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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 50 (1992), S. 524-526 
    ISSN: 1432-0827
    Keywords: Verapamil ; Bone ; Osteopenia ; Rat ; Female ; Intestinal calcium absorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Verapamil inhibits the intestinal absorption of calcium (Ca) and increases serum parathyroid hormone in rats. The effects of verapamil on bone tissue after long-term treatment is, however, not well described. Adult female and male Sprague-Dawley rats received verapamil in their drinking water at a dosage of 0.075 mg/ml (low dose) or 0.75 mg/ml (high dose) for 12 weeks; control rats received only drinking water. All rats were fed a diet containing 0.1% Ca and 0.5% P. In female rats, the amount of bone ash per volume was significantly reduced from 0.742 g/ml in controls to 0.713 g/ml after low-dose treatment of verapamil, and to 0.667 g/ml following high-dose treatment (P〈0.01). The tibial length was increased from 39.7 mm in controls to 40.3 mm or to 40.7 mm after low or high doses (P〈0.01). The tibial volume increased from 0.385 ml in controls to 0.397 ml after low doses and to 0.429 ml after high doses (P〈0.01). In contrast, in male rats the amount of bone ash per volume was significantly increased from 0.578 g/ml in controls to 0.580 g/ml after low doses and to 0.620 g/ml after high doses of verapamil (P〈0.01). The tibial bone volume in males as decreased from 0.633 ml in controls to 0.641 ml after low doses and to 0.583 ml after high doses (P〈0.05). The tibial length in the males was not changed by verapamil. The intestinal absorption of Ca was reduced in male rats from 5.28 in controls to 4.03 (serosa/mucosa) after low-dose treatment and to 2.46 after high-dose treatment with verapamil (P〈0.05). In female rats, the intestinal absorption of Ca did not change after verapamil treatment. Thus, chronic treatment with verapamil in female rats induced osteopenia whereas in male rats bone growth was inhibited.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 50 (1992), S. 391-396 
    ISSN: 1432-0827
    Keywords: Bone ; Matrix ; Phosphoproteins ; Biomineralization ; Calcium ; Nucleation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Osteopontin, bone sialoprotein, and bone acidic glycoprotein-75 are three acidic phosphoproteins that are isolated from the mineralized phase of bone matrix, are synthesized by osteoblastic cells, and are generally restricted in their distribution to calcified tissues. Although each is a distinct gene product, these proteins share aspartic/glutamic acid contents of 30–36% and each contains multiple phosphoryl and sialyl groups. These properties, plus a strict relationship of acidic macromolecules with cell-controlled mineralization throughout nature, suggest functions in calcium binding and nucleation of calcium hydroxyapatite crystal formation. However, direct proof for such roles is still largely indirect in nature. The purpose of this review is to present two speculative hypotheses regarding acidic phosphoprotein function. The goal was to use new sequence information along with database comparisons to develop a structural rationalization of how these proteins may function in calcium handling by bone. For example, our analysis has identified a conserved polyacidic stretch in all three phosphoproteins which we propose mediates metal binding. Also, conserved motifs were identified that are analogous with those for casein kinase II phosphorylation sites and whose number correlates well with that of phosphoryl groups/protein. A two-state conformational model of calcium binding by bone matrix acidic phosphoproteins is described which incorporates these findings.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0827
    Keywords: Histamine ; Polyamines ; Mast cells ; Histidine decarboxylase ; Bone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary A simple method for determining histamine and polyamines in various tissues was devised. The method, however, could not be applied to calcified tissues, because the high concentration of Ca2+ in the extract interferes with the chromatographic separation of these amines. By treating the extracts from calcified tissues with K2CO3, we succeeded in removing the Ca2+, and the method could then be applied to determine the amines in bone tissues of mice. By using this method, we examined the contribution of mast cells and histidine decarboxylae (HDC) to the amount of histamine in the bone. The results indicate that (1) the HDC activity in the bone is the highest among the tissues of normal mice, and the histamine produced by the HDC in the bone is metabolized rapidly; (2) a major part of HDC in the bone is present in the bone marrow cells other than mast cells, and most of histamine in the bone is attributable to the histamine pooled in mast cells; (3) mast cells in the diaphysis are located largely along the endosteal lining; and (4) the method devised in this study may be useful for studying the roles of histamine (or mast cells) and polyamines in calcified tissues.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Osteoporosis international 2 (1992), S. 201-204 
    ISSN: 1433-2965
    Keywords: Bone ; Distal radius ; Fracture ; Single photon absorptiometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Thirty-six women aged 60, 70 or 80 years who had fractured one of their distal radii (Colles' fracture) 0 to 35 (median 10) years earlier were examined in this population-based study. Single photon measurements (SPA) were performed on both arms 1 cm and 6 cm proximal to the styloid process of the ulna. All women were questioned about earlier wrist fractures and which, if any, side had been affected. Information about the type and site of the fracture was also gathered from the hospital records. The bone mineral content (BMC) was found to be increased by almost 20% in the once-fractured radius at the distal measuring site (1 cm) when compared with the unaffected side. This difference did not seem to diminish with time. At the proximal measuring site there was no difference between the once-fractured and the non-fractured side. There was a progressive loss of bone mineral in the once-fractured arm during the first years after the fracture however. This appeared to be reversed after about 10 years to a relative gain, even though the correlation was weak. Six of the 36 women could not remember which side had been fractured and five could not remember having had such a fracture at all. Determination of osteoporosis by measuring forearm BMC with single photon densitometry is therefore of limited value in some women of the oldest age groups.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Skeletal radiology 21 (1992), S. 509-513 
    ISSN: 1432-2161
    Keywords: Epithelioid hemangioendothelioma ; Bone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Epithelioid hemangioendothelioma is the prototype of a group of vascular tumors characterized by epithelioid or histiocytoid endothelial cells. Epithelioid hemangioendothelioma of bone is a rare lesion that constitutes fewer than 1% of primary malignant skeletal neoplasms. We describe two cases that illustrate the spectrum of radiographic features seen with this neoplasm, and also present its appearance on magnetic resonance imaging.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 50 (1992), S. 193-196 
    ISSN: 1432-0827
    Keywords: Bone ; Mechanical properties ; Fatigue microdamage ; Exercise
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The presence of microdamage in the tibiae and femora of rats following repetitive loading in vivo was investigated by subjecting 48 male rats, aged 12 weeks, to treadmill running (26.8 m.min-1 on 10% grade) for 0.56 hours (5,000 cycles, E1), 1.13 hours, (10,000 cycles, E2), 2.27 hours (20,000 cycles, E3), and 3.4 hours (30,000 cycles, E4) with Group C as control. Following exercise, tibiae and femora were excised and the right limbs were tested in torsion at 180°.sec-1. Transverse sections were cut from the proximal, mid- and distal diaphysis of left tibiae and femora, bulk stained in basic fuchsin, cut to 50 μm thick, and examined for the presence of microdamage. Following these periods of loading, tibiae and femora showed no evidence of microdamage initiation, as evidenced by light microscopy, or corresponding alterations in mechanical properties. It was concluded that the magnitude of loading produced by single bouts of intensive exercise, which encompassed up to 30,000 loading cycles, was insufficient to initiate fatigue microdamage in tibiae or femora of rats.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 51 (1992), S. 143-150 
    ISSN: 1432-0827
    Keywords: Adsorption ; Magnesium ; Calcium ; Apatite crystals ; Enamel ; Dentin ; Bone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Magnesium (Mg) is a conspicuous constituent of hard tissues but its possible role in biomineralization is poorly understood. It is possible that Mg2+ adsorbed onto bioapatites may contribute to the modulation of crystal growth as such inhibitory activity has been reported for synthetic apatites. The present study was undertaken to determine the adsorption isotherms of Mg ions onto synthetic apatites and biominerals in tooth and bone tissues in the presence of other ions of natural occurrence. Synthetic crystals used as adsorbents were hydroxyapatite and, as a better prototype for the biomineral, Mg-containing carbonatoapatite. Human enamel and dentin materials were obtained from extracted, caries-free, permanent teeth. Porcine dentin materials at two developmental stages were obtained from erupted deciduous and unerupted permanent teeth of a 6-month-old slaughtered piglet. Porcine bone was obtained from the cortical portion of the mandible of the same animal. All biomineral samples were pulverized and then treated by plasma ashing (deproteination) at about 60°C. Each of the powdered samples was equilibrated in solutions containing various initial concentrations of Mg2+, Ca2+, and Na+ (or K+) as nitrate salts. Following equilibration, concentrations (and activities) of magnesium and calcium ions in the experimental solution were determined. The pH values of the equilibrium solutions were in the range of 6.2–6.5. Experimental data of the Mg adsorption onto hydroxyapatite were interpreted on the basis of a Langmuir-type model for binary systems assuming competition of Mg2+ and Ca2+ for the same adsorption sites on the crystal surfaces of the apatites. According to this model, the adsorbed Mg is expressed as a function of the ionic activity ratio (Mg2+)/(Ca2+) in the equilibrium solution. The model contains two parameters, the adsorption selectivity constant Ks and the maximum number of adsorption sites N (μmol/g). The numerical values of Ks were similar for all adsorbents used (synthetic and biological) and indicated the preferential adsorption of Ca2+ probably due to spacial restrictions extending to the very surface of the crystals. The initial level of Mg2+ in the surface pool was different in the various biominerals, probably reflecting the composition of fluid in which the biominerals were formed. Whereas the surface pool of Mg of human enamel was marginal, only 5% of the total Mg, significant fractions of the total Mg in human and porcine dentins (about 20–30%), and porcine bone (about 40%) existed on the crystal surfaces. There were significant differences in the total Mg and the value of the parameter N between young (unerupted) and mature (erupted) dentin minerals. It was ascertained that the occupancy of adsorption sites by Mg ions became greater with maturation of the dentin tissues. The overall results suggest that the Mg-mineral interaction in tooth and bone tissues may be a highly tissue-specific process, presumably reflecting differences in fluid composition (particularly Ca and Mg activities) responsible for biomineralization.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 51 (1992), S. 72-77 
    ISSN: 1432-0827
    Keywords: Fixation ; FT-IR microscopy ; Infrared spectroscopy ; Bone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Fourier transform infrared microscopy is a powerful tool for the characterization of mineral and protein in histologic sections of bone. This study was concerned with determining whether techniques used to preserve these tissties and to prepare them for sectioning had an effect on spectral properties. The υ1, υ3 phosphate bands in the 900–1200 cm-1 spectral region were used to evaluate the structure of the apatitic mineral in fresh-frozen, ethanol-fixed, and formalin-fixed 35-day-old rat femurs; fresh-frozen and formalin-fixed 20-day-old fetal rat femurs; ground 35-day-old rat diaphyseal bone samples; and formalin-fixed, methacrylate-embedded ground diaphyseal bone. The crystallinity (crystal size and perfection) of the bone apatite was assessed by a curve-fitting analysis of the υ1, υ3 phosphate bands. Results indicate that ethanol or formalin fixation of the 35-day-old intact rat femur, and formalin fixation and embedding of the ground rat bone do not significantly alter the crystallinity of the apatite. However, formalin fixation of the fetal rat bone did alter the structure of the apatite mineral phase. In addition, evaluation of protein secondary structure in the 35-day-old rat femur from the Amide I and Amide II vibrations near 1650 and 1550 cm-1, respectively, revealed that protein conformation was altered by ethanol fixation.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1432-0827
    Keywords: Menopause ; Estrogens ; Bone ; Osteoporosis ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Biochemical parameters reflecting bone resorption [urinary calcium/creatinine (Ca/Cr) and hydroxyproline/ creatinine (OH/Cr)] were related to serum estrogens [estrone (E1) and estradiol (E2)] in 262 healthy women including 158 patients receiving estrogen replacement therapy (ERT) for at least 6 months, 49 eugonadal women, and 55 untreated postmenopausal women. A significant (P〈0.001) correlation exists between serum E2 and Ca/Cr: Ca/Cr (mg/dl)=-0.00044 E2 (pg/ml)+0.129 (n=262; r=-0.37), serum E2 and OH/Cr: (OH/Cr (mg/g)=-0.049 E2 (pg/ml)+18.76 (n=262; r=-0.36), serum E1 and Ca/Cr: Ca/Cr (mg/dl)=-0.0003 E1 (pg/ml)+0.127 (n=261; r=-0.28) but not between serum E1 and OH/Cr. Women with circulating levels of E2 between 60 and 90 pg/ml have a significant (P〈 0.01) reduction of Ca/Cr and OH/Cr when compared with those with lower levels of E2. Higher values of E2 do not provide additional benefit. We conclude that in postmenopausal women receiving an estrogen replacement therapy (ERT), a significant reduction of bone resorption is achieved when circulating levels of estradiol reach a value (60 pg/ml) corresponding to the one measured, in eugonadal women, during the last days of the early follicular phase of the menstrual cycle. We suggest that oral or percutaneous ERT should induce a minimal value of 60 pg/ml to prevent postmenopausal bone loss.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 51 (1992), S. 291-297 
    ISSN: 1432-0827
    Keywords: Bone ; Osteoblast ; Cyclosporin A ; Attachment ; Proliferation ; Alkaline phosphatase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The effects of the immunosuppressive drug cyclosporin A (CsA) were evaluated on ROS 17/2.8 cells in vitro. ROS cells were treated with CsA (0, 0.5, 1.0, 5.0 μg/ml) for 3 days with and without bovine parathyroid hormone (bPTH) (1–34) 10 nM. CsA at 0.5, 1.0, 5.0 μg/ml without PTH and at 5.0 μg/ml in the presence of PTH significantly inhibited proliferation, as determined by a tetrazolium colorimetric assay. In addition, ROS cell number was significantly reduced at 3 and 4 days with CsA (5.0 μg/ml) without affecting cell viability. Incorporation of [3H]-thymidine into DNA was significantly reduced by 3.0 and 5.0 μg/ml CsA after 12 and 24 hours exposure. Basal and 1,25-dihydroxyvitamin D3-stimulated alkaline phosphatase levels in confluent ROS cells were reduced (P〈0.05) with CsA (1.0 and 3.0 μg/ml). Pretreatment of ROS 17/2.8 cells with CsA did not alter PTH-stimulated cAMP levels or [125I]-PTHrP binding to ROS cells. CsA treatment of ROS 17/2.8 cells induced a spindle-shaped appearance with loss of attachment in confluent cultures. When ROS cells were cultured in CsA-containing media, cellular attachment at 6 and 12 hours was reduced (P〈0.05) compared with untreated ROS cells. These findings indicate that CsA was capable of inhibiting proliferation, cell number, mitogenesis, alkaline phosphatase levels, and cell attachment of ROS cells without affecting PTH binding or cAMP levels. This direct effect of CsA on osteoblasts may be important in changes of bone remodeling observed in CsA-treated humans and animals.
    Type of Medium: Electronic Resource
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  • 11
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 51 (1992), S. 255-258 
    ISSN: 1432-0827
    Keywords: Bone ; Densitometry ; Dual energy X-ray absorptiometry ; Lateral spine scanning ; Reproducibility
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Reproducibility of lateral spine dual energy X-ray absorptiometry (LAT DEXA) scans using a Lunar DPX-L scanner was assessed in a cadaveric phantom and in patients. One hundred phantom measurements over 7 months demonstrated a longitudinal stability of 1.7% (coefficient of variation, CV). Additional scans were performed with the phantom rotated by up to 20° in each of the three orthogonal planes to assess the effects of variable patient positioning. Horizontal and vertical rotation of the spine had little effect on the estimated bone mineral density (BMD), however, axial rotation of greater than 8° led to errors in the BMD measurement. One hundred consecutive patients had two lateral scans performed within 1 month. BMD (range 0.10–1.6 g/cm2) was determined for each scan by one operator. Significant overlap from ribs and pelvis was often seen with L2 and L4 vertebrae but one vertebra (L3) could be measured in every case. Intraoperator and interoperator variability was assessed by three experienced operators, each analyzing 10 patients' scans on five separate occasions, and was found to be less than 1.1% for a single vertebra. BMD estimation of vertebral bodies and midslices by lateral DEXA scans (CV% of 3.8% and 4.6%) have a 95% confidence interval of 0.074 g/cm2 and 0.096 g/cm2, respectively for two vertebrae. This variability is due mainly to axial rotation, with operator variability, horizontal rotation, and vertical rotation having little effect on BMD estimation.
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 51 (1992), S. 30-34 
    ISSN: 1432-0827
    Keywords: PTHRP ; Anabolic ; Rat ; Bone ; Potency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Parathyroid hormone-related protein (PTHRP) has recently been purified from human tumors associated with the syndrome of humoral hypercalcemia of malignancy. The gene encoding PTHRP has been cloned, and based on predicted amino acid sequence, polypeptides comprising the first 36 [36Tyr(1–36) PTHRP amide] and 74 [(1–74)PTHRP] amino acids have been synthesized. Human (h) PTHRP (1–36) and (1–74) are potent bone-resorbing agents, and are catabolic for bone in vivo when given continuously at high doses. Bovine parathyroid hormone (bPTH) (1–34) is also catabolic for bone at high dose levels, but when given in low doses for weeks to months, it is anabolic. Although PTHRP possess several PTH-like properties in bone, hPTHRP (1–34) is reported to be only weakly anabolic in vivo. As polypeptide length influences PTHRP action, we evaluated hPTHRP(1–74) as an anabolic agent for bone in vivo. Twenty-four 4-week-old male Sprague-Dawley rats were given daily subcutaneous injections of hPTHRP(1–74) (1 and 2 nmol/100 g body weight, bw), bPTH(1–34) (4 nmol/100 g bw) or vehicle. Rats were sacrificed on day 12, and serum calcium, phosphorus, and 1,25 dihydroxyvitamin D and femoral bone dry weight, calcium content, and hydroxyproline content were measured. Serum calcium and phosphorus were equivalent in all groups. A significant increase in dry bone weight was observed in both PTHRP-treated groups compared with controls. PTHRP also caused a significant, dose-dependent increase in bone calcium and hydroxypro-line content. Results of these studies indicate that PTHRP (1–74) is anabolic for bone in vivo when administered at low-dosage levels for a prolonged period.
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    Springer
    European journal of orthopaedic surgery & traumatology 2 (1992), S. 265-268 
    ISSN: 1432-1068
    Keywords: Bone ; Xenograft ; Young's modulus ; Biomechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary The aim of the present study was to compare the mechanical properties of two types of a new bone xenograft, T650 (Luddoc®) (Dense and Medium) with human and fresh bovine trabecular bone. Compressive testing was performed to destruction with a constant deformation rate of 0,025 mm min−1. Shear destructive testing was also carried out. Under our experimental conditions, Young's modulus of dense T650 (132.9 ± 52.3 MPa) do not differ significantly from that of fresh bovine bone (117.5 ± 61.5 MPa); and that of medium T650 (79.92 ± 37.3 MPa) did not differ significantly from human bone (77,36 ± 54,9 MPa). The shear force is required to destroy dense T650 (494 ± 167 N) did not differ significantly from those for fresh bovine bone (558 ± 104 N). Whereas the values for medium T650 were significantly lower (359 ± 155 N). The stress-strain curves obtained from all the specimens did not differ significantly. The process used to obtain T650 did not modify the mechanical properties of bovine trabecular bone.
    Notes: Résumé Le but de ce travail est de comparer les propriétés mécaniques d'une nouvelle xénogreffe osseuse le T650 (Luddoc®) répartie en deux sous groupes dits “dense” et “moyen” à celle de l'os trabéculaire humain et de bovin. Des tests de compression avec un rapport de déformation constant de 0,025 mm min−1 et des tests de rupture au cisaillement sont appliqués. Dans les conditions expérimentales utilisées, le module de Young du T650 dense (132,9 ± 52,3 MPa) est comparable à celui de l'os trabéculaire frais de bovin (117,5 ± 61,5 MPa), celui du T650 moyen (79,92 ± 37,3 MPa) à celui de l'os humain (77,36 ± 54,9 MPa). La résistance à la rupture au cisaillement du T650 dense (494 ± 167 N) est comparable à celle de l'os trabéculaire de veau frais (558 ± 104 N). Les valeurs du T650 moyen sont significativement plus faibles (359 ± 155 N). Les courbes compression/déformation sont similaires pour les différents types d'éprouvettes testés. Les traitements subis par l'os trabéculaire de veau pour l'obtention du T650 n'affectent pas ses propriétés mécaniques.
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  • 14
    Electronic Resource
    Electronic Resource
    Springer
    Archives of toxicology 66 (1992), S. 315-320 
    ISSN: 1432-0738
    Keywords: Cadmium ; Rat ; Bone ; Long-term administration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A decrease in mechanical strength of bones was observed both in young and old rats for long periods of administration of cadmium. Young (3-week-old) female rats were given 0 (control), 5 and 10 ppm cadmium in drinking water, respectively, for 20 weeks. Old (18-month old) female rats were given 0 (control) and 40 ppm cadmium in drinking water, respectively, for 7 months. The compression strengths of bones of young rats which were given 10 ppm cadmium, and those of old rats which were given 40 ppm cadmium, significantly decreased at the distal end portion of femur. Cadmium contents in bones in the 10 ppm and 40 ppm groups were about 110 and 210 ng/g dry weight, respectively. The present result confirmed that cadmium has a lesional effect on the mechanical strength of bone at the concentration of 100–200 ng/g in dry weight of bone, for both young and old rats.
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  • 15
    ISSN: 1432-2161
    Keywords: Ultrasound ; Bone ; Ilizarov ; Artifact ; Measurement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Thirty-three ultrasound examinations of the corticotomy interval of patients undergoing Ilizarov procedures were retrospectively evaluated for the presence or absence of an acoustic edge artifact. This artifact, consisting of a fine anechoic band, has been previously described in phantom models and is presumed to be due to phase cancellation effects. We demonstrated this artifact in 8 of 33 examinations. The artifact proved helpful in identifying the location of the corticotomy margin, even when this margin was obscured by the presence of developing periosteal new bone. Attention to technical factors is, however, important. We believe that this artifact may have a useful role in the routine monitoring of the Ilizarov patient.
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  • 16
    ISSN: 1432-0878
    Keywords: Parathyroid hormone-related peptide ; Osteocalcin-mRNA ; In situ hybridization histochemistry ; Bone ; Rat (Wistar)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Previous studies have indicated that 19-dayold fetal long bones of the rat contain an adenylyl cyclase-stimulating activity antigenically related to parathyroid hormone-related peptide. To ascertain its origin, Northern blotting and in situ hybridization histochemistry were performed. Results demonstrate that mRNA of parathyroid hormone-related peptide is present in RNA extracted from fetal long bones of the rat and that cells responsible for its production are localized in the periosteum. These cells are not mature osteoblasts because they do not synthesize mRNA of osteocalcin. Thus the present study shows that parathyroid hormone-related peptide could be produced locally, at least in part, in the skeleton of fetal rats.
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  • 17
    ISSN: 1434-9949
    Keywords: Total ; Body ; Bone ; Mineral ; Content ; Pelvic ; Bone ; Mineral ; Content ; Postmenopausal ; Osteoporosis ; Bone ; Mass
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Bibliographic references seem very controversill regarding the most appropriate anatomical area for bone mass estimation. Since some overlapping in the different bone mass measurements among normal and osteoporotic females has been observed, we have studied the bone mineral content of the pelvic bone through DEXA, and have correlated it with the total body bone mineral content, a highly discriminating measure, in order to observe whether pelvic bone mineral may be a useful measure in bone mass assessment. Pelvic and total body bone mineral values did not decrease until menopause in 104 normal premenopausal females aged 20 to 49 years. On the other hand, these values decreased in normal postmenopausal women (n=44) aged 50 to 65 years (p〈0.001), with a 16% pelvic bone mineral content and an 11% total body bone mineral content decrease. Osteoporotic females (n=30), showed lower values for both levels than normal postmenopausal ones (p〈0.001), with a 54% pelvic and a 24% total decrease. A 15% overlap was observed when pelvic values between normal postmenopausal and osteoporotic females were compared. The greater percentage decrease in pelvic BMC compared to total body bone mineral content and the lower overlap observed suggest that the pelvis may be an ideal anatomical area for bone mass evaluations.
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  • 18
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 35 (1992), S. 1941-1966 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In Part I of this paper the kinematic relationships between the absolute, elastic and joint accelerations are developed. In this paper, these kinematic equations are used with the generalized Newton-Euler equations and the relationship between the actual and generalized reaction forces to develop a recursive projection algorithm for the dynamic analysis of open-loop mechanical systems consisting of a set of interconnected rigid and deformable bodies. Optimal matrix permutation, partitioning and projection methods are used to eliminate the elastic accelerations while maintaining the inertia coupling between the rigid body motion and the elastic deformation. Recursive projection methods are then applied in order to project the inertia of the leaf bodies onto their parent bodies. This leads to an optimal symbolic factorization which recursively yields the absolute and joint accelerations, and the joint reaction forces. The method presented in this paper avoids the use of Newton-Raphson algorithms in the numerical solution of the constrained dynamic equations of open-loop kinematic chains since the joint accelerations are readily available from the solution of the resulting reduced system of equations. Furthermore, the method requires only the inversion or decomposition of relatively small matrices and the numerical integration of a minimum number of co-ordinates. Open-loop multibody robotic manipulator systems are used to compare the results and efficiency of the recursive methods with that of the augmented formulations that employ Newton-Raphson algorithms.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
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  • 19
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 35 (1992), S. 1991-2002 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper a new method for computing non-linear magnetostatic fields is introduced, which allows the simultaneous coupling of a finite element structure with a magnetic network. Combining the advantages of both methods while avoiding their drawbacks, this coupling yields both an accurate and time-efficient computation.The traditional method of the unknown mesh fluxes is applied for the solution of the magnetic network. The finite element solution, on the other hand, is based on a classical first-order interpolation of the unknown vector potential. The coupling is established by a proper organization of the unknowns on the boundary common to the finite element and network regions. In this way, a single system of non-linear equations is obtained.Moreover, it is shown that the coupled system of equations is equivalent to a single finite element system if generalized base functions are allowed. Consequently, various results from finite element theory may be applied. For instance, the matrix governing the iteratively linearized system of equations can directly be shown symmetrical and positive definite.Finally, the field inside a permanent magnet motor is calculated with the coupled method. Although the number of unknowns is dramatically reduced compared to a full FE calculation, the same level of accuracy is achieved. Hereby, the benefit of the coupled method is clearly proved.
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    International Journal for Numerical Methods in Engineering 35 (1992), S. 2049-2066 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The first-order shear deformation plate theory can be used in the small strain and moderate rotation non-linear elasticity by defining correctly the displacement vector form. In this paper, the problem of the consistency between the displacement vector form and the finite strain tensor approximation is analysed. Then, a new moderate rotation theory is proposed. The variational form of the governing equations is derived for the beam and the plate problems in a consistent way. Then, an iterative numerical procedure based on the finite element method and the secant striffness matrix is developed in order to solve the non-linear differential equation problem. Computations are made for one- and two-dimensional structures, in order to assess the performance of the von Kármán, finite elasticity, classical and the proposed moderate rotation theories.
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  • 21
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    International Journal for Numerical Methods in Engineering 35 (1992), S. 2103-2104 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 22
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    International Journal for Numerical Methods in Engineering 35 (1992), S. 2067-2078 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Development of techniques to provide rapid and accurate evaluation of the integrations required in boundary element method (BEM) formulations are receiving more attention in the literature. In this work, a series of direct expressions for surface integrals, required for a boundary element solution of the non-homogeneous biharmonic over a general two-dimensional curvilinear surface, are presented. The concept of an isoparametric representation, usually applied to the variation of the field variables and the geometry, is extended to the parametric mapping of the curvilinear geometry. The result renders the typically complicated Jacobian function into a series of polynomial expressions based on the shape function set and several discrete Jacobian values. An application of the isoparametric approximation of the Jacobian for a quadratic element representation is developed. Implementation of this approximation significantly improves the accuracy of the boundary integral solution by eliminating error associated with numerical quadrature. Overall computational efficiency is improved by reducing the time necessary to calculate individual surface integrals and evaluate field variables at internal points. A numerical solution of the boundary integral equations of phenomena governed by the biharmonic equation is presented and compared with an exact analysis.
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  • 23
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    International Journal for Numerical Methods in Engineering 35 (1992), S. 2079-2100 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An infinite boundary element (IBE) is presented for the analysis of three-dimensional potential problems in an unbounded medium. The IBE formulations are done to allow their coupling with the finite element (FE) matrices for finite domains and to obtain the overall matrices without destroying the banded structure of the FE matrices. The infinite body is divided into a number of zones whose contributions are expressed in terms of the nodal quantities at FE nodes by employing suitable decay functions and performing mainly analytical integrations of the boundary element kernels. The continuity and compatibility conditions for the potential and the flux at the FE-IBE interface are developed. The relationships for the contributions of the IBE flux vectors to the FE load vectors are given. The final equations for the IBE are obtained in the usual FE stiffness-load vector form and are easily assembled with the FE matrices for the finite object. A series of numerical examples in heat transfer and electromagnetics were solved and compared with alternative solutions to demonstrate the validity of the present formulations.
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  • 24
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    International Journal for Numerical Methods in Engineering 35 (1992), S. 1427-1442 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents a fast numerical algorithm for the implementation of material models for creep into finite element codes. First, an overview of existing algorithms for transient and steady-state creep is given. Next, a new formulation is presented which reduces the constitutive integration to the solution of a scalar non-linear algebraic equation. A solution is shown to exist without the need for subincrementation. Details of the numerical algorithm are then discussed. The paper closes with several numerical examples which illustrate the speed, robustness and accuracy of the proposed procedure as implemented in the Lawrence Livermore National Laboratory finite element codes NIKE2D and NIKE3D.
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  • 25
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    International Journal for Numerical Methods in Engineering 35 (1992), S. 1351-1395 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Structures presenting kinematical inderterminacy are usually called mechanisms. This paper is entirely concerned with assemblies which reveal themselves to be mechanisms at a null value of the load. Among them a first distinction is made between infinitesimal and finite ones, the former being characterized by one or several directions of lower (but not zero) stiffness, whereas the latter show at least one finite admissible displacement for which none of the bars undergoes any elongation. Moreover, there exists the possibility to make a further distinction among the infinitesimal mechanisms, according to which is the order of the stiffness along the direction considered above. The way of evaluating this order is to perform a local analysis of the strain energy of the assembly, once the displacement field is parametrized in terms of a suitable parameter. By means of a finite element technique, this analysis can be easily performed through the numerical approach presented in this report.
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    International Journal for Numerical Methods in Engineering 35 (1992), S. 1487-1502 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A solution strategy to find the shape and topology of structures that maximize a natural frequency is presented. The methodology is based on a homogenization method and the representation of the shape of the structure as a material property. The problem is formulated as a reinforcement problem in which a given structure is reinforced using a prescribed amount of material. Two dimensional, plane elasticity problems are considered. Examples are presented for illustration.
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    International Journal for Numerical Methods in Engineering 35 (1992), S. 1541-1542 
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  • 28
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    International Journal for Numerical Methods in Engineering 35 (1992) 
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    Keywords: Engineering ; Engineering General
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  • 29
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    International Journal for Numerical Methods in Engineering 33 (1992) 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 143-148 
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    Notes: An integral equation whose kernel presents logarithmic singularity is numerically solved by the method of arbitrary collocation points (ACP). As a first step a Gaussian quadrature of order n (hence of polynomial accuracy 2n- 1) is employed for the numerical approximation of the integral. Until now the collocation, which follows, was performed on special points x̄k, determined as roots of appropriate transcedental functions, in order to retain the 2n - 1 degree of polynomial accuracy of the Gaussian quadrature. In this paper an appropriate interpolatory technique is proposed, so that xk may be arbitrary and yet the high (2n - 1) accuracy of the Gaussian quadrature is retained.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 149-162 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: A rank-sufficient flat triangular shell element with drilling degrees-of-freedom is described. A variational basis for this element has been provided by a three-field variational principle with relaxed interelement compatibility and traction continuity conditions. A generalized spurious mode control procedure has been developed in order to stabilize zero energy kinematical modes. Excellent performance has been found in an obstacle course and buckling problems.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 213-215 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 33
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    Notes: The theory of optimal control and the theory of a substructural chain in static structural analysis are mutually simulated issues. From the minimum potential energy variational principle of the substructural chain, the generalized variational principle with two kinds of variables is derived first. By comparing that generalized variational principle with the variational principle in LQ control theory, the simulation relation is established. Based on that relation, the potential energy and mixed energy formulation of the algebraic Riccati equations are derived, then iterative algorithms are proposed which give the upper and lower bounds to the solution matrix. By using the solutions of the positive and negative co-ordinate algebraic Riccati equations, the canonical transformation matrices for the eigenproblems of the substructural chain and LQ control are constructed respectively, which reduce the eigenproblem to half-size. The properties of the solutions are analysed, which establishes the basis for expansion solutions.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 217-219 
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 220-220 
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 221-222 
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  • 37
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    International Journal for Numerical Methods in Engineering 33 (1992) 
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 235-268 
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    Notes: A theory is presented for the determination of the free vibration characteristics of anisotropic thin cylindrical shells, partially or completely filled with liquid, for two circumferential wave numbers, n = 0, axisymmetric and n = 1, beam-like. The method used was a combination of finite element analysis and classical shell theory. The shell was subdivided into cylindrical finite elements and the displacement functions were obtained using the shell equations. Expressions for the mass and stiffness matrices for a finite element and for the whole structure were obtained. A finite element was developed for the liquid in cases of potential flow. The natural frequencies of the shell, both empty and partially filled, were obtained and compared with existing experiments and other theories.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 469-502 
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    Notes: A simple, two-noded, finite element model for the three-dimensional buckling analysis of beam assemblages is developed. The underlying generalized-beam theory employed accounts for all coupled significant modes of deformations, including stretching, bending, shear and torsion, as well as warping. Its mixed formulation is of the two-field type, utilizing linear and constant interpolants for displacements and strain fields. Due considerations are given to the effect off inite rotations in space on the non-linear kinematic descriptions as well as the configuration-dependent behaviour of externally applied moment vectors of the conservative and non-conservative types. The performance of the model, and particularly the accuracy of its geometric and load-correction stiffnesses, is assessed in a fairly complete set of numerical simulations.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 907-927 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: The energy release rate G for 2-D rubbery material problems with non-conservative crack surface tractions is calculated by a modified version of virtual crack extension method with finite element solutions. The formulation is demonstrated to be ‘patch-independent’ and therefore a complicated finite element model around the crack tip is not required.
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  • 41
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 929-942 
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    Notes: The purpose of the present paper is the development of a numerical method for the evaluation of the Stress Intensity Factor in mode II at the tips of closed cracks subjected to compressive normal stresses and monotonically increasing shear stresses. A hybrid Boundary Element Technique, originally developed for the analysis of open cracks, has been suitably modified. The Stress Intensity Factor is evaluated directly on the basis of the displacement discontinuities computed at the crack tip element, by taking into account the development of frictional resistance on the crack surfaces. A limited number (10-15) of displacement discontinuity elements is found to be sufficient for an accurate evaluation of the Stress Intensity Factor. Some basic aspects of the mechanical behaviour of closed cracks are also investigated on the basis of the proposed method.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 963-973 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: A simple and efficient triangular finite element is introduced for plate bending applications. The element is a three-node triangular one with three basic degrees of freedom per node and two internal rotation degrees of freedom, using selective reduced integration. Numerical examples indicate that, despite its simplicity, the element is not only competitively accurate, but also useful as a thick-thin triangular plate bending element. It is also pointed out that this element using selective reduced integration is in fact a mixed element.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 943-961 
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    Notes: We investigate the Generalized Midpoint Rule for the time integration of elastoplastic constitutive equations for pressure-independent yield criteria. The incremental equations are divided into one scalar hydrostatic pressure/dilation rate equation, and a stress deviator/strain rate deviator tensorial equation, the solution of which reduces to one single scalar equation in the plastic multiplier. The existence and uniqueness of an incremental solution is discussed. The pressure/deviator decomposition is the basis for reduced integration of the pressure term in the Principle of Virtual Work, in order to avoid locking and spurious pressure oscillations. It is also shown that an optimal choice of the parameter of the Midpoint Rule can be computed by reference to the analytical solution of the equations assuming no work hardening. A benchmark test shows that this choice allows increased time steps. This formulation is applied to two classical problems: bulging of a tube under internal pressure and tension test on a notched specimen, and a comparison with the analytical solution is performed. Finally, the hypothesis which sustains these formulations of elastoplasticity (constant strain rate during an increment) is discussed with reference to elastic unloading and residual stress computation.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 975-995 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: This paper presents a method for creating a Delaunay triangulation connected to a set of specified points. The theoretical aspect is recalled for an arbitrary dimension and the method is discussed in order to derive a practical approach, valid for dimensions 2 and 3, which is simple, robust and well adapted to computation. Convex polyhedral and arbitrary polyhedral situations are introduced.
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  • 45
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1119-1138 
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    Notes: A geometrically non-linear thin shell element made from classical laminated materials is developed from three dimensional continuum concepts that admits arbitrarily large displacements and rotations. The development shows how explicit integration through the thickness of the element can be accomplished without sacrificing significant accuracy of the element.Computations obtained via the present formulation are compared with four test problems for which numerical data are available. All computations were carried out using the Crisfield-Riks arc length continuation algorithm with a full Newton-Raphson iterative scheme. Excellent agreement is observed for each test problem.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1165-1180 
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    Notes: A new explicit variable time-integration methodology and architecture which possesses self-starting attributes, eliminates the need to involve acceleration computations, and which has improved accuracy characteristics in comparison to the traditional central-difference-type formulations customarily advocated is described for applicability to computational structural dynamics. To sharpen the focus of the present study, an explicit variable time-integration architecture which is relatively simple, yet effective, is described. Unlike variable explicit time-integration formulations adopted in the past, the present self-starting variable time-integration architecture and implementation aspects facilitate a simplified representation and a straightforward and effective approach for combining finite element meshes requiring different time steps in a single analysis. Numerical test cases are provided which demonstrate the applicability of the proposed formulations.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1139-1163 
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    Notes: Dynamic substructuring or modal synthesis is established as a powerful means by which the computational effort required to perform dynamic analyses of large structures comprising many degrees of freedom can be reduced. For the case where the substructures are rigidly connected a method of synthesis is proposed which gives very substantial improvements in efficiency over existing methods both in terms of the number of floating-point operations which must take place and the on-board computer memory required. The proposed method makes use of a stable co-ordinate transformation which reduces the mass matrix for the constrained composite-system to the identity matrix and makes the stiffness matrix banded. The bandwidth is exactly equal to twice the total number of constraints plus 1. This is usually very small in comparison with the total number of degrees of freedom in the constrained composite-system. The proposed method is ideal for combining a number of substructures into a single new substructure in an efficient way without necessarily disposing of any degrees of freedom. Approximate formulae are presented which give the ratios of the number of operations required for established methods compared with the number needed for the proposed method. These formulae determine when it is appropriate to use the method proposed here.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1181-1195 
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    Notes: In this paper we derive the non-singular boundary integral representation of the field gradients for two-dimensional problems of classical potential field theory. Numerical implementation of this representation is developed too. The proposed method eliminates the most inaccurate influence coefficients which arise when singular integral representations are used and the internal point approaches the boundary. Since the integrands in this new method are finite at any internal point, accurate numerical results are achieved even in that portion of a solid which is very close to a discretized boundary. Two test problems are analysed in which the numerical results computed by strongly singular, weakly singular and non-singular integral representations are compared mutually and with exact solutions.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1197-1216 
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    Notes: Optimal plastic designs for structural frames can be obtained via static or kinematic considerations, each leading to a mathematical model requiring solution by linear programming. In both cases a mechanism can be found which satisfies the Foulkes optimality condition. However, this mechanism generally has many degrees of freedom and is most unlikely to be the actual collapse mode of the frame. A simple algorithm based on the method of redundant forces is presented for the automatic generation of the alternative optimal collapse mechanisms, any of which may be the actual collapse mode.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1217-1236 
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    Notes: In this paper, a ring rolling process is analysed by the Arbitrary Lagrangian Eulerian (ALE) finite element method. Phenomena associated with the process, such as large deformations, elastoplastic material behaviour and the friction on the interface, are included in the analysis. Special modelling on driven, idle and guide rolls is given. Results which include the overall shape of the formed ring, the time histories of roll separating force and driving torque, the distribution of the normal pressure on the ring-roll interface as well as the distribution of effective stresses in the formed ring, are also presented.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1237-1249 
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    Notes: The issue of developing effective and robust schemes to implement a class of the Ogden-type hypereiastic constitutive models, for large-strain analysis of rubber-like materials, is addressed. To this end, explicit forms for the corresponding material tangent-stiffness tensors are developed, and these are valid for the entire deformation range; i.e. with both distinct as well as repeated principal-stretch values. Throughout the analysis the various implications of the underlying property of separability of the strain-energy functions are exploited, thus leading to compact final forms of the tensor expressions. In particular, this facilitated the treatment of the complex cases of uncoupled volumetric/deviatoric formulations for incompressible materials, which are becoming increasingly popular in recent years. The forms derived are also amenable for use with symbolic-manipulation packages for systematic code generation.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1251-1267 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: Several old and new tetrahedral elements are tested and compared to some classical hexahedral elements for the solution of three-dimensional incompressible fluid flow problems. The proposed elements are created by adding velocity degrees of freedom to the basic trilinear velocity, constant pressure tetrahedron so as to satisfy the Brezzi condition. Numerical tests carried out for an artificial divergence-free flow problem and the lid-driven cubic cavity up to a Reynolds number of 400 are used to compare the proposed elements and assess their accuracy.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1269-1287 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: The present paper is concerned with the effective numerical implementation of the two-dimensional dual boundary element method, for linear elastic crack problems. The dual equations of the method are the displacement and the traction boundary integral equations. When the displacement equation is applied on one of the crack surfaces and the traction equation on the other, general mixed-mode crack problems can be solved with a single-region formulation. Both crack surfaces are discretized with discontinuous quadratic boundary elements; this strategy not only automatically satisfies the necessary conditions for the existence of the finite-part integrals, which occur naturally, but also circumvents the problem of collocation at crack tips, crack kinks and crack-edge corners. Examples of geometries with edge, and embedded crack are analysed with the present method. Highly accurate results are obtained, when the stress intensity factor is evaluated with the J-integral technique. The accuracy and efficiency of the implementation described herein make this formulation ideal for the study of crack growth problems under mixed-mode conditions.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1305-1320 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Finite elements based on Mindlin-Reissner theory and three-dimensional theory are used to study the distribution of shear forces and twisting moments in plates with various simple support conditions. Differences between the results obtained using these two theories are highlighted. A crude adaptive mesh refinement procedure is applied to improve the accuracy of the finite-element analysis.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1321-1323 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1325-1325 
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1329-1329 
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1327-1328 
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  • 59
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1611-1623 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper first presents the details of the development of a new six-noded plane triangular finite dynamic element. A block Lanczos algorithm is developed next for the accurate and efficient solution of the quadratic matrix eigenvalue problem associated with the finite dynamic element formulation. The resulting computer program fully exploits matrix sparsity inherent in such a discretization and proves to be most efficient for the extraction of the usually required first few roots and vectors, including repeated ones. Most importantly, the present eigenproblem solution effort is shown to be comparable to that of the corresponding finite element analysis, thereby rendering the associated dynamic element method rather attractive owing to superior convergence characteristics of such elements, presented herein.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1721-1736 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: Based on the incremental non-linear theory of solid bodies and the Hellinger-Reissncr principle, a mixed updated Lagrangian formulation of the large displacement motion of solid bodies is derived, and an associated mixed finite element model is developed. The model contains the displacements and stresses as the nodal degrees of freedom. The model is used for the large deformation elasto-plastic analysis of plane problems. In solving non-linear problems, the Newton-Raphson method with arc-length control is adopted to trace the post-buckling response. The computational steps to calculate the elasto-plastic stress increments at Gauss points in the elasto-plastic analysis by the present mixed model are described in detail. Numerical results are presented and compared with those of the displacement model and existing solutions to show the accuracy of the present mixed model in the large deformation elasto-plastic analysis of plane problems.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1737-1754 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: An accurate and efficient time domain BEM for 2-D scalar wave problems is presented. Emphasis is on developing analytical boundary elements (explicit solutions of the element matrices). The solutions are obtained under the condition of straight line elements and by bringing the problem to a simple and genral form of double convolution equation which is then solved by the Cagniard-De Hoop method. Six kinds of elements for any combination of the spatial interpolation functions of order 0, 1, 2 with the temporal interpolation functions of order 0, 1 are given in a compact form. It is pointed out that if the order of temporal interpolation function is higher than 1, or if the continuity of velocity or acceleration is required, the time-stepping technique will face difficulty. A method to solve this problem is also presented.Advantages of using the analytical elements instead of a numerical integral procedure are apparent. Problems with such things as singular integrals, accuracy and stability are solved. Methodology and solutions are demonstrated by a comparative study of two example problems. Numerical solutions reveal that the computation is efficient, accurate and stable.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1771-1773 
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    International Journal for Numerical Methods in Engineering 33 (1992) 
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1755-1769 
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    Notes: An a posteriori error estimation method for finite element solutions for three-dimensional elastic problems is presented based on the theory developed by the authors for two-dimensional problems.1 The error is estimated for the finite element solutions obtained using three-dimensional 8-node elements with a linear interpolation function in an arbitrary hexahedron. The method is successfully applied to three-dimensional elastic problems. In order to decrease computing time and memory use, the error is estimated element by element. The major difficulty in the element-wise error estimation technique is satisfying the self-equilibrium condition of applied forces, especially in three-dimensional problems. These forces are mainly due to traction discontinuity on the element boundaries. The difficulty is circumvented by employing an element-wise optimal procedure. It is also shown that a very accurate stress solution can be obtained by adding estimated error to the original finite element solutions.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1813-1822 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: This paper is concerned with the problem of modelling the motion of a bubble close to a rigid structure in an infinite fluid. It is well known that the boundary integral method is a powerful technique for modelling the motion of a single bubble in a fluid. In this paper we shall present a modified boundary integral method for modelling the motion of a bubble close to a fixed finite rigid structure, and discuss a numerical scheme for solving the resulting integral equation for three-dimensional problems. Finally, we illustrate our method with some typical numerical results.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1861-1874 
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    Notes: In recent years progress has been made in applying moving and deforming mesh systems to phase change problems. This allows the numerical attention where it is needed, near the migrating phase change zone. In spatially unbounded problems one hopes that numerically finite outer boundaries either escape significant activity or are automatically pushed further away as activity nears. Not infrequently this approach fails. Temperature activity often spreads more rapidly than phase change, thereby reaching far boundaries; stretching of the mesh by movement of far boundaries can challenge mesh control and cause ill-conditioning. In this paper the advantages of time dependent mesh adaption are enhanced by the joining of a new formulation for infinite elements to far boundaries. This is accomplished through a co-ordinate transformation within the framework of conventional 2-D quadratic, biquadratic, and linear-quadratic elements. Standard 2 by 2 Gauss-Legendre quadrature suffices throughout and normal Galerkin finite element features are undisturbed, including strict conservation of energy. The formulation is independent of global co-ordinates, entails no restrictions on the unknown function and should be applicable to other problem types. All test cases on quadrilateral and triangular grids show very significant improvements with infinite elements relative to comparable solution systems using strictly finite grids.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1843-1859 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: A general, well-structured and efficient method is advanced for the solution of-a large class of dynamic interaction problems including a non-linear dynamic system running at a prescribed time-dependent speed on a linear track or guideway. The method uses an extended state-space vector approach in conjunction with a complex modal superposition. It allows for the analysis of structures containing both physical and modal components. The physical components studied here are vehicles modelled as linear or non-linear discrete mass-spring-damper systems. The modal component studied is a linear continuous model of a track structure containing beam elements which can be generally damped and which can be embedded in a three-parameter damped Winkler-type foundation. The complex modal parameters of the track structure are solved for. Algebraic equations are established which impose constraints on the transverse forces and accelerations at the interfaces between the moving dynamic systems and the track. An irregularity function modelling a given non-straight profile of the non-loaded track or a non-circular periphery of the wheels is also accounted for. Loss of contact and recovered contact between a vehicle and the track can be treated. The system of coupled first-order differential equations governing the motion of the vehicles and the track and the set of algebraic constraint equations are together compactly expressed in one unified matrix format. A time-variant initial-value problem is thereby formulated such that its solution can be found in a straightforward way by use of standard time-stepping methods implemented in existing subroutine libraries. Examples for verification and application of the proposed method are given. The present study should be of particular value in railway engineering.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1891-1925 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: The primary aim of this research is to implement the arbitrary Lagrangian-Eulerian finite element description to model large deformation of interacting bodies. A pure Lagrangian description is often incapable of representing their contact with sufficient precision. In this work, the arbitrary Lagrangian-Eulerian (ALE) description has been extended to the surface nodes of interacting bodies to overcome these limitations. A penalty formulation has been implemented to account for the impenetrability constraint. The materials have been characterized as elastic-viscoplastic. Implicit integration schemes have been used at the global and constitutive levels for'improved stability.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1875-1890 
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    Notes: In order to obtain the curvature changes of the exterior surface of a shell subjected to an internal pressure, it is necessary to evaluate the displacement derivatives up to the second order. To this end, a hexahedronal element is developed with three-dimensional elastic properties utilized. At a nodal point on the surface of the shell, the first-order derivatives of the three displacement components are used as degrees of freedom (d.o.f.) in addition to the components themselves. However, at a nodal point not on the surface, only the three displacement components are used. Therefore, an element with aii exterior surface has a total of 48 d.o.f. and other elements have 24 d.o.f.The stiffness matrix of the 8-node subparametric hexahedronal high-order element is derived from the strain energy consideration. The cubic shape functions in the surface co-ordinates and linear shape functions through the shell thickness are used. The second derivatives of displacement components are continuous at any point on the exterior surface of the element, although they may not be continuous across the nodal line of two adjacent elements.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 1927-1940 
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    Notes: An efficient method is developed to compute the sensitivities of eigenvalues, eigenvectors and frequency responses in a reduced approximate rnodel. The reanalyses of a modified structure for those dynamic responses are also derived in the approximate model. An optimization process utilizing the efficiently calculated sensitivities and reanalyses of the modified structure is formed. The difficulties of finding eigenvector sensitivities for repeated modes have also been addressed and averted in the approximate model. Two numerical examples show satisfactory outcomes by using this proposed approach.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 2109-2127 
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    Notes: A finite element formulation for geometric non-linear analysis of elastic straight thin-walled beams is presented. The updated Lagrangian procedure is used for a stiffness matrix derivation-to analyse large displacements or buckling behaviour of space frames. The stiffness matrix is developed for a generic cross-section and is equally efficient for symmetric, monosymmetric or asymmetric open sections. Some non-linear strain terms usually neglected in the literature have been considered, resulting in a formulation which also includes the initial bimoment and torsion effect for all cross-sections analysed. The proposed method has been implemented and the results of sample problems are presented.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 2129-2143 
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    Notes: Linear and non-linear boundary eigenvalue problems are discretized by a new finite element like method. The reason for the new construction principle is the non-linear dependence of the dynamic stiffness element matrix on an eigenparameter. The dynamic stiffness element matrix is evaluated for a fixed number of parameters and is then elementwise replaced by a polynomial in the eigenparameter by solving least squares problems. A fast solver is introduced for the resulting non-linear matrix eigenvalue problem. It consists of a combination of bisection method and inverse iteration. The superiority of the newconstructionprinciple in comparison with the finite or dynamic element method is demonstrated finally for some numerical examples.
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 2201-2203 
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 2199-2199 
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 2181-2197 
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    Notes: Assumed field-consistent strain formulations of the displacement finite element procedure can lead to poor convergence and spurious stress oscillations if the assumed strain fields are not variationally correct, i.e. they do not satisfy an important orthogonality condition emerging from the equivalence sought between assumed strain displacement procedures and mixed procedures based on the Hellinger-Reissner theorem. Failure to ensure variational correctness introduces errors which can be equated to the presence of spurious loading mechanisms that cause stress oscillations. In this paper, we use the Timoshenko beam element to demonstrate that field-consistency and variational' consistency are two complementary but mutually exclusive principles - one does not imply the other and that both are necessary to successfully implement a displacement type finite element for constrained media.
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    International Journal for Numerical Methods in Engineering 34 (1992) 
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    International Journal for Numerical Methods in Engineering 34 (1992), S. 1-1 
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    International Journal for Numerical Methods in Engineering 33 (1992), S. 2145-2179 
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    Notes: The continuity and differentiability of object functions is a basic prerequisite for the application of gradient methods in optimization. However, for parameters defining the shape of an electromagnetic device, the finite element discretization in the field analysis introduces discontinuities into the object function which slow down the convergence rate. Additionally, depending on the geometric parametrizaiion employed, the optimization frequently yields shape contours that are impracticable for manufacturing purposes. This paper investigates the problems inherent in geometric parametrization and shows that the discontinuities in the object function are caused by changes in mesh topology as the geometric parameters vary; these changes inevitably follow from the use of free meshing algorithms. As a solution to these shortcomings a structural mapping technique is outlined that maps surface displacements onto the parameters of the finite element mesh and obtains the parameter dependent geometric variations without a change in mesh topology. This resulting geometric parametrization yields continuous object functions without artificial local minima and results in smooth surface contours of the optimized device. Using this new parametrization technique, design sensitivity analysis, is shown to be a reliable and essential part in the efficient application of gradient methods for shape optimization.
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    International Journal for Numerical Methods in Engineering 34 (1992), S. 3-3 
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    International Journal for Numerical Methods in Engineering 34 (1992), S. 61-71 
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    International Journal for Numerical Methods in Engineering 34 (1992), S. 39-59 
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    Notes: The first part of this study addresses the controversy ‘degenerated solid approach’ versus ‘shell theory’. It is shown that both formulations differ only in the kind of discretization if they are based on the same mechanical assumptions. In particular for degenerated shell elements different versions of explicit integration across the thickness are discussed. Among these are the approximation ‘Jacobian across the thickness is constant’, proven to be too restrictive, and the series expansion of the inverse Jacobian which turns out to be unnecessary although it leads to equations of the same order as those of a ‘best first approximation’ of a shell theory.The second part deals with the description of large rotations. It is demonstrated for problems formulated in three components of a rotation vector that a straightforward derivation results in a symmetric tangent stiffness matrix. However, a modified version is also added leading to an unsymmetric matrix already discussed in the literature. For shell problems with only two rotational variables both formulations coincide.
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    International Journal for Numerical Methods in Engineering 34 (1992), S. 73-115 
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    Notes: A non-linear shell theory, including transverse shear strains, with exact description of the kinematical fields is developed. The strain measures are derived via the polar decomposition theorem allowing for an explicit use of a three parametric rotation tensor. Thus in-plane rotations, also called drilling degrees of freedom, are included in a natural way. Various alternatives of the theory are derived. For a special version of the theory, with altogether six kinematical fields, different mixed variational principles are given. A hybrid finite element formulation, which does not exhibit locking phenomena, is developed. Numerical examples of shell deformation at finite rotations, with excellent element performance, are presented. Comparison with results reported in the literature demonstrates the features of the theory as well as the proposed finite element formulation.
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    International Journal for Numerical Methods in Engineering 34 (1992), S. 9-33 
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    Keywords: Engineering ; Engineering General
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    Notes: Computational Mechanics or Computational Applied Science is today the base on which most of the achievements of engineering and physics are built. Its concern is the solution of complex mathematical theories in numerical terms, without which the translation of these into practical artifacts would be impossible. Indeed, by providing such quantitative measures it enhances the understanding of the physical phenomena and stimulates further development of theory and physical experiment.Most of the theory underlying physical phenomena is cast in terms of, often involved, differential equations for which closed forms of solution are seldom possible. Numerical approximation or discretization processes are necessary for quantitative solution. Here the first steps were taken at the start of this century by the pioneering work of Richardson introducing finite difference approximations. The invention of relaxation methods by Southwell during the Second World War allowed many practical solutions to be achieved. However, it was the advent of the electronic digital computer that marked the turning point in Computational Mechanics. The dramatic escalation of the power of these machines, which still continues today, allowed the development of the field of Computational Mechanics as we know it.It is through this computer power that such methods of approximations as finite elements, finite differences, boundary solutions and spectral processes became a practical reality, though each was anticipated in the pre computer area. It is not surprising therefore, that the mathematical foundations and the full development of such methods have been accomplished only relatively recently.Today we see the field of activity subdivided between those specializing in the development of the various computational approximation processes and those seeking optimal numerical solutions for their particular field of application. It is the objective of this Congress and indeed of the International Association of Computational Mechanics to provide a forum at which an interdisciplinary exchange of information can take place between the various sections and disciplines of the whole field. Indeed, this is the way progress can best be achieved. Recent history indicates that substantial advances are as frequently made due to a method seeking a new application as through a problem requiring a solution.In recent history we have seen on occasion a liaison of a particular computational approximation method to a field of application occurring through historical accident. Here the intimate association of the finite method and the field of SOLID MECHANICS (CSM or Computational Solid Mechanics) and that of the finite differences with FLUID DYNAMICS (CDF or Computational Fluid Dynamics) can be observed as classical examples. Today the advent of new application fields and a better understanding of the approximation theory are helping to break down the barriers and ensure a more rational matching of objectives and methods. We shall illustrate the lecture with examples of such recent progress and state some possibilities as yet unexplored. Indeed, we are sure that the Congress will achieve in much more detail the same aims.This presentation stresses the essential unity of the subject and discusses some areas where progress and research are currently active. Two of such, adaptive error controlled analysis and treatment of hyperbolic (fluid) problems, are singled out due to their wide applications.
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  • 84
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    International Journal for Numerical Methods in Engineering 34 (1992), S. 165-169 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: For the analysis of shell structures with finite displacements and rotations displacement-based and mixed finite-rotation shell elements are developed starting from consistent tensorial shell theories. The constraints for the description of the deformed normal vector have been considered at the element level as subsidiary conditions so that finite rotations in arbitrary strongly nonlinear situations can be considered without any difficulty. The efficiency of the finite-rotation elements is demonstrated by numerical examples.
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  • 85
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    International Journal for Numerical Methods in Engineering 34 (1992), S. 117-164 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In Parts I to V of the present work, the formulation and finite element implementation of a non-linear stress resultant shell model are considered in detail. This paper is concerned with the extension of these results to incorporate completely general non-linear dynamic response. Of special interest here is the dynamics of very flexible shells undergoing large overall motion which conserves the total linear and angular momentum and, for the Hamiltonian case, the total energy. A main goal of this paper is the design of non-linear time-stepping algorithms, and the construction of finite element interpolations, which preserve exactly these fundamental constants of motion. It is shown that only a very special class of algorithms, namely a formulation of the mid-point rule in conservation form, exactly preserves the total linear and angular momentum. For the Hamiltonian case, a somewhat surprising result is proved: regardless of the degree of non-linearity in the stored-energy function, a generalized mid-point rule algorithm always exists which exactly conserves energy The conservation properties of a time-stepping algorithm need not, and in general will not, be preserved by the spatial discretization. Precise conditions which ensure preservation of these conservation properties are derived. A number of numerical simulations are presented which illustrate the exact conservation properties of the proposed methodology.
    Additional Material: 22 Ill.
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  • 86
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    International Journal for Numerical Methods in Engineering 34 (1992), S. 171-177 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A universal method which can be used to generalize thin plate elements to thick ones without adding any extra degree of freedom (DOF) is presented in this paper. To illustrate this method, a rectangular moderately thick plate element with 12 DOF is constructed on the basis of the well known thin plate ACM element. The element can be used in the analysis of both thin and thick plates. Shear locking is avoided.
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  • 87
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    International Journal for Numerical Methods in Engineering 34 (1992), S. 179-195 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents a method for a quick evaluation of stresses and displacements in a plate structure for elastostatic problems. First, an approximation is built from the mathematical structure of the solutions for starshaped domains, which is representative of long wavelength effects. Second, a variational formulation consistent with this approximation is proposed. Finally, two alternative procedures for coupling adjacent domains are demonstrated.
    Additional Material: 13 Ill.
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  • 88
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    International Journal for Numerical Methods in Engineering 34 (1992), S. 223-231 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
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  • 89
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    International Journal for Numerical Methods in Engineering 34 (1992), S. 197-208 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The present paper is concerned with the improvement of a finite element for the analysis of plate bending structures. The element formulation is based upon the Mindlin plate concept. The displacement field of this element is formed by adding non-conforming modes to two rotational displacement components of an 8-node plate element. The element has the requisite numbers of zero eigenvalues associated with rigid body modes to avoid the spurious zero energy mode. It is shown that the results obtained by the element converged to the exact solutions very rapidly as the mesh is refined and exhibited reliable solutions through numerical studies for standard benchmark problems. This element is shown to overcome the shear locking problem completely in a very thin plate situation, even for irregular meshes.
    Additional Material: 6 Ill.
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  • 90
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    International Journal for Numerical Methods in Engineering 34 (1992), S. 209-220 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In structural elements that allow shear deformation, uniformly reduced integration is used to avoid shear and membrane locking. The spurious modes of an underintegrated stiffness matrix can be filtered using perturbation methods. Although finite elements with perturbed stiffness show very good results, the displacements still conceal a component of spurious modes, albeit with very small magnitude depending on the perturbation factor. To desensitize the numerical results completely from the perturbation factor, a projection of the applied force is proposed to complement the perturbation of the stiffness such that spurious modes are not excited, thus providing robustness to the filtering of spurious modes. The proposed methodology is general in nature, but is applied in this paper to a 9-node shell element with uniformly reduced integration as an illustration. The perturbation of the stiffness matrix and the projection of the force vector are performed at the element level, avoiding expensive local-global transformations. As a consequence of the force projection, the perturbation factor for the stiffness can be arbitrarily small, and the element yields accurate results for a wide range of shell thickness.
    Additional Material: 4 Ill.
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  • 91
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    International Journal for Numerical Methods in Engineering 34 (1992), S. 233-247 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new computational model for the analysis of friction phenomena is presented in this work. The model is a regularized form of the Coulomb friction law, which stems from the analogy of friction and plasticity phenomena. The basic difference from the classical plasticity is the non-linear form of both the normal and the tangential elastic compliance. The numerical implementation of the model is also discussed. The methodology presented herein is used for the analysis of both dynamic and quasi-static problems. The dynamic substructuring and the static condensation are used to enhance the computational efficiency.
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  • 92
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    International Journal for Numerical Methods in Engineering 34 (1992), S. 279-302 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Additional Material: 17 Ill.
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  • 93
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    International Journal for Numerical Methods in Engineering 34 (1992), S. 271-277 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: We present a new algorithm for numerical solution of contactproblems without friction. The method is based on enhancing conjugate projector preconditioning into the standard conjugate gradient method for the solution of quadratic programming problems with inequality constraints. We show that the algorithm is correct and discuss the efficiency of the algorithm. The relation of the algorithm to the domain decomposition methods is also explained. The paper is supplied with numerical experiment.
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  • 94
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    International Journal for Numerical Methods in Engineering 34 (1992), S. 303-318 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Additional Material: 13 Ill.
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  • 95
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    International Journal for Numerical Methods in Engineering 34 (1992), S. 249-269 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This work is concerned with the formulation and numerical realization of large displacement contact problems with friction. A restricted class of contact problems is treated, where the deformation of one of the contacting bodies is prescribed. The formulation utilizes a particular convected co-ordinate chart to define, firstly, tangential components for all potential contact points and, secondly, the notion of incremental tangential displacement. By writing the discretized problem as a generalized equation in the sense of Robinson it is made clear how Newton's method may be extended to this kind of non-differentiable problems. The proposed algorithm is verified by several numerical examples.
    Additional Material: 6 Ill.
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  • 96
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 34 (1992) 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
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  • 97
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    International Journal for Numerical Methods in Engineering 34 (1992), S. 349-363 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Conditions of strain localization in multipotential elastoplasticity are studied in this paper for a strain discontinuity mode. The formulation is specialized to the case of a general anisotropic Mohr-Coulomb model, where plastic shear deformations are envisaged as the contribution of microstrains in several planes. Some finite element simulations with strain projection show the relationship between the predicted direction of localization and the post bifurcation modes.
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  • 98
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Softening, understood as unstable behaviour of material or structural components, is considered herein for its possible consequences on the overall behaviour of discrete dynamic models of elastic-plastic beam structures, in the absence of geometric effects. It is shown that multiplicity of incremental solutions (response bifurcations) and manifestations of overall instability may occur. The bifurcated responses may exhibit different scenarios for the same excitation: e.g. shakedown or local damage up to failure. An insight into and criteria for such occurrences are achieved by formulating the rate and the finite increment problem as linear complementarity problems. Period doubling and deterministic chaos under harmonic excitation are observed when reversible (holonomic) softening behaviour is assumed. The strong sensitivity of the phenomena investigated with respect to the choice of the structural model is pointed out. The findings are elucidated by illustrative examples.
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  • 99
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    International Journal for Numerical Methods in Engineering 34 (1992), S. 365-389 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The orthogonal metal cutting process for a controlled contact tool is simulated using a limit analysis theorem. The basic principles are stated in the form of a primal optimization problem with an objective function subjected to constraints of the equilibrium equation, its static boundary conditions and a constitutive inequality. An Eulerian reference co-ordinate is used to describe the steady state motion of the workpiece relative to the tool. Based on a duality theorem, a dual functional bounds the objective functional of the primal problem from above by a sharp inequality. The dual formulation seeks the least upper bound and thus recovers the maximum of the primal functional theoretically. A finite element approximation of the continuous variables in the dual problem reduces it to a convex programming. Since the original dual problem admits discontinuous solutions in the form of bounded variation functions, care must be taken in the finite element approximation to account for such a possibility. This is accomplished by a combined smoothing and successive approximation algorithm. Convergence is robust from any initial iterate. Results are obtained for a wide range of control parameters including cutting depth, rake angle, rake length and friction. The converged solutions provide information on cutting force, chip thickness, chip stream angle and shear angle which agree well both in values and trend with the published data. But the available data represent only a small subset in the range of parameters exhaustively investigated in this paper.
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  • 100
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    International Journal for Numerical Methods in Engineering 34 (1992), S. 395-415 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This survey paper is devoted to the description of numerical methods for modern problems of computational fluid dynamics (CFD). The problems of steady and unsteady aerodynamic flows, different transition turbulent regimes and motion around complex shape bodies (aircraft as a whole) are investigated. These approaches sharply reduce the level of demand on computer resources.
    Additional Material: 7 Ill.
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