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  • Electronic Resource  (3,297)
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  • Insulin
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  • Electronic Resource  (3,297)
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  • 1
    ISSN: 1534-4681
    Keywords: Insulin ; TPN ; Protein kinetics ; Amino acids ; Nutrition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Background: Cancer cachexia is a significant cause of postoperative morbidity and mortality in patients with tumors of the upper gastrointestinal tract. Standard parenteral nutrition (TPN) has failed to alter this. The anabolic effect of insulin has been well documented, and its positive effect on protein economy in cancer patients has been recently demonstrated. This study examines the effect of high-dose insulin and parenteral nutrition on protein kinetics in postoperative cancer patients. Methods: Eleven patients underwent surgery for pancreatic, esophageal, or gastric carcinoma. Postoperatively, patients received standard TPN for 4 days (1 g/kg/day amino acids, 1,000 kcal/day dextrose, 100 g/day lipid), and hyperinsulinemic parenteral nutrition for 4 days (same as standard TPN plus 1.44 U/kg/day regular human insulin) in a crossover design. All patients received both treatments, and the order of treatment was determined randomly. Euglycemia was maintained during insulin infusion via a variable 30% dextrose infusion. Patients underwent protein metabolic studies after each treatment period and rates of whole body and skeletal muscle protein synthesis, breakdown, and net balance were determined by radioisotopic tracer methods using14C-leucine and3H-phenylalanine. Results: Compared with standard TPN (STD), hyperinsulinemic TPN (INS) resulted in a significant increase in skeletal muscle protein synthesis (INS: 52.04±10.22 versus STD: 26.06±6.71 nmol phe/100 g/min, p〈0.05) and net balance of protein (INS: 7.75±4.61 versus STD: −15.10±6.44 nmol phe/100 g/min, p〈0.01), but no difference in skeletal muscle protein breakdown (INS: 44.29±11.54 versus STD: 41.17±5.89 nmol phe/100 g/min). Whole-body net balance of protein also significantly increased with insulin-based TPN, compared with standard TPN (INS: 0.04±0.05 versus STD: −0.08±0.07 µmol leu/kg/min, p〈0.05), but no difference in whole-body protein synthesis (INS: 2.52±0.15 versus STD: 2.49±0.15 µmol leu/kg/min) or whole-body protein breakdown (INS: 2.48±0.16 versus STD: 2.58±0.19 µmol leu/kg/min) was observed. Patients received significantly more calories during the hyperinsulinemic TPN period than during the standard TPN period. There was no difference in total, essential, or branched-chain amino acids, and no difference in serum free fatty acids, triglycerides, or cholesterol was observed between the two treatment periods. Conclusion: High-dose insulin in conjunction with hypercaloric parenteral nutrition causes improved skeletal muscle protein synthesis, skeletal muscle protein net balance, and whole-body protein net balance compared with standard TPN in postoperative cancer patients.
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  • 2
    ISSN: 1432-1440
    Keywords: Myotonic dystrophy ; Growth hormone ; Growth hormone releasing hormone ; Insulin ; C-Peptide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Growth hormone (GH) levels were measured in 12 patients with myotonic dystrophy (MD; 7 men and 5 women, aged 21–49 years) and 14 volunteers after administration of 100 μg GH-releasing hormone (GHRH; 1–29). A 75-g oral glucose tolerance test was carried out to determine glucose, insulin, plasma C-peptide, and urinary C-peptide. The GH level in six MD patients responded normally to GHRH (group I), with a peak of 17.1 ± 1.46 μg/l, compared withcontrols (27.8 ± 19.6 μg/l, NS), and that in the other six patients responded subnormally, with a peak of 3.15 ± 1.46 μg/l, lower than in controls and in group I patients (P 〈 0.001). In group I the insulin response to the glucose tolerance test showed hyperinsulinism and was lower than that in group II patients; stimulated C-peptide was also higher in group II than in group I and in controls; urinary C-peptide levels were parallel to those in previous data. In all MD patients there were a negative correlation between absolute values of GH response to GHRH and insulin response to glucose tolerance test (r = - 0.79, P 〈 0.001). Our data suggest that the failure in GH release and peripheral insulin action is due to a generalized defect in cellular membrane function in MD patients.
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  • 3
    ISSN: 1437-9813
    Keywords: Nesidioblastosis ; Insulin ; Radioimmunoassay ; Immunohistochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We present two cases of nesidioblastosis, a common cause of persistent hypoglycemia in infancy that, if inadequately treated, can lead to mental retardation. Tissue insulin data obtained from both radioimmunoassay and immunohistochemistry are presented. In each case, the insulin content correlated well with the quantity of insulinpositive cells in each portion of the pancreas. However, the insulin content varied from case to case and from portion to portion of the same pancreas. Thus, discrepancies in clinical results in nesidioblastosis may be due to variability of insulin content in the resected pancreas.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Virchows Archiv 425 (1994), S. 305-313 
    ISSN: 1432-2307
    Keywords: Rat ; Pancreatic beta cells ; Immunocytochemistry ; Ultrastructure ; Insulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract When studied morphologically in semi-thin sections in the rat in vivo, pancreatic beta cells displayed heterogeneous immunoreactivities for insulin and amylin, depending on the islet size and the intra-islet position of the beta cells. In larger islets, cortical beta cells (beta cells with contacts with all islet cell types and with the exocrine parenchyma) which are located in the periphery were more densely immunostained for insulin and amylin than medullary beta cells (beta cells with contacts only with other beta cells) which are located in the centre of the islet. Ultrastructurally, these findings were accompanied by differences in the number of secretory granules and mitochondria. Beta cells in small islets and at extra-islet sites exhibited a dense immunoreactivity. After administration of glibenclamide, immunoreactivities for insulin and amylin were diminished in a time-dependent manner, decreasing first in medullary and thereafter in cortical beta cells of larger islets. Ultrastructurally, the beta cells exhibited the typical signs of stimulation. A minority of beta cells in small islets and all beta cells in extra-islet locations remained unchanged. Thus pancreatic beta cells under basal and stimulatory conditions in vivo exhibit heterogeneity in hormone content and in ultrastructural features. These differences may represent the basis for a functional heterogeneity of the insulin secretory response of the individual beta cell both in vivo and in vitro in states of normal and impaired insulin secretion. As heterogeneity was observed only among beta cells in islets, while single beta cells surrounded by acinar cells exhibited no changes in insulin immunoreactivity, interactions between beta cells as well as between beta cells and other endocrine cells may be critical for expression of heterogeneity within the beta cell population.
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  • 5
    ISSN: 1432-0428
    Keywords: Insulin ; islet amyloid polypeptide ; pancreas ; secretion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary To determine whether chronic overproduction of islet amyloid polypeptide alters beta-cell function, we studied a line of transgenic mice which overexpress islet amyloid polypeptide in their beta-cells. At 3 months of age, these transgenic mice had greater pancreatic content of both islet amyloid polypeptide and insulin. Further, basal and glucose-stimulated secretion of both islet amyloid polypeptide and insulin were also elevated in the perfused pancreas of the transgenic animals. These findings demonstrate that chronic overproduction and secretion of islet amyloid polypeptide are associated with increased insulin storage and enhanced secretion of insulin in vitro. This increase in insulin storage and secretion may be due to a direct effect of islet amyloid polypeptide on the beta-cell or a betacell adaptation to islet amyloid polypeptide-induced insulin resistance.
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  • 6
    ISSN: 1432-0428
    Keywords: Insulin ; metformin ; 3-0-methylglucose transport ; non-insulin-dependent diabetes mellitus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Metformin has been demonstrated to lower blood glucose in vivo by a mechanism which increases peripheral glucose uptake. Furthermore, the therapeutic concentration of metformin has been estimated to be in the order of 0.01 mmol/l. We investigated the effect of metformin on insulin-stimulated 3-0-methylglucose transport in isolated skeletal muscle obtained from seven patients with non-insulin-dependent diabetes mellitus (NIDDM) and from eight healthy subjects. Whole body insulin-mediated glucose utilization was decreased by 45% (p〈0.05) in the diabetic subjects when studied at 8 mmol/l glucose, compared to the healthy subjects studied at 5 mmol/l glucose. Metformin, at concentrations of 0.1 and 0.01 mmol/l, had no effect on basal or insulin-stimulated (100 ΜU/ml) glucose transport in muscle strips from either of the groups. However, the two control subjects and three patients with NIDDM which displayed a low rate of insulin-mediated glucose utilization (〈20 Μmol·kg−1·min−1), as well as in vitro insulin resistance, demonstrated increased insulin-stimulated glucose transport in the presence of metformin at 0.1 mmol/l (p〈0.05). In conclusion, the concentration of metformin resulting in a potentiating effect on insulin-stimulated glucose transport in insulin-resistant human skeletal muscle is 10-fold higher than the therapeutic concentrations administered to patients with NIDDM. Thus, it is conceivable that the hypoglycaemic effect of metformin in vivo may be due to an accumulation of the drug in the extracellular space of skeletal muscle, or to an effect of the drug distal to the glucose transport step.
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  • 7
    ISSN: 1432-0428
    Keywords: Insulin ; C-peptide ; fructosamine ; triglyceride ; birthweight ; fatty acid ; non-insulin-dependent diabetes mellitus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Many ethnic groups at high risk of non-insulin-dependent diabetes mellitus are hyperinsulinaemic by early adult life. This study assessed whether such hyperinsulinaemia is present at birth. Cross sectional comparisons of maternal biochemistry, umbilical cord biochemistry and neonatal anthropometry were made between one ‘low risk’ and three ‘high risk’ ethnic groups, without diabetes in pregnancy in Auckland, New Zealand. The study comprised 123 European, Polynesian (Maori and Pacific Islands) and Indian normal pregnancies. Indian mothers were the smallest, with the highest insulin and non-esterified fatty acid concentrations. Polynesian mothers were the most obese with a higher fructosamine concentration. From these pregnancies, Indian neonates were smaller, slimmer, with the highest cord triglyceride (0.6 mmol/l vs 0.4 mmol/l, p〈0.01), and lowest cord insulin concentrations (7.1 mU/l vs 8.6 mU/l (European), 9.2 mU/l (Polynesian), p〈0.05). Polynesian babies had a high cord insulin: C-peptide ratio (52.5 mU/nmol vs 44.4 mU/ nmol (European), 44.1 mU/nmol (Indian), p=0.05). Although reduced intrauterine growth may contribute to the excess of diabetes and heart disease in Indians, it cannot explain the excess of diabetes in Polynesians. Exposure to minor relative maternal hyperglycaemia in the mother and abnormal neonatal insulin handling (as demonstrated by the higher insulin: C-peptide ratio) may be of long-term significance in Polynesians.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 55 (1994), S. 363-367 
    ISSN: 1432-0827
    Keywords: Skeletal unloading ; Bone formation ; Insulin ; Insulin-like growth factor-I ; Rat femur
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract The alteration of bone metabolism in the femur of rats with skeletal unloading for 4 days was investigated. Skeletal unloading was designed using the model of hindlimb hang in rats. Skeletal unloading caused a significant decrease in femoral weight, calcium, and phosphorus contents in the metaphysis but not diaphysis. Also, the unloading induced a significant decrease of zinc content, alkaline phosphatase activity, and deoxyribonucleic acid (DNA) content in the femoral diaphysis and metaphysis. When the femoraldiaphyseal and metaphyseal tissues from normal and skeletal-unloading rats were cultured in the presence of insulin (10-9 and 10-8 M) for 24 hours in vitro, the hormonal effect to increase alkaline phosphatase activity and DNA content in the diaphysis, but not metaphysis, was lost in the bone tissues from unloading rats. However, the culture with insulin-like growth factor-I (IGF-I; 10-8 and 10-7 M) produced a significant increase of alkaline phosphatase activity and DNA content in both the diaphyseal and metaphyseal tissues from normal and unloading rats. These results demonstrate that skeletal unloading causes an impairment of insulin effect, but not IGF-I effect, on bone metabolism in femoral tissues.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Pediatric nephrology 8 (1994), S. 309-312 
    ISSN: 1432-198X
    Keywords: Glucose ; Insulin ; Growth ; Chronic renal failure ; Uremia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We studied glucose metabolism using the hyperglycemic technique in a cross-section of 23 children (15 pubertal, 8 prepubertal) with stable chronic renal failure as a possible cause of their poor growth. Linear growth was expressed as growth velocity standard deviation score (GVSDS). GVSDS correlated with glucose disposal rate but not with insulin sensitivity index in the pubertal (r=0.87,P〈0.001) and prepubertal (r=0.86,P〈0.02) children with chronic renal failure. Thirteen children were followed longitudinally during medical suppression of hyperparathyroidism with dietary phosphate restriction and high-dose phosphate binders. Following significant suppression of serum parathyroid hormone (PTH) levels back to the normal range (932±240 ng/l to 199±50 ng/l), GVSDS, glucose disposal rate and insulin secretion all increased significantly (P〈0.01), with no change in insulin sensitivity index and renal function. The changes in GVSDS correlated with the changes in glucose disposal rate (r=0.86,P〈0.02) and with the changes in insulin secretion (r=0.80,P〈0.01). However, the changes in GVSDS did not correlate with the changes in PTH. The hypothesis that insulin may be more important than PTH in the pathogenesis of growth failure in chronic renal disease deserves further investigation.
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  • 10
    ISSN: 1432-0738
    Keywords: Key words Cell proliferation ; Pancreas ; 5-Bromo-2′-deoxyuridine (BrdU) ; Immunohistochemistry ; Hormones ; Insulin ; Glucagon ; Somatostatin ; Phenobarbitone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  A previous study demonstrated that administration of phenobarbitone to male AP Wistar rats for up to 7 days caused alterations in labelling indices (LIs) in several different tissues (including a reduction of the endocrine pancreas population LI) as determined by immunohistochemical visualisation of 5-bromo-2′-deoxyuridine (BrdU) incorporation into S-phase nuclei. The primary objective of this study was to determine whether treatment with phenobarbitone influenced the replicative states of specific cohorts of the islet (of Langerhans) cell population or generated a uniform depression of LI. Quantitation of the LIs of individual islet cell cohorts was achieved by utilisation of a dual immunohistochemical staining method for BrdU and islet hormones (insulin, glucagon and somatostatin) using a sequential peroxidase anti-peroxidase (PAP)/alkaline phosphatase anti-alkaline phosphatase (APAAP) method employing diaminobenzidine and New Fuchsin chromogens, respectively. We observed reductions, increases and no change in LIs of insulin-, glucagon- and somatostatin-positive cells, respectively. We conclude that the decreased LI of the insulin-positive cohort was not countered entirely by the LI increase in the glucagon-positive cohort due to the larger size of the former. Furthermore, the effects of phenobarbitone treatment are not manifested generally in the islet cell population but in the insulin- and glucagon-positive cohorts only. The causation of these effects is unknown but is likely to be due to enhanced carbohydrate and hormone metabolism. We believe that the visualisation and quantitation of replicating cells in specific hormone-positive cohorts of the islet cell population provide opportunities for understanding the influence of xenobiotics and disease processes on pancreatic function.
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  • 11
    Electronic Resource
    Electronic Resource
    Springer
    European journal of pediatrics 153 (1994), S. 409-410 
    ISSN: 1432-1076
    Keywords: Key words     Children ; Diabetes ; Insulin ; Jet injection ; Pain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract      The aim of this study was to investigate whether insulin application by jet injector is less painful than by needle. Pain was scored by 41 diabetic and seven healthy volunteers after injections with both methods. Injections by jet were no less painful than those by needle but produced several local side-effects.
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    European biophysics journal 23 (1994), S. 177-187 
    ISSN: 1432-1017
    Keywords: Molecular dynamics simulation ; Insulin ; Crosslinked insulin ; Single chain insulin ; Active conformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Molecular dynamics simulations were carried out on an insulin crosslinked between the N-terminal A chain and the C-terminal B chain to form a so-called mini-proinsulin: N α -A1-N ε -B29-diaminosuberoyl insulin (DASI). To investigate the influence of crosslinking on the dynamics of the insulin moiety, the bridge was removed from a transient DASI structure and simulation was carried on independently with the then unlinked (ULKI) as well as with the crosslinked species. The effects of crystal packing and quaternary interactions were checked by simulating both types of monomers and dimers known from the hexamer structure. All simulations were compared to previous ones of native insulin. DASI shows general similarity to the native simulations in most parts of the structure. Deviations are visible in the segments to which the bridge is directly connected, i.e. their flexibility is reduced. Upon removal of the bridge the ULKI simulations reapproach those of native insulin. The influence of the bridge spreads over the whole molecule, but all of its main structural features remain intact. The simulations suggest that the displacement of the C-terminal B chain of native insulin, considered important for receptor interaction, is prevented by the bridge, which also partially shields some binding residues. This is in accordance with the poor biological potency of A1-B29-crosslinked insulins.
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  • 13
    ISSN: 1432-2013
    Keywords: Glucose oxidation ; Glucose infusion ; Insulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract To determine the limits to oxidation of exogenous glucose by skeletal muscle, the effects of euglycaemia (plasma glucose 5 mM, ET) and hyperglycaemia (plasma glucose 10 mM, HT) on fuel substrate kinetics were evaluated in 12 trained subjects cycling at 70% of maximal oxygen uptake (VO2, max) for 2 h. During exercise, subjects ingested water labelled with traces of U-14C-glucose so that the rates of plasma glucose oxidation (R ox) could be determined from plasma 14C-glucose and expired 14CO2 radioactivities, and respiratory gas exchange. Simultaneously, 2-3H-glucose was infused at a constant rate to estimate rates of endogenous glucose turnover (R a), while unlabelled glucose (25% dextrose) was infused to maintain plasma glucose concentration at either 5 or 10 mM. During ET, endogenous liver glucose R a (total R a minus the rate of infusion) declined from 22.4±4.9 to 6.5±1.4 μmol/min per kg fat-free mass [FFM] (P〈0.05) and during HT it was completely suppressed. In contrast, R ox increased to 152±21 and 61±10 μmol/min per kg FFM at the end of HT and ET respectively (P〈0.05). HT (i. e., plasma glucose 10 mM) and hyperinsulinaemia (24.5±0.9 μU/ml) also increased total carbohydrate oxidation from 203±7 (ET) to 310±3 μmol/min per kg FFM (P〈0.0001) and suppressed fat oxidation from 51±3 (ET) to 18±2 μmol/min per kg FFM (P〈0.0001). As the rates of oxidation at more physiological euglycaemic concentrations of glucose were limited to 92±9 μmol/ min per kg FFM, and were similar to those reported when carbohydrate is ingested, the results of the current study suggest that the concentrations of glucose and insulin normally present during prolonged, intense exercise may limit the rate of muscle glucose uptake and oxidation.
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  • 14
    ISSN: 1432-1912
    Keywords: Insulin ; Dimerized insulin derivatives ; Insulin receptor antagonists ; Glucose transport ; 3T3-L1 cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effects of 7 covalently dimerized insulin derivatives on glucose transport in differentiated 3T3-L1 cells were investigated. Symmetric cross-linkage at lysine B29 with a bridge of 2 (oxalyl), 8 (suberoyl) or 12 (dodecanedioyl) carbon atoms produced derivatives with essentially unaltered receptor binding affinity but largely reduced intrinsic activity. Regardless of the chain length, these derivatives inhibited the effect of submaximal insulin concentrations. Insulin derivatives cross-linked at phenylalanine 131 or asymmetrically at 131/1129 were full agonists of the insulin receptor. When lysine B29 was cross-linked with the inactive desoctapeptide(B23-B30)insulin at phenylalanine B1, the intrinsic activity of the resulting dimer was lower than that of insulin, but higher than that of the symmetric B29-dimers. It is concluded that linkage at the B29-lysines, and not at the B1-phenylalanine, leads to partial agonism of dimerized insulin derivatives, regardless of the length of the crosslinker.
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  • 15
    ISSN: 1432-5233
    Keywords: Insulin ; VMH ; Cardiovascular response ; VMH lesion ; Blood pressure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The cardiovascular responses to insulin-induced hypoglycemia were studied in normal and ventral medial hypothalamic (VMH)-lesioned rats. The goal of this study was to investigate the role of the VMH in mediating the insulin-induced decreases in cardiovascular tone. Male Wistar rats were anesthetized with urethane/chloralose. Following the induction of anesthesia, the trachea, femoral artery, and femoral vein were cannulated. The femoral artery was attached to a pressure transducer for cardiovascular monitoring. The cardiovascular activity was recorded using a Modular Instruments Micro 5000 signal processing system. The mean arterial pressure and pulse pressures and heart rate were evaluated. In control studies, a stable plasma glucose and blood pressure were obtained with urethane/chloralose anesthesia for the duration of the experiments. Insulin (2.0 or 5.0 U/kg) significantly decreased the plasma glucose as well as the blood pressure. In VMH-lesioned rats, the lesions were accomplished by radiofrequency, and the cardiovascular response to insulin-induced hypoglycemia was investigated 1 or 6 weeks later. There was no difference in the cardiovascular response to insulin-induced hypoglycemia between the low or high insulin dose after 1 week in VMH-lesioned animals. The low dose after 6 weeks in VMH-lesioned animals did not produce a change in the mean arterial pressure response compared with controls. The pulse pressure was higher than in the sham-lesioned animals, and the plasma glucose response was greater. The high dose after 6 weeks in VMH-lesioned animals in contrast to sham-lesioned animals led to an increased cardiovascular response instead of a decrease. We propose that the decrease in cardiovascular activity in response to insulin-induced hypoglycemia in normal animals can be attributed to a direct or indirect effect on vascular dilation as well as possibly to an inhibition of sympathetic firing. However, it appears that insulin increases the vascular dilation as well as the parasympathetic tone after 1 week in the VMH-lesioned animals, similar to the findings in sham-lesioned animals. However, after 6 weeks, the insulin-induced decreased cardiovascular tone is minimal. Thus, we believe hat the VMH does not have a direct effect in modulating the insulin-induced decrease in cardiovascular tone, but its destruction appears to influence other regulatory centers.
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  • 16
    ISSN: 1439-6327
    Keywords: Catecholamines ; Insulin ; Growth hormone ; ACTH ; Erythropoietin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract To establish whether or not hypoxia influences the training-induced adaptation of hormonal responses to exercise, 21 healthy, untrained subjects [26 (2) years, mean (SE)] were studied in three groups before and after 5 weeks' training (cycle ergometer, 45 min· day−1, 5 days· week−1). Group 1 trained at sea level at 70% maximal oxygen uptake ( $$\dot V$$ O2max), group 2 in a hypobaric chamber at a simulated altitude of 2500 m at 70% of altitude $$\dot V$$ O2max, and group 3 at a simulated altitude of 2500 m at the same absolute work rate as group 1. Arterial blood was sampled before, during and at the end of exhaustive cycling at sea level (85% of pretraining of $$\dot V$$ O2max). $$\dot V$$ O2 increased by 12 (2)% with no significant difference between groups, whereas endurance improved most in group 1 (P 〈 0.05). Training-induced changes in response to exercise of noradrenaline, adrenaline, growth hormone, β-endorphin, glucagon, and insulin were similar in the three groups. Concentrations of erythropoietin and 2,3-diphosphoglycerate at rest did not change over the training period. In conclusion, within 5 weeks of training, no further adaptation of hormonal exercise responses takes place if intensity is increased above 70% $$\dot V$$ O2max. Furthermore, hypoxia per se does not add to the training-induced hormonal responses to exercise.
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  • 17
    ISSN: 1573-6903
    Keywords: Insulin ; chick embryo ; retina ; development ; HPLC analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Retinas of chick embryos contain insulin (1) and further, are capable of synthesizing it, as demonstrated by incubating retinas at different ages (7th–18th day) with [3H]leucine. The synthesized radioactive insulin was isolated and assayed by means of a HPLC procedure. The synthesis of insulin was found to be highest in the youngest retinas studied (day 7), afterwards it declined with age except for an increment found at 14–15 day. Explants of chick embryo retinas, cultured in vitro, rapidly degraded insulin. Nevertheless, the content of immunoreactive insulin in retinal explants diminished slowly with the age of culture, so that, after 8 days of incubation, it was about 60% of the content found in the retinas at the beginning of incubation. This was proof that cultured explants are capable of efficiently synthesizing insulin. The synthesized [3H]insulin was released from explants into the medium. This was evident also after 6–8 days in culture.
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  • 18
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 10 (1994) 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 19
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 10 (1994), S. 1-9 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An iterative method is introduced for computing second-order partial derivatives (sensitivities) of eigenvalues and eigenvectors of matrices which depend on a number of real design parameters. Numerical tests confirm the viability of the method and support our theoretical analysis. Alternative methods are reviewed briefly and compared with the one proposed here.
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  • 20
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 10 (1994), S. 11-19 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the formulation of the semi-Loof element the rotation of the tangent plane is derived from the interpolation of the transverse displacement, while the rotation of the normal is interpolated separately by another set of shape functions. The geometric stiffness matrix can be formulated by use of either of the two rotation representations. It is demonstrated that the use of the tangent plane representation in the geometric stiffness matrix is far superior to the common form at present.
    Additional Material: 4 Ill.
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  • 21
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 10 (1994), S. 21-32 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An efficient solution to boundary-value problems may be based on the application of a suitably truncated T-complete set of Trefftz functions over individual subdomains and on linking the fields by a least-squares procedure. Although it yields a symmetric system of linear equations, this approach as originally presented by Zielinski and Zienkiewicz is not suited for implementation into FE codes. The present paper presents two equivalent formulations, which take respectively the form of the finite (FE) and non-conventional boundary-element (BE) approach. Both allow the resulting simultaneous equations to be assembled following the standard direct stiffness methods and can readily be implemented into existing FE codes.As in the conventional p-method, the accuracy may be controlled within large limits without increasing the number of elements. The present approach allows substantial saving in computer time in comparison with the so-called hybrid-Trefftz (HT) elements, though the assumed displacement fields are identical. The practical efficiency of the new T-element approach is assessed on the problem of stress concentration in a symmetrically compressed perforated panel.
    Additional Material: 6 Ill.
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  • 22
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 10 (1994), S. 167-178 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A sixth-order polynomial shape function is developed for BIE analysis. The function is applied over only three-noded elements, but with the support for the function extending over adjacent elements. This avoids the oscillations near the ends of the range which otherwise are characteristic of high-order polynomial interpolation. Various test problems are explored, and it is shown that results as accurate as those from conventional quadratic elements are obtained with larger nodal spacings, and thus giving the potential for significant reductions in matrix storage requirements and solution times.
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  • 23
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    Communications in Numerical Methods in Engineering 10 (1994), S. 155-166 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A finite element formulation based on superposition is proposed for a lifting aerofoil in incompressible potential flow. An accuracy improvement technique for the singularity at the aerofoil trailing edge is discussed. It is shown that the quarter-node quadrilateral element can be readily employed to simulate this singularity. It is also demonstrated that the circulation in the flow field can be easily represented by a single constraint equation rather than introducing an artificial cut line in the mesh. The influence of finite-element mesh size on solution accuracy and the correct form of the boundary condition have been investigated as well. Numerical examples are given for both steady and quasisteady Joukowski aerofoils of various thicknesses and at a range of incidences. In all test cases, good agreement is observed between the analytical solution and the numerical result.
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  • 24
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    Communications in Numerical Methods in Engineering 10 (1994) 
    ISSN: 1069-8299
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    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 25
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    Communications in Numerical Methods in Engineering 10 (1994), S. 183-194 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An 8-node element (HMITC) for 3D non-linear analysis of solids is presented. The new element is based on an element developed by Wilson and Ibrahimbegovic, that incorporates incompatible modes, and on the method of mixed interpolation of tonsorial components. The HMITC element does not contain spurious zero energy modes and satisfies Irons' Patch Test. The numerical experimentation indicates that the HMITC has good performance even with distorted meshes.
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  • 26
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    Communications in Numerical Methods in Engineering 10 (1994), S. 203-215 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper we consider an explicit finite-element method, with elements adaptively oriented in space-time, for the solution of one-dimensional conservation laws, extending previous work dealing with linear convection-diffusion and incompressible flow. In particular we consider Burgers' equation and the compressible Euler equations.
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  • 27
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    Communications in Numerical Methods in Engineering 10 (1994), S. 195-201 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: A numerical method, based on neural-network-based functions, for solving partial differential equations is reported in the paper. Using a ‘universal approximator’ based on a neural network and point collocation, the numerical problem of solving the partial differential equation is transformed to an unconstrained minimization problem. The method is extremely easy to implement and is suitable for obtaining an approximate solution in a short period of time. The technique is illustrated with the aid of two numerical examples.
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  • 28
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    Communications in Numerical Methods in Engineering 10 (1994), S. 217-225 
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An efficient algorithm for consideration of axial and cyclic symmetry in the boundary-element method is presented. The appropriate transformation relationships was derived. The algorithm is then implemented in a boundary element program for the analysis of 2D elastostatic problems. Through analysis of typical problems the validity of the algorithm and its implementation is verified. A high level of accuracy and substantial reduction in computer time and storage was achieved.
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  • 29
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    Communications in Numerical Methods in Engineering 10 (1994), S. 227-235 
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The diffusion of oxygen into an absorbing medium as an example of an implicit moving boundary problem has been dealt with by a number of authors using various numerical techniques, and, where appropriate, approximate analytical expressions. To evaluate the time for complete absorption, extrapolation is usually employed. An unconditionally stable explicit numerical scheme that avoids the limitations of such methods is presented and tested herein. Unlike existing schemes this method is fully numerical; it avoids the large array size, generally required for existing methods, by using a variable-length time step. The time for complete absorption emerges from the final step in the normal computing procedure with no recourse to extrapolation. Furthermore, owing to the implicit condition prevailing at the moving boundary, no iterations are needed to evaluate the time step required for the moving boundary to move a single space increment. The numerical results obtained compare very favourably with those due to earlier authors.
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  • 30
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    Communications in Numerical Methods in Engineering 10 (1994), S. 237-248 
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    Topics: Mathematics , Technology
    Notes: In the paper we have developed a new formulation for solution of structural-acoustic coupling problems by boundary elements using the multiple reciprocity method. It is assumed that the structure is composed of plate components and is excited by the external or the internal noise source. The efficiency of the proposed formulation becomes especially remarkable if the boundary-value problem is to be solved repeatedly for different values of frequency. The accuracy of the numerical computations has been compared with the analytical solution in a test example.
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  • 31
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    Communications in Numerical Methods in Engineering 10 (1994), S. 257-265 
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    Keywords: Engineering ; Engineering General
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    Topics: Mathematics , Technology
    Notes: Techniques for stress- and strain-controlled in situ homogenization of inelastic periodic composites are presented. The results of homogenization computations on a specific elastoplastic composite solid are then employed to validate the form of an orthotropic elastoplasticity model with a tensorial kinematic hardening law.
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  • 32
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    Communications in Numerical Methods in Engineering 10 (1994), S. 249-255 
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    Keywords: Engineering ; Engineering General
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    Topics: Mathematics , Technology
    Notes: An algorithm for evaluation of friction in general contact-impact interfaces is described. The algorithm is based on an explicit finite-element method. Coulomb's friction law is assumed. The defence node algorithm is used such that the sticking condition can be imposed with the Lagrange multiplier method even in explicit dynamic analysis. The algorithm is supposed to be applicable in general situations, including large deformations of the contact-impact bodies and large relative sliding between the contact-impact boundaries. Numerical results are presented to demonstrate the performance of the algorithm.
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  • 33
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    Communications in Numerical Methods in Engineering 10 (1994), S. 275-277 
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  • 34
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    Communications in Numerical Methods in Engineering 10 (1994) 
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  • 35
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    Communications in Numerical Methods in Engineering 10 (1994), S. 267-273 
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    Notes: A generalization of the r(1-m)/m strain singularity of higher-order isoparametric elements is presented. It is shown that, by variable placement of the side nodes between their original and singular positions, the point of singularity sensed by the element can be controlled. The transition elements have a strain singularity outside their domain. The singular and non-singular elements are elements are special cases of the general mapping. The transition elements, together with the singular isoparametric elements, can be used for solving crack problems.
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  • 36
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    Communications in Numerical Methods in Engineering 10 (1994), S. 279-290 
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    Notes: In the design of members with flaws, it is necessary to keep the stress intensity factor K of any sharp crack below the fracture toughness Kcr of the materials. Stress-intensity factor equations for the more common basic specimen geometries and various loading conditions are available in the literature. The application of these equations to complex structures involves geometric problems such as the identification of the outline of each member and the sizing of the equivalent specimen for each flaw. The paper gives a response to such difficulties.
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    Communications in Numerical Methods in Engineering 10 (1994), S. 303-312 
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    Notes: A simple, yet storage-effective ‘linear’ programming code is given. The assumption of non-negative variables is bypassed without increasing the size of the problem. Furthermore, the objective is allowed to be summed over not just linear, but also concave, functions. A specific truss topology optimization example is shown.
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  • 38
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    Communications in Numerical Methods in Engineering 10 (1994), S. 291-296 
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    Notes: We propose in this paper a nine-point, fourth-order difference method for the numerical solution of the quasilinear Poisson equation \documentclass{article}\pagestyle{empty}\begin{document}$$ Au_{zz} + \frac{1}{r}u_r + Bu_{rr} = f\left({r,z,u,u_r,u_z} \right) $$\end{document} with appropriate boundary conditions. The method is based on five evaluations of f. The numerical results of four problems obtained using this method are listed. The results demonstrate the fourth-order accuracy of the method.
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  • 39
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    Communications in Numerical Methods in Engineering 10 (1994), S. 297-302 
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    Notes: Singularly perturbed second-order elliptic equations with boundary layers are considered. These may be considered as model problems for the advection of some quantity such as heat or a pollutant in a flow field or as linear approximations to the Navier-Stokes equations for fluid flow. Numerical methods composed of central-difference operators on special piece-wise-uniform meshes are constructed for the above problems. Numerical results are obtained which show that these methods give approximate solutions with error estimates that are independent of the singular perturbation parameter. An open theoretical problem is posed.
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  • 40
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    Communications in Numerical Methods in Engineering 10 (1994), S. 313-320 
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    Notes: In the paper we present a superconvergent patch recovery technique for obtaining higher-order-accurate finite-element solutions and thus a postprocessed type of L2 norm error estimate. Two modifications make our procedure different from the one proposed by Zienkiewicz and Zhu (1992), in which higher-order-accurate derivatives of the finite-element solution at nodes are determined. Firstly, the recovery process is made for element, not for nodes. An ‘element patch’, which represents the union of an element under consideration and the surrounding elements, is introduced. Secondly, the local error estimate is calculated directly from the improved solution for this element. Numerical tests on both 1D and 2D model problems show that this method can provide an asymptotically exact a posteriori L2 norm error estimate if the used element possesses superconvergent points for the solutions.
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  • 41
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    Communications in Numerical Methods in Engineering 10 (1994), S. 321-331 
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    Topics: Mathematics , Technology
    Notes: A new approach to developing serendipity quadrilateral infinite elements is presented. Using these elements universal matrices for quasiharmonic equation are developed. For a particular member of the family these matrices are independent of the size and shape of the element. Using these matrices the element stiffness matrix can be generated in a simpler manner by taking into account the size and shape of the element.
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  • 42
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    Communications in Numerical Methods in Engineering 10 (1994), S. 333-338 
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    Notes: A new global secant relaxation (GSR)-method-based improvement procedure is used to improve the overall convergency performance of the modified Newton-Raphson iteration in carrying out the solution of discrete systems resulting from the finite-element discretization of a certain class of structural problems involving non-linear deformation behaviour.
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  • 43
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    Communications in Numerical Methods in Engineering 10 (1994), S. 339-353 
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    Notes: Theoretical and experimental analysis of free-surface electrohydrodynamic flow is fragmented and incomplete. Simulation studies of this phenomenon are further limited by the inherent complexities in the modelling process. In this note a mathematical model is developed to analyse free-surface electrohydrodynamic flow in two dimensions, and preliminary results of the simulation are described. The configurations examined include electrified conducting surfaces, the dielectrophoretic forces, and a conducting jet. The simulation is compared with analytical results in the first two investigations and is shown to be quite accurate. In the last simulation it is demonstrated that in the initial formation of a conducting jet, a 10 per cent increase in applied voltage results in about a 10 per cent increase in fluid velocity.
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    Communications in Numerical Methods in Engineering 10 (1994), S. 355-357 
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  • 45
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    Communications in Numerical Methods in Engineering 10 (1994), S. 359-360 
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  • 46
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    Communications in Numerical Methods in Engineering 10 (1994) 
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  • 47
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    Communications in Numerical Methods in Engineering 10 (1994), S. 361-371 
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    Notes: The dual reciprocity boundary element method, first proposed by Nardini and Brebbia (1982, 1985), is a powerful technique for solving elliptic partial differential equations. Adopting this approach, a singular volume integral, which needs to be evaluated with a traditional boundary element method, can be converted into a boundary integral. However, when the governing equation is of a certain type, this conversion fails due to the singularities being introduced inside the physical domain and on the boundary arising by differentiating distance functions. We avoid these artificially created singularities by constructing a transformation which leads to improved numerical results.
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    Communications in Numerical Methods in Engineering 10 (1994), S. 743-749 
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    Notes: This is a study about one of the core questions in the GMRES(k) method regarding the obtaining of vector yk for the least-squares problem, argminy |Hky - β(n)e1|2 (see Saad and Schultz1). We propose a simple but efficient approach to the resolution of this problem and a low cost computation of the residual and the residual norm, including both in a complete and detailed FGMRES(k) algorithm. The whole algorithm of minimization only involves two backward substitutions with triangular matrices and a dot product. The residual and the residual norm are computed, making use of results in the least-squares problem.
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    Communications in Numerical Methods in Engineering 10 (1994), S. 759-760 
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    Communications in Numerical Methods in Engineering 10 (1994), S. 761-762 
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  • 51
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    Communications in Numerical Methods in Engineering 10 (1994) 
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  • 52
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 1481-1497 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: A procedure for the optimization of stretched triangular grids is described. The method is based on the construction and minimization of a function that represents a generalized version for stretched grids of a non-linear spring system. The function is minimized using a gradient method based on the steepest descent. Examples are provided to show the applicability of the method to computational fluid dynamics problems.
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 1465-1480 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: Multigrid method is used to accelerate the convergence of the numerical solution of the set of partial differential equations for generating the Body-Fitted Co-ordinate system (BFC) for both simply and doubly connected domain problems. The multigrid method is based on the full approximation scheme with bilinear interpolation as prolongation operator. The other components of the multigrid method such as the relaxation method, restriction operator, number of relaxation sweeps per cycle and direction of relaxation sweeps are varied with a view to obtaining the general principle in implementing an efficient multigrid algorithm for the generation of the BFCs.
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 1531-1555 
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    Notes: In Part I of this work, Paulino et al.1 have presented an algorithm for profile and wavefront reduction of large sparse matrices of symmetric configuration. This algorithm is based on spectral properties of a Finite Element Graph (FEG), An FEG has been defined as a nodal graph G, a dual graph G* or a communication graph G· associated with a generic finite element mesh. The novel algorithm has been called Spectral FEG Resequencing (SFR). This algorithm has specific features that distinguish it from previous algorithms. These features include (1) use of global information in the graph, (2) no need of a pseudoperipheral vertex or the endpoints of a pseudodiameter, and (3) no need of any type of level structure of the FEG. To validate this algorithm in a numerical sense, extensive computational testing on a variety of problems is presented here. This includes algorithmic performance evaluation using a library of benchmark test problems which contains both connected and non-connected graphs, study of the algebraic connectivity (λ2) of an FEG, eigensolver convergence verification, running time performance evaluation and assessment of the algorithm on a set of practical finite element examples. It is shown that the SFR algorithm is effective in reordering nodes and/or elements of generic finite element meshes. Moreover, it computes orderings which compare favourably with the ones obtained by some previous algorithms that have been published in the technical literature.
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 1557-1572 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: To exploit the benefits of parallel computer architectures for multibody system simulation, an interdisciplinary approach has been pursued, combining knowledge of the three disciplines of dynamics, numerical mathematics and computer science. An analysis of the options available for the formulation and numerical solution of the dynamical system equations yielded a surprising result. A method initially proposed to solve the inverse problem of dynamics is the best choice to generate the system equations required for solving the simulation problem, when relying on implicit integration routines. Such routines have the particular advantage of handling stiff systems, too. The new O(N)-residual formalism, generating the system equations in a form required for implicit numerical integration, has a high potential to benefit from parallel computer architectures. Two strategies of medium and coarse grain parallelization have been implemented on a Transputer network to obtain a package for parallel multibody simulation. An analysis of the performance of this package demonstrates for typical multibody simulation problems that the new code is five times faster than existing codes when implemented on a serial computer. An additional speed-up by the same order of magnitude is obtained when the code is implemented on a Transputer network.
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 181-201 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: A general Finite Volume Method (FVM) for the analysis of structural problems is presented. It is shown that the FVM can be considered to be a particular case of finite elements with a non-Galerkin weighting. For structural analysis this can readily be interpreted as equivalent to the unit displacement method which involves mainly surface integrals. Both displacement and mixed FV formulations are presented for static and dynamic problems.
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 229-256 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: An element-free Galerkin method which is applicable to arbitrary shapes but requires only nodal data is applied to elasticity and heat conduction problems. In this method, moving least-squares interpolants are used to construct the trial and test functions for the variational principle (weak form); the dependent variable and its gradient are continuous in the entire domain. In contrast to an earlier formulation by Nayroles and coworkers, certain key differences are introduced in the implementation to increase its accuracy. The numerical examples in this paper show that with these modifications, the method does not exhibit any volumetric locking, the rate of convergence can exceed that of finite elements significantly and a high resolution of localized steep gradients can be achieved. The moving least-squares interpolants and the choices of the weight function are also discussed in this paper.
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 37-48 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A pseudo-transient (static) linear, geometric, material and combined geometric and material non-linear analyses of composite laminates are presented. A nine-noded isoparametric quadrilateral finite element belonging to the Lagrangiar family is used in space discretization. An explicit time marching scheme is employed for time integration of the resulting discrete ordinary differential equations with the special forms of diagonal fictitious mass and/or damping matrices. Elasto-plastic material behaviour is incorporated using the flow theory of plasticity. In particular, a modified version of Hill's initial yield criterion is used in which anisotropy parameters of plasticity are introduced. The shear deformation is accounted for by assuming a constant transverse shear strain across the thickness of the laminate and the geometric non-linearity is considered in the sense of von Karman strains. The layered element approach is adopted for the treatment of plastic behaviour through the thickness. A wide range of numerical examples is presented to demonstrate the validity and efficiency of the present approach. The results for combined non-linearity are also presented. The variety of results presented here, which are based on realistic material properties of often-used advanced laminated composite plates, and especially those for combined non-linear analysis, should serve as a reference for future investigations.
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 91-105 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A variationally coupled finite element-boundary element method is developed for transient problems. A single variational statement is obtained for the entire domain and the unknown tractions, which may be discontinuous on the interface and are often a source of difficulties, are eliminated. Moreover, no interface conditions need be taken into consideration at the level of the discretized equation. The discrete equations for the coupled system can be obtained directly without any intermediate steps. The method generalizes a coupling method previously developed by the authors for statics. Numerical examples show that the solutions obtained by the present method agree very well with those obtained by analytical solutions.
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  • 60
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 431-455 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: A six-node triangle plate/shell element is developed for the analysis of laminated composite structures. This model is formulated using Hamilton's principle along with a first-order (Reissner/Mindlin) shear deformation theory. The element is based upon an isoparametric representation along with an interdependent interpolation strategy; bicubic polynomials for the transverse displacement and biquadratic polynomials for the element geometry, in-plane displacements and rotations. The resulting element, which is evaluated using exact numerical integration, has correct rank and is free of shear ‘locking’. Numerical results are presented that validate the new element and prove its outstanding convergence capabilities in comparison to existing triangular elements using standardized test problems (elastic eigenvalue analysis, patch test, static simply supported square-plate solutions) and experimentally measured vibration data of cantilevered isotropic and composite plates.
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  • 61
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 475-496 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The collapse of ordinary finite elements to generate the desired strain singularity at the crack tip for fracture mechanics applications can lead to unwanted additional singularities in that area. Although neither the quarter-point nor the half-point 8-node two-dimensional (2-D) and 20-node three-dimensional (3-D) elements exhibit this behaviour, the present article proves that arbitrarily small deviations from the quarter-point element can be constructed which do have additional singularities. Since the general behaviour of the half-point element is not affected by small modifications, this element is better suited to match complex body geometries.
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 537-538 
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  • 63
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 517-536 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: The superconvergent patch derivative recovery method of Zienkiewicz and Zhu is enhanced by adding the squares of the residuals of the equilibrium equation and natural boundary conditions. In addition, a new conjoint polynomial for interpolating the local patch stresses over the element which significantly improves the local projection scheme is presented. Results show that in the 4-node quadrilateral, the equilibrium and boundary condition residuals usually improve accuracy but not the rate of convergence, whereas in the 9-node quadrilateral, results are mixed. The conjoint polynomial always improves the accuracy of the derivative field within the element as compared to the standard nodal interpolation, particularly in 4-node quadrilaterals.
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 279-296 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An hybrid stress element formulation based on internal, incompatible displacements is used to develop efficient Mindlin plate elements. The 4-node quadrilateral Mindlin plate element is derived from a modified energy functional. Both displacements and stresses are defined in the natural co-ordinate interpolation system. The assumed stress field is obtained by tensor transformation and so chosen as to ensure that the element is co-ordinate invariant and stable. Shear locking is avoided through an appropriate identification of the internal, incompatible displacement field. The role played by incompatible displacements in the formulation of hybrid stress elements for thin and moderately thick plates is discussed. Numerical applications are presented to illustrate the accuracy and reliability of the suggested Mindlin plate element.
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 605-621 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: In the present paper, we analyse the computational performance of the Lanczos method and a recent optimization technique for the calculation of the p (p ≤ 40) leftmost eigenpairs of generalized symmetric eigenproblems arising from the finite element integration of elliptic PDEs. The accelerated conjugate gradient method is used to minimize successive Rayleigh quotients defined in deflated subspaces of decreasing size. The pointwise Lanczos scheme is employed in combination with both the Cholesky factorization of the stiffness matrix and the preconditioned conjugate gradient method for evaluating the recursive Lanczos vectors. The three algorithms are applied to five sample problems of varying size up to almost 5000. The numerical results show that the Lanczos approach with Cholesky triangularization is generally faster (up to a factor of 5) for small to moderately large matrices, while the optimization method is superior for large problems in terms of both storage requirement and CPU time. In the large case, the Lanczos-Cholesky scheme may be very expensive to run even on modern quite powerful computers.
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 387-411 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: A new eight-node quadrilateral shear-bending Reissner-Mindlin plate finite element for the very thin and thick plates without locking and spurious zero-energy modes is presented. The element has very good convergence characteristics both for thin and thick plates, is hardly insensitive to mesh distortions, and passes the patch tests. The formulation of the element is derived from a displacement variational principle and some general criteria to compute inconsistent transverse shear strains. These criteria have been applied with success to four- and eight-node quadrilateral plate finite elements and could be applied to construct triangular elements. The eight-node quadrilateral shear-bending plate finite element proposed has been found to be very efficient.
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 457-474 
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    Notes: A theory is proposed in this paper to explain, in a unified manner, the three rational approaches using the incompatible displacements uλ in the hybrid element formulation. Limited to the plane stress case, the theory suggests that the introduction of uλ is to constrain the total value of the invariant I2(= σxσy - τxy2) of the assumed stresses over the element to zero. In the plane stress case, this is the well-known condition for the stress distributions to be independent of the elastic constants of the material. The theory proposed is also used to explain the closeness of the performances of the four 4-node hybrid stress membrane elements, 5β-I, 5β-II, 5β-A and 5β-C, that have been developed previously. The differences among them are shown to be of the second degree in the distortion measures of the element shape, when they are compared on the basis of the non-vanishing total value of I2 of their respectively adopted assumed stress field. Several numerical examples are used to verify and to illustrate the proposed theory.
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    International Journal for Numerical Methods in Engineering 37 (1994) 
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 1825-1840 
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    Notes: This paper presents a boundary element formulation for the permanent Navier-Stokes equations in which the well-known closed-form fundamental solution for the steady Stokes equations is employed. In this way, from the integral representation formulae for the Stokes' equations, an integral equation is found in which the original non-linear convective terms of the Navier-Stokes equations appear as a domain integral. Additionally, the method of dual reciprocity is used to transform the domain integral to boundary integrals (this method is closely related to the method of particular integrals also used in the literature to transform domain integrals to boundary integrals). Numerical results are presented for the three-dimensional internal flow in a cylindrical container with a rotating cover, in which the accuracy of the method is shown.
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 2291-2309 
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    Notes: The helicoidal beam model developed in the first part of this work is applied here to the development of a mixed finite element for space-curved and twisted beams undergoing large displacements and finite rotations. Starting from the governing weak form expressed by the principle of virtual work, a consistent linearization is obtained in the following and a novel updated Lagrangian finite element implementation is thoroughly discussed.The unique features and the distinguishing properties previously claimed for the helicoidal model are shown here to imply remarkable numerical consequences. For this purpose, meaningful example problems regarding the non-linear static response of beams are addressed in the following and the results are compared with those available from the literature.Furthermore, a finite element in time for the rigid body dynamic problem is developed within the framework of the helicoidal geometry. The underlying philosophy of this novel finite element for dynamics is the realization of the helicoidal decomposition of the rigid body motion within a time step.
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    International Journal for Numerical Methods in Engineering 37 (1994) 
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 2311-2335 
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    Notes: A finite element approach for shape optimization in two-dimensional (2-D) frictionless contact problems is presented in this work. The goal is to find the shape that gives a constant distribution of stresses along the contact boundary.The whole formulation, including mathematical model for the unilateral problem, sensitivity analysis and geometry definition is treated in a continuous form, independently of the discretization in finite elements. Shape optimization is performed by direct modification of geometry through B-spline curves and an automatic mesh generator is used at each new configuration to provide the finite element input data for numerical analysis and sensitivity computations. Using augmented-Lagrangian techniques (to solve the contact problem) and an interior-point mathematical-programming algorithm (for shape optimization), we obtain several results reported at the end of the article.
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 2337-2338 
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 1881-1896 
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    Notes: This paper presents the first endeavour to exploit a generalized differential quadrature method as an accurate, efficient and simple numerical technique for structural analysis. Firstly, drawbacks existing in the method of differential quadrature (DQ) are evaluated and discussed. Then, an improved and simpler generalized differential quadrature method (GDQ) is introduced to overcome the existing drawback and to simplify the procedure for determining the weighting coefficients. Subsequently, the generalized differential quadrature is systematically employed to solve problems in structural analysis. Numerical examples have shown the superb accuracy, efficiency, convenience and the great potential of this method.
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 3015-3018 
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 3019-3021 
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    International Journal for Numerical Methods in Engineering 37 (1994) 
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 3005-3014 
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    Notes: Since Soize introduced the concept of fuzzy structures in structural acoustics there has been little activity clarifying the basic elements which underlie his theory. Soize's papers are not easy reading due to the high level of mathematical formalism. In addition Soize simultaneously bases this fuzzy structure theory on two components: (1) a model for one Degree Of Freedom (DOF) fuzzy oscillators, and (2) a medium frequency solution method developed previously. It is unclear as to the role of the two components, although others have already undertaken a study of the medium frequency method by itself.In the present paper a fundamental analysis of the first component, the one-DOF fuzzy oscillators, is undertaken. The symbolic manipulation program Mathematica is utilized to gain insight into this component of Soize's fuzzy theory. The resulting Mathematica simulations are easy to use and interpret, and they provide valuable insight into the parameters composing Soize's fuzzy oscillators. It is determined that in many cases of structural acoustics, where there is small damping and a medium to high modal density, the fuzzy mass primarily determines what effect a discrete fuzzy oscillator will have as an attachment.
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 3023-3036 
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    Notes: A new numerical approach has been devised for performing accurate absorbing-emitting non-scattering radiation calculations for Cartesian co-ordinate based problems with one ordinate symmetry using only the solution plane formed by the other two ordinates. To accomplish this, the method makes use of ‘effective intensity rays’ which only exist and have meaning in the solution plane of the problem but which are made, through a special procedure, to contain the information of the third dimension. This novel procedure thus eliminates the problem of solid angles and greatly reduces both the complexity and computational expense involved in the solution of such problems. Yet it can do this without producing loss in accuracy. The approach is ultimately intended for use in combustion problems involving high temperatures and optically thin media. For verification purposes the method is applied to the problem of heat exchange in infinitely long rectangular enclosures and is found to give excellent results over a optical thickness range that includes the optically very thin case.
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 1978-1979 
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 2525-2525 
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 2005-2039 
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    Notes: A method is described which constructs three-dimensional unstructured tetrahedral meshes using the Delaunay triangulation criterion. Several automatic point creation techniques will be highlighted and an algorithm will be presented which can ensure that, given an initial surface triangulation which bounds a domain, a valid boundary conforming assembly of tetrahedra will be produced. Statistics of measures of grid quality are presented for several grids. The efficiency of the proposed procedure reduces the computer time for the generation of realistic unstructured tetrahedral grids to the order of minutes on workstations of modest computational capabilities.
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 2109-2123 
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    Notes: A coupled transient thermoelastic behaviour of an axial-cracked hollow circular cylinder subjected to a sudden heating is investigated in this study. It is shown that surface heating may induce the compressive thermal stress near the inner surface of the cylinder which in turn may force the cracked surfaces to close together. Assuming that the existence of the crack does not alter the temperature distribution, we can divide this problem into two parts and solve it by the principle of superposition. First, the temperature and transient thermal stress distributions along the axisymmetric surface of the imaginary cylinder without crack are obtained by finite element implicit time integration method Secondly, the opposite sense of the stress distributions along the cracked surfaces, which is obtained previously, is treated as the traction boundary conditions; the contact length and contact pressure of the real cracked cylinder are obtained by modified elimination finite element scheme. Finally, we also obtained the normalized stress intensity factor for the crack tip of the cylinder. It is concluded that the effect due to thermoelastic coupling term on stress intensity factor becomes more important for higher coupling coefficient, and this coupling term also results in a small time lag in temperature, thermal stress and stress intensity factor.
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 2149-2150 
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 2699-2700 
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 2583-2608 
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    Notes: In continuum mechanics within specific classes of problems, one- or two-dimensional theories are often simpler to apply than the more complete three-dimensional one. This is, for example, the case of thin bodies, such as plates or shells, which may be studied using appropriate two-dimensionai theories.Within this approach, the reduction of the dimension is traded for a loss of information relative to the motion in the transverse direction. For example, in the case of non-linear material behaviour, classical plasticity plate theories are usually not able to model the effects related to the spreading of plasticity through the cross-section.In the present paper we discuss a generalized plasticity plate model, which can be used to reproduce some of the three-dimensional effects in a two-dimensional setting. We present the continuous and the discrete time model, including both isotropic and kinematic hardening mechanisms; moreover, the form of the tangent matrix consistent with the discrete model is addressed.Finally, some examples (cantilever beam, clamped circular plate and clamped square plate under monotonic and cyclic loading) are studied numerically using a three-dimensional classical plasticity theory, a classical plasticity plate theory and the proposed plate theory. The generalized plasticity plate model matches the three-dimensional response with greater accuracy, than the classical plasticity plate model.
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 2679-2697 
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    Notes: The dynamic behaviour of liquid-filled shells of revolution is investigated considering the soil-structure interaction and the fluid-structure interaction, respectively. In the circumferential direction the loads and variables are approximated by Fourier series. The shell is modelled through shell ring elements including non-linear behaviour, coupled with isoparametric continuum ring elements and special infinite elements for the soil and isoparametric pressure ring elements for the fluid. Transient loadings like earthquake excitation and the non-linearities of the shell and the soil require an analysis in the time domain. To reduce the size of the problem, linear parts of the system are condensed by the substructure technique. The soil region is divided into two parts, a near field permitting non-linearities like plastification or uplifting of the shell, and a far field for the treatment of radiation of energy.The boundary conditions for the shell footing have a strong influence on the distribution of the axial membrane forces and, hence, on the stability limit, which is mostly governed by plastic collapse and caused by the dynamically activated pressure acting on the tank wall. It is shown how the soil properties influence the dynamic stability of the shell under harmonic excitation and under realistic earthquake motion.
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 2701-2702 
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    International Journal for Numerical Methods in Engineering 37 (1994), S. 2717-2733 
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents a Wave Equation Model (WEM) to solve advection dominant Advection-Diffusion (A-D) equation. It is known that the operator-splitting approach is one of the effective methods to solve A-D equation. In the advection step the numerical solution of the advection equation is often troubled by numerical dispersion or numerical diffusion. Instead of directly solving the first-order advection equation, the present wave equation model solves a second-order equivalent wave equation whose solution is identical to that of the first-order advection equation. Numerical examples of 1-D and 2-D with constant flow velocities and varying flow velocities are presented. The truncation error and stability condition of 1-D wave equation model is given. The Fourier analysis of WEM is carried out. The numerical solutions are in good agreement with the exact solutions. The wave equation model introduces very little numerical oscillation. The numerical diffusion introduced by WEM is cancelled by inverse numerical diffusion introduced by WEM as well. It is found that the numerical solutions of WEM are not sensitive to Courant number under stability constraint. The computational cost is economical for practical applications.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 92
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 37 (1994), S. 3825-3842 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A flat shell element based on the free-formulation finite element concept is developed for analysing geometrically non-linear thin composite shells. A corotational form of the updated Lagrangian formulation is utilized. Numerical results for typical validation problems are presented in order to demonstrate the accuracy and validity of this element. These results are obtained by solving the incremental equilibrium equations through the cylindrical arc-length method.
    Additional Material: 13 Ill.
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  • 93
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 37 (1994), S. 3809-3823 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper we investigate the additional storage overhead needed for a parallel implementation of finite element applications. In particular, we compare the storage requirements for the factorization of the sparse matrices that would occur on a parallel processor vs. a uniprocessor. This variation in storage results from the factorization fill-in. We address the question of whether the storage overhead is so large for parallel implementations that it imposes severe limitations on the problem size in contrast to the problems executed sequentially on a uniprocessor. The storage requirements for the parallel implementation are based upon a new ordering scheme, the combination mesh-based scheme. This scheme uses a domain decomposition method which attempts to balance the processors' loads and decreases the interprocessor communication. The storage requirements for the sequential implementation is based upon the minimum degree algorithm. The difference between the two storage requirements corresponds to the storage overhead attributed to the parallel scheme.Experiments were conducted on regular and irregular, 2-D and 3-D problems. The meshes were decomposed into 2-256 subdomains which can be executed on 2-256 processors, respectively. The total storage requirements or fill-in for most of the 2-D problems were less than a factor of two increase over the sequential execution. In contrast, large 3-D problems had zero increase in storage or fill-in over the sequential execution; the fill-in was less for the parallel execution than the sequential execution. Thus, we conclude that the storage overhead attributed to the use of parallel processors will not impose severe constraints on the problem size. Further, for large 3-D applications, the combination mesh-based algorithm does better than minimum degree for reducing the fill-in.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 94
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 37 (1994), S. 3843-3868 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Incrementally objective integration schemes are proposed for the accurate and efficient determination of design sensitivity coefficients (DSCs) for solid mechanics problems with both material and geometrical non-linearities. The derivation of these schemes are based on the direct differentiation of objective schemes that are used in stress analysis for problems of this class. Two widely used objective stress rates, the Jaumann rate and the Green-Naghdi rate, are considered here within the same setting with only minor changes of the integration scheme. Numerical results are presented for a simple shear problem with different material constitutive laws, including a hypoelastic model and a unified isotropic viscoplastic model, for these two objective rates. The numerical results are compared with analytical solutions or direct integration solutions. The close agreement among these solutions demonstrates the accuracy and efficiency of the proposed scheme.
    Additional Material: 13 Ill.
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  • 95
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 37 (1994), S. 3869-3903 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Development of a finite deformation elasto-plasticity model based on the multiplicative decomposition of the deformation gradient is presented and discussed in detail. The formulation presented in this paper includes the derivation of the full set of equations for the Drucker-Prager yield criterion. The equations, which are not available elsewhere, are developed within a framework using a spectral decomposition approach. Further, expressions for the consistent (algorithmic) tangent moduli in the finite strain regime are developed. Since the finite deformation framework employed to obtain the expressions presented here collapses to the classical infinitesimal plasticity framework when the finite strain assumption is no longer necessary, the finite deformation consistent tangent moduli are compared to the consistent tangent moduli valid for use with infinitesimal plasticity. Validation of the implemented finite deformation elasto-plastic Drucker-Prager model is performed through the solution of the concrete slump test. Comparisons between an existing approximate analytical solution and experimental data are presented, and results are discussed in detail.
    Additional Material: 11 Ill.
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  • 96
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 37 (1994), S. 3905-3919 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents a parallel implementation of the boundary element method for MIMD computer architectures to determine the effective properties of two heterogeneous physical systems. The first physical system is comprised of spheres sedimenting in a viscous fluid at low Reynolds numbers. The effective property is characterized by the hindered settling function which is a measure of the average sedimentation velocity. The second physical system is a short-fibre reinforced composite. The effective property for this system is the composite modulus. The determination of effective properties of heterogeneous media requires performing statistical analyses of several realizations of physical systems based on defining characteristics of the media. The boundary element method is particularly well suited for studying such systems because of the simplification in the discretization associated with the method. However, as the number of heterogeneities to be modeled is increased so are the computational demands. Parallel computation offers the opportunity to model systems of greater complexity. We discuss a parallel boundary element formulation based on the torus-wrap mapping. In this approach, blocks of the coefficient matrix associated with the discretized boundary element equations are assigned to processors as opposed to more traditional parallel boundary element implementations where rows or columns are assigned to processors. The torus-wrap mapping can be shown to minimize communication volume between processors during the LU factorization. Therefore, the present formulation scales well with increases in the number of processors.
    Additional Material: 5 Ill.
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  • 97
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 37 (1994), S. 4263-4284 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The use of inconsistent displacement fields for Mindlin plate elements causes unmatched coefficients to appear in shear strain interpolations. The role of the numerical integration order in relation to these unmatched coefficients, and the existence of optimal stress points are explained through the use of the reduced minimization concept. This concept makes it possible to test whether assumed displacement fields or shear strain fields result in inconsistent strain fields which contain spurious constraints. We have included applications of reduced minimization to the conventional C0-continuous elements, which employ reduced integration, and to quadrilateral Mindlin plate elements of Hinton and Huang to demonstrate how these elements alleviate shear locking.
    Additional Material: 4 Ill.
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  • 98
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 37 (1994), S. 715-716 
    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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  • 99
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 37 (1994) 
    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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  • 100
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 37 (1994), S. 693-713 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A method using techniques of computational geometry for generating tetrahedral finite element meshes in three-dimensional polyhedral regions is presented. The input to the method consists of the boundary faces of the polyhedral region and possibly internal and hole interfaces, plus the desired number of tetrahedra and other scalar parameters. The region is decomposed into convex polyhedra in two stages so that tetrahedra of one length scale can be generated in each subregion. A mesh distribution function, which is either automatically constructed from the first-stage convex polyhedron decomposition or supplied by the user, is used to determine the tetrahedron sizes in the subregions. Then a boundary-constrained triangulation is constructed in each convex polyhedron, with local transformations being used to improve the quality of the tetrahedra. Experimental results from triangulations of three regions are provided.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
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