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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 7 (1995), S. 2831-2847 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This work focuses on subgrid-scale (SGS) modeling for finite-difference large-eddy simulations, employing filters in physical space. When a filter in physical space is used, an overlap is allowed between the unresolved and the resolved scales. For such a filter, all the three terms in the classical decomposition of the SGS stress tensor are present: the Leonard and cross-terms, due to the overlap between scales, and the true SGS Reynolds tensor, expressing the pure effect of the small scales. A dynamic subgrid-scale stress model is proposed, for finite-difference large-eddy simulation of incompressible and compressible flows in which the Leonard and cross-parts of the SGS stress tensor are assumed to be proportional to the resolved part (the "modified Leonard term''), which is computed explicity. The SGS Reynolds stress is modeled by the eddy-viscosity Smagorinsky model. The two unknown parameters in this model are computed dynamically, as in Germano et al. [Phys. Fluids A 3, 1790 (1991)], but using a least squares technique. The model is tested using direct numerical simulation data for fully developed turbulent incompressible flows in presence of solid boundaries and free surfaces, and for compressible homogeneous turbulence. A "box filter'' in physical space is used. Other SGS models are also tested, viz. the dynamic model of Germano et al. (DSM), and its compressible extension by Moin et al. [Phys. Fluids A 3, 2746 (1991)], and the dynamic mixed model in Zang et al. [Phys. Fluids A 5, 3186 (1993)] (DMM) and its compressible version developed here. Results on the behavior of the different models with regard to energy exchanges and correlation with the exact SGS stresses are presented for different filter widths. In particular high correlation is found between the modified Leonard and cross-terms thus justifying the basic assumption made in the model. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 13 (2001), S. 2728-2731 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A parametrization of the form drag due to airflow over sinusoidal wavy surfaces in the presence of significant flow separation is investigated; it is based on a bluff-body analogy. To this aim, the results of large-eddy simulations carried out for various Reynolds numbers and wave slopes are used, together with the data from experiments and other simulations available in the literature. It is shown that, as a first approximation, the drag coefficient may be considered independent of the wave slope and Reynolds number. The value obtained here for rigid sinusoidal waves is close to that computed for wind-ruffled breaking paddle waves. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 10 (1998), S. 3020-3022 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A priori tests are performed to study the effect of the filter on the subgrid scale term in large-eddy simulation. Several filters, corresponding to finite-difference schemes of different order of accuracy, are applied to direct numerical simulation data. In particular, the effect of the filter on the importance of the Leonard term and on its correlation with the subgrid scale stress is investigated to evaluate, for different numerical schemes, the capabilities of subgrid scale models accounting for this term, such as scale-similarity or mixed models. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 9 (1997), S. 2405-2419 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper describes large-eddy simulations of decaying turbulence in an open channel, using different dynamic subgrade-scale models, viz. the dynamic model of Germano et al. [Phys. Fluids A 3, 1790 (1991)] (DSM), the dynamic mixed model in Zang et al. [Phys. Fluids A 5, 3186 (1993)] (DMM), and the dynamic two-parameter model of Salvetti and Banerjee [Phys. Fluids 7, 2831 (1995)] (DTM). These models are incorporated in a finite-volume solver of the Navier–Stokes equations. A direct numerical simulation of this flow conducted by Pan and Banerjee [Phys. Fluids 7, 1649 (1995)] showed that near the free surface turbulence has a quasi-two-dimensional behavior. Moreover, the quasi-two-dimensional region increases in thickness with the decay time, although the structure remains three-dimensional in the central regions of the flow. The results of the large-eddy simulations show that both the DMM and the DTM are able to reproduce the features of the decay process observed in the direct simulation and to handle the anisotropic nature of the flow. Nevertheless, the addition of the second model coefficient in the DTM improves the agreement with the direct simulation. When the DSM is used, significant discrepancies are observed between the large-eddy and the direct simulations during the decay process at the free surface. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Journal of Computational Physics 60 (1985), S. 467-477 
    ISSN: 0021-9991
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Computer Science , Physics
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature medicine 3 (1997), S. 1176-1176 
    ISSN: 1546-170X
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] To the editor — Twin registries are considered unique research resources1. Concordance rate studies in monozygotic vs. dizygotic twins and biological studies in identical twins (concordant or discordant for a disease) substantially contribute to the definition of genetic and non-genetic ...
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-1084
    Keywords: Key words: Rectal cancer – Therapeutic radiology – Tumour staging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. Surgical treatment of carcinoma of the distal third of the rectum with anal sphincter preservation is increasingly used in accredited cancer centers. This study aimed to evaluate the diagnostic usefulness of radiological investigations in the management of patients who had undergone resection with coloanal anastomosis for carcinoma of the rectum, in the immediate post-operative period, during closure of the protective colostomy and in the follow-up of symptomatic recanalized patients. A total of 175 patients who had undergone total rectal resection with end-to-side anastomosis for carcinoma of the distal third of the rectal ampulla, most of whom had received postoperative radiotherapy, were evaluated radiologically. In the postoperative period radiological investigation was ordered only for symptomatic patients to detect pathology of the anastomosis and the pouch sutures and was used direct film abdominal radiography and contrast-enhanced radiography of the rectal stump with a water-soluble radio-opaque agent. Before closure of the colostomy, 2 months after rectal excision or approximately 4 months after if postoperative radiotherapy was given, the anastomosis and pouch of all patients, even asymptomatic ones, were studied with water-soluble contrast enema to check for normal canalization. In the follow-up after recanalization radiological examinations were done to complete the study of the large intestine if the endoscopist was not able to examine it up to the cecum. Of the 175 patients examined radiologically during the postoperative period and/or subsequent follow-up, 95 showed no pathological findings. Seventy-nine patients had fistulas of the coloanal anastomosis or the pouch, 23 of which supplied a presacral collection. In the absence of severe sepsis, the only therapeutic measures were systemic antibiotics and washing of the surgical catheters to maintain efficient operation. In 2 patients in whom transanal drainage was performed radiologically the fistula was cured in 1 week. In 36 cases of cicatricial stenosis, 17 at the coloanal anastomosis and 19 at the pouch, radiological examination always detected the lesion, correctly defining its anatomical characteristics, nature and extension. Of the 19 cases of stenosis treated radiologically, 15 recovered an adequate intestinal calibre for normal evacuation. During follow-up of the 175 patients operated on, 21 cases of recurrence were detected. Radiological examination was requested as the first investigation in only one of these cases, for a patient with subocclusion. Radiological investigations in patients who have undergone coloanal anastomosis are of real diagnostic value in the immediate post-operative period, during closure of the protective colostomy and in the follow-up of symptomatic recanalized patients.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    European radiology 5 (1995), S. 213-216 
    ISSN: 1432-1084
    Keywords: CT, technique ; Neoplasms, staging ; Rectum, CT ; Rectum, neoplasms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The use of a balloon catheter to distend the rectum for pelvic CT in patients with rectal cancer is described. The 20-cm long balloon, inserted over a 12F catheter and inflated with 180-200 ml of water, is simple to use, well tolerated by patients and allows high-quality CT scans. Preliminary results of the presurgical staging of rectal cancer by CT with rectal balloon in a series of 15 patients show a high accuracy when comapred with the pathological findings: involvement of perirectal nodes and adjacent structures was correctly identified in all cases, while CT overestimated the invasion of perirectal fat in two cases, due to the impossibility of distinguishing neoplastic from inflammatorry tissue. The operability statement (site and dimensions of the tumour) allowed correct surgical planning in all cases.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    European radiology 5 (1995), S. 213-216 
    ISSN: 1432-1084
    Keywords: CT, technique ; Neoplasms, staging ; Rectum, CT ; Rectum, neoplasms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The use of a balloon catheter to distend the rectum for pelvic CT in patients with rectal cancer is described. The 20-cm long balloon, inserted over a 12F catheter and inflated with 180-200 ml of water, is simple to use, well tolerated by patients and allows high-quality CT scans. Preliminary results of the presurgical staging of rectal cancer by CT with rectal balloon in a series of 15 patients show a high accuracy when comapred with the pathological findings: involvement of perirectal nodes and adjacent structures was correctly identified in all cases, while CT overestimated the invasion of perirectal fat in two cases, due to the impossibility of distinguishing neoplastic from inflammatorry tissue. The operability statement (site and dimensions of the tumour) allowed correct surgical planning in all cases.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1432-0509
    Keywords: Key words: Enteral feeding—Gastrojejunostomy—Gastrostomy—Interventional procedure, utilization—Stomach, interventional procedure.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Background: Percutaneous gastrostomy is generally performed for permanent enteral nutrition or gastric decompression. Methods: In our series of oncologic patients, percutaneous gastrostomy was also used temporarily in some patients for enteral nutrition while awaiting functional recovery of swallowing, in preparation for surgery, or for the treatment of fistulas in the upper digestive tract. Fifty-one procedures were performed in 50 patients: 42 for feeding, eight for decompression, and one for transgastric drainage of a duodenal fistula. Results: Of the 35 patients treated for permanent enteral nutrition, four are still alive, with a total survival time of 2167 days. In three patients, gastrostomy was performed for temporary feeding and was removed once the ability to swallow was restored. In four patients, it was created to restore metabolic balance before surgery. In the patient with a duodenal fistula, healing was achieved in 19 days. The seven patients in whom the procedure was performed for decompression survived for a mean of 19.2 days. There was only one major procedure-related complication (peritonitis). Conclusions: Percutaneous gastrostomy is a safe, low-cost method that allows the patient to maintain essential nutrition without the discomfort of a nasogastic tube and therefore warrants wider and earlier use. We feel that its application should also be extended to temporary feeding of patients about to undergo long courses of chemotherapy and radiotherapy, which can lead to severe deterioration of nutritional status.
    Type of Medium: Electronic Resource
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