Home About us Contact
|
Home About us Contact | ||
|
|
||
Likely Reason (likely + reason)
Selected AbstractsDynamics of unsaturated soils using various finite element formulationsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2009Nadarajah Ravichandran Abstract Unsaturated soils are three-phase porous media consisting of a solid skeleton, pore liquid, and pore gas. The coupled mathematical equations representing the dynamics of unsaturated soils can be derived based on the theory of mixtures. Solution of these fully coupled governing equations for unsaturated soils requires tremendous computational resources because three individual phases and interactions between them have to be taken into account. The fully coupled equations governing the dynamics of unsaturated soils are first presented and then two finite element formulations of the governing equations are presented and implemented within a finite element framework. The finite element implementation of all the terms in the governing equations results in the complete formulation and is solved for the first time in this paper. A computationally efficient reduced formulation is obtained by neglecting the relative accelerations and velocities of liquid and gas in the governing equations to investigate the effects of fluid flow in the overall behavior. These two formulations are used to simulate the behavior of an unsaturated silty soil embankment subjected to base shaking and compared with the results from another commonly used partially reduced formulation that neglects the relative accelerations, but takes into account the relative velocities. The stress,strain response of the solid skeleton is modeled as both elastic and elastoplastic in all three analyses. In the elastic analyses no permanent deformations are predicted and the displacements of the partially reduced formulation are in between those of the reduced and complete formulations. The frequency of vibration of the complete formulation in the elastic analysis is closer to the predominant frequency of the base motion and smaller than the frequencies of vibration of the other two analyses. Proper consideration of damping due to fluid flows in the complete formulation is the likely reason for this difference. Permanent deformations are predicted by all three formulations for the elastoplastic analyses. The complete formulation, however, predicts reductions in pore fluid pressures following strong shaking resulting in somewhat smaller displacements than the reduced formulation. The results from complete and reduced formulations are otherwise comparable for elastoplastic analyses. For the elastoplastic analysis, the partially reduced formulation leads to stiffer response than the other two formulations. The likely reason for this stiffer response in the elastoplastic analysis is the interpolation scheme (linear displacement and linear pore fluid pressures) used in the finite element implementation of the partially reduced formulation. Copyright © 2008 John Wiley & Sons, Ltd. [source] Evidence for an ice-free Wrangel Island, northeast Siberia during the Last Glacial MaximumBOREAS, Issue 3 2005LYN GUALTIERI 10Be and 26Al surface exposure ages from 22 tors and bedrock samples from Wrangel Island, northeast Siberia, indicate that the East Siberian and Chukchi shelves were ice-free during the Last Glacial Maximum (LGM). The paucity of glacial landforms and deposits, the absence of erratics and the presence of radiocarbon dates on plant and mammal fossils that span the LGM suggest that Wrangel Island also remained free of extensive glacial ice during the LGM. The lack of moisture due to the continental climate on the emergent Bering Land Bridge is the most likely reason for limited ice in this part of the Arctic. Alternative interpretations regarding the age and origin of ,glaciogenic' bedforms on the Chukchi shelf should be considered. [source] Sources of character conflict in a clade of water striders (Heteroptera: Gerridae)CLADISTICS, Issue 6 2003Jakob Damgaard Incongruence among trees reconstructed with different data may stem from historical (gene tree-species tree conflict) or process (character change biases) phenomena. Regardless of the source, incongruent data, as determined with "global" measures of homoplasy, have often been excluded from parsimony analysis of the combined data. Recent studies suggest that these homoplasy measures do not predict the contribution of each character to overall tree structure. Branch support measures identify, on a character to node basis, sources of support and conflict resulting from a simultaneous analysis of the data. We implement these branch support measures to identify sources of character conflict in a clade of water striders consisting of Gerris Fabricius, Aquarius Schellenberg, and Limnoporus Stål species. Separate analyses of morphology, mitochondrial cytochrome oxidase I (COI), large mitochondrial ribosomal subunit (16SrRNA), and elongation factor-1, (EF-1,) data resulted in cladograms that varied in resolution and topological concordance. Simultaneous analysis of the data resulted in two trees that were unresolved for one node in a strict consensus. The topology agreed with current classification except for the placements of Aquarius chilensis and the Aquarius remigis species group closer to Gerris than to congeneric species. Branch support measures indicated that support derived from each data set varied among nodes, but COI had an overall negative effect on branch support. However, Spearman rank correlation of partitioned branch support values indicated no negative associations of branch support between any data sets and a positive association between EF-1, and 16SrRNA. Thus incongruence among data sets was not drastic and the gene-tree versus species tree phenomenon was not implicated. Biases in character change were a more likely reason for incongruence, although saturation curves and incongruence length difference for COI indicated little potential for homoplasy. However, a posteriori inspection of COI nucleotide change with reference to the simultaneous analysis tree revealed AT and codon biases. These biases were not associated with branch support measures. Therefore, it is difficult to predict incongruence or identify its cause. Exclusion of data is ill advised because every character is potentially parsimony informative. [source] Should ileal pouch,anal anastomosis include mucosectomy?COLORECTAL DISEASE, Issue 5 2007W. M. Chambers Abstract Objective, Debate exists as to the benefits of performing mucosectomy as part of pouch surgery for ulcerative colitis (UC) and familial adenomatous polyposis (FAP). Whilst mucosectomy results in a more complete removal of diseased mucosa, this benefit may be at the price of poorer function. We examined these issues. Method, Using Medline, Embase, Ovid and Cochrane database searches papers were identified relating to the outcome following pouch surgery with and without mucosectomy. Potential reasons for functional problems were investigated, as were rates of ,cuffitis', dysplasia, polyposis and cancer in the ileal pouch and anal canal. Results, The available evidence suggests that performing a mucosectomy leads to a worse functional outcome. Meta-analysis suggested that nighttime seepage of stool and resting and squeeze pressure were worse after mucosectomy. The most likely reason for functional impairment following pouch surgery was the degree of anal manipulation. Mucosectomy does seem to confer benefit in terms of disease control but this benefit does not reach statistical significance. Conclusion, Stapled anastomosis avoiding mucosectomy is the approach of choice for ileal pouch anal anastomosis because this leads to superior functional outcome. Performing mucosectomy results in some clinical benefits in terms of lower rates of inflammation and dysplasia in the retained mucosa in UC patients and lower rates of cuff polyposis in FAP patients. However, on the basis of available evidence mucosectomy is only indicated in those cases where the patient is at a high risk of disease in the retained rectal cuff. [source] Sex roles, parental effort and offspring desertion in the monogamous Eurasian Curlew Numenius arquataIBIS, Issue 3 2001DAVE CURRIE The reasons for female desertion of offspring and the evolution of predominantly male care among monogamous bird species are not clearly understood. We studied parental effort during the incubation and chick rearing periods in the Eurasian Curlew Numenius arquata in western Finland, and compared timing of brood desertion with other populations in Europe. Males and females contributed equally to incubation and showed no differences in the intensity of mobbing behaviour towards a potential nest predator (stuffed crow) shortly after hatching. However, females deserted their offspring approximately halfway through the brooding period (c. 16 d after hatching), while males remained with chicks until independence (c. 35 d). Females with late-laid clutches deserted their offspring sooner after hatching than those with clutches produced earlier in the season. Curlew females deserted younger chicks in northeast Europe, where laying dates were later, breeding seasons shorter and migration distances were longer, than in western and central Europe. We suggest that the most likely reasons for offspring desertion by females may be associated with increased female survivorship and maintenance of pairbond between years. [source] Talking Tough, Acting Coy: What Happened to the Anti,Social Behaviour Order?THE HOWARD JOURNAL OF CRIMINAL JUSTICE, Issue 5 2002Elizabeth Burney The government blames local authorities for using anti,social behaviour orders too little. Are they really to be blamed? What are the likely reasons for the very patchy support of the ASBO? The article examines a range of explanations, including that local crime and disorder partnerships, paradoxically having been told by the government to consult and innovate, are adopting a variety of other methods for suppressing anti,social conduct. Patterns of ASBO usage are examined, revealing that it is essentially yet another tool for dealing with persistent young offenders. Legislation for extending the scope and availability of ASBOs is critically appraised. [source] | ||||||||||