178 research outputs found
Nesiritide: Harmful or Harmless?
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90328/1/phco.26.10.1465.pd
Global existence of solutions to 2-D Navier-Stokes flow with non-decaying initial data in half-plane
We investigate the Navier-Stokes initial boundary value problem in the
half-plane with initial data
or with non decaying initial data . We introduce a technique that allows to solve the two-dimesional
problem, further, but not least, it can be also employed to obtain weak
solutions, as regards the non decaying initial data, to the three-dimensional
Navier-Stokes IBVP. This last result is the first of its kind
Continuous, Semi-discrete, and Fully Discretized Navier-Stokes Equations
The Navier--Stokes equations are commonly used to model and to simulate flow
phenomena. We introduce the basic equations and discuss the standard methods
for the spatial and temporal discretization. We analyse the semi-discrete
equations -- a semi-explicit nonlinear DAE -- in terms of the strangeness index
and quantify the numerical difficulties in the fully discrete schemes, that are
induced by the strangeness of the system. By analyzing the Kronecker index of
the difference-algebraic equations, that represent commonly and successfully
used time stepping schemes for the Navier--Stokes equations, we show that those
time-integration schemes factually remove the strangeness. The theoretical
considerations are backed and illustrated by numerical examples.Comment: 28 pages, 2 figure, code available under DOI: 10.5281/zenodo.998909,
https://doi.org/10.5281/zenodo.99890
Cultural specificity versus institutional universalism: a critique of the National Integrity System (NIS) methodology
This article provides an assessment and critique of the National Integrity System approach and methodology, informed by the experience of conducting an NIS review in Cambodia. It explores four key issues that potentially undermine the relevance and value of NIS reports for developing democracies: the narrowly conceived institutional approach underpinning the NIS methodology; the insufficient appreciation of cultural distinctiveness; a failure properly to conceptualise and articulate the very notion of ‘integrity’; and an over emphasis on compliance-based approaches to combating corruption at the expense of the positive promotion of integrity. The article seeks to offer some pointers to how the NIS approach could be adapted to broaden its conceptualisation of institutions and integrity, and thereby provide reports that are more theoretically informed as well as being more constructive and actionable
Quantum value indefiniteness
The indeterministic outcome of a measurement of an individual quantum is
certified by the impossibility of the simultaneous, definite, deterministic
pre-existence of all conceivable observables from physical conditions of that
quantum alone. We discuss possible interpretations and consequences for quantum
oracles.Comment: 19 pages, 2 tables, 2 figures; contribution to PC0
A posteriori error estimates for fully discrete schemes for the time dependent Stokes problem
The final publication is available at Springer via http://dx.doi.org/10.1007/s10092-018-0259-2This work is devoted to a posteriori error analysis of fully discrete finite element approximations to the time dependent Stokes system. The space discretization is based on popular stable spaces, including Crouzeix–Raviart and Taylor–Hood finite element methods. Implicit Euler is applied for the time discretization. The finite element spaces are allowed to change with time steps and the projection steps include alternatives that is hoped to cope with possible numerical artifices and the loss of the discrete incompressibility of the schemes. The final estimates are of optimal order in L∞(L2) for the velocity error
Utilisation of an operative difficulty grading scale for laparoscopic cholecystectomy
Background
A reliable system for grading operative difficulty of laparoscopic cholecystectomy would standardise description of findings and reporting of outcomes. The aim of this study was to validate a difficulty grading system (Nassar scale), testing its applicability and consistency in two large prospective datasets.
Methods
Patient and disease-related variables and 30-day outcomes were identified in two prospective cholecystectomy databases: the multi-centre prospective cohort of 8820 patients from the recent CholeS Study and the single-surgeon series containing 4089 patients. Operative data and patient outcomes were correlated with Nassar operative difficultly scale, using Kendall’s tau for dichotomous variables, or Jonckheere–Terpstra tests for continuous variables. A ROC curve analysis was performed, to quantify the predictive accuracy of the scale for each outcome, with continuous outcomes dichotomised, prior to analysis.
Results
A higher operative difficulty grade was consistently associated with worse outcomes for the patients in both the reference and CholeS cohorts. The median length of stay increased from 0 to 4 days, and the 30-day complication rate from 7.6 to 24.4% as the difficulty grade increased from 1 to 4/5 (both p < 0.001). In the CholeS cohort, a higher difficulty grade was found to be most strongly associated with conversion to open and 30-day mortality (AUROC = 0.903, 0.822, respectively). On multivariable analysis, the Nassar operative difficultly scale was found to be a significant independent predictor of operative duration, conversion to open surgery, 30-day complications and 30-day reintervention (all p < 0.001).
Conclusion
We have shown that an operative difficulty scale can standardise the description of operative findings by multiple grades of surgeons to facilitate audit, training assessment and research. It provides a tool for reporting operative findings, disease severity and technical difficulty and can be utilised in future research to reliably compare outcomes according to case mix and intra-operative difficulty
Recommendations for increasing the use of HIV/AIDS resource allocation models
The article of record as published may be found at: http://dx.doi.org/10.1186/1471-2458-9-S1-S8Background: Resource allocation models have not had a substantial impact on HIV/AIDS
resource allocation decisions in spite of the important, additional insights they may provide. In this paper, we highlight six difficulties often encountered in attempts to implement such models in policy settings; these are: model complexity, data requirements, multiple stakeholders, funding
issues, and political and ethical considerations. We then make recommendations as to how each of these difficulties may be overcome.
Results: To ensure that models can inform the actual decision, modellers should understand the environment in which decision-makers operate, including full knowledge of the stakeholders' key issues and requirements. HIV/AIDS resource allocation model formulations should be contextualized and sensitive to societal concerns and decision-makers' realities. Modellers should provide the required education and training materials in order for decision-makers to be
reasonably well versed in understanding the capabilities, power and limitations of the model.
Conclusion: This paper addresses the issue of knowledge translation from the established
resource allocation modelling expertise in the academic realm to that of policymaking
Distribution of the anther-smut pathogen Microbotryum on species of the Caryophyllaceae
Artículo de publicación ISIUnderstanding disease distributions is of fundamental and applied importance,
yet few studies benefit from integrating broad sampling with ecological and phylogenetic
data. Here, anther-smut disease, caused by the fungus Microbotryum,
was assessed using herbarium specimens of Silene and allied genera of the
Caryophyllaceae.
• A total of 42 000 herbarium specimens were examined, and plant geographical
distributions and morphological and life history characteristics were tested as correlates
of disease occurrence. Phylogenetic comparative methods were used to
determine the association between disease and plant life-span.
• Disease was found on 391 herbarium specimens from 114 species and all continents
with native Silene. Anther smut occurred exclusively on perennial plants,
consistent with the pathogen requiring living hosts to overwinter. The disease was
estimated to occur in 80% of perennial species of Silene and allied genera. The
correlation between plant life-span and disease was highly significant while
controlling for the plant phylogeny, but the disease was not correlated with
differences in floral morphology.
• Using resources available in natural history collections, this study illustrates how
disease distribution can be determined, not by restriction to a clade of susceptible
hosts or to a limited geographical region, but by association with host life-span, a
trait that has undergone frequent evolutionary transitions.We acknowledge grant support from the John
Simon Guggenheim Memorial Foundation and the
National Science Foundation (DEB-0747222) to MEH,
the National Science Foundation Minority Postdoctoral
Fellowship (DBI-0706721) to JIMA, University of Chile
awards PFB-23 and ICM P05-002 to MTKA, and The
Swedish Research Council for Environment, Agricultural
Sciences and Spatial Planning (FORMAS) support to BO,
and Royal Society Incoming Fellowship and Center for
Infection, Immunity, and Evolution Advanced Fellowship
to ABP
The Ischemic Stroke Genetics Study (ISGS) Protocol
BACKGROUND: The molecular basis for the genetic risk of ischemic stroke is likely to be multigenic and influenced by environmental factors. Several small case-control studies have suggested associations between ischemic stroke and polymorphisms of genes that code for coagulation cascade proteins and platelet receptors. Our aim is to investigate potential associations between hemostatic gene polymorphisms and ischemic stroke, with particular emphasis on detailed characterization of the phenotype. METHODS/DESIGN: The Ischemic Stroke Genetic Study is a prospective, multicenter genetic association study in adults with recent first-ever ischemic stroke confirmed with computed tomography or magnetic resonance imaging. Patients are evaluated at academic medical centers in the United States and compared with sex- and age-matched controls. Stroke subtypes are determined by central blinded adjudication using standardized, validated mechanistic and syndromic classification systems. The panel of genes to be tested for polymorphisms includes β-fibrinogen and platelet glycoprotein Ia, Iba, and IIb/IIIa. Immortalized cell lines are created to allow for time- and cost-efficient testing of additional candidate genes in the future. DISCUSSION: The study is designed to minimize survival bias and to allow for exploring associations between specific polymorphisms and individual subtypes of ischemic stroke. The data set will also permit the study of genetic determinants of stroke outcome. Having cell lines will permit testing of future candidate risk factor genes
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