1,538 research outputs found
Risks and Benefits of Using a Commercially Available Ventricular Assist Device for Failing Fontan Cavopulmonary Support: A Modeling Investigation
Fontan patients often develop circulatory failure and are in desperate need
of a therapeutic solution. A blood pump surgically placed in the cavopulmonary
pathway can substitute the function of the absent sub-pulmonary ventricle by
generating a mild pressure boost. However, there is currently no commercially
available device designed for the cavopulmonary application; and the risks and
benefits of implanting a ventricular assist device (VAD) originally designed
for the left ventricular application on the right circulation of failing Fontan
patients is not yet clear. Moreover, further research is needed to compare the
hemodynamics between the two clinically-considered surgical configurations
(Full Support and IVC Support) for cavopulmonary assist, with Full and IVC
Support corresponding to the entire venous return or only the inferior venous
return, respectively, being routed through the VAD. In this study, we used a
numerical model of the failing Fontan physiology to evaluate the Fontan
hemodynamic response to a left VAD during the IVC and Full supports. We
observed that during the Full support the VAD improved the cardiac output while
maintaining blood pressures within safe ranges, and lowered the IVC pressure to
<15mmHg; however, we found a potential risk of lung damage at higher pump
speeds due to the excessive pulmonary pressure elevation. IVC support the other
hand, did not benefit the hemodynamics of the example failing Fontan patients,
resulting in the superior vena cava pressure increasing to an unsafe level of
>20 mmHg. The findings in this study may be helpful to surgeons for recognizing
the risks of a cavopulmonary VAD and developing coherent clinical strategies
for the implementation of cavopulmonary support
Evidence of package trading in a mature multi-species ITQ market
In multi-species fisheries managed under ITQs, the existence of joint production may lead to complex catch-quota balancing issues. Previous modelling and experimental research suggest that, in such fisheries, some fishers may benefit from the ability to trade packages of fishing quotas, rather than fulfil their quota needs by simultaneously bidding on separate single-species quota markets. This note presents evidence of naturally occurring package trades in a real fishery. Based on this evidence, we suggest that further empirical and modelling research is required on the potential and limitations of package quota trading in mixed fisheries managed with ITQs. © 2014
From Systematic Reviews to Clinical Recommendations for Evidence-Based Health Care: Validation of Revised Assessment of Multiple Systematic Reviews (R-AMSTAR) for Grading of Clinical Relevance
Research synthesis seeks to gather, examine and evaluate systematically research reports that converge toward answering a carefully crafted research question, which states the problem patient population, the intervention under consideration, and the clinical outcome of interest. The product of the process of systematically reviewing the research literature pertinent to the research question thusly stated is the “systematic review”
Dependence of the flux creep activation energy on current density and magnetic field for MgB2 superconductor
Systematic ac susceptibility measurements have been performed on a MgB
bulk sample. We demonstrate that the flux creep activation energy is a
nonlinear function of the current density , indicating a
nonlogarithmic relaxation of the current density in this material. The
dependence of the activation energy on the magnetic field is determined to be a
power law , showing a steep decline in the activation
energy with the magnetic field, which accounts for the steep drop in the
critical current density with magnetic field that is observed in MgB. The
irreversibility field is also found to be rather low, therefore, the pinning
properties of this new material will need to be enhanced for practical
applications.Comment: 11 pages, 6 figures, Revtex forma
Wave functions for arbitrary operator ordering in the de Sitter minisuperspace approximation
We derive exact series solutions for the Wheeler-DeWitt equation
corresponding to a spatially closed Friedmann-Robertson-Walker universe with
cosmological constant for arbitrary operator ordering of the scale factor of
the universe. The resulting wave functions are those relevant to the
approximation which has been widely used in two-dimensional minisuperspace
models with an inflationary scalar field for the purpose of predicting the
period of inflation which results from competing boundary condition proposals
for the wave function of the universe. The problem that Vilenkin's tunneling
wave function is not normalizable for general operator orderings, is shown to
persist for other values of the spatial curvature, and when additional matter
degrees of freedom such as radiation are included.Comment: 12 pages, revTeX-3.
Macrophage migration inhibitory factor stimulated by Helicobacter pylori increases proliferation of gastric epithelial cells
AIM: Helicobacter pylori (H pylori) is associated with increased gastric inflammatory and epithelial expression of macrophage migration inhibitory factor (MIF) and gastric epithelial cell proliferation. This study aimed at determining whether H pylori directly stimulates release of MIF in monocytes, whether the cag pathogenicity island (PAI) is involved for this function, and whether MIF stimulated by H pylori increases gastric epithelial cell proliferation in vitro. METHODS: A cytotoxic wild-type H pylori strain (TN2)and its three isogenic mutants (TN2△cag, TN2△cagA and TN2△cagE) were co-cultured with cells of a human monocyte cell line, THP-1, for 24 h at different organism/cell ratios. MIF in the supernatants was measured by an ELISA. Cells of a human gastric cancer cell line, MKN45, were then co-cultured with the supernatants, with and without monoclonal anti-MIF antibody for 24 h. The cells were further incubated for 12 h after addition of (3)H-thymidine, and the levels of incorporation of (3)H-thymidine were measured with a liquid scintillation counter. RESULTS: The wild-type strain and the isogenic mutants, TN2△cagA and TN2△cagE, increased MIF release at organism/cell ratios of 200/1 and 400/1, but not at the ratios of 50/1 and 100/1. However, the mutant TN2△cag did not increase the release of MIF at any of the four ratios. (3)H-thymidine readings for MKN-45 cells were significantly increased with supernatants derived from the wild-type strain and the mutants TN2△cagA and TN2△cagE, but not from the mutant TN2△cag. Moreover, in the presence of monoclonal anti-MIF antibody, the stimulatory effects of the wild-type strain on cell proliferation disappeared. CONCLUSION: H pylori stimulates MIF release in monocytes, likely through its cag PAI, but not related to cagA or cagE. H pylori-stimulated monocyte culture supernatant increases gastric cell proliferation, which is blocked by anti-MIF antibody, suggesting that MIF plays an important role in H pylori-induced gastric epithelial cell proliferation
Modified f(G) gravity models with curvature-matter coupling
A modified f(G) gravity model with coupling between matter and geometry is
proposed, which is described by the product of the Lagrange density of the
matter and an arbitrary function of the Gauss-Bonnet term. The field equations
and the equations of motion corresponding to this model show the
non-conservation of the energy-momentum tensor, the presence of an extra-force
acting on test particles and the non-geodesic motion. Moreover, the energy
conditions and the stability criterion at de Sitter point in the modified f(G)
gravity models with curvature-matter coupling are derived, which can degenerate
to the well-known energy conditions in general relativity. Furthermore, in
order to get some insight on the meaning of these energy conditions, we apply
them to the specific models of f(G) gravity and the corresponding constraints
on the models are given. In addition, the conditions and the candidate for
late-time cosmic accelerated expansion in the modified f(G) gravity are studied
by means of conditions of power-law expansion and the equation of state of
matter less than -1/ 3 .Comment: 13 pages, 4 figure
Hot and repulsive traffic flow
We study a message passing model, applicable also to traffic problems. The
model is implemented in a discrete lattice, where particles move towards their
destination, with fluctuations around the minimal distance path. A repulsive
interaction between particles is introduced in order to avoid the appearance of
traffic jam. We have studied the parameter space finding regions of fluid
traffic, and saturated ones, being separated by abrupt changes. The improvement
of the system performance is also explored, by the introduction of a
non-constant potential acting on the particles. Finally, we deal with the
behavior of the system when temporary failures in the transmission occurs.Comment: 22 pages, uuencoded gzipped postscript file. 11 figures include
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