155 research outputs found
A Family of Interleaved High Step-Up DC-DC Converters by Integrating a Voltage Multiplier and an Active Clamp Circuits
A family of interleaved current-fed high step-up dc-dc converters are
introduced and analyzed here by combining a voltage multiplier (VM) and an
active clamp circuit for high-voltage high-power applications. Low input
currents and output voltages ripples values and high voltage-gains
characteristics of these converters make them suitable for lots of dc-dc
applications. All power devices operate entirely under soft switching
conditions, even when wide load and input voltage variations are applied. Thus,
they can be designed at high switching frequencies to reduce passive components
sizes to achieve high-power density, one of the main targets of the power
electronics researches. Also, their input and output ports common ground
simplifies the gate-drives and control circuits. To verify the given analyses
and simulations, a 120-320 V to 1 kV, 50-1300 W three-stage two-leg prototype
converter has been implemented at 100 kHz. Based on the experimental results,
maximum efficiency of 96.5% is achieved.Comment: 14 pages, 15 figure
Impedance Probe to Measure Local Gas Volume Fraction and Bubble Velocity in a Bubbly Liquid
We have developed a dual impedance-based probe that can simultaneously measure the bubble velocity and the gas volume fraction in length scales comparable to the bubble diameter. The accurate determination of the profiles is very important for comparisons with existing theories that describe the rheological behavior of bubbly liquids. The gas volume fraction is determined by the residence time of bubble within the measuring volume of the probe. We have found that the details of the bubble-probe interactions must be taken into account to obtain an accurate measure of the gas volume fraction at a point. We are able to predict the apparent nonlinear behavior of the gas volume fraction measurement at large concentrations. The bubble velocity is obtained from the cross correlation of the signals of two closely spaced identical probes. Performance tests and results are shown for bubble velocity and bubble concentration profiles in a gravity driven shear flow of a bubbly liquid
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Fecal microbiota transplant rescues mice from human pathogen mediated sepsis by restoring systemic immunity.
Death due to sepsis remains a persistent threat to critically ill patients confined to the intensive care unit and is characterized by colonization with multi-drug-resistant healthcare-associated pathogens. Here we report that sepsis in mice caused by a defined four-member pathogen community isolated from a patient with lethal sepsis is associated with the systemic suppression of key elements of the host transcriptome required for pathogen clearance and decreased butyrate expression. More specifically, these pathogens directly suppress interferon regulatory factor 3. Fecal microbiota transplant (FMT) reverses the course of otherwise lethal sepsis by enhancing pathogen clearance via the restoration of host immunity in an interferon regulatory factor 3-dependent manner. This protective effect is linked to the expansion of butyrate-producing Bacteroidetes. Taken together these results suggest that fecal microbiota transplantation may be a treatment option in sepsis associated with immunosuppression
Simulating Three-Dimensional Hydrodynamics on a Cellular-Automata Machine
We demonstrate how three-dimensional fluid flow simulations can be carried
out on the Cellular Automata Machine 8 (CAM-8), a special-purpose computer for
cellular-automata computations. The principal algorithmic innovation is the use
of a lattice-gas model with a 16-bit collision operator that is specially
adapted to the machine architecture. It is shown how the collision rules can be
optimized to obtain a low viscosity of the fluid. Predictions of the viscosity
based on a Boltzmann approximation agree well with measurements of the
viscosity made on CAM-8. Several test simulations of flows in simple geometries
-- channels, pipes, and a cubic array of spheres -- are carried out.
Measurements of average flux in these geometries compare well with theoretical
predictions.Comment: 19 pages, REVTeX and epsf macros require
Free energy of colloidal particles at the surface of sessile drops
The influence of finite system size on the free energy of a spherical
particle floating at the surface of a sessile droplet is studied both
analytically and numerically. In the special case that the contact angle at the
substrate equals a capillary analogue of the method of images is
applied in order to calculate small deformations of the droplet shape if an
external force is applied to the particle. The type of boundary conditions for
the droplet shape at the substrate determines the sign of the capillary
monopole associated with the image particle. Therefore, the free energy of the
particle, which is proportional to the interaction energy of the original
particle with its image, can be of either sign, too. The analytic solutions,
given by the Green's function of the capillary equation, are constructed such
that the condition of the forces acting on the droplet being balanced and of
the volume constraint are fulfilled. Besides the known phenomena of attraction
of a particle to a free contact line and repulsion from a pinned one, we
observe a local free energy minimum for the particle being located at the drop
apex or at an intermediate angle, respectively. This peculiarity can be traced
back to a non-monotonic behavior of the Green's function, which reflects the
interplay between the deformations of the droplet shape and the volume
constraint.Comment: 24 pages, 19 figure
Rush to Judgment: The STI-Treatment Trials and HIV in Sub-Saharan Africa
Introduction: The extraordinarily high incidence of HIV in sub-Saharan Africa led to the search for cofactor infections that could explain the high rates of transmission in the region. Genital inflammation and lesions caused by sexually transmitted infections (STIs) were a probable mechanism, and numerous observational studies indicated several STI cofactors. Nine out of the ten randomized controlled trials (RCTs), however, failed to demonstrate that treating STIs could lower HIV incidence. We evaluate all 10 trials to determine if their design permits the conclusion, widely believed, that STI treatment is ineffective in reducing HIV incidence.
Discussion: Examination of the trials reveals critical methodological problems sufficient to account for statistically insignificant outcomes in nine of the ten trials. Shortcomings of the trials include weak exposure contrast, confounding, non-differential misclassification, contamination and effect modification, all of which consistently bias the results toward the null. In any future STI-HIV trial, ethical considerations will again require weak exposure contrast. The complexity posed by HIV transmission in the genital microbial environment means that any future STI-HIV trial will face confounding, non-differential misclassification and effect modification. As a result, it is unlikely that additional trials would be able to answer the question of whether STI control reduces HIV incidence.
Conclusions: Shortcomings in published RCTs render invalid the conclusion that treating STIs and other cofactor infections is ineffective in HIV prevention. Meta-analyses of observational studies conclude that STIs can raise HIV transmission efficiency two- to fourfold. Health policy is always implemented under uncertainty. Given the known benefits of STI control, the irreparable harm from not treating STIs and the likely decline in HIV incidence resulting from STI control, it is appropriate to expand STI control programmes and to use funds earmarked for HIV prevention to finance those programmes
Fecal microbiota transplant rescues mice from sepsis due to multi-drug resistant healthcare pathogens by restoring systemic immunity
Death due to sepsis remains a persistent threat to critically ill patients confined to the intensive care unit and is characterized by colonization with multi-drug-resistant healthcare-associated pathogens. Here we report that sepsis in mice caused by a defined four-member pathogen community isolated from a patient with lethal sepsis is associated with the systemic suppression of key elements of the host transcriptome required for pathogen clearance and decreased butyrate expression. More specifically, these pathogens directly suppress interferon regulatory factor 3. Fecal microbiota transplant (FMT) reverses the course of otherwise lethal sepsis by enhancing pathogen clearance via the restoration of host immunity in an interferon regulatory factor 3-dependent manner. This protective effect is linked to the expansion of butyrate-producing Bacteroidetes. Taken together these results suggest that fecal microbiota transplantation may be a treatment option in sepsis associated with immunosuppression
HIV, STI prevalence and risk behaviours among women selling sex in Lahore, Pakistan
<p>Abstract</p> <p>Background</p> <p>More than 340 million cases of curable sexually transmitted infections (STIs) were estimated to have occurred worldwide in 1995. Previous studies have shown that the presence of other concomitant STIs increases the likelihood of HIV transmission. The first national study of STIs conducted in Pakistan in 2004 revealed a high burden of STIs among women selling sex. The HIV epidemic in Pakistan has thus far followed the "Asian epidemic model". Earlier studies among women selling sex have shown a low prevalence of HIV coupled with a low level of knowledge about AIDS. The aim of our study was to estimate the prevalence of HIV and STIs, and assess knowledge and risk behaviours related to HIV/STI, among women selling sex in Lahore, Pakistan.</p> <p>Methods</p> <p>A total of 730 participants were recruited through respondent-driven sampling. The participants were women selling sex in three areas (referred to as "A", "B", and "C") of Lahore. A structured questionnaire addressing demographic information, sexual life history, sexual contacts, and knowledge and practices related to HIV/STI prevention was administered by face-to-face interview. Biological samples were obtained from all participants and tested for HIV, <it>Treponema pallidum</it>, <it>Neisseria gonorrhoeae</it>, <it>Chlamydia trachomatis </it>and <it>Trichomonas vaginalis</it>. Pearson's chi-square and multivariable logistic regression analysis were performed to test associations between potential risk factors and specified diagnosed infections.</p> <p>Results</p> <p>The prevalence of HIV infection was 0.7%, <it>T pallidum </it>4.5%, <it>N gonorrhoeae </it>7.5%, <it>C trachomatis </it>7.7% and <it>T vaginalis </it>5.1%. The participants had been selling sex for a median period of seven years and had a median of three clients per day. Sixty five percent of the participants reported that they "Always use condom". The median fee per sexual contact was Rs. 250 (3 Euro). Compared to Areas A and C, women selling sex in Area B had a significantly higher risk of chlamydial infection, gonorrhoea and trichomoniasis. Among the participants, 37% had correct knowledge about HIV/AIDS transmission and its prevention.</p> <p>Conclusions</p> <p>The prevalence of HIV was <1%, and of any other STI 18.5% among participating women selling sex in Lahore, Pakistan. A reasonably high condom use, a relatively low number of sexual partners, and a relatively low prevalence of STIs might have contributed to the low HIV prevalence.</p
Lattice Boltzmann simulations of soft matter systems
This article concerns numerical simulations of the dynamics of particles
immersed in a continuum solvent. As prototypical systems, we consider colloidal
dispersions of spherical particles and solutions of uncharged polymers. After a
brief explanation of the concept of hydrodynamic interactions, we give a
general overview over the various simulation methods that have been developed
to cope with the resulting computational problems. We then focus on the
approach we have developed, which couples a system of particles to a lattice
Boltzmann model representing the solvent degrees of freedom. The standard D3Q19
lattice Boltzmann model is derived and explained in depth, followed by a
detailed discussion of complementary methods for the coupling of solvent and
solute. Colloidal dispersions are best described in terms of extended particles
with appropriate boundary conditions at the surfaces, while particles with
internal degrees of freedom are easier to simulate as an arrangement of mass
points with frictional coupling to the solvent. In both cases, particular care
has been taken to simulate thermal fluctuations in a consistent way. The
usefulness of this methodology is illustrated by studies from our own research,
where the dynamics of colloidal and polymeric systems has been investigated in
both equilibrium and nonequilibrium situations.Comment: Review article, submitted to Advances in Polymer Science. 16 figures,
76 page
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