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Search Results: 1 - 10 of 297458 matches for " J. Benziger "
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The Autohumidification Polymer Electrolyte Membrane Fuel Cell
J. B. Benziger,J. Moxley,S. Tulyani,A. Turner,A. B. Bocarsly,Y. G. Kevrekidis
Physics , 2003,
Abstract: A PEM fuel cell was specially constructed to determine kinetics under conditions of well-defined gas phase composition and cell temperature. Steady state multiplicity was discovered in the autohumidification PEM fuel cell, resulting from a balance between water production and water removal. Ignition was observed in the PEM fuel cell for a critical water activity of about 0.1. Ignition is a consequence of the exponential increase of proton conductivity with water activity, which creates an autocatalytic feedback between the water production and the proton conduction. The steady state current in the ignited state decreases with increasing temperature between 50 to 105 deg C. At temperatures greater than 70 deg C five steady states were observed in the PEM fuel cell. The steady state performance has been followed with variable load resistance and hysteresis loops have been mapped. The dynamics of transitions between steady states are slow about 10^3 to 10^4 s. These slow dynamics are suggested to result from a coupling of mechanical and chemical properties of the membrane electrode assembly due to swelling of the membrane with water absorption.
Sex Differences in Risk Factors for Cardiovascular Disease: The PERU MIGRANT Study
Antonio Bernabe-Ortiz, Catherine Pastorius Benziger, Robert H. Gilman, Liam Smeeth, J. Jaime Miranda
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0035127
Abstract: Introduction Although men and women have similar risk factors for cardiovascular disease, many social behaviors in developing countries differ by sex. Rural-to-urban migrants have different cardiovascular risk profiles than rural or urban dwellers. The objective of this study was to evaluate the sex differences with specific cardiovascular risk factors in rural-to-urban migrants. Methods and Results We used the rural-to-urban migrant group of the PERU MIGRANT cross-sectional study to investigate the sex differences in specific cardiovascular risk factors: obesity, hypertension, metabolic syndrome, as well as exposures of socioeconomic status, acculturation surrogates and behavioral characteristics. Logistic regression analysis was used to characterize strength of association between sex and our outcomes adjusting for potential confounders. The sample of migrants was 589 (mean age 46.5 years) and 52.4% were female. In the adjusted models, women were more likely to be obese (OR=5.97; 95%CI: 3.21–11) and have metabolic syndrome (OR=2.22; 95%CI: 1.39–3.55) than men, explaining the greatest variability for obesity and metabolic syndrome but not for hypertension. Conclusions Our results suggest that interventions for CVD in Peru should be sex-specific and address the unique health needs of migrant populations living in urban shantytowns since the risk factors for obesity and metabolic syndrome differ between males and females.
Determining and addressing obstacles to the effective use of long-lasting insecticide-impregnated nets in rural Tanzania
Maria Widmar, Courtney J Nagel, Deborah Y Ho, Peter W Benziger, Nils Hennig
Malaria Journal , 2009, DOI: 10.1186/1475-2875-8-315
Abstract: Five practices and attitudes inconsistent with effective LLIN use were identified from household interviews (n = 10). A randomized survey of villagers (n = 132) verified local prevalence of these practices and attitudes. Community leaders held an educational session for two members of every household addressing these practice and attitudes, demonstrating proper LLIN use, and emphasizing behaviour modification. Attendees received one or two LLINs per household. Surveys distributed three weeks (n = 104) and 15 months (n = 104) post-intervention assessed corrected practices and attitudes. Project efficacy was defined by correction of baseline practices and attitudes as well as high rates of reported daily net use, with statistical significance determined by chi-square test.Baseline interviews and surveys revealed incorrect practices and attitudes regarding 1) use of nets in dry season, 2) need to retreat LLINs, 3) children napping under nets, 4) need to repair nets, and 5) net procurement as a priority, with 53- 88.6% incorrect responses (11.4-47% correct responses). A three-week follow-up demonstrated 83-95% correct responses. Fifteen-month follow-up showed statistically significant (p < 0.01) corrections from baseline in all five practice and attitudes (39.4-93.3% correct answers). 89.4% of respondents reported using their nets every night, and 93.3% affirmed purchase of nets as a financial priority.Results suggest that addressing community-specific practices and attitudes prior to LLIN distribution promotes consistent and correct use, and helps change attitudes towards bed nets as a preventative health measure. Future LLIN distributions can learn from the paradigm established in this project.In Tanzania, malaria is the leading cause of morbidity and mortality in both adults and children under five [1,2]. 97% of the population is currently considered at risk for infection, with 75% living in high intensity transmission areas [3]. This burden of disease costs Tanzania
Ignition and Front Propagation in Polymer Electrolyte Membrane Fuel Cells
J. B. Benziger,E. -S. Chia,Y. De Decker,I. G. Kevrekidis
Physics , 2006,
Abstract: Water produced in a Polymer Electrolyte Membrane (PEM) fuel cell enhances membrane proton conductivity; this positive feedback loop can lead to current ignition. Using a segmented anode fuel cell we study the effect of gas phase convection and membrane diffusion of water on the spatiotemporal nonlinear dynamics - localized ignition and front propagation - in the cell. Co-current gas flow causes ignition at the cell outlet, and membrane diffusion causes the front to slowly propagate to the inlet; counter-current flow causes ignition in the interior of the cell, with the fronts subsequently spreading towards both inlets. These instabilities critically affect fuel cell performance.
The Stirred Tank Reactor Polymer Electrolyte Membrane Fuel Cell
Jay Benziger,E. Chia,E. Karnas,J. Moxley,C. Teuscher,I. G. Kevrekidis
Physics , 2003,
Abstract: The design and operation of a differential Polymer Electrolyte Membrane (PEM) fuel cell is described. The fuel cell design is based on coupled Stirred Tank Reactors (STR); the gas phase in each reactor compartment was well mixed. The characteristic times for reactant flow, gas phase diffusion and reaction were chosen so that the gas compositions at both the anode and cathode are uniform. The STR PEM fuel cell is one-dimensional; the only spatial gradients are transverse to the membrane. The STR PEM fuel cell was employed to examine fuel cell start- up, and its dynamic responses to changes in load, temperature and reactant flow rates. Multiple time scales in systems response are found to correspond to water absorption by the membrane, water transport through the membrane and stress-related mechanical changes of the membrane.
A Comparison of Physical Properties and Fuel Cell Performance of Nafion and Zirconium Phosphate/Nafion Composite Membranes
Chris Yang,S. Srinivasan,A. B. Bocarsly,S. Tulyani,J. B. Benziger
Physics , 2003,
Abstract: The physio-chemical properties of Nafion 115 and a composite Nafion 115/Zirconium Phosphate (25wt%) membranes are compared. The composite membrane takes up more water than Nafion at the same water activity. However, the proton conductivity of the composite membrane is slightly less than that for Nafion 115. Small angle X-ray scattering shows the hydrophilic phase domains in the composite membrane are spaced further apart than in Nafion 115, and the composite membrane shows less restructuring with water uptake. Despite the lower proton conductivity of the composite membranes they display better fuel cell performance than Nafion 115 when the fuel cell is operated under-humidified. It is suggested that the composite membrane has a greater rigidity that accounts for its improved fuel cell performance.
Steady State Multiplicity in a Polymer Electrolyte Membrane Fuel Cell
Ee-Sunn J. Chia,Jay B. Benziger,Ioannis G. Kevrekidis
Physics , 2003,
Abstract: A simplified differential reactor model that embodies the essential physics controlling PEM fuel cell (PEM-FC) dynamics is presented. A remarkable analogy exists between water management in the differential PEM-FC and energy balance in the classical exothermic stirred tank reactor. Water, the reaction product in the PEM-FC autocatalytically accelerates the reaction rate by enhancing proton transport through the PEM. Established analyses of heat autocatalyticity in a CSTR are modified to present water management autocatalyticity in a stirred tank reactor PEM-FC.
The Nylon Scintillator Containment Vessels for the Borexino Solar Neutrino Experiment
J. Benziger,L. Cadonati,F. Calaprice,E. de Haas,R. Fernholz,R. Ford,C. Galbiati,A. Goretti,E. Harding,An. Ianni,S. Kidner,M. Leung,F. Loeser,K. McCarty,A. Nelson,R. Parsells,A. Pocar,T. Shutt,A. Sonnenschein,R. B. Vogelaar
Physics , 2007, DOI: 10.1016/j.nima.2007.08.176
Abstract: Borexino is a solar neutrino experiment designed to observe the 0.86 MeV Be-7 neutrinos emitted in the pp cycle of the sun. Neutrinos will be detected by their elastic scattering on electrons in 100 tons of liquid scintillator. The neutrino event rate in the scintillator is expected to be low (~0.35 events per day per ton), and the signals will be at energies below 1.5 MeV, where background from natural radioactivity is prominent. Scintillation light produced by the recoil electrons is observed by an array of 2240 photomultiplier tubes. Because of the intrinsic radioactive contaminants in these PMTs, the liquid scintillator is shielded from them by a thick barrier of buffer fluid. A spherical vessel made of thin nylon film contains the scintillator, separating it from the surrounding buffer. The buffer region itself is divided into two concentric shells by a second nylon vessel in order to prevent inward diffusion of radon atoms. The radioactive background requirements for Borexino are challenging to meet, especially for the scintillator and these nylon vessels. Besides meeting requirements for low radioactivity, the nylon vessels must also satisfy requirements for mechanical, optical, and chemical properties. The present paper describes the research and development, construction, and installation of the nylon vessels for the Borexino experiment.
A Scintillator Purification System for the Borexino Solar Neutrino Detector
J. Benziger,L. Cadonati,F. Calaprice,M. Chen,A. Corsi,F. Dalnoki-Veress,R. Fernholz,R. Ford,C. Galbiati,A. Goretti,E. Harding,Aldo Ianni,Andrea Ianni,S. Kidner,M. Leung,F. Loeser,K. McCarty,D. McKinsey,A. Nelson,A. Pocar,C. Salvo,D. Schimizzi,T. Shutt,A. Sonnenschein
Physics , 2007, DOI: 10.1016/j.nima.2007.12.043
Abstract: Purification of the 278 tons of liquid scintillator and 889 tons of buffer shielding for the Borexino solar neutrino detector was performed with a system that combined distillation, water extraction, gas stripping and filtration. The purification of the scintillator achieved unprecedented low backgrounds for the large scale liquid scintillation detector. This paper describes the principles of operation, design, construction and commissioning of the purification system, and reviews the requirements and methods to achieve system cleanliness and leak-tightness.
Unraveling a 146 Years Old Taxonomic Puzzle: Validation of Malabar Snakehead, Species-Status and Its Relevance for Channid Systematics and Evolution
Allen Benziger, Siby Philip, Rajeev Raghavan, Palakkaparambil Hamsa Anvar Ali, Mithun Sukumaran, Josin C. Tharian, Neelesh Dahanukar, Fibin Baby, Reynold Peter, Karunakaran Rema Devi, Kizhakke Veetil Radhakrishnan, Mohamed AbdulKather Haniffa, Ralf Britz, Agostinho Antunes
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0021272
Abstract: Background The Malabar snakehead Channa diplogramma is one of the most enigmatic and least understood species within the family Channidae, which comprise one of the most important groups of freshwater food fish in tropical Asia. Since its description from peninsular India in 1865, it has remained a taxonomic puzzle with many researchers questioning its validity, based on its striking similarity with the South East Asian C. micropeltes. In this study, we assessed the identity of the Malabar snakehead, C. diplogramma, using morphological and molecular genetic analyses, and also evaluated its phylogenetic relationships and evolutionary biogeography. Methodology/Principal Findings The morphometric and meristic analysis provided conclusive evidence to separate C. diplogramma and C. micropeltes as two distinct species. Number of caudal fin rays, lateral line scales, scales below lateral line; total vertebrae, pre-anal length and body depth were the most prominent characters that can be used to differentiate both the species. Channa diplogramma also shows several ontogenic color phases during its life history, which is shared with C. micropeltes. Finally, the genetic distance between both species for the partial mitochondrial 16S rRNA and COI sequences is also well above the intra-specific genetic distances of any other channid species compared in this study. Conclusions/Significance The current distribution of C. diplogramma and C. micropeltes is best explained by vicariance. The significant variation in the key taxonomic characters and the results of the molecular marker analysis points towards an allopatric speciation event or vicariant divergence from a common ancestor, which molecular data suggests to have occurred as early as 21.76 million years ago. The resurrection of C. diplogramma from the synonymy of C. micropeltes has hence been confirmed 146 years after its initial description and 134 years after it was synonymised, establishing it is an endemic species of peninsular India and prioritizing its conservation value.
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