120 research outputs found
A New Source of Reaction - Diffusion Coupling in Confined Systems due to Temperature Inhomogeneity
Diffusion is often accompanied by a reaction or sorption which can induce
temperature inhomogeneities. Monte Carlo simulations of Lennard-Jones atoms in
zeolite NaCaA are reported with a hot zone presumed to be created by a
reaction. Our simulations show that localised hot regions can alter both the
kinetic and transport properties. Further, enhancement of the diffusion
constant is greater for larger barrier height, a surprising result of
considerable significance to many chemical and biological processes. We find an
unanticipated coupling between reaction and diffusion due to the presence of
hot zone in addition to that which normally exists via concentration.Comment: to be published in Phys. Rev. Let
Reduced-Order Modeling of Turbulent Reacting Flows with Application to Ramjets and Scramjets
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90621/1/AIAA-50272-117.pd
Lattice Kinetics of Diffusion-Limited Coalescence and Annihilation with Sources
We study the 1D kinetics of diffusion-limited coalescence and annihilation
with back reactions and different kinds of particle input. By considering the
changes in occupation and parity of a given interval, we derive sets of
hierarchical equations from which exact expressions for the lattice coverage
and the particle concentration can be obtained. We compare the mean-field
approximation and the continuum approximation to the exact solutions and we
discuss their regime of validity.Comment: 24 pages and 3 eps figures, Revtex, accepted for publication in J.
Phys.
Extraction kinetics of saponins from quinoa seed (Chenopodium quinoa Willd)
Quinoa has higher protein content (11-16% m/m) and better amino acid profile than cereals and represents a valuable resource for healthy nutrition. The aim of this work was to study the saponins extraction kinetics during washing of soaked quinoa. The experimental curves of saponins content as a function of time was measured at water temperatures of 20, 40, 60, and 70ºC. A spectrophotometric method was proposed to determine total saponins content, while an unsteady state diffusional model was applied to this extraction problem, assuming strict internal control to the mass transfer rate. As a first analysis, the complete analytical solution for constant diffusion coefficient (Deff) using the initial radius (R0) provided an accurate predicted curve at each temperature. The diffusion coefficients (around 10−10 m2s-1), were correlated with temperature using an Arrhenius-type relationship to obtain an activation energy Ea of 16.9 kJ mol-1. The preliminary values of Ea and preexponential factor (D0) thus obtained were used as initial values of a second, more robust fitting where the whole dataset of saponins concentrations as a function of time for all temperatures. The Arrhenius equation was directly inserted into the diffusional solution. The following parameters were obtained: Ea= 17.2 kJ mol-1 and, D0= 3.232×107 m2 s-1, respectively with an overall r2=0.985. Saponins content agreed well with experimental values. As the equation is capable of predicting saponin extraction times for various operating conditions, it can be used within equipment design schemes
LANSCE Digital Low Level RF Upgrade
Incremental upgrades of the legacy low level RF (LLRF) equipment-50 years for
the Los Alamos Neutron Science Center (LANSCE)-involves challenges and problems
not seen with new and total replacement opportunities. The digital LLRF upgrade
at LANSCE has deployed 30 of the 53 required systems as of September 2022. This
paper describes the performance of the digital upgrade, current status, and
future installations along with the technical challenges, including unexpected
challenges, associated with deploying new digital systems in conjunction with
legacy analog equipment. In addition, this paper discusses the operational
details of simultaneous multi-energy beam operations using high energy
re-bunching, beam-type specific set points and simultaneous multi-beam
operations at LANSCE. The adaptability of the digital LLRF systems is essential
as the design is able to accommodate new control and beam parameters associated
with future systems without significant hardware modifications such as the
expected LANSCE Modernization Program. This adaptability of the digital LLRF
technology was recently demonstrated with the Module 1, 201.25-MHz high-power
RF upgrade completed in 2021.Comment: Talk presented at LLRF Workshop 2022 (LLRF2022, arXiv:2208.13680
Growth hormone therapy improves growth in children with cystic fibrosis related liver disease
Growth impairment in cystic fibrosis (CF) is worsened by liver disease. Children with CF have serum levels of insulin-like growth factor-I (IGF-I) that are lower than expected for their normal growth hormone (GH) production. In children with CF-related liver disease (CFLD), response to endogenous GH is further reduced. We present our experience with two young children with CFLD given recombinant human GH (rhGH). The first patient was a 5 year-old female with CFLD and poor growth who responded well for 1 1/2 years to rhGH therapy during her initial course and without a significant increase in serum IGF-I, but with a substantial increase in IGF-I concentration when the GH dose was increased. The second patient was a 5 month-old male with advanced liver disease who had transient improved growth and liver function following rhGH. These patients suggest that rhGH is safe and may be effective in children with CFLD
Decline in total serum IgE and soluble CD30 in the context of soil-transmitted helminth decline in Bolivia
In the Bolivian Chaco, recent surveys documented a dramatic decrease in the prevalence of soil-transmitted helminth (STH) infections as compared with the 1980s after thirty years of preventive chemotherapy (PC). Concomitant immunological rearrangements are expected. Because nematode infections are associated with increased levels of circulating IgE and glycoprotein CD30 soluble form (sCD30), this study aims to evaluate changes in serological markers of T helper (Th)2-cells activity between 1987 (high STH prevalence) and 2013 (low STH prevalence) in rural communities in the Bolivian Chaco area. We collected 151 sera during two different surveys in 1987 (n = 65) and 2013 (n = 86) and measured the concentration of total IgE and sCD30 by immunoassays. We found a statistically significant age-independent decrease in the total IgE (P < 0.0001) and sCD30 (P < 0.0001) from 1987 to 2013. The significant decrease in serological Th2 markers (IgE and sCD30) between 1987 and 2013 is consistent with the drop in STH prevalence in this geographical area during the same period of time. Further studies might elucidate the clinical and epidemiological impact of these serological rearrangements
Ancient mitochondrial DNA provides high-resolution time scale of the peopling of the Americas
The exact timing, route, and process of the initial peopling of the Americas remains uncertain despite much research. Archaeological evidence indicates the presence of humans as far as southern Chile by 14.6 thousand years ago (ka), shortly after the Pleistocene ice sheets blocking access from eastern Beringia began to retreat. Genetic estimates of the timing and route of entry have been constrained by the lack of suitable calibration points and low genetic diversity of Native Americans. We sequenced 92 whole mitochondrial genomes from pre-Columbian South American skeletons dating from 8.6 to 0.5 ka, allowing a detailed, temporally calibrated reconstruction of the peopling of the Americas in a Bayesian coalescent analysis. The data suggest that a small population entered the Americas via a coastal route around 16.0 ka, following previous isolation in eastern Beringia for ~2.4 to 9 thousand years after separation from eastern Siberian populations. Following a rapid movement throughout the Americas, limited gene flow in South America resulted in a marked phylogeographic structure of populations, which persisted through time. All of the ancient mitochondrial lineages detected in this study were absent from modern data sets, suggesting a high extinction rate. To investigate this further, we applied a novel principal components multiple logistic regression test to Bayesian serial coalescent simulations. The analysis supported a scenario in which European colonization caused a substantial loss of pre-Columbian lineages.Bastien Llamas, Lars Fehren-Schmitz, Guido Valverde, Julien Soubrier, Swapan Mallick, Nadin Rohland, Susanne Nordenfelt, Cristina Valdiosera, Stephen M. Richards, Adam Rohrlach, Maria Inés Barreto Romero, Isabel Flores Espinoza, Elsa Tomasto Cagigao, LucÃa Watson Jiménez, Krzysztof Makowski, Ilán Santiago Leboreiro Reyna, Josefina Mansilla Lory, Julio Alejandro Ballivián Torrez, Mario A. Rivera, Richard L. Burger, Maria Constanza Ceruti, Johan Reinhard, R. Spencer Wells, Gustavo Politis, Calogero M. Santoro, Vivien G. Standen, Colin Smith, David Reich, Simon Y. W. Ho, Alan Cooper and Wolfgang Haa
Caracterización fÃsica y obtención de parámetros de fluidización de germen de trigo
El germen de trigo es el embrión del grano de trigo, presenta un elevado contenido de tocoferoles y proteÃnas y ácidos grasos y proteÃnas de alta calidad. A su vez, contiene enzimas con elevada actividad que limitan su periodo de aptitud a unos pocos dÃas. El objetivo del presente trabajo fue caracterizar fÃsicamente las partÃculas de germen de trigo para determinar los parámetros de diseño para un proceso de fluidificación térmica con aire. Los ejes principales de las partÃculas fueron determinados mediante análisis de imágenes y sus dimensiones y parámetros geométricos fueron calculados. La densidad de lecho fijo y la porosidad del lecho fueron determinadas. Los estudios fluido-dinámicos nos permitieron determinar los coeficientes, laminar (277,46±17,48) y turbulento (7,79±0,69) de la ecuación de Ergun y la velocidad de mÃnima fluidificación (0,35±0,02 m/s).Wheat germ is the embryo of de wheat seed, it contains a high tocopherol and protein content, and high quality proteins and fatty acids. Also, wheat germ has a considerable enzymatic activity that limits its shelf life. The aims of the study were to physically characterize wheat germ particles to determine their design parameters of thermal fluidization process with air. The principal axes of the particle were measured by image analysis, and their dimensions and geometric parameters were calculated. The fixed bed density and the void fraction were measured. The fluid-dynamic studies allowed us to determine laminar (277.46±17.48) and turbulent (7.79±0.69) coefficients of the Ergun equation and the minimum fluidization velocity (0.35±0.02 m/s).Centro de Investigación y Desarrollo en CriotecnologÃa de Alimento
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