1,452 research outputs found
Porous Media Matric Potential and Water Content Measurements During Parabolic Flight
Control of water and air in the root zone of plants remains a challenge in the microgravity environment of space. Due to limited flight opportunities, research aimed at resolving microgravity porous media fluid dynamics must often be conducted on Earth. The NASA KC-135 reduced gravity flight program offers an opportunity for Earth-based researchers to study physical processes in a variable gravity environment. The objectives of this study were to obtain measurements of water content and matric potential during the parabolic profile flown by the KC-135 aircraft. The flight profile provided 20–25 s of microgravity at the top of the parabola, while pulling 1.8 g at the bottom. The soil moisture sensors (Temperature and Moisture Acquisition System: Orbital Technologies, Madison, WI) used a heat-pulse method to indirectly estimate water content from heat dissipation. Tensiometers were constructed using a stainless steel porous cup with a pressure transducer and were used to measure the matric potential of the medium. The two types of sensors were placed at different depths in a substrate compartment filled with 1–2 mm Turface (calcined clay). The ability of the heat-pulse sensors to monitor overall changes in water content in the substrate compartment decreased with water content. Differences in measured water content data recorded at 0, 1, and 1.8 g were not significant. Tensiometer readings tracked pressure differences due to the hydrostatic force changes with variable gravity. The readings may have been affected by changes in cabin air pressure that occurred during each parabola. Tensiometer porous membrane conductivity (function of pore size) and fluid volume both influence response time. Porous media sample height and water content influence time-to-equilibrium, where shorter samples and higher water content achieve faster equilibrium. Further testing is needed to develop these sensors for space flight applications
Two-Channel Totally Asymmetric Simple Exclusion Processes
Totally asymmetric simple exclusion processes, consisting of two coupled
parallel lattice chains with particles interacting with hard-core exclusion and
moving along the channels and between them, are considered. In the limit of
strong coupling between the channels, the particle currents, density profiles
and a phase diagram are calculated exactly by mapping the system into an
effective one-channel totally asymmetric exclusion model. For intermediate
couplings, a simple approximate theory, that describes the particle dynamics in
vertical clusters of two corresponding parallel sites exactly and neglects the
correlations between different vertical clusters, is developed. It is found
that, similarly to the case of one-channel totally asymmetric simple exclusion
processes, there are three stationary state phases, although the phase
boundaries and stationary properties strongly depend on inter-channel coupling.
An extensive computer Monte Carlo simulations fully support the theoretical
predictions.Comment: 13 pages, 10 figure
Theoretical Investigation of Totally Asymmetric Exclusion Processes on Lattices with Junctions
Totally asymmetric simple exclusion processes on lattices with junctions,
where particles interact with hard-core exclusion and move on parallel lattice
branches that at the junction combine into a single lattice segment, are
investigated. A simple approximate theory, that treats the correlations around
the junction position in a mean-field fashion, is developed in order to
calculate stationary particle currents, density profiles and a phase diagram.
It is shown that there are three possible stationary phases depending on the
state of each of the lattice branch. At first-order phase boundaries, where the
density correlations are important, a modified phenomenological domain-wall
theory, that accounts for correlations, is introduced. Extensive Monte Carlo
computer simulations are performed to investigate the system, and it is found
that they are in excellent agreement with theoretical predictions.Comment: 16 pages, 7 figure
Spontaneous Symmetry Breaking in Two-Channel Asymmetric Exclusion Processes with Narrow Entrances
Multi-particle non-equilibrium dynamics in two-channel asymmetric exclusion
processes with narrow entrances is investigated theoretically. Particles move
on two parallel lattices in opposite directions without changing them, while
the channels are coupled only at the boundaries. A particle cannot enter the
corresponding lane if the exit site of the other lane is occupied. Stationary
phase diagrams, particle currents and densities are calculated in a mean-field
approximation. It is shown that there are four stationary phases in the system,
with two of them exhibiting spontaneous symmetry breaking phenomena. Extensive
Monte Carlo computer simulations confirm qualitatively our predictions,
although the phase boundaries and stationary properties deviate from the
mean-field results. Computer simulations indicate that several dynamic and
phase properties of the system have a strong size dependency, and one of the
stationary phases predicted by the mean-field theory disappears in the
thermodynamic limit.Comment: 13 page
The relation of plasmacytoid dendritic cells (pDCs) and regulatory t-cells (Tregs) with HPV persistence in HIV-Infected and HIV-Uninfected women
Other than CD4+ count, the immunologic factors that underlie the relationship of HIV/AIDS with persistent oncogenic HPV (oncHPV) and cervical cancer are not well understood. Plasmacytoid dendritic cells (pDCs) and regulatory T-cells (Tregs) are of particular interest. pDCs have both effector and antigen presenting activity and, in HIV-positive patients, low pDC levels are associated with opportunistic infections. Tregs downregulate immune responses, and are present at high levels in HIV-positives. The current pilot study shows for the first time that low pDC and high Treg levels may be significantly associated with oncHPV persistence in both HIV-positive and HIV-negative women. Larger studies are now warranted
Mesoscopic conductance and its fluctuations at non-zero Hall angle
We consider the bilocal conductivity tensor, the two-probe conductance and
its fluctuations for a disordered phase-coherent two-dimensional system of
non-interacting electrons in the presence of a magnetic field, including
correctly the edge effects. Analytical results are obtained by perturbation
theory in the limit . For mesoscopic systems the conduction
process is dominated by diffusion but we show that, due to the lack of
time-reversal symmetry, the boundary condition for diffusion is altered at the
reflecting edges. Instead of the usual condition, that the derivative along the
direction normal to the wall of the diffusing variable vanishes, the derivative
at the Hall angle to the normal vanishes. We demonstrate the origin of this
boundary condition from different starting points, using (i) a simplified
Chalker-Coddington network model, (ii) the standard diagrammatic perturbation
expansion, and (iii) the nonlinear sigma-model with the topological term, thus
establishing connections between the different approaches. Further boundary
effects are found in quantum interference phenomena. We evaluate the mean
bilocal conductivity tensor , and the mean and variance
of the conductance, to leading order in and to order
, and find that the variance of the conductance
increases with the Hall ratio. Thus the conductance fluctuations are no longer
simply described by the unitary universality class of the case,
but instead there is a one-parameter family of probability distributions. In
the quasi-one-dimensional limit, the usual universal result for the conductance
fluctuations of the unitary ensemble is recovered, in contrast to results of
previous authors. Also, a long discussion of current conservation.Comment: Latex, uses RevTex, 58 pages, 5 figures available on request at
[email protected]. Submitted to Phys. Rev.
Surfactant protein D modulates HIV infection of both T-cells and dendritic cells
Surfactant Protein D (SP-D) is an oligomerized C-type lectin molecule with immunomodulatory properties and involvement in lung surfactant homeostasis in the respiratory tract. SP-D binds to the enveloped viruses, influenza A virus and respiratory syncytial virus and inhibits their replication in vitro and in vivo. SP-D has been shown to bind to HIV via the HIV envelope protein gp120 and inhibit infectivity in vitro. Here we show that SP-D binds to different strains of HIV (BaL and IIIB) and the binding occurs at both pH 7.4 and 5.0 resembling physiological relevant pH values found in the body and the female urogenital tract, respectively. The binding of SP-D to HIV particles and gp120 was inhibited by the presence of several hexoses with mannose found to be the strongest inhibitor. Competition studies showed that soluble CD4 and CVN did not interfere with the interaction between SP-D and gp120. However, soluble recombinant DC-SIGN was shown to inhibit the binding between SP-D and gp120. SP-D agglutinated HIV and gp120 in a calcium dependent manner. SP-D inhibited the infectivity of HIV strains at both pH values of 7.4 and 5.0 in a concentration dependent manner. The inhibition of the infectivity was abolished by the presence of mannose. SP-D enhanced the binding of HIV to immature monocyte derived dendritic cells (iMDDCs) and was also found to enhance HIV capture and transfer to the T-cell like line PM1. These results suggest that SP-D can bind to and inhibit direct infection of T-cells by HIV but also enhance the transfer of infectious HIV particles from DCs to T-cells in vivo
Response of the solar atmosphere to magnetic field evolution in a coronal hole region
Methods. We study an equatorial CH observed simultaneously by HINODE and
STEREO on July 27, 2007. The HINODE/SP maps are adopted to derive the physical
parameters of the photosphere and to research the magnetic field evolution and
distribution. The G band and Ca II H images with high tempo-spatial resolution
from HINODE/BFI and the multi-wavelength data from STEREO/EUVI are utilized to
study the corresponding atmospheric response of different overlying layers.
Results. We explore an emerging dipole locating at the CH boundary. Mini-scale
arch filaments (AFs) accompanying the emerging dipole were observed with the Ca
II H line. During the separation of the dipolar footpoints, three AFs appeared
and expanded in turn. The first AF divided into two segments in its late stage,
while the second and third AFs erupted in their late stages. The lifetimes of
these three AFs are 4, 6, 10 minutes, and the two intervals between the three
divisions or eruptions are 18 and 12 minutes, respectively. We display an
example of mixed-polarity flux emergence of IN fields within the CH and present
the corresponding chromospheric response. With the increase of the integrated
magnetic flux, the brightness of the Ca II H images exhibits an increasing
trend. We also study magnetic flux cancellations of NT fields locating at the
CH boundary and present the obvious chromospheric and coronal response. We
notice that the brighter regions seen in the 171 A images are relevant to the
interacting magnetic elements. By examining the magnetic NT and IN elements and
the response of different atmospheric layers, we obtain good positive linear
correlations between the NT magnetic flux densities and the brightness of both
G band (correlation coefficient 0.85) and Ca II H (correlation coefficient
0.58).Comment: 9 pages, 9 figures. A&A, in pres
The roles and values of wild foods in agricultural systems
Almost every ecosystem has been amended so that plants and animals can be used as food, fibre, fodder, medicines, traps and weapons. Historically, wild plants and animals were sole dietary components for hunter–gatherer and forager cultures. Today, they remain key to many agricultural communities. The mean use of wild foods by agricultural and forager communities in 22 countries of Asia and Africa (36 studies) is 90–100 species per location. Aggregate country estimates can reach 300–800 species (e.g. India, Ethiopia, Kenya). The mean use of wild species is 120 per community for indigenous communities in both industrialized and developing countries. Many of these wild foods are actively managed, suggesting there is a false dichotomy around ideas of the agricultural and the wild: hunter–gatherers and foragers farm and manage their environments, and cultivators use many wild plants and animals. Yet, provision of and access to these sources of food may be declining as natural habitats come under increasing pressure from development, conservation-exclusions and agricultural expansion. Despite their value, wild foods are excluded from official statistics on economic values of natural resources. It is clear that wild plants and animals continue to form a significant proportion of the global food basket, and while a variety of social and ecological drivers are acting to reduce wild food use, their importance may be set to grow as pressures on agricultural productivity increase.</jats:p
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Searches For High-Frequency Variations In The B-8 Solar Neutrino Flux At The Sudbury Neutrino Observatory
We have performed three searches for high-frequency signals in the solar neutrino flux measured by the Sudbury Neutrino Observatory, motivated by the possibility that solar g-mode oscillations could affect the production or propagation of solar B-8 neutrinos. The first search looked for any significant peak in the frequency range 1-144 day(-1), with a sensitivity to sinusoidal signals with amplitudes of 12% or greater. The second search focused on regions in which g-mode signals have been claimed by experiments aboard the Solar and Heliospheric Observatory satellite, and was sensitive to signals with amplitudes of 10% or greater. The third search looked for extra power across the entire frequency band. No statistically significant signal was detected in any of the three searches.Natural Sciences and Engineering Research Council, CanadaIndustry Canada, CanadaNational Research Council, CanadaNorthern Ontario Heritage Fund, CanadaAtomic Energy of Canada, Ltd., CanadaOntario Power Generation, CanadaHigh Performance Computing Virtual Laboratory, CanadaCanada Foundation for InnovationDept. of Energy, USNational Energy Research Scientific Computing Center, USScience and Technologies Facilities Council, UKAstronom
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