1,329 research outputs found
Clearance of endosymbionts in the tick vector Rhipicephalus sanguineus
Abstract only availableVector-borne diseases reduce livestock production in areas whose human populations are starving, such as the Tsetse belt in Africa. In the United States, people are infected every year with Lyme disease, Rocky Mountain Spotted Fever, and Human Monocytic Ehrlichiosis. A method of controlling vectors, such as ticks, would have many uses. Previous studies have indicated that all ticks of the species Amblyomma americanum are infected with a Coxiella sp. bacterial symbiont. After treatment with the antibiotics rifampin and tetracycline, nymphs and adults were shown to have lower numbers of this symbiont and treatment of engorged adult females was shown to result in decreased fecundity (Zhong et al. 2007). It was speculated that this Coxiella symbiont plays a vital role in tick fitness and female fecundity. The goals of the current experiment are to: demonstrate the presence of the same or similar symbiont in Rhipicephalus sanguineus adults and larvae, demonstrate clearance of the symbiont in larvae after treatment with antibiotics, observe any negative effects on the fecundity of the treated females, and test the acquisition rate of larvae that feed on a carrier of Ehrlichia canis, a pathogen of which ticks are a vector. A Coxiella sp. symbiont was shown in adult and larvae R. sanguineus using PCR. Adult females were then fed with males on dogs to repletion, with several groups receiving different treatments of antibiotics prior to mating. Three of the treatment groups suffered significantly lower fecundity than the control. DNA from the resulting larvae was PCR assayed for symbionts, and the Coxiella symbiont has been found in lower numbers in the larvae of these treated groups. The next phase of the experiment is to feed symbiont cleared or reduced larvae on an E. canis carrier and compare their rate of acquisition to untreated larvae.Dr. Roger W. Stich, Veterinary Pathobiolog
Effect of initial spin polarization on spin dephasing and electron g factor in a high-mobility two-dimensional electron system
We have investigated the spin dynamics of a high-mobility two-dimensional
electron system (2DES) in a GaAs--AlGaAs single quantum well by
time-resolved Faraday rotation (TRFR) in dependence on the initial degree of
spin polarization, , of the 2DES. From to %, we observe
an increase of the spin dephasing time, , by an order of magnitude,
from about 20 ps to 200 ps, in good agreement with theoretical predictions by
Weng and Wu [Phys. Rev. B {\bf 68}, 075312 (2003)]. Furthermore, by applying an
external magnetic field in the Voigt configuration, also the electron
factor is found to decrease for increasing . Fully microscopic calculations,
by numerically solving the kinetic spin Bloch equations considering the
D'yakonov-Perel' and the Bir-Aronov-Pikus mechanisms, reproduce the most
salient features of the experiments, {\em i.e}., a dramatic decrease of spin
dephasing and a moderate decrease of the electron factor with increasing
. We show that both results are determined dominantly by the Hartree-Fock
contribution of the Coulomb interaction.Comment: 4 pages, 4 figures, to be published in PR
Experimentelle Überprüfung einer evolutionstheoretischen Erklärung von Schlafplatzpräferenzen des Menschen
Obwohl Menschen einen großen Teil des Tages an ihrem
Schlafplatz verbringen, gibt es kaum experimentelle und
theoriegeleitete Studien zur Schlafplatzwahl des Menschen.
Da der Mensch im Schlaf relativ schutzlos gegenüber Angreifern ist und eine passende Wahl der Schlafumgebung Schutz und damit höhere Überlebenschancen bietet, wird die Schlafplatzwahl aus evolutionärer Perspektive untersucht.
Es wird ein Evolutionsbedingter Psychologischer Mechanismus (EPM) zur Schlafplatzwahl postuliert und daraus abgeleitete Hypothesen überprüft: Ein Schlafplatz sollte so gewählt werden, dass er schnelle Reaktionen auf Angreifer ermöglicht. Daher sollte (1) vom Bett aus die Tür im Blickfeld sein, (2) das Bett in deutlicher Weise von der Tür abgerückt sein und (3) bevorzugt in die Zimmerhälfte gestellt werden, in die sich die Tür öffnet. Eine Studie mit 138 Probanden, die Möbel auf experimentell manipulierten Grundrissen anrichten, kann diese Hypothesen bestätigen
Detection of large magneto-anisotropy of electron spin dephasing in a high-mobility two-dimensional electron system in a GaAs/AlGaAs quantum well
In time-resolved Faraday rotation experiments we have detected an inplane
anisotropy of the electron spin-dephasing time (SDT) in an
--modulation-doped GaAs/AlGaAs single quantum well. The SDT
was measured with magnetic fields of T, applied in the and
inplane crystal directions of the GaAs quantum well. For fields
along , we have found an up to a factor of about 2 larger SDT than
in the perpendicular direction. Fully microscopic calculations, by numerically
solving the kinetic spin Bloch equations considering the D'yakonov-Perel' and
the Bir-Aronov-Pikus mechanisms, reproduce the experimental findings
quantitatively. This quantitative analysis of the data allowed us to determine
the relative strengths of Rashba and Dresselhaus terms in our sample. Moreover,
we could estimate the SDT for spins aligned in the {\em inplane}
direction to be on the order of several nanoseconds, which is up to two orders
of magnitude larger than that in the perpendicular {\em inplane} direction.Comment: 4 pages, 4 figures, to be published in PR
How to integrate real-world user behavior into models of the market diffusion of alternative fuels in passenger cars - An in-depth comparison of three models for Germany
The future market diffusion of alternative fuels in the passenger car sector is of great interest to both carmakers and policymakers in order to decrease CO emissions. The decision to buy a car is not totally objective and only partly based on cost. For this reason, those modeling the future market evolution of cars powered by alternative fuels try to include behavioral and non-cost related aspects. This paper analyzes the integration of user behavior into market diffusion models and compares three models that include this aspect. The comparison comprises three parts: first, it compares the modeling approaches, then uses a harmonized data set to model the future market diffusion of alternative fuel vehicles, with and without behavioral aspects. The most important aspects of user behavior included in the models are the use of charging infrastructure, the limited model availability, the consideration of range anxiety as a hampering factor or the willingness-to-pay-more for alternative drivetrains as a supporting factor, as well as a distinction of users\u27 driving distances. User behavior is considered in various ways, but always has a limiting effect on electric vehicle market diffusion. While a model that distinguishes individual users and driving distances stresses the high relevance of this aspect, it is considered less important in models with a more aggregated inclusion of user behavior based on logit functions
Atomic layering at the liquid silicon surface: a first- principles simulation
We simulate the liquid silicon surface with first-principles molecular
dynamics in a slab geometry. We find that the atom-density profile presents a
pronounced layering, similar to those observed in low-temperature liquid metals
like Ga and Hg. The depth-dependent pair correlation function shows that the
effect originates from directional bonding of Si atoms at the surface, and
propagates into the bulk. The layering has no major effects in the electronic
and dynamical properties of the system, that are very similar to those of bulk
liquid Si. To our knowledge, this is the first study of a liquid surface by
first-principles molecular dynamics.Comment: 4 pages, 4 figures, submitted to PR
Dynamic Structure Factor of Liquid and Amorphous Ge From Ab Initio Simulations
We calculate the dynamic structure factor S(k,omega) of liquid Ge (l-Ge) at
temperature T = 1250 K, and of amorphous Ge (a-Ge) at T = 300 K, using ab
initio molecular dynamics. The electronic energy is computed using
density-functional theory, primarily in the generalized gradient approximation,
together with a plane wave representation of the wave functions and ultra-soft
pseudopotentials. We use a 64-atom cell with periodic boundary conditions, and
calculate averages over runs of up to 16 ps. The calculated liquid S(k,omega)
agrees qualitatively with that obtained by Hosokawa et al, using inelastic
X-ray scattering. In a-Ge, we find that the calculated S(k,omega) is in
qualitative agreement with that obtained experimentally by Maley et al. Our
results suggest that the ab initio approach is sufficient to allow approximate
calculations of S(k,omega) in both liquid and amorphous materials.Comment: 31 pages and 8 figures. Accepted for Phys. Rev.
Dependence of spin dephasing on initial spin polarization in a high-mobility two-dimensional electron system
We have studied the spin dynamics of a high-mobility two-dimensional electron
system in a GaAs/Al_{0.3}Ga_{0.7}As single quantum well by time-resolved
Faraday rotation and time-resolved Kerr rotation in dependence on the initial
degree of spin polarization, P, of the electrons. By increasing the initial
spin polarization from the low-P regime to a significant P of several percent,
we find that the spin dephasing time, , increases from about 20 ps to
200 ps; Moreover, increases with temperature at small spin
polarization but decreases with temperature at large spin polarization. All
these features are in good agreement with theoretical predictions by Weng and
Wu [Phys. Rev. B {\bf 68}, 075312 (2003)]. Measurements as a function of spin
polarization at fixed electron density are performed to further confirm the
theory. A fully microscopic calculation is performed by setting up and
numerically solving the kinetic spin Bloch equations, including the
D'yakonov-Perel' and the Bir-Aronov-Pikus mechanisms, with {\em all} the
scattering explicitly included. We reproduce all principal features of the
experiments, i.e., a dramatic decrease of spin dephasing with increasing
and the temperature dependences at different spin polarizations.Comment: 8 pages, 8 figures, to be published in PR
FAD binding, cobinamide binding and active site communication in the corrin reductase (CobR)
Adenosylcobalamin, the coenzyme form of vitamin B12, is one Nature's most complex coenzyme whose de novo biogenesis proceeds along either an anaerobic or aerobic metabolic pathway. The aerobic synthesis involves reduction of the centrally chelated cobalt metal ion of the corrin ring from Co(II) to Co(I) before adenosylation can take place. A corrin reductase (CobR) enzyme has been identified as the likely agent to catalyse this reduction of the metal ion. Herein, we reveal how Brucella melitensis CobR binds its coenzyme FAD (flavin dinucleotide) and we also show that the enzyme can bind a corrin substrate consistent with its role in reduction of the cobalt of the corrin ring. Stopped-flow kinetics and EPR reveal a mechanistic asymmetry in CobR dimer that provides a potential link between the two electron reduction by NADH to the single electron reduction of Co(II) to Co(I)
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