15,132 research outputs found
Power law tails of time correlations in a mesoscopic fluid model
In a quenched mesoscopic fluid, modelling transport processes at high
densities, we perform computer simulations of the single particle energy
autocorrelation function C_e(t), which is essentially a return probability.
This is done to test the predictions for power law tails, obtained from mode
coupling theory. We study both off and on-lattice systems in one- and
two-dimensions. The predicted long time tail ~ t^{-d/2} is in excellent
agreement with the results of computer simulations. We also account for finite
size effects, such that smaller systems are fully covered by the present theory
as well.Comment: 11 pages, 12 figure
Immunity in barren and enriched housed pigs differing in baseline cortisol concentration
It was shown recently that barren housed pigs (small pens, no substrate) have a blunted circadian rhythm of salivary cortisol as compared to enriched housed pigs (large pens with daily fresh bedding). In the light period, enriched housed pigs showed significantly higher concentrations of cortisol in saliva than barren housed pigs, whereas in the dark period, cortisol concentrations were low in both enriched and barren housed pigs. In the present study, the immunological consequences of the difference in baseline salivary cortisol concentration in the light period were evaluated. It appeared that leukocyte and lymphocyte distributions, and in vitro lymphocyte proliferation following ConcanavalineA (ConA) stimulation in the assay using purified lymphocytes were not affected. However, barren and enriched housed pigs did show a different proliferation response to ConA in the whole blood assay. At day 2 of culture, proliferation was higher in barren housed pigs than in enriched housed pigs, whereas at day 4 of culture, proliferation was higher in enriched housed pigs than in barren housed pigs. Lymphocyte proliferation at day 2 of culture in the whole blood assay correlated negatively with plasma cortisol levels, which might thus explain the higher proliferation in barren housed pigs at day 2 of culture. The in vivo humoral and cellular (delayed type hypersensitivity, DTH) immune response to KLH was not affected by housing conditions. We conclude that, although baseline salivary cortisol concentrations differ between enriched and barren housed pigs, immune function appears to be relatively unaffected.
Irreversible Thermodynamics in Multiscale Stochastic Dynamical Systems
This work extends the results of the recently developed theory of a rather
complete thermodynamic formalism for discrete-state, continuous-time Markov
processes with and without detailed balance. We aim at investigating the
question that whether and how the thermodynamic structure is invariant in a
multiscale stochastic system. That is, whether the relations between
thermodynamic functions of state and process variables remain unchanged when
the system is viewed at different time scales and resolutions. Our results show
that the dynamics on a fast time scale contribute an entropic term to the
"internal energy function", , for the slow dynamics. Based on the
conditional free energy , one can then treat the slow dynamics as if
the fast dynamics is nonexistent. Furthermore, we show that the free energy,
which characterizes the spontaneous organization in a system without detailed
balance, is invariant with or without the fast dynamics: The fast dynamics is
assumed to reach stationarity instantaneously on the slow time scale; they have
no effect on the system's free energy. The same can not be said for the entropy
and the internal energy, both of which contain the same contribution from the
fast dynamics. We also investigate the consequences of time-scale separation in
connection to the concepts of quasi-stationaryty and steady-adiabaticity
introduced in the phenomenological steady-state thermodynamics
Observation of two-orbital spin-exchange interactions with ultracold SU(N)-symmetric fermions
We report on the direct observation of spin-exchanging interactions in a
two-orbital SU(N)-symmetric quantum gas of ytterbium in an optical lattice. The
two orbital states are represented by two different (meta-)stable electronic
configurations of fermionic Yb-173. A strong spin-exchange between particles in
the two separate orbitals is mediated by the contact interaction between atoms,
which we characterize by clock shift spectroscopy in a 3D optical lattice. We
find the system to be SU(N)-symmetric within our measurement precision and
characterize all relevant scattering channels for atom pairs in combinations of
the ground and the excited state. Elastic scattering between the orbitals is
dominated by the antisymmetric channel, which leads to the strong spin-exchange
coupling. The exchange process is directly observed, by characterizing the
dynamic equilibration of spin imbalances between two large ensembles in the two
orbital states, as well as indirectly in atom pairs via interaction shift
spectroscopy in a 3D lattice. The realization of a stable SU(N)-symmetric
two-orbital Hubbard Hamiltonian opens the route towards experimental quantum
simulation of condensed-matter models based on orbital interactions, such as
the Kondo lattice model.Comment: Correction: In the original version of this preprint the assignment
of states with symmetric electronic wavefunction (|eg+>) and with
antisymmetric electronic wavefunction (|eg->) to the observed spectral lines
was inverted. This has been corrected in the current version. The results of
the paper remain unchanged, with the exchange coupling being inverted to a
ferromagnetic exchang
Magneto-resistance in a lithography defined single constrained domain wall spin valve
We have measured domain wall magnetoresistance in a single lithographically constrained domain wall. An H-shaped Ni nano-bridge was fabricated by e-beam lithography with the two sides being single magnetic do- mains showing independent magnetic switching. The connection between the sides constraining the domain wall when the sides line up anti-parallel. The magneto-resistance curve clearly identifies the magnetic con- figurations that are expected from a spin valve-like structure. The value of the magneto-resistance at room temperature is around 0.1% or 0.4 . This value is shown to be in agreement with a theoretical formulation based on spin accumulation. Micromagnetic simulations show it is possible to reduce the size of the domain wall further by shortening the length of the bridge
Letter to the Editor by M.C. DeRuiter and A.C. Gittenberger-de Groot relating to: Technical Improvements in Corrosion Casting of Small Specimens: A Study on Mesonephric Tubules and Vessels of Chicken Embryos. [by A. Carretero, H. Ditrich, M. Navarro, H. Splechtna, J. Ruberte, Scanning Microscopy Vol. 7(4), p. 1333-1338 (1993)].
Dear Editor,
The topic of scanning electron microscopy (SEM) investigation of casting of vessels in the embryo still holds our interest. We are particularly focused on the possibilities of early injection as a method to support angiogenesis and vasculogenesis research in the embryo. It is questionable whether our technique leads to unreliable results because of severe trauma to the embryo as suggested by the above mentioned authors. The lower success yield might very well be the result of the higher friability of the embryo in general in this young stage
Thermoelectric efficiency at maximum power in a quantum dot
We identify the operational conditions for maximum power of a
nanothermoelectric engine consisting of a single quantum level embedded between
two leads at different temperatures and chemical potentials. The corresponding
thermodynamic efficiency agrees with the Curzon-Ahlborn expression up to
quadratic terms in the gradients, supporting the thesis of universality beyond
linear response.Comment: 4 pages, 3 figure
Scattering Theory of Charge-Current Induced Magnetization Dynamics
In ferromagnets, charge currents can excite magnons via the spin-orbit
coupling. We develop a novel and general scattering theory of charge current
induced macrospin magnetization torques in normal metalferromagnetnormal
metal layers. We apply the formalism to a dirty GaAs(Ga,Mn)AsGaAs system.
By computing the charge current induced magnetization torques and solving the
Landau-Lifshitz-Gilbert equation, we find magnetization switching for current
densities as low as ~A/cm. Our results are in agreement
with a recent experimental observation of charge-current induced magnetization
switching in (Ga,Mn)As.Comment: Final version accepted by EP
Nonpolar resistive switching in Cu/SiC/Au non-volatile resistive memory devices
Amorphous silicon carbide (a-SiC) based resistive memory (RM) Cu/a-SiC/Au devices were fabricated and their resistive switching characteristics investigated. All four possible modes of nonpolar resistive switching were achieved with ON/OFF ratio in the range 10 6-10 8. Detailed current-voltage I-V characteristics analysis suggests that the conduction mechanism in low resistance state is due to the formation of metallic filaments. Schottky emission is proven to be the dominant conduction mechanism in high resistance state which results from the Schottky contacts between the metal electrodes and SiC. ON/OFF ratios exceeding 10 7 over 10 years were also predicted from state retention characterizations. These results suggest promising application potentials for Cu/a-SiC/Au RM
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