345 research outputs found
General properties of response functions of nonequilibrium steady states
We derive general properties, which hold for both quantum and classical
systems, of response functions of nonequilibrium steady states. We clarify
differences from those of equilibrium states. In particular, sum rules and
asymptotic behaviors are derived, and their implications are discussed. Since
almost no assumptions are made, our results are applicable to diverse physical
systems. We also demonstrate our results by a molecular dynamics simulation of
a many-body interacting system.Comment: After publication of this paper, several typos were found, which have
been fixed in the erratum (J. Phys. Soc. Jpn., 80 (2011) 128001). All the
corrections have been made in this updated arXive version. 13 pages with 3
figure
Indications of Universal Excess Fluctuations in Nonequilibrium Systems
The fluctuation in electric current in nonequilibrium steady states is
investigated by molecular dynamics simulation of macroscopically uniform
conductors. At low frequencies, appropriate decomposition of the spectral
intensity of current into thermal and excess fluctuations provides a simple
picture of excess fluctuations behaving as shot noise. This indicates that the
fluctuation-dissipation relation may be violated in a universal manner by the
appearance of shot noise for a wide range of systems with particle or momentum
transport.Comment: 4 pages, 4 figures; title changed, major revision; to appear in J.
Phys. Soc. Jp
Nonequilibrium Molecular Dynamics Simulation of Interacting Many Electrons Scattered by Lattice Vibrations
We propose a new model suitable for a nonequilibrium molecular dynamics (MD)
simulation of electrical conductors. The model consists of classical electrons
and atoms. The atoms compose a lattice vibration system. The electrons are
scattered by electron-electron and electron-atom interactions. Since the
scattering cross section is physically more important than the functional form
of a scattering potential, we propose to devise the electron-atom interaction
potential in such a way that its scattering cross section agrees with that of
quantum-mechanical one. To demonstrate advantages of the proposed model, we
perform a nonequilibrium MD simulation assuming a doped semiconductor at room
or higher temperature. In the linear response regime, we confirm Ohm's law, the
dispersion relations and the fluctuation-dissipation relation. Furthermore, we
obtain reasonable dependence of the electrical conductivity on temperature,
despite the fact that our model is a classical model.Comment: 21 pages, 11 figure
Long-Time Behavior of Velocity Autocorrelation Function for Interacting Particles in a Two-Dimensional Disordered System
The long-time behavior of the velocity autocorrelation function (VACF) is
investigated by the molecular dynamics simulation of a two-dimensional system
which has both a many-body interaction and a random potential. With
strengthening the random potential by increasing the density of impurities, a
crossover behavior of the VACF is observed from a positive tail, which is
proportional to t^{-1}, to a negative tail, proportional to -t^{-2}. The latter
tail exists even when the density of particles is the same order as the density
of impurities. The behavior of the VACF in a nonequilibrium steady state is
also studied. In the linear response regime the behavior is similar to that in
the equilibrium state, whereas it changes drastically in the nonlinear response
regime.Comment: 12 pages, 5 figure
Long-time Low-latency Quantum Memory by Dynamical Decoupling
Quantum memory is a central component for quantum information processing
devices, and will be required to provide high-fidelity storage of arbitrary
states, long storage times and small access latencies. Despite growing interest
in applying physical-layer error-suppression strategies to boost fidelities, it
has not previously been possible to meet such competing demands with a single
approach. Here we use an experimentally validated theoretical framework to
identify periodic repetition of a high-order dynamical decoupling sequence as a
systematic strategy to meet these challenges. We provide analytic
bounds-validated by numerical calculations-on the characteristics of the
relevant control sequences and show that a "stroboscopic saturation" of
coherence, or coherence plateau, can be engineered, even in the presence of
experimental imperfection. This permits high-fidelity storage for times that
can be exceptionally long, meaning that our device-independent results should
prove instrumental in producing practically useful quantum technologies.Comment: abstract and authors list fixe
Anomalous Heat Conduction in Three-Dimensional Nonlinear Lattices
Heat conduction in three-dimenisional nonlinear lattice models is studied
using nonequilibrium molecular dynamics simulations. We employ the FPU model,
in which there exists a nonlinearity in the interaction of biquadratic form. It
is confirmed that the thermal conductivity, the ratio of the energy flux to the
temperature gradient, diverges in systems up to 128x128x256 lattice sites. This
size corresponds to nanoscopic to mesoscopic scales of several tens of
nanometers. From these results, we conjecture that the energy transport in
insulators with perfect crystalline order exhibits anomalous behavior. The
effects of lattice structure, random impurities, and natural length in
interactions are also examined. We find that face-centered cubic (fcc) lattices
display stronger divergence than simple cubic lattices. When impurity sites of
infinitely large mass, which are hence fixed, are randomly distributed, such
divergence vanishes.Comment: 10pages, 10 figures, Fig. 1 is replaced and some minor corrections
were mad
Effects of Simulated Microgravity on Embryonic Stem Cells
There have been many studies on the biological effects of simulated microgravity (SMG) on differentiated cells or adult stem cells. However, there has been no systematic study on the effects of SMG on embryonic stem (ES) cells. In this study, we investigated various effects (including cell proliferation, cell cycle distribution, cell differentiation, cell adhesion, apoptosis, genomic integrity and DNA damage repair) of SMG on mouse embryonic stem (mES) cells. Mouse ES cells cultured under SMG condition had a significantly reduced total cell number compared with cells cultured under 1 g gravity (1G) condition. However, there was no significant difference in cell cycle distribution between SMG and 1G culture conditions, indicating that cell proliferation was not impaired significantly by SMG and was not a major factor contributing to the total cell number reduction. In contrast, a lower adhesion rate cultured under SMG condition contributed to the lower cell number in SMG. Our results also revealed that SMG alone could not induce DNA damage in mES cells while it could affect the repair of radiation-induced DNA lesions of mES cells. Taken together, mES cells were sensitive to SMG and the major alterations in cellular events were cell number expansion, adhesion rate decrease, increased apoptosis and delayed DNA repair progression, which are distinct from the responses of other types of cells to SMG
Wnt inhibitors Dkk1 and Sost are downstream targets of BMP signaling through the type IA receptor (BMPRIA) in osteoblasts
The bone morphogenetic protein (BMP) and Wnt signaling pathways both contribute essential roles in regulating bone mass. However, the molecular interactions between these pathways in osteoblasts are poorly understood. We recently reported that osteoblast-targeted conditional knockout (cKO) of BMP receptor type IA (BMPRIA) resulted in increased bone mass during embryonic development, where diminished expression of Sost as a downstream effector of BMPRIA resulted in increased Wnt/Β-catenin signaling. Here, we report that Bmpr1a cKO mice exhibit increased bone mass during weanling stages, again with evidence of enhanced Wnt/Β-catenin signaling as assessed by Wnt reporter TOPGAL mice and TOPFLASH luciferase. Consistent with negative regulation of the Wnt pathway by BMPRIA signaling, treatment of osteoblasts with dorsomorphin, an inhibitor of Smad-dependent BMP signaling, enhanced Wnt signaling. In addition to Sost , Wnt inhibitor Dkk1 also was downregulated in cKO bone. Expression levels of Dkk1 and Sost were upregulated by BMP2 treatment and downregulated by Noggin. Moreover, expression of a constitutively active Bmpr1a transgene in mice resulted in the upregulation of both Dkk1 and Sost and partially rescued the Bmpr1a cKO bone phenotype. These effectors are differentially regulated by mitogen-activated protein kinase (MAPK) p38 because pretreatment of osteoblasts with SB202190 blocked BMP2-induced Dkk1 expression but not Sost . These results demonstrate that BMPRIA in osteoblasts negatively regulates endogenous bone mass and Wnt/Β-catenin signaling and that this regulation may be mediated by the activities of Sost and Dkk1 . This study highlights several interactions between BMP and Wnt signaling cascades in osteoblasts that may be amenable to therapeutic intervention for the modification of bone mass density. © 2010 American Society for Bone and Mineral ResearchPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65056/1/90806_ftp.pd
Initial experience of transumbilical laparoendoscopic single-site surgery of partial adrenalectomy in patient with aldosterone-producing adenoma
<p>Abstract</p> <p>Background</p> <p>Laparoscopic single-site surgery has recently emerged in the field of urology and this minimally-invasive surgery has resulted in a further reduction in morbidity compared with traditional laparoscopy. We present our initial experience with laparoendoscopic single-site surgery of partial adrenalectomy (LESS-PA) to treat aldosterone-producing adenomas.</p> <p>Case presentation</p> <p>A 60-year-old woman was diagnosed with aldosterone-producing macroadenomas in the left adrenal and aldosterone-producing microadenomas in the right adrenal. A two-step operation was planned. The first step involved transumbilical LESS-PA for the left adrenal tumors. A multichannel port was inserted through the center of the umbilicus and the left adrenal gland was approached using bent instruments according to standard traditional laparoscopic procedures. The tumors were resected using an ultrasonic scalpel, and the resected site was coagulated using a vessel sealing instrument and then sealed with fibrin glue. Operative time was 123 minutes and blood loss was minimal. The patient was discharged from hospital within 72 hours. Her right adrenal microadenomas will be treated in the next several months.</p> <p>Conclusions</p> <p>Although our experience is limited, LESS-PA appears to be safe and feasible for treating aldosterone-producing adenomas. More cases and comparisons with the multiport technique are needed before drawing any definite conclusions concerning the technique.</p
Configurational Thermodynamics of Alloyed Nanoparticles with Adsorbates
Changes in the chemical configuration of alloyed nanoparticle (NP) catalysts induced by adsorbates under working conditions, such as reversal in core–shell preference, are crucial to understand and design NP functionality. We extend the cluster expansion method to predict the configurational thermodynamics of alloyed NPs with adsorbates based on density functional theory data. Exemplified with PdRh NPs having O-coverage up to a monolayer, we fully detail the core–shell behavior across the entire range of NP composition and O-coverage with quantitative agreement to in situ experimental data. Optimally fitted cluster interactions in the heterogeneous system are the key to enable quantitative Monte Carlo simulations and design
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