12,621 research outputs found
Generalizing Amdahlâs Law for Power and Energy
Extending Amdahl\u27s law to identify optimal power-performance configurations requires considering the interactive effects of power, performance, and parallel overhead
T-Shape Molecular Heat Pump
We report on the first molecular device of heat pump modeled by a T-shape
Frenkel-Kontorova lattice. The system is a three-terminal device with the
important feature that the heat can be pumped from the low-temperature region
to the high-temperature region through the third terminal. The pumping action
is achieved by applying a stochastic external force that periodically modulates
the atomic temperature. The temperature, the frequency and the system size
dependence of heat pump are briefly discussed.Comment: 6 figure
Effective potential for composite operators and for an auxiliary scalar field in a Nambu-Jona-Lasinio model
We derive the effective potentials for composite operators in a
Nambu-Jona-Lasinio (NJL) model at zero and finite temperature and show that in
each case they are equivalent to the corresponding effective potentials based
on an auxiliary scalar field. The both effective potentials could lead to the
same possible spontaneous breaking and restoration of symmetries including
chiral symmetry if the momentum cutoff in the loop integrals is large enough,
and can be transformed to each other when the Schwinger-Dyson (SD) equation of
the dynamical fermion mass from the fermion-antifermion vacuum (or thermal)
condensates is used. The results also generally indicate that two effective
potentials with the same single order parameter but rather different
mathematical expressions can still be considered physically equivalent if the
SD equation corresponding to the extreme value conditions of the two potentials
have the same form.Comment: 7 pages, no figur
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Changes in the milk metabolome of the Giant Panda (Ailuropoda melanoleuca) with time after birth: three phases in early lactation and progressive individual differences
Ursids (bears) in general, and giant pandas in particular, are highly altricial at birth. The components of bear milks and their changes with time may be uniquely adapted to nourish relatively immature neonates, protect them from pathogens, and support the maturation of neonatal digestive physiology. Serial milk samples collected from three giant pandas in early lactation were subjected to untargeted metabolite profiling and multivariate analysis. Changes in milk metabolites with time after birth were analysed by Principal Component Analysis, Hierarchical Cluster Analysis and further supported by Orthogonal Partial Least Square-Discriminant Analysis, revealing three phases of milk maturation: days 1â6 (Phase 1), days 7â20 (Phase 2), and beyond day 20 (Phase 3). While the compositions of Phase 1 milks were essentially indistinguishable among individuals, divergences emerged during the second week of lactation. OPLS regression analysis positioned against the growth rate of one cub tentatively inferred a correlation with changes in the abundance of a trisaccharide, isoglobotriose, previously observed to be a major oligosaccharide in ursid milks. Three artificial milk formulae used to feed giant panda cubs were also analysed, and were found to differ markedly in component content from natural panda milk. These findings have implications for the dependence of the ontogeny of all species of bears, and potentially other members of the Carnivora and beyond, on the complexity and sequential changes in maternal provision of micrometabolites in the immediate period after birth
Dynamical properties of the random Heisenberg chain
We use numerical techniques to study dynamical properties at finite
temperature () of the Heisenberg spin chain with random exchange couplings,
which realizes the random singlet (RS) fixed point in the low-energy limit.
Specifically, we study the dynamic spin structure factor , which
can be probed directly by inelastic neutron scattering experiments and, in the
limit of small , in nuclear magnetic resonance (NMR) experiments
through the spin-lattice relaxation rate . Our work combines three
complementary methods: exact diagonalization, matrix-product-state algorithms,
and stochastic analytic continuation of quantum Monte Carlo results in
imaginary time. Unlike the uniform system, whose low-energy excitations at low
are restricted to close to and , our study reveals a
continuous narrow band of low-energy excitations in , extending
throughout the Brillouin zone. Close to , the scaling properties of
these excitations are well captured by the RS theory, but we also see
disagreements with some aspects of the predicted -dependence further away
from . Furthermore we find spin diffusion effects close to that
are not contained within the RS theory but give non-negligible contributions to
the mean . To compare with NMR experiments, we consider the distribution
of the local values, which is broad, approximately described by a
stretched exponential. The mean value first decreases with , but starts to
increase and diverge below a crossover temperature. Although a similar
divergent behavior has been found for the static uniform susceptibility, this
divergent behavior of has never been seen in experiments. Our results
show that the divergence of the mean is due to rare events in the
disordered chains and is concealed in experiments, where the typical
value is accessed.Comment: 19 pages, 14 figure
PowerPack: Energy Profiling and Analysis of High-Performance Systems and Applications
Energy efficiency is a major concern in modern high-performance computing system design. In the past few years, there has been mounting evidence that power usage limits system scale and computing density, and thus, ultimately system performance. However, despite the impact of power and energy on the computer systems community, few studies provide insight to where and how power is consumed on high-performance systems and applications. In previous work, we designed a framework called PowerPack that was the first tool to isolate the power consumption of devices including disks, memory, NICs, and processors in a high-performance cluster and correlate these measurements to application functions. In this work, we extend our framework to support systems with multicore, multiprocessor-based nodes, and then provide in-depth analyses of the energy consumption of parallel applications on clusters of these systems. These analyses include the impacts of chip multiprocessing on power and energy efficiency, and its interaction with application executions. In addition, we use PowerPack to study the power dynamics and energy efficiencies of dynamic voltage and frequency scaling (DVFS) techniques on clusters. Our experiments reveal conclusively how intelligent DVFS scheduling can enhance system energy efficiency while maintaining performance
P2Xâ Knock-Out Mice Reveal a Major Sensory Role for Urothelially Released ATP
The present study explores the possible involvement of a purinergic mechanism in mechanosensory transduction in the bladder using P2Xâ receptor knock-out (P2Xâ â»ââ») and wild-type control (P2Xâ âșââș) mice. Immunohistochemistry revealed abundant nerve fibers in a suburothelial plexus in the mouse bladder that are immunoreactive to anti-P2Xâ. P2Xâ -positive staining was completely absent in the subepithelial plexus of the P2Xâ â»ââ» mice, whereas staining for calcitonin gene-related peptide and vanilloid receptor 1 receptors remained. Using a novel superfused mouse bladderâpelvic nerve preparation, we detected a release of ATP proportional to the extent of bladder distension in both P2Xâ â»ââ» mice, whereas staining for calcitonin gene-related peptide and vanilloid receptor 1 receptors remained. Using a novel superfused mouse bladderâpelvic nerve preparation, we detected a release of ATP proportional to the extent of bladder distension in both P2Xâ âșââș and P2Xâ â»ââ» mice, although P2Xâ â»ââ» bladder had an increased capacity compared with that of the P2Xâ âșââș bladder. The activity of multifiber pelvic nerve afferents increased progressively during gradual bladder distension (at a rate of 0.1 ml/min). However, the bladder afferents from P2Xâ â»ââ» mice showed an attenuated response to bladder distension. Mouse bladder afferents of P2Xâ âșââș, but not P2Xâ â»ââ», were rapidly activated by intravesical injections of P2X agonists (ATP or α,ÎČ-methylene ATP) and subsequently showed an augmented response to bladder distension. By contrast, P2X antagonists [2âČ,3âČ-O-(2,4,6-trinitrophenyl)-ATP and pyridoxal 5-phosphate 6-azophenyl-2âČ,4âČ-disulfonic acid] and capsaicin attenuated distension-induced discharges in bladder afferents. These data strongly suggest a major sensory role for urothelially released ATP acting via P2Xâ receptors on a subpopulation of pelvic afferent fibers
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