3,922 research outputs found
Mean-atom-trajectory model for the velocity autocorrelation function of monatomic liquids
We present a model for the motion of an average atom in a liquid or
supercooled liquid state and apply it to calculations of the velocity
autocorrelation function and diffusion coefficient . The model
trajectory consists of oscillations at a distribution of frequencies
characteristic of the normal modes of a single potential valley, interspersed
with position- and velocity-conserving transits to similar adjacent valleys.
The resulting predictions for and agree remarkably well with MD
simulations of Na at up to almost three times its melting temperature. Two
independent processes in the model relax velocity autocorrelations: (a)
dephasing due to the presence of many frequency components, which operates at
all temperatures but which produces no diffusion, and (b) the transit process,
which increases with increasing temperature and which produces diffusion.
Because the model provides a single-atom trajectory in real space and time,
including transits, it may be used to calculate all single-atom correlation
functions.Comment: LaTeX, 8 figs. This is an updated version of cond-mat/0002057 and
cond-mat/0002058 combined Minor changes made to coincide with published
versio
A Low-Power Hardware-Friendly Optimisation Algorithm With Absolute Numerical Stability and Convergence Guarantees
We propose Dual-Feedback Generalized Proximal Gradient Descent (DFGPGD) as a
new, hardware-friendly, operator splitting algorithm. We then establish
convergence guarantees under approximate computational errors and we derive
theoretical criteria for the numerical stability of DFGPGD based on absolute
stability of dynamical systems. We also propose a new generalized proximal ADMM
that can be used to instantiate most of existing proximal-based composite
optimization solvers. We implement DFGPGD and ADMM on FPGA ZCU106 board and
compare them in light of FPGA's timing as well as resource utilization and
power efficiency. We also perform a full-stack, application-to-hardware,
comparison between approximate versions of DFGPGD and ADMM based on dynamic
power/error rate trade-off, which is a new hardware-application combined
metric
Magnetic field-modulated exciton generation in organic semiconductors: an intermolecular quantum correlation effect
Magnetoelectroluminescence (MEL) of organic semiconductor has been
experimentally tuned by adopting blended emitting layer consisting of both hole
and electron transporting materials. A theoretical model considering
intermolecular quantum correlation is proposed to demonstrate two fundamental
issues: (1) two mechanisms, spin scattering and spin mixing, dominate the two
different steps respectively in the process of the magnetic field modulated
generation of exciton; (2) the hopping rate of carriers determines the
intensity of MEL. Calculation successfully predicts the increase of singlet
excitons in low field with little change of triplet exciton population.Comment: 16 pages, 4 figure
Direct Ascorbic Acid Detection with Ferritin Immobilized on Single-Walled Carbon Nanotubes
Association Among Acrylamide, Blood Insulin, and Insulin Resistance in Adults
OBJECTIVE - Exposure to acrylamide in foodstuffs and smoking has become a worldwide concern. The effect of acrylamide on glucose homeostasis is not known. The goal of the present study Was to test the hypothesis that trace acrylamide exposure might be independently associated With both reduced blood insulin and reduced insulin resistance. RESEARCH DESIGN AND METHODS - We examined 1,356 participants with reliable measures of glucose homeostasis and Hb adducts of acrylamide (HbAA) and glycidamide from the National Health and Nutrition Examination Survey, 2003-2004. Glucose homeostasis was assessed by the measurement of plasma glucose, serum insulin, and the homeostasis model assessment of insulin resistance (HOMA- IR). RESULTS - in a linear regression model, a 1-unit increase in log HbAA was associated with a decrease in serum insulin (beta coefficient = -0.20 +/- 0.05, P = 0.001) and HOMA-IR (beta coefficient = -0.23 +/- 0.05, P < 0.001). After HbAA concentrations were divided into quartiles in the fully adjusted models, the adjusted serum insulin level and HOMA- IR significantly decreased across quartiles of HbAA (P-trend < 0.001 for both ). In subgroup analysis, the association of HbAA levels with HOMA-IR and insulin levels was stronger in subjects who were white or had ever smoked or in subjects With a lower education level or a BMI <25 or >30 kg/m(2). CONCLUSIONS - Acrylamide is associated with reduced serum insulin levels in adults. Further clinical and animal studies are warranted to clarify the putative causal relationship
Atomic mass dependence of \Xi^- and \overline{\Xi}^+ production in central 250 GeV \pi^- nucleon interactions
We present the first measurement of the atomic mass dependence of central
\Xi^- and \overline{\Xi}^+ production. It is measured using a sample of 22,459
\Xi^-'s and \overline{\Xi}^+'s produced in collisions between a 250 GeV \pi^-
beam and targets of beryllium, aluminum, copper, and tungsten. The relative
cross sections are fit to the two parameter function \sigma_0 A^\alpha, where A
is the atomic mass. We measure \alpha = 0.924+-0.020+-0.025, for Feynman-x in
the range -0.09 < x_F < 0.15.Comment: 10 pages, revtex, 2 figures, submitted to Phys. Rev.
Impaired DNA replication within progenitor cell pools promotes leukemogenesis.
Impaired cell cycle progression can be paradoxically associated with increased rates of malignancies. Using retroviral transduction of bone marrow progenitors followed by transplantation into mice, we demonstrate that inhibition of hematopoietic progenitor cell proliferation impairs competition, promoting the expansion of progenitors that acquire oncogenic mutations which restore cell cycle progression. Conditions that impair DNA replication dramatically enhance the proliferative advantage provided by the expression of Bcr-Abl or mutant p53, which provide no apparent competitive advantage under conditions of healthy replication. Furthermore, for the Bcr-Abl oncogene the competitive advantage in contexts of impaired DNA replication dramatically increases leukemogenesis. Impaired replication within hematopoietic progenitor cell pools can select for oncogenic events and thereby promote leukemia, demonstrating the importance of replicative competence in the prevention of tumorigenesis. The demonstration that replication-impaired, poorly competitive progenitor cell pools can promote tumorigenesis provides a new rationale for links between tumorigenesis and common human conditions of impaired DNA replication such as dietary folate deficiency, chemotherapeutics targeting dNTP synthesis, and polymorphisms in genes important for DNA metabolism
Disorder-Induced Critical Phenomena in Hysteresis: Numerical Scaling in Three and Higher Dimensions
We present numerical simulations of avalanches and critical phenomena
associated with hysteresis loops, modeled using the zero-temperature
random-field Ising model. We study the transition between smooth hysteresis
loops and loops with a sharp jump in the magnetization, as the disorder in our
model is decreased. In a large region near the critical point, we find scaling
and critical phenomena, which are well described by the results of an epsilon
expansion about six dimensions. We present the results of simulations in 3, 4,
and 5 dimensions, with systems with up to a billion spins (1000^3).Comment: Condensed and updated version of cond-mat/9609072,``Disorder-Induced
Critical Phenomena in Hysteresis: A Numerical Scaling Analysis'
Multi-decadal modulations in the Aleutian-Icelandic Low seesaw and the axial symmetry of the Arctic Oscillation signature, as revealed in the 20th century reanalysis
Seesaw relationship in intensity between the surface Aleutian and Icelandic Lows (AIS) is a manifestation of atmospheric teleconnection that bridges the interannual variability over the Pacific and Atlantic in particular winter months. Analysis of the 20th Century Reanalysis data reveals that the strength and timing of AIS have undergone multi-decadal modulations in conjunction with those in structure of the Arctic Oscillation (AO) signature, extracted in the leading mode of interannual sea-level pressure (SLP) variability over the extratropical Northern Hemisphere. Specifically, events of what may be called ‘pure AO’, in which SLP anomalies exhibit a high degree of axial symmetry in association with in-phase SLP variability between the midlatitude Atlantic and Pacific, tended to occur during multi-decadal periods in which the inter-basin teleconnection through AIS was active under the enhanced interannual variability of the Aleutian Low. In contrast, the axial symmetry of the AO pattern was apparently reduced during a multi-decadal period in which the AIS teleconnection was inactive under the weakened interannual variability of the Aleutian Low. In this period, the leading mode of interannual SLP variability represented a meridional seesaw between the Atlantic and Arctic, which resembles SLP anomaly pattern associated with the cold-ocean/warm-land (COWL) temperature pattern. These multi-decadal modulations in interannual AIS signal and the axial symmetry of the interannual AO pattern occurred under multi-decadal changes in the background state that also represented the polarity changes of the COWL-like anomaly pattern
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