27,513 research outputs found
Effects of aminoperimidine on electrolyte transport across amphibian skin
The effect of aminoperimidine (AP)on transepithelial Na+ transport and Cl- conductance (G(Cl)) of isolated amphibian skin (Bufo viridis and Rana esculenta) was analyzed using transepithelial and intracellular electrophysiological techniques. AP, applied at concentrations between 30 and 100 mu M from the mucosal side, stimulated Na+ transport rapidly and reversibly by more than 30% of the control value due to an increase in apical membrane Na+ permeability. Influence of AP on basolateral membrane conductance and effective driving force for Na+ were negligible. Voltage-activated G(Cl) of toad skin, but not the resting, deactivated conductance, as well as spontaneously high G(Cl) in frog skin was rapidly inhibited by AP in a concentration-dependent manner. The half-maximal inhibitory concentration of 20 mu M is the highest hithero reported inhibitory power for G(Cl) in amphibian skin. The effect of AP on G(Cl) was slowly and incompletely reversible even after brief exposure to the agent. Serosal application of AP had similar, albeit delayed effects on both Nai and Cl- transport. AP did not interfere with the Cl- pathway after it was opened by 100-300 mu M CPT-cAMP, a membrane-permeable, nonhydrolyzed analogue of cAMP. Inhibition of the voltage-activated G(Cl) by AP was attenuated or missing when AP was applied during voltage perturbation to serosa-positive potentials. Since AP is positively charged at physiological pH, it suggests that the affected site is located inside the Cl- pathway at a certain distance from the external surface. AP affects then the Na+ and Cl- transport pathways independent of each other. The nature of chemical interference with AP, which is responsible for the influence on the transport of Na+ and Cl-, remains to be elucidated
Numerical Investigations of SO(4) Emergent Extended Symmetry in Spin-1/2 Heisenberg Antiferromagnetic Chains
The antiferromagnetic Heisenberg chain is expected to have an extended
symmetry, [SU(2)xSU(2)]/Z 2 , in the infrared limit, whose physical
interpretation is that the spin and dimer order parameters form the components
of a common 4-dimensional vector. Here we numerically in- vestigate this
emergent symmetry using quantum Monte Carlo simulations of a modified
Heisenberg chain (the J-Q model) in which the logarithmic scaling corrections
of the conventional Heisenberg chain can be avoided. We show how the two- and
three-point spin and dimer correlation func- tions approach their forms
constrained by conformal field theory as the system size increases and
numerically confirm the expected effects of the extended symmetry on various
correlation functions
Daily minimum and maximum temperature simulation over complex terrain
Spatiotemporal simulation of minimum and maximum temperature is a fundamental
requirement for climate impact studies and hydrological or agricultural models.
Particularly over regions with variable orography, these simulations are
difficult to produce due to terrain driven nonstationarity. We develop a
bivariate stochastic model for the spatiotemporal field of minimum and maximum
temperature. The proposed framework splits the bivariate field into two
components of "local climate" and "weather." The local climate component is a
linear model with spatially varying process coefficients capturing the annual
cycle and yielding local climate estimates at all locations, not only those
within the observation network. The weather component spatially correlates the
bivariate simulations, whose matrix-valued covariance function we estimate
using a nonparametric kernel smoother that retains nonnegative definiteness and
allows for substantial nonstationarity across the simulation domain. The
statistical model is augmented with a spatially varying nugget effect to allow
for locally varying small scale variability. Our model is applied to a daily
temperature data set covering the complex terrain of Colorado, USA, and
successfully accommodates substantial temporally varying nonstationarity in
both the direct-covariance and cross-covariance functions.Comment: Published in at http://dx.doi.org/10.1214/12-AOAS602 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
A simple method for designing or analyzing an optical communication link
A simple method is described for determining the performance of a free space optical communication link. The method can be used either in the system design (synthesis) mode or in the performance evaluation (analysis) mode. Although restricted to photo counting based detection of pulse position modulated signals, the method is still sufficiently general to accommodate space-based, as well as ground-based, reception
Boydbolt, a positive-latch, simple-release fastener
Fastener /Boydbolt/ has recently been designed to furnish positive lock and release characteristics that positively prevent accidental adverse functions of lock or release
Optimum predetection diversity receiving system Patent
Development of optimum pre-detection diversity combining receiving system adapted for use with amplitude modulation, phase modulation, and frequency modulation system
Project Fog Drops 5. Task 1: A numerical model of advection fog. Task 2: Recommendations for simplified individual zero-gravity cloud physics experiments
A two-dimensional numerical model was used to investigate the formation of marine advection fog. The model predicts the evolution of potential temperature, horizontal wind, water vapor content, and liquid water content in a vertical cross section of the atmosphere as determined by vertical turbulent transfer and horizontal advection, as well as radiative cooling and drop sedimentation. The model is designed to simulate the formation, development, or dissipation of advection fog in response to transfer of heat and moisture between the atmosphere and the surface as driven by advection over horizontal discontinuities in the surface temperature. Results from numerical simulations of advection fog formation are discussed with reference to observations of marine fog. A survey of candidate fog or cloud microphysics experiments which might be performed in the low gravity environment of a shuttle-type spacecraft in presented. Recommendations are given for relatively simple experiments which are relevent to fog modification problems
Indicators of Conformal Field Theory: entanglement entropy and multiple-point correlators
The entanglement entropy (EE) of quantum systems is often used as a test of
low-energy descriptions by conformal field theory (CFT). Here we point out that
this is not a reliable indicator, as the EE often shows the same behavior even
when a CFT description is not correct (as long as the system is asymptotically
scale-invariant). We use constraints on the scaling dimension given by the CFT
with SU(2) symmetry to provide alternative tests with two- and four-point
correlation functions, showing examples for quantum spin models in 1+1
dimensions. In the case of a critical amplitude-product state expressed in the
valence-bond basis (where the amplitudes decay as a power law of the bond
length and the wave function is the product of all bond amplitudes), we show
that even though the EE exhibits the expected CFT behavior, there is no CFT
description of this state. We provide numerical tests of the behavior predicted
by CFT for the correlation functions in the critical transverse-field Ising
chain and the - spin chain, where the conformal structure is well
understood. That behavior is not reproduced in the amplitude-product state.Comment: 9 pages, 11 figure
On the mass of a Kerr-anti-de Sitter spacetime in D dimensions
We show how to compute the mass of a Kerr-anti-de Sitter spacetime with
respect to the anti-de Sitter background in any dimension, using a
superpotential which has been derived from standard Noether identities. The
calculation takes no account of the source of the curvature and confirms
results obtained for black holes via the first law of thermodynamics.Comment: minor changes; accepted by CQ
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