240 research outputs found
Possible first order transition in the two-dimensional Ginzburg-Landau model induced by thermally fluctuating vortex cores
We study the two-dimensional Ginzburg-Landau model of a neutral superfluid in
the vicinity of the vortex unbinding transition. The model is mapped onto an
effective interacting vortex gas by a systematic perturbative elimination of
all fluctuating degrees of freedom (amplitude {\em and} phase of the order
parameter field) except the vortex positions. In the Coulomb gas descriptions
derived previously in the literature, thermal amplitude fluctuations were
neglected altogether. We argue that, if one includes the latter, the vortices
still form a two- dimensional Coulomb gas, but the vortex fugacity can be
substantially raised. Under the assumption that Minnhagen's generic phase
diagram of the two- dimensional Coulomb gas is correct, our results then point
to a first order transition rather than a Kosterlitz-Thouless transition,
provided the Ginzburg-Landau correlation length is large enough in units of a
microscopic cutoff length for fluctuations. The experimental relevance of these
results is briefly discussed. [Submitted to J. Stat. Phys.]Comment: 36 pages, LaTeX, 6 figures upon request, UATP2-DB1-9
Short report: Dynamics of Plasmodium falciparum malaria after sub-optimal therapy in Uganda.
We followed parasite genotypes of 75 patients for 42 days after treatment of uncomplicated malaria with chloroquine + sulfadoxine-pyrimethamine in Kampala, Uganda. Infections were complex (mean, 2.88 strains) and followed three patterns: 27% of patients eliminated all strains and remained parasite-free, 48% had a long aparasitemic interval followed by reappearance of original strains after 3-33 days (mean, 9.2 days), and 25% failed to clear original strains and required therapy after 3-35 days (mean, 17 days). These results highlight the complexity of malaria in Africa and have implications for efficacy trials, because missing late reappearances of strains could lead to misclassification of outcomes
Gender inequalities in transnational academic mobility and the ideal type of academic entrepreneur
Dynamic Scaling of Magnetic Flux Noise Near the KTB Transition in Overdamped Josephson Junction Arrays
We have used a dc Superconducting QUantum Interference Device to measure the
magnetic flux noise generated by the equilibrium vortex density fluctuations
associated with the Kosterlitz-Thouless-Berezinskii (KTB) transition in an
overdamped Josephson junction array. At temperatures slightly above the KTB
transition temperature, the noise is white for and scales as
for . Here , where is the correlation
length and is the dynamic exponent. Moreover, when all frequencies are
scaled by , data for different temperatures and frequencies collapse on
to a single curve. In addition, we have extracted the dynamic exponent and
found .Comment: 5 pages, LaTeX (REVTeX) format, requires epsfig and amstex style
files. 3 figures included. Tentatively scheduled for publication in Physical
Review Letters, 18 March, 199
DOSE REQUIREMENTS AND PLASMA CONCENTRATIONS OF PIPECURONIUM DURING BILATERAL RENAL EXCLUSION AND ORTHOTOPIC LIVER TRANSPLANTATION IN PIGS
We have studied five pigs undergoing bilateral clamping of the renal pedicles, seven pigs undergoing orthotopic liver transplantation and three control animals without surgery in order to examine the roles of the kidney and liver in the plasma clearance of pipecuronium. An i.v. infusion of pipecuronium was controlled to maintain a constant 90-95 % twitch depression throughout the investigation. The right sciatic nerve was stimulated continuously with supra-maximal stimuli at 0.1 Hz and the force of the corresponding evoked isometric muscle contraction was recorded continuously. Control pigs needed an infusion rate of pipecuronium 8-10.7 μg kg−1 min−1. In the renal group, it was necessary to reduce the infusion rate of pipecuronium by about 25% after clamping both renal vascular pedicles (P < 0.05 compared with controls); in pigs undergoing liver transplantation, it was necessary to reduce the rate by approximately 80% after clamping hepatic vessels (P < 0.05 compared with controls and from the period after clamping of renal vessels). After hepatic recirculation, the infusion rate of pipecuronium was increased progressively to a rate which corresponded to 50% of baseline values (P < 0.05 compared with the anhepatic phase and from controls). Plasma concentrations of pipecuronium were comparable in the three animal groups and did not change significantly during the study. These data suggest that the liver plays a more important role than the kidney in the plasma clearance of pipecuronium in pig
Fluctuation-dissipation theorem and flux noise in overdamped Josephson junction arrays
The form of the fluctuation-dissipation theorem for a resistively shunted
Josephson juction array is derived with the help of the method which
explicitely takes into acoount screening effects. This result is used to
express the flux noise power spectrum in terms of frequency dependent sheet
impedance of the array. The relation between noise amplitude and parameters of
the detection coil is analysed for the simplest case of a single-loop coil.Comment: ReVTeX, 8 page
The fully frustrated XY model with next nearest neighbor interaction
We introduce a fully frustrated XY model with nearest neighbor (nn) and next
nearest neighbor (nnn) couplings which can be realized in Josephson junction
arrays. We study the phase diagram for ( is the ratio
between nnn and nn couplings). When an Ising and a
Berezinskii-Kosterlitz-Thouless transitions are present. Both critical
temperatures decrease with increasing . For the array
undergoes a sequence of two transitions. On raising the temperature first the
two sublattices decouple from each other and then, at higher temperatures, each
sublattice becomes disorderd.Comment: 11 pages, 5 figure
The G0 Experiment: Apparatus for Parity-Violating Electron Scattering Measurements at Forward and Backward Angles
In the G0 experiment, performed at Jefferson Lab, the parity-violating
elastic scattering of electrons from protons and quasi-elastic scattering from
deuterons is measured in order to determine the neutral weak currents of the
nucleon. Asymmetries as small as 1 part per million in the scattering of a
polarized electron beam are determined using a dedicated apparatus. It consists
of specialized beam-monitoring and control systems, a cryogenic hydrogen (or
deuterium) target, and a superconducting, toroidal magnetic spectrometer
equipped with plastic scintillation and aerogel Cerenkov detectors, as well as
fast readout electronics for the measurement of individual events. The overall
design and performance of this experimental system is discussed.Comment: Submitted to Nuclear Instruments and Method
1/\omega-flux-noise and dynamical critical properties of two-dimensional XY-models
We have numerically studied the dynamic correlation functions in
thermodynamic equilibrium of two-dimensional O(2)-symmetry models with either
bond (RSJ) or site (TDGL) dissipation as a function of temperature T. We find
that above the critical temperature the frequency dependent flux noise
, with
and ,
while the dynamic critical exponents and .
Contrary to expectation the TDGL results are in closer agreement with the
experiments in Josephson-junction arrays by Shaw et al., than those from the
RSJ model. We find that these results are related to anomalous vortex diffusion
through vortex clusters.Comment: 4 pages Rev-Tex, two figures in postscript. To appear In Physical
Review Letter
Ingress of NaCl in concrete with alkali reactive aggregate: effect on silicon solubility
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