572 research outputs found
Ondansetron does not inhibit the analgesic effect of alfentanil
5-Hydroxytryptamine (5-HT) causes antinociception via presynaptic 5-HT3 (5-HT subtype 3) receptors on primary afferent nociceptive neurones in the spinal cord dorsal horn. Therefore, ondansetron (a 5-HT3 receptor antagonist) may increase the perception of a noxious stimulus or decrease the effects of concurrently administered antinociceptive drugs. Using a randomized, doubleblind, crossover study design, we have tested this hypothesis in eight healthy volunteers who, on three different days, received either ondansetron and placebo, ondansetron and alfentanil or placebo and alfentanil. Experimental pain was induced with heat, cold, mechanical pressure and electrical stimulation. Ondansetron alone did not change the response to any of the experimental tests, but alfentanil and the combination ondansetron- alfentanil significantly changed the response compared with ondansetron alone. There was no difference between alfentanil alone and the combination ondansetron-alfentanil. We conclude that ondansetron does not change the response to pressure, heat, cold or electrical nociceptive stimuli or antagonize the analgesic effect of alfentani
Tachyon Tube and Supertube
We search for tubular solutions in unstable D3-brane. With critical electric
field E=1, solutions representing supertubes, which are supersymmetric bound
states of fundamental strings, D0-branes, and a cylindrical D2-brane, are found
and shown to exhibit BPS-like property. We also point out that boosting such a
{\it tachyon tube} solution generates string flux winding around the tube,
resulting in helical electric fluxes on the D2-brane. We also discuss issues
related to fundamental string, absence of magnetic monopole, and finally more
tachyon tubes with noncritical electric field.Comment: 21 pages, 3 figure
Non-Abelian Chern-Simons Particles and their Quantization
A many--body Schr\"odinger equation for non--Abelian Chern--Simons particles
is obtained from both point--particle and field--theoretic pictures. We present
a particle Lagrangian and a field theoretic Lagrange density, and discuss their
properties. Both are quantized by the symplectic method of Hamiltonian
reduction. An --body Schr\"odinger equation for the particles is obtained
from both starting points. It is shown that the resulting interaction between
particles can be replaced by non--trivial boundary conditions. Also, the
equation is compared with the one given in the literature.Comment: 18 pages, MIT preprint CTP # 227
Critical behavior of certain antiferromagnets with complicated ordering: Four-loop \ve-expansion analysis
The critical behavior of a complex N-component order parameter
Ginzburg-Landau model with isotropic and cubic interactions describing
antiferromagnetic and structural phase transitions in certain crystals with
complicated ordering is studied in the framework of the four-loop
renormalization group (RG) approach in (4-\ve) dimensions. By using
dimensional regularization and the minimal subtraction scheme, the perturbative
expansions for RG functions are deduced and resummed by the Borel-Leroy
transformation combined with a conformal mapping. Investigation of the global
structure of RG flows for the physically significant cases N=2 and N=3 shows
that the model has an anisotropic stable fixed point governing the continuous
phase transitions with new critical exponents. This is supported by the
estimate of the critical dimensionality obtained from six loops
via the exact relation established for the complex and real
hypercubic models.Comment: LaTeX, 16 pages, no figures. Expands on cond-mat/0109338 and includes
detailed formula
Entanglement Entropy from a Holographic Viewpoint
The entanglement entropy has been historically studied by many authors in
order to obtain quantum mechanical interpretations of the gravitational
entropy. The discovery of AdS/CFT correspondence leads to the idea of
holographic entanglement entropy, which is a clear solution to this important
problem in gravity. In this article, we would like to give a quick survey of
recent progresses on the holographic entanglement entropy. We focus on its
gravitational aspects, so that it is comprehensible to those who are familiar
with general relativity and basics of quantum field theory.Comment: Latex, 30 pages, invited review for Classical and Quantum Gravity,
minor correction
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Dispersion measure variability for 36 millisecond pulsars at 150MHz with LOFAR
Context. Radio pulses from pulsars are affected by plasma dispersion, which results in a frequency-dependent propagation delay. Variations in the magnitude of this effect lead to an additional source of red noise in pulsar timing experiments, including pulsar timing arrays (PTAs) that aim to detect nanohertz gravitational waves.
Aims. We aim to quantify the time-variable dispersion with much improved precision and characterise the spectrum of these variations.
Methods. We use the pulsar timing technique to obtain highly precise dispersion measure (DM) time series. Our dataset consists of observations of 36 millisecond pulsars, which were observed for up to 7.1 yr with the LOw Frequency ARray (LOFAR) telescope at a centre frequency of ~150 MHz. Seventeen of these sources were observed with a weekly cadence, while the rest were observed at monthly cadence.
Results. We achieve a median DM precision of the order of 10−5 cm−3 pc for a significant fraction of our sources. We detect significant variations of the DM in all pulsars with a median DM uncertainty of less than 2 × 10−4 cm−3 pc. The noise contribution to pulsar timing experiments at higher frequencies is calculated to be at a level of 0.1–10 μs at 1.4 GHz over a timespan of a few years, which is in many cases larger than the typical timing precision of 1 μs or better that PTAs aim for. We found no evidence for a dependence of DM on radio frequency for any of the sources in our sample.
Conclusions. The DM time series we obtained using LOFAR could in principle be used to correct higher-frequency data for the variations of the dispersive delay. However, there is currently the practical restriction that pulsars tend to provide either highly precise times of arrival (ToAs) at 1.4 GHz or a high DM precision at low frequencies, but not both, due to spectral properties. Combining the higher-frequency ToAs with those from LOFAR to measure the infinite-frequency ToA and DM would improve the result
The LOFAR Tied-Array All-Sky Survey: Timing of 35 radio pulsars and an overview of the properties of the LOFAR pulsar discoveries
The LOFAR Tied-Array All-Sky Survey (LOTAAS) is the most sensitive untargeted radio pulsar survey performed at low radio frequencies (119-151 MHz) to date and has discovered 76 new radio pulsars, including the 23.5-s pulsar J0250+5854, which up until recently was the slowest spinning radio pulsar known. In this paper, we report on the timing solutions of 35 pulsars discovered by LOTAAS, which include a nulling pulsar and a mildly recycled pulsar, and thereby complete the full timing analysis of the LOTAAS pulsar discoveries. We give an overview of the findings from the full LOTAAS sample of 76 pulsars, discussing their pulse profiles, radio spectra, and timing parameters. We found that the pulse profiles of some of the pulsars show profile variations in time or frequency, and while some pulsars show signs of scattering, a large majority display no pulse broadening. The LOTAAS discoveries have on average steeper radio spectra and longer spin periods (1.4
7), as well as lower spin-down rates (3.1
7) compared to the known pulsar population. We discuss the cause of these differences and attribute them to a combination of selection effects of the LOTAAS survey as well as previous pulsar surveys, though we cannot rule out that older pulsars tend to have steeper radio spectra
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