3,625 research outputs found
Proposed New Test of Spin Effects in General Relativity
The recent discovery of a double-pulsar PSR J0737-3039A/B provides an
opportunity of unequivocally observing, for the first time, spin effects in
general relativity. Existing efforts involve detection of the precession of the
spinning body itself. However, for a close binary system, spin effects on the
orbit may also be discernable. Not only do they add to the advance of the
periastron (by an amount which is small compared to the conventional
contribution) but they also give rise to a precession of the orbit about the
spin direction. The measurement of such an effect would also give information
on the moment of inertia of pulsars
Viscosity of the Earth
Direct and indirect estimates of the variation of viscosity with depth in the mantle indicate that a low viscosity layer exists in the upper mantle. A viscosity varying with depth can be used to reconcile the various estimates of relaxation times. If the seismic anelasticity can be used as a guide the average viscosity of the lower mantle is about 10^(23)P. Combined with previous estimates of the upper mantle viscosity this gives a relaxation time of about 3000 years for the non-equilibrium bulge of the Earth. This is close to the time from the last ice age but is much less than the 10^7 years required if the non-equilibrium bulge is due to the changing rate of rotation which requires an average mantle viscosity of 10^(26) P. If the latter value is correct the activation volume for creep is much larger than for anelasticity or the effect of a phase change in the upper mantle is more effective in suppressing creep than attenuation.
The response of a layered viscous sphere to a surface load is calculated for a wide range of parameters including the above range of estimates for lower mantle viscosity. These results can be used to estimate the decay time, or the isostatic time scale, for various sized features
Self reported aggravating activities do not demonstrate a consistent directional pattern in chronic non specific low back pain patients: An observational study
Question: Do the self-reported aggravating activities of chronic non-specific low back pain
patients demonstrate a consistent directional pattern? Design: Cross-sectional observational
study. Participants: 240 chronic non specific low back pain patients. Outcome measure: We
invited experienced clinicians to classify each of the three self-nominated aggravating
activities from the Patient Specific Functional Scale by the direction of lumbar spine
movement. Patients were described as demonstrating a directional pattern if all nominated
activities moved the spine into the same direction. Analyses were undertaken to determine if
the proportion of patients demonstrating a directional pattern was greater than would be
expected by chance. Results: In some patients, all tasks did move the spine into the same
direction, but this proportion did not differ from chance (p = 0.328). There were no clinical or
demographic differences between those who displayed a directional pattern and those who did
not (all p > 0.05). Conclusion: Using patient self-reported aggravating activities we were
unable to demonstrate the existence of a consistent pattern of adverse movement in patients
with chronic non-specific low back pain
Disentanglement and Decoherence without dissipation at non-zero temperatures
Decoherence is well understood, in contrast to disentanglement. According to
common lore, irreversible coupling to a dissipative environment is the
mechanism for loss of entanglement. Here, we show that, on the contrary,
disentanglement can in fact occur at large enough temperatures even for
vanishingly small dissipation (as we have shown previously for decoherence).
However, whereas the effect of on decoherence increases exponentially with
time, the effect of on disentanglement is constant for all times,
reflecting a fundamental difference between the two phenomena. Also, the
possibility of disentanglement at a particular increases with decreasing
initial entanglement.Comment: 3 page
The Young Cluster Population of M82 Region B
We present observations obtained with the Advanced Camera for Surveys on
board the Hubble Space Telescope of the "fossil" starburst region B in the
nearby starburst galaxy M82. By comparing UBVI photometry with models, we
derive ages and extinctions for 35 U-band selected star clusters. We find that
the peak epoch of cluster formation occurred ~ 150 Myr ago, in contrast to
earlier work that found a peak formation age of 1.1 Gyr. The difference is most
likely due to our inclusion of U-band data, which are essential for accurate
age determinations of young cluster populations. We further show that the
previously reported turnover in the cluster luminosity function is probably due
to the neglect of the effect of extended sources on the detection limit. The
much younger cluster ages we derive clarifies the evolution of the M82
starburst. The M82-B age distribution now overlaps with the ages of: the
nuclear starburst; clusters formed on the opposite side of the disk; and the
last encounter with M81, some 220 Myr ago.Comment: 11 pages, 4 figures, accepted for publication in ApJ Letter
Far-Ultraviolet Color Gradients in Early-Type Galaxies
We discuss far-UV (1500 A) surface photometry and FUV-B color profiles for 8
E/S0 galaxies from images taken with the Ultraviolet Imaging Telescope,
primarily during the Astro-2 mission. In three cases, the FUV radial profiles
are more consistent with an exponential than a de Vaucouleurs function, but
there is no other evidence for the presence of a disk or of young, massive
stars. In all cases except M32 the FUV-B color becomes redder at larger radii.
There is a wide range of internal radial FUV-B color gradients. However, we
find no correlation between the FUV-B color gradients and internal metallicity
gradients based on Mg absorption features. We conclude that metallicity is not
the sole parameter controlling the "UV upturn component" in old populations.Comment: 11 pages; tar.gz file includes LaTeX text file, 3 PostScript figures.
Paper to be published in ApJ Letter
Diversity of gut microflora is required for the generation of B cell with regulatory properties in a skin graft model
B cells have been reported to promote graft rejection through alloantibody production. However, there is growing evidence that B cells can contribute to the maintenance of tolerance. Here, we used a mouse model of MHC-class I mismatched skin transplantation to investigate the contribution of B cells to graft survival. We demonstrate that adoptive transfer of B cells prolongs skin graft survival but only when the B cells were isolated from mice housed in low sterility "conventional" (CV) facilities and not from mice housed in pathogen free facilities (SPF). However, prolongation of skin graft survival was lost when B cells were isolated from IL-10 deficient mice housed in CV facilities. The suppressive function of B cells isolated from mice housed in CV facilities correlated with an anti-inflammatory environment and with the presence of a different gut microflora compared to mice maintained in SPF facilities. Treatment of mice in the CV facility with antibiotics abrogated the regulatory capacity of B cells. Finally, we identified transitional B cells isolated from CV facilities as possessing the regulatory function. These findings demonstrate that B cells, and in particular transitional B cells, can promote prolongation of graft survival, a function dependent on licensing by gut microflora
Reply to Comment on "Completely positive quantum dissipation"
This is the reply to a Comment by R. F. O'Connell (Phys. Rev. Lett. 87 (2001)
028901) on a paper written by the author (B. Vacchini, ``Completely positive
quantum dissipation'', Phys.Rev.Lett. 84 (2000) 1374, arXiv:quant-ph/0002094).Comment: 2 pages, revtex, no figure
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