40,014 research outputs found
Evidence For Intrinsic Magnetic Moments in Black Hole Candidates
We show that the power law part of the quiescent x-ray emissions of neutron stars in low mass x-ray binaries is magnetospheric in origin. It can be very accurately calculated from rates of spin and the times brighter luminosity at the transition to the hard spectral state. We establish that the spectral state transition for neutron stars is a magnetospheric propeller effect. We test the hypothesis that the similar spectral state switches and quiescent power law emissions of the black hole candidates might be magnetospheric effects. In the process we derive proposed magnetic moments and rates of spin for them and accurately predict their quiescent luminosities. We discuss other tests of the hypothesis and consider some attractive aspects of a unified magnetospheric model for low mass x-ray binaries. We also consider some of the changes that would be needed for strong-field gravity theories to accomodate intrinsic magnetic moments in collapsed objects
High-Redshift Superclustering of QSO Absorption Line Systems on 100 Mpc Scales
We have analyzed the clustering of C IV absorption line systems in an
extensive new catalog of heavy element QSO absorbers. The catalog permits
exploration of clustering over a large range in both scale (from about 1 to
over 300 Mpc) and redshift (z from 1.2 to 4.5). We find significant evidence
(5.0 sigma) that C IV absorbers are clustered on comoving scales of 100 Mpc and
less --- similar to the size of voids and walls found in galaxy redshift
surveys of the local universe --- with a mean correlation function over these scales. We find, on these scales, that the mean
correlation function at low (z=1.7), medium (z=2.4), and high redshift (z=3.0)
is , , and , respectively.
Thus, the superclustering is present even at high redshift; furthermore, it
does not appear that the superclustering scale, in comoving coordinates, has
changed significantly since then. We find 7 QSOs with rich groups of absorbers
(potential superclusters) that account for a significant portion of the
clustering signal, with 2 at redshift . We find that the
superclustering is just as evident if we take instead of 0.5;
however, the inferred scale of clustering is then 240 Mpc , which is larger
than the largest scales of clustering known at present. This discrepancy may be
indicative of a larger value of , and hence . The evolution of
the correlation function on 50 Mpc scales is consistent with that expected in
cosmologies with density parameter ranging from 0.1 to 1.
Finally, we find no evidence for clustering on scales greater than 100 Mpc
() or 240 Mpc ().Comment: 16 LaTeX pages with 3 encapsulated Postscript figures included, uses
AASTeX (v. 4.0) available at ftp://ftp.aas.org/pubs/ , to appear in The
Astrophysical Journal Letter
Anisotropy beta functions
The flow of couplings under anisotropic scaling of momenta is computed in
theory in 6 dimensions. It is shown that the coupling decreases as
momenta of two of the particles become large, keeping the third momentum fixed,
but at a slower rate than the decrease of the coupling if all three momenta
become large simultaneously. This effect serves as a simple test of effective
theories of high energy scattering, since such theories should reproduce these
deviations from the usual logarithmic scale dependence.Comment: uuencoded ps file, 6 page
Temperature dependence of the phonon entropy of vanadium
The phonon density-of-states (DOS) of elemental vanadium was measured at elevated temperatures by inelastic neutron scattering. The phonon softening predicted by thermal expansion against the bulk modulus is much larger than the measured shifts in phonon energies. We conclude that the phonon anharmonicities associated with thermal expansion are largely canceled by effects from phonon-phonon scattering. Prior measurements of the heat capacity and calculations of the electronic entropy of vanadium are assessed, and consistency requires an explicit temperature dependence of the phonon DOS. Using data from the literature, similar results are found for chromium, niobium, titanium, and zirconium
Scotin, a novel p53-inducible proapoptotic protein located in the ER and the nuclear membrane
p53 is a transcription factor that induces growth arrest or apoptosis in response to cellular stress. To identify new p53-inducible proapoptotic genes, we compared, by differential display, the expression of genes in spleen or thymus of normal and p53 nullizygote mice after γ-irradiation of whole animals. We report the identification and characterization of human and mouse Scotin homologues, a novel gene directly transactivated by p53. The Scotin protein is localized to the ER and the nuclear membrane. Scotin can induce apoptosis in a caspase-dependent manner. Inhibition of endogenous Scotin expression increases resistance to p53-dependent apoptosis induced by DNA damage, suggesting that Scotin plays a role in p53-dependent apoptosis. The discovery of Scotin brings to light a role of the ER in p53-dependent apoptosis
Diffuse Neutron Scattering Study of Relaxor Ferroelectric (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3(PZN-xPT)
Diffuse neutron scattering is a valuable tool to obtain information about the
size and orientation of the polar nanoregions that are a characteristic feature
of relaxor ferroelectrics. In this paper, we present new diffuse scattering
results obtained on Pb(Zn1/3Nb2/3)O3 (PZN for short) and
(1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3(PZN-xPT)single crystals (with x=4.5 and 9%),
around various Bragg reflections and along three symmetry directions in the
[100]-[011] zone. Diffuse scattering is observed around reflections with mixed
indices, (100), (011) and (300), and along transverse and diagonal directions
only. No diffuse scattering is found in longitudinal scans. The diffuse
scattering peaks can be fitted well with a Lorentzian function, from which a
correlation length is extracted. The correlation length increases with
decreasing temperatures down to the transition at Tc, first following a
Curie-Weiss law, then departing from it and becoming flat at very low
temperatures. These results are interpreted in terms of three temperature
regions: 1) dynamic polarization fluctuations (i.e. with a finite lifetime) at
high temperatures, 2) static polarization reorientations (condensation of polar
nanoregions) that can still reorient as a unit (relaxor behavior) at
intermediate temperatures and 3) orientational freezing of the polar
nanoregions with random strain fields in pure PZN or a structural phase
transition in PZN-xPT at low temperatures. The addition of PT leads to a
broadening of the diffuse scattering along the diagonal ([111]) relative to the
transverse ([100]) direction, indicating a change in the orientation of the
polar regions. Also, with the addition of PT, the polar nanoregions condense at
a higher temperature above Tc.Comment: AIP 6x9 style files, 9 pages, 5 figures, Conference-Fundamental
Physics of Ferroelectrics 200
Graph-Embedding Empowered Entity Retrieval
In this research, we improve upon the current state of the art in entity
retrieval by re-ranking the result list using graph embeddings. The paper shows
that graph embeddings are useful for entity-oriented search tasks. We
demonstrate empirically that encoding information from the knowledge graph into
(graph) embeddings contributes to a higher increase in effectiveness of entity
retrieval results than using plain word embeddings. We analyze the impact of
the accuracy of the entity linker on the overall retrieval effectiveness. Our
analysis further deploys the cluster hypothesis to explain the observed
advantages of graph embeddings over the more widely used word embeddings, for
user tasks involving ranking entities
Renormalization-group Calculation of Color-Coulomb Potential
We report here on the application of the perturbative renormalization-group
to the Coulomb gauge in QCD. We use it to determine the high-momentum
asymptotic form of the instantaneous color-Coulomb potential and
of the vacuum polarization . These quantities are
renormalization-group invariants, in the sense that they are independent of the
renormalization scheme. A scheme-independent definition of the running coupling
constant is provided by , and of , where , and
is a finite QCD mass scale. We also show how to calculate the
coefficients in the expansion of the invariant -function , where all coefficients are scheme-independent.Comment: 24 pages, 1 figure, TeX file. Minor modifications, incorporating
referee's suggestion
Large harmonic softening of the phonon density of states of uranium
Phonon density-of-states curves were obtained from inelastic neutron scattering spectra from the three crystalline phases of uranium at temperatures from 50 to 1213 K. The alpha -phase showed an unusually large thermal softening of phonon frequencies. Analysis of the vibrational power spectrum showed that this phonon softening originates with the softening of a harmonic solid, as opposed to vibrations in anharmonic potentials. It follows that thermal excitations of electronic states are more significant thermodynamically than are the classical volume effects. For the alpha-beta and beta-gamma phase transitions, vibrational and electronic entropies were comparable
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