1,251 research outputs found
Ordering in Heisenberg Spin Glasses
For five different Heisenberg spin glass systems, torque experiments were
performed in applied magnetic fields up to . The Dzyaloshinski-Moriya
random anisotropy strengths, the in-field torque onset temperatures, and the
torque relaxation were measured. Critical exponents were estimated
independently using a standard protocol. The data are strong evidence for a
true spin glass ordered state which survives under high applied magnetic
fields; they can be interpreted consistently in terms of a chiral ordering
model with replica symmetry breaking as proposed by Kawamura and coworkers.Comment: 4 pages 4 figures. Revised version accepted by PR
A Surprising Lack of LGRB Metallicity Evolution with Redshift
Recent additions to the population of Long-duration Gamma Ray Burst (LGRB)
host galaxies with measured metallicities and host masses allow us to
investigate how the distributions of both these properties change with
redshift. We form a sample out to z of 2.5 which we show does not have strong
redshift dependent populations biases in mass and metallicity measurements.
Using this sample, we find a surprising lack of evolution in the LGRB
metallicity distribution across different redshifts and in particular the
fraction of LGRB hosts with relatively high-metallicity, that is those with
12+log(O/H) > 8.4, remains essentially constant out to z = 2.5. This result is
at odds with the evolution in the mass metallicity relation of typical
galaxies, which become progressively more metal poor with increasing redshift.
By converting the measured LGRB host masses and redshifts to expected
metallicities using redshift appropriate mass-metallicity relations, we further
find that the increase in LGRB host galaxy mass distribution with redshift seen
in the Perley et al. (2016) SHOALS sample is consistent with that needed to
preserve a non-evolving LGRB metallicity distribution. However, the estimated
LGRB host metallicity distribution is at least a quarter dex higher at all
redshifts than the measured metallicity distribution. This corresponds to about
a factor of two in raw metallicity and resolves much of the difference between
the LGRB host metallicity cutoffs determined by Graham & Fruchter (2017) and
Perley et al. (2016). As LGRB hosts do not follow the general mass metallicity
relations, there is no substitute for actually measuring their metallicities.Comment: 20 pages, 7 figures, 10 table
Orbital Variability in the Eclipsing Pulsar Binary PSR B1957+20
We have conducted timing observations of the eclipsing millisecond binary
pulsar PSR~B1957+20, extending the span of data on this pulsar to more than
five years. During this time the orbital period of the system has varied by
roughly , changing quadratically with time
and displaying an orbital period second derivative s. The previous measurement of a large negative
orbital period derivative reflected only the short-term behavior of the system
during the early observations; the orbital period derivative is now positive
and increasing rapidly. If, as we suspect, the PSR~B1957+20 system is
undergoing quasi-cyclic orbital period variations similar to those found in
other close binaries such as Algol and RS CVn, then the
companion to PSR~B1957+20 is most likely non-degenerate, convective, and
magnetically active.Comment: 9 pages, 3 figures, LaTeX, submitted ApJL 13 Dec. 1993, arz-00
Non linear transport properties of an insulating YBCO nano-bridge
We have investigated the transport properties of an insulating
sub-micrometric YBa2Cu3O7-d bridge, patterned on a thin film. As expected for a
variable-range-hopping insulator, transport is found non linear. The reduced
dimension allows for the observation of an individual fluctuator generating
random telegraph noise, which dynamics could be explored as a function of the
temperature and transport current. Some recordings clearly exhibit three levels
fluctuating resistance, with comparable level separation and correlated
dynamics, which likely result from the existence of two states or correlated
clustered charge traps
The faint-galaxy hosts of gamma-ray bursts
The observed redshifts and magnitudes of the host galaxies of gamma-ray
bursts (GRBs) are compared with the predictions of three basic GRB models, in
which the comoving rate density of GRBs is (1) proportional to the cosmic star
formation rate density, (2) proportional to the total integrated stellar
density and (3) constant. All three models make the assumption that at every
epoch the probability of a GRB occuring in a galaxy is proportional to that
galaxy's broad-band luminosity. No assumption is made that GRBs are standard
candles or even that their luminosity function is narrow. All three rate
density models are consistent with the observed GRB host galaxies to date,
although model (2) is slightly disfavored relative to the others. Models (1)
and (3) make very similar predictions for host galaxy magnitude and redshift
distributions; these models will be probably not be distinguished without
measurements of host-galaxy star-formation rates. The fraction of host galaxies
fainter than 28 mag may constrain the faint end of the galaxy luminosity
function at high redshift, or, if the fraction is observed to be low, may
suggest that the bursters are expelled from low-luminosity hosts. In all
models, the probability of finding a z<0.008 GRB among a sample of 11 GRBs is
less than 10^(-4), strongly suggesting that GRB 980425, if associated with
supernova 1998bw, represents a distinct class of GRBs.Comment: 7 pages, ApJ in press, revised to incorporate yet more new and
revised observational result
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