33,921 research outputs found
The high-energy gamma-ray light curve of PSR B1259 -63
The high-energy gamma-ray light curve of the binary system PSR B1259 -63, is
computed using the approach that successfully predicted the spectrum at
periastron. The simultaneous INTEGRAL and H.E.S.S. spectra taken 16 days after
periastron currently permit both a model with dominant radiative losses, high
pulsar wind Lorentz factor and modest efficiency as well as one with dominant
adiabatic losses, a slower wind and higher efficiency. In this paper we shown
how the long-term light curve may help to lift this degeneracy.Comment: 4 pages, to appear in proceedings of: Astrophysical Sources of High
Energy Particles and Radiation, Torun (2005
Extension of Gutenberg-Richter Distribution to Mw -1.3, No Lower Limit in Sight
With twelve years of seismic data from TauTona Gold Mine, South Africa, we show that mining-induced earthquakes follow the Gutenberg-Richter relation with no scale break down to the completeness level of the catalog, at moment magnitude MW −1.3. Events recorded during relatively quiet hours in 2006 indicate that catalog detection limitations, not earthquake source physics, controlled the previously reported minimum magnitude in this mine. Within the Natural Earthquake Laboratory in South African Mines (NELSAM) experiment\u27s dense seismic array, earthquakes that exhibit shear failure at magnitudes as small as MW −3.9 are observed, but we find no evidence that MW −3.9 represents the minimum magnitude. In contrast to previous work, our results imply small nucleation zones and that earthquake processes in the mine can readily be scaled to those in either laboratory experiments or natural faults
Constraints on the total coupling strength to bosons in iron based superconductors
At present, there is still no consistent interpretation of the normal and
superconducting properties of Fe-based superconductors (FeSCs). The strength of
the el-el interaction and the role of correlation effects are under debate.
Here, we examine several common materials and illustrate various problems and
concepts that are generic for all FeSCs. Based on empirical observations and
qualitative insight from density functional theory, we show that the
superconducting and low-energy thermodynamic properties of the FeSCs can be
described semi-quantitively within multiband Eliashberg theory. We account for
an important high-energy mass renormalization phenomenologically,and in
agreement with constraints provided by thermodynamic, optical, and
angle-resolved photoemission data. When seen in this way, all FeSCs with
40~K studied so far are found to belong to an {\it
intermediate} coupling regime. This finding is in contrast to the strong
coupling scenarios proposed in the early period of the FeSC history.We also
discuss several related issues, including the role of band shifts as measured
by the positions of van Hove singularities, and the nature of a recently
suggested quantum critical point in the strongly hole-doped systems
AFeAs (A = K, Rb, Cs). Using high-precision full relativistic GGA-band
structure calculations, we arrive at a somewhat milder mass renormalization in
comparison with previous studies. From the calculated mass anisotropies of all
Fermi surface sheets, only the -pocket near the corner of the BZ
is compatible with the experimentally observed anisotropy of the upper critical
field. pointing to its dominant role in the superconductivity of these three
compounds.Comment: 19 pages, 9 figure
Shock absorbing support and restraint means Patent
Shock absorbing couch for body support under high acceleration or deceleration force
XMM-Newton observations of PSr B1259-63 near the 2004 periastron passage
PSR B1259-63 is in a highly eccentric 3.4 year orbit with a Be star and
crosses the Be star disc twice per orbit, just prior to and just after
periastron. Unpulsed radio, X-ray and gamma-ray emission observed from the
binary system is thought to be due to the collision of pulsar wind with the
wind of Be star. We present here the results of new XMM-Newton observations of
the PSR B1259-63 system during the beginning of 2004 as the pulsar approached
the disc of Be star.We combine these results with earlier unpublished X-ray
data from BeppoSAX and XMM-Newton as well as with ASCA data. The detailed X-ray
lightcurve of the system shows that the pulsar passes (twice per orbit) through
a well-defined gaussian-profile disk with the half-opening angle (projected on
the pulsar orbit plane) ~18.5 deg. The intersection of the disk middle plane
with the pulsar orbital plane is inclined at ~70 deg to the major axis of the
pulsar orbit. Comparing the X-ray lightcurve to the TeV lightcurve of the
system we find that the increase of the TeV flux some 10--100 days after the
periastron passage is unambiguously related to the disk passage. At the moment
of entrance to the disk the X-ray photon index hardens from 1.8 up to 1.2
before returning to the steeper value 1.5. Such behaviour is not easily
accounted for by the model in which the X-ray emission is synchrotron emission
from the shocked pulsar wind. We argue that the observed hardening of the X-ray
spectrum is due to the inverse Compton or bremsstrahlung emission from 10-100
MeV electrons responsible for the radio synchrotron emission.Comment: 9 pages, accepted to MNRA
Benefit Transfer from Multiple Contingent Experiments: A Flexible Two-Step Model Combining Individual Choice Data with Community Characteristics
This study proposes a new approach to utilize information from existing choice experiments to predict policy outcomes for a transfer setting. Recognizing the difficulties from pooling raw data from experiments with different designs and sub-populations we first re-estimate all underlying Random Utility Models individually, and then combine them in a second stage process to form a weighted mixture density for the generation of policy-relevant welfare estimates. Using data from recent choice experiments on farmland preservation we illustrate that our strategy is more robust to transfer inaccuracies than single-site approaches. The specification of "intelligent" mixture weights will be a fruitful ground for future research in the area of Benefit Transfer.
Space and biotechnology: An industry profile
The results of a study conducted by the Center for Space and Advanced Technology (CSAT) for NASA-JSC are presented. The objectives were to determine the interests and attitudes of the U.S. biotechnology industry toward space biotechnology and to prepare a concise review of the current activities of the biotechnology industry. In order to accomplish these objectives, two primary actions were taken. First, a questionnaire was designed, reviewed, and distributed to U.S. biotechnology companies. Second, reviews of the various biotechnology fields were prepared in several aspects of the industry. For each review, leading figures in the field were asked to prepare a brief review pointing out key trends and current industry technical problems. The result is a readable narrative of the biotechnology industry which will provide space scientists and engineers valuable clues as to where the space environment can be explored to advance the U.S. biotechnology industry
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