17,770 research outputs found
Apparent Clustering of Intermediate-redshift Galaxies as a Probe of Dark Energy
We show the apparent redshift-space clustering of galaxies in redshift range
of 0.2--0.4 provides surprisingly useful constraints on dark energy component
in the universe, because of the right balance between the density of objects
and the survey depth. We apply Fisher matrix analysis to the the Luminous Red
Galaxies (LRGs) in the Sloan Digital Sky Survey (SDSS), as a concrete example.
Possible degeneracies in the evolution of the equation of state (EOS) and the
other cosmological parameters are clarified.Comment: 5 pages, 3 figures, Phys.Rev.Lett., replaced with the accepted
versio
Novel Precursors for Boron Nanotubes: The Competition of Two-Center and Three-Center Bonding in Boron Sheets
We present a new class of boron sheets, composed of triangular and hexagonal
motifs, that are more stable than structures considered to date and thus are
likely to be the precursors of boron nanotubes. We describe a simple and clear
picture of electronic bonding in boron sheets and highlight the importance of
three-center bonding and its competition with two-center bonding, which can
also explain the stability of recently discovered boron fullerenes. Our
findings call for reconsideration of the literature on boron sheets, nanotubes,
and clusters.Comment: 4 pages, 4 figures, 1 tabl
Discovery of X-ray pulsations from "next Geminga" - PSR J1836+5925
We report the X-ray pulsation of ~173.3 ms for the "next Geminga", PSR
J1836+5925, with recent XMM-Newton investigations. The X-ray periodicity is
consistent wtih the gamma-ray ephemeris at the same epoch. The X-ray folded
light curve has a sinusoidal structure which is different from the
double-peaked gamma-ray pulse profile. We have also analysed the X-ray
phase-averaged spectra which shows the X-ray emission from PSR J1836+5925 is
thermal dominant. This suggests the X-ray pulsation mainly originates from the
modulated hot spot on the stellar surface.Comment: 7 pages, 3 figures, 1 table, accepted for publication in ApJ Lette
Progress in thin film GaAs solar cells
Solar cells using polycrystalline films of gallium arsenid
A NuSTAR Observation of the Gamma-ray Emitting Millisecond Pulsar PSR J1723-2837
We report on the first NuSTAR observation of the gamma-ray emitting
millisecond pulsar binary PSR J1723-2837. X-ray radiation up to 79 keV is
clearly detected and the simultaneous NuSTAR and Swift spectrum is well
described by an absorbed power-law with a photon index of ~1.3. We also find
X-ray modulations in the 3-10 keV, 10-20 keV, 20-79 keV, and 3-79 keV bands at
the 14.8-hr binary orbital period. All these are entirely consistent with
previous X-ray observations below 10 keV. This new hard X-ray observation of
PSR J1723-2837 provides strong evidence that the X-rays are from the
intrabinary shock via an interaction between the pulsar wind and the outflow
from the companion star. We discuss how the NuSTAR observation constrains the
physical parameters of the intrabinary shock model.Comment: Accepted for publication in ApJ. 5 pages, 3 figure
Multiwavelength properties of a new Geminga-like pulsar: PSR J2021+4026
In this paper, we report a detailed investigation of the multiwavelength
properties of a newly detected gamma-ray pulsar, PSR J2021+4026, in both
observational and theoretical aspects. We firstly identify an X-ray source in
the XMM-Newton serendipitous source catalogue, 2XMM J202131.0+402645, located
within the 95% confidence circle of PSR J2021+4026. With an archival Chandra
observation, this identification provides an X-ray position with arcsecond
accuracy which is helpful in facilitating further investigations. Searching for
the pulsed radio emission at the position of 2XMM J202131.0+402645 with a 25-m
telescope at Urumqi Astronomical Observatory resulted in null detection and
places an upper-limit of 0.1~mJy for any pulsed signal at 18~cm. Together with
the emission properties in X-ray and gamma-ray, the radio quietness suggests
PSR J2021+4026 to be another member of Geminga-like pulsars. In the radio sky
survey data, extended emission features have been identified in the gamma-ray
error circle of PSR J2021+4026. We have also re-analyzed the gamma-ray data
collected by FERMI's Large Area Telescope. We found that the X-ray position of
2XMM J202131.0+402645 is consistent with that of the optimal gamma-ray timing
solution. We have further modeled the results in the context of outer gap model
which provides us with constraints for the pulsar emission geometry such as
magnetic inclination angle and the viewing angle. We have also discussed the
possibility of whether PSR J2021+4026 has any physical association with the
supernova remnant G78.2+2.1 (gamma-Cygni).Comment: 11 pages, 14 figure
Experimental Quantum Cloning with Prior Partial Information
When prior partial information about a state to be cloned is available, it
can be cloned with a fidelity higher than that of universal quantum cloning. We
experimentally verify this intriguing relationship between the cloning fidelity
and the prior information by reporting the first experimental optimal quantum
state-dependent cloning, using nuclear magnetic resonance techniques. Our
experiments may further have important implications into many quantum
information processing protocols.Comment: 4 pages, 2 figure
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