4,584 research outputs found
The Fermi LAT detection of magnetar-like pulsar PSR J1846-0258 at high-energy gamma-rays
We report the detection of the pulsed signal of the radio-quiet magnetar-like
pulsar PSR J1846-0258 in the high-energy \gr-ray data of the Fermi Large Area
Telescope (Fermi LAT). We produced phase-coherent timing models exploiting RXTE
PCA and Swift XRT monitoring data for the post- (magnetar-like) outburst period
from 2007 August 28 to 2016 September 4, with independent verification using
INTEGRAL ISGRI and Fermi GBM data. Phase-folding barycentric arrival times of
selected Fermi LAT events from PSR J1846-0258, resulted in a 4.2 sigma
detection (30--100 MeV) of a broad pulse consistent in shape and aligned in
phase with the profiles that we measured with Swift XRT (2.5--10 keV), INTEGRAL
ISGRI (20--150 keV) and Fermi GBM (20--300 keV). The pulsed flux (30--100 MeV)
is (3.91 +/- 0.97)E-9 photons/(cm^2 s MeV). Declining significances of the
INTEGRAL ISGRI 20--150 keV pulse profiles suggest fading of the pulsed hard
X-ray emission during the post-outburst epochs. We revisited with greatly
improved statistics the timing and spectral characteristics of PSR B1509-58 as
measured with the Fermi LAT. The broad-band pulsed emission spectra (from 2 keV
up to GeV energies) of PSR J1846-0258 and PSR B1509-58 can be accurately
described with similarly curved shapes, with maximum luminosities at 3.5 +/-
1.1 MeV (PSR J1846-0258) and 2.23 +/- 0.11 MeV (PSR B1509-58). We discuss
possible explanations for observational differences between Fermi LAT detected
pulsars that reach maximum luminosities at GeV energies, like the second
magnetar-like pulsar PSR J1119-6127, and pulsars with maximum luminosities at
MeV energies, which might be due to geometric differences rather than exotic
physics in high-B fields.Comment: 13 pages, 8 figures, accepted by MNRAS on 2017 November 3
Preferred Basis in a Measurement Process
The effect of decoherence is analysed for a free particle, interacting with
an environment via a dissipative coupling. The interaction between the particle
and the environment occurs by a coupling of the position operator of the
particle with the environmental degrees of freedom. By examining the exact
solution of the density matrix equation one finds that the density matrix
becomes completely diagonal in momentum with time while the position space
density matrix remains nonlocal. This establishes the momentum basis as the
emergent 'preferred basis' selected by the environment which is contrary to the
general expectation that position should emerge as the preferred basis since
the coupling with the environment is via the position coordinate.Comment: Standard REVTeX format, 10 pages of output. Accepted for publication
in Phys. Rev
Structural and electronic properties of the metal-metal intramolecular junctions of single-walled carbon nanotubes
Several intramolecular junctions (IMJs) connecting two metallic (11, 8) and
(9, 6) carbon nanotubes along their common axis have been realized by using a
layer-divided technique to the nanotubes and introducing the topological
defects. Atomic structure of each IMJ configuration is optimized with a
combination of density-functional theory (DFT) and the universal force field
(UFF) method, based upon which a four-orbital tight-binding calculation is made
on its electronic properties. Different topological defect structures and their
distributions on the IMJ interfaces have been found, showing decisive effects
on the localized density of states, while the sigma-pi coupling effect is
negligible near Fermi energy (EF). Finally, a new IMJ model has been proposed,
which probably reflects a real atomic structure of the M-M IMJ observed in the
experiment [Science 291, 97 (2001)].Comment: 11 pages and 3 figure
Accuracy of computerized tomography in determining hepatic tumor size in patients receiving liver transplantation or resection
Computerized tomography (CT) of liver is used in oncologic practice for staging tumors, evaluating response to treatment, and screening patients for hepatic resection. Because of the impact of CT liver scan on major treatment decisions, it is important to assess its accuracy. Patients undergoing liver transplantation or resection provide a unique opportunity to test the accuracy of hepatic-imaging techniques by comparison of finding of preoperative CT scan with those at gross pathologic examination of resected specimens. Forty-one patients who had partial hepatic resection (34 patients) or liver transplantation (eight patients) for malignant (30 patients) or benign (11 patients) tumors were evaluable. Eight (47%) of 17 patients with primary malignant liver tumors, four (31%) of 13 patients with metastatic liver tumors, and two (20%) of 10 patients with benign liver tumors had tumor nodules in resected specimens that were not apparent on preoperative CT studies. These nodules varied in size from 0.1 to 1.6 cm. While 11 of 14 of these nodules were 1.0 cm. These results suggest that conventional CT alone may be insufficient to accurately determine the presence or absence of liver metastases, extent of liver involvement, or response of hepatic metastases to treatment
Through-membrane electron-beam lithography for ultrathin membrane applications
We present a technique to fabricate ultrathin (down to 20 nm) uniform
electron transparent windows at dedicated locations in a SiN membrane for in
situ transmission electron microscopy experiments. An electron-beam (e-beam)
resist is spray-coated on the backside of the membrane in a KOH- etched cavity
in silicon which is patterned using through-membrane electron-beam lithography.
This is a controlled way to make transparent windows in membranes, whilst the
topside of the membrane remains undamaged and retains its flatness. Our
approach was optimized for MEMS-based heating chips but can be applied to any
chip design. We show two different applications of this technique for (1)
fabrication of a nanogap electrode by means of electromigration in thin
free-standing metal films and (2) making low-noise graphene nanopore devices
Paraconductivity in Carbon Nanotubes
We report the calculation of paraconductivity in carbon nanotubes above the
superconducting transition temperature. The complex behavior of
paraconductivity depending upon the tube radius, temperature and magnetic field
strength is analyzed. The results are qualitatively compared with recent
experimental observations in carbon nanotubes of an inherent transition to the
superconducting state and pronounced thermodynamic fluctuations above .
The application of our results to single-wall and multi-wall carbon nanotubes
as well as ropes of nanotubes is discussed.Comment: 7 pages, 1 figur
Positive Quantum Brownian Evolution
Using the independent oscillator model with an arbitrary system potential, we
derive a quantum Brownian equation assuming a correlated total initial state.
Although not of Lindblad form, the equation preserves positivity of the density
operator on a restricted set of initial states
Completely Positive Quantum Dissipation
A completely positive master equation describing quantum dissipation for a
Brownian particle is derived starting from microphysical collisions, exploiting
a recently introduced approach to subdynamics of a macrosystem. The obtained
equation can be cast into Lindblad form with a single generator for each
Cartesian direction. Temperature dependent friction and diffusion coefficients
for both position and momentum are expressed in terms of the collision
cross-section.Comment: 8 pages, revtex, no figure
Wave function recombination instability in cold atom interferometers
Cold atom interferometers use guiding potentials that split the wave function
of the Bose-Einstein condensate and then recombine it. We present theoretical
analysis of the wave function recombination instability that is due to the weak
nonlinearity of the condensate. It is most pronounced when the accumulated
phase difference between the arms of the interferometer is close to an odd
multiple of PI and consists in exponential amplification of the weak ground
state mode by the strong first excited mode. The instability exists for both
trapped-atom and beam interferometers.Comment: 4 pages, 5 figure
Negative differential resistance in nanotube devices
Carbon nanotube junctions are predicted to exhibit negative differential
resistance, with very high peak-to-valley current ratios even at room
temperature. We treat both nanotube p-n junctions and undoped
metal-nanotube-metal junctions, calculating quantum transport through the
self-consistent potential within a tight-binding approximation. The undoped
junctions in particular may be suitable for device integration.Comment: 4 pages, 4 figures, to appear in Physical Review Letter
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