20,537 research outputs found
Dynamical stability of entanglement between spin ensembles
We study the dynamical stability of the entanglement between the two spin
ensembles in the presence of an environment. For a comparative study, we
consider the two cases: a single spin ensemble, and two ensembles linearly
coupled to a bath, respectively. In both circumstances, we assume the validity
of the Markovian approximation for the bath. We examine the robustness of the
state by means of the growth of the linear entropy which gives a measure of the
purity of the system. We find out macroscopic entangled states of two spin
ensembles can stably exist in a common bath. This result may be very useful to
generate and detect macroscopic entanglement in a common noisy environment and
even a stable macroscopic memory.Comment: 4 pages, 1 figur
Nanostructuring GaN using microsphere lithography
The authors report on the fabrication and characterization of nanopillar arrays on GaN substrates using the technique of microsphere lithography. Self-assembled hexagonally packed silica microsphere arrays were formed on GaN wafers by spin coating and tilting. By precision control of process parameters, a monolayer can be formed over a wide region. The silica microspheres act as a hard mask for pattern transfer of the nanostructures. After dry etching, arrays of nanopillars were formed on the surface of the wafer. The ordered nanostructures can be clearly seen in the scanning electron microscopy images, while photoluminescence measurements revealed a twofold enhancement of light emission intensity. © 2008 American Vacuum Society.published_or_final_versio
High-Energy emissions from the Pulsar/Be binary system PSR J2032+4127/MT91 213
PSR J2032+4127 is a radio-loud gamma-ray-emitting pulsar; it is orbiting
around a high-mass Be type star with a very long orbital period of 25-50years,
and is approaching periastron, which will occur in late 2017/early 2018. This
system comprises with a young pulsar and a Be type star, which is similar to
the so-called gamma-ray binary PSR~B1259-63/LS2883. It is expected therefore
that PSR J2032+4127 shows an enhancement of high-energy emission caused by the
interaction between the pulsar wind and Be wind/disk around periastron. Ho et
al. recently reported a rapid increase in the X-ray flux from this system. In
this paper, we also confirm a rapid increase in the X-ray flux along the orbit,
while the GeV flux shows no significant change. We discuss the high-energy
emissions from the shock caused by the pulsar wind and stellar wind interaction
and examine the properties of the pulsar wind in this binary system. We argue
that the rate of increase of the X-ray flux observed by Swift indicates (1) a
variation of the momentum ratio of the two-wind interaction region along the
orbit, or (2) an evolution of the magnetization parameter of the pulsar wind
with the radial distance from the pulsar. We also discuss the pulsar wind/Be
disk interaction at the periastron passage, and propose the possibility of
formation of an accretion disk around the pulsar. We model high-energy
emissions through the inverse-Compton scattering process of the
cold-relativistic pulsar wind off soft photons from the accretion disk.Comment: 18 pages, 23 figures, 1 Table, accepted for publication in Ap
Broken time-reversal symmetry in Josephson junction involving two-band superconductors
A novel time-reversal symmetry breaking state is found theoretically in the
Josephson junction between the two-gap superconductor and the conventional
s-wave superconductor. This occurs due to the frustration between the three
order parameters analogous to the two antiferromagnetically coupled XY-spins
put under a magnetic field. This leads to the interface states with the
energies inside the superconducting gap. Possible experimental observations of
this state with broken time-reversal symmetry are discussed.Comment: 9 pages, 1 figur
Probing spacetime foam with extragalactic sources
Due to quantum fluctuations, spacetime is probably ``foamy'' on very small
scales. We propose to detect this texture of spacetime foam by looking for
core-halo structures in the images of distant quasars. We find that the Very
Large Telescope interferometer will be on the verge of being able to probe the
fabric of spacetime when it reaches its design performance. Our method also
allows us to use spacetime foam physics and physics of computation to infer the
existence of dark energy/matter, independent of the evidence from recent
cosmological observations.Comment: LaTeX, 11 pages, 1 figure; version submitted to PRL; several
references added; very useful comments and suggestions by Eric Perlman
incorporate
The X-ray modulation of PSR J2032+4127/MT91 213 during the Periastron Passage in 2017
We present the Neil Gehrels Swift Observatory (Swift), Fermi Large Area
Telescope (Fermi-LAT), and Karl G. Jansky Very Large Array (VLA) observations
of the gamma-ray binary PSR J2032+4127/MT91 213, of which the periastron
passage has just occurred in November 2017. In the Swift X-ray light curve, the
flux was steadily increasing before mid-October 2017, however, a sharp X-ray
dip on a weekly time-scale is seen during the periastron passage, followed by a
post-periastron X-ray flare lasting for ~20 days. We suggest that the X-ray dip
is caused by (i) an increase of the magnetization parameter at the shock, and
(ii) the suppression due to the Doppler boosting effect. The 20-day
post-periastron flare could be a consequence of the Be stellar disk passage by
the pulsar. An orbital GeV modulation is also expected in our model, however,
no significant variability is seen in the Fermi-LAT light curve. We suspect
that the GeV emission resulted from the interaction between the binary's
members is hidden behind the bright magnetospheric emission of the pulsar.
Pulsar gating technique would be useful to remove the magnetospheric emission
and recover the predicted GeV modulation, if an accurate radio timing solution
over the periastron passage is provided in the future.Comment: 6 pages, including 2 figures. Accepted for publication in Ap
Parametrical optimization of laser surface alloyed NiTi shape memory alloy with Co and Nb by the Taguchi method
Different high-purity metal powders were successfully alloyed on to a nickel titanium (NiTi) shape memory alloy (SMA) with a 3 kW carbon dioxide (CO2) laser system. In order to produce an alloyed layer with complete penetration and acceptable composition profile, the Taguchi approach was used as a statistical technique for optimizing selected laser processing parameters. A systematic study of laser power, scanning velocity, and pre-paste powder thickness was conducted. The signal-to-noise ratios (S/N) for each control factor were calculated in order to assess the deviation from the average response. Analysis of variance (ANOVA) was carried out to understand the significance of process variables affecting the process effects. The Taguchi method was able to determine the laser process parameters for the laser surface alloying technique with high statistical accuracy and yield a laser surface alloying technique capable of achieving a desirable dilution ratio. Energy dispersive spectrometry consistently showed that the per cent by weight of Ni was reduced by 45 per cent as compared with untreated NiTi SMA when the Taguchi-determined laser processing parameters were employed, thus verifying the laser's processing parameters as optimum
Comparison of chemical profiles and effectiveness between Erxian decoction and mixtures of decoctions of its individual herbs : a novel approach for identification of the standard chemicals
Acknowledgements This study was partially supported by grants from the Seed Funding Programme for Basic Research (Project Number 201211159146 and 201411159213), the University of Hong Kong. We thank Mr Keith Wong and Ms Cindy Lee for their technical assistances.Peer reviewedPublisher PD
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