6,666 research outputs found
Continuous wave detector has wide frequency range
Portable battery-operated detector indicates the presence of steady state signals exceeding a predetermined value over a wide frequency range by the closure of output relay contacts. It was designed to monitor electronic equipment used in the Saturn 2 program
Time-Resolved Ultraviolet Observations of the Globular Cluster X-ray Source in NGC 6624: The Shortest Known Period Binary System
Using the Faint Object Spectrograph (FOS) aboard the Hubble Space Telescope,
we have obtained the first time-resolved spectra of the King et al.
ultraviolet-bright counterpart to the 11-minute binary X-ray source in the core
of the globular cluster NGC 6624. This object cannot be readily observed in the
visible, even from HST, due to a much brighter star superposed <0.1'' distant.
Our FOS data show a highly statistically significant UV flux modulation with a
period of 11.46+-0.04 min, very similar to the 685 sec period of the known
X-ray modulation, definitively confirming the association between the King et
al. UV counterpart and the intense X-ray source. The UV amplitude is very large
compared with the observed X-ray oscillations: X-ray variations are generally
reported as 2-3% peak-to-peak, whereas our data show an amplitude of about 16%
in the 126-251 nm range. A model for the system by Arons & King predicts
periodic UV fluctuations in this shortest-known period binary system, due to
the cyclically changing aspect of the X-ray heated face of the secondary star
(perhaps a very low mass helium degenerate). However, prior to our
observations, this predicted modulation has not been detected. Employing the
Arons & King formalism, which invokes a number of different physical
assumptions, we infer a system orbital inclination 35deg<i<50 deg. Amongst the
three best-studied UV/optical counterparts to the intense globular cluster
X-ray sources, two are now thought to consist of exotic double-degenerate
ultrashort period binary systems.Comment: 10 pages including 2 figures in Latex (AASTeX 4.0). Accepted for
publication in vol. 482 (1997 June 10 issue) of The Astrophysical Journal
(Letters
Specific heat of the ideal gas obeying the generalized exclusion statistics
We calculate the specific heat of the ideal gas obeying the generalized
exclusion statistics (GES) in the continuum model and the tight binding model
numerically. In the continuum model of 3-d space, the specific heat increases
with statistical parameter at low temperature whereas it decreases with
statistical parameter at high temperature. We find that the critical
temperature normalized by (Fermi energy) is 0.290. The specific heat of
2-d space was known to be independent of in the continuum model, but it
varies with drastically in the tight-binding model. From its unique
behavior, identification of GES particles will be possible from the specific
heat.Comment: 14 pages, 9 figures, to be published in Eur. Phys. J. B, References
and figures added, typos corrected, one section removed and two sections
merge
A Search for the Optical Counterpart of the Luminous X-ray Source in NGC 6652
We examine images of the field of X1832-330, the luminous (Lx ~ 10^36 erg/s)
X-ray burst source near the center of the globular cluster NGC 6652, in order
to identify the optical counterpart for further study. U and B ground-based
images allow us to set a limit M_B > 3.5 for the counterpart at the time of
those observations, provided that the color is (U-B)_0 ~ -1, similar to the
sources known in other clusters. Archival Hubble Space Telescope observations
survey most but not all of the 1 sigma X-ray error circle, and allow us to set
limits M_B > 5.9 and M_B > 5.2 in the WF/PC and WFPC2 regions, respectively. In
the WF/PC images we do weakly detect a faint object with UV-excess, but it is
located 11.7'' from the ROSAT X-ray position. This considerable (2.3 sigma)
discrepancy in position suggests that this candidate be treated with caution,
but it remains the only reasonable one advanced thus far. We measure for this
star m_439 = 20.2 +- 0.2, (m_336 - m_439) = -0.5 +- 0.2, and estimate M_B =
5.5, (U-B)_0 = -0.9, similar to other known optical counterparts. If this
candidate is not the identification, our limits imply that the true
counterpart, not yet identified, is probably the optically-faintest cluster
source yet known, or alternatively that it did not show significant UV excess
at the time of these observations. Finally, we assess the outlook for the
identification of the remaining luminous globular cluster X-ray sources.Comment: 15 pages including 5 figures and no tables. Accepted for publication
in The Astronomical Journal; to appear in Volume 116, September 1998. A
preprint with full resolution figures may be downloaded from
http://www.astro.washington.edu/deutsch/pubs
Adiabatic Quantum Computation in Open Systems
We analyze the performance of adiabatic quantum computation (AQC) under the
effect of decoherence. To this end, we introduce an inherently open-systems
approach, based on a recent generalization of the adiabatic approximation. In
contrast to closed systems, we show that a system may initially be in an
adiabatic regime, but then undergo a transition to a regime where adiabaticity
breaks down. As a consequence, the success of AQC depends sensitively on the
competition between various pertinent rates, giving rise to optimality
criteria.Comment: v2: 4 pages, 1 figure. Published versio
Calculating the relative entropy of entanglement
We extend Vedral and Plenio's theorem (theorem 3 in Phys. Rev. A 57, 1619) to
a more general case, and obtain the relative entropy of entanglement for a
class of mixed states, this result can also follow from Rains' theorem 9 in
Phys. Rev. A 60, 179.Comment: 2 pages, RevTex, an important reference adde
Multipartite pure-state entanglement and the generalized GHZ states
We show that not all 4-party pure states are GHZ reducible (i.e., can be
generated reversibly from a combination of 2-, 3- and 4-party maximally
entangled states by local quantum operations and classical communication
asymptotically) through an example, we also present some properties of the
relative entropy of entanglement for those 3-party pure states that are GHZ
reducible, and then we relate these properties to the additivity of the
relative entropy of entanglement.Comment: 7 pages, Revtex, type error correcte
Fiber-Cavity-Based Optomechanical Device
We describe an optomechanical device consisting of a fiber-based optical
cavity containing a silicon nitiride membrane. In comparison with typical
free-space cavities, the fiber-cavity's small mode size (10 {\mu}m waist, 80
{\mu}m length) allows the use of smaller, lighter membranes and increases the
cavity-membrane linear coupling to 3 GHz/nm and quadratic coupling to 20
GHz/nm^2. This device is also intrinsically fiber-coupled and uses glass
ferrules for passive alignment. These improvements will greatly simplify the
use of optomechanical systems, particularly in cryogenic settings. At room
temperature, we expect these devices to be able to detect the shot noise of
radiation pressure.Comment: 4 pages, 3 figures; the following article has been submitted to
Applied Physics Letter
Daubechies Wavelets for Linear Scaling Density Functional Theory
We demonstrate that Daubechies wavelets can be used to construct a minimal
set of optimized localized contracted basis functions in which the Kohn-Sham
orbitals can be represented with an arbitrarily high, controllable precision.
Ground state energies and the forces acting on the ions can be calculated in
this basis with the same accuracy as if they were calculated directly in a
Daubechies wavelets basis, provided that the amplitude of these contracted
basis functions is sufficiently small on the surface of the localization
region, which is guaranteed by the optimization procedure described in this
work. This approach reduces the computational costs of DFT calculations, and
can be combined with sparse matrix algebra to obtain linear scaling with
respect to the number of electrons in the system. Calculations on systems of
10,000 atoms or more thus become feasible in a systematic basis set with
moderate computational resources. Further computational savings can be achieved
by exploiting the similarity of the contracted basis functions for closely
related environments, e.g. in geometry optimizations or combined calculations
of neutral and charged systems
Magnetic Domain Patterns Depending on the Sweeping Rate of Magnetic Fields
The domain patterns in a thin ferromagnetic film are investigated in both
experiments and numerical simulations. Magnetic domain patterns under a zero
field are usually observed after an external magnetic field is removed. It is
demonstrated that the characteristics of the domain patterns depend on the
decreasing rate of the external field, although it can also depend on other
factors. Our numerical simulations and experiments show the following
properties of domain patterns: a sea-island structure appears when the field
decreases rapidly from the saturating field to the zero field, while a
labyrinth structure is observed for a slowly decreasing field. The mechanism of
the dependence on the field sweeping rate is discussed in terms of the concepts
of crystallization.Comment: 4 pages, 3 figure
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