18,673 research outputs found
Long-term EXOTIME photometry and follow-up spectroscopy of the sdB pulsator HS 0702+6043
Pulsating subdwarf B (sdB) stars oscillate in short-period p-modes or
long-period g-modes. HS0702+6043 (DW Lyn) is one of a few objects to show
characteristics of both types and is hence classified as hybrid pulsator. It is
one of our targets in the EXOTIME program to search for planetary companions
around extreme horizontal branch objects. In addition to the standard exercise
in asteroseismology to probe the instantaneous inner structure of a star,
measured changes in the pulsation frequencies as derived from an O-C diagram
can be compared to theoretical evolutionary timescales. Based on the
photometric data available so far, we are able to derive a high-resolution
frequency spectrum and to report on our efforts to construct a multi-season O-C
diagram. Additionally, we have gathered time-resolved spectroscopic data in
order to constrain stellar parameters and to derive mode parameters as well as
radial and rotational velocities.Comment: 2 pages, JENAM 2008 proceedings, to be published in 'Communications
in Asteroseismology', 15
Satisfiability of CTL* with constraints
We show that satisfiability for CTL* with equality-, order-, and
modulo-constraints over Z is decidable. Previously, decidability was only known
for certain fragments of CTL*, e.g., the existential and positive fragments and
EF.Comment: To appear at Concur 201
Constraint checking during error recovery
The system-level software onboard a spacecraft is responsible for recovery from communication, power, thermal, and computer-health anomalies that may occur. The recovery must occur without disrupting any critical scientific or engineering activity that is executing at the time of the error. Thus, the error-recovery software may have to execute concurrently with the ongoing acquisition of scientific data or with spacecraft maneuvers. This work provides a technique by which the rules that constrain the concurrent execution of these processes can be modeled in a graph. An algorithm is described that uses this model to validate that the constraints hold for all concurrent executions of the error-recovery software with the software that controls the science and engineering activities of the spacecraft. The results are applicable to a variety of control systems with critical constraints on the timing and ordering of the events they control
Memory erasure in small systems
We consider an overdamped nanoparticle in a driven double-well potential as a
generic model of an erasable one-bit memory. We study in detail the statistics
of the heat dissipated during an erasure process and show that full erasure may
be achieved by dissipating less heat than the Landauer bound. We quantify the
occurrence of such events and propose a single-particle experiment to verify
our predictions. Our results show that Landauer's principle has to be
generalized at the nanoscale to accommodate heat fluctuations.Comment: 4 pages, 4 figure
Quasi-deterministic transport of Brownian particles in an oscillating periodic potential
We consider overdamped Brownian dynamics in a periodic potential with
temporally oscillating amplitude. We analyze the transport which shows
effective diffusion enhanced by the oscillations and derive approximate
expressions for the diffusion coefficient. Furthermore we analyze the effect of
the oscillating potential on the transport if additionally a constant force is
applied. We show the existence of synchronization regimes at which the
deterministic dynamics is in resonance with the potential oscillations giving
rise to transport with extremely low dispersion. We distinguish slow and fast
oscillatory driving and give analytical expressions for the mean velocity and
effective diffusion.Comment: submitted: Feb 12th, 201
Measures of galaxy dust and gas mass with Herschel photometry and prospects for ALMA
(Abridged) Combining the deepest Herschel extragalactic surveys (PEP,
GOODS-H, HerMES), and Monte Carlo mock catalogs, we explore the robustness of
dust mass estimates based on modeling of broad band spectral energy
distributions (SEDs) with two popular approaches: Draine & Li (2007, DL07) and
a modified black body (MBB). As long as the observed SED extends to at least
160-200 micron in the rest frame, M(dust) can be recovered with a >3 sigma
significance and without the occurrence of systematics. An average offset of a
factor ~1.5 exists between DL07- and MBB-based dust masses, based on consistent
dust properties. At the depth of the deepest Herschel surveys (in the GOODS-S
field) it is possible to retrieve dust masses with a S/N>=3 for galaxies on the
main sequence of star formation (MS) down to M(stars)~1e10 [M(sun)] up to z~1.
At higher redshift (z<=2) the same result is achieved only for objects at the
tip of the MS or lying above it. Molecular gas masses, obtained converting
M(dust) through the metallicity-dependent gas-to-dust ratio delta(GDR), are
consistent with those based on the scaling of depletion time, and on CO
spectroscopy. Focusing on CO-detected galaxies at z>1, the delta(GDR)
dependence on metallicity is consistent with the local relation. We combine
far-IR Herschel data and sub-mm ALMA expected fluxes to study the advantages of
a full SED coverage.Comment: Accepted for publication in Astronomy and Astrophysics. Some figures
have degraded quality for filesize reason
Irreversibility and the arrow of time in a quenched quantum system
Irreversibility is one of the most intriguing concepts in physics. While
microscopic physical laws are perfectly reversible, macroscopic average
behavior has a preferred direction of time. According to the second law of
thermodynamics, this arrow of time is associated with a positive mean entropy
production. Using a nuclear magnetic resonance setup, we measure the
nonequilibrium entropy produced in an isolated spin-1/2 system following fast
quenches of an external magnetic field and experimentally demonstrate that it
is equal to the entropic distance, expressed by the Kullback-Leibler
divergence, between a microscopic process and its time-reverse. Our result
addresses the concept of irreversibility from a microscopic quantum standpoint.Comment: 8 pages, 7 figures, RevTeX4-1; Accepted for publication Phys. Rev.
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