97,257 research outputs found
Percentile residual life orders
In this paper we study a family of stochastic orders of random variables defined
via the comparison of their percentile residual life functions. Some interpretations
of these stochastic orders are given, and various properties of them are derived.
The relationships to other stochastic orders are also studied. Finally, some
applications in reliability theory and finance are described
The percentile residual life up to time t0: ordering and aging properties
Motivated by practical issues, a new stochastic order for random variables is introduced by comparing all their percentile residual life functions until a certain instant. Some interpretations of these stochastic orders are given, and various properties of them are derived. The relationships to other stochastic orders are studied, and also an application in Reliability Theory is described. Finally, we present some characterization results of the decreasing percentile residual life up to time t0 aging notion.Aging notion, Hazard rate, Mean residual life, Percentile residual life, Reliability, Stochastic ordering
Direct Imaging in Reflected Light: Characterization of Older, Temperate Exoplanets With 30-m Telescopes
Direct detection, also known as direct imaging, is a method for discovering
and characterizing the atmospheres of planets at intermediate and wide
separations. It is the only means of obtaining spectra of non-transiting
exoplanets. Characterizing the atmospheres of planets in the <5 AU regime,
where RV surveys have revealed an abundance of other worlds, requires a
30-m-class aperture in combination with an advanced adaptive optics system,
coronagraph, and suite of spectrometers and imagers - this concept underlies
planned instruments for both TMT (the Planetary Systems Imager, or PSI) and the
GMT (GMagAO-X). These instruments could provide astrometry, photometry, and
spectroscopy of an unprecedented sample of rocky planets, ice giants, and gas
giants. For the first time habitable zone exoplanets will become accessible to
direct imaging, and these instruments have the potential to detect and
characterize the innermost regions of nearby M-dwarf planetary systems in
reflected light. High-resolution spectroscopy will not only illuminate the
physics and chemistry of exo-atmospheres, but may also probe rocky, temperate
worlds for signs of life in the form of atmospheric biomarkers (combinations of
water, oxygen and other molecular species). By completing the census of
non-transiting worlds at a range of separations from their host stars, these
instruments will provide the final pieces to the puzzle of planetary
demographics. This whitepaper explores the science goals of direct imaging on
30-m telescopes and the technology development needed to achieve them.Comment: (March 2018) Submitted to the Exoplanet Science Strategy committee of
the NA
Observation of coherent backscattering of light by cold atoms
Coherent backscattering (CBS) of light waves by a random medium is a
signature of interference effects in multiple scattering. This effect has been
studied in many systems ranging from white paint to biological tissues.
Recently, we have observed CBS from a sample of laser-cooled atoms, a
scattering medium with interesting new properties. In this paper we discuss
various effects, which have to be taken into account for a quantitative study
of coherent backscattering of light by cold atoms.Comment: 25 pages LaTex2e, 17 figures, submitted to J. Opt. B: Quant. Semicl.
Op
Quantum and classical dynamics of a three-mode absorption refrigerator
We study the quantum and classical evolution of a system of three harmonic
modes interacting via a trilinear Hamiltonian. With the modes prepared in
thermal states of different temperatures, this model describes the working
principle of an absorption refrigerator that transfers energy from a cold to a
hot environment at the expense of free energy provided by a high-temperature
work reservoir. Inspired by a recent experimental realization with trapped
ions, we elucidate key features of the coupling Hamiltonian that are relevant
for the refrigerator performance. The coherent system dynamics exhibits rapid
effective equilibration of the mode energies and correlations, as well as a
transient enhancement of the cooling performance at short times. We find that
these features can be fully reproduced in a classical framework.Comment: 11 pages, 8 figures; additions and corrections; accepted in Quantum
on 2017-12-0
A temperature behavior of the frustrated translational mode of adsorbate and the nature of the "adsorbate-substrate" interaction
A temperature behavior of the frustrated translational mode (T-mode) of a
light particle, coupled by different regimes of ohmicity to the surface, is
studied within a formalism of the generalized diffusion coefficients. The
memory effects of the adsorbate motion are considered to be the main reason of
the T-mode origin. Numerical calculations yield a thermally induced shift and
broadening of the T-mode, which is found to be linear in temperature for Ohmic
and super-Ohmic systems and nonlinear for strongly sub-Ohmic ones. We obtain
analytical expressions for the T-mode shift and width at weak coupling for the
systems with integer "ohmicity" indexes n=0-2 in zero temperature and high
temperature limits. We provide an explanation of the experimentally observed
blue- or red-shifts of the T-mode on the basis of a comparative analysis of two
typical times of the system evolution: a time of decay of the
"velocity-velocity" autocorrelation function, and a correlation time of the
thermal bath random forces. A relation of the T-mode to the multiple jumps of
the adsorbate is discussed, and generalization of conditions of the multiple
hopping to the case of quantum surface diffusion is performed.Comment: 12 pages, 4 figure
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