36,501 research outputs found
Behavior of the sonic boom shock wave near the sonic cutoff altitude
Behavior of sonic boom shock wave near sonic cutoff altitud
The detection of markovian sequences of signals technical report no. 23
Detection of pure tone embedded in noise - Markov chains of signal
Introduction: The Challenge of Risk Communication in a Democratic Society
The symposium editors review key issues concerning the relationship between risk communication and public participation
Future directions in kaonic atom physics
Recent progress and open problems in kaonic atom physics are presented. A
connection between phenomenological deep potentials and the underlying
interaction is established as well as the need for a theory for multinucleon
absorption of kaons. absorption at rest to specific
hypernuclei states is briefly discussed.Comment: 6 pages, 3 figures, proceedings of the EXA2011 conference, to appear
in Hyperfine Interaction
Radiation- and Phonon-Bottleneck-Induced Tunneling in the Fe8 Single-Molecule Magnet
We measure magnetization changes in a single crystal of the single-molecule
magnet Fe8 when exposed to intense, short (<20 s) pulses of microwave
radiation resonant with the m = 10 to 9 transition. We find that radiation
induces a phonon bottleneck in the system with a time scale of ~5 s. The
phonon bottleneck, in turn, drives the spin dynamics, allowing observation of
thermally assisted resonant tunneling between spin states at the 100-ns time
scale. Detailed numerical simulations quantitatively reproduce the data and
yield a spin-phonon relaxation time of T1 ~ 40 ns.Comment: 6 RevTeX pages, including 4 EPS figures, version accepted for
publicatio
Quantum Lattice Fluctuations and Luminescence in C_60
We consider luminescence in photo-excited neutral C_60 using the
Su-Schrieffer-Heeger model applied to a single C_60 molecule. To calculate the
luminescence we use a collective coordinate method where our collective
coordinate resembles the displacement of the carbon atoms of the Hg(8) phonon
mode and extrapolates between the ground state "dimerisation" and the exciton
polaron. There is good agreement for the existing luminescence peak spacing and
fair agreement for the relative intensity. We predict the existence of further
peaks not yet resolved in experiment. PACS Numbers : 78.65.Hc, 74.70.Kn,
36.90+
Measurement of Magnetization Dynamics in Single-Molecule Magnets Induced by Pulsed Millimeter-Wave Radiation
We describe an experiment aimed at measuring the spin dynamics of the Fe8
single-molecule magnet in the presence of pulsed microwave radiation. In
earlier work, heating was observed after a 0.2-ms pulse of intense radiation,
indicating that the spin system and the lattice were out of thermal equilibrium
at millisecond time scale [Bal et al., Europhys. Lett. 71, 110 (2005)]. In the
current work, an inductive pick-up loop is used to probe the photon-induced
magnetization dynamics between only two levels of the spin system at much
shorter time scales (from ns to us). The relaxation time for the magnetization,
induced by a pulse of radiation, is found to be on the order of 10 us.Comment: 3 RevTeX pages, including 3 eps figures. The paper will appear in the
Journal of Applied Physics as MMM'05 conference proceeding
The Narrow-band Ultraviolet Imaging Experiment for Wide-field Surveys (NUVIEWS)-I: Dust scattered continuum
We report on the first results of the Narrow-band Ultraviolet Imaging
Experiment for Wide-field Surveys (NUVIEWS), a sounding rocket experiment
designed to map the far-ultraviolet background in four narrow bands. This is
the first imaging measurement of the UV background to cover a substantial
fraction of the sky. The narrow band responses (145, 155, 161, and 174 nm, 7-10
nm wide) allow us to isolate background contributions from dust-scattered
continuum, H2 fluorescence, and CIV 155 nm emission. In our first flight, we
mapped one quarter of the sky with 5-10 arcminute imaging resolution. In this
paper, we model the dominant contribution of the background, dust-scattered
continuum. Our data base consists of a map of over 10,000 sq. degrees with 468
independent measurements in 6.25 by 6.25 sq. degree bins. Stars and
instrumental stellar halos are removed from the data. We present a map of the
continuum background obtained in the 174 nm telescope. We use a model that
follows Witt, Friedman, and Sasseen (1997: WFS) to account for the
inhomogeneous radiation field and multiple scattering effects in clouds. We
find that the dust in the diffuse interstellar medium displays a moderate
albedo (a=0.55+/-0.1) and highly forward scattering phase function parameter
(g=0.75+/-0.1) over a large fraction of the sky, similar to dust in star
forming regions. We also have discovered a significant variance from the model.Comment: 16 pages, 3 ps figures, submitted to Astrophysical Journal Letter
Detecting many-body entanglements in noninteracting ultracold atomic fermi gases
We explore the possibility of detecting many-body entanglement using
time-of-flight (TOF) momentum correlations in ultracold atomic fermi gases. In
analogy to the vacuum correlations responsible for Bekenstein-Hawking black
hole entropy, a partitioned atomic gas will exhibit particle-hole correlations
responsible for entanglement entropy. The signature of these momentum
correlations might be detected by a sensitive TOF type experiment.Comment: 5 pages, 5 figures, fixed axes labels on figs. 3 and 5, added
reference
Spacetime Information
In usual quantum theory, the information available about a quantum system is
defined in terms of the density matrix describing it on a spacelike surface.
This definition must be generalized for extensions of quantum theory which do
not have a notion of state on a spacelike surface. It must be generalized for
the generalized quantum theories appropriate when spacetime geometry fluctuates
quantum mechanically or when geometry is fixed but not foliable by spacelike
surfaces. This paper introduces a four-dimensional notion of the information
available about a quantum system's boundary conditions in the various sets of
decohering histories it may display. The idea of spacetime information is
applied in several contexts: When spacetime geometry is fixed the information
available through alternatives restricted to a spacetime region is defined. The
information available through histories of alternatives of general operators is
compared to that obtained from the more limited coarse- grainings of
sum-over-histories quantum mechanics. The definition of information is
considered in generalized quantum theories. We consider as specific examples
time-neutral quantum mechanics with initial and final conditions, quantum
theories with non-unitary evolution, and the generalized quantum frameworks
appropriate for quantum spacetime. In such theories complete information about
a quantum system is not necessarily available on any spacelike surface but must
be searched for throughout spacetime. The information loss commonly associated
with the ``evolution of pure states into mixed states'' in black hole
evaporation is thus not in conflict with the principles of generalized quantum
mechanics.Comment: 47pages, 2 figures, UCSBTH 94-0
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