2,363 research outputs found
One-Parameter Squeezed Gaussian States of Time-Dependent Harmonic Oscillator and Selection Rule for Vacuum States
By using the invariant method we find one-parameter squeezed Gaussian states
for both time-independent and time-dependent oscillators. The squeezing
parameter is expressed in terms of energy expectation value for
time-independent case and represents the degree of mixing positive and negative
frequency solutions for time-dependent case. A {\it minimum uncertainty
proposal} is advanced to select uniquely vacuum states at each moment of time.
We show that the Gaussian states with minimum uncertainty coincide with the
true vacuum state for time-independent oscillator and the Bunch-Davies vacuum
for a massive scalar field in a de Sitter spacetime.Comment: 13 Pages, ReVTeX, no figure
The intracluster magnetic field power spectrum in Abell 2382
The goal of this work is to put constraints on the strength and structure of
the magnetic field in the cluster of galaxies A2382. We investigate the
relationship between magnetic field and Faraday rotation effects in the
cluster, using numerical simulations as a reference for the observed
polarization properties. For this purpose we present Very Large Array
observations at 20 cm and 6 cm of two polarized radio sources embedded in
A2382, and we obtained detailed rotation measure images for both of them. We
simulated random three-dimensional magnetic field models with different power
spectra and thus produced synthetic rotation measure images. By comparing our
simulations with the observed polarization properties of the radio sources, we
can determine the strength and the power spectrum of intra-cluster magnetic
field fluctuations that best reproduce the observations. The data are
consistent with a power law magnetic field power spectrum with the Kolmogorov
index , while the outer scale of the magnetic field fluctuations is of
the order of 35 kpc. The average magnetic field strength at the cluster center
is about 3 G and decreases in the external region as the square root of
the electron gas density. The average magnetic field strength in the central 1
Mpc is about 1 G.Comment: Comments: 18 pages, 13 figures, accepted by A&A. For a version with
high quality figures, see http://erg.ca.astro.it/preprints/guidetti2007
Magnetic power spectra from Faraday rotation maps - REALMAF and its use on Hydra A
We develop a novel maximum-a-posteriori method to measure magnetic power
spectra from Faraday rotation data and implement it in the REALMAF code. A
sophisticated model for the magnetic autocorrelation in real space permits us
to alleviate previously required simplifying assumptions in the processing. We
also introduce a way to treat the divergence relation of the magnetic field
with a multiplicative factor in Fourier space, with which we can model the
magnetic autocorrelation as a spherically symmetric function. Applied to the
dataset of Hydra A north, we find a power law power spectrum on spatial scales
between 0.3 kpc and 8 kpc, with no visible turnover at large scales within this
range and a spectral index consistent with a Kolmogorov-like power law regime.
The magnetic field strength profile seems to follow the electron density
profile with an index alpha=1. A variation of alpha from 0.5 to 1.5 would lead
to a spectral index between 1.55 and 2.05. The extrapolated magnetic field
strength in the cluster centre highly depends on the assumed projection angle
of the jet. For an angle of 45 degree we derive extrapolated 36 muG in the
centre and directly probed 16 muG at 50 kpc radius.Comment: 13 pages, 13 figures, version accepted by A&A with restructured
introduction and language improvement
Colossal Positive Magnetoresistance in a Doped Nearly Magnetic Semiconductor
We report on a positive colossal magnetoresistance (MR) induced by
metallization of FeSb, a nearly magnetic or "Kondo" semiconductor with 3d
ions. We discuss contribution of orbital MR and quantum interference to
enhanced magnetic field response of electrical resistivity.Comment: 5 pages, 5 figure
The Coma cluster magnetic field from Faraday rotation measures
The aim of the present work is to constrain the Coma cluster magnetic field
strength, its radial profile and power spectrum by comparing Faraday Rotation
Measure (RM) images with numerical simulations of the magnetic field. We have
analyzed polarization data for seven radio sources in the Coma cluster field
observed with the Very Large Array at 3.6, 6 and 20 cm, and derived Faraday
Rotation Measures with kiloparsec scale resolution. Random three dimensional
magnetic field models have been simulated for various values of the central
intensity B_0 and radial power-law slope eta, where eta indicates how the field
scales with respect to the gas density profile. We derive the central magnetic
field strength, and radial profile values that best reproduce the RM
observations. We find that the magnetic field power spectrum is well
represented by a Kolmogorov power spectrum with minimum scale ~ 2 kpc and
maximum scale ~ 34 kpc. The central magnetic field strength and radial slope
are constrained to be in the range (B_0=3.9 microG; eta=0.4) and (B_0=5.4
microG; eta=0.7) within 1sigma. The best agreement between observations and
simulations is achieved for B_0=4.7 microG; eta=0.5. Values of B_0>7 microG and
1.0 are incompatible with RM data at
99 % confidence level.Comment: 23 pages, 21 figures. Higher resolution available at
http://www.ira.inaf.it/~bonafede/paper.pdf. A&A accepte
Saturation intensity and time response of InGaAs-InGaP MQW optical modulators
Includes bibliographical references (page 260).We report modulation saturation and time response measurements on InGaAs-InGaP MQW modulators. The measurements yield a saturation intensity of (3.7 ± 0.1) kW/cm2 for a 0-10 V swing and switching times between 10 and 90 ns, depending on the bias voltage and incident light intensity. The observed dependence indicates that field screening due to carrier build-up is the dominant physical mechanism determining both the speed and the saturation intensity. This conclusion is supported by results of theoretical calculations
Hadron widths in mixed-phase matter
We derive classically an expression for a hadron width in a two-phase region
of hadron gas and quark-gluon plasma (QGP). The presence of QGP gives hadrons
larger widths than they would have in a pure hadron gas. We find that the
width observed in a central Au+Au collision at
GeV/nucleon is a few MeV greater than the width in a pure hadron gas. The part
of observed hadron widths due to QGP is approximately proportional to
.Comment: 8 pages, latex, no figures, KSUCNR-002-9
Probing Interstellar Dust with Infrared Echoes from the Cas A Supernova
We present the analysis of an IRS 5-38 {\mu}m spectrum and MIPS photometric
measurements of an infrared echo near the Cassiopeia A supernova remnant
observed with the Spitzer Space Telescope. We have modeled the recorded echo
accounting for PAHs, quantum-heated carbon and silicate grains, as well as
thermal carbon and silicate particles. Using the fact that optical light echo
spectroscopy has established that Cas A originated from a type IIb supernova
explosion showing an optical spectrum remarkably similar to the prototypical
type IIb SN 1993J, we use the latter to construct template data input for our
simulations. We are then able to reproduce the recorded infrared echo spectrum
by combining the emission of dust heated by the UV burst produced at the shock
breakout after the core-collapse and dust heated by optical light emitted near
the visual maximum of the supernova light curve, where the UV burst and optical
light curve characteristics are based on SN 1993J. We find a mean density of
\sim680 H cm^{-3} for the echo region, with a size of a few light years across.
We also find evidence of dust processing in the form of a lack of small PAHs
with less than \sim300 carbon atoms, consistent with a scenario of PAHs
destruction by the UV burst via photodissociation at the estimated distance of
the echo region from Cas A. Furthermore, our simulations suggest that the weak
11 {\mu}m features of our recorded infrared echo spectrum are consistent with a
strong dehydrogenated state of the PAHs. This exploratory study highlights the
potential of investigating dust processing in the interstellar medium through
infrared echoes.Comment: 16 pages, 14 figures, accepted for publication in the Astrophysical
Journa
Comprehending the responsible tourism practices through principles of sustainability: A case of Kinabalu Park
This study initiates a research into the practices of responsible tourism in the UNESCO National Park, a place with high levels of biodiversity and value that is worthy of preservation. The responsible tourism definitions, practices and challenges emerged through an intense scrutiny of textual data, which were collected through in-depth interviews with 25 tour operators and park management. Results indicated that responsibility was constructed around the principles of sustainability, or a reification of, ecological friendliness, economical viability and sociocultural amicability in Kinabalu Park, Sabah. Finally, the paper exemplified three implication practices to boost responsible tourism development in Kinabalu Park and other similar parks
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