1,719 research outputs found
Vibrational dynamics and boson peak in a supercooled polydisperse liquid
Vibrational density of states (VDOS) in a supercooled polydisperse liquid is
computed by diagonalizing the Hessian matrix evaluated at the potential energy
minima for systems with different values of polydispersity. An increase of
polydispersity leads to an increase in relative population of the localized
high-frequency modes. At low frequencies, the density of states show an excess
compared to the Debye squared-frequency law, which has been identified with the
boson peak. The height of the boson peak increases with polydispersity. The
values of the participation ratio as well as the level spacing statistics
demonstrate that the modes comprising the boson peak are largely delocalized.
Interestingly, the intensity of the boson peak shows a rather narrow
sensitivity to changes in temperature and is seen to persist even at high
temperatures. Study of the difference spectrum at two different polydispersity
reveals that the increase in the height of boson peak is due to a population
shift from modes with frequencies above the maximum in the VDOS to that below
the maximum, indicating an increase in the fraction of the unstable modes in
the system. The latter is further supported by the facilitation of the observed
dynamics by polydispersity. Since the strength of the liquid increases with
polydispersity, the present result provides an evidence that the intensity of
boson peak correlates positively with the strength of the liquid, as observed
earlier in many experimental systems
A transient high-coherence oscillation in 4U 1820-30
We re-analyzed two Rossi X-Ray Timing Explorer archival observations of the
atoll source 4U 1820-30 in order to investigate the detailed time-frequency
properties of the source during the intervals when a ~7 Hz QPO was detected by
Wijnands et al. (1999, ApJ, 512, L39). We find that in both observations, in
addition to a QPO signal lasting a couple of minutes as previously reported,
there is a much narrower transient oscillation with a life time of only a few
seconds. Within this time, the oscillation is consistent with being coherent.
Its integrated fractional rms is around 10% and its frequency 7.3 Hz and 5.7 Hz
in the two observations. We discuss the possible association of this QPO with
other oscillations known both in Neutron-Star and Black-Hole systems,
concentrating on the similarities with the narrow 5-7 Hz oscillations observed
at high flux in Black-Hole Candidates.Comment: 5 pages, 3 figures, accepted for publication in A&A. FIgure 1 is
reduced in resolution, full-resolution version of this text available at
http://www.merate.mi.astro.it/~belloni/ms0335.ps.g
Phase Change Observed in Ultrathin Ba0.5Sr0.5TiO3 Films by in-situ Resonant Photoemission Spectroscopy
Epitaxial Ba0.5Sr0.5TiO3 thin films were prepared on Nb-doped SrTiO3
(100)substrates by the pulsed laser deposition technique, and were studied by
measuring the Ti 2p - 3d resonant photoemission spectra in the valence-band
region as a function of film thickness, both at room temperature and low
temperature. Our results demonstrated an abrupt variation in the spectral
structures between 2.8 nm (~7 monolayers) and 2.0 nm (~5 monolayers)
Ba0.5Sr0.5TiO3 films, suggesting that there exists a critical thickness for
phase change in the range of 2.0 nm to 2.8 nm. This may be ascribed mainly to
the intrinsic size effects.Comment: 13 pages, 4 figure
Fully Dispersive Models for Moving Loads on Ice Sheets
The response of a floating elastic plate to the motion of a moving load is studied using a fully dispersive weakly nonlinear system of equations. The system allows for accurate description of waves across the whole spectrum of wavelengths and also incorporates nonlinearity, forcing and damping. The flexural-gravity waves described by the system are time-dependent responses to a forcing with a described weight distribution, moving at a time-dependent velocity. The model is versatile enough to allow the study of a wide range of situations including the motion of a combination of point loads and loads of arbitrary shape. Numerical solutions of the system are compared to data from a number of field campaigns on ice-covered lakes, and good agreement between the deflectometer records and the numerical simulations is observed in most cases. Consideration is also given to waves generated by an accelerating or decelerating load, and it is shown that a decelerating load may trigger a wave response with a far greater amplitude than a load moving at constant celerity
Sigma Exchange in the Nonmesonic Decays of Light Hypernuclei and Violation of the Delta I=1/2 Rule
Nonmesonic weak decays of s-shell hypernuclei are analyzed in microscopic
models for the Lambda N to NN weak interaction. A scalar-isoscalar meson,
sigma, is introduced and its importance in accounting the decay rates, n/p
ratios and proton asymmetry is demonstrated. Possible violation of the Delta
I=1/2 rule in the nonmesonic weak decay of Lambda is discussed in a
phenomenological analysis and several useful constraints are presented. The
microscopic calculation shows that the current experimental data indicate a
large violation of the Delta I=1/2 rule, although no definite conclusion can be
derived due to large ambiguity of the decay rate of {^4_Lambda H}.Comment: 13 pages, 5 figure
Enhanced Peculiar Velocities in Brane-Induced Gravity
The mounting evidence for anomalously large peculiar velocities in our
Universe presents a challenge for the LCDM paradigm. The recent estimates of
the large scale bulk flow by Watkins et al. are inconsistent at the nearly 3
sigma level with LCDM predictions. Meanwhile, Lee and Komatsu have recently
estimated that the occurrence of high-velocity merging systems such as the
Bullet Cluster (1E0657-57) is unlikely at a 6.5-5.8 sigma level, with an
estimated probability between 3.3x10^{-11} and 3.6x10^{-9} in LCDM cosmology.
We show that these anomalies are alleviated in a broad class of
infrared-modifed gravity theories, called brane-induced gravity, in which
gravity becomes higher-dimensional at ultra large distances. These theories
include additional scalar forces that enhance gravitational attraction and
therefore speed up structure formation at late times and on sufficiently large
scales. The peculiar velocities are enhanced by 24-34% compared to standard
gravity, with the maximal enhancement nearly consistent at the 2 sigma level
with bulk flow observations. The occurrence of the Bullet Cluster in these
theories is 10^4 times more probable than in LCDM cosmology.Comment: 15 pages, 6 figures. v2: added reference
The current status of orbital experiments for UHECR studies
Two types of orbital detectors of extreme energy cosmic rays are being
developed nowadays: (i) TUS and KLYPVE with reflecting optical systems
(mirrors) and (ii) JEM-EUSO with high-transmittance Fresnel lenses. They will
cover much larger areas than existing ground-based arrays and almost uniformly
monitor the celestial sphere. The TUS detector is the pioneering mission
developed in SINP MSU in cooperation with several Russian and foreign
institutions. It has relatively small field of view (+/-4.5 deg), which
corresponds to a ground area of 6.4x10^3 sq.km. The telescope consists of a
Fresnel-type mirror-concentrator (~2 sq.m) and a photo receiver (a matrix of
16x16 photomultiplier tubes). It is to be deployed on the Lomonosov satellite,
and is currently at the final stage of preflight tests. Recently, SINP MSU
began the KLYPVE project to be installed on board of the Russian segment of the
ISS. The optical system of this detector contains a larger primary mirror (10
sq.m), which allows decreasing the energy threshold. The total effective field
of view will be at least +/-14 degrees to exceed the annual exposure of the
existing ground-based experiments. Several configurations of the detector are
being currently considered. Finally, JEM-EUSO is a wide field of view (+/-30
deg) detector. The optics is composed of two curved double-sided Fresnel lenses
with 2.65 m external diameter, a precision diffractive middle lens and a pupil.
The ultraviolet photons are focused onto the focal surface, which consists of
nearly 5000 multi-anode photomultipliers. It is developed by a large
international collaboration. All three orbital detectors have multi-purpose
character due to continuous monitoring of various atmospheric phenomena. The
present status of development of the TUS and KLYPVE missions is reported, and a
brief comparison of the projects with JEM-EUSO is given.Comment: 18 pages; based on the rapporteur talk given by M.I. Panasyuk at
ECRS-2014; v2: a few minor language issues fixed thanks to the editor; to be
published in the proceeding
Hybridization between the conduction band and 3d orbitals in the oxide-based diluted magnetic semiconductor InVO
The electronic structure of InVO () has been
investigated using photoemission spectroscopy (PES) and x-ray absorption
spectroscopy (XAS). The V core-level PES and XAS spectra revealed
trivalent electronic state of the V ion, consistent with the substitution of
the V ion for the In site. The V 3d partial density of states obtained by the
resonant PES technique showed a sharp peak above the O band. While the O
XAS spectrum of InVO was similar to that of InO,
there were differences in the In and 3d XAS spectra between V-doped and
pure InO. The observations give clear evidence for hybridization
between the In conduction band and the V 3d orbitals in InVO.Comment: 5 pages, 4 figure
Photoemission and x-ray absorption studies of valence states in (Ni,Zn,Fe,Ti)O thin films exhibiting photo-induced magnetization
By means of photoemission and x-ray absorption spectroscopy, we have studied
the electronic structure of (Ni,Zn,Fe,Ti)O thin films, which
exhibits a cluster glass behavior with a spin-freezing temperature of
K and photo-induced magnetization (PIM) below . The Ni and Zn
ions were found to be in the divalent states. Most of the Fe and Ti ions in the
thin films were trivalent (Fe) and tetravalent (Ti),
respectively. While Ti doping did not affect the valence states of the Ni and
Zn ions, a small amount of Fe ions increased with Ti concentration,
consistent with the proposed charge-transfer mechanism of PIM.Comment: 4 pages, 4 figure
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