9,596 research outputs found
Molecular kinetics of solid and liquid CHCl
We present a detailed analysis of the molecular kinetics of CHCl in a
range of temperatures covering the solid and liquid phases. Using nuclear
quadrupolar resonance we determine the relaxation times for the molecular
rotations in solid at pre-melting conditions. Molecular dynamics simulations
are used to characterize the rotational dynamics in the solid and liquid phases
and to study the local structure of the liquid in terms of the molecular
relative orientations. We find that in the pre-melting regime the molecules
rotate about the C-H bond, but the rotations are isotropic in the liquid, even
at supercooled conditions.Comment: Chemical Physics Letter (in press). 14 pages, 7 figure
Diagnosing shock temperature with NH and HO profiles
In a previous study of the L1157 B1 shocked cavity, a comparison between
NH(1-) and HO(1--1) transitions showed a
striking difference in the profiles, with HO emitting at definitely higher
velocities. This behaviour was explained as a result of the high-temperature
gas-phase chemistry occurring in the postshock gas in the B1 cavity of this
outflow. If the differences in behaviour between ammonia and water are indeed a
consequence of the high gas temperatures reached during the passage of a shock,
then one should find such differences to be ubiquitous among chemically rich
outflows. In order to determine whether the difference in profiles observed
between NH and HO is unique to L1157 or a common characteristic of
chemically rich outflows, we have performed Herschel-HIFI observations of the
NH(1-0) line at 572.5 GHz in a sample of 8 bright low-mass outflow
spots already observed in the HO(1--1) line within
the WISH KP. We detected the ammonia emission at high-velocities at most of the
outflows positions. In all cases, the water emission reaches higher velocities
than NH, proving that this behaviour is not exclusive of the L1157-B1
position. Comparisons with a gas-grain chemical and shock model confirms, for
this larger sample, that the behaviour of ammonia is determined principally by
the temperature of the gas.Comment: Accepted for publication in the Monthly Notices of the Royal
Astronomical Societ
Harrison-Z'eldovich primordial spectrum is consistent with observations
Inflation predicts primordial scalar perturbations with a nearly
scale-invariant spectrum and a spectral index approximately unity (the
Harrison--Zel'dovich (HZ) spectrum). The first important step for inflationary
cosmology is to check the consistency of the HZ primordial spectrum with
current observations. Recent analyses have claimed that a HZ primordial
spectrum is excluded at more than 99% c.l.. Here we show that the HZ spectrum
is only marginally disfavored if one considers a more general reionization
scenario. Data from the Planck mission will settle the issue.Comment: 4 Pages, 2 Figure
Far-infrared edge modes in quantum dots
We have investigated edge modes of different multipolarity sustained by
quantum dots submitted to external magnetic fields. We present a microscopic
description based on a variational solution of the equation of motion for any
axially symmetric confining potential and multipole mode. Numerical results for
dots with different number of electrons whose ground-state is described within
a local Current Density Functional Theory are discussed. Two sum rules, which
are exact within this theory, are derived. In the limit of a large neutral dot
at B=0, we have shown that the classical hydrodynamic dispersion law for edge
waves \omega(q) \sim \sqrt{q \ln (q_0/q)} holds when quantum and finite size
effects are taken into account.Comment: We have changed some figures as well as a part of the tex
Control of Recoil Losses in Nanomechanical SiN Membrane Resonators
In the context of a recoil damping analysis, we have designed and produced a
membrane resonator equipped with a specific on-chip structure working as a
"loss shield" for a circular membrane. In this device the vibrations of the
membrane, with a quality factor of , reach the limit set by the intrinsic
dissipation in silicon nitride, for all the modes and regardless of the modal
shape, also at low frequency. Guided by our theoretical model of the loss
shield, we describe the design rationale of the device, which can be used as
effective replacement of commercial membrane resonators in advanced
optomechanical setups, also at cryogenic temperatures
Calibrated quantum thermometry in cavity optomechanics
Cavity optomechanics has achieved the major breakthrough of the preparation
and observation of macroscopic mechanical oscillators in peculiarly quantum
states. The development of reliable indicators of the oscillator properties in
these conditions is important also for applications to quantum technologies. We
compare two procedures to infer the oscillator occupation number, minimizing
the necessity of system calibrations. The former starts from homodyne spectra,
the latter is based on the measurement of the motional sidebands asymmetry in
heterodyne spectra. Moreover, we describe and discuss a method to control the
cavity detuning, that is a crucial parameter for the accuracy of the latter,
intrinsically superior procedure
Far-infrared edge modes in quantum dots
We have investigated edge modes of different multipolarity sustained by
quantum dots submitted to external magnetic fields. We present a microscopic
description based on a variational solution of the equation of motion for any
axially symmetric confining potential and multipole mode. Numerical results for
dots with different number of electrons whose ground-state is described within
a local Current Density Functional Theory are discussed. Two sum rules, which
are exact within this theory, are derived. In the limit of a large neutral dot
at B=0, we have shown that the classical hydrodynamic dispersion law for edge
waves \omega(q) \sim \sqrt{q \ln (q_0/q)} holds when quantum and finite size
effects are taken into account.Comment: We have changed some figures as well as a part of the tex
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.
Let
Application of large area SiPMs for the readout of a plastic scintillator based timing detector
In this study an array of eight 6 mm x 6 mm area SiPMs was coupled to the end
of a long plastic scintillator counter which was exposed to a 2.5 GeV/c muon
beam at the CERN PS. Timing characteristics of bars with dimensions 150 cm x 6
cm x 1 cm and 120 cm x 11 cm x 2.5 cm have been studied. An 8-channel SiPM
anode readout ASIC (MUSIC R1) based on a novel low input impedance current
conveyor has been used to read out and amplify SiPMs independently and sum the
signals at the end. Prospects for applications in large-scale particle physics
detectors with timing resolution below 100 ps are provided in light of the
results
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