1,041 research outputs found
Thermal Excitation of Broadband and Long-range Surface Waves on SiO 2 Submicron Films
We detect thermally excited surfaces waves on a submicron SiO 2 layer,
including Zenneck and guided modes in addition to Surface Phonon Polaritons.
The measurements show the existence of these hybrid thermal-electromagnetic
waves from near-(2.7 m) to far-(11.2 m) infrared. Their propagation
distances reach values on the order of the millimeter, several orders of
magnitude larger than on semi-infinite systems. These two features, spectral
broadness and long range propagation, make these waves good candidates for
near-field applications both in optics and thermics due to their dual nature.Comment: Applied Physics Letters, American Institute of Physics, 201
Increase of Thermal Resistance Between a Nanostructure and a Surface due to Phonon Multireflections
The thermal resistance between a nanostructure and a half-body is calculated
in the framework of particle-phonons physics. The current models approximate
the nanostructure as a thermal bath. We prove that the multireflections of heat
carriers in the nanostructure significantly increase resistance in
contradiction with former predictions. This increase depends on the shape of
the nanostructure and the heat carriers mean free path only. We provide a
general and simple expression for the contact resistance and examine the
specific cases of nanowires and nanoparticles
Two-phonon 1- state in 112Sn observed in resonant photon scattering
Results of a photon scattering experiment on 112Sn using bremsstrahlung with
an endpoint energy of E_0 = 3.8 MeV are reported. A J = 1 state at E_x =
3434(1) keV has been excited. Its decay width into the ground state amounts to
Gamma_0 = 151(17) meV, making it a candidate for a [2+ x 3-]1- two-phonon
state. The results for 112Sn are compared with quasiparticle-phonon model
calculations as well as the systematics of the lowest-lying 1- states
established in other even-mass tin isotopes. Contrary to findings in the
heavier stable even-mass Sn isotopes, no 2+ states between 2 and 3.5 MeV
excitation energy have been detected in the present experiment.Comment: 10 pages, including 2 figures, Phys. Rev. C, in pres
Collisional relaxation of Feshbach molecules and three-body recombination in 87Rb Bose-Einstein condensates
We predict the resonance enhanced magnetic field dependence of atom-dimer
relaxation and three-body recombination rates in a Rb Bose-Einstein
condensate (BEC) close to 1007 G. Our exact treatments of three-particle
scattering explicitly include the dependence of the interactions on the atomic
Zeeman levels. The Feshbach resonance distorts the entire diatomic energy
spectrum causing interferences in both loss phenomena. Our two independent
experiments confirm the predicted recombination loss over a range of rate
constants that spans four orders of magnitude.Comment: 4 pages, 3 eps figures (updated references
Lifetime Measurement of the 6s Level of Rubidium
We present a lifetime measurements of the 6s level of rubidium. We use a
time-correlated single-photon counting technique on two different samples of
rubidium atoms. A vapor cell with variable rubidium density and a sample of
atoms confined and cooled in a magneto-optical trap. The 5P_{1/2} level serves
as the resonant intermediate step for the two step excitation to the 6s level.
We detect the decay of the 6s level through the cascade fluorescence of the
5P_{3/2} level at 780 nm. The two samples have different systematic effects,
but we obtain consistent results that averaged give a lifetime of 45.57 +- 0.17
ns.Comment: 10 pages, 9 figure
A two-level Structural Equation Model for evaluating the external effectiveness of PhD
In recent years the number of PhDs in Italy has significantly grown and purposes of
PhD courses have expanded from the traditional ones. The analysis of the contribution of PhD
title for job placement and employment condition of PhDs is an important tool for evaluating
the quality and the effectiveness of PhD courses. For this reason, knowledge of the
employment status and career of PhDs becomes essential and can help to reduce the gap
between academia and labour market. The aim of this paper is to estimate a two-level
structural equation model with latent variables to assess the external effectiveness of PhD. The
analysis is performed using data from the research "Current situation and employment
prospects of PhDs", commissioned by National Committee for the Evaluation of the University
System (CNVSU) to the Department of Statistics "G. Parenti" of the University of Florence. The
proposed measure of "external effectiveness" is a latent variable obtained by evaluating the
level of satisfaction with the employment status of PhDs who achieved the title in 2008. The
opinion was expressed one year after obtaining PhD on a ten ordered point scale. External
effectiveness indicators used are Consistency with studies, Utilization of the acquired skills and
Compliance with the cultural interests
The origin of hysteresis in resistive switching in magnetite is Joule heating
In many transition metal oxides the electrical resistance is observed to
undergo dramatic changes induced by large biases. In magnetite, FeO,
below the Verwey temperature, an electric field driven transition to a state of
lower resistance was recently found, with hysteretic current-voltage response.
We report the results of pulsed electrical conduction measurements in epitaxial
magnetite thin films. We show that while the high- to low-resistance transition
is driven by electric field, the hysteresis observed in curves results
from Joule heating in the low resistance state. The shape of the hysteresis
loop depends on pulse parameters, and reduces to a hysteresis-free "jump" of
the current provided thermal relaxation is rapid compared to the time between
voltage pulses. A simple relaxation time thermal model is proposed that
captures the essentials of the hysteresis mechanism.Comment: 7 pages, 6 figure
Diagnosis delays in the UK according to pre- or post-migration acquisition of HIV
Objectives:
To evaluate whether infection occurred pre- or post-migration and the associated diagnosis delay in migrants diagnosed with HIV in the UK.
Design:
We analysed a cohort of individuals diagnosed with HIV in the UK in 2014–2016 born in Africa or elsewhere in Europe. Inclusion criteria were arrival within 15 years before diagnosis, availability of HIV pol sequence and viral subtype shared by at least 10 individuals.
Methods:
We examined phylogenies for evidence of infection after entry into the UK and incorporated this information into a Bayesian analysis of timing of infection using biomarkers of CD4+ cell count, avidity assays, proportion of ambiguous nucleotides in viral sequences and last negative test dates where available.
Results:
1256 individuals were included. The final model indicated that HIV was acquired post-migration for most men who have sex with men (MSM) born in Europe (posterior expectation 65%, 95% credibility interval 64%-67%) or Africa (65%, 62%-69%), whereas a minority (20%-30%) of men and women with heterosexual transmission acquired HIV post-migration. Estimated diagnosis delays were lower for MSM than for those with heterosexual transmission, and were lower for those with post-migration infection across all subgroups. For MSM acquiring HIV post-migration the estimated mean time to diagnosis was 5 years for all subgroups.
Conclusions:
Acquisition of HIV post-migration is common, particularly among MSM calling for prevention efforts aimed at migrant communities. Delays in diagnosis reinforce the need for targeted testing initiatives
The ACCENT-protocol: a framework for benchmarking and model evaluation
We summarise results from a workshop on “Model Benchmarking and Quality Assurance” of the EU-Network of Excellence ACCENT, including results from other activities (e.g. COST Action 732) and publications. A formalised evaluation protocol is presented, i.e. a generic formalism describing the procedure of how to perform a model evaluation. This includes eight steps and examples from global model applications which are given for illustration. The first and important step is concerning the purpose of the model application, i.e. the addressed underlying scientific or political question. We give examples to demonstrate that there is no model evaluation per se, i.e. without a focused purpose. Model evaluation is testing, whether a model is fit for its purpose. The following steps are deduced from the purpose and include model requirements, input data, key processes and quantities, benchmark data, quality indicators, sensitivities, as well as benchmarking and grading. We define “benchmarking” as the process of comparing the model output against either observational data or high fidelity model data, i.e. benchmark data. Special focus is given to the uncertainties, e.g. in observational data, which have the potential to lead to wrong conclusions in the model evaluation if not considered carefully.publishe
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