5,738 research outputs found
Isoscaling and the high Temperature limit
This study shows that isoscaling, usually studied in nuclear reactions, is a
phenomenon common to all cases of fair sampling. Exact expressions for the
yield ratio and approximate expressions for the isoscaling parameters
and are obtained and compared to experimental results. It is
concluded that nuclear isoscaling is bound to contain a component due to
sampling and, thus, a words of caution is issued to those interested in
extracting information about the nuclear equation of state from isoscaling.Comment: 7 pages, 1 figur
Adiabatic Electron-Phonon Interaction and High-Temperature Thermodynamics of A15 Compounds
Inelastic neutron scattering was used to measure the phonon densities of states of the A15 compounds V_3Si, V_3Ge, and V_3Co at temperatures from 10 to 1273 K. It was found that phonons in V_3Si and V_3Ge, which are superconducting at low temperatures, exhibit an anomalous stiffening with increasing temperature, whereas phonons in V_3Co have a normal softening behavior. First-principles calculations show that this anomalous increase in phonon frequencies at high temperatures originates with an adiabatic electron-phonon coupling mechanism. The anomaly is caused by the thermally induced broadening of sharp peaks in the electronic density of states of V_3Si and V_3Ge, which tends to decrease the electronic density at the Fermi level. These results show that the adiabatic electron-phonon coupling can influence the phonon thermodynamics at temperatures exceeding 1000 K
Measuring the purity of a qubit state: entanglement estimation with fully separable measurements
Given a finite number of copies of a qubit state we compute the maximum
fidelity that can be attained using joint-measurement protocols for estimating
its purity. We prove that in the asymptotic limit,
separable-measurement protocols can be as efficient as the optimal
joint-measurement one if classical communication is used. This in turn shows
that the optimal estimation of the entanglement of a two-qubit state can also
be achieved asymptotically with fully separable measurements. The relationship
between our global Bayesian approach and the quantum Cramer-Rao bound is also
discussed.Comment: 5 pages, 1 figure, RevTeX, improved versio
Limb imaging of the Venus O2 visible nightglow with the Venus Monitoring Camera
We investigated the Venus O2 visible nightglow with imagery from the Venus
Monitoring Camera on Venus Express. Drawing from data collected between April
2007 and January 2011, we study the global distribution of this emission,
discovered in the late 70s by the Venera 9 and 10 missions. The inferred
limb-viewing intensities are on the order of 150 kiloRayleighs at the lower
latitudes and seem to drop somewhat towards the poles. The emission is
generally stable, although there are episodes when the intensities rise up to
500 kR. We compare a set of Venus Monitoring Camera observations with
coincident measurements of the O2 nightglow at 1.27 {\mu}m made with the
Visible and Infrared Thermal Imaging Spectrometer, also on Venus Express. From
the evidence gathered in this and past works, we suggest a direct correlation
between the instantaneous emissions from the two O2 nightglow systems. Possible
implications regarding the uncertain origin of the atomic oxygen green line at
557.7 nm are noted.Comment: 7 pages, 3 figure
Exact Solution of the Munoz-Eaton Model for Protein Folding
A transfer-matrix formalism is introduced to evaluate exactly the partition
function of the Munoz-Eaton model, relating the folding kinetics of proteins of
known structure to their thermodynamics and topology. This technique can be
used for a generic protein, for any choice of the energy and entropy
parameters, and in principle allows the model to be used as a first tool to
characterize the dynamics of a protein of known native state and equilibrium
population. Applications to a -hairpin and to protein CI-2, with
comparisons to previous results, are also shown.Comment: 4 pages, 5 figures, RevTeX 4. To be published in Phys. Rev. Let
âThey bring AIDS to us and say we give it to themâ: Socio-structural context of female sex workersâ vulnerability to HIV infection in Ibadan Nigeria
The aim of the study was to examine and describe the individual and structural-environmental factors that shape the vulnerability of brothel-based female sex workers (FSWs) in Ibadan, southwest Nigeria to HIV infection. A descriptive qualitative research design was utilised to elicit data, using in-depth interviews and focus group discussions, from 60 randomly selected participants in four brothels. A thematic analysis of data was undertaken following transcription and validation of interviews. Five themes emerged from the data: (i) flawed knowledge and fatalistic attitudes; (ii) the psychosocial and economic context of sex work; (iii) religious beliefs, stigma and risk taking; (iv) barriers to HIV testing; and (v) legal and policy constraints to sex work. We describe the complex interaction between these themes and how they combine to increase the risk of HIV infection among FSWs. The impact of previous interventions to reduce the risk of HIV infection among FSWs has been limited by personal and structural factors; hence we recommend that new strategies that recognise the practical constraints to HIV prevention among FSWs are urgently needed to make the environment of commercial work safer for FSWs, their clients, and by extension the general population
Electron-phonon interactions and high-temperature thermodynamics of vanadium and its alloys
Inelastic neutron scattering was used to measure the phonon densities of states (DOSs) for pure V and solid solutions of V with 6 to 7at% of Co, Nb, and Pt, at temperatures from 10 K to 1323 K. Ancillary measurements of heat capacity and thermal expansion are reported on V and V-7at%Co and used to help identify the different sources of entropy. Pure V exhibits an anomalous anharmonic stiffening of phonons with increasing temperature. This anharmonicity is suppressed by Co and Pt, but not by isoelectronic Nb solutes. The changes in phonon frequency with alloying and with temperature both correlate to the decrease in electron density of states (DOS) at the Fermi level as calculated using density functional theory. The effects of both temperature and alloying can be understood in terms of an adiabatic electron-phonon interaction (EPI), which broadens sharp features in the electron DOS. These results show that the adiabatic EPI can influence the phonon thermodynamics at temperatures exceeding 1000 K, and that thermal trends of phonons may help assess the strength of the EPI
Critical wetting of a class of nonequilibrium interfaces: A mean-field picture
A self-consistent mean-field method is used to study critical wetting
transitions under nonequilibrium conditions by analyzing Kardar-Parisi-Zhang
(KPZ) interfaces in the presence of a bounding substrate. In the case of
positive KPZ nonlinearity a single (Gaussian) regime is found. On the contrary,
interfaces corresponding to negative nonlinearities lead to three different
regimes of critical behavior for the surface order-parameter: (i) a trivial
Gaussian regime, (ii) a weak-fluctuation regime with a trivially located
critical point and nontrivial exponents, and (iii) a highly non-trivial
strong-fluctuation regime, for which we provide a full solution by finding the
zeros of parabolic-cylinder functions. These analytical results are also
verified by solving numerically the self-consistent equation in each case.
Analogies with and differences from equilibrium critical wetting as well as
nonequilibrium complete wetting are also discussed.Comment: 11 pages, 2 figure
Magnetic and vibrational properties of high-entropy alloys
The magnetic properties of high-entropy alloys based on equimolar FeCoCrNi were investigated using vibrating sample magnetometry to determine their usefulness in high-temperature magnetic applications. Nuclear resonant inelastic x-ray scattering measurements were performed to evaluate the vibrational entropy of the ^(57)Fe atoms and to infer chemical order. The configurational and vibrational entropy of alloying are discussed as they apply to these high-entropy alloys
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