1,338 research outputs found
Isochoric, isobaric and ultrafast conductivities of aluminum, lithium and carbon in the warm dense matter (WDM) regime
We study the conductivities of (i) the equilibrium isochoric state
(), (ii) the equilibrium isobaric state (),
and also the (iii) non-equilibrium ultrafast matter (UFM) state () with the ion temperature less than the the electron temperature
. Aluminum, lithium and carbon are considered, being increasingly complex
warm dense matter (WDM) systems, with carbon having transient covalent bonds.
First-principles calculations, i.e., neutral-pseudoatom (NPA) calculations and
density-functional theory (DFT) with molecular-dynamics (MD) simulations, are
compared where possible with experimental data to characterize and . The NPA are
closest to the available experimental data when compared to results from
DFT+MD, where simulations of about 64-125 atoms are typically used. The
published conductivities for Li are reviewed and the value at a temperature of
4.5 eV is examined using supporting X-ray Thomson scattering calculations. A
physical picture of the variations of with temperature and density
applicable to these materials is given. The insensitivity of to
below 10 eV for carbon, compared to Al and Li, is clarified.Comment: 10 figure
Two-temperature pair potentials and phonon spectra for simple metals in the warm dense matter regime
We develop ion-ion pair potentials for Al, Na and K for densities and
temperatures relevant to the warm-dense-matter (WDM) regime. Furthermore, we
emphasize non-equilibrium states where the ion temperature differs from
the electron temperature . This work focuses mainly on ultra-fast
laser-metal interactions where the energy of the laser is almost exclusively
transferred to the electron sub-system over femtosecond time scales. This
results in a two-temperature system with and with the ions still at
the initial room temperature . First-principles calculations, such as
density functional theory (DFT) or quantum Monte Carlo, are as yet not fully
feasible for WDM conditions due to lack of finite- features, e.g.
pseudopotentials, and extensive CPU time requirements. Simpler methods are
needed to study these highly complex systems. We propose to use two-temperature
pair potentials constructed from linear-response theory
using the non-linear electron density obtained from finite-
DFT with a single ion immersed in the appropriate electron fluid. We compute
equilibrium phonon spectra at which are found to be in very good
agreement with experiments. This gives credibility to our non-equilibrium
phonon dispersion relations which are important in determining thermophysical
properties, stability, energy-relaxation mechanisms and transport coefficients.Comment: International Conf. on Strongly-Coupled Coulombo Systems (SCCS) 201
Ion-ion dynamic structure factor, acoustic modes and equation of state of two-temperature warm dense aluminum
The ion-ion dynamical structure factor and the equation of state of warm
dense aluminum in a two-temperature quasi-equilibrium state, with the electron
temperature higher than the ion temperature, are investigated using
molecular-dynamics simulations based on ion-ion pair potentials constructed
from a neutral pseudoatom model. Such pair potentials based on density
functional theory are parameter-free and depend directly on the electron
temperature and indirectly on the ion temperature, enabling efficient
computation of two-temperature properties. Comparison with ab initio
simulations and with other average-atom calculations for equilibrium aluminum
shows good agreement, justifying a study of quasi-equilibrium situations.
Analyzing the van Hove function, we find that ion-ion correlations vanish in a
time significantly smaller than the electron-ion relaxation time so that
dynamical properties have a physical meaning for the quasi-equilibrium state. A
significant increase in the speed of sound is predicted from the modification
of the dispersion relation of the ion acoustic mode as the electron temperature
is increased. The two-temperature equation of state including the free energy,
internal energy and pressure is also presented
Leveraging Ada 2012 and SPARK 2014 for assessing generated code from AADL models
Modeling of Distributed Real-time Embedded systems using Architecture Description Language provides the foundations for various levels of analysis: scheduling, reliability, consis- tency, etc.; but also allows for automatic code generation. A challenge is to demonstrate that generated code matches quality required for safety-critical systems. In the scope of the AADL, the Ocarina toolchain proposes code generation towards the Ada Ravenscar profile with restrictions for High- Integrity. It has been extensively used in the space domain as part of the TASTE project within the European Space Agency. In this paper, we illustrate how the combined use of Ada 2012 and SPARK 2014 significantly increases code quality and exhibits absence of run-time errors at both run-time and generated code levels
Nasal Carriage of Staphylococcus aureus in Australian (pre-clinical and clinical) Medical Students
The nasal carriage of Staphylococcus aureus in 808 Australian medical students was studied. Five groups of students experienced varying degrees of clinical exposure in a hospital environment ranging from 0 to 42 months. The overall percentage of carriers among the five groups did not vary. However, with increasing clinical exposure there was a decrease in the percentage of isolates sensitive to all antibiotics tested, and an increase in the carriage of S. aureus resistant to three or more antibiotics. No carriers of methicillin-resistant S. aureus (MRSA) were detected. The comparative rates of S. aureus carriage between female and male students varied. The relevance of medical students as nasal carriers of S. aureus in the hospital environment today is discussed
- …