1,465 research outputs found
Thermal effects on lattice strain in hcp Fe under pressure
We compute the c/a lattice strain versus temperature for nonmagnetic hcp iron
at high pressures using both first-principles linear response quasiharmonic
calculations based on the full potential linear-muffin-tin-orbital (LMTO)
method and the particle-in-cell (PIC) model for the vibrational partition
function using a tight-binding total-energy method. The tight-binding model
shows excellent agreement with the all-electron LMTO method. When hcp structure
is stable, the calculated geometric mean frequency and Helmholtz free energy of
hcp Fe from PIC and linear response lattice dynamics agree very well, as does
the axial ratio as a function of temperature and pressure. On-site
anharmonicity proves to be small up to the melting temperature, and PIC gives a
good estimate of its sign and magnitude. At low pressures, hcp Fe becomes
dynamically unstable at large c/a ratios, and the PIC model might fail where
the structure approaches lattice instability. The PIC approximation describes
well the vibrational behavior away from the instability, and thus is a
reasonable approach to compute high temperature properties of materials. Our
results show significant differences from earlier PIC studies, which gave much
larger axial ratio increases with increasing temperature, or reported large
differences between PIC and lattice dynamics results.Comment: 9 figure
First-principles thermoelasticity of bcc iron under pressure
We investigate the elastic and isotropic aggregate properties of
ferromagnetic bcc iron as a function of temperature and pressure by computing
the Helmholtz free energies for the volume-conserving strained structures using
the first-principles linear response linear-muffin-tin-orbital method and the
generalized-gradient approximation. We include the electronic excitation
contributions to the free energy from the band structures, and phonon
contributions from quasi-harmonic lattice dynamics. We make detailed
comparisons between our calculated elastic moduli and their temperature and
pressure dependences with available experimental and theoretical data.Comment: 5 figures, 2 table
First-principles thermal equation of state and thermoelasticity of hcp Fe at high pressures
We investigate the equation of state and elastic properties of hcp iron at
high pressures and high temperatures using first principles linear response
linear-muffin-tin-orbital method in the generalized-gradient approximation. We
calculate the Helmholtz free energy as a function of volume, temperature, and
volume-conserving strains, including the electronic excitation contributions
from band structures and lattice vibrational contributions from quasi-harmonic
lattice dynamics. We perform detailed investigations on the behavior of elastic
moduli and equation of state properties as functions of temperature and
pressure, including the pressure-volume equation of state, bulk modulus, the
thermal expansion coefficient, the Gruneisen ratio, and the shock Hugoniot.
Detailed comparison has been made with available experimental measurements and
theoretical predictions.Comment: 33 pages, 12 figure
Bivariate spline interpolation with optimal approximation order
Let be a triangulation of some polygonal domain f c R2 and let S9 (A) denote the space of all bivariate polynomial splines of smoothness r and degree q with respect to A. We develop the first Hermite-type interpolation scheme for S9 (A), q >_ 3r + 2, whose approximation error is bounded above by Kh4+i, where h is the maximal diameter of the triangles in A, and the constant K only depends on the smallest angle of the triangulation and is independent of near-degenerate edges and nearsingular vertices. Moreover, the fundamental functions of our scheme are minimally supported and form a locally linearly independent basis for a superspline subspace of Sr, (A). This shows that the optimal approximation order can be achieved by using minimally supported splines. Our method of proof is completely different from the quasi-interpolation techniques for the study of the approximation power of bivariate splines developed in [71 and [181
Acute cortical blindness caused by pre-eclampsia in the antepartum; posterior reversible encephalopathy syndrome (PRES)
We present a case report of a patient presenting posterior reversible encephalopathy syndrome (PRES), a rare acute neurological condition associated with pre-eclampsia. A possible common aetiology and successful clinical management approach is reported
Anomalous Heat Diffusion
Consider anomalous energy spread in solid phases, i.e., , as induced by a
small initial excess energy perturbation distribution away
from equilibrium. The associated total thermal equilibrium heat flux
autocorrelation function is shown to obey rigorously the intriguing
relation, , where is the specific
volumetric heat capacity. Its integral assumes a time-local Helfand-moment
relation; i.e. , where
the chosen cut-off time is determined by the maximal signal velocity for
heat transfer. Given the premise that the averaged nonequilibrium heat flux is
governed by an anomalous heat conductivity, energy diffusion scaling determines
a corresponding anomalous thermal conductivity scaling behaviour
SOTER on ROS: A Run-Time Assurance Framework on the Robot Operating System
We present an implementation of SOTER, a run-time assurance framework for
building safe distributed mobile robotic (DMR) systems, on top of the Robot
Operating System (ROS). The safety of DMR systems cannot always be guaranteed
at design time, especially when complex, off-the-shelf components are used that
cannot be verified easily. SOTER addresses this by providing a language-based
approach for run-time assurance for DMR systems. SOTER implements the reactive
robotic software using the language P, a domain-specific language designed for
implementing asynchronous event-driven systems, along with an integrated
run-time assurance system that allows programmers to use unfortified components
but still provide safety guarantees. We describe an implementation of SOTER for
ROS and demonstrate its efficacy using a multi-robot surveillance case study,
with multiple run-time assurance modules. Through rigorous simulation, we show
that SOTER enabled systems ensure safety, even when using unknown and untrusted
components.Comment: 20th International Conference on Runtime Verificatio
Protein Adducts of Iso[4]levuglandin E2, a Product of the Isoprostane Pathway, in Oxidized Low Density Lipoprotein
Levuglandin (LG) E2, a cytotoxic seco prostanoic acid co-generated with prostaglandins by nonenzymatic rearrangements of the cyclooxygenase-derived endoperoxide, prostaglandin H2, avidly binds to proteins. That LGE2-protein adducts can also be generated nonenzymatically is demonstrated by their production during free radical-induced oxidation of low density lipoprotein (LDL). Like oxidized LDL, LGE2-LDL, but not native LDL, undergoes receptor-mediated uptake and impaired processing by macrophage cells. Since radical-induced lipid oxidation produces isomers of prostaglandins, isoprostanes (isoPs), via endoperoxide intermediates, we postulated previously that a similar family of LG isomers, isoLGs, is cogenerated with isoPs. Now iso[4]LGE2-protein epitopes produced by radical-induced oxidation of arachidonic acid in the presence of protein were detected with an enzyme-linked immunosorbent assay. Iso[4]LGE2-protein epitopes are also generated during free radical-induced oxidation of LDL. All of the LGE2isomers generated upon oxidation of LDL are efficiently sequestered by covalent adduction with LDL-based amino groups. The potent electrophilic reactivity of iso-LGs can be anticipated to have biological consequences beyond their obvious potential as markers for specific arachidonate-derived protein modifications that may be of value for the quantitative assessment of oxidative injury
Labour Market and Social Policy in Italy: Challenges and Changes. Bertelsmann Policy Brief #2016/02
vEight years after the outbreak of the financial crisis, Italy has still to cope with and
overcome a plethora of economic and social challenges. On top of this, it faces an
unfavourable demographic structure and severe disparities between its northern and
southern regions. Some promising reforms have recently been enacted, specifically
targeting poverty and social exclusion. However, much more remains to be done on
the way towards greater economic stability and widely shared prosperity
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