533 research outputs found
On the ab initio calculation of CVV Auger spectra in closed-shell systems
We propose an ab initio method to evaluate the core-valence-valence (CVV)
Auger spectrum of systems with filled valence bands. The method is based on the
Cini-Sawatzky theory, and aims at estimating the parameters by first-principles
calculations in the framework of density-functional theory (DFT). Photoemission
energies and the interaction energy for the two holes in the final state are
evaluated by performing DFT simulations for the system with varied population
of electronic levels. Transition matrix elements are taken from atomic results.
The approach takes into account the non-sphericity of the density of states of
the emitting atom, spin-orbit interaction in core and valence, and non
quadratic terms in the total energy expansion with respect to fractional
occupation numbers. It is tested on two benchmark systems, Zn and Cu metals,
leading in both cases to L23M45M45 Auger peaks within 2 eV from the
experimental ones. Detailed analysis is presented on the relative weight of the
various contributions considered in our method, providing the basis for future
development. Especially problematic is the evaluation of the hole-hole
interaction for systems with broad valence bands: our method underestimates its
value in Cu, while we obtain excellent results for this quantity in Zn.Comment: 20 pages, 5 figures, 4 table
Equilibrium and time-dependent Josephson current in one-dimensional superconducting junctions
We investigate the transport properties of a one-dimensional
superconductor-normal metal-superconductor (S-N-S) system described within the
tight-binding approximation. We compute the equilibrium dc Josephson current
and the time-dependent oscillating current generated after the switch-on of a
constant bias. In the first case an exact embedding procedure to calculate the
Nambu-Gorkov Keldysh Green's function is employed and used to derive the
continuum and bound states contributions to the dc current. A general formalism
to obtain the Andreev bound states (ABS) of a normal chain connected to
superconducting leads is also presented. We identify a regime in which all
Josephson current is carried by the ABS and obtain an analytic formula for the
current-phase relation in the limit of long chains. In the latter case the
condition for perfect Andreev reflections is expressed in terms of the
microscopic parameters of the model, showing a limitation of the so called
wide-band-limit (WBL) approximation. When a finite bias is applied to the S-N-S
junction we compute the exact time-evolution of the system by solving
numerically the time-dependent Bogoliubov-deGennes equations. We provide a
microscopic description of the electron dynamics not only inside the normal
region but also in the superconductors, thus gaining more information with
respect to WBL-based approaches. Our scheme allows us to study the ac regime as
well as the transient dynamics whose characteristic time-scale is dictated by
the velocity of multiple Andreev reflections
Nine years of comparative effectiveness research education and training: initiative supported by the PhRMA Foundation
The term comparative effectiveness research (CER) took center stage with passage of the American Recovery and Reinvestment Act (2009). The companion US$1.1 billion in funding prompted the launch of initiatives to train the scientific workforce capable of conducting and using CER. Passage of the Patient Protection and Affordable Care Act (2010) focused these initiatives on patients, coining the term ‘patient-centered outcomes research’ (PCOR). Educational and training initiatives were soon launched. This report describes the initiative of the Pharmaceutical Research and Manufacturers Association of America (PhRMA) Foundation. Through provision of grant funding to six academic Centers of Excellence, to spearheading and sponsoring three national conferences, the PhRMA Foundation has made significant contributions to creation of the scientific workforce that conducts and uses CER/PCOR
Critical currents in graphene Josephson junctions
We study the superconducting correlations induced in graphene when it is
placed between two superconductors, focusing in particular on the supercurrents
supported by the 2D system. For this purpose we make use of a formalism placing
the emphasis on the many-body aspects of the problem, with the aim of
investigating the dependence of the critical currents on relevant variables
like the distance L between the superconducting contacts, the temperature, and
the doping level. Thus we show that, despite the vanishing density of states at
the Fermi level in undoped graphene, supercurrents may exist at zero
temperature with a natural 1/L^3 dependence at large L. When temperature
effects are taken into account, the supercurrents are further suppressed beyond
the thermal length L_T (~ v_F / k_B T, in terms of the Fermi velocity v_F of
graphene), entering a regime where the decay is given by a 1/L^5 dependence. On
the other hand, the supercurrents can be enhanced upon doping, as the Fermi
level is shifted by a chemical potential \mu from the charge neutrality point.
This introduces a new crossover length L* ~ v_F / \mu, at which the effects of
the finite charge density start being felt, marking the transition from the
short-distance 1/L^3 behavior to a softer 1/L^2 decay of the supercurrents at
large L. It turns out that the decay of the critical currents is given in
general by a power-law behavior, which can be seen as a consequence of the
perfect scaling of the Dirac theory applied to the low-energy description of
graphene.Comment: 11 pages, 6 figures, to appear in J. Phys.: Condens. Matte
Electromechanical dissociation of left atrium in patients with Cardiac Amyloidosis by Magnetic Resonance: Prognostic and clinical correlates
EchidnaCSI: engaging the public in research and conservation of the short-beaked echidna
The short-beaked echidna is an iconic Australian animal and the most-widespread native mammal, inhabiting diverse environments. The cryptic nature of echidnas has limited research into their ecology in most areas; however, from the well-researched and endangered Kangaroo Island echidna population, we understand that the threats include habitat loss, roads, and invasive species. To obtain more information about echidnas Australia-wide, we established the Echidna Conservation Science Initiative (EchidnaCSI) citizen science project. EchidnaCSI calls on members of the public to submit photographs of wild echidnas and learn to identify and collect echidna scats for molecular analysis. To facilitate participation, we developed a smartphone application as well as ongoing social and traditional media activities and community events. In 3 y, more than 9,000 members of the public have downloaded the EchidnaCSI app, collecting 400 scats and submitting over 8,000 sightings of echidnas from across Australia. A subset of submitted scat samples were subjected to DNA extraction and PCR, which validated the approach of using citizen science for scat collection and viability for molecular analysis. To assess the impact of the project through public participation, we surveyed our participants (n = 944) to understand their demographics and motivations for engagement. Survey results also revealed that EchidnaCSI served as a gateway into citizen science more generally for many participants. EchidnaCSI demonstrates the potential for using citizen science approaches to collect high-quality data and material from a cryptic species over a very large geographic area and the considerable engagement value of citizen science research.Tahlia Perry, Alan Stenhouse, Isabella Wilson, Imma Perfetto, Michael W. McKelvey, Michelle Coulson, Rachel A. Ankeny, Peggy D. Rismiller, and Frank Grützne
Identification, isolation and in vitro expansion of human and nonhuman primate T stem cell memory cell
The T cell compartment is phenotypically and functionally heterogeneous; subsets of naive and memory cells have different functional properties, and also differ with respect to homeostatic potential and the ability to persist in vivo. Human stem cell memory T (TSCM) cells, which possess superior immune reconstitution and antitumor response capabilities, can be identified by polychromatic flow cytometry on the basis of the simultaneous expression of several naive markers together with the memory marker CD95. We describe here a protocol based on the minimum set of markers required for optimal identification of human and nonhuman primate (NHP) TSCM cells with commonly available flow cytometers. By using flow sorters, TSCM cells can thereby be isolated efficiently at high yield and purity. With the use of the 5.5-h isolation procedure, depending on the number of cells needed, the sorting procedure can last for 2-15 h. We also indicate multiple strategies for their efficient expansion in vitro at consistent numbers for functional characterization or adoptive transfer experiments
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