125 research outputs found
Mott scattering at the interface between a metal and a topological insulator
We compute the spin-active scattering matrix and the local spectrum at the
interface between a metal and a three-dimensional topological band insulator.
We show that there exists a critical incident angle at which complete (100%)
spin flip reflection occurs and the spin rotation angle jumps by . We
discuss the origin of this phenomena, and systematically study the dependence
of spin-flip and spin-conserving scattering amplitudes on the interface
transparency and metal Fermi surface parameters. The interface spectrum
contains a well-defined Dirac cone in the tunneling limit, and smoothly evolves
into a continuum of metal induced gap states for good contacts. We also
investigate the complex band structure of BiSe.Comment: published versio
Hot electron transport in Ballistic Electron Emission Spectroscopy: band structure effects and k-space currents
Using a Green's function approach, we investigate band structure effects in
the BEEM current distribution in reciprocal space. In the elastic limit, this
formalism provides a 'parameter free' solution to the BEEM problem. At low
temperatures, and for thin metallic layers, the elastic approximation is enough
to explain the experimental I(V) curves at low voltages. At higher voltages
inelastic effects are approximately taken into account by introducing an
effective RPA-electron lifetime, much in similarity with LEED theory. For thick
films, however, additional damping mechanisms are required to obtain agreement
with experiment.Comment: 4 pages, 3 postscript figures, revte
A theoretical analysis of Ballistic Electron Emission Microscopy: k-space distributions and spectroscopy
We analyze BEEM experiments. At low temperatures and low voltages, near the
threshold value of the Schottky barrier, the BEEM current is dominated by the
elastic component. Elastic scattering by the lattice results in the formation
of focused beams and narrow lines in real space. To obtain the current injected
in the semiconductor, we compute the current distribution in reciprocal space
and, assuming energy and conservation. Our results show an
important focalization of the injected electron beam and explain the similarity
between BEEM currents for Au/Si(111) and Au/Si(100).Comment: 17 pages, 5 figures (postscript), Latex, APS,
http://www.icmm.csic.es/Pandres/pedro.htm. Appl. Surf. Sci. (in press
Magnetic-field effects on transport in carbon nanotube junctions
Here we address a theoretical study on the behaviour of electronic states of
heterojunctions and quantum dots based on carbon nanotubes under magnetic
fields. Emphasis is put on the analysis of the local density of states, the
conductance, and on the characteristic curves of current versus voltage. The
heterostructures are modeled by joining zigzag tubes through single
pentagon-heptagon pair defects, and described within a simple tight binding
calculation. The conductance is calculated using the Landauer formula in the
Green functions formalism. The used theoretical approach incorporates the
atomic details of the topological defects by performing an energy relaxation
via Monte Carlo calculation. The effect of a magnetic field on the conductance
gap of the system is investigated and compared to those of isolated constituent
tubes. It is found that the conductance gap of the studied CNHs exhibits
oscillations as a function of the magnetic flux. However, unlike the pristine
tubes case, they are not Aharonov-Bohm periodic oscillations
Negative differential resistance in molecular junctions: application to graphene ribbon junctions
Using self-consistent calculations based on Non-Equilibrium Green's Function
(NEGF) formalism, the origin of negative differential resistance (NDR) in
molecular junctions and quantum wires is investigated. Coupling of the molecule
to electrodes becomes asymmetric at high bias due to asymmetry between its
highest occupied molecular orbital (HOMO) and lowest unoccupied molecular
orbital (LUMO) levels. This causes appearance of an asymmetric potential
profile due to a depletion of charge and reduction of screening near the source
electrode. With increasing bias, this sharp potential drop leads to an enhanced
localization of the HOMO and LUMO states in different parts of the system. The
reduction in overlap, caused by localization, results in a significant
reduction in the transmission coefficient and current with increasing bias. An
atomic chain connected to two Graphene ribbons was investigated to illustrate
these effects. For a chain substituting a molecule, an even-odd effect is also
observed in the NDR characteristics.Comment: 8 pages, 8 figure
Evaluación del impacto de una intervención para mejorar las coberturas de vacunación frente a neumococo en pacientes con VIH
Fundamentos: Las personas infectadas por el vi-rus de la inmunodeficiencia humana (VIH) presentan riesgo elevado de sufrir la enfermedad neumocócica invasiva, motivo por el que se recomienda su vacuna-ción frente al neumococo. El objetivo de este trabajo fue evaluar el impacto de implementar una consulta hospitalaria de vacunas en las coberturas de vacuna-ción de estos pacientes.
Métodos: Se elaboró un estudio cuasiexperimental sin grupo control, de tipo antes/después, en el que se realizó un muestreo de casos consecutivos de pacientes con VIH remitidos a nuestra consulta entre el 1 noviembre de 2014 y el 30 junio de 2018. Las coberturas en el momento de la fecha de la cita para la valoración de su estado vacunal (en nuestra consulta) y después de ser atendido se compararon usando la prueba chi-cuadrado. Como referencia se utilizaron las del momento de la fecha de la primera cita.
Resultados: Se analizaron 209 pacientes, en los que se obtuvieron mejoras estadísticamente signifi-cativas en sus coberturas vacunales: 2, 9% en el mo-mento de la fecha de la cita para la valoración en nuestra consulta y 88% después de ser atendidos en nuestra consulta (RR [IC95%]= 30, 7 [13, 92-67, 58]) para la vacuna antineumocócica conjugada 13-valen-te, y 16, 3% en el momento de la primera cita y 83, 7% después de ser atendidos en nuestra consulta (RR [IC95%]=5, 2 [3, 76-7, 04]) para la vacuna antineumo-cócica polisacárida 23-valente.
Conclusiones: Implementar una consulta hospitalaria de vacunas representa una intervención efectiva para mejorar las coberturas de vacunación frente al neumococo en pacientes con VIH.
Background: People affected by the human immunodeficiency virus (HIV) have a higher risk of invasive pneumococcal disease. Therefore, vaccination against streptococcus pneumoniae is recommended for that group. The objective of this study was to analyze the impact of implementing a hospital appointment to assess vaccination status as part of the vaccination schedule of HIV patients.
Methods: We carried out a quasi-experimental uncontrolled before and after study with a sampling of consecutive cases of HIV patients referred to our department from November 1, 2014 to June 30, 2018. The study compared the vaccination coverage on the date of the appointment for an assessment of their vaccination status in our department and after the appointment. The analysis used the chi-squared test and the values on the date of the first appointment were taken as a reference.
Results: 209 patients were analyzed, and a statistically significant improvement was observed regarding their vaccination coverage: 2.9% of the patients had been vaccinated on the date in which they made an appointment for assessment by our department, and 88.0% were vaccinated after they left (OR [95%CI]: 30.7 [13.92-67.58]) with the 13-valent pneumococcal conjugate vaccine; and 16.3% had been vaccinated on the date they made the first appointment vs. 83.7% after they came to the appointment (OR [95%CI]: 5.2 [3.76-7.04]) with the 23-valent polysaccharide pneumococcal vaccine.
Conclusions: Implementing a hospital appointment for vaccination is an effective intervention to improve vaccination coverage against streptococcus pneumoniae in HIV patients
Multicentric standardization of protocols for the diagnosis of human mitochondrial respiratory chain defects
The quantification of mitochondrial respiratory chain (MRC) enzymatic activities is essential for diagnosis of a wide range of mitochondrial diseases, ranging from inherited defects to secondary dysfunctions. MRC lesion is frequently linked to extended cell damage through the generation of proton leak or oxidative stress, threatening organ viability and patient health. However, the intrinsic challenge of a methodological setup and the high variability in measuring MRC enzymatic activities represents a major obstacle for comparative analysis amongst institutions. To improve experimental and statistical robustness, seven Spanish centers with extensive experience in mitochondrial research and diagnosis joined to standardize common protocols for spectrophotometric MRC enzymatic measurements using minimum amounts of sample. Herein, we present the detailed protocols, reference ranges, tips and troubleshooting methods for experimental and analytical setups in different sample preparations and tissues that will allow an international standardization of common protocols for the diagnosis of MRC defects. Methodological standardization is a crucial step to obtain comparable reference ranges and international standards for laboratory assays to set the path for further diagnosis and research in the field of mitochondrial diseases. © 2022 by the authors. Licensee MDPI, Basel, Switzerland
Core reconstruction in pseudopotential calculations
A new method is presented for obtaining all-electron results from a
pseudopotential calculation. This is achieved by carrying out a localised
calculation in the region of an atomic nucleus using the embedding potential
method of Inglesfield [J.Phys. C {\bf 14}, 3795 (1981)]. In this method the
core region is \emph{reconstructed}, and none of the simplifying approximations
(such as spherical symmetry of the charge density/potential or frozen core
electrons) that previous solutions to this problem have required are made. The
embedding method requires an accurate real space Green function, and an
analysis of the errors introduced in constructing this from a set of numerical
eigenstates is given. Results are presented for an all-electron reconstruction
of bulk aluminium, for both the charge density and the density of states.Comment: 14 pages, 5 figure
Theory and simulation of quantum photovoltaic devices based on the non-equilibrium Green's function formalism
This article reviews the application of the non-equilibrium Green's function
formalism to the simulation of novel photovoltaic devices utilizing quantum
confinement effects in low dimensional absorber structures. It covers
well-known aspects of the fundamental NEGF theory for a system of interacting
electrons, photons and phonons with relevance for the simulation of
optoelectronic devices and introduces at the same time new approaches to the
theoretical description of the elementary processes of photovoltaic device
operation, such as photogeneration via coherent excitonic absorption,
phonon-mediated indirect optical transitions or non-radiative recombination via
defect states. While the description of the theoretical framework is kept as
general as possible, two specific prototypical quantum photovoltaic devices, a
single quantum well photodiode and a silicon-oxide based superlattice absorber,
are used to illustrated the kind of unique insight that numerical simulations
based on the theory are able to provide.Comment: 20 pages, 10 figures; invited review pape
Electronic transport in extended systems: Application to carbon nanotubes
Article on electronic transport in extended systems and the application to carbon nanotubes
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