2,724 research outputs found
Optimal quantum state reconstruction for cold trapped ions
We study the physical implementation of an optimal tomographic reconstruction
scheme for the case of determining the state of a multi-qubit system, where
trapped ions are used for defining qubits. The protocol is based on the use of
mutually unbiased measurements and on the physical information described in H.
H\"{a}ffner \emph{et. al} [Nature \textbf{438}, 643-646 (2005)]. We introduce
the concept of physical complexity for different types of unbiased measurements
and analyze their generation in terms of one and two qubit gates for trapped
ions.Comment: Accepted for publication in Phys. Rev. A as Rap. Com
Coherent transport in graphene nanoconstrictions
We study the effect of a structural nanoconstriction on the coherent
transport properties of otherwise ideal zig-zag-edged infinitely long graphene
ribbons. The electronic structure is calculated with the standard one-orbital
tight-binding model and the linear conductance is obtained using the Landauer
formula. We find that, since the zero-bias current is carried in the bulk of
the ribbon, this is very robust with respect to a variety of constriction
geometries and edge defects. In contrast, the curve of zero-bias conductance
versus gate voltage departs from the staircase of the ideal case
as soon as a single atom is removed from the sample. We also find that
wedge-shaped constrictions can present non-conducting states fully localized in
the constriction close to the Fermi energy. The interest of these localized
states in regards the formation of quantum dots in graphene is discussed.Comment: 9 pages, 9 figure
Spin splitting in a polarized quasi-two-dimensional exciton gas
We have observed a large spin splitting between "spin" and
heavy-hole excitons, having unbalanced populations, in undoped GaAs/AlAs
quantum wells in the absence of any external magnetic field. Time-resolved
photoluminescence spectroscopy, under excitation with circularly polarized
light, reveals that, for high excitonic density and short times after the
pulsed excitation, the emission from majority excitons lies above that of
minority ones. The amount of the splitting, which can be as large as 50% of the
binding energy, increases with excitonic density and presents a time evolution
closely connected with the degree of polarization of the luminescence. Our
results are interpreted on the light of a recently developed model, which shows
that, while intra-excitonic exchange interaction is responsible for the spin
relaxation processes, exciton-exciton interaction produces a breaking of the
spin degeneracy in two-dimensional semiconductors.Comment: Revtex, four pages; four figures, postscript file Accepted for
publication in Physical Review B (Rapid Commun.
HIV-1 and Alzheimer: a real conection?
La infección por el virus de inmunodeficiencia humana (VIH) causa alteraciones neurológicas que son más graves y frecuentes como consecuenia del envejecimieno de la población. Este daño se asocia a la disfunción neuronal, que patológicamente se caracteriza como una pérdida de sinapsis, acortamiento de neuritas, anormalidades dendríticas, así comon pérdida neuronal. A este respecto, varios estudios han observado un aumento significativo de placas amiloides en cerebros de individuos infectados por el VIH en comparación con controles sanos, así como en individuos VIH positivos que habían estado expuestos a la terapia antirretroviral. En este trabajo se ha investigado el efecto de la combinación del péptido β-amiloide e infección por VIH-1 en diferentes células del sistema nervioso. El pretratamiento de las células gliales y neuronales provoca un incremento en la replicación viral, así como el tratamiento combinado virus y formas de oligómeros y fibrillas producen un incremento en las especies reactivas de oxígeno y de la forma activa de la enzima proapoptótica caspasa-3, en astrocitos. Lo que podría traducirse como un incremento de neurotoxicidad y depositos de β-amiloide en el cerebro infectado.Infection by human immunodeficiency virus (HIV) promotes neurological alterations which are more severe and frequents, due to the aging of the population. This dementia is associated to neuronal disfunction, and is pathologicaly characterized as sinapse lose, dendritic abnormalities and neuronal death. Supporting this, several studies have shown a significant increase of the amyloid plaques in infected HIV brains compared to healthy controls as well as HIV positive individuals which were exposed to antiretroviral therapy. In the present study we have investigated the combined effect of amyloid-β and HIV-1 infection in diferent nervous cells. When we pretreated glial cells and neurons we found an increased viral replication, as well as the combined treatment of HIV and oligomeric and fibrils forms of amyloid-β which produce glial increased levels of oxygen reactive species and the proapoptotic enzyme caspase-3. These observations could be traduced in an increased neurotoxicity and amyloid-β deposits in infected brains
Osteoblastoma del sacro. A propósito de dos casos clínicos.
El osteoblastoma es un tumor óseo primitivo de frecuente localización en los elementos posteriores de la columna vertebral, aunque raro en el sacro. Se presentan dos osteoblastomas del sacro, con un seguimiento medio de ocho años, tratados mediante resección intralesional que, sin morbilidad, deparó un excelente resultado. El curetaje sería un procedimiento de resección válido en osteoblastomas sacros no agresivos, si bien obliga a un seguimiento prolongado del paciente para vigilar la posibilidad de recidivas locales.Osteoblastoma is a primary neoplasm of bone fre-
quently located in the posterior elements of the spine, alt-
hough rarely affecting the sacrum. Two cases in this location
are reported, with a mean follow-up of eight years, treated
with an intralesional resection that, without any morbidity, has
provided an excellent result. Curettage should be a valid re-
section procedure for nonagressive osteoblastomas of the
sacrum, although it makes necessary a long follow-up in or-
der to watch over the possibility of a local recurrence
Relationships between depth and age, and recruitment indexes of hake on Galicia and Portugal shelf
In this paper it is studied the relations between
the depth and the ages of the hake caugth in the six surveys
done between 1974 and 1979 in the Divisions Vlllc and IXa, as
soon as the recruitment levels in those years. It is observed
a clear stratification of the ages and a significant bathimetric
tendency to increase the mean age with the depth (1'=0.81).
On the other hand, it is noticed a serious decrease in the following years over the recruitment level detected in 1974.Dans ce papier on a studie les relations entre l'âge
et la profundeur du merlu capturée pendant six campagns realisées
entre 1974 et 1979 dans subaire Vlllc et Division IXa du CIEM
ainsi que les nivenux du recruitment durant ces annees.
On observe une claire stratification entre la bathymetrie
et l'âge et une tendence significatif a augmenter l'âge moyenne avec la profunder (r=0.81). D'antre coté, on constante une grave
chute dans 1es anneés suivantes un relation avec le niveaux de recruitement detecté en 1974
Influence of nanoscale defects on the improvement of photocatalytic activity of Ag/ZnO
This study presents the advances in the field of ZnO/Ag catalysts from the synthesis of hierarchical ZnO nanowires (NWs) decorated with Ag nanoparticles, prepared by a facile solvothermal method at 120°C. It evaluates the photocatalytic efficiency from studying the time reaction of Ag/Zn concentration ratio and the presence of cetyltrimethylammonium bromide (CTAB) as an organic dispersant. X-ray diffraction, scanning electron microscopy, and analytical/high-resolution transmission electron microscopy results confirmed the presence of homogeneous cylindrical ZnO nanowires and quasi-spherical Ag crystals. ZnO NWs exhibited hexagonal wurtzite structure and cubic FCC symmetry in Ag nanoparticles (NPS). Two types of nanostructures, including homogeneous cylindrical ZnO NWs in the absence of Ag and simultaneous presence of ZnO NWs and Ag NPs, formed depending on experimental conditions. The photocatalytic activity was evaluated by studying methylene blue (MB) degradation time under UV light excitation. Diffuse reflectance UV–Vis spectrophotometry (UV–Vis DRS) allowed identifying the ZnO absorption band at ~393 nm. Crystal size varied depending on the reaction time and the addition of CTAB. Synthesis time increased bandgap values, getting better photocatalytic performance in samples synthesized in intermediate times (6 h), higher Ag+/Zn2+ molar ratio (0.2/1.0), and CTAB. According to HRTEM observations, the presence of silver nanocrystals with high content of defects (twinning, stacking faults) could play an essential role in the photocatalytic response. In this context, the specific synthesis conditions of Ag/ZnO might be more appropriate for their use in organic dyes degradation in water and the potential use in protective treatments against materials biodeterioration processes.This work has been supported by the Innovation and Education Ministry (ref. MAT2013-47460-C5-5-P and MAT2016-80875-C3-3-R), the Autonomous Region Program of Madrid (ref. S2018/NMT-4411 and S2013/MIT-2862), the Geomateriales 2 program (S2013/MIT_2914), the TOP Heritage (P2018/NMT-4372) of the Community of Madrid, the Innovation and Education Ministry (MAT201347460-C5-5-P) and the Ministry of Education, Science and Technological Development of Serbia (projects No. 172035 and 45020). Besides, we would like to thank the Master of “Materials Science” of Carlos III University (Spain) for providing financial and laboratory equipment support
Estrés oxidativo y osteonecrosis de la cabeza femoral
La osteonecrosis no traumática de la cabeza femoral representa un problema clínico importante, ya
que hasta un 80% de los casos terminan en un colapso osteocondral con gran destrucción ósea y daño articular, con
dolor y pérdida de la función de la cadera, necesitando finalmente una intervención de prótesis de sustitución a una
edad temprana. La patogénesis de esta enfermedad es multifactorial y se conocen diversidad de factores etiológicos
asociados a ella: consumo de alcohol y tabaco, uso de costicosteroides, alteraciones hemostáticas, alteraciones en el
metabolismo lipídico y presencia de ciertos polimorfismos genéticos. Sin embargo, un gran número están descritas
como idiopáticas y no presentan factores de riesgo. Recientes estudios en modelos animales de ONF inducida por
esteroides sugieren que el estrés oxidativo podría estar involucrado en el desarrollo de la enfermedad. Estos estudios
muestran que la administración de sustancias oxidantes aumenta el riesgo de padecer la enfermedad y que la administración de antioxidantes podría prevenir el desarrollo de la misma.Non-traumatic osteonecrosis of the femoral head represents a significant clinical problem. Chondral
collapse occurs in up to 80% of the untreated cases resulting in bone destruction, pain and loss of joint function and
prosthetic hip replacement at an early age is needed. The pathogenesis of the disease is likely multifactorial and seve-
ral etiologic factors are known to be associated with it: alcohol intake, smoking, corticosteroid use, impaired hemos-
tasis and lipid metabolism, and the presence of certain polymorphisms. However, a significant number are described,
as idiopathic and do not present any risk factor. Recent studies in steroid-induced ONF animal models suggest that
oxidative stress could be involved in the development of the disease. These studies show that the administration of
pro-oxidant substances increase the risk of disease and antioxidants administration might prevent the development
thereo
Breakdown of anomalous channeling with ion energy for accurate strain determination in gan-based heterostructures
The influence of the beam energy on the determination of strain state with ion channeling in GaN-based heterostructures (HSs) is addressed. Experimental results show that anomalous channeling may hinder an accurate analysis due to the steering effects at the HS interface, which are more intense at lower ion energies. The experimental angular scans have been well reproduced by Monte Carlo simulations, correlating the steering effects with the close encounter probability at the interface. Consequently, limitations in the determination of the strain state by ion channeling can be overcome by selecting the adequate beam energy
Extended WKB method, resonances and supersymmetric radial barriers
Semiclassical approximations are implemented in the calculation of position
and width of low energy resonances for radial barriers. The numerical
integrations are delimited by t/T<<8, with t the period of a classical particle
in the barrier trap and T the resonance lifetime. These energies are used in
the construction of `haired' short range potentials as the supersymmetric
partners of a given radial barrier. The new potentials could be useful in the
study of the transient phenomena which give rise to the Moshinsky's diffraction
in time.Comment: 12 pages, 4 figures, 3 table
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