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 $(2n+1) e^2/h$ 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" $+1$ and $-1$ 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