Fabrication and Characterization of Multiband Solar Cells Based on Highly Mismatched Alloys

Multiband solar cells are one type of third generation photovoltaic devices in which an increase of the power conversion efficiency is achieved through the absorption of low energy photons while preserving a large band gap that determines the open circuit voltage. The ability to absorb photons from different parts of the solar spectrum originates from the presence of an intermediate energy band located within the band gap of the material. This intermediate band, acting as a stepping stone allows the absorption of low energy photons to transfer electrons from the valence band to the conduction band by a sequential two photons absorption process. It has been demonstrated that highly mismatched alloys offer a potential to be used as a model material system for practical realization of multiband solar cells. Dilute nitride GaAs1-xNx highly mismatched alloy with low mole fraction of N is a prototypical multiband semiconductor with a well-defined intermediate band. Currently, we are using chemical beam epitaxy to synthesize dilute nitride highly mismatched alloys. The materials are characterized by a variety of structural and optical methods to optimize their properties for multiband photovoltaic devices

Effect of a padel match on biochemical and haematological parameters in professional players with regard to gender-related differences

Haematological and biochemical parameters have not yet been analysed in professional padel players. The aim of this study was to determine the basal values of these parameters and to observe the effect of a simulated competition on them, including gender-related differences. A total of 14 male professional players (age: 28.2 ± 7.9 years), and 16 female professional players (age: 29.7 ± 3.7 years) participated in this study. Players were allowed to hydrate ad libitum during the matches. Haematological and biochemical values were obtained before and after a simulated competitive padel match. The men’s group showed higher baseline values in red blood cells, haematocrit, haemoglobin, urea, creatinine, uric acid, albumin, glutamic oxaloacetic transaminase (GOT), glutamic-pyruvic transaminase (GPT), lactate dehydrogenase (LDH) and creatine kinase (CK) (p < 0.01) than the women’s group. Attending to match effect, significant differences were obtained in urea, creatinine, CK and glucose (p < 0.05). Finally, the group x match interaction revealed significant differences in serum concentrations of sodium and chloride (p < 0.05). In conclusion, high-level padel matches provoke several changes in biochemical parameters related to muscle damage and protein catabolism. Recovery and fluid intake strategies could be added regarding gender. The results obtained could be due to the differences in the intensity and volume of the simulated competition

Effective interactions of colloids on nematic films

The elastic and capillary interactions between a pair of colloidal particles trapped on top of a nematic film are studied theoretically for large separations $d$. The elastic interaction is repulsive and of quadrupolar type, varying as $d^{-5}$. For macroscopically thick films, the capillary interaction is likewise repulsive and proportional to $d^{-5}$ as a consequence of mechanical isolation of the system comprised of the colloids and the interface. A finite film thickness introduces a nonvanishing force on the system (exerted by the substrate supporting the film) leading to logarithmically varying capillary attractions. However, their strength turns out to be too small to be of importance for the recently observed pattern formation of colloidal droplets on nematic films.Comment: 13 pages, accepted by EPJ

Black Hole Astrophysics in AdS Braneworlds

We consider astrophysics of large black holes localized on the brane in the infinite Randall-Sundrum model. Using their description in terms of a conformal field theory (CFT) coupled to gravity, deduced in Ref. [1], we show that they undergo a period of rapid decay via Hawking radiation of CFT modes. For example, a black hole of mass ${\rm few} \times M_\odot$ would shed most of its mass in $\sim 10^4 - 10^5$ years if the AdS radius is $L \sim 10^{-1}$ mm, currently the upper bound from table-top experiments. Since this is within the mass range of X-ray binary systems containing a black hole, the evaporation enhanced by the hidden sector CFT modes could cause the disappearance of X-ray sources on the sky. This would be a striking signature of RS2 with a large AdS radius. Alternatively, for shorter AdS radii, the evaporation would be slower. In such cases, the persistence of X-ray binaries with black holes already implies an upper bound on the AdS radius of L \la 10^{-2} mm, an order of magnitude better than the bounds from table-top experiments. The observation of primordial black holes with a mass in the MACHO range $M \sim 0.1 - 0.5 M_\odot$ and an age comparable to the age of the universe would further strengthen the bound on the AdS radius to L \la {\rm few} \times 10^{-6} mm.Comment: 14 pages, latex, no figures v2: added reference

Dynamics of a large extra dimension inspired hybrid inflation model

In low scale quantum gravity scenarios the fundamental scale of nature can be as low as TeV, in order to address the naturalness of the electroweak scale. A number of difficulties arise in constructing specific models; stabilisation of the radius of the extra dimensions, avoidance of overproduction of Kaluza Klein modes, achieving successful baryogenesis and production of a close to scale-invariant spectrum of density perturbations with the correct amplitude. We examine in detail the dynamics, including radion stabilisation, of a hybrid inflation model that has been proposed in order to address these difficulties, where the inflaton is a gauge singlet residing in the bulk. We find that for a low fundamental scale the phase transition, which in standard four dimensional hybrid models usually ends inflation, is slow and there is second phase of inflation lasting for a large number of e-foldings. The density perturbations on cosmologically interesting scales exit the Hubble radius during this second phase of inflation, and we find that their amplitude is far smaller than is required. We find that the duration of the second phase of inflation can be short, so that cosmologically interesting scales exit the Hubble radius prior to the phase transition, and the density perturbations have the correct amplitude, only if the fundamental scale takes an intermediate value. Finally we comment briefly on the implications of an intermediate fundamental scale for the production of primordial black holes and baryogenesis.Comment: 9 pages, 2 figures version to appear in Phys. Rev. D, additional references and minor changes to discussio

Valorización de ceniza de bagazo de caña de la industria azucarera Nicaragüense como sustituto parcial al cemento Portland

In this study, the use of the ashes of sugarcane bagasse (ASB) from Monte Rosa sugarcane mill (Nicaragua) as an alternative material to Portland Cement (PC) was evaluated. The evaluation was performed through studies of advanced characterization and mechanical properties in pastes with 15% and 45% substitution of PC. Moreover, 100% PC pastes were used as reference. The mechanical resistance (MR), the consumption of calcium hydroxide and the development of reaction products were measured. The results showed that the highest values of MR were obtained for the reference pastes, thus indicating that the MR decreased with increase in the degree of substitution. Through the analysis of X-ray diffraction (XRD) and thermal analysis TGA / DTA was found that the consumption of Ca(OH)2 gave rise to the formation of CSH gel as the main product of hydration and caused the gain in the mechanical properties. The reaction products were observed by scanning electron microscopy (SEM) where the mechanism in solid state was noticeable. From this result, it can be concluded that the ASB are pozzolanic material with a better reactivity to Ca(OH)2 with 15% of substitution. DOI: http://dx.doi.org/10.5377/nexo.v27i2.1944En este estudio, se presenta la valoración del uso de las cenizas de bagazo de caña (CBCA) proveniente del Ingenio Monte Rosa(Nicaragua) como material alternativo al cemento Portland (CP) mediante estudios de caracterización avanzada y propiedadesmecánicas, en pastas endurecidas de CP sustituidas en 15 y 45 % por CBCA; además se utilizó pastas de referencia con 100 %CP sobre las cuales se evaluó las resistencias mecánicas (RM), el consumo de hidróxido de calcio y el desarrollo de losproductos de reacción. Los resultados revelaron que los valores más altos de RM reportados fueron por el sistema de referencia,indicando que la RM disminuyó con el incremento en el porcentaje de sustitución. Por medio de los análisis de difracción derayos X (DRX) y análisis térmicos por ATG/ATD fue demostrado el consumo de Ca(OH)2 que dio lugar a la formación de gelCSH como principal producto de hidratación y responsable de la ganancia de las propiedades mecánicas. Los productos dereacción fueron observados también por microscopia electrónica de barrido (MEB) donde el mecanismo en estado sólido fuenotable. A partir de estos resultados se puede concluir que las CBCA son un material puzolánico con una mejor reactividadfrente al Ca(OH)2 con 15 % de sustitución.DOI: http://dx.doi.org/10.5377/nexo.v27i2.194

A Dissipative-Particle-Dynamics Model for Simulating Dynamics of Charged Colloid

A mesoscopic colloid model is developed in which a spherical colloid is represented by many interacting sites on its surface. The hydrodynamic interactions with thermal fluctuations are taken accounts in full using Dissipative Particle Dynamics, and the electrostatic interactions are simulated using Particle-Particle-Particle Mesh method. This new model is applied to investigate the electrophoretic mobility of a charged colloid under an external electric field, and the influence of salt concentration and colloid charge are systematically studied. The simulation results show good agreement with predictions from the electrokinetic theory.Comment: 17 pages, 8 figures, submitted to the proceedings of High Performance Computing in Science & Engineering '1

Constraining the primordial spectrum of metric perturbations from gravitino and moduli production

We consider the production of gravitinos and moduli fields from quantum vacuum fluctuations induced by the presence of scalar metric perturbations at the end of inflation. We obtain the corresponding occupation numbers, up to first order in perturbation theory, in terms of the power spectrum of the metric perturbations. We compute the limits imposed by nucleosynthesis on the spectral index $n_s$ for different models with constant $n_s$. The results show that, in certain cases, such limits can be as strong as $n_s<1.12$, which is more stringent than those coming from primordial black hole production.Comment: 16 pages, LaTeX, 5 figures. Corrected figures, new references included. Final version to appear in Phys. Rev.

Resonant x-ray diffraction study of the magnetoresistant perovskite Pr0.6Ca0.4MnO3

We report a x-ray resonant diffraction study of the perovskite Pr0.6Ca0.4MnO3. At the Mn K-edge, this technique is sensitive to details of the electronic structure of the Mn atoms. We discuss the resonant x-ray spectra measured above and below the charge and orbital ordering phase transition temperature (TCOO = 232 K), and present a detailed analysis of the energy and polarization dependence of the resonant scattering. The analysis confirms that the structural transition is a transition to an orbitally ordered phase in which inequivalent Mn atoms are ordered in a CE-type pattern. The Mn atoms differ mostly by their 3d orbital occupation. We find that the charge disproportionation is incomplete, 3d^{3.5-\delta} and 3d^{3.5+\delta} with \delta\ll0.5 . A revised CE-type model is considered in which there are two Mn sublattices, each with partial e_{g} occupancy. One sublattice consists of Mn atoms with the 3x^{2}-r^{2} or 3y^{2}-r^{2} orbitals partially occupied, the other sublattice with the x^{2}-y^{2} orbital partially occupied.Comment: 15 pages, 15 figure