A new device laboratory: Experimental validation

Postprint (published version

Optimum single-gap solar cells for missions to Mercury

The power supply for space probes is usually based on photovoltaic (PV) systems. The first solar cells used in these systems were single-gap solar cells fabricated with Si and GaAs. Later on, multijunction solar cells (MJSC) based on III–V semiconductors were developed because of their higher efficiency and tolerance to a radiation environment [1]. All these solar cells have been based on semiconductors that fulfill the needs of most near-Earth missions. However, those same semiconductors fail to meet the needs of some other missions involving harsh environments such as high-intensity high-temperature (HIHT) environments [2]. In this work, we investigate which semiconductor material is optimum to implement single-gap solar cells for missions to Mercury, where HIHT conditions are expected. Because solar cell efficiency decreases as temperature increases [3], achieving high-efficiency photovoltaic conversion at HIHT conditions is a big challenge. Previous works have pointed out the need of using wide-bandgap semiconductors to reach this goal [4,5]. In this context, we will study the potential of solar cells based on AlxGa1−xAs, a well-known semiconductor whose physical properties have been extensively investigated. The limiting efficiency of these solar cells performing in near-Mercury missions will be calculated to determine the optimum composition for AlxGa1−xAs

Outcome analysis of intracorneal ring segments for the treatment of keratoconus based on visual, refractive, and aberrometric impairment

PURPOSE: To analyze the outcomes of intracorneal ring segment (ICRS) implantation for the treatment of keratoconus based on preoperative visual impairment. DESIGN: Multicenter, retrospective, nonrandomized study. METHODS: A total of 611 eyes of 361 keratoconic patients were evaluated. Subjects were classified according to their preoperative corrected distance visual acuity (CDVA) into 5 different groups: grade I, CDVA of 0.90 or better; grade II, CDVA equal to or better than 0.60 and worse than 0.90; grade III, CDVA equal to or better than 0.40 and worse than 0.60; grade IV, CDVA equal to or better than 0.20 and worse than 0.40; and grade plus, CDVA worse than 0.20. Success and failure indices were defined based on visual, refractive, corneal topographic, and aberrometric data and evaluated in each group 6 months after ICRS implantation. RESULTS: Significant improvement after the procedure was observed regarding uncorrected distance visual acuity in all grades (P < .05). CDVA significantly decreased in grade I (P < .01) but significantly increased in all other grades (P < .05). A total of 37.9% of patients with preoperative CDVA 0.6 or better gained 1 or more lines of CDVA, whereas 82.8% of patients with preoperative CDVA 0.4 or worse gained 1 or more lines of CDVA (P < .01). Spherical equivalent and keratometry readings showed a significant reduction in all grades (P ≤ .02). Corneal higher-order aberrations did not change after the procedure (P ≥ .05). CONCLUSIONS: Based on preoperative visual impairment, ICRS implantation provides significantly better results in patients with a severe form of the disease. A notable loss of CDVA lines can be expected in patients with a milder form of keratoconus

Computational chemical analysis of unconjugated bilirubin anions and insights into pKa values clarification

The pKa, the negative logarithm of the acid dissociation equilibrium constant, of the carboxylic acid groups of unconjugated bilirubin in water is a discussed issue because there are quite different experimental values reported. Using quantum mechanical calculations we have studied the conformational behavior of unconjugated bilirubin species (in gas phase and in solution modeled implicitly and explicitly) to provide evidence that may clarify pKa values because of its pathophysiological relevance. Our results show that rotation of carboxylate group, which is not restricted, settles it in a suitable place to establish stronger interactions that stabilizes the monoanion and the dianion to be properly solvated, demonstrating that the rationalization used to justify the high pKa values of unconjugated bilirubin is inappropriate. Furthermore, low unconjugated bilirubin (UCB) pKa values were estimated from a linear regression analysis.Fil: Vega Hissi, Esteban Gabriel. Universidad Nacional de San Luis. Facultad de Quimica, Bioquimica y Farmacia. Departamento de Quimica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto Multidisciplinario de Investigaciones Biológicas de San Luis; ArgentinaFil: Estrada, Mario Rinaldo. Universidad Nacional de San Luis. Facultad de Quimica, Bioquimica y Farmacia. Departamento de Quimica; ArgentinaFil: Lavecchia, Martín José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Centro de Química Inorgánica; ArgentinaFil: Pis Diez, Reinaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Centro de Química Inorgánica; Argentin

Quality of Work Life and Mental Health in Primary Care Physicians

AbstractThe aim of this study was to find the relationship between the perception of Quality of Work Life (QWL) and the mental health of primary care physicians of a public health institution in Guadalajara, Mexico. The study was analytical and was carried out with a universe of 818 doctors from 92 health units and the probability sample of 154 people. In all of them, CVT-GOHISALO and Goldberg GHQ-28 questionnaires were applied in order to measure their perception of QWL and the risk of mental illness respectively. Both instruments were selected because of their high reliability. We measured the satisfaction of the people interviewed for each one of the seven dimensions of CVT-GOHISALO and related to the points assigned to GHQ-28 case or not to consider the case of mental illness. The percentages of dissatisfaction with the QWL were greater than 12% in all dimensions of the instrument, being the highest value of 20.5% dissatisfaction for the job satisfaction dimension. In the classification of the case or not according to the GHQ-28, 22% were considered cases and 78% non-cases. We sought correspondence of satisfaction with the QWL by dimensions and non-case of Goldberg's, as well as dissatisfaction with the QWL and Goldberg's case, finding a clear link between being satisfied and having mental health. All dimensions have a correspondence that goes from 79.7% to 82.3% between satisfaction and non-case, being in all the statistical significance value less than 0.05 For primary care physicians in the studied institution, there is a clear relationship between being satisfied with the QWL and present less risk of mental illness. It is alarming that the medical staff presents high rates of dissatisfaction with the QWL and risk of mental illness. It is necessary to provide preventive programs among health care workers in order to improve their QWL and mental health

HIT intermediate-band solar cells with self-assembled colloidal quantum dots and metal nanoparticles

The particular opto-electronic properties of chemically synthesized colloidal nanoparticles can be promising for functional materials, as those required for high efficient photovoltaic (PV) devices. In particular, appropriately-designed semiconductor colloids (quantum dots, QDs) can potentially allow sub-bandgap current generation in intermediate-band solar cells; while metal nanoparticles (MNPs) sustaining surface plasmons can provide both near and far-field light trapping to further boost the generated power. However, the incorporation of colloidal particles in inorganic PV materials is not trivial, therefore their implementation has so far been restricted to organic/polymeric based solar cells. In this work, PbS colloidal QDs have been incorporated in the intrinsic a-Si:H layer of HIT (substrate/a-Si:H hetero-junction) test structures. Both c-Si and GaAs substrates have been used, and in some cases colloidal Au NPs have also been included. The obtained devices are meant as probes to verify the feasibility of incorporating foreign nanoparticles in a cell structure and not as potentially efficient solar cells. Despite the radical novelties incorporated, the devices behaved similarly to the references, thus proving the compatibility of the proposed materials and processes

Self-organized colloidal quantum dots and metal nanoparticles for plasmon-enhanced intermediate-band solar cells

A colloidal deposition technique is presented to construct long-range ordered hybrid arrays of self-assembled quantum dots and metal nanoparticles. Quantum dots are promising for novel opto-electronic devices but, in most cases, their optical transitions of interest lack sufficient light absorption to provide a significant impact in their implementation. A potential solution is to couple the dots with localized plasmons in metal nanoparticles. The extreme confinement of light in the near-field produced by the nanoparticles can potentially boost the absorption in the quantum dots by up to two orders of magnitude. In this work, light extinction measurements are employed to probe the plasmon resonance of spherical gold nanoparticles in lead sulfide colloidal quantum dots and amorphous silicon thin-films. Mie theory computations are used to analyze the experimental results and determine the absorption enhancement that can be generated by the highly intense near-field produced in the vicinity of the gold nanoparticles at their surface plasmon resonance. The results presented here are of interest for the development of plasmon-enhanced colloidal nanostructured photovoltaic materials, such as colloidal quantum dot intermediate-band solar cells

Intermediate band to conduction band optical absorption in ZnTeO

ZnTe doped with high concentrations of oxygen has been proposed in previous works as an intermediate band (IB) material for photovoltaic applications. The existence of extra optical transitions related to the presence of an IB has already been demonstrated in this material and it has been possible to measure the absorption coefficient of the transitions from the valence band (VB) to the IB. In this study, we present the first measurement of the absorption coefficient associated with transitions from the IB to the conduction band (CB) in ZnTeO. The samples used are 4-mum-thick ZnTe layers with or without O in a concentration ~10 19 cm -3, which have been grown on semiinsulating GaAs substrates by molecular beam epitaxy (MBE). The IB-CB absorption coefficient peaks for photon energies ~0.4 eV. It is extracted from reflectance and transmittance spectra measured using Fourier transform infrared (FTIR) spectroscopy. Under typical FTIR measurement conditions (low light intensity, broadband spectrum), the absorption coefficient in IB-to-CB transitions reaches 700 cm -1. This is much weaker than the one observed for VB-IB absorption. This result is consistent with the fact that the IB is expected to be nearly empty of electrons under equilibrium conditions in ZnTe(O)

Intermediate Band to Conduction Band optical absorption in ZnTe:O

ZnTe doped with high concentrations of oxygen has been proposed in previous works as intermediate band (IB) material for photovoltaic applications. The existence of extra optical transitions related to the presence of an IB has already been demonstrated in this material and it has been possible to measure the absorption coefficient of the transitions from the valence band (VB) to the IB. In this work we present the first measurement of the absorption coefficient associated to transitions from the IB to the conduction band (CB) in ZnTe:O. The samples used are 4 ?m thick ZnTe layers with or without O in a concentration ~ 1019 cm-3, which have been grown on semi-insulating GaAs substrates by molecular beam epitaxy (MBE). The IB-CB absorption coefficient peaks for photon energies ~ 0.4 eV. It is extracted from reflectance and transmittance spectra measured using Fourier Transform Infrared (FTIR) spectroscopy. Under typical FTIR measurement conditions (low light intensity, broadband spectrum) the absorption coefficient in IB-to-CB transitions reaches 700 cm-1. This is much weaker than the one observed for VB-IB absorption. This result is consistent with the fact that the IB is expected to be nearly empty of electrons under equilibrium conditions in ZnTe(:O). The absorption for VB to IB transitions is also observed in the same samples through reflectance measurements performed in the visible range using a monochromator. These measurements are compared with the quantum efficiency (QE) from solar cells fabricated under similar conditions