Increased cell efficiency in InGaAs thin film solar cells with dielectric and metal back reflectors

Compound single junction and multijunction solar cells enable very high photovoltaic efficiencies by virtue of employing different band gap materials in seriesconnected tandem cells to access the full solar spectrum. Researchers focused on improving the electrical properties of solar cells by optimizing the material growth conditions, however relatively little work to date has been devoted to light trapping and enhanced absorption in III-V compound solar cells using back reflectors. We studied absorption enhancement in InGaAs and InGaAsP thin film solar cells by means of numerical modeling. Flat dielectric and metal back reflectors that might be introduced into the solar cell via wafer-bonding, epitaxial lift-off or deposition techniques have been shown to increase the short circuit current and the photovoltaic efficiency of solar cells

Lithography-Free, Omnidirectional, CMOS-Compatible AlCu Alloys for Thin-Film Superabsorbers

Superabsorbers based on metasurfaces have recently enabled the control of light at the nanoscale in unprecedented ways. Nevertheless, the sub‐wavelength features needed to modify the absorption band usually require complex fabrication methods, such as electron‐beam lithography. To overcome the scalability limitations associated with the fabrication of metallic nanostructures, engineering the optical response of superabsorbers by metal alloying is proposed, instead of tuning the geometry/size of the nanoscale building blocks. The superior performance of thin film AlCu alloys as the metallic component of planar bilayer superabsorbers is numerically demonstrated. This alloy outperforms its pure constituents as well as other metals, such as Ag, Au, and Cr. As a model system, a Si/AlCu structure is analyzed that presents \u3e99% absorption at selected wavelength ranging from the visible to the near‐infrared regions of the spectrum, depending on the subwavelength thickness of the semiconductor. The multi‐wavelength near‐unity absorption behavior of Si/AlCu persists even for oblique angle of incidence, up to 70°. Additionally, the findings are validated by fabricating and testing a‐Si/AlCu superabsorbers, where good agreement is found between the numerically and experimentally determined optical response. The system investigated here is relevant for integration in complementary metal‐oxide‐semiconductor (CMOS) technologies

Wide-band-gap InAlAs solar cell for an alternative multijunction approach

We have fabricated an In_(0.52)Al_(0.48)As solar cell lattice-matched to InP with efficiency higher than 14% and maximum external quantum efficiency equal to 81%. High quality, dislocation-free In_xAl_(1−x)As alloyed layers were used to fabricate the single junction solar cell. Photoluminescence of In_xAl_(1−x)As showed good material quality and lifetime of over 200 ps. A high band gap In_(0.35)Al_(0.65)As window was used to increase light absorption within the p-n absorber layer and improve cell efficiency, despite strain. The InAlAs top cell reported here is a key building block for an InP-based three junction high efficiency solar cell consisting of InAlAs/InGaAsP/InGaAs lattice-matched to the substrate

Towards an optimized all lattice-matched InAlAs/InGaAsP/InGaAs multijunction solar cell with efficiency >50%

An approach for an all lattice-matched multijunction solar cell optimized design is presented with 5.807 Å lattice constant, together with a detailed analysis of its performance by means of full device modeling. The simulations show that a (1.93 eV)In_(0.37)Al_(0.63)As/(1.39 eV)In_(0.38)Ga_(0.62)As_(0.57)P_(0.43)/(0.94 eV)In_(0.38)Ga_(0.62)As 3-junction solar cell can achieve efficiencies >51% under 100-suns illumination (with V_(oc) = 3.34 V). As a key proof of concept, an equivalent 3-junction solar cell lattice-matched to InP was fabricated and tested. The independently connected single junction solar cells were also tested in a spectrum splitting configuration, showing similar performance to a monolithic tandem device, with V_(oc) = 1.8 V

Stress e coping académico: Contributos para a adaptação da escala MMC

Este estudo enquadra-se na investigação do coping perante dificuldades associadas ao quotidiano escolar. Utilizando entrevistas a 30 alunos, o estudo (1) identificou as principais situações geradoras de stress, reconhecendo a importância relativa do stress académico na vida dos alunos, e (2) analisou a validade cultural para o contexto português das situações stressantes usadas na escala Multidimensional Measure of Coping (MMC), avaliando as perceções dos alunos quanto ao nível de stress induzido e controlo percebido relativamente a essas situações. Os resultados confirmaram a importância da escola enquanto fonte significativa de stress, e a adequação da MMC ao contexto português

Lipopolysaccharide modulates astrocytic S100B secretion: a study in cerebrospinal fluid and astrocyte cultures from rats

<p>Abstract</p> <p>Background</p> <p>Inflammatory responses in brain are primarily mediated by microglia, but growing evidence suggests a crucial importance of astrocytes. S100B, a calcium-binding protein secreted by astrocytes, has properties of a neurotrophic or an inflammatory cytokine. However, it is not known whether primary signals occurring during induction of an inflammatory response (e.g. lipopolysaccharide, LPS) directly modulate S100B.</p> <p>Methods</p> <p>In this work, we evaluated whether S100B levels in cerebrospinal fluid (CSF) and serum of Wistar rats are affected by LPS administered by intraperitoneal (IP) or intracerebroventricular (ICV) injection, as well as whether primary astrocyte cultures respond directly to lipopolysaccharide.</p> <p>Results</p> <p>Our data suggest that S100B secretion in brain tissue is stimulated rapidly and persistently (for at least 24 h) by ICV LPS administration. This increase in CSF S100B was transient when LPS was IP administered. In contrast to these S100B results, we observed an increase in in TNFα levels in serum, but not in CSF, after IP administration of LPS. In isolated astrocytes and in acute hippocampal slices, we observed a direct stimulation of S100B secretion by LPS at a concentration of 10 μg/mL. An involvement of TLR4 was confirmed by use of specific inhibitors. However, lower levels of LPS in astrocyte cultures were able to induce a decrease in S100B secretion after 24 h, without significant change in intracellular content of S100B. In addition, after 24 h exposure to LPS, we observed a decrease in astrocytic glutathione and an increase in astrocytic glial fibrillary acidic protein.</p> <p>Conclusions</p> <p>Together, these data contribute to the understanding of the effects of LPS on astrocytes, particularly on S100B secretion, and help us to interpret cerebrospinal fluid and serum changes for this protein in neuroinflammatory diseases. Moreover, non-brain S100B-expressing tissues may be differentially regulated, since LPS administration did not lead to increased serum levels of S100B.</p

Academic stress and coping: Contributions to the adaptation of the MMC

Este estudo enquadra-se na investiga??o das estrat?gias de coping utilizadas perante dificuldades associadas ao quotidiano escolar. Utilizando entrevistas a 30 alunos, o estudo (1) identificou as principais situa??es geradoras de stress, reconhecendo a import?ncia relativa do stress acad?mico na vida dos alunos, e (2) analisou a validade cultural para o contexto portugu?s das situa??es stressantes usadas na escala Multidimensional Measure of Coping (MMC), avaliando as perce??es dos alunos quanto ao n?vel de stress induzido e controlo percebido relativamente a essas situa??es. Os resultados confirmaram a import?ncia da escola enquanto fonte significativa de stress, e a adequa??o da MMC ao contexto portugu?s.8C1E-AFB9-6BE1 | Maria Teresa Martins Gon?alvesN/

The progressive onset of cholinergic and adrenergic control of heart rate during development in the green iguana, Iguana iguana

Made available in DSpace on 2018-11-26T16:16:38Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-10-01INCT in Comparative PhysiologyFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)National Science FoundationThe autonomic control of heart rate was studied throughout development in embryos of the green iguana, Iguana iguana by applying receptor agonists and antagonists of the parasympathetic and sympathetic systems. Acetylcholine (Ach) slowed or stopped the heart and atropine antagonized the response to Ach indicating the presence of muscarinic cholinoceptors on the heart of early embryos. However, atropine injections had no impact on heart rate until immediately before hatching, when it increased heart rate by 15%. This cholinergic tonus increased to 34% in hatchlings and dropped to 24% in adult iguanas. Although epinephrine was without effect, injection of propranolol slowed the heart throughout development, indicating the presence of beta-adrenergic receptors on the heart of early embryos, possibly stimulated by high levels of circulating catecholamines. The calculated excitatory tonus varied between 33% and 68% until immediately before hatching when it fell to 25% and 29%, a level retained in hatchlings and adults. Hypoxia caused a bradycardia in early embryos that was unaffected by injection of atropine indicating that hypoxia has a direct effect upon the heart. In later embryos and hatchlings hypoxia caused a tachycardia that was unaffected by injection of atropine. Subsequent injection of propranolol reduced heart rate both uncovering a hypoxic bradycardia in late embryos and abolishing tachycardia in hatchlings. Hypercapnia was without effect on heart rate in late stage embryos and in hatchlings. (C) 2015 Elsevier Inc All rights reserved.Univ Estadual Paulista, Inst Biociencias, Dept Zool, Rio Claro, SP, BrazilUniv Fed Sao Carlos, Dept Ciencias Fisiol, BR-13560 Sao Carlos, SP, BrazilUniv N Texas, Dept Biol Sci, Dev Integrat Biol Cluster, Denton, TX 76203 USAUniv Birmingham, Sch Biosci, Birmingham B15 2TT, W Midlands, EnglandUniv Estadual Paulista, Inst Biociencias, Dept Zool, Rio Claro, SP, BrazilINCT in Comparative Physiology: CNPq 573921/2008-3INCT in Comparative Physiology: FAPESP 2008/57712-4FAPESP: 2012/06938-8FAPESP: 2012/16537-0National Science Foundation: IBN-IOS 084574