UMA PROPOSTA DE OTIMIZAÇÃO NA CONVERSÃO DE ENERGIA SOLAR EM ENERGIA ELÉTRICA POR PAINEIS FOTOVOLTAICOS

O crescimento da demanda de energia observado nas últimas décadas vem sendo um estímulo para a utilização de novas fontes de energias, anteriormente consideradas caras. Sabe-se que a energia solar que chega à superfície terrestre supera a demanda de energia mundial, porém os equipamentos que convertem a radiação solar em algum tipo de energia útil possuem baixos rendimentos. Com base nesta perspectiva, esta dissertação de mestrado tem por objetivo conseguir a maior extração de energia elétrica de um painel fotovoltaico utilizando circuitos eletrônicos que buscam o ponto de máxima potência de operação da célula. Para tanto, implementou-se experimentalmente um circuito eletrônico que utiliza, como plano de controle, um algoritmo de busca do máximo ponto de potência (MPPT Maximum Power Point Tracking) com passo variável que é acoplado a um painel fotovoltaico. Desenvolveu-se também um sistema de gerenciamento microcontrolado que é capaz de coletar parâmetros do painel fotovoltaico para análise de resultados. Estudos de caso na avaliação do tempo de resposta do circuito e rendimento do arranjo proposto também foram realizados, conseguindo situações onde o ganho de potência foi superior a 100% e tempos de resposta do circuito variando de 0,88 a 11 segundos

Ferroelectricity in a quasiamorphous ultrathin BaTiO3 film

Until now, the quasiamorphous (QA) phase in BaTiO3 (BTO), SrTiO3 (STO), and BaZrO3 was achieved by pulling a thick film through a steep temperature gradient. Here, we show that a room-temperature deposited ultrathin film, subsequently annealed in O-2 can also produce a QA phase. The atomic, electronic, and ferroelectric (FE) structure of a QA, ultrathin BTO grown on STO were studied by x-ray diffraction (XRD), x-ray photoelectron diffraction (XPD), x-ray photoelectron spectroscopy (XPS), and piezoforce microscopy (PFM). The absence of long-range order is confirmed by in-and out-of-plane XRD as well as Ti 2p XPD. FE polarized domains with good retention have been successfully written into the QA film and exhibit a clear P-E hysteresis loop. Substrate clamping frustrates volume expansion during annealing leading to a QA film. Photoelectron spectroscopy confirms a similar overall electronic structure as for thicker films but with some significant differences. Simple charge-transfer arguments are not sufficient to explain the high-resolution core-level spectra. Ba, Ti, and O all show components associated with a surface region. We suggest that the observation of such a component in the Ti 2p spectrum is linked with the high dynamic charge tensor induced by the large off-center displacement of the Ti ion.8420French National Research Agency (ANR) [ANR-10-BLAN-1012]CEAFrench National Research Agency (ANR) [ANR-10-BLAN-1012

A-6G and A-20C Polymorphisms in the Angiotensinogen Promoter and Hypertension Risk in Chinese: A Meta-Analysis

BACKGROUND: Numerous studies in Chinese populations have evaluated the association between the A-6G and A-20C polymorphisms in the promoter region of angiotensinogen gene and hypertension. However, the results remain conflicting. We carried out a meta-analysis for these associations. METHODS AND RESULTS: Case-control studies in Chinese and English publications were identified by searching the MEDLINE, EMBASE, CNKI, Wanfang, CBM, and VIP databases. The random-effects model was applied for dichotomous outcomes to combine the results of the individual studies. We finally selected 24 studies containing 5932 hypertensive patients and 5231 normotensive controls. Overall, we found significant association between the A-6G polymorphism and the decreased risk of hypertension in the dominant genetic model (AA+AG vs. GG: P=0.001, OR=0.71, 95%CI 0.57-0.87, P(heterogeneity)=0.96). The A-20C polymorphism was significantly associated with the increased risk for hypertension in the allele comparison (C vs. A: P=0.03, OR=1.14, 95%CI 1.02-1.27, P(heterogeneity)=0.92) and recessive genetic model (CC vs. CA+AA: P=0.005, OR=1.71, 95%CI 1.18-2.48, P(heterogeneity)=0.99). In the subgroup analysis by ethnicity, significant association was also found among Han Chinese for both A-6G and A-20C polymorphisms. A borderline significantly decreased risk of hypertension between A-6G and Chinese Mongolian was seen in the allele comparison (A vs. G: P=0.05, OR=0.79, 95%CI 0.62-1.00, P(heterogeneity)=0.84). CONCLUSION: Our meta-analysis indicated significant association between angiotensinogen promoter polymorphisms and hypertension in the Chinese populations, especially in Han Chinese

Genotype determination for polymorphisms in linkage disequilibrium

<p>Abstract</p> <p>Background</p> <p>Genome-wide association studies with single nucleotide polymorphisms (SNPs) show great promise to identify genetic determinants of complex human traits. In current analyses, genotype calling and imputation of missing genotypes are usually considered as two separated tasks. The genotypes of SNPs are first determined one at a time from allele signal intensities. Then the missing genotypes, i.e., no-calls caused by not perfectly separated signal clouds, are imputed based on the linkage disequilibrium (LD) between multiple SNPs. Although many statistical methods have been developed to improve either genotype calling or imputation of missing genotypes, treating the two steps independently can lead to loss of genetic information.</p> <p>Results</p> <p>We propose a novel genotype calling framework. In this framework, we consider the signal intensities and underlying LD structure of SNPs simultaneously by estimating both cluster parameters and haplotype frequencies. As a result, our new method outperforms some existing algorithms in terms of both call rates and genotyping accuracy. Our studies also suggest that jointly analyzing multiple SNPs in LD provides more accurate estimation of haplotypes than haplotype reconstruction methods that only use called genotypes.</p> <p>Conclusion</p> <p>Our study demonstrates that jointly analyzing signal intensities and LD structure of multiple SNPs is a better way to determine genotypes and estimate LD parameters.</p

Large-scale Synthesis of β-SiC Nanochains and Their Raman/Photoluminescence Properties

Although the SiC/SiO2 nanochain heterojunction has been synthesized, the chained homogeneous nanostructure of SiC has not been reported before. Herein, the novel β-SiC nanochains are synthesized assisted by the AAO template. The characterized results demonstrate that the nanostructures are constructed by spheres of 25–30 nm and conjoint wires of 15–20 nm in diameters. Raman and photoluminescence measurements are used to explore the unique optical properties. A speed-alternating vapor–solid (SA-VS) growth mechanism is proposed to interpret the formation of this typical nanochains. The achieved nanochains enrich the species of one-dimensional (1D) nanostructures and may hold great potential applications in nanotechnology

Self-assembled foam-like graphene networks formed through nucleate boiling

Self-assembled foam-like graphene (SFG) structures were formed using a simple nucleate boiling method, which is governed by the dynamics of bubble generation and departure in the graphene colloid solution. The conductivity and sheet resistance of the calcined (400 degrees C) SFG film were 11.8 S.cm(-1) and 91.2 Omega square(-1), respectively, and were comparable to those of graphene obtained by chemical vapor deposition (CVD) (similar to 10 S.cm(-1))(.) The SFG structures can be directly formed on any substrate, including transparent conductive oxide (TCO) glasses, metals, bare glasses, and flexible polymers. As a potential application, SFG formed on fluorine-doped tin oxide (FTO) exhibited a slightly better overall efficiency (3.6%) than a conventional gold electrode (3.4%) as a cathode of quantum dot sensitized solar cells (QDSSCs)open232

Quantum-Dot Light-Emitting Diodes with Nitrogen-Doped Carbon Nanodot Hole Transport and Electronic Energy Transfer Layer

Electroluminescence efficiency is crucial for the application of quantum-dot light-emitting diodes (QD-LEDs) in practical devices. We demonstrate that nitrogen-doped carbon nanodot (N-CD) interlayer improves electrical and luminescent properties of QD-LEDs. The N-CDs were prepared by solution-based bottom up synthesis and were inserted as a hole transport layer (HTL) between other multilayer HTL heterojunction and the red-QD layer. The QD-LEDs with N-CD interlayer represented superior electrical rectification and electroluminescent efficiency than those without the N-CD interlayer. The insertion of N-CD layer was found to provoke the Forster resonance energy transfer (FRET) from N-CD to QD layer, as confirmed by time-integrated and - resolved photoluminescence spectroscopy. Moreover, hole-only devices (HODs) with N-CD interlayer presented high hole transport capability, and ultraviolet photoelectron spectroscopy also revealed that the N-CD interlayer reduced the highest hole barrier height. Thus, more balanced carrier injection with sufficient hole carrier transport feasibly lead to the superior electrical and electroluminescent properties of the QD-LEDs with N-CD interlayer. We further studied effect of N-CD interlayer thickness on electrical and luminescent performances for high-brightness QD-LEDs. The ability of the N-CD interlayer to improve both the electrical and luminescent characteristics of the QD-LEDs would be readily exploited as an emerging photoactive material for high-efficiency optoelectronic devices.ope

A Powerful Test of Parent-of-Origin Effects for Quantitative Traits Using Haplotypes

Imprinting is an epigenetic phenomenon where the same alleles have unequal transcriptions and thus contribute differently to a trait depending on their parent of origin. This mechanism has been found to affect a variety of human disorders. Although various methods for testing parent-of-origin effects have been proposed in linkage analysis settings, only a few are available for association analysis and they are usually restricted to small families and particular study designs. In this study, we develop a powerful maximum likelihood test to evaluate the parent-of-origin effects of SNPs on quantitative phenotypes in general family studies. Our method incorporates haplotype distribution to take advantage of inter-marker LD information in genome-wide association studies (GWAS). Our method also accommodates missing genotypes that often occur in genetic studies. Our simulation studies with various minor allele frequencies, LD structures, family sizes, and missing schemes have uniformly shown that using the new method significantly improves the power of detecting imprinted genes compared with the method using the SNP at the testing locus only. Our simulations suggest that the most efficient strategy to investigate parent-of-origin effects is to recruit one parent and as many offspring as possible under practical constraints. As a demonstration, we applied our method to a dataset from the Genetics of Lipid Lowering Drugs and Diet Network (GOLDN) to test the parent-of-origin effects of the SNPs within the PPARGC1A, MTP and FABP2 genes on diabetes-related phenotypes, and found that several SNPs in the MTP gene show parent-of-origin effects on insulin and glucose levels