Spin-Exchange Interaction in ZnO-based Quantum Wells

Wurtzitic ZnO/(Zn,Mg)O quantum wells grown along the (0001) direction permit unprecedented tunability of the short-range spin exchange interaction. In the context of large exciton binding energies and electron-hole exchange interaction in ZnO, this tunability results from the competition between quantum confinement and giant quantum confined Stark effect. By using time-resolved photoluminescence we identify, for well widths under 3 nm, the redistribution of oscillator strengths between the A and B excitonic transitions, due to the enhancement of the exchange interaction. Conversely, for wider wells, the redistribution is cancelled by the dominant effect of internal electric fields, which dramatically reduce the exchange energy.Comment: 14 pages, 3 figure

Avaliação do efeito de veranico na produção de matéria seca de milho e sorgo.

O presente trabalho teve como principal objetivo a influencia de veranicos nas fases inicial e reprodutiva na producao de materia seca de milho e sorgo. O ensaio foi instalado em um latossolo Vermelho-Escuro,distrofico, fase cerrado, durante os anos agricolas de 1982 a 1985. No primeiro ano aplicou-se 3,7 toneladas de calcario dolomitico e fez-se uma adubacao de correcao baseada em analises do solo. As cultivares de milho utilizadas foram BR 126 e CMSXS 201 Xe, as de sorgo, BR 505 e BR 601. Em cada ano agricola estes hibridos foram plantados em 4 diferentes epocas (8, 15 e 25 de outubro e 5 de novembro), com e sem irrigacao suplementar. O delineamento experimental utilizado foi blocos casualizados com 5 repeticoes. Quantificou-se a materia seca correspondente a parte aerea das plantas colhidas quando os graos encontravam-se na fase de grao macio. Embora os resultados tenham mostrado tanto para o milho como para o sorgo, que as producoes entre anos, nao diferiram significativamente, houve um aumento medio da producao das culturas irrigadas sobre as nao irrigadas de 12 a 27% para o milho e cerca de 36% para o sorgo. Estas diferencas podem ser atribuidas a ocorrencia de veranico durante o ciclo das culturas. A producao de milho foi superior a do sorgo, principalmente quando foi utilizada irrigacao suplementar Embora a ocorrencia de veranico na fase inicial de crescimento tenha influenciado na producao de ambas as culturas, o sorgo demonstrou-se mais sensivel ao deficit de agua ate 20 a 25 dias

SCOOTER: A compact and scalable dynamic labeling scheme for XML updates

Although dynamic labeling schemes for XML have been the focus of recent research activity, there are significant challenges still to be overcome. In particular, though there are labeling schemes that ensure a compact label representation when creating an XML document, when the document is subject to repeated and arbitrary deletions and insertions, the labels grow rapidly and consequently have a significant impact on query and update performance. We review the outstanding issues todate and in this paper we propose SCOOTER - a new dynamic labeling scheme for XML. The new labeling scheme can completely avoid relabeling existing labels. In particular, SCOOTER can handle frequently skewed insertions gracefully. Theoretical analysis and experimental results confirm the scalability, compact representation, efficient growth rate and performance of SCOOTER in comparison to existing dynamic labeling schemes

Influência da rotação de culturas no sistema radicular do milho e em algumas características químicas de um latossolo vermelho-escuro distrófico da região de Sete Lagoas.

Em experimento envolvendo rotacao de culturas e adubacao verde na cultura do milho, em um latossolo Vermelho-Escuro distrofico, observou-se um periodo de estiagem prolongada durante a fase de florescimento de milho, sintomas acentuados de murcha em areas de cultivo continuo com milho. Em areas onde se efetuava a rotacao de cultura soja-milho, mucuna-milho, milho + mucuna intercalar-milho, este sintoma nao se repetia. Procurando-se avaliar os beneficios de rotacao de culturas sobre o monocultivo, coletou-se amostras de solo de uma area com 0,20 m2, tendo-se como ponto central a linha de milho. O volume amostrado foi obtido atraves das seguintes profundidades: 0-2 cm, 2-4 cm, 4-6 cm, 6-10 cm, 10-14 cm, 14-18 cm, 18-26 cm, 26-34 cm e 34-42 cm. Apos a coleta do solo + raizes, estas foram separadas e quantificadas (peso) e o solo analisado quimicamente. Os resultados permitiram concluir que a rotacao soja-milho e mucuna-milho, promoveram maior aumento de peso de plantas de milho e maior quantidade de raizes abaixo de 30 cm de profundidade em relacao ao milho continuo e milho com mucuna intercalar. A rotacao soja-milho promoveu uma melhor distribuicao de bases nas camadas mais profundas do solo, aumentando a saturacao de calcio. Houve, nas areas com rotacao mucuna-milho, maiores teores de potassio, calcio e magnesio, em relacao aos demais manejos (soja-milho, milho continuo e milho apos milho + mucuna intercalar)

An autonomous organic reaction search engine for chemical reactivity

The exploration of chemical space for new reactivity, reactions and molecules is limited by the need for separate work-up-separation steps searching for molecules rather than reactivity. Herein we present a system that can autonomously evaluate chemical reactivity within a network of 64 possible reaction combinations and aims for new reactivity, rather than a predefined set of targets. The robotic system combines chemical handling, in-line spectroscopy and real-time feedback and analysis with an algorithm that is able to distinguish and select the most reactive pathways, generating a reaction selection index (RSI) without need for separate work-up or purification steps. This allows the automatic navigation of a chemical network, leading to previously unreported molecules while needing only to do a fraction of the total possible reactions without any prior knowledge of the chemistry. We show the RSI correlates with reactivity and is able to search chemical space using the most reactive pathways

SnS Thin Films Prepared by Chemical Spray Pyrolysis at Different Substrate Temperatures for Photovoltaic Applications

[EN] The preparation and analysis of morphological, structural, optical, vibrational and compositional properties of tin monosulfide (SnS) thin films deposited on glass substrate by chemical spray pyrolysis is reported herein. The growth conditions were evaluated to reduce the presence of residual phases different to the SnS orthorhombic phase. X-ray diffraction spectra revealed the polycrystalline nature of the SnS films with orthorhombic structure and a preferential grain orientation along the (111) direction. At high substrate temperature (450A degrees C), a crystalline phase corresponding to the Sn2S3 phase was observed. Raman spectroscopy confirmed the dominance of the SnS phase and the presence of an additional Sn2S3 phase. Scanning electron microscopy (SEM) images reveal that the SnS film morphology depends on the substrate temperature. Between 250A degrees C and 350A degrees C, SnS films were shaped as rounded grains with some cracks between them, while at substrate temperatures above 400A degrees C, films were denser and more compact. Energy-dispersive x-ray spectroscopy (EDS) analysis showed that the stoichiometry of sprayed SnS films improved with the increase of substrate temperature and atomic force microscopy micrographs showed films well covered at 350A degrees C resulting in a rougher and bigger grain size. Optical and electrical measurements showed that the optical bandgap and the resistivity decreased when the substrate temperature increased, and smaller values, 1.46 eV and 60 Omega cm, respectively, were attained at 450A degrees C. These SnS thin films could be used as an absorber layer for the development of tandem solar cell devices due to their high absorbability in the visible region with optimum bandgap energy.This work was supported by Ministerio de Economia y Competitividad (ENE2013-46624-C4-4-R) and Generalitat valenciana (Prometeus 2014/044).Sall, T.; Marí, B.; Mollar García, MA.; Sans-Tresserras, JÁ. (2017). SnS Thin Films Prepared by Chemical Spray Pyrolysis at Different Substrate Temperatures for Photovoltaic Applications. Journal of Electronic Materials. 46(3):1714-1719. https://doi.org/10.1007/s11664-016-5215-9S17141719463N.R. Mathews, H.B.M. Anaya, M.A. Cortes-Jacome, C. Angeles-Chavez, and J.A. Toledo-Antonio, J. Electrochem. Soc. 157, H337 (2010).N. Koteeswara Reddy, K. Ramesh, R. Ganesan, K. Reddy, K.R. Gunasekhar, and E. Gopal, Appl. Phys. A 83, 133 (2006).J.J. Loferski, J. Appl. Phys. 27, 777 (1956).K.T.R. Reddy, N.K. Reddy, and R.W. Miles, Sol. Energy Mat. Sol. C 90, 3041 (2006).C. Gao, H.L. Shen, L. Sun, H.B. Huang, L.F. Lu, and H. Cai, Mater. Lett. 64, 2177 (2010).D. Avellaneda, M.T.S. Nair, and P.K. Nair, J. Electrochem. Soc. 155, D517 (2008).J.R.S. Brownson, C. Georges, and C. Levy-Clement, Chem. Mater. 19, 3080 (2007).P. Sinsermsuksakul, J. Heo, W. Noh, A.S. Hock, and R.G. Gordon, Adv. Eng. Mat 1, 1116 (2011).T. Sall, M. Mollar, and B. Marí, J. Mater. Sci. 51, 7607 (2016).K. Otto, A. Katerski, O. Volobujeva, A. Mere, and M. Krunks, Energy Proc. 3, 63 (2011).J. Malaquias, P.A. Fernandes, P.M.P. Salomé, and A.F. da Cunha, Thin Solid Films 519, 7416 (2011).T.H. Sajeesh, A.R. Warrier, C. Sudha Kartha, and K.P. Vijayakumar, Thin Solid Films 518, 4370 (2010).M. Vasudeva Reddy, G. Sreedevi, C. Park, R.W. Miles, and K.T. Ramakrishna Reddy, Curr. Appl. Phys. 15, 588 (2015).A. Molenaar, Extended Abstracts, vol. 84-2, Pennington, N.J., 634 (1984)S. López, S. Granados, and A. Ortiz, Semicond. Sci. Technol. 11, 433 (1996).B. Cullity, Elements of X-ray Diffraction (New York: Addision-Wesley Publishing Company Inc, 1967), p. 501.G. Willeke, R. Dasbach, B. Sailer, and E. Bucher, Thin Solid Films 213, 271 (1992).H.R. Chandrasekhar, R.G. Humphreys, U. Zwick, and M. Cardona, Phys. Rev. B 15, 2177 (1977).S. Cheng and G. Conibeer, Thin Solid Films 520, 837 (2011)