Boson-boson effective nonrelativistic potential for higher-derivative electromagnetic theories in D dimensions

The problem of computing the effective nonrelativistic potential $U_{D}$ for the interaction of charged scalar bosons within the context of D-dimensional electromagnetism with a cutoff, is reduced to quadratures. It is shown that $U_3$ cannot bind a pair of identical charged scalar bosons; nevertheless, numerical calculations indicate that boson-boson bound states do exist in the framework of three-dimensional higher-derivative electromagnetism augmented by a topological Chern-Simons term.Comment: 6 page

Is it Physically Sound to Add a Topologically Massive Term to Three-Dimensional Massive Electromagnetic or Gravitational Models ?

The addition of a topologically massive term to an admittedly non-unitary three-dimensional massive model, be it an electromagnetic system or a gravitational one, does not cure its non-unitarity. What about the enlargement of avowedly unitary massive models by way of a topologically massive term? The electromagnetic models remain unitary after the topological augmentation but, surprisingly enough, the gravitational ones have their unitarity spoiled. Here we analyze these issues and present the explanation why unitary massive gravitational models, unlike unitary massive electromagnetic ones, cannot coexist from the viewpoint of unitarity with topologically massive terms. We also discuss the novel features of the three-term effective field models that are gauge-invariant

Unavoidable Conflict Between Massive Gravity Models and Massive Topological Terms

Massive gravity models in 2+1 dimensions, such as those obtained by adding to Einstein's gravity the usual Fierz-Pauli, or the more complicated Ricci scalar squared ($R^2$), terms, are tree level unitary. Interesting enough these seemingly harmless systems have their unitarity spoiled when they are augmented by a Chern-Simons term. Furthermore, if the massive topological term is added to $R + R_{\mu\nu}^2$ gravity, or to $R + R_{\mu\nu}^2 + R^2$ gravity (higher-derivative gravity), which are nonunitary at the tree level, the resulting models remain nonunitary. Therefore, unlike the common belief, as well as the claims in the literature, the coexistence between three-dimensional massive gravity models and massive topological terms is conflicting.Comment: 13 pages, no figure

Infestação do bicudo-do-algodoeiro em função da densidade de plantas e época do cultivo

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Agronomia e Medicina Veterinária, 2016.O bicudo-do-algodoeiro é uma das pragas de maior relevância da agricultura no Brasil. Apesar da sua importância, medidas de manejo efetivas em sistemas de cultivo restritivos ao uso de insumos sintéticos continuam escassas. O objetivo desse trabalho foi avaliar o efeito do espaçamento entre linhas e da época de semeadura sobre o ataque do bicudo-do-algodoeiro e características condicionantes da produção das plantas. Foram testados os espaçamentos de 0,50, 0,75 e 1,00 m entre linhas e as épocas de semeadura 20/11/14, 16/12/14 e 20/01/15, sendo os tratamentos arranjados no delineamento em blocos ao acaso com quatro repetições. Ao surgimento das primeiras estruturas reprodutivas, avaliou-se, semanalmente, o número total e o número de estruturas reprodutivas contendo sinais de alimentação e oviposição do bicudo-do-algodoeiro. Adicionalmente, as estruturas atacadas e caídas no solo foram coletadas, que também é uma medida de controle cultural por catação evitando um aumento na infestação da lavoura pelos indivíduos emergidos e destinadas ao laboratório e submetidas à mesma avaliação feita a campo sendo, em seguida, acondicionadas em recipientes plásticos de 5L de capacidade e submetidas à avaliação semanal quanto à emergência de adultos até 21 dias após a coleta. Na última avaliação, foi realizada análise destrutiva para contabilização das fases da praga presentes no interior das estruturas coletadas e que não emergiram. A partir da abertura de 80% dos capulhos, as avaliações a campo foram encerradas, quando foi realizada a colheita de 10 plantas ao acaso por parcela contabilizando-se o número total de capulhos e maçãs, o número de capulhos normais e defeituosos (carimã), o número total de ramos das plantas colhidas e o número de maçãs normais e com sinais de ataque do bicudo-do-algodoeiro. Após essa avaliação, os capulhos foram pesados com e sem caroço para estimativa da produção, rendimento e qualidade tecnológica da fibra. Os dados foram analisados por ANOVA por medidas repetidas e ANOVA seguida de teste de médias, para a verificação do efeito significativo de tratamentos. Observou-se que o espaçamento de 0,75 m entre linhas e a segunda época de cultivo (16/12/2014) adiaram a tomada de decisão de controle de A. grandis em uma e três semanas, respectivamente, além de terem produzido menor número de adultos e, em geral, menor número de estruturas reprodutivas danificadas. O espaçamento de 0,75 m e a primeira época de cultivo (20/11/2014) proporcionaram as maiores produções e permitiram a obtenção de melhores classificações em termos de qualidade da fibra.The boll weevil is one of the most important pest of cotton in Brazil. In spite of its relevance, management practices that are effective in controlling this pest in systems restrictive concerning pesticides use are scarce. Hence, this work evaluated the effect of row spacing and planting date over attack boll weevil, and over the production characteristics of cotton plants. Row spacing of 0.50, 0.75 and 1.00 m and planting dates of 11/20/14, 12/16/14 and 01/20/15 were tested, with the treatments being arranged in a completely randomized design with four replicates. The evaluations started at the appearance of the first reproductive structures. Weekly, from this point on, the total number of reproductive structures and those showing punctures of feeding and/or oviposition boll weevil were recorded. In addition, the falling attacked structures were collected, taken to the Lab and evaluated concerning the boll weevil adult emergence. Right after, these structures were placed in plastic containers of 5 L capacity where they were kept for 21 days. The number of emerging adults of boll weevil was weekly accounted. The last evaluation, a destructive observation, was performed in order to record the number of non-emerged insects. When the bolls opened, data recording stopped and 10 plants per plot were randomly harvested. The number of normal and attacked open and closed bolls and the number of branches per plant were recorded. The lint were manually separated from the seeds and weighted in order to obtain the fiber yield. The material was sent to Embrapa Cotton Campina Grande, PB, for fiber analysis. The data were subjected to repeated measures ANOVA and ANOVA followed by multiple comparison tests every time that a significant effect of treatments was verified. Row spacing of 0.75 m and the second planting date (12/16/2014) postponed the controlling decision of A. grandis in one and three weeks, respectively. Besides, those were the treatments where the lowest number of the boll weevil and damaged reproductive structures were obtained. Also, the highest yields were obtained at the row spacing of 0.75 and on the first planting date (11/20/2014). Finally, the quality of fiber in these treatments reached the best qualification

Renormalization of electron self-energies via their interaction with spin excitations: A first-principles investigation

Access to magnetic excitation spectra of single atoms deposited on surfaces is nowadays possible by means of low-temperature inelastic scanning tunneling spectroscopy. We present a first-principles method for the calculation of inelastic tunneling spectra utilizing the Korringa-Kohn-Rostoker Green function method combined with time-dependent density functional theory and many-body perturbation theory. The key quantity is the electron self-energy describing the coupling of the electrons to the spin excitation within the adsorbate. By investigating Cr, Mn, Fe and Co adatoms on a Cu(111) substrate, we spin-characterize the spectra and demonstrate that their shapes are altered by the magnetization of the adatoms, of the tip and the orbital decay into vacuum. Our method also predicts spectral features more complex than the steps obtained by simpler models for the adsorbate (e.g., localized spin models)

Perspectiva social del e-learning en la universidad

En la actual sociedad del conocimiento, los progresos en ciencia y tecnología conviven con una amplia problemática social que es necesario abordar para analizar los problemas relacionados con la educación. En los últimos años, la presencia del Estado ha disminuido en todos los ámbitos. El modelo estadounidense de privatización y comercialización ha creado nuevas realidades, como la necesidad de los países ricos de controlar, entre otras cosas, los servicios, el conocimiento y las nuevas tecnologías. En este contexto, y ante la creciente comercialización de la educación como servicio, incluso desde los organismos internacionales, los países en desarrollo necesitan más que nunca acceder a instituciones de educación superior y de investigación que les permitan avanzar hacia un desarrollo sostenible. Asistimos a un proceso de elitización en el que la educación deja de ser un bien público y pasa a convertirse en un bien privado, lo que se refleja en los sistemas educativos de distintos países. Son varios los procesos de reforma de los sistemas educativos de países en desarrollo que tienen como objetivo facilitar el acceso al conocimiento. Muchas de las medidas que deben aplicarse pasan por la utilización de las nuevas tecnologías y el intercambio de conocimientos mediante una cooperación internacional que se aleje de la comercialización y permita el acceso de todas las personas a la sociedad del conocimiento

Embedment of metal nanoparticles in GaAs and Si for plasmonic absorption enhancement in intermediate band solar cells

The high near-field enhancement occurring in the vicinity of metallic nanoparticles (MNPs) sustaining surface plasmons can only be fully exploited in photovoltaic devices if the MNPs are placed inside their semiconducting material, in the photoactive region. In this work an experimental procedure is studied to embed MNPs in gallium arsenide (GaAs) and silicon (Si), which can be applied to other semiconductor host materials. The approach consists in spin-coating colloidal MNPs dispersed in solution onto the substrate surface. Then a capping layer of the same material as the substrate is deposited on top to embed the MNPs in the semiconductor. The extinction spectra of silver (Ag) and gold (Au) MNPs embedded in GaAs and Si is modeled with Mie theory for comparison with optical measurements. This contribution constitutes the initial step towards the realization of quantum-dot intermediate band solar cells (QD-IBSC) with MN