Mass spectra of the particle-antiparticle system with a Dirac oscillator interaction

The present view about the structure of mesons is that they are a quark-antiquark system. The mass spectrum corresponding to this system should, in principle, be given by chromodynamics, but this turns out to be a complex affair. Thus it is of some interest to consider relativistic systems of particle-antiparticle, with a simple type of interaction, which could give some insight on the spectra we can expect for mesons. This analysis is carried out when the interaction is of the Dirac oscillator type. It is shown that the Dirac equation of the antiparticle can be obtained from that of the particle by just changing the frequency omega into -omega. Following a procedure suggested by Barut, the equation for the particle-antiparticle system is derived and it is solved by a perturbation procedure. Thus, explicit expressions for the square of the mass spectra are obtained and its implications in the meson case is discussed

ATP-dependent chromatosome remodeling

Chromatin serves to package, protect and organize the complex eukaryotic genomes to assure their stable inheritance over many cell generations. At the same time, chromatin must be dynamic to allow continued use of DNA during a cell's lifetime. One important principle that endows chromatin with flexibility involves ATP-dependent `remodeling' factors, which alter DNA-histone interactions to form, disrupt or move nucleosomes. Remodeling is well documented at the nucleosomal level, but little is known about the action of remodeling factors in a more physiological chromatin environment. Recent findings suggest that some remodeling machines can reorganize even folded chromatin fibers containing the linker histone H1, extending the potential scope of remodeling reactions to the bulk of euchromatin

Single-particle transfer and nuclear supersymmetry

Transfer reactions constitute a stringent test for nuclear supersymmetry, a theory that simultaneously describes neighboring nuclei with bosonic and fermionic character. We construct and analytically evaluate one-nucleon transfer matrix elements between supersymmetric partners with the U( 6/4) case as an example, and stress the need for a careful treatment of bosonic and fermionic operators in the construction of mixed tensor operators.CONACyT 32416-E 32397-EPAGA-UNAM IN106400DGICYT PB98-111

Global priorities for conservation across multiple dimensions of mammalian diversity

Conservation priorities that are based on species distribution, endemism, and vulnerability may underrepresent biologically unique species as well as their functional roles and evolutionary histories. To ensure that priorities are biologically comprehensive, multiple dimensions of diversity must be considered. Further, understanding how the different dimensions relate to one another spatially is important for conservation prioritization, but the relationship remains poorly understood. Here, we use spatial conservation planning to (i) identify and compare priority regions for global mammal conservation across three key dimensions of biodiversity-taxonomic, phylogenetic, and traits-and (ii) determine the overlap of these regions with the locations of threatened species and existing protected areas. We show that priority areas for mammal conservation exhibit low overlap across the three dimensions, highlighting the need for an integrative approach for biodiversity conservation. Additionally, currently protected areas poorly represent the three dimensions of mammalian biodiversity. We identify areas of high conservation priority among and across the dimensions that should receive special attention for expanding the global protected area network. These high-priority areas, combined with areas of high priority for other taxonomic groups and with social, economic, and political considerations, provide a biological foundation for future conservation planning efforts

Magnetismo e Propriedades Estruturais de Nanopartículas Magnéticas Obtidas por Processos Químicos.

Neste trabalho, objetivamos sintetizar, estabilizar e caracterizar estrutural e magneticamente, nanopartículas à base de Fe, produzidas através dos métodos químicos de redução e de precipitação. Em ambos os casos, utilizamos as técnicas de Espectroscopia Mössbauer, Difração de raios X, Microscopias Eletrônicas de Varredura e de Transmissão, além de medidas magnéticas realizadas nos modos DC e AC. Nanopartículas preparadas por Redução Química: realizamos, à temperatura ambiente, a hidrólise-redução do FeCl3 em água deionizada, utilizando diferentes quantidades de glicerol como agente controlador da concentração de íons de Fe3+, juntamente com o redutor NaBH4. Investigamos os efeitos da utilização de diferentes quantidades de glicerol, no processo de síntese, e do processo de secagem das amostras sobre a estabilização da fase -Fe. Como resultados, obtivemos nanopartículas de Fe com estrutura cúbica de corpo centrado ( -Fe) encapsuladas por superfícies amorfas de Fe2B (a-Fe2B) às quais nos referimos por -Fe/a-Fe2B. Verificamos o aumento na concentração fase -Fe ( ) como função do aumento na quantidade de glicerol ( ) utilizada na síntese, para as amostras secas a vácuo. Para as amostras úmidas notamos alta susceptibilidade a oxidação, enquanto que as amostras secas a vácuo se mantiveram estáveis por medidas de Espectroscopia Mössbauer realizadas 12 meses após a síntese. Para as quantidades de 2, 3 e 4 ml de glicerol, produzimos nanopartículas de -Fe/a-Fe2B sem a presença de óxido de Fe, adicionalmente observamos mudanças no formato das nanopartículas produzidas, utilizando 4 ml de glicerol, produzimos nanofolhas de -Fe/a-Fe2B e utilizando 5 ml, obtivemos nanopartículas de -Fe/a-Fe2B e -Fe2O3 com formato esférico irregular. Nanopartículas preparadas por Precipitação Química: produzimos nanocompósitos de Fe2P dispersos numa matriz de carbono poroso, através do método de precipitação química. Além da produção deste nanocompósito utilizando o carvão ativado (preparado por ativação química com H3PO4), a impregnação com sais de Fe3+ em meio aquoso, e subsequentes tratamentos térmicos, sob fluxo de N2, levaram a formação da fase hexagonal não estequiométrica Fe2-XP e da fase ortorrômbica Fe-P com razão de 4:1, respectivamente. Medidas de espectroscopia viii Mössbauer em baixas temperaturas revelam que parte da fração (~ 28 %) deste material se encontra no estado paramagnético, sugerindo que parte da fase não estequiométrica Fe2-XP é constituída por partículas muito pequenas. Observamos ainda uma transição de fase metamagnética em torno de 150 K, associada à nanopartículas pertencentes à fase Fe2-XP, por estar bem abaixo da temperatura de ordenamento do composto Fe2P (~ 230 K) e por ser dependente da frequência e dos campos externos AC e DC aplicados. Além disso, as nanopartículas de Fe2-XP possuem um caráter magneto-duro em baixas temperaturas, com campo coercivo . Considerando estas interessantes propriedades magnéticas e hiperfinas e a área de superfície elevada da matriz de carvão ativado, que não é fortemente reduzida após a impregnação com os compostos contendo Fe, podemos apontar aplicações tecnológicas promissoras para o nanocompósito produzido

Banking Efficiency in Chile: a Profit Frontier Approach

This paper characterizes the evolution of the efficiency X in the Chilean banking industry over 1987 to 2007, based on a profit frontier approach. Our results suggest that over this period the Chilean banking sector has attained just a 15% over its maximum profits. This inefficiency basically arises from a technical source rather than an assignative one, and mainly affects domestic and small banks. Nevertheless, the level of efficiency X of the industry as a whole has dramatically improved since the late 1990’s, which is consistent with important economic, technological and regulatory transformations.

Observaciones de planetas y pequeños planetas realizadas en 1983, en el círculo meridiano Repsold de Cerro Calán

Se presentan los resultados de 34 observaciones diferenciales , en ascensión recta de los planetas Urano y Neptuno y de los pequeños planetas Ceres, Juno y Vesta, realizadas con el Círculo Meridiano Repsold de Cerro Calán. El error medio de cada observación es ε_α cos δ ≃ ± 0ˢ.016 y se dan los valores de la ascensión recta observada y los (O-C) para cada una de las observaciones en el sentido instrumento - American Ephemeris.Asociación Argentina de Astronomí

Estudio farmacológico y fitoquímico de dos especies de salandra nativas de México

A pharmacological and phytochemical sreening study of two species of Solandra native of Mexico is reported due to their indigenous use in traditional medicine. Water extracts of flowers of S. nítida and barks of S. guerrerense have marked anticholinergic effectis inhibiting acetiylicholine induced contraction of the smooth muscle of isolated ileum of guinea pig and depressing EEG activity in rats after intraperitoneal injection. By gas chromatography and NMR spectrometry the prodomine is abundant in S. nítida flowers, vhile Hyoscyamine is the mayin alkaloid in S. guerrerense bark. The presence of these tropane alkaloids in Solandra extracts and popular use of the plants for ceremonial and medicinal procedures is discussed.Se realizó un screening farmacológico y fitoquírnico de dos especies de Solandra que se usan en México con propósitos medicinales y rituales. Los extractos de flores de S. nítida y de cortezas de S. guerrerense contienen escopolamina e hiosciamina respectivamente como alcaloides predominantes. El efecto anticolinérgico de los extractos acuosos de estas plantas se estudió en el íleon aislado del cobayo y su efecto sedante del sistema nervioso central en la rata implantada con electrodos y sometida a estímulos dolorosos. El uso como psicotrópico que se hace de estas especies se explica como una consecuencia de la intoxicación que producen los extractos administrados por vía oral. Se discute el papel de la acetilcolina y los alcaloides del tropano en la acción anestésica local atribuida a estas plantas

Bayesian additive regression trees for probabilistic programming

Bayesian additive regression trees (BART) is a non-parametric method to approximate functions. It is a black-box method based on the sum of many trees where priors are used to regularize inference, mainly by restricting trees' learning capacity so that no individual tree is able to explain the data, but rather the sum of trees. We discuss BART in the context of probabilistic programming languages (PPL), i.e., we present BART as a primitive that can be used as a component of a probabilistic model rather than as a standalone model. Specifically, we introduce the Python library PyMC-BART, which works by extending PyMC, a library for probabilistic programming. We showcase a few examples of models that can be built using PyMC-BART, discuss recommendations for the selection of hyperparameters, and finally, we close with limitations of our implementation and future directions for improvement.Comment: 22 pages, 17 figure