Una explicación de la conducta competitiva de las microempresas de subsistencia: evidencia para México

O objetivo deste trabalho é discutir dois elementos para a análise do setor microempresarial: a necessidade de repensar o enquadramento teórico de referência para representar seu comportamento de concorrência e a pertinência de diferenciá-lo segundo sua natureza, localização e objetivos. Para isso, utiliza-se uma metodologia a partir de contrastes entre evidências empíricas e pressupostos essenciais da teoria da organização industrial, bem como a aplicação de instrumentos de medida do grau de concorrência estratégica e classificação microempresarial com base num modelo logístico de escolha discreta. Dessa forma, chegam-se a resultados que sugerem que o desempenho competitivo de um subsetor importante das microempresas possa ser associado com modelos de concorrência imperfeita, dando diretrizes para sua pertinente análise.El objetivo de este trabajo es discutir dos elementos para el análisis del sector microempresarial: la necesidad de replantear el marco teórico de referencia para representar su comportamiento competitivo y la pertinencia de diferenciarlas según su naturaleza, localización y objetivos. Para ello se utiliza una metodología a partir de contrastes entre evidencias empíricas y supuestos esenciales de la teoría de la organización industrial, así como la aplicación de instrumentos de medida del grado de competencia estratégica y clasificación microempresarial con base en un modelo de elección discreta logístico. De esta forma, se recaban resultados que sugieren que el desempeño competitivo de un subsector importante de las microempresas puede ser asociado a modelos de competencia imperfecta, dando pautas para su pertinente análisis

Accretion properties of T Tauri stars in sigma Ori

Accretion disks around young stars evolve in time with time scales of few million years. We present here a study of the accretion properties of a sample of 35 stars in the ~3 million year old star-forming region sigma Ori. Of these, 31 are objects with evidence of disks, based on their IR excess emission. We use near-IR hydrogen recombination lines (Pa_gamma) to measure their mass accretion rate. We find that the accretion rates are significantly lower in sigma Ori than in younger regions, such as rho-Oph, consistently with viscous disk evolution. The He I 1.083 micron line is detected (either in absorption or in emission) in 72% of the stars with disks, providing evidence of accretion-powered activity also in very low accretors, where other accretion indicators dissapear.Comment: Astronomy and Astrophysics, accepte

FLAMES spectroscopy of low-mass stars in the young clusters sigma Ori and lambda Ori

Aims. We performed a detailed membership selection and studied the accretion properties of low-mass stars in the two apparently very similar young (1-10 Myr) clusters sigma Ori and lambda Ori. Methods. We observed 98 and 49 low-mass (0.2-1.0 M_sun) stars in sigma Ori and lambda Ori respectively, using the multi-object optical spectrograph FLAMES at the VLT, with the high-resolution (R=17,000) HR15N grating (6470-6790 AA). We used radial velocities, Li and Halpha to establish cluster membership and Halpha and other optical emission lines to analyze the accretion properties of members. Results. We identified 65 and 45 members of the sigma Ori and lambda Ori clusters, respectively and discovered 16 new candidate binary systems. We also measured rotational broadening for 20 stars and estimated the mass accretion rates in 25 stars of the sigma Ori cluster, finding values between 10^-11 and 10^-7.7 M_sun yr^-1 and in 4 stars of the lambda Ori cluster, finding values between 10^-11 and 10^-10.1 M_sun yr-1. Comparing our results with the infrared photometry obtained by the Spitzer satellite, we find that the fraction of stars with disks and the fraction of active disks is larger in the sigma Ori cluster (52+-9% and 78+-16%) than in lambda Ori (28+-8% and 40+-20%) Conclusions. The different disk and accretion properties of the two clusters could be due either to the effect of the high-mass stars and the supernova explosion in the lambda Ori cluster or to different ages of the cluster populations. Further observations are required to draw a definitive conclusion.Comment: 14 pages, 9 figures, 9 tables, accepted for publications in A&

Uma explicação do comportamento de concorrência das microempresas de subsistência: evidência para o México

The objective of this paper is to discuss two elements necessary when analyzing the microenterprise sector: the need to rethink the theoretical frame of reference to represent its competitive behavior; and the relevance of differentiating them according to their nature, location and objectives. The methodology is based on contrasting empirical evidences and essential assumptions made by the industrial organization theory, as well as applying measuring instruments for the degree of strategic competence and microenterprise classification, based on a discrete logistic choice model. Results suggest that the competitive performance of an important subsector of microenterprises can be associated with models of imperfect competition, giving guidelines for their pertinent analysis.El objetivo de este trabajo es discutir dos elementos para el análisis del sector microempresarial: la necesidad de replantear el marco teórico de referencia para representar su comportamiento competitivo y la pertinencia de diferenciarlas según su naturaleza, localización y objetivos. Para ello se utiliza una metodología a partir de contrastes entre evidencias empíricas y supuestos esenciales de la teoría de la organización industrial, así como la aplicación de instrumentos de medida del grado de competencia estratégica y clasificación microempresarial con base en un modelo de elección discreta logístico. De esta forma, se recaban resultados que sugieren que el desempeño competitivo de un subsector importante de las microempresas puede ser asociado a modelos de competencia imperfecta, dando pautas para su pertinente análisis.O objetivo deste trabalho é discutir dois elementos para a análise do setor microempresarial: a necessidade de repensar o enquadramento teórico de referência para representar seu comportamento de concorrência e a pertinência de diferenciá-lo segundo sua natureza, localização e objetivos. Para isso, utiliza-se uma metodologia a partir de contrastes entre evidências empíricas e pressupostos essenciais da teoria da organização industrial, bem como a aplicação de instrumentos de medida do grau de concorrência estratégica e classificação microempresarial com base num modelo logístico de escolha discreta. Dessa forma, chegam-se a resultados que sugerem que o desempenho competitivo de um subsetor importante das microempresas possa ser associado com modelos de concorrência imperfeita, dando diretrizes para sua pertinente análise

Comparative genomics reveals high biological diversity and specific adaptations in the industrially and medically important fungal genus Aspergillus

Incluye más de 100 autoresBackground: The fungal genus Aspergillus is of critical importance to humankind. Species include those with industrial applications, important pathogens of humans, animals and crops, a source of potent carcinogenic contaminants of food, and an important genetic model. The genome sequences of eight aspergilli have already been explored to investigate aspects of fungal biology, raising questions about evolution and specialization within this genus. Results: We have generated genome sequences for ten novel, highly diverse Aspergillus species and compared these in detail to sister and more distant genera. Comparative studies of key aspects of fungal biology, including primary and secondary metabolism, stress response, biomass degradation, and signal transduction, revealed both conservation and diversity among the species. Observed genomic differences were validated with experimental studies. This revealed several highlights, such as the potential for sex in asexual species, organic acid production genes being a key feature of black aspergilli, alternative approaches for degrading plant biomass, and indications for the genetic basis of stress response. A genome-wide phylogenetic analysis demonstrated in detail the relationship of the newly genome sequenced species with other aspergilli. Conclusions: Many aspects of biological differences between fungal species cannot be explained by current knowledge obtained from genome sequences. The comparative genomics and experimental study, presented here, allows for the first time a genus-wide view of the biological diversity of the aspergilli and in many, but not all, cases linked genome differences to phenotype. Insights gained could be exploited for biotechnological and medical applications of fungi

Interfaz Gráfica Computacional para Destilación Multicomponente utilizando Métodos Cortos

In this work, we developed a graphical interface that determines by steady-state simulation the number of plates required for multicomponent distillation process and the composition of distillate and bottoms flow of a distillation tower using short-cut methods. The graphical user interface was built in the programming language Python 2.5, allows to present the input and output data for the case of distillation columns operating in steady state. The results of using the graphical interface shows a simple way to make preliminary designs of distillation towers and its potential as support material for the study and understanding of basic concepts in multicomponent distillation. In a later work it will can display the dynamic model performance through scheduled disturbances in operating conditions.Keywords: multicomponent distillation, shorcut methods, graphical user interface, Phyton 2.5.DOI: http://dx.doi.org/10.5377/nexo.v24i2.660En este trabajo, se elaboró una interfaz gráfica que determina por medio de simulación en estado estacionario el número de platos necesarios en el proceso de destilación multicomponente, así como la composición en el flujo de destilado y fondos de una torre de destilación utilizando métodos cortos. La interfaz gráfica de usuario, se construyó en el lenguaje de programación Python 2.5, permite presentar los datos de entrada y salida para el caso de columnas de destilación operando en régimen permanente. Los resultados del uso de la interfaz gráfica muestran una forma simple de realizar diseños preliminares de torres de destilación y su potencialidad como material de apoyo para el estudio y comprensión de conceptos básicos en destilación multicomponente. En un trabajo posterior se podrá visualizar el desempeño del modelo dinámico a través de perturbaciones programadas en las condiciones de operación.Palabras claves: destilación multicomponente, métodos cortos, interfaz gráfica de usuario, Phyton 2.5.DOI: http://dx.doi.org/10.5377/nexo.v24i2.66

Productive response of lambs fed with fresh or dehydrated spineless cactus (Opuntia ficus-indica L.)

Abstract The objective of this study was to evaluate the effect of cactus (Opuntia ficus-indica L.) supplementation on lamb animal performance, during a 11-week period. For this purpose, 27 male lambs of commercial crossbreeds were used, with initial live weight mean of 21.4±3.8 kg. They were distributed homogeneously into three groups of nine each, and then randomly assigned to each of the following treatments: (T1) control diet, (2) diet with 17% (dry matter basis) of dehydrated cactus, and (3) diet with 17% (dry matter basis) of fresh cactus. Digestibility in situ of the diet, dry matter intake (DMI), daily gain weight (DGW), feeding conversion (FC) and efficiency (FE), back fat, hot and cold carcass yield, biological hot and cold carcass yield, and carcass pH at slaughtering and 24h post mortem, were evaluated. A completely random design using Proc GLM was used, and when statistical differences were observed, a mean comparison was done using the Tukey test. There were significant differences (P≤0.001) on DM digestibility, with higher value (42.0%) on the control diet during the first 6 hours of incubation, but after 48 hours, the highest digestibility (88.6%) was on the fresh cactus diet. There were not significant differences (P>0.05) between treatments on animal performance, except on back fat, being higher (P<0.001) on dehydrated (4.1 mm) and fresh (3.3 mm) diets, compared to the control one (7.8 mm). The means for hot and cold carcass yield, biological hot and cold carcass yield, and carcass pH at slaughtering and 24h post mortem were 50.6%, 47.0%, 55.4%, 49.5%, 6.6% and 5.8%, respectively. Diet including cactus had similar effect on productive parameters than that of the commercial one, which makes it a viable feeding strategy, and from the economical point of view, could be attractive to the farmer, since the cactus is a plant that grows over the year. However, there is a need of doing more research to confirm these results, not only on fattening lambs, but also on the different animal life stages, considering different levels of cactus, and working on different animal breed and species

The Monitor project: JW 380 -- a 0.26, 0.15 Msol pre main sequence eclipsing binary in the Orion Nebula Cluster

We report the discovery of a low-mass (0.26 +/- 0.02, 0.15 +/- 0.01 Msol) pre-main-sequence eclipsing binary with a 5.3 day orbital period. JW 380 was detected as part of a high-cadence time-resolved photometric survey (the Monitor project) using the 2.5m Isaac Newton Telescope and Wide Field Camera for a survey of a single field in the Orion Nebula Cluster (ONC) region in V and i bands. The star is assigned a 99 per cent membership probability from proper motion measurements, and radial velocity observations indicate a systemic velocity within 1 sigma of that of the ONC. Modelling of the combined light and radial velocity curves of the system gave stellar radii of 1.19 +0.04 -0.18 Rsol and 0.90 +0.17 -0.03 Rsol for the primary and secondary, with a significant third light contribution which is also visible as a third peak in the cross-correlation functions used to derive radial velocities. The masses and radii appear to be consistent with stellar models for 2-3 Myr age from several authors, within the present observational errors. These observations probe an important region of mass-radius parameter space, where there are currently only a handful of known pre-main-sequence eclipsing binary systems with precise measurements available in the literature.Comment: 11 pages, 9 figures, accepted for publication in MNRA

Transiciones, conflictos y democracia : estudios de coyuntura

México ha vivido un largo proceso de transición que ha desencadenado dinamismos económicos, culturales y políticos. En la actual coyuntura, estos dinamismos muestran toda su complejidad, su inevitable articulación y la tensión entre las fuerzas que intentan sostener un viejo modelo de gobernar y decidir el rumbo del país, y aquellas que buscan abrirse a un espectro mucho más amplio y diversificado de actores. En ellos se conjuntan las aspiraciones más legítimas de los mexicanos por avanzar en el reconocimiento y respeto de la pluralidad étnica, de género y entre generaciones, y por impulsar una dinámica en la que —en medio de los procesos de mundialización— los distintos grupos e intereses de los mexicanos puedan ser incluidos. La transición mexicana tiende a centrarse en la dimensión política. La intensidad que cobran los procesos políticos y el énfasis que importantes analistas ponen en dichos procesos, contribuyen a que esta asociación vaya cobrandoíuerza. En este sentido, es necesario advertir que en las transiciones la tendencia privatizadora, la reducción del gasto social, así como la necesidad de pactos sociales que sean respetados, la participación creciente de la sociedad civil, etc. son factores importantes que, en medio de contradicciones, van generando nuevos esquemas de relación entre gobierno y sociedad.ITESO, A.C

No silver bullet for digital soil mapping: country-specific soil organic carbon estimates across Latin America.

Country-specific soil organic carbon (SOC) estimates are the baseline for the Global SOC Map of the Global Soil Partnership (GSOCmap-GSP). This endeavor is key to explaining the uncertainty of global SOC estimates but requires harmonizing heterogeneous datasets and building country-specific capacities for digital soil mapping (DSM).We identified country-specific predictors for SOC and tested the performance of five predictive algorithms for mapping SOC across Latin America. The algorithms included support vector machines (SVMs), random forest (RF), kernel-weighted nearest neighbors (KK), partial least squares regression (PL), and regression kriging based on stepwise multiple linear models (RK). Country-specific training data and SOC predictors (5 x 5 km pixel resolution) were obtained from ISRIC - World Soil Information. Temperature, soil type, vegetation indices, and topographic constraints were the best predictors for SOC, but country-specific predictors and their respective weights varied across Latin America. We compared a large diversity of country-specific datasets and models, and were able to explain SOC variability in a range between ~ 1 and ~ 60 %, with no universal predictive algorithm among countries. A regional (n = 11 268 SOC estimates) ensemble of these five algorithms was able to explain ~ 39% of SOC variability from repeated 5-fold cross-validation.We report a combined SOC stock of 77.8 +- 43.6 Pg (uncertainty represented by the full conditional response of independent model residuals) across Latin America. SOC stocks were higher in tropical forests (30 +- 16.5 Pg) and croplands (13 +- 8.1 Pg). Country-specific and regional ensembles revealed spatial discrepancies across geopolitical borders, higher elevations, and coastal plains, but provided similar regional stocks (77.8 +- 42.2 and 76.8 +- 45.1 Pg, respectively). These results are conservative compared to global estimates (e.g., SoilGrids250m 185.8 Pg, the Harmonized World Soil Database 138.4 Pg, or the GSOCmap-GSP 99.7 Pg). Countries with large area (i.e., Brazil, Bolivia, Mexico, Peru) and large spatial SOC heterogeneity had lower SOC stocks per unit area and larger uncertainty in their predictions. We highlight that expert opinion is needed to set boundary prediction limits to avoid unrealistically high modeling estimates. For maximizing explained variance while minimizing prediction bias, the selection of predictive algorithms for SOC mapping should consider density of available data and variability of country-specific environmental gradients. This study highlights the large degree of spatial uncertainty in SOC estimates across Latin America. We provide a framework for improving country-specific mapping efforts and reducing current discrepancy of global, regional, and country-specific SOC estimates