3,581 research outputs found
On the consistency of universally non-minimally coupled theories
We discuss the consistency of a recently proposed class of theories described
by an arbitrary function of the Ricci scalar, the trace of the energy-momentum
tensor and the contraction of the Ricci tensor with the energy-momentum tensor.
We briefly discuss the limitations of including the energy-momentum tensor in
the action, as it is a non fundamental quantity, but a quantity that should be
derived from the action. The fact that theories containing non-linear
contractions of the Ricci tensor usually leads to the presence of pathologies
associated with higher-order equations of motion will be shown to constrain the
stability of this class of theories. We provide a general framework and show
that the conformal mode for these theories generally has higher-order equations
of motion and that non-minimal couplings to the matter fields usually lead to
higher-order equations of motion. In order to illustrate such limitations we
explicitly study the cases of a canonical scalar field, a K-essence field and a
massive vector field. Whereas for the scalar field cases it is possible to find
healthy theories, for the vector field case the presence of instabilities is
unavoidable.Comment: Minor changes, version published matching Phys. Rev. D 91 (2015)
104003. 15 pages, no figure
Soybean root rot caused by Fusarium oxysporum and Fusarium graminearum: interactions with biotic and abiotic factors
Fusarium oxysporum (Fo) and Fusarium graminearum (Fg) are important components of the Fusarium root rot complex in soybean. Fo is one of the species most frequently associated with soybean root rot, and Fg isolates that colonize wheat and maize have been found to be highly pathogenic on soybean, in the United States. Fo and Fg cause seed decay, damping-off, crown and root rots and pod blight.
The goal of this research was to characterize the biology of Fo and Fg and determine their role as soybean seedling pathogens in the Fusarium root rot complex. The objectives were to: i) assess the phenotypic characteristics of Fo isolates from soybean, including the interaction between Fo isolates and soybean cultivars, growth characteristics in culture, and sensitivity to fungicides, ii) evaluate the effect of pH and temperature on the development of soybean root rot caused by Fo, and iii) determine the impact of soil texture, soil pH and soil water content on seedling disease caused by Fg.
For objective 1, pathogenicity of fourteen Fo isolates was evaluated on eleven soybean cultivars in rolled-towel and petri-dish assays. Our study revealed that cultivars differed in susceptibility to Fo, and there were significant isolate ÃÂÃÂ cultivar interactions. These results suggests that the pattern of resistance or susceptibility for each soybean cultivar differs among isolates. In addition, soybean cultivars differed in susceptibility to Fo, illustrating the variability among Fo isolates from soybean and the potential for their management through cultivar selection.
Fo isolates also differed in radial growth on PDA. Pyraclostrobin and trifloxystrobin effectively reduced conidial germination, and ipconazole effectively reduced fungal growth, but fludioxonil was ineffective against Fo fungal growth. These results illustrate the variability among Fo isolates from soybean and the potential for their management through cultivar selection or seed treatment.
For objective 2, a growth chamber study was performed to assess the effects of pH and temperature on Fo fungal growth and seedling disease. Fo isolates were grown on artificial culture media at four pH levels (4, 5, 6, 7, 8), and incubated at four temperatures (15 20, 25, or 30áµ’C). In a rolled-towel assay, seeds were inoculated with a suspension of a pathogenic or a non-pathogenic Fo isolate. We found that Fo isolates had the greatest radial growth at pH 6 and 25áµ’C, and caused the most severe root rot at pH 6 and 25áµ’C. In addition, a Gaussian model was performed to estimate optimal pH and temperature for fungal growth and disease severity. Optimal conditions estimated using a Gaussian model were pH 6.4 at 27.4 áµ’C for maximal fungal growth, and pH 5.9 at 30áµ’C for maximal root rot severity. These results indicate that optimal pH and temperature conditions for Fo growth are similar to optimal conditions for infection and disease in soybean seedlings, and suggest that Fo may be a more important seedling pathogen when soybeans are planted later, under warm conditions.
For objective 3, we tested the effect of four artificial soil textures (sand, loamy sand, sandy loam and loam), two levels of soil pH (6 and 8), and three levels of soil moisture (permanent wilting point, field capacity and saturation) on root rot of soybean caused by Fg. We found a significant interaction between soil moisture and soil texture for root rot. The greatest severity (~70%) was observed at pH 6 and permanent wilting point in sandy loam soils. In contrast, pot saturation resulted in the lowest levels of disease in sandy loam and loam soils (11.6 and 10.8%, respectively). Percentages of reduction on seedling growth parameters relative to the non-inoculated control, such as root length, foliar area, shoot and root dry weights and root tips were significantly higher in sandy loam soils. In contrast, there were no relative growth reductions in sandy soils. Our results suggest root disease caused by Fg increases in water-stressed plants, resulting in detrimental effects on plant development
Two experiences of tourism policy and governance: Metepec and Toluca
En este artÃculo se contrastan los supuestos teóricos de la gobernanza con la polÃtica turÃstica implementada entre 2014 y 2016 en los municipios de Metepec y Toluca, Estado de México. El análisis muestra que en ambos casos la formación e implementación de dicha polÃtica dista de aquello que la gobernanza plantea respecto a la mayor participación de actores no gubernamentales en la toma de decisiones. El Enfoque de Redes de PolÃtica Pública (ERPP), utilizado como herramienta metodológica, permitió concluir que en esas demarcaciones está arraigado el ejercicio de poder en el actor gubernamental, lo que deja escasas posibilidades de acción a otros sectores que pudieran apoyar una mejor práctica turÃstic
Las dinámicas de dominación capitalista en el espacio rural: la configuración de paisajes turÃsticos
La pérdida de significación económica de las actividades primarias en el ámbito rural mexicano ha venido acompañada de una marcada terciarización de las actividades productivas, el campo ha comenzado a ser vinculado a actividades no agrÃcolas como el turismo que, además de deteriorar los ecosistemas, ha transformado el espacio rural en un tejido denso y tupido de infraestructuras o equipamientos destinados al ofrecimiento de servicios turÃsticos. El objetivo es reflexionar teóricamente sobre la configuración paisajÃstica de los espacios rurales como resultado del proceso de dominación capitalista a través del turismo, lo cual no es más que un proceso histórico conformado por dos dinámicas fundamentales: la apropiación de los espacios y recursos estratégicos para el turismo y, la valorización del espacio
La influencia que ejerce la atención al cliente en la competitividad de las pequeñas y medianas empresas en la ciudad de Matagalpa, durante el año 2010
El tema general para llevar a cabo este trabajo investigativo, radica en la competitividad de las pequeñas y medianas empresas en la ciudad de Matagalpa. Del tema general se desglosa el Sub _ tema: La influencia que ejerce la atención al cliente en la competitividad de las pequeñas y medianas empresas (PYMES) en la ciudad de Matagalpa, durante el año 2010. En la actualidad se vuelve indispensable que las pequeñas y medianas empresas (PYMES) opten por aplicar estrategias, identificar los factores, e implementar principios de atención al cliente como retos de competitividad. Una de las principales metas del presente documento, es analizar el papel importante que juega el aplicar una adecuada atención al cliente y por ende los beneficios que esta genera a cada empresa. En esta investigación se abordan los factores que inciden, estrategias aplicadas y principios que deben implementarse con el objetivo de lograr beneficios y una buena atención al cliente, asà como información de conceptos básicos, importancia, principios, factores y etapas de competitividad, además información general de las PYMES, tomando como referencia los sectores: metal mecánica y comercio de la ciudad de Matagalpa.
Las PYMES evaluadas, implementan de forma inconsciente o no planificada los factores que inciden en la atención al cliente asà como las estrategias y principios. Además han logrado una buena atención al cliente y competitivida
Child Employment, a Controversial Issue; Analysis in Two Touristic Destinations
El empleo de escasa capacitación laboral es una de las caracterÃsticas notorias de la actividad turÃstica en los destinos emergentes e incluso los consolidados. En el caso del empleo infantil, esta situación es fácilmente observable en distintos destinos turÃsticos de México. El objetivo general fue analizar la influencia del turismo hacia el trabajo infantil en Playa del Carmen y Cozumel, dos de los principales destinos turÃsticos de Quintana Roo. Se determinaron los factores que fomentan o inhiben la práctica que atenta contra los derechos de los menores: la imagen turÃstica, lagunas legales, situación de pobreza. Los resultados permitirán diseñar mejores polÃticas públicas para prevenir el trabajo infantil en los destinos turÃsticos. Low-skilled employment is one of the noteworthy features of tourism activity in emerging and sometimes even consolidated destinations. As for child employment, such a situation is widely observed throughout several tourist destinations in Mexico. In this context, the general objective was to analyze the influence of tourism on child labor in Playa del Carmen and Cozumel, the two main tourist destinations in Quintana Roo. The following were determined as factors that foster or inhibit any practice that violates the rights of minors: tourism reputation, legal deficiencies, poverty situation. Outcomes will allow the design of better public policies against child labor in tourist destinations.UAE
El turismo como instrumento de polÃtica ambiental en el Santuario de la Mariposa Monarca El Rosario
La polÃtica ambiental en México se implementó como un mecanismo para frenar el deterioro en áreas naturales como la Reserva de la Biosfera de la Mariposa Monarca, sin embargo, se cuestiona su eficacia debido al continuo deterioro, la pérdida de bosques, la mortandad de la mariposa, y la disminución de mantos freáticos; todo esto acentuado por el turismo masivo. Esto es consecuencia de las dificultades de implementación de la polÃtica ambiental y de los actores que participan en ella. El análisis se realizó bajo el enfoque de Redes de PolÃtica Pública. La principal conclusión es que existe una limitada coordinación interinstitucional y esto dificulta la comunicación y acuerdo entre actores
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