3,417 research outputs found
Quasinormal Modes and Stability Criterion of Dilatonic Black Hole in 1+1 and 4+1 Dimensions
We study the stability of black holes that are solutions of the dilaton
gravity derived from string-theoretical models in two and five dimensions
against to scalar field perturbations, using the Quasinormal Modes (QNMs)
approach. In order to find the QNMs corresponding to a black hole geometry, we
consider perturbations described by a massive scalar field non-minimally
coupled to gravity. We find that the QNM's frequencies turn out to be pure
imaginary leading to purely damped modes, that is in agreement with the
literature of dilatonic black holes. Our result exhibits the unstable behavior
of the considered geometry against the scalar perturbations. We consider both
the minimal coupling case, i.e., for which the coupling parameter
vanishes, and the case .Comment: sevarl changes, some reference was added, 10 pages, 4 figure
Non perturbative renormalization group and momentum dependence of n-point functions (II)
In a companion paper (hep-th/0512317), we have presented an approximation
scheme to solve the Non Perturbative Renormalization Group equations that
allows the calculation of the -point functions for arbitrary values of the
external momenta. The method was applied in its leading order to the
calculation of the self-energy of the O() model in the critical regime. The
purpose of the present paper is to extend this study to the next-to-leading
order of the approximation scheme. This involves the calculation of the 4-point
function at leading order, where new features arise, related to the occurrence
of exceptional configurations of momenta in the flow equations. These require a
special treatment, inviting us to improve the straightforward iteration scheme
that we originally proposed. The final result for the self-energy at
next-to-leading order exhibits a remarkable improvement as compared to the
leading order calculation. This is demonstrated by the calculation of the shift
, caused by weak interactions, in the temperature of Bose-Einstein
condensation. This quantity depends on the self-energy at all momentum scales
and can be used as a benchmark of the approximation. The improved
next-to-leading order calculation of the self-energy presented in this paper
leads to excellent agreement with lattice data and is within 4% of the exact
large result.Comment: 35 pages, 11 figure
Indeterminacy, Memory, and Motion in a Simple Granular Packing
We apply two theoretical and two numerical methods to the problem of a disk
placed in a groove and subjected to gravity and a torque. Methods assuming
rigid particles are indeterminate -- certain combinations of forces cannot be
calculated, but only constrained by inequalities. In methods assuming
deformable particles, these combinations of forces are determined by the
history of the packing. Thus indeterminacy in rigid particles becomes memory in
deformable ones. Furthermore, the torque needed to rotate the particle was
calculated. Two different paths to motion were identified. In the first,
contact forces change slowly, and the indeterminacy decreases continuously to
zero, and vanishes precisely at the onset of motion, and the torque needed to
rotate the disk is independent of method and packing history. In the second
way, this torque depends on method and on the history of the packing, and the
forces jump discontinuously at the onset of motion.Comment: 11 pages, 7 figures, submitted to Phys Rev
Non perturbative renormalisation group and momentum dependence of -point functions (I)
We present an approximation scheme to solve the Non Perturbative
Renormalization Group equations and obtain the full momentum dependence of the
-point functions. It is based on an iterative procedure where, in a first
step, an initial ansatz for the -point functions is constructed by solving
approximate flow equations derived from well motivated approximations. These
approximations exploit the derivative expansion and the decoupling of high
momentum modes. The method is applied to the O() model. In leading order,
the self energy is already accurate both in the perturbative and the scaling
regimes. A stringent test is provided by the calculation of the shift in the transition temperature of the weakly repulsive Bose gas, a quantity
which is particularly sensitive to all momentum scales. The leading order
result is in agreement with lattice calculations, albeit with a theoretical
uncertainty of about 25%.Comment: 48 pages, 15 figures A few minor corrections. A reference adde
On the 2-point function of the O(N) model
The self-energy of the critical 3-dimensional O(N) model is calculated. The
analysis is performed in the context of the Non-Perturbative Renormalization
Group, by exploiting an approximation which takes into account contributions of
an infinite number of vertices. A very simple calculation yields the 2-point
function in the whole range of momenta, from the UV Gaussian regime to the
scaling one. Results are in good agreement with best estimates in the
literature for any value of N in all momenta regimes. This encourages the use
of this simple approximation procedure to calculate correlation functions at
finite momenta in other physical situations
Development and validation of the Spanish hazard perception test
Objective: The aim of the current study is to develop and obtain validity evidence for a Hazard Perception test suitable for the Spanish driving population. To obtain validity evidence to support the use of the test, the effect of hazardous and quasi-hazardous situations on the participants’ Hazard Prediction is analysed and the pattern of results of drivers of different driving experience: learner, novice and expert drivers and re-offender vs. non-offender drivers, is compared. Potentially hazardous situations are those that develop without involving any real hazard (i.e., the driver didn’t actually have to decelerate or make any evasive manoeuvre to avoid a potential collision). The current study analysed multiple offender drivers attending compulsory re-education programmes as a result of reaching the maximum number of penalty points on their driving licence, due to repeated violations of traffic laws. Method: A new video-based hazard perception test was developed, using a total of 20 hazardous situation videos plus 8 quasi-hazardous situation videos. They were selected from 167 recordings of natural hazards in real Spanish driving settings
Transport coefficients for dense hard-disk systems
A study of the transport coefficients of a system of elastic hard disks,
based on the use of Helfand-Einstein expressions is reported. The
self-diffusion, the viscosity, and the heat conductivity are examined with
averaging techniques especially appropriate for the use in event-driven
molecular dynamics algorithms with periodic boundary conditions. The density
and size dependence of the results is analyzed, and comparison with the
predictions from Enskog's theory is carried out. In particular, the behavior of
the transport coefficients in the vicinity of the fluid-solid transition is
investigated and a striking power law divergence of the viscosity in this
region is obtained, while all other examined transport coefficients show a drop
in that density range.Comment: submitted to PR
Caracterización quÃmica y cuantificación del rendimiento de extracción de pigmento en siete accesiones mexicanas de Bixa orellana
Achiote (Bixa orellana) is a plant used for obtaining a natural dye rich on carotenoids (mainly bixin and norbixin); it is also the plant species with the highest content of tocotrienols in nature. In the present work, the pigment extraction yield of seven Mexican accessions of Bixa orellana was quantified. Also color parameters and content of tocotrienols, tocopherols, norbixin, bixin, total phenolic compounds and antioxidant capacity were evaluated in the corresponding annatto extracts. The highest percentage of pigment extraction yield was obtained with KOH (4.84%). Accessions 43 (L*= 4.01 ± 0.79, C*= 7.33 ± 1.07, h= 25.76 ± 6.35) and 50 (L*= 3.17 ± 0.64, C*= 6.81 ± 0.53, h= 26.41 ± 4.41) had the lowest color values, meaning these accessions had a darker and redder color. Four accessions showed the highest content of bixin: accession 48 (3.1%), 45 (2.6%) 43 (2.4%) and 47 (2.2%). Accession 50 had showed the highest content of total phenolic compounds and of tocotrienols (T3), mainly the isoform δ-T3 (5.03 ± 0.64 mg g−1 Seed Dry Weight), as well as the highest antioxidant capacity.El achiote (Bixa orellana) es una planta utilizada para obtener un colorante natural rico en carotenoides (principalmente bixina y norbixina); además, es la especie vegetal con el mayor contenido de tocotrienoles. En este trabajo, se determinó el rendimiento de extracción de pigmento de siete accesiones mexicanas de Bixa orellana. También se evaluaron los parámetros de color y el contenido de tocotrienoles, tocoferoles, norbixina, bixina, compuestos fenólicos totales y la capacidad antioxidante en extractos de annato. El mayor porcentaje de rendimiento de extracción de pigmento fue obtenido con KOH (4.847905%). Las accesiones 43 (L*= 4.01 ± 0.79, C*= 7.33 ± 1.07, h= 25.76 ± 6.35) y 50 (L*= 3.17 ± 0.64, C*= 6.81 ± 0.53, h= 26.41 ± 4.41) presentaron los valores más bajos de los párametros de color, lo que significa que estas accesiones tuvieron un color más oscuro y más rojo. Cuatro accesiones mostraron el mayor contenido de bixina: accesión 48 (3.1%), 45 (2.6%) 43 (2.4%) and 47 (2.2%). La accession 50 mostró el mayor contenido de compuestos fenólicos totales y de tocotrienoles (T3), principalmente la isoforma δ-T3 (5.03 ± 0.64 mg g-1 Peso Seco), asà como también la mayor capacidad antioxidante.Fil: Raddatz Mota, D.. Universidad Autónoma Metropolitana; MéxicoFil: Pérez Flores, L. J.. Universidad Autónoma Metropolitana; MéxicoFil: Carrari, Fernando Oscar. Instituto Nacional de TecnologÃa Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de BiotecnologÃa; ArgentinaFil: Insani, Ester Marina. Instituto Nacional de TecnologÃa Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de BiotecnologÃa; ArgentinaFil: Asis, Ramón. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Córdoba. Centro de Investigaciones en BioquÃmica ClÃnica e InmunologÃa; ArgentinaFil: Mendoza Espinoza, J. A.. Universidad Nacional Autónoma de México; MéxicoFil: DÃaz de León Sánchez, F.. Universidad Autónoma Metropolitana; MéxicoFil: Rivera Cabrera, F.. Universidad Autónoma Metropolitana; Méxic
Tumour-marker levels and prognosis in malignant teratoma of the testis
The effect of 6 putative prognostic factors on survival was studied in patients with Stages III and IV malignant teratoma of the testis. Differences between survival curves were tested for statistical significance. A diameter greater than 5 cm in the largest tumour mass, and greater than 8 pulmonary metastases were adverse prognostic factors (P = 0.004 and 0.008 respectively). Patients with malignant teratoma, trophoblastic, fared worse than those with malignant teratoma, undifferentiated, and malignant teratoma, intermediate (P = 0.011 and 0.023 respectively). Previous chemotherapy or radiotherapy had no significant effect. Serum alpha-foetoprotein (AFP) above 10(3) MRC u/ml and serum beta subunit of human chorionic gonadotrophin (hCG) above 10(5) miu/ml, were found to predict a poor prognosis (P = 0.010 and 0.001 respectively). A combination of measurements of the tumour markers gave the most consistent indication of prognosis, in that patients with either AFP greater than 10(3) MRC u/ml or hCG greater than 10(5) miu/ml, or both, fared much worse than those with neither factor (P = 0.001). Serum concentrations of AFP and hCG should be stated in reports of treatment of testicular teratoma in order to provide a basis for comparison with other series. Regular and frequent measurements of these markers are appropriate throughout the clinical management of patients with malignant teratoma
Tourist spaces and tourism policy in Spain and Portugal
Advances in Cultura, Tourism and Hospitality Research;10, 235-249This study analyses the relationship between the development of the tourism policy of Spain and Portugal and their effects on regional imbalances. Despite the proximity of the two countries and their specialisation in tourism, there are few comparative studies on tourism of the two Iberian countries. The study focuses on the two major phases of tourism policy: the period of mass tourism and post-Fordist stage. In the conclusions we refer the debate on the existence of a model of development based on tourism to the Latin countries of Southern Europe and we note the export process of the Spanish low-cost tourism model to other countries.Financiado por el Gobierno de España, Programa Fundamental de Investigación, Proyecto de I+D (CSO2012-30840) "GeografÃas de la crisis: análisis de los territorios urbanos y turÃsticos de las Islas Baleares, Costa del Sol y principales destinos del Caribe y América Central"
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