789 research outputs found

    Aharonov-Bohm effect for an exciton in a finite width nano-ring

    Get PDF
    We study the Aharonov-Bohm effect for an exciton on a nano-ring using a 2D attractive fermionic Hubbard model. We extend previous results obtained for a 1D ring in which only azimuthal motion is considered, to a more general case of 2D annular lattices. In general, we show that the existence of the localization effect, increased by the nonlinearity, makes the phenomenon in the 2D system similar to the 1D case. However, the introduction of radial motion introduces extra frequencies, different from the original isolated frequency corresponding to the excitonic Aharonov- Bohm oscillations. If the circumference of the system becomes large enough, the Aharonov-Bohm effect is suppressed

    The relationship between Mathematical Utility Theory and the Integrability Problem: some arguments in favour

    Get PDF
    The resort to utility-theoretical issues will permit us to propose a constructive procedure for deriving a homogeneous of degree one, continuous function that gives raise to a primitive demand function under suitably mild conditions. This constitutes the first elementary proof of a necessary and sufficient condition for an integrability problem to have a solution by continuous (subjective utility) functions. Such achievement reinforces the relevance of a technique that was succesfully formalized in Alcantud and Rodríguez-Palmero (2001). The analysis of these two works exposes deep relationships between two apparently separate fields: mathematical utility theory and the revealed preference approach to the integrability problem.Strong Axiom of Homothetic Revelation; revealed preference; continuous homogeneous of degree one utility; integrability of demand.

    Existence and uniqueness of solutions to the Bellman equation in the unbounded case

    Get PDF
    We study the problem of the existence and uniqueness of solutions to the Bellman equation in the presence of unbounded returns. We introduce a new approach based both on consideration of a metric on the space of all continuous functions over the state space, and on the application of some metric fixed point theorems. With appropriate conditions we prove uniqueness of solutions with respect to the whole space of continuous functions. Furthermore, the paper provides new sufficient conditions for the existence of solutions that can be applied to fairly general models. It is also proven that the fixed point coincides with the value function and that it can be approached by successive iterations of the Bellman operator.The research of J. P. Rincón-Zapatero was supported by Project VA108/01 of Junta de Castilla y León and Project BFM2002–00425 (FEDER) of Ministerio de Ciencia y Tecnología, Spain. C. Rodríguez-Palmero gratefully acknowledges financial support from Junta de Castilla y León, Project VA31/01.Publicad

    Mathematical utility theory and the representability of demand by continuous homogeneous functions

    Get PDF
    The resort to utility-theoretical issues will permit us to propose a constructive procedure for deriving a homogeneous of degree one continuous function that gives raise to a primitive demand function under suitably mild conditions. This constitutes the first self-contained and elementary proof of a necessary and sufficient condition for an integrability problem to have a solution by continuous (subjective utility) functions

    Magnetic behavior of NiCu nanowire arrays: Compositional, geometry and temperature dependence

    Get PDF
    Arrays of Ni100-xCux nanowires ranging in composition 0¿=¿x¿=¿75, diameter from 35 to 80¿nm, and length from 150¿nm to 28¿µm have been fabricated by electrochemical co-deposition of Ni and Cu into self-ordered anodic aluminum oxide membranes. As determined by X-ray diffraction and Transmission Electron Microscopy, the crystalline structure shows fcc cubic symmetry with [111] preferred texture and preferential Ni or Cu lattice depending on the composition. Their magnetic properties such as coercivity and squareness have been determined as a function of composition and geometry in a Vibrating Sample Magnetometer in the temperature range from 10 to 290¿K for applied magnetic fields parallel and perpendicular to the nanowires axis. Addition of Cu into the NiCu alloy up to 50% enhances both parallel coercivity and squareness. For the higher Cu content, these properties decrease and the magnetization easy axis becomes oriented perpendicular to the wires. In addition, coercivity and squareness increase by decreasing the diameter of nanowires which is ascribed to the increase of shape anisotropy. The temperature dependent measurements reflect a complex behavior of the magnetic anisotropy as a result of energy contributions with different evolution with temperature

    Microwave sintering of dense and lattice 3Y-TZP samples shaped by digital light processing

    Get PDF
    Nowadays it is possible to produce ceramic parts with solid and complex shapes with rapid and efficient shaping and sintering techniques. In this paper, 3mol% yttria stabilized zirconia (3Y-TZP) dense and lattice parts were shaped by Digital light processing method (DLP) and densified by conventional (CV) and microwave (MW) sintering. 3Y-TZP samples were MW sintered up to 1550 °C with different heating rates (10, 30, and 50 °C/min) for the dense samples and 30 °C/min for the lattice samples. Controlled thermal cycles with a homogenous heating and no thermal runaway was reached. CV sintering was carried out at 10 °C/min up to 1550 °C. No inter-layer delamination was detected after sintering by the two methods. Both dense and lattice MW-sintered samples reached high final densities (equivalent to obtained values with CV-sintered samples, i.e., ≥98% T.D.), but exhibited a lower average grain size than CV-sintered materials. The different architectures between dense and lattice samples resulted in a different specific absorbed power: the power absorbed by the dense sample is lower than that absorbed by the lattice one meaning that this sample architecture heats up easily

    Fungal microbiota from rain water and pathogenicity of Fusarium species isolated from atmospheric dust and rainfall dust

    Get PDF
    In order to determine the presence of Fusarium spp. in atmospheric dust and rainfall dust, samples were collected during September 2007, and July, August, and October 2008. The results reveal the prevalence of airborne Fusarium species coming from the atmosphere of the South East coast of Spain. Five different Fusarium species were isolated from the settling dust: Fusarium oxysporum, F. solani, F. equiseti, F. dimerum, and F. proliferatum. Moreover, rainwater samples were obtained during significant rainfall events in January and February 2009. Using the dilution-plate method, 12 fungal genera were identified from these rainwater samples. Specific analyses of the rainwater revealed the presence of three species of Fusarium: F. oxysporum, F. proliferatum and F. equiseti. A total of 57 isolates of Fusarium spp. obtained from both rainwater and atmospheric rainfall dust sampling were inoculated onto melon (Cucumis melo L.) cv. Piñonet and tomato (Lycopersicon esculentum Mill.) cv. San Pedro. These species were chosen because they are the main herbaceous crops in Almeria province. The results presented in this work indicate strongly that spores or propagules of Fusarium are able to cross the continental barrier carried by winds from the Sahara (Africa) to crop or coastal lands in Europe. Results show differences in the pathogenicity of the isolates tested. Both hosts showed root rot when inoculated with different species of Fusarium, although fresh weight measurements did not bring any information about the pathogenicity. The findings presented above are strong indications that long-distance transmission of Fusarium propagules may occur. Diseases caused by species of Fusarium are common in these areas. They were in the past, and are still today, a problem for greenhouses crops in Almería, and many species have been listed as pathogens on agricultural crops in this region. Saharan air masses dominate the Mediterranean regions. The evidence of long distance dispersal of Fusarium spp. by atmospheric dust and rainwater together with their proved pathogenicity must be taken into account in epidemiological studies

    METÁFORAS DEL VIAJE EN LA NOVELA LATINOAMERICANA DEL SIGLO XX: EL ARPA Y LA SOMBRA DE ALEJO CARPENTIER

    Get PDF
    Cuando Roland Barthes afirma que la historia de un novelista es la historia de  un  tema  y  sus  variaciones,  nos  da  una  clave  significativa  para  entender  la praxis artística de Alejo Carpentier. En la monumental obra del novelista cubano el viaje es uno de esos grandes temas. La recurrencia de este tópico en la obra del escritor cubano es expresiva de un singular entendimiento del hombre y sus coordenadas históricas, sin desconocer que toda reflexión sobre América en la obra de Carpentier transita necesariamente por la estetización de este cronotopo. Estudio en este ensayo la presencia del viaje en El arpa y la sombra (1979), obra que cierra todo un gran proyecto narrativo y en la que vuelve al tópico del viaje, esta vez asociado al tema de los orígenes de nuestra historia, de nuestra cultura y de nuestra escritura

    DISCURSOS DA MEMÓRIA NA LITERATURA DA DIÁSPORA CUBANA NOS ESTADOS UNIDOS

    Get PDF
    Neste estudo apresento alguns pressupostos para pensar as relações entre diáspora e memoria, discutindo a singularidade de um conjunto de textos pertencentes ao universo da literatura cubano-americana, cuja temática central e formas discursivas privilegiadas estão vinculadas à estetização de uma memoria diaspórica.Palavras -chave: Diáspora. Memória. Literatura cubano-americanaResumen En este estúdio presento algunos presupuestos para pensar las relaciones entre diáspora y memoria, discutiendo la singularidad de un conjunto de textos pertenecientes al universo de la literatura cubano- americana, cuya temática central y formas discursivas privilegiadas están vinculadas a la estetización de una memoria diaspórica.Palabras claves: Diáspora. Memoria. Literatura cubano-americanaAbstract In this paper I discuss some assumptions for approaching the relations between diaspora and memory, while discussing the singularity of a group of texts that belong to the realm of Cuban-American literature, and share a central theme and privileged discursive forms that are connected to the aesthetization of diasporic memory.Keywords: Diaspora. Memory. Cuban-American literatur
    corecore