7,480 research outputs found
Relativistic tunneling through opaque barriers
We propose an analytical study of relativistic tunneling through opaque
barriers. We obtain a closed formula for the phase time. This formula is in
excellent agreement with the numerical simulations and corrects the standard
formula obtained by the stationary phase method. An important result is found
when the upper limit of the incoming energy distribution coincides with the
upper limit of the tunneling zone. In this case, the phase time is proportional
to the barrier width.Comment: 11 pages, 3 figure
Ultrastructural Alterations in Lepocinclis acus (Euglenophyta) Induced by Medium with High Organic Matter Content
Ultrastructural changes induced by exposure to excess of organic matter were studied in Lepocinclis acus (ex Euglena acus). The cells isolated from the Matanza River, Buenos Aires, Argentina, were grown in soil water medium (SWM). When transferred to medium enriched with Bacteriological Peptone OXOID®, marked body deformation and a significant shortening and widening of the cells was observed. These changes were unexpected in a species with quite rigid cells, a condition previously shown in studies of the pellicle fine structure. Transmission electron microscopy observations suggest that cellular deformation might be facilitated by an increase in strip number, whereas in the original strips normal ultrastructure was maintained. An increase in number and volume of paramylon grains and vacuoles, as well as the presence of membrane whorls in vacuoles was observed. The fine structure of organisms grown in medium with and without organic matter enrichment was compared, and the systematic and ecological importance of morphological changes triggered by cell deformation was discussed.Fil: Conforti, Visitacion Teresa D.. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y BiologĂa Experimental; ArgentinaFil: Ruiz, Laura Beatriz. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y BiologĂa Experimental; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Leonardi, Patricia Ines. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - BahĂa Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentina. Universidad Nacional del Sur. Departamento de BiologĂa, BioquĂmica y Farmacia; Argentin
Facility Location with Spatially Interactive Travel Behavior
This paper sets out a spatially interactive facility location model that specifies client travel behavior according to a "gravity" formula. The well-known uncapacitated facility location model is a limiting case of this model. Analytical partial optimization yields a condensed formulation that can be solved by a nonlinear branch-and-bound approach. Computational results are presented for several problems having as many as 69 potential facility locations
JPIP Proxy Server for Remote Browsing of JPEG2000 Images
The JPEG2000 image compression standard offers scalability features in support of remote browsing applications. In particular Part 9 of the JPEG2000 standard defines a protocol called JPIP for interactivity with JPEG2000 code-streams and files. In client-server application based on JPIP, a client does not directly interact with the compressed file, but formulates requests using a simple syntax which identifies the current ldquoFocus Windowrdquo. In this kind of application particularly useful could be a proxy server, that potentially can improve the performance of the system through a better use of the network infrastructure. The aim of this work is to propose a proxy server with JPIP capabilities and shows the benefits that can be brought to remote browsing applications
CFD Model of a Specific Fire Scenario
Flashover is a complex and potentially very dangerous phenomenon. The NSW Fire Brigade currently conducts training courses in flashover and backdraft using a test cell made from a shipping container where chipboard is set alight in the test cell and the fire is allowed to develop into flashover. As part of a collaborative project with the NSWFB, computational models are being developed to aid in the training procedure. CFD models of the test cell in advancing flashover scenarios, using the code FDS are compared with qualitative experimental data, with good agreement shown for the fire behaviour. Models with different configurations of the test cell were also compared, with particular consideration on the effect on time to flashover and temperature trends
Analysis of different typologies of natural insulation materials with economic and performances evaluation of the same in building
Considering the significant impact that the residential sector has on energy consumption, it is particularly important to implement policies aimed at improving energy efficiency in buildings for saving primary energy, and also to spread the concept of sustainable development through the use of appropriate technology and proper project criteria both for new constructions and for the rehabilitation of existing ones. It is in this context and in an attempt to reduce as much as possible the consumption of resources that fits the possibility of utilizing "natural" materials for the insulation of buildings. In this work they have been analyzed the natural insulation materials present on the Italian building market, where for "natural" it is meant the ones that are derived from renewable materials, which emit no pollutants and that are recyclable or biodegradable. Then it has been created a database which highlights the physical and thermohygrometrical characteristics (density, conductivity, specific heat, vapor permeability, etc.), as well as the possible applications (ceiling, wall, roof). Then it has been carried out a performing and economic comparison related to the replacement of the traditional insulation of a residential building located in Perugia (Central Italy) with the majority of the insulating materials identified in relation to its type of use. The synthetic insulating materials have been replaced in order to reach, for the analysed building, the same thermal performances obtained with the application of traditional insulators. From the analysis of dynamic thermal parameters has been deduced that the building envelope insulated with natural products has better thermal summer performances compared to the same insulated with traditional materials such as XPS, with the same thermal winter performances. This improvement is mainly due to the high value of the specific heat characteristic of the natural insulators. Finally, it has been carried out an economic comparison between the two types of insulation from which it has been possible to deduce that the utilize of natural insulation products have meant an increase in the costs which is widely variable depending on the type of natural insulator used
Preferential attachment in the growth of social networks: the case of Wikipedia
We present an analysis of the statistical properties and growth of the free
on-line encyclopedia Wikipedia. By describing topics by vertices and hyperlinks
between them as edges, we can represent this encyclopedia as a directed graph.
The topological properties of this graph are in close analogy with that of the
World Wide Web, despite the very different growth mechanism. In particular we
measure a scale--invariant distribution of the in-- and out-- degree and we are
able to reproduce these features by means of a simple statistical model. As a
major consequence, Wikipedia growth can be described by local rules such as the
preferential attachment mechanism, though users can act globally on the
network.Comment: 4 pages, 4 figures, revte
Low-complexity motion estimation for the Scalable Video Coding extension of H.264/AVC
The recently standardized Scalable Video Coding(SVC) extension of H.264/AVC allows bitstream scalability with improved rate-distortion efficiency with respect to the classical Simulcasting approach, at the cost of an increased computational complexity of the encoding process. So one critical issue related to practical deployment of SVC is the complexity reduction, fundamental to use it in consumer applications. In this paper, we present a fully scalable fast motion estimation algorithm that enables an excellent complexity performance
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