18,815 research outputs found
Quantum evolution of scalar fields in Robertson-Walker space-time
We study the field theory in a flat Robertson-Walker
space-time using the functional Sch\"odinger picture. We introduce a simple
Gaussian approximation to analyze the time evolution of pure states and we
establish the renormalizability of the approximation. We also show that the
energy-momentum tensor in this approximation is finite once we consider the
usual mass and coupling constant renormalizations.Comment: Revtex file, 19 pages, no figures. Compressed ps version available at
http://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-912.ps.Z or at
ftp://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-912.ps.
Phases of granular segregation in a binary mixture
We present results from an extensive experimental investigation into granular
segregation of a shallow binary mixture in which particles are driven by
frictional interactions with the surface of a vibrating horizontal tray. Three
distinct phases of the mixture are established viz; binary gas (unsegregated),
segregation liquid and segregation crystal. Their ranges of existence are
mapped out as a function of the system's primary control parameters using a
number of measures based on Voronoi tessellation. We study the associated
transitions and show that segregation can be suppressed is the total filling
fraction of the granular layer, , is decreased below a critical value,
, or if the dimensionless acceleration of the driving, , is
increased above a value .Comment: 12 pages, 12 figures, submitted to Phys. Rev.
Locally perceived hard global constraints in multi-agenty schedulling
We propose how to model enterprise facilities (like factories, warehouses, etc.) in a multi-product production/distribution network, capacity management at those facilities, and scheduling agents which act as enterprise managers, taking decisions that affect the available capacity. A coordination mechanism through which scheduling agents can locally perceive hard global temporal constraints is also proposed
A Hamiltonian approach for explosive percolation
We introduce a cluster growth process that provides a clear connection
between equilibrium statistical mechanics and an explosive percolation model
similar to the one recently proposed by Achlioptas et al. [Science 323, 1453
(2009)]. We show that the following two ingredients are essential for obtaining
an abrupt (first-order) transition in the fraction of the system occupied by
the largest cluster: (i) the size of all growing clusters should be kept
approximately the same, and (ii) the inclusion of merging bonds (i.e., bonds
connecting vertices in different clusters) should dominate with respect to the
redundant bonds (i.e., bonds connecting vertices in the same cluster).
Moreover, in the extreme limit where only merging bonds are present, a complete
enumeration scheme based on tree-like graphs can be used to obtain an exact
solution of our model that displays a first-order transition. Finally, the
proposed mechanism can be viewed as a generalization of standard percolation
that discloses an entirely new family of models with potential application in
growth and fragmentation processes of real network systems.Comment: 4 pages, 4 figure
Marine polysaccharide multilayers: PH responsive systems for the surface modification of tissue engineering scaffolds
[Excerpt] The success of some polymeric scaffolds for Tissue Engineering is hindered by its surface chemistry, which in many cases leads to a significant foreign body response. To overcome this, the present project intend to explore a strategy of surface modification through electrostatic self-assembly, first reported in the 1990s, by the construction of multilayered systems by assembling a polycation and a polyanion in an alternate fashion. [...]info:eu-repo/semantics/publishedVersio
Simulations of Time-Resolved X-Ray Diffraction in Laue Geometry
A method of computer simulation of Time-Resolved X-ray Diffraction (TRXD) in
asymmetric Laue (transmission) geometry with an arbitrary propagating strain
perpendicular to the crystal surface is presented. We present two case studies
for possible strain generation by short-pulse laser irradiation: (i) a
thermoelastic-like analytic model; (ii) a numerical model including effects of
electron-hole diffusion, Auger recombination, deformation potential and thermal
diffusion. A comparison with recent experimental results is also presented.Comment: 9 pages, 11 figure
A sociodemographic and neuropsychological characterization of an illiterate population
The objectives of this article are to characterize the performance and to discuss the performance differences between literate and illiterate participants in a well-defined study population. We describe the participant-selection procedure used to investigate this population. Three groups with similar sociocultural backgrounds living in a relatively homogeneous fishing community in southern Portugal were characterized in terms of socioeconomic and sociocultural background variables and compared on a simple neuropsychological test battery; specifically, a literate group with more than 4 years of education (n = 9), a literate group with 4 years of education (n = 26), and an illiterate group (n = 31) were included in this study. We compare and discuss our results with other similar studies on the effects of literacy and illiteracy. The results indicate that naming and identification of real objects, verbal fluency using ecologically relevant semantic criteria, verbal memory, and orientation are not affected by literacy or level of formal education. In contrast, verbal working memory assessed with digit span, verbal abstraction, long-term semantic memory, and calculation (i.e., multiplication) are significantly affected by the level of literacy. We indicate that it is possible, with proper participant-selection procedures, to exclude general cognitive impairment and to control important sociocultural factors that potentially could introduce bias when studying the specific effects of literacy and level of formal education on cognitive brain function
Sistema de cultivo para cevada. III. Efeitos de algumas culturas de inverno sobre o rendimento de grãos da soja e da ervilhaca sobre o rendimento de grãos de milho, em plantio direto, no perÃodo de 1986/1987 a 1988/1989.
bitstream/item/133650/1/ID12384-1988-1989sojaresultados-p54-61.pdfTrabalho apresentado na XVII Reunião de Pesquisa de Soja da Região Sul, Porto Alegre, 1989
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