14 research outputs found
A proof of the Geroch-Horowitz-Penrose formulation of the strong cosmic censor conjecture motivated by computability theory
In this paper we present a proof of a mathematical version of the strong
cosmic censor conjecture attributed to Geroch-Horowitz and Penrose but
formulated explicitly by Wald. The proof is based on the existence of
future-inextendible causal curves in causal pasts of events on the future
Cauchy horizon in a non-globally hyperbolic space-time. By examining explicit
non-globally hyperbolic space-times we find that in case of several physically
relevant solutions these future-inextendible curves have in fact infinite
length. This way we recognize a close relationship between asymptotically flat
or anti-de Sitter, physically relevant extendible space-times and the so-called
Malament-Hogarth space-times which play a central role in recent investigations
in the theory of "gravitational computers". This motivates us to exhibit a more
sharp, more geometric formulation of the strong cosmic censor conjecture,
namely "all physically relevant, asymptotically flat or anti-de Sitter but
non-globally hyperbolic space-times are Malament-Hogarth ones".
Our observations may indicate a natural but hidden connection between the
strong cosmic censorship scenario and the Church-Turing thesis revealing an
unexpected conceptual depth beneath both conjectures.Comment: 16pp, LaTeX, no figures. Final published versio
Ecological Invasion, Roughened Fronts, and a Competitor's Extreme Advance: Integrating Stochastic Spatial-Growth Models
Both community ecology and conservation biology seek further understanding of
factors governing the advance of an invasive species. We model biological
invasion as an individual-based, stochastic process on a two-dimensional
landscape. An ecologically superior invader and a resident species compete for
space preemptively. Our general model includes the basic contact process and a
variant of the Eden model as special cases. We employ the concept of a
"roughened" front to quantify effects of discreteness and stochasticity on
invasion; we emphasize the probability distribution of the front-runner's
relative position. That is, we analyze the location of the most advanced
invader as the extreme deviation about the front's mean position. We find that
a class of models with different assumptions about neighborhood interactions
exhibit universal characteristics. That is, key features of the invasion
dynamics span a class of models, independently of locally detailed demographic
rules. Our results integrate theories of invasive spatial growth and generate
novel hypotheses linking habitat or landscape size (length of the invading
front) to invasion velocity, and to the relative position of the most advanced
invader.Comment: The original publication is available at
www.springerlink.com/content/8528v8563r7u2742
Caracterização eletroforética e análise de subgrupo de rotavírus em rebanhos bovinos leiteiros do Estado de São Paulo
Foi realizado um estudo para determinar a ocorrência de infecção por rotavírus em rebanhos bovinos leiteiros. Foram analisadas 375 amostras de fezes de bezerros, na faixa etária 1 a 45 dias, provenientes de animais pertencentes a nove propriedades rurais, situadas em seis municípios da região nordeste do Estado de São Paulo. Destas, 193 pertenciam a animais com diarréia e 182 foram obtidas de animais clinicamente sadios. As técnicas utilizadas para a detecção de rotavírus foram o ensaio imunoenzimático (EIE) e a eletroforese em gel de poliacrilamida (EGPA). Por meio do EIE foram detectadas 11,2% (42/375) de amostras positivas, 15% delas (29/193) obtidas de animais com diarréia e 7,1% (13/182) colhidas de animais sem diarréia. A análise do perfil do genoma indicou a presença de seis eletroferótipos distintos, característicos de rotavírus do grupo A. Um único eletroferótipo foi detectado em três rebanhos, o qual permaneceu constante durante o período de amostragem. em dois rebanhos diferentes eletroferótipos foram detectados, embora com maior prevalência de um dado perfil. A caracterização das amostras positivas em subgrupos foi realizada por meio do EIE com duplo sanduíche, utilizando-se anticorpos monoclonais (MAb) específicos para antígenos de subgrupo (I e II). Foram caracterizadas como subgrupo I 52,4% (22/42) das amostras testadas, nenhuma reagiu com MAb de subgrupo II, enquanto as demais, 47,6% (20/42), não reagiram com nenhum dos dois subgrupos.A study was accomplished to determine the occurrence of rotavirus in feces of calves, in the State of São Paulo, Brazil. A total of 375 samples of feces from calves 1 to 45 day-old were collected. The animals belonged to farms situated in six counties of the northeast region of the State. One hundred and ninety tree out of these samples belonged to animals with a clinical picture of diarrhea and 182 were obtained from clinically healthy animals. The techniques used for the detection of rotavirus were the enzyme immunoassay (EIA) and the polyacrilamide gel electrophoresis (PAGE). By the use of EIA, 11.2% (42/375) of the samples were positive for rotavirus. Among the samples of diarrheic calves, 15% (29/193) were found to be positive for rotavirus, whereas 7.1 (13/182) positive samples were obtained from clinically healthy animals. The PAGE test presented a lower sensitivity than EIA, since from the 42 positive samples in EIA, only 36 presented an electrophoretical profile characteristic of rotavirus. The genome analysis indicated the presence of six distinct electrophoretical types characteristic of group A rotavirus. A unique electropherotype was detected in tree farms, which remained constant during the sampling period. In two farms a second electropherotype was detected. The serological characterization of the positive samples in subgroups was accomplished through EIA with double sandwich, utilizing monoclonal antibodies ( I and II). Twenty two group A rotavirus strains I (52.4%, 22/42) reacted with MAb of subgroup I, none to subgroup II, and the remaining 47.6% (20/42) did not react with the two subgroups