35 research outputs found
Cluster persistence in one-dimensional diffusion--limited cluster--cluster aggregation
The persistence probability, , of a cluster to remain unaggregated is
studied in cluster-cluster aggregation, when the diffusion coefficient of a
cluster depends on its size as . In the mean-field the
problem maps to the survival of three annihilating random walkers with
time-dependent noise correlations. For the motion of persistent
clusters becomes asymptotically irrelevant and the mean-field theory provides a
correct description. For the spatial fluctuations remain relevant
and the persistence probability is overestimated by the random walk theory. The
decay of persistence determines the small size tail of the cluster size
distribution. For the distribution is flat and, surprisingly,
independent of .Comment: 11 pages, 6 figures, RevTeX4, submitted to Phys. Rev.
Survival probability of a diffusing particle in the presence of Poisson-distributed mobile traps
The problem of a diffusing particle moving among diffusing traps is analyzed
in general space dimension d. We consider the case where the traps are
initially randomly distributed in space, with uniform density rho, and derive
upper and lower bounds for the probability Q(t) (averaged over all particle and
trap trajectories) that the particle survives up to time t. We show that, for
1<=d<2, the bounds converge asymptotically to give where and D
is the diffusion constant of the traps, and that for d=2. For d>2 bounds can still be derived, but they no longer
converge for large t. For 1<=d<=2, these asymptotic form are independent of the
diffusion constant of the particle. The results are compared with simulation
results obtained using a new algorithm [V. Mehra and P. Grassberger, Phys. Rev.
E v65 050101 (2002)] which is described in detail. Deviations from the
predicted asymptotic forms are found to be large even for very small values of
Q(t), indicating slowly decaying corrections whose form is consistent with the
bounds. We also present results in d=1 for the case where the trap densities on
either side of the particle are different. For this case we can still obtain
exact bounds but they no longer converge.Comment: 13 pages, RevTeX4, 6 figures. Figures and references updated;
equations corrected; discussion clarifie
Persistence properties of a system of coagulating and annihilating random walkers
We study a d-dimensional system of diffusing particles that on contact either
annihilate with probability 1/(q-1) or coagulate with probability (q-2)/(q-1).
In 1-dimension, the system models the zero temperature Glauber dynamics of
domain walls in the q-state Potts model. We calculate P(m,t), the probability
that a randomly chosen lattice site contains a particle whose ancestors have
undergone exactly (m-1) coagulations. Using perturbative renormalization group
analysis for d < 2, we show that, if the number of coagulations m is much less
than the typical number M(t), then P(m,t) ~ m^(z/d) t^(-theta), with theta=d Q
+ Q(Q-1/2) epsilon + O(epsilon^2), z=(2Q-1) epsilon + (2 Q-1) (Q-1)(1/2+A Q)
epsilon^2 +O(epsilon^3), where Q=(q-1)/q, epsilon =2-d and A =-0.006. M(t) is
shown to scale as t^(d/2-delta), where delta = d (1 -Q)+(Q-1)(Q-1/2) epsilon+
O(epsilon^2). In two dimensions, we show that P(m,t) ~ ln(t)^(Q(3-2Q))
ln(m)^((2Q-1)^2) t^(-2Q) for m << t^(2 Q-1). The 1-dimensional results
corresponding to epsilon=1 are compared with results from Monte Carlo
simulations.Comment: 12 pages, revtex, 5 figure
A pervasive approach to a real-time intelligent decision support system in intensive medicine
The decision on the most appropriate procedure to provide to the
patients the best healthcare possible is a critical and complex task in Intensive
Care Units (ICU). Clinical Decision Support Systems (CDSS) should deal with
huge amounts of data and online monitoring, analyzing numerous parameters
and providing outputs in a short real-time. Although the advances attained in
this area of knowledge new challenges should be taken into account in future
CDSS developments, principally in ICUs environments. The next generation of
CDSS will be pervasive and ubiquitous providing the doctors with the
appropriate services and information in order to support decisions regardless the
time or the local where they are. Consequently new requirements arise namely
the privacy of data and the security in data access. This paper will present a
pervasive perspective of the decision making process in the context of INTCare
system, an intelligent decision support system for intensive medicine. Three
scenarios are explored using data mining models continuously assessed and
optimized. Some preliminary results are depicted and discussed.Fundação para a CiĂȘncia e a Tecnologia (FCT
Genetic loci and prioritization of genes for kidney function decline derived from a meta-analysis of 62 longitudinal genome-wide association studies
Estimated glomerular filtration rate (eGFR) reflects kidney function. Progressive eGFR-decline can lead to kidney failure, necessitating dialysis or transplantation. Hundreds of loci from genome-wide association studies (GWAS) for eGFR help explain population cross section variability. Since the contribution of these or other loci to eGFR-decline remains largely unknown, we derived GWAS for annual eGFR-decline and meta-analyzed 62 longitudinal studies with eGFR assessed twice over time in all 343,339 individuals and in high-risk groups. We also explored different covariate adjustment. Twelve genome-wide significant independent variants for eGFR-decline unadjusted or adjusted for eGFR-baseline (11 novel, one known for this phenotype), including nine variants robustly associated across models were identified. All loci for eGFR-decline were known for cross-sectional eGFR and thus distinguished a subgroup of eGFR loci. Seven of the nine variants showed variant-by-age interaction on eGFR cross section (further about 350,000 individuals), which linked genetic associations for eGFR-decline with age-dependency of genetic cross-section associations. Clinically important were two to four-fold greater genetic effects on eGFR-decline in high-risk subgroups. Five variants associated also with chronic kidney disease progression mapped to genes with functional in-silico evidence (UMOD, SPATA7, GALNTL5, TPPP). An unfavorable versus favorable nine-variant genetic profile showed increased risk odds ratios of 1.35 for kidney failure (95% confidence intervals 1.03-1.77) and 1.27 for acute kidney injury (95% confidence intervals 1.08-1.50) in over 2000 cases each, with matched controls). Thus, we provide a large data resource, genetic loci, and prioritized genes for kidney function decline, which help inform drug development pipelines revealing important insights into the age-dependency of kidney function genetics
Com o diabo no corpo: os terrĂveis papagaios do Brasil colĂŽnia
Desde a Antiguidade, papagaios, periquitos e afins (Psittacidae) fascinaram os europeus por seu vivo colorido e uma notĂĄvel capacidade de interação com seres humanos. A descoberta do Novo Mundo nada faria alĂ©m de acrescentar novos elementos ao trĂĄfico de animais exĂłticos hĂĄ muito estabelecido pelos europeus com a Ăfrica e o Oriente. Sem possuir grandes mamĂferos, a AmĂ©rica tropical participaria desse comĂ©rcio com o que tinha de mais atrativo, essencialmente felinos, primatas e aves - em particular os papagaios, os quais eram embarcados em bom nĂșmero. Contudo, a julgar pelos documentos do Brasil colĂŽnia, esses volĂĄteis podiam inspirar muito pouca simpatia, pois nenhum outro animal - exceto as formigas - foi tantas vezes mencionado como praga para a agricultura. AlĂ©m disso, alguns psitĂĄcidas mostravam-se tĂŁo loquazes que inspiravam a sĂ©ria desconfiança de serem animais demonĂacos ou possessos, pois sĂł trĂȘs classes de entidades - anjos, homens e demĂŽnios - possuĂam o dom da palavra. Nos dias de hoje, vĂĄrios representantes dos Psittacidae ainda constituem uma ameaça para a agricultura, enquanto os indivĂduos muito faladores continuam despertando a suspeita de estarem possuĂdos pelo demĂŽnio. Transcendendo a mera curiosidade, essa crença exemplifica o quĂŁo intrincadas podem ser as relaçÔes do homem com o chamado âmundo naturalâ, revelando um universo mais amplo e multifacetado do que se poderia supor a princĂpio. Nesse sentido, a existĂȘncia de aves capazes de falar torna essa relação ainda mais complexa e evidencia que as dificuldades de estabelecer o limite entre o animal e o humano se estendem alĂ©m dos primatas e envolvem as mais inusitadas espĂ©cies zoolĂłgicas.Since ancient times, parrots and their allies (Psittacidae) have fascinated Europeans by their striking colors and notable ability to interact with human beings. The discovery of the New World added new species to the international exotic animal trade, which for many centuries had brought beasts to Europe from Africa and the Orient. Lacking large mammals, tropical America participated in this trade with its most appealing species, essentially felines, primates and birds - especially parrots - which were shipped in large numbers. It should be noted, however, that at times these birds were not well liked. In fact, according to documents from colonial Brazil, only the ants rank higher than parrots as the animals most often mentioned as agricultural pests. On the other hand, some of these birds were so chatty that people suspected them to be demonic or possessed animals, since only three classes of beings - angels, men and demons - have the ability to speak. Nowadays, several Psittacidae still constitute a threat to agriculture, and the suspicion that extremely talkative birds were demon possessed has also survived. More than a joke or a mere curiosity, this belief exemplifies how intricate manâs relationships with the ânatural worldâ may be. In this sense, the existence of birds that are able to speak adds a further twist to these relationships, demonstrating that the problem of establishing a boundary between the animal and the human does not only involve primates, but also includes some unusual zoological species