64 research outputs found
Frazil ice formation during the spring flood and its role in transport of sediments to the ice cover
Ratio of the Isolated Photon Cross Sections at \sqrt{s} = 630 and 1800 GeV
The inclusive cross section for production of isolated photons has been
measured in \pbarp collisions at GeV with the \D0 detector at
the Fermilab Tevatron Collider. The photons span a transverse energy ()
range from 7-49 GeV and have pseudorapidity . This measurement is
combined with to previous \D0 result at GeV to form a ratio
of the cross sections. Comparison of next-to-leading order QCD with the
measured cross section at 630 GeV and ratio of cross sections show satisfactory
agreement in most of the range.Comment: 7 pages. Published in Phys. Rev. Lett. 87, 251805, (2001
Search for Kaluza-Klein Graviton Emission in Collisions at TeV using the Missing Energy Signature
We report on a search for direct Kaluza-Klein graviton production in a data
sample of 84 of \ppb collisions at = 1.8 TeV, recorded
by the Collider Detector at Fermilab. We investigate the final state of large
missing transverse energy and one or two high energy jets. We compare the data
with the predictions from a -dimensional Kaluza-Klein scenario in which
gravity becomes strong at the TeV scale. At 95% confidence level (C.L.) for
=2, 4, and 6 we exclude an effective Planck scale below 1.0, 0.77, and 0.71
TeV, respectively.Comment: Submitted to PRL, 7 pages 4 figures/Revision includes 5 figure
Measurement of the average time-integrated mixing probability of b-flavored hadrons produced at the Tevatron
We have measured the number of like-sign (LS) and opposite-sign (OS) lepton
pairs arising from double semileptonic decays of and -hadrons,
pair-produced at the Fermilab Tevatron collider. The data samples were
collected with the Collider Detector at Fermilab (CDF) during the 1992-1995
collider run by triggering on the existence of and candidates
in an event. The observed ratio of LS to OS dileptons leads to a measurement of
the average time-integrated mixing probability of all produced -flavored
hadrons which decay weakly, (stat.)
(syst.), that is significantly larger than the world average .Comment: 47 pages, 10 figures, 15 tables Submitted to Phys. Rev.
Evolutionism and genetics of posttraumatic stress disorder
The authors discuss, from the evolutionary concept, how flight and fight responses and tonic immobility can lead to a new understanding of posttraumatic stress disorder. Through the analysis of symptom clusters (revivals, avoidance and hyperexcitation), neurobiological and evolutionary findings are correlated. The current discoveries on posttraumatic stress disorder genetics are summarized and analyzed in this evolutionary perspective, using concepts to understand the gene-environment interaction, such as epigenetic. The proposal is that the research of susceptibility factors in posttraumatic stress disorder must be investigated from the factorial point of view, where their interactions increase the risk of developing the disorder, preventing a unique search of the cause of this disorder. The research of candidate genes in posttraumatic stress disorder must take into consideration all the systems associated with processes of stress response, such as the hypothalamus-pituitary-adrenal and sympathetic axes, mechanisms of learning, formation and extinguishing of declarative memories, neurogenesis and apoptosis, which involve many systems of neurotransmitters, neuropeptides and neurohormones.Os autores discutem, a partir do conceito evolutivo, como a resposta de estresse, nas suas possibilidades de fuga e luta e de imobilidade tônica, pode levar a uma nova compreensão etiológica do transtorno de estresse pós-traumático. Através da análise dos agrupamentos de sintomas desse diagnóstico - revivência, evitação e hiperexcitação -, procuram correlacionar os achados neurobiológicos e evolutivos. As descobertas atuais sobre a genética do transtorno de estresse pós-traumático são resumidas e colocadas nessa perspectiva evolutiva, dentro de conceitos que possibilitam o entendimento da interação gene/ambiente, como a epigenética. Propõem que a pesquisa dos fatores de risco do transtorno de estresse pós-traumático deva ser investigada do ponto de vista fatorial, onde a somatória destes aumenta o risco de desenvolvimento do quadro, não sendo possível a procura da causa do transtorno de forma única. A pesquisa de genes candidatos no transtorno de estresse pós-traumático deve levar em consideração todos os sistemas associados aos processos de respostas ao estresse, sistemas dos eixos hipotálamo-hipofisário-adrenal e simpático, mecanismos de aprendizado, formação de memórias declarativas, de extinção e esquecimento, da neurogênese e da apoptose, que envolvem vários sistemas de neurotransmissores, neuropeptídeos e neuro-hormônios.Universidade Federal de São Paulo (UNIFESP)(UNIFESP)UNIFESP Departamento de PsiquiatriaUniversidade de São Paulo Faculdade de Medicin Hospital de ClínicasUNIFESP, Depto. de PsiquiatriaSciEL
Smart Swarms of Bacteria-Inspired Agents with Performance Adaptable Interactions
Collective navigation and swarming have been studied in animal groups, such as fish schools, bird flocks, bacteria, and slime molds. Computer modeling has shown that collective behavior of simple agents can result from simple interactions between the agents, which include short range repulsion, intermediate range alignment, and long range attraction. Here we study collective navigation of bacteria-inspired smart agents in complex terrains, with adaptive interactions that depend on performance. More specifically, each agent adjusts its interactions with the other agents according to its local environment – by decreasing the peers' influence while navigating in a beneficial direction, and increasing it otherwise. We show that inclusion of such performance dependent adaptable interactions significantly improves the collective swarming performance, leading to highly efficient navigation, especially in complex terrains. Notably, to afford such adaptable interactions, each modeled agent requires only simple computational capabilities with short-term memory, which can easily be implemented in simple swarming robots
Search for single top quark production at D0 using neural networks
We present a search for electroweak production of single top quarks in ~90 pb^-1 of data collected with the DZero detector at the Fermilab Tevatron collider. Using arrays of neural networks to separate signals from backgrounds, we set upper limits on the cross sections of 17 pb for the s-channel process ppbar->tb+X, and 22 pb for the t-channel process ppbar->tqb+X, both at the 95% confidence level
Differential cross section for W boson production as a function of transverse momentum in proton-antiproton collisions at 1.8 TeV
We report a measurement of the differential cross section for W boson
production as a function of its transverse momentum in proton-antiproton
collisions at sqrt{s} = 1.8 TeV. The data were collected by the D0 experiment
at the Fermilab Tevatron Collider during 1994-1995 and correspond to an
integrated luminosity of 85 pb^{-1}. The results are in good agreement with
quantum chromodynamics over the entire range of transverse momentum.Comment: Accepted by Physics Letters
Measurement of the ratio of differential cross sections for W and Z boson production as a function of transverse momentum in pbar p collisions at sqrt(s)=1.8 TeV
We report on a measurement of the ratio of the differential cross sections
for W and Z boson production as a function of transverse momentum in
proton-antiproton collisions at sqrt(s) = 1.8 TeV. This measurement uses data
recorded by the D0 detector at the Fermilab Tevatron in 1994-1995. It
represents the first investigation of a proposal that ratios between W and Z
observables can be calculated reliably using perturbative QCD, even when the
individual observables are not. Using the ratio of differential cross sections
reduces both experimental and theoretical uncertainties, and can therefore
provide smaller overall uncertainties in the measured mass and width of the W
boson than current methods used at hadron colliders.Comment: 10 pages, 2 figures, to be published in Physics Letters
Search for narrow t(t)over-bar resonances in p(p)over-bar collisions at root s=1.8 TeV
A search for narrow resonances that decay into t (t) over bar pairs has been performed using 130 pb(-1) of data in the lepton + jets channel collected by the DO detector in p (p) over bar collisions at roots=1.8 TeV. There is no significant deviation observed from the standard-model predictions at a top-quark mass of 175 GeV/c(2). We therefore present upper limits at the 95% confidence level on the product of the production cross section and branching fraction to t (t) over bar for narrow resonances as a function of the resonance mass M-X. These limits are used to exclude the existence of a leptophobic top-color particle with mass M-X<560 GeV/c(2), using a theoretical cross section for a width Gamma(X)=0.012M(X)
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