246 research outputs found
French Parliamentary Documents
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Collapse dynamics of trapped Bose-Einstein condensates
We analyze the implosion and subsequent explosion of a trapped condensate
after the scattering length is switched to a negative value. Our results
compare very well qualitatively and fairly well quantitatively with the results
of recent experiments at JILA.Comment: 4 pages, 3 figure
Fluid models of congestion collapse in overloaded switched networks
We consider a switched network (i.e. a queueing network in which there are constraints on which queues may be served simultaneously), in a state of overload. We analyse the behaviour of two scheduling algorithms for multihop switched networks: a generalized version of max-weight, and the α-fair policy. We show that queue sizes grow linearly with time, under either algorithm, and we characterize the growth rates. We use this characterization to demonstrate examples of congestion
collapse, i.e. cases in which throughput drops as the switched network becomes more overloaded.We further show that the loss of throughput can be made arbitrarily small by the max-weight algorithm with weight function f (q) = q[superscript α] as α→0.National Science Foundation (U.S.) (Career CNS-0546590
Pulsar-wind nebulae and magnetar outflows: observations at radio, X-ray, and gamma-ray wavelengths
We review observations of several classes of neutron-star-powered outflows:
pulsar-wind nebulae (PWNe) inside shell supernova remnants (SNRs), PWNe
interacting directly with interstellar medium (ISM), and magnetar-powered
outflows. We describe radio, X-ray, and gamma-ray observations of PWNe,
focusing first on integrated spectral-energy distributions (SEDs) and global
spectral properties. High-resolution X-ray imaging of PWNe shows a bewildering
array of morphologies, with jets, trails, and other structures. Several of the
23 so far identified magnetars show evidence for continuous or sporadic
emission of material, sometimes associated with giant flares, and a few
possible "magnetar-wind nebulae" have been recently identified.Comment: 61 pages, 44 figures (reduced in quality for size reasons). Published
in Space Science Reviews, "Jets and Winds in Pulsar Wind Nebulae, Gamma-ray
Bursts and Blazars: Physics of Extreme Energy Release
Longevidade de sementes de camu-camu submetidas a diferentes ambientes e formas de conservação
O camu-camu (Myrciaria dubia (H.B.K.) McVaugh) produz fruto com grande potencial para extração de ácido ascórbico, que apresenta relevante importância econômica e social, com inúmeras aplicações industriais. O objetivo deste trabalho foi avaliar o efeito de diferentes formas de conservação e ambientes de armazenamento, sobre a manutenção da viabilidade das sementes. O delineamento experimental inteiramente casualizado, utilizando parcelas subsubdivididas, onde os fatores foram: ambiente de armazenamento (ao ar livre, em água, em câmara a 5 e a 10 ºC), forma de conservação (sementes com polpa - CP, sementes sem polpa - SP e sementes lavadas e tratadas - LT) e perÃodo de armazenamento (0; 2; 4 e 6 meses). O critério de avaliação adotado foi a protrusão da raiz primária. As sementes armazenadas em água, nas formas SP e LT, apresentaram germinação maior que 90%. As sementes nas formas CP e LT, armazenadas a 5 e a 10 ºC, tiveram germinação acima de 89%. O armazenamento em água e ao ar livre não afetou a germinação, podendo as sementes serem armazenadas durante o perÃodo de seis e quatro meses, respectivamente. As sementes CP, armazenadas em água, tiveram menor tempo médio para germinação. O Ãndice de velocidade de germinação aumentou com o perÃodo de armazenamento e foi maior nas sementes armazenadas na água em todos os perÃodos. As sementes com polpa apresentaram menor Ãndice de velocidade de germinação em todo o perÃodo de armazenamento avaliado
High-time Resolution Astrophysics and Pulsars
The discovery of pulsars in 1968 heralded an era where the temporal
characteristics of detectors had to be reassessed. Up to this point detector
integration times would normally be measured in minutes rather seconds and
definitely not on sub-second time scales. At the start of the 21st century
pulsar observations are still pushing the limits of detector telescope
capabilities. Flux variations on times scales less than 1 nsec have been
observed during giant radio pulses. Pulsar studies over the next 10 to 20 years
will require instruments with time resolutions down to microseconds and below,
high-quantum quantum efficiency, reasonable energy resolution and sensitive to
circular and linear polarisation of stochastic signals. This chapter is review
of temporally resolved optical observations of pulsars. It concludes with
estimates of the observability of pulsars with both existing telescopes and
into the ELT era.Comment: Review; 21 pages, 5 figures, 86 references. Book chapter to appear
in: D.Phelan, O.Ryan & A.Shearer, eds.: High Time Resolution Astrophysics
(Astrophysics and Space Science Library, Springer, 2007). The original
publication will be available at http://www.springerlink.co
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