4,299 research outputs found
The s-process branching at 185W
The neutron capture cross section of the unstable nucleus 185W has been
derived from experimental photoactivation data of the inverse reaction
186W(gamma,n)185W. The new result of sigma = (687 +- 110) mbarn confirms the
theoretically predicted neutron capture cross section of 185W of sigma = 700
mbarn at kT = 30 keV. A neutron density in the classical s-process of n_n =
(3.8 +0.9 -0.8} * 1e8 cm-3 is derived from the new data for the 185W branching.
In a stellar s-process model one finds a significant overproduction of the
residual s-only nucleus 186Os.Comment: ApJ, in pres
The role of body rotation in bacterial flagellar bundling
In bacterial chemotaxis, E. coli cells drift up chemical gradients by a
series of runs and tumbles. Runs are periods of directed swimming, and tumbles
are abrupt changes in swimming direction. Near the beginning of each run, the
rotating helical flagellar filaments which propel the cell form a bundle. Using
resistive-force theory, we show that the counter-rotation of the cell body
necessary for torque balance is sufficient to wrap the filaments into a bundle,
even in the absence of the swirling flows produced by each individual filament
A Rotating, Inhomogeneous Dust Interior for the BTZ Black Hole
We present exact solutions describing rotating, inhomogeneous dust with
generic initial data in 2+1 dimensional AdS spacetime and show how they are
smoothly matched to the Banados-Teitelboim-Zanelli (BTZ) solution in the
exterior. The metrics, which are the rotational analogues of the 2+1
dimensional LeMaitre-Tolman-Bondi (LTB) family, are described by their angular
momentum and one additional constant which, together with the angular momentum,
determines the energy density of the dust cloud. The weak energy condition
gives a constraint on the angular momentum profile inside the cloud. Solutions
can be stationary or time dependent, but only the time dependent solutions can
be matched consistently to a BTZ exterior. No singularity is formed in either
the stationary or the time dependent cases.Comment: 16 pages, no figure
Forestry restoration in abandoned pastures of Urochloa by different sizes of brushwood.
A galharia é um método de complexação ambiental, que consiste no aproveitamento de resíduos vegetais. Esse método, quando bem estabelecido tecnicamente, pode exercer influência sobre a qualidade da cama de sementes, favorecendo o estabelecimento de plantas nativas e a restauração do ecossistema. Dessa forma, objetivou-se avaliar a eficiência de galharia para a indução da regeneração natural de espécies nativas em área coberta por gramíneas exóticas inibidoras do gênero Urochloa, bem como verificar o tamanho mínimo necessário para conter a reinvasão das forrageiras. Como hipótese, adotou-se a largura mínima de 4 m como suficiente para o estabelecimento da regeneração natural, antes da reocupação das forrageiras. O experimento foi conduzido entre maio 2014 e maio 2016 em Morretes-PR, na Floresta Ombrófila Densa de Terras Baixas. Foram implantados sete tamanhos de galharia: 6 x 1, 6 x 2, 6 x 3, 6 x 4, 6 x 5, 6 x 6 m e testemunha. As espécies lenhosas foram identificadas e contadas e a porcentagem de cobertura herbácea estimada após 4, 8, 12, 18 e 24 meses. Não se verificou retomada da sucessão natural por espécies nativas. Independentemente do tamanho, a galharia foi ineficiente para conter a reinvasão pelas gramíneas a partir das bordas das parcelas e, como pilha de resíduos, dificultou o estabelecimento de espécies lenhosas. Para a criação de safe sites e consequente restauração via regeneração natural, faz-se necessária a eliminação local das forrageiras Urochloa, sem a qual espécies nativas terão pouca probabilidade de sobreviver
Price Discovery and the Accuracy of Consolidated Data Feeds in the U.S. Equity Markets
Both the scientific community and the popular press have paid much attention
to the speed of the Securities Information Processor, the data feed
consolidating all trades and quotes across the US stock market. Rather than the
speed of the Securities Information Processor, or SIP, we focus here on its
accuracy. Relying on Trade and Quote data, we provide various measures of SIP
latency relative to high-speed data feeds between exchanges, known as direct
feeds. We use first differences to highlight not only the divergence between
the direct feeds and the SIP, but also the fundamental inaccuracy of the SIP.
We find that as many as 60 percent or more of trades are reported out of
sequence for stocks with high trade volume, therefore skewing simple measures
such as returns. While not yet definitive, this analysis supports our
preliminary conclusion that the underlying infrastructure of the SIP is
currently unable to keep pace with the trading activity in today's stock
market.Comment: 18 pages, 20 figures, 2 table
Testing T Invariance in the Interaction of Slow Neutrons with Aligned Nuclei
The study of five-fold (P even, T odd) correlation in the interaction of slow
polarized neutrons with aligned nuclei is a possible way of testing the time
reversal invariance due to the expected enhancement of T violating effects in
compound resonances. Possible nuclear targets are discussed which can be
aligned both dynamically as well as by the "brute force" method at low
temperature. A statistical estimation is performed of the five-fold correlation
for low lying p wave compound resonances of the Sb, Sb and
I nuclei. It is shown that a significant improvement can be achieved
for the bound on the intensity of the fundamental parity conserving time
violating (PCTV) interaction.Comment: 22 pages, 5 figures, published versio
Recommended from our members
High-resolution neutron capture and transmission measurements and the stellar neutron capture cross sections of {sup 116,120}Sn
Improved astrophysical reaction rates for {sup 116,120}Sn(n, {gamma}) are of interest because nucleosynthesis models have not been able to reproduce the observed abundances in this mass region. For example, previous s-process calculations have consistently underproduced the s-only isotope {sup 116}Sn. Also, these studies have resulted in residual reprocess abundances for the tin isotopes which are systematically larger than predicted by reprocess calculations. It has been suggested that these problems could be solved by reducing the solar tin abundance by 10-20%, but there is no experimental evidence to justify this renormalization. Instead, it is possible that the problem lies in the (n,T) cross sections used in the reaction network calculations or in the s-process models. One reason to suspect the (n, {gamma}) data is that previous measurements did not extend to low enough energies to determine accurately the Maxwellian-averaged capture cross sections at the low temperatures (kT=6-8 keV) favored by the most recent stellar models of the s process. Also, the two most recent high-precision measurements of the {sup 120}Sn(n, {gamma}) cross section are in serious disagreement. Because of its small size, this cross section could affect (via the s-process branching at {sup 121}Sn) the relative abundances of the three s-only isotopes of Te
Neutron-skin thickness of Pb, and symmetry-energy constraints from the study of the anti-analog giant dipole resonance
The Pb(,) Pb reaction at a beam energy of
30 MeV has been used to excite the anti-analog of the giant dipole resonance
(AGDR) and to measure its -decay to the isobaric analog state in
coincidence with proton decay of IAS. The energy of the transition has also
been calculated with the self-consistent relativistic random-phase
approximation (RRPA), and found to be linearly correlated to the predicted
value of the neutron-skin thickness (). By comparing the
theoretical results with the measured transition energy, the value of 0.190
0.028 fm has been determined for of Pb, in
agreement with previous experimental results. The AGDR excitation energy has
also been used to calculate the symmetry energy at saturation (
MeV) and the slope of the symmetry energy ( MeV), resulting in
more stringent constraints than most of the previous studies.Comment: 6 pages, 5 figures. arXiv admin note: text overlap with
arXiv:1205.232
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