11,553 research outputs found
Analytical r-mode solution with gravitational radiation reaction force
We present and discuss the analytical r-mode solution to the linearized
hydrodynamic equations of a slowly rotating, Newtonian, barotropic,
non-magnetized, perfect-fluid star in which the gravitational radiation
reaction force is present.Comment: 3 pages, in Proceedings of the 5th International Workshop "New Worlds
in Astroparticle Physics", Faro, Portugal, 8-10 January 200
Nonlinear evolution of r-modes: the role of differential rotation
Recent work has shown that differential rotation, producing large scale
drifts of fluid elements along stellar latitudes, is an unavoidable feature of
r-modes in the nonlinear theory. We investigate the role of this differential
rotation in the evolution of the l=2 r-mode instability of a newly born, hot,
rapidly rotating neutron star. It is shown that the amplitude of the r-mode
saturates a few hundred seconds after the mode instability sets in. The
saturation amplitude depends on the amount of differential rotation at the time
the instability becomes active and can take values much smaller than unity. It
is also shown that, independently of the saturation amplitude of the mode, the
star spins down to rotation rates that are comparable to the inferred initial
rotation rates of the fastest pulsars associated with supernova remnants.
Finally, it is shown that, when the drift of fluid elements at the time the
instability sets in is significant, most of the initial angular momentum of the
star is transferred to the r-mode and, consequently, almost none is carried
away by gravitational radiation.Comment: 10 pages, 5 figure
Technology adoption and the investment climate : firm-level evidence for Eastern Europe and Central Asia
The international diffusion of technology presents an opportunity for developing economies distant from the world technological frontier to reduce their income gap relative to advanced economies. It is therefore crucial to understand why, when faced with similar technological alternatives different firms in different countries choose to adopt different vintages of capital. This paper examines technology adoption across firms in Eastern Europe and Central Asia. The findings show that access to complementary inputs - managerial capacity, skilled labor, finance, and good infrastructure - and to international knowledge - through foreign direct investment or exports - is an important correlate of technology adoption. The link between market incentives and technology adoption is more nuanced. Although consumer pressure results in technology adoption, competitor pressure does not, suggesting that only firms with rents are able to adopt technology given substantial resource constraints. Privatized firms exhibit better technology adoption outcomes but only when a clear private owner with a profit incentive is present. Better governance is associated with technology adoption only in the countries that joined the European Union in 2004. Future increases in technology adoption by firms in the region will require complementary reforms of the investment climate.E-Business,Technology Industry,ICT Policy and Strategies,Microfinance,
Heuristic for estimation of multiqubit genuine multipartite entanglement
For every N-qubit density matrix written in the computational basis, an
associated "X-density matrix" can be obtained by vanishing all entries out of
the main- and anti-diagonals. It is very simple to compute the genuine
multipartite (GM) concurrence of this associated N-qubit X-state, which,
moreover, lower bounds the GM-concurrence of the original (non-X) state. In
this paper, we rely on these facts to introduce and benchmark a heuristic for
estimating the GM-concurrence of an arbitrary multiqubit mixed state. By
explicitly considering two classes of mixed states, we illustrate that our
estimates are usually very close to the standard lower bound on the
GM-concurrence, being significantly easier to compute. In addition, while
evaluating the performance of our proposed heuristic, we provide the first
characterization of GM-entanglement in the steady states of the driven Dicke
model at zero temperature.Comment: 19 pages, 5 figure
The influence of differential rotation on the detectability of gravitational waves from the r-mode instability
Recently, it was shown that differential rotation is an unavoidable feature
of nonlinear r-modes. We investigate the influence of this differential
rotation on the detectability of gravitational waves emitted by a newly born,
hot, rapidly-rotating neutron star, as it spins down due to the r-mode
instability. We conclude that gravitational radiation may be detected by the
advanced laser interferometer detector LIGO if the amount of differential
rotation at the time the r-mode instability becomes active is not very high.Comment: 8 pages, 6 figures, revtex
Avaliação da retenção de metais pesados de escorrências rodoviárias por filtração adsorptiva
A degradação da qualidade de solos e águas subterrâneas causada por escorrências
rodoviárias constitui um assunto de crescente preocupação e de interesse
para a realização, a nível internacional, de variados programas de investigação e
desenvolvimento.
Um grande número de metais pesados e micropoluentes orgânicos aparecem
associados ao tráfego automóvel. Cu, Pb, Zn e Cd – às vezes também Ni e Cr –
são considerados os metais pesados mais importantes associadas, quer a fontes
móveis, quer estacionárias, podendo estes metais aparecer na forma dissolvida ou
ligados a partículas.
No presente trabalho descrevem-se alguns aspectos de um projecto de investigação
realizado com o objectivo de avaliar a eficiência de meios porosos na retenção
de metais pesados provenientes de escorrências rodoviárias, usando, para tal,
um meio filtrante constituído por materiais correntes e com propriedades conhecidas:
areia e caulinite. Os parâmetros de controlo para a experiência foram: pH,
condutividade, temperatura, Zn, Cu, Pb, caudal e carga hidráulica.
Os resultados preliminares mostram que o Zn é o metal com maior mobilidade.
Com as taxas de aplicação consideradas, as eficiências de retenção diminuíram
para valores inferiores a 50% num período de 15, 70 e 110 dias, para os três diferentes
meios filtrantes considerados. Para o Cu e Pb, e depois de um período
experimental de 260 dias, as eficiências de retenção registadas são superiores a
70% e 40% para o meio filtrante de areia, respectivamente, e superiores a 90%
para os meios filtrantes de areia e caulinite
The millisecond pulsar mass distribution: Evidence for bimodality and constraints on the maximum neutron star mass
The mass function of neutron stars (NSs) contains information about the late
evolution of massive stars, the supernova explosion mechanism, and the
equation-of-state of cold, nuclear matter beyond the nuclear saturation
density. A number of recent NS mass measurements in binary millisecond pulsar
(MSP) systems increase the fraction of massive NSs (with M)
to of the observed population. In light of these results, we
employ a Bayesian framework to revisit the MSP mass distribution. We find that
a single Gaussian model does not sufficiently describe the observed population.
We test alternative empirical models and infer that the MSP mass distribution
is strongly asymmetric. The diversity in spin and orbital properties of
high-mass NSs suggests that this is most likely not a result of the recycling
process, but rather reflects differences in the NS birth masses. The asymmetry
is best accounted for by a bimodal distribution with a low mass component
centred at M and dispersed by
M, and a high-mass component with a mean of
and a dispersion of
M. We also establish a lower limit of M
at 98% C.L. for the maximum NS mass, from the absence of a high-mass truncation
in the observed masses. Using our inferred model, we find that the measurement
of 350 MSP masses, expected after the conclusion of pulsar surveys with the
Square-Kilometre Array, can result in a precise localization of a maximum mass
up to 2.15 M, with a 5% accuracy. Finally, we identify possible
massive NSs within the known pulsar population and discuss birth masses of
MSPs.Comment: submitted to ApJ; 21 pages in aastex6 two-column format, 12 figures,
5 tables. Comments are welcom
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