5,740 research outputs found
Gravitation Wave Emission from Radio Pulsars Revisited
We report a new pulsar population synthesis based on Monte Carlo techniques,
aiming to estimate the contribution of galactic radio pulsars to the continuous
gravitational wave emission. Assuming that the rotation periods of pulsars at
birth have a Gaussian distribution, we find that the average initial period is
290 ms. The number of objects with periods equal to or less than 0.4 s, and
therefore capable of being detected by an interferometric gravitational antenna
like VIRGO, is of the order of 5100-7800. With integration times lasting
between 2 and 3 yr, our simulations suggest that about two detections should be
possible, if the mean equatorial ellipticity of the pulsars is
=10. A mean ellipticity an order of magnitude higher increases the
expected number of detections to 12-18, whereas for , no
detections are expectedComment: accepted for publication in A&A, 9 pages, 8 figure
Ages of Elliptical Galaxies: Single versus Multi Population Interpretation
New calibrations of spectrophotometric indices of elliptical galaxies as
functions of spectrophotometric indices are presented, permitting estimates of
mean stellar population ages and metallicities. These calibrations are based on
evolutionary models including a two-phase interstellar medium, infall and a
galactic wind.Free parameters were fixed by requiring that models reproduce the
mean trend of data in the color-magnitude diagram as well as in the plane of
indices Hbeta-Mg2 and Mg2-. To improve the location of faint ellipticals(MB
> -20) in the Hbeta-Mg2 diagram, down-sizing was introduced. An application of
our calibrations to a sample of ellipticals and a comparison with results
derived from single stellar population models is given. Our models indicate
that mean population ages span an interval of 7-12 Gyr and are correlated with
metallicities, which range from approximately half up to three times solar.Comment: 10 pages and 6 figures. Accepted for publication in Monthly Notices
of the Royal Astronomical Society Main Journa
Cosmic Background of Gravitational Waves from Rotating Neutron Stars
The extragalactic background of gravitational waves produced by tri-axial
rotating neutron stars was calculated, under the assumption that the properties
of the underlying pulsar population are the same of those of the galactic
population, recently derived by Regimbau & de Freitas Pacheco (2000). For an
equatorial ellipticity of = 10, the equivalent density
parameter due to gravitational waves has a maximum amplitude in the range
2, around 0.9-1.5 kHz. The main reasons
affecting the theoretical predictions are discussed. This background is
comparable to that produced by the ''ring-down'' emission from distorted black
holes. The detection possibility of this background by a future generation of
gravitational antennas is also examined.Comment: accepted for publication in Astronomy & Astrophysic
Relação entre o intervalo de partos e o custo total de produção de leite por vaca no rebanho.
O intervalo de partos foi a variavel de maior impacto nos custos de producao de vacas da raca holandesa de primeira e segunda lactacoes, seguida da producao total de leite. A idade ao primeiro parto e o valor genetico relacionaram-se apenas com o custo de producao de vacas holandesas de primeira lactacao. No caso de vacas mesticas (HZ) de primeira e segunda lactacao apenas o intervalo de partos e a producao total de leite relacionaram-se com o custo total.Resumo expandido
Quark core formation in spinning-down pulsars
Pulsars spin-down due to magnetic torque reducing its radius and increasing
the central energy density. Some pulsar which are born with central densities
close to the critical value of quark deconfinement may undergo a phase
transition and structural re-arrengement. This process may excite oscillation
modes and emmit gravitational waves. We determine the rate of quark core
formation in neutron stars using a realistic population synthesis code.Comment: Proceedings of the 2nd International Workshop on Astronomy and
Relativistic Astrophysics, to appear in IJMP
Searching Gravitational Waves from Pulsars, Using Laser Beam Interferometers
We use recent population synthesis results to investigate the distribution of
pulsars in the frequency space, having a gravitational strain high enough to be
detected by the future generations of laser beam interferometers.
We find that until detectors become able to recover the entire population,
the frequency distribution of the 'detectable' population will be very
dependent on the detector noise curve. Assuming a mean equatorial deformation
, the optimal frequency is around 450 Hz for interferometers
of the first generation (LIGO or VIRGO) and shifts toward 85 Hz for advanced
detectors. An interesting result for future detection stategies is the
significant narrowing of the distribution when improving the sensitivity: with
an advanced detector, it is possible to have 90% of detection probability while
exploring less than 20% of the parameter space (7.5% in the case of ). In addition, we show that in most cases the spindown of
'detectable' pulsars represents a period shift of less than a tens of
nanoseconds after one year of observation, making them easier to follow in the
frequency space.Comment: 5 pages, 3 figures accepted for publication in Astronomy &
Astrophysic
Distribuição das raízes do coqueiro-anão verde para o manejo da irrigação e a aplicação de fertilizantes.
O conhecimento da distribuicao do sistema radicular de uma cultura constitui-se em uma importate ferramenta para a otimizacao de praticas agricolas como a irrigacao e a adubacao; O sistema radicular do coqueiro; Distribuicao das raizes do coqueiro-anao em sequeiro; Aplicacao de fertilizantes; Distribuicao das raizes do coqueiro-anao verde irrigado; Informacoes para o manejo da irrigacao do coqueiro-anao; Profundidade efetiva do sistema radicular; Area molhada na irrigacao localizacao; Localizacao de sensores da umidade do solo; Informacoes para aplicacao de fertilizantesbitstream/CNPAT-2010/8607/1/Ci-016.pd
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