1,410 research outputs found
Acceleration disturbances due to local gravity gradients in ASTROD I
The Astrodynamical Space Test of Relativity using Optical Devices (ASTROD)
mission consists of three spacecraft in separate solar orbits and carries out
laser interferometric ranging. ASTROD aims at testing relativistic gravity,
measuring the solar system and detecting gravitational waves. Because of the
larger arm length, the sensitivity of ASTROD to gravitational waves is
estimated to be about 30 times better than Laser Interferometer Space Antenna
(LISA) in the frequency range lower than about 0.1 mHz. ASTROD I is a simple
version of ASTROD, employing one spacecraft in a solar orbit. It is the first
step for ASTROD and serves as a technology demonstration mission for ASTROD. In
addition, several scientific results are expected in the ASTROD I experiment.
The required acceleration noise level of ASTROD I is 10^-13 m s^-2 Hz^{-1/2} at
the frequency of 0.1 mHz. In this paper, we focus on local gravity gradient
noise that could be one of the largest acceleration disturbances in the ASTROD
I experiment. We have carried out gravitational modelling for the current
test-mass design and simplified configurations of ASTROD I by using an
analytical method and the Monte Carlo method. Our analyses can be applied to
figure out the optimal designs of the test mass and the constructing materials
of the spacecraft, and the configuration of compensation mass to reduce local
gravity gradients.Comment: 6 pages, presented at the 6th Edoardo Amaldi Conference (Okinawa
Japan, June 2005); to be published in Journal of Physics: Conference Serie
Geophysical constraint on a relic background of the dilatons
According to a scenario in string cosmology, a relic background of light
dilatons can be a significant component of the dark matter in the Universe. A
new approach of searching for such a dilatonic background by observing Earth's
surface gravity was proposed in my previous work. In this paper, the concept of
the geophysical search is briefly reviewed, and the geophysical constraint on
the dilaton background is presented as a function of the strength of the
dilaton coupling, . For simplicity, I focus on massless dilatons and
assume a simple Earth model. With the current upper limit on , we obtain
the upper limit on the dimensionless energy density of the massless background,
, which is about one-order of
magnitude more stringent than the one from astrophysical observations, at the
frequency of 7 10 Hz. If the magnitude of is
experimentally found to be smaller than the current upper limit by one order of
magnitude, the geophysical upper limit on becomes less
stringent and comparable to the one obtained from the astrophysical
observations.Comment: 6 pages, Proceedings for the 8th Edoardo Amaldi Conference on
Gravitational Waves, 21-26 June, 2009, Columbia University, New York, US
Electrothermal flow in Dielectrophoresis of Single-Walled Carbon Nanotubes
We theoretically investigate the impact of the electrothermal flow on the
dielectrophoretic separation of single-walled carbon nanotubes (SWNT). The
electrothermal flow is observed to control the motions of semiconducting SWNTs
in a sizeable domain near the electrodes under typical experimental conditions,
therefore helping the dielectrophoretic force to attract semiconducting SWNTs
in a broader range. Moreover, with the increase of the surfactant
concentration, the electrothermal flow is enhanced, and with the change of
frequency, the pattern of the electrothermal flow changes. It is shown that
under some typical experimental conditions of dielectrophoresis separation of
SWNTs, the electrothermal flow is a dominating factor in determining the motion
of SWNTs.Comment: 5 pages, 4 figures, Submitted to PR
Model-independent study of the QCD sum rule for the pi NN coupling constant
We reinvestigate the QCD sum rule for the pi NN coupling constant, g,
starting from the vacuum-to-pion matrix element of the correlation function of
the interpolating fields of two nucleons. We study in detail the physical
content of the correlation function without referring to the effective theory.
We consider the invariant correlation functions by splitting the correlation
function into different Dirac structures. We show that the coefficients of the
double-pole terms are proportional to g but that the coefficients of the
single-pole terms are not determined by g. In the chiral limit the single-pole
terms as well as the continuum terms are ill defined in the dispersion
integral. Therefore, the use of naive QCD sum rules obtained from the invariant
correlation functions is not justified. A possible procedure to avoid this
difficulty is discussed.Comment: 20 pages, 2 figure
An aerogel Cherenkov detector for multi-GeV photon detection with low sensitivity to neutrons
We describe a novel photon detector which operates under an intense flux of
neutrons. It is composed of lead-aerogel sandwich counter modules. Its salient
features are high photon detection efficiency and blindness to neutrons. As a
result of Monte Carlo (MC) simulations, the efficiency for photons with the
energy larger than 1 GeV is expected to be higher than 99.5% and that for 2
GeV/ neutrons less than 1%. The performance on the photon detection under
such a large flux of neutrons was measured for a part of the detector. It was
confirmed that the efficiency to photons with the energy 1 GeV was
consistent with the MC expectation within 8.2% uncertainty.Comment: 16 pages, 16 figures, submitted to Prog. Theor. Exp. Phy
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