1,512 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
Negative Parity Baryons in the QCD Sum Rule
Masses and couplings of the negative parity excited baryons are studied in
the QCD sum rule. Separation of the negative-parity spectrum is proposed and is
applied to the flavor octet and singlet baryons. We find that the quark
condensate is responsible for the mass splitting of the ground and the
negative-parity excited states. This is expected from the chiral symmetry and
supports the idea that the negative-parity baryon forms a parity doublet with
the ground state. The meson-baryon coupling constants are also computed for the
excited states in the QCD sum rule. It is found that the \pi NN^* coupling
vanishes in the chiral limit.Comment: 13pp, LaTeX, 1 EPS figure, uses epsf.sty, Talk given by M.O. at
CEBAF/INT workshop "N* physics", Seattle, September (1996), to appear in the
proceeding
Keep the course: travelling penguins consistently orient toward the destination
The Tenth Symposium on Polar Science/Ordinary sessions : [OB] Polar Biology, Wed. 4 Dec. / Entrance Hall (1st floor) , National Institute of Polar Researc
Anomalous Hall Effect in Ferromagnetic Metals: Role of Phonons at Finite Temperature
The anomalous Hall effect in a multiband tight-binding model is numerically
studied taking into account both elastic scattering by disorder and inelastic
scattering by the electron-phonon interaction. The Hall conductivity is
obtained as a function of temperature , inelastic scattering rate ,
chemical potential , and impurity concentration . We find
that the new scaling law holds over a wide range of these parameters;
, with () being the
conductivity tensor (with only elastic scattering), which corresponds to the
recent experimental observation [Phys. Rev. Lett. {\bf 103} (2009) 087206]. The
condition of this scaling is examined. Also, it is found that the intrinsic
mechanism depends on temperature under a resonance condition.Comment: 5 figure
Wide-Supply-Range All-Digital Leakage Variation Sensor for On-Chip Process and Temperature Monitoring
Variation in process, voltage and temperature is a major obstacle in achieving energy-efficient operation of LSI. This paper proposes an all-digital on-chip circuit to monitor leakage current variations of both of the nMOSFET and pMOSFET independently. As leakage current is highly sensitive to threshold voltage and temperature, the circuit is suitable for tracking process and temperature variation. The circuit uses reconfigurable inhomogeneity to obtain statistical properties from a single monitor instance. A compact reconfigurable inverter topology is proposed to implement the monitor circuit. The compact and digital nature of the inverter enables cell-based design, which will reduce design costs. Measurement results from a 65 nm test chip show the validity of the proposed circuit. For a 124 sample size for both of the nMOSFET and pMOSFET, the monitor area is 4500 μm2 and active power consumption is 76 nW at 0.8 V operation. The proposed technique enables area-efficient and low-cost implementation thus can be used in product chips for applications such as dynamic energy and thermal management, testing and post-silicon tuning
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