812 research outputs found
Characterization of Standardized Lunar Regolith Simulant Materials
Lunar exploration requires scientific and engineering studies using standardized testing procedures that ultimately support flight certification of technologies and hardware. This motivates the development of traceable, standardized lunar regolith simulant (SLRS) materials. For details, refer to the 2005 Workshop on Lunar Regolith Simulant Materials
The Weibull-Geometric distribution
In this paper we introduce, for the first time, the Weibull-Geometric
distribution which generalizes the exponential-geometric distribution proposed
by Adamidis and Loukas (1998). The hazard function of the last distribution is
monotone decreasing but the hazard function of the new distribution can take
more general forms. Unlike the Weibull distribution, the proposed distribution
is useful for modeling unimodal failure rates. We derive the cumulative
distribution and hazard functions, the density of the order statistics and
calculate expressions for its moments and for the moments of the order
statistics. We give expressions for the R\'enyi and Shannon entropies. The
maximum likelihood estimation procedure is discussed and an algorithm EM
(Dempster et al., 1977; McLachlan and Krishnan, 1997) is provided for
estimating the parameters. We obtain the information matrix and discuss
inference. Applications to real data sets are given to show the flexibility and
potentiality of the proposed distribution
Search for Optical Pulsation in M82 X-2
We report on a search for optical pulsation from M82 X-2 over a range of periods. M82 X-2 is an X-ray pulsar with a 1.37s average spin period and a 2.5 day sinusoidal modulation. The observations were done with the ARray Camera for Optical to Near-IR Spectrophotometry at the 200 inch Hale telescope at the Palomar Observatory. We performed H test and χ^2 statistical analysis. No significant optical pulsations were found in the wavelength range of 3000–11000 Å with a pulsation period between 1.36262 and 1.37462 s. We found an upper limit on pulsed emission in the 4000–8000 Å wavelength range to be fainter than ~20.5 mag_(AB) , corresponding to ~23 μJy
Wide-gap Couette flows of dense emulsions: Local concentration measurements, and comparison between macroscopic and local constitutive law measurements through magnetic resonance imaging
Flows of dense emulsions show many complex features among which long range
nonlocal effects pose a problem for macroscopic characterization. In order to
get around this problem, we study the flows of several dense emulsions in a
wide-gap Couette geometry. We couple macroscopic rheometric experiments and
local velocity measurements through MRI techniques. As concentration
heterogeneities can be expected, we designed a method to measure the local
droplet concentration in emulsions with a MRI device. In contrast to dense
suspensions of rigid particles where very fast migration occurs under shear, we
show that no migration takes place in dense emulsions even for strains as large
as 100 000 in our systems. As a result of the absence of migration and of
finite size effect, we are able to determine very precisely the local
rheological behavior of several dense emulsions. As the materials are
homogeneous, this behavior can also be inferred from purely macroscopic
measurements. We thus suggest that properly analyzed purely macroscopic
measurements in a wide-gap Couette geometry can be used as a tool to study the
local constitutive laws of dense emulsions. All behaviors are basically
consistent with Herschel-Bulkley laws of index 0.5, but discrepancies exist at
the approach of the yield stress due to slow shear flows below the apparent
yield stress in the case of a strongly adhesive emulsion. The existence of a
constitutive law accounting for all flows contrasts with previous results
obtained within a microchannel by Goyon et al. (2008): the use of a wide-gap
Couette geometry is likely to prevent here from nonlocal finite size effects;
it also contrasts with the observations of B\'ecu et al. (2006)
The Murchison Blue Angel Inclusion: Its Mineralogy and Petrology
Hibonite-bearing inclusions found in CV and CM chondrites are thought to contain some of the earliest phases condensed from the solar nebula. A well preserved inclusion of this type, found by R. Becker, has been isolated from the Murchison CM chondrite for extensive analysis
A titanium-nitride near-infrared kinetic inductance photon-counting detector and its anomalous electrodynamics
We demonstrate single-photon counting at 1550 nm with titanium-nitride (TiN)
microwave kinetic inductance detectors. Energy resolution of 0.4 eV and
arrival-time resolution of 1.2 microseconds are achieved. 0-, 1-, 2-photon
events are resolved and shown to follow Poisson statistics. We find that the
temperature-dependent frequency shift deviates from the Mattis-Bardeen theory,
and the dissipation response shows a shorter decay time than the frequency
response at low temperatures. We suggest that the observed anomalous
electrodynamics may be related to quasiparticle traps or subgap states in the
disordered TiN films. Finally, the electron density-of-states is derived from
the pulse response.Comment: 4 pages, 3 figure
Interaction and flocculation of spherical colloids wetted by a surface-induced corona of paranematic order
Particles dispersed in a liquid crystal above the nematic-isotropic phase
transition are wetted by a surface-induced corona of paranematic order. Such
coronas give rise to pronounced two-particle interactions. In this article, we
report details on the analytical and numerical study of these interactions
published recently [Phys. Rev. Lett. 86, 3915 (2001)]. We especially
demonstrate how for large particle separations the asymptotic form of a Yukawa
potential arises. We show that the Yukawa potential is a surprisingly good
description for the two-particle interactions down to distances of the order of
the nematic coherence length. Based on this fact, we extend earlier studies on
a temperature induced flocculation transition in electrostatically stabilized
colloidal dispersions [Phys. Rev. E 61, 2831 (2000)]. We employ the Yukawa
potential to establish a flocculation diagram for a much larger range of the
electrostatic parameters, namely the surface charge density and the Debye
screening length. As a new feature, a kinetically stabilized dispersion close
to the nematic-isotropic phase transition is found.Comment: Revtex v4.0, 16 pages, 12 Postscript figures. Accepted for
publication in Phys. Rev.
Simulating Particle Dispersions in Nematic Liquid-Crystal Solvents
A new method is presented for mesoscopic simulations of particle dispersions
in nematic liquid crystal solvents. It allows efficient first-principle
simulations of the dispersions involving many particles with many-body
interactions mediated by the solvents. A simple demonstration is shown for the
aggregation process of a two dimentional dispersion.Comment: 5 pages, 5 figure
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