36,782 research outputs found
Light weight fire resistant graphite composites
Composite structures with a honeycomb core and characterized by lightweight and excellent fire resistance are provided. These sandwich structures employ facesheets made up of bismaleimide-vinyl styrylpyridine copolymers with fiber reinforcement such as carbon fiber reinforcement. In preferred embodiments the facesheets are over layered with a decorative film. The properties of these composites make them attractive materials of construction aircraft and spacecraft
Lacie phase 1 Classification and Mensuration Subsystem (CAMS) rework experiment
An experiment was designed to test the ability of the Classification and Mensuration Subsystem rework operations to improve wheat proportion estimates for segments that had been processed previously. Sites selected for the experiment included three in Kansas and three in Texas, with the remaining five distributed in Montana and North and South Dakota. The acquisition dates were selected to be representative of imagery available in actual operations. No more than one acquisition per biophase were used, and biophases were determined by actual crop calendars. All sites were worked by each of four Analyst-Interpreter/Data Processing Analyst Teams who reviewed the initial processing of each segment and accepted or reworked it for an estimate of the proportion of small grains in the segment. Classification results, acquisitions and classification errors and performance results between CAMS regular and ITS rework are tabulated
Sagnac Interferometer Enhanced Particle Tracking in Optical Tweezers
A setup is proposed to enhance tracking of very small particles, by using
optical tweezers embedded within a Sagnac interferometer. The achievable
signal-to-noise ratio is shown to be enhanced over that for a standard optical
tweezers setup. The enhancement factor increases asymptotically as the
interferometer visibility approaches 100%, but is capped at a maximum given by
the ratio of the trapping field intensity to the detector saturation threshold.
For an achievable visibility of 99%, the signal-to-noise ratio is enhanced by a
factor of 200, and the minimum trackable particle size is 2.4 times smaller
than without the interferometer
Dragging a polymer chain into a nanotube and subsequent release
We present a scaling theory and Monte Carlo (MC) simulation results for a
flexible polymer chain slowly dragged by one end into a nanotube. We also
describe the situation when the completely confined chain is released and
gradually leaves the tube. MC simulations were performed for a self-avoiding
lattice model with a biased chain growth algorithm, the pruned-enriched
Rosenbluth method. The nanotube is a long channel opened at one end and its
diameter is much smaller than the size of the polymer coil in solution. We
analyze the following characteristics as functions of the chain end position
inside the tube: the free energy of confinement, the average end-to-end
distance, the average number of imprisoned monomers, and the average stretching
of the confined part of the chain for various values of and for the number
of monomers in the chain, . We show that when the chain end is dragged by a
certain critical distance into the tube, the polymer undergoes a
first-order phase transition whereby the remaining free tail is abruptly sucked
into the tube. This is accompanied by jumps in the average size, the number of
imprisoned segments, and in the average stretching parameter. The critical
distance scales as . The transition takes place when
approximately 3/4 of the chain units are dragged into the tube. The theory
presented is based on constructing the Landau free energy as a function of an
order parameter that provides a complete description of equilibrium and
metastable states. We argue that if the trapped chain is released with all
monomers allowed to fluctuate, the reverse process in which the chain leaves
the confinement occurs smoothly without any jumps. Finally, we apply the theory
to estimate the lifetime of confined DNA in metastable states in nanotubes.Comment: 13pages, 14figure
X-ray spectral modelling of the AGN obscuring region in the CDFS: Bayesian model selection and catalogue
AGN are known to have complex X-ray spectra that depend on both the
properties of the accreting SMBH (e.g. mass, accretion rate) and the
distribution of obscuring material in its vicinity ("torus"). Often however,
simple and even unphysical models are adopted to represent the X-ray spectra of
AGN. In the case of blank field surveys in particular, this should have an
impact on e.g. the determination of the AGN luminosity function, the inferred
accretion history of the Universe and also on our understanding of the relation
between AGN and their host galaxies. We develop a Bayesian framework for model
comparison and parameter estimation of X-ray spectra. We take into account
uncertainties associated with X-ray data and photometric redshifts. We also
demonstrate how Bayesian model comparison can be used to select among ten
different physically motivated X-ray spectral models the one that provides a
better representation of the observations. Despite the use of low-count
spectra, our methodology is able to draw strong inferences on the geometry of
the torus. For a sample of 350 AGN in the 4 Ms Chandra Deep Field South field,
our analysis identifies four components needed to represent the diversity of
the observed X-ray spectra: (abridged). Simpler models are ruled out with
decisive evidence in favour of a geometrically extended structure with
significant Compton scattering. Regarding the geometry of the obscurer, there
is strong evidence against both a completely closed or entirely open toroidal
geometry, in favour of an intermediate case. The additional Compton reflection
required by data over that predicted by toroidal geometry models, may be a sign
of a density gradient in the torus or reflection off the accretion disk.
Finally, we release a catalogue with estimated parameters such as the accretion
luminosity in the 2-10 keV band and the column density, , of the
obscurer.Comment: 28 pages, 18 figures, catalogue available from
https://www.mpe.mpg.de/~jbuchner/agn_torus/analysis/cdfs4Ms_cat/, software
available from https://github.com/JohannesBuchner/BX
Effective interactions between star polymers
We study numerically the effective pair potential between star polymers with
equal arm lengths and equal number of arms. The simulations were done for
the soft core Domb-Joyce model on the simple cubic lattice, to minimize
corrections to scaling and to allow for an unlimited number of arms. For the
sampling, we used the pruned-enriched Rosenbluth method (PERM). We find that
the potential is much less soft than claimed in previous papers, in particular
for . While we verify the logarithmic divergence of , with
being the distance between the two cores, predicted by Witten and Pincus, we
find for that the Mayer function is hardly distinguishable from that for
a Gaussian potential.Comment: 5 pages, 5 figure
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