30,728 research outputs found
Polymer packaging and ejection in viral capsids: shape matters
We use a mesoscale simulation approach to explore the impact of different
capsid geometries on the packaging and ejection dynamics of polymers of
different flexibility. We find that both packing and ejection times are faster
for flexible polymers. For such polymers a sphere packs more quickly and ejects
more slowly than an ellipsoid. For semiflexible polymers, however, the case
relevant to DNA, a sphere both packs and ejects more easily. We interpret our
results by considering both the thermodynamics and the relaxational dynamics of
the polymers. The predictions could be tested with bio-mimetic experiments with
synthetic polymers inside artificial vesicles. Our results suggest that phages
may have evolved to be roughly spherical in shape to optimise the speed of
genome ejection, which is the first stage in infection.Comment: 4 pages, 4 figure
Space processing of chalcogenide glass
The manner in which the weightless, containerless nature of in-space processing can be successfully utilized to improve the quality of infrared transmitting chalcogenide glasses is determined. The technique of space processing chalcogenide glass was developed, and the process and equipment necessary to do so was defined. Earthbound processing experiments with As2S3 and G28Sb12Se60 glasses were experimented with. Incorporated into these experiments is the use of an acoustic levitation device
A Generative Model for Parts-based Object Segmentation
The Shape Boltzmann Machine (SBM) [1] has recently been introduced as a stateof-the-art model of foreground/background object shape. We extend the SBM to account for the foreground object’s parts. Our new model, the Multinomial SBM (MSBM), can capture both local and global statistics of part shapes accurately. We combine the MSBM with an appearance model to form a fully generative model of images of objects. Parts-based object segmentations are obtained simply by performing probabilistic inference in the model. We apply the model to two challenging datasets which exhibit significant shape and appearance variability, and find that it obtains results that are comparable to the state-of-the-art. There has been significant focus in computer vision on object recognition and detection e.g. [2], but a strong desire remains to obtain richer descriptions of objects than just their bounding boxes. One such description is a parts-based object segmentation, in which an image is partitioned into multiple sets of pixels, each belonging to either a part of the object of interest, or its background. The significance of parts in computer vision has been recognized since the earliest days of th
Geometric Phase, Bundle Classification, and Group Representation
The line bundles which arise in the holonomy interpretations of the geometric
phase display curious similarities to those encountered in the statement of the
Borel-Weil-Bott theorem of the representation theory. The remarkable relation
of the geometric phase to the classification of complex line bundles provides
the necessary tools for establishing the relevance of the Borel-Weil-Bott
theorem to Berry's adiabatic phase. This enables one to define a set of
topological charges for arbitrary compact connected semisimple dynamical Lie
groups. In this paper, the problem of the determination of the parameter space
of the Hamiltonian is also addressed. A simple topological argument is
presented to indicate the relation between the Riemannian structure on the
parameter space and Berry's connection. The results about the fibre bundles and
group theory are used to introduce a procedure to reduce the problem of the
non-adiabatic (geometric) phase to Berry's adiabatic phase for cranked
Hamiltonians. Finally, the possible relevance of the topological charges of the
geometric phase to those of the non-abelian monopoles is pointed out.Comment: 30 pages (LaTeX); UT-CR-12-9
The measured compositions of Uranus and Neptune from their formation on the CO iceline
The formation mechanisms of the ice giants Uranus and Neptune, and the origin
of their elemental and isotopic compositions, have long been debated. The
density of solids in the outer protosolar nebula is too low to explain their
formation, and spectroscopic observations show that both planets are highly
enriched in carbon, very poor in nitrogen, and the ices from which they
originally formed might had deuterium-to-hydrogen ratios lower than the
predicted cometary value, unexplained properties observed in no other planets.
Here we show that all these properties can be explained naturally if Uranus and
Neptune both formed at the carbon monoxide iceline. Due to the diffusive
redistribution of vapors, this outer region of the protosolar nebula
intrinsically has enough surface density to form both planets from carbon-rich
solids but nitrogen-depleted gas, in abundances consistent with their observed
values. Water rich interiors originating mostly from transformed CO ices
reconcile the D/H value of Uranus and Neptune's building blocks with the
cometary value. Finally, Our scenario generalizes a well known hypothesis that
Jupiter formed on an iceline (water snowline) for the two ice giants, and might
be a first step towards generalizing this mechanism for other giant planets.Comment: The Astrophysical Journal (in press), 8 pages, 5 figure
Nutrient Digestibility and Productivity of Bali Cattle Fed Fermented Hymenachne Amplexiacalis Based Rations Supplemented with Leucaena Leucocephala
An experiment was conducted to study the effects of lamtoro (Leucaena leucocephala) leaf supplementation in fermented kumpai grass (Hymenachne amplexiacalis) based rations on the productivity of Bali cattle. Variables measured were dry matter and organic matter intakes, nutrient digestibility (dry matter, organic matter, crude protein, and crude fiber), body weight gain, and feed efficiency. The types of rations were: Ration A= 45% fermented kumpai grass + 40% benggala grass + 15% concentrate + 0% lamtoro leaf, Ration B= 45% fermented kumpai grass + 30% benggala grass + 15% concentrate + 10% lamtoro leaf, Ration C= 45% fermented kumpai grass + 20% benggala grass + 15% concentrate + 20% lamtoro leaf, and Ration D= 45% fermented kumpai grass + 10% benggala grass + 15% concentrate + 30% lamtoro leaf. The supplementation of lamtoro leaf up to 30% into the ration could increase (P<0.05) dry matter and organic matter intakes, and crude protein digestibility. The highest body weight gain and feed efficiency were found in Bali cattle fed ration with 20% lamtoro leaf supplementation. The level of lamtoro leaf supplementation in the ration did not affect the digestibility of dry matter, organic matter, and crude fiber. It was concluded that the supplementation of lamtoro leaf in the ration could increase dry matter, organic matter, and crude protein intakes. Addition of 20% lamtoro leaf gave the best effect on the increased body weight gain and feed efficiency in Bali cattle
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New Exploration in the Chitral Valley, Pakistan: An Extension of the Gandharan Grave Culture
NoNew survey in the Chitral Valley has doubled the number of recorded Gandharan Grave culture sites in the region and extended their geographical range. The numbers and location of sites indicates that the Gandharan Grave culture was well established in the Chitral valley, suggesting that the valley may have been central to this cultural development, rather than marginal
Tunneling and Non-Universality in Continuum Percolation Systems
The values obtained experimentally for the conductivity critical exponent in
numerous percolation systems, in which the interparticle conduction is by
tunnelling, were found to be in the range of and about , where
is the universal conductivity exponent. These latter values are however
considerably smaller than those predicted by the available ``one
dimensional"-like theory of tunneling-percolation. In this letter we show that
this long-standing discrepancy can be resolved by considering the more
realistic "three dimensional" model and the limited proximity to the
percolation threshold in all the many available experimental studiesComment: 4 pages, 2 figure
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