614 research outputs found
Elaboration and study of the thermo-mechanical properties of an aligned cnt - polypropylene nanocomposite by twin-screw mixer
This study presents first the fabrication of a nanocomposite material based on Multi-Walled Carbon Nanotubes, and on a thermoplastic polymer matrix. First, a twin-screw mixer had been employed for preparing polypropylene nanocomposites loaded at 0.1, 1, 2, and 5wt% of MWCNT. Second, a characterization of rheological behavior for polypropylene as well as polypropylene/multi-walled carbon nanotube mixtures, at three temperatures (180, 200, and 220 °C,) has been carried out using cone and plate rheometer. Then, its thermomechanical properties have been studied. The work demonstrates how the addition of functionalized CNTs to a polypropylene will allow it to act as thermal conductor rather than as insulator
Deterministic hierarchical networks
It has been shown that many networks associated with complex systems are
small-world (they have both a large local clustering coefficient and a small
diameter) and they are also scale-free (the degrees are distributed according
to a power law). Moreover, these networks are very often hierarchical, as they
describe the modularity of the systems that are modeled. Most of the studies
for complex networks are based on stochastic methods. However, a deterministic
method, with an exact determination of the main relevant parameters of the
networks, has proven useful. Indeed, this approach complements and enhances the
probabilistic and simulation techniques and, therefore, it provides a better
understanding of the systems modeled. In this paper we find the radius,
diameter, clustering coefficient and degree distribution of a generic family of
deterministic hierarchical small-world scale-free networks that has been
considered for modeling real-life complex systems
Developing a second generation Laue lens prototype: high reflectivity crystals and accurate assembly
Laue lenses are an emerging technology that will enhance gamma-ray telescope
sensitivity by one to two orders of magnitude in selected energy bands of the
\sim 100 keV to \sim 1.5 MeV range. This optic would be particularly well
adapted to the observation of faint gamma ray lines, as required for the study
of Supernovae and Galactic positron annihilation. It could also prove very
useful for the study of hard X-ray tails from a variety of compact objects,
especially making a difference by providing sufficient sensitivity for
polarization to be measured by the focal plane detector. Our group has been
addressing the two key issues relevant to improve performance with respect to
the first generation of Laue lens prototypes: obtaining large numbers of
efficient crystals and developing a method to fix them with accurate
orientation and dense packing factor onto a substrate. We present preliminary
results of an on-going study aiming to enable a large number of crystals
suitable for diffraction at energies above 500 keV. In addition, we show the
first results of the Laue lens prototype assembled using our beamline at SSL/UC
Berkeley, which demonstrates our ability to orient and glue crystals with
accuracy of a few arcsec, as required for an efficient Laue lens telescope.Comment: Published in the proceedings of the SPIE conference held in San Diego
in August 201
Defensive alliances in regular graphs and circulant graphs
In this paper we study defensive alliances in some regular graphs.
We determine which subgraphs could a critical defensive alliance
of a graph induce, if is -regular and the cardinality of the alliance is
at most .
In particular, we study the case of circulant graphs, i.e. Cayley graphs on a cyclic group.
The critical defensive alliances of a circulant graph of degree at most
are completely determined. For the general case, we give tight lower and upper bounds
on the alliance number of a circulant graph with generators.Preprin
A simple compensation method for the accurate measurement of magnetic losses with a single strip tester
International audienceWe present a new method for the accurate characterization of soft magnetic sheets using a permeameter based on the precise compensation of the magnetomotive force (MMF) drop in the flux-closing yoke. It has been developed in order to overcome the systematic uncertainty affecting the value of the magnetic fieldstrength in single sheet testers when obtained, according to the standards, through the measurement of the magnetizing current. This phenomenon is more critical for high permeability materials, because of the reduced MMF drop across the sample. While additional sensors and auxiliary windings have been proposed in the literature, a novel approach is demonstrated here, based on the use of the permeameter upper half yoke as the MMF drop sensor and of an auxiliary winding on the lower half yoke, implementing compensation. This solution, dispensing one from dealing with the usually small signal levels of the conventional MMF drop sensors (e.g. Chattock coils), provides best results with the introduction of wedge-shaped magnetic poles, in order to accurately define the magnetic path length. The method is validated by measurements of power loss, apparent power, and hysteresis cycles on non-oriented and grain-oriented Fe-Si steel sheets, which are compared with local measurements performed on the same samples using H-coil and B-coil across a uniformly magnetized region
Microsporidia Are Natural Intracellular Parasites of the Nematode Caenorhabditis elegans
For decades the soil nematode Caenorhabditis elegans has been an important model system for biology, but little is known about its natural ecology. Recently, C. elegans has become the focus of studies of innate immunity and several pathogens have been shown to cause lethal intestinal infections in C. elegans. However none of these pathogens has been shown to invade nematode intestinal cells, and no pathogen has been isolated from wild-caught C. elegans. Here we describe an intracellular pathogen isolated from wild-caught C. elegans that we show is a new species of microsporidia. Microsporidia comprise a large class of eukaryotic intracellular parasites that are medically and agriculturally important, but poorly understood. We show that microsporidian infection of the C. elegans intestine proceeds through distinct stages and is transmitted horizontally. Disruption of a conserved cytoskeletal structure in the intestine called the terminal web correlates with the release of microsporidian spores from infected cells, and appears to be part of a novel mechanism by which intracellular pathogens exit from infected cells. Unlike in bacterial intestinal infections, the p38 MAPK and insulin/insulin-like growth factor (IGF) signaling pathways do not appear to play substantial roles in resistance to microsporidian infection in C. elegans. We found microsporidia in multiple wild-caught isolates of Caenorhabditis nematodes from diverse geographic locations. These results indicate that microsporidia are common parasites of C. elegans in the wild. In addition, the interaction between C. elegans and its natural microsporidian parasites provides a system in which to dissect intracellular intestinal infection in vivo and insight into the diversity of pathogenic mechanisms used by intracellular microbes
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