Enhanced dielectrophoresis of nanocolloids by dimer formation

We investigate the dielectrophoretic motion of charge-neutral, polarizable nanocolloids through molecular dynamics simulations. Comparison to analytical results derived for continuum systems shows that the discrete charge distributions on the nanocolloids have a significant impact on their coupling to the external field. Aggregation of nanocolloids leads to enhanced dielectrophoretic transport, provided that increase in the dipole moment upon aggregation can overcome the related increase in friction. The dimer orientation and the exact structure of the nanocolloid charge distribution are shown to be important in the enhanced transport

Extinction and dust/gas ratio in LMC molecular clouds

Aims. The goal of this paper is to measure the dust content and distribution in the Large Magellanic Cloud (LMC) by comparing extinction maps produced in the near-infrared wavelengths and the spatial distribution of the neutral and molecular gas, as traced by Hi and CO observations. Methods. In order to derive an extinction map of the LMC, we have developed a new method to measure the color excess of dark clouds, using the 2MASS all-sky survey. Classical methods to measure the color excess (including the NICE method) tend to underestimate the true color excess if the clouds are significantly contaminated by unreddened foreground stars, as is the case in the LMC. We propose a new method that uses the color of the X percentile reddest stars and which is robust against such contamination. Using this method, it is possible to infer the positions of dark clouds with respect to the star distribution by comparing the observed color excess as a function of the percentile used and that predicted by a model. Results. On the basis of the resulting extinction map, we perform a correlation analysis for a set of dark molecular clouds. Assuming similar infrared absorption properties for the dust in the neutral and molecular phases, we derive the absorption-to-column density ratio AV/NH and the CO-to-H2 conversion factor X_(CO). We show that AV/NH increases from the outskirts of the LMC towards the 30 Dor star-forming region. This can be explained either by a systematic increase of the dust abundance, or by the presence of an additional gas component not traced by Hi or CO, but strongly correlated to the Hi distribution. If dust abundance is allowed to vary, the derived X_(CO) factors for the selected regions are several times lower than those derived from a virial analysis of the CO data. This could indicate that molecular clouds in the LMC are not gravitationally bound, or that they are bounded by substantial external pressure. However, the X_(CO) values derived from absorption can be reconciled with the virial results assuming a constant value for the dust abundance and the existence of an additional, unseen gas component. These results are in agreement with those derived for the LMC from diffuse far-infrared emission

Multiple and variable speed electrical generator systems for large wind turbines

A cost effective method to achieve increased wind turbine generator energy conversion and other operational benefits through variable speed operation is presented. Earlier studies of multiple and variable speed generators in wind turbines were extended for evaluation in the context of a specific large sized conceptual design. System design and simulation have defined the costs and performance benefits which can be expected from both two speed and variable speed configurations

The Radial Structure of SNR N103B

We report on the results from a Chandra ACIS observation of the young, compact, supernova remnant N103B. The unprecedented spatial resolution of Chandra reveals sub-arcsecond structure, both in the brightness and in spectral variations. Underlying these small-scale variations is a surprisingly simple radial structure in the equivalent widths of the strong Si and S emission lines. We investigate these radial variations through spatially resolved spectroscopy using a plane-parallel, non-equilibrium ionization model with multiple components. The majority of the emission arises from components with a temperature of 1 keV: a fully ionized hydrogen component; a high ionization timescale (n_e*t > 10^12 s cm^-3) component containing Si, S, Ar, Ca, and Fe; and a low ionization timescale (n_e*t ~ 10^{11} s cm^-3) O, Ne, and Mg component. To reproduce the strong Fe Kalpha line, it is necessary to include additional Fe in a hot (> 2 keV), low ionization (n_e*t ~ 10^10.8 s cm^-3) component. This hot Fe may be in the form of hot Fe bubbles, formed in the radioactive decay of clumps of 56Ni. We find no radial variation in the ionization timescales or temperatures of the various components. Rather, the Si and S equivalent widths increase at large radii because these lines, as well as those of Ar and Ca, are formed in a shell occupying the outer half of the remnant. A shell of hot Fe is located interior to this, but there is a large region of overlap between these two shells. In the inner 30% of the remnant, there is a core of cooler, 1 keV Fe. We find that the distribution of the ejecta and the yields of the intermediate mass species are consistent with model prediction for Type Ia events.Comment: 34 pages, including 7 tables and 7 figures, Accepted by Ap