We report (i) systematic studies of the growth rate for melt textured YBCO, (ii) top seeding growth techniques to determine the minimum seed size, and (iii) joining techniques for melt textured YBCO, enabling the fabrication of large single domain structures of arbitrary shape. Seeded growth of YBCO occurs in a narrow temperature window about 20 C below the peritectic decomposition temperature. Successful top seeding depends on the size of the NdBCO seed crystal. Small seeds are eventually dissolved in the melt before nucleation occurs, while large seeds regularly produce single domain monoliths. Joining techniques based on seeding of low melting point Tm123/Y211 filler material by neighboring YBCO are described. Magneto-optical images of the YBCO/TmBCO/YBCO assembly show no detectable penetration of magnetic field at the joints.

Collecting debris samples following a nuclear event requires that operations be conducted from a considerable stand-off distance. An ultra-wide range gamma detector system has been constructed to accomplish both long range radiation search and close range hot sample collection functions. Constructed and tested on a REMOTEC Andros platform, the system has demonstrated reliable operation over six orders of magnitude of gamma dose from 100's of uR/hr to over 100 R/hr. Functional elements include a remotely controlled variable collimator assembly, a NaI(Tl)/photomultiplier tube detector, a proprietary digital radiation instrument, a coaxially mounted video camera, a digital compass, and both local and remote control computers with a user interface designed for long range operations. Long range sensitivity and target location, as well as close range sample selection performance are presented.

We present the first results from a very deep Chandra X-ray observation of the core of the Perseus cluster of galaxies. A pressure map reveals a clear thick band of high pressure around the inner radio bubbles. The gas in the band must be expanding outward and the sharp front to it is identified as a shock front, yet we see no temperature jump across it; indeed there is more soft emission behind the shock than in front of it. We conclude that in this inner region either thermal conduction operates efficiently or the co-existing relativistic plasma seen as the radio mini-halo is mediating the shock. If common, isothermal shocks in cluster cores mean that we cannot diagnose the expansion speed of radio bubbles from temperature measurements alone. They can at times expand more rapidly than currently assumed without producing significant regions of hot gas. Bubbles may also be significantly more energetic. The pressure ripples found in earlier images are identified as isothermal sound waves. A simple estimate based on their amplitude confirms that they can be an effective distributed heat source able to balance radiative cooling.We see multiphase gas with about 10{sup 9}M{sub {circle_dot}} at a temperature of about …

This paper discusses the critical dependence of the open-circuit voltage (VOC) of crystalline Si solar cells on the emitter and base doping levels. Contrary to conventional models that try to ascribe VOC-limitations to (independent) bulk and surface recombination losses, the authors suggest, as the dominant mechanism, the formation of a compensated ``buffer layer'' that is formed as phosphorus is diffused into the p-type (boron-doped) base. The only purpose of the base doping is to optimize the buffer layer. Their calculations show that this model makes the achievement of high VOC and good carrier collection (JSC, FF) interdependent. Sanyo's ``HIT'' solar cells are an example of a different method to implement this buffer layer concept for crystalline Si solar cells. The general principle for a VOC-enhancing buffer layer relies on using materials with high lifetimes and low carrier mobilities that are capable of reducing surface or junction recombination by reducing the flow of carriers into this loss-pathway.

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