Analysis of a resonant-cavity enhanced GaAs/AlGaAs MSMphotodetector

The authors have developed a 2-D device simulator for heterostructure metal-semiconductor-metal (MSM) photodetectors. They have incorporated a model of multilayer optics into the simulator and used it to analyze the temporal response of a resonant-cavity enhanced heterostructure with a confining buffer layer and a distributed Bragg reflector (DBR). The authors show that through fine tuning the layer thicknesses, optical resonance enhancement of the light absorption can be obtained     

A cholera toxin-sensitive guanyl nucleotide binding protein mediates the movement of pituitary luteinizing hormone into a releasable pool: loss of this event is associated with the onset of homologous desensitization to gonadotropin-releasing hormone

Cholera toxin (CTX; 5 micrograms/ml), but not pertussis toxin (100 ng/ml), when preincubated with pituitary cells for 18 h, enhances the percentage of cellular LH released in response to continuous or pulsatile administration of 5 x 10(-9) M GnRH. This effect occurs without increasing total (intracellular plus extracellular) LH, indicating that it is best explained by redistribution of LH from a nonreleasable to a releasable pool. This site of action is consistent with the observation that CTX-pretreated cells are also sensitized to stimulation of LH release by the Ca2+ ionophore A23187. The observations that CTX stimulates the production of cAMP in these cells and that the sensitizing action of CTX is mimicked by (Bu)2cAMP (1 mM) are consistent with the view that a CTX-stimulated guanyl nucleotide binding protein, capable of activating adenylyl cyclase, is mediating this sensitization. We used a perifused cell system to show that the movement of LH into a releasable pool is lost with the onset of homologous desensitization due to high pulse frequency or constant administration of GnRH (5 x 10(-9) M, continuous or a pulse each 15 min). Sensitization to CTX is restored by stimulation with a high concentration of GnRH (10(-6) M) or by resetting the pulse frequency to the rate measured in vivo (a pulse each 90 min). Both of these treatments also circumvent the desensitized state, restoring LH release. These results identify a novel lesion associated with the development of desensitization in the gonadotrope and support the role of a CTX-sensitive guanyl nucleotide binding protein in regulation of pituitary responsiveness to GnRH.     

Invasiveness of LiTaO/sub 3/ and GaAs probes in external E-O sampling

Disturbances of signals on a coplanar waveguide (CPW) induced by the presence of LiTaO/sub 3/ and GaAs electrooptic probes in external electrooptic (EO) sampling have been simulated and compared quantitatively. The finite-difference-time-domain method is used to simulate the full wave field around a coplanar waveguide on a GaAs substrate in an external EO sampling configuration. The results indicate that the induced signal disturbance, or invasiveness, of a LiTaO/sub 3/ probe is almost ten times that of a GaAs probe in terms of the magnitude of S/sub 11/, but that LiTaO/sub 3/ yields about two times the EO response for a given S/sub 11/ and optical probing wavelength. The transparency of LiTaO/sub 3/ to shorter wavelengths, however, allows an even higher sensitivity for this material relative to GaAs. The results suggest that these probes do not exhibit significant invasiveness (magnitude of S/sub 11/ smaller than -40 dB), if they are removed from contact by the distance of CPWs center conductor width.<>     

"聪明的药丸"智能、可连网的药物分配机

本文介绍俄"聪明的药丸"可帮助解决许多错误用药的问题。它是一个具备数据库构件、网页连接、计时功能以及I/O设备控制等功能的小型嵌入式计算机。     

Studies of sintering of coal ash relevant to pulverized coal utility boilers: 1. Examination of the Raask shrinkage—electrical resistance method

The Raask shrinkage and electrical resistance method for determining the onset of sintering of fly ash has been tested on a soda lime glass, coal ASTM ashes, fly ashes and pulverized synthetic mineral mixtures. Results with the glass confirmed those of Raask and showed that particle size distribution and bulk density affected the resistance values: the sinter point was indicated by a change in the characteristic temperature coefficient of resistance. The shrinkage and electrical sinter points were usually the same, but a high Na content lignite gave 850°C for shrinkage but 600°C for characteristic resistance change. Sinter points were 200°C less for fly ash than for ASTM ash. The fly ashes had a slight enrichment of alkalies and a decrease in Fe content compared to the total ash. Holding a compact at a temperature above the sinter point gave increased strength and shrinkage, but no decrease in electrical resistance, indicating that the decrease in resistance as temperature increased was due to the establishment of contact points between particles, with little effect of the continued growth of a contact neck. Addition of pulverized sodium silicate or iron silicate glasses to a synthetic ash also reduced the sinter points, as did alkali additions, whereas addition of pyrite did not. It was concluded that the method was a valuable tool, but sources of variability had to be determined and controlled.     

The UWMAK-II study: A conceptual design of a helium cooled, solid breeder, Tokamak fusion reactor system

UWMAK-II is a conceptual design study of a low ß, circular Tokamak fusion power reactor. The aim of the study has been to perform a self-consistent analysis of a probable future fusion power system based on the philosophy that design decisions, wherever possible, should be conservative and should be based on present technology. As such, this system will not be the smallest, the least expensive, or the optimum Tokamak reactor. Rather, it represents a feasible system which we use to assess the technological problems uncovered and to examine possible solutions. The plasma is designed to generate 5000 MW(th) during a pulse and 1709 MW(e) continuously based upon a burn cycle with a 90 min burn and a 6.5 min rejuvenation period. The plasma carries a current of 14.9 MA and is designed with a double null poloidal divertor for impurity control and particle pumping. In addition, a low Z liner in the form of a carbon curtain is included to eliminate any source of high Z impurities. Plasma heating to ignition involves the use of neutral beam heating for a 10 sec period during which 200 MW of 500 keV deuterium atoms are injected into the plasma.The blanket design employs helium cooling and the solid lithium-bearing compound, lithium aluminate (Li₂Al₂O₄) for breeding tritium. The structural material is 316 stainless steel and beryllium is used as a neutron multiplier. The neutron radiation environment produces radiation damage that considerably influences blanket and system performance. The most significant effect is the loss of ductility which appears to limit the usable lifetime of the blanket first wall to about 2 yr at a 14 MeV neutron wall loading of 1.16 MW/m². The solid breeder blanket minimizes the tritium inventory but because of the low fractional burnup in the plasma and the need for roughly a one day reserve of fuel, the inventory is 17.7 kg. Induced radioactivity levels in the structure are of the order of 1 Ci/W(th) at shutdown after two years of operation. The main contributors to the activity are ) and ). Afterheat levels are slightly above 1% of thermal power but the afterheat power density is low, less than 0.1 w/g. The power cycle involves a He---Na intermediate heat exchanger followed by a sodium—steam system. The sodium intermediary is used to minimize tritium leakage through the power cycle and to provide a working fluid for thermal energy storage such that continuous electrical output is produced despite a pulse plasma cycle. A materials resource study has been completed for a UWMAK-II type system and beryllium appears to present a particular problem with regard to adequate resources. Other materials that could present problems of procurement include chromium and nickel. A preliminary economic analysis has been carried out to identify major cost areas and this is described.     

Nanostructured nanoparticles of self-assembled lipid pro-drugs as a route to improved chemotherapeutic agents

We demonstrate that oral delivery of self-assembled nanostructured nanoparticles consisting of 5-fluorouracil (5-FU) lipid prodrugs results in a highly effective, target-activated, chemotherapeutic agent, and offers significantly enhanced efficacy over a commercially available alternative that does not self-assemble. The lipid prodrug nanoparticles have been found to significantly slow the growth of a highly aggressive mouse 4T1 breast tumour, and essentially halt the growth of a human MDA-MB-231 breast tumour in mouse xenografts. Systemic toxicity is avoided as prodrug activation requires a three-step, enzymatic conversion to 5-FU, with the third step occurring preferentially at the tumour site. Additionally, differences in the lipid prodrug chemical structure and internal nanostructure of the nanoparticle dictate the enzymatic conversion rate and can be used to control sustained release profiles. Thus, we have developed novel oral nanomedicines that combine sustained release properties with target-selective activation.