Radio wave propagation experiments to probe the ionosphere

Ionospheric bias corrections associated with radio tracking of spacecraft depend on the following measuring techniques for integrated electron content: (1) Faraday rotation measurements from an earth synchronous satellite; (2) ranging measurements at two frequencies; and (3) group and phase velocity measurements obtained from tracking data. The extraction of the integrated electron content directly from tracking data is achieved by comparison of range-rate measurements based on Doppler shift with differentiated range measurements based on tone delay. This method is most desirable because the measured corrections pertain directly to the spacecraft whose orbit is being determined and can be used in near earth as well as deep space tracking data

Lunar far-side communication satellites

Data relay and tracking capability of lunar communication satellite

Heat exchanger method, ingot casting; fixed abrasive method, multi-wire slicing, phase 2. Silicon sheet growth development for the large area sheet task of the low cost silicon solar array project

A crack-free silicon ingot has been cast in a graded, semiconductor purity silica crucible. More than 90% single crystallinity has been achieved in 2.5 kg cast ingots. The impurities on the surface of the melt have been reduced with the use of a rapid heat-up cycle and absence of graphite retainers. Solar cells fabricated out of HEM cast material have shown conversion efficiency up to 14% under AM1 Xenon source illumination. Considerable progress has been achieved in casting square cross-section ingots. The growth in the corners has been obtained but the problem area is in fabricating a custom-made graded crucible. Kerf loss was reduced to 6.2 mil, 0.155 mm in slicing 4 cm x 4 cm cross-section with 100% yield. The abrasive life of plated impregnated blades was increased by hardening the electroless nickel layer. In an effort to prevent diamond pull-out and thereby improve the abrasive life, the plated layer was increased from 0.3 mil, 7.5 ..mu..m to 0.5 mil, 12.5 ..mu..m. The extra thickness buried the diamonds. A thinner copper sheath for impregnation and a thicker nickel coating to prevent diamond pull-out is expected to improve the abrasive life. Higher feed forces increased the cutting rates but resulted in deeper surface damage

Mirages, anti-mirages, and further surprises in quantum corrals with non-magnetic impurities

We investigate the local density of states (LDOS) for non-interacting electrons in a hard wall ellipse in the presence of a single non-magnetic scattering center. Using a T-matrix analysis we calculate the local Green's function and observe a variety of quantum mirage effects for different impurity positions. Locating the impurity near positions with LDOS maxima for the impurity free corral can either lead to a reduction or an enhancement of the LDOS at the mirror image point, i.e. a mirage or anti-mirage effect, or even suppress LDOS maxima in the entire area of the corral.Comment: 6 pages, 7 figure

Controlling diffusive transport in confined geometries

We analyze the diffusive transport of Brownian particles in narrow channels with periodically varying cross-section. The geometrical confinements lead to entropic barriers, the particle has to overcome in order to proceed in transport direction. The transport characteristics exhibit peculiar behaviors which are in contrast to what is observed for the transport in potentials with purely energetic barriers. By adjusting the geometric parameters of the channel one can effectively tune the transport and diffusion properties. A prominent example is the maximized enhancement of diffusion for particular channel parameters. The understanding of the role of channel-shape provides the possibility for a design of stylized channels wherein the quality of the transport can be efficiently optimized.Comment: accepted for publication in Acta Physica Polonica

Silicon ingot casting: Heat exchanger method. Multi-wire slicing: Fixed abrasive slicing technique, phase 3

In the area of ingot casting the proof of concept of heat exchanger method (HEM) was established. It was also established that HEM cast silicon yielded solar cell performance comparable to Czochralski grown material. Solar cells with conversion efficiencies of up to 15% were fabricated. It was shown that square cross-section ingots can be cast. In the area of crystal slicing, it was established that silicon can be sliced efficiently with the fixed abrasive slicing technique approach. This concept was carried forward to 10 cm diameter workpiece

Silicon ingot casting: Heat Exchange Method (HEM). Multi-wire slicing: Fixed Abrasive Slicing Technique (FAST). Phase 3 and phase 4: Silicon sheet growth development for the large area sheet task of the low-cost solar array project

Several areas of silicon sheet growth development are addressed including: silicon ingot casting, heat exchanger method, multiwire slicing, and fixed abrasive slicing technique

Steering the potential barriers: entropic to energetic

We propose a new mechanism to alter the nature of the potential barriers when a biased Brownian particle under goes a constrained motion in narrow, periodic channel. By changing the angle of the external bias, the nature of the potential barriers changes from purely entropic to energetic which in turn effects the diffusion process in the system. At an optimum angle of the bias, the nonlinear mobility exhibits a striking bell-shaped behavior. Moreover, the enhancement of the scaled effective diffusion coefficient can be efficiently controlled by the angle of the bias. This mechanism enables the proper design of channel structures for transport of molecules and small particles. The approximative analytical predictions have been verified by precise Brownian dynamic simulations.Comment: (6 pages, 7 figures) Submitted to PR