Slicing of silicon into sheet material: Silicon sheet growth development for the large area silicon sheet task of the Low Cost Silicon Solar Array project

The limits of blade tolerance were defined. The standard blades are T-2 thickness tolerance. Good results were obtained by using a slurry fluid consisting of mineral oil and a lubricity additive. Adjustments of the formulation and fine tuning of the cutting process with the new fluid are necessary. Test results and consultation indicate that the blade breakage encountered with water based slurries is unavoidable. Two full capacity (974 wafer) runs were made on the large prototype saw. Both runs resulted in extremely low yield. However, the reasons for the low yield were lack of proper technique rather than problems with machine function. The test on the effect of amount of material etched off of an as-sawn wafer on solar cell efficiency were completed. The results agree with previous work at JPL in that the minimum material removed per side that gives maximum efficiency is on the order of 10 microns

How well do domain wall fermions realize chiral symmetry?

In the domain wall fermion formulation, chiral symmetry breaking in full QCD is expected to fall exponentially with the length of the extra dimension. We measure the chiral symmetry breaking due to a finite extra dimension in two ways, which can be affected differently by finite volume and explicit fermion mass. For quenched QCD the two methods generally agree, except for the largest extent of the extra dimension, which makes the limit uncertain. We have less data for full QCD, but see exponential suppression for the method where we have data.Comment: 3 pages, 2 figures, LATTICE99(hightemp

Slicing of Silicon into Sheet Material: Silicon Sheet Growth Development for the Large Area Silicon Sheet Task of the Low Cost Silicon Solar Array Project

Testing of low cost low suspension power slurry vehicles is presented. Cutting oils are unlikely to work, but a mineral oil with additives should be workable. Two different abrasives were tested. A cheaper silicon carbide from Norton gave excellent results except for excessive kerf loss: the particles were too big. An abrasive treated for lubricity showed no lubricity improvement in mineral oil vehicle. The bounce fixture was tested for the first time under constant cut rate conditions (rather than constant force). Although the cut was not completed before the blades broke, the blade lifetime of thin (100 micrometer) blades was 120 times the lifetime without the fixture. The large prototype saw completed a successful run, producing 90% cutting yield (849 wafers) at 20 wafers/cm. Although inexperience with large numbers of wafers caused cleaning breakage to reduce this yield to 74%, the yield was high enough that the concept of the large saw is proven workable

Slicing of Silicon into Sheet Material. Silicon Sheet Growth Development for the Large Area Silicon Sheet Task of the Low Cost Silicon Solar Array Project

Tests on mineral oil slurries show that the potential for workability and low cost is present. However, slurries tested to date which had sufficient lubricity exhibited wafer breakage problems near the end of the run for as-yet unknown reasons. The first test of the large prototype saw under cutting force control was largely successful in that the controller worked perfectly. Unfortunately a technique error (excessive stroke shortening) caused blade breakage and low yield. The latest run of the large saw pointed up the fact that an indication of end-of-stoke vertical motion, or bounce, is necessary. A circuit to provide such indication was fabricated and installed. Preliminary tests show it to be excessively noise sensitive; therefore, work on grounding and shielding to reduce this sensitivity is in progress

Cryogenic fluid flow instabilities in heat exchangers

Analytical and experimental investigation determines the nature of oscillations and instabilities that occur in the flow of two-phase cryogenic fluids at both subcritical and supercritical pressures in heat exchangers. Test results with varying system parameters suggest certain design approaches with regard to heat exchanger geometry

Slicing of silicon into sheet material. Silicon sheet growth development for the large area silicon sheet task of the low cost silicon solar array project

Fabrication of a prototype large capacity multiple blade slurry saw is considered. Design of the bladehead which will tension up to 1000 blades, and cut a 45 cm long silicon ingot as large as 12 cm in diameter is given. The large blade tensioning force of 270,000 kg is applied through two bolts acting on a pair of scissor toggles, significantly reducing operator set-up time. Tests with an upside-down cutting technique resulted in 100% wafering yields and the highest wafer accuracy yet experienced with MS slicing. Variations in oil and abrasives resulted only in degraded slicing results. A technique of continuous abrasive slurry separation to remove silicon debris is described

Quasi-Bell inequalities from symmetrized products of noncommuting qubit observables

Noncommuting observables cannot be simultaneously measured, however, under local hidden variable models, they must simultaneously hold premeasurement values, implying the existence of a joint probability distribution. We study the joint distributions of noncommuting observables on qubits, with possible criteria of positivity and the Fr\'echet bounds limiting the joint probabilities, concluding that the latter may be negative. We use symmetrization, justified heuristically and then more carefully via the Moyal characteristic function, to find the quantum operator corresponding to the product of noncommuting observables. This is then used to construct Quasi-Bell inequalities, Bell inequalities containing products of noncommuting observables, on two qubits. These inequalities place limits on local hidden variable models that define joint probabilities for noncommuting observables. We find Quasi-Bell inequalities have a quantum to classical violation as high as $\frac{3}{2}$, higher than conventional Bell inequalities. The result demonstrates the theoretical importance of noncommutativity in the nonlocality of quantum mechanics, and provides an insightful generalization of Bell inequalities.Comment: 17 page

Very Low Mass Stellar and Substellar Companions to Solar-like Stars from MARVELS. II. A Short-period Companion Orbiting an F Star with Evidence of a Stellar Tertiary and Significant Mutual Inclination

We report the discovery via radial velocity (RV) measurements of a short-period (P = 2.430420 ± 0.000006 days) companion to the F-type main-sequence star TYC 2930-00872-1. A long-term trend in the RV data also suggests the presence of a tertiary stellar companion with P > 2000 days. High-resolution spectroscopy of the host star yields T_(eff) = 6427 ± 33 K, log g = 4.52 ± 0.14, and [Fe/H] = –0.04 ± 0.05. These parameters, combined with the broadband spectral energy distribution (SED) and a parallax, allow us to infer a mass and radius of the host star of M_1 = 1.21 ± 0.08 M_☉ and R_1 = 1.09^(+0.15)_(–0.13) R_☉. The minimum mass of the inner companion is below the hydrogen-burning limit; however, the true mass is likely to be substantially higher. We are able to exclude transits of the inner companion with high confidence. Further, the host star spectrum exhibits a clear signature of Ca H and K core emission, indicating stellar activity, but a lack of photometric variability and small v sin I suggest that the primary's spin axis is oriented in a pole-on configuration. The rotational period of the primary estimated through an activity-rotation relation matches the orbital period of the inner companion to within 1.5 σ, suggesting that the primary and inner companion are tidally locked. If the inner companion's orbital angular momentum vector is aligned with the stellar spin axis as expected through tidal evolution, then it has a stellar mass of ~0.3-0.4 M_☉. Direct imaging limits the existence of stellar companions to projected separations <30 AU. No set of spectral lines and no significant flux contribution to the SED from either companion are detected, which places individual upper mass limits of M_([2,3]) ≾ 1.0 M_☉, provided they are not stellar remnants. If the tertiary is not a stellar remnant, then it likely has a mass of ~0.5-0.6 M_☉, and its orbit is likely significantly inclined from that of the secondary, suggesting that the Kozai-Lidov mechanism may have driven the dynamical evolution of this system

Results of the 1977 southern California pismo clam survey

A Pismo clam, Tivela stultorum, survey was conducted in January 1977 on selected southern California beaches. Effort and catch information was collected through clammer interviews. Estimates for the two day survey were 1,596 clammers spending 2,506 hours to take 6,139 clams. Comparisons were made between the 1977 survey results and previous surveys. Clams were collected for length and age studies. Compliance to the 4.5-inch (114.3 mm) minimum size limit appeared to be good. (15pp.