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

Portable fiber optic coupled Doppler interferometer system for detonation and shock wave diagnostics

Testing and analysis of shock wave characteristics such as detonators and ground shock propagation frequently require a method of measuring velocity and displacement of the surface of interest. One method of measurement is Doppler interferometry. The VISAR (Velocity Interferometer System for Any Reflector) uses Doppler interferometry and has gained wide acceptance as the preferred tool for shock measurement. An important asset of VISAR is that it measures velocity and displacement nonintrusively

Measuring treasury market liquidity

This paper was presented at the conference "Economic Statistics: New Needs for the Twenty-First Century," cosponsored by the Federal Reserve Bank of New York, the Conference on Research in Income and Wealth, and the National Association for Business Economics, July 11, 2002. Securities liquidity is important to those who transact in markets, those who monitor market conditions, and those who analyze market developments. This article estimates and evaluates a comprehensive set of liquidity measures for the U.S. Treasury securities market. The author finds that the commonly used bid-ask spread-the difference between bid and offer prices-is a useful measure for assessing and tracking liquidity. The spread is highly correlated with a more sophisticated price impact measure and is correlated with episodes of reported poor liquidity in the expected manner. He also finds that other measures correlate less strongly with episodes of poor liquidity and with the bid-ask spread and price impact measures, indicating that they are only modest proxies for market liquidity. Trading volume and trading frequency, in particular, are found to be weak proxies for market liquidity, as both high and low levels of trading activity are associated with periods of poor liquidity.Liquidity (Economics) ; Treasury bills ; Treasury notes ; Government securities

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

Who buys Treasury securities at auction?

The U.S. Treasury Department now releases fuller information about its auctions than in the past, including new information on investor class and bidder category. The investor class data shed light on the distribution of demand for government securities, and the bidder category data, released first, offer an early read on demand. Purchases by indirect bidders, in particular, are a fairly good proxy for foreign purchases of Treasury notes, but not Treasury bills.Auctions ; Treasury notes ; Treasury bills ; Government securities

The benchmark U.S. Treasury market: recent performance and possible alternatives

Forecasting ; Economic indicators ; Treasury bills ; Government securities ; Budget ; Debts, Public

SUBOPT: A CAD program for suboptimal linear regulators

An interactive software package which provides design solutions for both standard linear quadratic regulator (LQR) and suboptimal linear regulator problems is described. Intended for time-invariant continuous systems, the package is easily modified to include sampled-data systems. LQR designs are obtained by established techniques while the large class of suboptimal problems containing controller and/or performance index options is solved using a robust gradient minimization technique. Numerical examples demonstrate features of the package and recent developments are described

‘Has anyone here seen Amos?’ – re-establishing ‘prophetic imagination’ at the centre of religious education and formation

In 1989 Australian author and illustrator Bob Graham published a children’s book entitled Has anyone here seen William? This article seeks to construct a parallel narrative in relation to the category of the prophet, with a particular focus on the need to engage in prophetic imagination within the twin contexts of religious education (hereafter R.E.) and formation. In doing so it also makes reference to one of the archetypical biblical prophets - Amos. The article’s primary interlocutor is scripture scholar Walter Brueggemann (1982, 2002a, 2002b) who has written on topics as diverse as scripture exegesis and the theology of pain and homecoming. He has also written prominently on prophetic imagination, understood as the capacity to stand outside the dominant discourse or power structure of one’s day and critique it. As we will demonstrate throughout the article, Brueggemann’s scholarship in this area is complemented and refined through contact with the African-American philosopher Cornel West’s (1999) approach to prophetic critique, along with other commentators. Held together, both thinkers impel us to consider why teaching ‘about prophets’ needs to be complemented by an explicit cultivation of prophetic imagination, and how this might be seeded in crucial contexts such as religious education and formation. Following a brief introduction (part one) the second part explores the nature of the prophetic challenge. Part three focuses on recovery of the prophetic imagination, while part four examines ways to cultivate the prophetic imagination today. The final section considers conclusions and future directions in relation to topics raised throughout the paper