Model reduction for optimization of rapid thermal chemical vapordeposition systems

A model of a three-zone rapid thermal chemical vapor deposition (RTCVD) system is developed to study the effects of spatial wafer temperature patterns on polysilicon deposition uniformity. A sequence of simulated runs is performed, varying the lamp power profiles so that different wafer temperature modes are excited. The dominant spatial wafer thermal modes are extracted via proper orthogonal decomposition and subsequently used as a set of trial functions to represent both the wafer temperature and deposition thickness. A collocation formulation of Galerkin's method is used to discretize the original modeling equations, giving a low-order model which loses little of the original, high order model's fidelity. We make use of the excellent predictive capabilities of the reduced model to optimize power inputs to the lamp banks to achieve a desired polysilicon deposition thickness at the end of a run with minimal deposition spatial nonuniformity. Since the results illustrate that the optimization procedure benefits from the use of the reduced-order model, our future goal is to integrate the model reduction methodology into real-time and run-to-run control algorithms. While developed in the context of optimizing a specific RTP process, the model reduction techniques presented in this paper are applicable to other materials processing systems     

On system design

The general, multiple attribute system design problem is formulated in total quality space which includes all of the microeconomic factors that influence the net value of a product to society. A hypothetical system design task—the development of improved system specifications and new subsystem requirements for the redesign of an automobile—is used to illustrate the approach. A new format is also given for describing design of experiment arrays which facilitates their use in spreadsheet calculations.     

An analysis of distributed feedback structures in ion exchangedwaveguides

The performance of distributed feedback (DFB) structures fabricated on ion exchanged waveguides has been numerically analyzed. Waveguide exchange time, grating order, period, number of periods, grating shape, and grating depth have been included as variables for the analysis. The results are for K⁺-Na⁺-type systems exchanged at 385°C     

An investigation of the use of heat pipes for machine tool spindle bearing cooling

The results of an experimental investigation into the practicality of using a heat pipe installed in the spindle of a milling machine to remove the heat produced in the spindle bearings which is capable of causing thermal distortion and cutting error are presented in the paper. Measurements of the variation of bearing temperature with time are reported at four different spindle speeds when there was no heat pipe installed, when the heat pipe was cooled by air and when the heat pipe was cooled by an ice/water mixture. Analysis of the results by a simple heat transfer model indicates that the particular heat pipe used was capable of removing up to 160 W with a corresponding 50% reduction in the rise of the bearing temperature above the temperature of the surrounding air at steady operating conditions.     

Effect of crystallinity on PVC physical properties

Crystallinity in PVC contributes significantly to the strength and resiliency of the polymer. Two types of crystallites have been described: a primary crystallite in the virgin powder state pictured as a platelet or flat needle-like lamellar crystallite, and a secondary, fringed micellar crystallite from melts or solutions. Both crystallites create loose, crosslinking networks. The secondary crystallite forms when plastisol melts are cooled or solutions are gelled. Crystallites exert a major effect on rheological properties. The thermal destruction of the primary crystallite networks in the melt phase results in a decrease in elastic modulus. Cooling from the fused state creates secondary crystallites that affect tensile and elongation.     

Laboratory and analytical studies of the effects of multipulselightning current on metal oxide arresters

Multiple stroke lightning ground flashes can impose surges of exceptional severity on the arresters used to protect exposed distribution system equipment. This paper reports laboratory and analytical studies of the effects of representative multiple impulse currents on zinc-oxide surge arresters of distribution class. The results indicate that sextuple 8/20 μs currents can cause damage to arresters not evident with standard lightning current tests and so are worthy of inclusion in testing Standards     

Effects of Ajoene on lymphocyte and macrophage membrane-dependent functions

An increasing flow of evidences collected on elementary forms of learning processes in selected animal models evidentiates some mechanisms which can represent the basic cellular principles underlying plastic changes: 1. 5HT and second messengers of nucleotide type (like cAMP) have a pivotal role in the learning process. 2. In almost all short-term learning processes the modifications are subserved by a mechanism of protein phosphorylation. 3. In various animal models the modulation of K+ and Ca2+ channels is the molecular mechanism for learning. Experiments performed in sensory T neuron of the leech indicate that the modulation of Na+/K+ electrogenic pump is one of the fundamental mechanism for learning. 4. In long-term plastic changes, the most important finding is that newly synthesized proteins are formed. 5. In addition to what has been observed in the Aplysia model, where changes in synaptic efficacy represent the basic principles of memory storage, in the leech it has been demonstrated that a molecular machinery present in a single neuron can adapt the activity of the cell to environmental stimuli.     

Keratin 17 gene expression during the murine hair cycle

Treatment of rats with phenytoin (DPH), an anti-epileptic drug, results in lower tissue thyroid hormone (TH) levels and interferes with the metabolic pathway of TH. To test the hypothesis that DPH affects the enterohepatic cycle of TH and, thus, the kinetics of TH turnover, we performed a kinetic experiment (three-compartment analysis) and a steady-state, double-isotope equilibrium experiment in rats treated for 3 weeks with DPH (50 mg/kg body weight per day) and in untreated controls. This included measurements of TH and TH metabolite levels, as well as the activities of enzymes involved in the TH metabolic pathway. DPH treatment resulted in a decrease in the production of thyroxine (T4) (by 25%) and tri-iodothyronine (T3) (by 37%), a decrease in the T3 concentration in all three pools, and a redistribution of T4 from the fast to the slow pool. The amount of T4 increased in intestinal contents and feces by 66% and 71% respectively. Expressed as a fraction of daily TH disposal, fecal loss of T4 was enhanced from 10 to 23% and that of T3 from 16 to 21%. An increase in T4 and T3 UDP-glucuronyltransferase activities was observed, suggesting that the increased fecal loss of T4 and T3 is secondary to an increased biliary output of their glucuronides. The reduced secretion of TH and increased fecal clearance during DPH treatment can lead in the long run to depletion of TH stores.     

CYSTINE LYASES IN PLANTS: A COMPREHENSIVE REVIEW

Cystine lyases cleave L-cystine through aβ-elimination reaction producing thiocysteine (cysteine persulfide), pyruvate and ammonia. They are responsible for the initial reaction that produces characteristic flavors and aromas in important vegetables of the genus Brassica. In this review, an overview of these plant C-S lyases, comparison with alliin lyases andβ-cystathionases, purification protocols, substrate specificity, function and biochemical characteristics will be discussed. The importance of these enzymes to food science will also be examined.