Fabrication of SiC-Whisker-Reinforced MoSi2 Composites by Tape Casting

In this paper, we describe a procedure for the processing of SiC-whisker-reinforced MoSi₂ composites via tape casting. Based on the characteristics of SiC whiskers and MoSi₂ powder in aqueous and nonaqueous solvents, a slip formulation (solvent, dispersant, binder, etc.) has been developed. The formulation developed allows for a uniform distribution of SiC whiskers in the matrix, easy separation of the tapes from the polymeric carrier, convenient control of both tape thickness and orientation of SiC whiskers, and a low binder burnout temperature. The latter is important for the prevention of the oxidation of MoSi₂ powder during the binder burnout in an oxidizing atmosphere.     

Multiobjective optimization of an industrial semibatch nylon 6 reactor

Multiobjective Pareto optimal solutions have been generated for three grades of nylon 6 being produced in an industrial semibatch reactor. The optimal operating conditions (called preferred solutions) for these three batches are easy to implement and lead to substantial improvements over current practice. The technique used is quite general and can easily be applied to improve the operation of other industrial polymerization reactors or design better (new) reactors. Good mathematical models, which account for the important physicochemical aspects actually operative in a reactor and which have been tested on industrial data, are a prerequisite for such optimization studies. © 1995 John Wiley & Sons, Inc.     

Information-Based Dynamic Manufacturing System Scheduling

Information about the state of the system is of paramount importance in determining the dynamics underlying manufacturing systems. In this paper, we present an adaptive scheduling policy for dynamic manufacturing system scheduling using information obtained from snapshots of the system at various points in time. Specifically, the framework presented allows for information-based dynamic scheduling where information collected about the system is used to (1) adjust appropriate parameters in the system and (2) search or optimize using genetic algorithms. The main feature of this policy is that it tailors the dispatching rule to be used at a given point in time to the prevailing state of the system. Experimental studies indicate the superiority of the suggested approach over the alternative approach involving the repeated application of a single dispatching rule for randomly generated test problems as well as a real system. In pa ticular, its relative performance improves further when there are frequent disruptions and when disruptions are caused by the introduction of tight due date jobs and machine breakdown—two of the most common sources of disruption in most manufacturing systems. From an operational perspective, the most important characteristics of the pattern-directed scheduling approach are its ability to incorporate the idiosyncratic characteristics of the given system into the dispatching rule selection process and its ability to refine itself incrementally on a continual basis by taking new system parameters into account.     

Ultraviolet radiometry with synchrotron radiation and cryogenic radiometry

The combination of a cryogenic radiometer and synchrotron radiation enables detector scale realization in spectral regions that are otherwise difficult to access. Cryogenic radiometry is the most accurate primary detector-based standard available to date, and synchrotron radiation gives a unique broadband and continuous spectrum that extends from x ray to far IR. We describe a new cryogenic radiometer-based UV radiometry facility at the Synchrotron Ultraviolet Radiation Facility II at the National Institute of Standards and Technology. The facility is designed to perform a variety of detector and optical materials characterizations. The facility combines a high-throughput, normal incidence monochromator with an absolute cryogenic radiometer optimized for UV measurements to provide absolute radiometric measurements in the spectral range from 125 nm to approximately 320 nm. We discuss results on photodetector characterizations, including absolute spectroradiometric calibration, spatial responsivity mapping, spectroreflectance, and internal quantum efficiency. In addition, such characterizations are used to study UV radiation damage in photodetectors that can shed light on the mechanism of the damage process. Examples are also given for UV optical materials characterization.     

Thermodynamics of Silicon Nitridation: Effect of Hydrogen

The effects of hydrogen on the equilibrium concentration of species formed during nitridation of silicon were studied using a computer program that calculates equilibrium compositions by minimizing the Gibbs free energy.     

On optimal ramp control of traffic jam queues

A queuing theory model is developed for the controlled merging of vehicles entering an expressway ramp. The flow of ramp vehicles is restricted in response to downstream congestion or traffic jams. An optimal on-off controller is found for the stochastic problem with random stopping time which results from minimizing the mean sum of the number of cars stopped in the jam and the number of cars diverted from the ramp.     

Evidence for defective skeletal mineralization in low-birthweight infants: the absorption of calcium and fat

Using serial metabolic balance techniques, the absorption and retention of calcium and the absorption of fat have beem measured over the first 30 to 70 days of life in 11 preterm and 2 full-term light-for-dates infants. They were fed either full-cream cow's milk, half-skimmed cow's milk, the proprietary filled milk S.M.A., or breast milk. The values for calcium intake, absorption and retention were compared with the rate of accumulation of calcium by the fetus in utero, which was calculated from published data on the chemical composition of fetal bodies. Infants fed breast milk had an absolute dietary deficiency of calcium. Those fed other milks ingested sufficient but they did not absorb enough. Though calcium absorption increased with increasing postnatal age, intrauterine rates of calcium retention were never achieved on any of the milks. The average retention of calcium by preterm infants as a percentage of intrauterine accumulation was, for cow's milk 38%, for S.M.A. 27%, and for breast milk 17%. The full-term light-for- dates infants absorbed and retained more calcium than the preterm infants; it was on average 52% of the amount accumulated by the human fetus for an equivalent weight gain. The average absorption of fat by preterm infants was, from the cow's milk preparations 55%, from S.M.A. 61%, and from breast milk 84%. The light-for-dates infants absorbed on average 87% of the breast milk fat. There was no evidence that the amount of calcium absorbed was materially influenced by fat malabsorption. The principal determinants of the amount of calcium absorbed were the length of gestation and postnatal age of the infant.     

The application of 1H HR-MAS NMR spectroscopy for the study of structures and associations of organic components at the solid-aqueous interface of a whole soil

High resolution-magic angle spinning nuclear magnetic resonance (HR-MAS NMR) allows the application of solution-state NMR experiments to samples that are not fully soluble and contain solids. Only the species in contact with the solvent system employed become NMR observable. In this study utilizing D2O as the solvent system we show it is possible to examine the structures at the solid-aqueous interface of a whole soil. Combining one- and two-dimensional HR-MAS NMR allowed, for the first time, the identification of fatty acids, aliphatic esters, and ethers/ alcohols as prominent species at the solid-aqueous interface of the soil with signals from sugars and amino acids also apparent. Few, if any signals from aromatic protons were observed when the soil was swollen in aqueous media, although these signals are observed in extracts from the same soil and when the soil is swollen with a more penetrating solvent(DMSO-d6)which is known to disassociate hydrogen bonds. These findings indicate that the soil aromatic moieties are protected in hydrophobic regions which are not water accessible. Furthermore, when the soil was amended with a herbicide (trifluralin), direct observations of interactions between the protons on a xenobiotic and the surrounding soil matrix were possible for the first time. HR-MAS promises to be a method that can be widely applicable to a range of complex environmental samples without the need for extraction, pretreatment, or purification.