Effect of Floodwater Extraction on Mountain Stream Morphology

Floodwater is often extracted for consumptive purposes from western mountain streams in the United States. The long-term extraction of floodwater may alter the morphological and ecological balance of such streams. Scale model experiments based on eight mountain gravel-bed streams in Idaho were conducted to test the effects of floodwater extraction on stream morphology. The model channel transported a poorly sorted mix of model “gravel,” as well as copious amounts of model “sand.” The channel had a discontinuous floodplain, developed its own bar morphology, and contained large model colluvium as well as a bedrock platform. A mobile-bed equilibrium was first developed using a repeated hydrograph. The experiment was then repeated using a sliding cutoff discharge. The discharges in the hydrograph that were below a given cutoff discharge were reduced to 30% of bankfull discharge. By raising the cutoff discharge, it was possible to study the effect of increasing severity of floodwater extraction on stream morphology. The experiments indicated an increase in sand content on the bed surface and a decrease in the standard deviation of fluctuations in bed elevation with increasing severity of floodwater extraction.     

Injury risk among children of low-income U.S.-born and immigrant mothers.

The number of immigrants in the United States is at an all time high, yet psychologists have largely ignored the domain of immigrant health. This article considers 1 aspect of immigrant health, risk for pediatric injury. A sample of over 5,000 5-year-old children from impoverished families was studied; approximately 13% had immigrant mothers. Children of immigrants had a significantly lower rate of injury in the prior year. This was particularly true of non-White children of immigrants. Three possible mediators for this finding--assistance with parenting, parenting style, and health care accessibility--were considered, but none explained the difference. The need for further research on the topic and implications of results for injury prevention are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modeling of multiple-quantum-well solar cells including capture, escape, and recombination of photoexcited carriers in quantum wells

A self-consistent numerical Poisson-Schrodinger-drift-diffusion solver is described for simulation of multiple-quantum-well (MQW) Al/sub x/Ga/sub 1-x/As-GaAs solar cells. The rates of escape, capture, and recombination of photoexcited carriers in quantum wells embedded in the intrinsic region of a p-i-n device are self-consistently incorporated in the model. The performance of the device for various quantum-well configurations is investigated and the device characteristics are related to the dynamics of capture, escape, absorption, and recombination of carriers in the quantum wells. Our results show that the incorporation of MQWs in the intrinsic region of a p-i-n solar cell can improve the conversion efficiency of non-optimal devices, if the device is designed based on careful consideration of the behavior of the photoexcited carriers in the quantum wells. Specifically, we found out that an Al/sub 0.1/Ga/sub 0.9/As-GaAs cell with multiple quantum wells of 150 /spl Aring/ is more efficient than an identical single bandgap Al/sub 0.1/Ga/sub 0.9/As cell with no quantum wells, but less efficient than a single bandgap GaAs cell without such quantum wells.     

3D Monte Carlo Modeling of Thin SOI MOSFETs Including the Effective Potential and Random Dopant Distribution

We use the effective potential to include quantum mechanical effects in thin SOI MOSFETs simulated with 3D Monte Carlo. We explore the role of discrete dopant distributions on the threshold voltage of the device within the framework of the effective potential by examining the current-voltage behavior as well as the electron distributions within the device. We find that simulations with the effective potential produce a similar shift in current as classical simulations when the dopants are considered to have a random discrete distribution instead of a uniform distribution.     

The Effective Potential in Device Modeling: The Good, the Bad and the Ugly

We discuss the use of the effective potential to incorporate quantum effects in device models. While threshold shifts and charge set-back are handled well, tunneling is not well handled by this approach, or by any other local potential approach.     

The Impact of Microcomputers on Devices to Aid the Handicapped

Proven prototypes too often do not go into production because of economic factors. The authors are using microcomputers to make devices less expensive, more flexible, and more producible.     

Threshold voltage calculation in ultrathin-film SOI MOSFETs using the effective potential

The success of the effective potential method of including quantum confinement effects in simulations of MOSFETs is based on the ability to calculate ahead of time the extent of the Gaussian wave packet used to describe the electron. In the calculation of the Gaussian, the inversion layer is assumed to form in a triangular potential well, from which a suitable standard deviation can be obtained. The situation in an ultrathin silicon-on-insulator (SOI) MOSFET is slightly different, in that the potential well has a triangular bottom, but there is a significant contribution to the confinement from the rectangular barriers formed by the gate oxide and the buried oxide. For this more complex potential well, it is of interest to determine the range of applicability of the effective potential model with a constant standard deviation. In this paper, we include this effective potential model in Monte Carlo calculations of the threshold voltage of ultrathin SOI MOSFETs. We find that the effective potential recovers the expected trend in threshold voltage shift with decreasing silicon thickness, down to a thickness of approximately 3 nm.     

Bridge Deck Construction Using Type K Cement

Because drying shrinkage cracking is a major source of bridge deck cracking, and because shrinkage compensating concrete (SCC) is known to substantially reduce shrinkage cracking, the use of SCC should be closely examined in an effort to increase the durability and service life of bridge decks. One of the concerns regarding the use of SCC is its more demanding construction requirements for placement time and for curing. This paper addresses relevant material and construction issues that have resulted in the successful use of SCC for bridge decks. The Ohio Turnpike Commission (OTC) has used SCC exclusively for its new and replacement bridge decks for the past 12 years, and they have been very satisfied with its performance to date. The OTC's evaluation of SCC is that it greatly mitigates shrinkage cracking. The OTC's requirements for SCC at the concrete plant, in-transit, and at the job site are included in this paper. The OTC's construction procedures are presented in the form of a chronological sequence of photographs illustrating the construction activities on a new SCC deck placement in 1994.     

Effects of packaging SrI2(Eu) scintillator crystals

Recent renewed emphasis placed on gamma-ray detectors for national security purposes has motivated researchers to identify and develop new scintillator materials capable of high energy resolution and growable to large sizes. We have discovered that SrI₂(Eu) has many desirable properties for gamma-ray detection and spectroscopy, including high light yield of ∼90,000 photons/MeV and excellent light yield proportionality. We have measured <2.7% FWHM at 662 keV with small detectors (<1 cm³) in direct contact with a photomultiplier tube, and ∼3% resolution at 662 keV is obtained for 1 in.³ crystals. Due to the hygroscopic nature of SrI₂(Eu), similar to NaI(Tl), proper packaging is required for field use. This work describes a systematic study performed to determine the key factors in the packaging process to optimize performance. These factors include proper polishing of the surface, the geometry of the crystal, reflector materials and windows. A technique based on use of a collimated ¹³⁷Cs source was developed to examine light collection uniformity. Employing this technique, we found that when the crystal is packaged properly, the variation in the pulse height at 662 keV from events near the bottom of the crystal compared to those near the top of the crystal could be reduced to <1%. This paper describes the design and engineering of our detector package in order to improve energy resolution of 1 in.³-scale SrI₂(Eu) crystals.