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Extreme ultraviolet (EUV) emission from laser-produced plasmas (LPP) centered at 13.5 nm is considered a leading candidate for the light source in future lithography systems. Tin is currently the best material for generating this EUV emission since it emits strongly within the 13.5 nm region due to its various ionic states (Sn8+-Sn14+). Highly efficient and low-debris LPPs are a pre-requisite for their use as light sources for EUV lithography. Tin plasmas generate debris that can damage collection optics over time. Techniques to mitigate debris are needed to extend the lifetime of these components and the system. Optimization of plasma conditions is necessary for increasing EUV emission and enhancing conversion efficiency (CE). Improving the source CE is necessary in order to reduce the cost of ownership and hence, develop a commercially viable lithography system for the semiconductor industry. One method to accomplish this is to reheat pre-formed plasma with a laser pulse to enhance EUV emission. This enhancement is achieved by controlling those plasma conditions necessary for optimizing EUV emission. We investigated the role of prepulse laser wavelength on prepulse plume formation and EUV in-band signal enhancement. A 6 ns Nd:YAG laser operating at 1064 nm and 266 nm was used for generating the prepulse plume. The expanding plume was then reheated by a 35 ns CO2laser operating at 10.6 m. The role of prepulse wavelength and energy on EUV conversion efficiency is discussed.

Material selection and lifetime issues for extreme ultraviolet (EUV) lithography are of critical importance to the success of this technology for commercial applications. This work reviews current trends in production and use of plasma-facing electrodes, insulators, and wall materials for EUV-type sources. Ideal candidate materials should be able to: withstand high thermal shock from the short pulsed plasma; withstand high thermal loads without structural failure; reduce debris generation during discharge; and be machined accurately. We reviewed the literature on current and proposed fusion plasma-facing materials as well as current experience with plasma gun and other simulation devices. Both fusion and EUV source materials involve issues of surface erosion by particle sputtering and heat-induced evaporation/melting. These materials are either bare structural materials or surface coatings. EUV materials can be divided into four categories: wall, electrode, optical, and insulator materials. For electric discharge sources, all four types are required, whereas laser-produced plasma EUV sources do not require electrode and insulator materials. Several types of candidate alloy and other materials and methods of manufacture are recommended for each component of EUV lithography light sources. © 2004 Society of Photo-Optical Instrumentation Engineers.

Discharge-produced plasma (DPP) devices have been proposed as a light source for EUV lithography. A key challenge for DPP is achieving sufficient brightness to support the throughput requirements of exposure tools for high-volume manufacturing lithography. To simulate the environment of the EUV source and optimize the output of the source, an integrated model is being developed to describe the hydrodynamic and optical processes that occur in DPP devices. The model includes both plasma evolution and magnetohydrodynamic processes as well as detailed photon radiation transport. The total variation diminishing scheme in the Lax-Friedrich formulation for the description of magnetic compression and diffusion in a cylindrical geometry is used. Several models are being developed for opacity calculations: a collisional radiation equilibrium model, a self-consistent field model with Auger processes, and a nonstationary kinetic model. Radiation transport for both continuum and lines with detailed spectral profiles are taken into account. The developed models are integrated into the HEIGHTS-EUV computer simulation package. Preliminary results of a numerical simulation of xenon gas hydrodynamics and EUV radiation output are presented for various plasma conditions. © 2004 Society of Photo-Optical Instrumentation Engineers.

Density functional calculations at the B3LYP/6-31G* level are used to generate electron-diffraction intensity curves for six conformers of hexahydro-1,3,5-trinitro-s-triazine (RDX). These are compared with an experimental curve (Shishkov, I. F.; Vilkov, L. V.; Lolonits, M.; Rozsondai, B. Struct. Chem. 1991, 2, 57) for which a structural model of gas-phase RDX was proposed. The calculations were done to investigate possible causes of the discrepancies between the theoretical structures and the molecular model proposed by Shishkov et al. The results show that alternative structures to that proposed from experiment can reproduce the measured intensities. Also, barriers to interconversion between the conformers were calculated to investigate the possibility of rapid interconversion at the temperature of the experiment (433 K). Barriers range from 1.5 to 5 kcal/mol, suggesting that measurements of RDX in the gas phase might reflect a dynamically averaged structure that represents contributions from the individual conformers.

A classical potential consisting of both intramolecular and intermolecular (Buckingham and Coulombic) terms that was developed for the simulation of crystalline nitromethane has been used to investigate the dynamics of liquid nitromethane at various temperatures and pressures. The validation of the proposed potential model was done for a large number of static and dynamic properties including the heat of vaporization, the variation of density with temperature and pressure, the thermal expansion coefficient, the self-diffusion coefficients, the viscosity coefficient, the dielectric constant, the bulk modulus, and the variation of vibrational frequencies with pressure. The analyses performed using constant pressure and temperature and constant volume and temperature molecular dynamics simulations show that the potential accurately reproduces the structural properties of liquid nitromethane at ambient pressure in the temperature range 260−374 K as well as the compression effects up to 14.2 GPa.

In vivoimaging of cells tagged with light-emitting probes, such as firefly luciferase or fluorescent proteins, is a powerful technology that enables a wide range of biological studies in small research animals. Reporters with emission in the red to infrared (>600 nm) are preferred due to the low absorption in tissue at these wavelengths. Modeling of photon diffusion through tissue indicates that bioluminescent cell counts as low as a few hundred can be detected subcutaneously, while ∼106cells are required to detect signals at ∼2 cm depth in tissue. Signal-to-noise estimates show that cooled back-thinned integrating charge coupled devices (CCDs) are preferred to image-intensified CCDs for this application, mainly due to their high quantum efficiency (∼85) at wavelengths >600 nm where tissue absorption is low. Instrumentation for in vivoimaging developed at Xenogen is described and several examples of images of mice with bioluminescent cells are presented. © 2001 Society of Photo-Optical Instrumentation Engineers.

A classical potential to simulate the dynamics of a nitromethane crystal as a function of temperature and pressure is described. The intramolecular part of the potential was taken as superposition of bond stretching, bond bending, and torsional angles terms. These terms were parametrized on the basis of the geometric and spectroscopic (vibrational frequencies and eigenvectors) data obtained using ab initio molecular orbital calculations performed at the B3LYP/6-31G* level on an isolated molecule. The intermolecular potential used is of the Buckingham 6-exp form plus charge−charge Coulombic interactions and has been previously developed by us (Sorescu, D. C.; Rice, B. M.; Thompson, D. L. J. Phys. Chem. 1997, B101, 798) to simulate crystals containing nitramine molecules and several other classes of nitro compounds. The analyses performed using constant pressure and temperature molecular dynamics simulations and molecular packing calculations indicate that the proposed potential model is able to reproduce accurately the changes of the structural crystallographic parameters as functions of temperature or pressure for the entire range of values investigated. In addition, the calculated bulk modulus of nitromethane was found in excellent agreement with the corresponding experimental results. Moreover, it was determined that the present potential predicts correctly an experimentally observed 45° change in methyl group orientation in the high-pressure regime relative to the low-temperature configuration. The analysis of the linear expansion coefficients and linear compression data indicate anisotropic behavior for the unit cell edges.

Abstract:  The traditional approach to developing propellants for specific gun applications relies heavily on trial and error. Candidate formulations must be made in small quantities and subjected to burning-rate measurements and small-scale vulnerability assessments. If the properties of these candidates fail to meet expectations, the process must be repeated. This approach, while historically unavoidable, is obviously inefficient in time and expense, but it also can generate considerable waste streams associated with unsuccessful formulations. With added considerations of life-cycle costs including environmental impact at all stages of development, use, and disposal, this traditional approach becomes increasingly unworkable. In this report a new approach is proposed which makes maximal use of scientific understanding embodied in models during the early phases of the propellant-development cycle. Through simple simulations, it is shown that this strategy can have a significant impact on the overall costs of the development process. In analogy to the DOE program to convert the nuclear-weapon stewardship from testing-based to science-based, we term the new approach "science-based design." It is argued that the modeling contribution to the propellant-development process is most efficiently implemented by subjecting candidate formulations to a hierarchy of models of different sophistication and input-data requirements, reserving the most rigorous models (usually the most data-intensive and least robust) for the most promising candidates. This new approach will require concentration and leveraging of resources toward the most critical early-phase development steps, but it may be the only credible strategy to reconcile the need for higher-performance weapons with the reality of declining resources.

Abstract:  The work presented here demonstrates the first phases of a newly-proposed gun propellant formulation process that will minimize life-cycle costs through science-based design. This new approach to gun propellant formulation proposes maximal use of modeling and simulation in the earliest phases of the developmental cycle to screen candidate formulations, resulting in the elimination of probable poor performers and the identification of the most promising candidates for further study and testing. The screening and identification of promising candidate formulations is demonstrated in the study presented here under the assumption of a specific weapon platform and user requirements. The process of selecting a propellant for the assumed gun system application has been distilled into a series of measurable steps leading from a set of candidate materials, through logical and numerical filters, to a shorter list of energetic materials demonstrated as viable choices for the weapon platform. Environmental filtering and performance modeling are used to screen propellants through a well-defined sequence of tests designed to weed out materials that do not meet standards in terms of safety, energy, or manufacturability. Because much of the testing is performed by computer modeling, the gun systems and energetic materials need not be present (nor even existent) in order to be described and matched against performance requirements for future applications. The calculations presented here demonstrate that utilizing computer models in the early developmental stages of the formulation process rather than physical testing produces enormous savings in labor, material, and environmental costs, along with a tremendous reduction in the time required to select a "best candidate" propellant.

Seedling traits have been described across 1744 species of Australian plants. Six traits were coded as binary alternatives: (1) phanerocotyly vs cryptocotyiy; (2) first leaf scale‐like vs leaf‐like; (3) first leaf single vs paired; (4) cotyledons hairy vs. glabrous; (5) hypocotyl hairy vs glabrous, and (6) embryo green vs non‐green at maturity. Seed volume was calculated from measurements of seed dimensions. Three approaches were used in analysing the data: (1) the taxonomic distribution of binary character states was described; (2) the strength of bivariate character associations was quantified at species level (‘cross‐species' correlations and regressions); (3) the data were arrayed on a phylogenetic tree in order to analyse by ‘phylogenetic regression’ for correlated evolutionary shifts in trait pairs. All die traits appeared evolutionarily malleable. For example, while cryptocotyiy was the minority condition (22% of species), it occurred in many different taxa (124 genera, 40 families, 24 orders) with high levels of polymorphy (16%, 25% and 42% for genera, families and orders). Similarly, the less common attribute states for first leaf type, hypocotyl texture, cotyledon texture and embryo colour occurred in species from right across die dicotyledon phylogeny, as did independent evolutionary divergences in each of mese characters. These patterns indicate that debate over which conditions are primitive and which are advanced will not have any general answer, only an answer for a specific branch‐step in die phylogenetic tree. In nearly all cases, correlated‐divergence analyses showed the same patterns as cross‐species analyses. The strongest associations were between seed volume and cryptocotyiy, seed volume and scale‐like first leaf, and seed volume and presence of green embryo. In addition, cryptocotyiy and scale‐like first leaf, and cotyledon and hypocotyl type, were strongly associated in bom correlated‐divergence and cross‐species analyses. Interpretation of results was mosdy presented wim respect to seed size, a trait which we consider to be pivotal in a species' seedling establishment strategy. All possible pairwise combinations ofbinary seedling traits were found in our study species. Taken togedier, the various lines of evidence presented here suggest that the traits have assorted more or less independendy of each odier and provide no evidence of functional groups based an mese attributes. Thus, the several existing seedling typologies should be regarded as classifications of convenience rather than as reflecting fundamental types.

A previously developed intermolecular potential for nitramines and several other classes of nitro-compound crystals has been used to investigate the behavior of the energetic materials hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX), 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX), 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (HNIW), and pentaerythritol tetranitrate (PETN) under hydrostatic compression. Isothermal−isobaric molecular simulations (assuming the rigid-molecule approximation) and molecular packing calculations were used to perform the analyses. In the case of the RDX, HMX, and HNIW crystals, the results indicate that the proposed potential model is able to reproduce accurately the changes in the structural crystallographic parameters as functions of pressure for the entire range of pressures that has been investigated experimentally. In addition, the calculated bulk moduli of RDX and HMX were found to be in good agreement with the corresponding experimental results. In the case of the PETN crystal, the crystallographic parameters have been reproduced with an acceptable accuracy at pressures up to about 5 GPa. The larger deviations from the experimental results at greater pressures indicate the limitations of the rigid-molecule model when applied to floppy molecules. The similarity of the results determined in molecular packing calculations relative to those from molecular dynamics simulations suggest that the former method can be used as an efficient tool for rapid tests of the crystal structure modification under pressure.

Hummock grasses in the genus TriodiaR. Br. were examined at 116 recently burned locations across mainland Australia, and were recorded as regenerating by resprouting, or by seed only. Prior to this survey it was known that the capacity to resprout varies considerably in Triodia, but it was unclear whether some species might be entirely resprouting and other species entirely fire-killed; whether this might be associated with particular traits of species or particular landscape types; or whether resprouting might be more common in particular regions such as the northern monsoonal grasslands. Seven species had both fire-killed and resprouting populations represented among the sites examined. Three species [T. basedowiiE. Pritzel, T. marginataN.T. Burbidge and T. melvillei(C.E. Hubbard) Lazarides] were recorded as fire-killed at all sites examined, and five species [T. bynoei(C.E. Hubbard) Lazarides, T. bunicola(S.W.L. Jacobs) Lazarides, T. intermediaCheel, T. molestaN.T. Burbidge and T. spicataN.T. Burbidge] were recorded as resprouting at all sites. Another seven species were recorded at one site only. There was no clear overall trend for fire-killed populations to be more prevalent in south rather than north, or east vswest, or coastal vsinland parts of the continent. No clear relationships were found between regeneration strategy and site attributes. Considered as a group, resprouting species were more likely to have an open growth form than a dense growth form, whereas the opposite was true for fire-killed species. Given that no trait either of species or of landscape was found to be a consistent correlate of resprouting, a likely inference is that resprouting might vary between different fires, even for a given population at a given site. Against this inference, fire-killed populations had substantial densities of seedlings much more often. Longitudinal studies would be needed to demonstrate directly whether resprouting varied between different fires at a site, and to investigate the implications of this for maintenance or extinction of local populations.

A new semi-empirical potential for Fe based on the quantum chemistry concept of bond order has been developed. The potential consists of two parts: the repulsive short-range exponential potential, and the attractive potential, also of the exponential form, with a bond-order prefactor. The latter depends on angles between the Fe-Fe bonds, and uses the environmental parameter similar to that of the Tersoff bond-order potential for tetrahedrally bonded semiconductors. The bond order function (depending on the above environmental parameter), however, is of a more general form than that of the Tersoff potential. The new potential was calibrated using the traditional fitting to the Universal Scaling and the equilibrium volume and cohesive energy of BCC Fe. The introduced 'punishment functions' also directed the multi-variate minimization process towards minimizing the deviations between the calculated and experimental values of the elastic moduli C′ and C44, the energies of FCC and HCP Fe modifications, and the (111) free surface energy. With the total of 15 fitted parameters, the potential reproduces with only minor deviations the elastic moduli, the volume–pressure equation of states in BCC phase, the energies in FCC and HCP modifications, the BCC-HCP phase transformation under pressure, and the energy of the (111) free surface. Other tests of the new potential are being currently performed. The potential will be used in atomistic simulations of lattice stability, and deformation and chemisorption processes in Fe.

We have analyzed the transferability of a previously proposed intermolecular potential for nitramine crystals to reproduce the experimentally determined crystal structures (within the approximation of rigid molecules) of 51 nitro compounds. These compounds include different types of acyclic, monocyclic, and polycyclic molecules. It is shown that this potential model accurately reproduces the experimentally determined crystallographic structures and lattice energies for the majority of these crystals. The best agreement with experimental structural and energetic data is obtained when the electrostatic charges have been determined using ab initio methods that include electron correlation effects, namely MP2 and B3LYP. The use of the electrostatic charges calculated at the Hartree−Fock level results in large differences between the predicted and the experimental values of the lattice energies. This difference can be significantly decreased by scaling the electrostatic charges with a general factor without introducing significant variations of the predicted crystallographic parameters. Further testing of the proposed intermolecular potential has been done by performing isothermal−isobaric molecular dynamics (MD) simulations over the temperature range 100−450 K, at atmospheric pressure, for the monoclinic phase of the 2,4,6-trinitrotoluene (TNT) crystal and for the polymorphic phase I of the pentaerythritol tetranitrate (PETN I) crystal. In each case, the results show that throughout the MD simulations the average structures of the crystals maintain the same space group symmetry as the one determined experimentally and there is a good agreement between the calculated crystallographic parameters and the experimental values. The thermal expansion coefficients calculated using the present model indicate an overall anisotropic behavior for both TNT and PETN I, with a thermal isotropy for PETN I along cell directions a and b.

Ab initio and nonlocal density functional theory (DFT) calculations were performed to determine reaction mechanisms for formation of the six-membered ring C3N3Cl3 (cyanuric chloride) from the monomer cyanogen chloride (ClCN). MP2 geometry optimizations followed by QCISD(T) energy refinements and corrections for zero-point energies for critical points on the potential energy surface were calculated using the 6-31G* and 6-311+G* basis sets. DFT (B3LYP) geometry optimizations and zero-point corrections for critical points on the potential energy surface were calculated with the 6-31G*, 6-311+G*, and cc-pVTZ basis sets. Good agreement is found for MP2 and DFT geometries and frequencies of cyanuric chloride and ClCN when compared with experimental values. Two formation mechanisms of cyanuric chloride were investigated, the concerted triple association (3 ClCN → cyanuric chloride) and the stepwise association (3ClCN → Cl2C2N2 + ClCN → cyanuric chloride). All calculations show that the lower energy path to formation of cyanuric chloride is the concerted triple-association. MP2 and DFT intrinsic reaction coordinate calculations starting from the transition state for concerted triple association reaction proceeding toward the isolated monomer resulted in the location of a local minimum, stable by as much as 8.0 kcal/mol, that corresponds to a weakly-bound cyclic (ClCN)3 cluster. The existence of this cluster on the reaction path for the concerted triple association could lower the entropic hindrance to this unusual association reaction mechanism. The DFT/cc-pVTZ barrier to concerted triple association relative to isolated ClCN is 42.9 kcal/mol. The QCISD(T)//MP2/6-311+G* barrier to concerted triple association is 41.0 kcal/mol. The DFT/cc-pVTZ barrier to formation of the dimer (stepwise association reaction) is 63.4 kcal/mol while the QCISD(T)//MP2/6-311+G* barrier is 76.7 kcal/mol. The barrier to formation of cyanuric chloride relative to the (ClCN)3 minimum requires ~46−49 kcal/mol, indicating that the concerted triple-association reaction via formation of the (ClCN)3 prereaction intermediate is the lower energy path to formation of cyanuric chloride. The temperature-corrected (T = 298 K) heats of reaction for formation of cyanuric chloride from ClCN are −63.4 and −61.2 kcal/mol for the B3LYP/cc-pVTZ and the QCISD(T)//MP2/6-311+G* predictions, respectively.

A group often spouses with aphasic partners participated in a support group. The group offered both a means of gaining emotional support and, through structured educational activities, relevant information. Comparisons between good and poor attenders on a range of measures of psychological adjustment were undertaken. It was found that good attenders showed significant improvement at various stages on tests of social dysfunction, somatic symptoms, and anxiety, and a broad measure of psychological well-being. Some functional improvement in the partners of good attenders was also noted. It is concluded that participation in a support group is of psychological benefit to spouses of aphasic patients.

We have developed an intermolecular potential that describes the structure of the α-form of the hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX) crystal. The potential is composed of pairwise atom−atom (6-exp) Buckingham interactions and charge−charge interactions. The parameters of the Buckingham repulsion−dispersion terms have been determined through a combination of nonlinear least-squares fitting to observed crystal structures and lattice energies and trial-and-error adjustment. Crystal packing calculations were performed to determine the equilibrium crystallographic structure and lattice energy of the model. There are no significant differences in the geometrical structures and crystal energies resulting from minimization of the lattice energy with and without symmetry constraints. Further testing of the intermolecular potential has been done by performing symmetry-constrained isothermal−isobaric Monte Carlo simulations. The properties of the crystal (lattice dimensions, molecular orientation, and lattice energy) determined from Monte Carlo simulations at temperatures over the range 4.2−300 K indicate good agreement with experimental data. The intermolecular potential was also subjected to isothermal−isobaric molecular dynamics calculations at ambient pressure for temperatures ranging from 4.2 to 325 K. Crystal structures at 300 K are in outstanding agreement with experiment (within 2% of lattice dimensions and almost no rotational and translational disorder of the molecules in the unit cell). The space-group symmetry was maintained throughout the simulations. Thermal expansion coefficients were determined for the model and are in reasonable accord with experiment.

The free energy of formation of magnesium sulfate and its solubility in magnesia have been determined. The salient feature of the results is that trace amounts of calcium impurity in magnesia noticeably lower the dissociation temperature and pressure of magnesium sulfate. A high-purity magnesia, which was prepared by oxidation of a high-purity magnesium, was used to determine the equilibrium constant for the formation of MgSO4. The sulfate solubil-ity In magnesia saturated with MgSO4was found to be higher than that in lime saturated with CaSO4. At 1100°C, CaSO4and CaS form in calcined dolomite at SO2partial pressures higher than those in pure CaO. From these findings it is estimated that at MgO saturation the ac-tivity coefficient relative to CaO is about 0.8.

In the present work the solid solubilities of CaS and CaSQ, in burnt lime were investigated by equilibrating lime with CO-CO2-SO2mixtures at temperatures from 950 to 1300°C. Also, the equilibrium constants for the formation of CaS and CaSO4were determined. At high oxy-gen activities, corresponding to a CO2/CO ratio >100 in the gas, the sulfur dissolves in lime primarily as sulfate ions. At lower oxygen activities (CO2/CO <30), the sulfur goes into so-lution in lime essentially as sulfide ions. Over the temperature range investigated the limit-ing sulfide solubility is within 0.01 to 0.03 pct S, whereas the sulfate solubility is within 0.03 to 0.1 pct S, increasing with increasing temperature.

Contamination of retail poultry by Campylobacter spp. is a significant source of human diarrheal disease. We have developed a colony-lift immunoassay (CLI) for the detection of Campylobacter jejuni, C. coli, and C. lari isolated from such sources and grown on selective agar medium or on filter membranes. This technique has been successfully utilized to quantify Campylobacter colonies within 18 to 28 h after sampling. Hydrophobic, high-protein-binding membranes were prewet with methanol and used to imprint bacterial cells from the agar or filter membrane, while leaving colonies intact and viable. The membranes were air dried, peroxidase neutralized, blocked with bovine serum albumin in phosphate-buffered saline, and hybridized for 5 min with an affinity-purified, horseradish peroxidase-labeled goat anti-Campylobacter antibody preparation (Kirkegaard and Perry Laboratories). The membranes were washed briefly, exposed to a 3,'5,5'-tetramethylbenzidine membrane substrate, rinsed in deionized water, and allowed to dry. Lifted colonies of Campylobacter were identified by a blue color reaction on the membrane. Replicas of the membranes were made by marking the location of the Campylobacter colonies on clear transparencies, which were subsequently utilized to locate the original colony on the filter membrane or agar plate. The specificity of this antibody preparation has been evaluated against a wide range of Campylobacter spp., including American Type Culture Collection type and references strains, retail poultry isolates, and isolates obtained from cloacal swabs of live commercial broiler chickens. Specificity against numerous non-Campylobacter spp. obtained from the same sources was also evaluated. The CLI provided a rapid and simple means for detection and enumeration of enteropathogenic Campylobacter organisms. We have successfully combined this CLI procedure with methods recently developed in our laboratories for retail meat and poultry sampling. Potentially, broader applications for use of this technique include detection and enumeration of campylobacters from clinical, veterinary, and environmental samples.

A pre-test, post-test, experimental design was used to evaluate the effects of peer counseling training with two samples of rehabilitation facility clients (N= 59). The following results were achieved with both samples, using different trainers: (1) both groups demonstrated improved basic helping skills as measured by the Communication and Discrimination Test(Carkhuff, 1976) and evaluated the training experience very positively; (2) neither group showed consistent improvement on a self-report measure of empathy, assertion, and decision making; and (3) neither group was rated significantly more assertive by their vocational training instructor.

We have investigated the transferability of a Buckingham repulsion−dispersion intermolecular potential previously developed [J. Phys. Chem. B 1997, 101, 798] for the explosive hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX) to predict the crystal structures (within the approximation of rigid molecules) of 30 nitramines, comprising acyclic, monocyclic, and polycyclic molecules. It is shown that this potential model accurately reproduces the experimentally determined crystallographic structures and lattice energies of these crystals. For the majority of these crystals, the best agreement with experiment is obtained when the electrostatic charges are determined using ab initio methods that include electron correlation effects, namely, MP2 and B3LYP. The use of the electrostatic charges calculated at the Hartree−Fock level results in large deviations of the predicted lattice energies from the experimental values. These deviations of the lattice energies can be significantly decreased, without significantly affecting the predicted crystallographic parameters, by scaling the electrostatic charges with a constant factor.

A 1988 community-based survey of 1,784 black adults aged 25-50 years in Pitt County, North Carolina, found mean waist-to-hip ratios of 0.890 for men and 0.852 for women. Based on guidelines from the US Department of Agriculture, 20% of the men and 76% of the women had an elevated waist-to-hip ratio. Sedentary behavior was associated with elevated waist-to-hip ratio in men, while a similar excess was associated with alcohol consumption in women. Weak, nonsignificant associations with waist-to-hip ratio were observed for smoking. Socioeconomic status was unrelated to waist-to-hip ratio in men, but it had a strong inverse relation for women.

The free energy of formation of magnesium sulfate and its solubility in magnesia have been determined. The salient feature of the results is that trace amounts of calcium impurity in magnesia noticeably lower the dissociation temperature and pressure of magnesium sulfate. A high-purity magnesia, which was prepared by oxidation of a high-purity magnesium, was used to determine the equilibrium constant for the formation of MgSO4. The sulfate solubil-ity In magnesia saturated with MgSO4was found to be higher than that in lime saturated with CaSO4. At 1100°C, CaSO4and CaS form in calcined dolomite at SO2partial pressures higher than those in pure CaO. From these findings it is estimated that at MgO saturation the ac-tivity coefficient relative to CaO is about 0.8.

In the present work the solid solubilities of CaS and CaSQ, in burnt lime were investigated by equilibrating lime with CO-CO2-SO2mixtures at temperatures from 950 to 1300°C. Also, the equilibrium constants for the formation of CaS and CaSO4were determined. At high oxy-gen activities, corresponding to a CO2/CO ratio >100 in the gas, the sulfur dissolves in lime primarily as sulfate ions. At lower oxygen activities (CO2/CO <30), the sulfur goes into so-lution in lime essentially as sulfide ions. Over the temperature range investigated the limit-ing sulfide solubility is within 0.01 to 0.03 pct S, whereas the sulfate solubility is within 0.03 to 0.1 pct S, increasing with increasing temperature.

The ecology of hummock-grass vegetation involves recurring fires. The hypothesis was tested that soil seed banks of hummock grass species are stimulated to germinate by the heat of fire or by ash addition. Hummocks of Plectrachne schinzii Henr., Triodia basedowii E. Pritz., and Triodia pungens R. Br. were burned, removed, or removed with the ash returned, and subsequent regeneration was recorded, in Ulum National Park. Regeneration of hummock grass was by seedlings only. Seedling emergence averaged 5/m2, with no differences between treatments or hummock grass species. This indicates the heat of fires and ash addition may not be important in stimulating seed germination of these hummock grass populations. Gemination was distributed over more than one rainfall event following the treatments.

We have explored the degree to which an intermolecular potential for the explosive hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX) (J. Phys. Chem. B 1997 101, 798) is transferable for predictions of crystal structures (within the approximation of rigid molecules) of a similar chemical system, in this case, polymorphic phases of the 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (HNIW) crystal. Molecular packing and isothermal−isobaric molecular dynamics calculations performed with this potential reproduce the main crystallographic features of the ε-, β-, and γ-HNIW crystals. Thermal expansion coefficients calculated using the present model predict near isotropic expansion for the ε- and γ-HNIW crystal phases and anisotropic expansion for β-HNIW.

The H + OCS potential-energy surface (PES) was used to evaluate the performance of density functional theory by comparing the results to ab initio calculations at the QCISD(T)//UMP2 and UMP2 levels using the aug-cc-pVTZ and 6-311+G(2df, 2p) basis sets. The two major reaction paths on this PES involve formation of OH(²Π) + CS(¹Σ) (reaction I) and SH(²Π) + CO(¹Σ) (reaction II). Experimental and QCISD(T)//UMP2/aug-cc-pVTZ activation barriers for (II) and reaction enthalpies for (I) and (II) were compared to values calculated by several density functionals (BLYP, B3LYP, B3PW91, BPW91, BP86, and B3P86) using the aug-cc-pVTZ basis set. All DFT/aug-cc-pVTZ predictions, except for the B3LYP prediction of the enthalpy of reaction I, were outside the range of experimental uncertainty. B3LYP predictions were in closest agreement with the experimental values and QCISD(T) predictions. B3LYP, BPW91, and B3PW91 predictions of the rate-limiting barrier to reaction II are within 3.5 kcal/mol of the QCISD(T) prediction, and all DFT values are below that of the QCISD(T). Reaction enthalpies for (I) and (II) were calculated using the BHandHLYP density functional and the 6-311+G(2df,2p) basis set. These predictions were closer to experiment and QCISD(T) values than any other DFT calculations, and the predicted enthalpy for reaction I is within the range of experimental values. The second portion of the study compared B3LYP and BLYP predictions of the 12 transition states and 6 stable intermediates within this PES with previously reported QCISD(T)//UMP2/6-311+G(2df,2p) predictions. The complexity of this surface allows for the evaluation of barrier heights for 28 reactions involving hydrogen addition, elimination, isomerization, migration, and radical diatomic elimination. With the exception of five reactions, all B3LYP barrier heights are within 3.7 kcal/mol of the QCISD(T) predictions and in several cases are in as good or better agreement than the UMP2 predictions. In addition, all but one of the B3LYP barriers lie below the QCISD(T) values. The most significant differences between the ab initio and DFT predictions were in the saddle points for radical elimination or addition. BLYP/6-311+G(2df, 2p) failed to find the two transition states associated with SH elimination from the cis- and trans-HSCO species. B3LYP located the saddle point for SH elimination from cis-HSCO, but its prediction of a saddle-point structure for SH elimination from trans-HSCO has an energy (without zero-point corrections) lower than that of the products. These transition states were subsequently optimized using the BHandHLYP functional and the 6-311+G(2df,2p) and 6-31G** basis sets. The geometries of these saddle points were in better agreement with UMP2/6-311+G(2df,2p) predictions than were the BLYP and B3LYP predictions. The BLYP predictions are in overall worse agreement with the QCISD(T) results than are the B3LYP predictions.

Symmetry-adapted perturbation theory (SAPT) has been used to investigate the intermolecular potential energy surface of CH3CN−CO2. A SAPT computation was performed for approximately 200 geometrical configurations using both a coarse grid in the five intermolecular coordinates and selected representative cuts. Four near-local minima are located on the potential energy surface. The deepest of these is −2.90 kcal/mol.

Results are presented from ab initio quantum chemical calculations on the ground-state potential energy surface for the open shell doublet reaction:  HNO + NO → N2O + OH (reaction I). This reaction is thought to be important in the sustained combustion of nitrogen-containing fuels. Geometry optimizations have been carried out at the QCISD/6-31G(d,p) level using unrestricted Hartree−Fock zeroth-order wave functions in search of local minima and transition states, followed by energy refinements for all critical points at the QCISD(T)/6-311+G(2df,2p) level. All saddle points were subjected to intrinsic reaction coordinate calculations to determine the minima to which they connect. We report two completed reaction pathways for reaction I. Some of these results will be compared with earlier work by others on the same reaction where geometry optimizations were carried out primarily at the UMP2/6-311G(d,p) level. The comparison brings to light some interesting differences between QCISD and UMP2 theories in the prediction of molecular structures and the connectivity of critical points (and therefore, connected reaction paths) for the doublet system in reaction I.

Geometry optimizations and normal-mode analyses of three conformers of 1,3,5-trinitro-s-triazine (RDX) are performed using second-order Moller−Plesset (MP2) and nonlocal density functional theory (DFT) methods. The density functional used in this study is B3LYP. The three conformers of RDX are distinguished mainly by the arrangement of the nitro groups relative to the ring atoms of the RDX molecule. NO2 groups arranged in either pseudo-equatorial or axial positions are denoted with (E) or (A), respectively. The AAE conformer has Cs symmetry and is the structure in the room-temperature stable crystal (α-RDX). The AAA and EEE conformers have C3v symmetry, a symmetry consistent with vapor and β-solid infrared spectra. The AAE and AAA conformers are studied at the MP2/6-31G*, B3LYP/6-31G*, and B3LYP/6-311+G** levels, and the EEE conformer is studied using the B3LYP density functional and the 6-31G* and 6-311+G** basis sets. The geometric parameters and infrared spectra of the AAA conformer are in good agreement with experimental gas-phase and β-solid data, supporting the hypotheses derived from experiment that the AAA structure is the most probable conformer in vapor-phase and β-solid RDX. The B3LYP/6-311+G** structures and simulated infrared spectra are in closest overall agreement with experimental data. The MP2/6-31G* structures and spectra are in poorest overall agreement with experiment.

The Vidas Chlamydia test (CHL) is an automated enzyme-linked immunofluorescence assay for the detection of Chlamydia trachomatis. Positive and equivocal results are confirmed with a blocking assay. A mouse monoclonal antibody directed against the chlamydial lipopolysaccharides was used for the test. The CHL assay is widely used in Europe, but U.S. experience with it is limited. Three clinical test sites (The Arlington Hospital, Arlington, Va., Indiana University, Indianapolis, and the University of California, San Francisco) compared CHL with tissue culture (TC) for the identification of chlamydia in urogenital specimens (2,453 females and 850 males). True positives (TP) were defined as either TC positive or TC negative and CHL positive by a positive direct fluorescent-antibody assay or PCR test. Overall prevalence was 5.5% for females, 10.3% for male urethral swabs, and 10.7% for combined male TC urethral swabs and CHL with first catch urine (FCU) specimens. Compared to TP, CHL and TC had sensitivities of 89.6 and 94.1% with female cervical swabs and 90.9 and 86.4% with male urethral swabs, respectively. CHL sensitivity was 81.2 for male FCU specimens and 77.7% for matching male TC swabs. There were relatively few false-positive results, with all specificities being >99.4%. With the blocking assay, Vidas CHL specificity was >99.7%. However, male FCU specimen sensitivity was compromised because 9.2% (7 of 76) of the TP were initially positive but were not confirmed. An improvement in the Vidas blocking assay is needed before we can recommend its use with male urine. Alternatively, one could argue that the specificity of the test is so high that a confirmatory assay is not needed. For male and female swabs, the Vidas CHL assay has a performance that is similar to that of TC.

Studies were performed to try to determine if gonadotrophins are altered during their interaction with tissue receptors. Immunologic, electrophoretic and binding properties of lactoperoxidase labelled [125I]HLH and [125I]HCG were examined before and after elution from mouse luteoma and human corpora lutea receptor preparations. The anti-HCG used in these studies at a 1:10 000 dilution precipitated 92% of a freshly iodinated [125I]HCG preparation. Receptor eluted [125I]HCG, derived from the same batch of labelled ligand, was virtually quantitatively precipitated by the same dilution of anti-HCG. [125I]HCG eluted from the human corpus luteum was electrophoretically more homogenous when compared to its heterogenous parent labelled preparation and migrated to a position similar to that of native HCG.In Ouchterlony double diffusion experiments against anti-HCG antiserum, corpus luteum eluted [125I]HCG and [125I]HLH showed immunologic identity with each other as well as with native HCG and HLH. Receptor eluted [125I]HCG from the mouse luteoma, following in vivoadministration via tail vein injection or after incubation in vitrowith labelled hormones, was immunologically indistinguishable from native HCG.The electrophoretic mobility of HCG was retarded when HCG was added to extracts of mouse luteoma, liver and kidney. Eluates of mouse luteoma, applied to Bio-Gel columns previously equilibrated with [125I]HCG showed the ability to concentrate [125I]HCG in the high molecular weight column fractions. Similar results were obtained with columns equilibrated with [125I]TSH and [125I]HGH. [125I]HCG eluted from the mouse luteoma was able to bind to fresh luteoma homogenate but, in contrast to an earlier report with [125I]HCG eluted from rat testis, no enhancement of binding of the eluted [125I]HCG was observed with fresh tissue. These results could be explained by the extraction of non-dialyzable intracellular component during the [125I]HCG elution procedure from the luteoma homogenate which combines with HCG to lower its binding and alter its electrophoretic mobility. This component could be extracted from other mouse tissues and combines with other labelled peptide hormones. Data in the present report support in part the hypothesis that gonadotrophins eluted from mouse luteoma and human corpus luteum are not altered by their interaction with tissue receptors.

This study examined the cognitive, affective, and behavioral effects of psychoeducational training with 28 multiply disabled “high-risk” clients in a vocational rehabilitation field office. The findings indicate that, with the exception of the measure of general adjustment, psychoeducational training had a significant positive effect on the degree to which clients expressed self-defeating beliefs, experienced non-productive emotions, emitted the relaxation response, and controlled stress. At six months follow-up, clients receiving the training had a more successful rehabilitation program status than did clients not receiving the training.

New data are reported, and literature data compiled, for species richness in 0.1 ha plots in Australian vegetation. We conclude that on present evidence the same vegetation types are rich, and the same types poor, at a 0.1 ha scale, in Australia as elsewhere. Tropical rainforest averages 140 species per 0.1 ha in permanently humid types. Temperate sclerophyll shrub-dominated types on low-nutrient soils are generally in the range 50–100 species, with open woodlands somewhat richer than scrublands. Warm semi-desert shrublands can have 50–80 species, counting ephemerals both of summer and of winter. Temperate closed forests generally have fewer than 50 species per 0.1 ha. For none of these types is there clear evidence that they are richer or poorer in species at a 0.1 ha scale than types in similar environments with similar growth-form mixes on other continents. We give data for grassy woodlands and sclerophyll scrublands in the monsoonal tropics; the fragments of data on such types available from other continents suggest there may be a wide range of species richness in sub-types of this very broad grouping. Generally, available data do not support the idea that floristic evolutionary history is a strong influence on the species richness of vegetation at the 0.1 ha scale, relative to the influence of the present-day climatic and soil environment.

Isothermal−isobaric molecular dynamics (NPT-MD) simulations of the β, α, and δ phases of crystalline 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX) were performed over the temperature range 4.2−553 K and 1 atm. The Buckingham repulsion−dispersion intermolecular potential developed for hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX) (J. Phys. Chem. 1997, B101, 798) with electrostatic charges determined by ab initio calculations was used to describe the HMX crystal phases. The predicted space group symmetries and structural parameters for the three phases of HMX are in close agreement with experimental values.

Recent legislation has extended rehabilitation services from the groups traditionally served to the socially and economically disadvantaged. Since many of these clients cannot be classified in the traditional modes, this study developed a system of classification according to personality traits intended to be useful to counselors in dealing with all types of clients.A sample of 135 clients was administered Form E of the Sixteen Personality Factor Questionnaire. Factor analysis (principle components method) and discriminant analysis differentiated three personality groups: (1) normal adjusted, (2) assertive-aggressive, and (3) passive-dependent. Appropriate counseling techniques for each group are suggested.

We present experimental and theoretical results on extended defects of hexagonal GaN grown by metal organic vapour deposition (MOCVD). Transmission electron microscopy (TEM) measurements indicate the presence of 3 nm wide type I1stacking faults (SFs) related to the MOCVD growth, and 2–4 nm SFs of unidentified type related to the ion implantation. We simulated infinite SFs of different types I1, I2and I3. First principles calculations were used to model Shockley partial dislocations, the core structure of the dislocations and intrinsic SFs. We estimate defect level positions and the formation energy of the infinite SFs. We also present results of the calculations and available experimental data on finite size SFs bounded by partial dislocations in wurtzite GaN. Calculation of the infinite SFs revealed shallow levels, but no deep levels. In the SFs bound by dislocations there are deep filled levels in the range of 0.4–0.8 eV from the valence band maximum (VBM) located at the atoms of the 90° dislocations. We also calculated the segregation of the C, n‐dopant, Si or O and the p‐dopant, Mg, to the dislocations and SFs. The effect of the segregation is found to be stronger for the SFs with partials. The results of the calculations are correlated with the experimental data on GaN obtained from high resolution TEM and Hall measurements. We suggest mechanisms of the formation of the SFs I1and I2after ion implantation and high temperature anneal and explain the difficulties of p‐type doping with the formation of the extended defects.