This article discusses symmetry-induced tunneling in one-dimensional disordered potentials.

Article on phase change enthalpies and entropies of liquid crystals.

Article on rate coefficients and mechanistic analysis for the reaction of hydroxyl radicals with 1,1-dichloroethylene and trans-1,2-dichloroethylene over an extended temperature range.

Article on kinetic studies of the reaction of hydroxyl radicals with trichloroethylene and tetrachloroethylene.

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The authors have performed first-principles calculations to examine the effects of biaxial strain and chemical ordering on the band gap of wurtzite In{sub x}Ga{sub 1{minus}x}N in the range 0 {le} x {le} 0.5. The results for unstrained, random alloys are in good agreement with theoretical estimates and measurements on unstrained zinc-blende alloys, but are in poor agreement with recent measurements on strained wurtzite alloys which display significantly lower gaps. Biaxial strain is found to have a non-linear effect on calculated alloy gaps, increasing them for x < 0.25 and decreasing them for x > 0.25. However, the overall agreement with measured wurtzite values remains poor. Chemical ordering along the [0001] direction in strained alloys is found to decrease the band gaps considerably, yielding much improved agreement with measurements. They discuss their results with regard to current theories concerning the optical properties of wurtzite InGaN alloys.

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With the availability of third-generation hard x-ray synchrotron radiation sources, such as the Advanced Photon Source (APS) at Argonne National Laboratory, x-ray inelastic scattering and x-ray nuclear resonant scattering provide powerful means for investigating the vibrational dynamics of a variety of materials and condensed matter systems. Novel high-resolution hard x-ray optics with meV energy resolution requires a compact positioning mechanism with 20--50-nrad angular resolution and stability. In this paper, the authors technical approach to this design challenge is presented. Sensitivity and stability test results are also discussed.

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Multi megawatt accelerators can deliver sufficient power to a target to destroy it in a few pulses. In order to look at the response of solid and liquid targets under these high power pulses, we are developing optical methods of measuring surface deformations with time resolutions limited by laser pulse lengths. These methods can be used to examine the surfaces of solids and liquids during elastic deformation and unstable hydrodynamic flows. We present preliminary results of a system designed for target tests using the Brookhaven AGS and the Argonne CHM linac.

We report on the experimental results of the dielectric based two beam accelerator (step-up transformer). By using a single high charge beam, we have generated and extracted a high power RF pulse from a 7.8 GHz primary dielectric structure and then subsequently transferred to a second accelerating structure with higher dielectric constant and smaller transverse dimensions. We have measured the energy change of a second (witness) beam passing through the acceleration stage. The measured gradient is > 4 times the deceleration gradient. The detailed experiment of set-up and results of the measurements are discussed. Future plans for the development of a 100 MeV demonstration accelerator based on this technique is presented.

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The Next Linear Collider (NLC) Collaboration is planning to construct an Engineering Test Facility (ETF) at Fermilab. As presently envisioned, the ETF would comprise a fundamental unit of the NLC main linac to include X-band klystrons and modulators, a delay-line power-distribution system (DLDS), and NLC accelerating structures that serve as loads. The principal purpose of the ETF is to validate stable operation of the power-distribution system, first without beam, then with a beam having the NLC pulse structure. This paper concerns the possibility of configuring and using the ETF to accelerate beam with an NLC pulse structure, as well as of doing experiments to measure beam-induced wakefields in the rf structures and their influence back on the beam.

One disadvantage of conventional iris-loaded accelerating structures is the high ratio of the peak surface electric field to the peak axial electric field useful for accelerating a beam. Typically this ratio E{sub s}/E{sub a} {ge} 2. The high surface electric field relative to the accelerating gradient may prove to be a limitation for realizing technologies for very high gradient accelerators. In this paper, we present a scheme that uses a hybrid dielectric and iris loaded periodic structure to reduce E{sub s}/E{sub a} to near unity, while the shunt impedance per unit length r and the quality factor Q compare favorably with conventional metallic structures. The analysis based on MAFIA simulations of such structures shows that we can lower the peak surface electric field close to the accelerating gradient while maintaining high acceleration efficiency as measured by r/Q. Numerical examples of X-band hybrid accelerating structures are given.

A brief review is given of recent progress in fabrication of high voltage GaN and AlGaN rectifiers, GaN/AlGaN heterojunction bipolar transistors, GaN heterostructure and metal-oxide semiconductor field effect transistors. Improvements in epitaxial layer quality and in fabrication techniques have led to significant advances in device performance.

Researchers at Brookhaven National Laboratory and the National Renewable Energy Laboratory have tested polymer-based coating systems to reduce the capital equipment and maintenance costs of heat exchangers in corrosive and fouling geothermal environments. These coating systems act as barriers to corrosion to protect low-cost carbon steel tubing; they are formulated to resist wear from hydroblasting and to have high thermal conductivity. Recently, new filler materials have been developed for coating systems that use polyphenylenesulphide as a matrix. These materials include boehmite crystals (orthorhombic aluminum hydroxide, which is grown in situ as a product of reaction with the geothermal fluid), which enhance wear and corrosion resistance, and carbon fibers, which improve mechanical, thermal, and corrosion-resistance properties of the composite.

There are a number of novel instrumentation issues relating to the generation cooling and acceleration of high power muon beams. Specific issues are monitoring the cooling water in the magnet nearest the target to minimize corrosion, monitoring the behavior of the target after the impact of the beam, and following the beam through the cooling accelerator chain. The muon cooling system also produces a number of unique issues such as making beam profile measurements in the presence of large backgrounds, measuring these backgrounds, losses, and the angular momentum of the beam. We describe the techniques we intend to use, and some of the constraints involved in their implementation.