The impressive performance improvements of laterally oxidized VCSELs come at the expense of increased fabrication complexity for 2-dimensional arrays. Since the epitaxial layers to be wet-thermally oxidized must be exposed, non-planarity can be an issue. This is particularly important in that electrical contact to both the anode and cathode of the diode must be brought out to a package. They have investigated four fabrication sequences suitable for the fabrication of 2-dimensional VCSEL arrays. These techniques include: mesa etched polymer planarized, mesa etched bridge contacted, mesa etched oxide isolated (where the electrical trace is isolated from the substrate during the oxidation) and oxide/implant isolation (oxidation through small via holes) all of which result in VCSELs with outstanding performance. The suitability of these processes for manufacturing are assessed relative to oxidation uniformity, device capacitance, and structural ruggedness for packaging.

The Li(Si)/FeS{sub 2} and Li(Si)/CoS{sub 2} couples were evaluated with a low-melting LiBr-KBr-LiF eutectic and all-Li LiCl-LiBr-LiF electrolyte for a battery application that required both high energy and high power for short duration. Screening studies were carried out with 1.25 inch-dia. triple cells and with 10-cell batteries. The Li(Si)/LiCl-LiBr-LiF/CoS{sub 2} couple performed the best under the power load and the Li(Si)/LiCl-LiBr-LiF/FeS{sub 2} was better under the energy load. The former system was selected as the best overall performer for the wide range of temperatures for both loads, because of the higher thermal stability of CoS{sub 2}.

Previously, an effective index optical model was introduced for the analysis of lateral waveguiding effects in vertical-cavity surface-emitting lasers. The authors show that the resultant transverse equation is almost identical to the one typically obtained in the analysis of dielectric waveguide problems, such as a step-index optical fiber. The solution to the transverse equation yields the lateral dependence of the optical field and, as is recognized in this paper, the discrete frequencies of the microcavity modes. As an example, they apply this technique to the analysis of vertical-cavity lasers that contain thin-oxide apertures. The model intuitively explains the experimental data and makes quantitative predictions in good agreement with a highly accurate numerical model.

This paper will concentrate on the progression of the bioassay and dose evaluation programs at Savannah River Site.

Shock loading techniques are often used to determine material response along a specific pressure loading curve referred to as the Hugoniot. However, many technological and scientific applications require accurate determination of dynamic material response that is off-Hugoniot, covering large regions of the equation-of-state surface. Unloading measurements from the shocked state provide off-Hugoniot information, but experimental techniques for measuring compressive off-Hugoniot response have been limited. A new pulsed magnetic loading technique is presented which provides previously unavailable information on isentropic loading of materials to pressures of several hundred kbar. This smoothly increasing pressure loading provides a good approximation to the high-pressure material isentrope centered at ambient conditions. The approach uses high current densities to create ramped magnetic loading to a few hundred kbar over time intervals of 100--200 ns. The method has successfully determined the isentropic mechanical response of copper to about 200 kbar and has been used to evaluate the kinetics of the alpha-epsilon phase transition occurring in iron at 130 kbar. With refinements in progress, the method shows promise for performing isentropic compression experiments to multi-Mbar pressures.

The authors report preliminary results from a study of {Lambda}{sup 0} polarization in the exclusive reaction pp {r_arrow} p{sub f} ({Lambda}{sup 0} K{sup +}) at 800 GeV/c. These data are a part of the 5 x 10{sup 9} diffractive event sample collected by Fermilab E690. They observe a large dependence of the polarization on the {Lambda}{sup 0} K{sup +} invariant mass. This observation confirms the result of the CERN ISR R608 experiment and extends the range over which the effect is observed.

Vertical cavity surface emitting laser (VCSEL) sources have been adopted into Gigabit Ethernet applications in a remarkably short time period. VCSELs are particularly suitable for multimode optical fiber local area networks (LANs), due to their reduced threshold current, circular output beam, and inexpensive and high volume manufacture. Moreover, selectively oxidized VCSELs are nearly ideal LAN sources since the oxide aperture within the laser cavity produces strong electrical and optical confinement which enables high electrical to optical conversion efficiency and minimal modal discrimination allowing emission into multiple transverse optical modes. In addition to the large demand for multimode lasers, VCSELs which emit into a single optical mode are also increasingly sought for emerging applications, which include data communication with single mode optical fiber, bar code scanning, laser printing, optical read/write heads, and modulation spectroscopy. To achieve single mode selectively oxidized VCSELs is a challenging task, since the inherent index confinement within these high performance lasers is very large.

Visapult is a prototype application and framework for remote visualization of large scientific datasets. We approach the technical challenges of tera-scale visualization with a unique architecture that employs high speed WANs and network data caches for data staging and transmission. This architecture allows for the use of available cache and compute resources at arbitrary locations on the network. High data throughput rates and network utilization are achieved by parallelizing I/O at each stage in the application, and by pipe-lining the visualization process. On the desktop, the graphics interactivity is effectively decoupled from the latency inherent in network applications. We present a detailed performance analysis of the application, and improvements resulting from field-test analysis conducted as part of the DOE Combustion Corridor project.

A new method for measuring the wavelength dependence of the transit time, material dispersion, and attenuation of an optical fiber is described. The authors inject light from a 4-ns risetime pulsed broad-band flashlamp into various length fibers and record the transmitted signals with a time-resolved spectrograph. Segments of data spanning an approximately 3,000 {angstrom} range are recorded from a single flashlamp pulse. Comparison of data acquired with short and long fibers enables the determination of the transit time and the material dispersion as functions of wavelength dependence for the entire recorded spectrum simultaneously. The wavelength dependent attenuation is also determined from the signal intensities. The method is demonstrated with experiments using a step index 200-{micro}m-diameter SiO{sub 2} fiber. The results agree with the transit time determined from the bulk glass refractive index to within {+-} 0.035% for the visible (4,000--7,200 {angstrom}) spectrum and 0.12% for the ultraviolet (2,650--4,000 {angstrom}) spectrum, and with the attenuation specified by the fiber manufacturer to within {+-} 10%.

We have shown that external hydrostatic pressure leads to the creation of structural defects, mainly in the vicinity of the II-VI/GaAs interface in the CdTe/Cd{sub 1-x}Mg{sub x}Te heterostructures grown by the molecular beam epitaxy method on GaAs substrates. These defects propagating across the epilayer cause permanent damage to the samples from the point of view of their electrical properties. In contrast, photoluminescence spectra are only weakly influenced by pressure. Our results shed light on the degradation process observed even without pressure in II-VI-based heterostructures.

Post-growth thermal annealing effects on InAs/GaAs quantum dots (QDs) near Stransky-Krastanow transformation were investigated. Self-assembled QDs of average size of about 10 nm were grown by metal organic vapour phase epitaxy. The photoluminescence (PL) due to emission from QDs as well as two peaks due to emission from the strained InAs wetting layer (WL) were observed in as-grown samples. Bimodal structure of the WL PL was attributed to WL regions of different thickness. There was almost no difference in the PL spectrum after 30 s annealing at 600 C. However, annealing at temperatures in the range between 700 C and 950 C resulted in quenching of the PL from QDs and the thinner WL. The PL peak from the new, thicker WL blue-shifted and narrowed with increasing annealing temperature. This behavior was in agreement with TEM observations. Complete dissolution of the QDs and substantial broadening of the WL was observed. All our results indicate that thermally induced modifications of the WL rather than QDs can be responsible for the blue-shift and narrowing of the PL peaks in structures containing InAs QDs.

Post-growth thermal annealing effects on InAs/GaAs quantum dots (QDs) near Stransky-Krastanow transformation were investigated. Self-assembled QDs of average size of about 10 nm were grown by metal-organic vapor phase epitaxy. The photoluminescence (PL) due to emission from QDs as well as two peaks due to emission from the strained InAs wetting layer (WL) were observed in as-grown samples. Bimodal structure of the WL PL was attributed to WL regions of different thickness. There was almost no difference in the PL spectrum after 30 s annealing at 600 C. However, annealing at temperatures in the range between 700 C and 950 C resulted in quenching of the PL from QDs and the thinner WL. The PL peak from the new, thicker WL blue-shifted and narrowed with increasing annealing temperature. This behavior was in agreement with TEM observations. Complete dissolution of the QDs and substantial broadening of the WL was observed. All our results indicate that thermally induced modifications of the WL rather than QDs can be responsible for the blue-shift and narrowing of the PL peaks in structures containing InAs QDs.

Deep centers and dislocation densities in undoped n GaN, grown by hydride vapor phase epitaxy (HVPE), were characterized as a function of the layer thickness by deep level transient spectroscopy and transmission electron microscopy, respectively. As the layer thickness decreases, the variety and concentration of deep centers increase, in conjunction with the increase of dislocation density. Based on comparison with electron irradiation induced centers, some dominant centers in HVPE GaN are identified as possible point defects.

A new scalable fiber laser approach is described and modeled, based on phase-locking multiple gain cores in an antiguided structure. In essence, the waveguide is comprised of a periodic sequence of gain-loaded and no-gain segments having uniform refractive index (referred to as the ''ribbon'') encapsulated within a reduced index cladding region. Our calculations reveal that the constant index profile within the ribbon structure provides optimal mode discrimination; the refractive index must be constant within {+-}0.001 to ensure single-mode operation for a 5-core design. Periodic variation in refractive index and gain of the ribbon laser lead to the emergence of a photonic bandgap, in analogy to so-called ''holey fibers''. Our constant index design, together with the periodic gain profile, may be described as a photonic metal.

Soft proton-antiproton interactions are selected from events collected with the CDF minimum-bias trigger at {radical}(s) = 1800 and 630 GeV. The analysis of their properties compared at the two energies reveals important and unexpected invariances. This paper describes an attempt to address the problem and the study of the properties of genuine soft interactions. These are identified as a subsample of proton antiproton interactions collected with the CDF minimum bias trigger. In the analysis a splitting procedure of the full minimum bias sample in two subsamples, one highly enriched in soft interactions and the other enriched in hard interactions, is applied. The two subsamples are analyzed separately through the compared measures of some inclusive distributions and final state correlations at different c.m.s. energies. The results evidence some interesting unobserved properties of the isolated soft sample and, in particular, a remarkably unpredicted invariance of some of the measured correlations and spectra between 630 and 1800 GeV.

Plutonium gamma-ray data analysis using MGA in the two-detector mode can provide information more refined than the gamma-ray analysis using MGA in the one-detector mode. Prior to the introduction of the new type of ORTEC coaxial detector, which has good resolution at 100-keV region and good efficiency at 1 MeV, the two-detector mode of the MGA could be used only with two separate HPGe detectors with appropriate characteristics. A recent study by us using small plutonium standards (less than 0.5g) suggests that this new detector indeed performed as well as combination of a high-resolution planar (''LEPS'') detector and a coaxial detector together. In this study, the CBNM plutonium gamma-ray standards were used to test this detector's ability with MGA, when measuring several grams of plutonium.

We offer a case for active technical management of the radiative forcing of the temperatures of the Earth's fluid envelopes, rather than administrative management of atmospheric greenhouse gas inputs, in order to stabilize both the global- and time-averaged climate and its mesoscale features. We suggest that active management of radiative forcing entails negligible--indeed, likely strongly negative--economic costs and environmental impacts, and thus best complies with the pertinent mandate of the UN Framework Convention on Climate Change. We propose that such approaches be swiftly evaluated in sub-scale in the course of an intensive international program.

This paper describes a study undertaken to explain the risk profile differences in the results of PRAs of two similar WER-1000 nuclear power plants. The risk profile differences are particularly significant in the area of small steam/feedwater line breaks, small-small LOCAs, support system initiators and containment bypass initiators. A top level (limited depth) approach was used in which we studied design differences, major assumptions, data differences, and also compared the two PRA analyses on an element-by-element basis in order to discern the major causative factors for the risk profile differences. We conclude that the major risk profile differences are due to differences in assumptions and engineering judgment (possibly combined with some design and data differences) involved in treatment of uncertain physical phenomena (primarily sump plugging in LOCAs and turbine building steaming effects in secondary system breaks). Additional major differences are attributable to support system characteristics.

In filled PDMS based composites, such as M97XX stress cushions, significant mechanical reinforcement of the polymer component is obtained from hydrogen bonding between the silica filler surface hydroxyls and the siloxane polymer backbone. It is expected that these interactions are influenced by the amount and structure of interfacial water. We have chosen to investigate in detail the effect of chemisorbed and physisorbed water on the interfacial structure and dynamics in silica-filled PDMS-based composites. Toward this end, we have combined classical molecular dynamics simulations and experimental studies employing nanoindentation, temperature programmed desorption (TPD), Dynamic Mechanical Analysis (DMA), and Nuclear Magnetic Resonance (NMR) analyses. Our TPD results suggest that moisture desorption and adsorption in M9787 can be approximated by the interaction of its silica constituents (Cab-0-Sil-M-7D and Hi-Sil-233) with moisture. Our experimental data also reveal that, in general, as heat-treated silica particles are exposed to moisture, chemisorbed states, then physisorbed states are gradually filled up in that order. Molecular modeling results suggest that the polymer-silica contact distance and the mobility of interfacial polymer chains significantly decreased as the hydration level at the interface was reduced. The reduced mobility of the PDMS chains in the interfacial domain reduced the bulk motional properties of …

We have synthesized a series of Ti-Si-N coatings with 0 to 20 at. % Si by high-density plasma-assisted vapor-phase deposition. Composition, structure, and atomic short-range order were characterized by Rutherford Backscattering Spectrometry (RBS), Transmission Electron Microscopy (TEM), {Theta}-2{Theta} X-ray Diffraction (XRD), and X-ray Absorption Near Edge Structure (XANES) spectroscopy. The mechanical properties of these coatings were characterized by instrumented nanoindentation, and compared to those of B1-TiN. Our experiments show that the present series of Ti-Si-N coatings are nanocomposites, consisting of a nm-scale mixture of crystalline titanium nitride (TiN) and amorphous silicon nitride (a-Si:N). The mechanical response of the present series of Ti-Si-N coatings was found to be essentially independent of the Si composition, and similar to that of B1-TiN.

We present a surface compression method that stores surfaces as wavelet-compressed signed-distance volumes. Our approach enables the representation of surfaces with complex topology and arbitrary numbers of components within a single multiresolution data structure. This data structure elegantly handles topological modification at high compression rates. Our method does not require the costly and sometimes infeasible base mesh construction step required by subdivision surface approaches. We present several improvements over previous attempts at compressing signed-distance functions, including an 0(n) distance transform, a zero set initialization method for triangle meshes, and a specialized thresholding algorithm. We demonstrate the potential of sampled distance volumes for surface compression and progressive reconstruction for complex high genus surfaces.

There are many options for the handling and storage of spent nuclear fuel from naval vessels. This paper summarizes the options that are available and explores the issues that are involved. In many cases choices have been made, not on the basis of which is the best engineering solution or the most cost-effective, but based on the political realities involved. For example, currently it seems that the most prevalent solution for spent fuel interim storage is in dual-purpose (transport-storage) casks. These casks are robust and, politically, they offer the visible evidence that the fuel is ''road-ready'' to be moved from the local area where the fuel is being stored in the interim. However, dual-purpose casks are the most expensive of the storage mediums. Drywell storage (storage in below grade or bermed pipes), on the other hand, the least expensive and most flexible storage option, suffers from an image of permanence (not politically acceptable) and from being improperly implemented in the past. Though these issues are easily resolved from a technical perspective, the option is often not seriously considered because of this past history. It wasn't too many years ago that spent fuel pools were the storage medium of choice. The …

Grids comprise an infrastructure that enables scientists to use a diverse set of distributed remote services and resources as part of complex scientific problem-solving processes. We analyze some of the challenges involved in deploying software and components transparently in Grids. We report on three practical solutions used by the Globus Project. Lessons learned from this experience lead us to believe that it is necessary to support a variety of software and component deployment strategies. These strategies are based on the hosting environment.

A thin metallic beam pipe reinforced by multi-layer spiral metallic ribs is proposed for rapid cycling proton synchrotrons. The pipe is made of Inconel 718 with thickness of a few tenths of mm. Each spiral rib has a cross section of about 0.3 mm{sup 2} and can be bonded to the pipe by using laser deposition technique (e.g., precision metal deposition, or PMD). Compared with other designs (e.g., ceramic beam pipe with a metallic cage used in the ISIS at the RAL), this new pipe will reduce the magnet aperture significantly, which, in turn, reduces the construction and operating cost of a synchrotron. Numerical simulations and analytical modeling are used to investigate the structural strength and deformation, and the eddy current effects, including heating, magnetic field distortion and the electro-magnetic force on the beam pipe. The results show that this new beam pipe will work. It can be employed to high intensity rapid cycling proton synchrotrons, such as the proton driver at FERMILAB and the JHF at JAERI/KEK. Effort to build a prototype is under way.