AR coating design for multi-junction solar cells can be more challenging than in the single junction case. Reasons for this are discussed. Analytical expressions used to optimize AR coatings for single junction solar cells are extended for use in monolithic, series interconnected multi-junction solar cell AR coating design. The result is an analytical expression which relates the solar cell performance (through J{sub SC}) directly to the AR coating design through the device reflectance. It is also illustrated how AR coating design can be used to provide an additional degree of freedom for current matching multi-junction devices.

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Daily newspaper from Perry, Oklahoma that includes local, state, and national news along with advertising.

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The goal of our research is to develop a fundamental quantitative understanding of the role of physical heterogeneities on DNAPL migration and remediation in aquifers. Such understanding is critical to cost effectively identify the location of the subsurface zone of contamination and design remediation schemes focused on removing the source of the contamination, the DNAPL itself. To reach this goal, the following objectives for the proposed research are defined: Objective 1: Develop fundamental understanding of the physics of DNAPL migration processes within heterogeneous porous media: (a) Conduct a suite of two-dimensional physical experiments within controlled and systematically varied heterogeneous porous media at scales up to one meter. Vary system parameters to consider a range of capillary and bond numbers within these heterogeneous porous structures. (b) Develop a new DNAPL migration model based on an up-scaling of invasion percolation (UP) to model the migration process. Compare the model predictions to experimental results. Accomplishing objective 1 provides a series of experiments against which we will be able to evaluate the validity of existing multi-phase flow theory as formulated in both percolation codes and in continuum flow codes. These experimental results will also provide new insights into DNAPL migration behavior. Development of the …

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We report development of a pilot process for the industrial rinsing of fabrics. This process combines hydraulic (pressure-driven) transport with electro-osmotic transport. It reduces the total amount of water required in certain rinsing operations by a factor of about five. Cotton exhibits an electro-osmotic transport coefficient of about 6 x 10{sup -9} m{sup 2}/s-V resulting from a partial ionization of hydroxyl groups on the cellulose polymer substrate. This process applies a field transverse to the fabric to effect the movement of water in the spaces between the 10 {micro}m cotton fibers which constitute the yam. The field strength is adjusted so that the induced electro-osmotic flux is comparable to a pressure-driven flux, which moves preferentially in the more open channels between the yams. For a fixed current density, solution conductivity and electro-osmotic transport vary inversely. The process is most practical for removal of liquids of relatively low conductivity (<500 {micro}S/cm). For removal of solutions of conductivity greater than 1200 {micro}S/cm, the rate of electro-osmotic flow may be too low to benefit the rinsing process if current densities are restricted to practical levels of about 30 mA/cm{sup 2}. Electra-osmotic transport may have important applications in wet processing of extremely fine textiles, …

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High resolution adsorption isotherms, temperature programmed desorption (TPD), x-ray diffraction (XRD) and x-ray absorption near edge spectroscopy (XANES) methods were used to investigate the interaction of SO{sub 2} with high quality MgO powders. The results of these investigations indicate that when SO{sub 2} is deposited on MgO in monolayer quantities at temperatures near 100K both SO{sub 2} and SO{sub 4} species form that are not removed by simply pumping on the pre-dosed samples at room temperature. TPD and XANES studies indicate that heating of pre-dosed MgO samples to temperatures above 350 C is required for full removal of the SO{sub 3}/SO{sub 4} species. XANES measurements made as a function of film thickness indicate for coverages near monolayer completion that the SO{sub 4} species form first.

Metal-doped diamond-like carbon films were produced for the purpose of an electrochemical nano-electrode. In this study we use Z-contrast scanning transmission electron microscopy to directly observe metal cluster formation and distributions within the chromium-doped carbon films. At low doping ({approximately}6at%Cr), Cr is uniformly distributed; at high doping ({approximately}12at%Cr), Cr-rich clusters are formed. Using electron energy loss spectroscopy, we find that the Cr clusters tend to be metallic-like at low doping levels and carbide-like at high doping levels according to the Cr L, white line ratios. The carbon is more diamond-like at low doping and more graphite/carbide like at high doping according to the sp1/sp3 electron percentage measurements.

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Inelastic nuclear resonant scattering spectra were measured on alloys of Fe{sub 3}Al that were chemically disordered, partially-ordered, and DO{sub 3}-ordered. The phonon partial DOS for {sup 57}Fe atoms were extracted from these data, and the change upon disordering in the partial vibrational entropy of Fe atoms was obtained. By comparison to previous calorimetry measurements, it is shown that the contribution of the Fe atoms to the vibrational entropy is a factor of 10 smaller than that of the Al atoms. With the assistance of Born - von Karman model calculations on the ordered alloy, it is shown that differences in the vibrational entropy originate primarily with changes in the optical modes upon disordering. The phonon DOS of {sup 57}Fe was found to change systematically with chemical short range order in the alloy. It is argued that changes in the vibrational entropy originate primarily with changes in the chemical short-range order in the alloy, as opposed to long-range order.

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The vertical motion of constant density atmospheric balloons has been considered via an equation of motion for the vertical displacement of a balloon, due to vertical air motion, which can be numerically solved for balloon positions. Initial calculations are made for a constant density atmosphere. Various vertical wind models with relatively large amplitudes are applied to the model to determine how tightly the balloons are coupled to the reference level and the time scale for the balloons to change to the wind driven reference altitude. A surface launch of a balloon to a 6 km reference altitude is modeled using a detailed atmospheric pressure-density-temperature profile in the equation of motion. The results show the balloons to be relatively tightly coupled ({approx} 50-100 m) to the reference altitude.

Ion-implantation and thermal-processing methods have been used to form nanophase magnetic precipitates of metallic cobalt that are embedded in the near-surface region of single crystals of Al{sub 2}O{sub 3}. The Co precipitates are isolated, single-crystal particles that are crystallographically oriented with respect to the host Al{sub 2}O{sub 3} lattice. Embedded nanophase Co precipitates were formed by the implantation of Co+ at an energy of 140 keV and a dose of 8 x l0{sup 16} ions/cm{sup 2} followed by annealing in a reducing atmosphere. The implanted/annealed Co depth profile, particle size distributions and shapes, and the orientational relationship between the nanophase precipitates and the host crystal lattice were determined using RBS/channeling, transmission electron microscopy, and x-ray diffraction.

Dispersion modeling of non-radiological airborne emissions associated with the construction and operation of three alternatives for high-level waste salt disposition at the Savannah River Site has been completed. The results will be used by Department of Energy-Savannah River in the preparation of the salt disposition supplemental environmental impact statement. Estimated maximum ground-level concentrations of applicable regulated air pollutants of the site boundary and at the distance to a hypothetical, co-located onsite worker are summarized in tables. In all cases, model estimated ambient concentrations are less than regulatory standards.

The National Society of Black Physicists will hold its Twentieth annual meeting and its XXIIII Day of Scientific Lectures at Lawrence Berkeley National Laboratory on March 27th - 30th, 1997. The meeting provides a major opportunity for African American physicists and students to present their current research and discuss issues germane to the constituency. It is therefore crucial to have the broadest cross-section of the membership at each meeting. The Lawrence Berkeley National Laboratory was chosen as the site of the 20th annual meeting because of its historical significance to Physics (being one of the first national laboratories in the United States) and the laboratories continuing support of the goals and objectives of the society.

Phase separation in nuclear waste glasses has an adverse effect on glass durability. Phase separation in glasses generally takes the form of two immiscible glass phases which differ in chemical composition, density, and surface tension. Usually one phase is more soluble than the other. Phase separation complicates modeling of glass durability as a function of composition because the composition of the overall glass is known but the compositions of the two immiscible phases is not known: the performance of the overall glass is unpredictable and the long term durability of the glass can not be modeled. A discriminate analysis of 110 homogeneous and phase separated waste glasses allowed a ''phase separation discriminate function'' to be defined. The discriminate function is calculated based on glass oxide wt percent and compositionally differentiates between immiscible phases of different density. The discriminate function is defined in 14 component composition space although greater than 95 percent of the glass chemistry is dominated by seven major components (Na2O- K2O-Li2O-SiO2-Al2O3-B2O3-Fe2O3). The compositionally dependent discriminator function is used to eliminate phase separated glasses from being processed in the Savannah River Site (SRS) Defense Waste Processing Facility (DWPF). All glasses produced are homogeneous and thus have predictable long term …

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The authors have applied Atomic Number Contrast Scanning Transmission Electron Microscopy (Z-Contrast STEM) towards the study of colloidal CdSe semiconductor nanocrystals embedded in MEH-PPV polymer films. For typical nanocrystal thicknesses, the image intensity is a monotonic function of thickness. Hence an atomic column-resolved image provides information both on the lateral shape of the nanocrystal, as well as the relative thickness of the individual columns. They show that the Z-Contrast image of a single CdSe nanocrystal is consistent with the predicted 3-D model derived from considering HRTEM images of several nanocrystals in different orientations. They further discuss the possibility of measuring absolute thicknesses of atomic columns if the crystal structure is known.

The understanding of electrical properties of grain boundaries in perovskites is essential for their application to capacitors, varistors and positive-temperature coefficient resistors. The origin of the electrical activity is generally attributed to the existence of charged defects in grain boundaries, usually assumed to be impurities, which set up a double Schottky barrier as they are screened by dopants in the adjacent bulk crystal. Microscopic understanding of the origin of the grain boundary charge, however, has not been achieved. It is not known yet if the charged grain boundary states are an intrinsic property of a stoichiometric grain boundary, arise from nonstoichiometry, or are caused by impurities. Here, the relation between atomic structure and electronic properties is studied by combining experiment with ab-initio calculations. The starting structures for theoretical calculations were obtained from Z-contrast images combined with electron energy loss spectroscopy to res olve the dislocation Core structures comprising the boundary. Dislocation core reconstructions are typical of all grain boundaries so far observed in this material. They avoid like-ion repulsion, and provide alternative sites for cation occupation in the grain boundaries. Optimized atomic positions are found by total energy calculations. Calculated differences in vacancy formation energies between the grain boundaries and …

Both x-ray diffuse reflectivity and laser light scattering have been used to investigate the temperature-dependent surface behavior of a Ni{sub 63}Al{sub 37} single crystal on different length scales. In-situ experiments were performed above the conventional martensitic start temperature M{sub s}. to search for premartensitic phenomena. X-ray experiments showed the presence of a surface precursor with second-order (continuous) character several 10 K above M{sub s}. This premonitory effect corresponds to a height-height-correlation function which changes on the nanometer scale as the martensitic transformation is approached. At the martensitic transformation, the surface morphology changed from nanoscopic roughness to macroscopic relief within a temperature interval of less than 1 K via intermediate stages. Laser light scattering was employed to study time-dependent aspects of the athermal martensitic transformation above M{sub s}. The occurrence of a martensitic transformation on isothermal holding after a certain incubation period was observed in Ni-Al for the first time. The measured incubation times increased by four orders of magnitude within a temperature interval of 0.5 K.

We are attempting to understand the solid phase chemistry of the high level nuclear waste (HLW) stored in tanks at Hanford. Because this waste is compositionally complex, our approach is to study experimentally the aging dynamics of simplified systems whose bulk chemistry approximates that of the tank sludges. After a basic understanding of these dynamics has been attained we plan to increase the compositional complexities one component at a time, in order to assess the influence of each component. Results will allow for reliable prediction of sludge phase chemistry over a range of sludge compositions. Iron and aluminum comprise the bulk of most HLW sludges, so we chose to begin by studying the behavior of iron-aluminum systems. Fe/Al ratios were chosen to approximate those relevant to the solutions that produced the sludge. Aluminum and iron concentrations in the various process fluids are summarized and compared to our experimental starting solutions in Table 1 (process solution data from Krumhansl, personal communication, 1998). Our low aluminum experiments serve as direct analogues to both Bismuth Phosphate and low-Fe PUREX waste. Cornell and Giovanoli (1985) found that, in a pure iron system at 70 C, a 10-fold or even 50-fold increase in suspension concentration …