Showing papers by "United States Department of Energy published in 1998"

Alkanethiolate Gold Cluster Molecules with Core Diameters from 1.5 to 5.2 nm: Core and Monolayer Properties as a Function of Core Size

Abstract: The mean size of the gold (Au) core in the synthesis of dodecanethiolate-stabilized Au cluster compounds can be finely adjusted by choice of the Au:dodecanethiolate ratio and the temperature and rate at which the reduction is conducted. The Au clusters have been examined with a large number of independent analytical tools, producing a remarkably consistent picture of these materials. Average cluster and core dimensions, as ascertained by 1H NMR line broadening, high-resolution transmission electron microscopy, small-angle X-ray scattering, and thermogravimetric analysis, vary between diameters of 1.5 and 5.2 nm (∼110−4800 Au atoms/core). The electronic properties of the Au core were examined by UV/vis and X-ray photoelectron spectroscopy; the core appears to remain largely metallic in nature even at the smallest core sizes examined. The alkanethiolate monolayer stabilizing the Au core ranges with core size from ∼53 to nearly 520 ligands/core, and was probed by Fourier transform infrared spectroscopy, diff...

New goals for the U.S. Human Genome Project: 1998-2003.

Abstract: The Human Genome Project has successfully completed all the major goals in its current 5-year plan, covering the period 1993–98. A new plan, for 1998–2003, is presented, in which human DNA sequencing will be the major emphasis. An ambitious schedule has been set to complete the full sequence by the end of 2003, 2 years ahead of previous projections. In the course of completing the sequence, a “working draft” of the human sequence will be produced by the end of 2001. The plan also includes goals for sequencing technology development; for studying human genome sequence variation; for developing technology for functional genomics; for completing the sequence of Caenorhabditis elegans and Drosophila melanogaster and starting the mouse genome; for studying the ethical, legal, and social implications of genome research; for bioinformatics and computational studies; and for training of genome scientists.

Fast, robust total variation-based reconstruction of noisy, blurred images

Abstract: Tikhonov regularization with a modified total variation regularization functional is used to recover an image from noisy, blurred data. This approach is appropriate for image processing in that it does not place a priori smoothness conditions on the solution image. An efficient algorithm is presented for the discretized problem that combines a fixed point iteration to handle nonlinearity with a new, effective preconditioned conjugate gradient iteration for large linear systems. Reconstructions, convergence results, and a direct comparison with a fast linear solver are presented for a satellite image reconstruction application.

Overview of combustion and gasification of rice husk in fluidized bed reactors

Abstract: Rice is cultivated in more than 75 countries in the world. The rice husk is the outer cover of the rice and on average it accounts for 20% of the paddy produced, on weight basis. The worldwide annual husk output is about 80 million tonnes with an annual energy potential of 1.210 9 GJ corre- sponding to a heating value of 15 MJ/kg. India alone generates about 22 million tonnes of rice husk per year. If an eAcient method is available, the husk can be converted to a useful form of energy to meet the thermal and mechanical energy requirements of the rice mills themselves. This paper provides an overview of previous works on combustion and gasification of rice husk in atmospheric bubbling fluidized bed reactors and summarizes the state of the art knowledge. As the high ash content, low bulk density, poor flow characteristics and low ash melting point makes the other types of reactors like grate furnaces and downdraft gasifiers either ineAcient or unsuitable for rice husk conversion to energy, the fluidized bed reactor seems to be the promising choice. The overview shows that the reported results are from only small bench or lab scale units. Although a combustion eAciency of about 80% can nor- mally be attained; the reported values in the literature, which are more than 95%, seem to be in higher order. Combustion intensity of about 530 kg/h/m 2 is reported. It is also technically feasible to gasify rice husk in a fluidized bed reactor to yield combustible producer gas, even with suAcient heating value for application in internal combustion engines. A combustible gas with heating value of 4-6 MJ/Nm 3 at a rate of 2.8-4.6 MWth/m 2 seems to be possible. Only very little information is available on the pol- lutant emissions in combustion and tar emissions from gasification. The major conclusion is that the results reported in the literature are limited and vary widely, emphasizing the need for further research to establish suitable and optimum operating conditions for commercial implementations. # 1998 Pub- lished by Elsevier Science Ltd. All rights reserved

Long-range electrostatic trapping of single-protein molecules at a liquid-solid interface.

Abstract: The motion of single, dye-labeled protein molecules was monitored at various pH and ionic strengths within the 180-nanometer-thick evanescent-field layer at a fused-silica surface. Below the isoelectric point, molecules partitioning into the excitation region increased in number but maintained a random spatial distribution, implying that surface charge can influence the charged protein at distances beyond that of the electrical double-layer thickness. The residence times of the molecules in the interfacial layer also increased below the isoelectric point. However, immobilization on the solid surface for extended periods was not observed. Histograms of residence times exhibit nearly identical asymmetry as the corresponding elution peaks in capillary electrophoresis. These results are a direct verification of the statistical theory of chromatography at the single-molecule level, with the caveat that long-range trapping rather than adsorption is the dominant mechanism.

Derivation of the equations of nonrelativistic quantum mechanics using the principle of minimum Fisher information

Abstract: The many-particle time-dependent Schr\"odinger equation is derived using the principle of minimum Fisher information. This application of information theory leads to a physically well motivated derivation of the Schr\"odinger equation, which distinguishes between subjective and objective elements of the theory.

Photometric separation of stellar properties using sdss filters

Abstract: Using synthetic photometry of Kurucz model spectra, we explore the colors of stars as a function of temperature, metallicity, and surface gravity with Sloan Digital Sky Survey (SDSS) filters, u'g'r'i'z'. The synthetic colors show qualitative agreement with the few published observations in these filters. We find that the locus of synthetic stars is basically two-dimensional for 4500 < T < 8000 K, which precludes simultaneous color separation of the three basic stellar characteristics we consider. Colors including u' contain the most information about normal stellar properties; measurements in this filter are also important for selecting white dwarfs. We identify two different subsets of the locus in which the loci separate by either metallicity or surface gravity. For 0.5 < g' - r' < 0.8 (corresponding roughly to G stars), the locus separates by metallicity; for photometric error of a few percent, we estimate metallicity to within ~0.5 dex in this range. In the range -0.15 < g' - r' < 0.00 (corresponding roughly to A stars), the locus shows separation by surface gravity. In both cases, we show that it is advantageous to use more than two colors when determining stellar properties by color. Strategic observations in SDSS filters are required to resolve the source of a ~5% discrepancy between synthetic colors of Gunn-Stryker stars, Kurucz models, and external determinations of the metallicities and surface gravities. The synthetic star colors can be used to investigate the properties of any normal star and to construct analytic expressions for the photometric prediction of stellar properties in special cases.

The IMADA-AVER Boundary Layer Experiment in the Mexico City Area

Abstract: A boundary layer field experiment in the Mexico City basin during the period 24 February–22 March 1997 is described. A total of six sites were instrumented. At four of the sites, 915-MHz radar wind profilers were deployed and radiosondes were released five times per day. Two of these sites also had sodars collocated with the profilers. Radiosondes were released twice per day at a fifth site to the south of the basin, and rawinsondes were flown from another location to the northeast of the city three times per day. Mixed layers grew to depths of 2500–3500 m, with a rapid period of growth beginning shortly before noon and lasting for several hours. Significant differences between the mixed-layer temperatures in the basin and outside the basin were observed. Three thermally and topographically driven flow patterns were observed that are consistent with previously hypothesized topographical and thermal forcing mechanisms. Despite these features, the circulation patterns in the basin important for the...

An Evaluation of the Dyslexia Training Program A Multisensory Method for Promoting Reading in Students with Reading Disabilities

Abstract: The development of reading and spelling skills in students with dyslexia, by definition, is delayed and often remains delayed despite years of instruction. Three qualities are thought to facilitate reading development in these children: the provision of a highly structured phonetic-instruction training program with heavy emphasis on the alphabetic system, drill and repetition to compensate for short-term verbal memory deficits, and multisensory methods to promote nonlanguage mental representations. The Dyslexia Training Program, a remedial reading program derived from Orton-Gillingham methods, embodies these qualities. Following their 2-year program, students displaying dyslexia demonstrated significantly higher reading recognition and comprehension compared with a control group. The two groups did not differ in spelling. In addition, the degree of improvement in reading demonstrated by students who received the Dyslexia Training Program by videotape and by those who received it live from instructors did ...

Biocatalytic Sulfur Removal from Fuels: Applicability for Producing Low Sulfur Gasoline

Abstract: Environmental regulations are driving R&D efforts to produce low sulfur fuels, including diesel fuel and gasoline for motor vehicles. Biocatalytic sulfur removal from fuels has potential applicability for producing low sulfur gasoline. Microbial biocatalysts have been identified that can biotransform sulfur compounds found in fuels, including ones that selectively remove sulfur from dibenzothiophene heterocyclic compounds. Most attention is give to the 4S pathway of Rhodococcus, which can remove sulfur from substituted and unsubstituted dibenzothiophenes, including sulfur compounds that hinder chemical catalysis and that resist removal by mild hydrotreatment. Various bioreactor and bioprocess designs are being tested for use with biocatalysts, including recombinant biocatalysts, for use in removing sulfur from fuels and feedstocks within the petroleum refinery stream. With bioprocess improvements that enhance biocatalyst stability, achieve faster kinetics, improve mass transfer limitations, temperature and solvent tolerance, as well as broaden substrate specificity to attack a greater range of heterocyclic compounds, biocatalysis may be a cost-effective approach to achieve the production of low sulfur gasoline. The challenge will be to accomplish these improvements by the time the regulations for low sulfur gasoline and other vehicle fuels go into effect in order to be competitive with emerging nonbiological desulfurization technologies.

Experimental determination of bed agglomeration tendencies of some common agricultural residues in fluidized bed combustion and gasification

Abstract: Ever increasing energy demand and the polluting nature of existing fossil fuel energy sources demonstrate the need for other non-polluting and renewable sources of energy. The agricultural residues available in abundance in many countries can be used for power generation. The fluidized bed technology seems to be suitable for converting a wide range of agricultural residues into energy, due to its inherent advantages of fuel flexibility, low operating temperature and isothermal operating condition. The major ash-related problem encountered in fluidized beds is bed agglomeration which, in the worst case, may result in total defluidization and unscheduled downtime. The initial agglomeration temperature for some common tropical agricultural residues were experimentally determined by using a newly developed method based on the controlled fluidized bed agglomeration test. The agricultural residues chosen for the study were rice husk, bagasse, cane trash and olive flesh. The results showed that the initial agglomeration temperatures were less than the initial deformation temperature predicted by the ASTM standard ash fusion tests for all fuels considered. The initial agglomeration temperatures of rice husk and bagasse were more than 1000°C. The agglomeration of cane trash and olive flesh was encountered at relatively low temperatures and their initial agglomeration temperatures in gasification were lower than those in combustion with both bed materials. The use of lime as bed material instead of quartz improved the agglomeration temperature of cane trash and olive flesh in combustion and decreased the same in gasification. The results indicate that rice husk and bagasse can be used in the fluidized bed for energy generation since their agglomeration temperatures are sufficiently high.

Zeolite-Supported Metal Oxide Sorbents for Hot-Gas Desulfurization

Abstract: This paper describes the results of the development of supported mixed-metal oxide sorbents for hot-gas desulfurization capable of withstanding multiple sulfidation/regeneration cycles at 871 °C (1600 °F). The sorbents consisted of various combinations of copper, molybdenum, and/or manganese oxides supported on a high silica-containing zeolite. These sorbents were tested in a fixed-bed reactor with simulated coal gas at 205 kPa (15 psig). The combination of all three metal oxides displayed synergism in enhancing efficiency for H2S removal and improved the crush strength on the pellets. Copper oxide was the most active component for reaction with H2S, while molybdenum and manganese oxides appeared to act as catalysts/promoters. During multicycle testing, this ternary metal oxide sorbent retained its reactivity and mechanical strength.

Emissions from Trucks using Fischer-Tropsch Diesel Fuel

Abstract: The Fischer-Tropsch (F-T) catalytic conversion process can be used to synthesize diesel fuels from a variety of feedstocks, including coal, natural gas and biomass. Synthetic diesel fuels can have very low sulfur and aromatic content, and excellent autoignition characteristics. Moreover, Fischer-Tropsch diesel fuels may also be economically competitive with California B- diesel fuel if produced in large volumes. overview of Fischer-Tropsch diesel fuel production and engine emissions testing is presented. Previous engine laboratory tests indicate that F-T diesel is a promising alternative fuel because it can be used in unmodified diesel engines, and substantial exhaust emissions reductions can be realized. The authors have performed preliminary tests to assess the real-world performance of F-T diesel fuels in heavy-duty trucks. Seven White-GMC Class 8 trucks equipped with Caterpillar 10.3 liter engines were tested using F-T diesel fuel. Vehicle emissions tests were performed using West Virginia University's unique transportable chassis dynamometer. The trucks were found to perform adequately on neat F-T diesel fuel. Compared to a California diesel fuel baseline, neat F-T diesel fuel emitted about 12% lower oxides of nitrogen (NOx) and 24% lower particulate matter over a five-mile driving cycle.

Electrothermal actuators fabricated in four-level planarized surface micromachined polycrystalline silicon

Abstract: This paper presents the results of tests performed on a variety of electrothermal microactuators and arrays of these actuators. The results are intended to aid designers of thermally actuated mechanisms, and they would apply to any surface micromachined polysilicon MEMS processes. Results presented include force and deflection vs. input power, maximum operating frequency, and the effects of long term operation. The end result is a set of proposed ideal actuator and array geometries for different applications' force requirements. In addition, various methods of arraying these actuators together are presented. Comparisons of these arraying methods allow the designer to choose which method best matches the fabrication process available and the application requirements. Finally, a thermally actuated stepper motor is used to demonstrate a useful application of these arrays.

Electrochemical incineration of benzoquinone in aqueous media using a quaternary metal oxide electrode in the absence of a soluble supporting electrolyte

Abstract: Electrochemical incineration of p-benzoquinone was evaluated as a model for the mineralization of carbon in toxic aromatic compounds. A Ti or Pt anode was coated with a film of the oxides of Ti, Ru, Sn and Sb. This quaternary metal oxide film was stable; elemental analysis of the electrolysed solution indicated the concentration of these metal ions to be 3μg L−1 or less. The anode showed good reactivity for the electrochemical incineration of benzoquinone. The use of a dissolved salt matrix as the so-called ‘supporting electrolyte’ was eliminated in favor of a solid-state electrolyte sandwiched between the anode and cathode. This substitution permitted the electrolysis solution to be analysed by electrospray mass spectrometry (ESMS); however, as a consequence, electrolysis periods were excessively long. Total organic carbon (TOC) and chemical oxygen demand (COD) decreased to 1–2 mgL−1 after 64h of electrolysis. The solution pH changed from 5 to 4. Phenolic and carboxylic acid intermediate products such as hydroquinone, maleic acid, fumaric acid, succinic acid, malonic acid, acetic acid and formic acids were identified and quantified using solid phase microextraction with gas chromatography with mass spectrometric detection (GCMS) or liquid chromatography (LC) with conductivity detection, absorbance detection, or electrosprary mass spectrometry (ESMS). Less than 1% of the carbon in benzoquinone was converted to acetone and acetaldehyde.

Effect of Fuel Nozzle Configuration on Premix Combustion Dynamics

Abstract: Combustion dynamics (or combustion oscillations) have emerged as a significant consideration in the development of low-emission gas turbines. To date, the effect of premix fuel nozzle geometry on combustion dynamics has not been well-documented. This paper presents experimental stability data from several different fuel nozzle geometries (i.e., changing the axial position of fuel injection in the premixer, and considering simultaneous injection from two axial positions). Tests are conducted in a can-style combustor designed specifically to study combustion dynamics. The operating pressure is fixed at 7.5 atmospheres and the inlet air temperature is fixed at 588K (600F). Tests are conducted with a nominal heat input of 1MWth (3MBTUH). Equivalence ratio and nozzle reference velocity are varied over the ranges typical of premix combustor design. The fuel is natural gas. Results show that observed dynamics can be understood from a time-lag model for oscillations, but the presence of multiple acoustic modes in this combustor makes it difficult to achieve stable combustion by simply re-locating the point of fuel injection. In contrast, reduced oscillating pressure amplitude was observed at most test conditions using simultaneous fuel injection from two axial positions.Copyright © 1998 by ASME

Model of banding in diffusive and convective regimes during directional solidification of peritectic systems

Abstract: The formation of banded microstructure in peritectic systems is examined theoretically in both diffusive and convective regimes. A rigorous model is developed in the diffusive regime that describes the non-steady-state growth of alternate solid α and β phase bands with a planar solid-liquid interface. The model is extended to incorporate the effect of convection by assuming that solute diffusion takes place within a boundary layer of constant thickness, with a uniform composition in the mixed liquid zone outside this layer. The model predicts that convection effects in a semi-infinite sample narrow the composition range over which extended banding can occur, and the spacing of bands is reduced compared to the diffusive growth model. In a finite length sample, convection is shown to lead only to the transient formation of bands. In this transient banding regime, only a few bands with a variable width are formed, and this transient banding process can occur over a wide range of compositions inside the two-phase peritectic region. Directional solidification studies in the Pb-Bi system show transient bands and agree qualitatively with these predictions. However, the basic mechanisms of band formation observed in this system is found to be significantly different from the one assumed in the model. A new mechanisms of banding is proposed in which continuous growth of both phases is present instead of nucleation at the boundary of the pre-existing phase. This mechanism yields an oscillatory structure with a shorter spatial periodicity than the band spacing predicted by the purely diffusive or boundary layer convective models.

Characterization of photovoltaic cells using poly(phenylenevinylene) doped with perylenediimide electron acceptors

Abstract: The performance of a sandwich junction device based on doped 1,4-bis(2-ethylhexyloxy)phenylenevinylene (BEH-PPV) is reported. The power conversion efficiency is dependent on the doping level, external load, and work function of the cathode. The increase in power conversion efficiency (ηe=0.8%) is due to efficient charge separation resulting from photoinduced electron transfer from the BEH-PPV donor to the perylene dicarboximide acceptor.

Iodine-129 and plutonium isotopes in Arctic kelp as historical indicators of transport of nuclear fuel-reprocessing wastes from mid-to-high latitudes in the Atlantic Ocean

Abstract: Iodine-129:iodine-127 ratios were determined using accelerator mass spectrometry in 34 Arctic marine algae collected between 1930 and 1993. A smaller set (5) of marine algae were also analyzed mass spectrometrically to determine plutonium-isotope ratios. The 129I:127I ratio increased as much as three orders of magnitude from a mean of <1×10−11 (atom/atom) in the pre-nuclear era (before 1945) to nearly 1000×10−11 in 1993 for marine algae collected from the Novaya Zemlya archipelago separating the Barents and Kara Seas. The predominant basis for the higher ratios in the Novaya Zemlya kelps appears to be upcurrent sources of 129I from nuclear fuel-reprocessing facilities at Sellafield (UK) and La Hague (France). Relatively high 241Pu:239Pu ratios (compared to observed bomb fallout at boreal latitudes, decay corrected to the date of collection) also corroborate the influence of non-fallout sources. The small size of the data set precludes determining if there are significant contributions of 129I and other radionuclides from Russian sources. In contrast, marine algae collected between 1969 and 1993 in the Bering, Beaufort and East Siberian Seas had much lower 129I:127I ratios (mean=14.04×10−11±3.15 SD) than those observed in the European Arctic. The narrow range of ratios in Ameriasian Arctic kelps, and the modest change over that time period, indicate that there were no major contributions of non-fallout 129I to North American Arctic surface waters at the time that the algae were collected. The potential for timing the transport of fuel-reprocessed 129I through analysis of additional archived samples is outlined.