Showing papers by "Oak Ridge National Laboratory published in 1999"

Fuzzy hierarchical analysis

Abstract: We present a new method of finding the fuzzy weights in fuzzy hierarchical analysis which is the direct fuzzification of the original method used by Saaty (1980) in the analytic hierarchy process. We test our new procedure in two cases where there are formulas for the crisp weights. An example is presented where there are five criteria and three alternatives.

Multilevel converters for large electric drives

Abstract: This paper presents transformerless multilevel power converters as an application for high-power and/or high-voltage electric motor drives. Multilevel converters: (1) can generate near-sinusoidal voltages with only fundamental frequency switching; (2) have almost no electromagnetic interference or common-mode voltage; and (3) are suitable for large voltampere-rated motor drives and high voltages. The cascade inverter is a natural fit for large automotive all-electric drives because it uses several levels of DC voltage sources, which would be available from batteries or fuel cells. The back-to-back diode-clamped converter is ideal where a source of AC voltage is available, such as in a hybrid electric vehicle. Simulation and experimental results show the superiority of these two converters over two-level pulsewidth-modulation-based drives.

Nucleosynthesis in Chandrasekhar Mass Models for Type Ia Supernovae and Constraints on Progenitor Systems and Burning-Front Propagation

Abstract: The major uncertainties involved in the Chandrasekhar mass models for Type Ia supernovae (SNe Ia) are related to the companion star of their accreting white dwarf progenitor (which determines the accretion rate and consequently the carbon ignition density) and the flame speed after the carbon ignition. We calculate explosive nucleosynthesis in relatively slow deflagrations with a variety of deflagration speeds and ignition densities to put new constraints on the above key quantities. The abundance of the Fe group, in particular of neutron-rich species like 48Ca,50Ti,54Cr,54,58Fe, and 58Ni, is highly sensitive to the electron captures taking place in the central layers. The yields obtained from such a slow central deflagration, and from a fast deflagration or delayed detonation in the outer layers, are combined and put to comparison with solar isotopic abundances. To avoid excessively large ratios of 54Cr/56Fe and 50Ti/56Fe, the central density of the average white dwarf progenitor at ignition should be as low as 2 ? 109 g cm-3. To avoid the overproduction of 58Ni and 54Fe, either the flame speed should not exceed a few percent of the sound speed in the central low Ye layers or the metallicity of the average progenitors has to be lower than solar. Such low central densities can be realized by a rapid accretion as fast as -->img1.gif 1 ? 10-7 M? yr-1. In order to reproduce the solar abundance of 48Ca, one also needs progenitor systems that undergo ignition at higher densities. Even the smallest laminar flame speeds after the low-density ignitions would not produce sufficient amount of this isotope. We also found that the total amount of 56Ni, the Si-Ca/Fe ratio, and the abundance of some elements like Mn and Cr (originating from incomplete Si burning), depend on the density of the deflagration-detonation transition in delayed detonations. Our nucleosynthesis results favor transition densities slightly below 2.2 ? 107 g cm-3.

The carbon balance of tropical, temperate and boreal forests

Abstract: Forest biomes are major reserves for terrestrial carbon, and major components of global primary productivity. The carbon balance of forests is determined by a number of component processes of carbon acquisition and carbon loss, and a small shift in the magnitude of these processes would have a large impact on the global carbon cycle. In this paper, we discuss the climatic influences on the carbon dynamics of boreal, temperate and tropical forests by presenting a new synthesis of micrometeorological, ecophysiological and forestry data, concentrating on three case-study sites. Historical changes in the carbon balance of each biome are also reviewed, and the evidence for a carbon sink in each forest biome and its likely behaviour under future global change are discussed. We conclude that there have been significant advances in determining the carbon balance of forests, but there are still critical uncertainties remaining, particularly in the behaviour of soil carbon stocks.

Tree responses to rising CO2 in field experiments: implications for the future forest

Abstract: The need to assess the role of forests in the global cycling of carbon and how that role will change as the atmospheric concentration of CO2 increases has spawned many experiments over a range of scales. Experiments using open-top chambers have been established at many sites to test whether the short-term responses of tree seedlings described in controlled environments would be sustained over several growing seasons under field conditions. Here we review the results of those experiments, using the framework of the interacting cycles of carbon, water and nutrients, because that is the framework of the ecosystem models that are being used to address the decades-long response of forests. Our analysis suggests that most of what was learned in seedling studies was qualitatively correct. The evidence from field-grown trees suggests a continued and consistent stimulation of photosynthesis of about 60% for a 300 p.p.m. increase in [CO2], and there is little evidence of the long-term loss of sensitivity to CO2 that was suggested by earlier experiments with tree seedlings in pots. Despite the importance of respiration to a tree's carbon budget, no strong scientific consensus has yet emerged concerning the potential direct or acclimation response of woody plant respiration to CO2 enrichment. The relative effect of CO2 on above-ground dry mass was highly variable and greater than that indicated by most syntheses of seedling studies. Effects of CO2 concentration on static measures of response are confounded with the acceleration of ontogeny observed in elevated CO2. The trees in these open-top chamber experiments were in an exponential growth phase, and the large growth responses to elevated CO2 resulted from the compound interest associated with an increasing leaf area. This effect cannot be expected to persist in a closed-canopy forest where growth potential is constrained by a steady-state leaf area index. A more robust and informative measure of tree growth in these experiments is the annual increment in wood mass per unit leaf area, which increased 27% in elevated CO2. There is no support for the conclusion from many studies of seedlings that root-to-shoot ratio is increased by elevated CO2; the production of fine roots may be enhanced, but it is not clear that this response would persist in a forest. Foliar nitrogen concentrations were lower in CO2-enriched trees, but to a lesser extent than was indicated in seedling studies and only when expressed on a leaf mass basis. The prediction that leaf litter C/N ratio would increase was not supported in field experiments. Also contrasting with seedling studies, there is little evidence from the field studies that stomatal conductance is consistently affected by CO2; however, this is a topic that demands more study. Experiments with trees in open-top chambers under field conditions have provided data on longer-term, larger-scale responses of trees to elevated CO2 under field conditions, confirmed some of the conclusions from previous seedling studies, and challenged other conclusions. There remain important obstacles to using these experimental results to predict forest responses to rising CO2, but the studies are valuable nonetheless for guiding ecosystem model development and revealing the critical questions that must be addressed in new, larger-scale CO2 experiments.

Local processes and regional patterns : appropriate scales for understanding variation in the diversity of plants and animals

Abstract: Determining the causes of variation in species diversity requires linking the scales at which variation in diversity is measured to the scales at which the processes hypothesized to affect diversity actually operate. Published analyses of the relative effects of local versus regional processes on species diversity have failed to measure diversity at spatial scales relevant to local processes. The effects of local processes. such as competition, can only be detected at appropriately small local scales, and are obscured by large samples that aggregate environmental heterogeneity. Relatively few ecological and evolutionary processes can be identified as uniquely regional in scale. and local processes are expected to produce regional-scale differences between regions that differ consistently in environmental conditions that affect local processes. The relative contributions of regional properties and local processes are hypothesized to vary predictably along certain environmental gradients, and to produce locally regulated patterns of species diversity at scales ranging from a few millimeters to the entire globe.

Global Change in Local Places: How Scale Matters

Abstract: Relationships between local and global scales deserve more attention than they have received in the global change research enterprise to date. This paper examines how and why scale matters, drawing on six basic arguments; examines the current state of the top-down global change research paradigm to evaluate the fit across relevant scale domains between global structure and local agency; and reviews current research efforts to better link the local and global scales of attention and action.

Microbial Population Changes during Bioremediation of an Experimental Oil Spill

Abstract: Three crude oil bioremediation techniques were applied in a randomized block field experiment simulating a coastal oil spill. Four treatments (no oil control, oil alone, oil plus nutrients, and oil plus nutrients plus an indigenous inoculum) were applied. In situ microbial community structures were monitored by phospholipid fatty acid (PLFA) analysis and 16S rDNA PCR-denaturing gradient gel electrophoresis (DGGE) to (i) identify the bacterial community members responsible for the decontamination of the site and (ii) define an end point for the removal of the hydrocarbon substrate. The results of PLFA analysis demonstrated a community shift in all plots from primarily eukaryotic biomass to gram-negative bacterial biomass with time. PLFA profiles from the oiled plots suggested increased gram-negative biomass and adaptation to metabolic stress compared to unoiled controls. DGGE analysis of untreated control plots revealed a simple, dynamic dominant population structure throughout the experiment. This banding pattern disappeared in all oiled plots, indicating that the structure and diversity of the dominant bacterial community changed substantially. No consistent differences were detected between nutrient-amended and indigenous inoculum-treated plots, but both differed from the oil-only plots. Prominent bands were excised for sequence analysis and indicated that oil treatment encouraged the growth of gram-negative microorganisms within the α-proteobacteria and Flexibacter-Cytophaga-Bacteroides phylum. α-Proteobacteria were never detected in unoiled controls. PLFA analysis indicated that by week 14 the microbial community structures of the oiled plots were becoming similar to those of the unoiled controls from the same time point, but DGGE analysis suggested that major differences in the bacterial communities remained.

The sources, fate, and toxicity of chemical warfare agent degradation products.

Abstract: We include in this review an assessment of the formation, environmental fate, and mammalian and ecotoxicity of CW agent degradation products relevant to environmental and occupational health. These parent CW agents include several vesicants: sulfur mustards [undistilled sulfur mustard (H), sulfur mustard (HD), and an HD/agent T mixture (HT)]; nitrogen mustards [ethylbis(2-chloroethyl)amine (HN1), methylbis(2-chloroethyl)amine (HN2), tris(2-chloroethyl)amine (HN3)], and Lewisite; four nerve agents (O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate (VX), tabun (GA), sarin (GB), and soman (GD)); and the blood agent cyanogen chloride. The degradation processes considered here include hydrolysis, microbial degradation, oxidation, and photolysis. We also briefly address decontamination but not combustion processes. Because CW agents are generally not considered very persistent, certain degradation products of significant persistence, even those that are not particularly toxic, may indicate previous CW agent presence or that degradation has occurred. Of those products for which there are data on both environmental fate and toxicity, only a few are both environmentally persistent and highly toxic. Major degradation products estimated to be of significant persistence (weeks to years) include thiodiglycol for HD; Lewisite oxide for Lewisite; and ethyl methyl phosphonic acid, methyl phosphonic acid, and possibly S-(2-diisopropylaminoethyl) methylphosphonothioic acid (EA 2192) for VX. Methyl phosphonic acid is also the ultimate hydrolysis product of both GB and GD. The GB product, isopropyl methylphosphonic acid, and a closely related contaminant of GB, diisopropyl methylphosphonate, are also persistent. Of all of these compounds, only Lewisite oxide and EA 2192 possess high mammalian toxicity. Unlike other CW agents, sulfur mustard agents (e.g., HD) are somewhat persistent; therefore, sites or conditions involving potential HD contamination should include an evaluation of both the agent and thiodiglycol.

Abiogenic Methane Formation and Isotopic Fractionation Under Hydrothermal Conditions

Abstract: Recently, methane (CH4) of possible abiogenic origin has been reported from many localities within Earth's crust. However, little is known about the mechanisms of abiogenic methane formation, or ab...

A critical examination of the fundamental relations used in the analysis of nanoindentation data

Abstract: Methods for analyzing nanoindentation load-displacement data to determine hardness and elastic modulus are based on analytical solutions for the indentation of an elastic half-space by rigid axisymmetric indenters. Careful examination of Sneddon's solution for indentation by a rigid cone reveals several largely ignored features that have important implications for nanoindentation property measurement. Finite element and analytical results are presented that show corrections to Sneddon's equations are needed if accurate results are to be obtained. Without the corrections, the equations underestimate the load and contact stiffness in a manner that leads to errors in the measured hardness and modulus, with the magnitudes of the errors depending on the angle of the indenter and Poisson's ratio of the half-space. First order corrections are derived, and general implications for the interpretation of nanoindentation data are discussed.

Nitroaromatic Munition Compounds: Environmental Effects and Screening Values

Abstract: Nitroaromatic compounds, including 2,4,6-trinitrotoluene (TNT), hexahydro-1,3, 5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5-tetrazocine (HMX), N-methyl-N,2,4,6-tetranitroaniline (tetryl), and associated byproducts and degradation products, were released to the environment during manufacturing and load, assembly, and pack (LAP) processes at U.S. Army Ammunition Plants (AAPs) and other military facilities. As a result of the release of these nitroaromatic compounds into the environment, many AAPs have been placed on the National Priorities List for Superfund cleanup (Fed. Reg. 60:20330). Many of these sites cover a wide expanse of relatively undisturbed land and provide diverse habitats that support a variety of aquatic and terrestrial species. Nitroaromatics are potentially toxic to the indigenous species at these sites and present a significant concern for site remediation. Table 1 presents an overview of ranges of detected concentrations of the nitroaromatic compounds in groundwater, surface water, sediment, and soil at military and manufacturing sites.

Shell structure of superheavy nuclei in self-consistent mean-field models

Abstract: We study the extrapolation of nuclear shell structure to the region of superheavy nuclei in self-consistent mean-field models[emdash]the Skyrme-Hartree-Fock approach and the relativistic mean-field model[emdash]using a large number of parametrizations which give similar results for stable nuclei but differ in detail. Results obtained with the folded-Yukawa potential which is widely used in macroscopic-macroscopic models are shown for comparison. We focus on differences in the isospin dependence of the spin-orbit interaction and the effective mass between the models and their influence on single-particle spectra. The predictive power of the mean-field models concerning single-particle spectra is discussed for the examples of [sup 208]Pb and the spin-orbit splittings of selected neutron and proton levels in [sup 16]O, [sup 132]Sn, and [sup 208]Pb. While all relativistic models give a reasonable description of spin-orbit splittings, all Skyrme interactions show a wrong trend with mass number. The spin-orbit splitting of heavy nuclei might be overestimated by 40[percent][endash]80[percent], which exposes a fundamental deficiency of the current nonrelativistic models. In most cases the occurrence of spherical shell closures is found to be nucleon-number dependent. Spherical doubly magic superheavy nuclei are found at [sub 184][sup 298]114, [sub 172][sup 292]120, or [sub 184][sup 310]126 depending on the parametrization. The Z=114more » proton shell closure, which is related to a large spin-orbit splitting of proton 2f states, is predicted only by forces which by far overestimate the proton spin-orbit splitting in [sup 208]Pb. The Z=120 and N=172 shell closures predicted by the relativistic models and some Skyrme interactions are found to be related to a central depression of the nuclear density distribution. This effect cannot appear in macroscopic-microscopic models or semiclassical approaches like the extended Thomas-Fermi-Strutinski integral approach which have a limited freedom for the density distribution only. In summary, our findings give a strong argument for [sub 172][sup 292]120 to be the next spherical doubly magic superheavy nucleus. [copyright] [ital 1999] [ital The American Physical Society]« less

Extinction Thresholds for Species in Fractal Landscapes

Abstract: Predicting species' responses to habitat loss and fragmentation is one of the greatest challenges fac- ing conservation biologists, particularly if extinction is a threshold phenomenon. Extinction thresholds are abrupt declines in the patch occupancy of a metapopulation across a narrow range of habitat loss. Metapop- ulation-type models have been used to predict extinction thresholds for endangered populations. These models often make simplifying assumptions about the distribution of habitat (random) and the search for suitable habitat sites (random dispersal). We relaxed these two assumptions in a modeling approach that combines a metapopulation model with neutral landscape models of fractal habitat distributions. Dispersal success for suitable, unoccupied sites was higher on fractal landscapes for nearest-neighbor dispersers (moving through adjacent cells of the landscape) than for dispersers searching at random (random distance and direction be- tween steps) on random landscapes. Consequently, species either did not suffer extinction thresholds or extinc- tion thresholds occurred later, at lower levels of habitat abundance, than predicted previously. The exception is for species with limited demographic potential, owing to low reproductive output ( R 9 o 5 1.01), in which ex- tinction thresholds occurred sooner than on random landscapes in all but the most clumped fractal land- scapes ( H 5 1.0). Furthermore, the threshold was more precipitous for these species. Many species of conserva- tion concern have limited demographic potential, and these species may be at greater risk from habitat loss and fragmentation than previously suspected.

Ion-beam modification of polymeric materials – fundamental principles and applications

Abstract: When an energetic ion traverses a polymer medium, it loses its energy by electronic and nuclear processes. In the past, considerable research efforts have been devoted to understand the effects of the electronic and nuclear processes in materials. There have been, however, some conflicting reports regarding the roles of electronic and nuclear stopping in producing property changes in polymeric materials, namely the magnitude of cross-linking and scission. A consensus derived from the work conducted at ORNL indicates that electronic stopping is largely responsible for cross-linking and nuclear stopping for scission, although both processes can cause cross-linking as well as scission. The most important parameter for cross-linking is found to be the energy deposited per unit ion path length or linear energy transfer (LET). The mechanisms involved with property changes are discussed by clarifying the concepts of nuclear and electronic stopping, LET, tracks, and spurs. Experimental evidence to support the views are presented. Also addressed are specific property changes induced by ion-beams, which may be of use for industrial applications.

Tansley Review No. 104

Abstract: Summary I INTRODUCTION – A HYPOTHESIS 374 II EFFECTS OF CALCIUM ON PHYSIOLOGICAL PROCESSES 376 1 The chemical uniqueness of calcium 376 (a) Cytotoxicity 376 (b) Binding properties 376 (c) Stimulation/displacement potential 376 2 Calcium signaling and plant responses to environmental stress 377 (a) Control principles 377 (b) Carbohydrate metabolism 378 (c) Synthesis and function of membranes and cell walls 379 (d) Disease resistance and wound repair 380 (e) Cold tolerance 381 (f) Stomatal regulation 382 III CALCIUM UPTAKE AND DISTRIBUTION AT THE WHOLE-PLANT LEVEL 382 1 Uptake at the root-soil interface 382 2 Transport and exchange in stems 384 3 Exchange of calcium by foliage 385 IV ECOSYSTEM PROCESSES AND CALCIUM SUPPLY 387 1 Plant succession and soil acidification 387 2 Plant adaptations to nutrient deficiency 389 (a) Morphological adaptations 389 (b) Physiological adaptations 390 V PLANT AND ECOSYSTEM RESPONSES TO HUMAN ALTERATIONS IN CALCIUM SUPPLY 391 1 Increased atmospheric inputs of acidity 391 (a) Reductions in soil cation pools 392 (b) Inhibition of calcium uptake and effects on root function 393 (c) Increased leaching of calcium from foliage 395 (d) Physiological indicators of altered forest function 397 (e) Wood chemistry, structure and function 402 2 Forest management 404 (a) Harvesting effects on nutrient supply 404 (b) Managing forest nutrient supply 405 VI CONCLUSION 407 1 Whole-tree perspectives 407 2 Ecosystem perspectives 408 VII EVALUATION OF THE HYPOTHESIS 410 Acknowledgements 411 References 411 Summary Calcium occupies a unique position among plant nutrients both chemically and functionally Its chemical properties allow it to exist in a wide range of binding states and to serve in both structural and messenger roles Despite its importance in many plant processes, Ca mobility is low, making Ca uptake and distribution rate a limiting process for many key plant functions Ca plays an essential role in regulating many physiological processes that influence both growth and responses to environmental stresses Included among these are: water and solute movement, influenced through effects on membrane structure and stomatal function; cell division and cell wall synthesis; direct or signaling roles in systems involved in plant defense and repair of damage from biotic and abiotic stress; rates of respiratory metabolism and translocation; and structural chemistry and function of woody support tissues Forest trees, because of their size and age capacity, have been examined for evidence of limitations imposed by the timing and level of Ca supply Examination of Ca physiology and biogeochemical cycling for forested systems reveals many indications that Ca supply places important limitations on forest structure and function These limitations are likely to be most significant with older trees, later successional stages, high levels of soil acidity and/or high canopy Ca leaching losses, or under conditions where plant competition is high or transpiration is limited by high humidity or low soil moisture Evidence of structural and physiological adaptations of forests to limited Ca supply; indicators of system dysfunction at many levels under reduced Ca supply; and the positive responses of diverse indicators of forest vitality in liming experiments indicate that Ca is more important to forest function and structure than has generally been recognized Lack of recognition of Ca limitations is due in part to that fact some important plant functions are controlled by changes in very small physiologically active pools within the cytoplasm, and whole-leaf Ca levels may not reflect these limitations An additional aspect is the fact that Ca availability has declined significantly for many forests in just the past few decades Additional research on the role of Ca supply in resistance of forests to disease, changes in structural integrity of woody tissues, restrictions on rooting patterns and function, and uptake of other nutrients, notably N, is needed Increased understanding of the physiological ecology of Ca supply can be anticipated to provide important insights that will aid in future protection and management of both natural and commercial forest systems

Effects of Particle Size of TiO2 on Photocatalytic Degradation of Methylene Blue in Aqueous Suspensions

Abstract: The influence of particle size of TiO2 on the photocatalytic degradation of methylene blue (MB) in a suspended aqueous solution has been studied. The results suggested that the adsorption rate and adsorbability of MB on suspended TiO2 particles increased as the particle sizes of TiO2 decreased. Photocatalytic activity of TiO2 also increased as the particle size of TiO2 became smaller, especially when the particle size is less than 30 nm. The half-life (t0.5) of the photocatalytic degradation of MB also decreased as the particle sizes of TiO2 decreased. The first-order reaction rate constant for photodegradation of MB increased as the particle size of TiO2 decreased. The initial degradation rate of MB in a suspended model was higher than that of a fixed-bed model. This will overcome the difficulty of preparation of ultrafine TiO2 catalyst particles. Once the problem of separation of fine TiO2 particles is solved, a TiO2 suspended photoreactor could be provided on an industrial basis.

Thermal properties of lithium-ion battery and components

Abstract: Experimental thermal property data of the Sony US-18650 lithium-ion battery and components are presented, as well as thermal property measuring techniques. The properties in question are specific heat capacity (C{sub p}), thermal diffusivity ({alpha}), and thermal conductivity ({kappa}), in the presence and absence of electrolyte [1 M LiPF{sub 6} in ethylene carbonate-dimethyl carbonate (EC:DMC, 1:1 wt %)]. The heat capacity of the battery, C{sub p}, is 0.96 {+-} 0.02 J/g K at an open-circuit voltage (OCV) of 2.75 V, and 1.04 {+-} 0.02 J/g K at 3.75 V. The thermal conductivity, {kappa}, was calculated from {kappa} {identical_to} {alpha}{rho}C{sub p} where {alpha} was measured by a xenon-flash technique. In the absence of electrolyte, {kappa} increases with OCV, for both the negative electrode (NE) and the positive electrode (PE). For the NE, the increase is 26% as the OCV increases from 2.75 to 3.75 V, whereas for the PE the increase is only 5 to 6%. The dependence of both C{sub p} and {kappa} on OCV is explained qualitatively by considering the effect of lithiation and delithiation on the electron carrier density, which leads to n-type semiconduction in the graphitic NE material, but a change from semiconducting to metallic character in Li{submore » x}CoO{sub 2} PE material. The overall effect is an increase of C{sub p} and {kappa} with OCV. For {kappa} this dependence is eliminated by electrolyte addition, which, however, greatly increases the effective {kappa} of the layered battery components by lowering the thermal contact resistance. For both NE and PE, the in-plane {kappa} value (measured along layers) is nearly one order of magnitude higher than the cross-plane {kappa}. This is ascribed mostly to the high thermal conductivity of the current collectors and to a lesser extent to the orientation of particles in the layers of electrodes.« less

Robust tracking of position and velocity with Kalman snakes

Abstract: A new Kalman-filter based active contour model is proposed for tracking of nonrigid objects in combined spatio-velocity space. The model employs measurements of gradient-based image potential and of optical-flow along the contour as system measurements. In order to improve robustness to image clutter and to occlusions an optical-flow based detection mechanism is proposed. The method detects and rejects spurious measurements which are not consistent with previous estimation of image motion.

Microfluidic devices for electrokinetically driven parallel and serial mixing

Abstract: Microfabricated devices for parallel and serial mixing of fluids are demonstrated. To simplify the voltage control hardware, electrokinetic mixing is effected using a single voltage source with the channels dimensioned to perform the desired voltage division. In addition, the number of fluid reservoirs is reduced by terminating multiple buffer, sample, or analysis channels in single reservoirs. The parallel mixing device is designed with a series of independent T-intersections, and the serial mixing device is based on an array of cross intersections and sample shunting. These devices were tested by mixing a sample with buffer in a dilution experiment. Sample fractions of 1.0, 0.84, 0.67, 0.51, 0.36, 0.19, and 0 were generated for the parallel mixing device, and sample fractions of 1.0, 0.36, 0.21, 0.12, and 0.06 for the serial mixing device.

Anomalous Dispersion of LO Phonons in La 1.85 Sr 0.15 CuO 4 at Low Temperatures

Abstract: Inelastic neutron scattering measurements of La1.85Sr0.15CuO4 show that a discontinuity in dispersion develops in the middle of the highest energy LO phonon branch at low temperatures. The result suggests dynamic short range unit cell doubling in the CuO2 plane along the direction of the Cu-O bond, such as charge ordering on every other row of oxygen. Such charge ordering is related to, but is different from, the stripe charge ordering observed for nonsuperconducting cuprates. The question of the influence of the electron-lattice interaction in the normal and superconducting electronic properties of high temperature superconductors remains open. Perhaps the most intriguing experimental evidence of a large and anomalous electron-lattice interaction comes from inelastic neutron scattering experiments on various high temperature superconducting materials [1‐ 6]. A signature of these materials is the strong renormalization of longitudinal high frequency (,80 meV) oxygen bond-stretching phonons in the CuO2 plane when holes are doped into the insulating compounds. The doping causes a large decrease in the frequency of the zone boundary s0.5, 0, 0d half-breathing phonon mode (15%‐ 20% softening compared to the insulating compound), indicating that there is a strong coupling of these phonons to the doped holes. This effect seems to be ubiquitous, and has been observed in single-crystal inelastic neutron scattering measurements of La22xSrxCuO4 [1], La2CuO41y [3], YBa2Cu3O61y [4,5], and even Ba12xKxBiO3 [6]. There are also indications of this effect from the observed softening of oxygen phonon bands in inelastic neutron scattering measurements of the phonon density of states in Pb2Sr2sCa,YdCu3O8 [7] and Li11xTi22xO4 [8]. It has proven quite difficult to interpret these results in terms of normal electron-phonon coupling in a metal, especially since the other measured phonon modes are, for the most part, unaffected (especially the oxygen breathing and quadrupole modes). Typical indications of electronphonon coupling, such as Kohn anomalies, seem to be inconsistent with the wave vector of the affected phonon. The Fermi surface should have strong nesting at 2kf which is close to q › s0.5, 0.5d, but not at s0.5, 0d, as demonstrated by the local-density approximation calculation [9] and ARPES measurements [10]. We have chosen to investigate these phonon phenomena more closely and have discovered that the anomalous nature of the bond-stretching branch is even more mysterious at low temperatures. The sample studied consisted of two single crystals of La1.85Sr0.15CuO4 which were comounted in an aluminum can filled with He exchange gas. Both samples were grown by the floating zone method and were obtained from the same batch. The total size of the sample is approximately 3.8 3 1.5 3 0.8 cm 3 . Previ

A Compilation of Physical, Spectroscopic and Photophysical Properties of Polycyclic Aromatic Hydrocarbons

Abstract: Polycyclic aromatic hydrocarbons (PAH),t also known as polynuclear aromatic hydrocarbons or polyarenes, constitute a large class of organic compounds. They are formed and released into the environment through natural and man-made sources. Natural sources include volcanoes and forest fire, while the man-made sources come from wood burning, automobile exhaust, industrial power generators, incinerators, production of coal tar, coke, asphalt and petroleum, incomplete combustion of coal, oil, gas, garbage, tobacco and charbroiled meat. Polycyclic aromatic heterocyclic analogs containing one or more nitrogen, oxygen or sulfur atoms are also present in substantial quantities in coal tar and petroleum residues produced during the refining process. In the atmosphere, they are principally generated from the combustion of fossil fuels, wood or forest burning, refuse burning and coal tar. Although anthropogenic sources account for the major portion of atmospheric PAH pollution (l), vehicle emissions are believed to be responsible for 35% of the total PAH emission in highly populated and industrialized urban areas of the United States (2). Deposition of PAH in surface and ground waters can take place from a variety of sources such as airborne PAH, municipal wastewater discharge, effluents from wood treatment plants and other industries, oil spills and petroleum pressing. Accumulation of PAH in soils is believed to result from atmospheric deposition after long-range transport. The concentration of PAH found in soil around urban and industrialized areas are sometimes up to two orders of magnitude higher than those in less-developed areas (derived from forest fires and airborne pollution). Once released into the environment, PAH can partition between air, water, soil or sediments. An extensive body of work on this subject has appeared in the literature in recent years. Representative examples include partitioning of PAH between the gas and suspended particle phase (3,4), aidwater

Microfabricated porous membrane structure for sample concentration and electrophoretic analysis.

Abstract: A microfabricated injection valve incorporating a porous membrane structure is reported that enables electrokinetic concentration of DNA samples using homogeneous buffer conditions followed by injection into a channel for electrophoretic analysis. The porous membrane was incorporated in the microchannel manifold by having two channels separated from each other by 3−12 μm and connected by a thin porous silicate layer. This design allows the passage of current to establish an electrical connection between the separated channels but prevents large molecules, e.g., DNA, from traversing the membrane. Concentrated DNA can be injected into the separation channel and electrophoretically analyzed. Experiments exhibit a nonlinear increase in concentration with time, and DNA fragments can be concentrated up to 2 orders of magnitude as shown by comparison of peak intensities for analysis performed with and without concentration.

Effect of Toxic Metals on Indigenous Soil β-Subgroup Proteobacterium Ammonia Oxidizer Community Structure and Protection against Toxicity by Inoculated Metal-Resistant Bacteria

Abstract: Contamination of soils with toxic metals is a major problem on military, industrial, and mining sites worldwide. Of particular interest to the field of bioremediation is the selection of biological markers for the end point of remediation. In this microcosm study, we focus on the effect of addition of a mixture of toxic metals (cadmium, cobalt, cesium, and strontium as chlorides) to soil on the population structure and size of the ammonia oxidizers that are members of the beta subgroup of the Proteobacteria (beta-subgroup ammonia oxidizers). In a parallel experiment, the soils were also treated by the addition of five strains of metal-resistant heterotrophic bacteria. Effects on nitrogen cycling were measured by monitoring the NH3 and NH4+ levels in soil samples. The gene encoding the alpha-subunit of ammonia monooxygenase (amoA) was selected as a functional molecular marker for the beta-subgroup ammonia oxidizing bacteria. Community structure comparisons were performed with clone libraries of PCR-amplified fragments of amoA recovered from contaminated and control microcosms for 8 weeks. Analysis was performed by restriction digestion and sequence comparison. The abundance of ammonia oxidizers in these microcosms was also monitored by competitive PCR. All amoA gene fragments recovered grouped with sequences derived from cultured Nitrosospira. These comprised four novel sequence clusters and a single unique clone. Specific changes in the community structure of beta-subgroup ammonia oxidizers were associated with the addition of metals. These changes were not seen in the presence of the inoculated metal-resistant bacteria. Neither treatment significantly altered the total number of beta-subgroup ammonia-oxidizing cells per gram of soil compared to untreated controls. Following an initial decrease in concentration, ammonia began to accumulate in metal-treated soils toward the end of the experiment.

Imprint coating : a novel synthesis of selective functionalized ordered mesoporous sorbents

Abstract: Molecular imprinting of surfaces of mesoporous sorbents is a novel method for introducing template-selective recognition sites. This method makes use of the unique surface environment of hexagonally packed mesopore surfaces of selected pore sizes (see the schematic representation) and coats such surfaces with functional ligands by binding to a metal ion template.