Showing papers by "United States Department of Energy published in 1986"

The Salmonella typhimurium/mammalian microsomal assay. A report of the U.S. Environmental Protection Agency Gene-Tox Program.

Abstract: The Salmonella assay has been in use for almost 15 years and can be defined as a routine test for mutagenicity and for predicting potential carcinogenicity It detects the majority of animal carcinogens and consequently plays an important role in safety assessment The test is also routinely used as the frontline screen for environmental samples (complex mixtures) isolated from air, water and food This role will continue to remain an area of growth as or because sample volumes associated with these testing areas are generally very limited and more extensive testing is generally impossible While this test, like all others, has some limitations, it is recommended that it be regularly included in all genetic testing batteries

C-H Activation Mechanisms and Regioselectivity in the Cyclometalation Reactions of Bis(pentamethylcyclopentadienyl)thorium Dialkyl Complexes

Abstract: This contribution reports on the syntheses, structures and cyclometalation reactions of a series of bis(pentamethylcyclopentadienyl)thorium dialkyl complexes of the type Cp'/sub 2/ThR/sub 2/ (Cp' = eta/sup 5/-C/sub 5/Me/sub 5/). It focuses upon the pathway of C-H ..-->.. C'-H hydrogen atom transfer, hydrogen atom positions in the ground states of Cp'/sub 2/Th(CH/sub 2/CMe/sub 3/)/sub 2/ by single-crystal neutron diffraction, and those structural/electronic factors influencing reaction rate and regioselectivity in both neopentyl and modified neopentyl complexes. While on the surface the present d/sup 0/,f/sup 0/ reaction patterns may appear to exhibit similarities to those of the d/sup 8/ and related systems, it will be seen that there are actually profound mechanistic differences. It will also be seen that Th-C bond enthalpy data are useful in understanding certain of the reaction patterns. 63 references, 7 figures, 7 tables.

Silicon carbide whisker reinforced ceramic composites and method for making same

Abstract: The present invention is directed to the fabrication of ceramic composites which possess improved mechanical properties especially increased fracture toughness. In the formation of these ceramic composites, the single crystal SiC whiskers are mixed with fine ceramic powders of a ceramic material such as Al2 O3, mullite, or B4 C. The mixtures which contain a homogeneous dispersion of the SiC whiskers are hot pressed at pressures in a range of about 28 to 70 MPa and temperatures in the range of about 1600° to 1950° C. with pressing times varying from about 0.75 to 2.5 hours. The resulting ceramic composites show an increase in fracture toughness of up to about 9 MPa.m1/2 which represents as much as a two-fold increase over that of the matrix material.

Fuel cell integrated with steam reformer

Abstract: A H 2 -air fuel cell integrated with a steam reformer is disclosed wherein a superheated water/methanol mixture is fed to a catalytic reformer to provide a continuous supply of hydrogen to the fuel cell, the gases exhausted from the anode of the fuel cell providing the thermal energy, via combustion, for superheating the water/methanol mixture.

Size polymorphism and heteroplasmy in the mitochondrial DNA of lower vertebrates.

Abstract: The mitochondrial DNA of the bowfin fish and each of two species of treefrogs displays large-scale size variation. Within each species, mitochondrial genomes span more than a 700 base pair range, and the size polymorphism is localized to one portion of the genome. In addition, about 5 percent of the total 357 individuals surveyed were observed to carry two size classes of mtDNA. These findings are among the few documented instances of extensive within-species mtDNA size polymorphism and individual heteroplasmy, and constitute exceptions to previously reached generalizations about the molecular basis of mtDNA variation.

Toxicological review of busulfan (Myleran).

Abstract: Busulfan is a bifunctional alkylating agent that appears to be cytotoxic to slowly proliferating or non-proliferating stem cell compartments, although its specific molecular and cellular mechanisms are unknown. It is the drug of preference in treatment of chronic myelogenous or granulocytic leukemia because its cytotoxic activity results in primary damage or destruction of hematopoietic cells. Additional effects resulting from the cytotoxicity of busulfan in hematological and other tissues, as documented by both human and animal model studies, include lethality, sterility, teratogenicity, and alteration of immune function. Busulfan has been shown to be mutagenic to microorganisms, mammalian cells in culture, Drosophila, and rodents. This agent is also considered potentially carcinogenic to humans. Various tissue hyperplasia and preneoplastic cells have been observed in animal model studies with busulfan, and case reports on human patients implicate busulfan as the causative agent in induction of secondary malignancies. Reports from human and animal studies of busulfan's cytotoxicity, teratogenicity, carcinogenicity, and mutagenicity have been reviewed. This information may be useful in a quantitative assessment of the effects of this agent and the identification of significant deficiencies in the data base. Demonstration that busulfan induces mutations in both somatic and germ cells suggests the need to assess its risk to humans.

Phase equilibrium in the LaMg (0 – 65 at.% Mg) and GdMg systems

Abstract: The phase relationships in the LaMg (up to 65 at.% Mg) and the GdMg phase diagrams were established. A special effort was made to determine the extent of the solid solubility of magnesium in the high temperature b.c.c. phases of lanthanum (γ) and gadolinium (β), and the eutectoid decomposition temperature and composition of these b.c.c. solid solution phases.

Quantum well multijunction photovoltaic cell

Abstract: A monolithic, quantum well, multilayer photovoltaic cell comprises a p-n junction comprising a p-region on one side and an n-region on the other side, each of which regions comprises a series of at least three semiconductor layers, all p-type in the p-region and all n-type in the n-region; each of said series of layers comprising alternating barrier and quantum well layers, each barrier layer comprising a semiconductor material having a first bandgap and each quantum well layer comprising a semiconductor material having a second bandgap when in bulk thickness which is narrower than said first bandgap, the barrier layers sandwiching each quantum well layer and each quantum well layer being sufficiently thin that the width of its bandgap is between said first and second bandgaps, such that radiation incident on said cell and above an energy determined by the bandgap of the quantum well layers will be absorbed and will produce an electrical potential across said junction.

Electromicroinjection of particles into living cells

Abstract: Method and apparatus for introducing particles into living cells. Fluorescently-stained human chromosomes are introduced into cultured, mitotic Chinese hamster cells using electromicroinjection. The recipient cells frequently survived the physiological perturbation imposed by a successful chromosome injection. Successfully injected recipient cells maintained viability as evidenced by their ability to be expanded. The technique relies on the surface charge of fluorescently stained chromosomes and their ability to be attracted and repelled to and from the tip of a micropipette. The apparatus includes a micropipette having a tip suitable for piercing the membrane of a target cell and an electrode inserted into the lumen thereof. The target cells and suspended particles are located in an electrically conducted solution, and the lumen of the micropipette is filled with an electrically conducting solution which contacts the electrode located therein. A second electrode is also located in the conducting solution containing the target cells and particles. Voltages applied to the electrode within the micropipette attract the particles to the region of the tip thereof. The particles adhere to the surface of the micropipette with sufficient force that insertion of the micropipette tip and attached particle through the membrane of a target cell will not dislodge the particle. By applying a voltage having the opposite polarity of the attraction voltage, the particles are expelled from the micropipette to which is then withdrawn from the cell body.

First-principles calculation of surface phonons on the Al(110) surface.

Abstract: The surface-phonon dispersion curves of Al(110) have been calculated with force constants determined from first-principles self-consistent total-energy calculations. Relaxation of the surface layers produces changes in the surface force constants which have a significant influence on the surface-phonon frequencies near the zone boundary.

Aneuploidy Data Review Committee: summary compilation of chemical data base and evaluation of test methodology.

Abstract: The Aneuploidy Data Review Commi.'ttee is composed of 9 working groups on different aneuploidy test systems (Dellarco et al., 1986); the reports of these working groups comprise the major part of this special issue of Mutation Research. This paper summarizes the conclusions of the committee and the data base of chemical test results. The data base on aneuploidy induction is too small at present for detailed comparisons of assay systems or assessments of chemical activity, but this systematic, critical reveiw of methodology provides guidelines for further test development and validation.

New Schrödinger equations for old: Inequivalence of the Darboux and Abraham-Moses constructions

Abstract: There exist two methods for generating families of isospectral Hamiltonians: one based on a theorem due to Darboux and the second due to Abraham and Moses based on the Gel'fand-Levitan equation. Both methods start with a general Hamiltonian operator H=-${d}^{2}$/${\mathrm{dx}}^{2}$+V(x), and generate infinite families of new Hamiltonians all with the same eigenvalue spectrum. The new spectrum corresponds either to the addition of new bound states with specified energy eigenvalues or to the deletion of bound-state eigenvalues. Neither process (addition or deletion) alters the reflection or transmission probabilities, although the amplitudes experience a phase change consistent with Levinson's theorem and the change in the number of bound states. In this paper we show that these two methods of generating families of isospectral Hamiltonians are, in general, inequivalent.

Silicon carbide whisker-zirconia reinforced mullite and alumina ceramics

Abstract: The flexural strength and/or fracture toughness of SiC whisker-reinforced composites utilizing mullite or alumina as the matrix material for the composite are increased by the addition of zirconia in a monoclinic or tetragonal phase to the matrix. The zirconia addition also provides for a lower hot-pressing temperature and increases the flexural strength and/or fracture toughness of the SiC whisker-reinforced composites over SiC whisker-reinforced composites of the similar matrix materials reinforced with similar concentrations of SiC whiskers.

Observation of negative s-wave proximity effect in superconducting UBe13.

Abstract: The Josephson ${I}_{c}$ between a Ta-wire probe and an induced, surface, singlet, superconducting state in U${\mathrm{Be}}_{13}$ decreases with decreasing temperature below the bulk U${\mathrm{Be}}_{13}$ ${T}_{c}$, in contrast to the increase seen in comparison Mo samples. This shows that the bulk U${\mathrm{Be}}_{13}$ superconductivity suppresses the induced singlet superconductivity. Such suppression is evidence of a triplet super-conducting state in U${\mathrm{Be}}_{13}$. Evidence is presented for phase slip between weakly coupled singlet and triplet order parameters.

A time resolution methodology for assessing the quality of lake sediment cores that are dated by 137Cs

Abstract: A methodology is proposed for grading the utility of lake sediment cores used to reconstruct pollution histories. The observed distribution of /sup 137/Cs with depth in the core is compared to that expected from independent, historic measurements of fallout deposition. The width of the /sup 137/Cs peak is the core profile that corresponds to the fallout maximum of 1963, or the combined maxima of 1959 and 1963, is used to infer the inherent time resolution of the core, i.e. the ability to distinguish events in the deposition history of the watershed. The method is applied to a number of core profiles from various lakes in the US and appears to provide self-consistent results.

A vibrational state‐selected study of the reaction H+2(v’0)+H2(v’’0=0)→H+3+H using the tandem photoionization mass spectrometry and radio frequency ion guide methods

Abstract: A new ion–molecule rection apparatus, which consists of a photoionization source, a tandem mass spectrometer, and a radio frequency octopole reaction cell is described. Using a quadrupole mass filter to reject H+3 background ions formed at the photoionization source, absolute total cross sections for the reaction H+2 (v’0) +H2 (v’0 =0)→H+3 +H, have been measured as a function of the vibrational state of reactant H+2, where v’0 =0–4, over the center‐of‐mass collision energy (Ec.m.) range of 0.04–15 eV. The experimental results are compared with phenomenological cross sections obtained in previous single gas cell studies, the quasiclassical trajectory calculations of Stine and Muckerman, and the recent similar calculations of Eaker and Schatz. The absolute total cross sections measured for v0 =0 and 3 at Ec.m. =0.5, 1, 3, and 5 eV are found to be in agreement with ‘‘trajectory surface hopping’’ calculations which include nonadiabatic surface hopping throughout the reaction.

Modified sedimentation‐dispersion model for solids in a three‐phase slurry column

Abstract: Solids distribution data for a three-phase, batch-fluidized slurry bubble column (SBC) are presented, using air as the gas phase, pure liquids and solutions as the liquid phase, and glass beads and carborundum catalyst powder as the solid phase. Solids distribution data for the three-phase SBC operated in a continuous mode of operation are also presented, using nitrogen as the gas phase, water as the liquid phase, and glass beads as the solid phase. A new model to provide a reasonable approach to predict solids concentration distributions for systems containing polydispersed solids is presented. The model is a modification of standard sedimentation-dispersion model published earlier. Empirical correlations for prediction of hindered settling velocity and solids dispersion coefficient for systems containing polydispersed solids are presented. A new method of evaluating critical gas velocity (CGV) from concentrations of the sample withdrawn at the same port of the SBC is presented. Also presented is a new mapping for CGV which separates the two regimes in the SBC, namely, incomplete fluidization and complete fluidization.

High gain and high extraction efficiency from a free electron laser amplifier operating in the millimeter wave regime

Abstract: Experiments at the Electron Laser Facility have generated peak microwave power of 180 MW at 35 GHz. The facility is operated as a single pass amplifier. Gain in excess of 30 dB/m has been observed up to saturation of the amplifier. For the 3.6 MeV, 850 A electron beam, the radiation corresponds to 6% energy extraction from the electron beam. Beyond saturation, the electron beam output power exhibits oscillations corresponding to the synchrotron motion of the trapped electrons in the ponderomotive well. In addition, the TE 21 and TM 21 modes have been studied and have power levels comparable to the fundamental. Third harmonic (105 GHz) radiation has been measured at power levels on the order of a few percent of the peak fundamental power.