Showing papers by "Lawrence Berkeley National Laboratory published in 1987"

Ranking possible carcinogenic hazards

Abstract: This review discusses reasons why animal cancer tests cannot be used to predict absolute human risks. Such tests, however, may be used to indicate that some chemicals might be of greater concern than others. Possible hazards to humans from a variety of rodent carcinogens are ranked by an index that relates the potency of each carcinogen in rodents to the exposure in humans. This ranking suggests that carcinogenic hazards from current levels of pesticide residues or water pollution are likely to be of minimal concern relative to the background levels of natural substances, though one cannot say whether these natural exposures are likely to be of major or minor importance.

The Influence of Extracellular Matrix on Gene Expression: Is Structure the Message?

Abstract: The study of the regulation of gene expression in cultured cells, particularly in epithelial cells, has been both hampered and facilitated by the loss of function that accompanies culture on traditional plastic substrata. Initially, investigations of differentiated function were thwarted by the inadequacy of tissue culture methods developed to support growth of mesenchymal cells. However, with the recognition that the unit of function in higher organisms is larger than the cell itself, and that gene expression is dependent upon cell interactions with hormones, substrata and other cells, came the understanding that the epithelial cell phenotype is profoundly influenced by the extracellular environment. In the last decade research on epithelial cells has centred on culture conditions that recreate the appropriate environment for function with very promising and important results. The investigations into the modulation of phenotype in culture produced not only a better model, but also contributed to a better understanding of the regulation of normal function. Using cultured mammary gland epithelial cells as a primary model of these interactions, our studies of gene expression are based on three premises. (1) That the extracellular matrix (ECM) on which the cells sit is an extension of the cells and an active participant in the regulation of cellular function; i.e. the ECM is an 'informational' entity in the sense that it receives, imparts and integrates structural and functional signals. (2) That ECM-induced functional differentiation in the mammary gland is mediated through changes in cell shape, i.e. that the structure is in large part 'the message' required to maintain differentiated gene expression. (3) That the unit of function includes the cell plus its extracellular matrix; in a larger context, the unit is the organ itself. These tenets and the data presented below are consistent with a model of 'Dynamic Reciprocity', where the ECM is postulated to exert an influence on gene expression via transmembrane proteins and cytoskeletal components. In turn, cytoskeletal association with polyribosomes affects mRNA stability and rates of protein synthesis, while its interaction with the nuclear matrix could affect mRNA processing and, possibly, rates of transcription.

Optimization of radiation therapy, III: A method of assessing complication probabilities from dose-volume histograms.

Abstract: To predict the likelihood of success of a therapeutic strategy, one must be able to assess the effects of the treatment upon both diseased and healthy tissues. This paper proposes a method for determining the probability that a healthy organ that receives a non-uniform distribution of X-irradiation, heat, chemotherapy, or other agent will escape complications. Starting with any given dose distribution, a dose-cumulative-volume histogram for the organ is generated. This is then reduced by an interpolation scheme (involving the volume-weighting of complication probabilities) to a slightly different histogram that corresponds to the same overall likelihood of complications, but which contains one less step. The procedure is repeated, one step at a time, until there remains a final, single-step histogram, for which the complication probability can be determined. The formalism makes use of a complication response function C(D, V) which, for the given treatment schedule, represents the probability of complications arising when the fraction V of the organ receives dose D and the rest of the organ gets none. Although the data required to generate this function are sparse at present, it should be possible to obtain the necessary information from in vivo and clinical studies. Volume effects are taken explicitly into account in two ways: the precise shape of the patient's histogram is employed in the calculation, and the complication response function is a function of the volume.

Electronic Shell Structure and Metal Clusters

Abstract: Publisher Summary The chapter presents a study on electronic shell structure and metal clusters. Unlike the “macroscopic” atoms, the metallic clusters described from both experimental and theoretical viewpoints in this chapter come far closer to having bulk properties, because they are 10–100 times bigger. The science of clusters is a rapidly growing interdisciplinary field with great promise for the production of new ideas and physical systems. Its ideas are relevant to related problems in the physics of atoms, molecules, condensed matter, and transitions among these systems. The chapter presents a review emphasizing on the electronic shell model, which is elegant and simple, avoids the complexity of elaborate quantum chemical computer calculations for clusters containing large numbers of atoms, and possesses the power of predictability. The study of the physical properties of states intermediate between the atom and the solid is called cluster physics. Lacking a precise definition, it is said that a cluster is a stable group of a few or a few hundred identical atoms or molecules. This chapter mainly discusses metal clusters. Atomic theory depends on the application of angular momentum conditions in the Coulomb field.

Hydraulic And Mechanical Properties of Natural Fractures In Low Permeability Rock

Abstract: The results of a comprehensive laboratory study of the mechanical displacement, permeability, and void geometry of single rock fractures in a quartz monzonite are summarized and analyzed. A metal-injection technique was developed that provided quantitative data on the precise geometry of the void spaces between the fracture surfaces and the areas of contact at different stresses. At effective stresses of less than 20 MPa fluid flow was proportional to the mean fracture aperture raised to a power greater than 3. As stress was increased, contact area was increased and void spaces become interconnected by small tortuous channels that constitute the principal impediment to fluid flow. At effective stresses higher than 20 MPa, the mean fracture aperture continued to diminish with increasing stress, but this had little effect on flow because the small tortuous flow channels deformed little with increasing stress.

The Potential of Vegetation in Reducing Summer Cooling Loads in Residential Buildings

Abstract: The potential of trees and other vegetation to reduce building cooling loads has been recorded in a number of studies but the meso- and microclimate changes producing such savings are not well understood. This paper describes a preliminary attempt to model the effects of landscaping on temperature, humidity, windspeed and solar gain in urban climates using information from existing agricultural and meteorological studies, with particular attention placed on quantifying the effects of plant evapotranspiration. The climate model is then used in conjunction with the DOE-2.1C building simulation program to calculate the net reductions in air-conditioning requirements due to trees and other vegetation. Preliminary results show that an additional 25% increase in the urban tree cover can save 40% of the annual cooling energy use of an average house in Sacramento, and 25% in Phoenix and Lake Charles. If this additional tree cover is located to optimize summer shading, the savings are further increased to...

Search for Isotope Effect in Superconducting Y-Ba-Cu-O

Abstract: An isotope effect has been searched for in the high-T/sub c/ superconductor YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ through substitution of /sup 18/O for /sup 16/O. No shift in the superconducting transition temperature T/sub c/ is observed by electrical resistivity or magnetic susceptibility measurements. We discuss the implications of this result for mechanisms of superconductivity in the high-T/sub c/ oxides.

Dynamic reciprocity: how do extracellular matrix and hormones direct gene expression?

Abstract: Using mouse mammary epithelial cells (MME) as a model, we show that extracellular matrix (ECM) plays a fundamental role in the maintenance of tissue-specific function in culture. The ECM affects both the level of mRNA and the rates of synthesis and secretion of milk proteins. Casein gene expression by primary mammary epithelial cells and cell strains is controlled by both ECM and lactogenic hormones (insulin, hydrocortisone and prolactin). In the case of transferrin, the major iron-binding protein of mouse milk, the ECM rather than prolactin, appears to modulate the level of its mRNA. We further show that both ECM and lactogenic hormones influence cell shape and polarity of mammary epithelial cells. The data are consistent with a model of "Dynamic Reciprocity" (Bissell et al. 1982) where the ECM is postulated to exert an influence on gene expression via transmembrane proteins and cytoskeletal components. Cytoskeleton, in turn, is associated with polyribosomes, affecting mRNA stability and rates of protein synthesis, and with the nuclear matrix, affecting mRNA processing and, possibly, rates of transcription. We postulate that hormones and ECM act synergistically to complete the 'reciprocity' loop.

Low‐frequency noise in dc superconducting quantum interference devices below 1 K

Abstract: At temperatures below about 1 K, a series of dc superconducting quantum interference devices (SQUID’s) exhibited an apparent flux noise with a spectral density scaling as 1/f α, where 0.58<α<0.80. Typically, the magnitude of the noise increased as the temperature was lowered below 1 K, tending to flatten out at low temperatures with a value of 7±3 μΦ0Hz−1/2 at 1 Hz that was nearly independent of the parameters and materials of the SQUID’s. Although a large number of hypothetical sources of the noise have been eliminated, the origin remains unidentified.

Third chronological supplement to the carcinogenic potency database: standardized results of animal bioassays published through December 1986 and by the National Toxicology Program through June 1987.

Abstract: This paper is the second chronological supplement to the Carcinogenic Potency Database, published earlier in this journal (1,2,4). We report here results of carcinogenesis bioassays published in the general literature between January 1983 and December 1984, and in Technical Reports of the National Cancer Institute/National Toxicology Program between January 1983 and May 1986. This supplement includes results of 525 long-term, chronic experiments of 199 test compounds, and reports the same information about each experiment in the same plot format as the earlier papers: e.g., the species and strain of test animal, the route and duration of compound administration, dose level and other aspects of experimental protocol, histopathology and tumor incidence, TD50 (carcinogenic potency) and its statistical significance, dose response, author's opinion about carcinogenicity, and literature citation. We refer the reader to the 1984 publications for a description of the numerical index of carcinogenic potency (TD50), a guide to the plot of the database, and a discussion of the sources of data, the rationale for the inclusion of particular experiments and particular target sites, and the conventions adopted in summarizing the literature. The three plots of the database are to be used together, since results of experiments published in earlier plots are not repeated. Taken together, the three plots include results for more than 3500 experiments on 975 chemicals. Appendix 14 is an index to all chemicals in the database and indicates which plot(s) each chemical appears in.

Ni, Pd, and Pt on GaAs: A comparative study of interfacial structures, compositions, and reacted film morphologies

Abstract: The reactions between (100) GaAs and the near-noble metals Ni, Pd, and Pt have been investigated by application of high-resolution transmission electron microscopy (TEM), energy-dispersive analysis of x-rays in the scanning TEM and Rutherford backscattering spectrometry. Emphasis is placed on the evolution of the phase distributions, film compositions, and interface morphologies during annealing at temperatures up to 480°C. The first phase in the Ni/GaAs reaction is shown to have the nominal composition Ni3GaAs. Ternary phases of the type PdxGaAs are also found to be the dominant products of the Pd/GaAs reaction. Conversely, only binary phases result from the Pt/GaAs reaction. These observations are used to construct isothermal sections of the M-Ga-As thin-film phase diagrams. The behavior of a thin (1–2 nm) native oxide-hydrocarbon layer during the Ni/GaAs, Pd/GaAs, and Pt/GaAs reactions is also investigated. Only the Ni/GaAs reaction is noticeably impeded in some regions by this intervening layer. In contrast, the Pd/GaAs and Pt/GaAs reactions tend to mechanically disperse the native oxide layers.

Observation of an oxygen isotope effect in YBa 2 Cu 3 O 7

Abstract: A small decrease in T/sub c/ of 0.3 K to 0.5 K is observed when as much as 90% of the /sup 16/O in YBa/sub 2/Cu/sub 3/O/sub 7/ is substituted with /sup 18/O. This result is consistent with our observation that there is an oxygen isotope effect in La/sub 1.85/Sr/sub 0.15/CuO/sub 4/, but in contrast with previous reports that there is no isotope effect for YBa/sub 2/Cu/sub 3/O/sub 7/. This new result suggests that phonons play an important role in the electron-pairing mechanism in YBa/sub 2/Cu/sub 3/O/sub 7/.

Local and nonlocal surface nonlinearities for surface optical second-harmonic generation.

Abstract: We investigate the physical origins of the surface nonlinear susceptibility responsible for surface optical second-harmonic generation. Experiments performed on simple covalent systems were designed to distinguish between the nonlocal electric-quadrupole-type nonlinearity induced by field discontinuity and the local intrinsic, electric-dipole-type nonlinearity of a surface or interface. We find that both mechanisms could operate: The latter usually dominates when the surface layer has a strong structural asymmetry with the fundamental or the second-harmonic frequency at resonance with a dipole-allowed transition.

Stochastic modeling of the independent roles of particle size and grain size in transgranular cleavage fracture

Abstract: The independent roles of grain size and particle size on sharp crack and rounded notch toughness are investigated over a range of temperatures from the lower shelf into the early ductile/brittle transition region. The results are interpreted in terms of a weakest link statistical model wherein the onset of failure coincides with the critical propagation of a particle microcrack into the matrix. It is shown that, for a fixed particle size distribution, both sharp-crack and rounded-notch toughness decrease with increasing grain size. However, at fixed grain size, the sharp-crack toughness increases, while the rounded-notch toughness decreases with increasing particle size. Such effects result primarily from the difference in the number of activated particles in the plastic zone.

Observation of an Isotope Shift in the Superconducting Transition Temperature of La 1.85 Sr 0.15 CuO 4

Abstract: An oxygen isotope shift is observed in superconducting ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_{4}$ when $^{18}\mathrm{O}$ is substituted partially for $^{16}\mathrm{O}$; the superconducting transition temperature ${T}_{c}$ is lowered by 0.3 to 1.0 K in different samples. We examine these results using conventioanl phonon-mediated BCS theory and conclude that, for ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_{4}$, phonons play an important role in the pairing mechanism.

Experiments on pollutant transport from soil into residential basements by pressure-driven airflow

Abstract: At two residences in Portland, OR, they have investigated (1) the coupling between residential basements and the air in nearby soil and (2) the influence of basement depressurization on the migration of air in soil. With the basements depressurized 25-50 Pa relative to outdoor air, underpressures as great as 20-40% of those in the basement were observed at sampling points in the soil. Sulfur hexafluoride was injected into the soil near the houses and its concentration monitored in soil air and in the house over time, both with and without basement depressurization. Depressurization was seen to have a substantial effect on the migration of the tracer within the soil. For basement depressurizations of 25-50 Pa, effective transport velocities through the soil and into the houses were observed to exceed 1 m h . Airborne SSSRn concentration was monitored in the basement of one house during the 6-day investigation and was seen to increase substantially on each of the seven occasions that the house was depressurized. The techniques employed are applicable to the study of problems of excessive radon entry into buildings and the migration of toxic vapors from waste dumps and landfills.

Intramolecular Electron Transfer in the Reductive Chromophore-Quencher Complex (bpy)Re(CO)3(py-PTZ)]

Abstract: Three metal complexes containing the reductive quencher ligand py-PTZ, ((bpy)Re(CO)/sub 3/(py-PTZ))/sup +/ and ((bpy)/sub 2/Ru/sup II/L(py-PTZ))/sup n+/ (where L = Cl/sup -/ (n = 1), PTZ = phenothiazine and acetonitrile ( n = 2)), were prepared and their redox and spectral properties investigated. The chromophore-quencher complex have essentially the same photophysical properties as their corresponding pyridine analogues at 77K in a 4:1 (v/v)) ethanol/methanol glass, but their properties are profoundly different in fluid solution. For the Re complex in fluid solution excitation of the Re..-->.. ..pi..*(bpy) metal to ligand charge-transfer (MLCT) chromophore at 355 nm is followed by rapid (<10 ns) appearance of transient absorption (TA) features at 350 and 500 nm consistent with formation of the charge-separated state ((bpy/sup.-/)Re(CO)/sub 3/(py-PTZ/sup.+))/sup +*/. Picosecond TA experiments monitored at 500 nm show that the PTZ/sup .+/ site grows in within approx.200 ps in polar organic solvents following laser excitation at 355 nm. The transient behavior observed leads to the conclusion that initial excitation of the MLCT chromophore is followed by rapid intramolecular electron-transfer quenching with k/sub q/(RT) = 4.8 x 10/sup 9/ s /sup -1/ in acetonitrile to give the charge-separated excited state ((bpy/sup .-)Re(CO)/sub 3/(py-PTZ/sup.+))/sup +/, which, in turn, decays tomore » the ground state with k/sub 2/ = 4.0 x 10/sup 7/ s/sup -1/. 36 references, 11 figures, 2 tables.« less

Elastic interface waves along a fracture

Abstract: Non-welded interfaces can be treated as a displacement discontinuity characterized by elastic stiffnesses. Applying this boundary condition to a generalized Rayleigh wave, it is shown that a fast and a slow dispersive wave can propagate along the fracture, even when the seismic properties of the rock on each side are identical.

Theory of quasiparticle energies in alkali metals.

Abstract: The quasiparticle band structures of Na and Li are calculated by evaluation of the electron self-energy to first order in the dynamically screened Coulomb interaction. For Na, our results explain quantitatively the large bandwidth reduction observed in recent angle-resolved photoemission experiments. The inclusion of exchange-correlation effects in the dielectric screening and the requirement that the energy dependence of the electron Green's function be treated self-consistently are found to be important in our obtaining the correct bandwidths.

Speciation and local structure in alkali and alkaline earth silicate glasses: Constraints from 29Si NMR spectroscopy

Abstract: 29 Si NMR spectroscopy provides important contributions to the understanding of silicate glass structure, as the resonance frequency is sensitive to several aspects of the local chemical environment (including intertetrahedral bond angles, bond distances, and number of bridging oxygens per silicon atom). New data on a series of binary alkali and alkaline earth glasses are presented which highlight the effects of composition, as well as the complications that can arise in the interpretation of spectra. In binary alkali silicate glasses, two partially resolved peaks may be observed, which are attributable to Si in sites with different numbers of bridging oxygens. These are present even in glasses which are almost certainly single, homogeneous phases. In alkaline earth and in aluminosilicate glasses, single, broad, often asymmetric resonances are found, whose linewidths span the frequency ranges of three or more structural species. Using a combination of slow sample spinning and non-spinning techniques, NMR spectra also provide data on local electronic symmetry, and indicate that silicon sites in glasses can be more symmetrical than those in crystalline materials.

The effect of Cu 6 Sn 5 whisker precipitates in bulk 60Sn-40Pb solder

Abstract: Hollow, Cu6Sn5 intermetallic rods form within molten 60Sn-40Pb solder when it reacts with Cu. It is suggested that these rods form at the Cu surface by a screw dislocation mechanism and break off into the bulk solder. Hollow hexagonal intermetallics result when the core of the rod dissolves away and fills with molten solder. The mechanical properties of bulk 60Sn-40Pb solder with and without the Cu6Sn5 intermetallic rods were tested in tension, at -196° C, 20° C, and 125° C. The intermetallics had no effect on strength, but decreased elongation at the lower temperatures. The intermetallics had a large effect on the fracture characteristics. At -196° C failures initiate by interfacial separation between the intermetallic and solder matrix. At 20° C failures initiate at cleaved intermetallic rods. At 125° C the intermetallic rods appear to have little effect on the mechanical properties.