Showing papers by "Pacific Northwest National Laboratory published in 1994"

Gaussian basis sets for use in correlated molecular calculations. IV. Calculation of static electrical response properties

Abstract: An accurate description of the electrical properties of atoms and molecules is critical for quantitative predictions of the nonlinear properties of molecules and of long‐range atomic and molecular interactions between both neutral and charged species. We report a systematic study of the basis sets required to obtain accurate correlated values for the static dipole (α1), quadrupole (α2), and octopole (α3) polarizabilities and the hyperpolarizability (γ) of the rare gas atoms He, Ne, and Ar. Several methods of correlation treatment were examined, including various orders of Moller–Plesset perturbation theory (MP2, MP3, MP4), coupled‐cluster theory with and without perturbative treatment of triple excitations [CCSD, CCSD(T)], and singles and doubles configuration interaction (CISD). All of the basis sets considered here were constructed by adding even‐tempered sets of diffuse functions to the correlation consistent basis sets of Dunning and co‐workers. With multiply‐augmented sets we find that the electrical properties of the rare gas atoms converge smoothly to values that are in excellent agreement with the available experimental data and/or previously computed results. As a further test of the basis sets presented here, the dipole polarizabilities of the F− and Cl− anions and of the HCl and N2 molecules are also reported.

Benchmark calculations with correlated molecular wave functions. IV. The classical barrier height of the H+H2→H2+H reaction

Abstract: Using systematic sequences of correlation consistent Gaussian basis sets from double to sextuple zeta quality, the classical barrier height of the H+H2 exchange reaction has been calculated by multireference configuration interaction (MRCI) methods. The MRCI calculations for collinear H3 have also been calibrated against large basis set full CI (FCI) results, which demonstrate that the MRCI treatment leads to energies less than 1 μhartree (≤0.001 kcal/mol) above the FCI energies. The dependence of both the H2 and H3 total energies on the basis set is found to be very regular, and this behavior has been used to extrapolate to the complete basis set (CBS) limits. The resulting estimate of the H–H–H CBS limit yields a classical barrier height, relative to exact H+H2, of 9.60±0.02 kcal/mol; the best directly calculated value for the barrier is equal to 9.62 kcal/mol. These results are in excellent agreement with recent quantum Monte Carlo calculations.

Probing single molecule dynamics.

Abstract: The room temperature dynamics of single sulforhodamine 101 molecules dispersed on a glass surface are investigated on two different time scales with near-field optics. On the 10(-2)- to 10(2)-second time scale, intensity fluctuations in the emission from single molecules are examined with polarization measurements, providing insight into their spectroscopic properties. On the nanosecond time scale, the fluorescence lifetimes of single molecules are measured, and their excited-state energy transfer to the aluminum coating of the near-field probe is characterized. A movie of the time-resolved emission demonstrates the feasibility of fluorescence lifetime imaging with single molecule sensitivity, picosecond temporal resolution, and a spatial resolving power beyond the diffraction limit.

Molecular mechanisms for corrosion of silica and silicate glasses

Abstract: Dissolution, selective leaching, and stress-corrosion cracking are all processes which can degrade the performance of silica and silicate glasses exposed to aqueous environments. Reactions which corrode glass in water include hydration, hydrolysis and condensation, and ion-exchange processes. Techniques such as solid-state nuclear magnetic resonance, Raman and Fourier transform infrared spectroscopies, pH stat titrations and elemental depth profiling have been used to establish the relative importance of the above reactions on glass degradation as a function of solution pH and composition, temperature and stress level. This paper reviews results obtained for silica, alkali silicate, and alkali boro- and aluminosilicate glasses. For most glasses, the rate at which water enters the glass structure controls the kinetics of the other glass-water reactions, explaining the corrosion characteristics of different glass compositions.

Automated multifilter rotating shadow-band radiometer: an instrument for optical depth and radiation measurements

Abstract: The multifilter rotating shadow-band radiometer is a ground-based instrument that uses independent interference-filter-photodiode detectors and the automated rotating shadow-band technique to make spectrally resolved measurements at seven wavelength passbands (chosen at the time of manufacture between 350 nm and 1.7 µm) of direct-normal, total-horizontal, and diffuse-horizontal irradiances. This instrument achieves an accuracy in direct-normal spectral irradiance comparable with that of tracking radiometers, and it is more accurate than conventional instruments for the determination of the diffuse and total-horizontal spectral irradiances because the angular acceptance function of the instrument closely approximates the ideal cosine response, and because the measured direct-normal component can be corrected for the remaining angular acceptance error. The three irradiance components are measured with the same detector for a given wavelength. Together with the automated shadow-band technique, this guarantees hat the calibration coefficients are identical for each, thus reducing errors when one compares them (as opposed to measurements made with independent instruments). One can use the direct-normal component observations for Langley analysis to obtain depths and to provide an ongoing calibration against the solar constant by extrapolation to zero air mass. Thus the long-term stability of all three measured components can be tied to the solar constant by an analysis of the routinely collected data.

The radiation-induced crystalline-to-amorphous transition in zircon

Abstract: A comprehensive understanding of radiation effects in zircon, ZrSiO4, over a broad range of time scales (0.5 h to 570 million years) has been obtained by a study of natural zircon, Pu-doped zircon, and ion-beam irradiated zircon. Radiation damage in zircon results in the simultaneous accumulation of both point defects and amorphous regions. The amorphization process is consistent with models based on the multiple overlap of particle tracks, suggesting that amorphization occurs as a result of a critical defect concentration. The amorphization dose increases with temperature in two stages (below 300 K and above 473 K) and is nearly independent of the damage source (α-decay events or heavy-ion beams) at 300 K. Recrystallization of completely amorphous zircon occurs above 1300 K and is a two-step process that involves the initial formation of pseudo-cubic ZrO2.

Moderate elevation of body iron level and increased risk of cancer occurrence and death

Abstract: The purpose of the study was to address the hypothesis that elevated body iron increases the risk of cancer occurrence and death, and to determine the dose response. Subjects were 3,287 men and 5,269 women participating in the first National Health and Nutrition Examination Survey who had a transferrin saturation determination at enrollment (1971-1975), who remained alive and cancer-free for at least 4 years, and who were followed to 1988 for cancer outcome. Among 379 men who developed cancer over the study period, the mean transferrin saturation at enrollment was 32.1% whereas among 2,908 who remained cancer-free it was 30.7%; the difference for mortality was 32.3% among 233 deaths vs. 30.8% among 3,054 men not dying of cancer. The mean differences among women were not significant. The mean differences in TIBC and serum iron among men were consistent with the findings for transferrin saturation, and all 3 differences were stable over time when examined by years since blood test. Men and women were divided into 5 groups on the basis of baseline transferrin saturation: 0 to 30%, 30-40%, 40-50%, 50-60%, and 60% and higher. Nineteen percent of men had a baseline transferrin saturation above 40% (the last 3 groups), whereas only 10 percent of women had transferrin saturation above 40%. For men and women combined, risk of cancer occurrence in each group relative to the first was 1.0, 0.95, 1.16, 1.38 and 1.81; for mortality the relative risks were 1.0, 0.96, 1.22, 1.29 and 1.73. There is evidence, in this cohort, of elevated cancer risk in those with moderately elevated iron level. This pattern was seen in women as well as in men.

Trapping, detection and reaction of very large single molecular ions by mass spectrometry

Abstract: RECENT developments have made electrospray-ionization (ESI) mass spectrometry1–3 an important technique for measuring molecular weights and studying the structures of large molecules of relative molecular masses approaching 200,000 (Mr 200K) Analysis of still larger molecules is difficult, however: to obtain a mass/charge ratio within the detectable limits, the ions must bear several charges, but a collection of ions of differing multiple charges presents a spectrum that is hard to interpret This problem would be avoided if sufficient sensitivity can be achieved to detect individual molecules Here we describe a technique that realizes this sensitivity for molecules of Mr to ~7 x 106, and which has the potential to be extended to Mr≈109 We use ESI and Fouriertransform ion cyclotron resonance mass spectrometry4 to obtain repeated measurements of the mass-to-charge ratio of single, highly charged molecular ions We are able to observe stepwise changes in the charge of an isolated ion owing to its reaction with small molecules introduced into the detection cell This technique should have wide applications for characterization of polymers and large biomolecules

Electrochemical Reduction of CO2 Catalyzed by Small Organophosphine Dendrimers Containing Palladium

Abstract: The sequential addition of diethyl vinylphosphonate to primary phosphines followed by reduction with lithium aluminum hydride can be used to synthesize small dendrimers containing up to 15 phosphorus atoms. A second approach uses the addition of bis((diethylphosphino)ethyl)phosphine to tetravinylsilane to produce a dendrimer containing 12 phosphorus atoms. The connectivities of these ligands are established unambiguously by {sup 31}P NMR spectroscopy. These dendrimers react with [Pd(CH{sub 3}CN){sub 4}](BF{sub 4}){sub 2} to produce metalated dendrimers which catalyze the electrochemical reduction of CO{sub 2} to CO. Relationships between catalytic properties and dendrimer structure are discussed.

Benchmark calculations with correlated molecular wave functions. V. The determination of accurate abinitio intermolecular potentials for He2, Ne2, and Ar2

Abstract: Dimer interactions of helium, neon, and argon have been studied using the augmented correlation consistent basis sets of Dunning and co‐workers. Two correlation methods have been employed throughout; Mo/ller–Plesset perturbation theory through fourth‐order (MP4) and single and double excitation coupled‐cluster theory with perturbative treatment of triple excitations [CCSD(T)]. Full configuration interaction (FCI) calculations were performed on He2 for some basis sets. In general, only valence electrons were correlated, although some calculations which also correlated the n=2 shell of Ar2 were performed. Dimer potential energy curves were determined using the supermolecule method with and without the counterpoise correction. A series of additional basis sets beyond the augmented correlation consistent sets were explored in which the diffuse region of the radial function space has been systematically saturated. In combination with the systematic expansion across angular function space which is inherent to the correlation consistent prescription, this approach guarantees very accurate atomic polarizabilities and hyperpolarizabilities and should lead to an accurate description of dispersion forces. The best counterpoise‐corrected MP4 values for the well depths of the three dimers are (in microhartrees, empirical values in parentheses) He2, 31.9 (34.6); Ne2, 123 (134); and Ar2, 430 (454). The corresponding CCSD(T) values are He2, 33.1; Ne2, 128; and Ar2, 417. Although these values are very good, the nearly exponential convergence of well depth as a function of basis quality afforded by using the various series of correlation consistent basis sets allows estimation of complete basis set (CBS) limiting values. The MP4 estimated CBS limits are He2, 32.2; Ne2, 126; and Ar2, 447. The corresponding CCSD(T) values are He2, 33.4; Ne2, 130; and Ar2, 430. Equilibrium separations are also reproduced with similar accuracy.

Comparison between geochemical and biological estimates of subsurface microbial activities.

Abstract: Geochemical and biological estimates of in situ microbial activities were compared from the aerobic and microaerophilic sediments of the Atlantic Coastal Plain. Radioisotope time-course experiments suggested oxidation rates greater than millimolar quantities per year for acetate and glucose. Geochemical analyses assessing oxygen consumption, soluble organic carbon utilization, sulfate reduction, and carbon dioxide production suggested organic oxidation rates of nano- to micromolar quantities per year. Radiotracer timecourse experiments appeared to overestimate rates of organic carbon oxidation, sulfate reduction, and biomass production by a factor of 103–106 greater than estimates calculated from groundwater analyses. Based on the geochemical evidence, in situ microbial metabolism was estimated to be in the nano- to micromolar range per year, and the average doubling time for the microbial community was estimated to be centuries.

Benchmark calculations with correlated molecular wave functions. VI. Second row A2 and first row/second row AB diatomic molecules

Abstract: Benchmark calculations employing the correlation consistent basis sets of Dunning and co‐workers are reported for the following diatomic species: Al2, Si2, P2, S2, Cl2, SiS, PS, PN, PO, and SO. Internally contracted multireference configuration interaction (CMRCI) calculations (correlating valence electrons only) have been performed for each species. For Cl2, P2, and PN, calculations have also been carried out using Mo/ller–Plesset perturbation theory (MP2, MP3, MP4) and the singles and doubles coupled‐cluster method with and without perturbative triples [CCSD, CCSD(T)]. Spectroscopic constants and dissociation energies are reported for the ground state of each species. In addition, the low‐lying excited states of Al2 and Si2 have been investigated. Estimated complete basis set (CBS) limits for the dissociation energies, De, and other spectroscopic constants are obtained from simple exponential extrapolations of the computed quantities. At the CBS limit the root‐mean‐square (rms) error in De for the CMRCI...

Transverse-current autocorrelation-function calculations of the shear viscosity for molecular liquids.

Abstract: The usual approach to calculating shear viscosities and other thermal transport coefficients from equilibrium molecular-dynamics simulations has been to evaluate the appropriate Green-Kubo relation. An alternative to this method is to examine the long-time behavior of correlations formed from the amplitudes of spontaneous fluctuations in transverse momentum fields (transverse-current autocorrelation functions). For systems in the hydrodynamic limit, long-wavelength fluctuations in transverse momentum fields decay exponentially with a decay constant 1/${\mathrm{\ensuremath{\tau}}}_{\mathit{H}}$=\ensuremath{\mu}${\mathit{k}}^{2}$/\ensuremath{\rho}, where k is the wave vector of the fluctuation, \ensuremath{\mu} is the shear viscosity, and \ensuremath{\rho} is the density. Thus, determination of ${\mathrm{\ensuremath{\tau}}}_{\mathit{H}}$ leads directly to \ensuremath{\mu}. This approach is used to calculate the shear viscosity for the Lennard-Jones fluid, liquid carbon dioxide, and the TIP4P model of water of Jorgensen et al. [J. Chem. Phys. 79, 926 (1983)].

Spatial relationships of soil microbial biomass and C and N Mineralization in a semi-arid shrub-steppe ecosystem

Abstract: Microbial mineralization of both C and N in the shrub-steppe soils of central Washington influence plant productivity and ecosystem stability. Microbial processes in arid ecosystems are in turn influenced by heterogeneously-spaced plants and abiotic variables. Our objective was to determine the spatial relationships of C and N mineralization and microbial biomass to plant location. We measured inorganic N pools, microbial biomass and C and N mineralization potentials (C o , N o ) from 205 soil samples positioned around five Artemisia tridentata shrub plants. Most variables showed log normal distributions and all were significantly correlated to each other. Microbial biomass had the highest positive correlation with C mineralization and soluble C. The metabolic C quotient ( q CO 2 ) was twice that of other natural forest and grassland ecosystems. In addition the metabolic N quotient ( q N) was lower in the shrub-steppe soil compared to other ecosystems. The coupled metabolic quotients indicate the shrub-steppe soil has low substrate quality with a high N immobilization capacity. Geostatistical analysis of spatial relationships showed that samples were spatially related with each other to a distance of 0.5–1.0 m. At sample locations where microbial biomass was high Co was also high. In contrast. No was low in these areas. Cross-correlation with plants showed that C o was spatially related to shrubs and not to grass plants and that No was not related to any plant location. Cross-correlation analysis revealed that variables that are linearly correlated may not necessarily be spatially correlated. Our study showed that the resource island effect of nutrients and microbial biomass in the shrub-steppe ecosystem is important when estimating microbial processes at the landscape level.

Effects of Climate Change on Commercial Building Energy Demand

Abstract: Most of the studies of the impact of global warming on energy use have employed aggregated utility models and have found that global warming would produce about a 2% decrease in heating requirements per PC and comparable increases in cooling requirements The one significant exception is a German study that utilized building energy models and determined that the increase in cooling would be somewhat larger, due to the effects of increased humidity with atmospheric warming This study utilizes the DOE2 building energy model on a prototype commercial building and demonstrates that increased humidity could be a significant factor in total building energy use, particularly in the more humid parts of the United States The study also demonstrates that the effect can be overcome with advanced building designs

Nonequilibrium Statistical Mechanics of Preasymptotic Dispersion.

Abstract: Turbulent transport in bulk-phase fluids and transport in porous media with fractal character involve fluctuations on all space and time scales. Consequently one anticipates constitutive theories should be nonlocal in character and involve constitutive parameters with arbitrary wavevector and frequency dependence. We provide here a nonequilibrium statistical mechanical theory of transport which involves both diffusive and convective mixing (dispersion) at all scales. The theory is based on a generalization of classical approaches used in molecular hydrodynamics and on time-correlation functions defined in terms of nonequilibrium expectations. The resulting constitutive laws are nonlocal and constitutive parameters are wavevector and frequency dependent. All results reduce to their convolution-Fickian quasi-Fickian, or Fickian counterparts in the appropriate limits.

A mouse model for calculating cross-organ beta doses from yttrium-90-labeled immunoconjugates

Abstract: Background. The organs of laboratory mice used in radioimmunotherapy experiments are relatively small compared to the ranges of high-energy yttrium-90 (Y-90) beta particles. Current Medical Internal Radiation Dose (MIRD) dosimetry methods do not account for beta energy that escapes an organ. A dosimetry model was developed to provide more realistic dose estimates for argans in mice who received Y-90-labeled antibodies by accounting for physical and geometric factors, loss of beta dose due to small organ sizes, and cross-organ doses, Methods. The dimensions, masses, surface areas, and overlapping areas of different organs of 10 athymic nude mice, each weighing approximately 25 g, were measured to form a realistic geometric model

Nitrous oxide flux from a shrub-steppe ecosystem: Sources and regulation

Abstract: The semi-arid shrub-steppe is the largest grassland-type ecosystem of North America and may make significant contributions to the global atmospheric N2O budget However, little information is available concerning sources and regulation of N2O flux in this ecosystem Experiments were made to determine the relative importance of nitrification, denitrification and abiotic sources to total N2O flux and to investigate the factors regulating N2O flux rates from an undisturbed shrub-steppe ecosystem The contributions to N2O flux by nitrification and denitrification were estimated using acetylene (10 Pa) to selectively inhibit N2O production by nitrifiers Abiotic sources of N2O were evaluated using sterilized soil Factors limiting N2O production were evaluated by monitoring N2O flux rates from soil-cores amended with combinations of NO3−-N, NH4+-N, soluble C and water The effect of wet-dry cycles on N2O flux was determined by wetting field dry soil to field capacity and monitoring N2O flux rates, soil NH4+-N, NO3−-N and water content throughout a drying period Our results showed that nitrification accounts for 61–98% of the N2O produced from soil at water contents below saturation and that denitrification is the primary N2O source at saturated water contents No detectable N2O was produced by abiotic sources In intact soil cores N2O flux rates were found to be most limited by water and N availability Wetting of dry soil resulted in a pulse of N2O flux due to increased N availability It is likely that this ecosystem exhibits relatively low N2O flux rates for much of the year due to low soil moisture and inorganic N contents Since soil moisture content is generally well below field capacity in this ecosystem, nitrification must be the dominant N2O source These results suggest that conditions favorable for substantial N2O production in shrub-steppe ecosystems probably exist only at times following precipitation events

Atomic and electronic structure of the corundum ( alpha -alumina) (0001) surface.

Abstract: Using a tight-binding, total-energy model, we predict the atomic and electronic structure of the relaxed (1\ifmmode\times\else\texttimes\fi{}1) corundum (0001) surface The surface shows a large, bond-length-conserving relaxation, which is allowed by the topology of the surface The relaxation is driven by a rehybridization of the surface Al atoms to ${\mathit{sp}}^{2}$, and an accompanying drop in the energy of occupied surface states, during the relaxation Displacements of surface atoms from bulk positions are as large as 07 \AA{}, and should be observable using a low-energy electron diffraction intensity analysis Full relaxed atomic positions are reported, as well as a wavelength-resolved surface band structure, including orbital characters of surface states

Observation of duplex DNA-drug noncovalent complexes by electrospray ionization mass spectrometry

Abstract: We have observed by ESI-MS the noncovalent complex formed between a minor groove binding molecule and a 12 base pair self-complementary oligonucleotide When the ratio of Distamycin Dm to oligonucleotide was varied, oligonucleotide duplex, 1:1 Dm/oligonucleotide duplex, and 2:1 Dm/oligonucleotide duplex noncovalent complexes were observed, consistent with NMR results for the same sequence and Dm to oligonucleotide duplex concentration ratios These results indicate that ESI-MS is an effective analytical technique for the detection of specific drug-oligonucleotide duplex noncovalent complexes and that specific noncovalent complexes can be observed reflecting stoichiometry in solution Additional experiments to determine if ESI-MS can provide information on the specificity and selectivity of additional minor groove binding and intercalating molecules are in progress 19 refs, 1 fig

Stability of vacancy defects in MgO: The role of charge neutrality

Abstract: The energetics and electronic structure of a series of neutral and charged oxygen and magnesium vacancy defects ([ital F], [ital F][sup +], [ital F][sup 2+], [ital V], [ital V][sup [minus]], [ital V][sup 2[minus]], and [ital P] centers) in MgO have been computed using the stationary total-energy functional. We find that contrary to the charge-compensation model for anion-cation defect pairs in ionic materials it is energetically unfavorable for an isolated neutral oxygen vacancy ([ital F] center) to transfer electrons to an isolated neutral magnesium vacancy ([ital V] center), and form isolated [ital F][sup 2+] and [ital V][sup 2[minus]] centers. Charge compensation is unfavorable because additional electrons at the [ital V] center induce new occupied states in the gap, which increase the energy of the defect. This result is consistent with the interpretation of spectroscopic experiments on MgO, in which the ground-state defects are either neutral or singly charged. The computed formation energies of both the [ital F] and [ital V] centers are larger than the cohesive energy of MgO per formula unit, but the binding energy of the defects in the [ital P] center configuration is 12.16 eV. This attraction between the [ital F] and [ital V] centers is enhanced whenmore » the defects carry a net charge. The position of the vacancy defect state in the fundamental energy gap of MgO is found to be in qualitative agreement with a model for optical absorption and emission, and is used as a simple model for the formation energies of the defects. The contribution of the band-structure energy to the stationary functional is found to account for more than 90% of the defect energies. This component of the defect formation energy is computed directly, using the recursion method, rather than as the difference between the total energies of our 8000-atom cluster with and without the defect.« less