Search Results - (Author, Cooperation:D. L. Lynch)

2014-01-05

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Animals ; Brain/*drug effects/metabolism ; Cannabinoid Receptor Antagonists/administration & dosage ; Cannabis/*toxicity ; Dronabinol/*toxicity ; Male ; Marijuana Abuse/drug therapy ; Mice ; Mice, Inbred C57BL ; Pregnenolone/*administration & dosage/*metabolism ; Rats ; Rats, Sprague-Dawley ; Rats, Wistar ; Receptor, Cannabinoid, CB1/*agonists/*antagonists & inhibitors

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

Recent experiments on the H/Ni(111) system have demonstrated that high-resolution electron-energy-loss spectra of subsurface absorbate species can be observed. We report here molecular-dynamics simulations for both the H/Ni(111) and H/Pd(111) systems. The necessary atomic forces are obtained from embedded atom method (EAM) potentials. From such calculations we have obtained the power spectra and compare our results to the available experimental data. These calculations reasonably reproduce the observed shifts upon embedding the H subsurface and we comment on the possibility of subsurface absorbates interfering with surface adsorbate assignments. Lastly, we illustrate the sensitivity of our results to the parametrization of the EAM potential.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

Clusters of rare gas atoms provide an interesting setting for the study of the issue of quantum mechanical localization. The properties of these clusters of 2–7 atoms are calculated using variational Monte Carlo methods. To our knowledge, this is the first variational Monte Carlo study of localized clusters and new solidlike wave function forms, including shadow, multiple bond length, and Boltzmann-like wave functions, are reported. Diffusion Monte Carlo methods provide an independent, exact value of the ground state energy, useful as a check of the variational results. The properties of the variational wave functions, when analyzed in terms of probability distribution functions, quench studies, and visual examination of the wave functions, indicate delocalized helium and localized argon and neon clusters.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

The surface diffusion constant for hydrogen and deuterium on the palladium(111) surface is calculated using quantum mechanical transition state theory. The rate constants for diffusion into the subsurface layer are also calculated. Quantum effects are seen to be most important for the surface/subsurface transition and cause an inverse isotope effect in which the rate for deuterium is greater than the rate for hydrogen. The results of ground and excited state wave function calculations show localized hydrogenic states, despite large zero point energies, and that the preferred binding site can vary with isotope between surface and subsurface sites. In addition, estimates of the tunneling rate between the surface and subsurface are in qualitative agreement with the low temperature transition state results.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

We employ a unified molecular dynamics (MD), quantum mechanical approach to simulate the behavior of large collections of atoms at finite temperature. The nuclei are moved according to classical mechanics while the forces are computed via quantum mechanical models. Two approaches have been used: (1) the extended Hückel method, which is an approximate molecular orbital approach and (2) density functional theory based on the local density approximation and plane wave pseudopotential formulation. We compute properties from the MD trajectories of up to 4 ps duration for samples containing up to 250 atoms of lithium, sodium, and potassium. These results are compared to both previous calculations and experimental results.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

In this paper, we report the results of ab initio calculations of photoelectron angular distributions and vibrational branching ratios for the (2+1) REMPI of H2 via the E,F 1Σ+g state, and compare these with the experimental data of Anderson et al. [Chem. Phys. Lett. 105, 22 (1984)]. These results show that the observed non-Franck–Condon behavior is predominantly due to the R dependence of the transition matrix elements, and to a lesser degree to the energy dependence. This work presents the first molecular REMPI study employing a correlated wave function to describe the Rydberg–valence mixing in the resonant intermediate state.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

We have studied the photoionization cross sections and photoelectron asymmetry parameters for ionization of the 1πg(X 2Πg), 5σg(A 2Σ+g), and 4σu(B 2Σ+u) levels of cyanogen using frozen-core Hartree–Fock photoelectron continuum orbitals. The main purpose of these studies has been to extend our understanding of the dynamics of shape resonances from earlier studies of diatomic and smaller polyatomic molecules to a larger polyatomic system. The results do, in fact, reveal a rich shape resonant structure in the electronic continuum of this polyatomic system. There is a low-energy σu resonance which, as expected, is the C–C analog of the l=3 shape resonance seen in N2(3σ−1g) and several other diatomics. In contrast to this diatomic-like behavior, the presence of the two CN groups in C2N2 results in a second σu and a σg resonance corresponding to linear combinations of a l=3 shape resonance localized on the CN sites. Moreover, our results also show a pronounced shape resonant behavior in the πu continuum, which, to our knowledge, has not been seen in smaller molecules.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

We report theoretical cross sections for direct photoionization of specific rovibrational levels of the B 1Σ+u electronic state of H2. The calculated cross sections differ considerably from values recently determined by resonant enhanced multiphoton ionization (REMPI) studies. In an attempt to understand the disagreement, we analyze in detail the REMPI dynamics and find that the multiphoton ionization probability is extremely sensitive to the spatial and temporal profiles of the laser pulses. Accurate characterization of laser profiles and their jitter is therefore necessary for a comparison between theory and experiment.

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] Several workers* have prepared synthetic protein lignin complexes simulating soil humic acid. While the reports are somewhat conflicting, in general, these complexes were attacked and degraded by the soil mieronora with some difficulty. A number of protein-lignin complexes were prepared from ...

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] Another clay mineral, attapulgite (pH. 8-5), intermediate in crystal structure between montmorillonite and kaolinite, has been studied using gelatin and cellulose dextrin (prepared from cellulose by degrading it with 72 per cent sulphuric acid)4 as the substrates. Gelatin alone (100 mgm.) and ...

Electronic Resource

1432-0800

Springer Online Journal Archives 1860-2000

Energy, Environment Protection, Nuclear Power Engineering

Medicine

Electronic Resource

1432-0800

Springer Online Journal Archives 1860-2000

Energy, Environment Protection, Nuclear Power Engineering

Medicine

Electronic Resource

1615-6102

Springer Online Journal Archives 1860-2000

Biology

Summary A comparative study was made of the ultrastructure and abundance of microbodies in the green algaBracteacoccus cinnabarinus grown photoautotrophically and heterotrophically on a conventional culture medium containing sodium acetate, potassium acetate and glucose. Several changes were observed in the cells maintained under these conditions. Most noticeably, cells grown on acetate in both light and dark were packed with lipid bodies. Microbodies were found to be closely appressed to the lipid bodies in cells grown heterotrophically in the dark on sodium acetate and potassium acetate. The average number of microbody profiles per cell was in general threefold greater in cells grown on sodium acetate than those grown on potassium acetate. No microbodies were observed in cells maintained photoautotrophically on the three carbon sources or in cells maintained photoautotrophically on Bristol's inorganic medium alone. Cytochemical staining with 3,3′-diaminobenzidine indicated the presence of catalase in the microbodies. The presence of microbodies suggests that the organelle may be performing functions similar to glyoxysomes in higher plants, namely the net conversion to succinate of acetyl CoA derived from lipid degredation. It is also apparent thatBracteacoccus can grow well as a heterotroph in the dark when acetate is included in the culture medium as a source of carbon.

Electronic Resource