Monte-Carlo studies of bosonic van der Waals clusters

In a previous paper (http://www.phys.uri.edu/people/nightingale/publications.html, chem-ph/9406003) we developed a form of variational trial wave function and applied it to van der Waals clusters: five or less atoms of Ar and Ne modeled by the Lennard-Jones potential. In addition, we tested the trial functions for a hypothetical, light atom resembling Ne but with only half its mass. We did not study atoms such as He with larger de Boer parameters, i.e., systems in which the zero point energy plays a more important role relative to the potential energy. This is the main purpose of the present paper. In fact, we study clusters to the very limit where the zero-point energy destroys the ground state as a bound state. A simple picture of this un-binding transition predicts the power law with which the energy vanishes as the de Boer parameter approaches its critical value and the power of the divergence of the the size of the clusters in this limit. Our numerical results are in agreement with these predictions.Comment: text and figures TeX form, 4 page

Van der Waals clusters in the ultra-quantum limit: a Monte Carlo study

Bosonic van der Waals clusters of sizes three, four and five are studied by diffusion quantum Monte-Carlo techniques. In particular we study the unbinding transition, the ultra-quantum limit where the ground state ceases to exist as a bound state. We discuss the quality of trial wave functions used in the calculations, the critical behavior in the vicinity of the unbinding transition, and simple improvements of the diffusion Monte Carlo algorithm.Comment: World Wide Web URL http://www.phys.uri.edu/people/mark_meierovich/visual/Main.html contains an informal presentation with color graphic

Decade-Scale Influences of Organic Matter Removal on Forest Soil Biogeochemistry and Microbial Ecology

One of the main goals of applied forest ecology is to utilize silvicultural practices that generate economic output from forest products while simultaneously maintaining the long-term sustainability of forest stand properties such as wildlife habitat, the ability to sequester carbon, soil nutrient stocks, and soil microbial community structure and function. To this regard, there are some forest management methods (such as clear-cutting, short rotations, whole-tree harvesting, and litter removal) that utilize intensive biomass removal techniques to increase economic output. These intensive methods could jeopardize the long-term sustainability of the forest ecosystem through the degradation and destabilization of soil biotic and abiotic properties. Because of this, the purpose of this study was to analyze specific soil biogeochemical and microbiological properties of Pinus taeda L. (loblolly pine) stands that were subjected to different harvest methods 18 years ago. Soil properties of intensively harvested stands (whole-tree harvest + forest floor removal) were compared to those of stands subjected to a less intensive method (bole-only harvest), and to unharvested control stands (tree age: 60-80 years old). Results indicate that increasing organic matter removal intensity can lead to reduced tree size and reduced soil organic carbon and soil total nitrogen; furthermore, soils from whole-tree harvest + forest floor removal plots were less enriched in δ13C and more enriched in δ15N suggesting that increasing forest harvest intensity decreases long-term carbon mineralization and decomposition potential as well as increases N-losses through volatilization and leaching. Increasing organic matter removal intensity also reduced microbial biomass carbon and microbial biomass nitrogen, NH4+, and NO2- + NO3- pools, increased the concentration of Mehlich-III extractable P, and altered the abundance of archaeal and bacterial amoA. Furthermore, intensive forest harvest led to decade-scale alterations in ammonia-oxidizer, fungal, and bacterial and community structure as well as functional fungal and bacterial groups relative to unharvested stands. These results imply that more intensive harvest methods not only lead to reduced tree size, but also create decade-long alterations in physical, chemical, and biological properties in surface and subsurface soils, which could be inherited by future rotations

Optimization of ground and excited state wavefunctions and van der Waals clusters

A quantum Monte Carlo method is introduced to optimize excited state trial wavefunctions. The method is applied in a correlation function Monte Carlo calculation to compute ground and excited state energies of bosonic van der Waals clusters of upto seven particles. The calculations are performed using trial wavefunctions with general three-body correlations

Localized helium excitations in 4He_N-benzene clusters

We compute ground and excited state properties of small helium clusters 4He_N containing a single benzene impurity molecule. Ground-state structures and energies are obtained for N=1,2,3,14 from importance-sampled, rigid-body diffusion Monte Carlo (DMC). Excited state energies due to helium vibrational motion near the molecule surface are evaluated using the projection operator, imaginary time spectral evolution (POITSE) method. We find excitation energies of up to ~23 K above the ground state. These states all possess vibrational character of helium atoms in a highly anisotropic potential due to the aromatic molecule, and can be categorized in terms of localized and collective vibrational modes. These results appear to provide precursors for a transition from localized to collective helium excitations at molecular nanosubstrates of increasing size. We discuss the implications of these results for analysis of anomalous spectral features in recent spectroscopic studies of large aromatic molecules in helium clusters.Comment: 15 pages, 5 figures, submitted to Phys. Rev.

Impact of new smoking trends on women's occupational health

Health problems and needs of females, particularly of working women, are discussed in relation to cigarette smoking and its effects. Problems encountered by working women with regard to understanding and knowledge of health risks are examined, as well as specific diseases and occupations presenting major health problems to the female worker. Smoking is shown to exert effects on females similar to those it exerts on males with regard to those cancers which are generally related to tobacco use. Various occupational exposures such as exposure to asbestos, known to act in synergism with tobacco as a carcinogen, are presented as hazards to the working woman. The cancer-promoting effect of alcohol, in conjunction with smoking, is also mentioned. Heart disease is another health problem which will be confronted by both the working and/or smoking woman, as it is by males. In addition, other occupations formerly thought of as “benevolent”, such as office work, are shown to present health hazards. It is concluded that more and greater health hazards will be faced by women, especially as they smoke more and take on more jobs that were traditionally filled by men. Closer monitoring and assessing of health status of women in the work force is called for to ensure that conditions in the workplace are not detriments to good health. Epidemiologic variables suggested for inclusion in future occupational health studies are presented

EVIDENCE FOR THE LINKAGE OF THE IGCH LOCUS TO A GENE CONTROLLING THE IDIOTYPIC SPECIFICITY OF ANTI-p-AZOPHENYLARSONATE ANTIBODIES IN STRAIN A MICE

Anti-p-azophenylarsonate (anti-Ar) antibodies elicited in all strain A/J mice tested share one or more idiotypic specificities. These specificities are also found in the anti-Ar antibodies of mice of the closely related strain, AL/N, but not in those of BALB/c mice. Anti-Ar antibodies were elicited in congenic mice in which the IgCH locus of AL/N mice, which controls allotypic markers in the constant regions of heavy chains, had been introgressively backcrossed for nine generations onto a BALB/c background; the mice were then rendered homozygous for the AL/N allotypic determinant. On the average, these antibodies were quantitatively equivalent, with respect to content of the cross-reactive idiotype, to those of AL/N mice. This indicates that the gene controlling the idiotype is closely linked to the IgCH locus. Since idiotype must be a function of V region sequences, the results suggest close linkage of VH and CH genes. The cross-reactive idiotype was found in nearly all F1 mice (C57/BL x A/J or BALB/c x A/J) tested

Tobacco Usage in France: An Epidemiological Study

A survey of tobacco and alcohol consumption was conducted among 3,453 noninstitutionalized men and women in 65 départements in France. Over four-fifths of the men and half of the women surveyed had smoked cigarettes. Men were far more likely than women to have stopped smoking, especially older men in higher social classes. Fifty-five percent of the men smoked cigarettes made with black tobacco (Gauloises, Gitanes), while women preferred blond tobacco products. Younger smokers of both sexes preferred filtered cigarettes, while older respondents smoked nonfiltered ones. Filter usage among men, but not women, increased with education. Inhalation was more prevalent among men than women, among the young than the old, and among the more educated than the less educated. “Drooping” or carrying a lighted cigarettes in the mouth without inhaling, was a practice more common in older, less educated male smokers. These data also provide some evidence in support of the hypothesis that black tobacco, with its higher pH, provides unprotonated nicotine which is easily absorbed by oral mucosa, thus making deep inhalation of the smoke less important to the smoker. The observed differences between the smoking practices of the French and those in the United States and United Kingdom along with the relatively higher alcohol consumption noted throughout France, may partially explain the lower rates of lung cancer and higher rates of larynx, esophagus, and oral cavity cancer found in French men