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

Spatiotemporal variations of soil reactive nitrogen oxide fluxes across the anthropogenic landscape

Volatile reactive nitrogen oxides (NO y ) are significant atmospheric pollutants, including NO x (nitric oxide [NO] + nitrogen dioxide [NO2]) and NO z (nitrous acid [HONO] + nitric acid [HNO3] + nitrogen trioxide [NO3] + ...). NO y species are products of nitrogen (N) cycle processes, particularly nitrification and denitrification. Biogenic sources, including soil, account for over 50% of natural NO y emissions to the atmosphere, yet emissions from soils are generally not included in atmospheric models as a result of a lack of mechanistic data. This work is a unique investigation of NO y fluxes on a landscape scale, taking a comprehensive set of land-use types, human influence, and seasonality into account to determine large-scale heterogeneity to provide a basis for future modeling and hypothesis generation. By coupling 16S rRNA amplicon sequencing and quantitative polymerase chain reaction, we have linked significant differences in functional potential and activity of nitrifying and denitrifying soil microbes to NO y emissions from soils. Further, we have identified soils subject to increased N deposition that are less microbially active despite increased available N, potentially as a result of poor soil health from anthropogenic pollution. Structural equation modeling suggests human influence on soils to be a more significant effector of soil NO y emissions than land-use type

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

Interactions of long-term grazing and woody encroachment can shift soil biogeochemistry and microbiomes in savanna ecosystems

Semi-arid grasslands and savannas in the southern Great Plains USA are extensively used for livestock grazing. Over the past century, Juniperus (juniper) and Quercus (oak) species abundance have increased due to intensive grazing and reduced fire frequency. We investigated the interactions between livestock grazing history (none, moderate, heavy) and vegetation cover (grassland, juniper, oak) using a ∼ 70-year grazing experiment in west-central Texas. We explored effects on soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), microbial community composition, and function. SOC and TN were 50–150 % higher under juniper and oak compared to grasslands, and 10–30 % lower in grazed vs. ungrazed areas. Vegetation × grazing interaction showed greater SOC and TN loss under oak than juniper or grasslands. Ungrazed controls had higher soil TP than grazed areas, with oak and juniper soils having more TP than grasslands. Bacterial and fungal communities differed between grassland and woody vegetation. Grazing affected only bacterial communities. SOC, TN, TP accounted for differences in community structure. Abundances of genes related to methane, nitrogen, sulfur metabolisms, and dominant fungal trophic modes were linked to soil C, N, P ratios. These findings highlight how long-term livestock grazing and woody plant encroachment influence soil C, N, P cycles, altering soil microbial community structure and function. This study provides insights for savanna ecosystem management and integrating land cover effects into biogeochemical models for global change scenarios

Chromosomal translocations activating myc sequences and transduction of v-abl are critical events in the rapid induction of plasmacytomas by Pristane and Abelson virus

Plasmacytomas with short latent periods can be induced in BALB/c mice by a single intraperitoneal (i.p.) injection of 0.5 ml pristane followed 20-40 d later by an injection of Abelson virus. The karyotypes of 18 such tumors were determined; 10 of these had rcpt 12;15, 5 had rcpt 6;15 and 3 had no translocations, but two of these have been shown to have interstitial deletions of chromosome 15. The specific breakpoints were the same as described in pristane-induced plasmacytomas, i.e., at 15D2/3, 6C2, and 12F2. Near diploid karyotypes and trisomy of chromosome 11 were frequently seen. All of the Abelson-plus-pristane-induced plasmacytomas (ABPC) were studied as transplanted tumors, contained integrated v-abl sequences, and actively transcribed v-abl mRNA. All but one of these tumors contained abundant myc RNA transcripts. The shortness of the latent periods of the ABPC suggests that the rcpt 12;15 and rcpt 6;15 occur soon after pristane administration and are present at the time Abelson virus is introduced. In this form of plasmacytomagenesis, activated v-abl genes appear to bypass other genetic changes that require a much longer period of time in pristane plasmacytomagenesis. Nonetheless, the consistent finding of chromosome-15 alterations and abundant myc expression in these plasmacytomas emphasize the apparent need for multiple events even in the genesis of some tumors induced by rapid transforming viruses