49 research outputs found
Itinerant electron metamagnetism in LaCoSi
The strongly exchange enhanced Pauli paramagnet LaCoSi is found to
exhibit an itinerant metamagnetic phase transition with indications for
metamagnetic quantum criticality. Our investigation comprises magnetic,
specific heat, and NMR measurements as well as ab-initio electronic structure
calculations. The critical field is about 3.5 T for and 6 T for , which is the lowest value ever found for rare earth intermetallic
compounds. In the ferromagnetic state there appears a moment of about 0.2
/Co at the Co-sites, but sigificantly smaller moments at the 4d
and Co-sites.Comment: 11 pages, 5 figures, PRB Rapid Communication, in prin
Environmental change and potential impacts: applied research priorities for Alaska\u27s North Slope
Statistical Theory of Spin Relaxation and Diffusion in Solids
A comprehensive theoretical description is given for the spin relaxation and
diffusion in solids. The formulation is made in a general
statistical-mechanical way. The method of the nonequilibrium statistical
operator (NSO) developed by D. N. Zubarev is employed to analyze a relaxation
dynamics of a spin subsystem. Perturbation of this subsystem in solids may
produce a nonequilibrium state which is then relaxed to an equilibrium state
due to the interaction between the particles or with a thermal bath (lattice).
The generalized kinetic equations were derived previously for a system weakly
coupled to a thermal bath to elucidate the nature of transport and relaxation
processes. In this paper, these results are used to describe the relaxation and
diffusion of nuclear spins in solids. The aim is to formulate a successive and
coherent microscopic description of the nuclear magnetic relaxation and
diffusion in solids. The nuclear spin-lattice relaxation is considered and the
Gorter relation is derived. As an example, a theory of spin diffusion of the
nuclear magnetic moment in dilute alloys (like Cu-Mn) is developed. It is shown
that due to the dipolar interaction between host nuclear spins and impurity
spins, a nonuniform distribution in the host nuclear spin system will occur and
consequently the macroscopic relaxation time will be strongly determined by the
spin diffusion. The explicit expressions for the relaxation time in certain
physically relevant cases are given.Comment: 41 pages, 119 Refs. Corrected typos, added reference
Meta-analysis of nature conservation values in Asia & Oceania: Data heterogeneity and benefit transfer issues
We conduct a meta-analysis (MA) of around 100 studies valuing nature conservation in Asia and Oceania. Dividing our dataset into two levels of heterogeneity in terms of good characteristics (endangered species vs. nature conservation more generally) and valuation methods, we show that the degree of regularity and conformity with theory and empirical expectations is higher for the more homogenous dataset of contingent valuation of endangered species. For example, we find that willingness to pay (WTP) for preservation of mammals tends to be higher than other species and that WTP for species preservation increases with income. Increasing the degree of heterogeneity in the valuation data, however, preserves much of the regularity, and the explanatory power of some of our models is in the range of other MA studies of goods typically assumed to be more homogenous (such as water quality). Subjecting our best MA models to a simple test forecasting values for out-of-sample observations, shows median (mean) forecasting errors of 24 (46) percent for endangered species and 46 (89) percent for nature conservation more generally, approaching levels that may be acceptable in benefit transfer for policy use. We recommend that the most prudent MA practice is to control for heterogeneity in regressions and sensitivity analysis, rather than to limit datasets by non-transparent criteria to a level of heterogeneity deemed acceptable to the individual analyst. However, the trade-off will always be present and the issue of acceptable level of heterogeneity in MA is far from settle
Recovery of the cave crayfish (Decapoda: Cambridae) population in Peacock Springs, Florida?
Volume: 22Start Page: 61End Page: 6
A Comparison of Fish Populations from Natural and Constructed Freshwater Marshes in Central Florida
In Florida, freshwater marshes are constructed as mitigation for wetland loss associated with phosphate strip mining, but little is known regarding the similarity of fish communities in natural and constructed marshes. Fish from five constructed and eight natural marshes were sampled quarterly via throw-traps for one year. Gambusia holbrooki, Heterandria formosa, Poecilia latiuinna, Elassoma everqladei, Fundulus chrysotus, Jordanella floridae, Fundulus rubifrons, and unidentified juvenile centrarchids were found in both constructed and natural marshes, while Lucania goodei was found only in constructed marshes. A comparison between constructed and natural marsh populations showed that differences in mean abundance and biomass at p \u3c 0.05 (Wilcoxon rank-sum teat) were present for G. holbrooki and E. everqladei. Differences in populations may be attributed to differences in conditions found in constructed and natural marshes