Electron-hole asymmetry in Co- and Mn-doped SrFe2As2

Phase diagram of electron and hole-doped SrFe2As2 single crystals is investigated using Co and Mn substitution at the Fe-sites. We found that the spin-density-wave state is suppressed by both dopants, but the superconducting phase appears only for Co (electron)-doping, not for Mn (hole)-doping. Absence of the superconductivity by Mn-doping is in sharp contrast to the hole-doped system with K-substitution at the Sr sites. Distinct structural change, in particular the increase of the Fe-As distance by Mn-doping is important to have a magnetic and semiconducting ground state as confirmed by first principles calculations. The absence of electron-hole symmetry in the Fe-site-doped SrFe2As2 suggests that the occurrence of high-Tc superconductivity is sensitive to the structural modification rather than the charge doping.Comment: 7 pages, 6 figure

Carbon dioxide fluxes from biologically-crusted Kalahari Sands after simulated wetting

We report surface CO2 efflux and subsoil CO2 concentrations in biologically-crusted soils from the Kalahari. Fluxes were determined in-situ using a closed chamber coupled to a portable gas chromatograph on dry soils and on soils subject to simulated light and heavy rainfall. Surface efflux was measured in an artificially darkened environment in order to determine by difference, whether photosynthesis was occurring. Dry soil efflux rates were 2.8–14.8 mg C m2 h−1 throughout a diurnal cycle. Light rainfall led to an immediate increase in efflux to a peak of 65.6 mg C m2 h−1. Heavy rainfall resulted in a large pulse of CO2 with efflux rates of 339.2 mg C m2 h−1 over the first hour after wetting. Peak rates remained high over the following 2 days (87.8 and 87.0 mg C m2 h−1). Given sufficient moisture, fluxes increased with temperature. We believe hydration of the subsoil stimulates microorganisms which repsire available C either from extracellular polysaccharide sheaths (EPS) or released into the soil through lysis of microbial cells. Higher fluxes from the soil kept in the dark suggests photosynthesis occurs in wetted crusts during the daytime but net C uptake is masked by respiration from other microorganisms

CP1CP^{1} model with Hopf term and fractional spin statistics

We reconsider the $CP^{1}$ model with the Hopf term by using the Batalin-Fradkin-Tyutin (BFT) scheme, which is an improved version of the Dirac quantization method. We also perform a semi-classical quantization of the topological charge Q sector by exploiting the collective coordinates to explicitly show the fractional spin statistics.Comment: 15 page

Envelope-kinetic analysis of the electron kinetic effects on Raman backscatter and Raman backward laser amplification

The electron kinetic effects on Raman backscattering and Raman backward laser amplification were analyzed. The analysis is based on the envelope-kinetic equations of a plasma wave, which are composed of the conventional envelope equation of a fluid plasma and the kinetic term. One major goal of this paper is to close the envelope-kinetic model by analyzing the kinetic term, which was not fully covered in the previous work [M. S. Hur et al., Phys. Rev. Lett. 95, 115003 (2005)]. It was found that the closed envelope-kinetic equation in the nontrapping regime takes the same form as the envelope equation of the fluid plasma used in the three-wave model. For the closure in the trapping-dominant regime, the test particle technique is employed to calculate the kinetic term. Results from the full kinetic and test particle simulations agree well with each other, while the latter has a great advantage in computation speed. The frequency shift and resonance breaking by the trapped particles are discussed with the help of a new diagnostic inserted in the full kinetic averaged particle-in-cell code.open5

Ideal Bose gas in fractal dimensions and superfluid 4^4He in porous media

Physical properties of ideal Bose gas with the fractal dimensionality between D=2 and D=3 are theoretically investigated. Calculation shows that the characteristic features of the specific heat and the superfluid density of ideal Bose gas in fractal dimensions are strikingly similar to those of superfluid Helium-4 in porous media. This result indicates that the geometrical factor is dominant over mutual interactions in determining physical properties of Helium-4 in porous media.Comment: 13 pages, 6 figure

The influence of trees, shrubs, and grasses on microclimate, soil carbon, nitrogen, and CO2 efflux:Potential implications of shrub encroachment for Kalahari rangelands

Shrub encroachment is a well-documented phenomenon affecting many of the world's drylands. The alteration of vegetation structure and species composition can lead to changes in local microclimate and soil properties which in turn affect carbon cycling. The objectives of this paper were to quantify differences in air temperatures, soil carbon, nitrogen, and CO2 efflux under trees (Vachellia erioloba), shrubs (Grewia flava), annual and perennial grasses (Schmidtia kalahariensis and Eragrostis lehmanniana) collected over three seasons at a site in Kgalagadi District, Botswana, in order to determine the vegetation-soil feedback mechanism affecting the carbon cycle. Air temperatures were logged continuously and soil CO2 efflux was determined throughout the day and evening using closed respiration chambers and an infrared gas analyser. There were significant differences in soil carbon, total nitrogen, CO2 efflux, light and temperatures beneath the canopies of trees, shrubs and grasses. Daytime air temperatures beneath shrubs and trees were cooler compared to grass sites, particularly in summer months. Night time air temperatures under shrubs and trees were, however, warmer than at the grass sites. There was also significantly more soil carbon, nitrogen and CO2 efflux under shrubs and trees compared to grasses. Whilst the differences observed in soils and microclimate may reinforce the competitive dominance of shrubs and present challenges to strategies designed to manage encroachment they should not be viewed as entirely negative. Our findings highlight some of the dichotomies and challenges to be addressed before interventions aiming to bring about more sustainable land management can be implementedpublishersversionPeer reviewe

Numerical Test of Disk Trial Wave function for Half-Filled Landau Level

The analyticity of the lowest Landau level wave functions and the relation between filling factor and the total angular momentum severely limits the possible forms of trial wave functions of a disk of electrons subject to a strong perpendicular magnetic field. For N, the number of electrons, up to 12 we have tested these disk trial wave functions for the half filled Landau level using Monte Carlo and exact diagonalization methods. The agreement between the results for the occupation numbers and ground state energies obtained from these two methods is excellent. We have also compared the profile of the occupation number near the edge with that obtained from a field-theoretical method. The results give qualitatively identical edge profiles. Experimental consequences are briefly discussed.Comment: To be published in Phys. Rev. B. 9 pages, 6 figure