Half-metallic antiferromagnets in double perovskites: LaAVRuO6_6 (A=Ca, Sr, and Ba)

Based on the theoretical exploration of electronic structures, we propose that the ordered double perovskites LaAVRuO$_6$ and LaVO$_3$/ARuO$_3$ (001) superlattice (A = Ca, Sr and Ba) are strong candidates for half-metallic (HM) antiferromagnets (AFMs). %LaAVRuO$_6$ and LaVO$_3$/ARuO$_3$ have the %100% spin polarizations at the Fermi level but with zero %total magnetic moments. We have shown that the HM-AFM nature in LaAVRuO$_6$ is very robust regardless of (i) divalent ion replacement at A-sites, (ii) oxygen site relaxation, (iii) the inclusion of the Coulomb correlation, and (iv) cation disorder. A type of the double exchange interaction is expected to be responsible for the half-metallicity and the antiferromagnetism in these systems.Comment: 4 pages, 4 figure

Testing Magnetic Field Models for the Class 0 Protostar L1527

For the Class 0 protostar, L1527, we compare 131 polarization vectors from SCUPOL/JCMT, SHARP/CSO and TADPOL/CARMA observations with the corresponding model polarization vectors of four ideal-MHD, non-turbulent, cloud core collapse models. These four models differ by their initial magnetic fields before collapse; two initially have aligned fields (strong and weak) and two initially have orthogonal fields (strong and weak) with respect to the rotation axis of the L1527 core. Only the initial weak orthogonal field model produces the observed circumstellar disk within L1527. This is a characteristic of nearly all ideal-MHD, non-turbulent, core collapse models. In this paper we test whether this weak orthogonal model also has the best agreement between its magnetic field structure and that inferred from the polarimetry observations of L1527. We found that this is not the case; based on the polarimetry observations the most favored model of the four is the weak aligned model. However, this model does not produce a circumstellar disk, so our result implies that a non-turbulent, ideal-MHD global collapse model probably does not represent the core collapse that has occurred in L1527. Our study also illustrates the importance of using polarization vectors covering a large area of a cloud core to determine the initial magnetic field orientation before collapse; the inner core magnetic field structure can be highly altered by a collapse and so measurements from this region alone can give unreliable estimates of the initial field configuration before collapse.Comment: 43 pages, 9 figures, 4 tables. Accepted by the Astrophysical Journa

Dynamic ploidy changes drive fluconazole resistance in human cryptococcal meningitis.

BACKGROUND: Cryptococcal meningitis (CM) causes an estimated 180,000 deaths annually, predominantly in sub-Saharan Africa, where most patients receive fluconazole (FLC) monotherapy. While relapse after FLC monotherapy with resistant strains is frequently observed, the mechanisms and impact of emergence of FLC resistance in human CM are poorly understood. Heteroresistance (HetR) - a resistant subpopulation within a susceptible strain - is a recently described phenomenon in Cryptococcus neoformans (Cn) and Cryptococcus gattii (Cg), the significance of which has not previously been studied in humans. METHODS: A cohort of 20 patients with HIV-associated CM in Tanzania was prospectively observed during therapy with either FLC monotherapy or in combination with flucytosine (5FC). Total and resistant subpopulations of Cryptococcus spp. were quantified directly from patient cerebrospinal fluid (CSF). Stored isolates underwent whole genome sequencing and phenotypic characterization. RESULTS: Heteroresistance was detectable in Cryptococcus spp. in the CSF of all patients at baseline (i.e., prior to initiation of therapy). During FLC monotherapy, the proportion of resistant colonies in the CSF increased during the first 2 weeks of treatment. In contrast, no resistant subpopulation was detectable in CSF by day 14 in those receiving a combination of FLC and 5FC. Genomic analysis revealed high rates of aneuploidy in heteroresistant colonies as well as in relapse isolates, with chromosome 1 (Chr1) disomy predominating. This is apparently due to the presence on Chr1 of ERG11, which is the FLC drug target, and AFR1, which encodes a drug efflux pump. In vitro efflux levels positively correlated with the level of heteroresistance. CONCLUSION: Our findings demonstrate for what we believe is the first time the presence and emergence of aneuploidy-driven FLC heteroresistance in human CM, association of efflux levels with heteroresistance, and the successful suppression of heteroresistance with 5FC/FLC combination therapy. FUNDING: This work was supported by the Wellcome Trust Strategic Award for Medical Mycology and Fungal Immunology 097377/Z/11/Z and the Daniel Turnberg Travel Fellowship

Effects of Backflow Correlation in the Three-Dimensional Electron Gas: Quantum Monte Carlo Study

The correlation energy of the homogeneous three-dimensional interacting electron gas is calculated using the variational and fixed-node diffusion Monte Carlo methods, with trial functions that include backflow and three-body correlations. In the high density regime the effects of backflow dominate over those due to three-body correlations, but the relative importance of the latter increases as the density decreases. Since the backflow correlations vary the nodes of the trial function, this leads to improved energies in the fixed-node diffusion Monte Carlo calculations. The effects are comparable to those found for the two-dimensional electron gas, leading to much improved variational energies and fixed-node diffusion energies equal to the release-node energies of Ceperley and Alder within statistical and systematic errors.Comment: 14 pages, 5 figures, submitted to Physical Review

Negative modes in the four-dimensional stringy wormholes

We study the Giddings-Strominger wormholes in string theories. We found negative modes among O(4)-symmetric fluctuations about the non-singular wormhole background. Hence the stringy wormhole contribution to the euclidean functional integral is purely imaginary. This means that the stringy wormhole is a bounce (not an instanton) and describes the nucleation and growth of wormholes in the Minkowski spacetime.Comment: 12 pages 2 figures, RevTe

Equivalence of operator-splitting schemes for the integration of the Langevin equation

We investigate the equivalence of different operator-splitting schemes for the integration of the Langevin equation. We consider a specific problem, so called the directed percolation process, which can be extended to a wider class of problems. We first give a compact mathematical description of the operator-splitting method and introduce two typical splitting schemes that will be useful in numerical studies. We show that the two schemes are essentially equivalent through the map that turns out to be an automorphism. An associated equivalent class of operator-splitting integrations is also defined by generalizing the specified equivalence.Comment: 4 page

Nonanalytic behavior of the spin susceptibility in clean Fermi systems

The wavevector and temperature dependent static spin susceptibility, \chi_s(Q,T), of clean interacting Fermi systems is considered in dimensions 1\leq d \leq 3. We show that at zero temperature \chi_s is a nonanalytic function of |Q|, with the leading nonanalyticity being |Q|^{d-1} for 1<d<3, and Q^2\ln|Q| for d=3. For the homogeneous spin susceptibility we find a nonanalytic temperature dependence T^{d-1} for 1<d<3. We give qualitative mode-mode coupling arguments to that effect, and corroborate these arguments by a perturbative calculation to second order in the electron-electron interaction amplitude. The implications of this, in particular for itinerant ferromagnetism, are discussed. We also point out the relation between our findings and established perturbative results for 1-d systems, as well as for the temperature dependence of \chi_s(Q=0) in d=3.Comment: 12pp., REVTeX, 5 eps figures, final version as publishe