5,644 research outputs found
Computer Program for the Calculation of Multicomponent Convective Diffusion Deposition Rates from Chemically Frozen Boundary Layer Theory
The computer program based on multicomponent chemically frozen boundary layer (CFBL) theory for calculating vapor and/or small particle deposition rates is documented. A specific application to perimter-averaged Na2SO4 deposition rate calculations on a cylindrical collector is demonstrated. The manual includes a typical program input and output for users
The two-dimensional frustrated Heisenberg model on the orthorhombic lattice
We discuss new high-field magnetization data recently obtained by Tsirlin et
al. for layered vanadium phosphates in the framework of the square-lattice
model. Our predictions for the saturation fields compare exceptionally well to
the experimental findings, and the strong bending of the curves below
saturation agrees very well with the experimental field dependence. Furthermore
we discuss the remarkably good agreement of the frustrated Heisenberg model on
the square lattice in spite of the fact that the compounds described with this
model actually have a lower crystallographic symmetry. We present results from
our calculations on the thermodynamics of the model on the orthorhombic (i.e.,
rectangular) lattice, in particular the temperature dependence of the magnetic
susceptibility. This analysis also sheds light on the discussion of magnetic
frustration and anisotropy of a class of iron pnictide parent compounds, where
several alternative suggestions for the magnetic exchange models were proposed.Comment: 4 pages, 3 figures, accepted for publication in Journal of Physics:
Conference Serie
Theoretical search for superconductivity in Sc3XB perovskites and weak ferromagnetism in Sc3X (X = Tl, In, Ga, Al)
A possibility for a new family of intermetallic perovskite superconductors
Sc3XB, with X = Tl, In, Ga and Al, is presented as a result of KKR electronic
structure and pseudopotential phonon calculations. The large values of computed
McMillan--Hopfield parameters on scandium suggest appearance of
superconductivity in Sc3XB compounds. On the other hand, the possibility of
weak itinerant ferromagnetic behavior of Sc3X systems is indicated by the small
magnetic moment on Sc atoms in two cases of X =~ l and In. Also the electronic
structure and resulting superconducting parameters for more realistic case of
boron--deficient systems Sc3XB_x are computed using KKR--CPA method, by
replacing boron atom with a vacancy. The comparison of the calculated
McMillan--Hopfield parameters of the Sc3XB series with corresponding values in
MgCNi3 and YRh3B superconductors is given, finding the favorable trends for
superconductivity.Comment: 13 pages, 13 figures. v3 - revise
Superconductivity in the New Platinum Germanides MPt4Ge12 (M = Rare-earth and Alkaline-earth Metals) with Filled Skutterudite Structure
New germanium-platinum compounds with the filled-skutterudite crystal
structure were synthesized. The structure and composition were investigated by
X-ray diffraction and microprobe analysis. Magnetic susceptibility, specific
heat, and electrical resistivity measurements evidence superconductivity in
LaPt4Ge12 and PrPt4Ge12 below 8.3K. The parameters of the normal and
superconducting states were established. Strong coupling and a crystal electric
field singlet groundstate is found for the Pr compound. Electronic structure
calculations show a large density of states at the Fermi level. Similar
behavior with lower T_c was observed for SrPt4Ge12 and BaPt4Ge12.Comment: RevTeX, 4 figures, submitted to Physical Review Letters July 12, 200
Interplay of atomic displacements in the quantum magnet (CuCl)LaNb2O7
We report on the crystal structure of the quantum magnet (CuCl)LaNb2O7 that
was controversially described with respect to its structural organization and
magnetic behavior. Using high-resolution synchrotron powder x-ray diffraction,
electron diffraction, transmission electron microscopy, and band structure
calculations, we solve the room-temperature structure of this compound
[alpha-(CuCl)LaNb2O7] and find two high-temperature polymorphs. The
gamma-(CuCl)LaNb2O7 phase, stable above 640K, is tetragonal with a(sub) = 3.889
A, c(sub) = 11.738 A, and the space group P4/mmm. In the gamma-(CuCl)LaNb2O7
structure, the Cu and Cl atoms are randomly displaced from the special
positions along the {100} directions. The beta-phase [a(sub) x 2a(sub) x
c(sub), space group Pbmm] and the alpha-phase [2a(sub) x 2a(sub) x c(sub),
space group Pbam] are stable between 640 K and 500 K and below 500 K,
respectively. The structural changes at 500 K and 640 K are identified as
order-disorder phase transitions. The displacement of the Cl atoms is frozen
upon the gamma --> beta transformation, while a cooperative tilting of the NbO6
octahedra in the alpha-phase further eliminates the disorder of the Cu atoms.
The low-temperature alpha-(CuCl)LaNb2O7 structure thus combines the two types
of the atomic displacements that interfere due to the bonding between the Cu
atoms and the apical oxygens of the NbO6 octahedra. The precise structural
information resolves the controversy between the previous computation-based
models and provides the long-sought input for understanding the magnetic
properties of (CuCl)LaNb2O7.Comment: 12 pages, 10 figures, 5 tables; crystallographic information (cif
files) include
Consequences of critical interchain couplings and anisotropy on a Haldane chain
Effects of interchain couplings and anisotropy on a Haldane chain have been
investigated by single crystal inelastic neutron scattering and density
functional theory (DFT) calculations on the model compound SrNiVO.
Significant effects on low energy excitation spectra are found where the
Haldane gap (; where is the intrachain exchange
interaction) is replaced by three energy minima at different antiferromagnetic
zone centers due to the complex interchain couplings. Further, the triplet
states are split into two branches by single-ion anisotropy. Quantitative
information on the intrachain and interchain interactions as well as on the
single-ion anisotropy are obtained from the analyses of the neutron scattering
spectra by the random phase approximation (RPA) method. The presence of
multiple competing interchain interactions is found from the analysis of the
experimental spectra and is also confirmed by the DFT calculations. The
interchain interactions are two orders of magnitude weaker than the
nearest-neighbour intrachain interaction = 8.7~meV. The DFT calculations
reveal that the dominant intrachain nearest-neighbor interaction occurs via
nontrivial extended superexchange pathways Ni--O--V--O--Ni involving the empty
orbital of V ions. The present single crystal study also allows us to
correctly position SrNiVO in the theoretical - phase
diagram [T. Sakai and M. Takahashi, Phys. Rev. B 42, 4537 (1990)] showing where
it lies within the spin-liquid phase.Comment: 12 pages, 12 figures, 3 tables PRB (accepted). in Phys. Rev. B (2015
Substance use among sexual minorities in the US – Linked to inequalities and unmet need for mental health treatment? Results from the National Survey on Drug Use and Health (NSDUH)
Background
A social group found to be particularly burdened by disparities in substance use is the group of sexual minorities (SM). We investigated the potential association between substance use among SM adults in the United States (US) and social inequality, with an additional focus on disparities in unmet need for mental health treatment.
Methods
A secondary cross-sectional data analysis was performed using National Survey on Drug Use and Health (NSDUH) data from 2015 to 2017 and including 126,463 individuals with 8,241 identifying as SM. Multivariable logistic regression models were implemented to quantify disparities in substance use, to calculate the effect of sociodemographic variables on substance use, and to examine associations to socioeconomic vulnerability.
Findings
SM showed higher odds of past-year substance use and lifetime chemsex drugs use. All SM except for bisexual men exhibited higher odds of past-month binge drinking relative to heterosexuals. Bisexual women had higher odds for use of all analysed substances relative to heterosexual women. Being older and being a woman were shown to be protective factors. Urbanity, being uninsured, and unmet need for mental health treatment were associated with significantly higher odds of substance use, chemsex drugs use and binge drinking. A link was established between drug use and health, with higher odds of drug use for lower health ratings. SM experienced significantly higher levels of socioeconomic vulnerability. Higher vulnerability indices were associated with increased odds for drug use.
Interpretation
This study is among the first nationally representative samples that analysed the effect of sociodemographic determinants and unmet need for mental health treatment on substance use in SM. It emphasises the multifactorial aetiology of vulnerability to substance use and highlights the distinct disparities in, and underlying mechanisms for substance use among SM. Approaches tailored to SM subgroups may be needed to address the problems of increased substance use for this population in the long-term. However, critical gaps in the literature remain and large-scale studies inclusive of SM individuals are needed to present causal links.
Funding: Gillings Fellowship SYOG054 to ARU
Antiferromagnetic fluctuations in the normal state of LiFeAs
We present a detailed study of 75As NMR Knight shift and spin-lattice
relaxation rate in the normal state of stoichiometric polycrystalline LiFeAs.
Our analysis of the Korringa relation suggests that LiFeAs exhibits strong
antiferromagnetic fluctuations, if transferred hyperfine coupling is a dominant
interaction between 75As nuclei and Fe electronic spins, whereas for an on-site
hyperfine coupling scenario, these are weaker, but still present to account for
our experimental observations. Density-functional calculations of electric
field gradient correctly reproduce the experimental values for both 75As and
7Li sites.Comment: 5 pages, 3 figures, thoroughly revised version with refined
experimental data, accepted for publication as a Rapid Communication in
Physical Review B
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