5,212 research outputs found
Electronic, dynamical, and thermal properties of ultra-incompressible superhard rhenium diboride: A combined first-principles and neutron scattering study
Rhenium diboride is a recently recognized ultra-incompressible superhard
material. Here we report the electronic (e), phonon (p), e-p coupling and
thermal properties of ReB from first-principles density-functional theory
(DFT) calculations and neutron scattering measurements. Our calculated elastic
constants ( = 641 GPa, = 159 GPa, = 128 GPa,
= 1037 GPa, and = 271 GPa), bulk modulus ( 350 GPa) and
hardness ( 46 GPa) are in good agreement with the reported
experimental data. The calculated phonon density of states (DOS) agrees very
well with our neutron vibrational spectroscopy result. Electronic and phonon
analysis indicates that the strong covalent B-B and Re-B bonding is the main
reason for the super incompressibility and hardness of ReB. The thermal
expansion coefficients, calculated within the quasi-harmonic approximation and
measured by neutron powder diffraction, are found to be nearly isotropic in
and directions and only slightly larger than that of diamond in terms of
magnitude. The excellent agreement found between calculations and experimental
measurements indicate that first-principles calculations capture the main
interactions in this class of superhard materials, and thus can be used to
search, predict, and design new materials with desired properties.Comment: submitted to pr
Magnetic Structure and Spin Waves in the Kagom\'{e} Jarosite compound
We present a detailed study of the magnetic structure and spin waves in the
Fe jarosite compound for the most general
Hamiltonian involving one- and two-spin interactions which are allowed by
symmetry. We compare the calculated spin-wave spectrum with the recent neutron
scattering data of Matan {\it et al.} for various model Hamiltonians which
include, in addition to isotropic Heisenberg exchange interactions between
nearest () and next-nearest () neighbors, single ion anisotropy and
Dzyaloshinskii-Moriya (DM) interactions. We concluded that DM interactions are
the dominant anisotropic interaction, which not only fits all the splittings in
the spin-wave spectrum but also reproduces the small canting of the spins out
of the Kagom\'e plane. A brief discussion of how representation theory
restricts the allowed magnetic structure is also given.Comment: 23 pages, 17 figures, submitted to Phys. Rev. B (March 2006
Transition Metal-Ethylene Complexes as High-Capacity Hydrogen Storage Media
From first-principles calculations, we predict that a single ethylene
molecule can form a stable complex with two transition metals (TM) such as Ti.
The resulting TM-ethylene complex then absorbs up to ten hydrogen molecules,
reaching to gravimetric storage capacity of 14 wt%. Dimerization,
polymerizations and incorporation of the TM-ethylene complexes in nanoporous
carbon materials have been also discussed. Our results are quite remarkable and
open a new approach to high-capacity hydrogen storage materials discovery.Comment: 5 pages, 4 figures, additional content, Phys. Rev. Lett. in pres
Cytotoxic and antibacterial activity of the mixture of olive oil and lime cream in vitro conditions
The mixture of olive oil and lime cream has been traditionally used to treat external burns in the region of Hatay/Antakya and middle Anatolia. Olive oil and lime cream have been employed by many physicians to treat many ailments in the past. A limited number of studies have shown the antibacterial effect of olive oil and that it does not have any toxic effect on the skin. But we did not find any reported studies on the mixture of olive oil and lime cream. The aim of this paper is to investigate the cytotoxic and antibacterial activity of olive oil and lime cream individually or/and in combination in vitro conditions, by using disk-diffusion method and in cell culture. The main purpose in using this mixture is usually to clear burns without a trace. Agar overlay, MTT (Cytotoxicity assay) and antibacterial susceptibility tests were used to investigate the cytotoxic and antibacterial activity of olive oil and lime cream. We found that lime cream has an antibacterial activity but also cytotoxic on the fibroblasts. On the other hand olive oil has limited or no antibacterial effect and it has little or no cytotoxic on the fibroblasts. When we combined lime cream and olive oil, olive oil reduced its cytotoxic impact. These results suggest that mixture of olive oil and lime cream is not cytotoxic and has antimicrobial activity.Keywords: Olive oil, lime cream, burn, in vitro, cytotoxic activity, antibacterial activit
Large-Scale Monte Carlo Study of a Realistic Lattice Model for Ga_(1-x)Mn_xAs
The properties of Mn-doped GaAs are studied at several doping levels and hole
compensations, using a real-space Hamiltonian on an fcc lattice that reproduces
the valence bands of undoped GaAs. Large-scale Monte Carlo (MC) simulations on
a Cray XT3 supercomputer, using up to a thousand nodes, were needed to make
this effort possible. Our analysis considers both the spin-orbit interaction
and the random distribution of the Mn ions. The hopping amplitudes are
functions of the GaAs Luttinger parameters. At the coupling J~1.2eV deduced
from photoemission experiments, the MC Curie temperature and the shape of the
magnetization curves are in agreement with experimental results for annealed
samples. Although there are sizable differences with mean-field predictions,
the system is found to be closer to a hole-fluid regime than to localized
carriers
Ohio Residency Law for Student Voters - Its Implications and a Proposal for More Effective Implementation of Residency Statutes
The task is to evaluate the traditional common law tests of domicile, many of which are outmoded, and to select those which are compatible with the new constitutional requirements of real fairness and equality in order to lay a firm foundation for the accomplishment of the original purposes of residency law in the modern world. Furthermore, the theoretical problems involved -constitutional exposition, common law analysis, statutory construction, and governmental policy- need to be synthesized into a system that is easily implemented by the Secretary of State, easily applied by local boards of election, and finally, easily understood by all new registrants for voting in Ohio. This article seeks to solve these problems in the soundest possible manner as a guide to the future and proposes a method of implementing them for boards of election and the general public
Hydrogen Absorption Properties of Metal-Ethylene Complexes
Recently, we have predicted [Phys. Rev. Lett. 97, 226102 (2006)] that a
single ethylene molecule can form stable complexes with light transition metals
(TM) such as Ti and the resulting TMn-ethylene complex can absorb up to ~12 and
14 wt % hydrogen for n=1 and 2, respectively. Here we extend this study to
include a large number of other metals and different isomeric structures. We
obtained interesting results for light metals such as Li. The ethylene molecule
is able to complex with two Li atoms with a binding energy of 0.7 eV/Li which
then binds up to two H2 molecules per Li with a binding energy of 0.24 eV/H2
and absorption capacity of 16 wt %, a record high value reported so far. The
stability of the proposed metal-ethylene complexes was tested by extensive
calculations such as normal-mode analysis, finite temperature first-principles
molecular dynamics (MD) simulations, and reaction path calculations. The phonon
and MD simulations indicate that the proposed structures are stable up to 500
K. The reaction path calculations indicate about 1 eV activation barrier for
the TM2-ethylene complex to transform into a possible lower energy
configuration where the ethylene molecule is dissociated. Importantly, no
matter which isometric configuration the TM2-ethylene complex possesses, the TM
atoms are able to bind multiple hydrogen molecules with suitable binding energy
for room temperature storage. These results suggest that co-deposition of
ethylene with a suitable precursor of TM or Li into nanopores of light-weight
host materials may be a very promising route to discovering new materials with
high-capacity hydrogen absorption properties
Linear and Non-Linear Causality Tests of Stock Price and Real Exchange Rate Interactions in Turkey
The purpose of this study is to determine whether there is a causality relationship between stock price and real exchange rates in Turkey. Within this context, the study employs monthly data for real exchange rates based on consumer price index and BIST 100 index as representing stock prices that cover the periods from January 2005 to August 2017. On the other side, Granger causality test, Toda-Yamamoto causality analysis and Diks and Panchenko nonlinear causality test used for this purpose. As a result, Linear Granger causality, Toda-Yamamoto and Nonlinear Granger causality tests reveal that there is a casual relationship between real exchange rate and stock price in Turkish economy for the period of 2005:01 - 2017:08 and the direction of the causality is from stock price to exchange rate. This evidence can be interpreted as the changes in stock prices may strongly have influences on the success of foreign exchange rate policies
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