1,296 research outputs found
Adsorption of Group-IV Elements on Graphene, Silicene, Germanene, Stanene: Dumbbell Formation
Silicene and germanene derivatives constructed from periodic dumbbell units
play a crucial role in multilayers of these honeycomb structures. Using
first-principles calculations based on density functional theory, here we
investigate the dumbbell formation mechanisms and energetics of Group IV atoms
adsorbed on graphene, silicene, germanene and stanene monolayer honeycomb
structures. The stabilities of the binding structures are further confirmed by
performing ab-initio molecular dynamics calculations at elevated temperatures,
except for stanene which is subject to structural instability upon the
adsorption of adatoms. Depending on the row number of the adatoms and
substrates we find three types of binding structures, which lead to significant
changes in the electronic, magnetic, and optical properties of substrates. In
particular, Si, Ge and Sn adatoms adsorbed on silicene and germanene form
dumbbell structures. Furthermore, dumbbell structures occur not only on single
layer, monatomic honeycomb structures, but also on their compounds like SiC and
SiGe. We show that the energy barrier to the migration of a dumbbell structure
is low due to the concerted action of atoms. This renders dumbbells rather
mobile on substrates to construct new single and multilayer Si and Ge phases.Comment: Accepted for publication in J. Phys. Chem.
An algorithm to obtain global solutions of the double confluent Heun equation
A procedure is proposed to construct solutions of the double confluent Heun
equation with a determinate behaviour at the singular points. The connection
factors are expressed as quotients of Wronskians of the involved solutions.
Asymptotic expansions are used in the computation of those Wronskians. The
feasibility of the method is shown in an example, namely, the Schroedinger
equation with a quasi-exactly-solvable potential
Supersymmetry and the relationship between a class of singular potentials in arbitrary dimensions
The eigenvalues of the potentials
and
, and of the special cases of these potentials such as the Kratzer and
Goldman-Krivchenkov potentials, are obtained in N-dimensional space. The
explicit dependence of these potentials in higher-dimensional space is
discussed, which have not been previously covered.Comment: 13 pages article in LaTEX (uses standard article.sty). Please check
"http://www1.gantep.edu.tr/~ozer" for other studies of Nuclear Physics Group
at University of Gaziante
Properties of Solutions in 2+1 Dimensions
We solve the Einstein equations for the 2+1 dimensions with and without
scalar fields. We calculate the entropy, Hawking temperature and the emission
probabilities for these cases. We also compute the Newman-Penrose coefficients
for different solutions and compare them.Comment: 16 pages, 1 figures, PlainTeX, Dedicated to Prof. Yavuz Nutku on his
60th birthday. References adde
Chemical Composition, Biological Activity, and Health-Promoting Effects of Withania somnifera for Pharma-Food Industry Applications
The Withania genus comes from the Solanaceae family and includes around 23 species, spread over some areas of the Mediterranean, Asia, and East Africa. Widely used in traditional medicine for thousands of years, these plants are rich in secondary metabolites, with special emphasis on steroidal lactones, named withanolides which are used as ingredients in numerous formulations for a plethora of diseases, such as asthma, diabetes, arthritis, impotence, amnesia, hypertension, anxiety, stress, cancer, neurodegenerative, and cardiovascular diseases, and many others. Among them, Withania somnifera (L.) Dunal is the most widely addressed species from a pharmacological and agroindustrial point of view. In this sense, this review provides an overview of the folk uses, phytochemical composition, and biological activity, such as antioxidant, antimicrobial, anti-inflammatory, and cytotoxic activity of W. somnifera, although more recently other species have also been increasingly investigated. In addition, their health-promoting effects, i.e., antistress, anxiolytic, adaptogenic, antirheumatoid arthritis, chemoprotective, and cardiorespiratory-enhancing abilities, along with safety and adverse effects are also discussed.N. C. -M. acknowledges the Portuguese Foundation for Science and Technology under the Horizon 2020 Program (PTDC/PSI-GER/28076/2017)
Constraints on the χ_(c1) versus χ_(c2) polarizations in proton-proton collisions at √s = 8 TeV
The polarizations of promptly produced χ_(c1) and χ_(c2) mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at √s=8 TeV. The χ_c states are reconstructed via their radiative decays χ_c → J/ψγ, with the photons being measured through conversions to e⁺e⁻, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χ_(c2) to χ_(c1) yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ → μ⁺μ⁻ decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum
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