1,000 research outputs found
An atlas of endohedral Sc2S cluster fullerenes
Structural identification is a difficult task in the study of metallofullerenes, but understanding of the mechanism of formation of these structures is a pre-requisite for new high-yield synthetic methods. Here, systematic density functional theory calculations demonstrate that metal sulfide fullerenes Sc2S@Cn have similar cage geometries from C70 to C84 and form a close-knit family of structures related by Endo-Kroto insertion/extrusion of C2 units and Stone-Wales isomerization transformations. The stabilities predicted for favoured isomers by DFT calculations are in good agreement with available experimental observations, have implications for the formation of metallofullerenes, and will aid structural identification from within the combinatorially vast pool of conceivable isomers
Ising model on nonorientable surfaces: Exact solution for the Moebius strip and the Klein bottle
Closed-form expressions are obtained for the partition function of the Ising
model on an M x N simple-quartic lattice embedded on a Moebius strip and a
Klein bottle for finite M and N. The finite-size effects at criticality are
analyzed and compared with those under cylindrical and toroidal boundary
conditions. Our analysis confirms that the central charge is c=1/2.Comment: 8 pages, 3 eps figure
The Effect of Nitrided Layer on Antibacterial Properties for Biomedical Stainless Steel
AbstractPlasma nitriding of AISI type 303 austenitic stainless steel using microwave system at various input powers was conducted in present study. The nitrided layers were characterized via scanning electron microscopy, transmission electron microscopy and Vickers microhardness tester. The anti-bacterial property of this nitrided layer was also evaluated. The analytical results revealed the hardness of AISI type 303 stainless steel could be enhanced with nitriding process. The microstructure of the nitrided layer comprised of nitrogen-expanded γ phase. Bacterial test demonstrated the nitrided layer processed the excellent an ti-bacterial properties. The enhanced hardness and anti-bacterial properties make the nitrided AISI type 303 austenitic stainless steel the potential material in the biomedical applications
Wavefunction statistics in open chaotic billiards
We study the statistical properties of wavefunctions in a chaotic billiard
that is opened up to the outside world. Upon increasing the openings, the
billiard wavefunctions cross over from real to complex. Each wavefunction is
characterized by a phase rigidity, which is itself a fluctuating quantity. We
calculate the probability distribution of the phase rigidity and discuss how
phase rigidity fluctuations cause long-range correlations of intensity and
current density. We also find that phase rigidities for wavefunctions with
different incoming wave boundary conditions are statistically correlated.Comment: 4 pages, RevTeX; 1 figur
Extended States in a One-dimensional Generalized Dimer Model
The transmission coefficient for a one dimensional system is given in terms
of Chebyshev polynomials using the tight-binding model. This result is applied
to a system composed of two impurities located between sites of a host
lattice. It is found that the system has extended states for several values of
the energy. Analytical expressions are given for the impurity site energy in
terms of the electron's energy. The number of resonant states grows like the
number of host sites between the impurities. This property makes the system
interesting since it is a simple task to design a configuration with resonant
energy very close to the Fermi level .Comment: 4 pages, 3 figure
Spin state and phase competition in TbBaCo_{2}O_{5.5} and the lanthanide series LnBaCo_{2}O_{5+\delta} (0<=\delta<=1)
A clear physics picture of TbBaCoO is revealed on the basis of
density functional theory calculations. An antiferromagnetic (AFM)
superexchange coupling between the almost high-spin Co ions competes
with a ferromagnetic (FM) interaction mediated by both p-d exchange and double
exchange, being responsible for the observed AFM-FM transition. And the
metal-insulator transition is accompanied by an xy/xz orbital-ordering
transition. Moreover, this picture can be generalized to the whole lanthanide
series, and it is predicted that a few room-temperature magnetoresistance
materials could be found in LnBaACoO
(Ln=Ho,Er,Tm,Yb,Lu; A=Sr,Ca,Mg).Comment: 13 pages, 2 figures; to be published in Phys. Rev. B on 1st Sept.
Title and Bylines are added to the revised versio
Electronic structure study of double perovskites FeReO (A=Ba,Sr,Ca) and SrMoO (M=Cr,Mn,Fe,Co) by LSDA and LSDA+U
We have implemented a systematic LSDA and LSDA+U study of the double
perovskites FeReO (A=Ba,Sr,Ca) and SrMoO
(M=Cr,Mn,Fe,Co) for understanding of their intriguing electronic and magnetic
properties. The results suggest a ferrimagnetic (FiM) and half-metallic (HM)
state of FeReO (A=Ba,Sr) due to a pdd- coupling between the
down-spin Re/Fe orbitals via the intermediate O
ones, also a very similar FiM and HM state of SrFeMoO.
In contrast, a decreasing Fe component at Fermi level () in the
distorted CaFeReO partly accounts for its nonmetallic behavior,
while a finite - coupling between the down-spin
Re/Fe orbitals being present at serves to
stabilize its FiM state. For SrCrMoO compared with
SrFeMoO, the coupling between the down-spin Mo/Cr
orbitals decreases as a noticeable shift up of the Cr 3d
levels, which is likely responsible for the decreasing value and weak
conductivity. Moreover, the calculated level distributions indicate a
Mn(Co)/Mo ionic state in SrMnMoO
(SrCoMoO), in terms of which their antiferromagnetic insulating
ground state can be interpreted. While orbital population analyses show that
owing to strong intrinsic pd covalence effects, SrMoO
(M=Cr,Mn,Fe,Co) have nearly the same valence state combinations, as accounts
for the similar M-independent spectral features observed in them.Comment: 21 pages, 3 figures. to be published in Phys. Rev. B on 15th Se
Higgs algebraic symmetry of screened system in a spherical geometry
The orbits and the dynamical symmetries for the screened Coulomb potentials
and isotropic harmonic oscillators have been studied by Wu and Zeng [Z. B. Wu
and J. Y. Zeng, Phys. Rev. A 62,032509 (2000)]. We find the similar properties
in the responding systems in a spherical space, whose dynamical symmetries are
described by Higgs Algebra. There exists a conserved aphelion and perihelion
vector, which, together with angular momentum, constitute the generators of the
geometrical symmetry group at the aphelia and perihelia points .Comment: 8 pages, 1 fi
Superconducting properties of RuSr2GdCu2O8 studied by SQUID magnetometry
For polycrystalline RuSr2GdCu2O8 (Ru-1212), distinct peaks have been reported
in d.c. magnetization in the superconducting state of the sample. Sr2GdRuO6
(Sr-2116), the precursor for the preparation of Ru-1212, shows similar peaks in
the same temperature regime. Based on measurements performed on both bulk and
powdered samples of Ru-1212 and Sr-2116, we exclude the possibility, that the
observed behavior of the magnetization of Ru-1212 is due to Sr-2116 impurities.
The effect is related to the superconductivity of Ru-1212, but it is not an
intrinsic property of this compound. We provide evidence that the observation
of magnetization peaks in the superconducting state of Ru-1212 is due to flux
motion generated by the movement of the sample in an inhomogeneous field,
during the measurement in the SQUID magnetometer. We propose several tests,
that help to decide, whether the features observed in a SQUID magnetization
measurement of Ru-1212 represent a property of the compound or not.Comment: 22 pages, 9 figure
Kinetic energy driven superconductivity in doped cuprates
Within the t-J model, the mechanism of superconductivity in doped cuprates is
studied based on the partial charge-spin separation fermion-spin theory. It is
shown that dressed holons interact occurring directly through the kinetic
energy by exchanging dressed spinon excitations, leading to a net attractive
force between dressed holons, then the electron Cooper pairs originating from
the dressed holon pairing state are due to the charge-spin recombination, and
their condensation reveals the superconducting ground-state. The electron
superconducting transition temperature is determined by the dressed holon pair
transition temperature, and is proportional to the concentration of doped holes
in the underdoped regime. With the common form of the electron Cooper pair, we
also show that there is a coexistence of the electron Cooper pair and
antiferromagnetic short-range correlation, and hence the antiferromagnetic
short-range fluctuation can persist into the superconducting state. Our results
are qualitatively consistent with experiments.Comment: 6 pages, Revtex, two figures are included, corrected typo
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