4,095 research outputs found
A relation between moduli space of D-branes on orbifolds and Ising model
We study D-branes transverse to an abelian orbifold C^3/Z_n Z_n. The moduli
space of the gauge theory on the D-branes is analyzed by combinatorial
calculation based on toric geometry. It is shown that the calculation is
related to a problemto count the number of ground states of an
antiferromagnetic Ising model. The lattice on which the Ising model is defined
is a triangular one defined on the McKay quiver of the orbifold.Comment: 20 pages, 13 figure
High-spin structures as the probes of proton-neutron pairing
Rotating nuclei in the mass region have been studied within
the framework of isovector mean field theory. Available data is well and
systematically described in the calculations. The present study supports the
presence of strong isovector pair field at low spin, which is, however,
destroyed at high spin. No clear evidence for the existence of the isoscalar
pairing has been found.Comment: Invited talk presented at the XIII Nuclear Physics Workshop,
Kazimierz Dolny, Sept. 27 - Oct. 1, Poland; submitted to International
Journal of Modern Physics
Stepwise Projection: Toward Brane Setups for Generic Orbifold Singularities
The construction of brane setups for the exceptional series E6,E7,E8 of SU(2)
orbifolds remains an ever-haunting conundrum. Motivated by techniques in some
works by Muto on non-Abelian SU(3) orbifolds, we here provide an algorithmic
outlook, a method which we call stepwise projection, that may shed some light
on this puzzle. We exemplify this method, consisting of transformation rules
for obtaining complex quivers and brane setups from more elementary ones, to
the cases of the D-series and E6 finite subgroups of SU(2). Furthermore, we
demonstrate the generality of the stepwise procedure by appealing to Frobenius'
theory of Induced Representations. Our algorithm suggests the existence of
generalisations of the orientifold plane in string theory.Comment: 22 pages, 3 figure
Analysis of the contributions of three-body potentials in the equation of state of 4He
The effect of three-body interatomic contributions in the equation of state
of 4He are investigated. A recent two-body potential together with the Cohen
and Murrell (Chem. Phys. Lett. 260, 371 (1996)) three-body potential are
applied to describe bulk helium. The triple-dipole dispersion and exchange
energies are evaluated subjected only to statistical uncertainties. An
extension of the diffusion Monte Carlo method is applied in order to compute
very small energies differences. The results show how the three-body
contributions affects the ground-state energy, the equilibrium, melting and
freezing densities.Comment: 18 pages, 3 figures, 4 table
Precise measurements of electron and hole g-factors of single quantum dots by using nuclear field
We demonstrated the cancellation of the external magnetic field by the
nuclear field at one edge of the nuclear polarization bistability in single
InAlAs quantum dots. The cancellation for the electron Zeeman splitting gives
the precise value of the hole g-factor. By combining with the exciton g-factor
that is obtained from the Zeeman splitting for linearly polarized excitation,
the magnitude and sign of the electron and hole g-factors in the growth
direction are evaluated.Comment: 3 pages, 2 figure
Understanding molecular representations in machine learning: The role of uniqueness and target similarity
The predictive accuracy of Machine Learning (ML) models of molecular
properties depends on the choice of the molecular representation. Based on the
postulates of quantum mechanics, we introduce a hierarchy of representations
which meet uniqueness and target similarity criteria. To systematically control
target similarity, we rely on interatomic many body expansions, as implemented
in universal force-fields, including Bonding, Angular, and higher order terms
(BA). Addition of higher order contributions systematically increases
similarity to the true potential energy and predictive accuracy of the
resulting ML models. We report numerical evidence for the performance of BAML
models trained on molecular properties pre-calculated at electron-correlated
and density functional theory level of theory for thousands of small organic
molecules. Properties studied include enthalpies and free energies of
atomization, heatcapacity, zero-point vibrational energies, dipole-moment,
polarizability, HOMO/LUMO energies and gap, ionization potential, electron
affinity, and electronic excitations. After training, BAML predicts energies or
electronic properties of out-of-sample molecules with unprecedented accuracy
and speed
The co-pyrolysis of flame retarded high impact polystyrene and polyolefins
The co-pyrolysis of brominated high impact polystyrene (Br-HIPS) with polyolefins using a fixed bed reactor has been investigated, in particular, the effect that different types brominated aryl compounds and antimony trioxide have on the pyrolysis products. The pyrolysis products were analysed using FT-IR, GC-FID, GC-MS, and GC-ECD. Liquid chromatography was used to separate the oils/waxes so that a more detailed analysis of the aliphatic, aromatic, and polar fractions could be carried out. It was found that interaction occurs between Br-HIPS and polyolefins during co-pyrolysis and that the presence of antimony trioxide influences the pyrolysis mass balance. Analysis of the Br-HIPS + polyolefin co-pyrolysis products showed that the presence of polyolefins led to an increase in the concentration of alkyl and vinyl mono-substituted benzene rings in the pyrolysis oil/wax resulting from Br-HIPS pyrolysis. The presence of Br-HIPS also had an impact on the oil/wax products of polyolefin pyrolysis, particularly on the polyethylene oil/wax composition which converted from being a mixture of 1-alkenes and n-alkanes to mostly n-alkanes. Antimony trioxide had very little impact on the polyolefin wax/oil composition but it did suppress the formation of styrene and alpha-methyl styrene and increase the formation of ethylbenzene and cumene during the pyrolysis of the Br-HIPS
Effect of doping and oxygen vacancies on the octahedral tilt transitions in the BaCeO3 perovskite
We present a systematic study of the effect of Y doping and hydration level
on the structural transformations of BaCeO3 based on anelastic spectroscopy
experiments. The temperature of the intermediate transformation between
rhombohedral and orthorhombic Imma phases rises with increasing the molar
fraction x of Y roughly as (500 K)x in the hydrated state, and is depressed of
more than twice that amount after complete dehydration. This is explained in
terms of the effect of doping on the average (Ce/Y)-O and Ba-O bond lengths,
and of lattice relaxation from O vacancies. The different behavior of the
transition to the lower temperature Pnma orthorhombic phase is tentatively
explained in terms of progressive flattening of the effective shape of the OH
ion and ordering of the O vacancies during cooling.Comment: 8 pages, 5 figure
Shell Model Study of the Double Beta Decays of Ge, Se and Xe
The lifetimes for the double beta decays of Ge, Se and
Xe are calculated using very large shell model spaces. The two neutrino
matrix elements obtained are in good agreement with the present experimental
data. For eV we predict the following upper bounds to the
half-lives for the neutrinoless mode: , and . These results are the first from a new generation of Shell
Model calculations reaching O(10) dimensions
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