784 research outputs found
Nonassociative differential geometry and gravity with non-geometric fluxes
We systematically develop the metric aspects of nonassociative differential
geometry tailored to the parabolic phase space model of constant locally
non-geometric closed string vacua, and use it to construct preliminary steps
towards a nonassociative theory of gravity on spacetime. We obtain explicit
expressions for the torsion, curvature, Ricci tensor and Levi-Civita connection
in nonassociative Riemannian geometry on phase space, and write down Einstein
field equations. We apply this formalism to construct R-flux corrections to the
Ricci tensor on spacetime, and comment on the potential implications of these
structures in non-geometric string theory and double field theory.Comment: 50 pages; v2: corrected comparison of curvature to ref. [14]; v3:
clarifying comments added; Final version to be published in JHE
The flux ratio of the [OIII] 5007,4959 lines in AGN: Comparison with theoretical calculations
By taking into account relativistic corrections to the magnetic dipole
operator, the theoretical [OIII] 5006.843/4958.511 line intensity ratio of 2.98
is obtained. In order to check this new value using AGN spectra we present the
measurements of the flux ratio of the [OIII] 4959,5007 emission lines for a
sample of 62 AGN, obtained from the Sloan Digital Sky Survey (SDSS) Database
and from published observations. We select only high signal-to-noise ratio
spectra for which the line shapes of the [OIII] 4959,5007 lines are the same.
We obtained an averaged flux ratio of 2.993 +/- 0.014, which is in a good
agreement with the theoretical one.Comment: Accepted for publication in the MNRA
A Method for Gradient Enhancement of Continuum Damage Models
A method for the regularization of continuum damage material models based on gradient-type enhancement of the free-energy functional is presented. Direct introduction of the gradient of the damage variable would require C1 interpolation of the displacements, which is a complicated task to achieve with quadrilateral elements. Therefore a new variable field is introduced, which makes the model non-local in nature, while preserving C0 interpolation order of the variables at the same time. The strategy is formulated as a pure minimization problem, therefore the LBB-condition does not apply in this case. However, we still take the interpolation of the displacement field one order higher than the interpolation of the field of additional (non-local) variables. That leads to increased accuracy and removes the post-processing step necessary to obtain consistent results in the case of equal interpolation order. Several numerical examples which show the performance of the proposed gradient enhancement are presented. The pathological mesh dependence of the damage model is efficiently removed, together with the difficulties of numerical calculations in the softening range. Calculations predict a development of the damage variable which is mesh-objective for fixed internal material length
Jordanian Quantum Deformations of D=4 Anti-de-Sitter and Poincare Superalgebras
We consider a superextension of the extended Jordanian twist, describing
nonstandard quantization of anti-de-Sitter () superalgebra in
the form of Hopf superalgebra. The super-Jordanian twisting function and
corresponding basic coproduct formulae for the generators of are
given in explicit form. The nonlinear transformation of the classical
superalgebra basis not modifying the defining algebraic relations but
simplifying coproducts and antipodes is proposed. Our physical application is
to interpret the new super-Jordanian deformation of superalgebra as
deformed D=4 supersymmetries. Subsequently we perform suitable
contraction of quantum Jordanian superalgebra and obtain new
-deformation of D=4 Poincare superalgebra, with the bosonic sector
describing the light cone -deformation of Poincare symmetries.Comment: LaTeX,13 pages, comments and references added, to be published in
Eur.Phys.J.
On the Schwarzschild-de Sitter metric of nonlocal de Sitter gravity
Earlier constructed a simple nonlocal de Sitter gravity model has a
cosmological solution in a very good agreement with astronomical observations.
In this paper, we continue the investigation of the nonlocal de Sitter model of
gravity, focusing on finding an appropriate solution for the Schwarzschild-de
Sitter metric. We succeeded to solve the equations of motion in a certain
approximation. The obtained approximate solution is of particular interest for
examining the possible role of non-local de Sitter gravity in describing the
effects in galactic dynamics that are usually attributed to dark matter.Comment: 10 page
High-resolution FUSE and HST ultraviolet spectroscopy of the white dwarf central star of Sh 2-216
LS V +4621 is the DAO-type central star of the planetary nebula Sh 2-216. We
perform a comprehensive spectral analysis of high-resolution, high-S/N
ultraviolet observations obtained with FUSE and STIS aboard the HST as well as
the optical spectrum of LS V +4621 by means of state-of-the-art NLTE
model-atmosphere techniques in order to compare its photospheric properties to
theoretical predictions from stellar evolution theory as well as from diffusion
calculations.
From the N IV - NV, O IV - O VI, Si IV - Si V, and Fe V - Fe VII ionization
equilibria, we determined an effective temperature of 95 +/- 2 kK with high
precision. The surface gravity is log g = 6.9 +/- 0.2. An unexplained
discrepancy appears between the spectroscopic distance d = 224 +46/-58 pc and
the parallax distance d = 129 +6/-5 pc of LS V +4621. For the first time, we
have identified Mg IV and Ar VI absorption lines in the spectrum of a
hydrogen-rich central star and determined the Mg and Ar abundances as well as
the individual abundances of iron-group elements (Cr, Mn, Fe, Co, and Ni). With
the realistic treatment of metal opacities up to the iron group in the
model-atmosphere calculations, the so-called Balmer-line problem (found in
models that neglect metal-line blanketing) vanishes.
Spectral analysis by means of NLTE model atmospheres has presently arrived at
a high level of sophistication, which is now hampered largely by the lack of
reliable atomic data and accurate line-broadening tables. Strong efforts should
be made to improve upon this situation.Comment: 13 pages, 20 figure
A Dynamical 2-dimensional Fuzzy Space
The noncommutative extension of a dynamical 2-dimensional space-time is given
and some of its properties discussed. Wick rotation to euclidean signature
yields a surface which has as commutative limit the doughnut but in a singular
limit in which the radius of the hole tends to zero.Comment: 13 pages, accepted for publication in Phys. Lett.
Body Measures in Endangered Domestic Balkan Donkey Breed
Information regarding morphology of endangered autochthonous donkey breed in Serbia is insufficient. The aim of the study was to establish 18 morphometric values for the Balkan donkey breed and to explore possible age dependence of the parameters tested. In addition, inter-breed similarity of morphometric parameters was assessed by comparing the data obtained for the Balkan donkey with available morphometric measurements of several previously characterized donkey breeds. The study population included 74 donkeys, divided in two age groups (group A ≤ 3 years; group B > 3 years). Significant morphometric differences (p<0.05) in body length, head length, chest circumference and body weight were found between two age groups. Significant differences in morphological parameters were revealed among the Balkan donkey and other donkey breeds (Catalonian, Croatian and Albanian). However, the smallest distance was between the Balkan donkey and Albanian donkeys as demonstrated by the results of cluster analysis. The results of morphometric analyses showed consistency of the obtained values within the breed, and diversity as compared to other donkey breeds, and, thus, could be taken as referent for the Domestic Balkan donkey. The information gained through this comprehensive morphometric characterization of the Balkan donkey breed provides a basis for conservation and development of the breed standard
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