2,123 research outputs found
Comparison of the simulation and experimental fatigue crack behaviors in the aluminum alloy HS6061-T6
AbstractThis work deals with rotating bending fatigue tests on aluminum alloy HS6061-T6. Results have been obtained for two sizes of narrow section diameter for specimens with one hole. Results show that fatigue endurance is reduced in the case of the hole. In order to explain this behavior, numerical analysis by FEM were carried out to determine the stress concentrations for the two types of specimens. It is found that the important factor affects fatigue life is the narrow section diameter of the specimens, and the maximum damage occurs in the outer part of the specimen at the first stages of loading, however, it moves toward the center of the bar under uniaxial loading. The number of cycles to failure predicted numerically is higher than the experimental one. This difference is attributed mainly to an upper stage of fatigue crack growth, particularly, the interaction between fatigue crack growth and growth that can not be accounted for in the numerical model
Numerical solution to the hermitian Yang-Mills equation on the Fermat quintic
We develop an iterative method for finding solutions to the hermitian
Yang-Mills equation on stable holomorphic vector bundles, following ideas
recently developed by Donaldson. As illustrations, we construct numerically the
hermitian Einstein metrics on the tangent bundle and a rank three vector bundle
on P^2. In addition, we find a hermitian Yang-Mills connection on a stable rank
three vector bundle on the Fermat quintic.Comment: 25 pages, 2 figure
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Long-range eye tracking: A feasibility study
The design considerations for a long-range Purkinje effects based video tracking system using current technology is presented. Past work, current experiments, and future directions are thoroughly discussed, with an emphasis on digital signal processing techniques and obstacles. It has been determined that while a robust, efficient, long-range, and non-invasive eye tracking system will be difficult to develop, such as a project is indeed feasible
Dipolar Bose-Einstein condensate soliton on a two-dimensional optical lattice
Using a three-dimensional mean-field model we study one-dimensional dipolar
Bose-Einstein condensate (BEC) solitons on a weak two-dimensional (2D) square
and triangular optical lattice (OL) potentials placed perpendicular to the
polarization direction. The stabilization against collapse and expansion of
these solitons for a fixed dipolar interaction and a fixed number of atoms is
possible for short-range atomic interaction lying between two critical limits.
The solitons collapse below the lower limit and escapes to infinity above the
upper limit. One can also stabilize identical tiny BEC solitons arranged on the
2D square OL sites forming a stable 2D array of interacting droplets when the
OL sites are filled with a filling factor of 1/2 or less. Such an array is
unstable when the filling factor is made more than 1/2 by occupying two
adjacent sites of OL. These stable 2D arrays of dipolar superfluid BEC solitons
are quite similar to the recently studied dipolar Mott insulator states on 2D
lattice in the Bose-Hubbard model by Capogrosso-Sansone et al. [B.
Capogrosso-Sansone, C. Trefzger, M. Lewenstein, P. Zoller, G. Pupillo, Phys.
Rev. Lett. 104 (2010) 125301].Comment: 8 pages, 5 figures and 2 table
Bergman Kernel from Path Integral
We rederive the expansion of the Bergman kernel on Kahler manifolds developed
by Tian, Yau, Zelditch, Lu and Catlin, using path integral and perturbation
theory, and generalize it to supersymmetric quantum mechanics. One physics
interpretation of this result is as an expansion of the projector of wave
functions on the lowest Landau level, in the special case that the magnetic
field is proportional to the Kahler form. This is relevant for the quantum Hall
effect in curved space, and for its higher dimensional generalizations. Other
applications include the theory of coherent states, the study of balanced
metrics, noncommutative field theory, and a conjecture on metrics in black hole
backgrounds. We give a short overview of these various topics. From a
conceptual point of view, this expansion is noteworthy as it is a geometric
expansion, somewhat similar to the DeWitt-Seeley-Gilkey et al short time
expansion for the heat kernel, but in this case describing the long time limit,
without depending on supersymmetry.Comment: 27 page
Evidence for and phases in the morphotropic phase boundary region of : A Rietveld study
We present here the results of the room temperature dielectric constant
measurements and Rietveld analysis of the powder x-ray diffraction data on
(PMN-PT) in the composition range
to show that the morphotropic phase boundary (MPB)
region contains two monoclinic phases with space groups Cm (or type) and
Pm (or type) stable in the composition ranges and
, respectively. The structure of PMN-PT in the
composition ranges 0.26, and is found to be
rhombohedral (R3m) and tetragonal (P4mm), respectively. These results are
compared with the predictions of Vanderbilt & Cohen's theory.Comment: 20 pages, 11 pdf figure
Chaotic Repellers in Antiferromagnetic Ising Model
For the first time we present the consideration of the antiferromagnetic
Ising model in case of fully developed chaos and obtain the exact connection
between this model and chaotic repellers. We describe the chaotic properties of
this statistical mechanical system via the invariants characterizing a fractal
set and show that in chaotic region it displays phase transition at {\it
positive} "temperature" . We obtain the density of the
invariant measure on the chaotic repeller.Comment: LaTeX file, 10 pages, 4 PS figurs upon reques
Wavefunction topology of two-dimensional time-reversal symmetric superconductors
We discuss the topology of the wavefunctions of two-dimensional time-reversal
symmetric superconductors. We consider (a) the planar state, (b) a system with
broken up-down reflection symmetry, and (c) a system with general spin-orbit
interaction. We show explicitly how the relative sign of the order parameter on
the two Fermi surfaces affects this topology, and clarify the meaning of the
classification for these topological states.Comment: only the Introduction has been modified from v
TNF-α and TNF-β Gene Polymorphism in Saudi Rheumatoid Arthritis Patients
Background Tumor necrosis factor (TNF)-α and -β are cytokines with a wide range of inflammatory, apoptotic and immunomodulatory activities. TNF-α promoter –308 G < A polymorphism has been reported to be associated with rheumatoid arthritis (RA) with inconsistent results. Objective The aim of this study is to elucidate a possible association of TNF-α (G–308A) and TNF-β (A+252G) polymorphisms with the susceptibility of RA in Saudi patients. Patients and Methods This case control study consisted of 232 Saudi subjects including 106 RA patients and 126 matched controls. Genomic DNA was extracted using QIAamp R DNA mini kit (Qiagen CA, USA). TNF-α and TNF-β genes were amplified using Arms primers. Results The frequencies of TNF-α (–308) allele G and genotype GG were significantly higher in RA patients as compared to controls while allele A and genotype AA were predominant in control group. On the other hand the frequency of TNF-β (+252) GG and AA genotypes were significantly higher in RA patients as compared to controls while GA genotype was predominant in controls. It was inferred that genotype GG positive individuals at position –308 of TNF-α were susceptible to RA while genotype AA might has a protective effect on RA susceptibility in Saudis. Whereas GG and AA genotype of TNF-β at +252 position might exert additive susceptibility to RA and GA might be refractory. However, there was no significant association between duration of morning stiffness, RF positivity and number of joints involved and distribution of alleles/genotypes of TNF-α (–308) or TNF-β (+252) polymorphism. It may be concluded that the TNF-α (–308) and TNF-β (+252) polymorphisms might influence the susceptibility to RA in Saudi population. These results might have prognostic value for future clinical observations
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