86 research outputs found
Resolving Exceptional Configurations
In lattice QCD with Wilson fermions, exceptional configurations arise in the
quenched approximation at small quark mass. The origin of these large
previously uncontrolled lattice artifacts is identified. A simple well-defined
procedure (MQA) is presented which removes the artifacts while preserving the
correct continuum limit.Comment: Talk presented by E. Eichten at Lattice 97, Edinburgh(UK), July97. 6
pages, LaTeX, 1 table, 5 figure
30S Beam Development and X-ray Bursts
Over the past three years, we have worked on developing a well-characterized
30S radioactive beam to be used in a future experiment aiming to directly
measure the 30S(alpha,p) stellar reaction rate within the Gamow window of Type
I X-ray bursts. The importance of the 30S(alpha,p) reaction to X-ray bursts is
discussed. Given the astrophysical motivation, the successful results of and
challenges involved in the production of a low-energy 30S beam are detailed.
Finally, an overview of our future plans regarding this on-going project are
presented.Comment: 7 pages, 2 figures, 5th European Summer School on Experimental
Nuclear Astrophysics, Santa Tecla, Sicily, September 200
Quenched Chiral Artifacts for Wilson-Dirac Fermions
We examine artifacts associated with the chiral symmetry breaking induced
through the use of Wilson-Dirac fermions in lattice Monte Carlo computations.
For light quark masses, the conventional quenched theory can not be defined
using direct Monte Carlo methods due to the existence of nonintegrable poles in
physical quantities. These poles are associated with the real eigenvalue
spectrum of the Wilson-Dirac operator. We show how this singularity structure
can be observed in the analysis of both QED in two dimensions and QCD in four
dimensions.Comment: 32 pages (Latex) including 13 figures (EPS
On the low fermionic eigenmode dominance in QCD on the lattice
We demonstrate the utility of a spectral approximation to fermion loop
operators using low-lying eigenmodes of the hermitian Dirac-Wilson matrix, Q.
The investigation is based on a total of 400 full QCD vacuum configurations,
with two degenerate flavors of dynamical Wilson fermions at beta =5.6, at two
different sea quark masses. The spectral approach is highly competitive for
accessing both topological charge and disconnected diagrams, on large lattices
and small quark masses. We propose suitable partial summation techniques that
provide sufficient saturation for estimating Tr Q^{-1}, which is related to the
topological charge. In the effective mass plot of the eta' meson we achieved a
consistent early plateau formation, by ground state projecting the connected
piece of its propagator.Comment: 15 pages, 25 figures, citations adde
Elasto-Plastic Stress Analysis in Rotating Disks and Pressure Vessels Made of Functionally Graded Materials
Abstract A new elastio-plastic stress solution in axisymmetric problems (rotating disk, cylindrical and spherical vessel) is presented. The rotating disk (cylindrical and spherical vessel) was made of a ceramic/metal functionally graded material, i.e. a particle-reinforced composite. It was assumed that the material's plastic deformation follows an isotropic strain-hardening rule based on the von-Mises yield criterion. The mechanical properties of the graded material were modeled by the modified rule of mixtures. By assuming small strains, Hencky's stress-strain relation was used to obtain the governing differential equations for the plastic region. A numerical method for solving those differential equations was then proposed that enabled the prediction of stress state within the structure. Selected finite element results were also presented to establish supporting evidence for the validation of the proposed approach
Flexural wave propagation in fluid-conveying carbon nanotubes with system uncertainties
Atomistic Simulation of Tension-Compression Asymmetry in Defect-Free Nickel Nanocrystals
In this paper the mechanical properties of a metallic nanowire are calculated using molecular dynamics (MD) method. Initially, a solid FCC metallic nanowire is modeled in nano-scale. The mechanical behavior of specimen under uniaxial tension loading is simulated. In this stage, the mechanical properties of material such as yield stress, strain and Young’s modulus are calculated and the deformed shape of uniaxial loading is investigated. The effects of strain rate and volume/area ratio on the mechanical properties are discussed. Also, the complementary results are presented for mechanical behavior of nickel nanowires in compression using molecular dynamic method. Furthermore, the effects of strain rate and volume/area ratio on the compressive yield stress are studied and compared with the results of tensile test. In this stage, by introducing the ration of tensile yield stress and compressive yield stress ( σ σ ), a general relation between volume/area ratio and tensile/ compressive yield stress is obtained
Atomistic Simulation of Tension-Compression Asymmetry in Defect-Free Nickel Nanocrystals
In this paper the mechanical properties of a metallic nanowire are calculated using molecular dynamics (MD) method. Initially, a solid FCC metallic nanowire is modeled in nano-scale. The mechanical behavior of specimen under uniaxial tension loading is simulated. In this stage, the mechanical properties of material such as yield stress, strain and Young’s modulus are calculated and the deformed shape of uniaxial loading is investigated. The effects of strain rate and volume/area ratio on the mechanical properties are discussed. Also, the complementary results are presented for mechanical behavior of nickel nanowires in compression using molecular dynamic method. Furthermore, the effects of strain rate and volume/area ratio on the compressive yield stress are studied and compared with the results of tensile test. In this stage, by introducing the ration of tensile yield stress and compressive yield stress ( σ σ ), a general relation between volume/area ratio and tensile/ compressive yield stress is obtained
In silico structural, functional and pathogenicity evaluation of a novel mutation: An overview of HSD3B2 gene mutations
Mutations of 3 beta hydroxysteroid dehydrogenase type II (HSD3B2) gene result in different clinical consequences. We explain a patient who demonstrated a salt wasting form of 3 beta HSD deficiency in infancy. Signs of hyponatremia and hyperkalemia were recognized in the infant with ambiguous genitalia and perineal hypospadias. The 46,XY male was genotyped by direct sequencing of HSD3B2 gene. Steroid profiles showed elevated concentration of 17 hydroxyprogesterone, and decrease in concentration of cortisol, and testosterone. Dehydroepiandrotone (DHEA) to androstenedione ratio had 6 fold increases. Direct sequencing of the patient revealed homozygous missense A82P mutation in exon 3. This mutation was confirmed by segregation analysis of the parents. Bioinformatic tools were used for in silico structural and functional analyses. Also, the pathological effect of the mutation was validated by different software. Alanine is a conserved amino acid in the membrane binding domain of the enzyme and proline substitution was predicted to destabilize the protein. This report may highlight the importance of the screening programs of the disorder in Iran. (C) 2012 Elsevier B.V. All rights reserved
Utilization of wheat straw for fungal phytase production
Purpose Wheat straw is an agricultural waste which can be used as a cost effective animal feed. However, high hemicellulose and phytic acid content in wheat straw prevents it as a primary feed choice. Utilization of wheat straw in solid-state fermentation may result in wheat straw valorization and enzyme production. In this study, phytase production in solid-state fermentation of wheat straw using Aspergillus ficuum and valorization of wheat straw were evaluated. Methods A two-step experimental design procedure was employed for screening and optimization of influencing factors on phytase production. Effects of different nutritional and environmental factors were investigated by one factor at the time method (OFATM). To reach higher amounts of phytase, response surface methodology (RSM) was employed to optimize phytase production as a function of three of the most effective factors. Results Optimization of the significant parameters resulted in an increase in the phytase activity from 0.74 ± 0.12 to a maximum of 16.46 ± 0.56 Units per gram dry substrate (U gds−1). The high degree of the fungal phytase activity on wheat straw resulted in the decrease in phytic acid content by 57.4%, as compared to the untreated sample. Scanning electron microscopy (SEM) and FTIR structural analysis showed intensive fungal growth on wheat straw, and partial removal of hemicelluloses, lignin and phytic acid. Conclusion The study demonstrated the feasibility of wheat straw utilization in solid-state fermentation using Aspergillus ficuum toward the production of phytase and valorization of wheat straw as an animal feed
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