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

Quenched QCD with domain-wall fermions on coarse lattices

We investigate the existence of chiral zero modes at a^{-1} \simeq 1 GeV in quenched domain-wall QCD. Simulations are carried out for the plaquette and an RG-improved gauge actions on a 12^3x24xN_s lattice with N_s=10-50. We find that the pion mass in the chiral limit remains non-vanishing as N_s\to\infty for both gauge actions. Possible origins of this non-vanishing pion mass are discussed.Comment: LATTICE99(chiral fermions), 3 pages, 6 ps figures, LaTex, espcrc2.st

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

Effect of Mono and Di-rhamnolipids on Biofilms Pre-formed by Bacillus subtilis BBK006.

Different microbial inhibition strategies based on the planktonic bacterial physiology have been known to have limited efficacy on the growth of biofilms communities. This problem can be exacerbated by the emergence of increasingly resistant clinical strains. Biosurfactants have merited renewed interest in both clinical and hygienic sectors due to their potential to disperse microbial biofilms. In this work, we explore the aspects of Bacillus subtilis BBK006 biofilms and examine the contribution of biologically derived surface-active agents (rhamnolipids) to the disruption or inhibition of microbial biofilms produced by Bacillus subtilis BBK006. The ability of mono-rhamnolipids (Rha-C10-C10) produced by Pseudomonas aeruginosa ATCC 9027 and the di-rhamnolipids (Rha-Rha-C14-C14) produced by Burkholderia thailandensis E264, and phosphate-buffered saline to disrupt biofilm of Bacillus subtilis BBK006 was evaluated. The biofilm produced by Bacillus subtilis BBK006 was more sensitive to the di-rhamnolipids (0.4 g/L) produced by Burkholderia thailandensis than the mono-rhamnolipids (0.4 g/L) produced by Pseudomonas aeruginosa ATCC 9027. Rhamnolipids are biologically produced compounds safe for human use. This makes them ideal candidates for use in new generations of bacterial dispersal agents and useful for use as adjuvants for existing microbial suppression or eradication strategies

Nanoscale Simulations of Bauschinger Effects on a Nickel Nanowire

In this paper, the Bauschinger effect on a nickel nanowire is studied implementing molecular dynamics simulations in nanoscale. The inter-atomic interactions are represented by employing embedded-atom potential. Initially, the stress–strain curves for tensile and compressive loading are simulated by applying suitable periodic boundary conditions on an infinitely long nanowire. The generated results demonstrate that the yield strength in compression is lower than the tensile yield strength. At the second stage, the tension-followed-by-compression process is applied to the specimen at a predetermined strain rate. It is observed that the resulted yield strength in the reloading or reverse loading is substantially lower than the compressive yield stress in the original direction, a phenomena known as the Bauschinger effect. The reverse loading process is then performed at different strain levels after yield to study the Bauschinger effect variations. To clarify the Bauschinger effects on Ni nanowire, the introduced Bauschinger stress parameter (BP) is employed in the analysis

Nanoscale Simulations of Bauschinger Effects on a Nickel Nanowire

In this paper, the Bauschinger effect on a nickel nanowire is studied implementing molecular dynamics simulations in nanoscale. The inter-atomic interactions are represented by employing embedded-atom potential. Initially, the stress–strain curves for tensile and compressive loading are simulated by applying suitable periodic boundary conditions on an infinitely long nanowire. The generated results demonstrate that the yield strength in compression is lower than the tensile yield strength. At the second stage, the tension-followed-by-compression process is applied to the specimen at a predetermined strain rate. It is observed that the resulted yield strength in the reloading or reverse loading is substantially lower than the compressive yield stress in the original direction, a phenomena known as the Bauschinger effect. The reverse loading process is then performed at different strain levels after yield to study the Bauschinger effect variations. To clarify the Bauschinger effects on Ni nanowire, the introduced Bauschinger stress parameter (BP) is employed in the analysis

Nickel Nanowires Under Uniaxial Loads: A Molecular Dynamics Simulation Study

The mechanical properties of nickel nanowire at different temperatures are studied using molecular dynamics (MD) simulations. The inter-atomic interactions are represented by employing embedded-atom potential. In the case of uniaxial loading, the stress–strain curve at different strain rates is simulated. The effects of volume/surface ratio and temperature on mechanical properties of nickel nanowire are discussed. In particular, the loading–unloading process is modeled and the effect of unloading process on the stress–strain curve in the plastic region is investigated. Furthermore, the mechanical characterization in compression loading is carried out and the mechanism of deformation is elucidated based on the present model. The results of compression modeling show that the obtained yield stress is lower than the computed tensile yield stress

Mechanical Properties of Silicon-Germanium Nanotubes under Tensile and Compressive Loadings

The mechanical response of single-walled zigzag silicon-germanium nanotubes (SiGeNTs) under tensile and compressive loadings is modeled via atomistic simulation method. The inter-atomic forces are described using the Tersoff\u27s empirical bond-order potential. Initially, the comparative simulations of the bond lengths are presented and quite accurate behavior of the model is demonstrated. Afterwards, the results of the total strain energy are used to establish an expression for evaluating Young\u27s modulus of the nanotubes. Since different choices of wall thickness significantly affect the calculation of Young\u27s modulus, the effective modulus of elasticity is introduced. This procedure provides an accurate means for predicting the elastic modulus of the nanotubes. Numerical simulations were also performed to investigate the buckling behavior of SiGeNTs. Dependence of the critical buckling load on diameter and length of the nanotubes is shown. Finally, the effect of temperature on the axial compressive load of SiGeNTs is also discussed