752 research outputs found
Continuous deformations of the Grover walk preserving localization
The three-state Grover walk on a line exhibits the localization effect
characterized by a non-vanishing probability of the particle to stay at the
origin. We present two continuous deformations of the Grover walk which
preserve its localization nature. The resulting quantum walks differ in the
rate at which they spread through the lattice. The velocities of the left and
right-traveling probability peaks are given by the maximum of the group
velocity. We find the explicit form of peak velocities in dependence on the
coin parameter. Our results show that localization of the quantum walk is not a
singular property of an isolated coin operator but can be found for entire
families of coins
Chemical composition and antimicrobial activity of propolis collected from some localities of Western Algeria
The chemical analysis and antibacterial activity of propolis collected from some parts of Western Algeria were investigated. The ethanolic extracts of propolis (EEP) were evaluated for further investigation. The major constituents in EEP were identified by high-performance liquid chromatography (HPLC) analysis. All EEP samples were active against Gram positive bacteria (Staphylococcus aureus, Bacillus subtilis, Bacillus cereus), but no activity was found against Gram negative bacteria (Pseudomonas aeruginosa, Escherichia coli). The mean diameters of growth inhibition of the EEP ranged between 8.05 and 21.4 mm. The propolis extract obtained from Sidi bel Abbés (SFS-SBA) was more active than other samples as well as showed unique HPLC profile. These results support the idea that propolis can be a promising natural food preservative in food industry and alternative candidate for management of bacterial infections caused by drug-resistant microorganisms
Study of the one-dimensional off-lattice hot-monomer reaction model
Hot monomers are particles having a transient mobility (a ballistic flight)
prior to being definitely absorbed on a surface. After arriving at a surface,
the excess energy coming from the kinetic energy in the gas phase is dissipated
through degrees of freedom parallel to the surface plane. In this paper we
study the hot monomer-monomer adsorption-reaction process on a continuum
(off-lattice) one-dimensional space by means of Monte Carlo simulations. The
system exhibits second-order irreversible phase transition between a reactive
and saturated (absorbing) phases which belong to the directed percolation (DP)
universality class. This result is interpreted by means of a coarse-grained
Langevin description which allows as to extend the DP conjecture to transitions
occurring in continuous media.Comment: 13 pages, 5 figures, final version to appear in J. Phys.
Direct Calculation of Spin-Stiffness for Spin-1/2 Heisenberg Models
The spin-stiffness of frustrated spin-1/2 Heisenberg models in one and two
dimensions is computed for the first time by exact diagonalizations on small
clusters that implement spin-dependent twisted boundary conditions. Finite-size
extrapolation to the thermodynamic limit yields a value of for
the spin-stiffness of the unfrustrated planar antiferromagnet. We also present
a general discussion of the linear-response theory for spin-twists, which
ultimately leads to the moment sum-rule.Comment: 11 pgs, TeX, LA-UR-94-94 (to be published in Phys. Rev. B
Branching annihilating random walks with parity conservation on a square lattice
Using Monte Carlo simulations we have studied the transition from an "active"
steady state to an absorbing "inactive" state for two versions of the branching
annihilating random walks with parity conservation on a square lattice. In the
first model the randomly walking particles annihilate when they meet and the
branching process creates two additional particles; in the second case we
distinguish particles and antiparticles created and annihilated in pairs. Quite
distinct critical behavior is found in the two cases, raising the question of
what determines universality in this kind of systems.Comment: 4 pages, 4 EPS figures include
Three-dimensional flux states as a model for the pseudogap phase of transition metal oxides
We propose that the pseudogap state observed in the transition metal oxides
can be explained by a three-dimensional flux state, which exhibits
spontaneously generated currents in its ground state due to electron-electron
correlations. We compare the energy of the flux state to other classes of mean
field states, and find that it is stabilized over a wide range of and
. The signature of the state will be peaks in the neutron diffraction
spectra, the location and intensity of which are presented. The dependence of
the pseudogap in the optical conductivity is calculated based on the parameters
in the model.Comment: submitted to Phys. Rev. B on January 8, 200
Damage spreading for one-dimensional, non-equilibrium models with parity conserving phase transitions
The damage spreading (DS) transitions of two one-dimensional stochastic
cellular automata suggested by Grassberger (A and B) and the kinetic Ising
model of Menyh\'ard (NEKIM) have been investigated on the level of kinks and
spins. On the level of spins the parity conservation is not satisfied and
therefore studying these models provides a convenient tool to understand the
dependence of DS properties on symmetries. For the model B the critical point
and the DS transition point is well separated and directed percolation damage
spreading transition universality was found for spin damage as well as for kink
damage in spite of the conservation of damage variables modulo 2 in the latter
case. For the A stochastic cellular automaton, and the NEKIM model the two
transition points coincide with drastic effects on the damage of spin and kink
variables showing different time dependent behaviours. While the kink DS
transition is continuous and shows regular PC class universality, the spin
damage exhibits a discontinuous phase transition with compact clusters and PC
like dynamical scaling (), () and () exponents whereas
the static exponents determined by FSS are consistent with that of the spins of
the NEKIM model at the PC transition point. The generalised hyper-scaling law
is satisfied.Comment: 11 pages, 20 figures embedded in the text, minor changes in the text,
a new table and new references are adde
Multipole State of Heavy Lanthanide Filled Skutterudites
We discuss multipole properties of filled skutterudites containing heavy
lanthanide Ln from a microscopic viewpoint on the basis of a seven-orbital
Anderson model. For Ln=Gd, in contrast to naive expectation, quadrupole moments
remain in addition to main dipole ones. For Ln=Ho, we find an exotic state
governed by octupole moment. For Ln=Tb and Tm, no significant multipole moments
appear at low temperatures, while for Ln=Dy, Er, and Yb, dipole and
higher-order multipoles are dominant. We briefly discuss possible relevance of
these multipole states with actual materials.Comment: 5 pages, 3 figure
Normal and lateral Casimir force: Advances and prospects
We discuss recent experimental and theoretical results on the Casimir force
between real material bodies made of different materials. Special attention is
paid to calculations of the normal Casimir force acting perpendicular to the
surface with the help of the Lifshitz theory taking into account the role of
free charge carriers. Theoretical results for the thermal Casimir force acting
between metallic, dielectric and semiconductor materials are presented and
compared with available experimental data. Main attention is concentrated on
the possibility to control the magnitude and sign of the Casimir force for
applications in nanotechnology. In this respect we consider experiments on the
optical modulation of the Casimir force between metal and semiconductor test
bodies with laser light. Another option is the use of ferromagnetic materials,
specifically, ferromagnetic dielectrics. Under some conditions this allows to
get Casimir repulsion. The lateral Casimir force acting between sinusoidally
corrugated surfaces can be considered as some kind of noncontact friction
caused by zero-point oscillations of the electromagnetic field. Recent
experiments and computations using the exact theory have demonstrated the role
of diffraction-type effects in this phenomenon and the possibility to get
asymmetric force profiles. Conclusion is made that the Casimir force may play
important role in the operation of different devices on the nanoscale.Comment: 27 pages, 13 figures; Invited keynote lecture at the 2nd
International Conference on Science of Friction, Ise-Shima, Mie, Japan,
September 13-18, 2010; to appear in J. Phys.: Conf. Se
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