Table of contents

We study the vortex formation in optical lattices submitted to artificial gauge potentials. We compute the superfluid density for Abelian and non-Abelian gauge potentials with a mean-field approach of the Bose-Hubbard model and we determine the rule describing the number of vortices as a function of the effective magnetic flux. This simple rule is represented by a remarkably rich figure that represents the superfluid density as a function of the flux. The phenomena which emanate from this work should be observed experimentally in optical lattices within which atom tunneling is laser-assisted and described by commutative or non-commutative tunneling operators.

By considering particles as smeared objects, we investigate the effects of space noncommutativity on the orbits of particles in Schwarzschild spacetime. The effects of space noncommutativity on the value of the precession of the perihelion of particle orbit and deflection of light ray in Schwarzschild geometry are calculated and the stability of circular orbits is discussed.

A noncommutative space is considered, the position operators of which satisfy the commutativity relations of a Lie algebra. The basic tools for calculation on this space, including the product of the fields, inner product and the proper measure for integration are derived. Some general aspects of perturbative field theory calculations on this space are also discussed. One of the features of such models is that they are free from ultraviolet divergences (and hence free from UV/IR mixing as well), if the group is compact. The example of the group SO(3) or SU(2) is investigated in more detail.

Thermal aspects of the Brans-Dicke analog of the Bonnor-type black dihole are commentarially described on the basis of a magnetic-dipole solution of Kim and Lee in the Brans-Dicke-Maxwell theory. It is then exemplified that the so-called area theorem of the horizon is broken and the entropy is divergent, irrespective of the finite area of the horizon.

By considering the nonperturbative effects associated with the fundamental modular region, a new phase of a Gluon Plasma at finite density is proposed. It corresponds to the transition from glueballs to nonperturbative gluons which condense at a nonvanishing momentum. In this respect the proposed phase is analogous to the color superconducting LOFF phase for fermionic systems.

A fundamental symmetry of nuclear and particle physics is isospin whose third component is the Gell-Mann/Nishijima expression I_Z=Q-(B+S)/2. The role of isospin symmetry in relativistic heavy-ion collisions is studied. An isospin I_Z, strangeness S correlation is shown to be a direct and simple measure of flavor correlations, vanishing in a Qg phase of uncorrelated flavors in both symmetric N=Z and asymmetric N≠Z systems. By contrast, in a hadron phase, a I_Z/S correlation exists as long as the electrostatic charge chemical potential μ_Q≠0 as in N≠Z asymmetric systems. A parallel is drawn with a Zeeman effect which breaks a spin degeneracy.

This paper reports a study of ring-like and jet-like events in terms of Scaled factorial Moments (SFMs) in two-dimensional space for pions produced in ¹⁶O-AgBr interactions at 60 A GeV. The analysis reveals an intermittent type of increase in SFMs with decreasing bin width in both types of events. The analysis further shows that stronger fluctuations occur in the case of ring-like events.

Gas flows in the Knudsen layer adjacent to a solid wall cannot be described by the classical Navier-Stokes constitution in general, and high-order models such as the Burnett and super-Burnett models encounter many difficulties in practical applications. In the present work we propose an extended Navier-Stokes constitution in which the effect of the collisions between the gas molecules and bounded walls is incorporated. With this model, it is found that the flow behaviors in the Knudsen layer can be effectively captured.

We show that the widespread concept of eigenmodes in lossless waveguide structures, which assumes the presence of propagating and evanescent modes only, fails in the case of metal-dielectric structures, such as single holes/slits and periodic arrays of holes/slits in metals. In addition to these modes, there is a sequence of new eigenstates with complex values of the propagation constant and non-zero lateral energy flows. The whole eigenproblem ceases to be Hermitian because of changing sign of the optical dielectric constant. The new anomalous modes are shown to be essential for the description of the extraordinary light transmission through subwavelength holes.

A Knudsen layer theory is presented within the framework of a high-order lattice Boltzmann model obtained from the fourth-order Gauss-Hermite quadrature. The Kramers problem is analyzed in detail. We employ a multi-relaxation collision operator which is shown to permit a variable layer width. Computer simulations are performed which give excellent agreement with the theoretical derivations. Good qualitative agreement is achieved with the accurate numerical solution of the Boltzmann equation for hard sphere molecules. Our theoretical result clearly indicates that the lattice Boltzmann models with high symmetric velocity sets naturally develop to physically relevant Knudsen layers due to the discrete ordinate origin of the method.

This paper reports the recorded breakdown curves for dual-frequency (27.12 MHz/2 MHz and 13.56 MHz/50 Hz) discharges in nitrogen. Applying the LF voltage shifts the RF breakdown curve to the region of higher voltages and gas pressures, which is associated with the increased loss of charged particles due to the drift in the LF field. At higher LF voltage amplitudes the LF field contributes to gas ionization, the breakdown voltage for the RF discharge decreases and approaches zero when a self-sustained discharge in the LF field ignites. Applying the RF voltage leads to the decrease in the breakdown LF voltage, possibly due to the decrease of electron losses because of the oscillations in the RF field.

We present experimental measurements of the absorption of ultrashort laser pulses by 15 μm diameter methanol microdroplets. The droplet absorbs upto 70% of the incidence laser energy in the presence of a prepulse at intensities of about 1.5×10¹⁶ W cm⁻². In the absence of a prepulse, the absorption is only about 20%. Simultaneous measurements of X-ray yield (12 keV to 350 keV) and the absorption in the droplet plasma, shows that our earlier measurements of efficient generation (Anand M. et al. Appl. Phys. Lett., 88 (2006) 181111) of hard X-rays from the droplet plasma is due to the increased absorption in the droplets in the presence of optimum prepulse. 1-D PIC simulations, mimicing the mass-limited droplet density profile, demonstrate the effectiveness of the large scale-length droplet plasma in providing optimal conditions for resonant laser absorption energy and generation of hot electrons.

In 1900, Otto Lehmann observed that the texture of a cholesteric droplet heated from below can rotate continuously (Ann. Phys. (Leipzig), 2 (1900) 649). This observation (which has never been reproduced, to our knowledge) was explained in 1968 by Leslie (Proc. R. Soc. London, Ser. A, 307 (1968) 359) from symmetry arguments accounting for the chirality of the material. In 1982, Éber and Jánossy showed experimentally that a similar thermomechanical effect also exists in a compensated cholesteric (in which the helix is completely unwound). This result was immediately questioned by Pleiner and Brand who claimed that only the symmetry of the phase (and not that of the molecule) determines the structure of the macroscopic constitutive equations (Mol. Cryst. Liq. Cryst. Lett., 5 (1987) 61). According to them, the Lehmann effect should necessarily vanish at the compensation temperature. In order to understand the correct interpretation, we conducted very carefully the experiment in two complementary geometries. Our results agree with those of Éber and Jánossy, confirming the predominance of microscopic symmetries over macroscopic ones.

We present a molecular dynamics test of the Central-Limit Theorem (CLT) in a paradigmatic long-range-interacting many-body classical Hamiltonian system, the HMF model. We calculate sums of velocities at equidistant times along deterministic trajectories for different sizes and energy densities. We show that, when the system is in a chaotic regime (specifically, at thermal equilibrium), ergodicity is essentially verified, and the Pdfs of the sums appear to be Gaussians, consistently with the standard CLT. When the system is, instead, only weakly chaotic (specifically, along longstanding metastable Quasi-Stationary States), nonergodicity (i.e., discrepant ensemble and time averages) is observed, and robust q-Gaussian attractors emerge, consistently with recently proved generalizations of the CLT.

Discussed in this paper are details of the Ohmic conduction of the solution of a binary 1-1 electrolyte. The study is motivated by the desire to have a consistent equation of motion for a charged particle in a normal (non-superfluid) liquid with finite viscosity η. Usually, employed for this purpose is the so-called Langevin equation where the particle mass M is assumed to be constant and the characteristic relaxation time is expressed through the viscosity η. However, this scenario is not self-consistent: If the friction force has Stokes origin, the effective ion mass consisting of its bare mass and the associated hydrodynamic mass due to the arising flow of the adjacent liquid should not be constant (for example, in case of oscillatory motion it exhibits a strong frequency dispersion: M^ass(ω→0)≃ω^−1/2). Although the scenario with M=const is also in principle possible (we refer to it as the Drude scenario, below), in that case the friction force which is linear in the ion velocity should have a different (non-Stokes) origin. The performed analysis of frequency dispersion of electrolyte conductivity for the two scenarios reveals qualitative differences which can be detected experimentally in their behaviour allowing to distinguish between the Drude and Stokes models. An important problem for ion dynamics in liquids is the structure of charged clusters (arising around the ions) whose radius R_s is usually considered to be an adjustable parameter. We discuss the physical mechanisms governing the formation of R_s.

Spatial heterogeneity in the elastic properties of soft random solids is examined via a semi-microscopic model network using replica statistical mechanics. The elastic heterogeneity is characterized by random residual stress and Lamé coefficient fields, and the statistics of these quantities is inferred. Correlations involving the residual-stress field are found to be long ranged and governed by a universal parameter that also gives the mean shear modulus.

The tetragonal layered compounds TbTiGe and ErTiGe order antiferromagnetically at 276 K and 39 K, respectively. Partial substitution of Mo for Ti in these two compounds modifies the magnetic interactions giving rise to a ferromagnetic ground state which results in an enhanced magnetocaloric effect. The magnetic entropy change in ErTi_0.85Mo_0.15Ge for a magnetic field change of 5 T is ∼10.5 J/kg/K as against ∼0.8 J/kg/K for ErTiGe in the vicinity of the magnetic transition. Thus, magnetocaloric properties of such layered materials may be tunable by suitable chemical substitutions.

Infrared reflectivity and time-domain terahertz transmission spectra of EuTiO₃ ceramics revealed a polar optic phonon at 6–300 K whose softening is fully responsible for the recently observed quantum paraelectric behaviour. Even if our EuTiO₃ ceramics show lower permittivity than the single crystal due to a reduced density and/or small amount of secondary pyrochlore Eu₂Ti₂O₇ phase, we confirmed a magnetic field dependence of the permittivity, also slightly smaller than in single crystal. An attempt to reveal the soft phonon dependence at 1.8 K on the magnetic field up to 13 T remained below the accuracy of our infrared reflectivity experiment.

We consider a two-dimensional electron gas with Rashba's spin-orbit interaction and two in-plane potentials superimposed along directions perpendicular to each other. The first of these potentials is assumed to be a general periodic potential while the second one is totally arbitrary. A general form for Bloch's amplitude is found and an eigen-value problem for the band structure of the system is derived. We apply the general result to the two particular cases in which either the second potential represents a harmonic in-plane confinement or it is zero. We find that for a harmonic confinement regions of the Brillouin zone with high polarizations are associated with the ones of large group velocity.

We report that in spite of the commonly accepted view that stable Single-Bubble Sonoluminescence (SBSL) can only be achieved in water in the presence of a noble gas or hydrogen, long term stable SBSL can in fact be sustained with only diatomic gases like e.g. nitrogen being present. Compared to that of a stable argon bubble, the emission is much weaker and the spectrum looks much colder. Simulations support that the above quoted view, based on the dissociation hypothesis, is an erroneous inference from this theory.

By muon spin rotation we investigated the magnetic properties of a series of highly Na-doped Na_xCoO₂ single crystals with 0.78(1)⩽x⩽0.97(1). Our data provide evidence for an intrinsically inhomogeneous magnetic state which can be described in terms of hole-doping (Na vacancy)-induced magnetic clusters that percolate at 1−x≳0.04 until they yield a bulk magnetic state near x=0.78. Evidence for a strong (likely geometrical) frustration of the magnetic order is obtained from the anomalous doping dependence of the spin fluctuation rate (above the ordering temperature) which is strongly enhanced at x=0.78 as compared to x=0.97.

We show how spatiotemporal fluctuations can induce spontaneous symmetry breaking in systems which are perfectly symmetric in the absence of fluctuations. We illustrate this in the context of the autocatalytic production of chiral enantiomers from achiral reactants in reaction-diffusion systems. The mean-field steady state is chiral symmetric; spatiotemporal fluctuations induce global and complete chiral ordering with sharp phase transitions including re-entrance. We find that advective mass transport enhances the tendency to break chiral symmetry. We discuss the relation between our study and recent experiments demonstrating complete chiral symmetry breaking (CSB), and its implications to the emergence of molecular homochirality.

The response of stress with strain is one of the fundamental quantities used to characterize fracture in materials. Exactly how this relationship appears depends on the microscopic structure, which can vary considerably from material to material. Presently, we study the breaking of materials where the structural disorder is varied within a broad range, using a model based on elastic beams. A large number of system sizes is then generated for each level of disorder in order to study the scaling properties of the force-displacement characteristic. Whereas maximum force and displacement is found to scale trivially, being simply proportional to system size, the scaling exponents relative to the extent of damage in the stable and unstable regimes of fracture are found to scale non-trivially. Our calculations contradict earlier findings which suggested that the scaling is universal with respect to the disorder.

A new Brownian dynamics model is presented to describe the coarse grain dynamics of particles with long-lived memory. Instead of solving a set of generalized Langevin equations we introduce a set of variables describing the slowly fluctuating thermodynamic state of the ignored degrees of freedom. These variables give rise to additional transient forces on the simulated particles, whose interpretation provides a new way of thinking about memory effects in soft-matter physics. We illustrate the proposed method by simulating shear thinning of synthetic resins.