Forward-backward multiplicity distribution in a two-component model

We calculate stochastic quantities in a two-component model which is a product of a negative binomial and a Poisson distribution. The generating function and the KNO scaling function are obtained. A formula for the forward-backward (F-B) multiplicity correlation is derived from the generating function. We consider the case in which particles are produced in pairs and compare with experiment.     

Entropy of a two-component fluid in a square-well model

An analytical expression valid for two approximations, notably, the random phase approximation (RPA) and the mean spherical approximation (MSA), is derived for entropy of a two-component system with the pair potential of a square well (SW). This expression is applied to calculate the excess entropy of mixing of the Na-K and Na-Cs equiatomic compositions. It is shown that the use of the SW model leads to better results than the application of the hard-sphere model. The MSA gives better convergence with the experiment compared with the RPA.     

Folding model potentials from realistic interactions for heavy-ion scattering

The double-folding model, with “realistic” nucleon-nucleon interactions based upon a G-matrix constructed from the Reid potential, is used to calculate the real part of the optical potential for heavy-ion scattering. The resulting potentials are shown to reproduce the observed elastic scattering for a large number of systems with bombarding energies from 5 to 20 MeV per nucleon. Some representative inelastic transitions are also reproduced. Exceptions are the elastic scattering of ⁶Li and ⁹Be for which the folded potentials must be reduced in strength by a factor of about two.The same effective interactions are shown to give a good account of two particular cases of alpha scattering as well as some cases of nucleon-nucleus scattering. Some typical examples of inelastic heavy-ion scattering are also predicted successfully.Some general properties of the folding model are reviewed and its theoretical basis is discussed. An explicit density-dependence is examined for one particular realistic interaction and found not to change the results. Single nucleon exchange is included in an approximate way and its importance is studied.In addition to being a study of the folding model, this work also provides a systematic and comprehensive optical model analysis of heavy-ion elastic scattering in this energy range.     

Towards a realistic composite model of quarks and leptons

Within the context of the 't Hooft anomaly matching scheme, some guiding principles for model building are discussed with an eye to low-energy phenomenology. It is argued that Λ_ch (chiral symmetry breaking scale of the global color-flavor group G_CF) ≈ Λ_MC (metacolor scale) and Λ_gCF (unification scale of the gauge subgroup of G_CF) ≲ Λ_ch. As illustrations of the method, two composite models are suggested that can give rise to three or four generations of ordinary quarks and leptons without exotic fermions.     

Towards a realistic model of Higgsless electroweak symmetry breaking

We present a 5D gauge theory in warped space based on a bulk SU(2)L x SU(2)R x U(1)(B-L) gauge group where the gauge symmetry is broken by boundary conditions. The symmetry breaking pattern and the mass spectrum resemble that in the standard model (SM). To leading order in the warp factor the rho parameter and the coupling of the Z (S parameter) are as in the SM, while corrections are expected at the level of a percent. From the anti-de Sitter (AdS) conformal field theory point of view the model presented here can be viewed as the AdS dual of a (walking) technicolorlike theory, in the sense that it is the presence of the IR brane itself that breaks electroweak symmetry, and not a localized Higgs on the IR brane (which should be interpreted as a composite Higgs model). This model predicts the lightest W, Z, and gamma resonances to be at around 1.2 TeV, and no fundamental (or composite) Higgs particles.     

Stochastic resonance in a realistic model for surface adsorption

We study a model for a monolayer single adsorbate system used to describe pattern formation on adsorbates with lateral interactions, when it is submitted to pressure oscillations. Through numerical and analytical (based on a two-state approximation) methods to analyze the existence of stochastic resonance in such a bistable system. This is a first step toward the study of resonant phenomena in adsorbate systems with moving fronts and/or with presence of micro-reactors or spots.     

Extended JC-Dicke model for two-component atomic BEC inside a cavity

We consider a trapped two-component atomic Bose-Einstein condensate (BEC), where each atom with three energy-levels is coupled to an optical cavity field and an external classical optical field as well as a microwave field to form the so-called Δ-type configuration. After adiabatically eliminating the atomic excited state, an extended JC-Dicke model is derived under the rotating-wave approximation. The scaled ground-state energy and the phase diagram of this model Hamiltonian are investigated in the framework of mean-field approach. A new phase transition is revealed when the amplitude of microwave field changes its sign.     

Intriguing properties of kinks in a simple model with a two-component field

We present a summary of the topological and non-topological solitons of a two component field in 1+1 dimensions with application in field theory and in condensed matter physics. We note several intriguing analytical and numerical relationships between these solutions, which we believe to suggest that the relevant coupled nonlinear differential equations may be integrable exactly.     

A conformally flat realistic anisotropic model for a compact star

A physically realistic stellar model with a simple expression for the energy density and conformally flat interior is found. The relations between the different conditions are used without graphic proofs. It may represent a real pulsar.     

Quantum Hall conductivity in a Landau type model with a realistic geometry

In this paper, we revisit some quantum mechanical aspects related to the quantum Hall effect. We consider a Landau type model, paying a special attention to the experimental and geometrical features of quantum Hall experiments. The resulting formalism is then used to compute explicitely the Hall conductivity from a Kubo formula.     

Static properties of two-component kink in a non-linear discrete polarizability model

We study analytically, in the low-velocity regime, the static properties of two-component kink in a discrete polarizability model with a quartic electron–ion interaction in one ionic species. Using a discretized Hamiltonian formalism, we derive the exact equations of motion for the two-component kink centre of the mass X(t) and coupled field variables. Numerical analysis is performed to estimate the amplitude of the dressing and its effects on the static properties of the discrete lattice for the potassium selenate (K₂SeO₄) at T=40 K. We find that dressing has important effects on dynamical quantities such as the pinning frequency and the depth of the Peierls–Nabarro potential. Two-component kink contributions to the specific heat have been also analysed both in the continuum and the discrete limits.     

Stationary and oscillatory fronts in a two-component genetic regulatory network model

We investigate a two-component gene network model, originally used to describe the spatiotemporal patterning of the gene products in early Drosophila development. By considering a particular mode of interaction between the two gene products, denoted proteins A and B, we find both stable stationary and time-oscillatory fronts can occur in the reaction-diffusion system. We reduce the system by replacing B with its spatial average (shadow system) and assume an abrupt “on-and-off” switch for the genes. In doing so, explicit formula are obtained for all steady-state solutions and their linear eigenvalues. Using the diffusion of A,D_a, and the basal production rate, r, as bifurcation parameters, we explore ranges in which a monotone, stationary front is stable, and show it can lose stability through a Hopf bifurcation, giving rise to oscillatory fronts. We also discuss the existence and stability of steady-state and time-oscillatory solutions with multiple extrema. An intuitive explanation for the occurrence of stable stationary and oscillatory front solutions is provided based on the behavior of A in the absence of B and the opposite regulation between A and B. Such behavior is also interpreted in terms of the biological parameters in the model, including those governing the connection of the gene network.     

Behaviour of semi-inclusive sphericity distributions and a two-component uncorrelated cascade model

A simple two component uncorrelated cascade model is proposed which reproduces the semi-inclusive Sphericity distributions observed in lowp _T hadron-hadron collisions. It is pointed out that if α is an exponential parameter inserted into the quark-quark structure function, theS dependence of the semi-inclusive sphericity distribution for multiplicityn goes as exp (?α/nS). This conclusion agrees extremely well with the experimental data.     

From realistic to primitive models: a primitive model of methanol

An attempt to develop a methodology to construct a primitive model which descends directly from a parent realistic short-range model and reproduces its structural properties has been made. The realistic three-site OPLS model of methanol has been chosen as a test case. The primitive model copies the geometry of the OPLS model and thus pictures the methanol molecule as a hard heteronuclear dumbbell (representing oxygen and carbon atoms) with one embedded hydrogen site. All sites interact as hard spheres with the exception of the oxygen-hydrogen pair which may form a hydrogen bond mimicked by a square-well attraction. To determine parameters of the model two routes have been followed: (i) theoretical, based on an effective sphericalized site-site potential obtained from the parent potential, and (ii) semitheoretical which makes use of the knowledge of the structure of the dense parent fluid. Both sets of parameters provide similar results and reproduce the structure (site-site correlation functions, distribution of H-bonds and H-bond geometry) of the parent OPLS fluid reasonably well.     

Coil-globule transition in a realistic model of N-isopropylacrylamide: Numerical simulation

A number of homopolymers and copolymers are studied in numerical experiments with allowance for the realistic chemical structure of macromolecules. The method of molecular dynamics is used to determine the temperature of the coil-globule transition in a single macromolecule of N-isopropylacrylamide, as well as to study the coil-globule transition temperature in relation to the degree of fragmentation of N-isopropylacrylamide and methacrylic acid copolymers.