Realistic Interaction Models Research Articles

Flavor mixing and solution structures in Dyson–Schwinger equations for a two-flavor system

We solved the Dyson–Schwinger (DS) equations for a two-flavor system with symmetry to study its flavor mixing effects. Initially, we employed the point interaction model and bare vertex approximation to reveal the structure of the solutions. Using the point interaction model, the DS equations can be solved analytically, and we found that these solutions can be classified into three groups, each forming an ellipse. These solutions exhibit SO(2) symmetry, while the original SU(2) symmetry at the Lagrangian level is dynamically broken to SO(2), corresponding to the emergence of flavor mixing effects. However, this flavor mixing effect does not manifest in the final physical state. By utilizing the system’s SO(2) symmetry, we can diagonalize the propagators of the DS equations, eliminating the flavor mixing effect but causing the originally degenerate masses at the Lagrangian level to split. These mass eigenstates have identical quantum numbers but different masses. If we can correspond these to quark particles of different generations, we can explain why the three generations of quarks have different masses and obtain the corresponding quark mass spectrum. Finally, we provide the corresponding numerical results using a more realistic interaction model.

Medium-induced gluon radiation with full resummation of multiple scatterings for realistic parton-medium interactions

The new precision era of jet quenching observables at both RHIC and the LHC calls for an improved and more precise description of in-medium gluon emissions. The development of new theoretical tools and analytical calculations to tackle this challenge has been hampered by the inability to include the effects of multiple scatterings with the medium using a realistic model for the parton-medium interactions. In this paper, we show how the analytical expressions for the full in-medium spectrum, including the resummation of all multiple scatterings, can be written in a form where the numerical evaluation can be easily performed without the need of the usually employed harmonic or single hard approximations. We present the transverse momentum and energy-dependent medium- induced gluon emission distributions for known realistic interaction models to illustrate how our framework can be applied beyond the limited kinematic regions of previous calculations.

Divergence of activity expansions: Is it actually a problem?

For realistic interaction models, which include both molecular attraction and repulsion (e.g., Lennard-Jones, modified Lennard-Jones, Morse, and square-well potentials), the asymptotic behavior of the virial expansions for pressure and density in powers of activity has been studied taking power terms of high orders into account on the basis of the known finite-order irreducible integrals as well as the recent approximations of infinite irreducible series. Even in the divergence region (at subcritical temperatures), this behavior stays thermodynamically adequate (in contrast to the behavior of the virial equation of state with the same set of irreducible integrals) and corresponds to the beginning of the first-order phase transition: the divergence yields the jump (discontinuity) in density at constant pressure and chemical potential. In general, it provides a statistical explanation of the condensation phenomenon, but for liquid or solid states, the physically proper description (which can turn the infinite discontinuity into a finite jump of density) still needs further study of high-order cluster integrals and, especially, their real dependence on the system volume (density).

Influence of carbon nanotubes on the buckling of microtubule bundles in viscoelastic cytoplasm using nonlocal strain gradient theory

Carbon nanotubes are a new class of microtubule-stabilizing agents since they interact with protein microtubules in living cells, interfering with cell division and inducing apoptosis. In the present work, a modified beam model is developed to investigate the effect of carbon nanotubes on the buckling of microtubule bundles in living cell. A realistic interaction model is employed using recent experimental data on the carbon nanotube-stabilized microtubules. Small scale and surface effects are taken into account applying the nonlocal strain gradient theory and surface elasticity theory. Pasternak model is used to describe the normal and shearing effects of enclosing filament matrix on the buckling behavior of the system. An exact solution is obtained for the buckling growth rates of the mixed bundle in viscoelastic surrounding cytoplasm. The present results are compared with those reported in the open literature for single microtubules and an excellent agreement is found. Finally, the effects of different parameters such as the size, chirality, position and surface energy of carbon nanotubes on the buckling growth rates of microtubule bundles are studied. It is found that the buckling growth rate may increase or decrease by adding carbon nanotubes, depending on the diameter and chirality of carbon nanotubes.

Properties of strongly dipolar Bose gases beyond the Born approximation

Strongly dipolar Bose gases can form liquid droplets stabilized by quantum fluctuations. In theoretical description of this phenomenon, low energy scattering amplitude is utilized as an effective potential. We show that for magnetic atoms corrections with respect to Born approximation arise, and derive modified pseudopotential using realistic interaction model. We discuss the resulting changes in collective mode frequencies and droplet stability diagram. Our results are relevant for recent experiments with erbium and dysprosium atoms.

Force Control for Robotic-Assisted Surgery Based on Viscoelastic Tissue Model

Usually, force control algorithms developed for medical applications use a basic elastic model to represent the interaction between the robot and soft tissue. It is known that soft tissues are complex structures with viscoelastic properties as well as nonheterogeneity and hysteresis behavior. This work intends to improve the performance and the robustness of a force control scheme using a more realistic interaction model. The proposed force control is a model based algorithm using a Kelvin-Boltzmann viscoelastic model as the interaction model.

Three-neutron resonance trajectories for realistic interaction models

Three-neutron resonances are investigated using realistic nucleon-nucleon interaction models. The resonance pole trajectories are explored by first adding an additional interaction to artificially bind the three-neutron system and then gradually removing it. The pole positions for the three-neutron states up to $J=5/2$ are localized in the third energy quadrant---$\mathrm{Im}\phantom{\rule{0.2em}{0ex}}(E)\ensuremath{\leqslant}0,\phantom{\rule{0.3em}{0ex}}\mathrm{Re}\phantom{\rule{0.2em}{0ex}}(E)\ensuremath{\leqslant}0$---well before the additional interaction is removed. Our study shows that realistic nucleon-nucleon interaction models exclude any possible experimental signature of three-neutron resonances.

Ultrasonic tracking reveals multiple behavioural modes of snapper (Pagrus auratus) in a temperate no-take marine reserve

Abstract Interactions between marine reserve populations and non-reserve populations of exploited fishes have generally been modelled using simplistic assumptions about behaviour. Consequently, there is a recognized need for better information on fish movement behaviour at the appropriate spatial scales to generate more realistic interaction models. Automated ultrasonic tracking of marine fish, applied in this study, offers the potential to continuously track individuals for periods of up to several years within the study area. Snapper (Pagrus auratus) (FL: 33–68 cm) were surgically implanted with individually coded ultrasonic transmitters to monitor their movement within the Cape Rodney to Okakari Point Marine Reserve in northeast New Zealand from October 2001 to September 2002. The range of movement patterns observed includes some fish resident for the entire tracking period, while others were more mobile. Of the latter group, some fish left the array permanently while others returned after up to 83 days of continuous absence. Nearly all fish showed some level of site fidelity for varying periods of the time they were tracked. Fish activity peaked in the summer, when highest densities are known to occur. Results suggest that snapper behaviour is variable, and that patterns of habitat utilization vary between fish and also seasonally. Such a complex range of behaviours may be a key component for achieving desirable outcomes for both conservation and fisheries in marine reserves.

Testing interaction models by using x-rayabsorption spectroscopy: solid Pb

Structural models obtained using classical molecular dynamics (MD)simulations and realistic interatomic potentials for solid metalsare tested using experimental results obtained by x-ray absorptionspectroscopy (XAS). Accurate L-edgeextended x-ray absorption fine-structure (EXAFS) measurements of Pbgrains dispersed in BN and graphite matrices have been collected fortemperatures up to the melting point. The thermal expansion of thegrains was measured by energy-dispersive x-ray diffractiontechniques and found to be coincident with that of pure Pb up to thelimit of the present measurements. L3-edge EXAFSmeasurements of solid Pb at various temperatures have been analysedusing advanced data-analysis techniques (GNXAS)based on exact spherical-wave multiple-scattering simulation of theabsorption cross-section. Realistic structural models for solid Pbwere obtained from MD simulations using an empirical pair potential(Dzugutov, Larsson and Ebbsjo (DLE)), a tight-binding (TB) square-root functional, and anembedded-atom (EA) model potential parametrized by us. Theshort-range pair distribution function g(r) reconstructed by meansof EXAFS is compared with those obtained by MD simulations. Theempirical DLE potential, originally designed for the liquid state,is too soft, showing too-large values for the average distance R,variance σ2, and skewness β. The TB and EA potentialsare both compatible with XAS data as regards the average distanceand skewness of the first neighbours. The distance variance,associated with the thermal vibration amplitudes, is underestimatedfor the TB potential, while the EA model is found to be in agreementwith XAS data. The present results are also compared with thosefrom a previous EXAFS study on solid lead, where the cumulantexpansion and a simple one-dimensional anharmonic oscillator modelwere used. The need for realistic interaction models andappropriate simulation schemes for reliable XAS data analysis isemphasized, while differences from and improvements with respect toprevious approaches are only briefly discussed.

Global view of classical clusters: the hyperspherical approach to structure and dynamics

Hyperspherical and related approaches to the dynamics of few particles have been extensively exploited in nuclear, atomic and molecular physics in order to successfully deal with demanding quantum mechanical problems, such as few-nucleon structures and triatomic chemical reactions. In this work, we explore the use of these tools for the study of the structure and dynamics of atomic clusters, for which an ample phenomenology is being accumulated from a classical mechanics perspective. The invariants associated to the inertia tensor were examined for known absolute minimum energy structures of Lennard-Jones clusters up to a number of particles N = 150, while for N ⩽ 12 the structures of all relative minima were determined and studied in relationship with their symmetries. Morse clusters and a realistic interaction model for argon clusters were also briefly considered. In order to deal with cluster dynamics the concept of grand angular momentum is formulated in classical mechanics as a sum of external, deformation and internal (or kinematic) angular momenta. A similar decomposition, of prospective use for the analysis of molecular dynamics simulations, is proposed for the classical kinetic energy. The example of a classical trajectory analysis is given for the isomerization by pseudorotation of an N = 5 cluster.

On accuracy of different cluster models used in describing ordering phase transitions in fcc alloys

A general formulation of cluster methods applied to calculations of thermodynamic quantities of alloys in terms of renormalizing fields describing interaction between a cluster and its environment is given. We have shown that the well-known cluster variation method and the cluster field method, which was suggested earlier, are special cases of our approach. These methods have been used in calculations of phase diagrams of fcc alloys with L12 and L10 ordering transitions with several realistic interaction models. It turns out that, for all these models, the simple tetrahedron version of the cluster field method suggested in this paper describes the phase diagrams almost as accurately as more complicated cluster variation techniques. Possible applications of the tetrahedron version of the cluster field method to inhomogeneous states and kinetics of phase transitions in fcc alloys are discussed.