Microcanonical Thermodynamics of First Order Phase Transitions studied in the Potts Model

Phase transitions of first and second order can easily be distinguished in small systems in the microcanonical ensemble. Configurations of phase coexistence, which are suppressed in the canonical formulation, carry important information about the main characteristics of first order phase transitions like the transition temperature, the latent heat, and the interphase surface tension. The characterisitc backbending of the micro- canonical caloric equation of state T(E) (not to be confused with the well known Van der Waals loops in ordinary thermodynamics) leading to a negative specific heat is intimatly linked to the interphase surface entropy.Comment: Latex, 4 eps-figures, graphicx.st

Kaon squeeze-out in heavy ion reactions

The squeeze-out phenomenon of $K^+$ and $K^-$ mesons, i.e. the azimuthal asymmetry of $K^+$ and $K^-$ mesons emitted at midrapidity in heavy ion reactions, is investigated for beam energies of 1-2 A.GeV. It is found that the squeeze-out signal is strongly affected by in-medium potentials of these mesons. The repulsive $K^+$-nucleus potential gives rise to a pronounced out-of-plane emission of $K^+$'s at midrapidity. With the $K^+$ potential we reproduce well the experimental data of the $K^+$ azimuthal distribution. It is found that the attractive $K^-$-nucleus potential cancels to a large extent the influence of rescattering and reabsorption of the $K^-$ mesons on the projectile and target residuals (i.e. shadowing). This results in an azimuthally isotropic emission of the midrapidity $K^-$ mesons with transverse momentum up to 0.8 GeV/c. Since it is well accepted that the shadowing alone would lead to a significant out-of-plane preference of particle emission, in particular at high transverse momenta, the disappearance of the out-of-plane preference for the $K^-$ mesons can serve as an unambiguous signal of the attractive $K^-$ potential. We also apply a covariant formalism of the kaon dynamics to the squeeze-out phenomenon. Discrepancies between the theory and the experiments and possible solutions are discussed.Comment: 24 pages Latex using Elsevier style, 7 PS figures, accepted for publication in Euro. Phys. Jour.

Density functional approach to finite temperature nuclear properties and the role of a momentum dependent isovector interaction

Using a density functional approach based on a Skyrme interaction, thermodynamic properties of finite nuclei are investigated at non-zero temperture. The role of a momentum dependent isovector term is now studied besides volume, symmetry, surface and Coulomb effects. Various features associated with both mechanical and chemical instability and the liquid-gas coexistence curve are sensitive to the Skyrme interaction. The separated effects of the isoscalar term and the isovector term of momentum dependent interaction are studied for a modified SKM($m^*=m$) interaction. The frequently used Skyrme interaction SLy4 is one of the cases considered and is shown to have better features for neutron star studies due to a larger symmetry energy.Comment: 14 pages, 6 figures, added more discussio

Impact of constrained rewiring on network structure and node dynamics

In this paper, we study an adaptive spatial network. We consider a susceptible-infected-susceptible (SIS) epidemic on the network, with a link or contact rewiring process constrained by spatial proximity. In particular, we assume that susceptible nodes break links with infected nodes independently of distance and reconnect at random to susceptible nodes available within a given radius. By systematically manipulating this radius we investigate the impact of rewiring on the structure of the network and characteristics of the epidemic.We adopt a step-by-step approach whereby we first study the impact of rewiring on the network structure in the absence of an epidemic, then with nodes assigned a disease status but without disease dynamics, and finally running network and epidemic dynamics simultaneously. In the case of no labeling and no epidemic dynamics, we provide both analytic and semianalytic formulas for the value of clustering achieved in the network. Our results also show that the rewiring radius and the network’s initial structure have a pronounced effect on the endemic equilibrium, with increasingly large rewiring radiuses yielding smaller disease prevalence

Investigation of planetary ionospheres

Feasibility of using radio sounding techniques to investigate ionospheric properties of planet

Gravitational coupling to two-particle bound states and momentum conservation in deep inelastic scattering

The momentum conservation sum rule for deep inelastic scattering (DIS) from composite particles is investigated using the general theory of relativity. For two 1+1 dimensional examples, it shown that covariant theories automatically satisy the DIS momentum conservation sum rule provided the bound state is covariantilly normalized. Therefore, in these cases the two DIS sum rules for baryon conservation and momentum conservation are equivalent

Nuclear Chemical and Mechanical Instability and the Liquid-Gas Phase Transition in Nuclei

The thermodynamic properties of nuclei are studied in a mean field model using a Skryme interaction. Properties of two component systems are investigated over the complete range of proton fraction from a system of pure neutrons to a system of only protons. Besides volume, symmetry, and Coulomb effects we also include momentum or velocity dependent forces. Applications of the results developed are then given which include nuclear mechanical and chemical instability and an associated liquid/gas phase transition in two component systems. The velocity dependence leads to further changes in the coexistence curve and nuclear mechanical and chemical instability curves.Comment: 21 pages, 9 figures, Results are changed due to error in progra

Regge Behavior of DIS Structure Functions

Building on previous works of the mid 1960's, we construct an integral equation for forward elastic scattering (t=0) at arbitrary virtuality Q^2 and large s=W^2. This equation sums the ladder production of massless intermediate bosons to all orders, and the solution exhibits Regge behavior. The equation is used to study scattering in a simple chi^2 phi scalar theory, where it is solved appoximately and applied to the study of DIS at small x. We find that the model can naturally describe the quark distribution in both the large x region and the small x region dominated by Reggeon exchange.Comment: 13 pages with 5 figure