A Contour Method on Cayley tree

We consider a finite range lattice models on Cayley tree with two basic properties: the existence of only a finite number of ground states and with Peierls type condition. We define notion of a contour for the model on the Cayley tree. By a contour argument we show the existence of $s$ different (where $s$ is the number of ground states) Gibbs measures.Comment: 12 page

The relationship between particle freeze-out distributions and HBT radius parameters

The relationship between pion and kaon space-time freeze-out distributions and the HBT radius parameters in high-energy nucleus-nucleus collisions is investigated. We show that the HBT radius parameters in general do not reflect the R.M.S. deviations of the single particle production points. Instead, the HBT radius parameters are most closely related to the curvature of the two-particle space-time relative position distribution at the origin. We support our arguments by studies with a dynamical model (RQMD 2.4).Comment: RevTex, 10 pages including 3 figures. v2: Discussion of the lambda parameter has been added. PRC, in prin

Seed banks as conservation tool for endangered wild plant species in ecozones of Nigeria

Seed banks have played the largest role in the conservation of endangered wild plant species in the world. The potential role of seed in the regeneration of plant species is threatened by a rapid decline in the longevity and viability of the seeds in their natural habitats. This study addresses the key role of seed banks in the conservation of floristic diversity. The increasing popularity of the seed bank as a tool in the conservation of wild plant species can be attributed to different significance, including; provision of immediate access to plant samples, allowing researchers and conservation biologists to evaluate them for properties such as new sources of medicines, nutrition, and genes. Also, wild plant seeds conserved in seed banks are immune to habitat destruction, diseases, and predators. The stored seeds can be used to reinstate species into existing, suitable habitats where they were once present, or to augment the diversity of small, genetically depleted populations. Conservation efforts, as sources for population reintroduction and restoration, have been cited as an important justification for seed banks. Thus, it is recommended that seed banks with state-of-the-art storage facilities should be established at the national and local levels; and all of such banks should be networked so that materials, knowledge, and expertise on particular wild plant species is available on a global scale.Key words: Conservation, Endangered, Floristic diversity, Plant species, Seeds bank, Storag

Flow effects on the freeze-out phase-space density in heavy ion collisions

The strong longitudinal expansion of the reaction zone formed in relativistic heavy-ion collisions is found to significantly reduce the spatially averaged pion phase-space density, compared to naive estimates based on thermal distributions. This has important implications for data interpretation and leads to larger values for the extracted pion chemical potential at kinetic freeze-out.Comment: 5 pages, 3 figures included via epsfig, added discussion of different transverse density profiles, 1 new figur

Symmetry constraints for the emission angle dependence of Hanbury Brown--Twiss radii

We discuss symmetry constraints on the azimuthal oscillations of two-particle correlation (Hanbury Brown--Twiss interferometry) radii for non-central collisions between equal spherical nuclei. We also propose a new method for correcting in a model-independent way the emission angle dependent correlation function for finite event plane resolution and angular binning effects.Comment: 8 pages revtex4, 2 tables, no figures. Short Section VI added and correction algorithm in Section VII made more explicit. Submitted to Physical Review

Jet Tomography in the Forward Direction at RHIC

Hadron production at high-$p_T$ displays a strong suppression pattern in a wide rapidity region in heavy ion collisions at RHIC energies. This finding indicates the presence of strong final state effects for both transversally and longitudinally traveling partons, namely induced energy loss. We have developed a perturbative QCD based model to describe hadron production in $pp$ collision, which can be combined with the Glauber -- Gribov model to describe hadron production in heavy ion collisions. Investigating $AuAu$ and $CuCu$ collisions at energy $\sqrt{s}=200$ $A$GeV at mid-rapidity, we find the opacity of the strongly interacting hot matter to be proportional to the participant nucleon number. Considering forward rapidities, the suppression pattern indicates the formation of a longitudinally contracted dense deconfined zone in central heavy ion collisions. We determine parameters for the initial geometry from the existing data.Comment: 6 pages for Hot Quarks '06 Conferenc

Squids-snapper fish dynamics model with fishing effects in Terengganu, Malaysia

Overexploitation of marine resources by human activities has become a pandemic issue nowadays. High fishing rates for example, may lead to the extinction of marine populations. In this paper, we introduce a mathematical model of prey-predator system for marine ecosystem with fishing rates for the case of Terengganu state. For this model, we use squids as prey while snapper fish as predator. The objectives of this paper are to analyze the sustainability of equilibrium populations of squids and snapper fish using stability analysis and to show the effect of fishing rates on both of these populations. This model shows that there are four potential equilibria solutions where both populations of squids and snapper fish may be extinct, mutual exclusions where either one of the species dies out as well as coexistence of both populations. The results for stability analysis reported that the equilibrium of coexistence of both populations was stable while the other was unstable. This means that populations of squids and snapper fish are estimated to sustain in the future with the current fishing activities in Terengganu. Hence, we conjectured that in order to guarantee both populations continue to exist, the fishing activities in Terengganu must be restricted within certain range of parameters that is lower than the population growth rates

Excitations of a Bose-Einstein condensate in a one-dimensional optical lattice

We investigate the low-lying excitations of a stack of weakly-coupled two-dimensional Bose-Einstein condensates that is formed by a one-dimensional optical lattice. In particular, we calculate the dispersion relations of the monopole and quadrupole modes, both for the ground state as well as for the case in which the system contains a vortex along the direction of the lasers creating the optical lattice. Our variational approach enables us to determine analytically the dispersion relations for an arbitrary number of atoms in every two-dimensional condensate and for an arbitrary momentum. We also discuss the feasibility of experimentally observing our results.Comment: 16 pages, 5 figures, minor changes,accepted for publication in Phys. Rev.

The Net Global Effects of Alternative U.S. Biofuel Mandates

One of the declared objectives of U.S. biofuel policy is the reduction of greenhouse gas (GHG) emissions from fossil fuel combustion, but many studies have questioned whether such a reduction would actually occur and, if so, how large it would be. This report describes the global market, land use, GHG emissions, and nitrogen use impacts of the U.S. Renewable Fuel Standard (RFS2) and several alternative biofuel policy designs, which differ in terms of mandate magnitude and feedstock composition, over the 2010-2030 period