Semiclassical analysis of the quantum interference corrections to the conductance of mesoscopic systems

The Kubo formula for the conductance of a mesoscopic system is analyzed semiclassically, yielding simple expressions for both weak localization and universal conductance fluctuations. In contrast to earlier work which dealt with times shorter than $O(\log \hbar^{-1})$, here longer times are taken to give the dominant contributions. For such long times, many distinct classical orbits may obey essentially the same initial and final conditions on positions and momenta, and the interference between pairs of such orbits is analyzed. Application to a chain of $k$ classically ergodic scatterers connected in series gives the following results: $-{1 \over 3} [ 1 - (k+1)^{-2} ]$ for the weak localization correction to the zero--temperature dimensionless conductance, and ${2 \over 15} [ 1 - (k+1)^{-4} ]$ for the variance of its fluctuations. These results interpolate between the well known ones of random scattering matrices for $k=1$, and those of the one--dimensional diffusive wire for $k \rightarrow \infty$.Comment: 53 pages, using RevTeX, plus 3 postscript figures mailed separately. A short version of this work is available as cond-mat/950207

What is the meaning of the statistical hadronization model?

The statistical model of hadronization succeeds in reproducing particle abundances and transverse momentum spectra in high energy collisions of elementary particles as well as of heavy ions. Despite its apparent success, the interpretation of these results is controversial and the validity of the approach very often questioned. In this paper, we would like to summarize the whole issue by first outlining a basic formulation of the model and then comment on the main criticisms and different kinds of interpretations, with special emphasis on the so-called "phase space dominance". While the ultimate answer to the question why the statistical model works should certainly be pursued, we stress that it is a priority to confirm or disprove the fundamental scheme of the statistical model by performing some detailed tests on the rates of exclusive channels at lower energy.Comment: 14 pages, to be published in the Proceedings of the International workshop "Focus on multiplicity", Bari (Italy) June 17-19 200

A Diagrammatic Theory of Random Scattering Matrices for Normal-Superconducting Mesoscopic Junctions

The planar-diagrammatic technique of large-$N$ random matrices is extended to evaluate averages over the circular ensemble of unitary matrices. It is then applied to study transport through a disordered metallic ``grain'', attached through ideal leads to a normal electrode and to a superconducting electrode. The latter enforces boundary conditions which coherently couple electrons and holes at the Fermi energy through Andreev scattering. Consequently, the {\it leading order} of the conductance is altered, and thus changes much larger than $e^2/h$ are observed when, e.g., a weak magnetic field is applied. This is in agreement with existing theories. The approach developed here is intermediate between the theory of dirty superconductors (the Usadel equations) and the random-matrix approach involving transmission eigenvalues (e.g. the DMPK equation) in the following sense: even though one starts from a scattering formalism, a quantity analogous to the superconducting order-parameter within the system naturally arises. The method can be applied to a variety of mesoscopic normal-superconducting structures, but for brevity we consider here only the case of a simple disordered N-S junction.Comment: 39 pages + 9 postscript figure

Experimental study of the quantum driven pendulum and its classical analogue in atoms optics

We present experimental results for the dynamics of cold atoms in a far detuned amplitude-modulated optical standing wave. Phase-space resonances constitute distinct peaks in the atomic momentum distribution containing up to 65% of all atoms resulting from a mixed quantum chaotic phase space. We characterize the atomic behavior in classical and quantum regimes and we present the applicable quantum and classical theory, which we have developed and refined. We show experimental proof that the size and the position of the resonances in phase space can be controlled by varying several parameters, such as the modulation frequency, the scaled well depth, the modulation amplitude, and the scaled Planck's constant of the system. We have found a surprising stability against amplitude noise. We present methods to accurately control the momentum of an ensemble of atoms using these phase-space resonances which could be used for efficient phase-space state preparation

Equation of State, Radial Flow and Freeze-out in High Energy Heavy Ion Collisions

We have shown that recent experimental data on radial flow, both from AGS and SPS energies, are in agreement with the Equation of State (EOS) including the QCD phase transition. New hydro-kinetic model (HKM) is developed, which incorporates hydrodynamical treatment of expansion and proper kinetics of the freeze-out. We show that the freeze-out surfaces for different secondaries and different collisions are very different, and they are not at all isotherms (as was assumed in most previous hydro works). Comparison of HKM results with cascade-based event generator RQMD is also made in some details: we found that both EOS and flow are in rather good agreement, while the space-time picture is still somewhat different

Statistical hadronization with exclusive channels in e+e- annihilation

We perform a systematic analysis of exclusive hadronic channels in e+e- collisions at centre-of-mass energies between 2.1 and 2.6 GeV within the statistical hadronization model. Because of the low multiplicities involved, calculations have been carried out in the full microcanonical ensemble, including conservation of energy-momentum, angular momentum, parity, isospin, and all relevant charges. We show that the data is in an overall good agreement with the model for an energy density of about 0.5 GeV/fm^3 and an extra strangeness suppression parameter gamma_S ~ 0.7, essentially the same values found with fits to inclusive multiplicities at higher energy.Comment: 27 pages, 12 figure

The Biodiversity of the Mediterranean Sea: Estimates, Patterns, and Threats

The Mediterranean Sea is a marine biodiversity hot spot. Here we combined an extensive literature analysis with expert opinions to update publicly available estimates of major taxa in this marine ecosystem and to revise and update several species lists. We also assessed overall spatial and temporal patterns of species diversity and identified major changes and threats. Our results listed approximately 17,000 marine species occurring in the Mediterranean Sea. However, our estimates of marine diversity are still incomplete as yet—undescribed species will be added in the future. Diversity for microbes is substantially underestimated, and the deep-sea areas and portions of the southern and eastern region are still poorly known. In addition, the invasion of alien species is a crucial factor that will continue to change the biodiversity of the Mediterranean, mainly in its eastern basin that can spread rapidly northwards and westwards due to the warming of the Mediterranean Sea. Spatial patterns showed a general decrease in biodiversity from northwestern to southeastern regions following a gradient of production, with some exceptions and caution due to gaps in our knowledge of the biota along the southern and eastern rims. Biodiversity was also generally higher in coastal areas and continental shelves, and decreases with depth. Temporal trends indicated that overexploitation and habitat loss have been the main human drivers of historical changes in biodiversity. At present, habitat loss and degradation, followed by fishing impacts, pollution, climate change, eutrophication, and the establishment of alien species are the most important threats and affect the greatest number of taxonomic groups. All these impacts are expected to grow in importance in the future, especially climate change and habitat degradation. The spatial identification of hot spots highlighted the ecological importance of most of the western Mediterranean shelves (and in particular, the Strait of Gibraltar and the adjacent Alboran Sea), western African coast, the Adriatic, and the Aegean Sea, which show high concentrations of endangered, threatened, or vulnerable species. The Levantine Basin, severely impacted by the invasion of species, is endangered as well