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

Effects of graphene oxide on aquatic macrophyte under the influence of humic substances.

The behavior of nanostructured graphene oxide (GO) in the environment is complex and must be completely understood to evaluate the risk involved. Studies show that humic acid (HA) can stabilize nanomaterials in water and change its behavior. The aquatic macrophyte duckweed (Lemna minor) is a good plant model for adverse effects evaluation of many test-materials due to its fast growth and small size. This study assessed the effect of GO, with and without HA, on the growth of L. minor on fronds number and biomass changes. The plants were exposed during 7 days to the nominal concentrations of GO equals to 0.0 (control), 0.1, 1.0, 10.0 and 100.0 mg L-1, in the absence or in the presence of 20 mg L-1 of HA. Tests were conducted in multiwell polystyreneplates where each well contained two fronds at the start of the experiment. The number of replicates for each test?concentration was 24 wells. The plants were exposed to a constant photoperiod (24:0, light:dark cycle) supplied by white fluorescent lamps (~700 lux) at the temperature of 20± 2 ºC. The fronds number was counted daily and the wet weight was assessed at the end of the experiment. The concentration that promoted 50% of inhibition in the growth rate in terms of fronds number (EC50-7d growth) and the concentration that promoted 50% of wet weight reduction (EC50-7d biomass) were calculated. The reduction of the growth rate by GO at the concentration of 100 mg L-1 was remarkable detected (P 100 mg L-1. This value attributes a practically non-toxicity for the test-material in terms of fronds production. On the other hand, the calculated EC50-7d biomass for the GO in the presence of HA or not was 2.8 and 2.4 mg L-1 respectively. These results indicate that the adverse effects of GO in L. minor are more pronounced on the biomass production since it was clearly observed that reductions in the fronds sizes were greater than in the fronds number. The EC50-7d biomass values assigns a moderate toxicity of GO to L. minor and these data may be useful for the establishment of maximum concentrations limits of this material in water bodies

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

Systematic Analytical Approach to Correlation Functions of Resonances in Quantum Chaotic Scattering

We solve the problem of resonance statistics in systems with broken time-reversal invariance by deriving the joint probability density of all resonances in the framework of a random matrix approach and calculating explicitly all n-point correlation functions in the complex plane. As a by-product, we establish the Ginibre-like statistics of resonances for many open channels. Our method is a combination of Itzykson-Zuber integration and a variant of nonlinear $\sigma-$model and can be applied when the use of orthogonal polynomials is problematic.Comment: 4 pages, no figures. Misprints corrected, some details on single-channel and many-channel cases are adde

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

Efeitos da exposição aguda ao dimetoato em microcrustáceos e anelídeos.

Resumo: O dimetoato é um inseticida organofosforado de amplo espectro que penetra no corpo através da ingestão, inalação e contato com a pele. Em animais, pode ser metabolizado em produtos de oxidação mais tóxicos afetando muitos organismos não-alvo, incluindo invertebrados aquáticos e do solo. Tanto o microcrustáceo Daphnia magna quanto a minhoca Eisenia fetida são organismos adequados para ensaios de toxicidade, uma vez que pode ser facilmente criados e possuem curto ciclo de vida. O objetivo desse estudo foi avaliar a toxicidade aguda (48h) do dimetoato no microcrustáceo Daphnia magna enquanto organismo-teste aquático e avaliar os efeitos do dimetoato grau técnico sobre a sobrevivência de Eisenia fetida. Procurou-se também verificar a viabilidade do método de contato com papel de filtro para avaliação de ensaios de toxicidade aguda com minhocas. A CE50 para Daphnia magna foi de 0,99 mg/L com intervalo de confiança 95% de 1,22 - 1,54. A CL50 foi de 1083,55 mg/L de dimetoato grau técnico com limites inferiores e superiores a 95% de 711,23 ? 1375,55 mg/L para a E. fetida. O dimetoato grau técnico apenas apresentou letalidade a 50% da população em concentração acima de 1000 mg/L o que pode ser considerado praticamente não tóxico a organismos não-alvo do solo. Foi evidenciada também a eficiência do método de contato com papel de filtro como ferramenta para avaliação de toxicidade para E. fetida.bitstream/item/138620/1/2015AA061.pd

Statistics of S-matrix poles for chaotic systems with broken time reversal invariance: a conjecture

In the framework of a random matrix description of chaotic quantum scattering the positions of $S-$matrix poles are given by complex eigenvalues $Z_i$ of an effective non-Hermitian random-matrix Hamiltonian. We put forward a conjecture on statistics of $Z_i$ for systems with broken time-reversal invariance and verify that it allows to reproduce statistical characteristics of Wigner time delays known from independent calculations. We analyze the ensuing two-point statistical measures as e.g. spectral form factor and the number variance. In addition we find the density of complex eigenvalues of real asymmetric matrices generalizing the recent result by Efetov\cite{Efnh}.Comment: 4 page

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

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