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Variance estimate and taxonomic resolution: an analysis of macrobenthic spatial patterns at different scales in a Western Mediterranean coastal lagoon
No full textSUMMARY- The effects of taxonomic resolution on the variance estimates of macrobenthic assemblages were studied at four spatial scales in a Mediterranean coastal lagoon. The assemblages exhibited significant differences at all the investigated scales; however, spatial variability was mainly associated with the smallest and the largest scales. The decrease of taxonomic resolution (from species to family) was not related to a decrease of the overall variability and similar estimates of variance components were obtained using species and family resolution levels. The ordination models derived from species and family abundances were very similar both in terms of location and dispersion effect, while further aggregation to the class level began to alter the observed spatial patterns. In future studies aimed at assessing changes in the lagoon, resources derived from the cost reductions achieved using family level could be employed to plan more frequent surveys and/or to adopt complex spatial sampling designs with a high number of replicates
Spectral gap global solutions for degenerate Kirchhoff equations
No full textWe consider the second order Cauchy problem View the MathML source where m:[0,+∞)→[0,+∞) is a continuous function, and A is a self-adjoint nonnegative operator with dense domain on a Hilbert space. It is well known that this problem admits local-in-time solutions provided that u0 and u1 are regular enough, depending on the continuity modulus of m, and on the strict/weak hyperbolicity of the equation. We prove that for such initial data (u0,u1) there exist two pairs of initial data View the MathML source, View the MathML source for which the solution is global, and such that View the MathML source, View the MathML source. This is a byproduct of a global existence result for initial data with a suitable spectral gap, which extends previous results obtained in the strictly hyperbolic case with a smooth nonlinearity m
FPGA/DSP-based Implementation of a High-Performance Multi-Channel Counter
No full textA high-performance configurable multi-channel counter is presented. The system has been implemented on a small-size and low-cost Commercial-Off-The-Shelf (COTS) FPGA/DSP-based board, and features 64 input channels, a maximum counting rate of 45 MHz, and a minimum integration window (time resolution) of 24 μs with a 23 b counting depth. In particular, the time resolution depends on both the selected counting bit-depth and the number of acquisition channels: indeed, with a 8 b counting depth, the time resolution reaches the value of 8 μs if all the 64 input channels are enabled, whereas it lowers to 378 ns if only 2 channels are used. Thanks to its flexible architecture and performance, the system is suitable in highly demanding photon counting applications based on SPAD arrays, as well as in many other scientific experiments. Moreover, the collected counting results are both real-time processed and transmitted over a high-speed IEEE 1394 serial link. The same link is used to remotely set up and control the entire acquisition process, thus giving the system a even higher degree of flexibility. Finally, a theoretical model of general use which immediately provides the overall system performance is described. The model is then validated by the reported experimental results
An experimental analysis of abrasive water jet engraving of Italian marbles / Analisi sperimentale del processo di marcatura su marmi italiani tramite getto d’acqua ad alta pressione con abrasivo
No full textEnglish: This article concerns characterizing and optimizing the process of water-jet engraving on stone materials through experimental analysis. The purpose is to find possible relationships between work parameters for an abrasive water-jet and the geometrical parameters created by grooves. Samples of White Carrara and Perlato of Coreno marbles were used in testing. An optical profilometer was used to measure the transversal profile of the groove, objectively characterized by a number of measurements described in the article, including two parameters of visual quality. Statistical analysis made it possible to indicate optimal settings to enter on the basis of desired results; for example, increases in width, depth or the degree of groove contrast. Italian: Questo articolo affronta la caratterizzazione e ottimizzazione del processo di incisione di materiali lapidei mediante water jet attraverso un’analisi sperimentale. La finalità è trovare possibili relazioni tra parametri impostati per la lavorazione, tramite idrogetto con abrasivo, e parametri geometrici ricavati dai solchi. Per questo studio sono stati analizzati dei campioni di marmo Bianco di Carrara e di Perlato di Coreno. Per mezzo di un profilometro ottico è stato possibile misurare il profilo trasversale del solco, caratterizzato in maniera oggettiva tramite alcune misure descritte nell’articolo, inclusi due parametri di qualità visiva. Attraverso un’analisi statistica è stato possibile indicare le impostazioni ottimali da settare in base al risultato desiderato: es. aumento della larghezza, profondità o livello di contrasto del solco
Characterization of the pheromone gene family of an antarctic and arctic protozoan ciliate, Euplotes nobilii
No full textSUMMARY: Allelic genes encoding water-borne signal proteins (pheromones) were amplified and sequenced from the somatic (macronuclear) sub-chromosomic genome of Antarctic and Arctic strains of the marine ciliate, Euplotes nobilii. Their open reading frames appeared to be specific for polypeptide sequences of 83 to 94 amino acids identifiable with cytoplasmic pheromone precursors (pre-pro-pheromones), requiring two proteolytic steps to remove the pre- and pro-segments and secrete the mature pheromones. Differently from most of the macronuclear genes that have so far been characterized from Euplotes and other hypotrich ciliates, the 5′ and 3′ non-coding regions of all the seven E. nobilii pheromone genes are much longer than the coding regions (621 to 700 versus 214 to 285 nucleotides), and the 5′ regions in particular show nearly identical sequences across the whole set of pheromone genes. These structural peculiarities of the noncoding regions are likely due to the presence of intron sequences and provide presumptive evidence that they are site of basic, conserved activities in the mechanism that regulates the expression of the E. nobilii pheromone genes
AN ANALYTICAL METHOD FOR THE OPTIMUM THERMAL DESIGN OF CONVECTIVE LONGITUDINAL FIN ARRAYS
No full textSUMMARY The paper analyzes the problem of the optimum thermal design of free and forced convection fin arrays composed of longitudinal fins with constant thickness. Two different optimization problems have been considered: the minimization of the weight for a given heat flow and the maximization of the heat flow for a given fin weight. Two different geometrical configurations of the fin array have been considered: closed array and open array. The procedure for the optimization is provided in a general case and a complete analytical solution of the problem, for the case with the tip approximated as being insulated, is developed. The paper contains several illustrative examples of the application of the proposed optimization procedure
Thermal monopoles and selfdual dyons in the Quark-Gluon Plasma
No full textWe perform a numerical study of the excess of non-abelian gauge invariant
gluonic action around thermal abelian monopoles which populate the deconfined
phase of Yang-Mills theories. Our results show that the excess of magnetic
action is close to that of the electric one, so that thermal abelian monopoles
may be associated with physical objects carrying both electric and magnetic
charge, i.e. dyons. Thus, the quark gluon plasma is likely to be populated by
selfdual dyons, which may manifest themselves in the heavy-ion collisions via
the chiral magnetic effect. Thermodynamically, thermal monopoles provide a
negative contribution to the pressure of the system
Maximal width of the separatrix chaotic layer
No full textSUMMARY The main goal of the paper is to find the {\it absolute maximum} of the width
of the separatrix chaotic layer as function of the frequency of the
time-periodic perturbation of a one-dimensional Hamiltonian system possessing a
separatrix, which is one of the major unsolved problems in the theory of
separatrix chaos. For a given small amplitude of the perturbation, the width is
shown to possess sharp peaks in the range from logarithmically small to
moderate frequencies. These peaks are universal, being the consequence of the
involvement of the nonlinear resonance dynamics into the separatrix chaotic
motion. Developing further the approach introduced in the recent paper by
Soskin et al. ({\it PRE} {\bf 77}, 036221 (2008)), we derive leading-order
asymptotic expressions for the shape of the low-frequency peaks. The maxima of
the peaks, including in particular the {\it absolute maximum} of the width, are
proportional to the perturbation amplitude times either a logarithmically large
factor or a numerical, still typically large, factor, depending on the type of
system. Thus, our theory predicts that the maximal width of the chaotic layer
may be much larger than that predicted by former theories. The theory is
verified in simulations. An application to the facilitation of global chaos
onset is discussed
Time-resolved measurement of Landau-Zener tunneling in periodic potentials
No full textSUMMARY We report time-resolved measurements of Landau-Zener tunneling of
Bose-Einstein condensates in accelerated optical lattices, clearly resolving
the step-like time dependence of the band populations. Using different
experimental protocols we were able to measure the tunneling probability both
in the adiabatic and in the diabatic bases of the system. We also
experimentally determine the contribution of the momentum width of the Bose
condensates to the width of the tunneling steps and discuss the implications
for measuring the jump time in the Landau-Zener problem
On some rescaled shape optimization problems
No full textSUMMARY We consider Cheeger-like shape optimization problems of the form
where is a
given bounded domain and is above the natural scaling. We show the
existence of a solution and analyze as the particular cases of the
compliance functional and of the first eigenvalue
of the Dirichlet Laplacian. We prove that optimal sets are
open and we obtain some necessary conditions of optimality