http://www.infn.it/pubblicazioni it-IT INFN - Dataweb 79,044001 (2009)

Viable models of modified gravity which satisfy both local as well as cosmological tests are investigated. It is demonstrated that some versions of such highly nonlinear models exhibit multiple de Sitter universe solutions, which often appear in pairs, one of them being stable and the other unstable. It is explicitly shown that, for some values of the parameters, it is possible to find several de Sitter spaces (as a rule, numerically); one of them may serve for the inflationary stage, while the other can be used for the description of the dark energy epoch. The numerical evolution of the effective equation of state parameter is also presented, showing that these models can be considered as natural candidates for the unification of early-time inflation with late-time acceleration through de Sitter critical points. Moreover, based on the de Sitter solutions, multiple Schwarzschild-de Sitter universes are constructed which might also appear at the (pre-)inflationary stage. Their thermodynamics are studied and free energies are compared.]]> Thu, 18 Mar 2010 11:01:37 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000263816800052 40, (2007)

Ideas and techniques (asymptotic decoupling of single-trace subspace, asymptotic operator algebras, duality and role of supersymmetry) relevant in current Fock space investigations of quantum field theories have very simple roles in a class of toy models.]]> Wed, 10 Mar 2010 14:03:28 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000245035200001 24, (2009)

Inflation is today a part of the Standard Model of the Universe supported by the cosmic microwave background (CMB) and large scale structure (LSS) datasets. Inflation solves the horizon and flatness problems and naturally generates density fluctuations that seed LSS and CMB anisotropies, and tensor perturbations (primordial gravitational waves). Inflation theory is based on a scalar field phi (the inflaton) whose potential is fairly. at, leading to a slow-roll evolution. This review focuses on the following new aspects of inflation. We present the effective theory of inflation a la Ginsburg and Landau, in which the inflaton potential is a polynomial in the field phi and has the universal form V (phi) = NM(4)w(phi/[root NMP1]), where w = O(1), M << M-P1 is the scale of inflation and N similar to 60 is the number of e-folds since the cosmologically relevant modes exit the horizon till inflation ends. The slow-roll expansion becomes a systematic 1/N expansion and the inflaton couplings become naturally small as powers of the ratio (M/M-P1)(2). The spectral index and the ratio of tensor/scalar fluctuations are n(s) - 1 = O(1/N), r = O(1/N), while the running index turns out to be dn(s)/d ln k = O(1/N-2) and therefore can be neglected. The energy scale of inflation M similar to 0.7 x 10(16) GeV is completely determined by the amplitude of the scalar adiabatic fluctuations. A complete analytic study plus the Monte Carlo Markov chain (MCMC) analysis of the available CMB+LSS data (including WMAP5) with fourth degree trinomial potentials showed: (a) the spontaneous breaking of the phi -> -phi symmetry of the inflaton potential; (b) a lower bound for r in new inflation: r > 0.023 (95% CL) and r > 0.046 (68 CL); (c) the preferred inflation potential is a double-well, even function of the field with a moderate quartic coupling yielding as the most probable values n(s) similar or equal to 0.964, r similar or equal to 0.051. This value for r is within reach of forthcoming CMB observations. The present data in the effective theory of inflation clearly prefer new inflation. Study of higher degree inflaton potentials shows that terms of degree higher than 4 do not affect the fit in a significant way. In addition, a horizon exit happens for phi/[root N M-P1] similar to 0.9, making higher order terms in the potential w negligible. We summarize the physical effects of generic initial conditions (different from Bunch-Davies) on the scalar and tensor perturbations during slow roll and introduce the transfer function D(k), which encodes the observable initial condition effects on the power spectra. These effects are more prominent in the low CMB multipoles: a change in the initial conditions during slow roll can account for the observed CMB quadrupole suppression. Slow-roll inflation is generically preceded by a short, fast-roll stage. Bunch-Davies initial conditions are the natural initial conditions for the fast-roll perturbations. During fast roll, the potential in the wave equations of curvature and tensor perturbations is purely attractive and leads to a suppression of the curvature and tensor CMB quadrupoles. An MCMC analysis of the WMAP+SDSS data including fast roll shows that the quadrupole mode exits the horizon about 0.2 e-fold before fast roll ends and its amplitude gets suppressed. In addition, fast roll fixes the initial inflation redshift to be z(init) = 0. 9 x 10(56) and the total number of e-folds of inflation to be N-tot &SIME 64. Fast roll fits the TT, the TE and the EE modes well, reproducing the quadrupole suppression. A thorough study of the quantum loop corrections reveals that they are very small and are controlled by powers of (H/M-P1)(2) similar to 10(-9), a conclusion that validates the reliability of the effective theory of inflation. The present review shows how powerful the Ginsburg-Landau effective theory of inflation is in predicting observables that are being or will soon be contrasted with observations.]]> Tue, 09 Mar 2010 19:18:50 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000269142400001 6,025012 (2009)

Circular DNA in viruses and bacteria is often knotted. While mathematically problematic, the determination of the knot size is crucial for the study of the physical and biological behaviour of long macromolecules. Here, we review work on the size distribution of these knots under equilibrium conditions. We discuss knot localization in good and poor solvents, or in polymers that are adsorbed on a surface. We also discuss recent evidence that knot size is a crucial quantity in relaxation processes of knotted polymers.]]> Tue, 09 Mar 2010 19:18:50 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000267941700013 76,051804 (2007)

We study by Monte Carlo simulations a model of a knotted polymer ring adsorbing onto an impenetrable, attractive wall. The polymer is described by a self-avoiding polygon on the cubic lattice. We find that the adsorption transition temperature, the crossover exponent phi, and the metric exponent nu are the same as in the model where the topology of the ring is unrestricted. By measuring the average length of the knotted portion of the ring, we are able to show that adsorbed knots are localized. This knot localization transition is triggered by the adsorption transition but is accompanied by a less sharp variation of the exponent related to the degree of localization. Indeed, for a whole interval below the adsorption transition, one can not exclude a contiuous variation with temperature of this exponent. Deep into the adsorbed phase we are able to verify that knot localization is strong and well described in terms of the flat knot model.]]> Tue, 09 Mar 2010 19:18:50 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000251326100069 75,041105 (2007)

We give two different, statistically consistent definitions of the length l of a prime knot tied into a polymer ring. In the good solvent regime the polymer is modeled by a self avoiding polygon of N steps on cubic lattice and l is the number of steps over which the knot "spreads" in a given configuration. An analysis of extensive Monte Carlo data in equilibrium shows that the probability distribution of l as a function of N obeys a scaling of the form p(l,N)similar to l(-c)f(l/N-D), with c similar or equal to 1.25 and D similar or equal to 1. Both D and c could be independent of knot type. As a consequence, the knot is weakly localized, i.e., < l >similar to N-t, with t=2-c similar or equal to 0.75. For a ring with fixed knot type, weak localization implies the existence of a peculiar characteristic length l(nu)similar to N-t nu. In the scaling similar to N-nu (nu similar or equal to 0.58) of the radius of gyration of the whole ring, this length determines a leading power law correction which is much stronger than that found in the case of unrestricted topology. The existence of this correction is confirmed by an analysis of extensive Monte Carlo data for the radius of gyration. The collapsed regime is studied by introducing in the model sufficiently strong attractive interactions for nearest neighbor sites visited by the self-avoiding polygon. In this regime knot length determinations can be based on the entropic competition between two knotted loops separated by a slip link. These measurements enable us to conclude that each knot is delocalized (t similar or equal to 1).]]> Tue, 09 Mar 2010 19:18:50 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000246073900021 106, (2009)

Recent experiments showed that the linear double-stranded DNA in bacteriophage capsids is both highly knotted and neatly structured. What is the physical basis of this organization? Here we show evidence fromstochastic simulation techniques that suggests that a key element is the tendency of contacting DNA strands to order, as in cholesteric liquid crystals. This interaction favors their preferential juxtaposition at a small twist angle, thus promoting an approximately nematic (and apolar) local order. The ordering effect dramatically impacts the geometry and topology of DNA inside phages. Accounting for this local potential allows us to reproduce the main experimental data on DNA organization in phages, including the cryo-EM observations and detailed features of the spectrum of DNA knots formed inside viral capsids. The DNA knots we observe are strongly delocalized and, intriguingly, this is shown not to interfere with genome ejection out of the phage.]]> Tue, 09 Mar 2010 19:18:49 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000273178700043 59, (2009)

We interpret the phase structure of hadronic matter in terms of the basic dynamical and geometrical features of hadrons. Increasing the density of constituents of finite spatial extension, by increasing the temperature T or the baryochemical potential mu, eventually "fills the box" and eliminates the physical vacuum. We determine the corresponding transition as a function of T and mu through percolation theory. At low baryon density, this means a fusion of overlapping mesonic bags to one large bag, while at high baryon density, hard-core repulsion restricts the spatial mobility of baryons. As a consequence, there are two distinct limiting regimes for hadronic matter. We compare our results to those from effective chiral model studies.]]> Mon, 08 Mar 2010 18:52:17 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000262316900005 ,038 (2007)

We consider then on commutative extension of Chern-Simons theory.We show the the theory can be fully expanded in power series of the non commutative parameter and that no non-analytical sector exists.The theory appears to be unstable under radiative corrections,but we show that the infinite set of instabilities,to all order sin h and in theta is confined to a BR Sexactcocycle. We show also that the theory is anomaly free.The quantum theory cannot be written in terms of the Groenewald-Moyal star product,and hence doubts arise on the interpretation of the noncommutative nature of the underlying spacetime. Nonetheless,the deformed theory is well defined as a quantum field theory,and the beta function of the Chern-Simons coupling constant vanishes, as in the ordinary Chern-Simons theory.]]> Mon, 08 Mar 2010 17:16:46 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000250759700073 69, (2007)

We introduce a degenerate nonlinear parabolic-elliptic system, which describes the chemical aggression of limestones under the attack of SO2, in high permeability regime. By means of a dimensional scaling, the qualitative behavior of the solutions in the fast reaction limit is investigated. Explicit asymptotic conditions for the front formation are derived.]]> Mon, 08 Mar 2010 17:07:35 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000247505700007 60, (2007)

We derive an asymptotic solution of the vacuum Einstein equations that describe the propagation and diffraction of a localized, large-amplitude, rapidly varying gravitational wave. We compare and contrast the resulting theory of strongly nonlinear geometrical optics for the Einstein equations with nonlinear geometrical optics theories for variational wave equations. (c) 2007 Wiley Periodicals, Inc.]]> Mon, 08 Mar 2010 17:07:35 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000249938100004 69, (2007)

We present a numerical investigation of a degenerate nonlinear parabolic-elliptic system, which describes the chemical aggression of limestones under the attack of SO2, in high permeability regime. This system has been introduced in the first part of this paper. We present a finite element scheme for our model and its numerical stability is given under suitable CFL conditions. Numerical tests are discussed as well as some examples of the numerical behavior of the solutions.]]> Mon, 08 Mar 2010 17:07:35 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000248307300003 78,031601 (2008)

With the aim at quantitatively investigating the longstanding problem concerning the effect of short-range nucleon-nucleon correlations on scattering processes at high energies, the total neutron-nucleus cross section is calculated within a parameter-free approach which, for the first time, takes into account, simultaneously, central, spin, isospin, spin-isospin, and tensor nucleon-nucleon correlations, and Glauber elastic and Gribov inelastic shadowing corrections. Nuclei ranging from He-4 to Pb-208 and incident neutron momenta in the range 3 GeV/c-300 GeV/c are considered; the commonly used approach which approximates the square of the nuclear wave function by a product of one-body densities is carefully analyzed, showing that NN correlations can play a non-negligible role in high energy scattering off nuclei.]]> Sat, 06 Mar 2010 18:57:19 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000259692300005 73,235341 (2006)

We calculate ground state energies in the Brueckner-Hartree-Fock theory for N electrons (with N <= 20) confined to a circular quantum dot and in presence of a static magnetic field. Comparison with the predictions of Hartree-Fock, local-spin-density and exact configuration-interaction theories is made. We find that the correlations taken into account in Brueckner-Hartree-Fock calculations give an important contribution to the ground state energies, especially in strongly confined dots. In this high-density range, corresponding in practice to self-assembled quantum dots, the results of Brueckner-Hartree-Fock calculations are close to the exact values and better than those obtained in the local-spin-density approximation.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238696600109 29, (2006)

Traditionally X-ray sources used in mammography are X-ray tubes. Synchrotron radiation sources have shown better imaging performances, but they cannot replace conventional X-ray tube systems in routine mammographic examinations. A new generation of quasi-mono chromatic, high-flux X-ray sources is currently under development, based on Thomson backscattering of photons produced by a laser on a highly focused electron beam. They offer important potential applications in the medical field. In this work, we will discuss an application in the field of mammography, by using a Monte Carlo code, in which the effect of different spectral distributions and different mean energies on the image quality is studied. A test object, consisting of a block of Polymethyl Methacrylate (PMMA) containing air-filled holes (Contrast Detail Phantom) is used for the simulations. Results show 1-2 keV of energy spread for a quasi-monochromatic source produce images whose quality is comparable within 3-4% with those obtained by monochromatic sources and whose visibility is dramatically enhanced with respect to images obtained with X-ray tubes.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238723600004 747, (2006)

A comprehensive study is performed of two-loop Feynman diagrams with three external legs which, due to the exchange of massless gauge-bosons, give raise to infrared and collinear divergencies. Their relevance in assembling realistic computations of next-to-next-to-leading corrections to physical observables is emphasized. A classification of infrared singular configurations, based on solutions of Landau equations, is introduced. Algorithms for the numerical evaluation of the residues of the infrared poles and of the infrared finite parts of diagrams are introduced and discussed within the scheme of dimensional regularization. Integral representations of Feynman diagrams which form a generalization of Nielsen-Goncharov polylogarithms are introduced and their numerical evaluation discussed. Numerical results are shown for all different families of multi-scale, two-loop, three-point infrared divergent diagrams and successful comparisons with analytical results, whenever available, are performed. Part of these results has already been included in a recent evaluation of electroweak pseudo-observables at the two-loop level. (c) 2006 Elsevier B.V. All rights reserved.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238722400005 562, (2006)

The design of a four sector compact superconducting cyclotron, able to accelerate up to 250 A MeV light ions with charge/mass ratio 0.5, is in progress. Light ions like C-12(6+) B-10(5+), Li-6(3+) will be extracted by electrostatic deflectors while H-2(+) ions can be extracted also by stripping, therefore a beam power of 10 kW or more is available. This cyclotron can be used for radiotherapy with protons or carbon ions and also to drive a facility for production of unusual medical radioisotopes. The main parameters and some features of the machine are here presented. (c) 2006 Elsevier B.V. All rights reserved.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238764500111 563, (2006)

A readout card based on the standard PCI 32-bit/33 MHz bus has been developed for the fast readout of digital systems. The PCI card exploits a PCI bridge chip with Direct Memory Access (DMA) capabilities which permits to obtain a measured throughput up to 90 Mbytes/s. The PCI card has two high-density 80-pin connectors for data I/O; an external system acquisition card can be connected through two flat cables. A powerful programmable logic FPGA provides the management of the I/O lines; by default, 32 input and 32 output single-ended lines (CMOS) plus six LVDS lines are provided, but the FPGA allows several different I/O configurations depending on the specific application requirements. Another programmable device manages the control and status signals of the local bus and the Synchronous Static RAM available for data storage. Due to its main features like the configurable I/O patterns and the high throughput, this PCI card is suitable for applications like the fast readout of imaging acquisition systems. (c) 2006 Elsevier B.V. All rights reserved.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238764700027 563, (2006)

In digital imaging the ability to detect low contrast details is an aim that must be pursued. In order to achieve this result we have developed an acquisition system based on silicon pixel detector. The detector is a matrix of 256 x 256 square pixels of 55 mu m size. It is bump-bonded to a readout chip developed by the Medipix2 Collaboration [X. Llopart, et al., IEEE Trans. Nucl. Sci, NS-49 (5) (2002) 2279]. To see the low contrast details with this system, it is necessary to reduce inside the image the fluctuations of pixel-to-pixel counts, [1] down to statistical fluctuations. This has been achieved equalizing the phantom image with a high statistics flat field acquired in the same irradiation condition. We have studied the dependence of the image uniformity for different flat field and we have investigated the dependence of the image quality on the thickness of the phantom and on the energy window selected inside the incident spectrum. (c) 2006 Elsevier B.V. All rights reserved.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238764700034 47,062104 (2006)

We show that a POV measure F on the Borel sigma-algebra of the reals B(R) is commutative if and only if there exists a PV measure E on B(R) and, for every lambda in the spectrum of E, a probability measure gamma((center dot))(lambda) on B(R) such that the effect F(Delta) coincides with gamma(Delta)(A), where A is the self-adjoint operator associated to E. The relevance of this result to the theory of the sharp reconstruction is analyzed. (c) 2006 American Institute of Physics.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238730900004 47,062901 (2006)

A one-dimensional system made up of a compressible fluid and several mechanical oscillators, coupled to the acoustic field in the fluid, is analyzed for different settings of the oscillator array. The dynamical models are formulated in terms of singular perturbations of the decoupled dynamics of the acoustic field and the mechanical oscillators. Detailed spectral properties of the generators of the dynamics are given for each model we consider. In the case of a periodic array of mechanical oscillators it is shown that the energy spectrum presents a band structure. (c) 2006 American Institute of Physics.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238730900023 47,063508 (2006)

The inverse scattering transform for the vector defocusing nonlinear Schrodinger (NLS) equation with nonvanishing boundary values at infinity is constructed. The direct scattering problem is formulated on a two-sheeted covering of the complex plane. Two out of the six Jost eigenfunctions, however, do not admit an analytic extension on either sheet of the Riemann surface. Therefore, a suitable modification of both the direct and the inverse problem formulations is necessary. On the direct side, this is accomplished by constructing two additional analytic eigenfunctions which are expressed in terms of the adjoint eigenfunctions. The discrete spectrum, bound states and symmetries of the direct problem are then discussed. In the most general situation, a discrete eigenvalue corresponds to a quartet of zeros (poles) of certain scattering data. The inverse scattering problem is formulated in terms of a generalized Riemann-Hilbert (RH) problem in the upper/lower half planes of a suitable uniformization variable. Special soliton solutions are constructed from the poles in the RH problem, and include dark-dark soliton solutions, which have dark solitonic behavior in both components, as well as dark-bright soliton solutions, which have one dark and one bright component. The linear limit is obtained from the RH problem and is shown to correspond to the Fourier transform solution obtained from the linearized vector NLS system. (c) 2006 American Institute of Physics.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238730900036 57, (2006)

We review the current status of neutrino mass and mixing parameters, as derived from an up-to-date phenomenological analysis of world neutrino oscillation and non-oscillation data, performed within the standard three-neutrino mixing framework. (c) 2005 Elsevier B.V. All rights reserved.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238001000008 57, (2006)

We present an innovation in the structure of a bolometer which overcomes one of the drawbacks of the calorimetric mode. In this work we prove that studying the dynamics of the heat flow in the detector we can obtain information on the particle impact point and we are able to develop a new technique for an active background discrimination, in particular in view of the CUORE experiment. (c) 2005 Elsevier B.V. All rights reserved.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238001000033 57, (2006)

LUNA, Laboratory for Underground Nuclear Astrophysics at Gran Sasso, is studying thermonuclear reactions down to the energy of the nucleosynthesis inside stars. Significant results, relevant for neutrino physics and cosmology, have been the measurements of He-3(He-3, 2p)He-4 within the Gamow peak of the Sun and of N-14(p, gamma)O-15 down to very low energy. The results will be presented and their implications will be discussed. (c) 2005 Elsevier B.V All rights reserved.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238001000043 51, (2006)

We investigate the electronic instabilities of the small-diameter (3, 3) carbon nanotubes by studying the low-energy perturbations of the normal Luttinger liquid regime. The bosonization approach is adopted to deal exactly with the interactions in the forward-scattering channels, while renormalization group methods are used to analyze the low-energy instabilities. In this respect, we take into account the competition between the effective e-e interaction mediated by phonons and the Coulomb interaction in backscattering and Umklapp channels. Moreover, we apply our analysis to relevant experimental conditions where the nanotubes are assembled into large three-dimensional arrays, which leads to an efficient screening of the Coulomb potential at small momentum-transfer. We find that the destabilization of the normal metallic behavior takes place through the onset of critical behavior in some of the two charge stiffnesses that characterize the Luttinger liquid state. From a physical point of view, this results in either a divergent compressibility or a vanishing renormalized velocity for current excitations at the point of the transition. We observe anyhow that this kind of critical behavior occurs without the development of any appreciable sign of superconducting correlations.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238670700014 16,023120 (2006)

Entropy creation rate is introduced for a system interacting with thermostats (i.e., for a system subject to internal conservative forces interacting with "external" thermostats via conservative forces) and a fluctuation theorem for it is proved. As an application, a time scale is introduced, to be interpreted as the time over which irreversibility becomes manifest in a process leading from an initial to a final stationary state of a mechanical system in a general nonequilibrium context. The time scale is evaluated in a few examples, including the classical Joule-Thompson process (gas expansion in a vacuum).]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238729600020 454, (2006)

Context. Recent 3-D analysis of the solar spectrum data suggests a significant change of the solar chemical composition. This may affect the temporal evolution of the surface abundance of light elements since the extension of the convective envelope is largely affected by the internal opacity value. Aims. We analyse the influence of the adopted solar mixture on the opacity in the convective envelope of pre-main sequence (PMS) stars and thus on PMS lithium depletion. The surface Li abundance depends on the relative efficiency of several processes, some of them still not known with the required precision; this paper thus analyses one of the aspects of this "puzzle". Methods. Focusing on PMS evolution, where the largest amount of Li burning occurs, we computed stellar models for three selected masses (0.8, 1.0 and 1.2 M-circle dot, with Z = 0.013, Y = 0.27, alpha = 1.9) by varying the chemical mixture, that is the internal element distribution in Z. We analysed the contribution of the single elements to the opacity at the temperatures and densities of interest for Li depletion. Several mixtures were obtained by varying the abundance of the most important elements one at a time; we then calculated the corresponding PMS Li abundance evolution. Results. We found that a mixture variation does change the Li abundance: at fixed total metallicity, the Li depletion increases when increasing the fraction of elements heavier than O.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238726300037 637, (2006)

In this Letter we study topological open string field theory on D-branes in a IIB background given by non-compact CY geometries O(n) circle plus O(-2-n) on P-1 with a singular point at which an extra fiber sits. We wrap N D5-branes on P-1 and M effective D3-branes at singular points, which are actually D5-branes wrapped on a shrinking cycle. We calculate the holomorphic Chem-Simons partition function for the above models in a deformed complex structure and find that it reduces to multi-matrix models with flavour. These are the matrix models whose resolvents have been shown to satisfy the generalized Konishi anomaly equations with flavour. In the n = 0 case, corresponding to a partial resolution of the A(2) singularity, the quantum superpotential in the N = 1 unitary SYM with one adjoint and M fundamentals is obtained. The n = 1 case is also studied and shown to give rise to two-matrix models which for a particular set of couplings can be exactly solved. We explicitly show how to solve such a class of models by a quantum equation of motion technique. (c) 2006 Elsevier B.V. All rights reserved.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238399200016 637, (2006)

]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238459400006 638, (2006)

An interesting connection between the Regge theory of scattering, the Veneziano amplitude, the Lee-Yang theorems in statistical mechanics and nonextensive Renyi entropy is addressed. In this scheme the standard entropy and the Renyi entropy appear to be different limits of a unique mathematical object. This framework sheds light on the physical origin of nonextensivity. A non-trivial application to spin glass theory is shortly outlined. (c) 2006 Elsevier B.V. All rights reserved.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238489700014 355, (2006)

The use of non-Gaussian flat laser beams is currently under study to reduce the thermoelastic noise in the advanced gravitational wave interferometers. In this work we present a system based on two deformable mirrors to transform a Gaussian beam in a non-Gaussian flat beam. We use an approximated representation of flat beam based on the usual Hermite-Gaussian modes which is particularly useful when the flat beam is generated by using deformable mirrors. This system can be used either for flat beams generation or for beam matching in the mexican-hat mirrors Fabry-Perot cavities proposed for next generation of gravitational wave interferometers. (c) 2006 Elsevier B.V. All rights reserved.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238496900004 355, (2006)

Isochronous variants are introduced of two integrable lattices introduced by A.B. Shabat and R.I. Yarnilov, their equilibrium configurations are found (in the cases when they exist), and by investigating the motions of these systems near equilibrium some diophantine relations are discovered. (c) 2006 Elsevier B.V. All rights reserved.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238496900005 355, (2006)

]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238489900012 11, (2006)

Using the new generation Earth's gravity field models EIGEN-2S, GGM01S and EIGEN-GRACE02S generated by the space missions CHAMP and GRACE, we have obtained an accurate measurement of the Lense-Thirring effect with the LAGEOS and LAGEOS 11 satellites analyzing about 10 years of data with the EIGEN-2S and GGM01S models and about I I years of data with EIGEN-GRACE02S. This new analysis is in agreement with our previous measurements of the Lense-Thirring effect using the LAGEOS satellites and obtained with the JGM-3 and EGM96 Earth's models. However, the new determinations are more accurate and, especially, more robust than our previous measurements. In the present analysis we are only using the nodal rates of the two satellites, making no use of the perigee rate, as in our previous analyses. The perigee is affected by a number of non-gravitational perturbations difficult to be modelled and whose impact in the total error budget is not easy to assess. Using the EIGEN-2S model, we obtain a total error budget between 18% and 36%, of the Lense-Thirring effect due to all the error sources. Specifically, by using EIGEN-2S, we obtain: mu = 0.85, with a total error between 0.18 and 0.36, with GGM01S we get p = 1.06 with a total error between 0.19 and 0.24 and with EIGEN-GRACE02S we obtain p = 0.99, with a total error between 0.05 and 0.1, i.e., between 5% and 10% of the general relativistic predicted value of the Lense-Thirring effect. In addition to the analyses using EIGEN-2S, GGM01S and EIGEN-GRACE02S without the use of the perigee, we have also performed an analysis using the older model EGM96 with our previous method of combining the nodes of the LAGEOS satellites with the perigee of LAGEOS II. However, this analysis was performed over a period of about 10 years, i.e. about 2.5 times longer than any our previous analysis. The result using EGM96 over this longer period of observation agrees with our previous results over much shorter periods and with the EIGEN-2S, GGM01S and EIGEN-GRACE02S measurements of it. In addition to the accurate determination of frame-dragging and in agreement with our previous analyses of the orbits of the LAGEOS satellites, we have observed, since 1998, an anomalous change in the Earth quadrupole Coefficient, J(2) which agrees with recent findings of other authors. This anomalous variation of J(2) is accurately observed both on the node of LAGEOS and LAGEOS 11 and it is independent of the model used, i.e., it is observed by using the model EGM96 or by using EIGEN-2S, GGM01S or EIGEN-GRACE02S. However, this anomalous variation of the Earth quadrupole coefficient does not affect at all our determination of the Lense-Thirring effect thanks to the total elimination of the J(2)-induced errors with our especially devised estimation technique. (c) 2006 Elsevier B.V. All rights reserved.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238543000001 18, (2006)

We describe the results obtained from an improved model for protein folding. We find that a good agreement with the native structure of a 46-residue-long, five-letter protein segment is obtained by carefully tuning the parameters of the self-avoiding energy. In particular we find an improved free-energy profile. We also compare the efficiency of the multidimensional replica exchange method with the widely used parallel tempering.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238592700011 32, (2006)

Theorems on zeros of the truncated generating function in the complex plane are reviewed. When examined in the framework of a statistical model of high energy collisions based on the negative binomial (Pascal) multiplicity distribution, these results lead to maps of zeros of the grand canonical partition function which allow us to interpret in a novel way different classes of events in pp collisions at LHC c.m. energies.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238646000012 39, (2006)

A suitable plane transmission line was developed and its behaviour analysed at 900MHz radiofrequency fields to study DNA mutability and the repair of micro-organisms. In this work, utilizing such a device, we investigated the behaviour of DNA mutability and repair of Escherichia coli strains. The transmission line was very simple and versatile in changing its characteristic resistance and field intensity by varying its sizes. In the absence of cell samples inside the transmission line, the relative modulation of the electric and/or magnetic field was +/- 31% with respect to the mean values, allowing the processing of more samples at different exposure fields in a single run. A slight decrease in spontaneous mutability to rifampicin-resistance of the E. coli JC411 strain was demonstrated in mismatch-repair proficient samples exposed to the radio-frequency fields during their growth on solid medium.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238674100036 39, (2006)

A Cauchy problem on the semiline for a nonlinear diffusion equation is considered, with a boundary condition corresponding to a prescribed thermal conductivity at the origin. The problem is mapped into a moving boundary problem for the linear heat equation with a Robin-type boundary condition. Such a problem is then reduced to a linear integral Volterra equation of II type which admits a unique solution.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238553800010 39, (2006)

We focus on the transformation matrices between the standard Young Yamanouchi basis of an irreducible representation for the symmetric group S-n and the split basis adapted to the direct product subgroups S-n1 x Sn - n1. We introduce the concept of subduction graph and show that it conveniently describes the combinatorial structure of the equation system arisen from the linear equation method. Thus we can outline an improved algorithm to solve the subduction problem in symmetric groups by a graph searching process. We conclude by observing that the general matrix form formultiplicity separations, resulting from orthonormalization, can be expressed in terms of Sylvester matrices relative to a suitable inner product in the multiplicity space.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238554000009 39, (2006)

Novel integrable systems of coupled first-order autonomous PDEs in 1 + 1 dimensions ( space x and time t) are presented. Integrable covariant 2-vector and 3-vector PDEs, as well as higher-order integrable PDEs for a single, or a couple, of scalar-dependent variables ( including an extension of the sine-Gordon equation and a remarkably neat, highly nonlinear third-order PDE), are also obtained by appropriate reductions of the basic matrix equations. The Lax pairs that characterize the integrable character of the basic matrix PDEs are also exhibited, as well as their single-soliton solutions. These solitons generally exhibit the boomeronic ( and, less generically, the trapponic) phenomenology, namely they do not move uniformly, but rather ( in an appropriate reference system) come in from one end in the remote past and boomerang back to that same end in the remote future (boomerons), or are trapped to oscillate around a value fixed by the initial data (trappons).]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238571200010 39, (2006)

The Hankel determinant representations for the partition function and boundary correlation functions of the six-vertex model with domain wall boundary conditions are investigated by the methods of orthogonal polynomial theory. For specific values of the parameters of the model, corresponding to 1-, 2- and 3-enumerations of alternating signmatrices (ASMs), these polynomials specialize to classical ones (continuous Hahn, Meixner-Pollaczek and continuous dual Hahn, respectively). As a consequence, a unified and simplified treatment of ASM enumerations turns out to be possible, leading also to some new results such as the refined 3-enumerations of ASMs. Furthermore, the use of orthogonal polynomials allows us to express, for generic values of the parameters of the model, the partition function of the (partially) inhomogeneous model in terms of the one-point boundary correlation functions of the homogeneous one.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238571800016 21, (2006)

After a review of the few attempts to define quantum mechanics in noninertial frames, we introduce a family of relativistic nonrigid noninertial frames (equal-time parallel hyperplanes with differentially rotating 3-coordinates) as a gauge fixing of the description of N positive energy particles in the framework of parametrized Minkowski theories. Then we define a multitemporal quantization scheme in which the particles are quantized, but not the gauge variables describing the noninertial frames: they are considered as c-number generalized times. We study the coupled Schrodinger-like equations produced by the first class constraints and we show that there is a physical scalar product independent both from time and generalized times and a unitary evolution. Since a path in the space of the generalized times defines a nonrigid noninertial frame, we can find the associated self-adjoint effective Hamiltonian (H) over cap (ni) for the noninertial evolution: it differs from the inertial energy operator for the presence of inertial potentials and turns out to be frame-dependent like the energy density in general relativity. After a separation of the relativistic center of mass from the relative variables by means of a recently developed relativistic kinematics, inside (H) over tilde (ni) we can identify the self-adjoint relative energy operator (the invariant mass) M corresponding to the inertial energy and producing the same levels for the spectra of atoms as in inertial frames. Instead the (in general time-dependent) effective Hamiltonian is responsible for the interferometric effects signaling the noninertiality of the frame. It cannot be interpreted as an energy (there is no relativity principle and no kinematic group in noninertial frames) and generically, like in the case of time-dependent c-number external electromagnetic fields, it has no associated eigenvalue equation defining a noninertial spectrum. This formulation should help to find relativistic Bel inequalities and to define a quantization scheme for canonical gravity after having found a ultraviolet regularization of the Tomonaga-Schwinger formalism in special relativity as required by the Torre-Varadarajan no-go theorem.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238584400003 3, (2006)

We introduce the notion of extended wavelet transform for locally compact topological groups that are semidirect products with abelian normal factor, and we study its main properties. In particular, we show that this notion allows to define a weak wavelet transform - enjoying 'essentially' the same properties as a standard wavelet transform - associated with a group representation which is not square integrable, provided that suitable conditions are satisfied. As an application, we show that this construction allows to define (weak) wavelet transforms for (the universal covering of) the Poincare group, in spite of the fact that the discrete series of representations of this group is empty, so opening the possibility of achieving a remarkable representation of relativistic particles.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238454500001 3, (2006)

The would-be theory of quantum gravity, from which one should deduce the holographic principle, is not available yet. Here it is shown that the classical gravitational interaction is well inside the set of potentials allowed by the holographic principle. The role which such a principle could have in lowering the value of the cosmological constant computed in QFT to the observed one is clarified. It is also argued that, according to the Holographic Principle, the matter-antimatter asymmetry could behave like a seed for the inflationary phase of the universe. This scheme is supported by a good prediction of the number of e-folds. It seems that such a mechanism can only work in the presence of a Hagedorn-like phase transition. The issue of the "graceful exit" can be also naturally accounted for.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238454500004 3, (2006)

Exact solutions of Einstein field equations invariant for a non-Abelian bidimensional Lie algebra of Killing fields are described. Physical properties of these gravitational fields are studied, their wave character is checked by making use of covariant criteria and the observable effects of such waves are outlined. The possibility of detection of these waves with modern detectors, spherical resonant antennas in particular, is sketched.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238454500005 3, (2006)

The structure of space-time is analyzed by introducing a coordinate-free formulation of reference frame. Relativity groups emerge through the notion of equivalent frames. By means of the notion of objective existence, we show that transformations connecting equivalent frames are either Lorentz or generalized Galilei.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238454500011 3, (2006)

We classify the irreducible quaternionic representations of the extensions of internal symmetry groups by the group of space-time discrete symmetries. We obtain the possible forms of time reversal violating Hamiltonians in the case that the generalized parity operator is of geometrical type.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238454500014 53, (2006)

The Oscillation Project with Emulsion-tRacking Apparatus (OPERA) experiment will use a massive nuclear emulsion detector to search for nu(mu) -> nu(tau) oscillation by identifying tau leptons through the direct detection of their decay topology. The feasibility of experiments using a large mass emulsion detector is linked to the impressive progress under way in the development of automatic emulsion analysis. A new generation of scanning systems requires the development of fast automatic microscopes for emulsion scanning and image analysis to reconstruct tracks of elementary particles. The paper presents the European Scanning System (ESS) developed in the framework of OPERA collaboration.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238581900003 53, (2006)

The Agilent's G-Link serializers-deserializers are long lasting and widely used devices to implement serial links in the range of similar to 1 Gbit/s on copper and fibres. They feature a wide clocking window spanning the 13-70 MHz range, the ability to compensate for a constant phase delay in the clock distribution between the Tx and Rx node, low and deterministic link latency. All that makes this old-fashioned, power-hungry bipolar chipset still a popular choice in the design of modern trigger and data acquisition systems. The last entry in the family, named HDMP-103xA, has been released in the second half of 2001, as a drop-in replacement for the previous HDMP-103x silicon version. Despite the recent upgrade, the latest G-Link chip-set still suffers from subtle misbehaviors and undocumented bugs which may jeopardize even a very conservative design. In this paper we report our experience with G-Link during the design and test of the optical link for Level-1 Muon Trigger of the ATLAS experiment. We describe an ad-hoc platform developed for debugging the link and present the results of tests conducted in the lab.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238581900025 53, (2006)

We report on measurements performed to test the reliability of high rate data transmission over copper Gigabit Ethernet for the LHCb online system. High reliability of such transmissions will be crucial for the functioning of the software trigger layers of the LHCb experiment, at the CERN's LHC accelerator. The technological challenge in the system implementation consists of handling the expected high data throughput of event fragments using, to a large extent, commodity equipment. We report on performance evaluations (throughput, error rates and frame drop) of the main components involved in data transmission: the Ethernet cable, the PCI bus and the operating system (the latest kernel versions of Linux). Three different platforms have been used.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238581900027 53, (2006)

ARGO-YBJ is a full coverage air shower detector under construction at the Yangbajing Laboratory (4300 m a.s.l., Tibet, People Republic of China). Its main fields of research are gamma ray astronomy and cosmic ray studies. The detector covers similar to 5800 m(2) with single layer Resistive Plate Counters (RPCs), surrounded by a partially instrumented guard ring. This paper describes in detail the ARGO-YBJ Trigger Supervisor, which provides the interface between the Data Acquisition and the Trigger System. It is a simple and robust control instrument that monitors continuously the dead time at different levels in the Data Acquisition architecture. We present in this paper the results of the first pilot runs at the Yangbajing laboratory.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238581900033 53, (2006)

The Large Hadron Collider at CERN offers unprecedented challenges to the design and construction of detectors and trigger/data acquisition systems. For ATLAS, a three level trigger system has been developed to extract interesting physics signatures with a 106 rate reduction. To accomplish this, components of physics analysis traditionally deferred to off-line physics analysis must be embedded within the on-line trigger system. For the Muon trigger, the specific off-line algorithms MOORE (Muon Object Oriented REconstruction) and Muld (Muon Identification) have been adopted so far for the on-line use, imposing an operation in a Bayesian-like environment where only specific hypotheses must be validated. After a short review of the ATLAS trigger, the paper shows the general strategy of the Moon Identification and Selection accessing the full event data, or being seeded from results derived at a previous stage of the trigger chain.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238581900037 53, (2006)

In order to fully exploit all the possibilities of digital pulse shape acquisition with AZ/4 pi-multidetectors for charged products, we developed a case study of data acquisition system. The proposed object-oriented scalable architecture is distributed over a network of processing and storage units and based on a set of objects, each one devoted to a specific job. It performs on-line real-time acquisition and product identification, using sampling VME-ADCs and proper algorithms for digital signal processing. A PCI-VME bridge is used to interface the ADCs to a gigabit network of personal computers. Preliminary benchmarking tests have been carried out to determine performances and actual possibilities of the system.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238581900040 53, (2006)

The LHCb experiment at CERN has a large number of custom electronics boards performing high-speed data-processing. As in any large experiment the control and monitoring of these crate-mounted boards must be integrated into the overall control-system. Traditionally this has been done by using buses on the back-plane of the crates, such as VME. LHCb has chosen to equip every board with an embedded micro-controller and connecting them in a large Local Area Network. The intelligence of these devices allows complex (soft) real-time control and monitoring, required for modern field programmable gate array (FPGA) driven electronics. Moreover, each board has its own, isolated control access path, which increases the robustness of the entire system. The system is now in pre-production at several sites and will go into full production during next year. The hardware and software will be discussed and experience from the R&D and pre-production will be reviewed, with an emphasis on the advantages and difficulties of this approach to board-control.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238581900049 53, (2006)

Versatile Power Supply (VPS) Control is a component of a network-based control system and SCADA software with a client/server architecture developed using the Dataloggingzand Supervisory Control (DSC) by National Instruments. Installing OLE for Process Control (OPC) in the data server of VPS allows access to every kind of CAEN power supply (SY1527, SY527, etc.) that supports OPC server functionality and achieves integration of data and operation. Using VPS Graphic Panels, graphical menus with various data presentations have been created, so a new CAEN modules can be added without writing new code but only extending the Citadel Data Base. The data acquired to the Data Base server are accessible from the network.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238581900050 53, (2006)

An electronic board, called floor control module (FCM), was developed for the NEMO project, an underwater neutrino telescope. The offshore FCM is in charge of providing interfaces toward instrumental control boards, collecting data from up to eight readout channels, packing and sending streams to the onshore laboratory through an optical fiber driven by a dense wavelength division multiplexing (DWDM) electro-optical transceiver. To obtain a common timing at each level of the apparatus, communication adopts the synchronous digital hierarchy (SDH) protocol, a standard telecommunication synchronous format which allows clock recovery from bitstream, thus simplifying the distribution network. The channel is fully bidirectional to allow underwater apparatus control. The same FCM, plugged into a PCI bus, can also be used onshore for data reception and transmission. This architecture provides a complete real-time data transport layer between the onshore laboratory and the underwater detector.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238581900051 53, (2006)

In modern high energy and nuclear physics experiments, the complexity of gas detectors and their operation in areas not accessible during the data-taking periods require dedicated gas and safety systems running automatically and controlled by PC. In the FINUDA experiment, to control the gas systems of the drift and He chambers and to monitor the relevant parameters such as helium atmosphere purity and gas mixture composition which affect the experimental performances, three programs were written in National Instruments (NI) LabVIEW and Datalogging and Supervisory Control environment. Two safety systems work continuously to check the hydrocarbon leakages, inside and outside the He Chamber: pre-alarm and alarm signals feed a NI Field Point, where a real time program sends, via Ethernet, the FINUDA safety status to all detectors.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238581900052 53, (2006)

The design of a data acquisition system (DAQ) for a novel positron emission tomography (PET) scanner is reported. The PET system, based on long axially oriented scintillation crystals, readout by hybrid photon detectors (HPD), allows 3-D parallax-error free Compton enhanced gamma reconstruction. The DAQ system is composed of several readout cards, each one associated with a module of the PET scanner, and of a main card that controls the whole system. Using fast triggering signals from the silicon sensor back-planes, the main card performs the coincidence analysis and, in case of coincidence, it enables the readout of the two modules involved. The other modules are left free to perform new acquisitions. This concept based on several independent, event-driven and parallel readout chains, drastically reduces the acquisition dead time. Each enabled readout card digitizes, encodes and stores data from the associated module. Data are stored in a local FIFO and then are transferred through a network into a single computer. The system is designed according to the specifications of the IDEAS VaTaGP5. chip. Each readout card is able to accommodate all the chip readout modes and the test procedures and can be used as a standalone readout system that allows reading out up to 16 daisy chained chips per channel. The DAQ system here reported, designed for a two module demonstrator setup, was developed to study and optimize the essential design parameters.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238582000015 53, (2006)

A digital technique for high-resolution estimation of occurrence time of detected events is presented. The method achieves timing precisions well below the sampling time interval through a nonrecursive processing strategy. Due to linearity of the procedure, the processing runs online, and the architecture has been implemented in a configurable field programmable gate array (FPGA) device with a very limited resource burden. The method has been validated through processing of simulated and measured data and a full experimental assessment of the technique in an acquisition and processing digital setup for different operative conditions is at present going on.]]> Fri, 05 Mar 2010 17:03:33 +0100 http://www.infn.it/pubblicazioni/dettaglio.php?UT=ISI:000238582300002