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Search Results: 1 - 10 of 192145 matches for " D. Moretti "
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Limitations in the Use of the Equivalent Diameter  [PDF]
Licia Del Frate, Fabio Moretti, Giorgio Galassi, Francesco D’Auria
World Journal of Nuclear Science and Technology (WJNST) , 2016, DOI: 10.4236/wjnst.2016.61005
Abstract: This paper deals with the inaccuracy assessment of the friction pressure loss estimation based on Darcy formula combined with an equivalent hydraulic diameter and a friction factor valid for circular pipes when applied to a square rod bundle. The assessment has been done by comparing the analytical and semi-empirical predictions with two different CFD codes results: CFX and NEPTUNE_CFD. Two different analytical approaches have been considered: the whole-bundle and sub-channel approaches, both for laminar and turbulent flow conditions. Looking at results, it is reasonable to assume that an error in the range of 11% - 23% is likely when using equivalent diameter in the laminar regime. In the case of turbulent regime, the equivalent diameter works better and the error is in the range between a few percent and ~12%.
Detecting heavy charged Higgs bosons at the LHC with triple b-tagging
S. Moretti,D. P. Roy
Physics , 1999, DOI: 10.1016/S0370-2693(99)01291-5
Abstract: We investigate the charged Higgs boson signal at the LHC using its dominant production and decay modes with triple b-tagging, i.e. $tH^- \to t\bar tb \to b\bar bb W^+ W^-$, followed by leptonic decay of one W and hadronic decay of the other. We consider the continuum background from the associated production of $t\bar t$ with a b- or a light quark or gluon jet, which can be mis-tagged as b-jet. We reconstruct the top quark masses to identify the 3rd b-jet accompanying the $t\bar t$ pair, and use its p_T distribution to distinguish the signal from the background. Combining this with the reconstruction of the $H^\pm$ mass gives a viable signature over two interesting regions of the parameter space - i.e. $\tan\beta \sim 1$ and $\sim m_t/m_b$.
The triple Higgs self-coupling at future e+e- colliders: a signal-to-background study for the standard model
D. J. Miller,S. Moretti
Physics , 2000,
Abstract: The experimental reconstruction of the Higgs self-energy potential is essential to a verification of the Higgs boson's role in spontaneous electroweak symmetry breaking. The first step towards this goal, the measurement of the triple Higgs self-coupling, can possibly be accomplished at the next generation of linear colliders. Here we present a background study of the most promising channel, double Higgs-strahlung off a Z boson, e+e- -> HHZ, with the subsequent decay H -> b bbar, and evaluate the feasibility of its measurement.
Can the trilinear Higgs self-coupling be measured at future linear colliders?
D. J. Miller,S. Moretti
Physics , 1999, DOI: 10.1007/s100520050709
Abstract: We assess the possibility of measuring the trilinear self-coupling of the Standard Model Higgs boson at future electron-positron linear colliders with centre-of-mass energies between 500 and 1500 GeV. We consider rather light Higgs scalars, with mass below the W+W- threshold, produced in the double Higgs-strahlung channel e+e- -> HHZ and decaying via the dominant mode H -> bbbar. Assuming ideal vertex tagging of the heavy-quark jets and mass reconstruction of the Z boson produced in association with the Higgs pair, we compare the yield of the above process to those of all irreducible electroweak and strong backgrounds proceeding through a bbbar bbbar Z intermediate state. Total cross sections and differential spectra of phenomenological relevance to the selection and analysis of the signal are given and discussed.
Does Barypenthus concolor Burmeister (Trichoptera: Odontoceridae) select particles of different sizes for case building?
Moretti, Marcelo S.;Loyola, Rafael D.;
Neotropical Entomology , 2005, DOI: 10.1590/S1519-566X2005000200024
Abstract: many species of trichoptera larvae use organic or inorganic particles to build cases that protect them from predators. the study of the wide variety of structures produced by trichopterans is important to understand the evolution of case building behavior. the objective of this work was to investigate if larvae of barypenthus concolor (burmeister) are capable of selecting particles of specific sizes to build their cases. the study site was an altitudinal stream in serra do cipó national park, mg, brazil). cases and substrate samples were collected at three sites of the stream and submitted to granulometric analyses. the average mass of each particle size found in each site was used to determine the particle size proportion present in the substrate. the proportions of particle size of each case (site i: n = 10, site ii: n = 19, site iii: n = 13) were also analyzed. possible differences between the proportions of the particle sizes of the substrate and of those used by b. concolor larvae were assessed by the chi-square test. medium and fine gravel predominated at the three sites (>70%). there were no significant differences between the expected and observed particle size proportion in the cases. therefore, b. concolor does not select specific particle sizes for case building.
Rotating Topological Black Holes
D. Klemm,V. Moretti,L. Vanzo
Physics , 1997, DOI: 10.1103/PhysRevD.60.109902
Abstract: A class of metrics solving Einstein's equations with negative cosmological constant and representing rotating, topological black holes is presented. All such solutions are in the Petrov type-$D$ class, and can be obtained from the most general metric known in this class by acting with suitably chosen discrete groups of isometries. First, by analytical continuation of the Kerr-de Sitter metric, a solution describing uncharged, rotating black holes whose event horizon is a Riemann surface of arbitrary genus $g > 1$, is obtained. Then a solution representing a rotating, uncharged toroidal black hole is also presented. The higher genus black holes appear to be quite exotic objects, they lack global axial symmetry and have an intricate causal structure. The toroidal blackholes appear to be simpler, they have rotational symmetry and the amount of rotation they can have is bounded by some power of the mass.
OECD/NRC PSBT Benchmark: Investigating the CATHARE2 Capability to Predict Void Fraction in PWR Fuel Bundle
A. Del Nevo,D. Rozzia,F. Moretti,F. D’Auria
Science and Technology of Nuclear Installations , 2012, DOI: 10.1155/2012/757356
Abstract: Accurate prediction of steam volume fraction and of the boiling crisis (either DNB or dryout) occurrence is a key safety-relevant issue. Decades of experience have been built up both in experimental investigation and code development and qualification; however, there is still a large margin to improve and refine the modelling approaches. The qualification of the traditional methods (system codes) can be further enhanced by validation against high-quality experimental data (e.g., including measurement of local parameters). One of these databases, related to the void fraction measurements, is the pressurized water reactor subchannel and bundle tests (PSBT) conducted by the Nuclear Power Engineering Corporation (NUPEC) in Japan. Selected experiments belonging to this database are used for the OECD/NRC PSBT benchmark. The activity presented in the paper is connected with the improvement of current approaches by comparing system code predictions with measured data on void production in PWR-type fuel bundles. It is aimed at contributing to the validation of the numerical models of CATHARE 2 code, particularly for the prediction of void fraction distribution both at subchannel and bundle scale, for different test bundle configurations and thermal-hydraulic conditions, both in steady-state and transient conditions. 1. Introductory Remarks A system code shall demonstrate that it is reliable in simulating and predicting the key phenomena of properly selected scenarios. This is a necessary prerequisite for its applicability in accident analysis aimed at demonstrating that a nuclear system is safe and unlikely to fail. The current generation of thermal-hydraulic system (TH-SYS) codes benefits decades of experience in experimental investigation and code development and qualification. They are considered mature tools to provide best estimate description of phenomena and detailed reactor system representation. However, there is still a large margin to improve and refine the modelling approaches taking advantage of more recent techniques that focus on microscopic mechanisms rather than on macroscopic effects, so that more accurate predictions can be obtained and reduction of uncertainties can be achieved. In this view, the qualification of the traditional methods (system codes) can be further enhanced by validation against high-quality experimental data (e.g., including measurement of local parameters), while in parallel more sophisticated 3D techniques (such as CFD) are developed and assessed. One of these databases, related to the void fraction measurments, is the
Dynamics of saturated Bragg diffraction in a stored light grating in cold atoms
D. Moretti,N. Gonzalez,D. Felinto,J. W. R. Tabosa
Physics , 2008, DOI: 10.1103/PhysRevA.78.023811
Abstract: We report on a detailed investigation of the dynamics and the saturation of a light grating stored in a sample of cold cesium atoms. We employ Bragg diffraction to retrieve the stored optical information impressed into the atomic coherence by the incident light fields. The diffracted efficiency is studied as a function of the intensities of both writing and reading laser beams. A theoretical model is developed to predict the temporal pulse shape of the retrieved signal and compares reasonably well with the observed results.
Dynamics of a stored Zeeman coherence grating in an external magnetic field
D. Moretti,D. Felinto,J. W. R. Tabosa,A. Lezama
Physics , 2010, DOI: 10.1088/0953-4075/43/11/115502
Abstract: We investigate the evolution of a Zeeman coherence grating induced in a cold atomic cesium sample in the presence of an external magnetic field. The gratings are created in a three-beam light storage configuration using two quasi-collinear writing laser pulses and reading with a counterpropagating pulse after a variable time delay. The phase conjugated pulse arising from the atomic sample is monitored. Collapses and revivals of the retrieved pulse are observed for different polarizations of the laser beams and for different directions of the applied magnetic field. While magnetic field inhomogeneities are responsible for the decay of the coherent atomic response, a five-fold increase in the coherence decay time, with respect to no applied magnetic field, is obtained for an appropriate choice of the direction of the applied magnetic field. A simplified theoretical model illustrates the role of the magnetic field mean and its inhomogeneity on the collective atomic response.
Pulse pair generation from coherently prepared atomic ensembles
D. Moretti,D. Felinto,J. W. R. Tabosa
Physics , 2010, DOI: 10.1140/epjd/e2010-00200-y
Abstract: We report a detailed investigation on the generation of pulse pairs during the readout of a coherence grating stored in a cold atomic ensemble. The pulse shapes and the split of the retrieved energy between the two pulses are studied as a function of the relative intensities of the two reading fields, and a minimum is observed for the total retrieved energy. We introduce a simplified analytical theory for the process, considering a three-level atomic system, which explains all the most striking experimental features.
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