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Search Results: 1 - 10 of 145281 matches for " F. Ricci "
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Rotational dynamics of the magnetic moments in ferrofluids
Scherer, Claudio;Ricci, Trieste F.;
Brazilian Journal of Physics , 2001, DOI: 10.1590/S0103-97332001000300007
Abstract: we present a set of six non-linear stochastic diffferential equations for the six variables which are relevant for the dynamical behavior of the magnetic moments in ferrofluids, namely, the three euler angles of the magnetic particle, the two polar angles of the magnetic moment relative to the particle and the modulus of the magnetic moment. the interaction between the magnetic particle and the solvent fluid is modeled by dissipative and random noise torques, and so is the interaction between the particle and its magnetic moment, treated as an independent physical entity. in the appropriate limits, the model system reduces to the cases of super-paramagnetic or of non-super-paramagnetic (blocked magnetic moments) particles. numerical results show that for non-zero moment of inertia the precession of the magnetic moment around the magnetic field is accompanied by "nutation". it is also indicated how the dynamic complex susceptibility may be calculated from the equations of motion and the numerical results show that the nutation leads to a second resonance peak.
Rotational dynamics of the magnetic moments in ferrofluids
Scherer Claudio,Ricci Trieste F.
Brazilian Journal of Physics , 2001,
Abstract: We present a set of six non-linear stochastic diffferential equations for the six variables which are relevant for the dynamical behavior of the magnetic moments in ferrofluids, namely, the three Euler angles of the magnetic particle, the two polar angles of the magnetic moment relative to the particle and the modulus of the magnetic moment. The interaction between the magnetic particle and the solvent fluid is modeled by dissipative and random noise torques, and so is the interaction between the particle and its magnetic moment, treated as an independent physical entity. In the appropriate limits, the model system reduces to the cases of super-paramagnetic or of non-super-paramagnetic (blocked magnetic moments) particles. Numerical results show that for non-zero moment of inertia the precession of the magnetic moment around the magnetic field is accompanied by "nutation". It is also indicated how the dynamic complex susceptibility may be calculated from the equations of motion and the numerical results show that the nutation leads to a second resonance peak.
Linear Solar Models
F. L. Villante,B. Ricci
Physics , 2009, DOI: 10.1088/0004-637X/714/1/944
Abstract: We present a new approach to study the properties of the sun. We consider small variations of the physical and chemical properties of the sun with respect to Standard Solar Model predictions and we linearize the structure equations to relate them to the properties of the solar plasma. By assuming that the (variation of) the present solar composition can be estimated from the (variation of) the nuclear reaction rates and elemental diffusion efficiency in the present sun, we obtain a linear system of ordinary differential equations which can be used to calculate the response of the sun to an arbitrary modification of the input parameters (opacity, cross sections, etc.). This new approach is intended to be a complement to the traditional methods for solar model calculation and allows to investigate in a more efficient and transparent way the role of parameters and assumptions in solar model construction. We verify that these Linear Solar Models recover the predictions of the traditional solar models with an high level of accuracy.
Gravitational Waves, Sources, and Detectors
Bernard F Schutz,Franco Ricci
Physics , 2010,
Abstract: Notes of lectures for graduate students that were given at Lake Como in 1999, covering the theory of linearized gravitational waves, their sources, and the prospects at the time for detecting gravitational waves. The lectures remain of interest for pedagogical reasons, and in particular because they contain a treatment of current-quadrupole gravitational radiation (in connection with the r-modes of neutron stars) that is not readily available in other sources.
The Sun and the Newton Constant
B. Ricci,F. L. Villante
Physics , 2002, DOI: 10.1016/S0370-2693(02)02866-6
Abstract: Several properties of the solar interior are determined with a very high accuracy, which in some cases is comparable to that achieved in the determination of the Newton constant $G_N$. We find that the present uncertainty $\Delta G_N/G_N=\pm 1.5\cdot 10^{-3}$ has significant effects on the profile of density and pressure, however it has negligible influence on the solar properties which can be measured by means of helioseismology and $^8{\rm B}$ neutrinos. Our result do not support recent claims that observational solar data can be used to determine the value of $G_N$ with an accuracy of few part in $10^{-4}$. Present data cannot constrain $G_N$ to much better than $10^{-2}$.
Helioseismic determination of Beryllium neutrinos produced in the Sun
B. Ricci,F. L. Villante
Physics , 2000, DOI: 10.1016/S0370-2693(00)00853-4
Abstract: We provide a determination of the Beryllium neutrino luminosity directly by means of helioseismology, without using additional assumptions. We have constructed solar models where Beryllium neutrino, ($\nu_{Be}$) production is artificially changed by varying in an arbitrary way the zero energy astrophysical S-factor $S_{34}$ for the reaction $^3{\rm He}+^4{\rm He}\to ^7{\rm Be}+ \gamma$. Next we have compared the properties of such models with helioseismic determinations of photospheric helium abundance, depth of the convective zone and sound speed profile. We find that helioseismology directly confirms the production rate of $\nu_{Be}$ as predicted by SSMs to within $\pm 25%$ ($1\sigma$ error). This constraint is somehow weaker than that estimated from uncertainties of the SSM ($\pm 10%$), however it relies on direct observational data.
Absence of aging in the remanent magnetization in Migdal-Kadanoff spin glasses
F. Ricci-Tersenghi,F. Ritort
Physics , 1999, DOI: 10.1088/0305-4470/33/20/301
Abstract: We study the non-equilibrium behavior of three-dimensional spin glasses in the Migdal-Kadanoff approximation, that is on a hierarchical lattice. In this approximation the model has an unique ground state and equilibrium properties correctly described by the droplet model. Extensive numerical simulations show that this model lacks aging in the remanent magnetization as well as a maximum in the magnetic viscosity in disagreement with experiments as well as with numerical studies of the Edwards-Anderson model. This result strongly limits the validity of the droplet model (at least in its simplest form) as a good model for real spin glasses.
Construindo uma unidade didática conceitual sobre Mecanica Quantica: um estudo na forma??o de professores de Física
Ostermann, Fernanda;Ricci, Trieste S. F.;
Ciência & Educa??o (Bauru) , 2004, DOI: 10.1590/S1516-73132004000200007
Abstract: in this work, we present the results obtained from the implementation of a conceptual quantum mechanics unit. the teaching of this unit took place in the subject "modern and contemporary physics topics i", pertaining to the graduate curriculum designed to prepare masters in physics education at the federal university of rio grande do sul (ufrgs), brazil. the learning evaluation of basic conceptual aspects of qm was done through the application of a questionnaire before and after the lectures. the results before the lectures have shown that the students had important conceptual shortcomings in qm. after the implementation of the conceptual qm unit, it was possible to observe changes in their conceptions, especially those involved with the distinction between classical and quantum objects.
The Statistical Mechanics of Random Set Packing and a Generalization of the Karp-Sipser Algorithm
C. Lucibello,F. Ricci-Tersenghi
International Journal of Statistical Mechanics , 2014, DOI: 10.1155/2014/136829
Abstract: We analyse the asymptotic behaviour of random instances of the maximum set packing (MSP) optimization problem, also known as maximum matching or maximum strong independent set on hypergraphs. We give an analytic prediction of the MSPs size using the 1RSB cavity method from statistical mechanics of disordered systems. We also propose a heuristic algorithm, a generalization of the celebrated Karp-Sipser one, which allows us to rigorously prove that the replica symmetric cavity method prediction is exact for certain problem ensembles and breaks down when a core survives the leaf removal process. The -phenomena threshold discovered by Karp and Sipser, marking the onset of core emergence and of replica symmetry breaking, is elegantly generalized to for one of the ensembles considered, where is the size of the sets. 1. Introduction The maximum set packing is a very much studied problem in combinatorial optimization, one of Karp’s twenty-one NP-complete problems. Given a set and a collection of its subsets labeled by ; a set packing (SP) is a collection of the subsets such that they are pairwise disjoint. The size of a SP is . A maximum set packing (MSP) is an SP of maximum size. The integer programming formulation of the MSP problem reads The MSP problem, also known in the literature as the matching problem on hypergraphs or the strong independent set problem on hypergraphs, is an NP-Hard problem. This general formulation, however, can be specialized to obtain two other famous optimization problems: the restriction of the MSP problem to sets of size 2 corresponds to the problem of maximum matching on ordinary graphs and can be solved in polynomial time [1]; the restriction where each element of appears exactly 2 times in is the maximum independent set and belongs to the NP-Hard class. The formulation ((1)–(3)) of the MSP problem, therefore, encodes an ample class of packing problems and, as all packing problems, is related by duality to a covering problem, the minimum set covering problem. Another common specialization of the general MSP problem, known as -set packing, is that in which all sets have size at most . This is one of the most studied specializations in the computer science community, the efforts concentrating on minimal degree conditions to obtain a perfect matching [2], linear relaxations [3, 4], and approximability conditions [5–7]. Motivated by this interest, we choose a -set packing problem ensemble as the principal application of the general analytical framework developed in the following sections. The asymptotic behaviour of random sparse
Helioseismology and Beryllium neutrino
B. Ricci,F. L. Villante,M. Lissia
Physics , 1999, DOI: 10.1016/S0370-2693(99)00497-9
Abstract: We derive a lower limit on the Beryllium neutrino flux on earth, $\Phi(Be)_{min} = 1\cdot 10^9 cm^{-2} s^{-1}$, in the absence of oscillations, by using helioseismic data, the B-neutrino flux measured by Superkamiokande and the hydrogen abundance at the solar center predicted by Standard Solar Model (SSM) calculations. We emphasize that this abundance is the only result of SSMs needed for getting $\Phi(Be)_{min}$. We also derive lower bounds for the Gallium signal, $G_{min}=(91 \pm 3) $ SNU, and for the Chlorine signal, $C_{min}=(3.24\pm 0.14)$ SNU, which are about $3\sigma$ above their corresponding experimental values, $G_{exp}= (72\pm 6)$ SNU and $C_{exp}= (2.56\pm 0.22) $ SNU.
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