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Search Results: 1 - 10 of 6719 matches for " Alessandro Magni "
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Hysteresis properties at zero temperature in the Dipolar-Random Field Ising Model
Alessandro Magni
Physics , 1999, DOI: 10.1103/PhysRevB.59.985
Abstract: We present a modified two-dimensional random field Ising model, where a dipolar interaction term is added to the classic random field Hamiltonian. In a similar model it was already verified that the system state can exhibit domains in the form of stripe patterns, typical of thin materials with strong perpendicular anisotropy. In this work we show that the hysteresis loops obtained at zero temperature can display a strict similarity with the loops obtained in thin magnetic materials such as garnet films. In our model the processes of domain nucleation and domain wall motion are well separated in time as the system evolves. This remarkable fact allowed us to better understand the nucleation process in this family of spin systems.
Dipolar random field Ising model: an application to garnet films
Alessandro Magni,Gabor Vertesy
Physics , 1999, DOI: 10.1103/PhysRevB.61.3203
Abstract: The dipolar-random field Ising model (DRFIM) recently introduced displays a behaviour that can be connected to the magnetization of bidimensional magnetic media. Epitaxial magnetic garnet films seem to be the ideal test material for such a model. In this work the results of the measurements performed on garnet samples are presented, as well as the comparisons with simulation results obtained by the DRFIM. The results prove that a variety of hysteresis loops are well described by the DRFIM. This capability does not derive from the fine tuning of a great number of parameters, but by the interplay of exchange and dipolar interactions.
Cough variant asthma and atopic cough
Chiara Magni, Elisa Chellini, Alessandro Zanasi
Multidisciplinary Respiratory Medicine , 2010, DOI: 10.1186/2049-6958-5-2-99
Abstract: In some patients cough is a chronic unremitting symptom leading to a marked decrement in quality of life [1,2]. Chronic cough has been reported to be the fifth most common complaint seen by primary care physicians [3]. For instance, in USA up to 38% of a pulmonologist's outpatient practice is accounted for by persistently troublesome chronic cough [4]. In Japan, cough is the most frequent reason (11.7% of all) why patients visit clinics [5]. In Italy, cough is the third most common cause of medical visits with about 25 million consultancies for cough per year of which 5 million for the acute problem and 2 million for the chronic one (Dal Negro, personal communication). According to questionnaire surveys, the prevalence of chronic cough in the general population, including children, may vary from 9 to 33% [6]. Chronic cough is present in older subjects as may be seen from the average age of patients seen in cough clinics (Table 1).The most common causes worldwide of chronic cough in non-smoking, non-treated with ACE-inhibitor adults with normal chest radiogram include the upper airway cough syndrome (UACS), gastroesophageal reflux disease (GERD) and asthma syndromes [4,7-15]. This indicates a group of related airway disorders including the "classic" asthma, the so-called cough variant asthma, nonasthmatic eosinophilic bronchitis (NAEB), and atopic cough. However, even if the guidelines on cough diagnosis and management [16-18] are followed in detail, the cause of chronic cough may remain unexplained in up to 33-46% of cases [6,19]. The prevalence of UACS, GERD and asthma syndromes varies in different reports [4,7-15]. This suggests the necessity of further examination to elucidate cough mechanisms and etiology [20]. The differences in prevalence may depend upon racial and life style differences, access to specialists or differences in the definition of some cough causes [21,22]. For instance, in the United Kingdom and Australia the two most common causes of cough are
Microscopic foundations of the Rayleigh law of hysteresis
Stefano Zapperi,Alessandro Magni,Gianfranco Durin
Physics , 2001, DOI: 10.1016/S0304-8853(01)01131-3
Abstract: The hysteresis properties of ferromagnetic materials at low field are described by the Rayleigh law. We analyze the problem in light of modern statistical mechanics models of hysteresis. In particular, we compute the demagnetization curve and derive the Rayleigh parameters a and b in the random-field Ising model and in a model of domain wall depinning. In the random-field Ising model the Rayleigh law is obeyed only in the disorder dominated phase, while in the low disorder phase it is not possible to demagnetize the sample. This approach allows us to link a and b to microstructural parameters, such as the domain wall energy, the internal disorder or the exchange interactions. Finally, our results are compared with experiments.
Stochastic Dynamics in Quenched-in Disorder and Hysteresis
Giorgio Bertotti,Vittorio Basso,Alessandro Magni
Physics , 1998, DOI: 10.1063/1.369782
Abstract: The conditions under which relaxation dynamics in the presence of quenched-in disorder lead to rate-independent hysteresis are discussed. The calculation of average hysteresis branches is reduced to the solution of the level-crossing problem for the stochastic field describing quenched-in disorder. Closed analytical solutions are derived for the case where the disorder is characterized by Wiener-Levy statistics. This case is shown to be equivalent to the Preisach model and the associated Preisach distribution is explicitly derived, as a function of the parameters describing the original dynamic problem.
Low field hysteresis in disordered ferromagnets
Lorenzo Dante,Gianfranco Durin,Alessandro Magni,Stefano Zapperi
Physics , 2001, DOI: 10.1103/PhysRevB.65.144441
Abstract: We analyze low field hysteresis close to the demagnetized state in disordered ferromagnets using the zero temperature random-field Ising model. We solve the demagnetization process exactly in one dimension and derive the Rayleigh law of hysteresis. The initial susceptibility a and the hysteretic coefficient b display a peak as a function of the disorder width. This behavior is confirmed by numerical simulations d=2,3 showing that in limit of weak disorder demagnetization is not possible and the Rayleigh law is not defined. These results are in agreement with experimental observations on nanocrystalline magnetic materials.
Extreme Events Assessment Methodology Coupling Debris Flow, Flooding and Tidal Levels in the Coastal Floodplain of the São Paulo North Coast (Brazil)  [PDF]
Rafael de Oliveira Sakai, Diego Louren?o Cartacho, Emilia Arasaki, Paolo Alfredini, Alessandro Pezzoli, Wilson Cabral de Sousa Júnior, Maurizio Rosso, Luca Magni
International Journal of Geosciences (IJG) , 2013, DOI: 10.4236/ijg.2013.45B006
Abstract:

The North Coastal Region of the State of S?o Paulo, which comprises the Municipalities of Caraguatatuba, S?o Sebasti?o, Ilhabela and Ubatuba, is one of the most prone to flooding and debris flow deposition Brazilian areas, owing to hydrological extreme rainfall events usually coupled with extreme tidal levels. This risk is also high due to human lives and material assets, with increasing population rates and the establishment of large companies such as the Oil industry, with reduced defense/prevention measures and works.The catastrophic scenario of the city of Caraguatatuba, in March 1967, resulting from one of the most serious natural disasters in Brazil, fosters discussions about probabilities of heavy rainfall-caused events and rise in the sea level in coastal areas. Hence, this research is a consequence of this reality. The research is founded on an innovative methodology based on the analysis of past data of rainfall and tidal stations, complemented with debris flow registers in the region of the north coastal zone of the State of S?o Paulo (Brazil). The anaysis developed involved the meteorological, hydraulic, geotechnical and statistical knowledge areas.Practical results are intended to be used for urban planning, designs of macro-drainage, fluvial, maritime projects and debris flow retention structures. These practical applications will then associate the probability of occurrence of certain types of heavy rainfall-caused events such as flooding or debris flow coupled with a corresponding increase in tidal levels.

Non-equilibrium thermodynamics of the longitudinal spin Seebeck effect
Vittorio Basso,Elena Ferraro,Alessandro Magni,Alessandro Sola,Michaela Kuepferling,Massimo Pasquale
Physics , 2015,
Abstract: In this paper we employ non equilibrium thermodynamics of fluxes and forces to describe magnetization and heat transport. By the theory we are able to identify the thermodynamic driving force of the magnetization current as the gradient of the effective field $\nabla H^*$. This definition permits to define the spin Seebeck coefficient $\epsilon_M$ which relates $\nabla H^*$ and the temperature gradient $\nabla T$. By applying the theory to the geometry of the longitudinal spin Seebeck effect we are able to obtain the optimal conditions for generating large magnetization currents. Furthermore, by using the results of recent experiments, we obtain an order of magnitude for the value of $\epsilon_{M} \sim 10^{-2}$ TK$^{-1}$ for yttrium iron garnet (Y$_3$Fe$_5$O$_{12}$).
Thermodynamics of the heat currents in the longitudinal spin Seebeck and spin Peltier effects
Vittorio Basso,Elena Ferraro,Alessandro Magni,Alessandro Sola,Michaela Kuepferling,Massimo Pasquale
Physics , 2015,
Abstract: We employ the non-equilibrium thermodynamics of currents and forces to describe the heat transport caused by a spin current in a Pt/YIG bilayer. By starting from the constitutive equations of the magnetization currents in both Pt and YIG, we derive the magnetization potentials and currents. We apply the theory to the spin Peltier experiments in which a spin current, generated by the spin Hall effect in Pt, is injected into YIG. We find that efficient injection is obtained when: i) the thickness of each layer is larger than its diffusion length: $t_{Pt} > l_{Pt}$ and $t_{YIG} > l_{YIG}$ and ii) the ratio $(l_{Pt}/\tau_{Pt})/(l_{YIG}/\tau_{YIG})$ is small, where $\tau_i$ is the time constant of the intrinsic damping ($i=Pt, YIG$). We finally derive the temperature profile in adiabatic conditions. The scale of the effect is given by the parameter $\Delta T_{SH}$ which is proportional to the electric current in Pt. Using known parameters for Pt and YIG we estimate $\Delta T_{SH}/j_e = 4 \cdot 10^{-13}$ K A$^{-1}$m$^2$. This value is of the same order of magnitude of the spin Peltier experiments.
Lazy or Greedy? Impact of Xenophobic Beliefs on Natives’ Attitudes towards Redistribution  [PDF]
Raul Magni Berton
Open Journal of Political Science (OJPS) , 2013, DOI: 10.4236/ojps.2013.31005
Abstract:

Several recent accounts have shown that anti-immigrant feeling among citizens seems to reduce the support for the welfare state. As a consequence, the rise of immigration could produce a deep change in industrialized countries’ social security systems. This paper provides evidence that support for redistribution is not decreased by generic xenophobia, but by a specific kind of xenophobic belief. It also shows that some other xenophobic beliefs tend rather to produce a demand for governmental protection programs. Based on a multivariate analysis on individual and contextual French data, findings show that the support for social protection programs is positively related to the fear of competition from immigrants and negatively with the fear that immigrants strain the welfare state. This result can be generalized to other countries where “redistributive xenophobia” is much more widespread.

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