4,438 research outputs found
Fluctuations of fragment observables
This contribution presents a review of our present theoretical as well as
experimental knowledge of different fluctuation observables relevant to nuclear
multifragmentation. The possible connection between the presence of a
fluctuation peak and the occurrence of a phase transition or a critical
phenomenon is critically analyzed. Many different phenomena can lead both to
the creation and to the suppression of a fluctuation peak. In particular, the
role of constraints due to conservation laws and to data sorting is shown to be
essential. From the experimental point of view, a comparison of the available
fragmentation data reveals that there is a good agreement between different
data sets of basic fluctuation observables, if the fragmenting source is of
comparable size. This compatibility suggests that the fragmentation process is
largely independent of the reaction mechanism (central versus peripheral
collisions, symmetric versus asymmetric systems, light ions versus heavy ion
induced reactions). Configurational energy fluctuations, that may give
important information on the heat capacity of the fragmenting system at the
freeze out stage, are not fully compatible among different data sets and
require further analysis to properly account for Coulomb effects and secondary
decays. Some basic theoretical questions, concerning the interplay between the
dynamics of the collision and the fragmentation process, and the cluster
definition in dense and hot media, are still open and are addressed at the end
of the paper. A comparison with realistic models and/or a quantitative analysis
of the fluctuation properties will be needed to clarify in the next future the
nature of the transition observed from compound nucleus evaporation to
multi-fragment production.Comment: Contribution to WCI (World Consensus Initiative) Book " "Dynamics and
Thermodynamics with Nuclear Degrees of Freedom", to appear on Euorpean
Physics Journal A as part of the Topical Volume. 9 pages, 12 figure
Tracking energy fluctuations from fragment partitions in the Lattice Gas model
Partial energy fluctuations are known tools to reconstruct microcanonical
heat capacities. For experimental applications, approximations have been
developed to infer fluctuations at freeze out from the observed fragment
partitions. The accuracy of this procedure as well as the underlying
independent fragment approximation is under debate already at the level of
equilibrated systems. Using a well controlled computer experiment, the Lattice
Gas model, we critically discuss the thermodynamic conditions under which
fragment partitions can be used to reconstruct the thermodynamics of an
equilibrated system.Comment: version accepted for publication in Phys.Rev.
Comment on "Partial energies fluctuations and negative heat capacities" by X. Campi et al
Studying the energy partioning published in nucl-th/0406056v2 we show that
the presented results do not fulfill the sum rule due to energy conservation.
The observed fluctuations of the energy conservation test point to a numerical
problem. Moreover, analysis of the binding energies show that the fragment
recognition algorithm adopted by Campi et al. leads with a sizeable probability
to fragments containing up to the total mass even for excitation energies as
large as 3/4 of the total binding. This surprising result points to another
problem since the published inter-fragment energy is not zero while a unique
fragment is present. This problem may be due to either the fragment recognition
algorithm or to the definition of the inter and intra-fragment energy. These
numerical inconsistencies should be settled before any conclusion on the
physics can be drawn
L\u2019Italiano e l\u2019alfabeto per i nuovi arrivati
In recent years, thousands of refugees and asylum seekers have arrived at the port of Palermo, including a large number of teenagers without any adult caregivers. They are called Unaccompanied Minors. A significant part of them remain in the city and are placed in Italian language courses of the University of Palermo, (ItaStra), within a large inclusion project. The focus of this paper will be address to describe this new profile of learner: they are minors, 15 to 17 years old, without much formal education or training, without competent skills in reading or writing, but with a vast life experience in a multilingual environment and exposure to learning a diversity of new languages
"Chiamo uomo chi \ue8 padrone delle sue lingue". modelli di plurilinguismo da Lampedusa in su.
Il plurilinguismo dei nuovi migranti viene analizzato insieme al ruolo della lingua nella costruzione di modelli di societ\ue0 inclusiva e plural
Experimental Signals of Phase Transition
The connection between the thermodynamics of charged finite nuclear systems
and the asymptotically measured partitions is presented. Some open questions,
concerning in particular equilibrium partitions are discussed. We show a
detailed comparison of the decay patterns in Au+ C,Cu,Au central collisions and
in Au quasi-projectile events. Observation of abnormally large fluctuations in
carefully selected samples of data is reported as an indication of a first
order phase transition (negative heat capacity) in the nuclear equation of
state.Comment: 8 pages, 8th International Conference on Nucleus-Nucleus Collisions,
Moscow 200
Self-attraction effect and correction on three absolute gravimeters
The perturbations of the gravitational field due to the mass distribution of
an absolute gravimeter have been studied. The so called Self Attraction Effect
(SAE) is crucial for the measurement accuracy, especially for the International
Comparisons, and for the uncertainty budget evaluation. Three instruments have
been analysed: MPG-2, FG5-238 and IMPG-02. The SAE has been calculated using a
numerical method based on FEM simulation. The observed effect has been treated
as an additional vertical gravity gradient. The correction (SAC) to be applied
to the computed g value has been associated with the specific height level,
where the measurement result is typically reported. The magnitude of the
obtained corrections is of order 1E-8 m/s2.Comment: 14 pages, 8 figures, submitted to Metrologi
Negative heat capacity in the critical region of nuclear fragmentation: an experimental evidence of the liquid-gas phase transition
An experimental indication of negative heat capacity in excited nuclear
systems is inferred from the event by event study of energy fluctuations in
quasi-projectile sources formed in collisions at 35 A.MeV. The
excited source configuration is reconstructed through a calorimetric analysis
of its de-excitation products. Fragment partitions show signs of a critical
behavior at about 5 A.MeV excitation energy. In the same energy range the heat
capacity shows a negative branch providing a direct evidence of a first order
liquid gas phase transition.Comment: 4 Postscript figures, submitted to Phys. Rev. Lett. on 14-apr-199
Color in context: psychological context moderates the influence of red on approach- and avoidance-motivated behavior.
A basic premise of the recently proffered color-in-context model is that the influence of color on psychological functioning varies as a function of the psychological context in which color is perceived. Some research has examined the appetitive and aversive implications of viewing the color red in romance- and achievement-relevant contexts, respectively, but in all existing empirical work approach and avoidance behavior has been studied in separate tasks and separate experiments. Research is needed to directly test whether red influences the same behavior differently depending entirely on psychological context. The present experiment was designed to put this premise to direct test in romance- and achievement-relevant contexts within the same experimental paradigm involving walking behavior. Our results revealed that exposure to red (but not blue) indeed has differential implications for walking behavior as a function of the context in which the color is perceived. Red increased the speed with which participants walked to an ostensible interview about dating (a romance-relevant context), but decreased the speed with which they walked to an ostensible interview about intelligence (an achievement-relevant context). These results are the first direct evidence that the influence of red on psychological functioning in humans varies by psychological context. Our findings contribute to both the literature on color psychology and the broader, emerging literature on the influence of context on basic psychological processes
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