328 research outputs found
On the role of non-equilibrium, relativistic hot electron population in Target Normal Sheath Acceleration
No full textNon-equilibrium effects in a relativistic plasma sheath model
No full textPlasma sheaths characterized by electrons with relativistic energies and far from thermodynamic equilibrium are governed by a rich and largely unexplored physics. A reliable kinetic description of relativistic non-equilibrium plasma sheaths - besides its interest from a fundamental point of view - is crucial to many application, from controlled nuclear fusion to laser-driven particle acceleration. Sheath models proposed in the literature adopt either relativistic equilibrium distribution functions or non-relativistic non-equilibrium distribution functions, making it impossible to properly capture the physics involved when both relativistic and non-equilibrium effects are important. Here we tackle this issue by solving the electrostatic Vlasov-Poisson equations with a new class of fully-relativistic distribution functions that can describe non-equilibrium features via a real scalar parameter. After having discussed the general properties of the distribution functions and the resulting plasma sheath model, we establish an approach to investigate the effect of non-equilibrium solely. Then, we apply our approach to describe laser-plasma ion acceleration in the target normal sheath acceleration scheme. Results show how different degrees of non-equilibrium lead to the formation of sheaths with significantly different features, thereby having a relevant impact on the ion acceleration process. We believe that this approach can offer a deeper understanding of relativistic plasma sheaths, opening new perspectives in view of their applications
Plasmando al receptor : un paseo por las prácticas discursivas de Jorge Guillén y Rafael Alberti
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Laser-Driven Neutron Generation with Near-Critical Targets and Application to Materials Characterization
No full textLaser-driven neutrons arouse outstanding interest because of their promising uses in several fields, from basic science to materials inspection. Many experiments achieved neutron yields [108 - 1010 n/(sr s)] suitable for applications. These results were obtained by exploiting high-energy (approximately 10-100 J) lasers working at low repetition rates. Instead, adopting advanced target configurations like near-critical double-layer targets (DLTs) and compact, commercial lasers was slightly considered. Here, a theoretical study is performed to address neutron generation with commercial (40-400 TW, 1-15 J) systems and DLTs. We investigate proton acceleration and interaction with various materials to induce (p, n) reactions. DLTs allow achieving 1-2 orders of magnitude larger neutron yields and maximum energies 3 times higher than with single-layer targets. Then, the feasibility of two materials characterization techniques, namely fast neutron activation analysis and pulsed fast neutron resonance radiography, is assessed. The results indicate that they can be performed with commercial lasers and DLTs
Reference-free evaluation of thin films mass thickness and composition through energy dispersive X-ray spectroscopy
No full textIn this paper we report the development of a new method for the evaluation of thin films mass thickness and composition based on the Energy Dispersive X-Ray Spectroscopy (EDS). The method exploits the theoretical calculation of the in-depth characteristic X-ray generation distribution function (φ(ρz))in multilayer samples, where φ(ρz)is obtained by the numerical solution of the electron transport equation. Once the substrate composition in known, this method gives reliable measurements without the need of a reference sample and/or multiple voltage acquisitions. The electron transport model is derived from the Boltzmann transport equation and it exploits the most updated and reliable physical parameters in order to obtain an accurate description of the phenomenon. The method for the calculation of film mass thickness and composition is validated with benchmarks from standard techniques. In addition, a model uncertainty and sensitivity analysis is carried out and it indicates that the mass thickness accuracy is of the order of 10 μg/cm2, which is comparable to the nuclear standard techniques resolution. We show the technique peculiarities in one example model: two-dimensional mass thickness and composition profiles are obtained for a ultra-low density, high roughness, nanostructured film
Suicide attempts in schizophrenic patients : Clinical variables
No full textIntroduction: Schizophrenia is associated with a significant risk of suicide: 40-50% of schizophrenic patients report suicidal ideation at some point in their lives, and 4-13% eventually commit suicide. In order to be able to predict and prevent suicide in schizophrenic patients, it is necessary to investigate and characterise suicide victims who meet the criteria for psychotic disorders and risk factors. Methods: The aim of this retrospective study was to verify the associations between suicide attempts (SAs) and the demographic and clinical variables of 106 patients who met the DSM-IV-TR criteria for schizophrenia.The patients were divided into two groups on the basis of the presence/absence of lifetime suicide attempts, and their main demographic and clinical characteristics were analysed and compared. Results: The patients with a history of SAs frequently had a duration of untreated psychosis (DUP) of ≥1 year (chi-squared test= 9.984, df= 1, p= 0.0016). They also showed significant associations with the presence of a depressive dimension (chi-squared test= 4.439, df= 1, p= 0.0351), hospitalisations before SAs (chi-squared test= 25.515, df= 1, p <0.001), and a family history of psychiatric disorders (chi-squared test= 12.668, df= 2, p= 0.0018) or suicidal behaviours (chi-squared test= 18.241, df= 2, p= 0.0001). Finally, they were more frequently prescribed typical antipsychotic agents. Conclusions: The severity of psychiatric symptoms indicates a high risk of suicide in schizophrenic patients. Further prospective studies of larger samples should investigate the role of early interventions and atypical antipsychotic treatment in reducing the risk
DEL ESPACIO DESHUMANIZADO AL ESPACIO DE LA MEMORIA: TRAYECTORIAS DE LOS POETAS DEL VEINTISIETE
No full textThis work was born as an attempt to answer the following questions: what happens to the members of a literary generation when this generation’s time is over? Do they stray on their own personal path or do they maintain some consistent bonds that witness the road they have walked together? In order to answer these questions we analysed some of the works by Dámaso Alonso, Vicente Aleixandre and Luis Cernuda, focusing on some key moments of their production, in particular: the phase of the “poesía pura”, surrealism, exile and memory. This chronological approach allowed us, on one hand, to shed new light on long-acquired critical evaluations –especially regarding the earlier works of these poets–; and, on the other hand, to pinpoint how, despite the distance that grew between some of them in their life experiences, these authors still shared a common sensibility, which led them to develop similar answers to similar problems.
This analysis was performed with special attention to the element of space. In fact, since the introduction of the concept of chronotope by Bakhtin, space and time have become useful categories for the analysis of literary works; yet, traditionally, they have been associated most frequently with prose. For this reason, the analysis of the poetical space is a kind of novelty, which provides an exceptional point of observation on texts, offering, with contributions from linguistics and traditional critical studies, new readings of classical works. This way, a correspondence can be established between the changes the concept of space itself experiments in these authors and the evolution of their poetical world.
We start from the artificial, claustrophobic space that is typical of the “poesía pura”, where the young poet keeps a separate stance from the outside world, lingering in his room in strict meditation, only to later assist to its definitive breakthrough, when the chaotic agglomerate of irrational objects floating into nothingness, which is the trademark of the surrealist period, takes over. Afterwards, the painful occurrence of the exile, experienced both inside and outside the Spanish peninsula, contributes in transforming again the concept of space, pointing out a severe division of its physical environment, which is somehow mended by resorting to a partly-metaphysical, partly-psychological reconstruction. The last modification of this poetical chronotope, induced by the increasing proximity of the end of these poets’ lives, is represented by a further dwelling on the idea of limit, both from a temporal and spatial point of view, which puts in peril the same possibility of writing poetry. The risk of this poetical aporia is finally eluded by Aleixandre’s appeal to dialogue, which doubles the space available, allowing a new configuration that comprises, in the counterpoint of two poetical voices, the finite and the infinite aspects of reality.
Thanks to this achievement, we can answer affirmatively to our initial question, and thus recognize in Aleixandre the point of equilibrium of this complex triangle of friendship and jealousy, where the emulation and the desire to surpass the other shaped marvellous spaces of poetical beauty
Laser-driven production with advanced targets of Copper-64 for medical applications
No full textISSN:2296-424
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