Assessment of antenna parameters for current drive in thermonuclear reactors by radio-frequency power

The most challenging conceptual problem of thermonuclear energy research based on deuterium plasmas magnetically trapped in toroidal machines, named tokamaks, consists in how to control and actively shape during operations the current density radial profile of plasma column. To achieve this control is of paramount importance, indeed, for the following reasons: i) to prevent the onset of unstable modes that detriment the figures of stability and fusion power gain from thermonuclear reactions, which are necessary for a reactor; ii) to remove the obstacle of tokamaks of being intrinsically inductive machines, i.e., capable of producing only transient plasma regimes, in front of the reactor’s need of operating in steady- state. In regard to the former problem, data of modelling and experiments available in the last 25 years showed that the growth rate of pernicious unstable plasma modes, of magneto-hydro-dynamic (MHD) nature, is strongly depressed when a relative maximum of the plasma current density is suitably located at radii close to the region that interests the unstable modes. They make challenging the possibility of achieving the desired thermal insulation that is necessary for allowing thermonuclear conditions of high temperatures (∼100 million of degrees) and high density (∼1020 m-3) of plasma. The limitation of pulsed operation was, instead, well known since the assessment (half century ago) of the tokamak concept, and this was soon perceived as the major conceptual obstacle against the development of a thermonuclear fusion reactor. Indeed, at that time, the further problem of the onset of unstable modes (which produces anomalous transport effects, on heat and matter, via micro-turbulence and MHD modes) did not appear yet. The discovery in 1981 at Princeton (USA) of the lower hybrid current drive (LHCD) effect was considered very attractive for facing both the mentioned major problems of a reactor. The LHCD effect consists in the capability of multimegawatt microwave power at several gigahertz, coupled to quasi-electrostatic natural modes of plasma, named lower hybrid (LH) waves, of non- inductively producing current in tokamak plasma. Consequently, the plasma current can flow with continuity in a tokamak under RF power injection. The antenna consists in phased arrays of rectangular waveguides that suitably fit the gaps of the tokamak’s magnet. Via electronic setting of the waveguide phasing, the refractive index (n//, in the direction parallel to the confinement magnetic field) of the RF power spectrum can be usefully determined in order to Landau-resonate with a tail of the electron distribution of plasma electrons, for the temperature that corresponds to the radial layer where the current drive effect would be desirably produced. As further support of attractiveness of the LHCD effect, it should be considered that other methods utilising radiofrequency power in the ion-cyclotron and electron-cyclotron resonant frequencies, as well those that exploit strong power injection of energetic ion beams, present much lower efficiency in driving plasma current than that possible by the LHCD effect. Unfortunately, for long time the LHCD effect was observed to occur successfully only when operating at too low plasma densities – of about a factor three lower than that required by reactor – despite of the many attempts carried out for decades in many laboratories in the world. In these experiments, the RF power was however successfully coupled by the antenna, but remained unexpectedly deposited at the plasma periphery, as a consequence of parasitic effects of plasma edge. Only recently, an original research performed in the ENEA-Frascati Lab. – whose results have been published on Nature Communications: 5,55,2010 – has assessed a new method for enabling the occurrence of the LHCD effect at reactor graded high plasma densities. This method is based on previous theoretical predictions of reduced parasitic effect under higher temperature of plasma edge (ENEA Laboratory work published on Physical Review Letters in 2004). These works demonstrated that the parasitic damping of the coupled RF power is produced by non-linear wave-plasma interaction, named parametric instability (PI), which is capable of strongly altering (namely, broadening) the n// spectrum launched by the antenna. Consequently, the temperature required for Landau-resonance of the RF power spectrum with plasma electrons is strongly diminished, which causes absorption in the cold region of plasma periphery. This Thesis is focused on helping solution of an important conceptual problem, which is part of this challenge, by means of a noticeable application of strong radiofrequency power coupled to quasi- electrostatic plasma waves (LH waves). From the engineering point of view, results produced by an originally developed numerical code (LHPI) have backed solving the problem (existing for decades) of how to enable the antenna parameters determining the deposition of the coupled RF power (of several gigahertz) at a desired radial layer of the plasma column. This task would be ideally required indeed by an antenna. With respect to other current drive tool, based on electron cyclotron resonance (at about 150 GHz), this cannot guarantee the coverage of the outer half radius of plasma necessary for a reactor. Thanks to results reported here, new understanding is provided that for the first time enables a waveguide antenna for current drive in tokamaks to tailor the deposition in the plasma, in different operating conditions, by electronically acting on the launched spectrum (via feeding/phasing of waveguides). In particular, a) in case of too high plasma densities at the plasma edge, as occurs in running experiments, operation with higher temperature of plasma is recommended to avoid parasitic effects of spectral broadening. b) in case of too high plasma temperature at the plasma periphery, as envisaged in a future reactor, the assessment of a new antenna parameter, Δn//, allows however guaranteeing useful penetration of the coupled RF power into the plasma bulk. More specifically, the following issues have been considered in the Thesis. 1) Available data of RF power spectral broadening, kept during experiments carried out on the EAST tokamak (China), have been interpreted on the basis of the parametric instability modelling. This work has been performed thanks to a new version of a numerical code (developed on the basis of a previously version available since 1989 at ENEA-Frascati) having much improved qualities of velocity and precision. 2) The work has also focused on the key problem of how to enable the occurrence of the LHCD effect also in conditions of high electron temperature of reactor plasmas. Indeed, precisely the high temperature that in a reactor is expected to occur even at large radii of the plasma column which usefully prevents the occurrence of the parasitic effects observed in the experiments – would also produce an undesired RF power deposition too far out in the plasma, owing too strong electron Landau damping, as shown by numerical results. This circumstance is in contrast with the primary goal of a reactor of being equipped by current profile control, so that the too high plasma temperature of reactor represents the remaining major conceptual problem preventing the exploitation of the LHCD tool. This problem has been solved by the new outcome described in the Thesis. This result consists in having identified in a sufficiently narrow n// antenna power spectrum the way for reducing the wave-plasma interaction at high temperatures, thus enabling the penetration of the coupled RF power in the hot and dense regions of reactor plasmas. This diminished wave-plasma interaction is consequence of the content of standard quasi-linear theory of plasma waves: this aspect remained singularly undisclosed so far. 3) Finally, the thesis has analysed the problem of how to design an antenna capable of producing the required power spectra necessary for envisaging a current profile control system in a thermonuclear reactor. For carrying out this work, a numerical code has been utilised capable of treating waveguide antenna geometries however complex. Consequently, the desired sufficiently narrow n// power spectrum can be produced, indeed, by suitable array of active and passive phased array of rectangular waveguides. Moreover, the scan of the main antenna parameters (power reflection coefficient, directivity, etc,) performed assuming realistic conditions of plasma edge, has shown that all requirements should be satisfied for envisaging a current profile control system for a tokamak reactor based on the exploitation of the LHCD effect. The lower hybrid current drive tool in now fully supported by know how necessary for enabling the current profile control in the warm and dense plasma of thermonuclear reactor. The current drive method assessed here is of paramount importance for conceiving antennas to be implemented in the system of current profile control, which a reactor mandatorily requires

Safety and impact on diagnostic accuracy of early analgesia in suspected acute appendicitis: A meta-analysis

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In vitro interactions between Bradyrhizobium spp. and Tuber magnatum mycelium

Tuber magnatum is the most expensive truffle, but its large-scale cultivation is still a challenge compared to other valuable Tuber species. T. magnatum mycelium has never been grown profitably until now, which has led to difficulties to studying it in vitro. This study describes beneficial interactions between T. magnatum mycelium and never before described bradyrhizobia, which allows the in vitro growth of T. magnatum mycelium. Three T. magnatum strains were co-isolated on modified Woody Plant Medium (mWPM) with aerobic bacteria and characterised through microscopic observations. The difficulties of growing alone both partners, bacteria and T. magnatum mycelium, on mWPM demonstrated the reciprocal dependency. Three bacterial isolates for each T. magnatum strain were obtained and molecularly characterised by sequencing the 16S rRNA, glnII, recA and nifH genes. Phylogenetic analyses showed that all nine bacterial strains were distributed among five subclades included in a new monophyletic lineage belonging to the Bradyrhizobium genus within the Bradyrhizobium jicamae supergroup. The nifH genes were detected in all bacterial isolates, suggesting nitrogen-fixing capacities. This is the first report of consistent T. magnatum mycelium growth in vitro conditions. It has important implications for the development of new technologies in white truffle cultivation and for further studies on T. magnatum biology and genetics

Non-destructive collection survey of the historical Classense Library. Part II: Conservation scenarios

The effects of environmental and conservation management scenarios on the permanence of the historical book collections housed at the Classense Library (Ravenna, Italy) were investigated. Non-destructive material surveys delivered paper pH and degree of polymerisation data that, in conjunction with the Collections Demography dose–response function, provide heritage managers with estimations of the predicted collection lifetimes in diverse environmental management scenarios. For the first time, quantitative measurements of paper properties obtained in a historical library collection were used to elaborate isochrone and demographic plots, evaluated against the long-term planning horizon of 500 years. The scenarios include preventive and interventive actions aiming to preserve the fitness-for-use of collection items in terms of their ability to withstand manual handling, and consider cooling, dehumidification and deacidification, as well as combinations thereof. The results inform the conservation decision-makers about the preservation outcomes of environmental management options, to be considered for further action, once environmental, economic and social sustainability of such scenarios is considered

Cultural diplomacy as a path of Italian foreign policy between the cold war and the post-bipolar period

Il soft power di uno Stato è l’immagine che questo dà di sé agli altri, ed è naturalmente riempito di suoi ideali e valori, della sua lingua e delle sue conoscenze. La cultura, nella sua più ampia declinazione, in tal senso si rivela uno strumento diplomatico rilevante nella politica estera dello Stato. Questa può affermarne la presenza, preservarne l’identità, sviluppare forme di solidarietà, favorire obiettivi politici attraverso l’influenza del pubblico internazionale. La diplomazia culturale italiana negli anni di guerra fredda si è rappresentata come “strada operativa” particolare nel più ampio ventaglio di scelte di politica estera del nostro paese, a volte precorrendo le mire e gli obiettivi della diplomazia cosiddetta “tradizionale”. La cultura ha offerto all’Italia una prospettiva aggiuntiva nei termini del dialogo internazionale, ponendosi come canale privilegiato di relazioni difficilmente concertabili altrimenti nel corso della seconda metà del Novecento, segnata dal conflitto bipolare. Nella sua tensione verso la pace e la stabilità, con il suo costante richiamo ai diritti ed ai valori della democrazia, la diplomazia culturale italiana ha potuto inoltre vantare un contributo non secondario nella transizione dalle dinamiche internazionali segnate dalla guerra fredda alla determinazione delle relazioni internazionali propriamente post-bipolari.The soft power of a State is the image that it gives of itself to others, filled with its ideals and values, its language and its knowledge. Culture, in its broadest declination, in this sense proves to be a relevant diplomatic tool in the foreign policy of a State. This can affirm its presence, preserve its identity, develop forms of solidarity, promote political objectives through the influence of the international public. Italian cultural diplomacy in the years of the Cold War represented itself as a particular "operational path" in the wider range of foreign policy choices of our country, sometimes anticipating the aims and objectives of so-called "traditional" diplomacy. Culture offered Italy an additional perspective in terms of international dialogue, acting as a privileged channel for relations that would otherwise be difficult to negotiate during the second half of the twentieth century, marked by bipolar conflict. In its tension towards peace and stability, with its constant reference to the rights and values of democracy, Italian cultural diplomacy has also been able to boast a non-secondary contribution in the transition from the international dynamics marked by the Cold War to the determination of post-bipolar international relations

Non-destructive collection survey of the historical Classense Library. Part I: Paper characterisation

An innovative survey was conducted of the collections of the historical Biblioteca Classense, located in the urban area of Ravenna (Northern Italy). The survey aimed to evaluate the current conservation state of the book collections, where 297 paper-based items, including incunabula, manuscripts and books, dating from the 14th to the 20th century, were selected for analysis. This innovative survey was carried out non-destructively by assessing degradation visually and by measuring NIR spectral data followed by multivariate data analysis. Chemical and physical paper properties, important for paper characterisation and implementation of conservation strategies were determined, including paper type, pH, degree of polymerisation (DP), tensile strength, lignin, protein, and rosin content. This survey provided a significant quantitative dataset for rag paper covering a 600-year period. The analysis of DP changes over time allowed the first experimental estimation of the rate constant for historical rag paper, i.e., (4.2 ± 0.6)·10−7 year−1, which was validated with predictions based on the Collections Demography dose response function for historic paper taking into account the past climate in Ravenna. Statistical methods were employed to describe the correlations between the measured variables and different features of the books, suggesting that the degree of polymerisation can be used as a general proxy for rag paper mechanical strength

Molecular and functional characterization of a Rho GDP dissociation inhibitor in the filamentous fungus Tuber borchii

<p>Abstract</p> <p>Background</p> <p>Small GTPases of the Rho family function as tightly regulated molecular switches that govern important cellular functions in eukaryotes. Several families of regulatory proteins control their activation cycle and subcellular localization. Members of the guanine nucleotide dissociation inhibitor (GDI) family sequester Rho GTPases from the plasma membrane and keep them in an inactive form.</p> <p>Results</p> <p>We report on the characterization the RhoGDI homolog of <it>Tuber borchii </it>Vittad., an ascomycetous ectomycorrhizal fungus. The Tb<it>gdi </it>gene is present in two copies in the <it>T. borchii </it>genome. The predicted amino acid sequence shows high similarity to other known RhoGDIs. Real time PCR analyses revealed an increased expression of Tb<it>gdi </it>during the phase preparative to the symbiosis instauration, in particular after stimulation with root exudates extracts, that correlates with expression of Tb<it>cdc42</it>. In a translocation assay TbRhoGDI was able to solubilize TbCdc42 from membranes. Surprisingly, TbRhoGDI appeared not to interact with <it>S. cerevisiae </it>Cdc42, precluding the use of yeast as a surrogate model for functional studies. To study the role of TbRhoGDI we performed complementation experiments using a RhoGDI null strain of <it>Dictyostelium discoideum</it>, a model organism where the roles of Rho signaling pathways are well established. For comparison, complementation with mammalian RhoGDI1 and LyGDI was also studied in the null strain. Although interacting with Rac1 isoforms, TbRhoGDI was not able to revert the defects of the <it>D. discoideum </it>RhoGDI null strain, but displayed an additional negative effect on the cAMP-stimulated actin polymerization response.</p> <p>Conclusion</p> <p>T. borchii expresses a functional RhoGDI homolog that appears as an important modulator of cytoskeleton reorganization during polarized apical growth that antecedes symbiosis instauration. The specificity of TbRhoGDI actions was underscored by its inability to elicit a growth defect in <it>S. cerevisiae </it>or to compensate the loss of a <it>D. discoideum </it>RhoGDI. Knowledge of the cell signaling at the basis of cytoskeleton reorganization of ectomycorrhizal fungi is essential for improvements in the production of mycorrhized plant seedlings used in timberland extension programs and fruit body production.</p

ESTÁGIO E SUPERVISÃO EM SERVIÇO SOCIAL: DESAFIOS E POSSIBILIDADES NOS CAMINHOS DA FORMAÇÃO PROFISSIONAL

O presente trabalho trata-se de uma reflexão teórica acerca do tema estágioe supervisão na formação profissional. Partimos da concepção que o estudante vivencia gradativamente os passos necessários ao conhecimento, a investigação e intervenção social quando realiza o estágio supervisionado. A supervisão de estágio nesse processo tem por objetivo propiciar a reflexão, análise crítica da realidade em que se concretiza o trabalho profissional, bem como a sua totalidade. Por isso, a  necessidade dessa atividade ser sistematizada e amplamente discutida em tempos de precarização da educação e trabalho profissional para que haja o fortalecimento dos sujeitos envolvidos nesse processo, bem como as entidades representativas do Serviço Social para o enfrentamento dessa realidade na direção de uma formação profissional competente, com qualidade, condicionada ao projeto ético-político profissional

Reliability evaluation of metal oxide varistors for maintenance scheduling

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Demographic, psychological, chronobiological, and work-related predictors of sleep disturbances during the COVID-19 lockdown in Italy

The first COVID-19 contagion wave caused unprecedented restraining measures worldwide. In Italy, a period of generalized lockdown involving home confinement of the entire population was imposed for almost two months (9 March–3 May 2020). The present is the most extensive investigation aimed to unravel the demographic, psychological, chronobiological, and work-related predictors of sleep disturbances throughout the pandemic emergency. A total of 13,989 Italians completed a web-based survey during the confinement period (25 March–3 May). We collected demographic and lockdown-related work changes information, and we evaluated sleep quality, insomnia and depression symptoms, chronotype, perceived stress, and anxiety using validated questionnaires. The majority of the respondents reported a negative impact of confinement on their sleep and a delayed sleep phase. We highlighted an alarming prevalence of sleep disturbances during the lockdown. Main predictors of sleep disturbances identified by regression models were: female gender, advanced age, being a healthcare worker, living in southern Italy, confinement duration, and a higher level of depression, stress, and anxiety. The evening chronotype emerged as a vulnerability factor, while morning-type individuals showed a lower predisposition to sleep and psychological problems. Finally, working from home was associated with less severe sleep disturbances. Besides confirming the role of specific demographic and psychological factors in developing sleep disorders during the COVID-19 pandemic, we propose that circadian typologies could react differently to a particular period of reduced social jetlag. Moreover, our results suggest that working from home could play a protective role against the development of sleep disturbances during the current pandemic emergency