Decay of geodesic acoustic modes due to the combined action of phase mixing and Landau damping

Geodesic acoustic modes (GAMs) are oscillations of the electric field whose importance in tokamak plasmas is due to their role in the regulation of turbulence. The linear collisionless damping of GAMs is investigated here by means of analytical theory and numerical simulations with the global gyrokinetic particle-in-cell code ORB5. The combined effect of the phase mixing and Landau damping is found to quickly redistribute the GAM energy in phase-space, due to the synergy of the finite orbit width of the passing ions and the cascade in wave number given by the phase mixing. When plasma parameters characteristic of realistic tokamak profiles are considered, the GAM decay time is found to be an order of magnitude lower than the decay due to the Landau damping alone, and in some cases of the same order of magnitude of the characteristic GAM drive time due to the nonlinear interaction with an ITG mode. In particular, the radial mode structure evolution in time is investigated here and reproduced quantitatively by means of a dedicated initial value code and diagnostics.Comment: Submitted to Phys. Plasma

Studi storici dedicati a Orazio Cancila

Non accade sempre, e non è neppure necessario, che le raccolte di studi in onore di personalità del mondo degli studi trattino temi relativi o affini a quelli coltivati dalla personalità celebrata. Se, però, accade, si può certamente parlare di una felice circostanza o coincidenza, ma può accadere anche che tale circostanza o coincidenza sia significativa di qualcosa d’altro. E, ad esempio, può essere significativa del fatto che la personalità destinataria della raccolta si è posta o si è trovata al centro di sviluppi della storiografia contemporanea importanti anche perché rispondono a interessi diffusi negli studi e nella cultura del suo tempo. Della raccolta di studi per Orazio Cancila si può dire – credo – che ci si trova senz’altro in quest’ultimo caso, e, ciò, anche quando la formulazione letterale dei temi dei singoli contributi alla raccolta non sembra autorizzare una tale constatazione. ... È un bel panorama, ed è singolarmente conforme alla serie degli ampii e varii interessi storici di Cancila. (Dall'introduzione di Giuseppe Galasso

Exact equilibrium distributions in statistical quantum field theory with rotation and acceleration: scalar field

We derive a general exact form of the phase space distribution function and the thermal expectation values of local operators for the free quantum scalar field at equilibrium with rotation and acceleration in flat space-time without solving field equations in curvilinear coordinates. After factorizing the density operator with group theoretical methods, we obtain the exact form of the phase space distribution function as a formal series in thermal vorticity through an iterative method and we calculate thermal expectation values by means of analytic continuation techniques. We separately discuss the cases of pure rotation and pure acceleration and derive analytic results for the stress-energy tensor of the massless field. The expressions found agree with the exact analytic solutions obtained by solving the field equation in suitable curvilinear coordinates for the two cases at stake and already - or implicitly - known in literature. In order to extract finite values for the pure acceleration case we introduce the concept of analytic distillation of a complex function. For the massless field, the obtained expressions of the currents are polynomials in the acceleration/temperature ratios which vanish at $2\pi$, in full accordance with the Unruh effect.Comment: 38 pages, 1 figure. Final proofread version published in JHE

Spin-thermal shear coupling in a relativistic fluid

We show that spin polarization of a fermion in a relativistic fluid at local thermodynamic equilibrium can be generated by the symmetric derivative of the four-temperature vector, defined as thermal shear. As a consequence, besides vorticity, acceleration and temperature gradient, also the shear tensor contributes to the polarization of particles in a fluid. This contribution to the spin polarization vector, which is entirely non-dissipative, adds to the well known term proportional to thermal vorticity and may thus have important consequences for the solution of the local polarization puzzles observed in relativistic heavy ion collisions.Comment: 10 pages, 1 figure; version accepted for publication in Physics Letters

Increased levels of RNA oxidation enhance the reversion frequency in aging pro-apoptotic yeast mutants

Despite recent advances in understanding the complexity of RNA processes, regulation of the metabolism of oxidized cellular RNAs and the mechanisms through which oxidized ribonucleotides affect mRNA translation, and consequently cell viability, are not well characterized. We show here that the level of oxidized RNAs is markedly increased in a yeast decapping Kllsm4Δ1 mutant, which accumulates mRNAs, ages much faster that the wild type strain and undergoes regulated-cell-death. We also found that in Kllsm4Δ1 cells the mutation rate increases during chronological life span indicating that the capacity to han- dle oxidized RNAs in yeast declines with aging. Lowering intracellular ROS levels by antioxidants recovers the wild- type phenotype of mutant cells, including reduced amount of oxidized RNAs and lower mutation rate. Since mRNA oxidation was reported to occur in different neurodegen- erative diseases, decapping-deficient cells may represent a useful tool for deciphering molecular mechanisms of cell response to such conditions, providing new insights into RNA modification-based pathogenesis

A simple beam model to analyse the durability of adhesively bonded tile floorings in presence of shrinkage

A simple beam model for the evaluation of tile debonding due to substrate shrinkage is presented. The tile-adhesive-substrate package is modeled as an Euler-Bernoulli beam laying on a two-layer elastic foundation. An effective discrete model for inter-tile grouting is introduced with the aim of modelling workmanship defects due to partial filled groutings. The model is validated using the results of a 2D FE model. Different defect configurations and adhesive typologies are analysed, focusing the attention on the prediction of normal stresses in the adhesive layer under the assumption of Mode I failure of the adhesive

Polarization as a signature of local parity violation in hot QCD matter

We show that local parity violation due to chirality imbalance in relativistic nuclear collisions can be revealed by measuring the projection of the polarization vector onto the momentum, i.e. the helicity, of final state baryons. The proposed method does not require a coupling to the electromagnetic field, like in the Chiral Magnetic Effect. By using linear response theory, we show that, in the presence of a chiral imbalance, the spin 1/2 baryons and anti-baryons receive an additional contribution to the polarization along their momentum and proportional to the axial chemical potential. The additional, parity-breaking, contribution to helicity can be detected by studying helicity-helicity azimuthal angular correlation

Polarization as a signature of local parity violation in hot QCD matter

We show that local parity violation due to chirality imbalance in relativistic nuclear collisions can be revealed by measuring the projection of the polarization vector onto the momentum, i.e. the helicity, of final state baryons. The proposed method does not require a coupling to the electromagnetic field, like in the Chiral Magnetic Effect. By using linear response theory, we show that, in the presence of a chiral imbalance, the spin 1/2 baryons and anti-baryons receive an additional contribution to the polarization along their momentum and proportional to the axial chemical potential. The additional, parity-breaking, contribution to helicity can be detected by studying its dependence on the angle with respect to the reaction plane or with helicity-helicity angular correlation.Comment: 5 pages, 4 pages of supplementary material, 3 figures; some minor additions to the text and added reference

LE REGIONI D'EUROPA TRA IDENTITÀ LOCALI, NUOVE COMUNITÀ E DISPARITÀ TERRITORIALI

L’Europa è oggi attraversata da una forte domanda di autonomia da parte dei territori: da un lato, a tutela dell’identità delle comunità locali e, dall’altro, per la crescente rivendicazione di una più ampia rappresentanza delle cittadinanze. Queste istanze possono, però, mettere a rischio gli obiettivi di equilibrio e di coesione economica, sociale e territoriale, da sempre al centro della riflessione e delle proposte sviluppate dagli studiosi delle scienze regionali. La recente crisi ha acuito l’instabilità e allargato i complessivi divari tra le regioni, anche nella loro dinamica interna di evoluzione. Alla resilienza economica non sempre è corrisposto, nell’attuale transizione verso un nuovo paradigma, il mantenimento di solidi livelli di coesione sociale e di integrazione tra aree e comunità. Il volume raccoglie una selezione di contributi presentati alla XXXIX Conferenza Italiana di Scienze Regionali, svoltasi a Bolzano il 17, 18 e 19 settembre 2018. Nella sua articolazione, esso si sviluppa in tre parti. La prima analizza il tema della domanda di autonomia da parte dei territori all’interno dello sviluppo economico e sociale di regioni e paesi, e dell’attuale dibattito sul federalismo differenziato. Nella seconda le riflessioni si estendono alla crescente disparità tra aree centrali e aree periferiche, tra aree interne e aree esposte, tra Nord e Sud dei Paesi e dell’Europa, mentre nella terza parte, l’analisi guarda ai mutevoli equilibri tra territori e sistemi locali urbani e rurali, tra pianura e montagna e, all’interno delle aree montane, tra i fondivalle maggiormente urbanizzati e i territori di alta quota, zone spesso di confine tra province, regioni e stati. La novità editoriale di quest’anno è rappresentata da uno spazio dedicato a brevi contributi a cura di giovani autori vincitori dei premi AISRe.Europe is today crossed by a strong demand for autonomy from the territories: to protect the identity of local communities and, also analyze the growing demand for a broader representation of citizens. However, these issues can jeopardize the objectives of balance and economic, social and territorial cohesion, which have always been at the center of the reflection and proposals developed by scholars of regional sciences. The recent crisis has worsened instability and widened the overall gaps between the regions, including in their internal dynamics of evolution. Economic resilience is not always matched, in the current transition towards a new paradigm, by maintaining solid levels of social cohesion and integration between areas and communities. The volume collects a selection of contributions presented at the XXXIX Italian Conference of Regional Science, held in Bolzano on 17, 18 and 19 September 2018. The volume is divided into three parts. The first analyzes the issue of the demand for autonomy by the territories within the economic and social development of regions and countries, and the current debate on differentiated federalism. In the second, the reflections extend to the growing disparity between central and peripheral areas, between internal and exposed areas, between North and South of countries and Europe, while in the third part, the analysis looks at the changing balance between territories and systems. urban and rural areas, between plains and mountains and, within mountain areas, between the most urbanized valleys and high altitude territories, areas often bordering provinces, regions and states. This year ia space is dedicated to short contributions by young authors who have won the AISRe Awards