A singular symplectic variety of dimension 6 with a Lagrangian Prymian fibration

A projective symplectic variety $\mathcal{P}$ of dimension 6, with only finite quotient singularities, $\pi(\mathcal{P})=0$ and $h^{(2,0)}(\mathcal{P}_{smooth})=1$, is described as a relative compactified Prym variety of a family of genus 4 curves with involution. It is a Lagrangian fibration associated to a K3 surface double cover of a generic cubic surface. It has no symplectic desingularization

Fire Hose instability driven by alpha particle temperature anisotropy

We investigate properties of a solar wind-like plasma including a secondary alpha particle population exhibiting a parallel temperature anisotropy with respect to the background magnetic field, using linear and quasi-linear predictions and by means of one-dimensional hybrid simulations. We show that anisotropic alpha particles can drive a parallel fire hose instability analogous to that generated by protons, but that, remarkably, the instability can be triggered also when the parallel plasma beta of alpha particles is below unity. The wave activity generated by the alpha anisotropy affects the evolution of the more abundant protons, leading to their anisotropic heating. When both ion species have sufficient parallel anisotropies both of them can drive the instability, and we observe generation of two distinct peaks in the spectra of the fluctuations, with longer wavelengths associated to alphas and shorter ones to protons. If a non-zero relative drift is present, the unstable modes propagate preferentially in the direction of the drift associated with the unstable species. The generated waves scatter particles and reduce their temperature anisotropy to marginally stable state, and, moreover, they significantly reduce the relative drift between the two ion populations. The coexistence of modes excited by both species leads to saturation of the plasma in distinct regions of the beta/anisotropy parameter space for protons and alpha particles, in good agreement with in situ solar wind observations. Our results confirm that fire hose instabilities are likely at work in the solar wind and limit the anisotropy of different ion species in the plasma.Comment: 10 pages, 9 figures, Accepted for publication in The Astrophysical Journa

Two-dimensional Hybrid Simulations of Kinetic Plasma Turbulence: Current and Vorticity vs Proton Temperature

Proton temperature anisotropies between the directions parallel and perpendicular to the mean magnetic field are usually observed in the solar wind plasma. Here, we employ a high-resolution hybrid particle-in-cell simulation in order to investigate the relation between spatial properties of the proton temperature and the peaks in the current density and in the flow vorticity. Our results indicate that, although regions where the proton temperature is enhanced and temperature anisotropies are larger correspond approximately to regions where many thin current sheets form, no firm quantitative evidence supports the idea of a direct causality between the two phenomena. On the other hand, quite a clear correlation between the behavior of the proton temperature and the out-of-plane vorticity is obtained.Comment: 4 pages, 2 figures, Proceedings of the Fourteenth International Solar Wind Conferenc

Solar wind turbulence from MHD to sub-ion scales: high-resolution hybrid simulations

We present results from a high-resolution and large-scale hybrid (fluid electrons and particle-in-cell protons) two-dimensional numerical simulation of decaying turbulence. Two distinct spectral regions (separated by a smooth break at proton scales) develop with clear power-law scaling, each one occupying about a decade in wave numbers. The simulation results exhibit simultaneously several properties of the observed solar wind fluctuations: spectral indices of the magnetic, kinetic, and residual energy spectra in the magneto-hydrodynamic (MHD) inertial range along with a flattening of the electric field spectrum, an increase in magnetic compressibility, and a strong coupling of the cascade with the density and the parallel component of the magnetic fluctuations at sub-proton scales. Our findings support the interpretation that in the solar wind large-scale MHD fluctuations naturally evolve beyond proton scales into a turbulent regime that is governed by the generalized Ohm's law.Comment: 5 pages, 5 figures; introduction and conclusions changed, references updated, accepted for publication in ApJ

PROGETTAZIONE E SPERIMENTAZIONE DI UN ENDOREATTORE BIPROPELLENTE H2/H2O2

Il lavoro di tesi tratta il progetto e la sperimentazione di un endoreattore bipropellente a perossido d’idrogeno e idrogeno da 8 N di spinta. Il progetto ha l’intento di verificare la fattibilità di un sistema a spinta regolabile che utilizzi un combustibile di nuova generazione contenente idrogeno gassoso ed ottenuto da un precursore solido. Dopo i capitoli introduttivi dove è descritto lo stato dell’arte degli endoreattori bipropellente “verdi” ed i propellenti scelti per il progetto, si passa nel capitolo 3 allo studio concettuale della miscelazione dei propellenti, della stabilità di fiamma e dell’espansione della miscela nell’ugello di scarico. Una sintesi sulla combustione ed accensione di miscele reattive è esposta, insieme ad alcuni modelli teorici e sperimentali, nel capitolo 4. Il progetto consiste anche di uno studio mediante modelli 3D agli elementi finiti della miscelazione ed espansione dei gas, studio esposto nel capitolo 5. Infine, nel capitolo 6, è descritta la prova d’accensione del dispositivo

Magnetic Field Rotations in the Solar Wind at Kinetic Scales

The solar wind magnetic field contains rotations at a broad range of scales, which have been extensively studied in the MHD range. Here we present an extension of this analysis to the range between ion and electron kinetic scales. The distribution of rotation angles was found to be approximately log-normal, shifting to smaller angles at smaller scales almost self-similarly, but with small, statistically significant changes of shape. The fraction of energy in fluctuations with angles larger than $\alpha$ was found to drop approximately exponentially with $\alpha$, with e-folding angle $9.8^\circ$ at ion scales and $0.66^\circ$ at electron scales, showing that large angles ($\alpha > 30^\circ$) do not contain a significant amount of energy at kinetic scales. Implications for kinetic turbulence theory and the dissipation of solar wind turbulence are discussed

Indagine sugli effetti provocati da un eccesso di radiazione UV-B su foglie di Populus Alba L. mediante miscrospettrofluorimetria e microimaging di fluorescenza

.Foglie di Populus Alba L. (pioppo bianco) sottoposte a trattamento UV-B (280 nm < ? < 315 nm) sono state analizzate mediante tecniche di microscopia a trasmissione, di microspettrofluorimetria e di microimaging di fluorescenza e confrontate con analoghe foglie di controllo prelevate da piante mantenute a livelli standard di irraggiamento. I campioni fogliari impiegati per l\u27esperimento sono stati prelevati a partire dal quindicesimo giorno di accrescimento da piante fatte sviluppare in vivaio. Il trattamento UV (12 h al giorno) realizzato in camera di crescita si ? protratto per un massimo di 7 giorni a partire dal quindicesimo giorno di accrescimento. La radiazione UV-B applicata aveva una densit? di energia pari a 0.15 Wm-2 stimata con uno spettroradiometro a scansione SUV 100 (Biospherical Instruments, San Diego, CA). La strumentazione impiegata per le misure consisteva in un microscopio invertito a epifluorescenza (Diaphoto, Nikon, Japan) equipaggiato con una lampada a mercurio e filtri interferenziali di 10 nm (Andover Corporation, Salem, NH), dotato di ruota portafiltri e CCD per l\u27acquisizione delle immagini di fluorescenza. L\u27analisi dei dati ottenuti durante il periodo di trattamento si articola in tre punti principali: 1)studio delle modificazioni cellulari 2)analisi delle caratteristiche di fluorescenza 3)analisi dei valori di intensit? di fluorescenza a tempi crescenti di trattamento

The long non-coding RNA Kcnq1ot1 controls maternal p57 expression in muscle cells by promoting H3K27me3 accumulation to an intragenic MyoD-binding region

BACKGROUND: The cell-cycle inhibitor p57kip2 plays a critical role in mammalian development by coordinating cell proliferation and differentiation in many cell types. p57kip2 expression is finely regulated by several epigenetic mechanisms, including paternal imprinting. Kcnq1ot1, a long non-coding RNA (LncRNA), whose gene maps to the p57Kip2 imprinting domain, is expressed exclusively from the paternal allele and participates in the cis-silencing of the neighboring imprinted genes through chromatin-level regulation. In light of our previous evidence of a functional interaction between myogenic factors and imprinting control elements in the regulation of the maternal p57Kip2 allele during muscle differentiation, we examined the possibility that also Kcnq1ot1 could play an imprinting-independent role in the control of p57Kip2 expression in muscle cells. RESULTS: We found that Kcnq1ot1 depletion by siRNA causes the upregulation of the maternal and functional p57Kip2 allele during differentiation, suggesting a previously undisclosed role for this LncRNA. Consistently, Chromatin Oligo-affinity Precipitation assays showed that Kcnq1ot1 physically interacts not only with the paternal imprinting control region of the locus, as already known, but also with both maternal and paternal alleles of a novel p57Kip2 regulatory region, located intragenically and containing two binding sites for the muscle-specific factor MyoD. Moreover, chromatin immunoprecipitation assays after Kcnq1ot1 depletion demonstrated that the LncRNA is required for the accumulation of H3K27me3, a chromatin modification catalyzed by the histone-methyl-transferase EZH2, at the maternal p57kip2 intragenic region. Finally, upon differentiation, the binding of MyoD to this region and its physical interaction with Kcnq1ot1, analyzed by ChIP and RNA immunoprecipitation assays, correlate with the loss of EZH2 and H3K27me3 from chromatin and with p57Kip2 de-repression. CONCLUSIONS: These findings highlight the existence of an imprinting-independent role of Kcnq1ot1, adding new insights into the biology of a still mysterious LncRNA. Moreover, they expand our knowledge about the molecular mechanisms underlying the tight and fine regulation of p57Kip2 during differentiation and, possibly, its aberrant silencing observed in several pathologic conditions