Disk Evolution in Young Binaries: from Observations to Theory

The formation of a binary system surrounded by disks is the most common outcome of stellar formation. Hence studying and understanding the formation and the evolution of binary systems and associated disks is a cornerstone of star formation science. Moreover, since the components within binary systems are coeval and the sizes of their disks are fixed by the tidal truncation of their companion, binary systems provide an ideal "laboratory" in which to study disk evolution under well defined boundary conditions. In this paper, we review observations of several inner disk diagnostics in multiple systems, including hydrogen emission lines (indicative of ongoing accretion), $K-L$ and $K-N$ color excesses (evidence of warm inner disks), and polarization (indicative of the relative orientations of the disks around each component). We examine to what degree these properties are correlated within binary systems and how this degree of correlation depends on parameters such as separation and binary mass ratio. These findings will be interpreted both in terms of models that treat each disk as an isolated reservoir and those in which the disks are subject to re-supply from some form of circumbinary reservoir, the observational evidence for which we will also critically review. The planet forming potential of multiple star systems is discussed in terms of the relative lifetimes of disks around single stars, binary primaries and binary secondaries. Finally, we summarize several potentially revealing observational problems and future projects that could provide further insight into disk evolution in the coming decadeComment: 16 pages, 7 figures, chapter in Protostars and Planets

Analysis of equilibrium states of Markov solutions to the 3D Navier-Stokes equations driven by additive noise

We prove that every Markov solution to the three dimensional Navier-Stokes equation with periodic boundary conditions driven by additive Gaussian noise is uniquely ergodic. The convergence to the (unique) invariant measure is exponentially fast. Moreover, we give a well-posedness criterion for the equations in terms of invariant measures. We also analyse the energy balance and identify the term which ensures equality in the balance.Comment: 32 page

The GL 569 Multiple System

We report the results of high spectral and angular resolution infrared observations of the multiple system GL 569 A and B that were intended to measure the dynamical masses of the brown dwarf binary believed to comprise GL 569 B. Our analysis did not yield this result but, instead, revealed two surprises. First, at age ~100 Myr, the system is younger than had been reported earlier. Second, our spectroscopic and photometric results provide support for earlier indications that GL 569 B is actually a hierarchical brown dwarf triple rather than a binary. Our results suggest that the three components of GL 569 B have roughly equal mass, ~0.04 Msun.Comment: 29 pages, 10 figures, accepted for publication in the Astrophysical Journal; minor corrections to Section 5.1; changed typo in 6.

Superdiffusion in Decoupled Continuous Time Random Walks

Continuous time random walk models with decoupled waiting time density are studied. When the spatial one jump probability density belongs to the Levy distribution type and the total time transition is exponential a generalized superdiffusive regime is established. This is verified by showing that the square width of the probability distribution (appropriately defined)grows as $t^{2/\gamma}$ with $0<\gamma\leq2$ when $t\to \infty$. An important connection of our results and those of Tsallis' nonextensive statistics is shown. The normalized q-expectation value of $x^2$ calculated with the corresponding probability distribution behaves exactly as $t^{2/\gamma}$ in the asymptotic limit.Comment: 9 pages (.tex file), 1 Postscript figures, uses revtex.st

Use of Perylene Diimides in Synthetic Photochemistry

Perylene diimides (PDIs) are valuable organic chromophores that stand out for their outstanding optical and redox properties. Owing to these features, PDIs have emerged as prominent dyes capable of acting as photocatalysts for numerous relevant organic transformations. This Minireview highlights the recent advances in the application of PDIs in organic photocatalysis. The various mechanistic pathways of the photo-reduction reaction of aryl halides, recently proposed in independent studies, are discussed with an eye to unsolved challenges and forward-looking opportunities regarding the use of PDIs within this field

Verification of Knoop indenters with Gal-Indent optical system

Le normative internazionali ISO 4545-2 e 4545-3 per i test di durezza Knoop richiedono la verifica geometrica dei penetratori. Il laboratorio di durezza INRiM, in collaborazione con la Galileo-LTF®, ha sviluppato uno specifico sistema ottico di misurazione(commercializzato da Galileo-LTF® come Gal-Indent) , utilizzato per la verifica dei penetratori Vickers. Questo sistema è in grado di misurare i due angoli al vertice tra due facce opposte, i quattro angoli della base quadrangolare e l'angolo tra l'asse della piramide di diamante e l'asse del codolo del penetratore. Usando le misure degli angoli al vertice e della base come input di un appropriato modello geometrico, gli angoli al vertice tra spigoli opposti di penetratori Knoop, nominalmente di 172.5° e 130°, e l'angolo tra l'asse della piramide di diamante e l'asse del supporto del penetratore, nominalmente di 0°, possono essere verificati con un'incertezza estesa di 0.05°, come richiesto dalle normative. Il confronto tra le misure sperimentali eseguite con questo metodo su tre diversi penetratori Knoop, precedentemente verificati da un laboratorio accreditato tedesco, mostrano risultati compatibili, in termini di errore normalizzato.ISO 4545-2 and 4545-3 of Knoop hardness tests require the geometrical verification of the indenters. INRiM hardness laboratory, in cooperation with Galileo-LTF® has developed a specific optical measuring system (commercialized by Galileo-LTF® as Gal-Indent) which is addressed for the verification of Vickers indenters. This system is able to measure the two vertex angles between two opposite faces, the four angles of the quadrilateral base and the angle between the axis of the diamond pyramid and the axis of the indenter holder. Using the measured quantities of the vertex and base angles as inputs of a suitable geometrical model, the angles from the opposite edges at the vertex of Knoop indenters, nominally 172.5° and 130°, and the angle between the axis of the diamond pyramid and the axis of the indenter holder, nominally 0°, can be verified with an expanded uncertainty of 0.05°, as required by the relevant Standard. Comparison of experimental measurements performed on three different Knoop indenters, previously verified by a German accredited laboratory, shows compatible results in terms of normalized error

Jensen-Shannon divergence as a measure of distinguishability between mixed quantum states

We discuss an alternative to relative entropy as a measure of distance between mixed quantum states. The proposed quantity is an extension to the realm of quantum theory of the Jensen-Shannon divergence (JSD) between probability distributions. The JSD has several interesting properties. It arises in information theory and, unlike the Kullback-Leibler divergence, it is symmetric, always well defined and bounded. We show that the quantum JSD (QJSD) shares with the relative entropy most of the physically relevant properties, in particular those required for a "good" quantum distinguishability measure. We relate it to other known quantum distances and we suggest possible applications in the field of the quantum information theory.Comment: 14 pages, corrected equation 1

Denoising Diffusion Models on Model-Based Latent Space

With the recent advancements in the field of diffusion generative models, it has been shown that defining the generative process in the latent space of a powerful pretrained autoencoder can offer substantial advantages. This approach, by abstracting away imperceptible image details and introducing substantial spatial compression, renders the learning of the generative process more manageable while significantly reducing computational and memory demands. In this work, we propose to replace autoencoder coding with a model-based coding scheme based on traditional lossy image compression techniques; this choice not only further diminishes computational expenses but also allows us to probe the boundaries of latent-space image generation. Our objectives culminate in the proposal of a valuable approximation for training continuous diffusion models within a discrete space, accompanied by enhancements to the generative model for categorical values. Beyond the good results obtained for the problem at hand, we believe that the proposed work holds promise for enhancing the adaptability of generative diffusion models across diverse data types beyond the realm of imagery

Electron-Electron Bremsstrahlung Emission and the Inference of Electron Flux Spectra in Solar Flares

Although both electron-ion and electron-electron bremsstrahlung contribute to the hard X-ray emission from solar flares, the latter is normally ignored. Such an omission is not justified at electron (and photon) energies above $\sim 300$ keV, and inclusion of the additional electron-electron bremsstrahlung in general makes the electron spectrum required to produce a given hard X-ray spectrum steeper at high energies. Unlike electron-ion bremsstrahlung, electron-electron bremsstrahlung cannot produce photons of all energies up to the maximum electron energy involved. The maximum possible photon energy depends on the angle between the direction of the emitting electron and the emitted photon, and this suggests a diagnostic for an upper cutoff energy and/or for the degree of beaming of the accelerated electrons. We analyze the large event of January 17, 2005 observed by RHESSI and show that the upward break around 400 keV in the observed hard X-ray spectrum is naturally accounted for by the inclusion of electron-electron bremsstrahlung. Indeed, the mean source electron spectrum recovered through a regularized inversion of the hard X-ray spectrum, using a cross-section that includes both electron-ion and electron-electron terms, has a relatively constant spectral index $\delta$ over the range from electron kinetic energy $E = 200$ keV to $E = 1$ MeV. However, the level of detail discernible in the recovered electron spectrum is not sufficient to determine whether or not any upper cutoff energy exists.Comment: 7 pages, 5 figures, submitted to Astrophysical Journa