Ab-initio Phonon Calculations for the layered compound TiOCl

We present first-principles frozen-phonon calculations for the three Raman-active $A_g$ modes in the spin-1/2 layered TiOCl system within two different well-known approaches: the local density approximation (LDA) and the so-called LDA+U approximation. We observe that the inclusion of electron correlation in a mean-field level as implemented in the LDA+U leads to a better overall agreement with experimental results. We also discuss the implications of the two approaches on the physics of TiOCl.Comment: Phys. Rev. B (Rapid Comm.) (in Press

Effects of Fe substitution on the electronic, transport, and magnetic properties of ZnGa2_2O4_4: A systematic ab-initio study

We present a density functional study of Fe doped into the tetrahedral and octahedral cation sites of the wide band gap spinel ZnGa$_2$O$_4$. We calculate the electronic structure for different substitutions and discuss the magnetic and transport properties for each case considering different approximations for the exchange-correlation potential. We show that for certain doped cases, significant differences in the predicted behavior are obtained depending on the exchange correlation potential adopted. Possible applications of the doped systems as magnetic semiconductors are outlined.Comment: 9 pages, 8 figures; to be published in Phys. Rev.

La scala elicoidale del Borromini a Palazzo Barberini. Rilievo scan laser e modellazione parametrica.

L’articolo riguarda lo studio della forma e della geometria della scala elicoidale di Palazzo Barberini. Partendo dai dati digitali di base acquisiti con uno scanner laser, elaborati e gestiti successivamente attraverso procedure di ottimizzazione della points-cloud si sono prodotti dei modelli di rappresentazione integrati di tipo infografico e tridimensionale. La realizzazione della scala elicoidale a Palazzo Barberini oltre a rivestire un interesse di per sé in quanto sviluppo costruttivo di una forma geometrica complessa qual è un elicoide a pianta ovale, va letta e interpretata anche come testimonianza di un periodo particolare del barocco romano, ricco di intrecci e sovrapposizioni di committenze ecclesiastiche e nobiliari, di avvicendamenti e compresenze dei più grandi artisti e architetti dell’epoca che operano, spesso in simultanea, nei diversi cantieri romani. Borromini propone una variante al progetto iniziale di Maderno, che prevedeva una scala elicoidale a destra del grande portico d’entrata al palazzo, immaginando una nuova scala a pianta ovale con un ritmo di sei colonne binate per ogni giro dell’elica, prendendo a modello la scala che era stata realizzata pochi anni prima, nel 1585, al Palazzo del Quirinale ad opera del Mascherino. Borromini aveva lavorato pochi anni prima, sempre sotto la direzione di Maderno, nel palazzo del Quirinale, e in quel cantiere aveva avuto la possibilità di studiare attentamente la scala ovale del Mascherino. Alla morte del Maderno (1629) nel cantiere del costruendo Palazzo Barberini subentra il Bernini, con il quale Borromini avvierà una collaborazione destinata però a concludersi poco dopo. La scala verrà costruita nel 1633 quando oramai Borromini aveva già abbandonato il cantiere. L’articolo vuole prima di tutto mettere in evidenza le correlazioni tra forma e geometria nel momento in cui si progetta una campagna di acquisizione digitale utilizzando uno scanner laser. Vi sono infatti importanti implicazioni nella scelta dei punti di posizionamento dello strumento in grado di condizionare il rapporto tra qualità e quantità di una points-cloud che assume dignità di vero e proprio modello 3D nel momento in cui è possibile eseguire sia operazioni metriche ma anche selezionare o visualizzare parti o dettagli dell’oggetto rilevato disvelando forme e geometrie altrimenti difficilmente percepibili. Un primo livello di lettura dei modelli, ottenuti secondo procedure di gestione della points-cloud ormai consolidate, ha messo in evidenza l’esatta matrice formale dell’ovale con l’individuazione dei centri della policentrica, il conseguente sviluppo tridimensionale delle diverse eliche appartenenti a porzioni di superfici cilindriche adiacenti tra loro e di diverso raggio, il rapporto con la pendenza delle stesse linee direttrici. All’interno di questa matrice formale di primo livello si inserisce la matrice formale dell’ordine architettonico scandito nel ritmo delle sei coppie di colonne alternate da balaustrini e nella trabeazione che si sviluppa come un nastro all’interno dello spazio centrale illuminato dal soprastante lucernario. La struttura modulare della scala ha suggerito anche una sperimentazione per mezzo delle tecniche di modellazione parametrica per cercare di risalire al modello ideale della scala elicoidale del Borromini. Il modello digitale parametrico qui sperimentato rappresenta una nuova modalità di rappresentazione rispetto ai modelli già consolidati sia di tipo analogico che digitale. Attraverso una selezione critica di alcuni punti notevoli appartenenti alle geometrie presenti e un’osservazione statistica e normalizzata delle misure ricorrenti, si è proceduto all’individuazione di un algoritmo generativo che possiamo ipotizzare essere rappresentativo delle intenzioni progettuali dell’autore. L’intero percorso di ricerca seguito per giungere alla definizione del modello generativo parametrico - dall’ analisi del modello reale, al progetto del modello parametrico virtuale; dallo sviluppo dell’algoritmo generativo al suo collaudo, realizzato attraverso il confronto fra il modello generato e il modello rilevato - si è rilevato vincolo metodologico rigoroso per una più completa e appropriata conoscenza dell’opera

Numerically Modeling the First Peak of the Type IIb SN 2016gkg

Many Type IIb supernovae (SNe) show a prominent additional early peak in their light curves, which is generally thought to be due to the shock cooling of extended hydrogen-rich material surrounding the helium core of the exploding star. The recent SN 2016gkg was a nearby Type IIb SN discovered shortly after explosion, which makes it an excellent candidate for studying this first peak. We numerically explode a large grid of extended envelope models and compare these to SN 2016gkg to investigate what constraints can be derived from its light curve. This includes exploring density profiles for both a convective envelope and an optically thick steady-state wind, the latter of which has not typically been considered for Type IIb SNe models. We find that roughly $\sim0.02\,M_\odot$ of extended material with a radius of $\approx180-260\,R_\odot$ reproduces the photometric light curve data, consistent with pre-explosion imaging. These values are independent of the assumed density profile of this material, although a convective profile provides a somewhat better fit. We infer from our modeling that the explosion must have occurred within $\approx2-3\,{\rm hrs}$ of the first observed data point, demonstrating that this event was caught very close to the moment of explosion. Nevertheless, our best-fitting one-dimensional models overpredict the earliest velocity measurements, which suggests that the hydrogen-rich material is not distributed in a spherically symmetric manner. We compare this to the asymmetries seen in the SN IIb remnant Cas A, and we discuss the implications of this for Type IIb SN progenitors and explosion models.Comment: 8 pages, 8 figures, updated version accepted for publication in The Astrophysical Journa

An empirical limit on the kilonova rate from the DLT40 one day cadence Supernova Survey

Binary neutron star mergers are important to understand stellar evolution, the chemical enrichment of the universe via the r-process, the physics of short gamma-ray bursts, gravitational waves and pulsars. The rates at which these coalescences happen is uncertain, but it can be constrained in different ways. One of those is to search for the optical transients produced at the moment of the merging, called a kilonova, in ongoing SN searches. However, until now, only theoretical models for kilonovae light curve were available to estimate their rates. The recent kilonova discovery AT~2017gfo/DLT17ck gives us the opportunity to constrain the rate of kilonovae using the light curve of a real event. We constrain the rate of binary neutron star mergers using the DLT40 Supernova search, and the native AT~2017gfo/DLT17ck light curve obtained with the same telescope and software system. Excluding AT~2017gfo/DLT17ck due to visibility issues, which was only discovered thanks to the aLIGO/aVirgo trigger, no other similar transients detected during 13 months of daily cadence observations of $\sim$ 2200 nearby ($<$40 Mpc) galaxies. We find that the rate of BNS mergers is lower than 0.47 - 0.55 kilonovae per 100 years per $10^{10}$ $L_{B_{\odot}}$ (depending on the adopted extinction distribution). In volume, this translates to <0.99\times 10^{-4}\,_{-0.15}^{+0.19},\rm{Mpc^{-3}}\,\rm{yr^{-1}}(SNe Ia-like extinction distribution), consistent with previous BNS coalescence rates. Based on our rate limit, and the sensitivity of aLIGO/aVirgo during O2, it is very unlikely that kilonova events are lurking in old pointed galaxy SN search datasets.Comment: 3 figures, 2 table

The discovery of the electromagnetic counterpart of GW170817: kilonova AT 2017gfo/DLT17ck

During the second observing run of the Laser Interferometer gravitational- wave Observatory (LIGO) and Virgo Interferometer, a gravitational-wave signal consistent with a binary neutron star coalescence was detected on 2017 August 17th (GW170817), quickly followed by a coincident short gamma-ray burst trigger by the Fermi satellite. The Distance Less Than 40 (DLT40) Mpc supernova search performed pointed follow-up observations of a sample of galaxies regularly monitored by the survey which fell within the combined LIGO+Virgo localization region, and the larger Fermi gamma ray burst error box. Here we report the discovery of a new optical transient (DLT17ck, also known as SSS17a; it has also been registered as AT 2017gfo) spatially and temporally coincident with GW170817. The photometric and spectroscopic evolution of DLT17ck are unique, with an absolute peak magnitude of Mr = -15.8 \pm 0.1 and an r-band decline rate of 1.1mag/d. This fast evolution is generically consistent with kilonova models, which have been predicted as the optical counterpart to binary neutron star coalescences. Analysis of archival DLT40 data do not show any sign of transient activity at the location of DLT17ck down to r~19 mag in the time period between 8 months and 21 days prior to GW170817. This discovery represents the beginning of a new era for multi-messenger astronomy opening a new path to study and understand binary neutron star coalescences, short gamma-ray bursts and their optical counterparts.Comment: ApJL in press, 4 figure

A review of the molecular mechanisms underlying the development and progression of cardiac remodeling

Pathological molecular mechanisms involved in myocardial remodeling contribute to alter the existing structure of the heart, leading to cardiac dysfunction. Among the complex signaling network that characterizes myocardial remodeling, the distinct processes are myocyte loss, cardiac hypertrophy, alteration of extracellular matrix homeostasis, fibrosis, defective autophagy, metabolic abnormalities, and mitochondrial dysfunction. Several pathophysiological stimuli, such as pressure and volume overload, trigger the remodeling cascade, a process that initially confers protection to the heart as a compensatory mechanism. Yet chronic inflammation after myocardial infarction also leads to cardiac remodeling that, when prolonged, leads to heart failure progression. Here we review the molecular pathways involved in cardiac remodeling, with particular emphasis on those associated with myocardial infarction. A better understanding of cell signaling involved in cardiac remodeling may support the development of new therapeutic strategies towards the treatment of heart failure and reduction of cardiac complications. We will also discuss data derived from gene therapy approaches for modulating key mediators of cardiac remodeling

Autohydrolysis pretreatment of Arundo donax: a comparison between microwave-assisted batch and fast heating rate flow-through reaction systems

Background: Autohydrolysis of lignocellulosic biomass in liquid hot water has been widely studied owing to its high efficiency and relatively low cost. In the perspective of industrial applications, continuous or semi-continuous processes are more interesting than batch systems. Moreover, microwave heating of pretreatment systems has been proposed to intensify the kinetics of the process. In this study, the autohydrolysis of Arundo donax was performed in pure liquid hot water using a microwave-heated batch reactor and a semi-continuous flow-through reaction system with fast heating rate at the same operating conditions with the aim of performing a systematic comparison between the two different experimental apparatuses. Results: The effect of process temperature and time, biomass to water mass to volume ratio and water flow rate on the concentration and yield of hydrolysis products was investigated. The flow-through set-up allowed us to reach biomass solubilization up to 44.5 wt% on dry basis, while the batch system stopped at 34.5 wt% suggesting that the mass transfer could be the rate-determining step in the solubilization of the constituting biopolymers. For example, in the flow-through layout, using a flow rate of 3.5 mL/min at 200 °C with 20 min of processing time, quantitative recovery of hemicellulose was obtained with limited formation of degradation products. Interestingly, higher cellulose/ hemicellulose extraction ratios were found using the microwave-assisted batch reactor. FTIR analyses of the solid residues recovered after the pretreatment offered independent information on the fractions of liquefied biopolymers complementary to those derived from HPLC and UV–Vis spectroscopy. Conclusions: Collected experimental results indicated that the flow-through system can be adopted to obtain complete solubilization of the hemicellulose fraction of Arundo donax addressing the product distribution in soluble compounds towards fermentable sugars with limited formation of sugar degradation products and with limited penalty in terms of dilution of the hydrolysate solution. It was also found that microwaves can promote cellulose depolymerization and solubilization, thus allowing a more comprehensive utilization of the biomass and that infrared spectroscopy can be a useful technique to estimate the effect of the pretreatment

Prediction of Impaired Performance in Trail Making Test in MCI Patients With Small Vessel Disease Using DTI Data

Mild cognitive impairment (MCI) is a common condition in patients with diffuse hyperintensities of cerebral white matter (WM) in T2-weighted magnetic resonance images and cerebral small vessel disease (SVD). In MCI due to SVD, the most prominent feature of cognitive impairment lies in degradation of executive functions, i.e., of processes that supervise the organization and execution of complex behavior. The trail making test is a widely employed test sensitive to cognitive processing speed and executive functioning. MCI due to SVD has been hypothesized to be the effect of WM damage, and diffusion tensor imaging (DTI) is a well-established technique for in vivo characterization of WM. We propose a machine learning scheme tailored to 1) predicting the impairment in executive functions in patients with MCI and SVD, and 2) examining the brain substrates of this impairment. We employed data from 40 MCI patients with SVD and created feature vectors by averaging mean diffusivity (MD) and fractional anisotropy maps within 50 WM regions of interest. We trained support vector machines (SVMs) with polynomial as well as radial basis function kernels using different DTI-derived features while simultaneously optimizing parameters in leave-one-out nested cross validation. The best performance was obtained using MD features only and linear kernel SVMs, which were able to distinguish an impaired performance with high sensitivity (72.7%-89.5%), specificity (71.4%-83.3%), and accuracy (77.5%-80.0%). While brain substrates of executive functions are still debated, feature ranking confirm that MD in several WM regions, not limited to the frontal lobes, are truly predictive of executive functions