Optical and infrared photometry of the blazar PKS0537-441

We present a large collection of photometric data on the Blazar PKS 0537-441 in the VRIJHK bands taken in 2004-2009. At least three flare-like episodes with months duration, and >3 mag amplitude are apparent. The spectral energy distribution is consistent with a power law, and no indication of a thermal component is found. We searched for short time scale variability, and an interesting event was identified in the J band, with a duration of ~25 minutes.Comment: 10 pages, 3 figures, in press in ApJ

Onset of thermal convection in a horizontal porous layer saturated by a power-law fluid

A horizontal porous layer saturated by a non-Newtonian fluid is taken into account. The fluid is a Ostwald-De Waele type of fluid. The layer is heated from below while the upper boundary is isothermal. The lower boundary is impermeable and the upper one is free. A fully developed basic throughflow is considered. The basic state is perturbed by employing small amplitude perturbations such that a linear stability analysis is performed. The disturbances are assumed to be normal modes and a system of ordinary differential equations governing the perturbation dynamics is obtained. These ODEs form an eigenvalue problem that is solved numerically: both the neutral stability curves and the threshold values for the onset of convection are presented

Analisi dell'instabilità convettiva di fluidi non newtoniani in mezzi porosi

L'instabilità termica di Rayleigh-Bénard in un mezzo poroso saturato da un fluido Newtoniano è stata ampiamente studiata negli ultimi decenni. L'analisi è stata estesa al caso in cui il fluido è soggetto a un flusso orizzontale stazionario e parallelo. E' stato dimostrato che il flusso orizzontale non altera le condizioni di innesco dell'instabilità convettiva. Va menzionato che, mentre la maggior parte della letteratura esistente su questo argomento è relativa ai fluidi Newtoniani che saturano mezzi porosi, alcuni studi hanno esteso l'indagine anche a fluidi non Newtoniani. Questo lavoro di ricerca vuole espandere ulteriormente le conoscenze sull'insorgere dell'instabilità convettiva innescata dal galleggiamento termico in strati porosi saturati da un fluido non Newtoniano. Nella prima parte della tesi viene effettuato uno studio preliminare per capire in che modo un fluido non Newtoniano si caratterizza rispetto ad un fluido Newtoniano. Tali fluidi vengono poi studiati quando si trovano a saturare un solido poroso, di conseguenza vengono introdotte le considerazioni che portano alla modifica dell'equazione della quantità di moto dei fluidi Newtoniani a quella dei fluidi non Newtoniani in mezzi porosi. La parte finale della tesi riguarda lo studio numerico dell'instabilità. Da uno studio preliminare dei diversi articoli scientifici pubblicati su riviste del settore, viene studiata l'instabilità convettiva di un fluido non Newtoniano che satura uno strato poroso, il quale strato viene riscaldato nella superficie inferiore a flusso di calore costante mentre lo strato superiore è una superficie libera. Grazie alle tecniche matematiche studiate in diversi articoli scientifici, viene fatta un'analisi perturbativa di tipo lineare considerando i modi normali. Dallo studio si riescono a ricavare dei parametri adimensionali che descrivono le instabilità per i diversi tipi di fluidi non Newtoniani

Use of the Peak-Detector mode for gain calibration of SiPM sensors with ASIC CITIROC read-out

The Cherenkov Imaging Telescope Integrated Read Out Chip (CITIROC) is a 32-channel fully analogue front-end ASIC dedicated to the read-out of silicon photo-multiplier (SiPM) sensors that can be used in a variety of experiments with different applications: nuclear physics, medical imaging, astrophysics, etc. It has been adopted as front-end for the focal plane detectors of the ASTRI-Horn Cherenkov telescope and, in this context, it was modified implementing the peak detector reading mode to satisfy the instrument requirements. For each channel, two parallel AC coupled voltage preamplifiers, one for the high gain and one for the low gain, ensure the read-out of the charge from 160 fC to 320 pC (i.e. from 1 to 2000 photo-electrons with SiPM gain = 10$^{6}$, with a photo-electron to noise ratio of 10). The signal in each of the two preamplifier chains is shaped and the maximum value is captured by activating the peak detector for an adjustable time interval. In this work, we illustrate the peak detector operation mode and, in particular, how this can be used to calibrate the SiPM gain without the need of external light sources. To demonstrate the validity of the method, we also present and discuss some laboratory measurements.Comment: 11 pages, 9 figures, 15th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD19) 14-17 October 2019 Siena, Italy (Submitted to JINST peer review on 05 January 2020

Computational framework for the prediction of transcription factor binding sites by multiple data integration

Control of gene expression is essential to the establishment and maintenance of all cell types, and its dysregulation is involved in pathogenesis of several diseases. Accurate computational predictions of transcription factor regulation may thus help in understanding complex diseases, including mental disorders in which dysregulation of neural gene expression is thought to play a key role. However, biological mechanisms underlying the regulation of gene expression are not completely understood, and predictions via bioinformatics tools are typically poorly specific. We developed a bioinformatics workflow for the prediction of transcription factor binding sites from several independent datasets. We show the advantages of integrating information based on evolutionary conservation and gene expression, when tackling the problem of binding site prediction. Consistent results were obtained on a large simulated dataset consisting of 13050 in silico promoter sequences, on a set of 161 human gene promoters for which binding sites are known, and on a smaller set of promoters of Myc target genes. Our computational framework for binding site prediction can integrate multiple sources of data, and its performance was tested on different datasets. Our results show that integrating information from multiple data sources, such as genomic sequence of genes' promoters, conservation over multiple species, and gene expression data, indeed improves the accuracy of computational predictions

Theoretical and Numerical Study on Buongiorno’s Model with a Couette Flow of a Nanofluid in a Channel with an Embedded Cavity

In the present paper, the fluid flow and heat transfer of a nanofluid are numerically investigated. More specifically, reference is made to a nanofluid, described by means of Buongiorno’s model, subjected to Couette flow. The considered domain consists of a channel that displays a cavity shortly after the inlet section. The transport model for the nanofluid, that is the mass conservation, momentum, and nanoparticles equation, is written in a dimensionless form and solved by employing the software package Comsol Multiphysics. Many ideas emerged from this work: the visualization of the velocity stream function, the dimensionless temperature, and nanoparticle concentration fields are provided, as a function of the governing parameters: Reynolds, Peclet, Lewis, Brownian diffusivity number, and thermophoretic diffusivity number. Concerning the nanofluid typical effects, the thermophoretic diffusion seems to affect the solution much more than the Brownian diffusion. The Nusselt number on the upper wall is calculated as well, and the results show that it proves to be, in most of the considered cases, an increasing function of the Reynolds number. Moreover, concerning the Nusselt number, the Brownian diffusion effects are shown to be negligible

Geometric optimization of complex thermal-fluid dynamic system by means of constructal design

In this work the Constructal Theory is exposed in its generality, trying to approach it through examples mostly of a physical-engineering nature. Constructal Theory proposes to see living bodies as elements subject to constraints, which are built with a goal, an objective, which is to obtain maximum efficiency. Constructal Theory is characterized by Constructal Law, which states that if a system has the freedom to morph it develops over time a flow architecture that provides easier access to the currents that pass through it. The Constructal Law is as general as the First and Second Laws of Thermodynamics, but it has a very different purpose which makes it unique and complementary to those laws. While the First Law points to the conservation of energy, both the Constructal Law and the Second Law point to change, that is, to a direction in time. Contrary to the Second Law, the Constructal Law applies to systems that are out of balance, that is, to systems that evolve over time. While the second law deals with state variables, the Constructal Law combines flows and design. The thesis continues with the application of the Constructal Theory for a cardiac bypass shape optimization. Through the Constructal Theory the constraints under which the system is free to morph are defined and, through the classical engineering optimization processes (numerical simulations and optimization algorithms) the optimum conditions are defined, i.e., those conditions that guarantee the minimum resistance to the passage of the fluid. The characterization of the blood flow was an important step in the study of this system, as the heartbeat induces a pulsed regime inside the veins. Therefore, the simulations conducted in transient regime consider the deformed velocity profile according to the conditions dictated by the pressure gradient established by the heartbeat