Age consistency between exoplanet hosts and field stars

Transiting planets around stars are discovered mostly through photometric surveys. Unlike radial velocity surveys, photometric surveys do not tend to target slow rotators, inactive or metal-rich stars. Nevertheless, we suspect that observational biases could also impact transiting-planet hosts. This paper aims to evaluate how selection effects reflect on the evolutionary stage of both a limited sample of transiting-planet host stars (TPH) and a wider sample of planet-hosting stars detected through radial velocity analysis. Then, thanks to uniform derivation of stellar ages, a homogeneous comparison between exoplanet hosts and field star age distributions is developed. Stellar parameters have been computed through our custom-developed isochrone placement algorithm, according to PARSEC models. The notable aspects of our algorithm include the treatment of element diffusion, activity checks in terms of $\log{R'_{HK}}$ and $v\sin{i}$, and the evaluation of the stellar evolutionary speed in the Hertzsprung-Russel diagram in order to better constrain age. Working with TPH, the observational stellar mean density $\rho_{\star}$ allows us to compute stellar luminosity even if the distance is not available, by combining $\rho_{\star}$ with the spectroscopic $\log{g}$. The median value of the TPH ages is $\sim5$ Gyr. Even if this sample is not very large, however, the result is very similar to what we found for the sample of spectroscopic hosts, whose modal and median values are [3, 3.5) Gyr and $\sim4.8$ Gyr, respectively. Thus, these stellar samples suffer almost the same selection effects. We also conclude that the age of our Sun is consistent with the age distribution of solar neighbourhood MS stars with spectral types from late F to early K, regardless of whether they harbour planets or not. We considered the possibility that our selected samples are older than the average disc population.Comment: 13 pages, 1 longtable, 9 figures. Accepted by A&

Revising the ages of planet-hosting stars

This article aims to measure the age of planet-hosting stars (SWP) through stellar tracks and isochrones computed with the \textsl{PA}dova \& T\textsl{R}ieste \textsl{S}tellar \textsl{E}volutionary \textsl{C}ode (PARSEC). We developed algorithms based on two different techniques for determining the ages of field stars: \emph{isochrone placement} and \emph{Bayesian estimation}. Their application to a synthetic sample of coeval stars shows the intrinsic limits of each method. For instance, the Bayesian computation of the modal age tends to select the extreme age values in the isochrones grid. Therefore, we used the isochrone placement technique to measure the ages of 317 SWP. We found that $\sim6\%$ of SWP have ages lower than 0.5 Gyr. The age distribution peaks in the interval [1.5, 2) Gyr, then it decreases. However, $\sim7\%$ of the stars are older than 11 Gyr. The Sun turns out to be a common star that hosts planets, when considering its evolutionary stage. Our SWP age distribution is less peaked and slightly shifted towards lower ages if compared with ages in the literature and based on the isochrone fit. In particular, there are no ages below 0.5 Gyr in the literature.Comment: 16 pages, 18 figures. Accepted by A&

An efficient tool for the assisted design of SAR ADCs capacitive DACs

The optimal design of SAR ADCs requires the accurate estimate of nonlinearity and parasitic capacitance effects in the feedback charge redistribution DAC. Since both contributions depend on the specific array topology, complex calculations, custom modeling and heavy simulations in common circuit design environments are often required. This paper presents a MATLAB-based numerical environment to assist the design of the charge redistribution DACs adopted in SAR ADCs. The tool performs both parametric and statistical simulations taking into account capacitive mismatch and parasitic capacitances computing both differential and integral nonlinearity (DNL, INL). An excellent agreement is obtained with the results of circuit simulators (e.g. Cadence Spectre) featuring up to 10^4 shorter simulation time, allowing statistical simulations that would be otherwise impracticable. The switching energy and SNDR degradation due to static nonlinear effects are also estimated. Simulations and measurements on three designed and two fabricated prototypes confirm that the proposed tool can be used as a valid instrument to assist the design of a charge redistribution SAR ADC and to predict its static and dynamic metrics

Between the Greater and Lesser Caucasus: An Analysis of the Belts from the Tli Burial Ground and Their Contexts (Graves 40b, 215b, 425)

This article presents a new study of three burial contexts from the important Tli graveyard located in the Southern Caucasus. The three tombs contained bronze belts with features mainly pertaining to an Assyro-Urartian tradition. An analysis of the belts’ iconographic apparatuses is given, together with a new chronological position proposed for the belts and the tombs: our idea is that a possible date for them should be within the period between the 7th and 6th centuries B.C.E. The analysis showed, moreover, that the Tli necropolis must be considered a great example of the complex contacts and cultural exchanges between multiple realities located both in the Caucasus and in the Mesopotamian region

The ages of exoplanet hosts and field stars

The thesis aims at homogeneously determining the ages of exoplanet hosts and generic field stars using stellar evolutionary tracks and isochrones computed with the PAdova & TRieste Stellar Evolutionary Code (PARSEC), v. 1.0. To achieve this goal, we fully developed two algorithms (MatLab/Octave language) based on two different statistical approaches: one is frequentistic, the other is Bayesian. The algorithms have been tested on several samples of synthetic stars, in order to evaluate their reliability and put in evidence their limits. After that, we applied our custom-developed algorithms to two different samples of stars, belonging to the same spectral type range. They were essentially main-sequence G type stars located in the solar neighbourhood. One sample is made up of planet-hosting stars, while the other contains field stars that do not harbour planets, as far as we know. First of all, we found that the age distribution of stars harbouring transiting planets is similar to that of stars whose planets have been discovered through the radial velocity technique. This suggests that these two subsets of stars with planets suffer essentially the same selection effects. Finally we homogeneously compare planet-hosting stars with field stars. The histograms displaying the two age distributions peaks in the same age bin, i.e. [3, 3.5) Gyr, and have the same median age, that is 4.8 Gyr. The median age is very similar to that of the Sun. On the one hand, this suggests that our star is in the typical evolutionary stage characterizing G-type stars of the solar neighbourhood. On the other hand, a median age of 4.8 Gyr results to be older than the typical age that is assumed for the thin disc, where the analyzed stars are located. The selection we made in spectral type does introduce a bias. Moreover, it is likely that the sampling of stars limited only to the solar neighbourhood is not representative of the entire thin disc. By extending the analysis to farther distances, so that to include young star-forming regions such as the Taurus-Auriga complex or the Orion Nebula, we expect to collect much more young stars

A 64-Channel 965-μW Neural Recording SoC with UWB Wireless Transmission in 130-nm CMOS

This brief presents a 64-channel neural recording system-on-chip (SoC) with a 20-Mb/s wireless telemetry. Each channel of the analog front end consists of a low-noise bandpass amplifier, featuring a noise efficiency factor of 3.11 with an input-referred noise of 5.6 μVrms in a 0.001- to 10-kHz band and a 31.25-kSps 6-fJ/conversion-step 10-bit SAR analog-to-digital converter. The recorded signals are multiplexed in the digital domain and transmitted via an 11.7% efficiency pulse-position modulation ultrawideband transmitter, reaching a transmission range in excess of 7.5 m. The chip has been fabricated in a 130-nm CMOS process, measures 25 mm2, and dissipates 965 μW from a 0.5-V supply. This SoC features the lowest power per channel (15 μW) and the lowest energy per bit (48.2 pJ) among state-of-the-art wireless neural recording systems with a number of channels larger than 32. The proposed circuit is able to transmit the raw neural signal in a large bandwidth (up to 10 kHz) without performing any data compression or losing vital information, such as local field potentials

On the Hyperparameters influencing a PINN's generalization beyond the training domain

Physics-Informed Neural Networks (PINNs) are Neural Network architectures trained to emulate solutions of differential equations without the necessity of solution data. They are currently ubiquitous in the scientific literature due to their flexible and promising settings. However, very little of the available research provides practical studies that aim for a better quantitative understanding of such architecture and its functioning. In this paper, we analyze the performance of PINNs for various architectural hyperparameters and algorithmic settings based on a novel error metric and other factors such as training time. The proposed metric and approach are tailored to evaluate how well a PINN generalizes to points outside its training domain. Besides, we investigate the effect of the algorithmic setup on the outcome prediction of a PINN, inside and outside its training domain, to explore the effect of each hyperparameter. Through our study, we assess how the algorithmic setup of PINNs influences their potential for generalization and deduce the settings which maximize the potential of a PINN for accurate generalization. The study that we present returns insightful and at times counterintuitive results on PINNs. These results can be useful in PINN applications when defining the model and evaluating it

MCMCI: A code to fully characterise an exoplanetary system

Useful information can be retrieved by analysing the transit light curve of a planet-hosting star or induced radial velocity oscillations. However, inferring the physical parameters of the planet, such as mass, size, and semi-major axis, requires preliminary knowledge of some parameters of the host star, especially its mass or radius, which are generally inferred through theoretical evolutionary models. We seek to present and test a whole algorithm devoted to the complete characterisation of an exoplanetary system thanks to the global analysis of photometric or radial velocity time series combined with observational stellar parameters derived either from spectroscopy or photometry. We developed an integrated tool called MCMCI. This tool combines the Markov chain Monte Carlo (MCMC) approach of analysing photometric or radial velocity time series with a proper interpolation within stellar evolutionary isochrones and tracks, known as isochrone placement, to be performed at each chain step, to retrieve stellar theoretical parameters such as age, mass, and radius. We tested the MCMCI on the HD 219134 multi-planetary system hosting two transiting rocky super Earths and on WASP-4, which hosts a bloated hot Jupiter. Even considering different input approaches, a final convergence was reached within the code, we found good agreement with the results already stated in the literature and we obtained more precise output parameters, especially concerning planetary masses. The MCMCI tool offers the opportunity to perform an integrated analysis of an exoplanetary system without splitting it into the preliminary stellar characterisation through theoretical models. Rather this approach favours a close interaction between light curve analysis and isochrones, so that the parameters recovered at each step of the MCMC enter as inputs for purposes of isochrone placement.Comment: 18 pages, 6 figures, 6 tables. Accepted for publication in A&A. Source code link: https://github.com/Bonfanti88/MCMC

The Antecedents of the Technology Acceptance Model in Microentrepreneurs’ Intention to Use Social Networking Sites

Social media platforms offer significant growth opportunities for enterprises, particularly microenterprises, due to the chance to establish direct contact with customers. Drawing on the Technology-Acceptance Model (TAM), in the present study, we investigate the psychological reasons that lead microentrepreneurs to use Social Networking Sites (SNSs) for their business. In doing so, we also extend TAM by taking into account entrepreneurs’ personalities (e.g., extraversion and openness to experience) and their perceived risk. We collected data by examining 247 microentrepreneurs engaged in the production of handmade objects. Our results confirm that of all the TAM behavioral antecedents tested, perceived usefulness and attitude toward SNSs’ usage for business proved to be the best predictors of the intention to use SNSs for business activity. The results also indicate that extraversion, openness to experience, and perceived risk, as external factors, significantly affect the TAM constructs. We discuss implications and suggestions for future research