Search for non-Poissonian behavior in nuclear beta-decay

We performed two independent counting experiments on a beta-emitting source of Sm151 by measuring the gamma-photon emitted in a fraction of the decays. For counting times ranging from 10**-3 to 5.12*10**4 seconds, our measurements show no evidence of deviations from Poissonian behavior and, in particular, no sign of 1/f noise. These measurements put strong limits on non-Poissonian components of the fluctuations for the subset of decays accompanied by gamma, and corresponding limits for the total number of beta-decays. In particular, the magnitude of a hypothetical flicker floor is strongly bounded also for the beta-decay. This result further constrains theories predicting anomalous fluctuations in nuclear decays.Comment: 10 pages, LaTeX, plus 2 figures added as separate uuencoded compressed postscript files. To appear in Phys. Rev. E 55 (1997

On the robustness of the Hβ\beta Lick index as a cosmic clock in passive early-type galaxies

We examine the H$\beta$ Lick index in a sample of $\sim 24000$ massive ($\rm log(M/M_{\odot})>10.75$) and passive early-type galaxies extracted from SDSS at z<0.3, in order to assess the reliability of this index to constrain the epoch of formation and age evolution of these systems. We further investigate the possibility of exploiting this index as "cosmic chronometer", i.e. to derive the Hubble parameter from its differential evolution with redshift, hence constraining cosmological models independently of other probes. We find that the H$\beta$ strength increases with redshift as expected in passive evolution models, and shows at each redshift weaker values in more massive galaxies. However, a detailed comparison of the observed index with the predictions of stellar population synthesis models highlights a significant tension, with the observed index being systematically lower than expected. By analyzing the stacked spectra, we find a weak [NII]$\lambda6584$ emission line (not detectable in the single spectra) which anti-correlates with the mass, that can be interpreted as a hint of the presence of ionized gas. We estimated the correction of the H$\beta$ index by the residual emission component exploiting different approaches, but find it very uncertain and model-dependent. We conclude that, while the qualitative trends of the observed H$\beta$-z relations are consistent with the expected passive and downsizing scenario, the possible presence of ionized gas even in the most massive and passive galaxies prevents to use this index for a quantitative estimate of the age evolution and for cosmological applications.Comment: 20 pages, 11 figures, 1 table. Accepted for publication in MNRAS Main Journa

Bulges and disks in the local Universe. Linking the galaxy structure to star formation activity

We use a sample built on the SDSS DR7 catalogue and the bulge-disc decomposition of Simard et al. (2011) to study how the bulge and disc components contribute to the parent galaxy's star formation activity, by determining its position in the star formation rate (SFR) - stellar mass (M$_{\star}$) plane at 0.02$<z<$0.1. We use the bulge and disc colours as proxy for their SFRs. We study the mean galaxy bulge-total mass ratio (B/T) as a function of the residual from the MS ($\Delta_{MS}$) and find that the B/T-$\Delta_{MS}$ relation exhibits a parabola-like shape with the peak of the MS corresponding to the lowest B/Ts at any stellar mass. The lower and upper envelop of the MS are populated by galaxies with similar B/T, velocity dispersion and concentration ($R_{90}/R_{50}$) values. Bulges above the MS are characterised by blue colours or, when red, by a high level of dust obscuration, thus indicating that in both cases they are actively star forming. When on the MS or below it, bulges are mostly red and dead. At stellar masses above $10^{10.5}$M$_{\odot}$, bulges on the MS or in the green valley tend to be significantly redder than their counterparts in the quiescence region, despite similar levels of dust obscuration. The disc color anti-correlates at any mass with the distance from the MS, getting redder when approaching the MS lower envelope and the quiescence region. We conclude that the position of a galaxy in the LogSFR-LogM$_{\star}$ plane depends on the star formation activity of its components: above the MS both bulge and disk are actively star forming. The nuclear activity is the first to be suppressed, moving the galaxies on the MS. Once the disk stops forming stars as well, the galaxy moves below the MS and eventually to the quiescence region. This is confirmed by a large fraction ($\sim45\%$) of passive galaxies with a secure two component morphology.Comment: Version modified after referee comment

Two-Face(s): ionized and neutral gas winds in the local Universe

We present a comprehensive study of the Na I $\lambda$5890, 5895 (Na I D) resonant lines in the Sloan Digital Sky Survey (SDSS, DR7) spectroscopic sample to look for neutral gas outflows in the local galaxies. Individual galaxy spectra are stacked in bins of M${\star}$ and SFR to investigate the dependence of galactic wind occurrence and velocity as a function of the galaxy position in the SFR-$M{\star}$ plane. In massive galaxies at the high SFR tail we find evidence of a significant blue-shifted Na I D absorption, which we interpret as evidence of neutral outflowing gas. The occurrence of the blue-shifted absorption is observed at the same significance for purely SF galaxies, AGN and composite systems at fixed SFR. In all classes of objects the blue-shift is the largest and the Na I D equivalent width the smallest for face-on galaxies while the absorption feature is at the systemic velocity for edge-on systems. This indicates that the neutral outflow is mostly perpendicular or biconical with respect to the galactic disk. We also compare the kinematics of the neutral gas with the ionized gas phase as traced by the [OIII]$\lambda$5007, H$\alpha$, [NII]$\lambda6548$ and [NII]$\lambda6584$ emission lines. Differently for the neutral gas phase, all the emission lines show evidence of perturbed kinematics only in galaxies with a significant level of nuclear activity and, they are independent from the disk inclination. In conclusion, we find that, in the local Universe, galactic winds show two faces which are related to two different ejection mechanisms, namely the neutral outflowing gas phase related to the SF activity along the galaxy disk and the ionized phase related to the AGN feedback. In both the neutral and ionized gas phases, the observed wind velocities suggest that the outflowing gas remains bound to the galaxy with no definitive effect on the gas reservoir.Comment: Accepted to A&A, 13 pages, 9 figure

Technical and economical evaluation of Power-to-Methane technologies, based on green H2 and biogenic CO2

The topic of this PhD thesis is focused on the techno-economic analysis of energy systems for the production of green fuels, such as hydrogen (H2) and biomethane (CH4), exploiting Renewable Energy Sources (RES) and biogenic CO2. In the frame of the Sardinia energy scenario, one of the biggest islands in Italy, the only one without a natural gas grid and, at the same time, a high availability of renewable resources, the present thesis offers a contribution to find a solution for the future decarbonization of the island. The contribution of the present study refers to the production, transport, distribution, and final economic analysis of green fuels to support the energy transition and can also be a model for other isolated energy systems. The analysis carried out allowed the evaluation of the effectiveness and economic feasibility of such innovative technologies, Power-to-Hydrogen and Power-to-Methane. With the focus on the Power-to-Methane system, different layouts have been designed to perform a comprehensive analysis of various solutions. Systems based on commercially mature or innovative technologies are analysed throughout the development of models using MATLAB software. Hydrogen is produced using RES and electric energy from the grid and converted to biomethane through biological methanation processes (BHM), employing the CO2 resulting from the biogas upgrading in anaerobic digestion plants. Two different solutions have been analysed: a BHM process with the injection of CO2 and H2, and a BHM process with the injection of Biogas and H2. Evaluation of the optimal location for the Power-to-Methane system was carried out to find the more profitable way of transporting the CH4 produced. Variations on the reference layout allow getting a comprehensive view of different approaches and integrations, with the common objective to find the solution with the lowest Levelized Cost of Biomethane (LCOBM) value. In addition, another interesting solution studied is the inclusion of a BHM process in a Hydrogen Valley, with a focus on the economic and environmental benefits. Depending on the chosen configuration, the minimum LCOBM was between 2.27 and 2.85 €/Nm3, in the case of polymeric electrolyser membrane technology (PEM) with 56% of energy from RES and alkaline electrolyser (AEL) with 75% of energy from RES, respectively. Finally, including such a system in the Sardinia energy scenario, can provide a contribution of about 44% to the forecast natural gas consumption in 2050

Identifying the lights position in photometric stereo under unknown lighting

Reconstructing the 3D shape of an object from a set of images is a classical problem in Computer Vision. Photometric stereo is one of the possible approaches. It stands on the assumption that the object is observed from a fixed point of view under different lighting conditions. The traditional approach requires that the position of the light sources is accurately known. It has been proved that the lights position can be estimated directly from the data, when at least 6 images of the observed object are available. In this paper, we give a Matlab implementation of the algorithm for solving the photometric stereo problem under unknown lighting, and propose a simple shooting technique to solve the bas-relief ambiguity.Comment: new versio