281 research outputs found

    Improving the modelling of redshift-space distortions: I. A bivariate Gaussian description for the galaxy pairwise velocity distributions

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    As a step towards a more accurate modelling of redshift-space distortions in galaxy surveys, we develop a general description of the probability distribution function of galaxy pairwise velocities within the framework of the so-called streaming model. For a given galaxy separation r⃗\vec{r}, such function can be described as a superposition of virtually infinite local distributions. We characterize these in terms of their moments and then consider the specific case in which they are Gaussian functions, each with its own mean μ\mu and dispersion σ\sigma. Based on physical considerations, we make the further crucial assumption that these two parameters are in turn distributed according to a bivariate Gaussian, with its own mean and covariance matrix. Tests using numerical simulations explicitly show that with this compact description one can correctly model redshift-space distorsions on all scales, fully capturing the overall linear and nonlinear dynamics of the galaxy flow at different separations. In particular, we naturally obtain Gaussian/exponential, skewed/unskewed distribution functions, depending on separation as observed in simulations and data. Also, the recently proposed single-Gaussian description of redshift-space distortions is included in this model as a limiting case, when the bivariate Gaussian is collapsed to a two-dimensional Dirac delta function. We also show how this description naturally allows for the Taylor expansion of 1+ξS(s⃗)1+\xi_S(\vec{s}) around 1+ξR(r)1+\xi_R(r), which leads to the Kaiser linear formula when truncated to second order, expliciting its connection with the moments of the velocity distribution functions. More work is needed, but these results indicate a very promising path to make definitive progress in our program to improve RSD estimators.Comment: 11 pages, 3 figures, 2 table

    A new model with Serpent for the first criticality benchmarks of the TRIGA Mark II reactor

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    We present a new model, developed with the Serpent Monte Carlo code, for neutronics simulation of the TRIGA Mark II reactor of Pavia (Italy). The complete 3D geometry of the reactor core is implemented with high accuracy and detail, exploiting all the available information about geometry and materials. The Serpent model of the reactor is validated in the fresh fuel configuration, through a benchmark analysis of the first criticality experiments and control rods calibrations. The accuracy of simulations in reproducing the reactivity difference between the low power (10 W) and full power (250 kW) reactor condition is also tested. Finally, a direct comparison between Serpent and MCNP simulations of the same reactor configurations is presented

    The impact of the electricity tariff reform on renewable energies and energy efficiency investments: The case of the Italian residential market

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    This article investigates the impact that the electricity tariff reform is likely to have on investments in renewable energies (i.e., photovoltaics) and the adoption of energy efficiency measures (i.e., installation of heat pumps and efficient home appliances) in the residential market in Italy. The study develops detailed cost comparisons and simulations considering two different investment scenarios (before and after the reform) to conclude that the reform will: (i) have a negative impact on investments in photovoltaic systems; (ii) favor the adoption of energy efficiency measures, such as efficient home appliances

    SISTEMA DI PROPULSIONE PER VELIVOLO E METODO DI CONTROLLO DEL SISTEMA DI PROPULSIONE PER VELIVOLO

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    Brevetto per invenzione industriale intitolato "Sistema di propulsione per velivolo e metodo di controllo di sistema di propulsione per velivolo". Titolari: Politecnico di Torino, Torino; Alenia Aermacchi S.P.A., Venegono Superiore (VA). Inventori: Ronchetto Davide, Chiesa Sergio, Ragusa Carlo Stefano, Armando Eric Giacomo, Farfaglia Salvatore

    Remineralizing effect of a zinc-hydroxyapatite toothpaste on enamel erosion caused by soft drinks : ultrastructural analysis

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    The aim of the present in vitro study was to evaluate the protective effects of a zinc-hydroxyapatite toothpaste on repairing enamel erosion produced by a soft drink (Coca-Cola) compared to toothpastes with and without fluoride using Scanning Electron Microscopy (SEM). Fifty specimens were assigned to 5 groups of 10 specimens each. (Group 1: no erosive challenge, no toothpaste treatment, group 2: erosive challenge, no toothpaste treatment, 3: erosive challenge, toothpaste without fluoride, group 4: erosive challenge, fluoride toothpaste treatment, group 5: erosive challenge, zinc-hydroxyapatite toothpaste treatment). Repeated erosive challenges were provided by immersing bovine enamel specimens (10 per group) in a soft drink for 2 min (6mL, room temperature) at 0, 8, 24 and 32 h. After each erosive challenge, the toothpastes were applied neat onto the surface of specimens for 3 min without brushing and removed with distilled water. Between treatments the specimens were kept in artificial saliva. The surface of each specimen was imaged by SEM. Statistically significant differences were found between the samples used as control and those immersed in Coca-Cola (group 1 and 2): indeed among all groups the highest grade of damage was found in group 2. Instead the lowest grade was recorded in the samples of group 5 (Zinc hydroxyapatite toothpaste). The results of this study confirmed the potential benefit the Zn-HAP technology could provide in protecting enamel from erosive acid challenges. The treatment of erosively challenged enamel with Zn-Hap toothpaste showed a clear protective effect

    Distribution of Pseudomonas species in a dairy plant affected by occasional blue discoloration

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    During 2010 many cases of discoloration in mozzarella, popularly termed as blue mozzarella, have been reported to the attention of public opinion. Causes of the alteration were bacteria belonging to the genus Pseudomonas. The strong media impact of such cases has created confusion, not only among consumers, but also among experts. In order to help improving the knowledge on microbial ecology of this microorganism a study has been set up with the collaboration of a medium-sized dairy plant producing fresh mozzarella cheese, with occasional blue discoloration, conducting surveys and sampling in the pre-operational, operational and post-operational process phase, milk before and after pasteurization, water (n=12), environmental surfaces (n=22) and the air (n=27). A shelf life test was conducted on finished products stored at different temperatures (4-8°C). Among the isolates obtained from the microbiological analysis of the samples, 60 were subjected to biomolecular tests in order to confirm the belonging to Pseudomonas genus and to get an identification at species level by the amplification and sequencing of the gyrB gene. The results of microbiological tests demonstrated the presence of microorganisms belonging to the genus Pseudomonas along the entire production lane; molecular tests showed 7 different species among the 40 isolates identified. One particular species (Pseudomonas koreensis) was isolated from blue discolored mozzarella cheese and was indicated as the most relevant for the production plant, both for the distribution along the processing chain and for the consequences on the finished product

    Resin infiltrant for non-cavitated caries lesions: evaluation of color stability

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    The objective of this in vitro study was to evaluate the over time color stability of one resin infiltrant (Icon) upon exposure to staining solutions (coffee and wine) compared with one nano-hybrid sealant (Grandio Seal), one transparent fissure sealant with fluoride (Control Seal) and one nanofilled composite (Filtek Supreme XTE). All materials were polymerized according to manufacturers’ instructions into silicon rings (height 1 mm; internal diameter 6 mm; external diameter 8 mm) to obtain specimens identical in size. The specimens were immersed in staining solutions at room temperature over a 28-day test period. The control samples have not been subjected to the staining process. A colorimetric evaluation according to the CIE L*a*b* system was performed by a blind trained operator at 7, 14, 21, 28 days of the staining process. Shapiro Wilk test and Kruskal Wallis ANOVA were applied to assess significant differences among different materials. Means were compared with Scheffe’s multiple-comparison test at the 0.05 level of significance. In the case of all materials, immersion in solutions resulted in clinically perceivable color changes after 1 week (∆E 0.05). Color coordinate CIE b* varied similarly for all materials tested (P > 0.05). Immersion in coffee or red wine resulted in clinically perceivable color changes for all materials tested. Icon showed the highest color variations both after 1 week and 1 month. Icon can fix the initial esthetic problem associated with white spot lesions, but the resin may become more discolored than other materials over time

    CO2 capture from natural gas combined cycles by CO2 selective membranes

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    This paper performs a techno-economic analysis of natural gas-fired combined cycle (NGCC) power plants integrated with CO2 selective membranes for post-combustion CO2 capture. The configuration assessed is based on a two-membrane system: a CO2 capture membrane that separates the CO2 for final sequestration and a CO2 recycle membrane that selectively recycles CO2 to the gas turbine compressor inlet in order to increase the CO2 concentration in the gas turbine flue gas. Three different membrane technologies with different permeability and selectivity have been investigated. The mass and energy balances are calculated by integrating a power plant model, a membrane model and a CO2 purification unit model. An economic model is then used to estimate the cost of electricity and of CO2 avoided. A sensitivity analysis on the main process parameters and economic assumptions is also performed. It was found that a combination of a high permeability membrane with moderate selectivity as a recycle membrane and a very high selectivity membrane with high permeability used for the capture membrane resulted in the lowest CO2 avoided cost of 75 US$/tCO2. This plant features a feed pressure of 1.5 bar and a permeate pressure of 0.2 bar for the capture membrane. This result suggests that membrane systems can be competitive for CO2 capture from NGCC power plants when compared with MEA absorption. However, to achieve significant advantages with respect to benchmark MEA capture, better membrane permeability and lower costs are needed with respect to the state of the art technology. In addition, due to the selective recycle, the gas turbine operates with a working fluid highly enriched with CO2. This requires redesigning gas turbine components, which may represent a major challenge for commercial deployment

    A conceptual design tool to support high-speed vehicle design

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    This paper aims at presenting an integrated multidisciplinary methodology and the related software tool, called ASTRID-H, developed at Politecnico di Torino to support the conceptual and preliminary design phases of high-speed vehicles. Based on the experience in the development of innovative methodologies to cope with complex and highly integrated aircraft, ASTRID-H has been developed to guide students, researchers and engineers through the very first phases of the design of high-speed vehicles. ASTRID-H supports the users to move from the statistical evaluation of the guess data and the identification of the design space to the geometrical characterization of the vehicle guaranteeing a proper integration of the main subsystems. Already available and widely used mathematical models are here integrated in a new algorithm to face the complexity of the design of high-speed vehicles. In addition, the coefficients of the semi-empirical models that were not focusing on high-speed vehicles have been updated to widen classical theories to cover high-speed vehicles. The resulting implemented methodology allows the users to cope with complex multidisciplinary problems, which encompass a variety of interrelated disciplines and heterogeneous levels of fidelity. Furthermore, this paper reports the some of the main results achieved during the validation of the methodology thanks to the application to the STRATOFLY MR3 vehicle case study. STRATOFLY MR3 is a Mach 8 waverider configuration that stems from more than a decade of European research activities in the field of high-speed and currently under investigation in the Horizon 2020 STRATOFLY Project
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