Friction forces in cosmological models

We investigate the dynamics of test particles undergoing friction forces in a Friedmann-Robertson-Walker (FRW) spacetime. The interaction with the background fluid is modeled by introducing a Poynting-Robertson-like friction force in the equations of motion, leading to measurable (at least in principle) deviations of the particle trajectories from geodesic motion. The effect on the peculiar velocities of the particles is investigated for various equations of state of the background fluid and different standard cosmological models. The friction force is found to have major effects on particle motion in closed FRW universes, where it turns the time-asymptotic value (approaching the recollapse) of the peculiar particle velocity from ultra-relativistic (close to light speed) to a co-moving one, i.e., zero peculiar speed. On the other hand, for open or flat universes the effect of the friction is not so significant, because the time-asymptotic peculiar particle speed is largely non-relativistic also in the geodesic case.Comment: 8 pages, 2 figures; published versio

Scientific careers and gender differences. A qualitative study

In Europe, much effort has been devoted to explore the causes of the decline in number of university matriculations of science students and to identify gender differences in career choice. Yet, the problem extends to the fulfillment of career plans: given their professional expectations and their attitudes when choosing a career, girls are much less likely to pursue scientific careers such as engineering or physics. Evidence of this is provided by the social research carried out within the framework of the GAPP project (Gender Awareness Participation Process). The Gapp project is intended to investigate differences between girls and boys in their perception of science careers and to propose a range of innovative and concrete participatory activities involving scientists, engineers and professionals from the public and private S&T sectors. In this letter, we report a synthesis of the results of the social research conducted as first step of the project: exploring how the perceptions of science professions affect interest, motivation and subject choice at school, at the university and consequently in their career

Structural analysis of the double-walled copper-steel cryogenic chamber of the ASTAROTH experiment

This document describes the verification process of structural performance of the double- walled copper-steel cryogenic chamber of the ASTAROTH (All Sensitive crysTal ARray with lOw THreshold) experiment and the evaluation of the stresses generated near the thermal bridge connecting the inner and outer wall. The chamber consists of an external AISI 316L stainless steel dewar and an inner double-walled OF (Oxygen Free) copper dewar connected to an AISI 316L stainless steel flanged collar. The results showed that close to the thermal bridge (copper-steel junction) the stresses slightly exceed the YS of copper at the estimated operating temperature (localised strain-hardening condition). On the other hand, the safety coefficient respect to fracture is well above one for both materials. This condition, together with the fact that limited cooling cycles are expected during the operating life of the system, leads to the assumption that a progressive material hardening will occur in this area, thus locally raising the YS limit

Experimental Investigation on the Aerodynamic Interaction Between a Helicopter and Ground Obstacles

In this study, experiments were performed to investigate the aerodynamic interaction between a helicopter and ground obstacles. A new experimental set-up was realised and validated. The motorised helicopter model, which included the fuselage, was positioned in different positions relative to a model building in order to replicate different hovering configurations. The use of a helicopter model with a six-component balance and a building model with several pressure taps allowed a database to be compiled for the loads on the helicopter and obstacle. First several tests were performed without the building in order to develop a reference database and assess the experimental set-up through a comparison with results in the literature. The measured loads were analysed to investigate the interference effects of the building model on the helicopter performance. A physical interpretation of the flow phenomena was obtained through analysis of the obstacle pressure measurements and particle image velocimetry surveys of relevant configurations

Optically Tunable Diffraction Efficiency in Reflection Grating Written in Photomobile Polymers

In this work, we report the fabrication and optical characterization of a one-dimensional reflection holographic volume phase grating recorded in a recently developed holographic photomobile composite polymer mixture. The reflection grating recorded on the photomobile material was a periodic one-dimensional arrangement of hard polymeric walls and viscous regions. The reflection notch was located in the near-infrared region of the electromagnetic spectrum. The transmission efficiency of the grating was modulated by an external CW laser light source operating at λ = 532 nm. The transmission efficiency increased with the increase in the power of the external laser source, and in the range of the used power values, the phenomenon was completely reversible. At the highest power levels, a 48% increase in the diffraction efficiency was achieved. The increase in the diffraction efficiency was related to the growth of the refractive-index contrast of the grating. In particular, under illumination, the viscous material escaped from the irradiated area. This feature explains the experimentally observed changes in the values of the grating’s refractive index

Efficient Generation of Multimodal Fluid Simulation Data

Applying the representational power of machine learning to the prediction of complex fluid dynamics has been a relevant subject of study for years. However, the amount of available fluid simulation data does not match the notoriously high requirements of machine learning methods. Researchers have typically addressed this issue by generating their own datasets, preventing a consistent evaluation of their proposed approaches. Our work introduces a generation procedure for synthetic multi-modal fluid simulations datasets. By leveraging a GPU implementation, our procedure is also efficient enough that no data needs to be exchanged between users, except for configuration files required to reproduce the dataset. Furthermore, our procedure allows multiple modalities (generating both geometry and photorealistic renderings) and is general enough for it to be applied to various tasks in data-driven fluid simulation. We then employ our framework to generate a set of thoughtfully designed benchmark datasets, which attempt to span specific fluid simulation scenarios in a meaningful way. The properties of our contributions are demonstrated by evaluating recently published algorithms for the neural fluid simulation and fluid inverse rendering tasks using our benchmark datasets. Our contribution aims to fulfill the community's need for standardized benchmarks, fostering research that is more reproducible and robust than previous endeavors.Comment: 10 pages, 7 figure

Thermal tests of a scaled down mock-up of CP5.2 packaging system: Post-test analysis

Abstract In this study, the thermal performances of an Italian CP5.2 packaging system aimed at the transportation of bituminised wastes (i.e. engulfing fire of 800 °C for 30 min according to the IAEA regulation) are presented. Due to the high risk of auto-ignition of the bituminised wastes, that are stowed in the drums, in turn, immersed in the cement matrix of the CP 5.2, it was decided to test firstly a small scale mock-up. The mock up, containing only one drum with bituminised waste, was designed and built at the Department of Civil and Industrial Engineering (DICI) of the University of Pisa. The experimental test was carried out at Lab. Guerrini of the University of Pisa. Results demonstrated that after half an hour of fire exposure at 800 °C, the temperature in the bituminised waste package is below that of auto-ignition of the bitumen. The obtained results allowed in addition to set up the test procedure to adopt for fire test of a full scale CP5.2 system. Post test analysis, which was carried out by performing FEM analysis, is also presented and results compared to the experimental ones

Sustainability of global feeding.Coopetitive interaction among vegan and non-vegan food firms

In this paper, we face the problem of global feeding sustainability and related environmental issues, with a strong attention to possible public heath improvements. Specifically, we shall consider food producers and sellers of vegan (or vegetarian) and non-vegan (or non-vegetarian) food. We propose possible quantitative agreements among different food producers, in order to develop a sustainable healthier diet for future generations, by using a mathematical co-opetitive approach and game theory. The co-opetitive approach used by the authors provides a game theory model, which could help producers of vegan food an easier entry in global market and obtain a considerable free publicity. Meanwhile, the model could allow big producers/sellers of non-vegetarian food a smooth rapid transaction to more sustainable and healthier vegan or vegetarian production/supply. In particular, we propose an exemplary complex agreement setting among McDonald's and Muscle of Wheat, a small but strongly innovative Italian food producer. We think that, on one hand, Muscle of Wheat cannot enter a global market without the help of a large globalized food producer already present in the market, on the other hand, we think equally difficult that a large static and poorly innovative producer cannot follow credibly and rapidly enough the increasing and challenging issues of global food sustainability. We remark that our game model represents an asymmetric R&D alliance between McDonald's and Muscle of Wheat. The aim of our contribution is twofold. Firstly, we explain the advantages of a vegan diet for the human health, environmental issues, food sustainability, population sustainability; in fact, the model explain how global food producers could improve environmental, social and health conditions of world population. Secondly, we show how game theory normal-form and extensive-form games can be used in coopetition studies in order to increase health conditions of people, address climate change, address hunger in the world, improve welfare in a particular market. The results of the mathematical study prove that we can find win-win solutions for both firms, which are also good for world environment, human healthy, human population sustainability and climate change