Photoinduced inverse spin Hall effect in Pt/Ge(001) at room temperature

We performed photoinduced inverse spin Hall effect (ISHE) measurements on a Pt/Ge(001) junction at room temperature. The spin-oriented electrons, photogenerated at the direct gap of Ge using circularly polarized light, provide a net spin current which yields an electromotive field E_ISHE in the Pt layer. Such a signal is clearly detected at room temperature despite the strong {\Gamma} to L scattering which electrons undergo in the Ge conduction band. The ISHE signal dependence on the exciting photon energy is in good agreement with the electron spin polarization expected for optical orientation at the direct gap of Ge

Development of an engine variable geometry intake system for a Formula SAE application

The Formula SAE is an international competition for vehicle fully designed and built by students from worldwide Universities. The engine and vehicle design in the Formula SAE competition has to comply with a strict regulation. Regarding the engine intake line an air restrictor of circular cross-section no greater than 20 mm must be fitted between the throttle valve and the engine inlet. The aim of the throat is to limit the engine air flow rate as it strongly influences the volumetric efficiency and then the maximum power. The present paper is focused on the design of the engine intake system of the Firenze Race Team vehicle in order to optimize its performance in terms of both the maximum power and the drivability of the vehicle. One of the typical solutions for limiting the air restrictor influence consists of a plenum chamber placed along the intake line downstream of the restrictor. However the plenum involves also a delay in the engine response during the transient phases. The greater is the plenum, the lower are the power losses but the greater is the engine response delay. Taking advantage of a calibrated 1D model of the engine and a simplified vehicle model, the authors numerically analyzed an innovative solution that is constituted by a variable length duct inside the plenum. When the duct is at the maximum extension, the plenum is excluded from the intake line improving the engine response time. The optimization of the plenum volume and the definition of a preliminary control logic of the innovative system were done in order to obtain the maximum advantages in terms of both performance and engine drivability

Influence of the Displacement Profile on the Performance and Mechanical Stresses of an Axial Piston Compressor for Refrigeration Applications

Abstract Axial piston compressors are commonly equipped with rotating disk plates that make the pistons following a sinusoidal displacement. The variation of the plate angle leads to stroke increments without changing the displacement profile. The axial piston architecture allows one to make piston displacement profiles that are different from a sinusoidal one by using rotating disk with a shaped circumferential profile. In this work, a detailed analysis on the thermodynamic cycle of compressors with different disk geometries was carried out.A lumped parameter numerical model of a compressor for refrigeration application was developed. The compressor performance (i.e. indicated power, compressed mass of gas and specific power) was estimated by imposing piston displacement profiles that are different from the sinusoidal one. The influence on the cycle COP in which the compressor runs was evaluated for each analysis. For each profile, the study of the forces acting on the rotating plate was also investigated. A sensitivity analysis allowed the definition of a profile design that guarantees the optimization of both the thermodynamic cycle and the mechanical stresses

Experimental investigation on industrial drying process of cotton yarn bobbins: energy consumption and drying time

Abstract In the textile industry, the drying process is a time consuming and energy expensive operation that influences strongly the cost of the textile finishing operations. For this reason, the study of innovative techniques plays a key role to decrease the energy consumption, the costs and the environmental impact. After a first mechanical process, the moisture is removed from yarn fibers by a thermal convection dryer that delivers hot air through the material. In this study, the drying process of cotton yarn bobbins is experimentally analyzed. With this aim, an experimental test rig was developed based on the geometry of industrial dryers. The influence of the drying air path and the air working conditions was assessed by performing tests with different configurations, temperatures and pressures. The results were analyzed in terms of drying time and energy consumption as the optimum drying condition is a trade-off between these parameters

Design guidelines for H-Darrieus wind turbines: Optimization of the annual energy yield

H-Darrieus wind turbines are gaining popularity in the wind energy market, particularly as they are thought to represent a suitable solution even in unconventional installation areas. To promote the diffusion of this technology, industrial manufacturers are continuously proposing new and appealing exterior solutions, coupled with tempting rated-power offers. The actual operating conditions of a rotor over a year can be, however, very different from the nominal one and strictly dependent on the features of the installation site. Based on these considerations, a turbine optimization oriented to maximize the annual energy yield, instead of the maximum power, is thought to represent a more interesting solution. With this goal in mind, 21,600 test cases of H-Darrieus rotors were compared on the basis of their energy-yield capabilities for different annual wind distributions in terms of average speed. The wind distributions were combined with the predicted performance maps of the rotors obtained with a specifically developed numerical code based on a Blade Element Momentum (BEM) approach. The influence on turbine performance of the cut-in speed was accounted for, as well as the limitations due to structural loads (i.e. maximum rotational speed and maximum wind velocity). The analysis, carried out in terms of dimensionless parameters, highlighted the aerodynamic configurations able to ensure the largest annual energy yield for each wind distribution and set of aerodynamic constraints

Optimization of the Performance of a Formula SAE Engine by Means of a Wastegate Valve Electronically Actuated

Abstract The engine and vehicle design in Formula SAE competition has to accomplish a strict regulation. In order to limit the maximum power, an air restrictor of 20mm of diameter is imposed in the intake line. To overcome the limitations caused by the restrictor, Firenze Race Team equipped its one-cylinder engine with a turbocharger, which is conventionally provided with a wastegate (WG) valve to limit the maximum boost pressure and avoid knocking phenomena. Typically, the WG valve is controlled by a pneumatic actuator, which opens the valve according to a defined and constant maximum boost pressure downstream the compressor in the whole engine operating range. Therefore, the boost pressure at high engine speed, in which knocking problems are less intense and the volumetric efficiency is lower, is limited by the threshold value defined at medium-low engine speeds, i.e. the pneumatic WG limits the maximum power that the engine can supply. In this study, the implementation of an electronic control system for the WG valve is described together with a dedicated control strategy aimed at providing the desired boost pressure at full load for each engine speed, in order to get the maximum power avoiding knocking phenomena. The electronic WG provided higher power values and a more extended torque curve in comparison to the conventional pneumatic one

Assigning UPDRS Scores in the Leg Agility Task of Parkinsonians: Can It Be Done through BSN-based Kinematic Variables?

In this paper, by characterizing the Leg Agility (LA) task, which contributes to the evaluation of the degree of severity of the Parkinson's Disease (PD), through kinematic variables (including the angular amplitude and speed of thighs' motion), we investigate the link between these variables and Unified Parkinson's Disease Rating Scale (UPDRS) scores. Our investigation relies on the use of a few body-worn wireless inertial nodes and represents a first step in the design of a portable system, amenable to be integrated in Internet of Things (IoT) scenarios, for automatic detection of the degree of severity (in terms of UPDRS score) of PD. The experimental investigation is carried out considering 24 PD patients.Comment: 10 page

Gravitational waves from newly born, hot neutron stars

We study the gravitational radiation associated to the non--radial oscillations of newly born, hot neutron stars. The frequencies and damping times of the relevant quasi--normal modes are computed for two different models of proto--neutron stars, at different times of evolution, from its birth until it settles down as a cold neutron star. We find that the oscillation properties of proto--neutron stars are remarkably different from those of their cold, old descendants and that this affects the characteristic features of the gravitational signal emitted during the post-collapse evolution. The consequences on the observability of these signals by resonant--mass and interferometric detectors are analyzed. We find that gravitational waves from the pulsations of a newborn proto--neutron star in the galaxy could be detected with a signal to noise ratio of 5 by the first generation interferometers, if the energy stored in the modes is greater than $\sim 10^{-8} M_\odot c^2$, or by a resonant antenna if it is greater than $\sim 10^{-4} M_\odot c^2$. In addition since at early times the frequency of the spacetime modes is much lower than that of a cold neutron star, they would be also detectable with the same signal to noise ratio if a comparable amount of energy is radiated into these modes.Comment: Minor changes in Section 4.1, Table 3 and Figure 5. Accepted for publication in MNRA

Virtual incidence effect on rotating airfoils in Darrieus wind turbines

Small Darrieus wind turbines are one of the most interesting emerging technologies in the renewable energies scenario, even if they still are characterized by lower efficiencies than those of conventional horizontal-axis wind turbines due to the more complex aerodynamics involved in their functioning. In case of small rotors, in which the chord-to-radius ratios are generally high not to limit the blade Reynolds number, the performance of turbine blades has been suggested to be moreover influenced by the so-called "flow curvature effects". Recent works have indeed shown that the curved flowpath encountered by the blades makes them work like virtually cambered airfoils in a rectilinear flow. In the present study, focus is instead given to a further effect that is generated in reason of the curved streamline incoming on the blades, i.e. an extra-incidence seen by the airfoil, generally referred to as "virtual incidence". In detail, a novel computational method to define the incidence angle has been applied to unsteady CFD simulations of three airfoils in a Darrieus-like motion and their effective angles of attack have been compared to theoretical expectations. The analysis confirmed the presence of an additional virtual incidence on the airfoils and quantified it for different airfoils, chord-to-radius ratios and tip-speed ratios. A comparative discussion on BEM prediction capabilities is finally reported in the study