Introduction. Carotid endarterectomy versus carotid stenting. A never-ending story

L'articolo discute le controversie relative all'accettazione in pratica clinica dello stentig carotide

Mode decomposition methods for the analysis of cavitating flows in turbomachinery

Abstract The present work is aimed at the characterization of the cavitating flow regimes by applying the coupled POD/DMD technique to the vapor volume fraction field. The proposed approach provided an improved spatio-temporal-frequency description of the flow, based on the detection of the most energetic flow structures with information about their shape and size, and their decomposition into wave patterns oscillating with specific frequency and decay rate. The novel technique was applied to numerical results concerning the bubble cavitation and the supercavitation regimes of 2D water flows around a NACA hydrofoil at ambient temperature. Numerical simulations were performed by using a homogenous mixture model equipped with an extended Schnerr-Sauer cavitation model, in combination with a Volume of Fluid (VOF) interface tracking method. The proposed approached provided a better characterization of the unsteady cavitating flow, and allowed for a deeper insight about the dynamics of the vapor cavity, especially in cases involving the more chaotic regime of supercavitation. In particular, POD results figured out the most energetic coherent vapor structures associated to each cavitation regime: the first mode highlighted the main sheet cavity which grew on the hydrofoil up to detached, the second mode pointed out the cavitating/condensating doublet structures and the third mode figured out the smaller structures owning less energy but a higher frequency content. DMD modes performed a decomposition of the coherent structures detected by means of the POD analysis, into a subset of vapor pattern periodically evolving with a single frequency and a characteristic decay rate. Furthermore, results showed that the supercavitating flow structures owned characteristic frequencies which ranged from 5 to 26 Hz, while the less intensive bubble cavitation regime was characterized by frequencies ranging from 15 to 42 Hz

Implementation and validation of an extended Schnerr-Sauer cavitation model for non-isothermal flows in OpenFOAM

Abstract In the present work cavitation in liquid hydrogen and nitrogen was investigated by using the open source toolbox OpenFOAM. Simulations were performed by means of a mass transfer model, based on the homogeneous mixture approach in combination with the Volume of Fluid (VOF) method for the reconstruction the liquid-vapor interface. Two additional transport equations were considered, i.e. the liquid volume fraction advection and the temperature equation. The implementation of an extended Schnerr- Sauer model allowed for the introduction of the thermal effects in terms of latent heat release/absorption and convective heat transfer inside the liquid-vapor interface. A set of Antoine-like equations relate the saturation conditions to the local conditions

Modeling viscous effects on boundary layer of rarefied gas flows inside micronozzles in the slip regime condition

Abstract The present work provided a numerical investigation of the supersonic flow of rarefied gas into a planar micronozzle characterized by small depth and long divergent section. 2D and 3D computational fluid dynamics (CFD) computations were performed using the continuum Navier-Stokes equations in combination with partial slip conditions at walls, based on a the establishment of the slip regime related to a Knudsen number ranging between 1 x 10-3 and 1 x 10-1. Different partial slip conditions were considered, i.e. the ideal case of pure slip conditions and the full viscous case with Maxwellian slip conditions on sidewalls and planar walls, as well as the case of Maxwellian slip just on sidewalls. The Maxwell slip model was set with a tangential accommodation coefficient equal (TMAC) to 0.8. Comparisons were based on the estimation of the global performance of the micronozzle in terms of thrust force, specific impulse, discharge coefficient and Isp-efficiency. It resulted that when the nozzle depth was neglected, 3D simulations led to the same solution obtained by means of 2D computations inside the micronozzle. The boundary layer thicknesses experienced a linear growth on the sidewalls, and the viscous losses produced a reduction of the performance of about the 95%. Significant differences were found in the prediction of the jet plume, which took the typical bell-shape form in cases involving 2D computations, yet 3D simulations estimated a plume characterized by the succession of oblique shock waves and expansion fan waves. Instead, when the nozzle depth was considered, 3D simulations underlined a completely different behavior of the flow because of the establishment of the nozzle blockage and a viscous heating. The performance suffered an intense degradation of about the 47%, and the analysis of the jet plume highlighted the formation of the Mach disk followed by the typical diamond-shaped subsonic recirculation region

Plasma actuation for lifted flame stabilization in coaxial methane-air flow

The flame stabilization represents a relevant issue in aero-engine design. In fact, the growing demand of pollutant emissions reduction without significant losses of the combustion efficiency has driven the efforts of the scientific community towards lean flames. Lean fuel mixtures, characterized by low temperature flames, could manifest an unstable behaviour which can easily lead to the flame extinction due to the establishment of the blowout condition. This requires the implementation of control systems to avoid flame instability occurrence. The present work shows an investigation of the impact of dielectric barrier discharge (DBD) plasma actuation on lifted flame stabilization in a methane CH4-air Bunsen burner at ambient conditions. Two different plasma actuator configurations, powered with a high voltage (HV)/high frequency sinusoidal signal, have been investigated. Once the best actuator configuration was selected, the efficiency of the plasma actuation has been evaluated in terms of the flame lift-off distance, length and shape. In particular, in order to change the actuator power dissipation, different peak-to-peak voltages Vpp were tested, while the actuation frequency was kept equal to 20 kHz. The application of plasma discharges to flame stabilization leads to plasma-attached flames or plasma-enhanced lifted flames, depending on the air and fuel flow rates. At air flow rate of 1.54 g/s, plasma actuation allowed to decrease the lift-off height until the fuel jet velocity was below about 0.05 m/s thanks to the extension of the flame region upstream, toward the burner exit section. Beyond this value, it had no significant impact on the flame lift-off height, even though the amplitude of the lift-off height oscillations reduced coupled with a more stable behaviour of the lifting flame. The benefit of the plasma actuation increased by reducing the air flow rate to 1.35 g/s. In this condition, plasma-assisted flame reattachment was evident at each fuel velocity, in combination with an increasing flame height proportionally to the fuel jet velocity

Numerical investigation of the performance of Contra-Rotating Propellers for a Remotely Piloted Aerial Vehicle

Abstract The present work aims at the numerical prediction of the performance of a Contra-Rotating Propellers (CRP) system for a Remotely Piloted Aerial Vehicles (RPAV). The CRP system was compared with an equivalent counter-rotating propellers configuration which was set by considering two eccentric propellers which were rotating at the same speed. Each contra-rotating test case was built by varying the pitch angle of blades of the rear propeller, while the front propeller preserved the original reconstructed geometry. Several pitch configurations and angular velocities of the rear propeller was simulated. Comparisons showed an improvement of the propulsive efficiency of the contra-rotating configuration in case of larger pitch angles combined with slower angular velocities of the rear propeller

Deep Learning for Processing Electromyographic Signals: a Taxonomy-based Survey

Deep Learning (DL) has been recently employed to build smart systems that perform incredibly well in a wide range of tasks, such as image recognition, machine translation, and self-driving cars. In several fields the considerable improvement in the computing hardware and the increasing need for big data analytics has boosted DL work. In recent years physiological signal processing has strongly benefited from deep learning. In general, there is an exponential increase in the number of studies concerning the processing of electromyographic (EMG) signals using DL methods. This phenomenon is mostly explained by the current limitation of myoelectric controlled prostheses as well as the recent release of large EMG recording datasets, e.g. Ninapro. Such a growing trend has inspired us to seek and review recent papers focusing on processing EMG signals using DL methods. Referring to the Scopus database, a systematic literature search of papers published between January 2014 and March 2019 was carried out, and sixty-five papers were chosen for review after a full text analysis. The bibliometric research revealed that the reviewed papers can be grouped in four main categories according to the final application of the EMG signal analysis: Hand Gesture Classification, Speech and Emotion Classification, Sleep Stage Classification and Other Applications. The review process also confirmed the increasing trend in terms of published papers, the number of papers published in 2018 is indeed four times the amount of papers published the year before. As expected, most of the analyzed papers (≈60 %) concern the identification of hand gestures, thus supporting our hypothesis. Finally, it is worth reporting that the convolutional neural network (CNN) is the most used topology among the several involved DL architectures, in fact, the sixty percent approximately of the reviewed articles consider a CNN

Cryopreservation of adipose tissue with and without cryoprotective agent addition for breast lipofilling: A cytological and histological study.

Abstract In the second reconstructive phase of the breast after mastectomy, lipofilling is often necessary. Currently, lipofilling occurs immediately after autologous adipose tissue harvesting procedure, but most of the patients, usually, require multiple sessions to obtain a satisfactory result. Therefore, the need of repeated surgical harvesting outputs implies high risk of patients' morbidity and discomfort as well as increasing medical time and costs. The aim of our pilot study was to find out a feasible method to cryopreserve adipose tissue, in order to avoid reiterated liposuctions. Lipoaspirates samples have been harvested from 10 women and preserved by three methods: (1) the first one, using 10% Me2SO and 20% human albumin from human plasma as cryoprotective agents; (2) the second one, adding 5% Me2SO as cryoprotective agent; 3) the last one, without any cryoprotective agent. Fresh and cryopreserved fat samples, obtained through the aforementioned processes, have been analyzed ex vivo. The efficiency of the cryopreservation methods used was determined by adipocyte viability and the expression of adipocytes surface markers. Lipoaspirates stored at −196 °C for 3 months, after thawing, retained comparable adipocyte viability and histology to fresh tissue and no significant differences were found between the three methods used. Although the current results, differences between the methodologies in terms of viability may not become evident until breast lipofilling using frozen-thawed cryopreserved tissue

Root system of ‘BRS Platina’ banana under irrigation levels and planting densities

Banana production stands out in Brazilian semiarid agriculture; however, due to little availability of water resources, associating water-saving technologies with knowledge on parameters involved in the interplay between plants and soil is critical to improving banana production systems. The objectives of this study were to evaluate the effect of planting densities and irrigation levels on root length density of ‘BRS Platina’ banana and to correlate root parameters to crop yield and leaf area. A randomized block design was used, with factors arranged in split plots and treatments replicated three times: four irrigation levels (55%, 70%, 85% and 100% ETc) were assigned to plots and four planting densities (1,600; 2,000; 2,666; and 3,333 plants ha-1) to subplots. Root length density (RLD) was measured at five distances from the pseudostem, longitudinally to a row of plants: 0.10, 0.25, 0.50, 0.75 and 1.10 m; and at three depths for each distance: 0 to 0.20 m, 0.20 to 0.40 m and 0.40 to 0.60 m from surface level. Root length densities were highest at 100% ETc irrigation level and at 2,666 plants ha-1 and 3,333 plants ha-1, within 0.31 m deep and within 0.78 m of the pseudostem. Irrigation interacts with root system, and coupled with higher planting densities, contributes to increasing crop yields of ‘BRS Platina’ banana plants.A bananicultura se destaca no setor agrícola do semiárido brasileiro, no entanto, com a baixa disponibilidade de água, torna-se necessário a associação de tecnologias que proporcionem alta eficiência de uso da água, e o conhecimento de parâmetros que inter-relacionam o sistema planta-solo é relevante para indicação de um sistema de produção. Assim, objetivou-se com este trabalho avaliar a densidade de comprimento de raízes de bananeira ‘BRS Platina’ sob diferentes densidades de plantio e lâminas de irrigação e as correlações com produtividade e área foliar. O delineamento experimental foi em blocos casualizados, em esquema de parcelas subdivididas, com três repetições, sendo quatro lâminas de irrigação (55%, 70%, 85% e 100% da ETc) na parcela e quatro densidades de plantio diferentes (1.600, 2.000, 2.666 e 3.333 plantas por hectare) na subparcela. A densidade de comprimento de raízes (DCR) foi analisada em cinco distâncias do pseudocaule, longitudinalmente à linha de plantas: 0,10 m, 0,25 m, 0,50 m, 0,75 m e 1,10 m e em três profundidades para cada distância: de 0 a 0,20 m, de 0,20 a 0,40 m e de 0,40 a 0,60 m da superfície do solo. Os maiores valores de DCR foram encontrados sob lâmina de irrigação de 100% da ETc, nas densidade de plantio de 2.666 plantas ha-1 e 3.333 plantas ha-1, em até 0,31 m de profundidade e até 0,78 m de distância do pseudocaule. A irrigação apresenta interação com sistema radicular que juntamente com a densidade de plantio contribuem para aumento da produtividade da ‘BRS Platina’

Numerical Drop Test of a Full Composite Fuselage Section Having Two Components of Velocity

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