1,721,011 research outputs found
Characteristics of visual evoked potentials related to the electro-clinical expression of reflex seizures in photosensitive patients with idiopathic occipital lobe epilepsy
Full text linkSeizures provoked by visual stimuli may be induced by abnormal responses to light (photosensitivity) and structured patterns (patternsensitivity). In this study, we analysed visual evoked potentials (VEPs) in three different samples: i) 38 photosensitive patients (21 males, 17 females; mean age 10.0 ± 2.9 years) with idiopathic occipital lobe epilepsy and reflex seizures (RS); ii) 13 non-photosensitive patients (6 males, 7 females; mean age 11.7 ± 5.3) with idiopathic occipital lobe epilepsy; 20 healthy controls (12 males, 8 females; mean age 10.0 ± 3.4). After written informed consent, all subjects underwent a standard procedure of visual stimulation with intermittent light and pattern stimulation, under digital video-EEG recording. The EEG signal was processed off-line by averaging analysis for each stimulus to obtain the corresponding VEP. Comparisons among groups showed no significant differences for P100 latency. Higher P100 amplitude as well as higher after-discharge (AD) were found in photosensitive patients with RS. Thirty-seven of these patients had one or more RS during the procedure of stimulation for a total of 66 episodes. Significant increases of P100 amplitude and higher values of AD amplitude were found in relation to the occurrence of photoparoxysmal response (PPR) and/or seizures during full-field pattern stimulation. The increase in amplitude of the AD was higher when PPR was associated with seizures. The high amplitude of early VEP components confirms the abnormal hyperexcitability in the cortex of photosensitive patients with occipital lobe epilepsy. Moreover, the AD amplitude appears to be related to electro-clinical expression, being greater when PPR evolves into clinically evident seizures
Simulazione Numerica di Apparati di Iniezione ad Alte Pressioni in Fase di Regolazione
No full textPubblicazione Diparimento di Energetic
Shock Event Analysis, Characteristics Considerations and Conservativeness Influence in High-pressure Injection System Cavitating Flow Simulations
No full textA comparison between conservative and nonconservative models has been carried out for evaluating the influence of conservativeness on predicting transient flows in presence of cavitation induced discontinuities inside high-pressure injection systems. Even if nonconservative models can assure satisfactory accuracy in the evaluation of the wave propagation phenomena, they introduce fictitious source terms in the discretized equations. Such terms are usually negligible, but can play a significant role when discontinuities in the flow properties occur, producing appreciable errors on the pressure wave speed estimation. An analysis based on fluid characteristics around both the rarefaction and compression wave fronts has been carried out, showing that cavitation desinence is a shock occurrence, leading to a transition from a supersonic to a subsonic flow. For a significant evaluation of conservative and nonconservative model performances a conventional pumpline-nozzle injection system was considered because the pipe flow presented interesting cases of cavitation-induced shocks. The validity of the conservative model is substantiated by the comparison between computed pressure time-histories and experimental results at two pipe locations. The Rankine-Hugoniot jump conditions have been usefully applied to the numerical results obtained by the conservative model in order to calculate the sound speed of the traveling compression waves in the presence of cavitation. A novel algorithm of general application to calculate the shock speed predicted by nonconservative models, which points out the contribution of the internal fictitious fluxes in the wrong estimation of the shock velocity, has been introduced and validated through its application to Burgers' equatio
Effects of Rate-Shaped and Multiple Injection Strategies on Pollutant Emissions, Combustion Noise and Fuel Consumption in a Low Compression Ratio Diesel Engine
Full text linkAn experimental investigation has been carried out to highlight the effects of different injection strategies on the performance and emissions of a low compression ratio Euro 5 diesel engine operated with high EGR rates. Rate-shaped main injections, achieved with piezoelectric and solenoid injectors by means of boot and injection fusion, respectively, as well as optimized multiple injection patterns have been compared. The results of the comparisons, performed with reference to a state-of-the-art double pilot-Main (pM) strategy, are presented in terms of engine-out exhaust emissions, combustion noise (CN) and fuel consumption. Rate-shaped main injections, when included in delayed multiple injection patterns, have shown a minor influence on reducing NOx, while a slight deterioration in soot has been found. Both a double pilot and a boot injection schedule have been able to reduce CN at low loads. A higher reduction in CN has been obtained with an injection fusion event. Finally, DoE optimized triple and quadruple injection strategies have led to improved soot-NOx trade-offs, with respect to the pM calibration. In fact, splitting the injection helps to entrain air inside the fuel plumes, thus creating locally leaner mixture (less prone to forming soot) and allowing increasing the EGR rates (reducing NOx formation)
Cavitation Analogy to Gasdynamic Shocks: Model Conservativeness Effects on the Simulation of Transient Flows in High-Pressure Pipelines
No full textA comparison between conservative and nonconservative models has been carried out for evaluating the influence of conservativeness on the prediction of transient flows in high-pressure pipelines. For the numerical tests, a pump-line-nozzle Diesel injection system was considered because the pipe flow presented interesting cases of cavitation. The validity of a conservative model in the simulation of cavitating transient flows was substantiated by the comparison between computed pressure time histories and experimental results at two pipeline locations in the injection system. Although nonconservative models can assure satisfactory accuracy in the evaluation of the wave propagation phenomena, they introduce fictitious source terms in the discretized equations. Such terms are usually negligible, but can play a significant role in the presence of acoustic cavitation, i.e., pressure-wave-induced cavitation, producing errors in the pressure-wave speed prediction. A theoretical analysis based on unsteady characteristic lines was carried out, showing that the cavitation desinence is a shock gas-dynamic-like event, whereas cavitation inception is a supersonic expansion. The Rankine–Hugoniot jump conditions were applied to evaluate the shock wave speed in the presence of cavitation. Analytical relations to calculate the flow property variations across the cavitation-induced discontinuities were also derived. A previously published analytical expression of the sound speed in a homogeneous two-phase flow model was also derived from the eigenvalues of the Euler flow equations for the two distinct phases and a comparison was made with Wallis' formula, which is commonly applied to cavitating flow simulation in transmission lines. Finally, a novel algorithm for calculating the shock speed, as is predicted by nonconservative models, was presented and applied to Burgers' equation, pointing out the contribution of internal fictitious fluxes in the shock-speed wrong estimation
Dependence of combustion noise on engine calibration parameters by means of the response surface methodology in passenger car diesel engines
No full textCombustion noise from a passenger car diesel engine has been expressed as a function of the heat release rate peaks of pilot and main combustions as well as of the crankshaft angles at which these peaks occur, using a statistical regression model. Furthermore, the values of these heat release rate peaks and of their angles have been correlated with the main engine calibration parameters by means of second-order polynomial regressions. The values of the coefficients of these polynoms have been found to depend on the engine working condition. As a result, it has been possible to calculate the combustion noise as a function of the main engine calibration parameters at different engine working points, which are representative of low, medium and high load and speed conditions within the NEDC working zone.The effects of the pilot injection quantity and timing, of the main combustion phasing and of the rail pressure level have been analyzed for both late PCCI and conventional combustion modes. The definition of the pilot injection quantity and timing has resulted to be relevant for a reduction in combustion noise at low and medium speeds and loads, while a pilot injection should be removed for an optimized combustion noise engine calibration at high speeds and loads
Lateralization and outcome of EEG abnormalities in benign epilepsy with centro-temporal spikes.
No full textL’ Epilessia parziale Benigna a punte Centro-Temporali (BECTS) è stata messa in relazione con altre forme di epilessia parziale idiopatica per il riscontro di analogie morfologiche e topologiche nei patterns EEG. Tali ipotetiche relazioni derivano da osservazioni di singoli casi, non essendo mai stati effettuati studi sistematici su campioni omogenei di BECTS. Lo studio si basa sulla valutazione longitudinale dei patterns EEG (follow up medio 6,3 anni), in 36 pazienti con BECTS. Le anomalie EEG all’ esordio erano prevalentemente unilaterali e regredivano nel 50% dei casi al termine del follow up. Patterns EEG extrarolandici erano presenti in 8 pazienti, in tutti la sede era occipitale; 5 di loro presentavano anche una risposta fotoparossistica alla SLI; 4 di loro presentavano anche altri tipi di crisi con sintomi tipici delle Epilessie Idiopatiche del Lobo Occipitale (Sindrome di Panayotopoulos e Sindrome di Gastaut). E’ probabile che alcuni pazienti con BECTS abbiano una predisposizione genetica a uno spettro più ampio di espressività elettroclinica età-dipendente. Ulteriori informazioni da studi clinici e genetici sono necessarie per capire il tipo di relazione che intercorre tra le diverse forme di Epilessia Parziale Idiopatica dell’ infanzia
Experimental analysis on the effects of multiple injection strategies on pollutant emissions, combustion noise, and fuel consumption in a premixed charge compression ignition engine
No full textEarly single-injection premixed charge compression ignition (PCCI) strategies in compression ignition engines have been widely studied as a promising solution to meet the ever-increasing stringent emissions regulations. Although their application to diesel engines may provide several upsides (such as a massive and simultaneous reduction of NOx and soot engine-out emissions), especially at low to medium loads, several drawbacks, including an excessive amount of engine-out carbon monoxide (CO) and unburned hydrocarbons (HC) as well as intense combustion noise (CN), usually reveal to be major constraints. As a matter of fact, PCCI combustion systems are not yet consolidated enough for practical applications, although intensive research has been carried out to overcome its common limitations. Indeed, further research is still required. In this work, an experimental analysis has been carried out to highlight the potential benefits derived from the introduction of multiple (i.e., double and triple) fuel injection PCCI strategies on a 3.0-liter diesel engine, purposely designed to be operated with PCCI combustion concepts at low to medium engine loads. The experimental tests include the application of several fuel injection strategies: double- and triple-pulse PCCI schemes, featuring various fuel injection timing sweeps, and different fuel quantity distributions among each fuel shot were compared with a baseline single-pulse PCCI and a triple-injection conventional diesel combustion (CDC) pattern. The results are presented in terms of exhaust pollutant emissions, CN, and fuel consumption at two different engine operating points within a low to medium speed and load area of the engine map. Splitting the fuel injection into a double-stage pattern turned out ensuring appreciable drops of both engine-out HC and CO emissions, up to 50% lower than the single-injection PCCI levels, but still significantly worse than CDC outcomes, with penalties above +120%. Engine-out soot and nitrogen oxides (NOx) emissions retained considerably smaller than typical CDC values (with abatement ranging between −50% and −99%), while double-pulse PCCI calibrations featuring delayed second injection timings allowed to effectively dampen excessive CN intensity (of up to 7 dBA below the CN of the reference single-stage PCCI schedule), while slightly improving fuel economy. Finally, the introduction of a triple-stage pattern in PCCI revealed to have the potential to further reduce the emissions of incomplete combustion species and fuel consumption, when compared with single- and double-injection patterns (especially at low load), as well as to further deadening CN. However, besides being still ineffective in reaching the CDC performance even at low load (bsfc slightly over +4%, HC no better than +100%), when increasing the engine load, these benefits become milder to the point that the soaring calibration complexity required by a triple-stage PCCI pattern might not render it worthwhile
- …
