Impact of Pointing Errors on the Performances of Double Rician FSO Channels

In this paper we will propose new analytically traceable probability density function (PDF) model for free space optics (FSO) turbulence, obtained as a generalization of double Ricean turbulence model, that encompasses both large-scale and small-scale turbulence eddy effects along by taking into account performance decreasing influence of misalignment introduced through boresight pointing error model. Consequently, after delivering the closed-form expressions for the newly introduced double FSO model, we obtain the analytical expressions for the bit error rate (BER) performance for the Double Rician distribution affected by misalignment. Numerical results will show the impact of system parameters on FSO link performance and we will provide full performance analysis. © 2021.

Study on lifted flame stabilization under different background pressures

A numerical experimental investigation is presented for a steady methane lifted-flame and a non-reaction jet flow in a co-flow of hot combustion products from lean premixed air/hydrogen combustion. A pressurized vitiated co-flow burner has been employed to study the methane lifted flame and non-reaction jet flow under different background pressures. The lift-off height has been measured with a high-speed camera, and the central jet flow velocity has been measured by means of a Schlieren imaging system. The experimental results show that the lift-off height decreases for an increment in the background pressure and in the co-flow temperature. As far as the experimental tests on the non-reaction jet flow is concerned, the jet velocity becomes extinct faster as the background pressure rises. The evolution of the jet velocity has been proved to be another important factor that affects the lift-off height under different background pressures, in addition to the fuel autoignition delay. The simulation data led with a RANS/PDF model show that an increment in the background pressure makes the temperatures increase and induces a brighter yellow part of lifted flame, which leads to more soot production. This proves that the flame is not completely premixed. On the other hand, the Schlieren images of a non-reaction jet flow highlight that the flame is partially premixed, since the edge of the jet is not well defined, as the jet penetration increases with time.

CFD Analysis and NOx Prediction in H2 and Ch4 Turbulent Non-premixed Flame Compared with Swirling Flame

This work is devoted to the comparative study for the formation and dissociation of nitrogen oxides by the numerical simulation of turbulent combustion without premix in a combustion chamber having a cylindrical shape with two coaxial jets, two flames using the ANSYS fluent software16.0. The study focuses on the influence of the type of fuel on the composition of discharges in content with NOx, that is to say two cases are treated and compared. Turbulence is modeled by the k-ε model and the chemical aspect of combustion is treated by the PDF model for each flame. The calculation results relate to the characteristics of dynamic fields, temperature, the mass fractions of different species involved in the combustion process and the NOx prediction. The effect of the swirl is also tested in this study with a CFD prediction of non premixed swirling g flame. These results are compared with measurements and confrontations is satisfactory.

FSO system performance analysis based on novel Gamma–Chi-square irradiance PDF model

In order to provide a novel analytically traceable free space optics (FSO) channel model for describing turbulence based irradiance fluctuations, following basic scintillation theory principles, we have derived closed-form expression for probability density function (PDF) of a new statistical Gamma–Chi-square model. Further, capitalizing on provided model, error performances of FSO system over on–off keying (OOK) transmission scheme both in the presence of atmospheric turbulence and misalignment fading (pointing error) is investigated. For both cases, the average bit error rate (ABER) at the receiving side of the system is determined in an analytically closed form. The results are graphically presented in order to analyze the impact of different levels of turbulence, as well as other relevant parameters, on the quality of the received signal in the OOK modulated FSO system.

Alternative diastolic function models of ventricular longitudinal filling velocity are mathematically identical

The spatiotemporal features of normal in vivo cardiac motion are well established. Longitudinal velocity has become a focus of diastolic function (DF) characterization, particularly the tissue Doppler e′-wave, manifesting in early diastole when the left ventricle (LV) is a mechanical suction pump (dP/dV < 0). To characterize DF and elucidate mechanistic features, several models have been proposed and have been previously compared algebraically, numerically, and in their ability to fit physiological velocity data. We analyze two previously noncompared models of early rapid-filling lengthening velocity (Doppler e′-wave): parametrized diastolic filling (PDF) and force balance model (FBM). Our initial numerical experiments sampled FBM-generated e′( t) contours as input to determine PDF model predicted fit. The resulting exact numerical agreement [standard error of regression (SER) = 9.06 × 10−16] was not anticipated. Therefore, we analyzed all published FBM-generated e′( t) contours and observed identical agreement. We re-expressed FBM’s algebraic expressions for e′( t) and observed for the first time that model-based predictions for lengthening velocity by the FBM and the PDF model are mathematically identical: e′( t) = γe−α tsinh(β t), thereby providing exact algebraic relations between the three PDF parameters and the six FBM parameters. Previous pioneering experiments have independently established the unique determinants of e′( t) to be LV relaxation, restoring forces (stiffness), and load. In light of the exact intermodel agreement, we conclude that the three PDF parameters, relaxation, stiffness (restoring forces), and load, are unique determinants of DF and e′( t). Thus, we show that only the PDF formalism can compute the three unique, independent, physiological determinants of long-axis LV myocardial velocity from e′( t). NEW & NOTEWORTHY We show that two separate, independently derived physiological (kinematic) models predict mathematically identical expressions for LV-lengthening velocity (Doppler e′-wave), indicating that damped harmonic oscillatory motion is a physiologically accurate model of diastolic function. Although both models predict the same “overdamped” velocity contour, only one model solves the “inverse problem” and generates unique, lumped parameters of relaxation, stiffness (restoring force), and load from the e′-wave.