Hearing screening in schoolchildren: accuracy of different criteria used to analyze transient evoked otoacoustic emissions

ABSTRACT Purpose: to compare the accuracy of different criteria used to analyze transient evoked otoacoustic emissions in schoolchildren. Methods: an accuracy study, where an audiological assessment (audiometry, logoaudiometry, tympanometry) and transient emissions were performed with 70 schoolchildren, from the first to the fifth grade of a municipal school, in Northeastern Brazil (6-14 years, 9.9 ± 2 years), with four criteria, all with signal-to-noise ratio ≥ 3 dB, being: criterion A, in all frequency bands; B, in three consecutive frequency bands; C, in three of the five non-consecutive frequency bands; D, in 2, 3 and 4 kHz. Sensitivity, specificity, accuracy and predictive values with their respective confidence intervals of 95% were analyzed. Results: criterion A showed higher sensitivity (92.31%, 95% CI: 67-98%) and lower specificity (17.35%, 95% CI: 10-29%); criterion C higher specificity (84.21%, 95% CI: 72-91%) and higher positive predictive value (52.63%; 95% CI: 51.63-54.63). Accuracy was 82.85% (95% CI 78.23-87.47) in criterion C and 70% (95% CI: 65.38-74.62) in criterion B. Conclusion: criterion C, signal-to-noise ratio ≥ 3dB in three non-consecutive frequency bands, showed the best accuracy, being considered the best choice as a criterion for the isolated use of transient emissions as a hearing screening procedure, in schoolchildren.

Piston temperature model oriented to control applications in diesel engines

In this paper, the development of a control-oriented piston temperature model for diesel engines is discussed. Using the underlying energy balance at the piston, a one-state piston temperature model was developed based on a thermal resistance concept. The model is composed of five sub-models: an engine model, a heat distribution model, a piston temperature model, an initial piston temperature model, and a maximum piston temperature model. In the engine model, the combustion heat transferred to the engine is calculated based on the energy balance in the cylinder chamber. The heat distribution model, which is a main feature in this model, determines the heat transferred to the piston using two maps as a function of engine speed and fuel depending on the piston cooling jet (PCJ) operation. The energy balance at the piston is applied to calculate the mean piston temperature, and the initial piston temperature is determined by the arbitration between the piston and the oil temperatures. The maximum piston temperature is estimated using a simple linear correction to the mean piston temperature. Integrating all sub-models in the Simulink platform, the model was identified and validated using piston temperature measurements under steady-state fuel steps as well as transient tests. There is a good agreement between the modeled and the measured piston temperatures with less than 4.1°C of root-mean-square-error (RMSE) over transient emissions cycles (FTP-75, LA92, and HWEFT). The modeled piston temperature can be used as an input to the control strategy of variable cooling devices, such as a variable displacement oil pump.

NOx, Soot, and Fuel Consumption Predictions under Transient Operating Cycle for Common Rail High Power Density Diesel Engines

Diesel engine is presently facing the challenge of controlling NOx and soot emissions on transient cycles, to meet stricter emission norms and to control emissions during field operations. Development of a simulation tool for NOx and soot emissions prediction on transient operating cycles has become the most important objective, which can significantly reduce the experimentation time and cost required for tuning these emissions. Hence, in this work, a 0D comprehensive predictive model has been formulated with selection and coupling of appropriate combustion and emissions models to engine cycle models. Selected combustion and emissions models are further modified to improve their prediction accuracy in the full operating zone. Responses of the combustion and emissions models have been validated for load and “start of injection” changes. Model predicted transient fuel consumption, air handling system parameters, and NOx and soot emissions are in good agreement with measured data on a turbocharged high power density common rail engine for the “nonroad transient cycle” (NRTC). It can be concluded that 0D models can be used for prediction of transient emissions on modern engines. How the formulated approach can also be extended to transient emissions prediction for other applications and fuels is also discussed.

GE Rapid Response Plant Design: Operational Flexibility and Transient Emissions Control

The GE Rapid Response plant design is described and compared to conventional combined cycle plant design. Advantages of the Rapid Response improved operational flexibility are explained and compared to conventional combined cycle plants. Improvements include faster power delivery to the grid, more economical plant startup, more profitable plant startup and lower emissions during plant startup. The capability of a drum type HRSG for the Rapid Response cycling service is explored. Joint studies between GE and HRSG suppliers are highlighted supporting the adoption of drum type HRSGs for this cycling service. Necessary modifications to other plant equipment are explained. Quantitative comparisons of Rapid Response and conventional combined cycle plant operability are given for electrical energy production and emissions reduction. An advanced Selective Catalytic Reduction SCR control is shown providing improvements in combined cycle plant transient emissions control. Elements of the new control are explained. Argument is made to designate the new control as a second generation GEN II control compared to all other currently existing controls designated GEN I. A brief outline of the current state of Rapid Response plant deployment is provided.

Fast Measurement of Soot by In-Situ LII on a Production Engine

The contribution of transient emissions to total emissions is becoming more important in view of the improvement of steady state emissions and after-treatment systems. For a critical pollutant, namely soot, there is no commercially available measurement system able to measure sufficiently fast on production engines. This paper presents a measurement setup based on in-situ Laser Induced Incandescence (LII) allowing high speed, frequent soot measurements in a production engine. The setup consists of a pulsed laser system, a fast optical detector and a special, compact designed in-situ optical LII probe which makes it possible to change the measurement location easily. System speed is assessed among other approaches, by using eleven well defined soot steps obtained by injection pulses under controlled conditions on a highly dynamic test bench. The effect of these pulses for a production four-cylinder 2 lt. Euro 5 Diesel engine is measured at three different positions (at tailpipe, downstream of the turbine and in exhaust manifold). The features of LII intensity are extracted by principle component analyses (PCA) and compared with a fast and commercially available device (AVL Opacimeter) at last. The results show that the measurements with the proposed setup are able to detect all peaks in contrast to the commercially available device.