Regularity analysis of nocturnal oximetry recordings to assist in the diagnosis of sleep apnoea syndrome

The relationship between sleep apnoea–hypopnoea syndrome (SAHS) severity and the regularity of nocturnal oxygen saturation (SaO2) recordings was analysed. Three different methods were proposed to quantify regularity: approximate entropy (AEn), sample entropy (SEn) and kernel entropy (KEn). A total of 240 subjects suspected of suffering from SAHS took part in the study. They were randomly divided into a training set (96 subjects) and a test set (144 subjects) for the adjustment and assessment of the proposed methods, respectively. According to the measurements provided by AEn, SEn and KEn, higher irregularity of oximetry signals is associated with SAHS-positive patients. Receiver operating characteristic (ROC) and Pearson correlation analyses showed that KEn was the most reliable predictor of SAHS. It provided an area under the ROC curve of 0.91 in two-class classification of subjects as SAHS-negative or SAHS-positive. Moreover, KEn measurements from oximetry data exhibited a linear dependence on the apnoea–hypopnoea index, as shown by a correlation coefficient of 0.87. Therefore, these measurements could be used for the development of simplified diagnostic techniques in order to reduce the demand for polysomnographies. Furthermore, KEn represents a convincing alternative to AEn and SEn for the diagnostic analysis of noisy biomedical signals.

Some studies relating to the design of shallow, fluidized bed boilers

The concept of shallow fluidized bed boilers is defined and a preliminary working design for a gas-fired package boiler has been produced. Those areas of the design requiring further study have been specified. Experimental investigations concerning these areas have been carried out. A two-dimensional, conducting paper analog has been developed for the specific purpose of evaluating sheet fins. The analog has been generalised and is presented as a simple means of simulating the general, two-dimensional Helmholtz equation. By recording the transient response of spherical, calorimetric probes when plunged into heated air-fluidized beds, heat transfer coefficients have been measured at bed temperatures up to 1 100°C. A correlation fitting all the data to within ±10% has been obtained. A model of heat transfer to surfaces immersed in high temperature beds has been proposed. The model solutions are, however, only in qualitative agreement with the experimental data. A simple experimental investigation has revealed that the effective, radial, thermal conductivities of shallow fluidized beds are an order of magnitude lower than the axial conductivities. These must, consequently, be taken into account when considering heat transfer to surfaces immersed within fluidized beds. Preliminary work on pre-mixed gas combustion and some further qualitative experiments have been used as the basis for discussing the feasibility of combusting heavy fuel oils within shallow beds. The use of binary beds, within which the fuel could be both gasified and subsequently burnt, is proposed. Finally, the consequences of the experimental studies on the initial design are considered, and suggestions for further work are made.

Bed expansion:extending correlations for fluidized beds with inserts to open fluidized beds

Bed expansion occurs during the operation of gas-fluidized beds and is influenced by particle properties, gas properties and distributor characteristics. It has a significant bearing on heat and mass transfer phenomena within the bed. A method of predicting bed expansion behavior from other fluidizing parameters would be a useful tool in the design process, dispensing with the need for small-scale trials. This study builds on previous work on fluidized beds with vertical inserts to produce a correlation that links a modified particle terminal velocity, minimum fluidizing velocity and distributor characteristics with bed voidage in the relationship with P as the pitch between holes in the perforated distributor plate. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.