A broad spectrum of techniques for electrocardiogram (ECG) data compression have been proposed during the last three decades. Such techniques have been vital in reducing the digital ECG data volume for storage and transmission. These techniques are essential to a wide variety of applications ranging from diagnostic to ambulatory ECG's. Due to the diverse procedures that have been employed, comparison of ECG compression methods is a major problem. Present evaluation methods preclude any direct comparison among existing ECG compression techniques. The main purpose of this paper is to address this issue and to establish a unified view of ECG compression techniques. ECG data compression schemes are presented in two major groups: direct data compression and transformation methods. The direct data compression techniques are: ECG differential pulse code modulation and entropy coding, AZTEC, Turning-point, CORTES, Fan and SAPA algorithms, peak-picking, and cycle-to-cycle compression methods. The transformation methods briefly presented, include: Fourier, Walsh, and K-L transforms. The theoretical basis behind the direct ECG data compression schemes are presented and classified into three categories: tolerance-comparison compression, differential pulse code modulation (DPCM), and entropy coding methods. The paper concludes with the presentation of a framework for evaluation and comparison of ECG compression schemes.

A total of 29 two-phase flow tests was conducted in two 3-mile-long flow lines in the Prudhoe Bay field of Alaska. Of these, II were for a 12-in.-diameter line and 18 were for a 16-in. line. Nine of the tests were in slug flow, and 20 were in froth flow. Flow rates, inlet and outlet pressures, and temperatures were measured for each test. Gamma densitometers were used to monitor flow pattern and to determine mixture densities and slug characteristics.It was found that a modified Beggs-Brill 1 pressureloss correlation predicted culled data to within -1.5070 on the average compared with + 11.4% for a modified Dukler-Eaton 2 ,3 correlation. Very little scatter was observed with either method.Analysis of flow-pattern observations showed that none of the slug-flow tests were in the Schmidt 4 severe slug region characterized by extremely long slugs. It also was found that the slug/froth (dispersed) flow-pattern boundary existed at a much lower liquid flow rate than predicted by either Mandhane et al. 5 or Taitel and Dukler. 6

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In this note, we give necessary and sufficient conditions for a maximum-likelihood estimate of a subset of the proportions in a mixture of specified distributions. From these conditions, we derive likelihood equations satisfied by the maximum-likelihood estimate and discuss a successive-approximations procedure suggested by these equations for numerically evaluating the maximum-likelihood estimate. It is shown that, with probability for large samples, this procedure converges locally to the maximumlikelihood estimate whenever a certain step-size lies between 0 and 2. Furthermore, optimal rates of local convergence are obtained for a step-size which is bounded below by a number between and 2. *

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