Oxygen uptake rate measurements for evaluation of ozonation of municipal wastewater.

Ozonation has become more frequently used as oxidant to reduce chemical oxygen demand (COD) and toxic substances in wastewater originating from different industrial processes. An ozonation pilot plant followed by two parallel biological filters are used to investigate the possibility to reduce the high concentration of refractory COD in the effluent from a municipal wastewater treatment plant, partly loaded with biologically treated wastewater from a large pharmaceutical industry. COD measurements are used to evaluate the overall reduction of organic matter, oxygen uptake rate (OUR) and volatile fatty acids measurements are used for evaluation of the biodegradability of the remaining COD after ozonation. The impact of the ozone dose on the overall COD degradation and degradability of the remaining COD has been estimated. Biochemical oxygen demand (BOD) measurements confirm that parts of the COD are converted into biodegradable organic matter by ozonation. Biofilters following the ozonation plant secure that any degradable organic matter produced by ozonation is removed, which is confirmed from OUR-measurements.

Principles for transformation of scalp EEG from potential field into source distribution.

Tracings representing simultaneously recorded values of EEG potentials from different positions on the scalp surface describe how the instantaneous potential field over the scalp surface changes with time. Each instantaneous distribution of potential can be seen as resulting from spatial integration of primary components into the potential field. These components may be derived by means of the reverse procedure: subjecting the data from the potential field to spatial differentiation as provided by the Laplacian source operator. The result is a "deblurred," i.e., a more differentiated, distribution of source components hypothetically associated with the generators of the potential field. The Laplacian source operator can be implemented as a linear combination of the instantaneous potential values, either by means of very simple electronic circuitry or in a computer. The linear combination is a standard operation in matrix algebra and is widely applied in signal processing. The formalism of matrix algebra simplifies a precise evaluation of the method in relation to conventional derivation techniques and provides further methods for analysis of the EEG data.

Eigenvectors and eigenfunctions in spatiotemporal EEG analysis.

As a supplement to the article "An Eigenfunction Approach to the Inverse Problem of EEG" by Hjorth and Rodin in Brain Topography, 1988, 1 (2): 79-86, this paper discusses in greater detail the interrelations between the concepts of EEG sample vector, eigenvalue and eigenvector. It also describes how the method for assigning locations to uncorrelated EEG basic waveforms named eigenfunctions can be further developed by normalizing the EEG samples to unity global field power before computation of covariance. This enhances local persistence as a feature for revealing low-amplitude activity of possible diagnostic significance, even in the presence of more dominant activity.

An eigenfunction approach to the inverse problem of EEG.

A mathematical method of extracting salient features from electroencephalographic data called eigenfunction analysis is presented. It allows the reduction of 21 channels of EEG data to a few components which can be separated into those which are likely to originate relatively close to the surface and others of deeper origin. It was demonstrated that the original tracings can be reconstituted from these few components. The eigenvectors given an indication of the location of sources and the degree to which the eigenfunction appears on source derivation and average reference recordings allows an estimation of relative depth. The method has been successfully applied to EEG tracings from 10 patients and is illustrated in the case of a young woman suffering from complex partial seizures associated with a deep left temporal lesion. The implications for marked data reduction and the development of objective assessment of clinical neurophysiologic data are discussed.

Extraction of "deep" components from scalp EEG.

In an attempt to delineate the relative contribution of surface versus deep components in the EEG of patients with 3 per second generalized spike-wave discharges and clinical petit mal seizures, a mathematical method was devised which allows the splitting of the EEG into two major subsystems. It is based on the observation that broad electrical fields tend to represent activity at deeper structures while discrete narrow fields centered at one electrode position tend to be of more superficial origin. Since source derivation intentionally suppresses broad potential fields, a differentiation between superficial and deep activity can be achieved by subtracting the source density values from the corresponding electrode potential values. This will provide those aspects of the EEG which are contributed mainly by deep generators. The resultant data can then be subjected to eigenfunction analysis which yields few uncorrelated components. The percentage of contribution of each electrode to the total component thus derived can then be displayed as a topographic map. When this methodology was applied to ictal EEGs of three patients consistent results were obtained. The "deep" data yielded mainly two components with mutually perpendicular directions.

EEG topogram--an aid in describing EEG to the clinician.

The investigation presents a simple, reliable method to show localized EEG abnormalities in a topographical display. The aim of the study was to find a method which could be used in clinical practice, and which in topographical form could complement the written EEG report with information about degree and localization of an EEG abnormality. The EEG was recorded on a 21-channel polygraph (Siemens-Elema). The source derivation recording technique was used. Besides being displayed as a conventional EEG record, the signals were fed to a small computer that calculated an abnormality feature based on the time domain descriptors activity, mobility and complexity. Obtained values were converted into ink density in topograms by modulating the displacement velocity of the ink jet beam. The dynamic range was chosen so that maximum and minimum densities represented 1.5 and 0.5 times the average for each descriptor. The ink density in the topogram was thus related to the degree of EEG abnormality. The recording procedure followed the ordinary clinical routine except that the conventional EEG display was interrupted several times for a few seconds, on command by the EEG technician, to write out the topogram on the EEG paper. It is concluded that EEG topograms produced on line as part of the EEG examination procedure may greatly enhance EEG information conveyed from the neurophysiologist to the clinician. Furthermore, they permit direct visual comparison with other diagnostic topographic displays such as CT scan.

An adaptive EEG derivation technique.

The amount of common components in EEG tracings relating to any two electrodes in the 10-20 array depends partly on the distance between these electrodes, i.e. potentials on the scalp surface have an average mutual coupling which is related to distance along the surface. This coupling is expressed by the spatial correlation function which can be computed from the tracings. Information contained in the correlation functions relating to 30 individual subjects was used to modify the derivation technique to yield 'focussed' tracings in each case, i.e., tracings from which the distance-related coupling ('blur') had been removed. Obtained results were considered representative of the topographical resolution achievable within the limitations of the 10-20 system of electrode placement. The tracings were in most cases found to be almost identical to those obtained by means of the non-adaptive deconvolving technique known as source derivation. In some cases the adaptive technique produced tracings with slightly higher topographical differentiation than did source derivation.

EEG and haemodialysis. A structural survey of EEG spectral analysis, Hjorth's EEG descriptors, blood variables and psychological data.

Computerized EEG was performed in 20 patients with renal failure before and after haemodialysis (HD), applying spectral analysis and Hjorth's EEG descriptors in EEG quantification, correlation and factor analysis as statistical procedures to analyse the connections of EEG, blood variables and psychological performance. The main results were: (1) Moderate uraemic encephalopathy -- according to Kiley's (1971) standards -- was present in most of our patients, before and after HD. (2) Before HD, EEG slowing was most strongly connected with the creatinine level and EEG acceleration with hyperkalaemia, which in most cases accompanied a high urea level. (3) Significant EEG changes after HD were: decrease of percentage delta activity, increase of Hjorth's 'mobility', decrease of Hjorth's 'complexity'. (4) The theta/alpha ratio (Matousek 1968) was significantly correlated with the patient's general clinical state after HD. (5) Visual discrimination, memory and maximal tapping speed improved significantly after HD. Only Hjorth's EEG parameters were correlated with test performance in that patients with low voltage and fast EEGs did worse in visual discrimination.

Determination of coagulation factors (II-VII-X) and kaolin partial thromboplastin time by the LKB 8600 Reaction Rate Analyser.

Testing of a modified Reaction Rate Analyser 8600 in the automatic determination of coagulation time was accomplished with the assays Thrombotest Normotest and Kaolin Partial Thromboplastin Time. Variations in extinctions, from the adding of start reagent until coagulation, were recorded. The coagulation activities, found by the automatic method for the assays Thrombotest and Normotest, were compared with a manual method. Thrombotest showed a good correlation: 0.30 greater than P greater than 0.25 (paired t test). Normotest showed significantly different values by the methods: P less than 0.001 (paired t test). Kaolin Partial Thromboplastin Time (Activated Partial Thromboplastin Time with kaolin as activator) gave significantly lower vales--the difference was 3 sec--compared with a manual method, and the precision was considerably improved.

An on-line transformation of EEG scalp potentials into orthogonal source derivations.

A new type of EEG derivation has been investigated. This derivation, constituting a practical implementation of the Laplace operator, detects source activity as it appears at the surface level of the scalp. It is realized in the 10-20 system of electrode placement basically as an analogue superposition of four bipolar derivations, forming a star-like configuration around each electrode. Visual estimation of the topographical origins of a pattern, is thus replaced by a more efficient on-line process, which derives the source activity at the position of each individual electrode. Practical correlation tests have shown that the separation of adjacent derivations is improved by a factor of between two and four, compared to the corresponding bipolar and common reference derivations. Any feature of local origin will therefore have a correspondingly increased signal-to-noise ratio prior to the stage of visual or automatic interpretation. As a consequence of the partition of the scalp field into 19 source zreas, instead of utilizing an arbitrary number of potential differences, one fixed montage with 19 recorder channels is sufficient to present the total surface activity, within the limits of resolution of the electrode system.