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Biomedical subjects

W Reichardt

Publications and source records attributed to W Reichardt.

At least 55 records · Page 3Linked to original sources
PubMed1989

Computational structure of a biological motion-detection system as revealed by local detector analysis in the fly's nervous system.

The computations performed by individual movement detectors are analyzed by intracellularly recording from an identified direction-selective motion-sensitive interneuron in the fly's brain and by comparing these results with model predictions based on movement detectors of the correlation type. Three main conclusions were drawn with respect to the movement-detection system of the fly: (1) The essential nonlinear interaction between the two movement-detector input channels can be characterized formally by a mathematically almost perfect multiplication process. (2) Even at high contrasts no significant nonlinearities seem to distort the time course of the movement-detector input signals. (3) The movement detectors of the fly are not perfectly antisymmetrical; i.e., they respond with different time courses and amplitudes to motion in their preferred and null directions. As a consequence of this property, the motion detectors can respond to some degree to stationary patterns whose brightness is modulated in time. Moreover, the direction selectivity, i.e., the relative difference of the responses to motion in the preferred and null directions, depends on the contrast and on the spatial-frequency content of the stimulus pattern.

Animals↗
PubMed1989

[The determination of ammonia in rumen fluid].

The following 3 methods of NH3 determination were compared to each other for accuracy, on the basis of their results: microdiffusion acidimetric NH3 analysis, photometric NH3 analysis, using bivalent potassium tetra-iodomercurate, and steam distillation/acidimetric NH3 analysis. The results obtained from steam distillation at pH 7.6 were found to agree with those recorded from microdiffusion. However, photometric NH3 determination, using Nessler reagent, yielded overestimated values due to interference by other rumen juice substances.

Ammonia↗
PubMed1987

Computation of optical motion by movement detectors.

The first part of this paper deals with a system-theoretical approach for the decomposition of multi-input systems into the sum of simpler systems. This approach is applied here to analyse the algorithm which represents the computations underlying the extraction of motion information from the optical environment by biological movement detectors. The second part concentrates on a specific model for motion computation known to be realized by the visual system of insects and of man. These detectors provide the visual system with information on both the velocity and structural properties of a moving pattern. In the third part of this article the properties of two-dimensional arrays of movement detectors are analyzed and their relations to meaningful physiological responses are discussed.

Journal Article↗
PubMed1987

[Quantitative determination of the protein content of milk by ultraviolet spectrophotometry. 3. The protein content of whole milk].

It is possible to determine the protein content of unskimmed milk after dilution with a detergent solution by measuring of absorbance at 210 and 220 nm. If milk samples are not elder than 36 h the difference A210-A220 shows a high correlation to the values of Kjeldahl nitrogen analysis (r = 0.97). Similar coincidence was found to the values of absorbance measurements in skimmed milk (A210: r = 0.98; A235-A280: r = 0.96). With decreasing age of unskimmed milk samples the coincidence diminished. Absorbance data measured at 210, 215, 220, 225, 235 and 280 nm as well as the differences A215-A225 and A235-A280 do not much agree with analogous results from skimmed milk. Elderly creamed milk samples allow the determination of protein content from milk plasma. It could be proved by Kjeldahl nitrogen analysis, that differences in the nitrogen content of unskimmed and skimmed milk depend on the nitrogen-loss during centrifugation, on the protein content and the protein-fat-ratio.

Animals↗
PubMed1987

[Quantitative determination of the protein content of milk by ultraviolet spectrophotometry. 3. Determination of proteins in preserved milk samples].

It is reported upon the results of the quantitative estimation of protein content from preserved milk by means of ultraviolet spectrophotometry. In addition to the preservation by boric acid, bronopol, copper sulphate, potassium dichromate and ammonium peroxodisulphate storage at temperatures below 0 degrees C and freeze drying were tested. Besides bronopol and copper sulphate especially physical preservation methods proves fit for the protein estimation by measurements of absorbance at 210 nm, 235 and 280 nm or 210 and 220 nm. It is recommended to use solutions and filters of quartz with evaluated absorbance in daily calibrating of the spectrophotometer.

Animals↗
PubMed1987

Evaluation of optical motion information by movement detectors.

The paper is dealing in its first part with a system-theoretical approach for the decomposition of multi-input systems into the sum of simpler systems. By this approach the algorithm for the computations underlying the extraction of motion information from the optical environment by biological movement detectors is analysed. In the second part it concentrates on a specific model for motion computation known to be realized by the visual system of insects and of man. These motion detectors provide the visual system with information on both, velocity and structural properties of a moving pattern. The last part of the paper deals with the functional properties of two-dimensional arrays of movement detectors. They are analyzed and their relations to meaningful physiological responses are discussed.

Algorithms↗
PubMed1986

Processing of optical information by the visual system of the fly.

A detailed understanding of the principles of sensory information processing by the nervous system require investigations with a variety of "model" systems at different levels of complexity. The fly as a model system represents a compromise in the sense that the properties of information processing are taking place in a rather complex nervous system that is amenable to a quantitative analysis at three different levels: at the phenomenological level the overall function of the system, its input-output behaviour, and its logical organization are studied. At the second level, the functional principles of the subsystems, expressed by its algorithmic properties are the object of the analysis. At the third level the investigation focusses on the individual nerve cells and the neuronal circuitry involved in the computations. The approach, reviewed here, deals with an analysis of the visio-motor control system of the fly at the phenomenological level which leads to an algorithmic description of the main subsystems for extraction of motion- and position-information. The analysis at the third level is connected with the investigation of the so called figure-ground and pattern discrimination problem by the visual system of the fly. In this connection the elements of a new movement detector theory are mentioned.

Animals↗
PubMed1986

[Diagnostic problems of alveolar cell carcinoma].

The clinical and radiological symptoms and differential diagnosis of four out of seven cases of alveolar cell carcinomas of the lung, which were observed during the last years, have been compared. Some characteristics are shown, which make the differentiation possible between tuberculosis, sarcoidosis, chronic carcinogenic pneumonia and interstitial lung diseases. Early diagnosis by histological investigation of cells from sputum or from bronchial secretion and by needle biopsy seems possible. During the earliest stage alveolar cell carcinoma can be cured by surgery.

Adenocarcinoma, Bronchiolo-Alveolar↗
PubMed1984

[The quantitative determination of protein content in milk by means of ultraviolet spectrophotometry. 2. The suitability of the difference of absorbance at 235 and 280 nm for quantitative milk protein analysis].

The protein content of skimmed milk was determined by measuring the absorbance at 235 and 280 nm after dilution with alkylpolyglycolethersulphate solution. The difference of absorbance A235-A280 shows a high correlation to the values of KJELDAHL nitrogen analysis (r = 0.99). The protein content of casein and milkserum solutions could be determined in the same way. The method has the advantage, that their results are approximately independent of the amino acid composition of proteins, the content of nucleic acids, salts, lactose and non protein nitrogen. Both absorbances are obtainable from one solution. The dependence of the absorbance difference from the age of solution, the age of milk and from the temperature was investigated as well as the influence of preservatives.

Animals↗