Frequency limitations of the two-point central difference differentiation algorithm.

A two-point central difference algorithm is often used to calculate the derivative of a function. This estimate is only valid over a limited frequency range. Therefore, the algorithm can be modeled as an ideal differentiator in series with a low-pass filter. The filter cutoff frequency is a function of the time between the points. We discuss the accuracy and limitations of using this algorithm on human saccadic eye movement data. To calculate the velocity of saccadic eye movements the algorithm should have a cutoff frequency of 74 Hz or above.

Hereditary haemolytic anaemia due to red cell pyrimidine 5'-nucleotidase deficiency in two Irish families with a note on the benefit of splenectomy.

Hereditary haemolytic anaemia with basophilic stippling caused by pyrimidine 5'-nucleotidase deficiency is described in three members of two unrelated Irish families. In one family, the disease was moderately severe and the patient's condition was improved by splenectomy. In the other family the haemolytic anaemia was well compensated. In neither family was there a marked elevation of reduced glutathione. The implications are that pyrimidine 5'-nucleotidase deficiency is a heterogeneous disorder, both clinically and biochemically. In more severe forms splenectomy may be beneficial.

Red cell pyrimidine 5'-nucleotidase and glutathione in myeloproliferative and lymphoproliferative disorders.

Red cell reduced glutatione (GSH) and pyrimidine 5'-nucleotidase (Pry 5'-NT) were measured in a variety of myeloproliferative and lymphoproliferative disorders. Raised levels of GSH were found in chronic lymphocytic leukaemia, Hodgkin's disease, non-Hodgkin's lymphoma, Waldenstrom's macroglobulinaemia and myeloma. Decreased activity of Pyr 5'-NT was found in acute myeloblastic leukaemia, acute lymphoblastic leukaemia, chronic granulocytic leukaemia, chronic lymphocytic leukaemia, Hodgkin's disease and non-Hodgkin's lymphoma. There was no correlation between the raised GSH levels and decrease Pry 5'-NT levels.

Clinical evaluation of a prototype intraoral source x-ray system.

A prototype dental roentgenographic system which incorporates a tightly collimated intraoral x-ray source and an extraoral Polaroid film screen cassette was evaluated both in vitro and in vivo. Findings indicate that the detectability of artificially induced incipient enamel lesions was significantly less than that demonstrable for conventional roentgenograms produced with an extraoral source, long-cone geometry, and Kodak Ultra Speed D film. Larger lesions were found to be reliably detected by either technique. The new intraoral approach reduces the dose to the patient by possibly as much as 98 per cent and yields positive dry prints in 15 seconds. This system was clinically tested and found to be useful in endodontics and presurgical evaluation. Modifications are discussed which could reduce some of the technical problems and many of the shortcomings encountered.