Notes: Zusammenfassung Es werden die optischen Übergangswahrscheinlichkeiten für Elektronenübergänge zwischen Bandrändern und Zwischenbandtermen als Einelektronenproblem berechnet. Der Rechnung zugrunde gelegt wird ein ruhendes gestörtes Gitter, dessen Potentialverlauf modellmäßig durch ein gestörtesKronig-Potential beschrieben wird. Für die optischen Elektronenübergänge wird eine Auswahlregel gewonnen, die von der energetischen Lage der Zwischenbandterme unabhängig ist. Sodann wird die Wahrscheinlichkeit erlaubter Übergänge bei spontaner Emission in Abhängigkeit von der energetischen Lage der Zwischenbandterme berechnet. Es zeigt sich, daß die Übergangswahrscheinlichkeit mit zunehmendem energetischen Abstand Bandkanten—Zwischenbandterm ansteigt.

Notes: Abstract Seventeen patients were investigated to localize carcinoid tumor growth in the small intestine and liver. Portography, selective phlebography of the intestinal veins, arteriography, and hormone assay (Serotonin, substance P) after simultaneous catheterization of the celiac artery and portal and caval veins were performed. Most of the patients have been operated on and findings at surgery have been compared with the preoperative localization methods. In 3 cases with small bowel carcinoids and typical fibroplastic changes of the mesentery, phlebography as well as arteriography demonstrated well the degree of mesenteric involvement. None of the methods demonstrated the primary tumors. Arteriography was superior in demonstration of liver metastasis. The hormone assay was a useful complement to angiographic techniques in the diagnosis and localization of tumor growth.

Notes: Abstract The experiments and their analysis, presented in this paper, deal with the tracking behaviour of tethered flying flies (Musca domestica) towards moving black objects in front of white or randomly contrasted backgrounds. Experiments were carried out under closed—as well as under open-loop conditions. Under closed-loop the fly is coupled to its environment, whereas under open-loop its motor output does not influence the visual input. The following expeeiments have been carried out: Tracking of a black object in front of a white background (Section 3.1); under closed-loop, a fly follows an object, moved at constant angular speed ω, however, lagging behind it by the tracking angle ψtr. ψtr is linearly related to ω. Stable tracking in Musca is confined to about±20o both sides of the flight direction. Tracking of a black object, imbedded in a randomly contrasted pattern of different contrast (Section 3.2): under these conditions the same tracking rules as in the case of a white background are observed. With decreasing contrast difference between the object and the random pattern, the steepness of the linear relation between ω and ψtr increases. These observations are consistent with earlier experimental results and can be explained in terms of a phenomenological theory describing visual orientation in Musca; Poggio and Reichardt (1973a), Reichardt and Poggio (1975). Detection and tracking of a black object, hidden in a random background pattern of the same contrast (Sections 3.3 and 3.4): it is shown that the necessary condition for detection and tracking of an object under these conditions is the presence of relative motion between the object and the background. When the background is moved and the object is stationary, no detection is observed. The effect strongly depends upon parameters such as the object and the background configurations and their contrast differences. Full independence between the nervous correlates induced by the object and the background is also reached when the object is moved with constant angular speed against the background. In this case the phenomenological theory is easily applicable. Detection is demonstrated under closed—as well as under open-loop conditions. Analysis and interpretation of the detection phenomenon requires a mathematical formalism describing the responsible nonlinear interaction processes in the Central Nervous System of the fly. The Volterra description is such a formalism; Poggio and Reichardt (1973b). In terms of this formalism and in view of more recent experiments by Pick (1974) and by Heimburger et al. (1975), the detection effect can be accounted for by fourth order nonlinear interactions between the signals received from two to four receptors. The latter observations and their interpretations might lead to a better understanding of the discrmination of the optical environment into figure and ground.