Familial periventricular nodular heterotopia

Twenty patients with carcinoma of the ampulla of Vater were studied with sonography (N = 9) or both sonography and CT (N = 11). The tumor was shown by sonography in 16 patients (80%) as a small, round or oval, fairly well delineated mass in between the dilated distal common bile duct and duodenum which was delineated owing to luminal fluid or gas (N = 13); or as a polypoid mass within the dilated distal common bile duct resulting in abrupt obstruction (N = 3). In the remaining four patients, the mass was not delineated. Bile ducts were dilated down to the level of mass or ampullary region in all cases (100%), while the pancreatic duct was dilated in five cases (45%). We believe that sonography is the technique of initial choice in the diagnosis of carcinoma of the ampulla of Vater by identifying the mass at the distal end of the dilated common bile duct and/or pancreatic duct.     

Electrical and optical properties of ZnTe-GaSb heterojunctions

Heterojunctions between ZnTe and GaSb is produced by the interface-alloy technique with the use of movable quartz tube loaded in a furnace instead of a strip-heater. X-ray measurement shows that the recrystallized GaSb is monocrystalline and oriented parallel to the ZnTe substrate with (111) as the growth direction. Photoresponse for p-p ZnTe-GaSb heterojunctions decreases exponentially with decreasing incident photon energy for hν < 2·18 eV at room temperature. This behavior is explained by a model of linearly-graded bandgap region of the order of 500 Å long, which was first proposed for GaAs-InSb heterojunction by Hinkley and Rediker. The photocurrent is produced by hot holes generated by absorbed photons in the graded-gap region which traverse this region with a mean free path of about 40 Å. Space-charge-limited current observed in I–V characteristics of p-p ZnTe-GaSb heterojunctions is explained by Lampert theory. The thickness of semi-insulating region is estimated at about 1 to 3 μm from the capacitance measurements without d.c. bias. This thickness is much larger than the graded bandgap region. Capacitance depends strongly on both forward d.c. bias voltage and a.c. frequency, but is almost independent of reverse bias voltage. The results of capacitance measurements for forward bias are qualitatively interpreted in terms of a change in the trapped charge density in the semi-insulating region. A significant discrepancy between the theory and experimental results exists in the region of trap-free limit.