The capture of an optical image in the plane of a semiconductor quantum well and the subsequent re-emission of this image in the form of a two-dimensional photon flux is demonstrated. Spatially resolved storage of photonic signals in a two-dimensional lateral potential landscape of the quantum well is employed to imprint optical images in the form of trapped photogenerated charges into the solid. The lateral two-dimensional potential modulation leads to very long storage times by a deliberate spatial separation of photogenerated electron-hole pairs. Once the potential modulation is lifted, the initial optical information is restored and the photographed image is released in a flash of light.
Voltage-controlled lateral potential superlattices are used to dramatically increase the lifetime of photogenerated carriers in a quantum well. These long lifetimes, together with the ability to deliberately trigger radiative recombination, enable us to directly visualize the spreading character of nonlinear Maxwell relaxation of 2D charges along narrow channels. Our system allows for temporal and spatial resolution of Maxwell kinetics, usually a very fast process and difficult to observe. The observed spreading dynamics of a 2D hole plasma is in perfect agreement with our nonlinear model.
Astrocytoma vasculature patterns differ according to histological grade of malignancy with glioblastoma multiforme (WHO grade IV) showing most extensive endothelial proliferation. Here, we determined whether the vascular patterns of medulloblastoma and supratentorial primitive neuroectodermal tumors (PNETs), which can be hardly distinguished histopathologically, differ. We evaluated the spatial organization of vessels in medulloblastomas and PNETs using antibodies to von Willebrand factor (vWF) and CD34. Medulloblastoma capillaries showed slight endothelial cell hyperplasia. Microvessels sprouted from the capillaries and formed glomeruloid clusters. There were areas with chains of unopposed endothelial cells (3-10 cells). Supratentorial PNETs had highly branched capillaries with extensive endothelial cell hyperplasia. Glomeruloid arrays of microvessels extended from the capillaries. Small fragments of endothelial tubes were scattered throughout the tumor. Therefore, medulloblastomas and supratentorial PNETs showed different spatial organization of tumor vessels which can be used for differentiation of each tumor entity. These vascular patterns may reflect different tumor derived angiogenic stimuli.
Metathesis. -Ring closing metathesis to title compounds (IV) is achieved by using Grubbs' catalyst. The resulting E/Z mixtures are separable by GLC. The lactones (IV) and the ring opening product (VI) show weak cytotoxic activitiy against HL-60 cells.
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