Advanced design of a low energy electron source
A multiphysics-based modeling design of a low energy electron source using a thermionic cathode is described in this paper. The proposed device produces a narrow beam employable in delicate applications where dimensions are critical. The effects of multiple physics influencing factors due to the cathode heating over the beam dynamics have been predicted through a multiphysics design approach. This paper would provide the needed knowledge for virtual prototyping of such devices. For this aim, several strategies have been adopted to obtain a simple model, which shows clearly the investigated mechanisms. According to this study, the appropriate materials and shapes can be chosen.
DEVELOPMENT OF A THERMIONIC RF GUN FOR COHERENT THz SOURCE AT TOHOKU UNIVERSITY * BETWEEN THE CATHODE ENDPLATE
A test accelerator for the coherent terahertz source (t-ACTS) has been under development at Research Center for Electron Photon Science, Tohoku University. Intense coherent terahertz radiation will be generated by the very short electron bunch less than 100 fs using a thermionic RF gun. The RF gun has been already manufactured and the measurement of RF characteristics is now in progress. We present the results of low-power measurement and also discuss the effect of the cathode misalignment on the beam parameters such as transverse emittance and longitudinal phase space distribution.
Calyculins and Related Marine Natural Products as Serine-Threonine Protein Phosphatase PP1 and PP2A Inhibitors and Total Syntheses of Calyculin A, B, and C
Calyculins, highly cytotoxic polyketides, originally isolated from the marine sponge Discodermia calyx by Fusetani and co-workers, belong to the lithistid sponges group. These molecules have become interesting targets for cell biologists and synthetic organic chemists. The serine/threonine protein phosphatases play an essential role in the cellular signalling, metabolism, and cell cycle control. Calyculins express potent protein phosphatase 1 and 2A inhibitory activity, and have therefore become valuable tools for cellular biologists studying intracellular processes and their control by reversible phosphorylation. Calyculins might also play an important role in the development of several diseases such as cancer, neurodegenerative diseases, and type 2-diabetes mellitus. The fascinating structures of calyculins have inspired various groups of synthetic organic chemists to develop total syntheses of the most abundant calyculins A and C. However, with fifteen chiral centres, a cyano-capped tetraene unit, a phosphate-bearing spiroketal, an anti, anti, anti dipropionate segment, an α-chiral oxazole, and a trihydroxylated γ-amino acid, calyculins reach versatility that only few natural products can surpass, and truly challenge modern chemists’ asymmetric synthesis skills.