Precision Control of the Electron Longitudinal Bunch Shape Using an Emittance-Exchange Beam Line.

We report on the experimental generation of relativistic electron bunches with a tunable longitudinal bunch shape. A longitudinal bunch-shaping (LBS) beam line, consisting of a transverse mask followed by a transverse-to-longitudinal emittance exchange (EEX) beam line, is used to tailor the longitudinal bunch shape (or current profile) of the electron bunch. The mask shapes the bunch's horizontal profile, and the EEX beam line converts it to a corresponding longitudinal profile. The Argonne wakefield accelerator rf photoinjector delivers electron bunches into a LBS beam line to generate a variety of longitudinal bunch shapes. The quality of the longitudinal bunch shape is limited by various perturbations in the exchange process. We develop a simple method, based on the incident slope of the bunch, to significantly suppress the perturbations.

Heterogeneity in the processing defect of SLC26A4 mutants.

BACKGROUND: Mutations in the SLC26A4 gene are responsible for Pendred syndrome and non-syndromic hearing loss (DFNB4). This study analysed non-synonymous SLC26A4 mutations newly identified in East Asians, as well as three common mutations in Caucasians, to characterise their molecular pathogenic mechanisms and to explore the possibility of rescuing their processing defects. METHODS: A total of 11 non-synonymous disease associated mutations were generated and their effects on protein processing and on ion transporting activities were examined. RESULTS: Most of the mutations caused retention of the SLC26A4 gene product (pendrin) in the intracellular region, while wild-type pendrin reached the plasma membrane. Accordingly, these mutations abolished complex glycosylation and Cl(-)/HCO(3)(-) exchange activities of pendrin. However, significant heterogeneity in the processing of mutant pendrin molecules was observed. Each mutant protein exhibited a different cellular localisation, a different degree of N-glycosylation, and a different degree of sensitivity to the treatments that rescue processing defects. For example, H723R-pendrin, the most common mutation in East Asians, was mostly expressed in endoplasmic reticulum (ER), and its defects in protein processing and ion transporting activities were restored considerably by low temperature incubation. On the other hand, L236P-pendrin, the most common mutation in Caucasians, was mainly in the centrosomal region and was temperature insensitive. CONCLUSION: These results indicate that the processing of pendrin mutant protein is determined by mutant specific mechanisms, and that a mutant specific method would be required to rescue the conformational defects of each folding mutant.

Spatial resolution study and power calibration of the high-k scattering system on NSTX.

NSTX high-k scattering system has been extensively utilized in studying the microturbulence and coherent waves. An absolute calibration of the scattering system was performed employing a new millimeter-wave source and calibrated attenuators. One of the key parameters essential for the calibration of the multichannel scattering system is the interaction length. This interaction length is significantly different from the conventional one due to the curvature and magnetic shear effect.

Present status of the pohang light source.

The Pohang Light Source (PLS), the first large-scale accelerator complex in Korea, is a national users facility for basic and applied science research using synchrotron radiation. It consists of a 2 GeV linac as a full-energy injector and a low-emittance storage ring. The PLS linac is 150 m long with eleven 80 MW klystrons for a high accelerating gradient; the storage ring has the TBA-lattice with 12 super-periods and a 280 m circumference. Since the accelerators were commissioned in December 1994, the annual operation time exceeded 4600 h in 1996, and the user service time is expected to reach 3500 h in 1997. The facility was opened to general users in 1995 with two beamlines. Six beamlines are now operating: white-beam, NIM for ARUPS and gas-phase, photoemission spectroscopy, EXAFS, X-ray diffraction and lithography. Our long-term plan is to construct three new beamlines every year.