Electronic excitations during grazing scattering of hydrogen atoms on KI(001) and LiF(001) surfaces

The energy loss of hydrogen atoms with energies of 400 eV and 1 keV is studied in coincidence with the number of emitted electrons during grazing scattering from atomically clean and flat KI(001) and LiF(001) surfaces. The energy loss spectra for specific numbers of emitted electrons are analyzed in terms of a binary interaction model based on the formation of transient negative ions via local capture of valence band electrons from anion sites. Based on computer simulations we derive for this interaction scenario probabilities for the production of surface excitons, for electron loss to the conduction band of KI, for emission of electrons, and for formation of negative hydrogen ions. The pronounced differences of data obtained for the two surfaces are attributed to the different electronic structures of KI and LiF.     

14.5GHz紧凑型、低成本、全永磁ECR离子源

A compact 14.5GHz electron cyclotron resonance (ECR) ion source for the production of slow, multiply charged ions has been constructed,with the plasma-confining magnetic field produced exclusively by permanent magnets.Microwave power of up to 175W in the frequency range from 12.75 to 14.SGHz is transmitted from ground potential via a PTFE window into the water-cooled plasma chamber which can be equipped with an aluminum liner.The waveguide coupling system serves also as biased electrode,and two remotely-controlled gas inlet valves connected via an insulating break permit plasma operation in the gas- mixing mode.A triode extraction system sustains ion acceleration voltages between 1kV and 10kV.The ECR ion source is fully computer-controlled and can be remotely operated from any desired location via Ethernet.     

Virtual two-dimensional gel electrophoresis of high-density lipoproteins

High-density lipoproteins (HDLs) isolated by immunoaffinity chromatography and separated by immobilized pH gradient-isoelectric focusing (IPG-IEF) were examined by mass spectrometry directly, applying a new proteomics technology, virtual two-dimensional (2-D) gel electrophoresis. A preliminary examination of HDL particles has revealed at least 42 unique masses for protein species with isoelectric points between pH 5.47-5.04, some of which have not been observed previously. By delivering masses of intact proteins from complex cellular mixtures in a format that correlates directly to classical 2-D gel analyses, virtual 2-D gel electrophoresis constitutes a general discovery tool to expose and monitor protein isoforms and post-translational modifications. Furthermore, its general ability to deliver ions from sub-picomole level proteins enmeshed in complex cellular mixtures potentially fulfills the need of top-down proteomics to obtain intact protein ions from microscale samples. Additional comparison of such data to 2-D gel analyses and their identified proteins may elucidate the functions of the individual apolipoprotein components and the cardioprotective effects of HDL.