A comparison of ion and atom behavior in the first stage of an inductively coupled plasma mass spectrometer vacuum interface: Evidence of the effect of an ambipolar electric field

Velocities of argon atoms and calcium ions were measured in the first vacuum stage of an inductively coupled plasma mass spectrometer using high-resolution laser-excited fluorescence spectroscopy. The calcium ions reached terminal velocities in the supersonic expansion that were consistently 5–6% higher than those of argon atoms, despite minimal differences in the masses of the two species. A computational model of the expansion was developed that shows the development of an ambipolar electric field along the expansion axis. With reasonable assumptions about electron temperatures in the expansion, the model accounts for the differences between the terminal velocities of the neutral argon atoms and the singly-charged calcium ions.     

Steady vortical flow around a finite plate

An explicit solution for a layer of fluid with constant vorticitysurrounding a thin plate of finite length is obtained usingelementary conformal mapping methods. In the limit of largeplate length the behaviour of the solution near the ends ofthe plate tends to that of the previously known solution fora semi-infinite plate. Contour dynamics is used to investigatethe stability of the steady solutions.     

Measurements of a stator-induced circumferentially varying flow

The flow physics associated with the generation of both axisymmetric and non-axisymmetric swirl by various deflection patterns of a stator array was investigated experimentally through surface pressure and Stereoscopic Particle Image Velocimetry measurements. A three-dimensional rendering technique was developed to reconstruct the flow field around the model and in its wake. The three-dimensional fluid volume was reconstructed from multiple two-dimensional measurement planes. A cyclic distribution of the stators’ deflections resulted in non-axisymmetric distributions of the surface pressure and the flow field downstream of the stator array. The addition of a shroud had an amplifying effect: accelerating the flow through the stator array while reducing the non-uniform tangential velocity component generated by the stators. In the model near wake the flow field is associated with secondary flow patterns in the form of coherent streamwise vortical structures that can be described by potential flow mechanisms. The collective pitch distribution of the stators produces a flow field that resembles a potential Rankine vortex, whereas the cyclic pitch distribution generates a flow pattern that can be described by a potential vortex pair in a cross-flow.     

Hankel operators, the Segal-Bargmann space, and symmetrically-normed ideals

Starting with the Segal-Bargmann space, we investigate the Hankel operators with symbol functions in a certain linear space. Given an appropriate symbol function, we consider the associated Hankel operator together with the Hankel operator associated with that symbol function's complex conjugate. We give a necessary and sufficient condition for the simultaneous membership of these two operators in the symmetrically-normed ideal associated with any given symmetric norming function.     

Student presentations in the classroom

For many years, the author has been involving his students in classroom teaching of their own classes. The day-to-day practice is described, and the advantages and disadvantages for both the instructor and the students are discussed. Comparisons with the Moore Method of teaching are made.     

Excitation processes in an r.f.-boosted,pulsed hollow cathode lamp

Time and space resolved emission spectroscopy was used to examine the excitation processes in an r.f.-boosted, pulsed hollow cathode lamp. Sealed commercial hollow cathode lamps with copper cathodes and neon or argon buffer gases were driven with temporally spaced unidirectional current pulses and radio frequency bursts. The neon filled lamp was studied most extensively; the argon lamp was used for comparison.Three excitation periods were considered: the current pulse, the r.f. burst, and the afterglow. Each of these periods was marked by a unique set of emission characteristics that suggested different combinations of excitation processes. Excitation during the current pulse appears to be a combination electron impact and charge exchange. Charge exchange excites the 3d⁹5s levels of Cull while electron impact excites the other ion levels and the neutral levels. Charge exchange continues to excite the ion spectrum during the afterglow. Afterglow emission from the neutral spectrum apparently results from two types of recombination processes. The exact recombination mechanisms could not be unambiguously assigned. Emission results from the r.f. burst suggest that electron impact is the dominant excitation process. Excitation of the neutral and ion spectra are from their respective ground states. There appears to be little ionization by electron impact.To evaluate the lamp's suitability as a line source for analytical atomic spectroscopy the profile of the 324.8 nm neutral resonance line was examined during the current pulse and the r.f. burst. The profile during the current pulse is strongly dependent on radial position in the cathode bore. Near the edges of the cathode the line is severely self-reversed. The profile during the r.f. burst is uniform across the cathode bore and is affected only slightly by self-absorption.     

Dioxadispiroketal Compounds and a Potential Acyclic Precursor from Amomum aculeatum

Four new compounds having an unusual 1,7-dioxadispiro[5.1.5.2]-12-ene-11-one tricyclic ring system (1-4), their potential precursor, 5R-hydroxy-1-(4-hydroxyphenyl)-eicosan-3-one (5), and two known compounds, aculeatins A (6) and B (7), have been isolated from Amomum aculeatum. All compounds were characterized by spectroscopic methods and the configurations were established by 2D NOE correlations. Compounds 1-4, 6, and 7 showed cytotoxic activity against several human cancer cell lines.     

Constituents of the Leaves and Stem Bark of Aglaia foveolata

The previously known potent cytotoxic agent silvestrol (1) (0.002% w/w yield) and five new flavagline derivatives (2-6) were isolated from the leaves of Aglaia foveolata collected in Indonesia. The new compound 5 has an unprecedented cyclic amide moiety in its cyclopenta[b]benzopyran skeleton, while compound 6 is a novel benzo[b]oxepine derivative in which the oxepine ring is cleaved. Pyramidatine (7), a biogenetic precursor of the new flavaglines 2-6, was isolated from the leaf extract investigated. Silvestrol was also isolated from the stem bark of A. foveolata (yield of 0.02% w/w) along with a new baccharane-type triterpenoid (8). The structures of the new compounds were elucidated on the basis of their NMR and mass spectrometric data. All new compounds isolated were tested against a panel of cancer cell lines, but only compound 2 was cytotoxic (IC₅₀ range=1.4-1.8 μM), and is the first member of the cyclopenta[b]benzopyran class found to exhibit this type of activity. Compound 2 also showed significant NF-κB inhibitory activity in an Elisa assay (IC₅₀=0.37 μM).