Application of Ion Cyclotron Resonance to the Study of Inelastic Excitation by Low-Energy Electrons

The geometry of the resonance cell employed for ion cyclotron resonance spectroscopy (1-3) is ideally suited for studying inelastic excitation by low-energy electrons. It has been shown that the electron beam traverses a parabolic potential well between the trapping electrodes, the depth of which is approximately half the applied trapping voltage (3,4). Low-energy electrons generated by impact excitation of an atomic or molecular energy level can be trapped in the resonance cell if their final translational energy is insufficient to escape the preset depth of the potential well. These electrons can be drifted from the source of the resonance region by applying the usual static drift field E normal to the primary magnetic field H (4). The electron drift velocity in this crossed field geometry, given by cE/H, is independent of both charge and mass. For typical values of E and H the drift velocity is in the range of 10^1-10^3 cm/sec. In the lower range of accessible drift velocities, the residence time of electrons in the resonance cell approaches 0.1 sec

Ion molecule reactions in vinyl fluoride by photoionization. Effects of vibrational excitation on major reaction pathways

Photoionization methods have been used to study the reactions of the molecular ion in vinyl fluoride to yield the ionic products C_3H_3F_2^+, C_3H_4F^+, and C_3H_5^+. Quantitative measurements are reported of the effect of the vibrational state of the reactant ion on the product distribution and overall reaction cross section. Reaction cross sections for all three channels decrease with reactant internal energy. The effect on the reaction pathway producing C_3H_3F_2^+ is especially pronounced, with 0.18 eV of vibrational excitation being sufficient to reduce the reaction probability by 75%. Deactivation of vibrationally excited reactant ions competes with the reaction and is shown to be an efficient process

Evaporation and Discharge Dynamics of Highly Charged Multicomponent Droplets Generated by Electrospray Ionization

We investigate the Rayleigh discharge and evaporation dynamics of highly charged two-component droplets consisting principally of methanol with 2-methoxyethanol, tert-butanol, or m-nitrobenzyl alcohol. A phase Doppler anemometer (PDA) characterizes droplets generated by electrospray ionization (ESI) according to size, velocity, and charge as they move through a uniform electric field within an ion mobility spectrometer (IMS). Repeated field reversals result in droplet “ping-pong” through the PDA. This generates individual droplet histories of solvent evaporation behavior and the dynamics of charge loss to progeny droplets during Rayleigh discharge events. On average, methanol droplets discharge at 127% their Rayleigh limit of charge, q_R, and release 25% of the net charge. Charge loss from methanol/2-methoxyethanol droplets behaves similarly to pure 2-methoxyethanol droplets which release ~28% of their net charge. Binary methanol droplets containing up to 50% tert-butanol discharge at a lower percent q_R than pure methanol and release a greater fraction of their net charge. Mixed 99% methanol/1% m-nitrobenzyl alcohol droplets possess discharge characteristics similar to those of methanol. However, droplets of methanol containing 2% m-nitrobenzyl evaporate down to a fixed size and charge that remains constant with no observable discharges. Quasi-steady-state evaporation models accurately describe observed evaporation phenomena in which methanol/tert-butanol droplets evaporate at a rate similar to that of pure methanol and methanol/2-methoxyethanol droplets evaporate at a rate similar to that of 2-methoxyethanol. We compare these results to previous Rayleigh discharge experiments and discuss the implications for binary solvents in electrospray mass spectrometry (ESI-MS) and field-induced droplet ionization mass spectrometry (FIDI-MS)

Simultaneous estimation by partial totals for compartmental models

Simultaneous estimation procedure for parameters in multiple equation regression mode

Spearman simultaneous estimation for a compartmental model Technical report no. 9

Compartmental model, represented as system of linear combination of exponentials with common exponential parameters, for tracer experiment

Dustbuster: a compact impact-ionization time-of-flight mass spectrometer for in situ analysis of cosmic dust

We report on the design and testing of a compact impact-ionization time-of-flight mass spectrometer for analysis of cosmic dust, suitable for use on deep space missions. The instrument, Dustbuster, incorporates a large target area with a reflectron, simultaneously optimizing mass resolution, particle detection, and ion collection. Dust particles hit the 65-cm2 target plate and are partially ionized by the impact. The resulting ions, with broad energy and angular distributions, are accelerated through a modified reflectron, focusing ions of specific m/z in space and time to produce high-resolution mass spectra. The cylindrically symmetric instrument is 10 cm in diameter and 20 cm in length, considerably smaller than previous in situ dust analyzers, and can be easily scaled as needed for specific mission requirements. Laser desorption ionization of metal and mineral samples embedded in the impact plate simulated particle impacts for evaluations of instrument performance. Mass resolution in these experiments ranged from 60–180, permitting resolution of isotopes. The mass spectrometer can be combined with other instrument components to determine dust particle trajectories and sizes

Research and Teacher Education: The BERA-RSA inquiry. Policy and Practice within the United Kingdom.

Across the four jurisdictions of the United Kingdom (England, Northern Ireland, Scotland and Wales) initial teacher education (ITE) is under active development, with its content, location, control and quality often the focuses of sustained debate. Statutory and professional requirements for the sector inevitably reflect differing assumptions about teaching, teacher knowledge and governance. In exploring ITE across the four jurisdictions, this paper reviews policies and practices through two major focuses: first, the relationships between the declared teacher standards (competencies/competences) and research-informed teacher education provision; second, the ‘turn or (re)turn to the practical’ in teacher education, including policy declarations, changes in practices, and emphases and effects of the discourse(s) of relevance

User community development for the space transportation system/Skylab

The New User Function plan for identifying beneficial uses of space is described. Critical issues such as funding, manpower, and protection of user proprietary rights are discussed along with common barriers which impede the development of a user community. Studies for developing methodologies of identifying new users and uses of the space transportation system are included

First principles determination of the Peierls stress of the shuffle screw dislocation in silicon

The Peierls stress of the a/2 screw dislocation belonging to the shuffle set is calculated for silicon using density functional theory. We have checked the effect of boundary conditions by using two models, the supercell method where one considers a periodic array of dislocations, and the cluster method where a single dislocation is embedded in a small cluster. The Peierls stress is underestimated with the supercell and overestimated with the cluster. These contributions have been calculated and the Peierls stress is determined in the range between 2.4 x 10-2 and 2.8 x 10-2 eV {\AA}-3. When moving, the dislocation follows the {111} plane going through a low energy metastable configuration and never follows the 100 plane, which includes a higher energy metastable core configuration