ALBERT

Notes: Developments in the tokamak fusion test reactor (TFTR) data-management system supporting data acquisition and off-line physics data reduction are described. Data from monitor points, timing channels, transient recorder channels, and other devices are acquired and stored for use by on-line tasks. Files are transferred off line automatically. A configuration utility determines data acquired and files transferred. An event system driven by file arrival activates off-line reduction processes. A post-run process transfers files not shipped during runs. Files are archived to tape and are retrievable by digraph and shot number. Automatic skimming based on most recent access, file type, shot numbers, and user-set protections maintains the files required for post-run data reduction.

Notes: The nf Rydberg levels of 14N2 converging to the X 2Σ+g ground state of N+2 have been studied from n=4–9 in the high-resolution absorption spectra of supersonically expanding nitrogen at wavelengths ranging from 843.2 to 802.6 A(ring) (118 600–124 600 cm−1). The best experimental results, achieving rotational temperatures on the order of 20 to 40 K and a resolution of 0.5 cm−1, were obtained by photographing the jet absorption against the background continuum from a synchrotron radiation source. Complementary data for 14N2 and 15N2 come from the analyses of spectra recorded under equilibrium conditions at 70 K with a resolution of 1 cm−1, using the He continuum as background source. The observations are interpreted with the help of multichannel quantum defect calculations and lead to the conclusion that, to varying degrees and with the exception of 4f(v=0), all the complexes studied here show the effects of interactions with core excited d and s Rydberg levels built on the A 2Πu first excited state of N+2. Also, the 9f(v=0) complex is shown to be perturbed by 10p(v=0), and the strength of the p–f interaction has been determined.

Notes: A fast low-cost device to detect the phase shift between the excitation and the response of a cantilever in tapping-mode atomic force microscopy is described. For cantilever signals with a good signal to noise ratio, as is commonly found, the device presented can replace a lock-in amplifier. The setup is based on indirect time measurements realized by a combination of commonly used analog and digital integrated circuits. Phase measurement can already be achieved within one cycle. Signal output rates up to 100 kHz allow the use of the phase shift as an auxiliary imaging channel. Cantilever frequencies may range from 6 to more than 500 kHz. The principle of the setup is illustrated together with technical data. Images of a hydrophobic–hydrophilic structured silicon surface obtained in air and of purple membrane obtained in fluid are presented. © 1999 American Institute of Physics.

Notes: A theoretical study is made of dislocation pipe self-diffusion in an fcc crystal for three differing dislocation structures to ascertain the correlation factor, diffusivity, and mobility in an electric field. The three structures may be described as a pure edge dislocation with the usual Burgers vector b=a/2[110]. The other two are mixed dislocations with b=a[01¯0] and either a line sense of ξ=a[100] or ξ=a[101]. The latter two are similar to an edge-type dislocation and are formed by the removal of one-half of a (010) plane of atoms whose edge follows these directions. It is found that very little difference exists in the transport processes in these three structures. Thus, although the latter two dislocations have a major screw character in the sense of a mixed dislocation, the transport is dominated by the edge character which in turn is controlled by the binding energy of the vacancy to the core. Additionally, the ratio of the mobility to diffusivity in an electric field is proportional to the reciprocal of the correlation factor as found in the past for other self-diffusion situations, and these authors conclude that such a result is an unprovable axiom of correlated crystalline transport.

Notes: The conceptual design of the data handling system for the Compact Ignition Tokamak (CIT) takes advantage of the recent and upcoming advances in the technologies of database management systems, workstations, networking, and front-end processing. The software configuration of a diagnostic's front-end signal conditioning, data acquisition, and data reduction by means of filling in tables and specifying "objects'' for the data transformations will provide a more powerful tool for efficient application "programming.'' The maintenance of an audit trail of chains of transformations (input data and processes) will permit identification and recalculation of results which are affected by modifications of calibrations and processing.

Notes: Relaxation phenomena associated with ion transport through planar bimolecular lipid membranes may be studied by measurement of current transients which are induced by a temperature jump. The T jump is obtained by absorption of an IR-light pulse from a Nd-glass laser by the membrane and its aqueous environment. The apparatus described allows the detection of characteristic time constants between approximately 10 μs and several seconds. Processes can be resolved if the underlying change of enthalpy exceeds 1 kcal/mol.

Notes: The application of nanosecond voltage pulses to weakly ionized atmospheric pressure plasmas allows heating the electrons without considerably increasing the gas temperature, provided that the duration of the pulses is less than the critical time for the development of glow-to-arc transitions. The shift in the electron energy distribution towards higher energies causes a temporary increase in the ionization rate, and consequently a strong rise in electron density. This increase in electron density is reflected in an increased decay time of the plasma after the pulse application. Experiments in atmospheric pressure air glow discharges with gas temperatures of approximately 2000 K have been performed to explore the electron heating effect. Measurements of the temporal development of the voltage across the discharge and the optical emission in the visible after applying a 10 ns high voltage pulse to a weakly ionized steady state plasma demonstrated increasing plasma decay times from tens of nanoseconds to microseconds when the pulsed electric field was raised from 10 to 40 kV/cm. Temporally resolved photographs of the discharge have shown that the plasma column expands during this process. The nonlinear electron heating effect can be used to reduce the power consumption in a repetitively operated air plasma considerably compared to a dc plasma operation. Besides allowing power reduction, pulsed electron heating also has the potential to enhance plasma processes, which require elevated electron energies, such as excimer generation for ultraviolet lamps. © 2001 American Institute of Physics.

Notes: In this letter we report quantum mechanical integral and differential cross sections for the title reactions as calculated on a new ab initio potential energy surface. The calculations, all carried out in the reagents arrangement channel employing negative imaginary potentials, were done within the coupled-states approximation. The final vibrational state-to-state differential and integral cross sections were compared with experiment. Altogether, a very encouraging agreement was obtained. © 1996 American Institute of Physics.

Notes: Quantum mechanical integral and differential cross sections have been calculated for the title reaction at the three collision energies studied in the 1985 molecular beam experiment of Lee and co-workers, using the new ab initio potential energy surface of Stark and Werner (preceding paper). Although the overall agreement between the calculated and experimental center-of-mass frame angular distributions is satisfactory, there are still some noticeable differences. In particular, the forward scattering of HF(v′=3) is more pronounced in the present calculations than it is in the experiment and the calculations also predict some forward scattering of HF(v′=2). A comparison with the quasiclassical trajectory results of Aoiz and co-workers on the same potential energy surface shows that the forward scattering is largely a quantum mechanical effect in both cases, being dominated by high orbital angular momenta in the tunneling region where the combined centrifugal and potential energy barrier prevents classical trajectories from reacting. The possible role of a reactive scattering resonance in contributing to the quantum mechanical forward scattering is also discussed in some detail. © 1996 American Institute of Physics.

Notes: A three dimensional potential energy surface for the F+H2→HF+H reaction has been computed using the internally contracted multireference configuration interaction (MRCI) method with complete active space self-consistent field (CASSCF) reference functions and a very large basis set. Calibration calculations have been performed using the triple-zeta plus polarization basis set employed in previous nine-electron full CI (FCI) calculations of Knowles, Stark, and Werner [Chem. Phys. Lett. 185, 555 (1991)]. While all variational MRCI wave functions yield considerably larger barrier heights than the FCI, excellent agreement with the FCI barrier height and the exothermicity was obtained when the Davidson correction was applied (MRCI+Q). The convergence of the barrier height and exothermicity, spectroscopic constants of the HF and H2 fragments, and the electron affinity of the fluorine atom with respect to the basis set has been carefully tested. Using the largest basis sets, which included 5d, 4f, 3g, and 2h functions on fluorine, a linear barrier height of 1.84 kcal/mol and an exothermicity of 31.77 kcal/mol (exp. 31.73 kcal/mol) was obtained. The true saddle point has a bent structure and the barrier height is predicted to be (1.45±0.25) kcal/mol. About 700 points on the three-dimensional potential energy surface have been computed using a slightly smaller basis set, which yield F–HH barrier heights of 1.92 kcal/mol (linear), 1.54 kcal/mol (bent), and an exothermicity of 31.3 kcal/mol. The barrier height for the H+FH→HF+H exchange reaction is predicted to be 41.2 kcal/mol. In the entrance channel cuts through the three potentials correlating with F(2P3/2,1/2)+H2(1Σ+g) have been computed, and the effect of spin–orbit coupling is investigated. It is found that the spin–orbit coupling increases the barrier height relative to the asymptotic F(2P3/2)+H2(1Σ+g) ground state by about 0.35 kcal/mol, leading to final estimates for the effective collinear and bent barriers of (2.18±0.25) kcal/mol and (1.80±0.25) kcal/mol, respectively. An accurate global analytical fit of the potential (without the effect of spin–orbit coupling) has been obtained using the method of Aguado and Paniagua. Our new ab initio potential is compared to various potentials used so far in dynamics calculations for the F+H2 reaction. © 1996 American Institute of Physics.