New ion trap for atomic frequency standard applications

A novel linear ion trap that permits storage of a large number of ions with reduced susceptibility to the second-order Doppler effect caused by the radio frequency (RF) confining fields has been designed and built. This new trap should store about 20 times the number of ions a conventional RF trap stores with no corresponding increase in second-order Doppler shift from the confining field. In addition, the sensitivity of this shift to trapping parameters, i.e., RF voltage, RF frequency, and trap size, is greatly reduced

Atomic frequency standards for ultra-high-frequency stability

The general features of the Hg-199(+) trapped-ion frequency standard are outlined and compared to other atomic frequency standards, especially the hydrogen maser. The points discussed are those which make the trapped Hg-199(+) standard attractive: high line Q, reduced sensitivity to external magnetic fields, and simplicity of state selection, among others

The JPL trapped mercury ion frequency standard

In order to provide frequency standards for the Deep Space Network (DSN) which are more stable than present-day hydrogen masers, a research task was established under the Advanced Systems Program of the TDA to develop a Hg-199(+) trapped ion frequency standard. The first closed-loop operation of this kind is described. Mercury-199 ions are confined in an RF trap and are state-selected through the use of optical pumping with 194 nm UV light from a Hg-202 discharge lamp. Absorption of microwave radiation at the hyperfine frequency (40.5 GHz) is signaled by atomic fluorescence of the UV light. The frequency of a 40.5 GHz oscillator is locked to a 1.6 Hz wide atomic absorption line of the trapped ions. The measured Allan variance of this locked oscillator is currently gamma sub y (pi) = 4.4 x 10 to the minus 12th/square root of pi for 20 is less than pi is less than 320 seconds, which is better stability than the best commercial cesium standards by almost a factor of 2. This initial result was achieved without magnetic shielding and without regulation of ion number

Statistical evaluation of control inputs and eye movements in the use of instruments clusters during aircraft landing

Two different types of analyses were done on data from a study in which eye movements and other variables were recorded while four pilots executed landing sequences in a Boeing 737 simulation. Various conditions were manupulated, including changes in turbulence, starting position, and instrumentation. Control inputs were analyzed in the context of the various conditions and compared against ratings of workload obtained using the Cooper-Harper scale. A number of eye-scanning measures including mean dwell time and transition from one instrument to another were entered into a principal components factor analysis. The results show a differentiation between control inputs and eye-scanning behavior. This shows the need for improved definition of workload and experiments to uncover the important differences among control inputs, eye-scanning and cognitive processes of the pilot

Enantiomerically pure β-phenylalanine analogues from α–β-phenylalanine mixtures in a single reactive extraction step

An efficient and selective method for the extraction of α-amino acids in preference over their β-isomers using PdCl2(PPh3)2 was discovered, which enables the separation of product mixtures obtained in the enantioselective enzymatic formation of β-amino acids.

Structured multimedia authoring

We present the user interface to the CMIF authoring environment for constructing and playing multimedia presentations. The CMIF authoring environment supports a rich hypermedia document model allowing structure-based composition of multimedia presentations and the specification of synchronization constraints between constituent media items. An author constructs a multimedia presentation in terms of its structure and additional synchronization constraints, from which the CMIF player derives the precise timing information for the presentation. We discuss the advantages of a structured approach to authoring multimedia, and describe the facilities in the CMIF authoring environment for supporting this approach. The authoring environment presents three main views of a multimedia presentation: the hierarchy view is used for manipulating and viewing a presentation's hierarchical structure; the channel view is used for managing logical resources and specifying and viewing precise timing constra..

Structured Multimedia Authoring

Authoring context sensitive, interactive multimedia presentations is much more complex than authoring either purely audiovisual applications or text. Interactions among media objects need to be described as a set of spatio-temporal relationships that account for synchronous and asynchronous interactions, as well as on-demand linking behavior. This article considers the issues that need to be addressed by an authoring environment. We begin with a partitioning of concerns based on seven classes of authoring problems. We then describe a selection of multimedia authoring environments within four different authoring paradigms: structured, timeline, graph and scripting. We next provide observations and insights into the authoring process and argue that the structured paradigm provides the most useful framework for presentation authoring. We close with an example application of the structured multimedia authoring paradigm in the context of our own structure-based system GRiNS

Fragmentation pathways of nanofractal structures on surface

We present a detailed systematical theoretical analysis of the post-growth processes occurring in nanofractals grown on surface. For this study we developed a method which accounts for the internal dynamics of particles in a fractal. We demonstrate that particle diffusion and detachment controls the shape of the emerging stable islands on surface. We consider different scenarios of fractal post-growth relaxation and analyze the time evolution of the island's morphology. The results of our calculations are compared with available experimental observations, and experiments in which the post-growth relaxation of deposited nanostructures can be probed are suggested.Comment: 34 pages, 11 figure