272 research outputs found
Graphical explanation in an expert system for Space Station Freedom rack integration
The rationale and methodology used to incorporate graphics into explanations provided by an expert system for Space Station Freedom rack integration is examined. The rack integration task is typical of a class of constraint satisfaction problems for large programs where expertise from several areas is required. Graphically oriented approaches are used to explain the conclusions made by the system, the knowledge base content, and even at more abstract levels the control strategies employed by the system. The implemented architecture combines hypermedia and inference engine capabilities. The advantages of this architecture include: closer integration of user interface, explanation system, and knowledge base; the ability to embed links to deeper knowledge underlying the compiled knowledge used in the knowledge base; and allowing for more direct control of explanation depth and duration by the user. The graphical techniques employed range from simple statis presentation of schematics to dynamic creation of a series of pictures presented motion picture style. User models control the type, amount, and order of information presented
A knowledge-based approach to configuration layout, justification, and documentation
The design, development, and implementation is described of a prototype expert system which could aid designers and system engineers in the placement of racks aboard modules on Space Station Freedom. This type of problem is relevant to any program with multiple constraints and requirements demanding solutions which minimize usage of limited resources. This process is generally performed by a single, highly experienced engineer who integrates all the diverse mission requirements and limitations, and develops an overall technical solution which meets program and system requirements with minimal cost, weight, volume, power, etc. This system architect performs an intellectual integration process in which the underlying design rationale is often not fully documented. This is a situation which lends itself to an expert system solution for enhanced consistency, thoroughness, documentation, and change assessment capabilities
A Knowledge-Based Approach to Configuration Layout, Justification, and Documentation
The design, development, and implementation of a prototype expert system which could aid designers and system engineers in the placement of racks aboard modules on the Space Station Freedom are described. This type of problem is relevant to any program with multiple constraints and requirements demanding solutions which minimize usage of limited resources. This process is generally performed by a single, highly experienced engineer who integrates all the diverse mission requirements and limitations, and develops an overall technical solution which meets program and system requirements with minimal cost, weight, volume, power, etc. This system architect performs an intellectual integration process in which the underlying design rationale is often not fully documented. This is a situation which lends itself to an expert system solution for enhanced consistency, thoroughness, documentation, and change assessment capabilities
Tracing Electron-Ion Recombination in Nanoplasmas Produced by Extreme- Ultraviolet Irradiation of Rare-Gas Clusters
We investigate electron-ion recombination in nanoplasmas produced by the
ionization of rare-gas clusters with intense femtosecond extreme-ultraviolet
(XUV) pulses. The relaxation dynamics following XUV irradiation is studied
using time-delayed 790-nm pulses, revealing the generation of a large number
of excited atoms resulting from electron-ion recombination. In medium-sized
Ar-Xe clusters, these atoms are preferentially created in the Xe core within
10 ps after the cluster ionization. The ionization of excited atoms serves as
a sensitive probe for monitoring the cluster expansion dynamics up to the ns
time scale
Evolution of dopant-induced helium nanoplasmas
Two-component nanoplasmas generated by strong-field ionization of doped
helium nanodroplets are studied in a pump-probe experiment using few-cycle
laser pulses in combination with molecular dynamics simulations. High yields of
helium ions and a pronounced, droplet size-dependent resonance structure in the
pump-probe transients reveal the evolution of the dopant-induced helium
nanoplasma. The pump-probe dynamics is interpreted in terms of strong inner
ionization by the pump pulse and resonant heating by the probe pulse which
controls the final charge states detected via the frustration of electron-ion
recombination
Phase- and intensity-resolved measurements of above threshold ionization by few-cycle pulses
We investigate the carrier-envelope phase and intensity dependence of the
longitudinal momentum distribution of photoelectrons resulting from
above-threshold ionization of argon by few-cycle laser pulses. The intensity of
the pulses with a center wavelength of 750\,nm is varied in a range between
and \unit[5.5 \times 10^{14}]{W/cm^2}. Our measurements
reveal a prominent maximum in the carrier-envelope phase-dependent asymmetry at
photoelectron energies of 2\, ( being the
ponderomotive potential), that is persistent over the entire intensity range.
Further local maxima are observed at 0.3 and 0.8\,. The
experimental results are in good agreement with theoretical results obtained by
solving the three-dimensional time-dependent Schr\"{o}dinger equation (3D
TDSE). We show that for few-cycle pulses, the carrier-envelope phase-dependent
asymmetry amplitude provides a reliable measure for the peak intensity on
target. Moreover, the measured asymmetry amplitude exhibits an
intensity-dependent interference structure at low photoelectron energy, which
could be used to benchmark model potentials for complex atoms
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Attosecond streaking metrology with isolated nanotargets
The development of attosecond metrology has enabled time-resolved studies on atoms, molecules, and (nanostructured) solids. Despite a wealth of theoretical work, attosecond experiments on isolated nanotargets, such as nanoparticles, clusters, and droplets have been lacking. Only recently, attosecond streaking metrology could be extended to isolated silica nanospheres, enabling real-time measurements of the inelastic scattering time in dielectric materials. Here, we revisit these experiments and describe the single-shot analysis of velocity-map images, which permits to evaluate the recorded number of electrons. Modeling of the recorded electron histograms allows deriving the irradiated nanoparticle statistics. Theoretically, we analyze the influence of the nanoparticle size on the field-induced delay, which is one of the terms contributing to the measured streaking delay. The obtained new insight into attosecond streaking experiments on nanoparticles is expected to guide wider implementation of the approach on other types of nanoparticles, clusters, and droplets
Attosecond physics at the nanoscale
Recently two emerging areas of research, attosecond and nanoscale physics, have started to come together. Attosecond physics deals with phenomena occurring when ultrashort laser pulses, with duration on the femto- and sub-femtosecond time scales, interact with atoms, molecules or solids. The laser-induced electron dynamics occurs natively on a timescale down to a few hundred or even tens of attoseconds, which is comparable with the optical field. On the other hand, the second branch involves the manipulation and engineering of mesoscopic systems, such as solids, metals and dielectrics, with nanometric precision. Although nano-engineering is a vast and well-established research field on its own, the merger with intense laser physics is relatively recent. In this article we present a comprehensive experimental and theoretical overview of physics that takes place when short and intense laser pulses interact with nanosystems, such as metallic and dielectric nanostructures. In particular we elucidate how the spatially inhomogeneous laser induced fields at a nanometer scale modify the laser-driven electron dynamics. Consequently, this has important impact on pivotal processes such as ATI and HHG. The deep understanding of the coupled dynamics between these spatially inhomogeneous fields and matter configures a promising way to new avenues of research and applications. Thanks to the maturity that attosecond physics has reached, together with the tremendous advance in material engineering and manipulation techniques, the age of atto-nano physics has begun, but it is in the initial stage. We present thus some of the open questions, challenges and prospects for experimental confirmation of theoretical predictions, as well as experiments aimed at characterizing the induced fields and the unique electron dynamics initiated by them with high temporal and spatial resolution
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