9,623 research outputs found
Performance constraints and compensation for teleoperation with delay
A classical control perspective is used to characterize performance constraints and evaluate compensation techniques for teleoperation with delay. Use of control concepts such as open and closed loop performance, stability, and bandwidth yield insight to the delay problem. Teleoperator performance constraints are viewed as an open loop time delay lag and as a delay-induced closed loop bandwidth constraint. These constraints are illustrated with a simple analytical tracking example which is corroborated by a real time, 'man-in-the-loop' tracking experiment. The experiment also provides insight to those controller characteristics which are unique to a human operator. Predictive displays and feedforward commands are shown to provide open loop compensation for delay lag. Low pass filtering of telemetry or feedback signals is interpreted as closed loop compensation used to maintain a sufficiently low bandwidth for stability. A new closed loop compensation approach is proposed that uses a reactive (or force feedback) hand controller to restrict system bandwidth by impeding operator inputs
Adaptive Bayesian decision feedback equalizer for dispersive mobile radio channels
The paper investigates adaptive equalization of time dispersive mobile ratio fading channels and develops a robust high performance Bayesian decision feedback equalizer (DFE). The characteristics and implementation aspects of this Bayesian DFE are analyzed, and its performance is compared with those of the conventional symbol or fractional spaced DFE and the maximum likelihood sequence estimator (MLSE). In terms of computational complexity, the adaptive Bayesian DFE is slightly more complex than the conventional DFE but is much simpler than the adaptive MLSE. In terms of error rate in symbol detection, the adaptive Bayesian DFE outperforms the conventional DFE dramatically. Moreover, for severely fading multipath channels, the adaptive MLSE exhibits significant degradation from the theoretical optimal performance and becomes inferior to the adaptive Bayesian DFE
K-shell x-ray spectroscopy of atomic nitrogen
Absolute {\it K}-shell photoionization cross sections for atomic nitrogen
have been obtained from both experiment and state-of-the-art theoretical
techniques. Due to the difficulty of creating a target of neutral atomic
nitrogen, no high-resolution {\it K}-edge spectroscopy measurements have been
reported for this important atom. Interplay between theory and experiment
enabled identification and characterization of the strong
resonance features throughout the threshold region. An experimental value
of 409.64 0.02 eV was determined for the {\it K}-shell binding energy.Comment: 4 pages, 2 graphs, 1 tabl
Fatigue of notched fiber composite laminates. Part 2: Analytical and experimental evaluation
The analytical/experimental correlation study was performed to develop an understanding of the behavior of notched Boron/epoxy laminates subjected to tension/tension fatigue loading. It is postulated that the fatigue induced property changes (stiffness as well as strength) of the laminate can be obtained from the lamina fatigue properties. To that end, the Boron/epoxy lamina static and fatigue data (lifetime, residual stiffness and strength) were obtained initially. The longitudinal and transverse tension data were determined from the (0) and (90) laminate tests while the in-plane shear data were obtained from the (+ or - 45) sub s laminates. The static tests obtained the notched strength and mode of failure while the fatigue tests determined lifetime, damage propagation and residual strength. The failure in static tension occurred in a transverse crack propagation mode
Fatigue of notched fiber composite laminates. Part 1: Analytical model
A description is given of a semi-empirical, deterministic analysis for prediction and correlation of fatigue crack growth, residual strength, and fatigue lifetime for fiber composite laminates containing notches (holes). The failure model used for the analysis is based upon composite heterogeneous behavior and experimentally observed failure modes under both static and fatigue loading. The analysis is consistent with the wearout philosophy. Axial cracking and transverse cracking failure modes are treated together in the analysis. Cracking off-axis is handled by making a modification to the axial cracking analysis. The analysis predicts notched laminate failure from unidirectional material fatique properties using constant strain laminate analysis techniques. For multidirectional laminates, it is necessary to know lamina fatique behavior under axial normal stress, transverse normal stress and axial shear stress. Examples of the analysis method are given
Potentiating effect of heparin in the activation of procollagenase by a low-Mr angiogenesis factor
AbstractA low-Mr freely dialysable endothelial cell-stimulating angiogenesis factor (ESAF) from conditioned medium of a mouse lymphoma cell line has previously been shown to activate latent skin fibroblast procollagenase. Activation comparable with the maximum that can be achieved with trypsin is obtained with chemically undetectable amounts of the factor. We now show that when even smaller amounts of ESAF are used heparin is able to potentiate its action in this system. The relationship between this activity and the mechanism of angiogenesis, which is itself potentiated by heparin, is discussed
Photoionization of tungsten ions: experiment and theory for W
Experimental and theoretical results are reported for single-photon single
ionization of the tungsten ion W. Absolute cross sections have been
measured employing the photon-ion merged-beams setup at the Advanced Light
Source in Berkeley. Detailed photon-energy scans were performed at 200~meV
bandwidth in the 40 -- 105~eV range. Theoretical results have been obtained
from a Dirac-Coulomb R-matrix approach employing basis sets of 730 levels for
the photoionization of W. Calculations were carried out for the
, =2, ground level and the
associated fine-structure levels with =3 and 4 for the W ions. In
addition, cross sections have been calculated for the metastable levels
. Very satisfying agreement of theory and experiment is
found for the photoionization cross section of W which is remarkable
given the complexity of the electronic structure of tungsten ions in low charge
states.Comment: 15 pages, 3 figures, to appear in the Journal of Physics B: Atomic,
Molecular and Optical Physic
Fission Cycling in Supernova Nucleosynthesis: Active-Sterile Neutrino Oscillations
We investigate nucleosynthesis in the supernovae post-core bounce
neutrino-driven wind environment in the presence of active-sterile neutrino
transformation. We consider active-sterile neutrino oscillations for a range of
mixing parameters: vacuum mass-squared differences of 0.1 eV^2 < dm^2 < 100
eV^2, and vacuum mixing angles of sin^2(2 theta_v) > 10^-4. We find a
consistent r-process pattern for a large range of mixing parameters that is in
rough agreement with the halo star CS 22892-052 abundances and the pattern
shape is determined by fission cycling. We find that the allowed region for the
formation of the r-process peaks overlaps the LSND and NSBL (3+1) allowed
region.Comment: 11 pages, 7 figures, Corrected Typo
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