66,113 research outputs found
Ride quality and international standard ISO 2631 (Guide for the evaluation of human exposure to whole-body vibration)
The evolution of the standard, which is aimed at promoting research and production of more data, and providing some design guidance, is outlined and its contents summarized. Some of the assumptions and information on which it is based are analyzed. Its application to vehicle ride quality is considered in the context of the safety, efficiency and comfort of crew and passengers. The importance of establishing the precise criteria against which vibration limits are required is underlined, particularly the difficulties of first defining comfort and then postulating appropriate levels. Some current and future work related to improving the standard is outlined and additional suggestions offered
NASA three-laser airborne differential absorption lidar system electronics
The system control and signal conditioning electronics of the NASA three laser airborne differential absorption lidar (DIAL) system are described. The multipurpose DIAL system was developed for the remote measurement of gas and aerosol profiles in the troposphere and lower stratosphere. A brief description and photographs of the majority of electronics units developed under this contract are presented. The precision control system; which includes a master control unit, three combined NASA laser control interface/quantel control units, and three noise pulse discriminator/pockels cell pulser units; is described in detail. The need and design considerations for precision timing and control are discussed. Calibration procedures are included
Kernel-based high-dimensional histogram estimation for visual tracking
©2008 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or distribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.Presented at the 15th IEEE International Conference on Image Processing, October 12–15, 2008, San Diego, California, U.S.A.DOI: 10.1109/ICIP.2008.4711862We propose an approach for non-rigid tracking that represents objects by their set of distribution parameters. Compared to joint histogram representations, a set of parameters such as mixed moments provides a significantly reduced size representation. The discriminating power is comparable to that of the corresponding full high dimensional histogram yet at far less spatial and computational complexity. The proposed method is robust in the presence of noise and illumination changes, and provides a natural extension to the use of mixture models. Experiments demonstrate that the proposed method outperforms both full color mean-shift and global covariance searches
Quantum Entanglement Initiated Super Raman Scattering
It has now been possible to prepare chain of ions in an entangled state and
thus question arises --- how the optical properties of a chain of entangled
ions differ from say a chain of independent particles. We investigate nonlinear
optical processes in such chains. We explicitly demonstrate the possibility of
entanglement produced super Raman scattering. Our results in contrast to
Dicke's work on superradiance are applicable to stimulated processes and are
thus free from the standard complications of multimode quantum electrodynamics.
Our results suggest the possibility of similar enhancement factors in other
nonlinear processes like four wave mixing.Comment: 4 pages, 1 figur
Semiflexible polymers under external fields confined to two dimensions
The non-equilibrium structural and dynamical properties of semiflexible
polymers confined to two dimensions are investigated by molecular dynamics
simulations. Three different scenarios are considered: The force-extension
relation of tethered polymers, the relaxation of an initially stretched
semiflexible polymer, and semiflexible polymers under shear flow. We find
quantitative agreement with theoretical predictions for the force-extension
relation and the time dependence of the entropically contracting polymer. The
semiflexible polymers under shear flow exhibit significant conformational
changes at large shear rates, where less stiff polymers are extended by the
flow, whereas rather stiff polymers are contracted. In addition, the polymers
are aligned by the flow, thereby the two-dimensional semiflexible polymers
behave similarly to flexible polymers in three dimensions. The tumbling times
display a power-law dependence at high shear rate rates with an exponent
comparable to the one of flexible polymers in three-dimensional systems.Comment: Accepted for publication in J. Chem. Phy
The visual standards for the selection and retention of astronauts, part 2
In preparation for the various studies planned for assessing visual capabilities and tasks in order to set vision standards for astronauts, the following pieces of equipment have been assembled and tested: a spectacle obstruction measuring device, a biometric glare susceptibility tester, a variable vergence amplitude testing device, an eye movement recorder, a lunar illumination simulation chamber, a night myopia testing apparatus, and retinal adaption measuring devices
The effect of extreme response and non-extreme response styles on testing measurement invariance
Extreme and non-extreme response styles (RSs) are prevalent in survey research using
Likert-type scales. Their effects on measurement invariance (MI) in the context of
confirmatory factor analysis are systematically investigated here via a Monte Carlo
simulation study. Using the parameter estimates obtained from analyzing a 2007 Trends
in International Mathematics and Science Study data set, a population model was
constructed. Original and contaminated data with one of two RSs were generated and
analyzed via multi-group confirmatory factor analysis with different constraints of MI.
The results indicated that the detrimental effects of response style on MI have been
underestimated. More specifically, these two RSs had a substantially negative impact on
both model fit and parameter recovery, suggesting that the lack of MI between groups
may have been caused by the RSs, not the measured factors of focal interest. Practical
implications are provided to help practitioners to detect RSs and determine whether RSs
are a serious threat to MI
Charge ordering induces a smectic phase in oblate ionic liquid crystals
We report a computer simulation study of an electroneutral mixture of
oppositely charged oblate ellipsoids of revolution with aspect ratio A = 1/3.
In contrast to hard or soft repulsive ellipsoids, which are purely nematic,
this system exhibits a smectic-A phase in which charges of equal sign are
counterintuitively packed in layers perpendicular to the nematic director
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