31,290 research outputs found
Influence of blade aerodynamic model on prediction of helicopter rotor aeroacoustic signatures
Brownâs vorticity transport model has been used to investigate how the local blade aerodynamic model influences the quality of the prediction of the high-frequency airloads associated with bladeâvortex interactions, and thus the accuracy with which the acoustic signature of a helicopter rotor can be predicted. The vorticity transport model can accurately resolve the structure of the wake of the rotor and allows significant flexibility in the way that the blade loading can be represented. The Second Higher-Harmonic Control Aeroacoustics Rotor Test was initiated to provide experimental insight into the acoustic signature of a rotor in cases of strong bladeâvortex interaction. Predictions of two models for the local blade aerodynamics are compared with the test data. A marked improvement in accuracy of the predicted high-frequency airloads and acoustic signature is obtained when a lifting-chord model for the blade aerodynamics is used instead of a lifting-line-type approach. Errors in the amplitude and phase of the acoustic peaks are reduced, and the quality of the prediction is affected to a lesser extent by the computational resolution of the wake, with the lifting-chord model producing the best representation of the distribution of sound pressure below the rotor
Detection of Minimal Supersymmetric Model Higgs Bosons in \gam\gam Collisions: Influence of SUSY Decay Modes
We demonstrate that supersymmetric decay modes of the neutral Higgs bosons of
the MSSM could well make their detection extremely difficult when produced
singly in \gam\gam collisions at a back-scattered laser beam facility.Comment: 12 pages, requires phyzzx.tex and tables.tex, full postscript file
including embedded tables available via anonymous ftp at ucdhep.ucdavis.edu
as [anonymous.gunion]gamgamsusy.ps, preprint UCD-94-3
The Boltzmann Equation in Scalar Field Theory
We derive the classical transport equation, in scalar field theory with a
V(phi) interaction, from the equation of motion for the quantum field. We
obtain a very simple, but iterative, expression for the effective action which
generates all the n-point Green functions in the high-temperature limit. An
explicit closed form is given in the static case.Comment: 10 pages, using RevTeX (corrected TeX misprints
RCM-SLAM: Visual localisation and mapping under remote centre of motion constraints
In robotic surgery the motion of instruments
and the laparoscopic camera is constrained by their insertion
ports, i. e. a remote centre of motion (RCM). We propose a
Simultaneous Localisation and Mapping (SLAM) approach that
estimates laparoscopic camera motion under RCM constraints.
To achieve this we derive a minimal solver for the absolute
camera pose given two 2D-3D point correspondences (RCMPnP) and also a bundle adjustment optimiser that refines
camera poses within an RCM-constrained parameterisation.
These two methods are used together with previous work on
relative pose estimation under RCM [1] to assemble a SLAM
pipeline suitable for robotic surgery. Our simulations show that
RCM-PnP outperforms conventional PnP for a wide noise range
in the RCM position. Results with video footage from a robotic
prostatectomy show that RCM constraints significantly improve
camera pose estimatio
RCM-SLAM: Visual localisation and mapping under remote centre of motion constraints
In robotic surgery the motion of instruments and the laparoscopic camera is constrained by their insertion ports, i. e. a remote centre of motion (RCM). We propose a Simultaneous Localisation and Mapping (SLAM) approach that estimates laparoscopic camera motion under RCM constraints. To achieve this we derive a minimal solver for the absolute camera pose given two 2D-3D point correspondences (RCM-PnP) and also a bundle adjustment optimiser that refines camera poses within an RCM-constrained parameterisation. These two methods are used together with previous work on relative pose estimation under RCM [1] to assemble a SLAM pipeline suitable for robotic surgery. Our simulations show that RCM-PnP outperforms conventional PnP for a wide noise range in the RCM position. Results with video footage from a robotic prostatectomy show that RCM constraints significantly improve camera pose estimation
Measuring longitudinal amplitudes for electroproduction of pseudoscalar mesons using recoil polarization in parallel kinematics
We propose a new method for measuring longitudinal amplitudes for
electroproduction of pseudoscalar mesons that exploits a symmetry relation for
polarization observables in parallel kinematics. This polarization technique
does not require variation of electron scattering kinematics and avoids the
major sources of systematic errors in Rosenbluth separation.Comment: intended for Phys. Rev. C as a Brief Repor
Millimeter wave satellite concepts. Volume 1: Executive summary
The objectives of the program were: (1) development of methodology based on the technical requirements of potential services that might be assigned to millimeter wave bands for identifying the viable and appropriate technologies for future NASA millimeter research and development programs, and (2) testing of this methodology with user applications and services. The scope of the program included the entire communications network, both ground and space subsystems. The reports include: (1) cost, weight, and performance models for the subsystems, (2) conceptual design for point-to-point and broadcast communications satellites, (3) analytic relationships between subsystem parameters and an overall link performance, (4) baseline conceptual systems, (5) sensitivity studies, (6) model adjustment analyses, (7) identification of critical technologies and their risks, (8) brief R&D program scenarios for the technologies judged to be moderate or extensive risks
Synthesis and antibacterial effects of cobaltâcellulose magnetic nanocomposites
© The Royal Society of Chemistry. Green synthesis is employed to prepare cobalt/cellulose nanocomposites with cubic (α-cobalt) cobalt as a main component with antibacterial and magnetic properties. An in situ reduction of aqueous solutions of cobalt ions on a model cellulose substrate surface using hydrogen gas affords spherical, cellulose-stabilised cobalt nanoclusters with magnetic properties and an average diameter of 7 nm that are distributed evenly over the surface of the cellulose fibres. These cobalt/cellulose nanocomposites exhibit good antibacterial action against opportunistic pathogens both Gram-positive (S. aureus) and Gram-negative (E. coli, A. baumannii and P. aeruginosa), with zones of inhibition up to 15 mm, thereby encouraging the deployment of these advanced materials for the treatment of wastewater or within medical dressings. This method of preparation is compared with the analogous in situ reduction of cobalt ions on a cellulose surface using sodium borohydride as reducing agent
Long period polytype boundaries in silicon carbide
A significant gap in our understanding of polytypism exists, caused partly by the lack of experimental data on the spatial distribution of polytype coalescence and knowledge of the regions between adjoining polytypes. Few observations, Takei & Francombe (1967) apart, of the relative location of different polytypes have been reported. A phenomenological description of the boundaries, exact position of one-dimensional disorder (1DD) and long period polytypes (LPPâs) has been made possible by synchrotron X-ray diffraction topography (XRDT)
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