178,231 research outputs found
Recommended from our members
The optimisation of shot peen forming processes
An optimisation method based on an effective process model is presented. The calibrated and verified process model simulates peening on realistic components and provides a non-linear relationship between peening parameters and deflections. An optimal solution can be found by minimising the deviation of the computed deformed shape from the desired shape subject to certain constraints. This optimal solution of peening parameters can be directly used for practical operations. An optimisation example for forming a cylindrical shape on a 76x76x3 mm sample is provided. The experimental results demonstrate the applicability of the present optimisation method
Quantum Holonomies for Quantum Computing
Holonomic Quantum Computation (HQC) is an all-geometrical approach to quantum
information processing. In the HQC strategy information is encoded in
degenerate eigen-spaces of a parametric family of Hamiltonians. The
computational network of unitary quantum gates is realized by driving
adiabatically the Hamiltonian parameters along loops in a control manifold. By
properly designing such loops the non-trivial curvature of the underlying
bundle geometry gives rise to unitary transformations i.e., holonomies that
implement the desired unitary transformations. Conditions necessary for
universal QC are stated in terms of the curvature associated to the non-abelian
gauge potential (connection) over the control manifold. In view of their
geometrical nature the holonomic gates are robust against several kind of
perturbations and imperfections. This fact along with the adiabatic fashion in
which gates are performed makes in principle HQC an appealing way towards
universal fault-tolerant QC.Comment: 16 pages, 2 figures, REVTE
Precise near-earth navigation with GPS: A survey of techniques
The tracking accuracy of the low earth orbiters (below about 3000 km altitude) can be brought below 10 cm with a variety of differential techniques that exploit the Global Positioning System (GPS). All of these techniques require a precisely known global network of GPS ground receivers and a receiver aboard the user satellite, and all simultaneously estimate the user and GPS satellite orbits. Three basic approaches are the geometric, dynamic, and nondynamic strategies. The last combines dynamic GPS solutions with a geometric user solution. Two powerful extensions of the nondynamic strategy show considerable promise. The first uses an optimized synthesis of dynamics and geometry in the user solution, while the second uses a novel gravity-adjustment method to exploit data from repeat ground tracks. These techniques will offer sub-decimeter accuracy for dynamically unpredictable satellites down to the lowesst possible altitudes
Review study and evaluation of possible flight experiments relating to cloud physics experiments in space
The general objectives of the Zero-Gravity Atmospheric Cloud Physics Laboratory Program are to improve the level of knowledge in atmospheric cloud research by placing at the disposal of the terrestrial-bound atmospheric cloud physicist a laboratory that can be operated in the environment of zero-gravity or near zero-gravity. This laboratory will allow studies to be performed without mechanical, aerodynamic, electrical, or other techniques to support the object under study. The inhouse analysis of the Skylab 3 and 4 experiments in dynamics of oscillations, rotations, collisions and coalescence of water droplets under low gravity-environment is presented
Phased models for evaluating the performability of computing systems
A phase-by-phase modelling technique is introduced to evaluate a fault tolerant system's ability to execute different sets of computational tasks during different phases of the control process. Intraphase processes are allowed to differ from phase to phase. The probabilities of interphase state transitions are specified by interphase transition matrices. Based on constraints imposed on the intraphase and interphase transition probabilities, various iterative solution methods are developed for calculating system performability
A theoretical model of the wave particle interaction of plasma in space
A theoretical model, based on the kinetic theory for the perturbation of plasma in the magnetosphere, is proposed to study the observed disturbances which are caused by both natural and artificial sources that generate wave-like perturbations propagating around the globe. The proposed model covers the wave propagation through a media of transitional (from collisional to collisionless) fully ionized magnetoactive plasma. A systematic formulation of the problem is presented and the method of solution for the transitional model of magnetosphere is discussed. The possible emission of hydromagnetic waves in the magnetosphere during the quiet and disturbed time are also discussed
Multifluids description of dynamics of upper atmosphere
A multifluids model to investigate ionospheric dynamics was established on kinetic theory. Its resultant equations are used to examine the following dynamic problems in the gamma region of 80-2000 Km of the ionosphere: (1) propagation of acoustic modes in the 500-2,000 Km of the ionosphere (two fluid model); (2) the relation between the cross field plasma drift instabilities and type I and type II ionospheric irregularities; and (3) time dependent neutral wind structure and horizontal pressure gradient
Crystal orientation and thickness dependence of superconductivity on tetragonal FeSe1-x thin films
Superconductivity was recently found in the simple tetragonal FeSe structure.
Recent studies suggest that FeSe is unconventional, with the symmetry of the
superconducting pairing state still under debate. To tackle these problems,
clean single crystals and thin films are required. Here we report the
fabrication of superconducting beta-phase FeSe1-x thin films on different
substrates using a pulsed laser deposition (PLD) technique. Quite
interestingly, the crystal orientation, and thus, superconductivity in these
thin films is sensitive to the growth temperature. At 320C, films grow
preferably along c-axis, but the onset of superconductivity depends on film
thickness. At 500C, films grow along (101), with little thickness dependence.
These results suggest that the low temperature structural deformation
previously found is crucial to the superconductivity of this material
- …