224,160 research outputs found
Motion of a sphere in the presence of a plane interface. Part 2. An exact solution in bipolar co-ordinates
A general solution for Stokes’ equation in bipolar co-ordinates is derived, and then applied to the arbitrary motion of a sphere in the presence of a plane fluid/fluid interface. The drag force and hydrodynamic torque on the sphere are then calculated for four specific motions of the sphere; namely, translation perpendicular and parallel to the interface and rotation about an axis which is perpendicular and parallel, respectively, to the interface. The most significant result of the present work is the comparison between these numerically exact solutions and the approximate solutions from part 1. The latter can be generalized to a variety of particle shapes, and it is thus important to assess their accuracy for this case of spherical particles where an exact solution can be obtained. In addition to comparisons with the approximate solutions, we also examine the predicted changes in the velocity, pressure and vorticity fields due to the presence of the plane interface. One particularly interesting feature of the solutions is the fact that the direction of rotation of a freely suspended sphere moving parallel to the interface can either be the same as for a sphere rolling along the interface (as might be intuitively expected), or opposite depending upon the location of the sphere centre and the ratio of viscosities for the two fluids
Response analysis of an automobile shipping container
The design and development of automobile shipping containers to reduce enroute damage are discussed. Vibration tests were conducted to determine the system structural integrity. A dynamic analysis was made using NASTRAN and the results of the test and the analysis are compared
The creeping motion of a spherical particle normal to a deformable interface
Numerical results are presented for the approach of a rigid sphere normal to a deformable fluid-fluid interface in the velocity range for which inertial effects may be neglected. Both the case of a sphere moving with constant velocity, and that of a sphere moving under the action of a constant non-hydrodynamic body force are considered for several values of the viscosity ratio, density difference and interfacial tension between the two fluids. Two distinct modes of interface deformation are demonstrated: a film drainage mode in which fluid drains away in front of the sphere leaving an ever-thinning film, and a tailing mode where the sphere passes several radii beyond the plane of the initially undeformed interface, while remaining encapsulated by the original surrounding fluid which is connected with its main body by a thin thread-like tail behind the sphere. We consider the influence of the viscosity ratio, density difference, interfacial tension and starting position of the sphere in deter-mining which of these two modes of deformation will occur
Inverse Modelling to Obtain Head Movement Controller Signal
Experimentally obtained dynamics of time-optimal, horizontal head rotations have previously been simulated by a sixth order, nonlinear model driven by rectangular control signals. Electromyography (EMG) recordings have spects which differ in detail from the theoretical rectangular pulsed control signal. Control signals for time-optimal as well as sub-optimal horizontal head rotations were obtained by means of an inverse modelling procedures. With experimentally measured dynamical data serving as the input, this procedure inverts the model to produce the neurological control signals driving muscles and plant. The relationships between these controller signals, and EMG records should contribute to the understanding of the neurological control of movements
Giant Shapiro Resonances in a Flux Driven Josephson Junction Necklace
We present a detailed study of the dynamic response of a ring of equally
spaced Josephson junctions to a time-periodic external flux, including
screening current effects. The dynamics are described by the resistively
shunted Josephson junction model, appropriate for proximity effect junctions,
and we include Faraday's law for the flux. We find that the time-averaged
characteristics show novel {\em subharmonic giant Shapiro voltage resonances},
which strongly depend on having phase slips or not, on , on the inductance
and on the external drive frequency. We include an estimate of the possible
experimental parameters needed to observe these quantized voltage spikes.Comment: 8 pages RevTeX, 3 figures available upon reques
Reduction of blocking artifacts in both spatial domain and transformed domain
In this paper, we propose a bi-domain technique to reduce the blocking artifacts commonly incurred in image processing. Some pixels are sampled in the shifted image block and some high frequency components of the corresponding transformed block are discarded. By solving for the remaining unknown pixel values and the transformed coefficients, a less blocky image is obtained. Simulation results using the Discrete Cosine Transform and the Slant Transform show that the proposed algorithm gives a better quantitative result and image quality than that of the existing methods
On the Correct Convergence of Complex Langevin Simulations for Polynomial Actions
There are problems in physics and particularly in field theory which are
defined by complex valued weight functions where is a polynomial
action . The conditions under which a convergent complex
Langevin calculation correctly simulates such integrals are discussed. All
conditions on the process which are used to prove proper convergence are
defined in the stationary limit.Comment: 8 pages, LaTeX file, preprint UNIGRAZ-UTP 29-09-9
Dynamical renormalization group approach to the Altarelli-Parisi-Lipatov equations
The Altarelli-Parisi-Lipatov equations for the parton distribution functions
are rederived using the dynamical renormalization group approach to quantum
kinetics. This method systematically treats the ln Q^2 corrections that arises
in perturbation theory as a renormalization of the parton distribution function
and unambiguously indicates that the strong coupling must be allowed to run
with the scale in the evolution kernel. To leading logarithmic accuracy the
evolution equation is Markovian and the logarithmic divergences in the
perturbative expansion are identified with the secular divergences (terms that
grow in time) that emerge in a perturbative treatment of the kinetic equations
in nonequilibrium systems. The resummation of the leading logarithms by the
Altarelli-Parisi-Lipatov equation is thus similar to the resummation of the
leading secular terms by the Boltzmann kinetic equation.Comment: 8 pages, version to appear in Phys. Rev.
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