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Standing Wave (standing + wave)
Selected AbstractsNumerical analysis of microwave heating of a dielectricHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2003Yuichi Funawatashi Abstract Microwave heating of a dielectric in a cavity was analyzed numerically with the FDTD method with the aim of devising new methods for reducing uneven heating typical of microwaving. The dielectric was assumed to be water and the frequency of a microwave was taken to be 1 GHz. It was found that the electric field is highly dependent on the position of the dielectric in a cavity. The temperature distribution reflects the profile of the RMS value of the electric field in the dielectric, although there appears to be no effect of the short wavelength typical of the electric field. The heating rate depends on the position of the dielectric. In the case of a higher effective loss factor a microwave decays immediately after entering the dielectric, and the temperature of the interior remains low. These results indicate that the uneven heating is due to at least two causes: standing wave and rapid decay of a microwave. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(3): 227,236, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10087 [source] Influence of inertia, topography and gravity on transient axisymmetric thin-film flowINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2004Roger E. Khayat Abstract This study examines theoretically the development of early transients for axisymmetric flow of a thin film over a stationary cylindrical substrate of arbitrary shape. The fluid is assumed to emerge from an annular tube as it is driven by a pressure gradient maintained inside the annulus, and/or by gravity in the axial direction. The interplay between inertia, annulus aspect ratio, substrate topography and gravity is particularly emphasized. Initial conditions are found to have a drastic effect on the ensuing flow. The flow is governed by the thin-film equations of the ,boundary-layer' type, which are solved by expanding the flow field in terms of orthonormal modes in the radial direction. The formulation is validated upon comparison with the similarity solution of Watson (J. Fluid Mech 1964; 20:481) leading to an excellent agreement when only 2,3 modes are included. The wave and flow structure are examined for high and low inertia. It is found that low-inertia fluids tend to accumulate near the annulus exit, exhibiting a standing wave that grows with time. This behaviour clearly illustrates the difficulty faced with coating high-viscosity fluids. The annulus aspect is found to be influential only when inertia is significant; there is less flow resistance for a film over a cylinder of smaller diameter. For high inertia, the free surface evolves similarly to two-dimensional flow. The substrate topography is found to have a significant effect on transient behaviour, but this effect depends strongly on inertia. It is observed that the flow of a high-inertia fluid over a step-down exhibits the formation of a secondary wave that moves upstream of the primary wave. Gravity is found to help the film (coating) flow by halting or prohibiting the wave growth. The initial film profile and velocity distribution dictate whether the fluid will flow downstream or accumulate near the annulus exit. Copyright © 2004 John Wiley & Sons, Ltd. [source] Observation of interference effects in coherent diffraction of nanocrystals under X-ray standing-wave illuminationJOURNAL OF SYNCHROTRON RADIATION, Issue 6 2007Piotr Gryko Coherent X-ray diffraction is a useful technique for understanding the structure of compact objects including those which can be represented as phase objects. X-rays are highly penetrating and have wavelengths very close to atomic spacing. In this work, gold nanocrystals (on a reflecting substrate) were imaged at the Advanced Photon Source and found to produce a novel double diffraction pattern. Simulations were carried out to explain the experimental diffraction pattern in terms of reflection of the incident beam from the substrate to produce a standing wave. The experimental data were then phased to produce a two-dimensional real-space image of the gold. It is expected that the standing-wave illumination may be a useful tool to aid the convergence of the phasing algorithms for nanocrystals. [source] Trabecular bone volume fraction mapping by low-resolution MRIMAGNETIC RESONANCE IN MEDICINE, Issue 1 2001M.A. Fernández-Seara Abstract Trabecular bone volume fraction (TBVF) is highly associated with the mechanical competence of trabecular bone. TBVF is ordinarily measured by histomorphometry from bone biopsies or, noninvasively, by means of high-resolution microcomputed tomography and, more recently, by micro-MRI. The latter methods require spatial resolution sufficient to resolve trabeculae, along with segmentation techniques that allow unambiguous assignment of the signal to bone or bone marrow. In this article it is shown that TBVF can be measured under low-resolution conditions by exploiting the attenuation of the MR signal resulting from fractional occupancy of the imaging voxel by bone and bone marrow, provided that a reference signal is available from a marrow volume devoid of trabeculation. The method requires accurate measurement of apparent proton density, which entails correction for various sources of error. Key among these are the spatial nonuniformity in the RF field amplitude and effects of the slice profile, which are determined by B1 field mapping and numerical integration of the Bloch equations, respectively. By contrast, errors from variations in bone marrow composition (hematopoietic vs. fatty) between trabecular and reference site are predicted to be small and usually negligible. The method was evaluated in phantoms and in vivo in the distal radius and found to be accurate to 1% in marrow volume fraction. Finally, in a group of 12 patients of varying skeletal status, TBVF in the calcaneus was found to strongly correlate with integral bone mineral density of the lumbar vertebrae (r2 = 0.83, p < 0.0001). The method may fail in large imaging objects such as the human trunk at high magnetic field where standing wave and RF penetration effects cause intensity variations that cannot be corrected. Magn Reson Med 46:103,113, 2001. © 2001 Wiley-Liss, Inc. [source] On the standing wave in coupled non-linear Klein,Gordon equationsMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 1 2003Jian Zhang This paper is concerned with the standing wave in coupled non-linear Klein,Gordon equations. By an intricate variational argument we establish the existence of standing wave with the ground state. Then we derive out the sharp criterion for blowing up and global existence by applying the potential well argument and the concavity method. We also show the instability of the standing wave. Copyright © 2003 John Wiley & Sons, Ltd. [source] MHD waves in the solar north polar coronal holeASTRONOMISCHE NACHRICHTEN, Issue 7 2010E. Devlen Abstract The effects, hitherto not treated, of the temperature and the number density gradients, both in the parallel and the perpendicular direction to the magnetic field, of O VI ions, on the MHD wave propagation characteristics in the solar North Polar Coronal Hole are investigated. We investigate the magnetosonic wave propagation in a resistive MHD regime where only the thermal conduction is taken into account. Heat conduction across the magnetic field is treated in a non-classical approach wherein the heat is assumed to be conducted by the plasma waves emitted by ions and absorbed at a distance from the source by other ions. Anisotropic temperature and the number density distributions of O VI ions revealed the chaotic nature of MHD standing wave, especially near the plume/interplume lane borders. Attenuation length scales of the fast mode is shown not to be smoothly varying function of the radial distance from the Sun (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Purely nonlinear instability of standing waves with minimal energyCOMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 11 2003Andrew Comech We consider Hamiltonian systems with U(1) symmetry. We prove that in the generic situation the standing wave that has the minimal energy among all other standing waves is unstable, in spite of the absence of linear instability. Essentially, the instability is caused by higher algebraic degeneracy of the zero eigenvalue in the spectrum of the linearized system. We apply our theory to the nonlinear Schrödinger equation. © 2003 Wiley Periodicals, Inc. [source] An implicit three-dimensional fully non-hydrostatic model for free-surface flowsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2004Hengliang Yuan Abstract An implicit method is developed for solving the complete three-dimensional (3D) Navier,Stokes equations. The algorithm is based upon a staggered finite difference Crank-Nicholson scheme on a Cartesian grid. A new top-layer pressure treatment and a partial cell bottom treatment are introduced so that the 3D model is fully non-hydrostatic and is free of any hydrostatic assumption. A domain decomposition method is used to segregate the resulting 3D matrix system into a series of two-dimensional vertical plane problems, for each of which a block tri-diagonal system can be directly solved for the unknown horizontal velocity. Numerical tests including linear standing waves, nonlinear sloshing motions, and progressive wave interactions with uneven bottoms are performed. It is found that the model is capable to simulate accurately a range of free-surface flow problems using a very small number of vertical layers (e.g. two,four layers). The developed model is second-order accuracy in time and space and is unconditionally stable; and it can be effectively used to model 3D surface wave motions. Copyright © 2004 John Wiley & Sons, Ltd. [source] Backscattering X-ray standing waves in the XUV regionJOURNAL OF SYNCHROTRON RADIATION, Issue 3 2001T. M. Grehk It is demonstrated that Bragg reflection of XUV radiation can be used to study structural properties of crystalline materials with large unit cells. A standing-wave field is formed in a layered TiSe2 single crystal for a near-backscattering geometry (, = 88.5°). The partial electron yield is measured as a function of photon energy across the (001) Bragg reflection condition (h,, 1033,eV) and its characteristic modulation is compared with the results derived from dynamical diffraction theory in the two-wave approximation. The data reveal a large amount of disorder along the c -axis. [source] Characterization of freshwater pearl mussel (Margaritifera margaritifera) riverine habitat using River Habitat Survey dataAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 3 2003L.C. Hastie Abstract 1.The feasibility of using River Habitat Survey (RHS) data to describe freshwater pearl mussel (Margaritifera margaritifera) macrohabitat in the River Spey, north-east Scotland, was investigated. 2.Mussels were found to be positively associated with a number of RHS variables. These included: boulder/cobble river bed substrates, broken/unbroken standing waves (channel flow types), aquatic liverworts/mosses/lichens and broadleaf/mixed woodland/bankside tree cover. Negative associations with gravel-pebble/silt substrates and emergent reeds/sedges/herbs were also found. 3.Two binary logistic regression models, based on seven and four variables, respectively, were constructed in order to predict the presence/absence of mussels at any given site. Predictive success rates of 83% and 78% were achieved. 4.Another binary logistic regression model, based on four variables, was constructed in order to predict the occurrence of ,optimal' M. margaritifera habitat (overall mussel densities , 1 m,2). A predictive success rate of 83% was achieved. 5.The results indicate two potentially important applications of RHS for the conservation management of M. margaritifera: (1) for monitoring the effects of physical changes on extant mussel beds (and predicting their effects on mussel populations), and (2) for determining the habitat suitability of historically occupied sites for re-introductions. Copyright © 2003 John Wiley & Sons, Ltd. [source] Multiple three-dimensional mammalian cell aggregates formed away from solid substrata in ultrasound standing wavesBIOTECHNOLOGY PROGRESS, Issue 3 2009Larisa A. Kuznetsova Abstract Single and multiple three-dimensional cell aggregates of human red blood cells (RBCs) and HepG2 cells were formed rapidly in low mega-Hertz ultrasound standing wave fields of different geometries. A single discoid aggregate was formed in a half-wavelength pathlength resonator at a cell concentration sufficient to produce a 3D structure. Multiple cell aggregates were formed on the axis of a cylindrical resonator with a plane transducer (discoid aggregates); in a resonator with a tubular transducer and in the cross-fields of plane and tubular transducers and two plane orthogonal transducers (all cylindrical aggregates). Mechanically strong RBC aggregates were obtained by crosslinking with wheat germ agglutinin (WGA, a lectin). Scanning electron microscopy showed aggregate surface porous structures when RBCs were mixed with WGA before sonication and tighter packing when ultrasonically preformed aggregates were subsequently exposed to a flow containing WGA. HepG2 cell aggregates showed strong accumulation of F-actin at sites of cell,cell contact consistent with increased mechanical stability. The aggregates had a porous surface, and yet confocal microscopy revealed a tight packing of cells in the aggregate's inner core. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] Purely nonlinear instability of standing waves with minimal energyCOMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 11 2003Andrew Comech We consider Hamiltonian systems with U(1) symmetry. We prove that in the generic situation the standing wave that has the minimal energy among all other standing waves is unstable, in spite of the absence of linear instability. Essentially, the instability is caused by higher algebraic degeneracy of the zero eigenvalue in the spectrum of the linearized system. We apply our theory to the nonlinear Schrödinger equation. © 2003 Wiley Periodicals, Inc. [source] | ||||||||||||||||