DEFF Research Database (Denmark)
Burcharth, H. F.; Larsen, Brian Juul
The investigation concerns the design of a new internal breakwater in the main port of Ibiza. The objective of the model tests was in the first hand to optimize the cross section to make the wave reflection low enough to ensure that unacceptable wave agitation will not occur in the port. Secondly...
Wave reflections from breakwaters
Dickson, William S.
1994-01-01
A new method is presented for estimating the reflection of a random, multi-directional sea from a coastal structure. The technique is applicable to an array of wave gauges of arbitrary geometry deployed seaward of the reflector. An expansion for small oblique wave incidence angles is used to derive an approximate relationship between measured array cross-spectra and a small number of parameters that describe the incident wave properties and the reflectivity of the structure. Model tests with ...
Alfven Wave Reflection Model of Field-Aligned Currents at Mercury
Lyatsky, Wladislaw; Khazanov, George V.; Slavin, James
2010-01-01
An Alfven Wave Reflection (AWR) model is proposed that provides closure for strong field-aligned currents (FACs) driven by the magnetopause reconnection in the magnetospheres of planets having no significant ionospheric and surface electrical conductance. The model is based on properties of the Alfven waves, generated at high altitudes and reflected from the low-conductivity surface of the planet. When magnetospheric convection is very slow, the incident and reflected Alfven waves propagate along approximately the same path. In this case, the net field-aligned currents will be small. However, as the convection speed increases. the reflected wave is displaced relatively to the incident wave so that the incident and reflected waves no longer compensate each other. In this case, the net field-aligned current may be large despite the lack of significant ionospheric and surface conductivity. Our estimate shows that for typical solar wind conditions at Mercury, the magnitude of Region 1-type FACs in Mercury's magnetosphere may reach hundreds of kilo-Amperes. This AWR model of field-aligned currents may provide a solution to the long-standing problem of the closure of FACs in the Mercury's magnetosphere. c2009 Elsevier Inc. All rights reserved.
A hybrid scheme for absorbing edge reflections in numerical modeling of wave propagation
Liu, Yang; Sen, Mrinal K.
2010-01-01
We propose an efficient scheme to absorb reflections from the model boundaries in numerical solutions of wave equations. This scheme divides the computational domain into boundary, transition, and inner areas. The wavefields within the inner and boundary areas are computed by the wave equation and the one-way wave equation, respectively. The wavefields within the transition area are determined by a weighted combination of the wavefields computed by the wave equation and the one-way wave equation to obtain a smooth variation from the inner area to the boundary via the transition zone. The results from our finite-difference numerical modeling tests of the 2D acoustic wave equation show that the absorption enforced by this scheme gradually increases with increasing width of the transition area. We obtain equally good performance using pseudospectral and finite-element modeling with the same scheme. Our numerical experiments demonstrate that use of 10 grid points for absorbing edge reflections attains nearly perfect absorption. © 2010 Society of Exploration Geophysicists.
A hybrid scheme for absorbing edge reflections in numerical modeling of wave propagation
Liu, Yang
2010-03-01
We propose an efficient scheme to absorb reflections from the model boundaries in numerical solutions of wave equations. This scheme divides the computational domain into boundary, transition, and inner areas. The wavefields within the inner and boundary areas are computed by the wave equation and the one-way wave equation, respectively. The wavefields within the transition area are determined by a weighted combination of the wavefields computed by the wave equation and the one-way wave equation to obtain a smooth variation from the inner area to the boundary via the transition zone. The results from our finite-difference numerical modeling tests of the 2D acoustic wave equation show that the absorption enforced by this scheme gradually increases with increasing width of the transition area. We obtain equally good performance using pseudospectral and finite-element modeling with the same scheme. Our numerical experiments demonstrate that use of 10 grid points for absorbing edge reflections attains nearly perfect absorption. © 2010 Society of Exploration Geophysicists.
Sun, Li-Chung; Chang, Young-Fo; Chang, Chih-Hsiung; Chung, Chia-Lung
2012-05-01
In reflection seismology, detailed knowledge of how seismic waves propagate in anisotropic media is important for locating reservoirs accurately. The SH-wave possesses a pure mode polarization which does not convert to P- and SV-waves when reflecting from a horizontal interface, and vice versa. The simplicity of the SH-wave thus provides an easy way to view the details of SH-wave propagation in anisotropic media. In this study, we attempt to inspect the theoretical reflection moveouts of SH-waves reflected from transversely isotropic (TI) layers with tilted symmetry axes and to verify the reflection point, which could be shifted away from the common midpoint (CMP), by numerical calculations and physical modelling. In travel time-offset analyses, the moveout curves of SH-waves reflected from horizontal TI media (TIM) with different tilted angles of symmetry axes are computed by the TI modified hyperbolic equation and Fermat's principle, respectively. It turns out that both the computed moveout curves are similar and fit well to the observed physical data. The reflection points of SH-waves for a CMP gather computed by Fermat's principle show that they are close to the CMP for TIM with the vertical and horizontal symmetry axes, but they shift away from the CMP for the other tilted angles of symmetry axes. The shifts of the reflection points of the SH-waves from the CMP were verified by physical modelling.
MODELING OF REFLECTIVE PROPAGATING SLOW-MODE WAVE IN A FLARING LOOP
Energy Technology Data Exchange (ETDEWEB)
Fang, X.; Yuan, D.; Van Doorsselaere, T.; Keppens, R.; Xia, C. [Centre for mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Celestijnenlaan 200B, B-3001 Leuven (Belgium)
2015-11-01
Quasi-periodic propagating intensity disturbances have been observed in large coronal loops in extreme ultraviolet images over a decade, and are widely accepted to be slow magnetosonic waves. However, spectroscopic observations from Hinode/EIS revealed their association with persistent coronal upflows, making this interpretation debatable. We perform a 2.5D magnetohydrodynamic simulation to imitate the chromospheric evaporation and the following reflected patterns in a flare loop. Our model encompasses the corona, transition region, and chromosphere. We demonstrate that the quasi periodic propagating intensity variations captured by the synthesized Solar Dynamics Observatory/Atmospheric Imaging Assembly 131, 94 Å emission images match the previous observations well. With particle tracers in the simulation, we confirm that these quasi periodic propagating intensity variations consist of reflected slow mode waves and mass flows with an average speed of 310 km s{sup −1} in an 80 Mm length loop with an average temperature of 9 MK. With the synthesized Doppler shift velocity and intensity maps of the Solar and Heliospheric Observatory/Solar Ultraviolet Measurement of Emitted Radiation Fe xix line emission, we confirm that these reflected slow mode waves are propagating waves.
Modeling Transmission and Reflection Mueller Matrices of Dielectric Half-Wave Plates
Salatino, Maria; de Bernardis, Paolo; Masi, Silvia
2017-02-01
We present a simple analytical model describing multiple reflections in dielectric and optically active waveplates, for both normal and slant incidence, including absorption. We compute from first principles the transmission and reflection Mueller matrices of the waveplate. The model is used to simulate the performance of a Stokes polarimeter for mm-waves, in the framework of current attempts to precisely measure the linear polarization of the Cosmic Microwave Background (CMB). We study the spectral response of these optical devices, taking into account band and angle averaging effects and confirm the presence of a much richer spectral dependence than in an ideal phase retarder. We also present the matrix elements for the reflection matrix, which is useful to estimate systematic effects in some polarimeter configurations. The formulas we have derived can be used to quickly simulate the performance of future CMB polarimeters.
CFD Analysis of Water Solitary Wave Reflection
Directory of Open Access Journals (Sweden)
K. Smida
2011-12-01
Full Text Available A new numerical wave generation method is used to investigate the head-on collision of two solitary waves. The reflection at vertical wall of a solitary wave is also presented. The originality of this model, based on the Navier-Stokes equations, is the specification of an internal inlet velocity, defined as a source line within the computational domain for the generation of these non linear waves. This model was successfully implemented in the PHOENICS (Parabolic Hyperbolic Or Elliptic Numerical Integration Code Series code. The collision of two counter-propagating solitary waves is similar to the interaction of a soliton with a vertical wall. This wave generation method allows the saving of considerable time for this collision process since the counter-propagating wave is generated directly without reflection at vertical wall. For the collision of two solitary waves, numerical results show that the run-up phenomenon can be well explained, the solution of the maximum wave run-up is almost equal to experimental measurement. The simulated wave profiles during the collision are in good agreement with experimental results. For the reflection at vertical wall, the spatial profiles of the wave at fixed instants show that this problem is equivalent to the collision process.
Smith, J. A.; Cooper, K.; Randolph, M.
1984-01-01
A classical description of the one dimensional radiative transfer treatment of vegetation canopies was completed and the results were tested against measured prairie (blue grama) and agricultural canopies (soybean). Phase functions are calculated in terms of directly measurable biophysical characteristics of the canopy medium. While the phase functions tend to exhibit backscattering anisotropy, their exact behavior is somewhat more complex and wavelength dependent. A Monte Carlo model was developed that treats soil surfaces with large periodic variations in three dimensions. A photon-ray tracing technology is used. Currently, the rough soil surface is described by analytic functions and appropriate geometric calculations performed. A bidirectional reflectance distribution function is calculated and, hence, available for other atmospheric or canopy reflectance models as a lower boundary condition. This technique is used together with an adding model to calculate several cases where Lambertian leaves possessing anisotropic leaf angle distributions yield non-Lambertian reflectance; similar behavior is exhibited for simulated soil surfaces.
Energy Technology Data Exchange (ETDEWEB)
Mandal, Sudip; Banerjee, Dipankar; Pant, Vaibhav [Indian Institute of Astrophysics, Koramangala, Bangalore 560034 (India); Yuan, Ding; Fang, Xia; Doorsselaere, Tom Van, E-mail: sudip@iiap.res.in, E-mail: xia.fang@wis.kuleuven.be [Centre for mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Celestijnenlaan 200B, bus 2400, 3001, Leuven (Belgium)
2016-09-10
Slow MHD waves are important tools for understanding coronal structures and dynamics. In this paper, we report a number of observations from the X-Ray Telescope (XRT) on board HINODE and Solar Dynamic Observatory /Atmospheric Imaging Assembly (AIA) of reflecting longitudinal waves in hot coronal loops. To our knowledge, this is the first report of this kind as seen from the XRT and simultaneously with the AIA. The wave appears after a micro-flare occurs at one of the footpoints. We estimate the density and temperature of the loop plasma by performing differential emission measure (DEM) analysis on the AIA image sequence. The estimated speed of propagation is comparable to or lower than the local sound speed, suggesting it to be a propagating slow wave. The intensity perturbation amplitude, in every case, falls very rapidly as the perturbation moves along the loop and eventually vanishes after one or more reflections. To check the consistency of such reflection signatures with the obtained loop parameters, we perform a 2.5D MHD simulation, which uses the parameters obtained from our observation as inputs, and perform forward modeling to synthesize AIA 94 Å images. Analyzing the synthesized images, we obtain the same properties of the observables as for the real observation. From the analysis we conclude that a footpoint heating can generate a slow wave which then reflects back and forth in the coronal loop before fading. Our analysis of the simulated data shows that the main agent for this damping is anisotropic thermal conduction.
Thermal and ghost reflection modeling for a 180-deg. field-of-view long-wave infrared lens
Shi, Weimin; Couture, Michael E.
2001-03-01
Optics 1, Inc. has successfully designed and developed a 180 degree(s) field of view long wave infrared lens for USAF/AFRL under SBIR phase I and II funded projects in support of the multi-national Programmable Integrated Ordinance Suite (PIOS) program. In this paper, a procedure is presented on how to evaluate image degradation caused by asymmetric aerodynamic dome heating. In addition, a thermal gradient model is proposed to evaluate degradation caused by axial temperature gradient throughout the entire PIOS lens. Finally, a ghost reflection analysis is demonstrated with non-sequential model.
Wave-equation reflection traveltime inversion
Zhang, Sanzong
2011-01-01
The main difficulty with iterative waveform inversion using a gradient optimization method is that it tends to get stuck in local minima associated within the waveform misfit function. This is because the waveform misfit function is highly nonlinear with respect to changes in the velocity model. To reduce this nonlinearity, we present a reflection traveltime tomography method based on the wave equation which enjoys a more quasi-linear relationship between the model and the data. A local crosscorrelation of the windowed downgoing direct wave and the upgoing reflection wave at the image point yields the lag time that maximizes the correlation. This lag time represents the reflection traveltime residual that is back-projected into the earth model to update the velocity in the same way as wave-equation transmission traveltime inversion. No travel-time picking is needed and no high-frequency approximation is assumed. The mathematical derivation and the numerical examples are presented to partly demonstrate its efficiency and robustness. © 2011 Society of Exploration Geophysicists.
DEFF Research Database (Denmark)
Zanuttigh, Barbara; van der Meer, Jentsje W.; Andersen, Thomas Lykke
2009-01-01
This paper analyses wave reflection from permeable structures with a berm, including reshaping cases. Data are obtained from recent wave flume experiments and from 2DV numerical simulations performed with the COBRAS-UC code. The objectives of this research were to identify the proper representation...
Wave Reflection in 3D Conditions
DEFF Research Database (Denmark)
Zanuttigh, Barbara; Andersen, Thomas Lykke
2010-01-01
Based on recent experiments carried out in wave basin on breakwaters with armour layer of rocks and cubes, this paper examines the dependence of the reflection coefficient on wave directional spreading and obliquity. Results suggest that long-crested and short-crested waves give similar reflectio...
Fracture diagnostics with tube wave reflection logs
International Nuclear Information System (INIS)
Medlin, W.L.
1991-01-01
This paper reports on the Tube Wave Reflection Log (TWRL) which is acoustic logging method which provides information about the height, location and conductivity of hydraulically induced fractures behind perforated casing. The TWRL tool consists of a transmitter and closely spaced receiver. The transmitter is driven with a short, low frequency tone burst to generate long wavelength tube waves which are little attenuated in unperforated casing. They are partially reflected when they pass perforated intervals communicating with a hydraulically induced fracture. The tool listens for such reflections for 0.1 seconds following each excitation burst. As the tool is moved uphole at logging speed, the transmitter is excited at each foot of depth. VDL displays of the TWRL records provide reflection traces whose projections define the uppermost and lower-most perforations communicating with the fracture. The strength of the reflections depends on the ease of fluid flow into the fracture and thus, is an indicator of fracture conductivity
Flow control for oblique shock wave reflections
Giepman, R.H.M.
2016-01-01
Shock wave-boundary layer interactions are prevalent in many aerospace applications that involve transonic or supersonic flows. Such interactions may lead to boundary layer separation, flow unsteadiness and substantial losses in the total pressure. Flow control techniques can help to mitigate these adverse effects and stabilize the interaction. This thesis focuses on passive flow control techniques for oblique shock wave reflections on flat plates and presents experimental results for both la...
Gravitational wave sources: reflections and echoes
Price, Richard H.; Khanna, Gaurav
2017-11-01
The recent detection of gravitational waves has generated interest in alternatives to the black hole interpretation of sources. A subset of such alternatives involves a prediction of gravitational wave ‘echoes’. We consider two aspects of possible echoes: first, general features of echoes coming from spacetime reflecting conditions. We find that the detailed nature of such echoes does not bear any clear relationship to quasi-normal frequencies. Second, we point out the pitfalls in the analysis of local reflecting ‘walls’ near the horizon of rapidly rotating black holes.
Gravitational wave sources: reflections and echoes
International Nuclear Information System (INIS)
Price, Richard H; Khanna, Gaurav
2017-01-01
The recent detection of gravitational waves has generated interest in alternatives to the black hole interpretation of sources. A subset of such alternatives involves a prediction of gravitational wave ‘echoes’. We consider two aspects of possible echoes: first, general features of echoes coming from spacetime reflecting conditions. We find that the detailed nature of such echoes does not bear any clear relationship to quasi-normal frequencies. Second, we point out the pitfalls in the analysis of local reflecting ‘walls’ near the horizon of rapidly rotating black holes. (paper)
Music decreases aortic stiffness and wave reflections.
Vlachopoulos, Charalambos; Aggelakas, Angelos; Ioakeimidis, Nikolaos; Xaplanteris, Panagiotis; Terentes-Printzios, Dimitrios; Abdelrasoul, Mahmoud; Lazaros, George; Tousoulis, Dimitris
2015-05-01
Music has been related to cardiovascular health and used as adjunct therapy in patients with cardiovascular disease. Aortic stiffness and wave reflections are predictors of cardiovascular risk. We investigated the short-term effect of classical and rock music on arterial stiffness and wave reflections. Twenty healthy individuals (22.5±2.5 years) were studied on three different occasions and listened to a 30-min music track compilation (classical, rock, or no music for the sham procedure). Both classical and rock music resulted in a decrease of carotid-femoral pulse wave velocity (PWV) immediately after the end of music listening (all pclassical or rock music in a more sustained way (nadir by 6.0% and 5.8%, respectively, at time zero post-music listening, all pmusic preference was taken into consideration, both classical and rock music had a more potent effect on PWV in classical aficionados (by 0.20 m/s, p=0.003 and 0.13 m/s, p=0.015, respectively), whereas there was no effect in rock aficionados (all p=NS). Regarding wave reflections, classical music led to a more potent response in classical aficionados (AIx decrease by 9.45%), whereas rock led to a more potent response to rock aficionados (by 10.7%, all pMusic, both classical and rock, decreases aortic stiffness and wave reflections. Effect on aortic stiffness lasts for as long as music is listened to, while classical music has a sustained effect on wave reflections. These findings may have important implications, extending the spectrum of lifestyle modifications that can ameliorate arterial function. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.
Wang, T.
2017-05-26
Elastic full waveform inversion (EFWI) provides high-resolution parameter estimation of the subsurface but requires good initial guess of the true model. The traveltime inversion only minimizes traveltime misfits which are more sensitive and linearly related to the low-wavenumber model perturbation. Therefore, building initial P and S wave velocity models for EFWI by using elastic wave-equation reflections traveltime inversion (WERTI) would be effective and robust, especially for the deeper part. In order to distinguish the reflection travletimes of P or S-waves in elastic media, we decompose the surface multicomponent data into vector P- and S-wave seismogram. We utilize the dynamic image warping to extract the reflected P- or S-wave traveltimes. The P-wave velocity are first inverted using P-wave traveltime followed by the S-wave velocity inversion with S-wave traveltime, during which the wave mode decomposition is applied to the gradients calculation. Synthetic example on the Sigbee2A model proves the validity of our method for recovering the long wavelength components of the model.
Born reflection kernel analysis and wave-equation reflection traveltime inversion in elastic media
Wang, Tengfei
2017-08-17
Elastic reflection waveform inversion (ERWI) utilize the reflections to update the low and intermediate wavenumbers in the deeper part of model. However, ERWI suffers from the cycle-skipping problem due to the objective function of waveform residual. Since traveltime information relates to the background model more linearly, we use the traveltime residuals as objective function to update background velocity model using wave equation reflected traveltime inversion (WERTI). The reflection kernel analysis shows that mode decomposition can suppress the artifacts in gradient calculation. We design a two-step inversion strategy, in which PP reflections are firstly used to invert P wave velocity (Vp), followed by S wave velocity (Vs) inversion with PS reflections. P/S separation of multi-component seismograms and spatial wave mode decomposition can reduce the nonlinearity of inversion effectively by selecting suitable P or S wave subsets for hierarchical inversion. Numerical example of Sigsbee2A model validates the effectiveness of the algorithms and strategies for elastic WERTI (E-WERTI).
Beilecke, Thies; Krawczyk, Charlotte M.; Tanner, David C.; Ziesch, Jennifer; Research Group Protect
2014-05-01
Compressional wave (P-wave) reflection seismic field measurements are a standard tool for subsurface exploration. 2-D seismic measurements are often used for overview measurements, but also as near-surface supplement to fill gaps that often exist in 3-D seismic data sets. Such supplementing 2-D measurements are typically simple with respect to field layout. This is an opportunity for the use of shear waves (S-waves). Within the last years, S-waves have become more and more important. One reason is that P- and S-waves are differently sensitive to fluids and pore fill so that the additional S-wave information can be used to enhance lithological studies. Another reason is that S-waves have the advantage of higher spatial resolution. Within the same signal bandwidth they typically have about half the wavelength of P-waves. In near-surface unconsolidated sediments they can even enhance the structural resolution by one order of magnitude. We make use of these capabilities within the PROTECT project. In addition to already existing 2-D P-wave data, we carried out a near surface 2-D S-wave field survey at the CO2CRC Otway Project pilot site, close to Warrnambool, Australia in November 2013. The combined analysis of P-wave and S-wave data is used to construct a Poisson's Ratio 2-D model down to roughly 600 m depth. The Poisson's ratio values along a 1 km long profile at the site are surprisingly high, ranging from 0.47 in the carbonate-dominated near surface to 0.4 at depth. In the literature, average lab measurements of 0.22 for unfissured carbonates and 0.37 for fissured examples have been reported. The high values that we found may indicate areas of rather unconsolidated or fractured material, or enhanced fluid contents, and will be subject of further studies. This work is integrated in a larger workflow towards prediction of CO2 leakage and monitoring strategies for subsurface storage in general. Acknowledgement: This work was sponsored in part by the Australian
High resolution shear wave reflection surveying for hydrogeological investigations
International Nuclear Information System (INIS)
Johnson, W.J.; Clark, J.C.
1992-08-01
The high resolution S-wave method has been developed to be a powerful tool in mapping subsurface lithology and in conducting groundwater investigations. The research has demonstrated that the resolution obtainable using S-waves in a Coastal Plain environment is more than double than that obtained using conventional reflection, which already offers a higher resolution than any other surface method. Where the mapping of thin clay layers functioning as aquitards or thin sand layers functioning as aquifers are critical to the understanding of groundwater flow, S-wave reflections offer unparalleled possibilities for nondestructive exploration. The field experiment at Cooke Crossroads, South Carolina enabled the detection and mapping of beds in the thickness range of one to three feet. The S-wave reflection technique, in combination with conventional P-wave reflection, has potential to directly detect confined and unconfined aquifers. This is a breakthrough technology that still requires additional research before it can be applied on a commercial basis. Aquifer systems were interpreted from the test data at Cooke Crossroads consistent with theoretical model. Additional research is need in assessing the theoretical response of P- and S-waves to subsurface interfaces within unconsolidated sediments of varying moisture content and lithology. More theoretical modeling and in situ testing are needed to bring our knowledge of these phenomena to the level that oil and gas researchers have done for fluids in sandstones
Reflection of Alfven waves at an open magnetopause
International Nuclear Information System (INIS)
Cao, F.; Kan, J.R.
1990-01-01
Reflection of an Alfven wave incident on an open magnetopause form the magnetospheric side is examined. An open magnetopause, whose structure is different from the standard rotational discontinuity, is assumed to be a parameterized discontinuity with a nonzero normal field component. When an Alfven wave is incident on the open magnetopause, reflected and transmitted waves are generated. The emanating waves can be analyzed using linearized MHD conservation relations across the magnetopause, together with Snell's law. Under the assumption that the magnetic fields on the two sides of the open magnetopause are coplanar with the normal direction of the magnetopause, the governing equations are solved numerically. The results show that the electric fields of emanating Alfven waves depend mainly on the number density and the magnetic field jumps across the magnetopause. Under conditions representing the open magnetopause, it turns out that the open magnetopause behaves like a near perfect reflector. The corresponding reflection coefficient for the wave electric field can be approximated by R E = E r /E i ∼ -1 as has been deduced by Kan and Sun (1985) based on physical arguments. In other words, the solar wind flow is more or less unchanged by the loading effect of the Alfven wave incident on the magnetopause from the magnetospheric side. Therefore, under the assumptions of the model, the open magnetopause can be viewed as a constant voltage source
Terahertz wave reflective sensing and imaging
Zhong, Hua
Sensing and imaging technologies using terahertz (THz) radiation have found diverse applications as they approach maturity. Since the burgeoning of this technique in the 1990's, many THz sensing and imaging investigations have been designed and conducted in transmission geometry, which provides sufficient phase and amplitude contrast for the study of the spectral properties of targets in the THz domain. Driven by rising expectations that THz technology will be a potential candidate in the next generation of security screening, remote sensing, biomedical imaging and non-destructive testing (NDT), most THz sensing and imaging modalities are being extended to reflection geometry, which offers unique and adaptive solutions, and multi-dimensional information in many real scenarios. This thesis takes an application-focused approach to the advancement of THz wave reflective sensing and imaging systems: The absorption signature of the explosive material hexahydro-1,3,5-trinitro-1,3,5triazine (RDX) is measured at 30 m---the longest standoff distance so far attained by THz time-domain spectroscopy (THz-TDS). The standoff distance sensing ability of THz-TDS is investigated along with discussions specifying the influences of a variety of factors such as propagation distance, water vapor absorption and collection efficiency. Highly directional THz radiation from four-wave mixing in laser-induced air plasmas is first observed and measured, which provides a potential solution for the atmospheric absorption effect in standoff THz sensing. The simulations of the beam profiles also illuminate the underlying physics behind the interaction of the optical beam with the plasma. THz wave reflective spectroscopic focal-plane imaging is realized the first time. Absorption features of some explosives and related compounds (ERCs) and biochemical materials are identified by using adaptive feature extraction method. Good classification results using multiple pattern recognition methods are
The effects of core-reflected waves on finite fault inversions with teleseismic body wave data
Qian, Yunyi; Ni, Sidao; Wei, Shengji; Almeida, Rafael; Zhang, Han
2017-11-01
Teleseismic body waves are essential for imaging rupture processes of large earthquakes. Earthquake source parameters are usually characterized by waveform analyses such as finite fault inversions using only turning (direct) P and SH waves without considering the reflected phases from the core-mantle boundary (CMB). However, core-reflected waves such as ScS usually have amplitudes comparable to direct S waves due to the total reflection from the CMB and might interfere with the S waves used for inversion, especially at large epicentral distances for long duration earthquakes. In order to understand how core-reflected waves affect teleseismic body wave inversion results, we develop a procedure named Multitel3 to compute Green's functions that contain turning waves (direct P, pP, sP, direct S, sS and reverberations in the crust) and core-reflected waves (PcP, pPcP, sPcP, ScS, sScS and associated reflected phases from the CMB). This ray-based method can efficiently generate synthetic seismograms for turning and core-reflected waves independently, with the flexibility to take into account the 3-D Earth structure effect on the timing between these phases. The performance of this approach is assessed through a series of numerical inversion tests on synthetic waveforms of the 2008 Mw7.9 Wenchuan earthquake and the 2015 Mw7.8 Nepal earthquake. We also compare this improved method with the turning-wave only inversions and explore the stability of the new procedure when there are uncertainties in a priori information (such as fault geometry and epicentre location) or arrival time of core-reflected phases. Finally, a finite fault inversion of the 2005 Mw8.7 Nias-Simeulue earthquake is carried out using the improved Green's functions. Using enhanced Green's functions yields better inversion results as expected. While the finite source inversion with conventional P and SH waves is able to recover large-scale characteristics of the earthquake source, by adding PcP and ScS phases
Theory of reflection reflection and transmission of electromagnetic, particle and acoustic waves
Lekner, John
2016-01-01
This book deals with the reflection of electromagnetic and particle waves by interfaces. The interfaces can be sharp or diffuse. The topics of the book contain absorption, inverse problems, anisotropy, pulses and finite beams, rough surfaces, matrix methods, numerical methods, reflection of particle waves and neutron reflection. Exact general results are presented, followed by long wave reflection, variational theory, reflection amplitude equations of the Riccati type, and reflection of short waves. The Second Edition of the Theory of Reflection is an updated and much enlarged revision of the 1987 monograph. There are new chapters on periodically stratified media, ellipsometry, chiral media, neutron reflection and reflection of acoustic waves. The chapter on anisotropy is much extended, with a complete treatment of the reflection and transmission properties of arbitrarily oriented uniaxial crystals. The book gives a systematic and unified treatment reflection and transmission of electromagnetic and particle...
International Nuclear Information System (INIS)
Kaufman, A.N.; Brizard, A.J.; Cook, D.R.
1993-01-01
The analysis of the minority-ion gyroresonant heating process by a magnetosonic wave in a general magnetic field geometry with one ignorable spatial coordinate can be divided into several steps, each defined in terms of a precise mathematical problem to be solved. In this work, the authors focus their attention on the magnetosonic wave reflection problem in axisymmetric tokamak geometry; the conversion and absorption of the minority-ion gyroresonant ballistic waves are treated elsewhere. In contrast to their previous work, they employ a kinetic model based on the perturbation generating function S for the gyroresonant minority-ions. The bulk plasma response is represented by the perturbation magnetic vector potential A, corresponding to a shielded magnetosonic wave. The set of coupled equations for S and A can be derived from an action principle, which can also be used to derive explicit wave-action conservation laws in ray phase space. The reflection problem is solved in ray phase space by considering three separate steps. In the first step, the incident magnetosonic ray propagates towards the first linear mode conversion region, where action is transferred to the minority-ion gyroresonant ballistic waves. In the second step, the continuum of excited gyroresonant ballistic rays propagate towards the second linear mode conversion region. In the third step, the reflected magnetosonic wave field is excited by linear mode conversion from the minority gyroresonant ballistic rays
Arterial wave reflection decreases gradually from supine to upright
DEFF Research Database (Denmark)
van den Bogaard, Bas; Westerhof, Berend E; Best, Hendrik
2011-01-01
BACKGROUND. An increase in total peripheral resistance (TPR) usually increases arterial wave reflection. During passive head-up tilt (HUT), however, arterial wave reflection decreases with increasing TPR. This study addressed whether arterial wave reflection gradually decreases during HUT. METHODS....... In 10 healthy volunteers (22-39 years, nine males), we recorded finger arterial pressures in supine position (0°), and 30°and 70°degrees HUT and active standing (90°). Aortic pressure was constructed from the finger pressure signal and hemodynamics were calculated. Arterial wave reflection...... from 0.9 dyn s/cm(5) at 0? to 1.2, 1.4 and 1.4 dyn s/cm(5) at 30°, 70° and 90° (p wave reflection...
Full-waveform inversion with reflected waves for 2D VTI media
Pattnaik, Sonali; Tsvankin, Ilya; Wang, Hui; Alkhalifah, Tariq
2016-01-01
Full-waveform inversion in anisotropic media using reflected waves suffers from the strong non-linearity of the objective function and trade-offs between model parameters. Estimating long-wavelength model components by fixing parameter perturbations
Reflection and Transmission of Acoustic Waves through the Layer of Multifractional Bubbly Liquid
Directory of Open Access Journals (Sweden)
Gubaidullin Damir Anvarovich
2018-01-01
Full Text Available The mathematical model that determines reflection and transmission of acoustic wave through a medium containing multifractioanl bubbly liquid is presented. For the water-water with bubbles-water model the wave reflection and transmission coefficients are calculated. The influence of the bubble layer thickness on the investigated coefficients is shown. The theory compared with the experiment. It is shown that the theoretical results describe and explain well the available experimental data. It is revealed that the special dispersion and dissipative properties of the layer of bubbly liquid can significantly influence on the reflection and transmission of acoustic waves in multilayer medium
Nonlinear reflection of shock shear waves in soft elastic media.
Pinton, Gianmarco; Coulouvrat, François; Gennisson, Jean-Luc; Tanter, Mickaël
2010-02-01
For fluids, the theoretical investigation of shock wave reflection has a good agreement with experiments when the incident shock Mach number is large. But when it is small, theory predicts that Mach reflections are physically unrealistic, which contradicts experimental evidence. This von Neumann paradox is investigated for shear shock waves in soft elastic solids with theory and simulations. The nonlinear elastic wave equation is approximated by a paraxial wave equation with a cubic nonlinear term. This equation is solved numerically with finite differences and the Godunov scheme. Three reflection regimes are observed. Theory is developed for shock propagation by applying the Rankine-Hugoniot relations and entropic constraints. A characteristic parameter relating diffraction and non-linearity is introduced and its theoretical values are shown to match numerical observations. The numerical solution is then applied to von Neumann reflection, where curved reflected and Mach shocks are observed. Finally, the case of weak von Neumann reflection, where there is no reflected shock, is examined. The smooth but non-monotonic transition between these three reflection regimes, from linear Snell-Descartes to perfect grazing case, provides a solution to the acoustical von Neumann paradox for the shear wave equation. This transition is similar to the quadratic non-linearity in fluids.
Manipulating acoustic wave reflection by a nonlinear elastic metasurface
Guo, Xinxin; Gusev, Vitalyi E.; Bertoldi, Katia; Tournat, Vincent
2018-03-01
The acoustic wave reflection properties of a nonlinear elastic metasurface, derived from resonant nonlinear elastic elements, are theoretically and numerically studied. The metasurface is composed of a two degree-of-freedom mass-spring system with quadratic elastic nonlinearity. The possibility of converting, during the reflection process, most of the fundamental incoming wave energy into the second harmonic wave is shown, both theoretically and numerically, by means of a proper design of the nonlinear metasurface. The theoretical results from the harmonic balance method for a monochromatic source are compared with time domain simulations for a wave packet source. This protocol allows analyzing the dynamics of the nonlinear reflection process in the metasurface as well as exploring the limits of the operating frequency bandwidth. The reported methodology can be applied to a wide variety of nonlinear metasurfaces, thus possibly extending the family of exotic nonlinear reflection processes.
Reflected rarefactions, double regular reflection, and mach waves in aluminum and beryllium
International Nuclear Information System (INIS)
Neal, T.
1975-01-01
A number of shock techniques which can be used to obtain high-pressure equation-of-state information between the principal Hugoniot and the principal adiabat are illustrated. A rarefaction wave in aluminum shocked to 27.7 GPa [277 kbar] is examined with radiographic techniques and the bulk sound speed is determined. The two stage compression which occurs in a double shock may be attained by colliding two shocks and observing regular reflection. A radiographic method which uses this phenomenon to measure a three-stage compression of aluminum to a density of 4.7 Mg/m 3 and beryllium to a density of 3.1 Mg/m 3 is presented. The results of a Mach reflection experiment in aluminum are found to disagree substantially with the simple three-shock model. A modified model, consistent with observations, is discussed. In all cases the Gruneisen parameter is determined. (U.S.)
Flow control for oblique shock wave reflections
Giepman, R.H.M.
2016-01-01
Shock wave-boundary layer interactions are prevalent in many aerospace applications that involve transonic or supersonic flows. Such interactions may lead to boundary layer separation, flow unsteadiness and substantial losses in the total pressure. Flow control techniques can help to mitigate these
X-ray reflectivity study of thermal capillary waves on liquid surfaces
International Nuclear Information System (INIS)
Ocko, B.M.; Wu, X.Z.; Sirota, E.B.; Sinha, S.K.; Deutsch, M.
1994-01-01
X-ray reflectivity measurements have been carried out at the liquid/vapor interface of normal alkanes. The reflectivities over a large temperature range of different chain lengths (C20 and C36) provide a critical test of the various capillary wave models. Our data are most consistent with the hybrid model which allows for a molecular size dependent cutoff q max for the capillary waves and an intrinsic interface width σ 0
Kochetov, A. V.
2018-05-01
This work was initiated by experiments on studying the self-action of radio waves incident on the ionosphere from a ground-based transmitter at the stage of electromagnetic excitation of Langmuir turbulence (Langmuir effect). The emphasis is on the impact of "self-consistent" collisionless absorption of radio waves by the Langmuir turbulence, which develops when the incident-wave field swells in the resonant region of a smoothly inhomogeneous plasma, on the dynamics of the radio wave reflection. Electrodynamic characteristics of the nonlinear-plasma layer, which has a linear unperturbed profile of the plasma density, with different features of the absorption development are obtained for a high intensity of the incident radiation. Calculations of "soft" and "hard" regimes of the absorption occurrence, as well as hysteresis modes in which the damping switch-on and off thresholds differ several times, are carried out. The algorithms we devised and the results of the study can serve as the basis for a more adequate and more detailed numerical simulation for interpretation of the experimental data obtained at the stage of the Langmuir effect in the ionosphere.
The high resolution shear wave seismic reflection technique
International Nuclear Information System (INIS)
Johnson, W.J.; Clark, J.C.
1991-04-01
This report presents the state-of-the-art of the high resolution S-wave reflection technique. Published and unpublished literature has been reviewed and discussions have been held with experts. Result is to confirm that the proposed theoretical and practical basis for identifying aquifer systems using both P- and S-wave reflections is sound. Knowledge of S-wave velocity and P-wave velocity is a powerful tool for assessing the fluid characteristics of subsurface layers. Material properties and lateral changes in material properties such as change from clay to sand, can be inferred from careful dual evaluation of P and S-wave records. The high resolution S-wave reflection technique has seen its greatest application to date as part of geotechnical studies for building foundations in the Far East. Information from this type of study has been evaluated and will be incorporated in field studies. In particular, useful information regarding S-wave sources, noise suppression and recording procedures will be incorporated within the field studies. Case histories indicate that the best type of site for demonstrating the power of the high resolution S-wave technique will be in unconsolidated soil without excessive structural complexities. More complex sites can form the basis for subsequent research after the basic principles of the technique can be established under relatively uncomplicated conditions
Instantaneous wave emission model
International Nuclear Information System (INIS)
Kruer, W.L.
1970-12-01
A useful treatment of electrostatic wave emission by fast particles in a plasma is given. First, the potential due to a fast particle is expressed as a simple integration over the particle orbit; several interesting results readily follow. The potential in the wake of an accelerating particle is shown to be essentially that produced through local excitation of the plasma by the particle free-streaming about its instantaneous orbit. Application is made to one dimension, and it is shown that the wave emission and adsorption synchronize to the instantaneous velocity distribution function. Guided by these calculations, we then formulate a test particle model for computing the instantaneous wave emission by fast particles in a Vlasov plasma. This model lends itself to physical interpretation and provides a direct approach to many problems. By adopting a Fokker-Planck description for the particle dynamics, we calculate the broadening of the wave-particle resonance due to velocity diffusion and drag
Quantitative Estimation of Transmitted and Reflected Lamb Waves at Discontinuity
International Nuclear Information System (INIS)
Lim, Hyung Jin; Sohn, Hoon
2010-01-01
For the application of Lamb wave to structural health monitoring(SHM), understanding its physical characteristic and interaction between Lamb wave and defect of the host structure is an important issue. In this study, reflected, transmitted and mode converted Lamb waves at discontinuity of a plate structure were simulated and the amplitude ratios are calculated theoretically using Modal decomposition method. The predicted results were verified comparing with finite element method(FEM) and experimental results simulating attached PZTs. The result shows that the theoretical prediction is close to the FEM and the experimental verification. Moreover, quantitative estimation method was suggested using amplitude ratio of Lamb wave at discontinuity
Self-reflection of intense electromagnetic waves in plasmas
Energy Technology Data Exchange (ETDEWEB)
Tewari, D P; Kumar, A; Sharma, J K [Indian Inst. of Tech., New Delhi. Dept. of Physics
1977-10-01
A uniform electromagnetic wave of high power density, propagating in a collisional plasma gives rise to a modification in temperature-dependent collision frequency and in turn induces a gradient in the complex refractive index of the medium. A WKB solution of the problem predicts a backward propagating wave on account of the self-induced inhomogeneity. The amplitude of the backward (i.e. reflected) wave increases with increasing power density of the wave. This is a volume nonlinear effect and is appreciable for usually employed power densities.
International Nuclear Information System (INIS)
Benoit, M.; Marcos, F.; Teisson, Ch.
1999-01-01
Nuclear power stations located on the coast take the water they use to cool their circuits from the sea. The water intake and discharge devices must be able to operate in all weathers, notably during extreme storms, with waves 10 m high and over. To predict the impact of the waves on the equipment, they are modeled digitally from the moment they form in the middle of the ocean right up to the moment they break on the shore. (authors)
Deryabin, M. S.; Kasyanov, D. A.; Kurin, V. V.; Garasyov, M. A.
2016-05-01
We show that a significant energy redistribution occurs in the spectrum of reflected nonlinear waves, when an intense acoustic beam is reflected from an acoustically soft boundary, which manifests itself at short wave distances from a reflecting boundary. This effect leads to the appearance of extrema in the distributions of the amplitude and intensity of the field of the reflected acoustic beam near the reflecting boundary. The results of physical experiments are confirmed by numerical modeling of the process of transformation of nonlinear waves reflected from an acoustically soft boundary. Numerical modeling was performed by means of the Khokhlov—Zabolotskaya—Kuznetsov (KZK) equation.
Berberyan, A. Kh; Garakov, V. G.
2018-04-01
A large number of works have been devoted to investigation of the influence of the piezoelectric properties of a material on the propagation of elastic waves [1–3]. Herewith, the quasi-static piezoelasticity model was mainly used. In the problem of an electromagnetic wave reflection from an elastic medium with piezoelectric properties, it is necessary to consider hyperbolic equations [4].
Bulakhov, M. G.; Buyanov, Yu. I.; Yakubov, V. P.
1996-10-01
It has been shown that a full vector measurement of the total field allows one to uniquely distinguish the incident and reflected waves at each observation point without the use of a spatial difference based on an analysis of the polarization structure of the interference pattern which arises during reflection of electromagnetic waves from an intermedia boundary. We have investigated the stability of these procedures with respect to measurement noise by means of numerical modeling.
Reflection and transmission of electromagnetic waves in planarly stratified media
International Nuclear Information System (INIS)
Caviglia, G.
1999-01-01
Propagation of time-harmonic electromagnetic waves in planarly stratified multilayers is investigated. Each layer is allowed to be inhomogeneous and the layers are separated by interfaces. The procedure is based on the representation of the electromagnetic field in the basis of the eigenvectors of the matrix characterizing the first-order system. Hence the local reflection and transmission matrices are defined and the corresponding differential equations, in the pertinent space variable are determined. The jump conditions at interfaces are also established. The present model incorporates dissipative materials and the procedure holds without any restrictions to material symmetries. Differential equations appeared in the literature are shown to hold in particular (one-dimensional) cases or to represent homogeneous layers only
Arterial wave reflection and subclinical left ventricular systolic dysfunction.
Russo, Cesare; Jin, Zhezhen; Takei, Yasuyoshi; Hasegawa, Takuya; Koshaka, Shun; Palmieri, Vittorio; Elkind, Mitchell Sv; Homma, Shunichi; Sacco, Ralph L; Di Tullio, Marco R
2011-03-01
Increased arterial wave reflection is a predictor of cardiovascular events and has been hypothesized to be a cofactor in the pathophysiology of heart failure. Whether increased wave reflection is inversely associated with left-ventricular (LV) systolic function in individuals without heart failure is not clear. Arterial wave reflection and LV systolic function were assessed in 301 participants from the Cardiovascular Abnormalities and Brain Lesions (CABL) study using two-dimensional echocardiography and applanation tonometry of the radial artery to derive central arterial waveform by a validated transfer function. Aortic augmentation index (AIx) and wasted energy index (WEi) were used as indices of wave reflection. LV systolic function was measured by LV ejection fraction (LVEF) and tissue Doppler imaging (TDI). Mitral annulus peak systolic velocity (Sm), peak longitudinal strain and strain rate were measured. Participants with history of coronary artery disease, atrial fibrillation, LVEF less than 50% or wall motion abnormalities were excluded. Mean age of the study population was 68.3 ± 10.2 years (64.1% women, 65% hypertensive). LV systolic function by TDI was lower with increasing wave reflection, whereas LVEF was not. In multivariate analysis, TDI parameters of LV longitudinal systolic function were significantly and inversely correlated to AIx and WEi (P values from 0.05 to 0.002). In a community cohort without heart failure and with normal LVEF, an increased arterial wave reflection was associated with subclinical reduction in LV systolic function assessed by novel TDI techniques. Further studies are needed to investigate the prognostic implications of this relationship.
Energy Relations for Plane Waves Reflected from Moving Media
DEFF Research Database (Denmark)
Daly, P.; Gruenberg, Harry
1967-01-01
When a plane wave is obliquely incident from vacuum on a semi-infinite moving medium, the energy flow carried by the incident wave, is in general, not carried away by the reflected and transmitted waves. This is only the case when the medium velocity is parallel to its vacuum interface. Otherwise...... there is a net inflow or outflow of electromagnetic energy, which can be accounted for by the change of stored energy in the system, and the work done by the mechanical forces acting on the medium. A detailed energy balance is drawn up for two different media moving normal to their vacuum interfaces: (a...
A model to predict the sound reflection from forests
Wunderli, J.M.; Salomons, E.M.
2009-01-01
A model is presented to predict the reflection of sound at forest edges. A single tree is modelled as a vertical cylinder. For the reflection at a cylinder an analytical solution is given based on the theory of scattering of spherical waves. The entire forest is represented by a line of cylinders
Kashchenko, Serguey
2015-01-01
This monograph examines in detail models of neural systems described by delay-differential equations. Each element of the medium (neuron) is an oscillator that generates, in standalone mode, short impulses also known as spikes. The book discusses models of synaptic interaction between neurons, which lead to complex oscillatory modes in the system. In addition, it presents a solution to the problem of choosing the parameters of interaction in order to obtain attractors with predetermined structure. These attractors are represented as images encoded in the form of autowaves (wave memory). The target audience primarily comprises researchers and experts in the field, but it will also be beneficial for graduate students.
Parandaman, A.; Sudhakar, G.; Rajakumar, B.
Thermal reactions of Tetramethylsilane (TMS) diluted in argon were studied behind the reflected shock waves in a single-pulse shock tube (SPST) over the temperature range of 1085-1221 K and pressures varied between 10.6 and 22.8 atm. The stable products resulting from the decomposition of TMS were identified and quantified using gas chromatography and also verified with Fourier Transform Infrared (FTIR) spectrometer. The major reaction products are methane (CH4) and ethylene (C2H4). The minor reaction products are ethane (C2H6) and propylene (C3H6). The initiation of mechanism in the decomposition of TMS takes plays via the Si-C bond scission by ejecting the methyl radicals (CH3) and trimethylsilyl radicals ((CH3)3Si). The measured temperature dependent rate coefficient for the total decomposition of TMS was to be ktotal = 1.66 ×1015 exp (-64.46/RT) s-1 and for the formation of CH4 reaction channel was to be k = 2.20 × 1014 exp (-60.15/RT) s-1, where the activation energies are given in kcal mol-1. A kinetic scheme containing 17 species and 28 elementary reactions was used for the simulation using chemical kinetic simulator over the temperature range of 1085-1221 K. The agreement between the experimental and simulated results was satisfactory.
Born reflection kernel analysis and wave-equation reflection traveltime inversion in elastic media
Wang, Tengfei; Cheng, Jiubing
2017-01-01
Elastic reflection waveform inversion (ERWI) utilize the reflections to update the low and intermediate wavenumbers in the deeper part of model. However, ERWI suffers from the cycle-skipping problem due to the objective function of waveform residual
Reflection of equatorial Kelvin waves at eastern ocean boundaries Part I: hypothetical boundaries
Directory of Open Access Journals (Sweden)
J. Soares
1999-06-01
Full Text Available A baroclinic shallow-water model is developed to investigate the effect of the orientation of the eastern ocean boundary on the behavior of equatorial Kelvin waves. The model is formulated in a spherical polar coordinate system and includes dissipation and non-linear terms, effects which have not been previously included in analytical approaches to the problem. Both equatorial and middle latitude response are considered given the large latitudinal extent used in the model. Baroclinic equatorial Kelvin waves of intraseasonal, seasonal and annual periods are introduced into the domain as pulses of finite width. Their subsequent reflection, transmission and dissipation are investigated. It is found that dissipation is very important for the transmission of wave energy along the boundary and for reflections from the boundary. The dissipation was found to be dependent not only on the presence of the coastal Kelvin waves in the domain, but also on the period of these coastal waves. In particular the dissipation increases with wave period. It is also shown that the equatorial β-plane approximation can allow an anomalous generation of Rossby waves at higher latitudes. Nonlinearities generally have a small effect on the solutions, within the confines of this model.Key words. Oceanography: general (equatorial oceanography; numerical modeling · Oceanography: physical (eastern boundary currents
Arterial wave reflection and aortic valve calcification in an elderly community-based cohort.
Sera, Fusako; Russo, Cesare; Iwata, Shinichi; Jin, Zhezhen; Rundek, Tatjana; Elkind, Mitchell S V; Homma, Shunichi; Sacco, Ralph L; Di Tullio, Marco R
2015-04-01
Aortic valve calcification (AVC) without stenosis is common in the elderly, is associated with cardiovascular morbidity and mortality, and may progress to aortic valve stenosis. Arterial stiffness and pulse-wave reflection are important components of proximal aortic hemodynamics, but their relationship with AVC is not established. To investigate the relationship of arterial wave reflection and stiffness with AVC, pulse wave analysis and AVC evaluation by echocardiography were performed in 867 participants from the Cardiovascular Abnormalities and Brain Lesions study. Participants were divided into four categories on the basis of the severity and extent of AVC: (1) none or mild focal AVC, (2) mild diffuse AVC, (3) moderate to severe focal AVC, and (4) moderate to severe diffuse AVC. Central blood pressures and pulse pressure, total arterial compliance, augmentation index, and time to wave reflection were assessed using applanation tonometry. Indicators of arterial stiffness and wave reflection were significantly associated with AVC severity, except for central systolic and diastolic pressures and time to reflection. After adjustment for pertinent covariates (age, sex, race/ethnicity, and estimated glomerular filtration rate), only augmentation pressure (P = .02) and augmentation index (P = .002) were associated with the severity of AVC. Multivariate logistic regression analysis revealed that augmentation pressure (odds ratio per mm Hg, 1.14; 95% confidence interval, 1.02-1.27; P = .02) and augmentation index (odds ratio per percentage point, 1.07; 95% confidence interval, 1.01-1.13; P = .02) were associated with an increased risk for moderate to severe diffuse AVC, even when central blood pressure value was included in the same model. Arterial wave reflection is associated with AVC severity, independent of blood pressure values. Increased contribution of wave reflection to central blood pressure could be involved in the process leading to AVC. Copyright © 2015
Analytical computation of reflection and transmission coefficients for love waves
International Nuclear Information System (INIS)
Romanelli, F.; Vaccari, F.
1995-09-01
The computation of the transmission and reflection coefficients is an important step in the construction, if modal summation technique is used, of synthetic seismograms for 2-D or 3-D media. These coupling coefficients for Love waves at a vertical discontinuity are computed analytically. Numerical test for realistic structures show how the energy carried by an incoming mode is redistributed on the various modes existing on both sides of the vertical interface. (author). 15 refs, 8 figs
Reflection and absorption of ordinary waves in an inhomogeneous plasma
International Nuclear Information System (INIS)
Croci, R.
1990-11-01
This study treats the system of Vlasov and Maxwell equations for the Fourier transform in space and time of a plasma referred to Cartesian coordinates with the coordinate z parallel to the uniform equilibrium magnetic field with the equilibrium plasma density dependent on ηx, where η is a parameter. The k y component of the wave vector is taken equal to zero, whereas k z is different from zero. When the interaction of ordinary and extraordinary waves is neglected, the Fourier transform of the electric field of the ordinary waves obeys a homogeneous integral equation with principal part integrals, which is solved in the case of weak absorption and sufficiently small η (essentially smaller than vacuum wave vector), but without limitations on the ratio of the wavelength to the Larmor radius (the usual approximation being limited to wavelengths much smaller than the Larmor radius). The reflection and transmission coefficients and the total energy absorption are given in this approximation, whereas the energy conservation theorem for the reflection and transmission coefficients in an absorption-free plasma are derived for every value of η without explicit knowledge of the solutions. Finally, a general and compact equation for the eigenvalues which does not require complex analysis and knowledge of all solutions of the dispersion relation is given. (orig.)
A three-microphone acoustic reflection technique using transmitted acoustic waves in the airway.
Fujimoto, Yuki; Huang, Jyongsu; Fukunaga, Toshiharu; Kato, Ryo; Higashino, Mari; Shinomiya, Shohei; Kitadate, Shoko; Takahara, Yutaka; Yamaya, Atsuyo; Saito, Masatoshi; Kobayashi, Makoto; Kojima, Koji; Oikawa, Taku; Nakagawa, Ken; Tsuchihara, Katsuma; Iguchi, Masaharu; Takahashi, Masakatsu; Mizuno, Shiro; Osanai, Kazuhiro; Toga, Hirohisa
2013-10-15
The acoustic reflection technique noninvasively measures airway cross-sectional area vs. distance functions and uses a wave tube with a constant cross-sectional area to separate incidental and reflected waves introduced into the mouth or nostril. The accuracy of estimated cross-sectional areas gets worse in the deeper distances due to the nature of marching algorithms, i.e., errors of the estimated areas in the closer distances accumulate to those in the further distances. Here we present a new technique of acoustic reflection from measuring transmitted acoustic waves in the airway with three microphones and without employing a wave tube. Using miniaturized microphones mounted on a catheter, we estimated reflection coefficients among the microphones and separated incidental and reflected waves. A model study showed that the estimated cross-sectional area vs. distance function was coincident with the conventional two-microphone method, and it did not change with altered cross-sectional areas at the microphone position, although the estimated cross-sectional areas are relative values to that at the microphone position. The pharyngeal cross-sectional areas including retropalatal and retroglossal regions and the closing site during sleep was visualized in patients with obstructive sleep apnea. The method can be applicable to larger or smaller bronchi to evaluate the airspace and function in these localized airways.
Reflection and diffraction of atomic de Broglie waves by evanescent laser waves. Bare-state method
International Nuclear Information System (INIS)
Feng, Xiaoping; Witte, N.S.; Hollenberg, C.L.; Opat, G.
1994-01-01
Two methods are presented for the investigation of the reflection and diffraction of atoms by gratings formed either by standing or travelling evanescent laser waves. Both methods use the bare-state rather than dressed-state picture. One method is based on the Born series, whereas the other is based on the Laplace transformation of the coupled differential equations. The two methods yield the same theoretical expressions for the reflected and diffracted atomic waves in the whole space including the interaction and the asymptotic regions. 1 ref., 1 fig
Background velocity inversion by phase along reflection wave paths
Yu, Han; Guo, Bowen; Schuster, Gerard T.
2014-01-01
A background velocity model containing the correct lowwavenumber information is desired for both the quality of the migration image and the success of waveform inversion. We propose to invert for the low-wavenumber part of the velocity model by minimizing the phase difference between predicted and observed reflections. The velocity update is exclusively along the reflection wavepaths and, unlike conventional FWI, not along the reflection ellipses. This allows for reconstructing the smoothly varying parts of the background velocity model. Tests with synthetic data show both the benefits and limitations of this method.
Background velocity inversion by phase along reflection wave paths
Yu, Han
2014-08-05
A background velocity model containing the correct lowwavenumber information is desired for both the quality of the migration image and the success of waveform inversion. We propose to invert for the low-wavenumber part of the velocity model by minimizing the phase difference between predicted and observed reflections. The velocity update is exclusively along the reflection wavepaths and, unlike conventional FWI, not along the reflection ellipses. This allows for reconstructing the smoothly varying parts of the background velocity model. Tests with synthetic data show both the benefits and limitations of this method.
Angle-domain Migration Velocity Analysis using Wave-equation Reflection Traveltime Inversion
Zhang, Sanzong
2012-11-04
The main difficulty with an iterative waveform inversion is that it tends to get stuck in a local minima associated with the waveform misfit function. This is because the waveform misfit function is highly non-linear with respect to changes in the velocity model. To reduce this nonlinearity, we present a reflection traveltime tomography method based on the wave equation which enjoys a more quasi-linear relationship between the model and the data. A local crosscorrelation of the windowed downgoing direct wave and the upgoing reflection wave at the image point yields the lag time that maximizes the correlation. This lag time represents the reflection traveltime residual that is back-projected into the earth model to update the velocity in the same way as wave-equation transmission traveltime inversion. The residual movemout analysis in the angle-domain common image gathers provides a robust estimate of the depth residual which is converted to the reflection traveltime residual for the velocity inversion. We present numerical examples to demonstrate its efficiency in inverting seismic data for complex velocity model.
Brossier, Romain; Zhou, Wei; Operto, Stéphane; Virieux, Jean
2015-04-01
Full Waveform Inversion (FWI) is an appealing method for quantitative high-resolution subsurface imaging (Virieux et al., 2009). For crustal-scales exploration from surface seismic, FWI generally succeeds in recovering a broadband of wavenumbers in the shallow part of the targeted medium taking advantage of the broad scattering-angle provided by both reflected and diving waves. In contrast, deeper targets are often only illuminated by short-spread reflections, which favor the reconstruction of the short wavelengths at the expense of the longer ones, leading to a possible notch in the intermediate part of the wavenumber spectrum. To update the velocity macromodel from reflection data, image-domain strategies (e.g., Symes & Carazzone, 1991) aim to maximize a semblance criterion in the migrated domain. Alternatively, recent data-domain strategies (e.g., Xu et al., 2012, Ma & Hale, 2013, Brossier et al., 2014), called Reflection FWI (RFWI), inspired by Chavent et al. (1994), rely on a scale separation between the velocity macromodel and prior knowledge of the reflectivity to emphasize the transmission regime in the sensitivity kernel of the inversion. However, all these strategies focus on reflected waves only, discarding the low-wavenumber information carried out by diving waves. With the current development of very long-offset and wide-azimuth acquisitions, a significant part of the recorded energy is provided by diving waves and subcritical reflections, and high-resolution tomographic methods should take advantage of all types of waves. In this presentation, we will first review the issues of classical FWI when applied to reflected waves and how RFWI is able to retrieve the long wavelength of the model. We then propose a unified formulation of FWI (Zhou et al., 2014) to update the low wavenumbers of the velocity model by the joint inversion of diving and reflected arrivals, while the impedance model is updated thanks to reflected wave only. An alternate inversion of
Continuous wave terahertz reflection imaging of human colorectal tissue
Doradla, Pallavi; Alavi, Karim; Joseph, Cecil S.; Giles, Robert H.
2013-03-01
Continuous wave terahertz (THz) imaging has the potential to offer a safe, non-ionizing, and nondestructive medical imaging modality for delineating colorectal cancer. Fresh excisions of normal colon tissue were obtained from surgeries performed at the University of Massachusetts Medical School, Worcester. Reflection measurements of thick sections of colorectal tissues, mounted in an aluminum sample holder, were obtained for both fresh and formalin fixed tissues. The two-dimensional reflection images were acquired by using an optically pumped far-infrared molecular gas laser operating at 584 GHz with liquid Helium cooled silicon bolometer detector. Using polarizers in the experiment both co-polarized and cross-polarized remittance form the samples was collected. Analysis of the images showed the importance of understanding the effects of formalin fixation while determining reflectance level of tissue response. The resulting co- and cross-polarized images of both normal and formalin fixed tissues showed uniform terahertz response over the entire sample area. Initial measurements indicated a co-polarized reflectance of 16%, and a cross-polarized reflectance of 0.55% from fresh excisions of normal colonic tissues.
Reflection of ion acoustic waves by the plasma sheath
International Nuclear Information System (INIS)
Ibrahim, I.; Kuehl, H.H.
1984-01-01
The reflection coefficient R for linear monochromatic ion acoustic waves incident on the transonic layer and sheath from the plasma interior is calculated. The treatment differs from previous analyses in that (1) the exact zero-order ion density and velocity profiles for a planar, bounded plasma are used, and the zero-order charge separation is not neglected, and (2) the first-order quantities near the transonic layer are considered in detail, including first-order charge separation, whereby it is found that no coupling to the beam modes exists, and that the functional form of the first-order solution is completely determined. It is shown that the upper bound for Vertical BarRVertical Bar is (1)/(3) . The largest reflection occurs for frequencies which are small compared with the ionization frequency, and generally decreases with increasing frequency. By Fourier superposition, the reflection of a pulse is computed. For a narrow incident pulse, the reflected pulse is greatly distorted and is small compared with the incident pulse. For a broad pulse, the reflected pulse is similar in shape to the incident pulse, and has a magnitude which is approximately (1)/(3) of the incident pulse
Waves reflected by solid wall and wave interaction in vapour bubbly liquids
International Nuclear Information System (INIS)
Duong, N.H.; Nguyen, V.T.
2004-01-01
The vapour bubbly liquids are met in many natural and industrial processes, including in energy equipment. In the nuclear power plants this kind of medium appears in reactor cores (PWR, BWR and etc.), in turbine generators and in heat transfer loops. Due to some circumstances (for example, a hit caused by detonations or strong collisions) the pressure waves can appear in the bubbly liquid medium contained in those facilities. These waves propagate in the mixtures and interact with themselves and with structures. It is important that what will occur during mentioned above processes. The knowledge of this kind processes will be useful for analysing the different sorts of the processes occurred in the energy facilities where the vapor bubbly liquids are used as working or heat transfer medium, like nuclear power plants, and also useful in finding the measures for prevention of unfavourable phenomena (for example, during wave interactions maybe appear too high pressures, which could lead into damages of facilities and etc.) and safety operating the equipment. From the physical point of view, the waves in this kind of medium are interesting that owing to non-linear, dispersion and dissipation effects the wave patterns in them may be diverse and easy altered. In the paper the investigation results of the waves reflected by solid wall or structure of the moderate intensity shock waves, and the behaviour of pressure in the process of wave interaction in some mixtures of liquid with vapour bubbles (of radium ∼1 mm) are presented. (author)
Analysis of Wave Reflection from Wave Energy Converters Installed as Breakwaters in Harbour
DEFF Research Database (Denmark)
Zanuttigh, B.; Margheritini, Lucia; Gambles, L.
2009-01-01
loads on the structure, i.e. better survivability. Nevertheless these devices must comply with the requirements of harbour protection structures and thus cope with problems due to reflection of incoming waves, i.e. dangerous sea states close to harbors entrances and intensified sediment scour, which can...
Improved Wave-vessel Transfer Functions by Uncertainty Modelling
DEFF Research Database (Denmark)
Nielsen, Ulrik Dam; Fønss Bach, Kasper; Iseki, Toshio
2016-01-01
This paper deals with uncertainty modelling of wave-vessel transfer functions used to calculate or predict wave-induced responses of a ship in a seaway. Although transfer functions, in theory, can be calculated to exactly reflect the behaviour of the ship when exposed to waves, uncertainty in inp...
Properties of backward electromagnetic waves and negative reflection in ferrite films
International Nuclear Information System (INIS)
Vashkovsky, Anatolii V; Lock, Edwin H
2006-01-01
For a backward electromagnetic wave (magnetostatic wave) in a ferrite film, reflection from a perfect mirror formed by the straight edge of the film is investigated experimentally and theoretically. It is found that when the incident wave is collinear (the group velocity vector and the wave vector have opposite directions), negative reflection occurs at any angle of incidence, i.e., the incident and reflected beams are on the same side of the normal to the boundary. It is discovered that a noncollinear backward wave is nonreciprocal in the sense that its energy can be localized both near the surface and in the middle of the film. This property, previously observed only for surface magnetostatic waves, provides both the efficiency of generating and receiving the wave and the possibility of observing the reflected beam. A situation is realized where wave reflection results in two reflected beams. The properties of backward electromagnetic waves propagating in ferrite films are briefly analyzed. (methodological notes)
Viscoelasticity evaluation of rubber by surface reflection of supersonic wave.
Omata, Nobuaki; Suga, Takahiro; Furusawa, Hirokazu; Urabe, Shinichi; Kondo, Takeru; Ni, Qing-Qing
2006-12-22
The main characteristic of rubber is a viscoelasticity. So it is important to research the characteristic of the viscoelasticity of the high frequency band for the friction between a rubber material and the hard one with roughness, for instance, the tire and the road. As for the measurement of the viscoelasticity of rubber, DMA (dynamic mechanical analysis) is general. However, some problems are pointed out to the measurement of the high frequency band by DMA. Then, we evaluated the viscoelasticity characteristic by the supersonic wave measurement. However, attenuation of rubber is large, and when the viscoelasticity is measured by the supersonic wave therefore, it is inconvenient and limited in a past method by means of bottom reflection. In this report, we tried the viscoelasticity evaluation by the method of using complex surface reflection coefficient and we compared with the friction coefficient under wide-range friction velocity. As a result, some relationships had been found for two properties. We report the result that character of viscoelasticity of rubber was comparable to friction coefficient.
International Nuclear Information System (INIS)
Chandran, Benjamin D. G.; Hollweg, Joseph V.
2009-01-01
We study the propagation, reflection, and turbulent dissipation of Alfven waves in coronal holes and the solar wind. We start with the Heinemann-Olbert equations, which describe non-compressive magnetohydrodynamic fluctuations in an inhomogeneous medium with a background flow parallel to the background magnetic field. Following the approach of Dmitruk et al., we model the nonlinear terms in these equations using a simple phenomenology for the cascade and dissipation of wave energy and assume that there is much more energy in waves propagating away from the Sun than waves propagating toward the Sun. We then solve the equations analytically for waves with periods of hours and longer to obtain expressions for the wave amplitudes and turbulent heating rate as a function of heliocentric distance. We also develop a second approximate model that includes waves with periods of roughly one minute to one hour, which undergo less reflection than the longer-period waves, and compare our models to observations. Our models generalize the phenomenological model of Dmitruk et al. by accounting for the solar wind velocity, so that the turbulent heating rate can be evaluated from the coronal base out past the Alfven critical point-that is, throughout the region in which most of the heating and acceleration occurs. The simple analytical expressions that we obtain can be used to incorporate Alfven-wave reflection and turbulent heating into fluid models of the solar wind.
Full-waveform inversion with reflected waves for 2D VTI media
Pattnaik, Sonali
2016-09-06
Full-waveform inversion in anisotropic media using reflected waves suffers from the strong non-linearity of the objective function and trade-offs between model parameters. Estimating long-wavelength model components by fixing parameter perturbations, referred to as reflection-waveform inversion (RWI), can mitigate nonlinearity-related inversion issues. Here, we extend RWI to acoustic VTI (transversely isotropic with a vertical symmetry axis) media. To minimize trade-offs between the model parameters, we employ a new hierarchical two-stage approach that operates with the P-wave normal-moveout velocity and anisotropy coefficents ζ and η. First, is estimated using a fixed perturbation in ζ, and then we invert for η by fixing the updated perturbation in . The proposed 2D algorithm is tested on a horizontally layered VTI model.
Sound excitation at reflection of two electromagnetic waves from dence semibounded plasma
International Nuclear Information System (INIS)
Livdan, D.O.; Muratov, V.I.; Shuklin, A.P.
1988-01-01
The problem of two electromagnetic waves reflection by semibounded plasma which is nontransparent for each of these waves is solved. The reflection coefficients are obtained for normally incident waves. It is shown that the moduli of the reflection coefficients differ from the unit and this is due to the interaction of the external raiation with the acoustic wave excited in plasma. The energy flux in plasma is calculated
Development of pneumatic actuator with low-wave reflection characteristics
Chang, H.; Tsung, T. T.; Jwo, C. S.; Chiang, J. C.
2010-08-01
This study aims at the development of a less reflective electromagnetic pneumatic actuator often used in the anechoic chamber. Because a pneumatic actuator on the market is not appropriate for use in such a chamber and a metallic one has high dielectric constant which generates reflective electromagnetic waves to influence test parameters in the chamber. The newly developed pneumatic actuator is made from low dielectric constant plastics with less reflective of electromagnetic. A turbine-type air motor is used to develop the pneumatic actuator and a employ Prony tester is used to run the brake horsepower test for the performance test of pneumatic actuator. Test results indicate that the pneumatic actuator in the minimal starting flow is 17 l/min, and it generates a brake horsepower of 48 mW; in the maximum flow is 26 l/min, it generates a brake horsepower of 108 mW. Therefore, it works with a torque between 0.24 N-m and 0.55 N-m, and such a torque will be sufficient to drive the target button.
Observation of strong reflection of electron waves exiting a ballistic channel at low energy
Energy Technology Data Exchange (ETDEWEB)
Vaz, Canute I.; Campbell, Jason P.; Ryan, Jason T.; Gundlach, David; Cheung, Kin. P., E-mail: Kin.Cheung@NIST.gov [National Institute of Standards and Technology, Gaithersburg, MD 20899-8120 (United States); Liu, Changze [National Institute of Standards and Technology, Gaithersburg, MD 20899-8120 (United States); Institute of Microelectronics, Peking University, Beijing 100871 (China); Southwick, Richard G. [National Institute of Standards and Technology, Gaithersburg, MD 20899-8120 (United States); IBM Research, Albany, NY 12205 (United States); Oates, Anthony S. [Taiwan Semiconductor Manufacturing Corporation, Hsinchu 30844, Taiwan (China); Huang, Ru [Institute of Microelectronics, Peking University, Beijing 100871 (China)
2016-06-15
Wave scattering by a potential step is a ubiquitous concept. Thus, it is surprising that theoretical treatments of ballistic transport in nanoscale devices, from quantum point contacts to ballistic transistors, assume no reflection even when the potential step is encountered upon exiting the device. Experiments so far seem to support this even if it is not clear why. Here we report clear evidence of coherent reflection when electron wave exits the channel of a nanoscale transistor and when the electron energy is low. The observed behavior is well described by a simple rectangular potential barrier model which the Schrodinger’s equation can be solved exactly. We can explain why reflection is not observed in most situations but cannot be ignored in some important situations. Our experiment also represents a direct measurement of electron injection velocity - a critical quantity in nanoscale transistors that is widely considered not measurable.
Wave Generation in Physical Models
DEFF Research Database (Denmark)
Andersen, Thomas Lykke; Frigaard, Peter
The present book describes the most important aspects of wave generation techniques in physical models. Moreover, the book serves as technical documentation for the wave generation software AwaSys 6, cf. Aalborg University (2012). In addition to the two main authors also Tue Hald and Michael...
Kasimov, Aslan R.; Faria, Luiz; Rosales, Rodolfo R.
2013-01-01
: steady traveling wave solutions, instability of such solutions, and the onset of chaos. Our model is the first (to our knowledge) to describe chaos in shock waves by a scalar first-order partial differential equation. The chaos arises in the equation
Reflective coating optimization for interferometric detectors of gravitational waves.
Principe, Maria
2015-05-04
Brownian fluctuations in the highly reflective test-mass coatings are the dominant noise source, in a frequency band from a few tens to a few hundreds Hz, for Earth-bound detectors of Gravitational Waves. Minimizing such noise is mandatory to increase the visibility distance of these instruments, and eventually reach their quantum-limited sensitivity. Several strategies exist to achieve this goal. Layer thickness and material properties optimization have been proposed and effectively implemented, and are reviewed in this paper, together with other, so far less well developed, options. The former is the simplest option, yielding a sensible noise reduction with limited technological challenges; the latter is more technologically demanding, but is needed for future (cryogenic) detectors.
Modeling ionization by helicon waves
International Nuclear Information System (INIS)
Degeling, A.W.; Boswell, R.W.
1997-01-01
The response of the electron distribution function in one dimension to a traveling wave electric field is modeled for parameters relevant to a low-pressure helicon wave plasma source, and the resulting change in the ionization rate calculated. This is done by calculating the trajectories of individual electrons in a given wave field and assuming no collisions to build up the distribution function as the distance from the antenna is increased. The ionization rate is calculated for argon by considering the ionization cross section and electron flux at a specified position and time relative to the left-hand boundary, where the distribution function is assumed to be Maxwellian and the wave travels to the right. The simulation shows pulses in the ionization rate that move away from the antenna at the phase velocity of the wave, demonstrating the effect of resonant electrons trapped in the wave close-quote s frame of reference. It is found that the ionization rate is highest when the phase velocity of the wave is between 2 and 3x10 6 m/s, where the electrons interacting strongly with the wave (i.e., electrons with velocities inside the wave close-quote s open-quotes trapping widthclose quotes) have initial energies just below the ionization threshold. Results from the model are compared with experimental data and show reasonable qualitative agreement. copyright 1997 American Institute of Physics
Binumol, S.; Rao, Subba; Hegde, Arkal Vittal
2017-09-01
Breakwaters are one of the most important harbour structures constructed to withstand and dissipate the dynamic energy due to the action of the waves. Due to fast growing need of the universe and advances in technology different types of breakwaters are being developed. Quarter circle breakwater is a new type of breakwater emerged from semi circular breakwater and the first model was developed in Peoples Republic of China (2006). Quarter circle breakwater with perforations posses merits of caisson as well as perforated breakwaters such as low weight, requires less materials, suited for poor soil conditions, easily transported, handled and placed at the site, aesthetically pleasing, cost effective, eco-friendly and stable. Therefore it is necessary to carry out detailed studies on hydrodynamic characteristics to investigate the suitability and applicability of various types of quarter circle breakwaters. The present study investigates the wave reflection and loss characteristics of an emerged seaside perforated quarter circle breakwater of radius 55 cm and with varying ratios of spacing to diameter of perforations, for different water depths and wave conditions. The tests were conducted in the two-dimensional monochromatic wave flume available in Marine Structures laboratory of Department of Applied Mechanics and Hydraulics of National Institute of Technology, Surathkal, Karnataka, India. The results were plotted as non-dimensional graphs and it was observed that the reflection coefficient increases with increase in wave steepness for all values of ratio of height of breakwater structure to water depth. For a constant water depth, wave reflection increases with increase in ratio of spacing to diameter of perforations. It was also found that the loss coefficient decreases with increase in wave steepness for all values of ratio of height of breakwater structure to water depth, and ratio of spacing to diameter of perforations.
Reflective measurement of water concentration using millimeter wave illumination
Sung, Shijun; Bennett, David; Taylor, Zachary; Bajwa, Neha; Tewari, Priyamvada; Maccabi, Ashkan; Culjat, Martin; Singh, Rahul; Grundfest, Warren
2011-04-01
THz and millimeter wave technology have shown the potential to become a valuable medical imaging tool because of its sensitivity to water and safe, non-ionizing photon energy. Using the high dielectric constant of water in these frequency bands, reflectionmode THz sensing systems can be employed to measure water content in a target with high sensitivity. This phenomenology may lead to the development of clinical systems to measure the hydration state of biological targets. Such measurements may be useful in fast and convenient diagnosis of conditions whose symptoms can be characterized by changes in water concentration such as skin burns, dehydration, or chemical exposure. To explore millimeter wave sensitivity to hydration, a reflectometry system is constructed to make water concentration measurements at 100 GHz, and the minimum detectable water concentration difference is measured. This system employs a 100 GHz Gunn diode source and Golay cell detector to perform point reflectivity measurements of a wetted polypropylene towel as it dries on a mass balance. A noise limited, minimum detectable concentration difference of less than 0.5% by mass can be detected in water concentrations ranging from 70% to 80%. This sensitivity is sufficient to detect hydration changes caused by many diseases and pathologies and may be useful in the future as a diagnostic tool for the assessment of burns and other surface pathologies.
Directory of Open Access Journals (Sweden)
Narottam Maity
2016-01-01
Full Text Available Reflection of longitudinal displacement waves in a generalized thermoelastic half space under the action of uniform magnetic field has been investigated. The magnetic field is applied in such a direction that the problem can be considered as a two-dimensional one. The discussion is based on the three theories of generalized thermoelasticity: Lord-Shulman (L-S, Green-Lindsay (G-L, and Green-Naghdi (G-N with energy dissipation. We compute the possible wave velocities for different models. Amplitude ratios have been presented. The effects of magnetic field on various subjects of interest are discussed and shown graphically.
Sung, Shih-Hsien; Cheng, Hao-Min; Wang, Kang-Ling; Yu, Wen-Chung; Chuang, Shao-Yuan; Ting, Chih-Tai; Lakatta, Edward G; Yin, Frank C P; Chou, Pesus; Chen, Chen-Huan
2013-06-01
Arterial aging may link cardiovascular risk to white coat hypertension (WCH). The aims of the present study were to investigate the role of arterial aging in the white coat effect, defined as the difference between office and 24-hour ambulatory systolic blood pressures, and to compare WCH with prehypertension (PH) with respect to target organ damage and long-term cardiovascular mortality. A total of 1257 never-been-treated volunteer subjects from a community-based survey were studied. WCH and PH were defined by office and 24-hour ambulatory blood pressures. Left ventricular mass index, carotid intima-media thickness, estimated glomerular filtration rate, carotid-femoral pulse wave velocity, carotid augmentation index, amplitude of the reflection pressure wave, and 15-year cardiovascular mortality were determined. Subjects with WCH were significantly older and had greater body mass index, blood pressure values, intima-media thickness, carotid-femoral pulse wave velocity, augmentation index, amplitude of the backward pressure wave, and a lower estimated glomerular filtration rate than PH. Amplitude of the backward pressure wave was the most important independent correlate of the white coat effect in multivariate analysis (model r(2)=0.451; partial r(2)/model r(2)=90.5%). WCH had significantly greater cardiovascular mortality than PH (hazard ratio, 2.94; 95% confidence interval, 1.09-7.91), after accounting for age, sex, body mass index, smoking, fasting plasma glucose, and total cholesterol/high-density lipoprotein-cholesterol ratio. Further adjustment of the model for amplitude of the backward pressure wave eliminated the statistical significance of the WCH effect. In conclusion, the white coat effect is mainly caused by arterial aging. WCH carries higher risk for cardiovascular mortality than PH, probably via enhanced wave reflections that accompany arterial aging.
Reflection of a shock wave from a thermally accommodating wall - Molecular simulation.
Deiwert, G. S.
1973-01-01
Reflection of a plane shock wave from a wall has been simulated on a microscopic scale using a direct simulation Monte Carlo technique of the type developed by Bird. A monatomic gas model representing argon was used to describe the fluid medium and a simple one-parameter accommodation coefficient model was used to describe the gas-surface interaction. The influence of surface accommodation was studied parametrically by varying the accommodation coefficient from zero to one. Results are presented showing the temporal variations of flow field density, and mass, momentum, and energy fluxes to the wall during the shock wave reflection process. The energy flux was used to determine the wall temperature history. Comparisons with experiment are found to be satisfactory where data are available.
Constrained reaction volume approach for studying chemical kinetics behind reflected shock waves
Hanson, Ronald K.
2013-09-01
We report a constrained-reaction-volume strategy for conducting kinetics experiments behind reflected shock waves, achieved in the present work by staged filling in a shock tube. Using hydrogen-oxygen ignition experiments as an example, we demonstrate that this strategy eliminates the possibility of non-localized (remote) ignition in shock tubes. Furthermore, we show that this same strategy can also effectively eliminate or minimize pressure changes due to combustion heat release, thereby enabling quantitative modeling of the kinetics throughout the combustion event using a simple assumption of specified pressure and enthalpy. We measure temperature and OH radical time-histories during ethylene-oxygen combustion behind reflected shock waves in a constrained reaction volume and verify that the results can be accurately modeled using a detailed mechanism and a specified pressure and enthalpy constraint. © 2013 The Combustion Institute.
An asymptotic model of seismic reflection from a permeable layer
Energy Technology Data Exchange (ETDEWEB)
Silin, D.; Goloshubin, G.
2009-10-15
Analysis of compression wave propagation in a poroelastic medium predicts a peak of reflection from a high-permeability layer in the low-frequency end of the spectrum. An explicit formula expresses the resonant frequency through the elastic moduli of the solid skeleton, the permeability of the reservoir rock, the fluid viscosity and compressibility, and the reservoir thickness. This result is obtained through a low-frequency asymptotic analysis of Biot's model of poroelasticity. A review of the derivation of the main equations from the Hooke's law, momentum and mass balance equations, and Darcy's law suggests an alternative new physical interpretation of some coefficients of the classical poroelasticity. The velocity of wave propagation, the attenuation factor, and the wave number, are expressed in the form of power series with respect to a small dimensionless parameter. The absolute value of this parameter is equal to the product of the kinematic reservoir fluid mobility and the wave frequency. Retaining only the leading terms of the series leads to explicit and relatively simple expressions for the reflection and transmission coefficients for a planar wave crossing an interface between two permeable media, as well as wave reflection from a thin highly-permeable layer (a lens). Practical applications of the obtained asymptotic formulae are seismic modeling, inversion, and at-tribute analysis.
Reflection and absorption of ion-acoustic waves in a plasma density gradient
International Nuclear Information System (INIS)
Ishihara, O.
1977-01-01
Plasma is characterized by electrical quasineutrality and the collective behavior. There exists a longitudinal low-frequency wave called an ion-acoustic wave in a plasma. One problem in the experimental study of ion-acoustic waves has been that sometimes they are observed to be reflected from discharge tube walls, and sometimes to be absorbed. Theoretical computation reveals that a velocity gradient produced by a density gradient plays a significant role in the reflection. The velocity gradient produces the subsonic-supersonic transition and long wavelength waves are reflected before reaching the transition while short wavelength waves penetrate over the transition and are absorbed in the supersonic flow plasma
Treadmill walking with load carriage increases aortic pressure wave reflection.
Ribeiro, Fernando; Oliveira, Nórton L; Pires, Joana; Alves, Alberto J; Oliveira, José
2014-01-01
The study examined the effects of treadmill walking with load carriage on derived measures of central pressure and augmentation index in young healthy subjects. Fourteen male subjects (age 31.0 ± 1.0 years) volunteered in this study. Subjects walked 10 minutes on a treadmill at a speed of 5 km/h carrying no load during one session and a load of 10% of their body weight on both upper limbs in two water carboys with handle during the other session. Pulse wave analysis was performed at rest and immediately after exercise in the radial artery of the right upper limb by applanation tonometry. The main result indicates that walking with load carriage sharply increased augmentation index at 75 bpm (-5.5 ± 2.2 to -1.4 ± 2.2% vs. -5.2 ± 2.8 to -5.5 ± 2.1%, p<0.05), and also induced twice as high increments in central pulse pressure (7.4 ± 1.5 vs. 3.1 ± 1.4 mmHg, p<0.05) and peripheral (20.5 ± 2.7 vs. 10.3 ± 2.5 mmHg, p<0.05) and central systolic pressure (14.7 ± 2.1 vs. 7.4 ± 2.0 mmHg, p<0.05). Walking with additional load of 10% of their body weight (aerobic exercise accompanied by upper limb isometric contraction) increases derived measures of central pressure and augmentation index, an index of wave reflection and arterial stiffness. Copyright © 2013 Sociedade Portuguesa de Cardiologia. Published by Elsevier España. All rights reserved.
Variation of wave speed determined by the PU-loop with proximity to a reflection site.
Li, Ye; Borlotti, Alessandra; Parker, Kim H; Khir, Ashraf W
2011-01-01
Wave speed is directly related to arterial distensibility and is widely used by clinicians to assess arterial stiffness. The PU-loop method for determining wave speed is based on the water hammer equation for flow in flexible tubes and artery using the method of characteristics. This technique determines wave speed using simultaneous measurements of pressure and velocity at a single point. The method shows that during the early part of systole, the relationship between pressure and velocity is generally linear, and the initial slope of the PU-loop is proportional to wave speed. In this work, we designed an in-vitro experiment to investigate the effect of proximity to a reflection site on the wave speed determined by the PU-loop through varying the distance between the measurement and reflection sites. Measurements were made in a flexible tube with a reflection site at the distal end formed by joining the tube to another tube with a different diameter and material properties. Six different flexible tubes were used to generate both positive and negative reflection coefficients of different magnitudes. We found that the wave speed determined by the PU-loop did not change when the measurement site was far from the reflection site but did change as the distance to the reflection site decreased. The calculated wave speed increased with positive reflections and decreased with negative reflections. The magnitude of the change in wave speed at a fixed distance from the reflection site increased with increasing the value of the reflection coefficient.
Zhang, Sanzong
2015-05-26
Full-waveform inversion requires the accurate simulation of the dynamics and kinematics of wave propagation. This is difficult in practice because the amplitudes cannot be precisely reproduced for seismic waves in the earth. Wave-equation reflection traveltime tomography (WT) is proposed to avoid this problem by directly inverting the reflection-traveltime residuals without the use of the high-frequency approximation. We inverted synthetic traces and recorded seismic data for the velocity model by WT. Our results demonstrated that the wave-equation solution overcame the high-frequency approximation of ray-based tomography, was largely insensitive to the accurate modeling of amplitudes, and mitigated problems with ambiguous event identification. The synthetic examples illustrated the effectiveness of the WT method in providing a highly resolved estimate of the velocity model. A real data example from the Gulf of Mexico demonstrated these benefits of WT, but also found the limitations in traveltime residual estimation for complex models.
Reflection and transformation of acoustic waves at the interface in superfluid 3He-A
International Nuclear Information System (INIS)
Kekutiya, Sh.E.; Chkhaidze, N.D.
1997-01-01
Reflection and transformation of acoustic waves in 3 He-A and 3 He-A 1 are considered for two cases: (1) at the boundary with a solid impermeable wall at an arbitrary angle of incidence of a wave and (2) for normal incidence of waves on the interface between a free liquid and a system of periodic plane-parallel capillaries filling the semi-space. For the first case we have calculated the reflection coefficients of the first and the second sounds and spin and spin-temperature waves as well as the coefficients of transformation of these waves into each other. It is shown that the longitudinal wave undergoes no transformation into other waves, there occurs instead its complete reflection from the solid wall. The angle of incidence at which the energy attenuation coefficient of the first sound is maximum, and the interval of angles corresponding to the attenuation and the total interval reflection of the second sound are estimated. For the second case we have obtained: the coefficients of excitation of the fourth sound and the magneto-acoustic wave by the first and the second sounds; the reflection coefficients for the first and the second sounds and the longitudinal spin wave; the coefficient of transformation of the first sound into the second one and vice versa; the coefficient of reflection of the fourth sound from the capillary system - free liquid interface; the coefficient of excitation of longitudinal spin wave in free helium by the same wave in a capillary
Light reflection from a rough liquid surface including wind-wave effects in a scattering atmosphere
International Nuclear Information System (INIS)
Salinas, Santo V.; Liew, S.C.
2007-01-01
Visible and near-IR images of the ocean surface, taken from remote satellites, often contain important information of near-surface or sub-surface processes, which occur on, or over the ocean. Remote measurements of near surface winds, sea surface temperature and salinity, ocean color and underwater bathymetry, all, one way or another, depend on how well we understand sea surface roughness. However, in order to extract useful information from our remote measurements, we need to construct accurate models of the transfer of solar radiation inside the atmosphere as well as, its reflection from the sea surface. To approach this problem, we numerically solve the radiative transfer equation (RTE) by implementing a model for the atmosphere-ocean system. A one-dimensional atmospheric radiation model is solved via the widely known doubling and adding method and the ocean body is treated as a boundary condition to the problem. The ocean surface is modeled as a rough liquid surface which includes wind interaction and wave states, such as wave age. The model can have possible applications to the retrieval of wind and wave states, such as wave age, near a Sun glint region
Modelling offshore sand wave evolution
Nemeth, Attila; Hulscher, Suzanne J.M.H.; van Damme, Rudolf M.J.
2007-01-01
We present a two-dimensional vertical (2DV) flow and morphological numerical model describing the behaviour of offshore sand waves. The model contains the 2DV shallow water equations, with a free water surface and a general bed load formula. The water movement is coupled to the sediment transport
Toy models of crossed Andreev reflection
International Nuclear Information System (INIS)
Melin, R; Jirari, H; Peysson, S
2003-01-01
We propose toy models of crossed Andreev reflection in multiterminal hybrid structures containing out-of-equilibrium conductors. We apply the description to two possible experiments: (i) to a device containing a large quantum dot inserted in a crossed Andreev reflection circuit, and (ii) to a device containing an Aharonov-Bohm loop inserted in a crossed Andreev reflection circuit
Reflection and transmission of full-vector X-waves normally incident on dielectric half spaces
Salem, Mohamed
2011-08-01
The reflection and transmission of full-vector X-Waves incident normally on a planar interface between two lossless dielectric half-spaces are investigated. Full-vector X-Waves are obtained by superimposing transverse electric and magnetic polarization components, which are derived from the scalar X-Wave solution. The analysis of transmission and reflection is carried out via a straightforward but yet effective method: First, the X-Wave is decomposed into vector Bessel beams via the Bessel-Fourier transform. Then, the reflection and transmission coefficients of the beams are obtained in the spectral domain. Finally, the transmitted and reflected X-Waves are obtained via the inverse Bessel-Fourier transform carried out on the X-wave spectrum weighted with the corresponding coefficient. © 2011 IEEE.
Vignati, F.; Guardone, A.
2017-11-01
An analytical model for the evolution of regular reflections of cylindrical converging shock waves over circular-arc obstacles is proposed. The model based on the new (local) parameter, the perceived wedge angle, which substitutes the (global) wedge angle of planar surfaces and accounts for the time-dependent curvature of both the shock and the obstacle at the reflection point, is introduced. The new model compares fairly well with numerical results. Results from numerical simulations of the regular to Mach transition—eventually occurring further downstream along the obstacle—point to the perceived wedge angle as the most significant parameter to identify regular to Mach transitions. Indeed, at the transition point, the value of the perceived wedge angle is between 39° and 42° for all investigated configurations, whereas, e.g., the absolute local wedge angle varies in between 10° and 45° in the same conditions.
Directory of Open Access Journals (Sweden)
J. Soares
1999-06-01
Full Text Available The effect of viscosity, non linearities, incident wave period and realistic eastern coastline geometry on energy fluxes are investigated using a shallow water model with a spatial resolution of 1/4 degree in both meridional and zonal directions. Equatorial and mid-latitude responses are considered. It is found that (1 the influence of the coastline geometry and the incident wave period is more important for the westward energy flux than for the poleward flux, and (2 the effect of the inclination of the eastern ocean boundary on the poleward energy flux, for the Pacific and Atlantic Oceans, decline as the period of the incident wave increases. Furthermore, the model simulations suggest that the poleward energy fluxes from meridional boundaries give plausible results for motions of seasonal and annual periods. For comparatively shorter periods, a realistic coastline geometry has to be included for more accurate results. It is recommended that any numerical model involving the reflection of baroclinic Rossby waves (of intraseasonal, seasonal or annual periods on the eastern Pacific or Atlantic Oceans, should consider the effect of the coastline geometry in order to improve the accuracy of the results.Key words. Oceanography: general (climate and interannual variability; equatorial oceanography. Oceanography: physical (eastern boundary currents.
A Data-Driven Reflectance Model
Matusik, Wojciech; Pfister, Hanspeter; Brand, Matt; McMillan, Leonard
2003-01-01
We present a generative model for isotropic bidirectional reflectance distribution functions (BRDFs) based on acquired reflectance data. Instead of using analytical reflectance models, we represent each BRDF as a dense set of measurements. This allows us to interpolate and extrapolate in the space of acquired BRDFs to create new BRDFs. We treat each acquired BRDF as a single high-dimensional vector taken from a space of all possible BRDFs. We apply both linear (subspace) and non-linear (manif...
Boulanger, Jean-Philippe; Fu, Lee-Lueng
1996-01-01
The TOPEX/POSEIDON sea level data lead to new opportunities to investigate some theoretical mechanisms suggested to be involved in the El Nino-Southern Oscillation phenomenon in the tropical Pacific ocean. In particular, we are interested in studying the western boundary reflection, a process crucial for the delayed action oscillator theory, by using the TOPEX/POSEIDON data from November 1992 to May 1995. We first projected the sea level data onto Kelvin and first-mode Ross waves. Then we estimated the contribution of wind forcing to these waves by using a single baroclinic mode simple wave model forced by the ERS-1 wind data. Wave propagation was clearly observed with amplitudes well explained by the wind forcing in the ocean interior. Evidence of wave reflection was detected at both the western and eastern boundaries of the tropical Pacific ocean. At the eastern boundary, Kelvin waves were seen to reflect as first-mode Rossby waves during the entire period. The reflection efficiency (in terms of wave amplitude) of the South American coasts was estimated to be 80% of that of an infinite meridional wall. At the western boundary, reflection was observed in April-August 1993, in January-June 1994, and, later, in December 1994 to February 1995. Although the general roles of these reflection events in the variability observed in the equatorial Pacific ocean are not clear, the data suggest that the reflections in January-June 1994 have played a role in the onset of the warm conditions observed in late 1994 to early 1995. Indeed, during the January-June 1994 period, as strong downwelling first-mode Rossby waves reflected into downwelling Kelvin waves, easterly wind and cold sea surface temperature anomalies located near the date line weakened and eventually reversed in June-July 1994. The presence of the warm anomalies near the date line then favored convection and westerly wind anomalies that triggered strong downwelling Kelvin waves propagating throughout the basin
REFLECT: a program to integrate the wave equation through a plane stratified plasma
International Nuclear Information System (INIS)
Greene, J.W.
1975-01-01
A program was developed to integrate the wave equation through a plane stratified plasma with a general density distribution. The reflection and transmission of a plane wave are computed as a function of the angle of incidence. The polarization of the electric vector is assumed to be perpendicular to the plane of incidence. The model for absorption by classical inverse bremsstrahlung avoids the improper extrapolation of underdense formulae that are singular at the plasma critical surface. Surprisingly good agreement with the geometric-optics analysis of a linear layer was found. The system of ordinary differential equations is integrated by the variable-step, variable-order Adams method in the Lawrence Livermore Laboratory Gear package. Parametric studies of the absorption are summarized, and some possibilities for further development of the code are discussed. (auth)
International Nuclear Information System (INIS)
Totović, A R; Crnjanski, J V; Krstić, M M; Gvozdić, D M
2014-01-01
In this paper, we analyze two semiconductor optical amplifier (SOA) structures, traveling-wave and reflective, with the active region made of the bulk material. The model is based on the stationary traveling-wave equations for forward and backward propagating photon densities of the signal and the amplified spontaneous emission, along with the stationary carrier rate equation. We start by introducing linear approximation of the carrier density spatial distribution, which enables us to find solutions for the photon densities in a closed analytical form. An analytical approach ensures a low computational resource occupation and an easy analysis of the parameters influencing the SOA’s response. The comparison of the analytical and numerical results shows high agreement for a wide range of the input optical powers and bias currents. (paper)
Influence of ionization on reflection of solitary waves in a magnetized plasma
International Nuclear Information System (INIS)
Jyoti,; Malik, Hitendra K.; Kumar, Ravinder; Dahiya, Raj P.
2013-01-01
The reflection of nonlinear solitary waves is studied in a nonuniform, magnetized plasma diffusing from an ionization source along the magnetic field lines. Contribution of the ionization term is included in the continuity equation. The behavior of solitary waves is governed by modified form of Korteweg–de Vries equation (called mKdV equation). In order to investigate the reflection of solitary waves, the mKdV equations for the right and left going waves are derived, and solved by finding new transformations coupled at the point of reflection, for obtaining the expression of reflection coefficient. Contrary to the case of usual inhomogeneous plasma, the present analysis shows that a combination of usual sech 2 structure and tanh structure (called the tail of soliton) arises due to the influence of ionization term. Interestingly, this tailing structure disappears after the reflection of the soliton and hence, the soliton is downshifted prominently
Hu, T. C. J.; Glass, I. I.
Results are reported from experimental and analytical investigations of real-gas effects in the propagation of shock waves through SF6, a gas with 15 vibrational degrees of freedom. Shock waves with speeds ranging from Mach 1.25-8 were directed toward sharp steel wedges in a hypervelocity shock tube. Mach-Zehnder interferometry was used to obtain shock shape and geometry, isopycnic and density field data. Frozen-gas and equilibrium-gas (EQM) analyses modeling were performed for comparisons with experimental data, which depicted four types of reflection and transitions among them. Transition boundaries were best predicted with EQM treatment. A new criterion was derived for transition between single-Mach and complex-Mach reflection. Regular reflection continued past the boundary line defined by the transition criterion because of boundary layer growth produced on the wedge surface by passage of the shock wave.
Characteristics of Wave Reflection for Vertical and Slit Caissons with Porous Structures
Directory of Open Access Journals (Sweden)
Tae-Hwa Jung
2012-01-01
Full Text Available Offshore structures are occasionally located at a relatively deep water region, the outside of breakwater. In this case, these structures may be damaged by the supposition of incident and reflected waves from a vertical breakwater. To prevent the damage, the reflected waves are controlled by installing porous structures at the face of the vertical breakwater. In this study, numerical experiments are carried out to identify the characteristics of wave reflection from the porous structures installing in front of a vertical or slit caisson.
Sutherland models for complex reflection groups
International Nuclear Information System (INIS)
Crampe, N.; Young, C.A.S.
2008-01-01
There are known to be integrable Sutherland models associated to every real root system, or, which is almost equivalent, to every real reflection group. Real reflection groups are special cases of complex reflection groups. In this paper we associate certain integrable Sutherland models to the classical family of complex reflection groups. Internal degrees of freedom are introduced, defining dynamical spin chains, and the freezing limit taken to obtain static chains of Haldane-Shastry type. By considering the relation of these models to the usual BC N case, we are led to systems with both real and complex reflection groups as symmetries. We demonstrate their integrability by means of new Dunkl operators, associated to wreath products of dihedral groups
Using wave intensity analysis to determine local reflection coefficient in flexible tubes.
Li, Ye; Parker, Kim H; Khir, Ashraf W
2016-09-06
It has been shown that reflected waves affect the shape and magnitude of the arterial pressure waveform, and that reflected waves have physiological and clinical prognostic values. In general the reflection coefficient is defined as the ratio of the energy of the reflected to the incident wave. Since pressure has the units of energy per unit volume, arterial reflection coefficient are traditionally defined as the ratio of reflected to the incident pressure. We demonstrate that this approach maybe prone to inaccuracies when applied locally. One of the main objectives of this work is to examine the possibility of using wave intensity, which has units of energy flux per unit area, to determine the reflection coefficient. We used an in vitro experimental setting with a single inlet tube joined to a second tube with different properties to form a single reflection site. The second tube was long enough to ensure that reflections from its outlet did not obscure the interactions of the initial wave. We generated an approximately half sinusoidal wave at the inlet of the tube and took measurements of pressure and flow along the tube. We calculated the reflection coefficient using wave intensity (R dI and R dI 0.5 ) and wave energy (R I and R I 0.5 ) as well as the measured pressure (R dP ) and compared these results with the reflection coefficient calculated theoretically based on the mechanical properties of the tubes. The experimental results show that the reflection coefficients determined by all the techniques we studied increased or decreased with distance from the reflection site, depending on the type of reflection. In our experiments, R dP , R dI 0.5 and R I 0.5 are the most reliable parameters to measure the mean reflection coefficient, whilst R dI and R I provide the best measure of the local reflection coefficient, closest to the reflection site. Additional work with bifurcations, tapered tubes and in vivo experiments are needed to further understand, validate the
Overview of Wave to Wire Models
DEFF Research Database (Denmark)
Nielsen, Kim; Kramer, Morten Mejlhede; Ferri, Francesco
A “Wave to Wire” (W2W) model is a numerical tool that can calculate the power output from a specified Wave Energy Converter (WEC), under specified ocean wave conditions. The tool can be used to assess and optimize the performance of a Wave Energy Converter (WEC) design and provide knowledge...
Directory of Open Access Journals (Sweden)
Sukhendu Dey
1980-01-01
Full Text Available In the present paper the influence of the initial stress is shown on the reflection and transmission of P waves at the core-mantle boundary. Taking a particular value of the inherent initial stress, the variations of reflection and transmission coefficients with respect to the angle of emergence are represented by graphs. These graphs when compared with those having no initial stress show that the effect of the initial stress is to produce a reflected P and S waves with numerically higher amplitudes but a transmitted P wave with smaller amplitude. A method is also indicated in this paper to calculate the actual value of the initial stress near the core-mantle boundary by measuring the amplitudes of incident and reflected P waves.
Constrained reaction volume approach for studying chemical kinetics behind reflected shock waves
Hanson, Ronald K.; Pang, Genny A.; Chakraborty, Sreyashi; Ren, Wei; Wang, Shengkai; Davidson, David Frank
2013-01-01
We report a constrained-reaction-volume strategy for conducting kinetics experiments behind reflected shock waves, achieved in the present work by staged filling in a shock tube. Using hydrogen-oxygen ignition experiments as an example, we
Reflection of Lamb waves obliquely incident on the free edge of a plate.
Santhanam, Sridhar; Demirli, Ramazan
2013-01-01
The reflection of obliquely incident symmetric and anti-symmetric Lamb wave modes at the edge of a plate is studied. Both in-plane and Shear-Horizontal (SH) reflected wave modes are spawned by an obliquely incident in-plane Lamb wave mode. Energy reflection coefficients are calculated for the reflected wave modes as a function of frequency and angle of incidence. This is done by using the method of orthogonal mode decomposition and by enforcing traction free conditions at the plate edge using the method of collocation. A PZT sensor network, affixed to an Aluminum plate, is used to experimentally verify the predictions of the analysis. Experimental results provide support for the analytically determined results. Copyright © 2012 Elsevier B.V. All rights reserved.
Angle-domain Migration Velocity Analysis using Wave-equation Reflection Traveltime Inversion
Zhang, Sanzong; Schuster, Gerard T.; Luo, Yi
2012-01-01
way as wave-equation transmission traveltime inversion. The residual movemout analysis in the angle-domain common image gathers provides a robust estimate of the depth residual which is converted to the reflection traveltime residual for the velocity
Kasimov, Aslan R.
2013-03-08
We propose the following model equation, ut+1/2(u2−uus)x=f(x,us) that predicts chaotic shock waves, similar to those in detonations in chemically reacting mixtures. The equation is given on the half line, x<0, and the shock is located at x=0 for any t≥0. Here, us(t) is the shock state and the source term f is taken to mimic the chemical energy release in detonations. This equation retains the essential physics needed to reproduce many properties of detonations in gaseous reactive mixtures: steady traveling wave solutions, instability of such solutions, and the onset of chaos. Our model is the first (to our knowledge) to describe chaos in shock waves by a scalar first-order partial differential equation. The chaos arises in the equation thanks to an interplay between the nonlinearity of the inviscid Burgers equation and a novel forcing term that is nonlocal in nature and has deep physical roots in reactive Euler equations.
DISPELLING ILLUSIONS OF REFLECTION: A NEW ANALYSIS OF THE 2007 MAY 19 CORONAL 'WAVE' EVENT
International Nuclear Information System (INIS)
Attrill, Gemma D. R.
2010-01-01
A new analysis of the 2007 May 19 coronal wave-coronal mass ejection-dimmings event is offered employing base difference extreme-ultraviolet (EUV) images. Previous work analyzing the coronal wave associated with this event concluded strongly in favor of purely an MHD wave interpretation for the expanding bright front. This conclusion was based to a significant extent on the identification of multiple reflections of the coronal wave front. The analysis presented here shows that the previously identified 'reflections' are actually optical illusions and result from a misinterpretation of the running difference EUV data. The results of this new multiwavelength analysis indicate that two coronal wave fronts actually developed during the eruption. This new analysis has implications for our understanding of diffuse coronal waves and questions the validity of the analysis and conclusions reached in previous studies.
NONLINEAR REFLECTION PROCESS OF LINEARLY POLARIZED, BROADBAND ALFVÉN WAVES IN THE FAST SOLAR WIND
Energy Technology Data Exchange (ETDEWEB)
Shoda, M.; Yokoyama, T., E-mail: shoda@eps.s.u-tokyo.ac.jp [Department of Earth and Planetary Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan)
2016-04-01
Using one-dimensional numerical simulations, we study the elementary process of Alfvén wave reflection in a uniform medium, including nonlinear effects. In the linear regime, Alfvén wave reflection is triggered only by the inhomogeneity of the medium, whereas in the nonlinear regime, it can occur via nonlinear wave–wave interactions. Such nonlinear reflection (backscattering) is typified by decay instability. In most studies of decay instabilities, the initial condition has been a circularly polarized Alfvén wave. In this study we consider a linearly polarized Alfvén wave, which drives density fluctuations by its magnetic pressure force. For generality, we also assume a broadband wave with a red-noise spectrum. In the data analysis, we decompose the fluctuations into characteristic variables using local eigenvectors, thus revealing the behaviors of the individual modes. Different from the circular-polarization case, we find that the wave steepening produces a new energy channel from the parent Alfvén wave to the backscattered one. Such nonlinear reflection explains the observed increasing energy ratio of the sunward to the anti-sunward Alfvénic fluctuations in the solar wind with distance against the dynamical alignment effect.
Iterative calculation of reflected and transmitted acoustic waves at a rough interface
Berkhoff, Arthur P.; van den Berg, P.M.; Thijssen, J.M.
A rigorous iterative technique is described for calculating the acoustic wave reflection and transmission at an irregular interface between two different media. The method is based upon a plane-wave expansion technique in which the acoustic field equations and the radiation condition are satisfied
Reflection and transmission of normally incident full-vector X waves on planar interfaces
Salem, Mohamed; Bagci, Hakan
2011-01-01
The reflection and transmission of full-vector X waves normally incident on planar half-spaces and slabs are studied. For this purpose, X waves are expanded in terms of weighted vector Bessel beams; this new decomposition and reconstruction method
Reflection of P and SV waves at the free surface of a monoclinic ...
Indian Academy of Sciences (India)
R.Narasimhan(krishtel emaging)1461 1996 Oct 15 13:05:22
The propagation of plane waves in an anisotropic elastic medium possessing monoclinic symmetry is discussed. The expressions for ... Keywords. Anisotropic medium; elastic waves; monoclinic half-space; reflection coefficients. Proc. Indian Acad. Sci. ...... In contrast, for C < 0, the angle of reflec- tion is less than the angle of ...
Reflection and transmission of full-vector X-waves normally incident on dielectric half spaces
Salem, Mohamed; Bagci, Hakan
2011-01-01
polarization components, which are derived from the scalar X-Wave solution. The analysis of transmission and reflection is carried out via a straightforward but yet effective method: First, the X-Wave is decomposed into vector Bessel beams via the Bessel-Fourier
Directory of Open Access Journals (Sweden)
Dong Yan
2017-01-01
Full Text Available Strong shock waves can be generated by pulse discharge in water, and the characteristics due to the shock wave normal reflection from rigid walls have important significance to many fields, such as industrial production and defense construction. This paper investigates the effects of hydrostatic pressures and perturbation of wave source (i.e., charging voltage on normal reflection of one-dimensional unsteady flow shock waves. Basic properties of the incidence and reflection waves were analyzed theoretically and experimentally to identify the reflection mechanisms and hence the influencing factors and characteristics. The results indicated that increased perturbation (i.e., charging voltage leads to increased peak pressure and velocity of the reflected shock wave, whereas increased hydrostatic pressure obviously inhibited superposition of the reflection waves close to the rigid wall. The perturbation of wave source influence on the reflected wave was much lower than that on the incident wave, while the hydrostatic pressure obviously affected both incident and reflection waves. The reflection wave from the rigid wall in water exhibited the characteristics of a weak shock wave, and with increased hydrostatic pressure, these weak shock wave characteristics became more obvious.
Energy Technology Data Exchange (ETDEWEB)
Erlangga, Mokhammad Puput [Geophysical Engineering, Institut Teknologi Bandung, Ganesha Street no.10 Basic Science B Buliding fl.2-3 Bandung, 40132, West Java Indonesia puput.erlangga@gmail.com (Indonesia)
2015-04-16
Separation between signal and noise, incoherent or coherent, is important in seismic data processing. Although we have processed the seismic data, the coherent noise is still mixing with the primary signal. Multiple reflections are a kind of coherent noise. In this research, we processed seismic data to attenuate multiple reflections in the both synthetic and real seismic data of Mentawai. There are several methods to attenuate multiple reflection, one of them is Radon filter method that discriminates between primary reflection and multiple reflection in the τ-p domain based on move out difference between primary reflection and multiple reflection. However, in case where the move out difference is too small, the Radon filter method is not enough to attenuate the multiple reflections. The Radon filter also produces the artifacts on the gathers data. Except the Radon filter method, we also use the Wave Equation Multiple Elimination (WEMR) method to attenuate the long period multiple reflection. The WEMR method can attenuate the long period multiple reflection based on wave equation inversion. Refer to the inversion of wave equation and the magnitude of the seismic wave amplitude that observed on the free surface, we get the water bottom reflectivity which is used to eliminate the multiple reflections. The WEMR method does not depend on the move out difference to attenuate the long period multiple reflection. Therefore, the WEMR method can be applied to the seismic data which has small move out difference as the Mentawai seismic data. The small move out difference on the Mentawai seismic data is caused by the restrictiveness of far offset, which is only 705 meter. We compared the real free multiple stacking data after processing with Radon filter and WEMR process. The conclusion is the WEMR method can more attenuate the long period multiple reflection than the Radon filter method on the real (Mentawai) seismic data.
International Nuclear Information System (INIS)
Shiozawa, Toshiyuki
2010-01-01
For the purpose of providing for a theoretical background for the study of electromagnetic fields generated by precursory effects of earthquakes, the problem of transmission and total reflection at the earth-atmosphere interface is investigated in detail for a subhertz plane electromagnetic wave incident from the earth's crust. The term ''subhertz'' means 'below 1 Hz'. First, for the special case of normal incidence, the overall power transmission coefficient at the earth-atmosphere interface is found to take a maximum value at a definite frequency f 0 which is inversely proportional to the square of the depth of a virtual hypocenter. A typical value of f 0 falls around 0.01 Hz. For oblique incidence as well, this feature of the overall power transmission coefficient is retained except in the vicinity of the critical angle of incidence for the H-wave. At the critical angle of incidence, the power flow carried by a surface wave along the interface becomes anomalously large for the H-wave. However, over a wide range of angles of incidence greater than the critical angle, the power flow carried by the E-wave exceeds that carried by the H-wave by orders of magnitude. Finally, the energy conservation relations for the incident, reflected, and transmitted waves at the earth-atmosphere interface are discussed. For an incident wave coming from the earth's crust, the interactive power between the incident and reflected waves plays a crucial role for the conservation of energy at the interface.
Masy, J.; Niu, F.; Levander, A.; Schmitz, M.
2012-12-01
The Caribbean (CAR) and South American (SA) plate boundary in Venezuela is a broad zone of diffuse deformation and faulting. GPS measurements indicate that the CAR is moving approximately 2 cm/yr respect to SA, parallel to the strike slip fault system in the east, but with an oblique convergence component in the west (Weber et al., 2001). Along the central and eastern Venezuela coast, most of the motion is accommodated by both transpression and transtension along the right lateral strike-slip San Sebastian- El Pilar fault system. The main tectonic features of the area include accretionary wedges and coastal thrust belts with their associated foreland basins (e.g. Sierra del Interior and Espino Graben). Southern of the plate boundary is located the Guayana Shield, which is part of the Amazonian Craton, and is an elevated plain consisting of Precambrian rocks. BOLIVAR (Broadband Onshore-Offshore Lithospheric Investigation of Venezuela and the Antilles Arc Region) was a multidisciplinary, international investigation to determine the evolution of the CAR-SA plate boundary (Levander et al., 2006) that included a 47 station broadband seismic array to complement the 40 station Venezuelan national array operated by FUNVISIS. The goal of this study is to map out lithosphere thickness across the region in order to understand its role for the various types of deformations observed at surface. We combined surface wave tomography and body wave reflectivity to locate the depth of the lithosphere-asthenosphere boundary (LAB). To generate a coherent 3D reflectivity volume of the study area, we used both P- and S-wave receiver-function data, as well as the ScS reverberation records of two deep earthquakes occurring in South America. We also measured Rayleigh phase velocities in the frequency range of 20-100 s using the two plane-wave method to remove multi-pathing effects (Forsyth and Li, 2005). Finite-frequency kernels were computed for a total of 63 teleseismic events to improve
Numerical Modelling of Wave Run-Up
DEFF Research Database (Denmark)
Ramirez, Jorge Robert Rodriguez; Frigaard, Peter; Andersen, Thomas Lykke
2011-01-01
Wave loads are important in problems related to offshore structure, such as wave run-up, slamming. The computation of such wave problems are carried out by CFD models. This paper presents one model, NS3, which solve 3D Navier-Stokes equations and use Volume of Fluid (VOF) method to treat the free...
Macroscopic balance model for wave rotors
Welch, Gerard E.
1996-01-01
A mathematical model for multi-port wave rotors is described. The wave processes that effect energy exchange within the rotor passage are modeled using one-dimensional gas dynamics. Macroscopic mass and energy balances relate volume-averaged thermodynamic properties in the rotor passage control volume to the mass, momentum, and energy fluxes at the ports. Loss models account for entropy production in boundary layers and in separating flows caused by blade-blockage, incidence, and gradual opening and closing of rotor passages. The mathematical model provides a basis for predicting design-point wave rotor performance, port timing, and machine size. Model predictions are evaluated through comparisons with CFD calculations and three-port wave rotor experimental data. A four-port wave rotor design example is provided to demonstrate model applicability. The modeling approach is amenable to wave rotor optimization studies and rapid assessment of the trade-offs associated with integrating wave rotors into gas turbine engine systems.
International Nuclear Information System (INIS)
Saito, Yukimasa
1977-01-01
The transient reflection and transmission waves of E polarized electromagnetic waves coming into the boundary surface between air and moving isotropic plasma were theoretically investigated. By using the Laplace transformation in the moving system, the formulae of Lorentz and inverse Lorentz transformations concerning electromagnetic field were transformed, thus the transient reflection and transmission waves were obtained. These waves were normalized with the angular frequency of the incident waves, and the variation of the wave form was obtained. Examples of the numerical calculation of reflected waves are shown for the plasma moving in parallel to the boundary surface. (Kato, T.)
TURBULENCE IN THE SUB-ALFVENIC SOLAR WIND DRIVEN BY REFLECTION OF LOW-FREQUENCY ALFVEN WAVES
International Nuclear Information System (INIS)
Verdini, A.; Velli, M.; Buchlin, E.
2009-01-01
We study the formation and evolution of a turbulent spectrum of Alfven waves driven by reflection off the solar wind density gradients, starting from the coronal base up to 17 solar radii, well beyond the Alfvenic critical point. The background solar wind is assigned and two-dimensional shell models are used to describe nonlinear interactions. We find that the turbulent spectra are influenced by the nature of the reflected waves. Close to the base, these give rise to a flatter and steeper spectrum for the outgoing and reflected waves, respectively. At higher heliocentric distance both spectra evolve toward an asymptotic Kolmogorov spectrum. The turbulent dissipation is found to account for at least half of the heating required to sustain the background imposed solar wind and its shape is found to be determined by the reflection-determined turbulent heating below 1.5 solar radii. Therefore, reflection and reflection-driven turbulence are shown to play a key role in the acceleration of the fast solar wind and origin of the turbulent spectrum found at 0.3 AU in the heliosphere.
Kasimov, Aslan R; Faria, Luiz M; Rosales, Rodolfo R
2013-03-08
We propose the following model equation, u(t) + 1/2(u(2)-uu(s))x = f(x,u(s)) that predicts chaotic shock waves, similar to those in detonations in chemically reacting mixtures. The equation is given on the half line, xorder partial differential equation. The chaos arises in the equation thanks to an interplay between the nonlinearity of the inviscid Burgers equation and a novel forcing term that is nonlocal in nature and has deep physical roots in reactive Euler equations.
Light reflection models for computer graphics.
Greenberg, D P
1989-04-14
During the past 20 years, computer graphic techniques for simulating the reflection of light have progressed so that today images of photorealistic quality can be produced. Early algorithms considered direct lighting only, but global illumination phenomena with indirect lighting, surface interreflections, and shadows can now be modeled with ray tracing, radiosity, and Monte Carlo simulations. This article describes the historical development of computer graphic algorithms for light reflection and pictorially illustrates what will be commonly available in the near future.
Reflection and transmission of ion acoustic waves from a plasma discontinuity
International Nuclear Information System (INIS)
Gary, S.P.; Alexeff, I.; Bloomberg, H.W.
1975-01-01
Transmission and reflection coefficients are calculated for an ion acoustic wave incident from the upstream direction upon a plasma discontinuity of width much less than the wavelength. In the limit of an infinitely strong discontinuity there is complete in phase reflection. (U.S.)
Reflection and transmission of normally incident full-vector X waves on planar interfaces
Salem, Mohamed
2011-12-23
The reflection and transmission of full-vector X waves normally incident on planar half-spaces and slabs are studied. For this purpose, X waves are expanded in terms of weighted vector Bessel beams; this new decomposition and reconstruction method offers a more lucid and intuitive interpretation of the physical phenomena observed upon the reflection or transmission of X waves when compared to the conventional plane-wave decomposition technique. Using the Bessel beam expansion approach, we have characterized changes in the field shape and the intensity distribution of the transmitted and reflected full-vector X waves. We have also identified a novel longitudinal shift, which is observed when a full-vector X wave is transmitted through a dielectric slab under frustrated total reflection condition. The results of our studies presented here are valuable in understanding the behavior of full-vector X waves when they are utilized in practical applications in electromagnetics, optics, and photonics, such as trap and tweezer setups, optical lithography, and immaterial probing. © 2011 Optical Society of America.
Phase mixing of Alfvén waves in axisymmetric non-reflective magnetic plasma configurations
Petrukhin, N. S.; Ruderman, M. S.; Shurgalina, E. G.
2018-02-01
We study damping of phase-mixed Alfvén waves propagating in non-reflective axisymmetric magnetic plasma configurations. We derive the general equation describing the attenuation of the Alfvén wave amplitude. Then we applied the general theory to a particular case with the exponentially divergent magnetic field lines. The condition that the configuration is non-reflective determines the variation of the plasma density along the magnetic field lines. The density profiles exponentially decreasing with the height are not among non-reflective density profiles. However, we managed to find non-reflective profiles that fairly well approximate exponentially decreasing density. We calculate the variation of the total wave energy flux with the height for various values of shear viscosity. We found that to have a substantial amount of wave energy dissipated at the lower corona, one needs to increase shear viscosity by seven orders of magnitude in comparison with the value given by the classical plasma theory. An important result that we obtained is that the efficiency of the wave damping strongly depends on the density variation with the height. The stronger the density decrease, the weaker the wave damping is. On the basis of this result, we suggested a physical explanation of the phenomenon of the enhanced wave damping in equilibrium configurations with exponentially diverging magnetic field lines.
The reflection of an electromagnetic wave from the self-produced plasma
International Nuclear Information System (INIS)
Mirzaie, M.; Shokri, B.; Rukhadze, A. A.
2010-01-01
The dynamic behavior of a high power microwave beam propagating through a gaseous medium, which is ionized in the wave field is investigated. By solving the wave equation, the reflection index of the produced plasma is obtained. It is shown that the cut off condition is different from that of the steady state approximation. The reflection index is less than unity when the plasma density reaches the critical value estimated in the steady state approximation. So, the wave can still propagate through the plasma. By comparing the reflection indexes in the presence and absence of the time delay of the ionization process at different points of the medium, it is shown that it becomes unity much later in the first case. Therefore, the wave propagation takes much more time and consequently the medium is ionized much more.
DEFF Research Database (Denmark)
Ilic, C; Chadwick, A; Helm-Petersen, Jacob
2000-01-01
, non-phased locked methods are more appropriate. In this paper, the accuracy of two non-phased locked methods of directional analysis, the maximum likelihood method (MLM) and the Bayesian directional method (BDM) have been quantitatively evaluated using numerical simulations for the case...... of multidirectional waves with partial reflections. It is shown that the results are influenced by the ratio of distance from the reflector (L) to the length of the time series (S) used in the spectral analysis. Both methods are found to be capable of determining the incident and reflective wave fields when US > 0......Recent studies of advanced directional analysis techniques have mainly centred on incident wave fields. In the study of coastal structures, however, partially reflective wave fields are commonly present. In the near structure field, phase locked methods can be successfully applied. In the far field...
Large Blast and Thermal Simulator Reflected Wave Eliminator Study
1990-03-01
it delays the passage of this wave through the test section until after the test is complete. The required length of extra duct depends on the strength...tube axis, which acts like an additional contraction effect since Se = Sj/[Cqsin(aj)]. Tii extra area is illustrated best by plotting (Se-Ae)/Ac versus...34Simulation de Choc et de Soaffie. Comimpensateur d’Ondes de Detente de Bouche pour tube a Choc de 2400 mm de diametre de Veine. Description, Compte- Renda
Modelization of highly nonlinear waves in coastal regions
Gouin, Maïté; Ducrozet, Guillaume; Ferrant, Pierre
2015-04-01
The proposed work deals with the development of a highly non-linear model for water wave propagation in coastal regions. The accurate modelization of surface gravity waves is of major interest in ocean engineering, especially in the field of marine renewable energy. These marine structures are intended to be settled in coastal regions where the effect of variable bathymetry may be significant on local wave conditions. This study presents a numerical model for the wave propagation with complex bathymetry. It is based on High-Order Spectral (HOS) method, initially limited to the propagation of non-linear wave fields over flat bottom. Such a model has been developed and validated at the LHEEA Lab. (Ecole Centrale Nantes) over the past few years and the current developments will enlarge its application range. This new numerical model will keep the interesting numerical properties of the original pseudo-spectral approach (convergence, efficiency with the use of FFTs, …) and enable the possibility to propagate highly non-linear wave fields over long time and large distance. Different validations will be provided in addition to the presentation of the method. At first, Bragg reflection will be studied with the proposed approach. If the Bragg condition is satisfied, the reflected wave generated by a sinusoidal bottom patch should be amplified as a result of resonant quadratic interactions between incident wave and bottom. Comparisons will be provided with experiments and reference solutions. Then, the method will be used to consider the transformation of a non-linear monochromatic wave as it propagates up and over a submerged bar. As the waves travel up the front slope of the bar, it steepens and high harmonics are generated due to non-linear interactions. Comparisons with experimental data will be provided. The different test cases will assess the accuracy and efficiency of the method proposed.
Model wave functions for the deuteron
International Nuclear Information System (INIS)
Certov, A.; Mathelitsch, L.; Moravcsik, M.J.
1987-01-01
Model wave functions are constructed for the deuteron to facilitate the unambiguous exploration of dependencies on the percentage D state and on the small-, medium-, and large-distance parts of the deuteron wave function. The wave functions are constrained by those deuteron properties which are accurately known experimentally, and are in an analytic form which is easily integrable in expressions usually encountered in the use of such wave functions
Modelling and Simulation of Wave Loads
DEFF Research Database (Denmark)
Sørensen, John Dalsgaard; Thoft-Christensen, Palle
velocity can be approximated by a Gaussian Markov process. Known approximate results for the first-passage density or equivalently, the distribution of the extremes of wave loads are presented and compared with rather precise simulation results. It is demonstrated that the approximate results......A simple model of the wave load on slender members of offshore structures is described. The wave elevation of the sea state is modelled by a stationary Gaussian process. A new procedure to simulate realizations of the wave loads is developed. The simulation method assumes that the wave particle...
Modelling and Simulation of Wave Loads
DEFF Research Database (Denmark)
Sørensen, John Dalsgaard; Thoft-Christensen, Palle
1985-01-01
velocity can be approximated by a Gaussian Markov process. Known approximate results for the first passage density or equivalently, the distribution of the extremes of wave loads are presented and compared with rather precise simulation results. It is demonstrated that the approximate results......A simple model of the wave load on stender members of offshore structures is described . The wave elevation of the sea stateis modelled by a stationary Gaussian process. A new procedure to simulate realizations of the wave loads is developed. The simulation method assumes that the wave particle...
Wave model downscaling for coastal applications
Valchev, Nikolay; Davidan, Georgi; Trifonova, Ekaterina; Andreeva, Nataliya
2010-05-01
Downscaling is a suitable technique for obtaining high-resolution estimates from relatively coarse-resolution global models. Dynamical and statistical downscaling has been applied to the multidecadal simulations of ocean waves. Even as large-scale variability might be plausibly estimated from these simulations, their value for the small scale applications such as design of coastal protection structures and coastal risk assessment is limited due to their relatively coarse spatial and temporal resolutions. Another advantage of the high resolution wave modeling is that it accounts for shallow water effects. Therefore, it can be used for both wave forecasting at specific coastal locations and engineering applications that require knowledge about extreme wave statistics at or near the coastal facilities. In the present study downscaling is applied to both ECMWF and NCEP/NCAR global reanalysis of atmospheric pressure over the Black Sea with 2.5 degrees spatial resolution. A simplified regional atmospheric model is employed for calculation of the surface wind field at 0.5 degrees resolution that serves as forcing for the wave models. Further, a high-resolution nested WAM/SWAN wave model suite of nested wave models is applied for spatial downscaling. It aims at resolving the wave conditions in a limited area at the close proximity to the shore. The pilot site is located in the northern part the Bulgarian Black Sea shore. The system involves the WAM wave model adapted for basin scale simulation at 0.5 degrees spatial resolution. The WAM output for significant wave height, mean wave period and mean angle of wave approach is used in terms of external boundary conditions for the SWAN wave model, which is set up for the western Black Sea shelf at 4km resolution. The same model set up on about 400m resolution is nested to the first SWAN run. In this case the SWAN 2D spectral output provides boundary conditions for the high-resolution model run. The models are implemented for a
Primary and Reflected Compaction Waves in a Foam Rod Due to an Axial Impact by a Small Mass
Directory of Open Access Journals (Sweden)
D. Karagiozova
Full Text Available AbstractThe propagation of compaction waves in a stationary foam block subjected to an impact by a small mass is studied in order to examine the mechanism of compaction within the primary and reflected stress waves. The analysis is focused on aluminium strain rate insensitive foam that exhibits strain hardening under quasistatic compression. A theoretical approach is applied using a uniaxial model of compaction in which the compacted strains, being functions of the velocity variation, are not predefined but are obtained as a part of the solution. The present approach allows one to obtain the strain histories and strain distributions within the primary compaction wave as well as within the reflected wave, which propagates in a media with non-uniform density increasing monotonically in the direction of loading. FE simulations considering aluminium based foam Cymat with density 411.5 kg/m3 are carried out in order to verify the proposed theoretical model. A comparison between the impact velocity attenuation predicted by the present model and classical Rigid Perfectly-Plastic Locking material model for cellular materials is discussed.
Self-exchange of oxygen behind reflected shock waves
International Nuclear Information System (INIS)
Bopp, A.F.; Kern, R.D.; Niki, T.; Stack, G.M.
1979-01-01
The rate of isotopic exchange of equimolar mixtures of 32 O 2 + 36 O 2 dilute in Ne-1% Ar was studied over the temperature range 2625 to 3700 K. the reacting gas was analyzed from the reflected shock zone at 20-μs intervals with a time-of-flight mass spectrometer. Each experimental product profile obtained was compared to the corresponding computer-simulated profile calculation from an atomic mechanism by using previously published rate constants. It was observed that the growth of the exchange product exceeded that predicted by the atomic mechanism at the lower temperatures of this study. However, these differences diminished as the temperature increased. Static analysis of the gas mixtures investigated revealed that H 2 or D 2 if present were at a level of less than 2.5 ppM. Computer simulation of product profiles demonstrated that this impurity level was insufficient to affect the observed rate of product formation. It is proposed that contributions from molecular channels are operative at the lower temperatures while atomic pathways dominate at the higher temperatures
Bifurcation parameters of a reflected shock wave in cylindrical channels of different roughnesses
Penyazkov, O.; Skilandz, A.
2018-03-01
To investigate the effect of bifurcation on the induction time in cylindrical shock tubes used for chemical kinetic experiments, one should know the parameters of the bifurcation structure of a reflected shock wave. The dynamics and parameters of the shock wave bifurcation, which are caused by reflected shock wave-boundary layer interactions, are studied experimentally in argon, in air, and in a hydrogen-nitrogen mixture for Mach numbers M = 1.3-3.5 in a 76-mm-diameter shock tube without any ramp. Measurements were taken at a constant gas density behind the reflected shock wave. Over a wide range of experimental conditions, we studied the axial projection of the oblique shock wave and the pressure distribution in the vicinity of the triple Mach configuration at 50, 150, and 250 mm from the endwall, using side-wall schlieren and pressure measurements. Experiments on a polished shock tube and a shock tube with a surface roughness of 20 {μ }m Ra were carried out. The surface roughness was used for initiating small-scale turbulence in the boundary layer behind the incident shock wave. The effect of small-scale turbulence on the homogenization of the transition zone from the laminar to turbulent boundary layer along the shock tube perimeter was assessed, assuming its influence on a subsequent stabilization of the bifurcation structure size versus incident shock wave Mach number, as well as local flow parameters behind the reflected shock wave. The influence of surface roughness on the bifurcation development and pressure fluctuations near the wall, as well as on the Mach number, at which the bifurcation first develops, was analyzed. It was found that even small additional surface roughness can lead to an overshoot in pressure growth by a factor of two, but it can stabilize the bifurcation structure along the shock tube perimeter.
FORMATIVE AND REFLECTIVE MODELS IN MARKETING RESEARCH
Directory of Open Access Journals (Sweden)
Claudia Ioana CIOBANU
2017-06-01
Full Text Available Compliance with the construct validity criteria is necessary for the correct assessment of the research in terms of quality and for further development of the marketing models. The identification of formative and reflective constructs as well as the correct testing of their validity and reliability are important methodological steps for marketing research as described in this article. The first part defines the reflective and the formative constructs and highlighst their particularities by analysing the theoretical criteria that differentiate them. In the second part of the study aspects of validity and trust for the formative and reflective constructs are presented as well as some empirical considerations from research literature regarding their measurement.
Ray splitting in the reflection and refraction of surface acoustic waves in anisotropic solids.
Every, A G; Maznev, A A
2010-05-01
This paper examines the conditions for, and provides examples of, ray splitting in the reflection and refraction of surface acoustic waves (SAW) in elastically anisotropic solids at straight obstacles such as edges, surface breaking cracks, and interfaces between different solids. The concern here is not with the partial scattering of an incident SAW's energy into bulk waves, but with the occurrence of more than one SAW ray in the reflected and/or transmitted wave fields, by analogy with birefringence in optics and mode conversion of bulk elastic waves at interfaces. SAW ray splitting is dependent on the SAW slowness curve possessing concave regions, which within the constraint of wave vector conservation parallel to the obstacle allows multiple outgoing SAW modes for certain directions of incidence and orientation of obstacle. The existence of pseudo-SAW for a given surface provides a further channel for ray splitting. This paper discusses some typical material configurations for which SAW ray splitting occurs. An example is provided of mode conversion entailing backward reflection or negative refraction. Experimental demonstration of ray splitting in the reflection of a laser generated SAW in GaAs(111) is provided. The calculation of SAW mode conversion amplitudes lies outside the scope of this paper.
Generation of neutron standing waves at total reflection of polarized neutrons
International Nuclear Information System (INIS)
Aksenov, V.L.; Nikitenko, Yu.V.; Kozhevnikov, S.V.; Radu, F.; Kruijs, R.; Rekveldt, M.Th.
1999-01-01
The regime of neutron standing waves at reflection of polarized thermal neutrons from the structure glass/Cu (1000 A Angstrom)/Ti (2000 A Angstrom)/Co (60 A Angstrom)/Ti (300 A Angstrom) in a magnetic field directed at an angle to the sample plane is realized. The intensity of neutrons with a particular spin projection on the external magnetic field direction appears to be a periodic function of the neutron wavelength and the glancing angle of the reflected beam. It is shown that the neutron standing wave regime can be a very sensitive method for the determination of changes in the spatial position of magnetic noncollinear layers. (author)
Jiu-Sheng, Li; Ze-Jiang, Zhao; Jian-Quan, Yao
2017-11-27
In order to extend to 3-bit encoding, we propose notched-wheel structures as polarization insensitive coding metasurfaces to control terahertz wave reflection and suppress backward scattering. By using a coding sequence of "00110011…" along x-axis direction and 16 × 16 random coding sequence, we investigate the polarization insensitive properties of the coding metasurfaces. By designing the coding sequences of the basic coding elements, the terahertz wave reflection can be flexibly manipulated. Additionally, radar cross section (RCS) reduction in the backward direction is less than -10dB in a wide band. The present approach can offer application for novel terahertz manipulation devices.
Phase locking in backward-wave oscillators with strong end reflections
International Nuclear Information System (INIS)
Nusinovich, G. S.; Sinitsyn, O. V.; Rodgers, J.; Shkvarunets, A. G.; Carmel, Y.
2007-01-01
The theory of phase-locked oscillations in a backward-wave oscillator with strong end reflections is developed. Numerical results demonstrate that the locking bandwidth of such a device phase-locked by a prebunched electron beam can be twice the bandwidth of a resonator formed by a waveguide with strong end reflections. It is also shown that the device can operate with the efficiency exceeding 50% and that, in some cases, it can exhibit a hysteresis in the process of tuning the signal frequency. The applicability of the results obtained to the experiments with the plasma-assisted backward-wave oscillator currently underway at the University of Maryland is discussed
Shot- and angle-domain wave-equation traveltime inversion of reflection data: Theory
Zhang, Sanzong
2015-05-26
The main difficulty with iterative waveform inversion is that it tends to get stuck in local minima associated with the waveform misfit function. To mitigate this problem and avoid the need to fit amplitudes in the data, we have developed a wave-equation method that inverts the traveltimes of reflection events, and so it is less prone to the local minima problem. Instead of a waveform misfit function, the penalty function was a crosscorrelation of the downgoing direct wave and the upgoing reflection wave at the trial image point. The time lag, which maximized the crosscorrelation amplitude, represented the reflection-traveltime residual (RTR) that was back projected along the reflection wavepath to update the velocity. Shot- and angle-domain crosscorrelation functions were introduced to estimate the RTR by semblance analysis and scanning. In theory, only the traveltime information was inverted and there was no need to precisely fit the amplitudes or assume a high-frequency approximation. Results with synthetic data and field records revealed the benefits and limitations of wave-equation reflection traveltime inversion.
Effect of end reflections on conversion efficiency of coaxial relativistic backward wave oscillator
Energy Technology Data Exchange (ETDEWEB)
Teng, Yan; Chen, Changhua; Sun, Jun; Shi, Yanchao; Ye, Hu; Wu, Ping; Li, Shuang; Xiong, Xiaolong [Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi' an 710024 (China)
2015-11-07
This paper theoretically investigates the effect of end reflections on the operation of the coaxial relativistic backward wave oscillator (CRBWO). It is found that the considerable enhancement of the end reflection at one end increases the conversion efficiency, but excessively large end reflections at both ends weaken the asynchronous wave-beam interaction and thus reduce the conversion efficiency. Perfect reflection at the post end significantly improves the interaction between the electron beam and the asynchronous harmonic so that the conversion efficiency is notably increased. Based on the theoretical research, the diffraction-CRBWO with the generated microwave diffracted and output through the front end of the coaxial slow wave structure cavity is proposed. The post end is conductively closed to provide the perfect reflection. This promotes the amplitude and uniformity of the longitudinal electric field on the beam transmission line and improves the asynchronous wave-beam interaction. In numerical simulations under the diode voltage and current of 450 kV and 5.84 kA, microwave generation with the power of 1.45 GW and the conversion efficiency of 55% are obtained at the frequency of 7.45 GHz.
Shot- and angle-domain wave-equation traveltime inversion of reflection data: Theory
Zhang, Sanzong; Luo, Yi; Schuster, Gerard T.
2015-01-01
The main difficulty with iterative waveform inversion is that it tends to get stuck in local minima associated with the waveform misfit function. To mitigate this problem and avoid the need to fit amplitudes in the data, we have developed a wave-equation method that inverts the traveltimes of reflection events, and so it is less prone to the local minima problem. Instead of a waveform misfit function, the penalty function was a crosscorrelation of the downgoing direct wave and the upgoing reflection wave at the trial image point. The time lag, which maximized the crosscorrelation amplitude, represented the reflection-traveltime residual (RTR) that was back projected along the reflection wavepath to update the velocity. Shot- and angle-domain crosscorrelation functions were introduced to estimate the RTR by semblance analysis and scanning. In theory, only the traveltime information was inverted and there was no need to precisely fit the amplitudes or assume a high-frequency approximation. Results with synthetic data and field records revealed the benefits and limitations of wave-equation reflection traveltime inversion.
Model-based internal wave processing
Energy Technology Data Exchange (ETDEWEB)
Candy, J.V.; Chambers, D.H.
1995-06-09
A model-based approach is proposed to solve the oceanic internal wave signal processing problem that is based on state-space representations of the normal-mode vertical velocity and plane wave horizontal velocity propagation models. It is shown that these representations can be utilized to spatially propagate the modal (dept) vertical velocity functions given the basic parameters (wave numbers, Brunt-Vaisala frequency profile etc.) developed from the solution of the associated boundary value problem as well as the horizontal velocity components. Based on this framework, investigations are made of model-based solutions to the signal enhancement problem for internal waves.
Optimal reflection-free complex absorbing potentials for quantum propagation of wave packets
International Nuclear Information System (INIS)
Shemer, Oded; Brisker, Daria; Moiseyev, Nimrod
2005-01-01
The conditions for optimal reflection-free complex-absorbing potentials (CAPs) are discussed. It is shown that the CAPs as derived from the smooth-exterior-scaling transformation of the Hamiltonian [J. Phys. B 31, 1431 (1998)] serve as optimal reflection-free CAPs (RF CAPs) in wave-packet propagation calculations of open systems. The initial wave packet, Φ(t=0), can be located in the interaction region (as in half collision experiments) where the CAPs have vanished or in the asymptote where V CAP ≠0. As we show, the optimal CAPs can be introduced also in the region where the physical potential has not vanished. The unavoided reflections due to the use of a finite number of grid points (or basis functions) are discussed. A simple way to reduce the 'edge-grid' reflection effect is described
Extreme Wave Analysis by Integrating Model and Wave Buoy Data
Directory of Open Access Journals (Sweden)
Fabio Dentale
2018-03-01
Full Text Available Estimating the extreme values of significant wave height (HS, generally described by the HS return period TR function HS(TR and by its confidence intervals, is a necessity in many branches of coastal science and engineering. The availability of indirect wave data generated by global and regional wind and wave model chains have brought radical changes to the estimation procedures of such probability distribution—weather and wave modeling systems are routinely run all over the world, and HS time series for each grid point are produced and published after assimilation (analysis of the ground truth. However, while the sources of such indirect data are numerous, and generally of good quality, many aspects of their procedures are hidden to the users, who cannot evaluate the reliability and the limits of the HS(TR deriving from such data. In order to provide a simple engineering tool to evaluate the probability of extreme sea-states as well as the quality of such estimates, we propose here a procedure based on integrating HS time series generated by model chains with those recorded by wave buoys in the same area.
Kleinstein, G. G.; Gunzburger, M. D.
1976-01-01
An integral conservation law for wave numbers is considered. In order to test the validity of the proposed conservation law, a complete solution for the reflection and transmission of an acoustic wave impinging normally on a material interface moving at a constant speed is derived. The agreement between the frequency condition thus deduced from the dynamic equations of motion and the frequency condition derived from the jump condition associated with the integral equation supports the proposed law as a true conservation law. Additional comparisons such as amplitude discontinuities and Snells' law in a moving media further confirm the stated proposition. Results are stated concerning frequency and wave number relations across a shock front as predicted by the proposed conservation law.
Opdriftsbaserede modeller for Wave Star
DEFF Research Database (Denmark)
Kramer, Morten
Formålet med dette skrift er at få en forhåndsvurdering af mulige effektforøgelser for Wave Star ved anvendelse af aktiv akkumulatordrift. Disse vurderinger baseres på simuleringsmodeller for driften af Wave Star i uregelmæssige bølger. Modellen er udarbejdet i programmeringssproget Delphi og er en...
Radio wave propagation and parabolic equation modeling
Apaydin, Gokhan
2018-01-01
A thorough understanding of electromagnetic wave propagation is fundamental to the development of sophisticated communication and detection technologies. The powerful numerical methods described in this book represent a major step forward in our ability to accurately model electromagnetic wave propagation in order to establish and maintain reliable communication links, to detect targets in radar systems, and to maintain robust mobile phone and broadcasting networks. The first new book on guided wave propagation modeling and simulation to appear in nearly two decades, Radio Wave Propagation and Parabolic Equation Modeling addresses the fundamentals of electromagnetic wave propagation generally, with a specific focus on radio wave propagation through various media. The authors explore an array of new applications, and detail various v rtual electromagnetic tools for solving several frequent electromagnetic propagation problems. All of the methods described are presented within the context of real-world scenari...
Porous models for wave-seabed interactions
Energy Technology Data Exchange (ETDEWEB)
Jeng, Dong-Sheng [Shanghai Jiaotong Univ., SH (China)
2013-02-01
Detailed discussion about the phenomenon of wave-seabed interactions. Novel models for wave-induced seabed response. Intensive theoretical derivations for wave-seabed interactions. Practical examples for engineering applications. ''Porous Models for Wave-seabed Interactions'' discusses the Phenomenon of wave-seabed interactions, which is a vital issue for coastal and geotechnical engineers involved in the design of foundations for marine structures such as pipelines, breakwaters, platforms, etc. The most important sections of this book will be the fully detailed theoretical models of wave-seabed interaction problem, which are particularly useful for postgraduate students and junior researchers entering the discipline of marine geotechnics and offshore engineering. This book also converts the research outcomes of theoretical studies to engineering applications that will provide front-line engineers with practical and effective tools in the assessment of seabed instability in engineering design.
Laughman, Brian; Wang, Ling; Lund, Thomas S.; Collins, Richard L.
2018-01-01
Abstract An anelastic numerical model is employed to explore the dynamics of gravity waves (GWs) encountering a mesosphere inversion layer (MIL) having a moderate static stability enhancement and a layer of weaker static stability above. Instabilities occur within the MIL when the GW amplitude approaches that required for GW breaking due to compression of the vertical wavelength accompanying the increasing static stability. Thus, MILs can cause large‐amplitude GWs to yield instabilities and turbulence below the altitude where they would otherwise arise. Smaller‐amplitude GWs encountering a MIL do not lead to instability and turbulence but do exhibit partial reflection and transmission, and the transmission is a smaller fraction of the incident GW when instabilities and turbulence arise within the MIL. Additionally, greater GW transmission occurs for weaker MILs and for GWs having larger vertical wavelengths relative to the MIL depth and for lower GW intrinsic frequencies. These results imply similar dynamics for inversions due to other sources, including the tropopause inversion layer, the high stability capping the polar summer mesopause, and lower frequency GWs or tides having sufficient amplitudes to yield significant variations in stability at large and small vertical scales. MILs also imply much stronger reflections and less coherent GW propagation in environments having significant fine structure in the stability and velocity fields than in environments that are smoothly varying. PMID:29576994
Magnetospherically reflected chorus waves revealed by ray tracing with CLUSTER data
Directory of Open Access Journals (Sweden)
M. Parrot
Full Text Available This paper is related to the propagation characteristics of a chorus emission recorded simultaneously by the 4 satellites of the CLUSTER mission on 29 October 2001 between 01:00 and 05:00 UT. During this day, the spacecraft (SC 1, 2, and 4 are relatively close to each other but SC3 has been delayed by half an hour. We use the data recorded aboard CLUSTER by the STAFF spectrum analyser. This instrument provides the cross spectral matrix of three magnetic and two electric field components. Dedicated software processes this spectral matrix in order to determine the wave normal directions relative to the Earth’s magnetic field. This calculation is done for the 4 satellites at different times and different frequencies and allows us to check the directions of these waves. Measurements around the magnetic equator show that the parallel component of the Poynting vector changes its sign when the satellites cross the equator region. It indicates that the chorus waves propagate away from this region which is considered as the source area of these emissions. This is valid for the most intense waves observed on the magnetic and electric power spectrograms. But it is also observed on SC1, SC2, and SC4 that lower intensity waves propagate toward the equator simultaneously with the SC3 intense chorus waves propagating away from the equator. Both waves are at the same frequency. Using the wave normal directions of these waves, a ray tracing study shows that the waves observed by SC1, SC2, and SC4 cross the equatorial plane at the same location as the waves observed by SC3. SC3 which is 30 minutes late observes the waves that originate first from the equator; meanwhile, SC1, SC2, and SC4 observe the same waves that have suffered a Lower Hybrid Resonance (LHR reflection at low altitudes (based on the ray tracing analysis and now return to the equator at a different location with a lower intensity. Similar phenomenon is observed when all SC are on the other side
Magnetospherically reflected chorus waves revealed by ray tracing with CLUSTER data
Directory of Open Access Journals (Sweden)
M. Parrot
2003-05-01
Full Text Available This paper is related to the propagation characteristics of a chorus emission recorded simultaneously by the 4 satellites of the CLUSTER mission on 29 October 2001 between 01:00 and 05:00 UT. During this day, the spacecraft (SC 1, 2, and 4 are relatively close to each other but SC3 has been delayed by half an hour. We use the data recorded aboard CLUSTER by the STAFF spectrum analyser. This instrument provides the cross spectral matrix of three magnetic and two electric field components. Dedicated software processes this spectral matrix in order to determine the wave normal directions relative to the Earth’s magnetic field. This calculation is done for the 4 satellites at different times and different frequencies and allows us to check the directions of these waves. Measurements around the magnetic equator show that the parallel component of the Poynting vector changes its sign when the satellites cross the equator region. It indicates that the chorus waves propagate away from this region which is considered as the source area of these emissions. This is valid for the most intense waves observed on the magnetic and electric power spectrograms. But it is also observed on SC1, SC2, and SC4 that lower intensity waves propagate toward the equator simultaneously with the SC3 intense chorus waves propagating away from the equator. Both waves are at the same frequency. Using the wave normal directions of these waves, a ray tracing study shows that the waves observed by SC1, SC2, and SC4 cross the equatorial plane at the same location as the waves observed by SC3. SC3 which is 30 minutes late observes the waves that originate first from the equator; meanwhile, SC1, SC2, and SC4 observe the same waves that have suffered a Lower Hybrid Resonance (LHR reflection at low altitudes (based on the ray tracing analysis and now return to the equator at a different location with a lower intensity. Similar phenomenon is observed when all SC are on the other side
Reflective array modeling for reflective and directional SAW transducers.
Morgan, D P
1998-01-01
This paper presents a new approximate method for analyzing reflective SAW transducers, with much of the convenience of the coupled-mode (COM) method but with better accuracy. Transduction accuracy is obtained by incorporating the accurate electrostatic solution, giving for example correct harmonics, and allowance for electrode width variation, in a simple manner. Results are shown for a single-electrode transducer, Natural SPUDT and DART SPUDT, each using theoretically derived parameters. In contrast to the COM, the RAM can give accurate results for short or withdrawal-weighted transducers and for wide analysis bandwidth.
Parsons, L. C.; Andrews, G. T.
2012-09-01
Pseudo-reflection geometry Brillouin spectroscopy can be used to probe acoustic wave dispersion approximately along the surface normal of a material system while avoiding the difficulties associated with specularly reflected light encountered in an ideal reflection configuration. As an example of its application, we show analytically that it can be used to determine both the refractive index and bulk acoustic mode velocities of optically-isotropic non-metallic materials and confirm the utility of the approach via a series of experiments on fused quartz, gallium phosphide, water, and porous silicon films.
Epoxy-based broadband anti-reflection coating for millimeter-wave optics
Rosen, Darin; Suzuki, Aritoki; Keating, Brian; Krantz, William; Lee, Adrian T.; Quealy, Erin; Richards, Paul L.; Siritanasak, Praween; Walker, William
2013-01-01
We have developed epoxy-based, broadband anti-reflection coatings for millimeter-wave astrophysics experiments with cryogenic optics. By using multiple-layer coatings where each layer steps in dielectric constant, we achieved low reflection over a wide bandwidth. We suppressed the reflection from an alumina disk to 10% over fractional bandwidths of 92% and 104% using two-layer and three-layer coatings, respectively. The dielectric constants of epoxies were tuned between 2.06 and 7.44 by mixin...
Antiferromagnetism and d-wave superconductivity in the Hubbard model
Energy Technology Data Exchange (ETDEWEB)
Krahl, H.C.
2007-07-25
The two-dimensional Hubbard model is a promising effective model for the electronic degrees of freedom in the copper-oxide planes of high temperature superconductors. We present a functional renormalization group approach to this model with focus on antiferromagnetism and d-wave superconductivity. In order to make the relevant degrees of freedom more explicitly accessible on all length scales, we introduce composite bosonic fields mediating the interaction between the fermions. Spontaneous symmetry breaking is reflected in a non-vanishing expectation value of a bosonic field. The emergence of a coupling in the d-wave pairing channel triggered by spin wave fluctuations is demonstrated. Furthermore, the highest temperature at which the interaction strength for the electrons diverges in the renormalization flow is calculated for both antiferromagnetism and d-wave superconductivity over a wide range of doping. This ''pseudo-critical'' temperature signals the onset of local ordering. Moreover, the temperature dependence of d-wave superconducting order is studied within a simplified model characterized by a single coupling in the d-wave pairing channel. The phase transition within this model is found to be of the Kosterlitz-Thouless type. (orig.)
Inner core boundary topography explored with reflected and diffracted P waves
deSilva, Susini; Cormier, Vernon F.; Zheng, Yingcai
2018-03-01
The existence of topography of the inner core boundary (ICB) can affect the amplitude, phase, and coda of body waves incident on the inner core. By applying pseudospectral and boundary element methods to synthesize compressional waves interacting with the ICB, these effects are predicted and compared with waveform observations in pre-critical, critical, post-critical, and diffraction ranges of the PKiKP wave reflected from the ICB. These data sample overlapping regions of the inner core beneath the circum-Pacific belt and the Eurasian, North American, and Australian continents, but exclude large areas beneath the Pacific and Indian Oceans and the poles. In the pre-critical range, PKiKP waveforms require an upper bound of 2 km at 1-20 km wavelength for any ICB topography. Higher topography sharply reduces PKiKP amplitude and produces time-extended coda not observed in PKiKP waveforms. The existence of topography of this scale smooths over minima and zeros in the pre-critical ICB reflection coefficient predicted from standard earth models. In the range surrounding critical incidence (108-130 °), this upper bound of topography does not strongly affect the amplitude and waveform behavior of PKIKP + PKiKP at 1.5 Hz, which is relatively insensitive to 10-20 km wavelength topography height approaching 5 km. These data, however, have a strong overlap in the regions of the ICB sampled by pre-critical PKiKP that require a 2 km upper bound to topography height. In the diffracted range (>152°), topography as high as 5 km attenuates the peak amplitudes of PKIKP and PKPCdiff by similar amounts, leaving the PKPCdiff/PKIKP amplitude ratio unchanged from that predicted by a smooth ICB. The observed decay of PKPCdiff into the inner core shadow and the PKIKP-PKPCdiff differential travel time are consistent with a flattening of the outer core P velocity gradient near the ICB and iron enrichment at the bottom of the outer core.
International Nuclear Information System (INIS)
De Vine, G.; Shaddock, D.; McClelland, D.
2002-01-01
Full text: One technique of improving the sensitivity of interferometric gravitational wave detectors is to implement a signal mirror. This involves placing a mirror at the output of the Michelson interferometer. The gravitational wave signal is then 'recycled' back into the interferometer where it can coherently add with the gravitational wave signal still being produced. The frequency of the improved sensitivity is dependent on the position of the signal mirror, while the peak height and bandwidth are dependent on the reflectivity of the signal mirror. This is because the signal mirror forms a cavity with the Michelson interferometer and this cavity has a resonant frequency dependent on its length and a bandwidth dependent on its finesse, which are a function of signal mirror position and reflectivity, respectively. Due to the varying and/or unknown nature of the gravitational wave frequencies and wave-forms, it is desirable to be able to control both the peak frequency and bandwidth of the detector. The peak frequency can be easily adjusted by altering the signal mirror position. The bandwidth, however, is fixed with the signal mirror reflectivity. In a long base-line gravitational wave detector it is impractical to swap the signal mirror with one of different reflectivity for a number of reasons, for example, the detector's high vacuum would have to be broken, realignment performed and locking re-acquired. This is addressed by the proposal of two different forms of variable reflectivity signal mirror (VRSM): a Fabry-Perot cavity and a Michelson interferometer. These are analysed and the reasons for choosing to investigate the Michelson VRSM are given. The reasons include the potential for easier control and the smooth variation in reflectivity with arm length difference. The experiment is discussed and the results of the first demonstration of variable reflectivity signal recycling are presented in the form of frequency responses obtained by injecting a second
Directional wave measurements and modelling
Digital Repository Service at National Institute of Oceanography (India)
Anand, N.M.; Nayak, B.U.; Bhat, S.S.; SanilKumar, V.
Some of the results obtained from analysis of the monsoon directional wave data measured over 4 years in shallow waters off the west coast of India are presented. The directional spectrum computed from the time series data seems to indicate...
Russo, Cesare; Jin, Zhezhen; Palmieri, Vittorio; Homma, Shunichi; Rundek, Tatjana; Elkind, Mitchell S V; Sacco, Ralph L; Di Tullio, Marco R
2012-08-01
Increased arterial stiffness and wave reflection have been reported in heart failure with normal ejection fraction (HFNEF) and in asymptomatic left ventricular (LV) diastolic dysfunction, a precursor of HFNEF. It is unclear whether women, who have higher frequency of HFNEF, are more vulnerable than men to the deleterious effects of arterial stiffness on LV diastolic function. We investigated, in a large community-based cohort, whether sex differences exist in the relationship among arterial stiffness, wave reflection, and LV diastolic function. Arterial stiffness and wave reflection were assessed in 983 participants from the Cardiovascular Abnormalities and Brain Lesions study using applanation tonometry. The central pulse pressure/stroke volume index, total arterial compliance, pulse pressure amplification, and augmentation index were used as parameters of arterial stiffness and wave reflection. LV diastolic function was evaluated by 2-dimensional echocardiography and tissue-Doppler imaging. Arterial stiffness and wave reflection were greater in women compared with men, independent of body size and heart rate (all Pfunction in both sexes. Further adjustment for cardiovascular risk factors attenuated these relationships; however, a higher central pulse pressure/stroke volume index predicted LV diastolic dysfunction in women (odds ratio, 1.54; 95% confidence intervals, 1.03 to 2.30) and men (odds ratio, 2.09; 95% confidence interval, 1.30 to 3.39), independent of other risk factors. In conclusion, in our community-based cohort study, higher arterial stiffness was associated with worse LV diastolic function in men and women. Women's higher arterial stiffness, independent of body size, may contribute to their greater susceptibility to develop HFNEF.
Hanson, R. K.; Presley, L. L.; Williams, E. V.
1972-01-01
The method of characteristics for a chemically reacting gas is used in the construction of the time-dependent, one-dimensional flow field resulting from the normal reflection of an incident shock wave at the end wall of a shock tube. Nonequilibrium chemical reactions are allowed behind both the incident and reflected shock waves. All the solutions are evaluated for oxygen, but the results are generally representative of any inviscid, nonconducting, and nonradiating diatomic gas. The solutions clearly show that: (1) both the incident- and reflected-shock chemical relaxation times are important in governing the time to attain steady state thermodynamic properties; and (2) adjacent to the end wall, an excess-entropy layer develops wherein the steady state values of all the thermodynamic variables except pressure differ significantly from their corresponding Rankine-Hugoniot equilibrium values.
International Nuclear Information System (INIS)
Wang, L.; Feng, S.
1989-01-01
The relation between the reflection coefficients and the Green's function for a coherent wave propagation in a disordered elastic-scattering medium is derived. The sum rule of the reflection and transmission coefficients corresponding to probability conservation is shown rigorously for an arbitrary scattering potential. The correlation function of the reflection coefficients is then calculated by using a Feynman-diagrammatic approach in the weak-localized multiple-scattering regime (L much-gt l much-gt λ). The result is in agreement with recent experiments on the so-called ''memory effect'' in reflection coefficients. A more general condition under which the memory effect can occur is derived. Differences between the the correlation functions for reflection and that for transmission are discussed
DEFF Research Database (Denmark)
Helm-Petersen, J.; Frigaard, Peter
1994-01-01
This report is Aalborg University's first contribution to the MAS2-CT92 project: Full scale dynamic load monitoring of rubble mound breakwaters.......This report is Aalborg University's first contribution to the MAS2-CT92 project: Full scale dynamic load monitoring of rubble mound breakwaters....
Modeling of Mud-Wave Interaction: Mud-Induced Wave Transport & Wave-Induced Mud Transport
National Research Council Canada - National Science Library
Winterwerp, Johan C
2007-01-01
.... Also a new rheological model has been proposed to describe liquefaction of soft mud by waves, and the subsequent strength recovery after the passage of the waves. A scheme is presented on how to implement these formulations in Delft3D.
International Nuclear Information System (INIS)
Hollender, F.
1999-01-01
Within the framework of research for waste disposal in deep geological formations, the French agency for nuclear waste management (ANDRA) has to dispose of non-destructive investigation methods to characterize the medium. Ground penetrating radar (GPR) could be used for this purpose in the case of granitic sites. The work presented here deals with this geophysical method. The classical interpretation of GPR data consists in the localization of geological discontinuities by signal amplitude or arrival time analysis. The main objective of our studies is the interpretation of the radar wave distortion (due to propagation and reflection phenomena), not only to localize discontinuities but also to contribute to their identification. Three preliminary studies have been carried out in order to understand on the one hand, the complexity of the electromagnetic phenomena in the geological medium at radar frequency, and on the other hand, the radar equipment constraints. First, the dispersion and the attenuation characterized by a Q variable factor of the GPR waves are shown with the support of dielectric laboratory measurements. A model, which only requires three parameters, is proposed in order to describe this behavior. Second, the radiation patterns of borehole radar antenna are studied. We show that the amplitude and frequency content of the emitted signal are variable versus the emission angle. An analytical method is proposed to study these phenomena. Finally, instrumental drifts of GPR equipment are studied. Emission time, sampling frequency and amplitude fluctuations are described. These elements are taken into account for the processing of propagated signals by tomographic inversion. Medium anisotropy and borehole trajectory errors are inserted in algorithms in order to cancel artifacts which compromised the previous interpretation. A pre-processing method, based on wave separation algorithm, is applied on data in order to increase tomogram resolution. A new
Multi reflection of Lamb wave emission in an acoustic waveguide sensor.
Schmitt, Martin; Olfert, Sergei; Rautenberg, Jens; Lindner, Gerhard; Henning, Bernd; Reindl, Leonhard Michael
2013-02-27
Recently, an acoustic waveguide sensor based on multiple mode conversion of surface acoustic waves at the solid-liquid interfaces has been introduced for the concentration measurement of binary and ternary mixtures, liquid level sensing, investigation of spatial inhomogenities or bubble detection. In this contribution the sound wave propagation within this acoustic waveguide sensor is visualized by Schlieren imaging for continuous and burst operation the first time. In the acoustic waveguide the antisymmetrical zero order Lamb wave mode is excited by a single phase transducer of 1 MHz on thin glass plates of 1 mm thickness. By contact to the investigated liquid Lamb waves propagating on the first plate emit pressure waves into the adjacent liquid, which excites Lamb waves on the second plate, what again causes pressure waves traveling inside the liquid back to the first plate and so on. The Schlieren images prove this multi reflection within the acoustic waveguide, which confirms former considerations and calculations based on the receiver signal. With this knowledge the sensor concepts with the acoustic waveguide sensor can be interpreted in a better manner.
Model of bidirectional reflectance distribution function for metallic materials
International Nuclear Information System (INIS)
Wang Kai; Zhu Jing-Ping; Liu Hong; Hou Xun
2016-01-01
Based on the three-component assumption that the reflection is divided into specular reflection, directional diffuse reflection, and ideal diffuse reflection, a bidirectional reflectance distribution function (BRDF) model of metallic materials is presented. Compared with the two-component assumption that the reflection is composed of specular reflection and diffuse reflection, the three-component assumption divides the diffuse reflection into directional diffuse and ideal diffuse reflection. This model effectively resolves the problem that constant diffuse reflection leads to considerable error for metallic materials. Simulation and measurement results validate that this three-component BRDF model can improve the modeling accuracy significantly and describe the reflection properties in the hemisphere space precisely for the metallic materials. (paper)
Model of bidirectional reflectance distribution function for metallic materials
Wang, Kai; Zhu, Jing-Ping; Liu, Hong; Hou, Xun
2016-09-01
Based on the three-component assumption that the reflection is divided into specular reflection, directional diffuse reflection, and ideal diffuse reflection, a bidirectional reflectance distribution function (BRDF) model of metallic materials is presented. Compared with the two-component assumption that the reflection is composed of specular reflection and diffuse reflection, the three-component assumption divides the diffuse reflection into directional diffuse and ideal diffuse reflection. This model effectively resolves the problem that constant diffuse reflection leads to considerable error for metallic materials. Simulation and measurement results validate that this three-component BRDF model can improve the modeling accuracy significantly and describe the reflection properties in the hemisphere space precisely for the metallic materials.
Comparison of Transmission Line Methods for Surface Acoustic Wave Modeling
Wilson, William; Atkinson, Gary
2009-01-01
Surface Acoustic Wave (SAW) technology is low cost, rugged, lightweight, extremely low power and can be used to develop passive wireless sensors. For these reasons, NASA is investigating the use of SAW technology for Integrated Vehicle Health Monitoring (IVHM) of aerospace structures. To facilitate rapid prototyping of passive SAW sensors for aerospace applications, SAW models have been developed. This paper reports on the comparison of three methods of modeling SAWs. The three models are the Impulse Response Method (a first order model), and two second order matrix methods; the conventional matrix approach, and a modified matrix approach that is extended to include internal finger reflections. The second order models are based upon matrices that were originally developed for analyzing microwave circuits using transmission line theory. Results from the models are presented with measured data from devices. Keywords: Surface Acoustic Wave, SAW, transmission line models, Impulse Response Method.
Gravitational waves in hybrid quintessential inflationary models
Energy Technology Data Exchange (ETDEWEB)
Sa, Paulo M [Departamento de Fisica, Faculdade de Ciencias e Tecnologia, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro (Portugal); Henriques, Alfredo B, E-mail: pmsa@ualg.pt, E-mail: alfredo.henriques@ist.utl.pt [Centro Multidisciplinar de Astrofisica - CENTRA and Departamento de Fisica, Instituto Superior Tecnico, UTL, Av. Rovisco Pais, 1049-001 Lisboa (Portugal)
2011-09-22
The generation of primordial gravitational waves is investigated within the hybrid quintessential inflationary model. Using the method of continuous Bogoliubov coefficients, we calculate the full gravitational-wave energy spectrum. The post-inflationary kination period, characteristic of quintessential inflationary models, leaves a clear signature on the spectrum, namely, a sharp rise of the gravitational-wave spectral energy density {Omega}{sub GW} at high frequencies. For appropriate values of the parameters of the model, {Omega}{sub GW} can be as high as 10{sup -12} in the MHz-GHz range of frequencies.
Gravitational waves in hybrid quintessential inflationary models
International Nuclear Information System (INIS)
Sa, Paulo M; Henriques, Alfredo B
2011-01-01
The generation of primordial gravitational waves is investigated within the hybrid quintessential inflationary model. Using the method of continuous Bogoliubov coefficients, we calculate the full gravitational-wave energy spectrum. The post-inflationary kination period, characteristic of quintessential inflationary models, leaves a clear signature on the spectrum, namely, a sharp rise of the gravitational-wave spectral energy density Ω GW at high frequencies. For appropriate values of the parameters of the model, Ω GW can be as high as 10 -12 in the MHz-GHz range of frequencies.
Guided wave imaging of oblique reflecting interfaces in pipes using common-source synthetic focusing
Sun, Zeqing; Sun, Anyu; Ju, Bing-Feng
2018-04-01
Cross-mode-family mode conversion and secondary reflection of guided waves in pipes complicate the processing of guided waves signals, and can cause false detection. In this paper, filters operating in the spectral domain of wavenumber, circumferential order and frequency are designed to suppress the signal components of unwanted mode-family and unwanted traveling direction. Common-source synthetic focusing is used to reconstruct defect images from the guided wave signals. Simulations of the reflections from linear oblique defects and a semicircle defect are separately implemented. Defect images, which are reconstructed from the simulation results under different excitation conditions, are comparatively studied in terms of axial resolution, reflection amplitude, detectable oblique angle and so on. Further, the proposed method is experimentally validated by detecting linear cracks with various oblique angles (10-40°). The proposed method relies on the guided wave signals that are captured during 2-D scanning of a cylindrical area on the pipe. The redundancy of the signals is analyzed to reduce the time-consumption of the scanning process and to enhance the practicability of the proposed method.
Spontaneous acoustic emission of a corrugated shock wave in the presence of a reflecting surface
International Nuclear Information System (INIS)
Wouchuk, J.G.; Lopez Cavada, J.
2004-01-01
An analytic model to study perturbation evolution in the space between a corrugated shock and a piston surface is presented. The conditions for stable oscillation patterns are obtained by looking at the poles of the exact Laplace transform. It is seen that besides the standard D'yakov-Kontorovich (DK) mode of oscillation, the shock surface can exhibit an additional finite set of discrete frequencies, due to the interaction with the piston which reflects sound waves from behind. The additional eigenmodes are excited when the shock is launched at t=0 + . The first eigenmode (the DK mode) is always present, if the Hugoniot curve has the correct slope in the V-p plane. However, the additional frequencies could be excited for strong enough shocks. The predictions of the model are verified for particular cases by studying a van der Waals gas, as in the work of Bates and Montgomery [Phys. Fluids 11, 462 (1999); Phys. Rev. Lett. 84, 1180 (2000)]. Only acoustic emission modes are considered
Energy Technology Data Exchange (ETDEWEB)
Minegishi, M; Tsuru, T [Japan National Oil Corp., Tokyo (Japan); Matsuoka, T [Japan Petroleum Exploration Corp., Tokyo (Japan)
1996-05-01
Introduced herein is a reflection wave velocity analysis method using model scanning as a method for velocity estimation across a section, the estimation being useful in the construction of a velocity structure model in seismic exploration. In this method, a stripping type analysis is carried out, wherein optimum structure parameters are determined for reflection waves one after the other beginning with those from shallower parts. During this process, the velocity structures previously determined for the shallower parts are fixed and only the lowest of the layers undergoing analysis at the time is subjected to model scanning. To consider the bending of ray paths at each velocity boundaries involving shallower parts, the ray path tracing method is utilized for the calculation of the reflection travel time curve for the reflection surface being analyzed. Out of the reflection wave travel time curves calculated using various velocity structure models, one that suits best the actual reflection travel time is detected. The degree of matching between the calculated result and actual result is measured by use of data semblance in a time window provided centering about the calculated reflective wave travel time. The structure parameter is estimated on the basis of conditions for the maximum semblance. 1 ref., 4 figs.
International Nuclear Information System (INIS)
Witte, N.S.
1997-01-01
The exact solution to the problem of reflection and diffraction of atomic de Broglie waves by a travelling evanescent wave is found starting with a bare-state formulation. The solution for the wavefunctions, the tunnelling losses and the non-adiabatic losses are given exactly in terms of hyper-Bessel functions, and are valid for all detuning and Rabi frequencies, thus generalizing previous approximate methods. Furthermore we give the limiting cases of all amplitudes in the uniform semiclassical limit, which is valid in all regions including near the classical turning points, and in the large and weak coupling cases. Exact results for the zero detuning case are obtained in terms of Bessel functions. We find our uniform semiclassical limit to be closer to the exact result over the full range of parameter values than the previously reported calculations. The current knowledge of hyper-Bessel function properties is reviewed in order to apply this to the physical problems imposed
Travelling Waves in Hybrid Chemotaxis Models
Franz, Benjamin
2013-12-18
Hybrid models of chemotaxis combine agent-based models of cells with partial differential equation models of extracellular chemical signals. In this paper, travelling wave properties of hybrid models of bacterial chemotaxis are investigated. Bacteria are modelled using an agent-based (individual-based) approach with internal dynamics describing signal transduction. In addition to the chemotactic behaviour of the bacteria, the individual-based model also includes cell proliferation and death. Cells consume the extracellular nutrient field (chemoattractant), which is modelled using a partial differential equation. Mesoscopic and macroscopic equations representing the behaviour of the hybrid model are derived and the existence of travelling wave solutions for these models is established. It is shown that cell proliferation is necessary for the existence of non-transient (stationary) travelling waves in hybrid models. Additionally, a numerical comparison between the wave speeds of the continuum models and the hybrid models shows good agreement in the case of weak chemotaxis and qualitative agreement for the strong chemotaxis case. In the case of slow cell adaptation, we detect oscillating behaviour of the wave, which cannot be explained by mean-field approximations. © 2013 Society for Mathematical Biology.
The simplest models of the reflection nebulae
International Nuclear Information System (INIS)
Voshchinnikov, N.V.
1977-01-01
Some models of the reflection nebulue have been considered. The (U-B), (B-V) and (V-R) colors and the U, B, V and R polarization have been calculated for a model of a reflection nebula associated with a large dust cloud. For the cases in which the illuminating star is far from the surface of the cloud, the form of the nebula has been considered to be spherical. If the star is close to the surface of the cloud, a part of the nebura boundary has been considered to be flat. Single scattering within the homogeneous nebula has been assumed. All the calculations use the scattering by spheres as given by the Mie's theory. The effect of variations of chemical composition and size distribution function of the grains and the position of the illuminating star has been examined. Comparison of the theoretical results with the observations of the Merope nebula shows that the dirty ice grains with the refraction index m=1.30-0.02i and size parameter asub(o)=0.5μ represent satisfactorily the observation if the star is embedded 0.7 pc behind the front surface of the nebula
TE Wave Measurement and Modeling
Sikora, John P; Sonnad, Kiran G; Alesini, David; De Santis, Stefano
2013-01-01
In the TE wave method, microwaves are coupled into the beam-pipe and the effect of the electron cloud on these microwaves is measured. An electron cloud (EC) density can then be calculated from this measurement. There are two analysis methods currently in use. The first treats the microwaves as being transmitted from one point to another in the accelerator. The second more recent method, treats the beam-pipe as a resonant cavity. This paper will summarize the reasons for adopting the resonant TE wave analysis as well as give examples from CESRTA and DA{\\Phi}NE of resonant beam-pipe. The results of bead-pull bench measurements will show some possible standing wave patterns, including a cutoff mode (evanescent) where the field decreases exponentially with distance from the drive point. We will outline other recent developments in the TE wave method including VORPAL simulations of microwave resonances, as well as the simulation of transmission in the presence of both an electron cloud and magnetic fields.
An investigation of the structure of plasma produced by reflected shock waves
International Nuclear Information System (INIS)
Phillips, M.G.R.; Pugatschew, A.A.
1979-05-01
Space and time resolved measurements of electron density and temperature have been made in the reflected-shock plasma produced by a Mach 20 incident shock wave propagating in argon at an initial pressure of 1.5 Torr. The peak electron density was found to decrease away from the reflecting wall in such a way that the plasma was fairly uniform at all times. Close to the reflecting wall (0.2 cm away) the measured peak electron density was close to (i.e. about 20% lower than) the predicted equilibrium value but further away (1.0 cm) it was lower by a factor 4. Possible reasons for this discrepancy are discussed. Calculations of reflected-shock plasma structure based on incident shock structure are only partially supported by available experimental evidence
Hydraulic Model Tests on Modified Wave Dragon
DEFF Research Database (Denmark)
Hald, Tue; Lynggaard, Jakob
A floating model of the Wave Dragon (WD) was built in autumn 1998 by the Danish Maritime Institute in scale 1:50, see Sørensen and Friis-Madsen (1999) for reference. This model was subjected to a series of model tests and subsequent modifications at Aalborg University and in the following...... are found in Hald and Lynggaard (2001). Model tests and reconstruction are carried out during the phase 3 project: ”Wave Dragon. Reconstruction of an existing model in scale 1:50 and sequentiel tests of changes to the model geometry and mass distribution parameters” sponsored by the Danish Energy Agency...
Energy Technology Data Exchange (ETDEWEB)
Soler, Roberto; Terradas, Jaume; Oliver, Ramón; Ballester, José Luis, E-mail: roberto.soler@uib.es [Departament de Física, Universitat de les Illes Balears, E-07122 Palma de Mallorca (Spain)
2017-05-01
It has been proposed that Alfvén waves play an important role in the energy propagation through the solar atmospheric plasma and its heating. Here we theoretically investigate the propagation of torsional Alfvén waves in magnetic flux tubes expanding from the photosphere up to the low corona and explore the reflection, transmission, and dissipation of wave energy. We use a realistic variation of the plasma properties and the magnetic field strength with height. Dissipation by ion–neutral collisions in the chromosphere is included using a multifluid partially ionized plasma model. Considering the stationary state, we assume that the waves are driven below the photosphere and propagate to the corona, while they are partially reflected and damped in the chromosphere and transition region. The results reveal the existence of three different propagation regimes depending on the wave frequency: low frequencies are reflected back to the photosphere, intermediate frequencies are transmitted to the corona, and high frequencies are completely damped in the chromosphere. The frequency of maximum transmissivity depends on the magnetic field expansion rate and the atmospheric model, but is typically in the range of 0.04–0.3 Hz. Magnetic field expansion favors the transmission of waves to the corona and lowers the reflectivity of the chromosphere and transition region compared to the case with a straight field. As a consequence, the chromospheric heating due to ion–neutral dissipation systematically decreases when the expansion rate of the magnetic flux tube increases.
A Blast Wave Model With Viscous Corrections
Yang, Z.; Fries, R. J.
2017-04-01
Hadronic observables in the final stage of heavy ion collision can be described well by fluid dynamics or blast wave parameterizations. We improve existing blast wave models by adding shear viscous corrections to the particle distributions in the Navier-Stokes approximation. The specific shear viscosity η/s of a hadron gas at the freeze-out temperature is a new parameter in this model. We extract the blast wave parameters with viscous corrections from experimental data which leads to constraints on the specific shear viscosity at kinetic freeze-out. Preliminary results show η/s is rather small.
A Blast Wave Model With Viscous Corrections
International Nuclear Information System (INIS)
Yang, Z; Fries, R J
2017-01-01
Hadronic observables in the final stage of heavy ion collision can be described well by fluid dynamics or blast wave parameterizations. We improve existing blast wave models by adding shear viscous corrections to the particle distributions in the Navier-Stokes approximation. The specific shear viscosity η/s of a hadron gas at the freeze-out temperature is a new parameter in this model. We extract the blast wave parameters with viscous corrections from experimental data which leads to constraints on the specific shear viscosity at kinetic freeze-out. Preliminary results show η/s is rather small. (paper)
International Nuclear Information System (INIS)
Sparks, W.M.; Kutter, G.S.
1980-01-01
The rapid coherent oscillation during a dwarf nova outburst is attributed to an accretion-driven wave going around the white dwarf component of the binary system. The increase and decrease in the period of this oscillation is due to the change in the velocity of the wave as it is first being driven and then damped. Qualitatively, a large number of observations can be explained with such a model. The beginnings of a mathematical representation of this model are developed. (orig.)
Observation of reflected waves on the SABRE positive polarity inductive adder MITL
International Nuclear Information System (INIS)
Cuneo, M.E.; Poukey, J.W.; Mendel, C.W.; Rosenthal, S.E.; Hanson, D.L.; Smith, J.R.; Maenchen, J.E.; Wenger, D.F.; Bernard, M.A.
1993-01-01
We are studying the coupling of extraction applied-B ion diodes to Magnetically Insulated Transmission Line (MITLs) on the SABRE (Sandia Accelerator and Beam Research Experiment, 6 MV, 300 kA) positive polarity inductive voltage adder. Our goal is to determine conditions under which efficient coupling occurs. The best total power efficiency for an ideal ion diode load (i.e., without parasitic losses) is obtained by maximizing the product of cathode current and gap voltage. MITLs require that the load impedance be undermatched to the self-limited line operating impedance for efficient transfer of power to ion diodes, independent of transit time isolation, and even in the case of multiple cathode system with significant vacuum electron flow. We observe that this undermatched condition results in a reflected wave which decreases the line voltage and gap electron sheath current, and increases the anode and cathode current in a time-dependent way. The MITL diode coupling is determined by the flow impedance at the adder exit. We also show that the flow impedance increases along the extension MITL on SABRE. Experimental measurements of current and peak voltage are compared to analytical models and TWOQUICK 2.5-D PIC code simulations
Updated thermal model using simplified short-wave radiosity calculations
International Nuclear Information System (INIS)
Smith, J.A.; Goltz, S.M.
1994-01-01
An extension to a forest canopy thermal radiance model is described that computes the short-wave energy flux absorbed within the canopy by solving simplified radiosity equations describing flux transfers between canopy ensemble classes partitioned by vegetation layer and leaf slope. Integrated short-wave reflectance and transmittance-factors obtained from measured leaf optical properties were found to be nearly equal for the canopy studied. Short-wave view factor matrices were approximated by combining the average leaf scattering coefficient with the long-wave view factor matrices already incorporated in the model. Both the updated and original models were evaluated for a dense spruce fir forest study site in Central Maine. Canopy short-wave absorption coefficients estimated from detailed Monte Carlo ray tracing calculations were 0.60, 0.04, and 0.03 for the top, middle, and lower canopy layers corresponding to leaf area indices of 4.0, 1.05, and 0.25. The simplified radiosity technique yielded analogous absorption values of 0.55, 0.03, and 0.01. The resulting root mean square error in modeled versus measured canopy temperatures for all layers was less than 1°C with either technique. Maximum error in predicted temperature using the simplified radiosity technique was approximately 2°C during peak solar heating. (author)
Updated thermal model using simplified short-wave radiosity calculations
Energy Technology Data Exchange (ETDEWEB)
Smith, J. A.; Goltz, S. M.
1994-02-15
An extension to a forest canopy thermal radiance model is described that computes the short-wave energy flux absorbed within the canopy by solving simplified radiosity equations describing flux transfers between canopy ensemble classes partitioned by vegetation layer and leaf slope. Integrated short-wave reflectance and transmittance-factors obtained from measured leaf optical properties were found to be nearly equal for the canopy studied. Short-wave view factor matrices were approximated by combining the average leaf scattering coefficient with the long-wave view factor matrices already incorporated in the model. Both the updated and original models were evaluated for a dense spruce fir forest study site in Central Maine. Canopy short-wave absorption coefficients estimated from detailed Monte Carlo ray tracing calculations were 0.60, 0.04, and 0.03 for the top, middle, and lower canopy layers corresponding to leaf area indices of 4.0, 1.05, and 0.25. The simplified radiosity technique yielded analogous absorption values of 0.55, 0.03, and 0.01. The resulting root mean square error in modeled versus measured canopy temperatures for all layers was less than 1°C with either technique. Maximum error in predicted temperature using the simplified radiosity technique was approximately 2°C during peak solar heating. (author)
Takata, Tomoaki; Koda, Masahiko; Sugihara, Takaaki; Sugihara, Shinobu; Okamoto, Toshiaki; Miyoshi, Kenichi; Matono, Tomomitsu; Hosho, Keiko; Mae, Yukari; Iyama, Takuji; Fukui, Takeaki; Fukuda, Satoko; Munemura, Chishio; Isomoto, Hajime
2016-12-01
Acoustic radiation force impulse is a noninvasive method for evaluating tissue elasticity on ultrasound. Renal shear wave velocity measured by this technique has not been fully investigated in patients with renal disease. The aim of the present study was to compare renal shear wave velocity in end-stage renal disease patients and that in patients without chronic kidney disease and to investigate influencing factors. Renal shear wave velocities were measured in 59 healthy young subjects (control group), 31 subjects without chronic kidney disease (non-CKD group), and 39 end-stage renal disease patients (ESRD group). Each measurement was performed 10 times at both kidneys, and the mean value of eight of 10 measurements, excluding the maximum and minimum values, was compared. Renal shear wave velocity could be measured in all subjects. Renal shear wave velocity in the control group was higher than in the non-CKD group and in the ESRD group, and no difference was found between the non-CKD group and the ESRD group. Age and depth were negatively correlated to the renal shear wave velocity. In multiple regression analysis, age and depth were independent factors for renal shear wave velocity, while renal impairment was not. There was no difference between the non-CKD group and the ESRD group, even when ages were matched and depth was adjusted. Renal shear wave velocity was not associated with advanced renal impairment. However, it reflected alteration of renal aging, and this technique may be useful to detect renal impairment in the earlier stages. © 2015 Asian Pacific Society of Nephrology.
Wu, Meiyi; Burcklen, Catherine; André, Jean-Michel; Guen, Karine Le; Giglia, Angelo; Koshmak, Konstantin; Nannarone, Stefano; Bridou, Françoise; Meltchakov, Evgueni; Rossi, Sébastien de; Delmotte, Franck; Jonnard, Philippe
2017-11-01
We study Cr/Sc-based multilayer mirrors designed to work in the water window range using hard and soft x-ray reflectivity as well as x-ray fluorescence enhanced by standing waves. Samples differ by the elemental composition of the stack, the thickness of each layer, and the order of deposition. This paper mainly consists of two parts. In the first part, the optical performances of different Cr/Sc-based multilayers are reported, and in the second part, we extend further the characterization of the structural parameters of the multilayers, which can be extracted by comparing the experimental data with simulations. The methodology is detailed in the case of Cr/B4C/Sc sample for which a three-layer model is used. Structural parameters determined by fitting reflectivity curve are then introduced as fixed parameters to plot the x-ray standing wave curve, to compare with the experiment, and confirm the determined structure of the stack.
Study on Reflected Shock Wave/Boundary Layer Interaction in a Shock Tube
Energy Technology Data Exchange (ETDEWEB)
Kim, Dong Wook; Kim, Tae Ho; Kim, Heuy Dong [Andong Nat’l Univ., Andong (Korea, Republic of)
2017-07-15
The interaction between a shock wave and a boundary layer causes boundary layer separation, shock train, and in some cases, strong unsteadiness in the flow field. Such a situation is also observed in a shock tube, where the reflected shock wave interacts with the unsteady boundary layer. However, only a few studies have been conducted to investigate the shock train phenomenon in a shock tube. In the present study, numerical studies were conducted using the two-dimensional axisymmetric domain of a shock tube, and compressible Navier-Stokes equations were solved to clarify the flow characteristics of shock train phenomenon inside a shock tube. A detailed wave diagram was developed based on the present computational results, which were validated with existing experimental data.
Observation of neutron standing waves at total reflection by precision gamma spectroscopy
International Nuclear Information System (INIS)
Aksenov, V.L.; Gundorin, N.A.; Nikitenko, Yu.V.; Popov, Yu.P.; Cser, L.
1998-01-01
Total reflection of polarized neutrons from the layered structure glass/Fe (1000 A Angstrom)/Gd (50 A Angstrom) is investigated by registering neutrons and gamma-quanta from thermal neutron capture. The polarization ratio of gamma counts of neutron beams polarized in and opposite the direction of the magnetic field is measured. The polarization ratio is larger than unity for the neutron wavelengths λ 2.2 A Angstrom. Such behaviour of the wavelength dependence of the gamma-quanta polarization ratio points to the fact that over the surface of the Fe Layer a neutron standing wave caused by the interference of the incident neutron wave and the wave refracted from the magnetized Fe layer is formed
-Advanced Models for Tsunami and Rogue Waves
Directory of Open Access Journals (Sweden)
D. W. Pravica
2012-01-01
Full Text Available A wavelet , that satisfies the q-advanced differential equation for , is used to model N-wave oscillations observed in tsunamis. Although q-advanced ODEs may seem nonphysical, we present an application that model tsunamis, in particular the Japanese tsunami of March 11, 2011, by utilizing a one-dimensional wave equation that is forced by . The profile is similar to tsunami models in present use. The function is a wavelet that satisfies a q-advanced harmonic oscillator equation. It is also shown that another wavelet, , matches a rogue-wave profile. This is explained in terms of a resonance wherein two small amplitude forcing waves eventually lead to a large amplitude rogue. Since wavelets are used in the detection of tsunamis and rogues, the signal-analysis performance of and is examined on actual data.
Castelain, V; Hervé, P; Lecarpentier, Y; Duroux, P; Simonneau, G; Chemla, D
2001-03-15
The purpose of this time-domain study was to compare pulmonary artery (PA) pulse pressure and wave reflection in chronic pulmonary thromboembolism (CPTE) and primary pulmonary hypertension (PPH). Pulmonary artery pressure waveform analysis provides a simple and accurate estimation of right ventricular afterload in the time-domain. Chronic pulmonary thromboembolism and PPH are both responsible for severe pulmonary hypertension. Chronic pulmonary thromboembolism and PPH predominantly involve proximal and distal arteries, respectively, and may lead to differences in PA pressure waveform. High-fidelity PA pressure was recorded in 14 patients (7 men/7 women, 46 +/- 14 years) with CPTE (n = 7) and PPH (n = 7). We measured thermodilution cardiac output, mean PA pressure (MPAP), PA pulse pressure (PAPP = systolic - diastolic PAP) and normalized PAPP (nPAPP = PPAP/MPAP). Wave reflection was quantified by measuring Ti, that is, the time between pressure upstroke and the systolic inflection point (Pi), deltaP, that is, the systolic PAP minus Pi difference, and the augmentation index (deltaP/PPAP). At baseline, CPTE and PPH had similar cardiac index (2.4 +/- 0.4 vs. 2.5 +/- 0.5 l/min/m2), mean PAP (59 +/- 9 vs. 59 +/- 10 mm Hg), PPAP (57 +/- 13 vs. 53 +/- 13 mm Hg) and nPPAP (0.97 +/- 0.16 vs. 0.89 +/- 0.13). Chronic pulmonary thromboembolism had shorter Ti (90 +/- 17 vs. 126 +/- 16 ms, p PPAP (0.26 +/- 0.01 vs. 0.09 +/- 0.07, p < 0.01). Our study indicated that: 1) CPTE and PPH with severe pulmonary hypertension had similar PA pulse pressure, and 2) wave reflection is elevated in both groups, and CPTE had increased and anticipated wave reflection as compared with PPH, thus suggesting differences in the pulsatile component of right ventricular afterload.
Internal-wave reflection from uniform slopes: higher harmonics and Coriolis effects
Directory of Open Access Journals (Sweden)
T. Gerkema
2006-01-01
Full Text Available Weakly nonlinear reflection of internal waves from uniform slopes produces higher harmonics and mean fields; the expressions are here derived for constant stratification and with Coriolis effects fully included, i.e. the horizontal component of the earth rotation vector (referred to as 'non-traditional'' is taken into account. Uniformity in one of the horizontal directions is assumed. It is shown that solutions can be as readily derived with as without ; hence there is no need to make the so-called Traditional Approximation. Examples of reflecting internal-wave beams are presented for super-inertial, inertial and sub-inertial frequencies. The problem of resonant and non-resonant forcing of the second harmonic is studied for single plane waves; unlike under the Traditional Approximation, the problem of reflection from a horizontal bottom no longer forms a singular case. Non-traditional effects are favourable to resonant forcing at near-tidal rather than near-inertial frequencies, and generally increase the intensity of the second harmonic. Strong stratification tends to suppress non-traditional effects, but a near-total suppression is only attained for high values of stratification that are characteristic of the seasonal thermocline; in most parts of the ocean, non-traditional effects can therefore be expected to be important.
User's Manual for the Simulating Waves Nearshore Model (SWAN)
National Research Council Canada - National Science Library
Allard, Richard
2002-01-01
The Simulating WAves Nearshore (SWAN) model is a numerical wave model used to obtain realistic estimates of wave parameters in coastal areas, lakes, and estuaries from given wind, bottom, and current conditions...
Ocean wave prediction using numerical and neural network models
Digital Repository Service at National Institute of Oceanography (India)
Mandal, S.; Prabaharan, N.
This paper presents an overview of the development of the numerical wave prediction models and recently used neural networks for ocean wave hindcasting and forecasting. The numerical wave models express the physical concepts of the phenomena...
Assessment of multi class kinematic wave models
Van Wageningen-Kessels, F.L.M.; Van Lint, J.W.C.; Vuik, C.; Hoogendoorn, S.P.
2012-01-01
In the last decade many multi class kinematic wave (MCKW) traffic ow models have been proposed. MCKW models introduce heterogeneity among vehicles and drivers. For example, they take into account differences in (maximum) velocities and driving style. Nevertheless, the models are macroscopic and the
Turbulent Spot Pressure Fluctuation Wave Packet Model
Energy Technology Data Exchange (ETDEWEB)
Dechant, Lawrence J. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2017-05-01
Wave packet analysis provides a connection between linear small disturbance theory and subsequent nonlinear turbulent spot flow behavior. The traditional association between linear stability analysis and nonlinear wave form is developed via the method of stationary phase whereby asymptotic (simplified) mean flow solutions are used to estimate dispersion behavior and stationary phase approximation are used to invert the associated Fourier transform. The resulting process typically requires nonlinear algebraic equations inversions that can be best performed numerically, which partially mitigates the value of the approximation as compared to a more complete, e.g. DNS or linear/nonlinear adjoint methods. To obtain a simpler, closed-form analytical result, the complete packet solution is modeled via approximate amplitude (linear convected kinematic wave initial value problem) and local sinusoidal (wave equation) expressions. Significantly, the initial value for the kinematic wave transport expression follows from a separable variable coefficient approximation to the linearized pressure fluctuation Poisson expression. The resulting amplitude solution, while approximate in nature, nonetheless, appears to mimic many of the global features, e.g. transitional flow intermittency and pressure fluctuation magnitude behavior. A low wave number wave packet models also recover meaningful auto-correlation and low frequency spectral behaviors.
Wang, T.; Cheng, J.B.; Guo, Qiang; Wang, C.L.
2017-01-01
Elastic full waveform inversion (EFWI) provides high-resolution parameter estimation of the subsurface but requires good initial guess of the true model. The traveltime inversion only minimizes traveltime misfits which are more sensitive
Groundwater exploration in a Quaternary sediment body by shear-wave reflection seismics
Pirrung, M.; Polom, U.; Krawczyk, C. M.
2008-12-01
The detailed investigation of a shallow aquifer structure is the prerequisite for choosing a proper well location for groundwater exploration drilling for human drinking water supply and subsequent managing of the aquifer system. In the case of shallow aquifers of some 10 m in depth, this task is still a challenge for high-resolution geophysical methods, especially in populated areas. In areas of paved surfaces, shallow shear-wave reflection seismics is advantageous compared to conventional P-wave seismic methods. The sediment body of the Alfbach valley within the Vulkaneifel region in Germany, partly covered by the village Gillenfeld, was estimated to have a maximum thickness of nearly 60 m. It lies on top of a complicated basement structure, constituted by an incorporated lava flow near the basement. For the positioning of new well locations, a combination of a SH-wave land streamer receiver system and a small, wheelbarrow-mounted SH-wave source was used for the seismic investigations. This equipment can be easily applied also in residential areas without notable trouble for the inhabitants. The results of the 2.5D profiling show a clear image of the sediment body down to the bedrock with high resolution. Along a 1 km seismic profile, the sediment thickness varies between 20 to more than 60 m in the centre of the valley. The reflection behaviour from the bedrock surface corroborates the hypothesis of a basement structure with distinct topography, including strong dipping events from the flanks of the valley and strong diffractions from subsurface discontinuities. The reflection seismic imaging leads to an estimation of the former shape of the valley and a reconstruction of the flow conditions at the beginning of the sedimentation process.
Imaging near-subsurface subrosion structures and faults using SH-wave reflection seismics
Wadas, Sonja; Polom, Ulrich; Buness, Hermann; Krawczyk, Charlotte
2016-04-01
Subrosion is a term for underground leaching of soluble rocks and is a global phenomenon. It involves dissolution of evaporites due to the presence of unsaturated water, fractures and faults. Fractures and faults are pathways for water to circulate and to generate subsurface cavities. Depending on the leached material and the parameters of the generation process, especially the dissolution rate, different kinds of subrosion structures evolve in the subsurface. The two end members are collapse and depression structures. Subrosion is a natural process, but it can be enhanced by anthropogenic factors like manipulation of the aquifer system and groundwater flow and by e.g. extraction of saline water. The formation of sinkholes and depressions are a dangerous geohazard, especially if they occur in urban areas, which often leads to building and infrastructural damage and life-threatening situations. For this reason investigations of the processes that induce subrosion and a detailed analysis of the resulting structures are of importance. To develop a comprehensive model of near-subsurface subrosion structures, reflection seismics is one of the methods used by the Leibniz Institute for Applied Geophysics. The study area is located in the city of Bad Frankenhausen in northern Thuringia, Germany. Most of the geological underground of Thuringia is characterized by Permian deposits. Bad Frankenhausen is situated directly south of the Kyffhäuser mountain range at the Kyffhäuser Southern Margin Fault. This major fault is one of the main pathways for the circulating ground- and meteoric waters that leach the Permian deposits, especially the Leine-, Staßfurt- and Werra Formations. 2014 and 2015 eight shear wave reflection seismic profiles were carried out in the urban area of Bad Frankenhausen and three profiles in the countrified surroundings. Altogether ca. 3.6 km were surveyed using a landstreamer as receiver and an electro-dynamic vibrator as source. The surveys were
Elder, Robert M.; O'Connor, Thomas C.; Chantawansri, Tanya L.; Sliozberg, Yelena R.; Sirk, Timothy W.; Yeh, In-Chul; Robbins, Mark O.; Andzelm, Jan W.
2017-09-01
Semicrystalline polyethylene (PE) is attractive for a variety of mechanically demanding applications, where shock compression can occur. Although often highly crystalline, PE invariably contains nanoscale amorphous domains that influence shock propagation. Our objective in this work is to study the effects of such domains. To this end, we adopt a novel approach wherein we parametrize a simple continuum-level theory based on the shock impedance from molecular dynamics (MD) simulations. Using this theory, we predict how crystalline/amorphous interfaces attenuate shocks via energy reflection due to the impedance mismatch between the phases. The theory predicts that these interfaces attenuate weak shocks more effectively than strong shocks. We compare the theory to explicit nonequilibrium MD simulations of compressive shocks in semicrystalline PE containing nanometer-scale amorphous regions of varying size, where we analyze the pressure response and reflection of energy. The theory and simulations show good agreement for strong shocks (≥1.0 km /s ), but for weak shocks (shock front. However, the simulations show that when amorphous domains are narrow—with widths comparable to the shock front—reflection is reduced compared to the predictions. We identify several nanoscale mechanisms that reduce the impedance mismatch, and thus reduce reflection, at thin amorphous domains. First, the two-wave elastic-plastic structure of shocks in crystalline PE allows the faster-moving elastic precursor wave to compress small amorphous domains before the plastic wave arrives. Second, confinement between stiff, ordered crystalline domains increases the stiffness and chain ordering in small amorphous regions. Moreover, in terms of stiffness the interfaces are similar in width to the shock front, which may contribute to the underprediction of the theory for weak shocks, where the shock front is widest. We conclude by discussing the significance of these results, namely, how they can
Simple opdriftsbaserede modeller for Wave Star
DEFF Research Database (Denmark)
Kramer, Morten
Wave Star modellen er udarbejdet i programmeringssproget Delphi. Modellerne er en videre udarbejdelse af tidligere anvendte Excel-modeller. I forhold til Excelmodellerne udmærker de nye Dephi-modeller sig ved at beregningerne udføres mange gange hurtigere og modellerne kan håndtere lange tidsserier...
Wave and Wind Model Performance Metrics Tools
Choi, J. K.; Wang, D. W.
2016-02-01
Continual improvements and upgrades of Navy ocean wave and wind models are essential to the assurance of battlespace environment predictability of ocean surface wave and surf conditions in support of Naval global operations. Thus, constant verification and validation of model performance is equally essential to assure the progress of model developments and maintain confidence in the predictions. Global and regional scale model evaluations may require large areas and long periods of time. For observational data to compare against, altimeter winds and waves along the tracks from past and current operational satellites as well as moored/drifting buoys can be used for global and regional coverage. Using data and model runs in previous trials such as the planned experiment, the Dynamics of the Adriatic in Real Time (DART), we demonstrated the use of accumulated altimeter wind and wave data over several years to obtain an objective evaluation of the performance the SWAN (Simulating Waves Nearshore) model running in the Adriatic Sea. The assessment provided detailed performance of wind and wave models by using cell-averaged statistical variables maps with spatial statistics including slope, correlation, and scatter index to summarize model performance. Such a methodology is easily generalized to other regions and at global scales. Operational technology currently used by subject matter experts evaluating the Navy Coastal Ocean Model and the Hybrid Coordinate Ocean Model can be expanded to evaluate wave and wind models using tools developed for ArcMAP, a GIS application developed by ESRI. Recent inclusion of altimeter and buoy data into a format through the Naval Oceanographic Office's (NAVOCEANO) quality control system and the netCDF standards applicable to all model output makes it possible for the fusion of these data and direct model verification. Also, procedures were developed for the accumulation of match-ups of modelled and observed parameters to form a data base
Backscattered EM-wave manipulation using low cost 1-bit reflective surface at W-band
Taher Al-Nuaimi, Mustafa K.; Hong, Wei; He, Yejun
2018-04-01
The design of low cost 1-bit reflective (non-absorptive) surfaces for manipulation of backscattered EM-waves and radar cross section (RCS) reduction at W-band is presented in this article. The presented surface is designed based on the reflection phase cancellation principle. The unit cell used to compose the proposed surface has an obelus (division symbol of short wire and two disks above and below) like shape printed on a grounded dielectric material. Using this unit cell, surfaces that can efficiently manipulate the backscattered RCS pattern by using the proposed obelus-shaped unit cell (as ‘0’ element) and its mirrored unit cell (as ‘1’ element) in one surface with a 180° ± 35° reflection phase difference between their reflection phases are designed. The proposed surfaces can generate various kinds of backscattered RCS patterns, such as single, three, or four lobes or even a low-level (reduced RCS) diffused reflection pattern when those two unit cells are distributed randomly across the surface aperture. For experimental characterization purposes, a 50 × 50 mm2 surface is fabricated and measured.
Lagrangian modelling of ocean surface waves and synthetic aperture radar wave measurements
Energy Technology Data Exchange (ETDEWEB)
Fouques, Sebastien
2005-07-01
The present thesis is concerned with the estimation of the ocean wave spectrum from synthetic aperture radar imaging and the modelling of ocean surface waves using the Lagrangian formalism. The first part gives a short overview of the theories of ocean surface waves and synthetic aperture radar (SAR) whereas the second part consists of five independent publications. The first two articles investigate the influence of the radar backscatter model on the SAR imaging of ocean waves. In Article I, Monte Carlo simulations of SAR images of the ocean surface are carried out using a nonlinear backscatter model that include both specular reflection and Bragg scattering and the results are compared to simulations from the classical Hasselmann integral transform (Hasselmann and Hasselmann, 1991). It is shown that nonlinearities in the backscatter model strongly influence the imaging of range-travelling waves and that the former can suppress the range-splitting effect (Bruning et al., 1988). Furthermore, in Article II a database of Envisat-ASAR Wave Mode products co-located with directional wave spectra from the numerical model WAM and which contains range-travelling wave cases only, is set up. The WAM spectra are used as input to several ocean-to-SAR integral transforms, with various real aperture radar (RAR) models and the obtained SAR image cross-spectra are compared to the Envisat-ASAR observations. A first result is that the use of a linear backscatter model leads to a high proportion of non-physical negative backscatter values in the RAR image, as suggested by Schulz-Stellenfleth (2001). Then, a comparison between the observed SAR cross-spectra and the ones simulated through Hasselmann's integral transform reveals that only twenty percents of the observations show a range-splitting effect as strong as in the simulations. A much better agreement is obtained when using the integral transform by Schulz-Stellenfleth (2003), which is based on a nonlinear hackscatter model
International Nuclear Information System (INIS)
Shad-Manamen, N.; Eskandari-Ghadi, M.
2008-01-01
The existing theory for wave propagation through a soil layer are not compatible with the real soil layers because in the theory the layers are flat and the sub-layers are parallel, while in real the soil layers are not flat and they may not be parallel. Thus, wave propagations through a corrugated interface are so important. In this paper, a two dimensional SH-wave propagation through a corrugated interface between two linear transversely isotropic half-spaces is assessed. In order to do this, Lord Rayleigh's method is accepted to express the non-flat surface by a Fourier series. In this way, the amplitude of the reflected and transmitted waves is analytically determined in terms of the incident SH-wave amplitude. It is shown that except for the regular reflected and refracted waves, some irregular reflected and refracted waves are exist, and the amplitudes of these waves vary in terms of the angle and frequency of incident wave, equation of surface, and the material properties of the domains. The numerical computations for some cases of different amplitude/wave-length ratio of the interface are done. This work is an extension of Asano's paper (1960) for a more complicated interface, where more non-zero coefficients are considered in expressing the equation of surface in the form of Fourier series. The analytical results for some simpler case of isotropic domain are collapsed on Asano's results (1960). In addition, the numerical evaluation is in good agreement with Asano's.
Genetic influence on the relation between exhaled nitric oxide and pulse wave reflection.
Tarnoki, David Laszlo; Tarnoki, Adam Domonkos; Medda, Emanuela; Littvay, Levente; Lazar, Zsofia; Toccaceli, Virgilia; Fagnani, Corrado; Stazi, Maria Antonietta; Nisticó, Lorenza; Brescianini, Sonia; Penna, Luana; Lucatelli, Pierleone; Boatta, Emanuele; Zini, Chiara; Fanelli, Fabrizio; Baracchini, Claudio; Meneghetti, Giorgio; Koller, Akos; Osztovits, Janos; Jermendy, Gyorgy; Preda, Istvan; Kiss, Robert Gabor; Karlinger, Kinga; Lannert, Agnes; Horvath, Tamas; Schillaci, Giuseppe; Molnar, Andrea Agnes; Garami, Zsolt; Berczi, Viktor; Horvath, Ildiko
2013-06-01
Nitric oxide has an important role in the development of the structure and function of the airways and vessel walls. Fractional exhaled nitric oxide (FE(NO)) is inversely related to the markers and risk factors of atherosclerosis. We aimed to estimate the relative contribution of genes and shared and non-shared environmental influences to variations and covariation of FE(NO) levels and the marker of elasticity function of arteries. Adult Caucasian twin pairs (n = 117) were recruited in Hungary, Italy and in the United States (83 monozygotic and 34 dizygotic pairs; age: 48 ± 16 SD years). FE(NO) was measured by an electrochemical sensor-based device. Pulse wave reflection (aortic augmentation index, Aix(ao)) was determined by an oscillometric method (Arteriograph). A bivariate Cholesky decomposition model was applied to investigate whether the heritabilities of FE(NO) and Aix(ao) were linked. Genetic effects accounted for 58% (95% confidence interval (CI): 42%, 71%) of the variation in FE(NO) with the remaining 42% (95%CI: 29%, 58%) due to non-shared environmental influences. A modest negative correlation was observed between FE(NO) and Aix(ao) (r = -0.17; 95%CI:-0.32,-0.02). FE(NO) showed a significant negative genetic correlation with Aix(ao) (r(g) = -0.25; 95%CI:-0.46,-0.02). Thus in humans, variations in FE(NO) are explained both by genetic and non-shared environmental effects. Covariance between FE(NO) and Aix(ao) is explained entirely by shared genetic factors. This is consistent with an overlap among the sets of genes involved in the expression of these phenotypes and provides a basis for further genetic studies on cardiovascular and respiratory diseases.
Directory of Open Access Journals (Sweden)
K. Meziane
2004-07-01
Full Text Available An energetic ion (E≤40 event observed by the CLUSTER/CIS experiment upstream of the Earth's bow shock is studied in detail. The ion event is observed in association with quasi-monochromatic ULF MHD-like waves, which we show modulate the ion fluxes. According to three statistical bow shock position models, the Cluster spacecrafts are located at ~0.5 Re from the shock and the averaged bow shock θBn0 is about ~30°. The analysis of the three-dimensional angular distribution indicates that ions propagating roughly along the magnetic field direction are observed at the onset of the event. Later on, the angular distribution is gyrophase-bunched and the pitch-angle distribution is peaked at α0~θBn0, consistent with the specular reflection production mechanism. The analysis of the waves shows that they are left-handed in the spacecraft frame of reference (right-handed in the solar wind frame and propagate roughly along the ambient magnetic field; we have found that they are in cyclotron-resonance with the field-aligned beam observed just upstream. Using properties of the waves and particles, we explain the observed particle flux-modulation in the context of θBn changes at the shock caused by the convected ULF waves. We have found that the high count rates coincide with particles leaving the shock when θBn angles are less than ~40°, consistent with the specular reflection hypothesis as the production mechanism of ions.
Shallow shear-wave reflection seismics in the tsunami struck Krueng Aceh River Basin, Sumatra
Directory of Open Access Journals (Sweden)
U. Polom
2008-01-01
Full Text Available As part of the project "Management of Georisk" (MANGEONAD of the Federal Institute for Geosciences and Natural Resources (BGR, Hanover, high resolution shallow shear-wave reflection seismics was applied in the Indonesian province Nanggroe Aceh Darussalam, North Sumatra in cooperation with the Government of Indonesia, local counterparts, and the Leibniz Institute for Applied Geosciences, Hanover. The investigations were expected to support classification of earthquake site effects for the reconstruction of buildings and infrastructure as well as for groundwater exploration. The study focussed on the city of Banda Aceh and the surroundings of Aceh Besar. The shear-wave seismic surveys were done parallel to standard geoengineering investigations like cone penetrometer tests to support subsequent site specific statistical calibration. They were also partly supplemented by shallow p-wave seismics for the identification of (a elastic subsurface parameters and (b zones with abundance of groundwater. Evaluation of seismic site effects based on shallow reflection seismics has in fact been found to be a highly useful method in Aceh province. In particular, use of a vibratory seismic source was essential for successful application of shear-wave seismics in the city of Banda Aceh and in areas with compacted ground like on farm tracks in the surroundings, presenting mostly agricultural land use areas. We thus were able to explore the mechanical stiffness of the subsurface down to 100 m depth, occasionally even deeper, with remarkably high resolution. The results were transferred into geotechnical site classification in terms of the International Building Code (IBC, 2003. The seismic images give also insights into the history of the basin sedimentation processes of the Krueng Aceh River delta, which is relevant for the exploration of new areas for construction of safe foundations of buildings and for identification of fresh water aquifers in the tsunami
Wave propagation in the Lorenz-96 model
van Kekem, Dirk L.; Sterk, Alef E.
2018-04-01
In this paper we study the spatiotemporal properties of waves in the Lorenz-96 model and their dependence on the dimension parameter n and the forcing parameter F. For F > 0 the first bifurcation is either a supercritical Hopf or a double-Hopf bifurcation and the periodic attractor born at these bifurcations represents a traveling wave. Its spatial wave number increases linearly with n, but its period tends to a finite limit as n → ∞. For F traveling wave also grows linearly with n. For F < 0 and even n, however, a Hopf bifurcation is preceded by either one or two pitchfork bifurcations, where the number of the latter bifurcations depends on whether n has remainder 2 or 0 upon division by 4. This bifurcation sequence leads to stationary waves and their spatiotemporal properties also depend on the remainder after dividing n by 4. Finally, we explain how the double-Hopf bifurcation can generate two or more stable waves with different spatiotemporal properties that coexist for the same parameter values n and F.
Wave propagation in the Lorenz-96 model
Directory of Open Access Journals (Sweden)
D. L. van Kekem
2018-04-01
Full Text Available In this paper we study the spatiotemporal properties of waves in the Lorenz-96 model and their dependence on the dimension parameter n and the forcing parameter F. For F > 0 the first bifurcation is either a supercritical Hopf or a double-Hopf bifurcation and the periodic attractor born at these bifurcations represents a traveling wave. Its spatial wave number increases linearly with n, but its period tends to a finite limit as n → ∞. For F < 0 and odd n, the first bifurcation is again a supercritical Hopf bifurcation, but in this case the period of the traveling wave also grows linearly with n. For F < 0 and even n, however, a Hopf bifurcation is preceded by either one or two pitchfork bifurcations, where the number of the latter bifurcations depends on whether n has remainder 2 or 0 upon division by 4. This bifurcation sequence leads to stationary waves and their spatiotemporal properties also depend on the remainder after dividing n by 4. Finally, we explain how the double-Hopf bifurcation can generate two or more stable waves with different spatiotemporal properties that coexist for the same parameter values n and F.
Acute resistance exercise using free weights on aortic wave reflection characteristics.
Tai, Yu Lun; Gerhart, Hayden; Mayo, Xián; Kingsley, J Derek
2018-01-01
Aortic wave reflection characteristics such as the augmentation index (AIx), wasted left ventricular pressure energy (ΔE w ) and aortic haemodynamics, such as aortic systolic blood pressure (ASBP), strongly predict cardiovascular events. The effects of acute resistance exercise (ARE) using free-weight exercises on these characteristics are unknown. Therefore, we sought to determine the effects of acute free-weight resistance exercise on aortic wave reflection characteristics and aortic haemodynamics in resistance-trained individuals. Fifteen young, healthy resistance-trained (9 ± 3 years) individuals performed two randomized sessions consisting of an acute bout of free-weight resistance exercise (ARE) or a quiet control (CON). The ARE consisted of three sets of 10 repetitions at 75% one repetition maximum for squat, bench press and deadlift. In CON, the participants rested in the supine position for 30 min. Measurements were made at baseline before sessions and 10 min after sessions. A two-way ANOVA was used to compare the effects of condition across time. There were no significant interactions for aortic or brachial blood pressures. Compared to rest, there were significant increases in augmentation pressure (rest: 5·7 ± 3·0 mmHg; recovery: 10·4 ± 5·7 mmHg, P = 0·002), AIx (rest: 116·8 ± 4·2%; recovery: 123·2 ± 8·4%, P = 0·002), AIx normalized at 75 bpm (rest: 5·2 ± 7·6%; recovery: 27·3 ± 13·2%, Pfree-weight exercises may have no effect on aortic and brachial blood pressure but may significantly alter aortic wave reflection characteristics. © 2016 Scandinavian Society of Clinical Physiology and Nuclear Medicine. Published by John Wiley & Sons Ltd.
Hanssen, Henner; Nussbaumer, Monique; Moor, Christoph; Cordes, Mareike; Schindler, Christian; Schmidt-Trucksäss, Arno
2015-02-01
Our aim was to investigate the acute and 24-hour (h) effects of high-intensity interval training (HIIT) and moderate continuous training (MCT) on arterial pulse wave reflection, an established marker of arterial stiffness and cardiovascular risk. In a randomized cross-over design, 21 young healthy male participants performed a HIIT or a MCT on separate visits. Before and 5 (t5), 20 (t20), 35 (t35), and 50 (t50) minutes after the acute exercise bouts, the crude augmentation index (AIx) and the AIx at a set heart rate (AIx@75) were analysed by applanation tonometry. Starting 1 h post-exercise, both indices were captured over 24-h with an oscillometric monitoring device. AIx did not change significantly after MCT but declined progressively after HIIT, reaching significantly lower values compared to MCT at t35 (P = 0.045) and t50 (P = 0.008). AIx@75 increased after both acute exercise types but was higher after HIIT at t5 (P HIIT (P = 0.007) but not after MCT (P = 0.813). Exercise intensity affects pulse wave reflection, with different time courses for AIx and AIx@75 post-exercise. Although initially higher after HIIT, AIx@75 declines in the 24-h recovery period indicating more favourable effects on pulse wave reflection compared to MCT. This may result in substantial positive chronic training effects on arterial stiffness in health and cardiovascular disease. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.
Ludeno, Giovanni; Natale, Antonio; Soldovieri, Francesco; Vicinanza, Diego; Serafino, Francesco
2014-05-01
The observation of nearshore waves and the knowledge of the sea state parameters can play a crucial role for the safety of harbors and ocean engineering. In the last two decades, different algorithms for the estimation of sea state parameters, surface currents and bathymetry from X-band radar data have been developed and validated [1, 2]. The retrieval of ocean wave parameters such as significant height, period, direction and wavelength of the dominant wave is based on the spectral analysis of data sequences collected by nautical X-band radars [3]. In particular, the reconstruction of the wave motion is carried out through the inversion procedure explained in [1-3], which exploits the dispersion relationship to define a band pass filter used to separate the energy associated with the ocean waves from the background noise. It is worth to note that the shape of such a band pass filter depends upon the value of both the surface currents and bathymetry; in our reconstruction algorithm these parameters are estimated through the (Normalized Scalar Product) procedure [1], which outperforms other existing methods (e.g., the Least Squares) [4]. From the reconstructed wave elevation sequences we can get the directional spectrum that provides useful information (i.e., wavelength, period, direction and amplitude) relevant to the main waves contributing to the wave motion. Of course, in coastal zones a number of diffraction and reflection phenomena can be observed, due to sea-waves impinging obstacles as jetties, breakwaters and boats. In the present paper we want to show the capability to detect reflected and diffracted sea-waves offered by the processing of X-band radar data. Further details relevant to the obtained results will be provided in the full paper and at the conference time. References [1] F. Serafino, C. Lugni, F. Soldovieri, "A novel strategy for the surface current determination from marine X-Band radar data", IEEE Geosci. and Remote Sensing Letters, vol. 7, no
Highly directive Fabry-Perot leaky-wave nanoantennas based on optical partially reflective surfaces
Energy Technology Data Exchange (ETDEWEB)
Lorente-Crespo, M.; Mateo-Segura, C., E-mail: C.Mateo-Segura@hw.ac.uk [Institute of Sensors, Signals and Systems, Heriot-Watt University, EH14 4AS Edinburgh (United Kingdom)
2015-05-04
Nanoantennas enhance the conversion between highly localized electromagnetic fields and far-field radiation. Here, we investigate the response of a nano-patch partially reflective surface backed with a silver mirror to an optical source embedded at the centre of the structure. Using full wave simulations, we demonstrate a two orders of magnitude increased directivity compared to the isotropic radiator, 50% power confinement to a 13.8° width beam and a ±16 nm bandwidth. Our antenna does not rely on plasmonic phenomena thus reducing non-radiative losses and conserving source coherence.
DEFF Research Database (Denmark)
Ambühl, Simon; Kofoed, Jens Peter; Sørensen, John Dalsgaard
2015-01-01
Wave models used for site assessments are subjected to model uncertainties, which need to be quantified when using wave model results for probabilistic reliability assessments. This paper focuses on determination of wave model uncertainties. Four different wave models are considered, and validation...... data are collected from published scientific research. The bias and the root-mean-square error, as well as the scatter index, are considered for the significant wave height as well as the mean zero-crossing wave period. Based on an illustrative generic example, this paper presents how the quantified...... uncertainties can be implemented in probabilistic reliability assessments....
DEFF Research Database (Denmark)
Ambühl, Simon; Kofoed, Jens Peter; Sørensen, John Dalsgaard
2014-01-01
Wave models used for site assessments are subject to model uncertainties, which need to be quantified when using wave model results for probabilistic reliability assessments. This paper focuses on determination of wave model uncertainties. Considered are four different wave models and validation...... data is collected from published scientific research. The bias, the root-mean-square error as well as the scatter index are considered for the significant wave height as well as the mean zero-crossing wave period. Based on an illustrative generic example it is shown how the estimated uncertainties can...... be implemented in probabilistic reliability assessments....
Abnormal Waves Modelled as Second-order Conditional Waves
DEFF Research Database (Denmark)
Jensen, Jørgen Juncher
2005-01-01
The paper presents results for the expected second order short-crested wave conditional of a given wave crest at a specific point in time and space. The analysis is based on the second order Sharma and Dean shallow water wave theory. Numerical results showing the importance of the spectral densit...
Modeling of Rayleigh wave dispersion in Iberia
Directory of Open Access Journals (Sweden)
José Badal
2011-01-01
Full Text Available Phase and group velocities of 15–70 s Rayleigh waves propagating across the Iberian Peninsula have been transformed into local dispersion curves by linear inversion of travel times. The procedure permits that the waveform dispersion to be obtained as a continuous period-dependent velocity function at grid points belonging to the area probed by the waves, thus providing phase- and group-velocity contour maps for several periods within the interval of interest. The regionalization process rests on a homogeneous initial data set in which the number of observations remains almost constant for all periods of reference. Damped least-squares inversion of the local dispersion curves for shear-wave velocity structure is performed to obtain depth-dependent S-wave velocity profiles at the grid points covering the model region. The reliability of the results should improve significantly owing to the use of phase and group velocities simultaneously. On this basis, we have built horizontal depth sections that give an updated view of the seismic velocity structure of the peninsula at lithospheric and upper mantle depths (20–200 km. After averaging all the pure-path S-wave velocities previously determined at each grid point, the velocity-depth models so obtained for major tectonic units allow the comparison between the Hercynian basement and other areas of Mesozoic folding and Tertiary basins.
Radio Spectral Imaging of Reflective MHD Waves during the Impulsive Phase of a Solar Flare
Yu, S.; Chen, B.; Reeves, K.
2017-12-01
We report a new type of coherent radio bursts observed by the Karl G. Jansky Very Large Array (VLA) in 1-2 GHz during the impulsive phase of a two-ribbon flare on 2014 November 1, which we interpret as MHD waves reflected near the footpoint of flaring loops. In the dynamic spectrum, this burst starts with a positive frequency drift toward higher frequencies until it slows down near its highest-frequency boundary. Then it turns over and drifts toward lower frequencies. The frequency drift rate in its descending and ascending branch is between 50-150 MHz/s, which is much slower than type III radio bursts associated with fast electron beams but close to the well-known intermediate drift bursts, or fiber bursts, which are usually attributed to propagating whistler or Alfvenic waves. Thanks to VLA's unique capability of imaging with spectrometer-like temporal and spectral resolution (50 ms and 2 MHz), we are able to obtain an image of the radio source at every time and frequency in the dynamic spectrum where the burst is present and trace its spatial evolution. From the imaging results, we find that the radio source firstly moves downward toward one of the flaring ribbons before it "bounces off" at the lowest height (corresponding to the turnover frequency in the dynamic spectrum) and moves upward again. The measured speed in projection is at the order of 1-2 Mm/s, which is characteristic of Alfvenic or fast-mode MHD waves in the low corona. We conclude that the radio burst is emitted by trapped nonthermal electrons in the flaring loop carried along by a large-scale MHD wave. The waves are probably launched during the eruption of a magnetic flux rope in the flare impulsive phase.
Monitoring the reflection from an artificial defect in rail track using guided wave ultrasound
Loveday, Philip W.; Taylor, Rebecca M. C.; Long, Craig S.; Ramatlo, Dineo A.
2018-04-01
Guided wave ultrasound has the potential to detect relatively large defects in continuously welded rail track at long range. As monitoring can be performed in near real time it would be acceptable to only detect fairly large cracks provided this is achieved prior to complete rail breakage. Heavy haul rail lines are inspected periodically by conventional ultrasound and sections with even relatively small cracks are removed; therefore, no sizable defects are available to demonstrate monitoring in the presence of realistic environmental operating conditions. Instead, we glued a small mass to the rail to simulate reflection from a crack and monitored the guided wave signals as the glue joint deteriorated over time. Data was collected over a two week period on an operational heavy haul line. A piezoelectric transducer mounted under the head of the rail was used in pulse-echo mode to transmit and receive a mode of propagation with energy confined mainly in the head of the rail. The small mass was attached under the head of the rail, at a distance of 375m from the transducer, using a cyanoacrylate glue, which was not expected to remain intact for long. Pre-processing of the collected signals involved rejection of signals containing train noise, averaging, filtering and dispersion compensation. Reflections from aluminothermic welds were used to stretch and scale the signals to reduce the influence of temperature variations. Singular value decomposition and independent component analysis were then applied to the signals with the aim of separating the reflection caused by the artificial defect from the background signal. The performance of these techniques was compared for different time spans. The reflection from the artificial defect showed unanticipated fluctuations.
How Reflected Wave Fronts Dynamically Establish Hooke's Law in a Spring
Fahy, Stephen; O'Riordan, John; O'Sullivan, Colm; Twomey, Patrick
2012-01-01
A simple benchtop experiment in which a moving cart collides with a fixed spring is described. Force-time and force-distance data recorded during the collision display the transit of compression wave fronts through the spring following impact. These data can be used by students to develop a computational model of the dynamics of this simple…
A low-frequency asymptotic model of seismic reflection from a high-permeability layer
Energy Technology Data Exchange (ETDEWEB)
Silin, Dmitriy; Goloshubin, Gennady
2009-03-01
Analysis of compression wave propagation through a high-permeability layer in a homogeneous poroelastic medium predicts a peak of reflection in the low-frequency end of the spectrum. An explicit formula expresses the resonant frequency through the elastic moduli of the solid skeleton, the permeability of the reservoir rock, the fluid viscosity and compressibility, and the reservoir thickness. This result is obtained through a low-frequency asymptotic analysis of the Biot's model of poroelasticity. A new physical interpretation of some coefficients of the classical poroelasticity is a result of the derivation of the main equations from the Hooke's law, momentum and mass balance equations, and the Darcy's law. The velocity of wave propagation, the attenuation factor, and the wave number, are expressed in the form of power series with respect to a small dimensionless parameter. The latter is equal to the product of the kinematic reservoir fluid mobility, an imaginary unit, and the frequency of the signal. Retaining only the leading terms of the series leads to explicit and relatively simple expressions for the reflection and transmission coefficients for a planar wave crossing an interface between two permeable media, as well as wave reflection from a thin highly-permeable layer (a lens). The practical implications of the theory developed here are seismic modeling, inversion, and attribute analysis.
Coherent reflection from surface gravity water waves during reciprocal acoustic transmissions.
Badiey, Mohsen; Song, Aijun; Smith, Kevin B
2012-10-01
During a recent experiment in Kauai, Hawaii, reciprocal transmissions were conducted between two acoustic transceivers mounted on the seafloor at a depth of 100 m. The passage of moving surface wave crests was shown to generate focused and intense coherent acoustic returns, which had increasing or decreasing delay depending on the direction of propagation relative to the direction of surface wave crests. It is shown that a rough surface two-dimensional parabolic equation model with an evolving sea surface can produce qualitative agreement with data for the dynamic surface returns.
How reflected wave fronts dynamically establish Hooke's law in a spring
International Nuclear Information System (INIS)
Fahy, Stephen; O'Riordan, John; O'Sullivan, Colm; Twomey, Patrick
2012-01-01
A simple benchtop experiment in which a moving cart collides with a fixed spring is described. Force-time and force-distance data recorded during the collision display the transit of compression wave fronts through the spring following impact. These data can be used by students to develop a computational model of the dynamics of this simple mass-spring-sensor system using a simple application of the wave equation and thereby develop an intriguing picture of how a spring realizes Hooke's law approximately in this dynamic physical problem. (paper)
A Comparison of Surface Acoustic Wave Modeling Methods
Wilson, W. c.; Atkinson, G. M.
2009-01-01
Surface Acoustic Wave (SAW) technology is low cost, rugged, lightweight, extremely low power and can be used to develop passive wireless sensors. For these reasons, NASA is investigating the use of SAW technology for Integrated Vehicle Health Monitoring (IVHM) of aerospace structures. To facilitate rapid prototyping of passive SAW sensors for aerospace applications, SAW models have been developed. This paper reports on the comparison of three methods of modeling SAWs. The three models are the Impulse Response Method a first order model, and two second order matrix methods; the conventional matrix approach, and a modified matrix approach that is extended to include internal finger reflections. The second order models are based upon matrices that were originally developed for analyzing microwave circuits using transmission line theory. Results from the models are presented with measured data from devices.
Xu, Yanlong
2015-01-21
We report high quality broadband spatial reflections of Rayleigh surface acoustic waves (SAWs) through a graded grooved surface. High quality means that no wave is allowed to transmit and the incident wave is nearly all reflected to the input side. The graded grooved surface is structured by drilling one dimensional array of graded grooves with increased depths on a flat surface. We investigate SAW dispersion relations, wave field distribution at several typical SAW wavelengths, and time evolution of a Gaussian pulse through the graded grooved surface. Results show that the input broadband Rayleigh SAWs can be slowed, spatially enhanced and stopped, and finally reflected to the input side. The study suggests that engraving the flat surface can be used as an efficient and economical way to manipulate Rayleigh SAWs, which has potential application in novel SAW devices such as filters, reflectors, sensors, energy harvesters, and diodes.
On the tunneling of full-vector X-Waves through a slab under frustrated total reflection condition
Salem, Mohamed; Bagci, Hakan
2012-01-01
Tunneling of full-vector X-Waves through a dielectric slab under frustrated total reflection condition is investigated. Full-vector X-Waves are obtained by superimposing transverse electric and magnetic polarization components, which are derived from the scalar X-Wave solution. The analysis of reflection and transmission at the dielectric interfaces is carried out analytically in a straightforward fashion using vector Bessel beam expansion. Investigation of the fields propagating away from the farther end of the slab (transmitted fields) shows an advanced (superluminal) transmission of the X-Wave peak. Additionally, a similar advanced reflection is also observed. The apparent tunneling of the peak is shown to be due to the phase shift in the fields' spectra and not to be causally related to the incident peak. © 2012 IEEE.
On the tunneling of full-vector X-Waves through a slab under frustrated total reflection condition
Salem, Mohamed
2012-07-01
Tunneling of full-vector X-Waves through a dielectric slab under frustrated total reflection condition is investigated. Full-vector X-Waves are obtained by superimposing transverse electric and magnetic polarization components, which are derived from the scalar X-Wave solution. The analysis of reflection and transmission at the dielectric interfaces is carried out analytically in a straightforward fashion using vector Bessel beam expansion. Investigation of the fields propagating away from the farther end of the slab (transmitted fields) shows an advanced (superluminal) transmission of the X-Wave peak. Additionally, a similar advanced reflection is also observed. The apparent tunneling of the peak is shown to be due to the phase shift in the fields\\' spectra and not to be causally related to the incident peak. © 2012 IEEE.
International Nuclear Information System (INIS)
Yang Hongwei; Nanjing Agricultural Univ., Nanjing; Chen Rushan; Zhang Yun
2006-01-01
The dielectric property of dispersive media is written as rational polynomial function, the relation between D and E is derived in time domain. It is named shift operator FDTD (SO-FDTD) method. The high accuracy and efficiency of this method is confirmed by computing the reflection coefficients of electromagnetic waves by a collisional plasma slab. The reflection coefficients between plasma and the atmosphere or vacuum can be calculated by using the SO-FDTD method. The result is that the reflection coefficients are affected by plasma thickness, electron numerical density, the distributing orderliness of electron density, and incidence wave frequency. (authors)
Barashkov, M. S.; Bel'Diugin, I. M.; Zolotarev, M. V.; Kruzhilin, Iu. I.; Krymskii, M. I.
1989-04-01
A four-wave mirror with thermal nonlinearity has been experimentally realized with the interaction of corunning waves under parametric feedback with a nonreciprocal element. The effective reflection of a sequence of pulses with duration of about 300 ns from a neodymium-glass laser with maximal reflection coefficients greater than 30 has been demonstrated. The quality of the radiation reflected from the mirror is studied. A significant reduction in the steady-state lasing threshold has been shown with thermal nonlinearity at small angles of the interacting beam convergence, compared to the case of counterrunning convergence.
Energy Technology Data Exchange (ETDEWEB)
Naunyka, V. N.; Shepelevich, V. V., E-mail: vasshep@inbox.ru [Mozyr State Pedagogical University (Belarus)
2011-05-15
The mutual transformation of light waves in the case of their simultaneous diffraction from a bulk reflection phase hologram, which was formed in a cubic photorefractive crystal of the 4-bar 3m symmetry class, has been studied. The indicator surfaces of the polarization-optimized values of the relative intensity of the object wave, which make it possible to determine the amplification of this wave for any crystal cut, are constructed. The linear polarization azimuths at which the energy exchange between the light waves reaches a maximum are found numerically for crystals of different cuts.
Continuous-wave cavity ringdown spectroscopy based on the control of cavity reflection.
Li, Zhixin; Ma, Weiguang; Fu, Xiaofang; Tan, Wei; Zhao, Gang; Dong, Lei; Zhang, Lei; Yin, Wangbao; Jia, Suotang
2013-07-29
A new type of continuous-wave cavity ringdown spectrometer based on the control of cavity reflection for trace gas detection was designed and evaluated. The technique separated the acquisitions of the ringdown event and the trigger signal to optical switch by detecting the cavity reflection and transmission, respectively. A detailed description of the time sequence of the measurement process was presented. In order to avoid the wrong extraction of ringdown time encountered accidentally in fitting procedure, the laser frequency and cavity length were scanned synchronously. Based on the statistical analysis of measured ringdown times, the frequency normalized minimum detectable absorption in the reflection control mode was 1.7 × 10(-9)cm(-1)Hz(-1/2), which was 5.4 times smaller than that in the transmission control mode. However the signal-to-noise ratio of the absorption spectrum was only 3 times improved since the etalon effect existed. Finally, the peak absorption coefficients of the C(2)H(2) transition near 1530.9nm under different pressures showed a good agreement with the theoretical values.
A Model for Using Reflection to Enhance Interprofessional Education
Zarezadeh, Yadolah; Pearson, Pauline; Dickinson, Clair
2009-01-01
Both Reflective Practice and Interprofessional Education (IPE) have gained a considerable attention in the past three decades. Although a plethora of literature exists on either topic, few articles address the issue of using reflective techniques to enhance IPE (King &Ross, 2003; Ross et al, 2005; Goosey & Barr, 2002; Craddock, O'Halloran, Borthwick, & McPherson, 2006) and fewer provide a model to achieve this. The aim of this article is to propose a simple model for employing reflection in t...
Repairing process models to reflect reality
Fahland, D.; Aalst, van der W.M.P.; Barros, A.; Gal, A.; Kindler, E.
2012-01-01
Process mining techniques relate observed behavior (i.e., event logs) to modeled behavior (e.g., a BPMN model or a Petri net). Processes models can be discovered from event logs and conformance checking techniques can be used to detect and diagnose differences between observed and modeled behavior.
Kim, Sangbum; Kim, Kihong
2017-12-11
We study theoretically the interplay between the surface confined wave modes and the linear and nonlinear gain of the dielectric layer in the Otto configuration. The surface confined wave modes, such as surface plasmons or waveguide modes, are excited in the dielectric-metal bilayer by obliquely incident p waves. In the purely linear case, we find that the interplay between linear gain and surface confined wave modes can generate a large reflectance peak with its value much greater than 1. As the linear gain parameter increases, the peak appears at smaller incident angles, and the associated modes also change from surface plasmons to waveguide modes. When the nonlinear gain is turned on, the reflectance shows very strong multistability near the incident angles associated with surface confined wave modes. As the nonlinear gain parameter is varied, the reflectance curve undergoes complicated topological changes and sometimes displays separated closed curves. When the nonlinear gain parameter takes an optimally small value, a giant amplification of the reflectance by three orders of magnitude occurs near the incident angle associated with a waveguide mode. We also find that there exists a range of the incident angle where the wave is dissipated rather than amplified even in the presence of gain. We suggest that this can provide the basis for a possible new technology for thermal control in the subwavelength scale.
Ethical Issues in Engineering Models : Personal Reflections
Kleijnen, Jack P.C.
2010-01-01
I start this contribution with an overview of my personal involvement—as an Operations Research consultant—in several engineering case-studies that may raise ethical questions; these case studies employ simulation models. Next, I present an overview of the recent literature on ethical issues in modeling, focusing on the validation of the model’s assumptions; the decisive role of these assumptions leads to the quest for robust models. Actually, models are meant to solve practical problems; the...
Entanglement entropy in a holographic p-wave superconductor model
Directory of Open Access Journals (Sweden)
Li-Fang Li
2015-05-01
Full Text Available In a recent paper, arXiv:1309.4877, a holographic p-wave model has been proposed in an Einstein–Maxwell-complex vector field theory with a negative cosmological constant. The model exhibits rich phase structure depending on the mass and the charge of the vector field. We investigate the behavior of the entanglement entropy of dual field theory in this model. When the above two model parameters change, we observe the second order, first order and zeroth order phase transitions from the behavior of the entanglement entropy at some intermediate temperatures. These imply that the entanglement entropy can indicate not only the occurrence of the phase transition, but also the order of the phase transition. The entanglement entropy is indeed a good probe to phase transition. Furthermore, the “retrograde condensation” which is a sub-dominated phase is also reflected on the entanglement entropy.
Entanglement entropy in a holographic p-wave superconductor model
Energy Technology Data Exchange (ETDEWEB)
Li, Li-Fang, E-mail: lilf@itp.ac.cn [State Key Laboratory of Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190 (China); Cai, Rong-Gen, E-mail: cairg@itp.ac.cn [State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190 (China); Li, Li, E-mail: liliphy@itp.ac.cn [State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190 (China); Shen, Chao, E-mail: sc@nssc.ac.cn [State Key Laboratory of Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190 (China)
2015-05-15
In a recent paper, (arXiv:1309.4877), a holographic p-wave model has been proposed in an Einstein–Maxwell-complex vector field theory with a negative cosmological constant. The model exhibits rich phase structure depending on the mass and the charge of the vector field. We investigate the behavior of the entanglement entropy of dual field theory in this model. When the above two model parameters change, we observe the second order, first order and zeroth order phase transitions from the behavior of the entanglement entropy at some intermediate temperatures. These imply that the entanglement entropy can indicate not only the occurrence of the phase transition, but also the order of the phase transition. The entanglement entropy is indeed a good probe to phase transition. Furthermore, the “retrograde condensation” which is a sub-dominated phase is also reflected on the entanglement entropy.
Astrophysical Model Selection in Gravitational Wave Astronomy
Adams, Matthew R.; Cornish, Neil J.; Littenberg, Tyson B.
2012-01-01
Theoretical studies in gravitational wave astronomy have mostly focused on the information that can be extracted from individual detections, such as the mass of a binary system and its location in space. Here we consider how the information from multiple detections can be used to constrain astrophysical population models. This seemingly simple problem is made challenging by the high dimensionality and high degree of correlation in the parameter spaces that describe the signals, and by the complexity of the astrophysical models, which can also depend on a large number of parameters, some of which might not be directly constrained by the observations. We present a method for constraining population models using a hierarchical Bayesian modeling approach which simultaneously infers the source parameters and population model and provides the joint probability distributions for both. We illustrate this approach by considering the constraints that can be placed on population models for galactic white dwarf binaries using a future space-based gravitational wave detector. We find that a mission that is able to resolve approximately 5000 of the shortest period binaries will be able to constrain the population model parameters, including the chirp mass distribution and a characteristic galaxy disk radius to within a few percent. This compares favorably to existing bounds, where electromagnetic observations of stars in the galaxy constrain disk radii to within 20%.
Jose, Sumy; Jansman, Andreas; Hueting, Raymond Josephus Engelbart
The quality factor of the traditional Solidly Mounted Resonator (SMR) is limited by substrate losses, as the traditionally employed acoustic mirror reflects longitudinal waves but not shear waves. Modern mirrors do reflect both waves, but design rules for such mirrors have not been published so far.
Detailed modeling of mountain wave PSCs
Directory of Open Access Journals (Sweden)
S. Fueglistaler
2003-01-01
Full Text Available Polar stratospheric clouds (PSCs play a key role in polar ozone depletion. In the Arctic, PSCs can occur on the mesoscale due to orographically induced gravity waves. Here we present a detailed study of a mountain wave PSC event on 25-27 January 2000 over Scandinavia. The mountain wave PSCs were intensively observed by in-situ and remote-sensing techniques during the second phase of the SOLVE/THESEO-2000 Arctic campaign. We use these excellent data of PSC observations on 3 successive days to analyze the PSCs and to perform a detailed comparison with modeled clouds. We simulated the 3-dimensional PSC structure on all 3 days with a mesoscale numerical weather prediction (NWP model and a microphysical box model (using best available nucleation rates for ice and nitric acid trihydrate particles. We show that the combined mesoscale/microphysical model is capable of reproducing the PSC measurements within the uncertainty of data interpretation with respect to spatial dimensions, temporal development and microphysical properties, without manipulating temperatures or using other tuning parameters. In contrast, microphysical modeling based upon coarser scale global NWP data, e.g. current ECMWF analysis data, cannot reproduce observations, in particular the occurrence of ice and nitric acid trihydrate clouds. Combined mesoscale/microphysical modeling may be used for detailed a posteriori PSC analysis and for future Arctic campaign flight and mission planning. The fact that remote sensing alone cannot further constrain model results due to uncertainities in the interpretation of measurements, underlines the need for synchronous in-situ PSC observations in campaigns.
Modeling and Simulation of a Wave Energy Converter INWAVE
Directory of Open Access Journals (Sweden)
Seung Kwan Song
2017-01-01
Full Text Available INGINE Inc. developed its own wave energy converter (WEC named INWAVE and has currently installed three prototype modules in Jeju Island, Korea. This device is an on-shore-type WEC that consists of a buoy, pulleys fixed to the sea-floor and a power take off module (PTO. Three ropes are moored tightly on the bottom of the buoy and connected to the PTO via the pulleys, which are moving back and forth according to the motion of the buoy. Since the device can harness wave energy from all six degrees of movement of the buoy, it is possible to extract energy efficiently even under low energy density conditions provided in the coastal areas. In the PTO module, the ratchet gears convert the reciprocating movement of the rope drum into a uni-directional rotation and determine the transmission of power from the relation of the angular velocities between the rope drum and the generator. In this process, the discontinuity of the power transmission occurs and causes the modeling divergence. Therefore, we introduce the concept of the virtual torsion spring in order to prevent the impact error in the ratchet gear module, thereby completing the PTO modeling. In this paper, we deal with dynamic analysis in the time domain, based on Newtonian mechanics and linear wave theory. We derive the combined dynamics of the buoy and PTO modules via geometric relation between the buoy and mooring ropes, then suggest the ratchet gear mechanism with the virtual torsion spring element to reduce the dynamic errors during the phase transitions. Time domain simulation is carried out under irregular waves that reflect the actual wave states of the installation area, and we evaluate the theoretical performance using the capture width ratio.
Directory of Open Access Journals (Sweden)
M. E. Gorbunov
2018-03-01
Full Text Available Linear and non-linear representations of wave fields constitute the basis of modern algorithms for analysis of radio occultation (RO data. Linear representations are implemented by Fourier Integral Operators, which allow for high-resolution retrieval of bending angles. Non-linear representations include Wigner Distribution Function (WDF, which equals the pseudo-density of energy in the ray space. Representations allow for filtering wave fields by suppressing some areas of the ray space and mapping the field back from the transformed space to the initial one. We apply this technique to the retrieval of reflected rays from RO observations. The use of reflected rays may increase the accuracy of the retrieval of the atmospheric refractivity. Reflected rays can be identified by the visual inspection of WDF or spectrogram plots. Numerous examples from COSMIC data indicate that reflections are mostly observed over oceans or snow, in particular over Antarctica. We introduce the reflection index that characterizes the relative intensity of the reflected ray with respect to the direct ray. The index allows for the automatic identification of events with reflections. We use the radio holographic estimate of the errors of the retrieved bending angle profiles of reflected rays. A comparison of indices evaluated for a large base of events including the visual identification of reflections indicated a good agreement with our definition of reflection index.
Gorbunov, Michael E.; Cardellach, Estel; Lauritsen, Kent B.
2018-03-01
Linear and non-linear representations of wave fields constitute the basis of modern algorithms for analysis of radio occultation (RO) data. Linear representations are implemented by Fourier Integral Operators, which allow for high-resolution retrieval of bending angles. Non-linear representations include Wigner Distribution Function (WDF), which equals the pseudo-density of energy in the ray space. Representations allow for filtering wave fields by suppressing some areas of the ray space and mapping the field back from the transformed space to the initial one. We apply this technique to the retrieval of reflected rays from RO observations. The use of reflected rays may increase the accuracy of the retrieval of the atmospheric refractivity. Reflected rays can be identified by the visual inspection of WDF or spectrogram plots. Numerous examples from COSMIC data indicate that reflections are mostly observed over oceans or snow, in particular over Antarctica. We introduce the reflection index that characterizes the relative intensity of the reflected ray with respect to the direct ray. The index allows for the automatic identification of events with reflections. We use the radio holographic estimate of the errors of the retrieved bending angle profiles of reflected rays. A comparison of indices evaluated for a large base of events including the visual identification of reflections indicated a good agreement with our definition of reflection index.
A generalized multivariate regression model for modelling ocean wave heights
Wang, X. L.; Feng, Y.; Swail, V. R.
2012-04-01
In this study, a generalized multivariate linear regression model is developed to represent the relationship between 6-hourly ocean significant wave heights (Hs) and the corresponding 6-hourly mean sea level pressure (MSLP) fields. The model is calibrated using the ERA-Interim reanalysis of Hs and MSLP fields for 1981-2000, and is validated using the ERA-Interim reanalysis for 2001-2010 and ERA40 reanalysis of Hs and MSLP for 1958-2001. The performance of the fitted model is evaluated in terms of Pierce skill score, frequency bias index, and correlation skill score. Being not normally distributed, wave heights are subjected to a data adaptive Box-Cox transformation before being used in the model fitting. Also, since 6-hourly data are being modelled, lag-1 autocorrelation must be and is accounted for. The models with and without Box-Cox transformation, and with and without accounting for autocorrelation, are inter-compared in terms of their prediction skills. The fitted MSLP-Hs relationship is then used to reconstruct historical wave height climate from the 6-hourly MSLP fields taken from the Twentieth Century Reanalysis (20CR, Compo et al. 2011), and to project possible future wave height climates using CMIP5 model simulations of MSLP fields. The reconstructed and projected wave heights, both seasonal means and maxima, are subject to a trend analysis that allows for non-linear (polynomial) trends.
Do arterial stiffness and wave reflection underlie cardiovascular risk in ethnic minorities?
Faconti, Luca; Nanino, Elisa; Mills, Charlotte E; Cruickshank, Kennedy J
2016-01-01
Increasing evidence indicates that remarkable differences in cardiovascular risk between ethnic groups cannot be fully explained by traditional risk factors such as hypertension, diabetes or dislipidemia measured in midlife. Therefore, the underlying pathophysiology leading to this "excess risk" in ethnic minority groups is still poorly understood, and one way to address this issue is to shift the focus from "risk" to examine target organs, particularly blood vessels and their arterial properties more directly. In fact, structural and functional changes of the vascular system may be identifiable at very early stages of life when traditional factors are not yet developed. Arterial stiffening, measured as aortic pulse wave velocity, and wave reflection parameters, especially augmentation index, seem to be an important pathophysiological mechanism for the development of cardiovascular disease and predict mortality independent of other risk factors. However, data regarding these arterial indices in ethnic minorities are relatively rare and the heterogeneity between populations, techniques and statistical methods make it difficult to fully understand their role.
Energy Technology Data Exchange (ETDEWEB)
Kano, N; Yamaguchi, K; Yokota, T; Kiguchi, T [Geological Survey of Japan, Tsukuba (Japan)
1996-10-01
Anisotropy has been investigated using S-wave as a technique for detecting fractures. In this study, fundamental experiments were carried out with slightly changing the measuring conditions at a place where anisotropy was expected. This paper describes the fundamental data acquisition of anisotropy analysis using S-wave, and a part of the results. The experiments were conducted on the agricultural road in Yamadera district, Matsuyama-machi, Yamagata Prefecture. Two flat unpaved roads meeting at right angles were used as traverse lines. In this place, several reflection surfaces were certainly detected by P-wave, and anisotropy of S-wave was confirmed from the velocity of refracted wave of S-wave. Data were processed for individual traverse lines meeting at right angles. Firstly, signal sweeping, correlation, and vertical superposition were made. Six kinds of data were prepared, i.e., three-component receiving records of data at 0{degree} of generating direction and three-component receiving records of data at 90{degree} of generating direction. Records of T-component at 0{degree} and R-component at 90{degree} were used for processing of the seismic reflection method. These records would be considered to be data of SH-wave and SV-wave, respectively. 4 figs.
A wave model test bed study for wave energy resource characterization
Energy Technology Data Exchange (ETDEWEB)
Yang, Zhaoqing; Neary, Vincent S.; Wang, Taiping; Gunawan, Budi; Dallman, Annie R.; Wu, Wei-Cheng
2017-12-01
This paper presents a test bed study conducted to evaluate best practices in wave modeling to characterize energy resources. The model test bed off the central Oregon Coast was selected because of the high wave energy and available measured data at the site. Two third-generation spectral wave models, SWAN and WWIII, were evaluated. A four-level nested-grid approach—from global to test bed scale—was employed. Model skills were assessed using a set of model performance metrics based on comparing six simulated wave resource parameters to observations from a wave buoy inside the test bed. Both WWIII and SWAN performed well at the test bed site and exhibited similar modeling skills. The ST4 package with WWIII, which represents better physics for wave growth and dissipation, out-performed ST2 physics and improved wave power density and significant wave height predictions. However, ST4 physics tended to overpredict the wave energy period. The newly developed ST6 physics did not improve the overall model skill for predicting the six wave resource parameters. Sensitivity analysis using different wave frequencies and direction resolutions indicated the model results were not sensitive to spectral resolutions at the test bed site, likely due to the absence of complex bathymetric and geometric features.
Inflationary gravitational waves in collapse scheme models
Energy Technology Data Exchange (ETDEWEB)
Mariani, Mauro, E-mail: mariani@carina.fcaglp.unlp.edu.ar [Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque S/N, 1900 La Plata (Argentina); Bengochea, Gabriel R., E-mail: gabriel@iafe.uba.ar [Instituto de Astronomía y Física del Espacio (IAFE), UBA-CONICET, CC 67, Suc. 28, 1428 Buenos Aires (Argentina); León, Gabriel, E-mail: gleon@df.uba.ar [Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria – Pab. I, 1428 Buenos Aires (Argentina)
2016-01-10
The inflationary paradigm is an important cornerstone of the concordance cosmological model. However, standard inflation cannot fully address the transition from an early homogeneous and isotropic stage, to another one lacking such symmetries corresponding to our present universe. In previous works, a self-induced collapse of the wave function has been suggested as the missing ingredient of inflation. Most of the analysis regarding the collapse hypothesis has been solely focused on the characteristics of the spectrum associated to scalar perturbations, and within a semiclassical gravity framework. In this Letter, working in terms of a joint metric-matter quantization for inflation, we calculate, for the first time, the tensor power spectrum and the tensor-to-scalar ratio corresponding to the amplitude of primordial gravitational waves resulting from considering a generic self-induced collapse.
International Nuclear Information System (INIS)
Zaytsev, S.G.; Lazareva, E.V.; Mikhailova, A.V.; Nikolaev-Kozlov, V.L.; Chebotareva, E.I.
1979-01-01
Propagation of intensive shock waves with a temperature of about 1 eV has been studied in a two-dimensional reflection nozzle mounted at the exit of a shock tube. The Toepler technique has been involved along with the interference scheme with a laser light source allowing the multiple-frame recording to be done. Density distribution in the nozzle as well as the wave pattern occurring at the shock propagation are presented. (author)
A test-bed modeling study for wave resource assessment
Yang, Z.; Neary, V. S.; Wang, T.; Gunawan, B.; Dallman, A.
2016-02-01
Hindcasts from phase-averaged wave models are commonly used to estimate standard statistics used in wave energy resource assessments. However, the research community and wave energy converter industry is lacking a well-documented and consistent modeling approach for conducting these resource assessments at different phases of WEC project development, and at different spatial scales, e.g., from small-scale pilot study to large-scale commercial deployment. Therefore, it is necessary to evaluate current wave model codes, as well as limitations and knowledge gaps for predicting sea states, in order to establish best wave modeling practices, and to identify future research needs to improve wave prediction for resource assessment. This paper presents the first phase of an on-going modeling study to address these concerns. The modeling study is being conducted at a test-bed site off the Central Oregon Coast using two of the most widely-used third-generation wave models - WaveWatchIII and SWAN. A nested-grid modeling approach, with domain dimension ranging from global to regional scales, was used to provide wave spectral boundary condition to a local scale model domain, which has a spatial dimension around 60km by 60km and a grid resolution of 250m - 300m. Model results simulated by WaveWatchIII and SWAN in a structured-grid framework are compared to NOAA wave buoy data for the six wave parameters, including omnidirectional wave power, significant wave height, energy period, spectral width, direction of maximum directionally resolved wave power, and directionality coefficient. Model performance and computational efficiency are evaluated, and the best practices for wave resource assessments are discussed, based on a set of standard error statistics and model run times.
Energy Technology Data Exchange (ETDEWEB)
Wang, Hongjuan; Liu, Siqing; Gong, Jiancun [Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190 (China); Wu, Ning [School of Tourism and Geography, Yunnan Normal University, Kunming, Yunnan 650031 (China); Lin, Jun [Yunnan Observatories, Chinese Academy of Sciences, Kunming, Yunnan 650011 (China)
2015-06-01
We numerically study the detailed evolutionary features of the wave-like disturbance and its propagation in the eruption. This work is a follow-up to Wang et al., using significantly upgraded new simulations. We focus on the contribution of the velocity vortices and the fast shock reflection and refraction in the solar corona to the formation of the EUV waves. Following the loss of equilibrium in the coronal magnetic structure, the flux rope exhibits rapid motions and invokes the fast-mode shock at the front of the rope, which then produces a type II radio burst. The expansion of the fast shock, which is associated with outward motion, takes place in various directions, and the downward expansion shows the reflection and the refraction as a result of the non-uniform background plasma. The reflected component of the fast shock propagates upward and the refracted component propagates downward. As the refracted component reaches the boundary surface, a weak echo is excited. The Moreton wave is invoked as the fast shock touches the bottom boundary, so the Moreton wave lags the type II burst. A secondary echo occurs in the area where reflection of the fast shock encounters the slow-mode shock, and the nearby magnetic field lines are further distorted because of the interaction between the secondary echo and the velocity vortices. Our results indicate that the EUV wave may arise from various processes that are revealed in the new simulations.
International Nuclear Information System (INIS)
Tang Deli; Sun Aiping; Qiu Xiaoming
2002-01-01
The absorption, reflection, and transmission of radar waves by a uniform and magnetized plasma slab are studied. The effect of various plasma parameters and different values of magnetic field intensity on the absorbed, reflected and transmitted power are discussed. The calculated results show that the effects of magnetic field on the absorbed power as well as the frequency band of resonant absorption are very significant. More than 90% of radar wave power can be absorbed and the resonant absorption band is about 2G Hz
Applicability of WaveWatch-III wave model to fatigue assessment of offshore floating structures
Zou, T.; Kaminski, M.L.
2016-01-01
In design and operation of floating offshore structures, one has to avoid fatigue failures caused by action of ocean waves. The aim of this paper is to investigate the applicability of WaveWatch-III wave model to fatigue assessment of offshore floating structures. The applicability was investigated
Ethical Issues in Engineering Models : Personal Reflections
Kleijnen, Jack P.C.
2010-01-01
I start this contribution with an overview of my personal involvement—as an Operations Research consultant—in several engineering case-studies that may raise ethical questions; these case studies employ simulation models. Next, I present an overview of the recent literature on ethical issues in
Nath, Debashis; Chen, Wen; Zelin, Cai; Pogoreltsev, Alexander Ivanovich; Wei, Ke
2016-04-07
In the present study, we investigate the impact of stratospheric planetary wave reflection on tropospheric weather over Central Eurasia during the 2013 Sudden Stratospheric Warming (SSW) event. We analyze EP fluxes and Plumb wave activity fluxes to study the two and three dimensional aspects of wave propagation, respectively. The 2013 SSW event is excited by the combined influence of wavenumber 1 (WN1) and wavenumber 2 (WN2) planetary waves, which makes the event an unusual one and seems to have significant impact on tropospheric weather regime. We observe an extraordinary development of a ridge over the Siberian Tundra and the North Pacific during first development stage (last week of December 2012) and later from the North Atlantic in the second development stage (first week of January 2013), and these waves appear to be responsible for the excitation of the WN2 pattern during the SSW. The wave packets propagated upward and were then reflected back down to central Eurasia due to strong negative wind shear in the upper stratospheric polar jet, caused by the SSW event. Waves that propagated downward led to the formation of a deep trough over Eurasia and brought extreme cold weather over Kazakhstan, the Southern part of Russia and the Northwestern part of China during mid-January 2013.
International Nuclear Information System (INIS)
Lashmore-Davies, C.N.; Fuchs, V.; Dendy, R.O.
1993-01-01
A full-wave equation has been obtained from the gyrokinetic theory for the fast wave traversing a minority cyclotron resonance [Phys. Fluids B 4, 493 (1992)] with the aid of the fast wave approximation [Phys. Fluids 31, 1614 (1988)]. This theory describes the transmission, reflection, and absorption of the fast wave for arbitrary values of the parallel wave number. For oblique propagation the absorption is due to both ion cyclotron damping by minority ions and mode conversion to the ion Bernstein wave. The results for a 3 He minority in a D plasma indicate that for perpendicular propagation and minority temperatures of a few keV the power lost by the fast wave is all mode converted whereas for minority temperatures ∼100 keV∼30% of the incident power is dissipated by the minority ions due to the gyrokinetic correction. The gyrokinetic correction also results in a significant reduction in the reflection coefficient for low field side incidence when k zLB approx-lt 1 and the minority and hybrid resonances overlap
Waves, currents and sediment transport modelling at the Wave Hub site
Gonzalez-Santamaria, Raul
2013-01-01
Primary supervisory team: Qingping Zou and Shunqi Pan This research project uses an integrated modelling system to investigate the effects of a wave farm on nearshore sediment transport at the Wave Hub site. The Wave Hub project is a large scale demonstration site for the development of the operation of arrays of wave energy generation devices located at the southwest coast of the UK where multiple field measurements took place. Particular attention of this study was paid to th...
Horizontal circulation and jumps in Hamiltonian wave models
Gagarina, Elena; van der Vegt, Jacobus J.W.; Bokhove, Onno
2013-01-01
We are interested in the numerical modeling of wave-current interactions around surf zones at beaches. Any model that aims to predict the onset of wave breaking at the breaker line needs to capture both the nonlinearity of the wave and its dispersion. We have therefore formulated the Hamiltonian
Energy Technology Data Exchange (ETDEWEB)
Tang, Jau
1996-02-01
As an alternative to better physical explanations of the mechanisms of quantum interference and the origins of uncertainty broadening, a linear hopping model is proposed with ``color-varying`` dynamics to reflect fast exchange between time-reversed states. Intricate relations between this model, particle-wave dualism, and relativity are discussed. The wave function is shown to possess dual characteristics of a stable, localized ``soliton-like`` de Broglie wavelet and a delocalized, interfering Schroedinger carrier wave function.
Wilken, Dennis; Wölz, Susanne; Müller, Christof; Rabbel, Wolfgang
2009-05-01
As part of the FINOSEIS project we present the development of new seismic acquisition and inversion concepts for offshore-building foundation soil analysis. FINOSEIS is a subproject of the FINO3 project, which is aimed at the construction of an offshore research platform based in 28 m water depth, hosting eight research projects dealing with offshore wind energy topics. Our investigations focus on the determination of seismic parameters and structural information of the building plot of FINO3. We infer the shear-wave velocity structure by exploiting the dispersive properties of Scholte-waves and use high resolution 2.5D reflection seismic acquisition to determine seismic stratigraphy in three dimensions. Our work is motivated regarding possible hazards to offshore foundations such as wind parks and the FINO3 platform itself, e.g. permanent mechanical load by wind- and wave-forces possibly leading to an impairment of the soil. We conducted a pre-investigation of the site of the future platform in order to help finding a suitable foundation soil by improving common site investigation methods. In May 2006 we did a survey covering an area of 2 km square employing high resolution 2.5D reflection seismic. Along three 2 km airgun profiles Scholte-waves were recorded with Ocean-Bottom-Seismometers. Spectral analysis of these led to pseudo-2D shear-wave velocity models along the profiles. The reflection seismic area is characterized by glacial stratigraphy and diffractions documented within the penetration range of 30 m. With respect to the topography of the identified horizons as well as to the distribution of diffracting objects, a suitable foundation area for the platform was suggested. The results of the Scholte-wave experiment provide valuable information for further inversion models as well as for the dimensioning of further measurements. We also implemented an inversion strategy using the particle swarm optimization method. The inverted layers of shear-wave velocity
Mayr, Hans G.; Mengel, J. G.; Chan, K. L.; Huang, F. T.
2010-01-01
As Lindzen (1981) had shown, small-scale gravity waves (GW) produce the observed reversals of the zonal-mean circulation and temperature variations in the upper mesosphere. The waves also play a major role in modulating and amplifying the diurnal tides (DT) (e.g., Waltersheid, 1981; Fritts and Vincent, 1987; Fritts, 1995a). We summarize here the modeling studies with the mechanistic numerical spectral model (NSM) with Doppler spread parameterization for GW (Hines, 1997a, b), which describes in the middle atmosphere: (a) migrating and non-migrating DT, (b) planetary waves (PW), and (c) global-scale inertio gravity waves. Numerical experiments are discussed that illuminate the influence of GW filtering and nonlinear interactions between DT, PW, and zonal mean variations. Keywords: Theoretical modeling, Middle atmosphere dynamics, Gravity wave interactions, Migrating and non-migrating tides, Planetary waves, Global-scale inertio gravity waves.
Singh, Pooja; Chattopadhyay, Amares; Srivastava, Akanksha; Singh, Abhishek Kumar
2018-05-01
With a motivation to gain physical insight of reflection as well as transmission phenomena in frozen (river/ocean) situation for example in Antarctica and other coldest place on Earth, the present article undertakes the analysis of reflection and transmission of a plane wave at the interfaces of layered structured comprised of a water layer of finite thickness sandwiched between an upper half-space constituted of ice and a lower isotropic elastic half-space, which may be useful in geophysical exploration in such conditions. A closed form expression of reflection/transmission coefficients of reflected and transmitted waves has been derived in terms of angles of incidence, propagation vector, displacement vector and elastic constants of the media. Expressions corresponding to the energy partition of various reflected and transmitted waves have also been established analytically. It has been remarkably shown that the law of conservation of energy holds good in the entire reflection and transmission phenomena for different angles of incidence. A numerical examples were performed so to graphically portray the analytical findings. Further the deduced results are validated with the pre-established classical results.
Wave Modelling - The State of the Art
2007-09-27
8217) - -16 C-Ax( M) (I - 2y) -N +1CgAx’(1 -y)(6y’ - 6y + 1) + O(At4), (8.2) 24OX where p is the Courant- Friedrichs -Lewy (CFL) number, j = CgxAt/Ax. Thus...attainable time step is at the best of the order of min- utes . For early third generation wave models, this was unacceptable, and methods were developed to be... Barbara Channel. In: Beal, R. (Ed.), 5th California Islands Symposium, March 29-31. Mineral Management Service, Santa Barbara , CA. Onorato, M., Osborne
Nishino, Ko; Lombardi, Stephen
2011-01-01
We introduce a novel parametric bidirectional reflectance distribution function (BRDF) model that can accurately encode a wide variety of real-world isotropic BRDFs with a small number of parameters. The key observation we make is that a BRDF may be viewed as a statistical distribution on a unit hemisphere. We derive a novel directional statistics distribution, which we refer to as the hemispherical exponential power distribution, and model real-world isotropic BRDFs as mixtures of it. We derive a canonical probabilistic method for estimating the parameters, including the number of components, of this novel directional statistics BRDF model. We show that the model captures the full spectrum of real-world isotropic BRDFs with high accuracy, but a small footprint. We also demonstrate the advantages of the novel BRDF model by showing its use for reflection component separation and for exploring the space of isotropic BRDFs.
Widlowski, J.L.; Taberner, M.; Pinty, B.; Bruniquel-Pinel, V.; Disney, M.I.; Fernandes, R.; Gastellu-Etchegorry, J.P.; Gobron, N.; Kuusk, A.; Lavergne, T.; LeBlanc, S.; Lewis, P.E.; Martin, E.; Mõttus, M.; North, P.R.J.; Qin, W.; Robustelli, M.; Rochdi, N.; Ruiloba, R.; Thompson, R.; Verhoef, W.; Verstraete, M.M.; Xie, D.
2007-01-01
[1] The Radiation Transfer Model Intercomparison ( RAMI) initiative benchmarks canopy reflectance models under well-controlled experimental conditions. Launched for the first time in 1999, this triennial community exercise encourages the systematic evaluation of canopy reflectance models on a
Widlowski, J.-L.; Taberner, M.; Pinty, B.; Bruniquel-Pinel, V.; Disney, M.; Fernandes, R.; Gastellu-Etchegorry, J.P.; Gobron, N.; Kuusk, A.; Lavergne, T.; Leblanc, S.; Lewis, P.E.; Martin, E.; Mottus, M.; North, P.R.J.; Qin, W.; Robustelli, M.; Rochdi, N.; Ruiloba, R.; Soler, C.; Thompson, R.; Verhoef, W.; Xie, D.; Thompson, R.
2007-01-01
The Radiation Transfer Model Intercomparison (RAMI) initiative benchmarks canopy reflectance models under well‐controlled experimental conditions. Launched for the first time in 1999, this triennial community exercise encourages the systematic evaluation of canopy reflectance models on a voluntary
Reflection and Transmission of Plane Electromagnetic Waves by a Geologic Layer.
Energy Technology Data Exchange (ETDEWEB)
Aldridge, David F. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2017-04-01
Electric field and magnetic field reflection and transmission responses generated by a plane wave normally incident onto a finite - thickness geologic layer are mathematically derived and numerically evaluated. A thin layer with enhanced electric current conductivity and/or magnetic permeability is a reasonable geophysical representation of a hydraulic fracture inject ed with a high - contrast proppant pack. Both theory and numerics indicate that backward - and forward - scattered electromagnetic wavefields are potentially observable in a field experiment, despite the extreme thinness of a fracture compared to a typical low - frequency electromagnetic wavelength. The First Born Approximation (FBA) representation of layer scattering, significant for inversion studies, is shown to be accurate for a thin layer with mild medium parameter (i.e., conductivity, permeability, and per mittivity) contrasts with the surrounding homogeneous wholespace. However, FBA scattering theory breaks down for thick layers and strong parameter contrasts. ACKNOWLEDGEMENTS Sandia National Laboratories is a multi - mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the US Department of Energy's National Nuclear Security Administration under contract DE - AC04 - 94AL85000. This research is conducted under the auspices of CRADA (Cooperative Research and Development Agreement) SC11/01780.00 between Carbo Ceramics Inc. and Sandia National Laboratories. The author acknowledges former Carbo R&D Vic e - President Mr. Chad Cannan and former SNL Geophysics Department manage r Ms. Amy Halloran for their interest i n and support of this work. Technical discussions with Project Manager and Principal Investigator Dr. Chester J. Weiss of the SNL Geophysics Department greatly benefited this work. Dr. Lewis C. Bartel, formerly with S NL and presently a consultant to Carbo Ceramics, provided many useful and intuitive insights, and
Experimental Modeling of the Overtopping Flow on the Wave Dragon Wave Energy Converter
DEFF Research Database (Denmark)
Parmeggiani, Stefano; Kofoed, Jens Peter; Friis-Madsen, Erik
2011-01-01
The Wave Dragon Wave Energy Converter is currently facing a precommercial phase. At this stage of development a reliable overtopping model is highly required, in order to predict the performance of the device at possible deployment locations. A model formulation derived for an overtopping device...... with general geometry has been used so far. The paper presents an updated formulation drawn through the tank testing of a scaled model the Wave Dragon. The sensitivity analysis of the main features influencing the overtopping flow led to an updated model formulation which can be specifically suited...... for the Wave Dragon....
Rogue waves in a water tank: Experiments and modeling
Lechuga, Antonio
2013-04-01
Recently many rogue waves have been reported as the main cause of ship incidents on the sea. One of the main characteristics of rogue waves is its elusiveness: they present unexpectedly and disappear in the same wave. Some authors (Zakharov and al.2010) are attempting to find the probability of their appearances apart from studyingthe mechanism of the formation. As an effort on this topic we tried the generation of rogue waves in a water wave tank using a symmetric spectrum(Akhmediev et al. 2011) as input on the wave maker. The produced waves were clearly rogue waves with a rate (maximum wave height/ Significant wave height) of 2.33 and a kurtosis of 4.77 (Janssen 2003, Onorato 2006). These results were already presented (Lechuga 2012). Similar waves (in pattern aspect, but without being extreme waves) were described as crossing waves in a water tank(Shemer and Lichter1988). To go on further the next step has been to apply a theoretical model to the envelope of these waves. After some considerations the best model has been an analogue of the Ginzburg-Landau equation. This apparently amazing result is easily explained: We know that the Ginzburg-Landau model is related to some regular structures on the surface of a liquid and also in plasmas, electric and magnetic fields and other media. Another important characteristic of the model is that their solutions are invariants with respectto the translation group. The main aim of this presentation is to extract conclusions of the model and the comparison with the measured waves in the water tank.The nonlinear structure of waves and their regularity make suitable the use of the Ginzburg-Landau model to the envelope of generated waves in the tank,so giving us a powerful tool to cope with the results of our experiment.
Shear-wave seismic reflection imaging and impedance inversion for a near-surface point-bar
Benton, N. W.; Morrison, M.; Lorenzo, J. M.; Odom, B.; Clift, P. D.; Olson, E.; Gostic, A.
2017-12-01
Imaging and inversion of SH-waves are useful to detect, map, and quantitatively characterize near-surface point-bar strata. We conduct a horizontally-polarized (SH) reflection survey across and along a near-surface (9 - 40 m) downstream point-bar. We invert for shear-impedance profiles and correlate our interpretation to electrical conductivity (EC) logs in adjacent wells to study the internal architecture and lithology of point-bars. We acquire two common-midpoint (CMP) SH-wave seismic reflection lines at False River (Point Coupee Parish, Louisiana). A 104 m long seismic line (L1) is oriented orthogonal (NW - SE) to point-bar strike. A second line (L2) is 48 m long and set parallel to point-bar strike (NE - SW). Two EC wells lie 33 m apart. Both wells are parallel with respect to the L1 survey and offset from it by 15 m. EC log measurements range from 1 - 25 m depth. Interference of Love-waves prevents seismic imaging at depths less than 9 m. The L1 and L2 data sets are inverted for shear-impedance using a model-based band-limited impedance (BLIMP) algorithm that incorporates a low-frequency velocity model. This model is also used for the depthing processing. The L1 cross-section shows coherent dipping reflection events ( 4 - 7º) from 0.15 - 0.35 s (10 - 40 m). The corresponding shear-impedance profile also reveals coherent and dipping impedance contrasts that grow in magnitude with increasing depth. The L2 cross-section shows comparatively less dip ( 1º) as well as sharper and shallower continuity of reflection events (0.1 - 0.28 s TWT or 9 - 25 m). Depth-converted (TVD) seismic amplitudes and impedance values correlate to near-surface point-bar geology via superposition of log data. The first well (W5) shows distinct EC local maxima (+50 - 70 mS/m) at 14.5 and 15.5 m depth that correlate well with the seismic amplitudes and impedance values from both L1 and L2 data sets. The second well (W7) shows comparatively lower local maxima (+40 - 60 mS/m) but at greater
International Nuclear Information System (INIS)
Cho, G.S.; Cho, B.H.
1981-01-01
As to the backscatter instability which is one of nonlinear three-wave resonant interactions, the reflectivity(r) in the case of homogeneous-slab medium is calculated, assuming all the three wavepackets negligible damping caused by medium. The expression has turned out such that r = tanh 2 KAsub(p)L, where K, Asub(p), and L are the constant coupling coefficient, the constant pump-wave amplitude, and the thickness of the medium engaged in the interaction each. When this result is interpreted in terms of the stimulated Brillouin back-scattering in a so-called underdense plasma in controlled fusion, we find the reflectivity twice as large as that by others in the limit of large pump-wave damping, and unfitting to former experiments in the independence on the incident laser-light intensity. We see the incompatibility rise chiefly from neglecting the damping of pump-wave in the plasma. In contrast to the former results by others in the limit of large pump-wave damping, our result might be regarded as that for cases of negligible pump-wave damping, in general stimulated back-scattering phenomena. (author)
Forecasting ocean wave energy: A Comparison of the ECMWF wave model with time series methods
DEFF Research Database (Denmark)
Reikard, Gordon; Pinson, Pierre; Bidlot, Jean
2011-01-01
Recently, the technology has been developed to make wave farms commercially viable. Since electricity is perishable, utilities will be interested in forecasting ocean wave energy. The horizons involved in short-term management of power grids range from as little as a few hours to as long as several...... days. In selecting a method, the forecaster has a choice between physics-based models and statistical techniques. A further idea is to combine both types of models. This paper analyzes the forecasting properties of a well-known physics-based model, the European Center for Medium-Range Weather Forecasts...... (ECMWF) Wave Model, and two statistical techniques, time-varying parameter regressions and neural networks. Thirteen data sets at locations in the Atlantic and Pacific Oceans and the Gulf of Mexico are tested. The quantities to be predicted are the significant wave height, the wave period, and the wave...
A methodology for spectral wave model evaluation
Siqueira, S. A.; Edwards, K. L.; Rogers, W. E.
2017-12-01
Model evaluation is accomplished by comparing bulk parameters (e.g., significant wave height, energy period, and mean square slope (MSS)) calculated from the model energy spectra with those calculated from buoy energy spectra. Quality control of the observed data and choice of the frequency range from which the bulk parameters are calculated are critical steps in ensuring the validity of the model-data comparison. The compared frequency range of each observation and the analogous model output must be identical, and the optimal frequency range depends in part on the reliability of the observed spectra. National Data Buoy Center 3-m discus buoy spectra are unreliable above 0.3 Hz due to a non-optimal buoy response function correction. As such, the upper end of the spectrum should not be included when comparing a model to these data. Bioufouling of Waverider buoys must be detected, as it can harm the hydrodynamic response of the buoy at high frequencies, thereby rendering the upper part of the spectrum unsuitable for comparison. An important consideration is that the intentional exclusion of high frequency energy from a validation due to data quality concerns (above) can have major implications for validation exercises, especially for parameters such as the third and fourth moments of the spectrum (related to Stokes drift and MSS, respectively); final conclusions can be strongly altered. We demonstrate this by comparing outcomes with and without the exclusion, in a case where a Waverider buoy is believed to be free of biofouling. Determination of the appropriate frequency range is not limited to the observed spectra. Model evaluation involves considering whether all relevant frequencies are included. Guidance to make this decision is based on analysis of observed spectra. Two model frequency lower limits were considered. Energy in the observed spectrum below the model lower limit was calculated for each. For locations where long swell is a component of the wave
Spin-Wave Wave Function for Quantum Spin Models : Condensed Matter and Statistical Physics
Franjo, FRANJIC; Sandro, SORELLA; Istituto Nazionale di Fisica della Materia International School for Advance Studies; Istituto Nazionale di Fisica della Materia International School for Advance Studies
1997-01-01
We present a new approach to determine an accurate variational wave function for general quantum spin models, completely defined by a consistency requirement with the simple and well-known linear spin-wave expansion. With this wave function, it is also possible to obtain the correct behavior of the long distance correlation functions for the 1D S=1/2 antiferromagnet. In 2D the proposed spin-wave wave function represents an excellent approximation to the exact ground state of the S=1.2 XY mode...
Modelling of ground penetrating radar data in stratified media using the reflectivity technique
International Nuclear Information System (INIS)
Sena, Armando R; Sen, Mrinal K; Stoffa, Paul L
2008-01-01
Horizontally layered media are often encountered in shallow exploration geophysics. Ground penetrating radar (GPR) data in these environments can be modelled by techniques that are more efficient than finite difference (FD) or finite element (FE) schemes because the lateral homogeneity of the media allows us to reduce the dependence on the horizontal spatial variables through Fourier transforms on these coordinates. We adapt and implement the invariant embedding or reflectivity technique used to model elastic waves in layered media to model GPR data. The results obtained with the reflectivity and FDTD modelling techniques are in excellent agreement and the effects of the air–soil interface on the radiation pattern are correctly taken into account by the reflectivity technique. Comparison with real wide-angle GPR data shows that the reflectivity technique can satisfactorily reproduce the real GPR data. These results and the computationally efficient characteristics of the reflectivity technique (compared to FD or FE) demonstrate its usefulness in interpretation and possible model-based inversion schemes of GPR data in stratified media
International Nuclear Information System (INIS)
Liu Shaobin; Mo Jinjun; Yuan Naichang
2003-01-01
A finite-difference time-domain (FDTD) algorithm is applied to study the electro-magnetic reflection of conduction plane covered with inhomogeneous time-varying plasma, homogeneous plasma and inhomogeneous plasma. The collisions frequency of plasma is a function of electron density and plasma temperature. The number density profile follows a parabolic function. A discussion on the effect of various plasma parameters on the reflection coefficient is presented. Under the one-dimensional case, transient electromagnetic propagation through various plasmas has been obtained, and the reflection coefficients of EM wave through various plasma are calculated under different conditions. The results illustrate that a plasma cloaking system can successfully absorb the incident EM wave
Directory of Open Access Journals (Sweden)
Joanne Embree
2001-01-01
Full Text Available Ideally, editorials are written one to two months before publication in the Journal. It was my turn to write this one. I had planned to write the first draft the evening after my clinic on Tuesday, September 11. It didn't get done that night or during the next week. Somehow, the topic that I had originally chosen just didn't seem that important anymore as I, along my friends and colleagues, reflected on the changes that the events of that day were likely to have on our lives.
Traveling waves and conservation laws for highly nonlinear wave equations modeling Hertz chains
Przedborski, Michelle; Anco, Stephen C.
2017-09-01
A highly nonlinear, fourth-order wave equation that models the continuum theory of long wavelength pulses in weakly compressed, homogeneous, discrete chains with a general power-law contact interaction is studied. For this wave equation, all solitary wave solutions and all nonlinear periodic wave solutions, along with all conservation laws, are derived. The solutions are explicitly parameterized in terms of the asymptotic value of the wave amplitude in the case of solitary waves and the peak of the wave amplitude in the case of nonlinear periodic waves. All cases in which the solution expressions can be stated in an explicit analytic form using elementary functions are worked out. In these cases, explicit expressions for the total energy and total momentum for all solutions are obtained as well. The derivation of the solutions uses the conservation laws combined with an energy analysis argument to reduce the wave equation directly to a separable first-order differential equation that determines the wave amplitude in terms of the traveling wave variable. This method can be applied more generally to other highly nonlinear wave equations.
Numerical modelling of nearshore wave transformation
Digital Repository Service at National Institute of Oceanography (India)
Chandramohan, P.; Nayak, B.U.; SanilKumar, V.
A software has been developed for numerical refraction study based on finite amplitude wave theories. Wave attenuation due to shoaling, bottom friction, bottom percolation and viscous dissipation has also been incorporated. The software...
Impact of surface waves in a Regional Climate Model
DEFF Research Database (Denmark)
Rutgersson, Anna; Sætra, Oyvind; Semedo, Alvaro
2010-01-01
A coupled regional atmosphere-wave model system is developed with the purpose of investigating the impact of climate changes on the wave field, as well as feed-back effects of the wave field on the atmospheric parameters. This study focuses on the effects of introducing a two-way atmosphere...
O'Boyle, Louise; Whittaker, Trevor; Cox, Ronadh; Elsäßer, Björn
2017-04-01
During the winter of 2013-2014 the west coast of Ireland was exposed to 6 storms over a period of 8 weeks with wind speeds equating to hurricane categories 3 and 4. During this period, the largest significant wave height recorded at the Marine Institute M6 wave buoy, approximately 300km from the site, was 13.6m (on 26th January 2014). However, this may not be the largest sea state of that winter, because the buoy stopped logging on 30th January and therefore failed to capture the full winter period. During the February 12th 2014 "Darwin" storm, the Kinsale Energy Gas Platform off Ireland's south coast measured a wave height of 25 m, which remains the highest wave measured off Ireland's coasts[1]. Following these storms, significant dislocation and transportation of boulders and megagravel was observed on the Aran Islands, Co. Galway at elevations of up to 25m above the high water mark and distances up to 220 m inland including numerous clasts with masses >50t, and at least one megagravel block weighing >500t [2]. Clast movements of this magnitude would not have been predicted from the measured wave heights. This highlights a significant gap in our understanding of the relationships between storms and the coastal environment: how are storm waves amplified and modified by interactions with bathymetry? To gain further understanding of wave amplification, especially over steep and irregular bathymetry, we have designed Froude-scaled wave tank experiments using the 3D coastal wave basin facility at Queen's University Belfast. The basin is 18m long by 16m wide with wave generation by means of a 12m wide bank of 24 top hinged, force feedback, sector carrier wave paddles at one end. The basin is equipped with gravel beaches to dissipate wave energy on the remaining three sides, capable of absorbing up to 99% of the incident wave energy, to prevent unwanted reflections. Representative bathymetry for the Aran Islands is modelled in the basin based on a high resolution
Chen, Pengzhen; Wang, Xiaoqing; Liu, Li; Chong, Jinsong
2016-06-01
According to Bragg theory, capillary waves are the predominant scatterers of high-frequency band (such as Ka-band) microwave radiation from the surface of the ocean. Therefore, understanding the modulation mechanism of capillary waves is an important foundation for interpreting high-frequency microwave remote sensing images of the surface of the sea. In our experiments, we discovered that modulations of capillary waves are significantly larger than the values predicted by the classical theory. Further, analysis shows that the difference in restoring force results in an inflection point while the phase velocity changes from gravity waves region to capillary waves region, and this results in the capillary waves being able to resonate with gravity waves when the phase velocity of the gravity waves is equal to the group velocity of the capillary waves. Consequently, we propose a coupling modulation model in which the current modulates the capillary wave indirectly by modulating the resonant gravity waves, and the modulation of the former is approximated by that of the latter. This model very effectively explains the results discovered in our experiments. Further, based on Bragg scattering theory and this coupling modulation model, we simulate the modulation of normalized radar cross section (NRCS) of typical internal waves and show that the high-frequency bands are superior to the low-frequency bands because of their greater modulation of NRCS and better radiometric resolution. This result provides new support for choice of radar band for observation of wave-current modulation oceanic phenomena such as internal waves, fronts, and shears.
Boussinesq Modeling of Wave Propagation and Runup over Fringing Coral Reefs, Model Evaluation Report
National Research Council Canada - National Science Library
Demirbilek, Zeki; Nwogu, Okey G
2007-01-01
..., for waves propagating over fringing reefs. The model evaluation had two goals: (a) investigate differences between laboratory and field characteristics of wave transformation processes over reefs, and (b...
Wave Resource Characterization Using an Unstructured Grid Modeling Approach
Directory of Open Access Journals (Sweden)
Wei-Cheng Wu
2018-03-01
Full Text Available This paper presents a modeling study conducted on the central Oregon coast for wave resource characterization, using the unstructured grid Simulating WAve Nearshore (SWAN model coupled with a nested grid WAVEWATCH III® (WWIII model. The flexibility of models with various spatial resolutions and the effects of open boundary conditions simulated by a nested grid WWIII model with different physics packages were evaluated. The model results demonstrate the advantage of the unstructured grid-modeling approach for flexible model resolution and good model skills in simulating the six wave resource parameters recommended by the International Electrotechnical Commission in comparison to the observed data in Year 2009 at National Data Buoy Center Buoy 46050. Notably, spectral analysis indicates that the ST4 physics package improves upon the ST2 physics package’s ability to predict wave power density for large waves, which is important for wave resource assessment, load calculation of devices, and risk management. In addition, bivariate distributions show that the simulated sea state of maximum occurrence with the ST4 physics package matched the observed data better than with the ST2 physics package. This study demonstrated that the unstructured grid wave modeling approach, driven by regional nested grid WWIII outputs along with the ST4 physics package, can efficiently provide accurate wave hindcasts to support wave resource characterization. Our study also suggests that wind effects need to be considered if the dimension of the model domain is greater than approximately 100 km, or O (102 km.
Reflection and trapping of Alfvén waves in the open field lines of a neutron star
Mofiz, U A
2002-01-01
We have studied Alfvén wave propagation in the polar cap region of a neutron star at isothermal atmosphere using linear MHD equations. The study demonstrates reflection and trapping of the wave from the steep gradient region of Alfvén speed. The trapping efficiency depends sensitively on a dimensionless parameter $\\beta_{g}$ which is proportional to the mass and inversely proportional to thetemperature of the plasma. A scaling of radius, Schwarzchild radius and acceleration due to gravity of neutron stars of different masses are performed. The effective temperature of hydrostatic equilibrium is also scaled. For a neutron star with mass 1.4 solar mass and radius 10 km the temperature is to be of $10^8$ degree K. The Alfvén wave propagation near the event horizon is investigated. It is found that the wave length of Alfvén wave is shorter near the horizon while it becomes longer away from it. Pulsar wind acceleration by Alfvén wave is also examined. It is found that wave pressure force is predominant for lo...
Modelling of the Overtopping Flow on the Wave Dragon Wave Energy Converter
DEFF Research Database (Denmark)
Parmeggiani, Stefano; Pecher, Arthur; Kofoed, Jens Peter
2010-01-01
The Wave Dragon is a floating slack-moored Wave Energy Converter of the overtopping type, which is facing now the last phase of development before the commercial exploitation: the deployment of a full-scale demonstrator. In this phase a modelling tool allowing for accurate predictions of the perf......The Wave Dragon is a floating slack-moored Wave Energy Converter of the overtopping type, which is facing now the last phase of development before the commercial exploitation: the deployment of a full-scale demonstrator. In this phase a modelling tool allowing for accurate predictions...
Emission of OH* and CO2* during the high-temperature oxidation of acetone in reflected shock waves
Tereza, A. M.; Smirnov, V. N.; Vlasov, P. A.; Shumova, V. V.; Garmash, A. A.
2018-01-01
Experimental and kinetic modeling study of the ignition of a stoichiometric mixture of acetone with oxygen diluted by argon was carried out behind reflected shock waves within the temperature range of 1350-1810 K for the total mixture concentration [M 50] ~ 10-5 mol/cm3. Emission signals were recorded simultaneously for three different wavelengths: OH* (λ = 308 nm) and {{{CO}}}2* (λ1 = 365 nm; λ2 = 451 nm). It was revealed that the time it takes to reach the maximum of emission of OH* and {{{CO}}}2* is practically the same over the whole temperature range. At the same time, the emission profiles of {{{CO}}}2* after the maximum was attained, recorded at λ2 = 451 nm, differ noticeably from the profiles recorded at λ1 = 365 nm. For numerical modeling of the emission profiles of OH* and {{{CO}}}2* , the corresponding sets of excitation and quenching reactions available in the literature were used. In the course of our numerical simulations we succeeded in good agreement of our own experimental and simulation results on acetone ignition and the results available in the literature for conditions under consideration.
Millen, Aletta M E; Woodiwiss, Angela J; Norton, Gavin R
2016-07-01
Decreases in brachial blood pressure (BP) may occur for several hours following a bout of exercise. Although aortic backward waves predict cardiovascular damage independent of brachial BP, whether decreases in aortic backward waves also occur post-exercise in young-to-middle-aged hypertensives, the extent to which these changes exceed brachial BP changes, and the best method of identifying these changes is uncertain. We examined aortic function at baseline and 15-min post-exercise in 20 pre-hypertensive or hypertensive men and women (age 45 ± 7 years). Central aortic pressure, forward (Pf) and backward (Pb) wave pressures, the reflection index (RI) and augmentation pressure (AP) and index (AIx) were determined using applanation tonometry, and SphygmoCor software. Decreases in central aortic (p exercise. In addition, decreases in post-exercise (baseline versus post-exercise) Pb (19 ± 4 vs 13 ± 3 mm Hg p aged pre-hypertensive and hypertensive individuals, aortic backward waves decrease post-exercise; this change is not reflected in brachial BP measurements and is poorly indexed by measures of pressure augmentation.
Personal Coaching: Reflection on a Model for Effective Learning
Griffiths, Kerryn
2015-01-01
The article "Personal Coaching: A Model for Effective Learning" (Griffiths, 2006) appeared in the "Journal of Learning Design" Volume 1, Issue 2 in 2006. Almost ten years on, Kerryn Griffiths reflects upon her original article. Specifically, Griffiths looks back at the combined coaching-learning model she suggested in her…
Algebraic Bethe ansatz for 19-vertex models with reflection conditions
International Nuclear Information System (INIS)
Utiel, Wagner
2003-01-01
In this work we solve the 19-vertex models with the use of algebraic Bethe ansatz for diagonal reflection matrices (Sklyanin K-matrices). The eigenvectors, eigenvalues and Bethe equations are given in a general form. Quantum spin chains of spin one derived from the 19-vertex models were also discussed
Improving Intercultural Competence in the Classroom: A Reflective Development Model
Feng, Jing Betty
2016-01-01
To meet the increased demand for international business education that prepares college students for studying, living, or working overseas, I propose a four-stage reflective development model to be used in the traditional classroom context to enhance intercultural competence for undergraduate students. I employ the model in a personal development…
Social Perception and Social Reality: A Reflection-Construction Model.
Jussim, Lee
1991-01-01
A reflection-construction model of relations between social perception and social reality is presented that explicitly specifies several ways in which social perception may relate to social reality. Evidence supporting this model also supports a weaker version of the social-constructivist view. (SLD)
Stochastic volatility models and Kelvin waves
Energy Technology Data Exchange (ETDEWEB)
Lipton, Alex [Merrill Lynch, Mlfc Main, 2 King Edward Street, London EC1A 1HQ (United Kingdom); Sepp, Artur [Merrill Lynch, 4 World Financial Center, New York, NY 10080 (United States)], E-mail: Alex_Lipton@ml.com, E-mail: Artur_Sepp@ml.com
2008-08-29
We use stochastic volatility models to describe the evolution of an asset price, its instantaneous volatility and its realized volatility. In particular, we concentrate on the Stein and Stein model (SSM) (1991) for the stochastic asset volatility and the Heston model (HM) (1993) for the stochastic asset variance. By construction, the volatility is not sign definite in SSM and is non-negative in HM. It is well known that both models produce closed-form expressions for the prices of vanilla option via the Lewis-Lipton formula. However, the numerical pricing of exotic options by means of the finite difference and Monte Carlo methods is much more complex for HM than for SSM. Until now, this complexity was considered to be an acceptable price to pay for ensuring that the asset volatility is non-negative. We argue that having negative stochastic volatility is a psychological rather than financial or mathematical problem, and advocate using SSM rather than HM in most applications. We extend SSM by adding volatility jumps and obtain a closed-form expression for the density of the asset price and its realized volatility. We also show that the current method of choice for solving pricing problems with stochastic volatility (via the affine ansatz for the Fourier-transformed density function) can be traced back to the Kelvin method designed in the 19th century for studying wave motion problems arising in fluid dynamics.
Stochastic volatility models and Kelvin waves
Lipton, Alex; Sepp, Artur
2008-08-01
We use stochastic volatility models to describe the evolution of an asset price, its instantaneous volatility and its realized volatility. In particular, we concentrate on the Stein and Stein model (SSM) (1991) for the stochastic asset volatility and the Heston model (HM) (1993) for the stochastic asset variance. By construction, the volatility is not sign definite in SSM and is non-negative in HM. It is well known that both models produce closed-form expressions for the prices of vanilla option via the Lewis-Lipton formula. However, the numerical pricing of exotic options by means of the finite difference and Monte Carlo methods is much more complex for HM than for SSM. Until now, this complexity was considered to be an acceptable price to pay for ensuring that the asset volatility is non-negative. We argue that having negative stochastic volatility is a psychological rather than financial or mathematical problem, and advocate using SSM rather than HM in most applications. We extend SSM by adding volatility jumps and obtain a closed-form expression for the density of the asset price and its realized volatility. We also show that the current method of choice for solving pricing problems with stochastic volatility (via the affine ansatz for the Fourier-transformed density function) can be traced back to the Kelvin method designed in the 19th century for studying wave motion problems arising in fluid dynamics.
Stochastic volatility models and Kelvin waves
International Nuclear Information System (INIS)
Lipton, Alex; Sepp, Artur
2008-01-01
We use stochastic volatility models to describe the evolution of an asset price, its instantaneous volatility and its realized volatility. In particular, we concentrate on the Stein and Stein model (SSM) (1991) for the stochastic asset volatility and the Heston model (HM) (1993) for the stochastic asset variance. By construction, the volatility is not sign definite in SSM and is non-negative in HM. It is well known that both models produce closed-form expressions for the prices of vanilla option via the Lewis-Lipton formula. However, the numerical pricing of exotic options by means of the finite difference and Monte Carlo methods is much more complex for HM than for SSM. Until now, this complexity was considered to be an acceptable price to pay for ensuring that the asset volatility is non-negative. We argue that having negative stochastic volatility is a psychological rather than financial or mathematical problem, and advocate using SSM rather than HM in most applications. We extend SSM by adding volatility jumps and obtain a closed-form expression for the density of the asset price and its realized volatility. We also show that the current method of choice for solving pricing problems with stochastic volatility (via the affine ansatz for the Fourier-transformed density function) can be traced back to the Kelvin method designed in the 19th century for studying wave motion problems arising in fluid dynamics
Directory of Open Access Journals (Sweden)
Davide Grassi
2015-02-01
Full Text Available Hypertension and arterial stiffening are independent predictors of cardiovascular mortality. Flavonoids may exert some vascular protection. We investigated the effects of black tea on blood pressure (BP and wave reflections before and after fat load in hypertensives. According to a randomized, double-blind, controlled, cross-over design, 19 patients were assigned to consume black tea (129 mg flavonoids or placebo twice a day for eight days (13 day wash-out period. Digital volume pulse and BP were measured before and 1, 2, 3 and 4 h after tea consumption. Measurements were performed in a fasted state and after a fat load. Compared to placebo, reflection index and stiffness index decreased after tea consumption (p < 0.0001. Fat challenge increased wave reflection, which was counteracted by tea consumption (p < 0.0001. Black tea decreased systolic and diastolic BP (−3.2 mmHg, p < 0.005 and −2.6 mmHg, p < 0.0001; respectively and prevented BP increase after a fat load (p < 0.0001. Black tea consumption lowers wave reflections and BP in the fasting state, and during the challenging haemodynamic conditions after a fat load in hypertensives. Considering lipemia-induced impairment of arterial function may occur frequently during the day, our findings suggest regular consumption of black tea may be relevant for cardiovascular protection.
Model Predictive Control of a Wave Energy Converter
DEFF Research Database (Denmark)
Andersen, Palle; Pedersen, Tom Søndergård; Nielsen, Kirsten Mølgaard
2015-01-01
In this paper reactive control and Model Predictive Control (MPC) for a Wave Energy Converter (WEC) are compared. The analysis is based on a WEC from Wave Star A/S designed as a point absorber. The model predictive controller uses wave models based on the dominating sea states combined with a model...... connecting undisturbed wave sequences to sequences of torque. Losses in the conversion from mechanical to electrical power are taken into account in two ways. Conventional reactive controllers are tuned for each sea state with the assumption that the converter has the same efficiency back and forth. MPC...
Rosner, R.; An, C.-H.; Musielak, Z. E.; Moore, R. L.; Suess, S. T.
1991-01-01
A simple qualitative model for the origin of the coronal and mass-loss dividing lines separating late-type giants and supergiants with and without hot, X-ray-emitting corona, and with and without significant mass loss is discussed. The basic physical effects considered are the necessity of magnetic confinement for hot coronal material on the surface of such stars and the large reflection efficiency for Alfven waves in cool exponential atmospheres. The model assumes that the magnetic field geometry of these stars changes across the observed 'dividing lines' from being mostly closed on the high effective temperature side to being mostly open on the low effective temperature side.
Energy Technology Data Exchange (ETDEWEB)
Hull, Lawrence Mark [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Miller, Phillip Isaac [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Moro, Erik Allan [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2016-11-28
In the instance of multiple fragment impact on cased explosive, isolated curved shocks are generated in the explosive. These curved shocks propagate and may interact and form irregular or Mach reflections along the interaction loci, thereby producing a single shock that may be sufficient to initiate PBX-9501. However, the incident shocks are divergent and their intensity generally decreases as they expand, and the regions behind the Mach stem interaction loci are generally unsupported and allow release waves to rapidly affect the flow. The effects of release waves and divergent shocks may be considered theoretically through a “Shock Change Equation”.
International Nuclear Information System (INIS)
Eritsyan, O. S.; Lalayan, A. A.; Arakelyan, O. M.; Papoyan, A. A.; Kostanyan, R. B.
2010-01-01
The frequency dependence of the reflection coefficient of MgF 2 crystal in the frequency range of 200-800 cm -1 at different orientations of the optical axis has been investigated. The experimental data are compared with the calculation results. This comparison confirms that the wave vectors for the extraordinary wave have an open surface. This makes it possible to focus a divergent beam refracted at a flat boundary ori- ented perpendicularly to the optical crystal axis. The focusing effect of a plane-parallel MgF 2 crystal plate is calculated.
International Nuclear Information System (INIS)
Haynie, A.; Min, T.-J.; Luan, L.; Mu, W.; Ketterson, J. B.
2009-01-01
We describe an extension of the total-internal-reflection microscopy technique that permits direct in-plane distance measurements with high accuracy (<10 nm) over a wide range of separations. This high position accuracy arises from the creation of a standing evanescent wave and the ability to sweep the nodal positions (intensity minima of the standing wave) in a controlled manner via both the incident angle and the relative phase of the incoming laser beams. Some control over the vertical resolution is available through the ability to scan the incoming angle and with it the evanescent penetration depth.
Hsu, Jeffrey J; Katz, Ronit; Chirinos, Julio A; Jacobs, David R; Duprez, Daniel A; Peralta, Carmen A
2016-05-01
Differences in arterial wave reflections have been associated with increased risk for heart failure and mortality. Whether these measures are also associated with kidney function decline is not well established. Reflection magnitude (RM, defined as the ratio of the backward wave [Pb] to that of the forward wave [Pf]), augmentation index (AIx), and pulse pressure amplification (PPA) were derived from radial tonometry measures among 5232 participants free of cardiovascular disease who were enrolled in the Multiethnic Study of Atherosclerosis. Kidney function was estimated by creatinine and cystatin C measurements, as well as albumin-to-creatinine ratio. We evaluated the associations of Pb, Pf, RM, AIx, and PPA with annualized estimated glomerular filtration rate (eGFR) change and rapid kidney function decline over 5 years, using generalized linear mixed models and logistic regression, respectively. Of the study participants, 48% were male, mean age was 62 years, mean eGFR and median albumin-to-creatinine ratio at baseline were 84 mL/min/1.73 m(2) and 5.3 mg/g, respectively. In demographically adjusted models, both Pb and Pf had similarly strong associations with kidney function decline; compared to those in the lowest tertiles, the persons in the highest tertiles of Pb and Pf had a 1.01 and 0.99 mL/min/1.73 m(2)/year faster eGFR decline, respectively (P function decline. In conclusion, the reflected and forward wave components were similarly associated with kidney function decline, and these associations were explained by differences in systolic blood pressure. Copyright © 2016 American Society of Hypertension. Published by Elsevier Inc. All rights reserved.
Tschache, Saskia; Wadas, Sonja; Polom, Ulrich; Krawczyk, Charlotte M.
2017-04-01
Sinkholes pose a serious geohazard for humans and infrastructure in populated areas. The Junior Research Group Subrosion within the Leibniz Institute for Applied Geophysics and the joint project SIMULTAN work on the multi-scale investigation of subrosion processes in the subsurface, which cause natural sinkholes. In two case studies in sinkhole areas of Thuringia in Germany, we applied 2D shear wave reflection seismics using SH-waves with the aim to detect suitable parameters for the characterisation of critical zones. This method has the potential to image near-surface collapse and faulting structures in improved resolution compared to P-wave surveys resulting from the shorter wavelength of shear waves. Additionally, the shear wave velocity field derived by NMO velocity analysis is a basis to calculate further physical parameters, as e.g. the dynamic shear modulus. In both investigation areas, vertical seismic profiles (VSP) were acquired by generating P- and SH-waves (6 component VSP) directly next to a borehole equipped with a 3C downhole sensor. They provide shear and compressional wave velocity profiles, which are used to improve the 2D shear wave velocity field from surface seismics, to perform a depth calibration of the seismic image and to calculate the Vp/Vs ratio. The signals in the VSP data are analysed with respect to changes in polarisation and attenuation with depth and/or azimuth. The VSP data reveal low shear wave velocities of 200-300 m/s in rock layers known to be heavily affected by subrosion and confirm the low velocities calculated from the surface seismic data. A discrepancy of the shear wave velocities is observed in other intervals probably due to unsymmetrical travel paths in the surface seismics. In some VSP data dominant conversion of the direct SH-wave to P-wave is observed that is assumed to be caused by an increased presence of cavities. A potential fault distorting the vertical travel paths was detected by abnormal P-wave first
Active Absorption of Irregular Gravity Waves in BEM-Models
DEFF Research Database (Denmark)
Brorsen, Michael; Frigaard, Peter
1992-01-01
The boundary element method is applied to the computation of irregular gravity waves. The boundary conditions at the open boundaries are obtained by a digital filtering technique, where the surface elevations in front of the open boundary are filtered numerically yielding the velocity to be presc...... to be prescribed at the boundary. By numerical examples it is shown that well designed filters can reduce the wave reflection to a few per cent over a frequency range corresponding to a Jonswap spectrum....
Hemispherical reflectance model for passive images in an outdoor environment.
Kim, Charles C; Thai, Bea; Yamaoka, Neil; Aboutalib, Omar
2015-05-01
We present a hemispherical reflectance model for simulating passive images in an outdoor environment where illumination is provided by natural sources such as the sun and the clouds. While the bidirectional reflectance distribution function (BRDF) accurately produces radiance from any objects after the illumination, using the BRDF in calculating radiance requires double integration. Replacing the BRDF by hemispherical reflectance under the natural sources transforms the double integration into a multiplication. This reduces both storage space and computation time. We present the formalism for the radiance of the scene using hemispherical reflectance instead of BRDF. This enables us to generate passive images in an outdoor environment taking advantage of the computational and storage efficiencies. We show some examples for illustration.
Wang, Xiao-Qi; Yi, Guang-Yu; Han, Yu; Jiang, Cui; Gong, Wei-Jiang
2018-07-01
We construct one mesoscopic circuit in which one quantum dot couples to one DIII-class topological superconductor and one s-wave superconductor, in addition to its connection with the metallic lead. And then, the Andreev reflection current in the metallic lead is evaluated. It is found that the two kinds of superconductors drive the Andreev reflection in the constructive manner. Next as finite superconducting phase difference is taken into account, the Andreev reflection oscillates in period π/2, and it can be suppressed in the low-energy region if the superconducting phase difference is (n + 1/2) π/2 (n ∈ Integer). Such a result is almost independent of the increase of the intradot Coulomb interaction. Therefore, this structure can assist to realize the manipulation of the Andreev reflection. Also, the result in this work provides useful information for understanding the property of the DIII-class topological superconductor.
A hydrodynamic model of nearshore waves and wave-induced currents
Directory of Open Access Journals (Sweden)
Ahmed Khaled Seif
2011-09-01
Full Text Available In This study develops a quasi-three dimensional numerical model of wave driven coastal currents with accounting the effects of the wave-current interaction and the surface rollers. In the wave model, the current effects on wave breaking and energy dissipation are taken into account as well as the wave diffraction effect. The surface roller associated with wave breaking was modeled based on a modification of the equations by Dally and Brown (1995 and Larson and Kraus (2002. Furthermore, the quasi-three dimensional model, which based on Navier-Stokes equations, was modified in association with the surface roller effect, and solved using frictional step method. The model was validated by data sets obtained during experiments on the Large Scale Sediment Transport Facility (LSTF basin and the Hazaki Oceanographical Research Station (HORS. Then, a model test against detached breakwater was carried out to investigate the performance of the model around coastal structures. Finally, the model was applied to Akasaki port to verify the hydrodynamics around coastal structures. Good agreements between computations and measurements were obtained with regard to the cross-shore variation in waves and currents in nearshore and surf zone.
Coupling atmospheric and ocean wave models for storm simulation
DEFF Research Database (Denmark)
Du, Jianting
the atmosphere must, by conservation, result in the generation of the surface waves and currents. The physics-based methods are sensitive to the choice of wind-input source function (Sin), parameterization of high-frequency wave spectra tail, and numerical cut-off frequencies. Unfortunately, literature survey......This thesis studies the wind-wave interactions through the coupling between the atmospheric model and ocean surface wave models. Special attention is put on storm simulations in the North Sea for wind energy applications in the coastal zones. The two aspects, namely storm conditions and coastal...... shows that in most wind-wave coupling systems, either the Sin in the wave model is different from the one used for the momentum flux estimation in the atmospheric model, or the methods are too sensitive to the parameterization of high-frequency spectra tail and numerical cut-off frequencies. To confront...
Modeling deflagration waves out of hot spots
Partom, Yehuda
2017-01-01
It is widely accepted that shock initiation and detonation of heterogeneous explosives comes about by a two-step process known as ignition and growth. In the first step a shock sweeping through an explosive cell (control volume) creates hot spots that become ignition sites. In the second step, deflagration waves (or burn waves) propagate out of those hot spots and transform the reactant in the cell into reaction products. The macroscopic (or average) reaction rate of the reactant in the cell depends on the speed of those deflagration waves and on the average distance between neighboring hot spots. Here we simulate the propagation of deflagration waves out of hot spots on the mesoscale in axial symmetry using a 2D hydrocode, to which we add heat conduction and bulk reaction. The propagation speed of the deflagration waves may depend on both pressure and temperature. It depends on pressure for quasistatic loading near ambient temperature, and on temperature at high temperatures resulting from shock loading. From the simulation we obtain deflagration fronts emanating out of the hot spots. For 8 to 13 GPa shocks, the emanating fronts propagate as deflagration waves to consume the explosive between hot spots. For higher shock levels deflagration waves may interact with the sweeping shock to become detonation waves on the mesoscale. From the simulation results we extract average deflagration wave speeds.
Experimental Update of the Overtopping Model Used for the Wave Dragon Wave Energy Converter
DEFF Research Database (Denmark)
Parmeggiani, Stefano; Kofoed, Jens Peter; Friis-Madsen, Erik
2013-01-01
An overtopping model specifically suited for Wave Dragon is needed in order to improve the reliability of its performance estimates. The model shall be comprehensive of all relevant physical processes that affect overtopping and flexible to adapt to any local conditions and device configuration....... An experimental investigation is carried out to update an existing formulation suited for 2D draft-limited, low-crested structures, in order to include the effects on the overtopping flow of the wave steepness, the 3D geometry of Wave Dragon, the wing reflectors, the device motions and the non-rigid connection...... of which can be measured in real-time. Instead of using new fitting coefficients, this approach allows a broader applicability of the model beyond the Wave Dragon case, to any overtopping WEC or structure within the range of tested conditions. Predictions reliability of overtopping over Wave Dragon...
SH-wave reflection seismic and VSP as tools for the investigation of sinkhole areas in Germany
Wadas, Sonja; Tschache, Saskia; Polom, Ulrich; Buness, Hermann; Krawczyk, Charlotte M.
2017-04-01
Sinkholes can lead to damage of buildings and infrastructure and they can cause life-threatening situations, if they occur in urban areas. The process behind this phenomenon is called subrosion. Subrosion is the underground leaching of soluble rocks, e.g. anhydrite and gypsum, due to the contact with ground- and meteoric water. Depending on the leached material, and especially the dissolution rate, different kinds of subrosion structures evolve in the subsurface. The two end members are collapse and depression structures. For a better understanding of the subrosion processes a detailed characterization of the resulting structures is necessary. In Germany sinkholes are a problem in many areas. In northern Germany salt and in central and southern Germany sulfate and carbonate deposits are affected by subrosion. The study areas described here are located in Thuringia in central Germany and the underground is characterized by soluble Permian deposits. The occurrence of 20 to 50 sinkholes is reported per year. Two regions, Bad Frankenhausen and Schmalkalden, are investigated, showing a leaning church tower and a sinkhole of 30 m diameter and 20 m depth, respectively. In Bad Frankenhausen four P-wave and 16 SH-wave reflection seismic profiles were carried out, supplemented by three zero-offset VSPs. In Schmalkalden five SH-wave reflection seismic profiles and one zero-offset VSP were acquired. The 2-D seismic sections, in particular the SH-wave profiles, showed known and unknown near-surface faults in the vicinity of sinkholes and depressions. For imaging the near-surface ( 2,5, probably indicating unstable areas due to subrosion. We conclude, that SH-wave reflection seismic offer an important tool for the imaging and characterization of near-surface subrosion structures and the identification of unstable zones, especially in combination with P-wave reflection seismic and zero-offset VSP with P- and S-waves. Presumably there is a connection between the presence of large
A Reflectance Model for Relatively Clear and Turbid Waters
Directory of Open Access Journals (Sweden)
S. P. Tiwari
2013-02-01
Full Text Available Accurate modeling of spectral remote sensing reflectance (Rrs is of great interest for ocean colour studies in highly turbid and relatively clear waters. In this work a semianalytical model that simulates the spectral curves of remote sensing reflectance of these waters is developed based on the inherent optical properties (IOPs and f and Q factors. For accommodating differences in the optical properties of the water and accounting for their directional variations, IOPs and f and Q factors are derived as a function of phytoplankton pigments, suspended sediments and solar zenith angle. Results of this model are compared with in-situ bio-optical data collected at 83 stations encompassing highly turbid/relatively cleared waters of the South Sea of Korea. Measured and modeled remote sensing reflectances agree favorably in both magnitude and spectral shape, with considerably low errors (mean relative error MRE -0.0327; root mean square error RMSE 0.205, bias -0.0727 and slope 1.15 and correlation coefficient R2 0.74. These results suggest that the new model has the ability to reproduce measured reflectance values and has potentially profound implications for remote sensing of complex waters in this region.
Improving wave forecasting by integrating ensemble modelling and machine learning
O'Donncha, F.; Zhang, Y.; James, S. C.
2017-12-01
Modern smart-grid networks use technologies to instantly relay information on supply and demand to support effective decision making. Integration of renewable-energy resources with these systems demands accurate forecasting of energy production (and demand) capacities. For wave-energy converters, this requires wave-condition forecasting to enable estimates of energy production. Current operational wave forecasting systems exhibit substantial errors with wave-height RMSEs of 40 to 60 cm being typical, which limits the reliability of energy-generation predictions thereby impeding integration with the distribution grid. In this study, we integrate physics-based models with statistical learning aggregation techniques that combine forecasts from multiple, independent models into a single "best-estimate" prediction of the true state. The Simulating Waves Nearshore physics-based model is used to compute wind- and currents-augmented waves in the Monterey Bay area. Ensembles are developed based on multiple simulations perturbing input data (wave characteristics supplied at the model boundaries and winds) to the model. A learning-aggregation technique uses past observations and past model forecasts to calculate a weight for each model. The aggregated forecasts are compared to observation data to quantify the performance of the model ensemble and aggregation techniques. The appropriately weighted ensemble model outperforms an individual ensemble member with regard to forecasting wave conditions.
Huang, Hao; Ouyang, Zhengbiao
2018-01-01
We propose a general method for eliminating the reflection of waves in 2 dimensional photonic crystal waveguides (2D-PCWs), a kind of 2D material, by introducing extra scatterers inside the 2D-PCWs. The intrinsic reflection in 2D-PCWs is compensated by the backward-scattered waves from these scatterers, so that the overall reflection is greatly reduced and the insertion loss is improved accordingly. We first present the basic theory for the compensation method. Then, as a demonstration, we give four examples of extremely-low-reflection and high-transmission 90°bent 2D-PCWs created according to the method proposed. In the four examples, it is demonstrated by plane-wave expansion method and finite-difference time-domain method that the 90°bent 2D-PCWs can have high transmission ratio greater than 90% in a wide range of operating frequency, and the highest transmission ratio can be greater than 99.95% with a return loss higher than 43 dB, better than that in other typical 90°bent 2D-PCWs. With our method, the bent 2D-PCWs can be optimized to obtain high transmission ratio at different operating wavelengths. As a further application of this method, a waveguide-based optical bridge for light crossing is presented, showing an optimum return loss of 46.85 dB, transmission ratio of 99.95%, and isolation rates greater than 41.77 dB. The method proposed provides also a useful way for improving conventional waveguides made of cables, fibers, or metal walls in the optical, infrared, terahertz, and microwave bands.
International Nuclear Information System (INIS)
Petrzilka, V.
1991-09-01
The nonlinear changes of the reflection coefficient R of fast waves launched by waveguide arrays may be significant even for power densities S in the range of 3 or 4 kW/cm 2 . For the input parameters chosen in the computations, the effects of ponderomotive forces lead to an increase in plasma density in front of the grill , whereas for the slow wave the plasma density always decreases with growing S. For small plasma density in front of the grill, ponderomotive forces thus lead to the decrease of R, whereas for high plasma densities R grows with growing power density S. The heating of the edge plasma by the wave tends to weaken these changes. (Z.S.) 6 figs., 17 refs
Tian, Zhen; Huo, Linsheng; Gao, Weihang; Li, Hongnan; Song, Gangbing
2017-10-01
Wave-based concrete structural health monitoring has attracted much attention. A stress wave experiences significant attenuation in concrete, however there is a lack of a unified method for predicting the attenuation coefficient of the stress wave. In this paper, a simple and effective absorption attenuation model of stress waves in concrete is developed based on the Rayleigh damping model, which indicates that the absorption attenuation coefficient of stress waves in concrete is directly proportional to the square of the stress wave frequency when the damping ratio is small. In order to verify the theoretical model, related experiments were carried out. During the experiments, a concrete beam was designed in which the d33-model piezoelectric smart aggregates were embedded to detect the propagation of stress waves. It is difficult to distinguish direct stress waves due to the complex propagation paths and the reflection and scattering of stress waves in concrete. Hence, as another innovation of this paper, a new method for computing the absorption attenuation coefficient based on the time-reversal method is developed. Due to the self-adaptive focusing properties of the time-reversal method, the time-reversed stress wave focuses and generates a peak value. The time-reversal method eliminates the adverse effects of multipaths, reflection, and scattering. The absorption attenuation coefficient is computed by analyzing the peak value changes of the time-reversal focused signal. Finally, the experimental results are found to be in good agreement with the theoretical model.
Czech Academy of Sciences Publication Activity Database
Farra, V.; Pšenčík, Ivan
2010-01-01
Roč. 183, č. 3 (2010), s. 1443-1454 ISSN 0956-540X R&D Projects: GA ČR GA205/08/0332 Institutional research plan: CEZ:AV0Z30120515 Keywords : body waves * seismic anisotropy * wave propagation Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.411, year: 2010
Reflection of P and SV waves at the free surface of a monoclinic ...
Indian Academy of Sciences (India)
The propagation of plane waves in an anisotropic elastic medium possessing monoclinic symmetry is discussed. The expressions for the phase velocity of qP and qSV waves propagating in the plane of elastic symmetry are obtained in terms of the direction cosines of the propagation vector. It is shown that, in general, ...
Wave Tank Testing and Model Validation of an Autonomous Wave Energy Converter
Directory of Open Access Journals (Sweden)
Bret Bosma
2015-08-01
Full Text Available A key component in bringing ocean wave energy converters from concept to commercialization is the building and testing of scaled prototypes to provide model validation. A one quarter scale prototype of an autonomous two body heaving point absorber was modeled, built, and tested for this work. Wave tank testing results are compared with two hydrodynamic and system models—implemented in both ANSYS AQWA and MATLAB/Simulink—and show model validation over certain regions of operation. This work will serve as a guide for future developers of wave energy converter devices, providing insight in taking their design from concept to prototype stage.
Model-based dispersive wave processing: A recursive Bayesian solution
International Nuclear Information System (INIS)
Candy, J.V.; Chambers, D.H.
1999-01-01
Wave propagation through dispersive media represents a significant problem in many acoustic applications, especially in ocean acoustics, seismology, and nondestructive evaluation. In this paper we propose a propagation model that can easily represent many classes of dispersive waves and proceed to develop the model-based solution to the wave processing problem. It is shown that the underlying wave system is nonlinear and time-variable requiring a recursive processor. Thus the general solution to the model-based dispersive wave enhancement problem is developed using a Bayesian maximum a posteriori (MAP) approach and shown to lead to the recursive, nonlinear extended Kalman filter (EKF) processor. The problem of internal wave estimation is cast within this framework. The specific processor is developed and applied to data synthesized by a sophisticated simulator demonstrating the feasibility of this approach. copyright 1999 Acoustical Society of America.
Petronio, Lorenzo; Boaga, Jacopo; Cassiani, Giorgio
2016-05-01
The mechanisms of the disastrous Vajont rockslide (North-Eastern Italy, October 9, 1963) have been studied in great detail over the past five decades. Nevertheless, the reconstruction of the rockslide dynamics still presents several uncertainties, including those related to the accurate estimation of the actual landslide mass. This work presents the results of a geophysical characterization of the Vajont landslide body in terms of material properties and buried geometry. Both aspects add new information to the existing dataset and will help a better understanding of the rockslide failure mechanisms and dynamics. In addition, some general considerations concerning the intricacies of landslide characterization can be drawn, with due attention to potential pitfalls. The employed techniques are: (i) high resolution P-wave reflection, (ii) high resolution SH-wave reflection, (iii) controlled source surface wave analysis. We adopted as a seismic source a vibrator both for P waves and SH waves, using vertical and horizontal geophones respectively. For the surface wave seismic survey we used a heavy drop-weight source and low frequency receivers. Despite the high noise level caused by the fractured conditions of the large rock body, a common situation in landslide studies, we managed to achieve a satisfying imaging quality of the landslide structure thanks to the large number of active channels, the short receiver interval and the test of appropriate seismic sources. The joint use of different seismic techniques help focus the investigation on the rock mass mechanical properties. Results are in good agreement with the available borehole data, the geological sections and the mechanical properties of the rockmass estimated by other studies. In general the proposed approach is likely to be applicable successfully to similar situations where scattering and other noise sources are a typical bottleneck to geophysical data acquisition on landslide bodies.
The use of a wave boundary layer model in SWAN
DEFF Research Database (Denmark)
Du, Jianting; Bolaños, Rodolfo; Larsén, Xiaoli Guo
2017-01-01
A Wave Boundary Layer Model (WBLM) is implemented in the third-generation ocean wave model SWAN to improve the wind-input source function under idealized, fetch-limited condition. Accordingly, the white capping dissipation parameters are re-calibrated to fit the new wind-input source function...
International Nuclear Information System (INIS)
Karzova, M.; Yuldashev, P.; Khokhlova, V.; Ollivier, S.; Blanc-Benon, Ph.
2015-01-01
Mach stem is a well-known structure typically observed in the process of strong (acoustic Mach numbers greater than 0.4) step-shock waves reflection from a rigid boundary. However, this phenomenon has been much less studied for weak shocks in nonlinear acoustic fields where Mach numbers are in the range from 0.001 to 0.01 and pressure waveforms have more complicated waveforms than step shocks. The goal of this work was to demonstrate experimentally how nonlinear reflection occurs in air for very weak spherically divergent acoustic spark-generated pulses resembling an N-wave. Measurements of reflection patterns were performed using a Mach-Zehnder interferometer. A thin laser beam with sub-millimeter cross-section was used to obtain the time resolution of 0.4 µs, which is 6 times higher than the time resolution of the condenser microphones. Pressure waveforms were reconstructed using the inverse Abel transform applied to the phase of the signal measured by the interferometer. The Mach stem formation was observed experimentally as a result of collision of the incident and reflected shock pulses. It was shown that irregular reflection of the pulse occurred in a dynamic way and the length of the Mach stem increased linearly while the pulse propagated along the surface. Since the front shock of the spark-generated pulse was steeper than the rear shock, irregular type of reflection was observed only for the front shock of the pulse while the rear shock reflection occurred in a regular regime
Energy Technology Data Exchange (ETDEWEB)
Karzova, M., E-mail: masha@acs366.phys.msu.ru [Laboratoire de Mécanique des Fluides et d’Acoustique, Ecole Centrale de Lyon, 36 Avenue Guy de Collongue, 69134 Ecully (France); Physics Faculty, Moscow State University, Leninskie Gory, 119991 Moscow (Russian Federation); Yuldashev, P.; Khokhlova, V. [Physics Faculty, Moscow State University, Leninskie Gory, 119991 Moscow (Russian Federation); Ollivier, S.; Blanc-Benon, Ph. [Laboratoire de Mécanique des Fluides et d’Acoustique, Ecole Centrale de Lyon, 36 Avenue Guy de Collongue, 69134 Ecully (France)
2015-10-28
Mach stem is a well-known structure typically observed in the process of strong (acoustic Mach numbers greater than 0.4) step-shock waves reflection from a rigid boundary. However, this phenomenon has been much less studied for weak shocks in nonlinear acoustic fields where Mach numbers are in the range from 0.001 to 0.01 and pressure waveforms have more complicated waveforms than step shocks. The goal of this work was to demonstrate experimentally how nonlinear reflection occurs in air for very weak spherically divergent acoustic spark-generated pulses resembling an N-wave. Measurements of reflection patterns were performed using a Mach-Zehnder interferometer. A thin laser beam with sub-millimeter cross-section was used to obtain the time resolution of 0.4 µs, which is 6 times higher than the time resolution of the condenser microphones. Pressure waveforms were reconstructed using the inverse Abel transform applied to the phase of the signal measured by the interferometer. The Mach stem formation was observed experimentally as a result of collision of the incident and reflected shock pulses. It was shown that irregular reflection of the pulse occurred in a dynamic way and the length of the Mach stem increased linearly while the pulse propagated along the surface. Since the front shock of the spark-generated pulse was steeper than the rear shock, irregular type of reflection was observed only for the front shock of the pulse while the rear shock reflection occurred in a regular regime.
Modelling of Performance of Caisson Type Breakwaters under Extreme Waves
Güney Doǧan, Gözde; Özyurt Tarakcıoǧlu, Gülizar; Baykal, Cüneyt
2016-04-01
Many coastal structures are designed without considering loads of tsunami-like waves or long waves although they are constructed in areas prone to encounter these waves. Performance of caisson type breakwaters under extreme swells is tested in Middle East Technical University (METU) Coastal and Ocean Engineering Laboratory. This paper presents the comparison of pressure measurements taken along the surface of caisson type breakwaters and obtained from numerical modelling of them using IH2VOF as well as damage behavior of the breakwater under the same extreme swells tested in a wave flume at METU. Experiments are conducted in the 1.5 m wide wave flume, which is divided into two parallel sections (0.74 m wide each). A piston type of wave maker is used to generate the long wave conditions located at one end of the wave basin. Water depth is determined as 0.4m and kept constant during the experiments. A caisson type breakwater is constructed to one side of the divided flume. The model scale, based on the Froude similitude law, is chosen as 1:50. 7 different wave conditions are applied in the tests as the wave period ranging from 14.6 s to 34.7 s, wave heights from 3.5 m to 7.5 m and steepness from 0.002 to 0.015 in prototype scale. The design wave parameters for the breakwater were 5m wave height and 9.5s wave period in prototype. To determine the damage of the breakwater which were designed according to this wave but tested under swell waves, video and photo analysis as well as breakwater profile measurements before and after each test are performed. Further investigations are carried out about the acting wave forces on the concrete blocks of the caisson structures via pressure measurements on the surfaces of these structures where the structures are fixed to the channel bottom minimizing. Finally, these pressure measurements will be compared with the results obtained from the numerical study using IH2VOF which is one of the RANS models that can be applied to simulate
Numerical modelling of extreme waves by Smoothed Particle Hydrodynamics
Directory of Open Access Journals (Sweden)
M. H. Dao
2011-02-01
Full Text Available The impact of extreme/rogue waves can lead to serious damage of vessels as well as marine and coastal structures. Such extreme waves in deep water are characterized by steep wave fronts and an energetic wave crest. The process of wave breaking is highly complex and, apart from the general knowledge that impact loadings are highly impulsive, the dynamics of the breaking and impact are still poorly understood. Using an advanced numerical method, the Smoothed Particle Hydrodynamics enhanced with parallel computing is able to reproduce well the extreme waves and their breaking process. Once the waves and their breaking process are modelled successfully, the dynamics of the breaking and the characteristics of their impact on offshore structures could be studied. The computational methodology and numerical results are presented in this paper.
Dias, Frédéric; Renzi, Emiliano; Gallagher, Sarah; Sarkar, Dripta; Wei, Yanji; Abadie, Thomas; Cummins, Cathal; Rafiee, Ashkan
2017-08-01
The development of new wave energy converters has shed light on a number of unanswered questions in fluid mechanics, but has also identified a number of new issues of importance for their future deployment. The main concerns relevant to the practical use of wave energy converters are sustainability, survivability, and maintainability. Of course, it is also necessary to maximize the capture per unit area of the structure as well as to minimize the cost. In this review, we consider some of the questions related to the topics of sustainability, survivability, and maintenance access, with respect to sea conditions, for generic wave energy converters with an emphasis on the oscillating wave surge converter. New analytical models that have been developed are a topic of particular discussion. It is also shown how existing numerical models have been pushed to their limits to provide answers to open questions relating to the operation and characteristics of wave energy converters.
Dias, Frédéric; Renzi, Emiliano; Gallagher, Sarah; Sarkar, Dripta; Wei, Yanji; Abadie, Thomas; Cummins, Cathal; Rafiee, Ashkan
2017-01-01
The development of new wave energy converters has shed light on a number of unanswered questions in fluid mechanics, but has also identified a number of new issues of importance for their future deployment. The main concerns relevant to the practical use of wave energy converters are sustainability, survivability, and maintainability. Of course, it is also necessary to maximize the capture per unit area of the structure as well as to minimize the cost. In this review, we consider some of the questions related to the topics of sustainability, survivability, and maintenance access, with respect to sea conditions, for generic wave energy converters with an emphasis on the oscillating wave surge converter. New analytical models that have been developed are a topic of particular discussion. It is also shown how existing numerical models have been pushed to their limits to provide answers to open questions relating to the operation and characteristics of wave energy converters.
Does the cognitive reflection test measure cognitive reflection? A mathematical modeling approach.
Campitelli, Guillermo; Gerrans, Paul
2014-04-01
We used a mathematical modeling approach, based on a sample of 2,019 participants, to better understand what the cognitive reflection test (CRT; Frederick In Journal of Economic Perspectives, 19, 25-42, 2005) measures. This test, which is typically completed in less than 10 min, contains three problems and aims to measure the ability or disposition to resist reporting the response that first comes to mind. However, since the test contains three mathematically based problems, it is possible that the test only measures mathematical abilities, and not cognitive reflection. We found that the models that included an inhibition parameter (i.e., the probability of inhibiting an intuitive response), as well as a mathematical parameter (i.e., the probability of using an adequate mathematical procedure), fitted the data better than a model that only included a mathematical parameter. We also found that the inhibition parameter in males is best explained by both rational thinking ability and the disposition toward actively open-minded thinking, whereas in females this parameter was better explained by rational thinking only. With these findings, this study contributes to the understanding of the processes involved in solving the CRT, and will be particularly useful for researchers who are considering using this test in their research.
Energy Technology Data Exchange (ETDEWEB)
Kano, N; Kiguchi, T; Yamaguchi, K [Geological Survey of Japan, Tsukuba (Japan); Yokota, T [Japan National Oil Corp., Tokyo (Japan). Technology Research Center
1997-10-22
Investigations and discussions were given by using P-S logging on anisotropy of refracted waves in the fundamental experiments conducted in the Matsuyama town, Yamagata Prefecture. In the investigations, S-wave was transmitted into two to three directions at four locations in total: one at the opening of a well with a depth of 100 m and three locations having offset of 50 m from the well opening, and anisotropy of direct waves in the depth direction was investigated. Data were recorded on the ground at the same time by using a 3-component receiver. As a result of the experiment, detection of the anisotropy by means of measurement inside the well was found more difficult than anticipated due to anomaly in the refracted waves, hence no clear velocity anisotropy has been observed. It appears that no azimuth anisotropy exists at depths shallower than at least 24 m. No anisotropy due to incident angles was made clear in the present experiment. Offset recording experienced poor S/N ratio, having made the data analysis difficult. The data for zero offset do not harmonize with the refracted wave analysis on the data derived by using the reflection method, whose cause requires further discussions. 4 figs., 2 tabs.
Directory of Open Access Journals (Sweden)
Tim Verbrugghe
2017-10-01
Full Text Available Wave Energy Converters (WECs need to be deployed in large numbers in an array layout in order to have a significant power production. Each WEC has an impact on the incoming wave field, by diffracting, reflecting and radiating waves. Simulating the wave transformations within and around a WEC array is complex; it is difficult, or in some cases impossible, to simulate both these near-field and far-field wake effects using a single numerical model, in a time- and cost-efficient way in terms of computational time and effort. Within this research, a generic coupling methodology is developed to model both near-field and far-field wake effects caused by floating (e.g., WECs, platforms or fixed offshore structures. The methodology is based on the coupling of a wave-structure interaction solver (Nemoh and a wave propagation model. In this paper, this methodology is applied to two wave propagation models (OceanWave3D and MILDwave, which are compared to each other in a wide spectrum of tests. Additionally, the Nemoh-OceanWave3D model is validated by comparing it to experimental wave basin data. The methodology proves to be a reliable instrument to model wake effects of WEC arrays; results demonstrate a high degree of agreement between the numerical simulations with relative errors lower than 5 % and to a lesser extent for the experimental data, where errors range from 4 % to 17 % .
Evaluation of the numerical wave model (SWAN) for wave simulation in the Black Sea
Akpınar, Adem; van Vledder, Gerbrant Ph.; Kömürcü, Murat İhsan; Özger, Mehmet
2012-12-01
This study summaries the implementation of the SWAN model forced by the ECMWF ERA Interim dataset reanalyzed 10 m winds over the Black Sea which will be used to study the wind-wave climate and wave energy potential in the region, and its verification. The SWAN model results were compared with directional buoy measurements at three locations along the north and south coasts of the Black Sea, parametric model results based on the JONSWAP growth relations, and the results of previous studies. The SWAN model has been applied in a third generation and non-stationary mode with spherical coordinates. The linear and exponential growth from wind input, depth-induced wave breaking, bottom friction, whitecapping, four-wave (for deep water) and triad-wave (for shallow water) nonlinear interactions have been activated in the simulations. The results of this study indicate that agreement between simulated and observed wave parameters is satisfactory and it is slightly more accurate than the results of the previous studies. However, it still has lower estimates for the maximum values of both wave parameters. These lower estimates are probably due to too low wind speeds in the applied ECMWF wind fields, which is probably caused by orographic effects, and due to the relatively course resolution in time and space of the ECMWF (ERA-Interim) wind fields for the Black Sea.
International Nuclear Information System (INIS)
Lowe, M.J.S.; Cawley, P.; Kao, J-Y; Diligent, O.
2000-01-01
The interaction of the fundamental antisymmetric Lamb wave (a o ) with cracks and with notches of different depth and width has been investigated both experimentally and by finite element analysis. Excellent agreement between the predictions and the measurements has been obtained. It has been shown that the reflection coefficient is a function of both the notch width to wavelength and notch depth to wavelength ratios. Both the relationship between the reflection coefficient and notch, depth, and the frequency dependence of the reflection coefficient, are very different for the a o mode compared to the s o mode which was studied earlier. Physical insight into the reasons for the different behavior is given by examination of the stress fields and opening displacements at the crack or notch
International Nuclear Information System (INIS)
Ghosal, S.K.; Sen, S.N.
1977-01-01
The problem of transmission of sonic waves through a weakly ionised plasma bounded in each side by a neutral gas medium has been treated by assuming the plasma to be a mixture of two intermingled fluids viz., neutral particle fluid and ion fluid in equilibrium. From a hydrodynamic analysis the wave equation for 'p', the macroscopic pressure perturbation has been obtained and it is shown that two independent wave motions, one due to the neutral particles and the other due to ions are propagated through the plasma with two different phase velocities. Assuming the usual boundary conditions at the interface, the amplitude of the transmitted wave has been calculated in case of weakly ionized plasma; the theory can be utilized for the determination of electron temperature from the measured value of attenuation if the percentage of ionization and collision cross section can be obtained independently. (author)
Spectral analysis of surface waves method to assess shear wave velocity within centrifuge models
MURILLO, Carol Andrea; THOREL, Luc; CAICEDO, Bernardo
2009-01-01
The method of the spectral analysis of surface waves (SASW) is tested out on reduced scale centrifuge models, with a specific device, called the mini Falling Weight, developed for this purpose. Tests are performed on layered materials made of a mixture of sand and clay. The shear wave velocity VS determined within the models using the SASW is compared with the laboratory measurements carried out using the bender element test. The results show that the SASW technique applied to centrifuge test...
Wind-wave modelling aspects within complicate topography
Directory of Open Access Journals (Sweden)
S. Christopoulos
Full Text Available Wave forecasting aspects for basins with complicate geomorphology, such as the Aegean Sea, are investigated through an intercomparison study. The efficiency of the available wind models (ECMWF, UKMO to reproduce wind patterns over special basins, as well as three wave models incorporating different physics and characteristics (WAM, AUT, WACCAS, are tested for selected storm cases representing the typical wind situations over the basin. From the wave results, discussed in terms of time-series and statistical parameters, the crucial role is pointed out of the wind resolution and the reliability of the different wave models to estimate the wave climate in such a basin. The necessary grid resolution is also tested, while for a specific test case (December 1991 ERS-1 satellite data are compared with those of the model.
TWO-DIMENSIONAL MODELLING OF ACCIDENTAL FLOOD WAVES PROPAGATION
Lorand Catalin STOENESCU
2011-01-01
The study presented in this article describes a modern modeling methodology of the propagation of accidental flood waves in case a dam break; this methodology is applied in Romania for the first time for the pilot project „Breaking scenarios of Poiana Uzului dam”. The calculation programs used help us obtain a bidimensional calculation (2D) of the propagation of flood waves, taking into consideration the diminishing of the flood wave on a normal direction to the main direction; this diminishi...
Jacobian elliptic wave solutions in an anharmonic molecular crystal model
International Nuclear Information System (INIS)
Teh, C.G.R.; Lee, B.S.; Koo, W.K.
1997-07-01
Explicit Jacobian elliptic wave solutions are found in the anharmonic molecular crystal model for both the continuum limit and discrete modes. This class of wave solutions include the famous pulse-like and kink-like solitary modes. We would also like to report on the existence of some highly discrete staggered solitary wave modes not found in the continuum limit. (author). 9 refs, 1 fig
Energy Technology Data Exchange (ETDEWEB)
Uesaka, S [Kyoto University, Kyoto (Japan). Faculty of Engineering; Watanabe, T; Sassa, K [Kyoto University, Kyoto (Japan)
1997-05-27
Algorithm is constructed and a program developed for a full-wave inversion (FWI) method utilizing the elastic wave equation in seismic exploration. The FWI method is a method for obtaining a physical property distribution using the whole observed waveforms as the data. It is capable of high resolution which is several times smaller than the wavelength since it can handle such phenomena as wave reflection and dispersion. The method for determining the P-wave velocity structure by use of the acoustic wave equation does not provide information about the S-wave velocity since it does not consider S-waves or converted waves. In an analysis using the elastic wave equation, on the other hand, not only P-wave data but also S-wave data can be utilized. In this report, under such circumstances, an inverse analysis algorithm is constructed on the basis of the elastic wave equation, and a basic program is developed. On the basis of the methods of Mora and of Luo and Schuster, the correction factors for P-wave and S-wave velocities are formulated directly from the elastic wave equation. Computations are performed and the effects of the hypocenter frequency and vibration transmission direction are examined. 6 refs., 8 figs.
Short-Term Wave Forecasting with AR models in Real-Time Optimal Control of Wave Energy Converters
Fusco, Francesco; Ringwood, John
2010-01-01
Time domain control of wave energy converters requires knowledge of future incident wave elevation in order to approach conditions for optimal energy extraction. Autoregressive models revealed to be a promising approach to the prediction of future values of the wave elevation only from its past history. Results on real wave observations from different ocean locations show that AR models allow to achieve very good predictions for more than one wave period in the future if ...
Modeling stress wave propagation in rocks by distinct lattice spring model
Directory of Open Access Journals (Sweden)
Gaofeng Zhao
2014-08-01
Full Text Available In this paper, the ability of the distinct lattice spring model (DLSM for modeling stress wave propagation in rocks was fully investigated. The influence of particle size on simulation of different types of stress waves (e.g. one-dimensional (1D P-wave, 1D S-wave and two-dimensional (2D cylindrical wave was studied through comparing results predicted by the DLSM with different mesh ratios (lr and those obtained from the corresponding analytical solutions. Suggested values of lr were obtained for modeling these stress waves accurately. Moreover, the weak material layer method and virtual joint plane method were used to model P-wave and S-wave propagating through a single discontinuity. The results were compared with the classical analytical solutions, indicating that the virtual joint plane method can give better results and is recommended. Finally, some remarks of the DLSM on modeling of stress wave propagation in rocks were provided.
Experimental Update of the Overtopping Model Used for the Wave Dragon Wave Energy Converter
Directory of Open Access Journals (Sweden)
Erik Friis-Madsen
2013-04-01
Full Text Available An overtopping model specifically suited for Wave Dragon is needed in order to improve the reliability of its performance estimates. The model shall be comprehensive of all relevant physical processes that affect overtopping and flexible to adapt to any local conditions and device configuration. An experimental investigation is carried out to update an existing formulation suited for 2D draft-limited, low-crested structures, in order to include the effects on the overtopping flow of the wave steepness, the 3D geometry of Wave Dragon, the wing reflectors, the device motions and the non-rigid connection between platform and reflectors. The study is carried out in four phases, each of them specifically targeted at quantifying one of these effects through a sensitivity analysis and at modeling it through custom-made parameters. These are depending on features of the wave or the device configuration, all of which can be measured in real-time. Instead of using new fitting coefficients, this approach allows a broader applicability of the model beyond the Wave Dragon case, to any overtopping WEC or structure within the range of tested conditions. Predictions reliability of overtopping over Wave Dragon increased, as the updated model allows improved accuracy and precision respect to the former version.
Modeling the Buoyancy System of a Wave Energy Power Plant
DEFF Research Database (Denmark)
Pedersen, Tom S.; Nielsen, Kirsten M.
2009-01-01
A nonlinear dynamic model of the buoyancy system in a wave energy power plant is presented. The plant ("Wave Dragon") is a floating device using the potential energy in overtopping waves to produce power. A water reservoir is placed on top of the WD, and hydro turbines lead the water to the sea...... producing electrical power. Through air chambers it is possible to control the level of the WD. It is important to control the level in order to maximize the power production in proportion to the wave height, here the amount of overtopping water and the amount of potential energy is conflicting...
Modeling sheet-flow sand transport under progressive surface waves
Kranenburg, Wouter
2013-01-01
In the near-shore zone, energetic sea waves generate sheet-flow sand transport. In present day coastal models, wave-induced sheet-flow sand transport rates are usually predicted with semi-empirical transport formulas, based on extensive research on this phenomenon in oscillatory flow tunnels.
Variational Boussinesq model for strongly nonlinear dispersive waves
Lawrence, C.; Adytia, D.; van Groesen, E.
2018-01-01
For wave tank, coastal and oceanic applications, a fully nonlinear Variational Boussinesq model with optimized dispersion is derived and a simple Finite Element implementation is described. Improving a previous weakly nonlinear version, high waves over flat and varying bottom are shown to be
Models for seismic wave propagation in periodically layered porous media
Kudarova, A.; Van Dalen, K.N.; Drijkoningen, G.G.
2014-01-01
Several models are discussed for seismic wave propagation in periodically layered poroelastic media where layers represent mesoscopic-scale heterogeneities that are larger than the pore and grain sizes but smaller than the wavelength. The layers behave according to Biot’s theory. Wave propagation
Particle transport model sensitivity on wave-induced processes
Staneva, Joanna; Ricker, Marcel; Krüger, Oliver; Breivik, Oyvind; Stanev, Emil; Schrum, Corinna
2017-04-01
Different effects of wind waves on the hydrodynamics in the North Sea are investigated using a coupled wave (WAM) and circulation (NEMO) model system. The terms accounting for the wave-current interaction are: the Stokes-Coriolis force, the sea-state dependent momentum and energy flux. The role of the different Stokes drift parameterizations is investigated using a particle-drift model. Those particles can be considered as simple representations of either oil fractions, or fish larvae. In the ocean circulation models the momentum flux from the atmosphere, which is related to the wind speed, is passed directly to the ocean and this is controlled by the drag coefficient. However, in the real ocean, the waves play also the role of a reservoir for momentum and energy because different amounts of the momentum flux from the atmosphere is taken up by the waves. In the coupled model system the momentum transferred into the ocean model is estimated as the fraction of the total flux that goes directly to the currents plus the momentum lost from wave dissipation. Additionally, we demonstrate that the wave-induced Stokes-Coriolis force leads to a deflection of the current. During the extreme events the Stokes velocity is comparable in magnitude to the current velocity. The resulting wave-induced drift is crucial for the transport of particles in the upper ocean. The performed sensitivity analyses demonstrate that the model skill depends on the chosen processes. The results are validated using surface drifters, ADCP, HF radar data and other in-situ measurements in different regions of the North Sea with a focus on the coastal areas. The using of a coupled model system reveals that the newly introduced wave effects are important for the drift-model performance, especially during extremes. Those effects cannot be neglected by search and rescue, oil-spill, transport of biological material, or larva drift modelling.
A rapid radiative transfer model for reflection of solar radiation
Xiang, X.; Smith, E. A.; Justus, C. G.
1994-01-01
A rapid analytical radiative transfer model for reflection of solar radiation in plane-parallel atmospheres is developed based on the Sobolev approach and the delta function transformation technique. A distinct advantage of this model over alternative two-stream solutions is that in addition to yielding the irradiance components, which turn out to be mathematically equivalent to the delta-Eddington approximation, the radiance field can also be expanded in a mathematically consistent fashion. Tests with the model against a more precise multistream discrete ordinate model over a wide range of input parameters demonstrate that the new approximate method typically produces average radiance differences of less than 5%, with worst average differences of approximately 10%-15%. By the same token, the computational speed of the new model is some tens to thousands times faster than that of the more precise model when its stream resolution is set to generate precise calculations.
Attenuation of surface waves due to monsoon rains: A model study for the north Indian Ocean
Digital Repository Service at National Institute of Oceanography (India)
Vethamony, P.; Kumar, B.P.; Sarma, Y.V.B.
The dynamic interaction of intense rain with waves based on momentum exchange is applied to a second generation wave model to predict wave attenuation during monsoon. The scheme takes into account the characteristics of rain and wave parameters...
Modeling aspects of wave kinematics in offshore structures dynamics
International Nuclear Information System (INIS)
Spanos, P.D.; Ghanem, R.; Bhattacharjee, S.
1993-01-01
Magnitude and phase related issues of modeling of ocean wave kinematics are addressed. Causal and non-causal filters are examined. It is shown that if for a particular ocean engineering problem only the magnitude representation of wave spectra spatial relation is critical, analog filters can be quite useful models in conjunction with the technique of statistical linearization, for calculating dynamic analyses. This is illustrated by considering the dynamic response of a simple model of a guyed tower
Determining integral density distribution in the mach reflection of shock waves
Shevchenko, A. M.; Golubev, M. P.; Pavlov, A. A.; Pavlov, Al. A.; Khotyanovsky, D. V.; Shmakov, A. S.
2017-05-01
We present a method for and results of determination of the field of integral density in the structure of flow corresponding to the Mach interaction of shock waves at Mach number M = 3. The optical diagnostics of flow was performed using an interference technique based on self-adjusting Zernike filters (SA-AVT method). Numerical simulations were carried out using the CFS3D program package for solving the Euler and Navier-Stokes equations. Quantitative data on the distribution of integral density on the path of probing radiation in one direction of 3D flow transillumination in the region of Mach interaction of shock waves were obtained for the first time.
Energy Technology Data Exchange (ETDEWEB)
Yoshida, T; Asanuma, H; Niitsuma, H [Tohoku University, Sendai (Japan). Faculty of Engineering
1996-05-01
This paper reports a method to detect reflected wave components contained in an elastic wave caused in association with well drilling. Measurement was made on an elastic wave caused in association with well drilling in an experimental field by using a triaxial elastic wave detector disposed in a measurement well. Analyzing the particle motion tracks in the derived elastic wave signals (to derive the main axial direction of a three-dimensional hologram) revealed that oscillation direction of the signals changes non-steadily by time centering around the S-wave oscillation direction. In addition, a sound source position was estimated during the drilling. Existence probability of the S-wave signal in the non-steady continuous signals was estimated by handling the particle motion tracks stochastically. In addition, this existence probability was used as a weighting function for a correlative analysis to detect a reflected wave from directly reaching wave components in the non-steady continuous signals. Thus, improvement in reliability of reflected wave detection was attempted. Effectiveness of this method was endorsed by the field data. 3 refs., 7 figs.
Solvable model of spiral wave chimeras.
Martens, Erik A; Laing, Carlo R; Strogatz, Steven H
2010-01-29
Spiral waves are ubiquitous in two-dimensional systems of chemical or biological oscillators coupled locally by diffusion. At the center of such spirals is a phase singularity, a topological defect where the oscillator amplitude drops to zero. But if the coupling is nonlocal, a new kind of spiral can occur, with a circular core consisting of desynchronized oscillators running at full amplitude. Here, we provide the first analytical description of such a spiral wave chimera and use perturbation theory to calculate its rotation speed and the size of its incoherent core.
Solvable Model of Spiral Wave Chimeras
DEFF Research Database (Denmark)
Martens, Erik Andreas; Laing, Carlo R.; Strogatz, Steven H.
2010-01-01
Spiral waves are ubiquitous in two-dimensional systems of chemical or biological oscillators coupled locally by diffusion. At the center of such spirals is a phase singularity, a topological defect where the oscillator amplitude drops to zero. But if the coupling is nonlocal, a new kind of spiral...... can occur, with a circular core consisting of desynchronized oscillators running at full amplitude. Here, we provide the first analytical description of such a spiral wave chimera and use perturbation theory to calculate its rotation speed and the size of its incoherent core....
Computational study of nonlinear plasma waves. I. Simulation model and monochromatic wave propagtion
International Nuclear Information System (INIS)
Matda, Y.; Crawford, F.W.
1974-12-01
An economical low noise plasma simulation model is applied to a series of problems associated with electrostatic wave propagation in a one-dimensional, collisionless, Maxwellian plasma, in the absence of magnetic field. The model is described and tested, first in the absence of an applied signal, and then with a small amplitude perturbation, to establish the low noise features and to verify the theoretical linear dispersion relation at wave energy levels as low as 0.000,001 of the plasma thermal energy. The method is then used to study propagation of an essentially monochromatic plane wave. Results on amplitude oscillation and nonlinear frequency shift are compared with available theories. The additional phenomena of sideband instability and satellite growth, stimulated by large amplitude wave propagation and the resulting particle trapping, are described. (auth)
Traveling waves in an optimal velocity model of freeway traffic
Berg, Peter; Woods, Andrew
2001-03-01
Car-following models provide both a tool to describe traffic flow and algorithms for autonomous cruise control systems. Recently developed optimal velocity models contain a relaxation term that assigns a desirable speed to each headway and a response time over which drivers adjust to optimal velocity conditions. These models predict traffic breakdown phenomena analogous to real traffic instabilities. In order to deepen our understanding of these models, in this paper, we examine the transition from a linear stable stream of cars of one headway into a linear stable stream of a second headway. Numerical results of the governing equations identify a range of transition phenomena, including monotonic and oscillating travelling waves and a time- dependent dispersive adjustment wave. However, for certain conditions, we find that the adjustment takes the form of a nonlinear traveling wave from the upstream headway to a third, intermediate headway, followed by either another traveling wave or a dispersive wave further downstream matching the downstream headway. This intermediate value of the headway is selected such that the nonlinear traveling wave is the fastest stable traveling wave which is observed to develop in the numerical calculations. The development of these nonlinear waves, connecting linear stable flows of two different headways, is somewhat reminiscent of stop-start waves in congested flow on freeways. The different types of adjustments are classified in a phase diagram depending on the upstream and downstream headway and the response time of the model. The results have profound consequences for autonomous cruise control systems. For an autocade of both identical and different vehicles, the control system itself may trigger formations of nonlinear, steep wave transitions. Further information is available [Y. Sugiyama, Traffic and Granular Flow (World Scientific, Singapore, 1995), p. 137].
Modelling of Resonantly Forced Density Waves in Dense Planetary Rings
Lehmann, M.; Schmidt, J.; Salo, H.
2014-04-01
Density wave theory, originally proposed to explain the spiral structure of galactic disks, has been applied to explain parts of the complex sub-structure in Saturn's rings, such as the wavetrains excited at the inner Lindblad resonances (ILR) of various satellites. The linear theory for the excitation and damping of density waves in Saturn's rings is fairly well developed (e.g. Goldreich & Tremaine [1979]; Shu [1984]). However, it fails to describe certain aspects of the observed waves. The non-applicability of the linear theory is already indicated by the "cusplike" shape of many of the observed wave profiles. This is a typical nonlinear feature which is also present in overstability wavetrains (Schmidt & Salo [2003]; Latter & Ogilvie [2010]). In particular, it turns out that the detailed damping mechanism, as well as the role of different nonlinear effects on the propagation of density waves remain intransparent. First attemps are being made to investigate the excitation and propagation of nonlinear density waves within a hydrodynamical formalism, which is also the natural formalism for describing linear density waves. A simple weakly nonlinear model, derived from a multiple-scale expansion of the hydrodynamic equations, is presented. This model describes the damping of "free" spiral density waves in a vertically integrated fluid disk with density dependent transport coefficients, where the effects of the hydrodynamic nonlinearities are included. The model predicts that density waves are linearly unstable in a ring region where the conditions for viscous overstability are met, which translates to a steep dependence of the shear viscosity with respect to the disk's surface density. The possibility that this dependence could lead to a growth of density waves with increasing distance from the resonance, was already mentioned in Goldreich & Tremaine [1978]. Sufficiently far away from the ILR, the surface density perturbation caused by the wave, is predicted to
New Gravity Wave Treatments for GISS Climate Models
Geller, Marvin A.; Zhou, Tiehan; Ruedy, Reto; Aleinov, Igor; Nazarenko, Larissa; Tausnev, Nikolai L.; Sun, Shan; Kelley, Maxwell; Cheng, Ye
2011-01-01
Previous versions of GISS climate models have either used formulations of Rayleigh drag to represent unresolved gravity wave interactions with the model-resolved flow or have included a rather complicated treatment of unresolved gravity waves that, while being climate interactive, involved the specification of a relatively large number of parameters that were not well constrained by observations and also was computationally very expensive. Here, the authors introduce a relatively simple and computationally efficient specification of unresolved orographic and nonorographic gravity waves and their interaction with the resolved flow. Comparisons of the GISS model winds and temperatures with no gravity wave parameterization; with only orographic gravity wave parameterization; and with both orographic and nonorographic gravity wave parameterizations are shown to illustrate how the zonal mean winds and temperatures converge toward observations. The authors also show that the specifications of orographic and nonorographic gravity waves must be different in the Northern and Southern Hemispheres. Then results are presented where the nonorographic gravity wave sources are specified to represent sources from convection in the intertropical convergence zone and spontaneous emission from jet imbalances. Finally, a strategy to include these effects in a climate-dependent manner is suggested.
Energy Technology Data Exchange (ETDEWEB)
Neary, Vincent Sinclair [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Water Power Technologies; Yang, Zhaoqing [Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Coastal Sciences Division; Wang, Taiping [Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Coastal Sciences Division; Gunawan, Budi [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Water Power Technologies; Dallman, Ann Renee [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Water Power Technologies
2016-03-01
A wave model test bed is established to benchmark, test and evaluate spectral wave models and modeling methodologies (i.e., best practices) for predicting the wave energy resource parameters recommended by the International Electrotechnical Commission, IEC TS 62600-101Ed. 1.0 ©2015. Among other benefits, the model test bed can be used to investigate the suitability of different models, specifically what source terms should be included in spectral wave models under different wave climate conditions and for different classes of resource assessment. The overarching goal is to use these investigations to provide industry guidance for model selection and modeling best practices depending on the wave site conditions and desired class of resource assessment. Modeling best practices are reviewed, and limitations and knowledge gaps in predicting wave energy resource parameters are identified.
Reflected stochastic differential equation models for constrained animal movement
Hanks, Ephraim M.; Johnson, Devin S.; Hooten, Mevin B.
2017-01-01
Movement for many animal species is constrained in space by barriers such as rivers, shorelines, or impassable cliffs. We develop an approach for modeling animal movement constrained in space by considering a class of constrained stochastic processes, reflected stochastic differential equations. Our approach generalizes existing methods for modeling unconstrained animal movement. We present methods for simulation and inference based on augmenting the constrained movement path with a latent unconstrained path and illustrate this augmentation with a simulation example and an analysis of telemetry data from a Steller sea lion (Eumatopias jubatus) in southeast Alaska.
Reflection of plane waves from free surface of a microstretch elastic ...
Indian Academy of Sciences (India)
R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22
Department of Mathematics, Jat College, Rohtak 124 001, Haryana, India. e-mail: baljeet−gill@hotmail.com. In the present investigation, it is shown that there exists five basic waves in a ..... in layered media, (New York: McGraw-Hill). Gauthier ...
Czech Academy of Sciences Publication Activity Database
Pšenčík, Ivan; Farra, V.
2017-01-01
Roč. 82, č. 5 (2017), C175-C185 ISSN 0016-8033 R&D Projects: GA ČR(CZ) GA16-05237S Institutional support: RVO:67985530 Keywords : VTI media * velocity * seismic waves Subject RIV: DC - Siesmology, Volcanology, Earth Structure OBOR OECD: Volcanology Impact factor: 2.391, year: 2016
Identification and modeling of internal waves
Digital Repository Service at National Institute of Oceanography (India)
Murty, T.V.R.; Sadhuram, Y.; Rao, M.M.M.; SujithKumar, S.; Maneesha, K.; Sandhya, K.S.; Prakash, S.S.; Chandramouli, P.; Murthy, K.S.R.
Analyses of Internal Wave (IW) signatures by insitu observations off Visakhapatnam have been presented to study the impact of IWs on acoustic field. Temperature data were collected for 44 hours off Visakhapatnam (17° 26.46’N and 83° 31.20’E...
Modelling biochemical reaction systems by stochastic differential equations with reflection.
Niu, Yuanling; Burrage, Kevin; Chen, Luonan
2016-05-07
In this paper, we gave a new framework for modelling and simulating biochemical reaction systems by stochastic differential equations with reflection not in a heuristic way but in a mathematical way. The model is computationally efficient compared with the discrete-state Markov chain approach, and it ensures that both analytic and numerical solutions remain in a biologically plausible region. Specifically, our model mathematically ensures that species numbers lie in the domain D, which is a physical constraint for biochemical reactions, in contrast to the previous models. The domain D is actually obtained according to the structure of the corresponding chemical Langevin equations, i.e., the boundary is inherent in the biochemical reaction system. A variant of projection method was employed to solve the reflected stochastic differential equation model, and it includes three simple steps, i.e., Euler-Maruyama method was applied to the equations first, and then check whether or not the point lies within the domain D, and if not perform an orthogonal projection. It is found that the projection onto the closure D¯ is the solution to a convex quadratic programming problem. Thus, existing methods for the convex quadratic programming problem can be employed for the orthogonal projection map. Numerical tests on several important problems in biological systems confirmed the efficiency and accuracy of this approach. Copyright © 2016 Elsevier Ltd. All rights reserved.
Tellier, Gildas; Boisrobert, Christian
2007-11-01
The Maker fringes technique is commonly used for the determination of nonlinear optical coefficients. In this article, we present a new formulation of Maker fringes in parallel-surface samples, using boundary conditions taking into account the anisotropy of the crystal, the refractive-index dispersion, and the reflections of the fundamental and the second harmonic waves inside the material. Complete expressions for the generated second harmonic intensity are given for birefringent crystals for the case of no pump depletion. A comparison between theory and experimental results is made, showing the accuracy of our theoretical expressions.
Alfven waves in the auroral ionosphere: A numerical model compared with measurements
International Nuclear Information System (INIS)
Knudsen, D.J.; Kelley, M.C.; Vickrey, J.F.
1992-01-01
The authors solve a linear numerical model of Alfven waves reflecting from the high-latitude ionosphere, both to better understanding the role of the ionosphere in the magnetosphere/ionosphere coupling process and to compare model results with in situ measurements. They use the model to compute the frequency-dependent amplitude and phase relations between the meridional electric and the zonal magnetic fields due to Alfven waves. These relations are compared with measurements taken by an auroral sounding rocket flow in the morningside oval and by the HILAT satellite traversing the oval at local noon. The sounding rocket's trajectory was mostly parallel to the auroral oval, and is measured enhanced fluctuating field energy in regions of electron precipitation. The rocket-measured phase data are in excellent agreement with the Alfven wave model, and the relation between the modeled and the measured by HILAT are related by the height-integrated Pedersen conductivity Σ p , indicating that the measured field fluctuations were due mainly to structured field-aligned current systems. A reason for the relative lack of Alfven wave energy in the HILAT measurements could be the fact that the satellite traveled mostly perpendicular to the oval and therefore quickly traversed narrow regions of electron precipitation and associated wave activity
Magnetospheric pulsations: Models and observations of compressional waves
International Nuclear Information System (INIS)
Zhu, Xiaoming.
1989-01-01
The first part of the dissertation models ultralow frequency (ULF) waves in a simplified geometry in order to understand the physics of the mode coupling between the compressional and shear Alfven waves in an inhomogeneous magnetized plasma. Wave mode coupling occurs when a field line resonant frequency (defined by the shear Alfven mode) matches the global mode frequency (defined by the compressional mode). Large wave amplitudes occur near the resonant field line. Although the wave amplitude of the global mode is small away from resonant field lines, significant wave energy is stored in the wave mode due to its large scale nature. It serves as a reservoir to continuously feed energy to resonant field lines. This mechanism may explain why some field line resonances can last for times longer than that predicted from the ionospheric Joule dissipation. A nonmonotonic Alfven velocity divides the magnetosphere into two or more cavities by the local maxima of the Alfven velocity. The global mode is typically localized in one of the cavities except at some preferred frequencies, the global mode can extend through more than one cavity. This may explain ULF wave excitations in the low latitude magnetosphere. The second part of the dissertation is devoted to study compressional waves in the outer magnetosphere using magnetic field and plasma data. Statistical information on the distribution of compressional Pc 5 waves in the outer magnetosphere is obtained. Large amplitude, long period compressional Pc 5 pulsations are found very common near the magnetic equator. They are polarized mainly in a meridian plane with comparable compressional and transverse amplitudes. Close correlation between compressional wave amplitude and plasma β is also found. Several case studies show that compressional waves are quenched in the region where β < 1
Wave speeds in the macroscopic extended model for ultrarelativistic gases
Energy Technology Data Exchange (ETDEWEB)
Borghero, F., E-mail: borghero@unica.it [Dip. Matematica e Informatica, Università di Cagliari, Via Ospedale 72, 09124 Cagliari (Italy); Demontis, F., E-mail: fdemontis@unica.it [Dip. Matematica, Università di Cagliari, Viale Merello 92, 09123 Cagliari (Italy); Pennisi, S., E-mail: spennisi@unica.it [Dip. Matematica, Università di Cagliari, Via Ospedale 72, 09124 Cagliari (Italy)
2013-11-15
Equations determining wave speeds for a model of ultrarelativistic gases are investigated. This model is already present in literature; it deals with an arbitrary number of moments and it was proposed in the context of exact macroscopic approaches in Extended Thermodynamics. We find these results: the whole system for the determination of the wave speeds can be divided into independent subsystems which are expressed by linear combinations, through scalar coefficients, of tensors all of the same order; some wave speeds, but not all of them, are expressed by square roots of rational numbers; finally, we prove that these wave speeds for the macroscopic model are the same of those furnished by the kinetic model.
Can plane wave modes be physical modes in soliton models?
International Nuclear Information System (INIS)
Aldabe, F.
1995-08-01
I show that plane waves may not be used as asymptotic states in soliton models because they describe unphysical states. When asymptotic states are taken to the physical there is not T-matrix of O(1). (author). 9 refs
Computer modeling of inelastic wave propagation in porous rock
International Nuclear Information System (INIS)
Cheney, J.A.; Schatz, J.F.; Snell, C.
1979-01-01
Computer modeling of wave propagation in porous rock has several important applications. Among them are prediction of fragmentation and permeability changes to be caused by chemical explosions used for in situ resource recovery, and the understanding of nuclear explosion effects such as seismic wave generation, containment, and site hardness. Of interest in all these applications are the distance from the source to which inelastic effects persist and the amount of porosity change within the inelastic region. In order to study phenomena related to these applications, the Cam Clay family of models developed at Cambridge University was used to develop a similar model that is applicable to wave propagation in porous rock. That model was incorporated into a finite-difference wave propagation computer code SOC. 10 figures, 1 table
International Nuclear Information System (INIS)
Matsuda, Y.; Crawford, F.W.
1975-01-01
An economical low-noise plasma simulation model originated by Denavit is applied to a series of problems associated with electrostatic wave propagation in a one-dimensional, collisionless, Maxwellian plasma, in the absence of magnetic field. The model is described and tested, first in the absence of an applied signal, and then with a small amplitude perturbation. These tests serve to establish the low-noise features of the model, and to verify the theoretical linear dispersion relation at wave energy levels as low as 10 -6 of the plasma thermal energy: Better quantitative results are obtained, for comparable computing time, than can be obtained by conventional particle simulation models, or direct solution of the Vlasov equation. The method is then used to study propagation of an essentially monochromatic plane wave. Results on amplitude oscillation and nonlinear frequency shift are compared with available theories
The Pedagogical Reflection Model - an educational perspective on clinical decisions
DEFF Research Database (Denmark)
Voergaard Poulsen, Bettina; Vibholm Persson, Stine; Skriver, Mette
Clinical decision-making is important in patient-centred nursing, which is known in nursing education and research (1) The Pedagogical Reflection Model (PRM) can provide a framework that supports students’ decision-making in patient-specific situations. PRM is based on the assumption that clinical......) The aims of this study were to explore how nurse students and clinical supervisors use PRM as method to reflect before, during and after PRM guidance in relation to clinical decisions in the first year of clinical practice...... decision-making needs to take into account; 1) clinical experiences, 2) the perspective of the patient, 3) clinical observations and investigations, 4) knowledge about patients experiences of being a patient and ill, 5) medical knowledge about diseases, and 6) the organizational framework (2,3,4)(Figure 1...
Ocean wave characteristic in the Sunda Strait using Wave Spectrum Model
Rachmayani, R.; Ningsih, N. S.; Adiprabowo, S. R.; Nurfitri, S.
2018-03-01
The wave characteristics including significant wave height and direction, seas and swell in the Sunda Strait are analyzed seasonally to provide marine weather information. This is crucial for establishing secured marine activities between islands of Sumatera and Java. Ocean wave characteristics in the Sunda Strait are simulated for one year (July 1996–June 1977) by using SWAN numerical model. The ocean wave characteristics in the Sunda Strait are divided into three areas of interest; southern, centre and northern part of the Sunda Strait. Despite a weaker local wind, the maximum significant wave height is captured at the southern part with its height of 2.6 m in November compared to other seasonally months. This is associated with the dominated swell from the Indian Ocean contributes on wave energy toward the Sunda Strait. The 2D spectrum analysis exhibits the monthly wave characteristic at southern part that is dominated by seas along the year and swell propagating from the Indian Ocean to the Sunda Strait during December to February (northwest monsoon), May, and November. Seas and swell at northern part of the Sunda Strait are apprehended weaker compared to other parts of the Sunda Strait due to its location is farther from the Indian Ocean.
Shen, Yizhu; Yang, Jiawei; Meng, Hongfu; Dou, Wenbin; Hu, Sanming
2018-04-01
Metasurfaces, orbital angular momenta (OAM), and non-diffractive Bessel beams have been attracting worldwide research. Combining the benefits of these three promising techniques, this paper proposes a metasurface-based reflective-type approach to generate a first-order Bessel beam carrying OAM. To validate this approach, a millimeter-wave metasurface is analyzed, designed, fabricated, and measured. Experimental results agree well with simulation. Moreover, this reflective-type metasurface, generating a Bessel beam with OAM, is inherently integrated with a planar feeding source in the same single-layer printed circuit board. Therefore, the proposed design features low profile, low cost, easy integration with front-end active circuits, and no alignment error between the feeding source and the metasurface.
An Arctic Ice/Ocean Coupled Model with Wave Interactions
2015-09-30
discussed by DRI participants may aid our understanding as well, e.g. those conducted in the Hamburg Ship Model Basin. Our theoretical advances benefit...the project are – continued modifications to the Arctic wide WIM code in association with advances relating to a new ice/ocean model known as... Auckland , December 2014. Montiel, F. Transmission of ocean waves through a row of randomly perturbed circular ice floes. Minisymposium on Wave Motions of
Modeling Stop-and-Go Waves in Pedestrian Dynamics
Portz, Andrea; Seyfried, Armin
2010-01-01
Several spatially continuous pedestrian dynamics models have been validated against empirical data. We try to reproduce the experimental fundamental diagram (velocity versus density) with simulations. In addition to this quantitative criterion, we tried to reproduce stop-and-go waves as a qualitative criterion. Stop-and-go waves are a characteristic phenomenon for the single file movement. Only one of three investigated models satisfies both criteria.
Kuklik, Pawel; Sanders, Prashanthan; Szumowski, Lukasz; Żebrowski, Jan J
2013-01-01
Various forms of heart disease are associated with remodeling of the heart muscle, which results in a perturbation of cell-to-cell electrical coupling. These perturbations may alter the trajectory of spiral wave drift in the heart muscle. We investigate the effect of spatially extended inhomogeneity of transverse cell coupling on the spiral wave trajectory using a simple active media model. The spiral wave was either attracted or repelled from the center of inhomogeneity as a function of cell excitability and gradient of the cell coupling. High levels of excitability resulted in an attraction of the wave to the center of inhomogeneity, whereas low levels resulted in an escape and termination of the spiral wave. The spiral wave drift velocity was related to the gradient of the coupling and the initial position of the wave. In a diseased heart, a region of altered transverse coupling corresponds with local gap junction remodeling that may be responsible for stabilization-destabilization of spiral waves and hence reflect potentially important targets in the treatment of heart arrhythmias.
Grassi, Davide; Desideri, Giovambattista; Necozione, Stefano; Ruggieri, Fabrizio; Blumberg, Jeffrey B; Stornello, Michele; Ferri, Claudio
2012-09-01
Nitric oxide plays a pivotal role in regulating vascular tone. Different studies show endothelial function is impaired during hyperglycemia. Dark chocolate increases flow-mediated dilation in healthy and hypertensive subjects with and without glucose intolerance; however, the effect of pretreatment with dark chocolate on endothelial function and other vascular responses to hyperglycemia has not been examined. Therefore, we aimed to investigate the effects of flavanol-rich dark chocolate administration on (1) flow-mediated dilation and wave reflections; (2) blood pressure, endothelin-1 and oxidative stress, before and after oral glucose tolerance test (OGTT). Twelve healthy volunteers (5 males, 28.2±2.7 years) randomly received either 100 g/d dark chocolate or flavanol-free white chocolate for 3 days. After 7 days washout period, volunteers were switched to the other treatment. Flow-mediated dilation, stiffness index, reflection index, peak-to-peak time, blood pressure, endothelin-1 and 8-iso-PGF(2α) were evaluated after each treatment phase and OGTT. Compared with white chocolate, dark chocolate ingestion improved flow-mediated dilation (P=0.03), wave reflections, endothelin-1 and 8-iso-PGF(2α) (Pwave reflections, blood pressure, and endothelin-1 and 8-iso-PGF(2α) increased after OGTT. OGTT causes acute, transient impairment of endothelial function and oxidative stress, which is attenuated by flavanol-rich dark chocolate. These results suggest cocoa flavanols may contribute to vascular health by reducing the postprandial impairment of arterial function associated with the pathogenesis of atherosclerosis.
Lin, Shangfei; Sheng, Jinyu
2017-12-01
Depth-induced wave breaking is the primary dissipation mechanism for ocean surface waves in shallow waters. Different parametrizations were developed for parameterizing depth-induced wave breaking process in ocean surface wave models. The performance of six commonly-used parameterizations in simulating significant wave heights (SWHs) is assessed in this study. The main differences between these six parameterizations are representations of the breaker index and the fraction of breaking waves. Laboratory and field observations consisting of 882 cases from 14 sources of published observational data are used in the assessment. We demonstrate that the six parameterizations have reasonable performance in parameterizing depth-induced wave breaking in shallow waters, but with their own limitations and drawbacks. The widely-used parameterization suggested by Battjes and Janssen (1978, BJ78) has a drawback of underpredicting the SWHs in the locally-generated wave conditions and overpredicting in the remotely-generated wave conditions over flat bottoms. The drawback of BJ78 was addressed by a parameterization suggested by Salmon et al. (2015, SA15). But SA15 had relatively larger errors in SWHs over sloping bottoms than BJ78. We follow SA15 and propose a new parameterization with a dependence of the breaker index on the normalized water depth in deep waters similar to SA15. In shallow waters, the breaker index of the new parameterization has a nonlinear dependence on the local bottom slope rather than the linear dependence used in SA15. Overall, this new parameterization has the best performance with an average scatter index of ∼8.2% in comparison with the three best performing existing parameterizations with the average scatter index between 9.2% and 13.6%.
Modeling elastic wave propagation in kidney stones with application to shock wave lithotripsy.
Cleveland, Robin O; Sapozhnikov, Oleg A
2005-10-01
A time-domain finite-difference solution to the equations of linear elasticity was used to model the propagation of lithotripsy waves in kidney stones. The model was used to determine the loading on the stone (principal stresses and strains and maximum shear stresses and strains) due to the impact of lithotripsy shock waves. The simulations show that the peak loading induced in kidney stones is generated by constructive interference from shear waves launched from the outer edge of the stone with other waves in the stone. Notably the shear wave induced loads were significantly larger than the loads generated by the classic Hopkinson or spall effect. For simulations where the diameter of the focal spot of the lithotripter was smaller than that of the stone the loading decreased by more than 50%. The constructive interference was also sensitive to shock rise time and it was found that the peak tensile stress reduced by 30% as rise time increased from 25 to 150 ns. These results demonstrate that shear waves likely play a critical role in stone comminution and that lithotripters with large focal widths and short rise times should be effective at generating high stresses inside kidney stones.
International Nuclear Information System (INIS)
Chang, C C; Hsiao, T C; Kao, S C; Hsu, H Y
2014-01-01
Arterial blood pressure (ABP) is an important indicator of cardiovascular circulation and presents various intrinsic regulations. It has been found that the intrinsic characteristics of blood vessels can be assessed quantitatively by ABP analysis (called reflection wave analysis (RWA)), but conventional RWA is insufficient for assessment during non-stationary conditions, such as the Valsalva maneuver. Recently, a novel adaptive method called empirical mode decomposition (EMD) was proposed for non-stationary data analysis. This study proposed a RWA algorithm based on EMD (EMD-RWA). A total of 51 subjects participated in this study, including 39 healthy subjects and 12 patients with autonomic nervous system (ANS) dysfunction. The results showed that EMD-RWA provided a reliable estimation of reflection time in baseline and head-up tilt (HUT). Moreover, the estimated reflection time is able to assess the ANS function non-invasively, both in normal, healthy subjects and in the patients with ANS dysfunction. EMD-RWA provides a new approach for reflection time estimation in non-stationary conditions, and also helps with non-invasive ANS assessment. (paper)
Effects of Defect Size and Number Density on the Transmission and Reflection of Guided Elastic Waves
2016-04-22
localized region, a photoacoustic source generates elastic waves on one side of the damaged region, and then two ultrasound transducers measure the...Panther OPO) operating at 1.55um and with a pulse width of 7ns, a repetition rate of 30Hz and an average power of 65mW. This configuration seems...where the defects are of the same order as the wavelength of the ultrasound , we find ourselves confronted with Mie scattering, which has weaker
Geometric models of nested field wave forms
International Nuclear Information System (INIS)
Winters, D.
1984-01-01
The authors start with two dimensions. ''Maybe there's this thing we ought to call a 'compressible medium' that seems to be around here''. Maybe it's air or ether. There seems to be this compressible medium which has this quality which is that it conveys inertia momentum. And it is compressible. So, given that, and given not much else, they ought to be able to build things like atomic tables and fundamental concepts of physics. The idea is that the principles of creation are principles of superposition of wave shapes. The suggestion is that wave shape archetypally, naturally builds geometry, and that is the clue to the information structure of atoms and molecules and people
Nonlinear plasma wave models in 3D fluid simulations of laser-plasma interaction
Chapman, Thomas; Berger, Richard; Arrighi, Bill; Langer, Steve; Banks, Jeffrey; Brunner, Stephan
2017-10-01
Simulations of laser-plasma interaction (LPI) in inertial confinement fusion (ICF) conditions require multi-mm spatial scales due to the typical laser beam size and durations of order 100 ps in order for numerical laser reflectivities to converge. To be computationally achievable, these scales necessitate a fluid-like treatment of light and plasma waves with a spatial grid size on the order of the light wave length. Plasma waves experience many nonlinear phenomena not naturally described by a fluid treatment, such as frequency shifts induced by trapping, a nonlinear (typically suppressed) Landau damping, and mode couplings leading to instabilities that can cause the plasma wave to decay rapidly. These processes affect the onset and saturation of stimulated Raman and Brillouin scattering, and are of direct interest to the modeling and prediction of deleterious LPI in ICF. It is not currently computationally feasible to simulate these Debye length-scale phenomena in 3D across experimental scales. Analytically-derived and/or numerically benchmarked models of processes occurring at scales finer than the fluid simulation grid offer a path forward. We demonstrate the impact of a range of kinetic processes on plasma reflectivity via models included in the LPI simulation code pF3D. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Larmat, C. S.; Rougier, E.; Delorey, A.; Steedman, D. W.; Bradley, C. R.
2016-12-01
The goal of the Source Physics Experiment (SPE) is to bring empirical and theoretical advances to the problem of detection and identification of underground nuclear explosions. For this, the SPE program includes a strong modeling effort based on first principles calculations with the challenge to capture both the source and near-source processes and those taking place later in time as seismic waves propagate within complex 3D geologic environments. In this paper, we report on results of modeling that uses hydrodynamic simulation codes (Abaqus and CASH) coupled with a 3D full waveform propagation code, SPECFEM3D. For modeling the near source region, we employ a fully-coupled Euler-Lagrange (CEL) modeling capability with a new continuum-based visco-plastic fracture model for simulation of damage processes, called AZ_Frac. These capabilities produce high-fidelity models of various factors believed to be key in the generation of seismic waves: the explosion dynamics, a weak grout-filled borehole, the surrounding jointed rock, and damage creation and deformations happening around the source and the free surface. SPECFEM3D, based on the Spectral Element Method (SEM) is a direct numerical method for full wave modeling with mathematical accuracy. The coupling interface consists of a series of grid points of the SEM mesh situated inside of the hydrodynamic code's domain. Displacement time series at these points are computed using output data from CASH or Abaqus (by interpolation if needed) and fed into the time marching scheme of SPECFEM3D. We will present validation tests with the Sharpe's model and comparisons of waveforms modeled with Rg waves (2-8Hz) that were recorded up to 2 km for SPE. We especially show effects of the local topography, velocity structure and spallation. Our models predict smaller amplitudes of Rg waves for the first five SPE shots compared to pure elastic models such as Denny &Johnson (1991).
Winter radiation extinction and reflection in a boreal pine canopy: measurements and modelling
International Nuclear Information System (INIS)
Pomeroy, J.W.; Dion, K.
1996-01-01
Predicting the rate of snow melt and intercepted snow sublimation in boreal forests requires an understanding of the effects of snow-covered conifers on the exchange of radiant energy. This study examined the amount of intercepted snow on a jack pine canopy in the boreal forest of central Saskatchewan and the shortwave and net radiation exchange with this canopy, to determine the effect of intercepted snow and canopy structure on shortwave radiation reflection and extinction and net radiation attenuation in a boreal forest. The study focused on clear sky conditions, which are common during winter in the continental boreal forest. Intercepted snow was found to have no influence on the clear-sky albedo of the canopy, the extinction of short wave radiation by the canopy or ratio of net radiation at the canopy top to that at the surface snow cover. Because of the low albedo of the snow-covered canopy, net radiation at the canopy top remains positive and a large potential source of energy for sublimation. The canopy albedo declines somewhat as the extinction efficiency of the underlying canopy increases. The extinction efficiency of short wave radiation in the canopy depends on solar angle because of the approximately horizontal orientation of pine branches. For low solar angles above the horizon, the extinction efficiency is quite low and short wave transmissivity through the canopy is relatively high. As the solar angle increases, extinction increases up to angles of about 50°, and then declines. Extinction of short wave radiation in the canopy strongly influences the attenuation of net radiation by the canopy. Short wave radiation that is extinguished by branches is radiated as long wave, partly downwards to the snow cover. The ratio of net radiation at the canopy top to that at the snow cover surface increases with the extinction of short wave radiation and is negative for low extinction efficiencies. For the pine canopy examined, the daily mean net radiation at
Holographic p-wave superconductor models with Weyl corrections
Directory of Open Access Journals (Sweden)
Lu Zhang
2015-04-01
Full Text Available We study the effect of the Weyl corrections on the holographic p-wave dual models in the backgrounds of AdS soliton and AdS black hole via a Maxwell complex vector field model by using the numerical and analytical methods. We find that, in the soliton background, the Weyl corrections do not influence the properties of the holographic p-wave insulator/superconductor phase transition, which is different from that of the Yang–Mills theory. However, in the black hole background, we observe that similarly to the Weyl correction effects in the Yang–Mills theory, the higher Weyl corrections make it easier for the p-wave metal/superconductor phase transition to be triggered, which shows that these two p-wave models with Weyl corrections share some similar features for the condensation of the vector operator.
Wave Model Development in Multi-Ion Plasmas
Directory of Open Access Journals (Sweden)
Sung-Hee Song
1999-06-01
Full Text Available Near-earth space is composed of plasmas which embed a number of plasma waves. Space plasmas consist of electrons and multi-ion that determine local wave propagation characteristics. In multi-ion plasmas, it is di cult to find out analytic solution from the dispersion relation in general. In this work, we have developed a model with an arbitrary magnetic field and density as well as multi-ion plasmas. This model allows us to investigate how plasma waves behave when they propagate along realistic magnetic field lines, which are assumed by IGRF(International Geomagnetic Reference Field. The results are found to be useful for the analysis of the in situ observational data in space. For instance, if waves are assumed to propagate into the polar region, from the equatorial region, our model quantitatively shows how polarization is altered along earth travel path.
Collapse of the wave function models, ontology, origin, and implications
2018-01-01
This is the first single volume about the collapse theories of quantum mechanics, which is becoming a very active field of research in both physics and philosophy. In standard quantum mechanics, it is postulated that when the wave function of a quantum system is measured, it no longer follows the Schrödinger equation, but instantaneously and randomly collapses to one of the wave functions that correspond to definite measurement results. However, why and how a definite measurement result appears is unknown. A promising solution to this problem are collapse theories in which the collapse of the wave function is spontaneous and dynamical. Chapters written by distinguished physicists and philosophers of physics discuss the origin and implications of wave-function collapse, the controversies around collapse models and their ontologies, and new arguments for the reality of wave function collapse. This is an invaluable resource for students and researchers interested in the philosophy of physics and foundations of ...
DEFF Research Database (Denmark)
Rasmussen, Anders Rønne; Sørensen, Mads Peter; Gaididei, Yuri Borisovich
2011-01-01
A wave equation including nonlinear terms up to the second order for a thermoviscous Newtonian fluid is proposed. In the lossless case this equation results from an expansion to third order of the Lagrangian for the fundamental non-dissipative fluid dynamical equations. Thus it preserves the Hami...... is proposed. The dynamics of the rarefaction wave is approximated by a collective coordinate approach in the energy balance equation. © 2010 Springer Science+Business Media B.V.......A wave equation including nonlinear terms up to the second order for a thermoviscous Newtonian fluid is proposed. In the lossless case this equation results from an expansion to third order of the Lagrangian for the fundamental non-dissipative fluid dynamical equations. Thus it preserves...... the Hamiltonian structure, in contrast to the Kuznetsov equation, a model often used in nonlinear acoustics. An exact traveling wave front solution is derived from a generalized traveling wave assumption for the velocity potential. Numerical studies of the evolution of a number of arbitrary initial conditions...
DEFF Research Database (Denmark)
Larsén, Xiaoli Guo; Bolanos, Rodolfo; Du, Jianting
modeling for oshore wind farms. This modeling system consists of the atmospheric Weather Research and Forecasting (WRF) model, the wave model SWAN and an interface the Wave Boundary Layer Model WBLM, within the framework of coupled-ocean-atmosphere-wave-sediment transport modeling system COAWST...... (Hereinafter the WRF-WBLM-SWAN model). WBLM is implemented in SWAN, and it calculates stress and kinetic energy budgets in the lowest atmospheric layer where the wave-induced stress is introduced to the atmospheric modeling. WBLM ensures consistent calculation of stress for both the atmospheric and wave......, which can aect the choice of the off-shore wind turbine type. X-WiWa examined various methodologies for wave modeling. The offline coupling system using atmospheric data such as WRF or global reanalysis wind field to the MIKE 21 SW model has been improved with considerations of stability, air density...
Hybrid Modelling of a Traveling Wave Piezoelectric Motor
DEFF Research Database (Denmark)
El, Ghouti N.
a theoretical model is derived. Since the dynamic characteristics of the real motor are difficult to capture in an analytical model, and the parameters of the motor are time varying and highly nonlinear, then some assumptions are required in order to simplify the modeling task and thus provide a suitable model......This thesis considers the modeling of the traveling wave piezoelectric motor (PEM). The rotary traveling wave ultrasonic motor "Shinsei type USR60" is the case study considered in this work. The traveling wave PEM has excellent performance and many useful features such as high holding torque, high....... Despite many attempts a lumped motor model of the PEM is unavailable so far. The dynamical characteristics of the PEM are complicated, highly nonlinear, and the motor parameters are time varying due to temperature rise and changes in motor drive operating conditions. Therefore it is difficult to predict...
Spectral analysis of surface waves method to assess shear wave velocity within centrifuge models
Murillo, Carol Andrea; Thorel, Luc; Caicedo, Bernardo
2009-06-01
The method of the spectral analysis of surface waves (SASW) is tested out on reduced scale centrifuge models, with a specific device, called the mini Falling Weight, developed for this purpose. Tests are performed on layered materials made of a mixture of sand and clay. The shear wave velocity VS determined within the models using the SASW is compared with the laboratory measurements carried out using the bender element test. The results show that the SASW technique applied to centrifuge testing is a relevant method to characterize VS near the surface.
A model for calculating specular and diffuse reflections in outdoor sound propagation
Salomons, E.M.
2006-01-01
In many practical outdoor situations, the direct sound path between a noise source and a receiver is screened by an obstacle. In these situations indirect sound paths become important, in particular reflections of sound waves. Reflections may occur at objects such as a vertical wall, but also at the
Modelling of wave propagation over a submerged sand bar using SWASH
Digital Repository Service at National Institute of Oceanography (India)
Jishad, M.; Vu, T.T.T.; JayaKumar, S.
cases The wave heights and wave induced velocities obtained from the model and the laboratory experimental resultsare compared The model without the morphology feedback provided good correlation with the measurements for case of low wave energy, whereas...
Asteroid thermal modeling in the presence of reflected sunlight
Myhrvold, Nathan
2018-03-01
A new derivation of simple asteroid thermal models is presented, investigating the need to account correctly for Kirchhoff's law of thermal radiation when IR observations contain substantial reflected sunlight. The framework applies to both the NEATM and related thermal models. A new parameterization of these models eliminates the dependence of thermal modeling on visible absolute magnitude H, which is not always available. Monte Carlo simulations are used to assess the potential impact of violating Kirchhoff's law on estimates of physical parameters such as diameter and IR albedo, with an emphasis on NEOWISE results. The NEOWISE papers use ten different models, applied to 12 different combinations of WISE data bands, in 47 different combinations. The most prevalent combinations are simulated and the accuracy of diameter estimates is found to be depend critically on the model and data band combination. In the best case of full thermal modeling of all four band the errors in an idealized model the 1σ (68.27%) confidence interval is -5% to +6%, but this combination is just 1.9% of NEOWISE results. Other combinations representing 42% of the NEOWISE results have about twice the CI at -10% to +12%, before accounting for errors due to irregular shape or other real world effects that are not simulated. The model and data band combinations found for the majority of NEOWISE results have much larger systematic and random errors. Kirchhoff's law violation by NEOWISE models leads to errors in estimation accuracy that are strongest for asteroids with W1, W2 band emissivity ɛ12 in both the lowest (0.605 ≤ɛ12 ≤ 0 . 780), and highest decile (0.969 ≤ɛ12 ≤ 0 . 988), corresponding to the highest and lowest deciles of near-IR albedo pIR. Systematic accuracy error between deciles ranges from a low of 5% to as much as 45%, and there are also differences in the random errors. Kirchhoff's law effects also produce large errors in NEOWISE estimates of pIR, particularly for high
Unstructured Spectral Element Model for Dispersive and Nonlinear Wave Propagation
DEFF Research Database (Denmark)
Engsig-Karup, Allan Peter; Eskilsson, Claes; Bigoni, Daniele
2016-01-01
We introduce a new stabilized high-order and unstructured numerical model for modeling fully nonlinear and dispersive water waves. The model is based on a nodal spectral element method of arbitrary order in space and a -transformed formulation due to Cai, Langtangen, Nielsen and Tveito (1998). In...
Characteristics of light reflected from a dense ionization wave with a tunable velocity
Zhidkov, A.; Esirkepov, T.; Fujii, T.; Nemoto, K.; Koga, J.; Bulanov, S. V.
2009-01-01
An optically-dense ionization wave (IW) produced by two femtosecond laser pulses focused cylindrically and crossing each other is shown to be an efficient coherent x-ray converter. The resulting velocity of a quasi-plane IW in the vicinity of pulse intersection increases with the angle between the pulses from the group velocity of ionizing pulses to infinity allowing an easy tuning the wavelength of x-rays. The x-ray spectra of a converted, lower frequency coherent light change from the monoc...
Characteristics of light reflected from a dense ionization wave with a tunable velocity.
Zhidkov, A; Esirkepov, T; Fujii, T; Nemoto, K; Koga, J; Bulanov, S V
2009-11-20
An optically dense ionization wave (IW) produced by two femtosecond (approximately 10/30 fs) laser pulses focused cylindrically and crossing each other may become an efficient coherent x-ray converter in accordance with the Semenova-Lampe theory. The resulting velocity of a quasiplane IW in the vicinity of pulse intersection changes with the angle between the pulses from the group velocity of ionizing pulses to infinity allowing a tuning of the wavelength of x rays and their bunching. The x-ray spectra after scattering of a lower frequency and long coherent light pulse change from the monochromatic to high order harmoniclike with the duration of the ionizing pulses.
Self-organized Criticality Model for Ocean Internal Waves
International Nuclear Information System (INIS)
Wang Gang; Hou Yijun; Lin Min; Qiao Fangli
2009-01-01
In this paper, we present a simple spring-block model for ocean internal waves based on the self-organized criticality (SOC). The oscillations of the water blocks in the model display power-law behavior with an exponent of -2 in the frequency domain, which is similar to the current and sea water temperature spectra in the actual ocean and the universal Garrett and Munk deep ocean internal wave model [Geophysical Fluid Dynamics 2 (1972) 225; J. Geophys. Res. 80 (1975) 291]. The influence of the ratio of the driving force to the spring coefficient to SOC behaviors in the model is also discussed. (general)
Modelling Acoustic Wave Propagation in Axisymmetric Varying-Radius Waveguides
DEFF Research Database (Denmark)
Bæk, David; Willatzen, Morten
2008-01-01
A computationally fast and accurate model (a set of coupled ordinary differential equations) for fluid sound-wave propagation in infinite axisymmetric waveguides of varying radius is proposed. The model accounts for fluid heat conduction and fluid irrotational viscosity. The model problem is solved...... by expanding solutions in terms of cross-sectional eigenfunctions following Stevenson’s method. A transfer matrix can be easily constructed from simple model responses of a given waveguide and later used in computing the response to any complex wave input. Energy losses due to heat conduction and viscous...
Test particle modeling of wave-induced energetic electron precipitation
International Nuclear Information System (INIS)
Chang, H.C.; Inan, U.S.
1985-01-01
A test particle computer model of the precipitation of radiation belt electrons is extended to compute the dynamic energy spectrum of transient electron fluxes induced by short-duration VLF wave packets traveling along the geomagnetic field lines. The model is adapted to estimate the count rate and associated spectrum of precipitated electrons that would be observed by satellite-based particle detectors with given geometric factor and orientation with respect to the magnetic field. A constant-frequency wave pulse and a lightning-induced whistler wave packet are used as examples of the stimulating wave signals. The effects of asymmetry of particle mirror heights in the two hemispheres and the atmospheric backscatter of loss cone particles on the computed precipitated fluxes are discussed
Suppression of Spiral Wave in Modified Orengonator Model
International Nuclear Information System (INIS)
Ma Jun; Wang Chunni; Jin Wuyin; Yi Ming
2008-01-01
In this paper, a spatial perturbation scheme is proposed to suppress the spiral wave in the modified Orengonator model, which is used to describe the chemical reaction in the light-sensitive media. The controllable external illumination Φ is perturbed with a spatial linear function. In our numerical simulation, the scheme is investigated by imposing the external controllable illumination on the space continuously and/or intermittently. The numerical simulation results confirm that the stable rotating spiral wave still can be removed with the scheme proposed in this paper even if the controllable Φ changed vs. time and space synchronously. Then the scheme is also used to control the spiral wave and turbulence in the modified Fitzhugh-Nagumo model. It is found that the scheme is effective to remove the sable rotating and meandering spiral wave but it costs long transient period and intensity of the gradient parameter to eliminate the spiral turbulence
DLCQ and plane wave matrix Big Bang models
Blau, Matthias; O'Loughlin, Martin
2008-09-01
We study the generalisations of the Craps-Sethi-Verlinde matrix big bang model to curved, in particular plane wave, space-times, beginning with a careful discussion of the DLCQ procedure. Singular homogeneous plane waves are ideal toy-models of realistic space-time singularities since they have been shown to arise universally as their Penrose limits, and we emphasise the role played by the symmetries of these plane waves in implementing the flat space Seiberg-Sen DLCQ prescription for these curved backgrounds. We then analyse various aspects of the resulting matrix string Yang-Mills theories, such as the relation between strong coupling space-time singularities and world-sheet tachyonic mass terms. In order to have concrete examples at hand, in an appendix we determine and analyse the IIA singular homogeneous plane wave - null dilaton backgrounds.
DLCQ and plane wave matrix Big Bang models
International Nuclear Information System (INIS)
Blau, Matthias; O'Loughlin, Martin
2008-01-01
We study the generalisations of the Craps-Sethi-Verlinde matrix big bang model to curved, in particular plane wave, space-times, beginning with a careful discussion of the DLCQ procedure. Singular homogeneous plane waves are ideal toy-models of realistic space-time singularities since they have been shown to arise universally as their Penrose limits, and we emphasise the role played by the symmetries of these plane waves in implementing the flat space Seiberg-Sen DLCQ prescription for these curved backgrounds. We then analyse various aspects of the resulting matrix string Yang-Mills theories, such as the relation between strong coupling space-time singularities and world-sheet tachyonic mass terms. In order to have concrete examples at hand, in an appendix we determine and analyse the IIA singular homogeneous plane wave - null dilaton backgrounds.
Winter Radiation Extinction and Reflection in a Boreal Pine Canopy: Measurements and Modelling
Pomeroy, J. W.; Dion, K.
1996-12-01
Predicting the rate of snowmelt and intercepted snow sublimation in boreal forests requires an understanding of the effects of snow-covered conifers on the exchange of radiant energy. This study examined the amount of intercepted snow on a jack pine canopy in the boreal forest of central Saskatchewan and the shortwave and net radiation exchange with this canopy, to determine the effect of intercepted snow and canopy structure on shortwave radiation reflection and extinction and net radiation attenuation in a boreal forest. The study focused on clear sky conditions, which are common during winter in the continental boreal forest. Intercepted snow was found to have no influence on the clear-sky albedo of the canopy, the extinction of short wave radiation by the canopy or ratio of net radiation at the canopy top to that at the surface snow cover. Because of the low albedo of the snow-covered canopy, net radiation at the canopy top remains positive and a large potential source of energy for sublimation. The canopy albedo declines somewhat as the extinction efficiency of the underlying canopy increases. The extinction efficiency of short wave radiation in the canopy depends on solar angle because of the approximately horizontal orientation of pine branches. For low solar angles above the horizon, the extinction efficiency is quite low and short wave transmissivity through the canopy is relatively high. As the solar angle increases, extinction increases up to angles of about 50̂, and then declines. Extinction of short wave radiation in the canopy strongly influences the attenuation of net radiation by the canopy. Short wave radiation that is extinguished by branches is radiated as long wave, partly downwards to the snow cover. The ratio of net radiation at the canopy top to that at the snow cover surface increases with the extinction of short wave radiation and is negative for low extinction efficiencies. For the pine canopy examined, the daily mean net radiation at the
Wavefronts, light rays and caustic of a circular wave reflected by an arbitrary smooth curve
International Nuclear Information System (INIS)
Marciano-Melchor, Magdalena; Silva-Ortigoza, Ramón; Montiel-Piña, Enrique; Román-Hernández, Edwin; Santiago-Santiago, José Guadalupe; Silva-Ortigoza, Gilberto; Rosado, Alfonso; Suárez-Xique, Román
2011-01-01
The aim of the present work is to obtain expressions for both the wavefront train and the caustic associated with the light rays reflected by an arbitrary smooth curve after being emitted by a point light source located at an arbitrary position in the two-dimensional free space. To this end, we obtain an expression for the k-function associated with the general integral of Stavroudis to the eikonal equation that describes the evolution of the reflected light rays. The caustic is computed by using the definitions of the critical and caustic sets of the two-dimensional map that describes the evolution of an arbitrary wavefront associated with the general integral. The general results are applied to circular and parabolic mirrors. The main motivation to carry out this research is to establish, in future work, the caustic touching theorem in a two-dimensional optical medium and to study the diffraction problem by using the k-function concept. Both problems are important in the computation of the image of an arbitrary object under reflection and refraction
Loi, Shyeh Tjing; Papaloizou, John C. B.
2018-04-01
The spectrum of oscillation modes of a star provides information not only about its material properties (e.g. mean density), but also its symmetries. Spherical symmetry can be broken by rotation and/or magnetic fields. It has been postulated that strong magnetic fields in the cores of some red giants are responsible for their anomalously weak dipole mode amplitudes (the "dipole dichotomy" problem), but a detailed understanding of how gravity waves interact with strong fields is thus far lacking. In this work, we attack the problem through a variety of analytical and numerical techniques, applied to a localised region centred on a null line of a confined axisymmetric magnetic field which is approximated as being cylindrically symmetric. We uncover a rich variety of phenomena that manifest when the field strength exceeds a critical value, beyond which the symmetry is drastically broken by the Lorentz force. When this threshold is reached, the spatial structure of the g-modes becomes heavily altered. The dynamics of wave packet propagation transitions from regular to chaotic, which is expected to fundamentally change the organisation of the mode spectrum. In addition, depending on their frequency and the orientation of field lines with respect to the stratification, waves impinging on different parts of the magnetised region are found to undergo either reflection or trapping. Trapping regions provide an avenue for energy loss through Alfvén wave phase mixing. Our results may find application in various astrophysical contexts, including the dipole dichotomy problem, the solar interior, and compact star oscillations.
Modeling wave attenuation by salt marshes in Jamaica Bay, New York, using a new rapid wave model
Marsooli, Reza; Orton, Philip M.; Mellor, George
2017-07-01
Using a new rapid-computation wave model, improved and validated in the present study, we quantify the value of salt marshes in Jamaica Bay—a highly urbanized estuary located in New York City—as natural buffers against storm waves. We augment the MDO phase-averaged wave model by incorporating a vegetation-drag-induced energy dissipation term into its wave energy balance equation. We adopt an empirical formula from literature to determine the vegetation drag coefficient as a function of environmental conditions. Model evaluation using data from laboratory-scale experiments show that the improved MDO model accurately captures wave height attenuation due to submerged and emergent vegetation. We apply the validated model to Jamaica Bay to quantify the influence of coastal-scale salt marshes on storm waves. It is found that the impact of marsh islands is largest for storms with lower flood levels, due to wave breaking on the marsh island substrate. However, the role of the actual marsh plants, Spartina alterniflora, grows larger for storms with higher flood levels, when wave breaking does not occur and the vegetative drag becomes the main source of energy dissipation. For the latter case, seasonality of marsh height is important; at its maximum height in early fall, S. alterniflora causes twice the reduction as when it is at a shorter height in early summer. The model results also indicate that the vegetation drag coefficient varies 1 order of magnitude in the study area, and suggest exercising extra caution in using a constant drag coefficient in coastal wetlands.
Directory of Open Access Journals (Sweden)
Doris R. Pierce
2018-02-01
Full Text Available Background: This systematic review and meta-analysis quantified the effect of acute exercise mode on arterial stiffness and wave reflection measures including carotid-femoral pulse wave velocity (cf-PWV, augmentation index (AIx, and heart rate corrected AIx (AIx75.Methods: Using standardized terms, database searches from inception until 2017 identified 45 studies. Eligible studies included acute aerobic and/or resistance exercise in healthy adults, pre- and post-intervention measurements or change values, and described their study design. Data from included studies were analyzed and reported in accordance with the Cochrane Handbook for Systematic Reviews of Interventions and PRISMA guidelines. Meta-analytical data were reported via forest plots using absolute differences with 95% confidence intervals with the random effects model accounting for between-study heterogeneity. Reporting bias was assessed via funnel plots and, individual studies were evaluated for bias using the Cochrane Collaboration's tool for assessing risk of bias. A modified PEDro Scale was applied to appraise methodological concerns inherent to included studies.Results: Acute aerobic exercise failed to change cf-PWV (mean difference: 0.00 ms−1 [95% confidence interval: −0.11, 0.11], p = 0.96, significantly reduced AIx (−4.54% [−7.05, −2.04], p = 0.0004 and significantly increased AIx75 (3.58% [0.56, 6.61], p = 0.02. Contrastingly, acute resistance exercise significantly increased cf-PWV (0.42 ms−1 [0.17, 0.66], p = 0.0008, did not change AIx (1.63% [−3.83, 7.09], p = 0.56, and significantly increased AIx75 (15.02% [8.71, 21.33], p < 0.00001. Significant heterogeneity was evident within all comparisons except cf-PWV following resistance exercise, and several methodological concerns including low applicability of exercise protocols and lack of control intervention were identified.Conclusions: Distinct arterial stiffness and wave reflection responses were identified
Numerical Modeling of a Wave Energy Point Absorber
DEFF Research Database (Denmark)
Hernandez, Lorenzo Banos; Frigaard, Peter; Kirkegaard, Poul Henning
2009-01-01
The present study deals with numerical modelling of the Wave Star Energy WSE device. Hereby, linear potential theory is applied via a BEM code on the wave hydrodynamics exciting the floaters. Time and frequency domain solutions of the floater response are determined for regular and irregular seas....... Furthermore, these results are used to estimate the power and the energy absorbed by a single oscillating floater. Finally, a latching control strategy is analysed in open-loop configuration for energy maximization....
Modeling storm waves; Modeliser les houles de tempete
Energy Technology Data Exchange (ETDEWEB)
Benoit, M.; Marcos, F.; Teisson, Ch
1999-07-01
Nuclear power stations located on the coast take the water they use to cool their circuits from the sea. The water intake and discharge devices must be able to operate in all weathers, notably during extreme storms, with waves 10 m high and over. To predict the impact of the waves on the equipment, they are modeled digitally from the moment they form in the middle of the ocean right up to the moment they break on the shore. (authors)
Modeling Waves and Coastal Flooding along the Connecticut Coast
Cifuentes-Lorenzen, A.; Howard-Strobel, M. M.; Fake, T.; McCardell, G.; O'Donnell, J.; Asthita, M.
2015-12-01
We have used a hydrodynamic- wave coupled numerical model (FVCOM-SWAVE) to simulate flooding at the Connecticut coastline during severe storms. The model employed a one-way nesting scheme and an unstructured grid. The parent domain spanned most of the southern New England shelf and the fine resolution grid covered Long Island Sound (LIS) and extended across the Connecticut coast to the 10m elevation contour. The model results for sea level, current and wave statistics from the parent grid have been tested with data from several field campaigns at different locations spanning the western, central and eastern portions of LIS. Waves are fetch limited and improvements to the model-data comparison required modifications to spectral coefficients in the wave model. Finally, the nested results were validated with two field campaigns in shallow water environments (i.e. New Haven and Old Saybrook). To assess the spatial variability of storm wave characteristics the domain was forced with the hindcast winds obtained from meteorological models (NAM and WRF) for 13 severe weather events that affected LIS in the past 15 years. We have also forced the system with a simulation of Superstorm Sandy in a warmer climate to assess the impact a climate change on the character of flooding. The nested grid is currently being used to map flooding risks under severe weather events including the effects of precipitation on river flow and discharge.
Source modelling at the dawn of gravitational-wave astronomy
Gerosa, Davide
2016-09-01
The age of gravitational-wave astronomy has begun. Gravitational waves are propagating spacetime perturbations ("ripples in the fabric of space-time") predicted by Einstein's theory of General Relativity. These signals propagate at the speed of light and are generated by powerful astrophysical events, such as the merger of two black holes and supernova explosions. The first detection of gravitational waves was performed in 2015 with the LIGO interferometers. This constitutes a tremendous breakthrough in fundamental physics and astronomy: it is not only the first direct detection of such elusive signals, but also the first irrefutable observation of a black-hole binary system. The future of gravitational-wave astronomy is bright and loud: the LIGO experiments will soon be joined by a network of ground-based interferometers; the space mission eLISA has now been fully approved by the European Space Agency with a proof-of-concept mission called LISA Pathfinder launched in 2015. Gravitational-wave observations will provide unprecedented tests of gravity as well as a qualitatively new window on the Universe. Careful theoretical modelling of the astrophysical sources of gravitational-waves is crucial to maximize the scientific outcome of the detectors. In this Thesis, we present several advances on gravitational-wave source modelling, studying in particular: (i) the precessional dynamics of spinning black-hole binaries; (ii) the astrophysical consequences of black-hole recoils; and (iii) the formation of compact objects in the framework of scalar-tensor theories of gravity. All these phenomena are deeply characterized by a continuous interplay between General Relativity and astrophysics: despite being a truly relativistic messenger, gravitational waves encode details of the astrophysical formation and evolution processes of their sources. We work out signatures and predictions to extract such information from current and future observations. At the dawn of a revolutionary
Henriksen, Ellen Karoline; Angell, Carl; Vistnes, Arnt Inge; Bungum, Berit
2018-03-01
Quantum physics describes light as having both particle and wave properties; however, there is no consensus about how to interpret this duality on an ontological level. This article explores how pre-university physics students, while working with learning material focusing on historical-philosophical aspects of quantum physics, interpreted the wave-particle duality of light and which views they expressed on the nature of physics. A thematic analysis was performed on 133 written responses about the nature of light, given in the beginning of the teaching sequence, and 55 audio-recorded small-group discussions addressing the wave-particle duality, given later in the sequence. Most students initially expressed a wave and particle view of light, but some of these gave an "uncritical duality description", accepting without question the two ontologically different descriptions of light. In the small-group discussions, students expressed more nuanced views. Many tried to reconcile the two descriptions using semi-classical reasoning; others entered into philosophical discussions about the status of the current scientific description of light and expected science to come up with a better model. Some found the wave description of light particularly challenging and lacked a conception of "what is waving". Many seemed to implicitly take a realist view on the description of physical phenomena, contrary with the Copenhagen interpretation which is prevalent in textbooks. Results are discussed in light of different interpretations of quantum physics, and we conclude by arguing for a historical-philosophical perspective as an entry point for upper secondary physics students to explore the development and interpretation of quantum physical concepts.
Bryan, Sean A; Montroy, Thomas E; Ruhl, John E
2010-11-10
We derive an analytic formula using the Mueller matrix formalism that parameterizes the nonidealities of a half-wave plate (HWP) made from dielectric antireflection-coated birefringent slabs. This model accounts for frequency-dependent effects at normal incidence, including effects driven by the reflections at dielectric boundaries. The model also may be used to guide the characterization of an instrument that uses a HWP. We discuss the coupling of a HWP to different source spectra, and the potential impact of that effect on foreground removal for the SPIDER cosmic microwave background experiment. We also describe a way to use this model in a mapmaking algorithm that fully corrects for HWP nonidealities.
Wave climatology of the Indian Ocean derived from altimetry and wave model
Digital Repository Service at National Institute of Oceanography (India)
Vethamony, P.; Rao, L.V.G.; Kumar, R.; Sarkar, A.; Mohan, M.; Sudheesh, K.; Karthikeyan, S.B.
are found to be low compared to model values. As expected, central Indian Ocean region is found to have higher waves, generally swells, generated by strong winds prevailing over there in all seasons. In July, the entire Arabian Sea is under the influence...
Travelling waves in models of neural tissue: from localised structures to periodic waves
Meijer, Hil Gaétan Ellart; Coombes, Stephen
2014-01-01
We consider travelling waves (fronts, pulses and periodics) in spatially extended one dimensional neural field models. We demonstrate for an excitatory field with linear adaptation that, in addition to an expected stable pulse solution, a stable anti-pulse can exist. Varying the adaptation strength
Attenuation of surface waves in porous media: Shock wave experiments and modelling
Chao, G.E; Smeulders, D.M.J.; Dongen, van M.E.H.
2005-01-01
In this project we conduct experimental and numerical investigations on the attenuation mechanisms of surface waves in poroelastic materials. Viscous dissipation effects are modelled in the framework of Biot's theory. The experiments are performed using a shock tube technique. Quantitative agreement
A REFLECTION ON THE WAVE OF AMALGAMATIONS IN THE ROMANIAN HEALTH SECTOR
Directory of Open Access Journals (Sweden)
Ina MITU
2014-12-01
Full Text Available In the context of New Public Management (NPM and good governance, in the last decade the Romanian public health system has undergone a reform process. One of its consequences is the wave of public hospitals amalgamations that have occurred especially since the adoption of the new health law. Thus, in 2011 the Ministry of Health has made public a list of proposed amalgamations of hospitals (around 25% from total hospitals with beds that existed in that period. The aim of this research is to examine the wave of hospital mergers that occurred in Romania between 2011 and 2012. In particular, the study focuses on the drivers, social impact, typology and purpose of the analysed amalgamations. The study uses primary resources documents and it is based on a content analysis of 25 Government Decisions and Substantiation Notes from 2011 to 2012. An important generalization of the paper is that all the amalgamations from the analysed period are involuntary and are selected on territorial criteria and depending on the distance, the specific health services for the purpose of efficient use of human and material resources in order to enhance public health services. Additionally, the expected social impact of these events is materialized mainly in improving the quality of medical services provided to the population and providing unconditional access to medical services for policyholders. The expected changes include: reduction of staff costs; efficient use of public services; classifying the amalgamated hospitals in a higher category; reduction of management positions; optimizing medical activity in terms of economic efficiency; and achieving a management capable of the best use of existing financial resources.
Simulating Freak Waves in the Ocean with CFD Modeling
Manolidis, M.; Orzech, M.; Simeonov, J.
2017-12-01
Rogue, or freak, waves constitute an active topic of research within the world scientific community, as various maritime authorities around the globe seek to better understand and more accurately assess the risks that the occurrence of such phenomena entail. Several experimental studies have shed some light on the mechanics of rogue wave formation. In our work we numerically simulate the formation of such waves in oceanic conditions by means of Computational Fluid Dynamics (CFD) software. For this purpose we implement the NHWAVE and OpenFOAM software packages. Both are non-hydrostatic, turbulent flow solvers, but NHWAVE implements a shock-capturing scheme at the free surface-interface, while OpenFOAM utilizes the Volume Of Fluid (VOF) method. NHWAVE has been shown to accurately reproduce highly nonlinear surface wave phenomena, such as soliton propagation and wave shoaling. We conducted a range of tests simulating rogue wave formation and horizontally varying currents to evaluate and compare the capabilities of the two software packages. Then we used each model to investigate the effect of ocean currents and current gradients on the formation of rogue waves. We present preliminary results.
Kingsley, J Derek; Tai, Yu Lun; Mayo, Xian; Glasgow, Alaina; Marshall, Erica
2017-09-01
We sought to determine the sex-specific effects of an acute bout of free-weight resistance exercise (RE) on pulse wave reflection (aortic blood pressures, augmentation index (AIx), AIx at 75 bpm (AIx@75), augmentation pressure (AP), time of the reflected wave (Tr), subendocardial viability ratio (SEVR)), and aortic arterial stiffness in resistance-trained individuals. Resistance-trained men (n = 14) and women (n = 12) volunteered to participate in the study. Measurements were taken in the supine position at rest, and 10 minutes after 3 sets of 10 repetitions at 75% 1-repetition maximum on the squat, bench press, and deadlift. A 2 × 2 × 2 ANOVA was used to analyse the effects of sex (men, women) across condition (RE, control) and time (rest, recovery). There were no differences between sexes across conditions and time. There was no effect of the RE on brachial or aortic blood pressures. There were significant condition × time interactions for AIx (rest: 12.1 ± 7.9%; recovery: 19.9 ± 10.5%, p = .003), AIx@75 (rest: 5.3 ± 7.9%; recovery: 24.5 ± 14.3%, p = .0001), AP (rest: 4.9 ± 2.8 mmHg; recovery: 8.3 ± 6.0 mmHg, p = .004), and aortic arterial stiffness (rest: 5.3 ± 0.6 ms; recovery: 5.9 ± 0.7 ms, p = .02) with significant increases during recovery from the acute RE. There was also a significant condition × time for time of the reflected wave (rest: 150 ± 7 ms; recovery: 147 ± 9 ms, p = .02) and SEVR (rest: 147 ± 17%; recovery: 83 ± 24%, p = .0001) such that they were reduced during recovery from the acute RE compared to the control. These data suggest that an acute bout of RE increases AIx, AIx@75, and aortic arterial stiffness similarly between men and women without significantly altering aortic blood pressures.
Nixon, C.; Kofman, R.; Schmitt, D. R.; Lofi, J.; Gulick, S. P. S.; Christeson, G. L.; Saustrup, S., Sr.; Morgan, J. V.
2017-12-01
We acquired a closely-spaced vertical seismic profile (VSP) in the Chicxulub K-Pg Impact Crater drilling program borehole to calibrate the existing surface seismic profiles and provide complementary measurements of in situ seismic wave speeds. Downhole seismic records were obtained at spacings ranging from 1.25 m to 5 m along the borehole from 47.5 m to 1325 mwsf (meters wireline below sea floor) (Fig 1a) using a Sercel SlimwaveTM geophone chain (University of Alberta). The seismic source was a 30/30ci Sercel Mini GI airgun (University of Texas), fired a minimum of 5 times per station. Seismic data processing used a combination of a commercial processing package (Schlumberger's VISTA) and MatlabTM codes. The VSP displays detailed reflectivity (Fig. 1a) with the strongest reflection seen at 600 mwsf (280 ms one-way time), geologically corresponding to the sharp contact between the post-impact sediments and the target peak ring rock, thus confirming the pre-drilling interpretations of the seismic profiles. A two-way time trace extracted from the separated up-going wavefield matches the major reflection both in travel time and character. In the granitic rocks that form the peak ring of the Chicxulub impact crater, we observe P-wave velocities of 4000-4500 m/s which are significantly less than the expected values of granitoids ( 6000 m/s) (Fig. 1b). The VSP measured wave speeds are confirmed against downhole sonic logging and in laboratory velocimetry measurements; these data provide additional evidence that the crustal material displaced by the impact experienced a significant amount of damage. Samples and data provided by IODP. Samples can be requested at http://web.iodp.tamu.edu/sdrm after 19 October 2017. Expedition 364 was jointly funded by ECORD, ICDP, and IODP with contributions and logistical support from the Yucatan State Government and UNAM. The downhole seismic chain and wireline system is funded by grants to DRS from the Canada Foundation for Innovation and
A parametric costing model for wave energy technology
International Nuclear Information System (INIS)
1992-01-01
This document describes the philosophy and technical approach to a parametric cost model for offshore wave energy systems. Consideration is given both to existing known devices and other devices yet to be conceptualised. The report is complementary to a spreadsheet based cost estimating model. The latter permits users to derive capital cost estimates using either inherent default data or user provided data, if a particular scheme provides sufficient design definition for more accurate estimation. The model relies on design default data obtained from wave energy device designs and a set of specifically collected cost data. (author)
International Nuclear Information System (INIS)
Reichle, R; Desgranges, C; Faisse, F; Pocheau, C; Lasserre, J-P; Oelhoffen, F; Eupherte, L; Todeschini, M
2009-01-01
Tore Supra has-like ITER-reflecting internal surfaces, which can perturb the machine protection systems based on infrared (IR) thermography. To ameliorate this situation, we have measured and modelled in the 3-5 μm wavelength range the bi-directional reflection distribution function (BRDF) of wall material samples from Tore Supra and conducted in situ reflection measurements and simulated them with the CEA COSMOS code. BRDF results are presented for B 4 C and carbon fibre composite (CFC) tiles. The hemispherical integrated reflection ranges from 0.12 for the B 4 C sample to 0.39 for a CFC tile from the limiter erosion zone. In situ measurements of the IR reflection of a blackbody source off an ICRH and an LHCD antenna of Tore Supra are well reproduced by the simulation.
Energy Technology Data Exchange (ETDEWEB)
Reichle, R; Desgranges, C; Faisse, F; Pocheau, C [CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France); Lasserre, J-P; Oelhoffen, F; Eupherte, L; Todeschini, M [CEA, DAM, CESTA, F-33114 Le Barp (France)
2009-12-15
Tore Supra has-like ITER-reflecting internal surfaces, which can perturb the machine protection systems based on infrared (IR) thermography. To ameliorate this situation, we have measured and modelled in the 3-5 {mu}m wavelength range the bi-directional reflection distribution function (BRDF) of wall material samples from Tore Supra and conducted in situ reflection measurements and simulated them with the CEA COSMOS code. BRDF results are presented for B{sub 4}C and carbon fibre composite (CFC) tiles. The hemispherical integrated reflection ranges from 0.12 for the B{sub 4}C sample to 0.39 for a CFC tile from the limiter erosion zone. In situ measurements of the IR reflection of a blackbody source off an ICRH and an LHCD antenna of Tore Supra are well reproduced by the simulation.
Heat waves over Central Europe in regional climate model simulations
Lhotka, Ondřej; Kyselý, Jan
2014-05-01
Regional climate models (RCMs) have become a powerful tool for exploring impacts of global climate change on a regional scale. The aim of the study is to evaluate the capability of RCMs to reproduce characteristics of major heat waves over Central Europe in their simulations of the recent climate (1961-2000), with a focus on the most severe and longest Central European heat wave that occurred in 1994. We analyzed 7 RCM simulations with a high resolution (0.22°) from the ENSEMBLES project, driven by the ERA-40 reanalysis. In observed data (the E-OBS 9.0 dataset), heat waves were defined on the basis of deviations of daily maximum temperature (Tmax) from the 95% quantile of summer Tmax distribution in grid points over Central Europe. The same methodology was applied in the RCM simulations; we used corresponding 95% quantiles (calculated for each RCM and grid point) in order to remove the bias of modelled Tmax. While climatological characteristics of heat waves are reproduced reasonably well in the RCM ensemble, we found major deficiencies in simulating heat waves in individual years. For example, METNOHIRHAM simulated very severe heat waves in 1996, when no heat wave was observed. Focusing on the major 1994 heat wave, considerable differences in simulated temperature patterns were found among the RCMs. The differences in the temperature patterns were clearly linked to the simulated amount of precipitation during this event. The 1994 heat wave was almost absent in all RCMs that did not capture the observed precipitation deficit, while it was by far most pronounced in KNMI-RACMO that simulated virtually no precipitation over Central Europe during the 15-day period of the heat wave. By contrast to precipitation, values of evaporative fraction in the RCMs were not linked to severity of the simulated 1994 heat wave. This suggests a possible major contribution of other factors such as cloud cover and associated downward shortwave radiation. Therefore, a more detailed
Identification of wind fields for wave modeling near Qatar
Nayak, Sashikant; Balan Sobhana, Sandeepan; Panchang, Vijay
2016-04-01
Due to the development of coastal and offshore infrastructure in and around the Arabian Gulf, a large semi-enclosed sea, knowledge of met-ocean factors like prevailing wind systems, wind generated waves, and currents etc. are of great importance. Primarily it is important to identify the wind fields that are used as forcing functions for wave and circulation models for hindcasting and forecasting purposes. The present study investigates the effects of using two sources of wind-fields on the modeling of wind-waves in the Arabian Gulf, in particular near the coastal regions of Qatar. Two wind sources are considered here, those obtained from ECMWF and those generated by us using the WRF model. The wave model SWAN was first forced with the 6 hourly ERA Interim daily winds (from ECMWF) having spatial resolution of 0.125°. For the second option, wind fields were generated by us using the mesoscale wind model (WRF) with a high spatial resolution (0.1°) at every 30 minute intervals. The simulations were carried out for a period of two months (7th October-7th December, 2015) during which measurements were available from two moored buoys (deployed and operated by the Qatar Meteorological Department), one in the north of Qatar ("Qatar North", in water depth of 58.7 m) and other in the south ("Shiraouh Island", in water depth of 16.64 m). This period included a high-sea event on 11-12th of October, recorded by the two buoys where the significant wave heights (Hs) reached as high as 2.9 m (i.e. max wave height H ~ 5.22 m) and 1.9 (max wave height H ~ 3.4 m) respectively. Model results were compared with the data for this period. The scatter index (SI) of the Hs simulated using the WRF wind fields and the observed Hs was found to be about 30% and 32% for the two buoys (total period). The observed Hs were generally reproduced but there was consistent underestimation. (Maximum 27% for the high-sea event). For the Hs obtained with ERA interim wind fields, the underestimation was
Analytical model of diffuse reflectance spectrum of skin tissue
Energy Technology Data Exchange (ETDEWEB)
Lisenko, S A; Kugeiko, M M; Firago, V A [Belarusian State University, Minsk (Belarus); Sobchuk, A N [B.I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, Minsk (Belarus)
2014-01-31
We have derived simple analytical expressions that enable highly accurate calculation of diffusely reflected light signals of skin in the spectral range from 450 to 800 nm at a distance from the region of delivery of exciting radiation. The expressions, taking into account the dependence of the detected signals on the refractive index, transport scattering coefficient, absorption coefficient and anisotropy factor of the medium, have been obtained in the approximation of a two-layer medium model (epidermis and dermis) for the same parameters of light scattering but different absorption coefficients of layers. Numerical experiments on the retrieval of the skin biophysical parameters from the diffuse reflectance spectra simulated by the Monte Carlo method show that commercially available fibre-optic spectrophotometers with a fixed distance between the radiation source and detector can reliably determine the concentration of bilirubin, oxy- and deoxyhaemoglobin in the dermis tissues and the tissue structure parameter characterising the size of its effective scatterers. We present the examples of quantitative analysis of the experimental data, confirming the correctness of estimates of biophysical parameters of skin using the obtained analytical expressions. (biophotonics)
Travelling Waves in Hybrid Chemotaxis Models
Franz, Benjamin; Xue, Chuan; Painter, Kevin J.; Erban, Radek
2013-01-01
. Bacteria are modelled using an agent-based (individual-based) approach with internal dynamics describing signal transduction. In addition to the chemotactic behaviour of the bacteria, the individual-based model also includes cell proliferation and death
Wave attenuation model for dephasing and measurement of ...
Indian Academy of Sciences (India)
An analysis of previous models to simulate inelastic scattering in such systems is presented and a relatively new model based on wave attenuation is introduced. The problem of Aharonov–Bohm (AB) oscillations in conductance of a mesoscopic ring is studied. We show that the conductance is symmetric under ﬂux reversal ...
A water wave model with horizontal circulation and accurate dispersion
Cotter, C.; Bokhove, Onno
We describe a new water wave model which is variational, and combines a depth-averaged vertical (component of) vorticity with depth-dependent potential flow. The model facilitates the further restriction of the vertical profile of the velocity potential to n-th order polynomials or a finite element
Simple model for decay of laser generated shock waves
International Nuclear Information System (INIS)
Trainor, R.J.
1980-01-01
A simple model is derived to calculate the hydrodynamic decay of laser-generated shock waves. Comparison with detailed hydrocode simulations shows good agreement between calculated time evolution of shock pressure, position, and instantaneous pressure profile. Reliability of the model decreases in regions of the target where superthermal-electron preheat effects become comparable to shock effects
Non-homogeneous polymer model for wave propagation and its ...
African Journals Online (AJOL)
This article concerns certain aspects of four parameter polymer models to study harmonic waves in the non-homogeneous polymer rods of varying density. There are two sections of this paper, in first section, the rheological behaviour of the model is discussed numerically and then it is solved analytically with the help of ...
Numerical modeling of shoreline undulations part 1: Constant wave climate
DEFF Research Database (Denmark)
Kærgaard, Kasper Hauberg; Fredsøe, Jørgen
2013-01-01
integrated flow model, a wave-phase resolving sediment transport description and a one-line shoreline model.First the length of the shoreline undulations is determined in the linear regime using a stability analysis. Next the further evolution from the linear to the fully non-linear regime is described...
Wave-particle duality in a quark model
International Nuclear Information System (INIS)
Gudder, S.P.
1984-01-01
A quark model based on finite-dimensional quantum mechanics is presented. Observables associated with color, flavor, charge, and spin are considered. Using these observables, quark and baryon Hamiltonians are constructed. Wave-particle dualities in this model are pointed out. (Auth.)
TWO-DIMENSIONAL MODELLING OF ACCIDENTAL FLOOD WAVES PROPAGATION
Directory of Open Access Journals (Sweden)
Lorand Catalin STOENESCU
2011-05-01
Full Text Available The study presented in this article describes a modern modeling methodology of the propagation of accidental flood waves in case a dam break; this methodology is applied in Romania for the first time for the pilot project „Breaking scenarios of Poiana Uzului dam”. The calculation programs used help us obtain a bidimensional calculation (2D of the propagation of flood waves, taking into consideration the diminishing of the flood wave on a normal direction to the main direction; this diminishing of the flood wave is important in the case of sinuous courses of water or with urban settlements very close to the minor river bed. In the case of Poiana Uzului dam, 2 scenarios were simulated with the help of Ph.D. Eng. Dan Stematiu, plausible scenarios but with very little chances of actually producing. The results were presented as animations with flooded surfaces at certain time steps successively.
Models for short-wave instability in inviscid shear flows
Grimshaw, Roger
1999-11-01
The generation of instability in an invsicid fluid occurs by a resonance between two wave modes, where here the resonance occurs by a coincidence of phase speeds for a finite, non-zero wavenumber. We show that in the weakly nonlinear limit, the appropriate model consists of two coupled equations for the envelopes of the wave modes, in which the nonlinear terms are balanced with low-order cross-coupling linear dispersive terms rather than the more familiar high-order terms which arise in the nonlinear Schrodinger equation, for instance. We will show that this system may either contain gap solitons as solutions in the linearly stable case, or wave breakdown in the linearly unstable case. In this latter circumstance, the system either exhibits wave collapse in finite time, or disintegration into fine-scale structures.
The Clinical Learning Spiral: A Model to Develop Reflective Practitioners.
Stockhausen, Lynette
1994-01-01
The Clinical Learning Spiral incorporates reflective processes into undergraduate nursing education. It entails successive cycles of four phases: preparative (briefing, planning), constructive (practice development), reflective (debriefing), and reconstructive (planning for change and commitment to action). (SK)
DEFF Research Database (Denmark)
Victor, L.; Troch, P.; Kofoed, Jens Peter
2009-01-01
For overtopping wave energy converters (WECs) a more efficient energy conversion can be achieved when the volumes of water, wave by wave, that enter their reservoir are known and can be predicted. A numerical tool is being developed using a commercial CFD-solver to study and optimize...... nearshore 2Dstructure. First numerical model results are given for a specific test with regular waves, and are compared with the corresponding experimental results in this paper....
Beneduci, Amerigo; Chidichimo, Giuseppe
2012-05-01
Open-ended waveguide reflectometry is a promising tool for permittivity and other material properties calculation at mm-waves (30-300 GHz). Measurement of the reflection coefficient does not require sample manipulation, allowing in vivo and in vitro non destructive studies on cells. Here we used this technique for measuring the power reflection coefficient (reflectivity) of water and Petri dish supported human skin melanoma and keratinocyte cell cultures, in the 53-72 GHz frequency range. The dependence of the reflectivity on polystyrene or glass thickness of the Petri base plate and on the cell layer thickness was analyzed. Permittivity data were then easily retrieved by using a plane wave-dominant mode approach for formulating the reflectivity at the aperture of the flange-mounted open-ended rectangular waveguide probe. Limits and validity of such an approximate approach were analyzed and compared with full-wave near field formulations for which magnitude and phase of the reflection coefficient must be measured and solved using complicated systems of integral equations and extensive numerical calculation. Finally, Petri dish reflectivity measured by the open-ended waveguide method was compared with that numerically simulated under far-field exposure conditions used in a large number of in vitro studies. Such an analysis showed that, under certain conditions, open-ended reflectivity values approach the far field ones.
'Oscillator-wave' model: properties and heuristic instances
International Nuclear Information System (INIS)
Damgov, Vladimir; Trenchev, Plamen; Sheiretsky, Kostadin
2003-01-01
The article considers a generalized model of an oscillator, subjected to the influence of an external wave. It is shown that the systems of diverse physical background, which this model encompasses by their nature, should belong to the broader, proposed in previous works class of 'kick-excited self-adaptive dynamical systems'. The theoretical treatment includes an analytic approach to the conditions for emergence of small and large amplitudes, i.e. weak and strong non-linearity of the system. Derived also are generalized conditions for the transition of systems of this 'oscillator-wave' type to non-regular and chaotic behaviour. For the purpose of demonstrating the heuristic properties of the generalized oscillator-wave model from this point of view are considered the relevant systems and phenomena of the quantized cyclotron resonance and the megaquantum resonance-wave model of the Solar System. We point to a number of other natural and scientific phenomena, which can be effectively analyzed from the point of view of the developed approach. In particular we stress on the possibility for development and the wide applicability of specific wave influences, for example for the improvement and the speeding up of technological processes
Kachkouch, F; Franklin, H; Tinel, A
2018-07-01
The characteristics of the reflection and transmission by a fluid-loaded double porosity layer are studied. The medium obeys the two-pressure field poroelastic phenomenological model of Berryman and Wang. The open pore hydraulic conditions applied at the interfaces yield factorized expressions for the coefficients exhibiting on the one hand a separation allowing to distinguish between symmetrical and antisymmetrical motions and on the other hand the way each of the three dilatational waves associate with the shear wave. The numerical study done for a layer of Berea sandstone saturated by water shows clearly the role of each of the dilatational waves. There are peculiarities such as the absence of the fundamental antisymmetrical mode (zero order) and a singular behaviour of the symmetrical fundamental mode. The low frequency approximation for this latter is derived from the proposed formulas and compared with the numerical results. Copyright © 2018 Elsevier B.V. All rights reserved.
Forward modeling of space-borne gravitational wave detectors
International Nuclear Information System (INIS)
Rubbo, Louis J.; Cornish, Neil J.; Poujade, Olivier
2004-01-01
Planning is underway for several space-borne gravitational wave observatories to be built in the next 10 to 20 years. Realistic and efficient forward modeling will play a key role in the design and operation of these observatories. Space-borne interferometric gravitational wave detectors operate very differently from their ground-based counterparts. Complex orbital motion, virtual interferometry, and finite size effects complicate the description of space-based systems, while nonlinear control systems complicate the description of ground-based systems. Here we explore the forward modeling of space-based gravitational wave detectors and introduce an adiabatic approximation to the detector response that significantly extends the range of the standard low frequency approximation. The adiabatic approximation will aid in the development of data analysis techniques, and improve the modeling of astrophysical parameter extraction
Improvements on Semi-Classical Distorted-Wave model
Energy Technology Data Exchange (ETDEWEB)
Sun Weili; Watanabe, Y.; Kuwata, R. [Kyushu Univ., Fukuoka (Japan); Kohno, M.; Ogata, K.; Kawai, M.
1998-03-01
A method of improving the Semi-Classical Distorted Wave (SCDW) model in terms of the Wigner transform of the one-body density matrix is presented. Finite size effect of atomic nuclei can be taken into account by using the single particle wave functions for harmonic oscillator or Wood-Saxon potential, instead of those based on the local Fermi-gas model which were incorporated into previous SCDW model. We carried out a preliminary SCDW calculation of 160 MeV (p,p`x) reaction on {sup 90}Zr with the Wigner transform of harmonic oscillator wave functions. It is shown that the present calculation of angular distributions increase remarkably at backward angles than the previous ones and the agreement with the experimental data is improved. (author)
Yamauchi, Kazuto; Yamamura, Kazuya; Mimura, Hidekazu; Sano, Yasuhisa; Saito, Akira; Endo, Katsuyoshi; Souvorov, Alexei; Yabashi, Makina; Tamasaku, Kenji; Ishikawa, Tetsuya; Mori, Yuzo
2005-11-10
The intensity flatness and wavefront shape in a coherent hard-x-ray beam totally reflected by flat mirrors that have surface bumps modeled by Gaussian functions were investigated by use of a wave-optical simulation code. Simulated results revealed the necessity for peak-to-valley height accuracy of better than 1 nm at a lateral resolution near 0.1 mm to remove high-contrast interference fringes and appreciable wavefront phase errors. Three mirrors that had different surface qualities were tested at the 1 km-long beam line at the SPring-8/Japan Synchrotron Radiation Research Institute. Interference fringes faded when the surface figure was corrected below the subnanometer level to a spatial resolution close to 0.1 mm, as indicated by the simulated results.
DEFF Research Database (Denmark)
Verbrugghe, Tim; Troch, Peter; Kortenhaus, Andreas
2016-01-01
Wave energy converters (WECs) need to be deployed in large numbers in an array layout in order to have a significant power production. Each WEC has an impact on the incoming wave field, diffracting, reflecting and radiating waves. Simulating the wave transformations within and around a WEC farm...... of a wave-structure interaction solver and a wave propagation model, both based on the potential flow theory. This paper discusses the coupling method and illustrates the functionality with a proof-of-concept. Additionally, a projection of the evolution of the numerical tool is given. It can be concluded...... is complex; it is difficult to simulate both near field and far field effects with a single numerical model, with relatively fast computing times. Within this research a numerical tool is developed to model near-field and far-field wave transformations caused by WECs. The tool is based on the coupling...
Modeling Tides, Planetary Waves, and Equatorial Oscillations in the MLT
Mengel, J. G.; Mayr, H. G.; Drob, D. P.; Porter, H. S.; Bhartia, P. K. (Technical Monitor)
2001-01-01
Applying Hines Doppler Spread Parameterization for gravity waves (GW), our 3D model reproduces some essential features that characterize the observed seasonal variations of tides and planetary waves in the upper mesosphere. In 2D, our model also reproduces the large Semi-Annual Oscillation (SAO) and Quasi Biennial Oscillation (QBO) observed in this region at low latitudes. It is more challenging to describe these features combined in a more comprehensive self consistent model, and we give a progress report that outlines the difficulties and reports some success. In 3D, the GW's are partially absorbed by tides and planetary waves to amplify them. Thus the waves are less efficient in generating the QBO and SAO at equatorial latitudes. Some of this deficiency is compensated by the fact that the GW activity is observed to be enhanced at low latitudes. Increasing the GW source has the desired effect to boost the QBO, but the effect is confined primarily to the stratosphere. With increasing altitude, the meridional circulation becomes more important in redistributing the momentum deposited in the background flow by the GW's. Another factor involved is the altitude at which the GW's originate, which we had originally chosen to be the surface. Numerical experiments show that moving this source altitude to the top of the troposphere significantly increases the efficiency for generating the QBO without affecting much the tides and planetary waves in the model. Attention to the details in which the GW source comes into play thus appears to be of critical importance in modeling the phenomenology of the MLT. Among the suite of numerical experiments reported, we present a simulation that produced significant variations of tides and planetary waves in the upper mesosphere. The effect is related to the QBO generated in the model, and GW filtering is the likely cause.
Lappa, Marcello; Drikakis, Dimitris; Kokkinakis, Ioannis
2017-03-01
This paper concerns the propagation of shock waves in an enclosure filled with dusty gas. The main motivation for this problem is to probe the effect on such dynamics of solid particles dispersed in the fluid medium. This subject, which has attracted so much attention over recent years given its important implications in the study of the structural stability of systems exposed to high-energy internal detonations, is approached here in the framework of a hybrid numerical two-way coupled Eulerian-Lagrangian methodology. In particular, insights are sought by considering a relatively simple archetypal setting corresponding to a shock wave originating from a small spherical region initialized on the basis of available analytic solutions. The response of the system is explored numerically with respect to several parameters, including the blast intensity (via the related value of the initial shock Mach number), the solid mass fraction (mass load), and the particle size (Stokes number). Results are presented in terms of pressure-load diagrams. Beyond practical applications, it is shown that a kaleidoscope of fascinating patterns is produced by the "triadic" relationships among multiple shock reflection events and particle-fluid and particle-wall interaction dynamics. These would be of great interest to researchers and scientists interested in fundamental problems relating to the general theory of pattern formation in complex nonlinear multiphase systems.
Improved Modeling and Prediction of Surface Wave Amplitudes
2017-05-31
AFRL-RV-PS- AFRL-RV-PS- TR-2017-0162 TR-2017-0162 IMPROVED MODELING AND PREDICTION OF SURFACE WAVE AMPLITUDES Jeffry L. Stevens, et al. Leidos...data does not license the holder or any other person or corporation; or convey any rights or permission to manufacture, use, or sell any patented...SUBTITLE Improved Modeling and Prediction of Surface Wave Amplitudes 5a. CONTRACT NUMBER FA9453-14-C-0225 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER
Wave Transformation Over Reefs: Evaluation of One-Dimensional Numerical Models
National Research Council Canada - National Science Library
Demirbilek, Zeki; Nwogu, Okey G; Ward, Donald L; Sanchez, Alejandro
2009-01-01
Three one-dimensional (1D) numerical wave models are evaluated for wave transformation over reefs and estimates of wave setup, runup, and ponding levels in an island setting where the beach is fronted by fringing reef and lagoons...
International Nuclear Information System (INIS)
Wang, Xiaojuan; Tse, Peter W; Dordjevich, Alexandar
2011-01-01
The reflection signal from a defect in the process of guided wave-based pipeline inspection usually includes sufficient information to detect and define the defect. In previous research, it has been found that the reflection of guided waves from even a complex defect primarily results from the interference between reflection components generated at the front and the back edges of the defect. The respective contribution of different parameters of a defect to the overall reflection can be affected by the features of the two primary reflection components. The identification of these components embedded in the reflection signal is therefore useful in characterizing the concerned defect. In this research, we propose a method of model-based parameter estimation with the aid of the Hilbert–Huang transform technique for the purpose of decomposition of a reflection signal to enable characterization of the pipeline defect. Once two primary edge reflection components are decomposed and identified, the distance between the reflection positions, which closely relates to the axial length of the defect, could be easily and accurately determined. Considering the irregular profiles of complex pipeline defects at their two edges, which is often the case in real situations, the average of varied axial lengths of such a defect along the circumference of the pipeline is used in this paper as the characteristic value of actual axial length for comparison purpose. The experimental results of artificial defects and real corrosion in sample pipes were considered in this paper to demonstrate the effectiveness of the proposed method
Effective Orthorhombic Anisotropic Models for Wave field Extrapolation
Ibanez Jacome, Wilson
2013-05-01
Wavefield extrapolation in orthorhombic anisotropic media incorporates complicated but realistic models, to reproduce wave propagation phenomena in the Earth\\'s subsurface. Compared with the representations used for simpler symmetries, such as transversely isotropic or isotropic, orthorhombic models require an extended and more elaborated formulation that also involves more expensive computational processes. The acoustic assumption yields more efficient description of the orthorhombic wave equation that also provides a simplified representation for the orthorhombic dispersion relation. However, such representation is hampered by the sixth-order nature of the acoustic wave equation, as it also encompasses the contribution of shear waves. To reduce the computational cost of wavefield extrapolation in such media, I generate effective isotropic inhomogeneous models that are capable of reproducing the first-arrival kinematic aspects of the orthorhombic wavefield. First, in order to compute traveltimes in vertical orthorhombic media, I develop a stable, efficient and accurate algorithm based on the fast marching method. The derived orthorhombic acoustic dispersion relation, unlike the isotropic or transversely isotropic one, is represented by a sixth order polynomial equation that includes the fastest solution corresponding to outgoing P-waves in acoustic media. The effective velocity models are then computed by evaluating the traveltime gradients of the orthorhombic traveltime solution, which is done by explicitly solving the isotropic eikonal equation for the corresponding inhomogeneous isotropic velocity field. The inverted effective velocity fields are source dependent and produce equivalent first-arrival kinematic descriptions of wave propagation in orthorhombic media. I extrapolate wavefields in these isotropic effective velocity models using the more efficient isotropic operator, and the results compare well, especially kinematically, with those obtained from the
Barashkov, M. S.; Bel'dyugin, Igor'M.; Zolotarev, M. V.; Kruzhilin, Yu I.; Krymskiĭ, M. I.; Oshkin, S. P.; Starkov, G. S.; Umnov, A. F.; Kharchenko, M. A.
1989-04-01
A four-wave mirror exhibiting a thermal nonlinearity was used in a study of the interaction of concurrent waves under parametric feedback conditions in the presence of a nonreciprocal element. Strong reflection of a series of pulses of ~ 300 ns duration from a neodymium glass laser was demonstrated: the maximum reflection coefficient was in excess of 30. An analysis was made of the quality of the radiation reflected from this four-mirror parametric feedback system. A considerable reduction was observed in the steady-state threshold for the operation of this mirror with a thermal nonlinearity when the angles of convergence of the interacting beams were small compared with the case of head-on collision of the waves.
Quasi-optical reflective polarimeter for wide millimeter-wave band
Shinnaga, Hiroko; Tsuboi, Masato; Kasuga, Takashi
1998-11-01
We constructed a new reflective-type polarimeter system at 35 - 250 GHz for the 45 m telescope at Nobeyama Radio Observatory (NRO). Using the system, we can measure both linear polarization and circular polarization for our needs. The new system has two key points. First is that we can tune the center frequency of the polarimeter in the available frequency range, second is that insertion loss is low (0.15 plus or minus 0.03 dB at 86 GHz). These characteristics extended achievable scientific aims. In this paper, we present the design and the performance of the system. Using the system, we measured linear polarizations of some astronomical objects at 86 GHz, with SiO (nu) equals 0,1 and 2 at J equals 2 - 1 and 29SiO (nu) equals 0 J equals 2 - 1 simultaneously. As a result, the observation revealed SiO (nu) equals 0 J equals 2 - 1 of VY Canis Majoris is highly linearly polarized, the degree of linear polarization is up to 64%, in spite of SiO J equals 2 - 1 (nu) equals 1 is not highly linearly polarized. The highly linearly polarized feature is a strong evidence that 28SiO J equals 2 - 1 transition at the ground vibrational state originate through maser action. This is the first detection of the cosmic maser emission of SiO (nu) equals 0 J equals 2 - 1 transition.
Converted waves in a shallow marine environment : Experimental and modeling studies
El Allouche, N.; Drijkoningen, G.G.; Versteeg, W.; Ghose, R.
2011-01-01
Seismic waves converted from compressional to shear mode in the shallow subsurface can be useful not only for obtaining shear-wave velocity information but also for improved processing of deeper reflection data. These waves generated at deep seas have been used successfully in hydrocarbon
The development of efficient numerical time-domain modeling methods for geophysical wave propagation
Zhu, Lieyuan
This Ph.D. dissertation focuses on the numerical simulation of geophysical wave propagation in the time domain including elastic waves in solid media, the acoustic waves in fluid media, and the electromagnetic waves in dielectric media. This thesis shows that a linear system model can describe accurately the physical processes of those geophysical waves' propagation and can be used as a sound basis for modeling geophysical wave propagation phenomena. The generalized stability condition for numerical modeling of wave propagation is therefore discussed in the context of linear system theory. The efficiency of a series of different numerical algorithms in the time-domain for modeling geophysical wave propagation are discussed and compared. These algorithms include the finite-difference time-domain method, pseudospectral time domain method, alternating directional implicit (ADI) finite-difference time domain method. The advantages and disadvantages of these numerical methods are discussed and the specific stability condition for each modeling scheme is carefully derived in the context of the linear system theory. Based on the review and discussion of these existing approaches, the split step, ADI pseudospectral time domain (SS-ADI-PSTD) method is developed and tested for several cases. Moreover, the state-of-the-art stretched-coordinate perfect matched layer (SCPML) has also been implemented in SS-ADI-PSTD algorithm as the absorbing boundary condition for truncating the computational domain and absorbing the artificial reflection from the domain boundaries. After algorithmic development, a few case studies serve as the real-world examples to verify the capacities of the numerical algorithms and understand the capabilities and limitations of geophysical methods for detection of subsurface contamination. The first case is a study using ground penetrating radar (GPR) amplitude variation with offset (AVO) for subsurface non-aqueous-liquid (NAPL) contamination. The
Optimal parametric modelling of measured short waves
Digital Repository Service at National Institute of Oceanography (India)
Mandal, S.
the importance of selecting a suitable sampling interval for better estimates of parametric modelling and also for better statistical representation. Implementation of the above algorithms in a structural monitoring system has the potential advantage of storing...
Frontiers in Anisotropic Shock-Wave Modeling
2012-02-01
Epoxy IFPT simulated and experimental back surface velocities for 572, 788, and 1015 m/s. The experimental data Kevlar / Epoxy materials recovered after...model development for the Nextel and Kevlar / Epoxy materials subject to hypervelocity impact. They also performed the experimental inverse flyer test...IFPT) for Nextel and Kevlar / Epoxy . Their models were to be macro-mechanically based and suitable for implementation into a hydrocode coupled with EOS
A Coupled Atmospheric and Wave Modeling System for Storm Simulations
DEFF Research Database (Denmark)
Du, Jianting; Larsén, Xiaoli Guo; Bolanos, R.
2015-01-01
to parametrize z0. The results are validated through QuikScat data and point measurements from an open ocean site Ekosk and a coastal, relatively shallow water site Horns Rev. It is found that the modeling system captures in general better strong wind and strong wave characteristics for open ocean condition than......This study aims at improving the simulation of wind and waves during storms in connection with wind turbine design and operations in coastal areas. For this particular purpose, we investigated the Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) Modeling System which couples the Weather...... resolution ranging from 25km to 2km. Meanwhile, the atmospheric forcing data of dierent spatial resolution, with one about 100km (FNL) and the other about 38km (CFSR) are both used. In addition, bathymatry data of diferent resolutions (1arc-minute and 30arc-seconds) are used. We used three approaches...
Monitoring and modeling of ultrasonic wave propagation in crystallizing mixtures
Marshall, T.; Challis, R. E.; Tebbutt, J. S.
2002-05-01
The utility of ultrasonic compression wave techniques for monitoring crystallization processes is investigated in a study of the seeded crystallization of copper II sulfate pentahydrate from aqueous solution. Simple models are applied to predict crystal yield, crystal size distribution and the changing nature of the continuous phase. A scattering model is used to predict the ultrasonic attenuation as crystallization proceeds. Experiments confirm that modeled attenuation is in agreement with measured results.
Seismic waves and earthquakes in a global monolithic model
Roubíček, Tomáš
2018-03-01
The philosophy that a single "monolithic" model can "asymptotically" replace and couple in a simple elegant way several specialized models relevant on various Earth layers is presented and, in special situations, also rigorously justified. In particular, global seismicity and tectonics is coupled to capture, e.g., (here by a simplified model) ruptures of lithospheric faults generating seismic waves which then propagate through the solid-like mantle and inner core both as shear (S) or pressure (P) waves, while S-waves are suppressed in the fluidic outer core and also in the oceans. The "monolithic-type" models have the capacity to describe all the mentioned features globally in a unified way together with corresponding interfacial conditions implicitly involved, only when scaling its parameters appropriately in different Earth's layers. Coupling of seismic waves with seismic sources due to tectonic events is thus an automatic side effect. The global ansatz is here based, rather for an illustration, only on a relatively simple Jeffreys' viscoelastic damageable material at small strains whose various scaling (limits) can lead to Boger's viscoelastic fluid or even to purely elastic (inviscid) fluid. Self-induced gravity field, Coriolis, centrifugal, and tidal forces are counted in our global model, as well. The rigorous mathematical analysis as far as the existence of solutions, convergence of the mentioned scalings, and energy conservation is briefly presented.
A delay differential equation model of follicle waves in women.
Panza, Nicole M; Wright, Andrew A; Selgrade, James F
2016-01-01
This article presents a mathematical model for hormonal regulation of the menstrual cycle which predicts the occurrence of follicle waves in normally cycling women. Several follicles of ovulatory size that develop sequentially during one menstrual cycle are referred to as follicle waves. The model consists of 13 nonlinear, delay differential equations with 51 parameters. Model simulations exhibit a unique stable periodic cycle and this menstrual cycle accurately approximates blood levels of ovarian and pituitary hormones found in the biological literature. Numerical experiments illustrate that the number of follicle waves corresponds to the number of rises in pituitary follicle stimulating hormone. Modifications of the model equations result in simulations which predict the possibility of two ovulations at different times during the same menstrual cycle and, hence, the occurrence of dizygotic twins via a phenomenon referred to as superfecundation. Sensitive parameters are identified and bifurcations in model behaviour with respect to parameter changes are discussed. Studying follicle waves may be helpful for improving female fertility and for understanding some aspects of female reproductive ageing.
Herman, Agnieszka
2017-11-01
In this paper, a coupled sea ice-wave model is developed and used to analyze wave-induced stress and breaking in sea ice for a range of wave and ice conditions. The sea ice module is a discrete-element bonded-particle model, in which ice is represented as cuboid grains floating on the water surface that can be connected to their neighbors by elastic joints. The joints may break if instantaneous stresses acting on them exceed their strength. The wave module is based on an open-source version of the Non-Hydrostatic WAVE model (NHWAVE). The two modules are coupled with proper boundary conditions for pressure and velocity, exchanged at every wave model time step. In the present version, the model operates in two dimensions (one vertical and one horizontal) and is suitable for simulating compact ice in which heave and pitch motion dominates over surge. In a series of simulations with varying sea ice properties and incoming wavelength it is shown that wave-induced stress reaches maximum values at a certain distance from the ice edge. The value of maximum stress depends on both ice properties and characteristics of incoming waves, but, crucially for ice breaking, the location at which the maximum occurs does not change with the incoming wavelength. Consequently, both regular and random (Jonswap spectrum) waves break the ice into floes with almost identical sizes. The width of the zone of broken ice depends on ice strength and wave attenuation rates in the ice.
Modeling of the Voltage Waves in the LHC Main Dipole Circuits
Ravaioli, E; Formenti, F; Steckert, J; Thiesen, H; Verweij, A
2012-01-01
When a fast power abort is triggered in the LHC main dipole chain, voltage transients are generated at the output of the power converter and across the energy-extraction switches. The voltage waves propagate through the chain of 154 superconducting dipoles and can have undesired effects leading to spurious triggering of the quench protection system and firing of the quench heaters. The phase velocity of the waves travelling along the chain changes due to the inhomogeneous AC behavior of the dipoles. Furthermore, complex phenomena of reflection and superposition are present in the circuit. For these reasons analytical calculations are not sufficient for properly analyzing the circuit behavior after a fast power abort. The transients following the switch-off of the power converter and the opening of the switches are analyzed by means of a complete electrical model, developed with the Cadence© suite (PSpice© based). The model comprises all the electrical components of the circuit, additional components simula...
Unstable spiral waves and local Euclidean symmetry in a model of cardiac tissue
International Nuclear Information System (INIS)
Marcotte, Christopher D.; Grigoriev, Roman O.
2015-01-01
This paper investigates the properties of unstable single-spiral wave solutions arising in the Karma model of two-dimensional cardiac tissue. In particular, we discuss how such solutions can be computed numerically on domains of arbitrary shape and study how their stability, rotational frequency, and spatial drift depend on the size of the domain as well as the position of the spiral core with respect to the boundaries. We also discuss how the breaking of local Euclidean symmetry due to finite size effects as well as the spatial discretization of the model is reflected in the structure and dynamics of spiral waves. This analysis allows identification of a self-sustaining process responsible for maintaining the state of spiral chaos featuring multiple interacting spirals
Unstable spiral waves and local Euclidean symmetry in a model of cardiac tissue.
Marcotte, Christopher D; Grigoriev, Roman O
2015-06-01
This paper investigates the properties of unstable single-spiral wave solutions arising in the Karma model of two-dimensional cardiac tissue. In particular, we discuss how such solutions can be computed numerically on domains of arbitrary shape and study how their stability, rotational frequency, and spatial drift depend on the size of the domain as well as the position of the spiral core with respect to the boundaries. We also discuss how the breaking of local Euclidean symmetry due to finite size effects as well as the spatial discretization of the model is reflected in the structure and dynamics of spiral waves. This analysis allows identification of a self-sustaining process responsible for maintaining the state of spiral chaos featuring multiple interacting spirals.
On observational foundations of models with a wave spiral structure
International Nuclear Information System (INIS)
Suchkov, A.A.
1978-01-01
The validity of the density wave models of the spiral structure is considered. It is shown that the density wave in the Galaxy is doverned by its flat subsystem only, whereas the disk and the halo do not contribute significantly into the wave. It is found that the density wave model of the spiral structure of the Galaxy is confirmed by the value of the pattern speed derived from observational data (Ω = 20-25 km s -1 kpc -1 ). The position and the properties of the outer Lindblad resonance are confirmed by the existence and position of gas ring features in outer regions of our Galaxy and external galaxies. The corotation region in the Galaxy is situated at R=10/12 kpc. Near the corotation region the galactic shock wave is not expected to develop. The observed rapid decrease in the number of H2 regions while moving from R=5 kpc to R=10 kpc confirms this conclusion. The similar consistency between the positions of corotation region and outer resonance and the observed properties of H2 and H1 distribution has also been found for a number of extermal galaxies
Theoretical models for designing a 220-GHz folded waveguide backward wave oscillator
International Nuclear Information System (INIS)
Cai Jin-Chi; Chen Huai-Bi; Hu Lin-Lin; Ma Guo-Wu; Chen Hong-Bin; Jin Xiao
2015-01-01
In this paper, the basic equations of beam-wave interaction for designing the 220 GHz folded waveguide (FW) backward wave oscillator (BWO) are described. On the whole, these equations are mainly classified into small signal model (SSM), large signal model (LSM), and simplified small signal model (SSSM). Using these linear and nonlinear one-dimensional (1D) models, the oscillation characteristics of the FW BWO of a given configuration of slow wave structure (SWS) can be calculated by numerical iteration algorithm, which is more time efficient than three-dimensional (3D) particle-in-cell (PIC) simulation. The SSSM expressed by analytical formulas is innovatively derived for determining the initial values of the FW SWS conveniently. The dispersion characteristics of the FW are obtained by equivalent circuit analysis. The space charge effect, the end reflection effect, the lossy wall effect, and the relativistic effect are all considered in our models to offer more accurate results. The design process of the FW BWO tube with output power of watt scale in a frequency range between 215 GHz and 225 GHz based on these 1D models is demonstrated. The 3D PIC method is adopted to verify the theoretical design results, which shows that they are in good agreement with each other. (paper)
Full-wave modeling of ICRF waves: global and quasi-local descriptions
International Nuclear Information System (INIS)
Dumont, R. J.
2007-01-01
Waves in the Ion Cyclotron Range of Frequencies (ICRF) undergo significant space dispersion as they propagate in magnetic fusion plasmas, making it necessary to incorporate non-local effects in their physical description. Full-wave codes are routinely employed to simulate ICRF heating experiments in tokamaks. The vast majority of these codes rely on a description of the plasma based on a 'quasi-local' derivation of the dielectric tensor, i.e. assuming that the range of space dispersion remains small compared to the system dimensions. However, non-local effects caused by wide particle orbits are expected to play a significant role in current and future experiments featuring wave-driven fast ions, fusion-born alpha particles... Global formalisms have thus been proposed to include these effects in a more comprehensive fashion. Based on a description of the particle dynamics in terms of action-angle variables, a full-wave code, named EVE, is currently under development. Its first version, presented here, incorporates quasi-local expressions valid to second order in Larmor radius, derived from the more general Hamiltonian formalism. The obtained tool has the advantage of being compatible with the current requirements of integrated modeling, and lends itself to direct comparisons with existing codes
Wave Climate and Wave Mixing in the Marginal Ice Zones of Arctic Seas, Observations and Modelling
2015-09-30
measured by R/V Lance ( black solid line) and predicted by SWAN ( black dashed line) and the ship velocity (grey solid line). (c) BFI ( black solid line) and...and potential future trends; and WAVEWATCH-III® and SWAN wave models with new physics, adapted and validated for the Beaufort and Chukchi Seas...nondimensional spectral width ν ( black dashed line). (d–i) Selected photographs from the ship show local sea ice state. Fig. 6 illustrates a
Variational Boussinesq model for simulation of coastal waves and tsunamis
Adytia, D.; Adytia, Didit; van Groesen, Embrecht W.C.; Tan, Soon Keat; Huang, Zhenhua
2009-01-01
In this paper we describe the basic ideas of a so-called Variational Boussinesq Model which is based on the Hamiltonian structure of gravity surface waves. By using a rather simple approach to prescribe the profile of vertical fluid potential in the expression for the kinetic energy, we obtain a set
Non-homogeneous polymer model for wave propagation and its ...
African Journals Online (AJOL)
user
density are functions of space i.e. non-homogeneous engineering material. .... The Solution of equation Eq. (9) in the form of Eq. (10) can be obtained by taking a phase ..... Viscoelastic Model Applied to a Particular Case .... p m i exp m α α σ σ σ. = −. +. −. (35). The progressive harmonic wave which starts from the end. 0 x =.
The second-order decomposition model of nonlinear irregular waves
DEFF Research Database (Denmark)
Yang, Zhi Wen; Bingham, Harry B.; Li, Jin Xuan
2013-01-01
into the first- and the second-order super-harmonic as well as the second-order sub-harmonic components by transferring them into an identical Fourier frequency-space and using a Newton-Raphson iteration method. In order to evaluate the present model, a variety of monochromatic waves and the second...
FDTD Modelling of Electromagnetic waves in Stratified Medium ...
African Journals Online (AJOL)
The technique is an adaptation of the finite-difference time domain (FDTD) approach usually applied to model electromagnetic wave propagation. In this paper a simple 2D implementation of FDTD algorithm in mathematica environment is presented. Source implementation and the effect of conductivity on the incident field ...
Gravitational Jaynes–Cummings model beyond the rotating wave
Indian Academy of Sciences (India)
In this paper, the quantum properties of a two-level atom and the cavity-ﬁeld in the Jaynes–Cummings model with the gravity beyond the rotating wave approximation are investigated. For this purpose, by solving the Schrödinger equation in the interaction picture, the evolving state of the system is found by which the ...
Lake St. Clair: Storm Wave and Water Level Modeling
2013-06-01
R. A. Luettich, C. Dawson, V. J. Cardone , A. T. Cox, M. D. Powell, H. J. Westerink, and H. J. Roberts. 2010. A high resolution coupled riverine flow...Storm Wave and Water Level Modeling 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Tyler J. Hesser
Innovative technologies to accurately model waves and moored ship motions
CSIR Research Space (South Africa)
van der Molen, W
2010-09-01
Full Text Available Late in 2009 CSIR Built Environment in Stellenbosch was awarded a contract to carry out extensive physical and numerical modelling to study the wave conditions and associated moored ship motions, for the design of a new iron ore export jetty for BHP...
Yasui, Kyuichi; Kozuka, Teruyuki; Yasuoka, Masaki; Kato, Kazumi
2015-11-01
There are two major categories in a thermoacoustic prime-mover. One is the traveling-wave type and the other is the standing-wave type. A simple analytical model of a standing-wave thermoacoustic prime-mover is proposed at relatively low heat-flux for a stack much shorter than the acoustic wavelength, which approximately describes the Brayton cycle. Numerical simulations of Rott's equations have revealed that the work flow (acoustic power) increases by increasing of the amplitude of the particle velocity (| U|) for the traveling-wave type and by increasing cosΦ for the standing-wave type, where Φ is the phase difference between the particle velocity and the acoustic pressure. In other words, the standing-wave type is a phase-dominant type while the traveling-wave type is an amplitude-dominant one. The ratio of the absolute value of the traveling-wave component (| U|cosΦ) to that of the standing-wave component (| U|sinΦ) of any thermoacoustic engine roughly equals the ratio of the absolute value of the increasing rate of | U| to that of cosΦ. The different mechanism between the traveling-wave and the standing-wave type is discussed regarding the dependence of the energy efficiency on the acoustic impedance of a stack as well as that on ωτα, where ω is the angular frequency of an acoustic wave and τα is the thermal relaxation time. While the energy efficiency of the traveling-wave type at the optimal ωτα is much higher than that of the standing-wave type, the energy efficiency of the standing-wave type is higher than that of the traveling-wave type at much higher ωτα under a fixed temperature difference between the cold and the hot ends of the stack.
Millimeter Wave Radio Frequency Propagation Model Development
2014-08-28
be not be exceeded due to rain could be 95%. However, if the location were in a tropical rain forest , then then threshold might not be exceeded for...molecules grows. Approved for Public Release; Distribution is Unlimited. 14 Figure 3. Specific Attenuation Due to Water Vapor and Dry Air 3.1.1.2 Rain ... rain being the most detrimental and uncertain. Predictive models of rain attenuation claim some degree of accuracy up to 55 GHz, although they are
Shock waves and rarefaction waves in magnetohydrodynamics. Pt. 1: A model system
International Nuclear Information System (INIS)
Myong, R.S.; Roe, P.L.
1997-01-01
The present study consists of two parts. Here in Part I, a model set of conservation laws exactly preserving the MHD hyperbolic singularities is investigated to develop the general theory of the nonlinear evolution of MHD shock waves. Great emphasis is placed on shock admissibility conditions. By developing the viscosity admissibility condition, it is shown that the intermediate shocks are necessary to ensure that the planar Riemann problem is well-posed. In contrast, it turns out that the evolutionary condition is inappropriate for determining physically relevant MHD, shocks. In the general non-planar case, by studying canonical cases, we show that the solution of the Riemann problem is not necessarily unique - in particular, that it depends not only on reference states but also on the associated internal structure. Finally, the stability of intermediate shocks is discussed, and a theory of their nonlinear evolution is proposed. In Part 2, the theory of nonlinear waves developed for the model is applied to the MHD problem. It is shown that the topology of the MHD Hugoniot and wave curves is identical to that of the model problem. (Author)
Energy Technology Data Exchange (ETDEWEB)
Zargham, Ardalan, E-mail: zargham@ifp.uni-bremen.d [Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen (Germany); Schmidt, Thomas; Flege, Jan Ingo; Sauerbrey, Marc; Hildebrand, Radowan [Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen (Germany); Roehe, Sarah; Baeumer, Marcus [Applied and Physical Chemistry, University of Bremen, Leobener Str. 2, 28359, Bremen (Germany); Falta, Jens [Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen (Germany)
2010-02-15
We present a promising combination of methods to precisely determine the morphology of nanostructures, drawing on the example of monodisperse CoPt{sub 3} nanoparticle films deposited by spin coating and dip coating techniques on functionalized Au substrates. Ex-situ X-ray standing waves in total external reflection combined with X-ray reflectivity measurements were employed to determine element-specific atomic-density distributions in vertical direction.
International Nuclear Information System (INIS)
Nihan Onder; Alberto Teyssedou; Danila Roubtsov
2005-01-01
Full text of publication follows: In CANDU reactors the fuel channels are connected to inlet and outlet headers by feeder-pipes that consist of vertical and horizontal legs. In some feeders, orifices are installed for flow adjustment. During a postulated Loss of Coolant Accidents, the emergency cooling water injected into the inlet and outlet headers enters the fuel channels through the feeder pipes. Steam produced in the feeders and in the fuel channels may flow in the direction opposite to that of the water, thereby creating vertical to horizontal Counter-Current Flow (CCF). The rate at which the cooling water enters the fuel channel may be substantially limited by the flooding phenomena that entrains the water in the same direction as the steam flow. Steam flowing in the direction opposite to the cooling water can bring about the formation of slug flow. Long slugs of liquid moving at relatively high speed are transported back towards the headers by the steam. This phenomenon substantially reduces the amount of cooling water that can reach the reactor core. We conducted CCF experiments using a vertical-to-horizontal test section connected by 90 deg. elbows, with an orifice installed in the horizontal leg. Four different orifices were used to carry out the experiments. We have observed that soliton-type waves generated close to the elbow propagate in the horizontal leg towards the orifice, where a partial reflection takes place. Without an orifice, the soliton waves are reflected from the second elbow. The reflected waves move in the opposite direction to that of the incident wave. Since soliton-type waves are periodically generated, the incident and reflected waves interfere at some place in the horizontal leg. If the amplitude of the interference wave is high enough, the bridging of the tubes occur, which generates the slugs. During the experiments the water and air flow rates, pressures and void fraction distributions were measured. The slug propagation
DEFF Research Database (Denmark)
Buchholz, Jörg
2007-01-01
Masked thresholds were measured for a single test reflection, masked by the direct sound, as a function of the reflection delay. This was done for diotic as well as for dichotic stimulus presentations and all stimuli were presented via headphones. The input signal was a 200-ms long broadband noise......, such as normalized cross-correlation models (e.g., Bernstein et al., 1999, JASA, pp. 870-876), the power-addition model (Zurek, 1979, JASA, pp. 1750-1757), or Equalization-Cancellation-based models (e.g., Breebaart et al., 2001, JASA, pp. 1074-1088), cannot account for the psychoacoustical data. The present talk...
Animal model for schizophrenia that reflects gene-environment interactions.
Nagai, Taku; Ibi, Daisuke; Yamada, Kiyofumi
2011-01-01
Schizophrenia is a devastating psychiatric disorder that impairs mental and social functioning and affects approximately 1% of the population worldwide. Genetic susceptibility factors for schizophrenia have recently been reported, some of which are known to play a role in neurodevelopment; these include neuregulin-1, dysbindin, and disrupted-in-schizophrenia 1 (DISC1). Moreover, epidemiologic studies suggest that environmental insults, such as prenatal infection and perinatal complication, are involved in the development of schizophrenia. The possible interaction between environment and genetic susceptibility factors, especially during neurodevelopment, is proposed as a promising disease etiology of schizophrenia. Polyriboinosinic-polyribocytidilic acid (polyI : C) is a synthetic analogue of double-stranded RNA that leads to the pronounced but time-limited production of pro-inflammatory cytokines. Maternal immune activation by polyI : C exposure in rodents is known to precipitate a wide spectrum of behavioral, cognitive, and pharmacological abnormalities in adult offspring. Recently, we have reported that neonatal injection of polyI : C in mice results in schizophrenia-like behavioral alterations in adulthood. In this review, we show how gene-environment interactions during neurodevelopment result in phenotypic changes in adulthood by injecting polyI : C into transgenic mice that express a dominant-negative form of human DISC1 (DN-DISC1). Our findings suggest that polyI : C-treated DN-DISC1 mice are a well-validated animal model for schizophrenia that reflects gene-environment interactions.
Wave propagation model of heat conduction and group speed
Zhang, Long; Zhang, Xiaomin; Peng, Song
2018-03-01
In view of the finite relaxation model of non-Fourier's law, the Cattaneo and Vernotte (CV) model and Fourier's law are presented in this work for comparing wave propagation modes. Independent variable translation is applied to solve the partial differential equation. Results show that the general form of the time spatial distribution of temperature for the three media comprises two solutions: those corresponding to the positive and negative logarithmic heating rates. The former shows that a group of heat waves whose spatial distribution follows the exponential function law propagates at a group speed; the speed of propagation is related to the logarithmic heating rate. The total speed of all the possible heat waves can be combined to form the group speed of the wave propagation. The latter indicates that the spatial distribution of temperature, which follows the exponential function law, decays with time. These features show that propagation accelerates when heated and decelerates when cooled. For the model media that follow Fourier's law and correspond to the positive heat rate of heat conduction, the propagation mode is also considered the propagation of a group of heat waves because the group speed has no upper bound. For the finite relaxation model with non-Fourier media, the interval of group speed is bounded and the maximum speed can be obtained when the logarithmic heating rate is exactly the reciprocal of relaxation time. And for the CV model with a non-Fourier medium, the interval of group speed is also bounded and the maximum value can be obtained when the logarithmic heating rate is infinite.
Energy Technology Data Exchange (ETDEWEB)
Roberts, Jesse D.; Grace Chang; Jason Magalen; Craig Jones
2014-08-01
A n indust ry standard wave modeling tool was utilized to investigate model sensitivity to input parameters and wave energy converter ( WEC ) array deploym ent scenarios. Wave propagation was investigated d ownstream of the WECs to evaluate overall near - and far - field effects of WEC arrays. The sensitivity study illustrate d that b oth wave height and near - bottom orbital velocity we re subject to the largest pote ntial variations, each decreas ed in sensitivity as transmission coefficient increase d , as number and spacing of WEC devices decrease d , and as the deployment location move d offshore. Wave direction wa s affected consistently for all parameters and wave perio d was not affected (or negligibly affected) by varying model parameters or WEC configuration .
Latitudinal amplitude-phase structure of MHD waves: STARE radar observations and modeling
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Pilipenko V.
2016-09-01
Full Text Available We have developed a numerical model that yields a steady-state distribution of field components of MHD wave in an inhomogeneous plasma box simulating the realistic magnetosphere. The problem of adequate boundary condition at the ionosphere–magnetosphere interface for coupled MHD mode is considered. To justify the model’s assumptions, we have derived the explicit inequality showing when the ionospheric inductive Hall effect can be neglected upon the consideration of Alfven wave reflection from the ionospheric boundaries. The model predicts a feature of the ULF spatial amplitude/phase distribution that has not been noticed by the field line resonance theory: the existence of a region with opposite phase delays on the source side of the resonance. This theoretical prediction is supported by the amplitude-phase latitudinal structures of Pc5 waves observed by STARE radar and IMAGE magnetometers. A gradual decrease in azimuthal wave number m at smaller L-shells was observed at longitudinally separated radar beams.
A robust absorbing layer method for anisotropic seismic wave modeling
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Métivier, L., E-mail: ludovic.metivier@ujf-grenoble.fr [LJK, CNRS, Université de Grenoble, BP 53, 38041 Grenoble Cedex 09 (France); ISTerre, Université de Grenoble I, BP 53, 38041 Grenoble Cedex 09 (France); Brossier, R. [ISTerre, Université de Grenoble I, BP 53, 38041 Grenoble Cedex 09 (France); Labbé, S. [LJK, CNRS, Université de Grenoble, BP 53, 38041 Grenoble Cedex 09 (France); Operto, S. [Géoazur, Université de Nice Sophia-Antipolis, CNRS, IRD, OCA, Villefranche-sur-Mer (France); Virieux, J. [ISTerre, Université de Grenoble I, BP 53, 38041 Grenoble Cedex 09 (France)
2014-12-15
When applied to wave propagation modeling in anisotropic media, Perfectly Matched Layers (PML) exhibit instabilities. Incoming waves are amplified instead of being absorbed. Overcoming this difficulty is crucial as in many seismic imaging applications, accounting accurately for the subsurface anisotropy is mandatory. In this study, we present the SMART layer method as an alternative to PML approach. This method is based on the decomposition of the wavefield into components propagating inward and outward the domain of interest. Only outgoing components are damped. We show that for elastic and acoustic wave propagation in Transverse Isotropic media, the SMART layer is unconditionally dissipative: no amplification of the wavefield is possible. The SMART layers are not perfectly matched, therefore less accurate than conventional PML. However, a reasonable increase of the layer size yields an accuracy similar to PML. Finally, we illustrate that the selective damping strategy on which is based the SMART method can prevent the generation of spurious S-waves by embedding the source in a small zone where only S-waves are damped.