Design and Implementation of an Electronic Front-End Based on Square Wave Excitation for Ultrasonic Torsional Guided Wave Viscosity Sensor.

PubMed

Rabani, Amir

2016-10-12

The market for process instruments generally requires low cost devices that are robust, small in size, portable, and usable in-plant. Ultrasonic torsional guided wave sensors have received much attention by researchers for measurement of viscosity and/or density of fluids in recent years. The supporting electronic systems for these sensors providing many different settings of sine-wave signals are bulky and expensive. In contrast, a system based on bursts of square waves instead of sine waves would have a considerable advantage in that respect and could be built using simple integrated circuits at a cost that is orders of magnitude lower than for a windowed sine wave device. This paper explores the possibility of using square wave bursts as the driving signal source for the ultrasonic torsional guided wave viscosity sensor. A simple design of a compact and fully automatic analogue square wave front-end for the sensor is also proposed. The successful operation of the system is demonstrated by using the sensor for measuring the viscosity in a representative fluid. This work provides the basis for design and manufacture of low cost compact standalone ultrasonic guided wave sensors and enlightens the possibility of using coded excitation techniques utilising square wave sequences in such applications.

Sharp-front wave of strong magnetic field diffusion in solid metal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiao, Bo; Gu, Zhuo-wei; Kan, Ming-xian

When a strong magnetic field diffuses into a solid metal, if the metal's resistance possesses an abrupt rise at some critical temperature and the magnetic field strength is above some critical value, the magnetic field will diffuse into the metal in the form of a sharp-front wave. Formulas for the critical conditions under which a sharp-front magnetic diffusion wave emerges and a formula for the wave-front velocity are derived in this work.

Highly Efficient Wave-Front Reshaping of Surface Waves with Dielectric Metawalls

NASA Astrophysics Data System (ADS)

Dong, Shaohua; Zhang, Yu; Guo, Huijie; Duan, Jingwen; Guan, Fuxin; He, Qiong; Zhao, Haibin; Zhou, Lei; Sun, Shulin

2018-01-01

Controlling the wave fronts of surface waves (including surface-plamon polaritons and their equivalent counterparts) at will is highly important in photonics research, but the available mechanisms suffer from the issues of low efficiency, bulky size, and/or limited functionalities. Inspired by recent studies of metasurfaces that can freely control the wave fronts of propagating waves, we propose to use metawalls placed on a plasmonic surface to efficiently reshape the wave fronts of incident surface waves (SWs). Here, the metawall is constructed by specifically designed meta-atoms that can reflect SWs with desired phases and nearly unit amplitudes. As a proof of concept, we design and fabricate a metawall in the microwave regime (around 12 GHz) that can anomalously reflect the SWs following the generalized Snell's law with high efficiency (approximately 70%). Our results, in excellent agreement with full-wave simulations, provide an alternative yet efficient way to control the wave fronts of SWs in different frequency domains. We finally employ full-wave simulations to demonstrate a surface-plasmon-polariton focusing effect at telecom wavelength based on our scheme.

Nonlinear waves in reaction-diffusion systems: The effect of transport memory

NASA Astrophysics Data System (ADS)

Manne, K. K.; Hurd, A. J.; Kenkre, V. M.

2000-04-01

Motivated by the problem of determining stress distributions in granular materials, we study the effect of finite transport correlation times on the propagation of nonlinear wave fronts in reaction-diffusion systems. We obtain results such as the possibility of spatial oscillations in the wave-front shape for certain values of the system parameters and high enough wave-front speeds. We also generalize earlier known results concerning the minimum wave-front speed and shape-speed relationships stemming from the finiteness of the correlation times. Analytic investigations are made possible by a piecewise linear representation of the nonlinearity.

Sequential deconvolution from wave-front sensing using bivariate simplex splines

NASA Astrophysics Data System (ADS)

Guo, Shiping; Zhang, Rongzhi; Li, Jisheng; Zou, Jianhua; Xu, Rong; Liu, Changhai

2015-05-01

Deconvolution from wave-front sensing (DWFS) is an imaging compensation technique for turbulence degraded images based on simultaneous recording of short exposure images and wave-front sensor data. This paper employs the multivariate splines method for the sequential DWFS: a bivariate simplex splines based average slopes measurement model is built firstly for Shack-Hartmann wave-front sensor; next, a well-conditioned least squares estimator for the spline coefficients is constructed using multiple Shack-Hartmann measurements; then, the distorted wave-front is uniquely determined by the estimated spline coefficients; the object image is finally obtained by non-blind deconvolution processing. Simulated experiments in different turbulence strength show that our method performs superior image restoration results and noise rejection capability especially when extracting the multidirectional phase derivatives.

Nonlinear Wave Propagation

DTIC Science & Technology

2009-02-09

grey) soliton , to a nearly linear wavetrain at the front moving with its group velocity ; like KdV the NLS DSW has two speeds. The 1-D NLS theory was...studies of wave phenomena in nonlinear optics include ultrashort pulse dynamics in mode- locked lasers, dynamics and perturbations of dark solitons ...nonlinear Kerr response and has a large normal group - velocity dispersion (GVD). This requires a set of prisms and/or mirrors specially designed to have

Impacts of storms on coastal circulation in Long Bay, South Carolina

NASA Astrophysics Data System (ADS)

Kim, H.; Warner, J. C.; Voulgaris, G.; Work, P.

2006-12-01

We investigate the effects of coastal storms on the regional circulation in Long Bay, South Carolina, using a coupled ROMS (Regional Ocean Modeling System)- SWAN (Simulating WAves Nearshore) model. Meteorological observations during the South Carolina Coastal Erosion Study (October 2003 April 2004) reveal three dominant types of storms in the region warm fronts, cold fronts, and tropical storms. Each storm has a characteristic progression of wind patterns: (1) Warm fronts start with southwestward winds and change to northeastward after the front passes; (2) Cold fronts begin with northeastward winds and shift to southeastward when the front moves out; and (3) Tropical storms change wind directions from the southwest to the southeast during the storm. It is observed the coastal circulation distinctly responds to such atmospheric disturbances in either a upwelling-favorable condition to the northeastward winds or a downwelling-favorable condition to the southwestward winds. The study domain encompasses 300-km of gently arcing shoreline between Cape Romain to Cape Fear, and approximately 100-km offshore to the shelf edge. The model domain is resolved by a 300×130 mesh at 1-km intervals in the horizontal and twenty terrain-following layers in the vertical. The ROMS model is driven by tides and wind stress, and it includes wave-current interactions via dynamic coupling to the surface wave model SWAN. Salinity and temperature along the open boundaries are included by nudging to climatological values. A time period of six months is simulated from October 2003 to April 2004, concurrent with the observation study. Model results are compared to an extensive set of measurements collected at eight sites in the inner part of Long Bay, and are used to identify varying circulation response to each storm type. In addition, we investigate the significance of the Capes on the development of the alongshore pressure gradients, and examine the importance of wave-current interactions in the study region.

Statistical analysis of wavefront fluctuations from measurements of a wave-front sensor

NASA Astrophysics Data System (ADS)

Botygina, N. N.; Emaleev, O. N.; Konyaev, P. A.; Lukin, V. P.

2017-11-01

Measurements of the wave front aberrations at the input aperture of the Big Solar Vacuum Telescope (LSVT) were carried out by a wave-front sensor (WFS) of an adaptive optical system when the controlled deformable mirror was replaced by a plane one.

Mode Conversion of a Solar Extreme-ultraviolet Wave over a Coronal Cavity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zong, Weiguo; Dai, Yu, E-mail: ydai@nju.edu.cn

2017-01-10

We report on observations of an extreme-ultraviolet (EUV) wave event in the Sun on 2011 January 13 by Solar Terrestrial Relations Observatory and Solar Dynamics Observatory in quadrature. Both the trailing edge and the leading edge of the EUV wave front in the north direction are reliably traced, revealing generally compatible propagation velocities in both perspectives and a velocity ratio of about 1/3. When the wave front encounters a coronal cavity near the northern polar coronal hole, the trailing edge of the front stops while its leading edge just shows a small gap and extends over the cavity, meanwhile gettingmore » significantly decelerated but intensified. We propose that the trailing edge and the leading edge of the northward propagating wave front correspond to a non-wave coronal mass ejection component and a fast-mode magnetohydrodynamic wave component, respectively. The interaction of the fast-mode wave and the coronal cavity may involve a mode conversion process, through which part of the fast-mode wave is converted to a slow-mode wave that is trapped along the magnetic field lines. This scenario can reasonably account for the unusual behavior of the wave front over the coronal cavity.« less

A cryogenic 'set-and-forget' deformable mirror

NASA Astrophysics Data System (ADS)

Trines, Robin; Janssen, Huub; Paalvast, Sander; Teuwen, Maurice; Brandl, Bernhard; Rodenhuis, Michiel

2016-07-01

This paper discusses the development, realization and initial characterization of a demonstrator for a cryogenic 'set and forget' deformable mirror. Many optical and cryogenic infrared instruments on modern very and extremely large telescopes aim at diffraction-limited performance and require total wave front errors in the order of 50 nanometers or less. At the same time, their complex optical functionality requires either a large number of spherical mirrors or several complex free-form mirrors. Due to manufacturing and alignment tolerances, each mirror contributes static aberrations to the wave front. Many of these aberrations are not known in the design phase and can only be measured once the system has been assembled. A 'set-and-forget' deformable mirror can be used to compensate for these aberrations, making it especially interesting for systems with complex free-form mirrors or cryogenic systems where access to iterative realignment is very difficult or time consuming. The mirror with an optical diameter of 200 mm is designed to correct wave front aberrations of up to 2 μm root-mean square (rms). The shape of the wave front is approximated by the first 15 Zernike modes. Finite element analysis of the mirror shows a theoretically possible reduction of the wave front error from 2 μm to 53 nm rms. To produce the desired shapes, the mirror surface is controlled by 19 identical actuator modules at the back of the mirror. The actuator modules use commercially available Piezo-Knob actuators with a high technology readiness level (TRL). These provide nanometer resolution at cryogenic temperatures combined with high positional stability, and allow for the system to be powered off once the desired shape is obtained. The stiff design provides a high resonance frequency (>200 Hz) to suppress external disturbances. A full-size demonstrator of the deformable mirror containing 6 actuators and 13 dummy actuators is realized and characterized. Measurement results show that the actuators can provide sufficient stroke to correct the 2 μm rms WFE. The resolution of the actuator influence functions is found to be 0.24 nm rms or better depending on the position of the actuator within the grid. Superposition of the actuator influence functions shows that a 2 μm rms WFE can be accurately corrected with a 38 nm fitting error. Due to the manufacturing method of the demonstrator an artificially large print-through error of 182 nm is observed. The main cause of this print-through error has been identified and will be reduced in future design iterations. After these design changes the system is expected to have a total residual error of less than 70 nm and offer diffraction limited performance (λ14) for wavelengths of 1 μm and above.

STEREO OBSERVATIONS OF FAST MAGNETOSONIC WAVES IN THE EXTENDED SOLAR CORONA ASSOCIATED WITH EIT/EUV WAVES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kwon, Ryun-Young; Ofman, Leon; Kramar, Maxim

2013-03-20

We report white-light observations of a fast magnetosonic wave associated with a coronal mass ejection observed by STEREO/SECCHI/COR1 inner coronagraphs on 2011 August 4. The wave front is observed in the form of density compression passing through various coronal regions such as quiet/active corona, coronal holes, and streamers. Together with measured electron densities determined with STEREO COR1 and Extreme UltraViolet Imager (EUVI) data, we use our kinematic measurements of the wave front to calculate coronal magnetic fields and find that the measured speeds are consistent with characteristic fast magnetosonic speeds in the corona. In addition, the wave front turns outmore » to be the upper coronal counterpart of the EIT wave observed by STEREO EUVI traveling against the solar coronal disk; moreover, stationary fronts of the EIT wave are found to be located at the footpoints of deflected streamers and boundaries of coronal holes, after the wave front in the upper solar corona passes through open magnetic field lines in the streamers. Our findings suggest that the observed EIT wave should be in fact a fast magnetosonic shock/wave traveling in the inhomogeneous solar corona, as part of the fast magnetosonic wave propagating in the extended solar corona.« less

Last results of MADRAS, a space active optics demonstrator

NASA Astrophysics Data System (ADS)

Laslandes, Marie; Hourtoule, Claire; Hugot, Emmanuel; Ferrari, Marc; Devilliers, Christophe; Liotard, Arnaud; Lopez, Céline; Chazallet, Frédéric

2017-11-01

The goal of the MADRAS project (Mirror Active, Deformable and Regulated for Applications in Space) is to highlight the interest of Active Optics for the next generation of space telescope and instrumentation. Wave-front errors in future space telescopes will mainly come from thermal dilatation and zero gravity, inducing large lightweight primary mirrors deformation. To compensate for these effects, a 24 actuators, 100 mm diameter deformable mirror has been designed to be inserted in a pupil relay. Within the project, such a system has been optimized, integrated and experimentally characterized. The system is designed considering wave-front errors expected in 3m-class primary mirrors, and taking into account space constraints such as compactness, low weight, low power consumption and mechanical strength. Finite Element Analysis allowed an optimization of the system in order to reach a precision of correction better than 10 nm rms. A dedicated test-bed has been designed to fully characterize the integrated mirror performance in representative conditions. The test set up is made of three main parts: a telescope aberrations generator, a correction loop with the MADRAS mirror and a Shack-Hartman wave-front sensor, and PSF imaging. In addition, Fizeau interferometry monitors the optical surface shape. We have developed and characterized an active optics system with a limited number of actuators and a design fitting space requirements. All the conducted tests tend to demonstrate the efficiency of such a system for a real-time, in situ wave-front. It would allow a significant improvement for future space telescopes optical performance while relaxing the specifications on the others components.

Experimental study of an adaptive CFRC reflector for high order wave-front error correction

NASA Astrophysics Data System (ADS)

Lan, Lan; Fang, Houfei; Wu, Ke; Jiang, Shuidong; Zhou, Yang

2018-03-01

The recent radio frequency communication system developments are generating the need for creating space antennas with lightweight and high precision. The carbon fiber reinforced composite (CFRC) materials have been used to manufacture the high precision reflector. The wave-front errors caused by fabrication and on-orbit distortion are inevitable. The adaptive CFRC reflector has received much attention to do the wave-front error correction. Due to uneven stress distribution that is introduced by actuation force and fabrication, the high order wave-front errors such as print-through error is found on the reflector surface. However, the adaptive CFRC reflector with PZT actuators basically has no control authority over the high order wave-front errors. A new design architecture assembled secondary ribs at the weak triangular surfaces is presented in this paper. The virtual experimental study of the new adaptive CFRC reflector has conducted. The controllability of the original adaptive CFRC reflector and the new adaptive CFRC reflector with secondary ribs are investigated. The virtual experimental investigation shows that the new adaptive CFRC reflector is feasible and efficient to diminish the high order wave-front error.

On the Stability of the Detonation Wave Front in the High Explosive Liquid Mixture Tetranitromethane/Nitrobenzene

NASA Astrophysics Data System (ADS)

Fedorov, A. V.; Mikhaylov, A. L.; Men'Shikh, A. V.; Nazarov, D. V.; Finyushin, S. A.; Davydov, V. A.

2010-10-01

We performed experimental studies on the stability of the detonation wave front in mixtures of the liquids tetranitromethane (TNM) and nitrobenzene (NB). Tetranitromethane is an oxygen-rich explosive and nitrobenzene was used as a solvent or dilutant. (NB is not classed as an explosive but as an explosive would be oxygen poor and fuel rich.) The primary diagnostic was a laser velocimetry method with high temporal resolution. Data obtained were compared with the detonation parameters of the TNM/NB mixtures. In previous experimental work [1,2] it was shown that the detonation wave front in liquid explosives may be either smooth or rough. Rough detonation fronts have been reported in nitromethane, as well as nitromethane mixed with a solvent. Smooth detonation fronts have been reported in tetranitromethane. Previously, we conducted studies on the structure of the detonation wave front in liquid explosives containing tetranitromethane [3-5]. Smooth, stable fronts were recorded in pure tetranitromethane and in a 46/54 mixture of tetranitromethane and nitromethane. A pulsating, unstable detonation wave front was recorded in a 74/26 mixture of tetranitromethane and nitrobenzene. The goal of the present work is to extend our research on the structure of the detonation wave front in mixtures of tetranitromethane diluted with less energetic nitrobenzene. To this end, the following TNM/NB mixtures were studied: 95/5, 90/10, 85/15, 80/20, 74/26, and 50/50.

Transport of pollutants and sediment in the area of the Wave Hub (Celtic Sea)

NASA Astrophysics Data System (ADS)

Shapiro, Georgy; Huntley, David

2010-05-01

Ocean waves are a sustainable source of alternative energy that, if properly developed, will provide a quarter of current electricity demand and contribute to lowering the UK's reliance on fossil fuels. The UK government has given planning approval for a pilot power plant called the Wave Hub located in the eastern Celtic Sea off the Cornish north coast. The impact of a small number of devices on the physical environment is expected to be subtle outside the exclusion zone. However, such pilot projects are considered as the launching pad in the UK's ambitious programme to create a new wave energy industry. Large scale off-shore industrial activity can interact with the physical environment of the shelf sea in a two-fold manner: (i) the wave farm is affected by the waves, currents, variation in temperature and movements of sediment, and (ii) it can impact on the marine environment via a number of ways including release of dissolved and suspended matter during construction, operational and decommission stages of the project. These changes in the physical environment can then be translated into changes of the ecosystem and corresponding human activities. The Celtic Sea has a highly variable and complex thermal structure. In the spring and summer the water column becomes stratified due to solar heating of the surface layer, particularly in the areas of greater depth and/or low currents, where the turbulence is insufficient to mix the entire water column. Fronts form at the junctions of stratified and mixed water columns and these fronts generate currents which flow along the fronts. These frontal currents are subject to baroclinic instability and generate a whole set of mesoscale (i.e. comparable with the baroclinic Rossby radius) features such as eddies, filaments and mushroom currents, which are clearly seen on satellite images. Ecosystems are particularly concentrated in the vicinity of fronts so changes in frontal strength or location can have significant biological consequences. This paper presents some preliminary modelling results of a baseline study focussed on hind-cast and now-cast simulation of the 3D structure of temperature, salinity and current velocity in the area immediately adjacent to the location of the Wave Hub. Of the range of available 3D numerical models for shelf sea hydrodynamics, we have selected the Proudman Oceanographic Laboratory Coastal Modelling System (POLCOMS). The POLCOMS has successfully been used in a number of coastal/shelf sea regions to simulate circulation of coastal waters. Modelling is carried out in the region of approximately 200x 200 km with the variable vertical resolution typically less than 2 m. Such parameters allow resololution of the formation of coastal density fronts both within and outside the wave shadow zone, expected to be of the order of tens of kilometres. The meteorological parameters are obtained from the publicly available NCEP re-analyses data base. These parameters include components of the wind velocity and the surface heat fluxes, air pressure at sea level; temperature and humidity in the low troposphere; precipitation and cloudiness. In this study, the transport of pollution is simulated by a number of passive drifters located at a certain depth at a number of locations including the central point of the Wave Hub. Sediment transport is modelled using the Engelund-Hansen algorithm taking the current velocities produced by the POLCOMS as an input parameter. The Celtic sea is a tidally dominated region, and the modelling is run both in full-forcing and in tide-only modes in order to assess effects of density fronts on the residual (tidally averaged) circulation pattern. The results show that the pollution pathways are very sensitive to the formation of temperature fronts. In some cases the passive traces move in nearly opposite directions when the effect of temperature fronts is disregarded. Sediment transport is highly non-uniform spatially with some four areas along the Cornish coast being particularly affected. Sediment transport is also sensitive to the neap-spring phase of the tidal cycle. Residual currents caused by the non-linear tidal stream rectification are comparable or slower (depending on location) than the density driven currents caused by formation of temperature fronts. Location of the Wave Hub is particularly prone to strong transport of suspended particulate matter subject to availability of sediment on the seabed. These preliminary results suggest that the region of the Celtic Sea where the proposed Wave Hub is sited is an excellent location for assessing potential impacts of wave energy extraction. The authors wish to thank D. L. Aleynik for his help in setting up the POLCOMS model and the PRIMaRE project for providing computing facilities.

Geometrical shock dynamics, formation of singularities and topological bifurcations of converging shock fronts

NASA Astrophysics Data System (ADS)

Suramlishvili, Nugzar; Eggers, Jens; Fontelos, Marco

2014-11-01

We are concerned with singularities of the shock fronts of converging perturbed shock waves. Our considerations are based on Whitham's theory of geometrical shock dynamics. The recently developed method of local analysis is applied in order to determine generic singularities. In this case the solutions of partial differential equations describing the geometry of the shock fronts are presented as families of smooth maps with state variables and the set of control parameters dependent on Mach number, time and initial conditions. The space of control parameters of the singularities is analysed, the unfoldings describing the deformations of the canonical germs of shock front singularities are found and corresponding bifurcation diagrams are constructed. Research is supported by the Leverhulme Trust, Grant Number RPG-2012-568.

Twisted gravitational waves

NASA Astrophysics Data System (ADS)

Bini, Donato; Chicone, Carmen; Mashhoon, Bahram

2018-03-01

In general relativity (GR), linearized gravitational waves propagating in empty Minkowski spacetime along a fixed spatial direction have the property that the wave front is the Euclidean plane. Beyond the linear regime, exact plane waves in GR have been studied theoretically for a long time and many exact vacuum solutions of the gravitational field equations are known that represent plane gravitational waves. These have parallel rays and uniform wave fronts. It turns out, however, that GR also admits exact solutions representing gravitational waves propagating along a fixed direction that are nonplanar. The wave front is then nonuniform and the bundle of rays is twisted. We find a class of solutions representing nonplanar unidirectional gravitational waves and study some of the properties of these twisted waves.

Activation patterns of Purkinje fibers during long-duration ventricular fibrillation in an isolated canine heart model.

PubMed

Tabereaux, Paul B; Walcott, Greg P; Rogers, Jack M; Kim, Jong; Dosdall, Derek J; Robertson, Peter G; Killingsworth, Cheryl R; Smith, William M; Ideker, Raymond E

2007-09-04

The roles of Purkinje fibers (PFs) and focal wave fronts, if any, in the maintenance of ventricular fibrillation (VF) are unknown. If PFs are involved in VF maintenance, it should be possible to map wave fronts propagating from PFs into the working ventricular myocardium during VF. If wave fronts ever arise focally during VF, it should be possible to map them appearing de novo. Six canine hearts were isolated, and the left main coronary artery was cannulated and perfused. The left ventricular cavity was exposed, which allowed direct endocardial mapping of the anterior papillary muscle insertion. Nonperfused VF was induced, and 6 segments of data, each 5 seconds long, were analyzed during 10 minutes of VF. During 36 segments of data that were analyzed, 1018 PF or focal wave fronts of activation were identified. In 534 wave fronts, activation was mapped propagating from working ventricular myocardium to PF. In 142 wave fronts, activation was mapped propagating from PF to working ventricular myocardium. In 342 wave fronts, activation was mapped arising focally. More than 1 of these 3 patterns could occur in the same wave front. PFs are highly active throughout the first 10 minutes of VF. In addition to retrograde propagation from the working ventricular myocardium to PFs, antegrade propagation occurs from PFs to working ventricular myocardium, which suggests PFs are important in VF maintenance. Prior plunge needle recordings in dogs indicate activation propagates from the endocardium toward the epicardium after 1 minute of VF, which suggests that focal sites on the endocardium may represent foci and not breakthrough. If so, in addition to reentry, abnormal automaticity or triggered activity may also occur during VF.

Influence of wave-front sampling in adaptive optics retinal imaging

PubMed Central

Laslandes, Marie; Salas, Matthias; Hitzenberger, Christoph K.; Pircher, Michael

2017-01-01

A wide range of sampling densities of the wave-front has been used in retinal adaptive optics (AO) instruments, compared to the number of corrector elements. We developed a model in order to characterize the link between number of actuators, number of wave-front sampling points and AO correction performance. Based on available data from aberration measurements in the human eye, 1000 wave-fronts were generated for the simulations. The AO correction performance in the presence of these representative aberrations was simulated for different deformable mirror and Shack Hartmann wave-front sensor combinations. Predictions of the model were experimentally tested through in vivo measurements in 10 eyes including retinal imaging with an AO scanning laser ophthalmoscope. According to our study, a ratio between wavefront sampling points and actuator elements of 2 is sufficient to achieve high resolution in vivo images of photoreceptors. PMID:28271004

Spatial Dynamics of Multilayer Cellular Neural Networks

NASA Astrophysics Data System (ADS)

Wu, Shi-Liang; Hsu, Cheng-Hsiung

2018-02-01

The purpose of this work is to study the spatial dynamics of one-dimensional multilayer cellular neural networks. We first establish the existence of rightward and leftward spreading speeds of the model. Then we show that the spreading speeds coincide with the minimum wave speeds of the traveling wave fronts in the right and left directions. Moreover, we obtain the asymptotic behavior of the traveling wave fronts when the wave speeds are positive and greater than the spreading speeds. According to the asymptotic behavior and using various kinds of comparison theorems, some front-like entire solutions are constructed by combining the rightward and leftward traveling wave fronts with different speeds and a spatially homogeneous solution of the model. Finally, various qualitative features of such entire solutions are investigated.

Chilean Tsunami Rocks the Ross Ice Shelf

NASA Astrophysics Data System (ADS)

Bromirski, P. D.; Gerstoft, P.; Chen, Z.; Stephen, R. A.; Diez, A.; Arcas, D.; Wiens, D.; Aster, R. C.; Nyblade, A.

2016-12-01

The response of the Ross Ice Shelf (RIS) to the September 16, 2015 9.3 Mb Chilean earthquake tsunami (> 75 s period) and infragravity (IG) waves (50 - 300 s period) were recorded by a broadband seismic array deployed on the RIS from November 2014 to November 2015. The array included two linear transects, one approximately orthogonal to the shelf front extending 430 km southward toward the grounding zone, and an east-west transect spanning the RIS roughly parallel to the front about 100 km south of the ice edge (https://scripps.ucsd.edu/centers/iceshelfvibes/). Signals generated by both the tsunami and IG waves were recorded at all stations on floating ice, with little ocean wave-induced energy reaching stations on grounded ice. Cross-correlation and dispersion curve analyses indicate that tsunami and IG wave-generated signals propagate across the RIS at gravity wave speeds (about 70 m/s), consistent with coupled water-ice flexural-gravity waves propagating through the ice shelf from the north. Gravity wave excitation at periods > 100 s is continuously observed during the austral winter, providing mechanical excitation of the RIS throughout the year. Horizontal displacements are typically about 3 times larger than vertical displacements, producing extensional motions that could facilitate expansion of existing fractures. The vertical and horizontal spectra in the IG band attenuate exponentially with distance from the front. Tsunami model data are used to assess variability of excitation of the RIS by long period gravity waves. Substantial variability across the RIS roughly parallel to the front is observed, likely resulting from a combination of gravity wave amplitude variability along the front, signal attenuation, incident angle of the wave forcing at the front that depends on wave generation location as well as bathymetry under and north of the shelf, and water layer and ice shelf thickness and properties.

Robust Wave-front Correction in a Small Scale Adaptive Optics System Using a Membrane Deformable Mirror

NASA Astrophysics Data System (ADS)

Choi, Y.; Park, S.; Baik, S.; Jung, J.; Lee, S.; Yoo, J.

A small scale laboratory adaptive optics system using a Shack-Hartmann wave-front sensor (WFS) and a membrane deformable mirror (DM) has been built for robust image acquisition. In this study, an adaptive limited control technique is adopted to maintain the long-term correction stability of an adaptive optics system. To prevent the waste of dynamic correction range for correcting small residual wave-front distortions which are inefficient to correct, the built system tries to limit wave-front correction when a similar small difference wave-front pattern is repeatedly generated. Also, the effect of mechanical distortion in an adaptive optics system is studied and a pre-recognition method for the distortion is devised to prevent low-performance system operation. A confirmation process for a balanced work assignment among deformable mirror (DM) actuators is adopted for the pre-recognition. The corrected experimental results obtained by using a built small scale adaptive optics system are described in this paper.

Space-borne observation of mesospheric bore by Visible and near Infrared Spectral Imager onboard the International Space Station

NASA Astrophysics Data System (ADS)

Hozumi, Y.; Saito, A.; Sakanoi, T.; Yamazaki, A.; Hosokawa, K.

2017-12-01

Mesospheric bores were observed by Visible and near Infrared Spectral Imager (VISI) of the ISS-IMAP mission (Ionosphere, Mesosphere, upper Atmosphere and Plasmasphere mapping mission from the International Space Station) in O2 airglow at 762 nm wavelength. The mesospheric bore is moving front of sharp jump followed by undulations or turbulence in the mesopause region. Since previous studies of mesospheric bore were mainly based on ground-based airglow imaging that is limited in field-of-view and observing site, little is known about its horizontal extent and global behavior. Space-borne imaging by ISS-IMAP/VISI provides an opportunity to study the mesospheric bore with a wide field-of-view and global coverage. A mesospheric bore was captured by VISI in two consecutive paths on 9 July 2015 over the south of African continent (48ºS - 54ºS and 15ºE). The wave front aligned with south-north direction and propagated to west. The phase velocity and wave length of the following undulation were estimated to 100 m/s and 30 km, respectively. Those parameters are similar to those reported by previous studies. 30º anti-clockwise rotation of the wave front was recognized in 100 min. Another mesospheric bore was captured on 9 May 2013 over the south Atlantic ocean (35ºS - 43ºS and 24ºW - 1ºE) with more than 2,200 km horizontal extent of wave front. The wave front aligned with southeast-northwest direction. Because the following undulation is recognized in the southwest side of the wave front, it is estimated to propagate to northeast direction. The wave front was modulated with 1,000 km wave length. This modulation implies inhomogeneity of the phase velocity.

3D structure and kinematics characteristics of EUV wave front

NASA Astrophysics Data System (ADS)

Podladchikova, T.; Veronig, A.; Dissauer, K.

2017-12-01

We present 3D reconstructions of EUV wave fronts using multi-point observations from the STEREO-A and STEREO-B spacecraft. EUV waves are large-scale disturbances in the solar corona that are initiated by coronal mass ejections, and are thought to be large-amplitude fast-mode MHD waves or shocks. The aim of our study is to investigate the dynamic evolution of the 3D structure and wave kinematics of EUV wave fronts. We study the events on December 7, 2007 and February 13, 2009 using data from the STEREO/EUVI-A and EUVI-B instruments in the 195 Å filter. The proposed approach is based on a complementary combination of epipolar geometry of stereo vision and perturbation profiles. We propose two different solutions to the matching problem of the wave crest on images from the two spacecraft. One solution is suitable for the early and maximum stage of event development when STEREO-A and STEREO-B see the different facets of the wave, and the wave crest is clearly outlined. The second one is applicable also at the later stage of event development when the wave front becomes diffuse and is faintly visible. This approach allows us to identify automatically the segments of the diffuse front on pairs of STEREO-A and STEREO-B images and to solve the problem of identification and matching of the objects. We find that the EUV wave observed on December 7, 2007 starts with a height of 30-50 Mm, sharply increases to a height of 100-120 Mm about 10 min later, and decreases to 10-20 Mm in the decay phase. Including the 3D evolution of the EUV wave front allowed us to correct the wave kinematics for projection and changing height effects. The velocity of the wave crest (V=215-266 km/s) is larger than the trailing part of the wave pulse (V=103-163 km/s). For the February 9, 2009 event, the upward movement of the wave crest shows an increase from 20 to 100 Mm over a period of 30 min. The velocity of wave crest reaches values of 208-211 km/s.

Mathematical Methods in Wave Propagation: Part 2--Non-Linear Wave Front Analysis

ERIC Educational Resources Information Center

Jeffrey, Alan

1971-01-01

The paper presents applications and methods of analysis for non-linear hyperbolic partial differential equations. The paper is concluded by an account of wave front analysis as applied to the piston problem of gas dynamics. (JG)

A comparison of the Maslov integral seismogram and the finite-difference method

NASA Astrophysics Data System (ADS)

Huang, X.; Kendall, J.-M.; Thomson, C. J.; West, G. F.

1998-03-01

The Maslov asymptotic method addresses some of the problems with standard ray theory, such as caustics and shadows. However, it has been applied relatively little, perhaps because its accuracy remains untested. In this study we examine Maslov integral (MI) seismograms by comparing them with finite-difference (FD) seismograms for several cases of interest, such as (1) velocity gradients generating traveltime triplications and shadows, (2) wave-front bending, kinking and folding in a low-velocity waveguide, and (3) wavefield propagation perturbed by a high-velocity slab. The results show that many features of high- and intermediate-frequency waveforms are reliably predicted by Maslov's technique, but also that it is far less reliable and even fails for low frequencies. The terms `high' and `low' are model-dependent, but we mean the range over which it is sensible to discuss signals associated with identifiable wave fronts and local (if complicated) effects that potentially can be unravelled in interpretation. Of the high- and intermediate-frequency wave components, those wave- front anomalies due to wave-front bending, kinking, folding or rapid ray divergence can be accurately given by MI. True diffractions due to secondary wave-front sections are theoretically not included in Maslov theory (as they require true diffracted rays), but in practice they can often be satisfactorily predicted. This occurs roughly within a wavelength of the truncated geometrical wave front, where such diffractions are most important since their amplitudes may still be as large as half that on the geometrical wave front itself. Outside this region MI is inaccurate (although then the diffractions are usually small). Thus waveforms of high and intermediate frequencies are essentially controlled by classical wave-front geometry. Our results also show that the accuracy of MI can be improved by rotating the Maslov integration axis so that the nearest wave-front anomaly is adequately `sampled'. This rotation can be performed after ray tracing and it can serve to avoid pseudo-caustics by using it in conjunction with the phase-partitioning approach. The effort needed in phase partitioning has been reduced by using an interactive graphics technique. It is difficult to formulate a general rule prescribing the limitations of MI accuracy because of model dependency. However, our experiences indicate that two space- and two timescales need to be considered. These are the pulse width in space, the length scale over which the instantaneous wave-front curvature changes, and the timescales of pulse width and significant features in the ray traveltime curve. It seems, from our examples, that when these scales are comparable, the Maslov method gives very acceptable results.

A new wave front shape-based approach for acoustic source localization in an anisotropic plate without knowing its material properties.

PubMed

Sen, Novonil; Kundu, Tribikram

2018-07-01

Estimating the location of an acoustic source in a structure is an important step towards passive structural health monitoring. Techniques for localizing an acoustic source in isotropic structures are well developed in the literature. Development of similar techniques for anisotropic structures, however, has gained attention only in the recent years and has a scope of further improvement. Most of the existing techniques for anisotropic structures either assume a straight line wave propagation path between the source and an ultrasonic sensor or require the material properties to be known. This study considers different shapes of the wave front generated during an acoustic event and develops a methodology to localize the acoustic source in an anisotropic plate from those wave front shapes. An elliptical wave front shape-based technique was developed first, followed by the development of a parametric curve-based technique for non-elliptical wave front shapes. The source coordinates are obtained by minimizing an objective function. The proposed methodology does not assume a straight line wave propagation path and can predict the source location without any knowledge of the elastic properties of the material. A numerical study presented here illustrates how the proposed methodology can accurately estimate the source coordinates. Copyright © 2018 Elsevier B.V. All rights reserved.

Traveling waves in a spring-block chain sliding down a slope

NASA Astrophysics Data System (ADS)

Morales, J. E.; James, G.; Tonnelier, A.

2017-07-01

Traveling waves are studied in a spring slider-block model. We explicitly construct front waves (kinks) for a piecewise-linear spinodal friction force. Pulse waves are obtained as the matching of two traveling fronts with identical speeds. Explicit formulas are obtained for the wavespeed and the wave form in the anticontinuum limit. The link with localized waves in a Burridge-Knopoff model of an earthquake fault is briefly discussed.

Traveling waves in a spring-block chain sliding down a slope.

PubMed

Morales, J E; James, G; Tonnelier, A

2017-07-01

Traveling waves are studied in a spring slider-block model. We explicitly construct front waves (kinks) for a piecewise-linear spinodal friction force. Pulse waves are obtained as the matching of two traveling fronts with identical speeds. Explicit formulas are obtained for the wavespeed and the wave form in the anticontinuum limit. The link with localized waves in a Burridge-Knopoff model of an earthquake fault is briefly discussed.

Characterising a holographic modal phase mask for the detection of ocular aberrations

NASA Astrophysics Data System (ADS)

Corbett, A. D.; Leyva, D. Gil; Diaz-Santana, L.; Wilkinson, T. D.; Zhong, J. J.

2005-12-01

The accurate measurement of the double-pass ocular wave front has been shown to have a broad range of applications from LASIK surgery to adaptively corrected retinal imaging. The ocular wave front can be accurately described by a small number of Zernike circle polynomials. The modal wave front sensor was first proposed by Neil et al. and allows the coefficients of the individual Zernike modes to be measured directly. Typically the aberrations measured with the modal sensor are smaller than those seen in the ocular wave front. In this work, we investigated a technique for adapting a modal phase mask for the sensing of the ocular wave front. This involved extending the dynamic range of the sensor by increasing the pinhole size to 2.4mm and optimising the mask bias to 0.75λ. This was found to decrease the RMS error by up to a factor of three for eye-like aberrations with amplitudes up to 0.2μm. For aberrations taken from a sample of real-eye measurements a 20% decrease in the RMS error was observed.

Storms or cold fronts? What is really responsible for the extreme waves regime in the Colombian Caribbean coast

NASA Astrophysics Data System (ADS)

Otero, L. J.; Ortiz-Royero, J. C.; Ruiz-Merchan, J. K.; Higgins, A. E.; Henriquez, S. A.

2015-05-01

On Friday, 7 March 2009, a 200 m-long section of the tourist pier in Puerto Colombia collapsed under the impact of the waves generated by a cold front in the area. The aim of this study is to determine the contribution and importance of cold fronts and storms on extreme waves in different areas of the Colombian Caribbean to determine the degree of the threat posed by the flood processes to which these coastal populations are exposed and the actions to which coastal engineering constructions should be subject. In the calculation of maritime constructions, the most important parameter is the wave's height; therefore, it is necessary to definitively know the design wave height to which a coastal engineering structure should be resistant. This wave height varies according to the return period considered. Using Gumbel's extreme value methodology, the significant height values for the study area were calculated. The methodology was evaluated using data from the re-analysis of the spectral NOAA Wavewatch III (WW3) model for 15 points along the 1600 km of the Colombia Caribbean coast (continental and insular) of the last 15 years. The results demonstrated that the extreme waves caused by tropical cyclones and cold fronts have different effects along the Colombian Caribbean coast. Storms and hurricanes are of greater importance in the Guajira Peninsula (Alta Guajira). In the central area formed by Baja Guajira, Santa Marta, Barranquilla, and Cartagena, the strong influence of cold fronts on extreme waves is evident. On the other hand, in the southern region of the Colombian Caribbean coast, from the Gulf of Morrosquillo to the Gulf of Urabá, even though extreme waves are lower than in the previous regions, extreme waves are dominated mainly by the passage of cold fronts. Extreme waves in the San Andrés and Providencia insular region present a different dynamic from that in the continental area due to its geographic location. The wave heights in the extreme regime are similar in magnitude to those found in Alta Guajira, but the extreme waves associated with the passage of cold fronts in this region have lower return periods than the extreme waves associated with hurricane season. These results are of great importance when evaluating the threat of extreme waves in the coastal and port infrastructure, for purposes of the design of new constructions, and in the coastal flood processes due to run-up because, according to the site of interest in the coast, the forces that shape extreme waves are not the same.

Smoldering wave-front velocity in fiberboard

Treesearch

John J. Brenden; Erwin L. Schaffer

1980-01-01

In fiberboard, the phenomena of smoldering can be visualized as decomposition resulting from the motion of a thermal wave-front through the material. The tendency to smolder is then directly proportional to the velocity of the front. Velocity measurements were made on four fiberboards and were compared to values given in the literature for several substances....

Target-in-the-loop beam control: basic considerations for analysis and wave-front sensing

NASA Astrophysics Data System (ADS)

Vorontsov, Mikhail A.; Kolosov, Valeriy

2005-01-01

Target-in-the-loop (TIL) wave propagation geometry represents perhaps the most challenging case for adaptive optics applications that are related to maximization of irradiance power density on extended remotely located surfaces in the presence of dynamically changing refractive-index inhomogeneities in the propagation medium. We introduce a TIL propagation model that uses a combination of the parabolic equation describing coherent outgoing-wave propagation, and the equation describing evolution of the mutual correlation function (MCF) for the backscattered wave (return wave). The resulting evolution equation for the MCF is further simplified by use of the smooth-refractive-index approximation. This approximation permits derivation of the transport equation for the return-wave brightness function, analyzed here by the method of characteristics (brightness function trajectories). The equations for the brightness function trajectories (ray equations) can be efficiently integrated numerically. We also consider wave-front sensors that perform sensing of speckle-averaged characteristics of the wave-front phase (TIL sensors). Analysis of the wave-front phase reconstructed from Shack-Hartmann TIL sensor measurements shows that an extended target introduces a phase modulation (target-induced phase) that cannot be easily separated from the atmospheric-turbulence-related phase aberrations. We also show that wave-front sensing results depend on the extended target shape, surface roughness, and outgoing-beam intensity distribution on the target surface. For targets with smooth surfaces and nonflat shapes, the target-induced phase can contain aberrations. The presence of target-induced aberrations in the conjugated phase may result in a deterioration of adaptive system performance.

Target-in-the-loop beam control: basic considerations for analysis and wave-front sensing.

PubMed

Vorontsov, Mikhail A; Kolosov, Valeriy

2005-01-01

Target-in-the-loop (TIL) wave propagation geometry represents perhaps the most challenging case for adaptive optics applications that are related to maximization of irradiance power density on extended remotely located surfaces in the presence of dynamically changing refractive-index inhomogeneities in the propagation medium. We introduce a TIL propagation model that uses a combination of the parabolic equation describing coherent outgoing-wave propagation, and the equation describing evolution of the mutual correlation function (MCF) for the backscattered wave (return wave). The resulting evolution equation for the MCF is further simplified by use of the smooth-refractive-index approximation. This approximation permits derivation of the transport equation for the return-wave brightness function, analyzed here by the method of characteristics (brightness function trajectories). The equations for the brightness function trajectories (ray equations) can be efficiently integrated numerically. We also consider wave-front sensors that perform sensing of speckle-averaged characteristics of the wave-front phase (TIL sensors). Analysis of the wave-front phase reconstructed from Shack-Hartmann TIL sensor measurements shows that an extended target introduces a phase modulation (target-induced phase) that cannot be easily separated from the atmospheric-turbulence-related phase aberrations. We also show that wave-front sensing results depend on the extended target shape, surface roughness, and outgoing-beam intensity distribution on the target surface. For targets with smooth surfaces and nonflat shapes, the target-induced phase can contain aberrations. The presence of target-induced aberrations in the conjugated phase may result in a deterioration of adaptive system performance.

SLOW PATCHY EXTREME-ULTRAVIOLET PROPAGATING FRONTS ASSOCIATED WITH FAST CORONAL MAGNETO-ACOUSTIC WAVES IN SOLAR ERUPTIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Y.; Ding, M. D.; Chen, P. F., E-mail: guoyang@nju.edu.cn

2015-08-15

Using the high spatiotemporal resolution extreme ultraviolet (EUV) observations of the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we conduct a statistical study of the observational properties of the coronal EUV propagating fronts. We find that it might be a universal phenomenon for two types of fronts to coexist in a large solar eruptive event. It is consistent with the hybrid model of EUV propagating fronts, which predicts that coronal EUV propagating fronts consist of both a fast magneto-acoustic wave and a nonwave component. We find that the morphologies, propagation behaviors, and kinematic features of the two EUVmore » propagating fronts are completely different from each other. The fast magneto-acoustic wave fronts are almost isotropic. They travel continuously from the flaring region across multiple magnetic polarities to global distances. On the other hand, the slow nonwave fronts appear as anisotropic and sequential patches of EUV brightening. Each patch propagates locally in the magnetic domains where the magnetic field lines connect to the bottom boundary and stops at the magnetic domain boundaries. Within each magnetic domain, the velocities of the slow patchy nonwave component are an order of magnitude lower than that of the fast-wave component. However, the patches of the slow EUV propagating front can jump from one magnetic domain to a remote one. The velocities of such a transit between different magnetic domains are about one-third to one-half of those of the fast-wave component. The results show that the velocities of the nonwave component, both within one magnetic domain and between different magnetic domains, are highly nonuniform due to the inhomogeneity of the magnetic field in the lower atmosphere.« less

Analysis of moving surface structures at a laser-induced boiling front

NASA Astrophysics Data System (ADS)

Matti, R. S.; Kaplan, A. F. H.

2014-10-01

Recently ultra-high speed imaging enabled to observe moving wave patterns on metal melts that experience laser-induced boiling. In laser materials processing a vertical laser-induced boiling front governs processes like keyhole laser welding, laser remote fusion cutting, laser drilling or laser ablation. The observed waves originate from temperature variations that are closely related to the melt topology. For improved understanding of the essential front mechanisms and of the front topology, for the first time a deeper systematic analysis of the wave patterns was carried out. Seven geometrical shapes of bright or dark domains were distinguished and categorized, in particular bright peaks of three kinds and dark valleys, often inclined. Two categories describe special flow patterns at the top and bottom of the front. Dynamic and statistical analysis has revealed that the shapes often combine or separate from one category to another when streaming down the front. The brightness of wave peaks typically fluctuates during 20-50 μs. This variety of thermal wave observations is interpreted with respect to the accompanying surface topology of the melt and in turn for governing local mechanisms like absorption, shadowing, boiling, ablation pressure and melt acceleration. The findings can be of importance for understanding the key process mechanisms and for optimizing laser materials processing.

Cold fronts in the Colombian Caribbean Sea and their relationship to extreme wave events

NASA Astrophysics Data System (ADS)

Ortiz-Royero, J. C.; Otero, L. J.; Restrepo, J. C.; Ruiz, J.; Cadena, M.

2013-11-01

Extreme ocean waves in the Caribbean Sea are commonly related to the effects of storms and hurricanes during the months of June through November. The collapse of 200 m of the Puerto Colombia pier in March 2009 revealed the effects of meteorological phenomena other than storms and hurricanes that may be influencing the extreme wave regime in the Colombian Caribbean. The marked seasonality of these atmospheric fronts was established by analyzing the meteorological-marine reports of the Instituto de Hidrología, Meteorología y Estudios Ambientales of Colombia (IDEAM, based on its initials in Spanish) and the Centro de Investigación en Oceanografía y Meteorología of Colombia (CIOH, based on its initials in Spanish) during the last 16 yr. The highest number of cold fronts was observed during the months of January, February, and March, with 6 fronts occurring per year. An annual trend was observed and the highest number of fronts occurred in 2010 (20 in total); moreover, an annual strong relationship between the maximum average wave values and the cold fronts in the central zone of the Colombian Caribbean during the first three months of the year was established. In addition, the maximum values of the significant height produced by the passage of cold fronts during the last 16 yr were identified. Although the Colombian Caribbean has been affected by storms and hurricanes in the past, this research allows us to conclude that there is a strong relationship between cold fronts and the largest waves in the Colombian Caribbean during the last 16 yr, which have caused damage to coastal infrastructure. We verified that the passage of a cold front corresponded to the most significant extreme wave event of the last two decades in the Colombian Caribbean, which caused the structural collapse of the Puerto Colombia pier, located near the city of Barranquilla, between 5 and 10 March 2009. This information is invaluable when evaluating average and extreme wave regimes for the purpose of informing the design of structures in this region of the Caribbean.

Diffraction of a plane wave by a three-dimensional corner

NASA Technical Reports Server (NTRS)

Ting, L.; Kung, F.

1971-01-01

By the superposition of the conical solution for the diffraction of a plane pulse by a three dimensional corner, the solution for a general incident plane wave is constructed. A numerical program is presented for the computation of the pressure distribution on the surface due to an incident plane wave of any wave form and at any incident angle. Numerical examples are presented to show the pressure signature at several points on the surface due to incident wave with a front shock wave, two shock waves in succession, or a compression wave with same peak pressure. The examples show that when the distance of a point on the surface from the edges or the vertex is comparable to the distance for the front pressure raise to reach the maximum, the peak pressure at that point can be much less than that given by a regular reflection, because the diffracted wave front arrives at that point prior to the arrival of the peak incident wave.

Pion and kaon valence-quark parton quasidistributions

NASA Astrophysics Data System (ADS)

Xu, Shu-Sheng; Chang, Lei; Roberts, Craig D.; Zong, Hong-Shi

2018-05-01

Algebraic Ansätze for the Poincaré-covariant Bethe-Salpeter wave functions of the pion and kaon are used to calculate their light-front wave functions, parton distribution amplitudes, parton quasidistribution amplitudes, valence parton distribution functions, and parton quasidistribution functions (PqDFs). The light-front wave functions are broad, concave functions, and the scale of flavor-symmetry violation in the kaon is roughly 15%, being set by the ratio of emergent masses in the s - and u -quark sectors. Parton quasidistribution amplitudes computed with longitudinal momentum Pz=1.75 GeV provide a semiquantitatively accurate representation of the objective parton distribution amplitude, but even with Pz=3 GeV , they cannot provide information about this amplitude's end point behavior. On the valence-quark domain, similar outcomes characterize PqDFs. In this connection, however, the ratio of kaon-to-pion u -quark PqDFs is found to provide a good approximation to the true parton distribution function ratio on 0.4 ≲x ≲0.8 , suggesting that with existing resources computations of ratios of parton quasidistributions can yield results that support empirical comparison.

Hydrodynamic and thermal mechanisms of filtration combustion inclinational instability based on non-uniform distribution of initial preheating temperature

NASA Astrophysics Data System (ADS)

Xia, Yongfang; Shi, Junrui; Xu, Youning; Ma, Rui

2018-03-01

Filtration combustion (FC) is one style of porous media combustion with inert matrix, in which the combustion wave front propagates, only downstream or reciprocally. In this paper, we investigate the FC flame front inclinational instability of lean methane/air mixtures flowing through a packed bed as a combustion wave front perturbation of the initial preheating temperature non-uniformity is assumed. The predicted results show that the growth rate of the flame front inclinational angle is proportional to the magnitude of the initial preheating temperature difference. Additionally, depending on gas inlet gas velocity and equivalence ratio, it is demonstrated that increase of gas inlet gas velocity accelerates the FC wave front deformation, and the inclinational instability evolves faster at lower equivalence ratio. The development of the flame front inclinational angle may be regarded as a two-staged evolution, which includes rapid increase, and approaching maximum value of inclinational angle due to the quasi-steady condition of the combustion system. The hydrodynamic and thermal mechanisms of the FC inclinational instability are analyzed. Consequently, the local propagation velocity of the FC wave front is non-uniform to result in the development of inclinational angle at the first stage of rapid increase.

Unsteady self-sustained detonation in flake aluminum dust/air mixtures

NASA Astrophysics Data System (ADS)

Liu, Q.; Li, S.; Huang, J.; Zhang, Y.

2017-07-01

Self-sustained detonation waves in flake aluminum dust/air mixtures have been studied in a tube of diameter 199 mm and length 32.4 m. A pressure sensor array of 32 sensors mounted around certain circumferences of the tube was used to measure the shape of the detonation front in the circumferential direction and pressure histories of the detonation wave. A two-head spin detonation wave front was observed for the aluminum dust/air mixtures, and the cellular structure resulting from the spinning movement of the triple point was analyzed. The variations in velocity and overpressure of the detonation wave with propagation distance in a cell were studied. The interactions of waves in triple-point configurations were analyzed and the flow-field parameters were calculated. Three types of triple-point configuration have been found in the wave front of the detonation wave of an aluminum dust/air mixture. Both strong and weak transverse waves exist in the unstable self-sustained detonation wave.

PECULIAR STATIONARY EUV WAVE FRONTS IN THE ERUPTION ON 2011 MAY 11

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chandra, R.; Fulara, A.; Chen, P. F.

We present and interpret the observations of extreme ultraviolet (EUV) waves associated with a filament eruption on 2011 May 11. The filament eruption also produces a small B-class two ribbon flare and a coronal mass ejection. The event is observed by the Solar Dynamic Observatory with high spatio-temporal resolution data recorded by the Atmospheric Imaging Assembly. As the filament erupts, we observe two types of EUV waves (slow and fast) propagating outwards. The faster EUV wave has a propagation velocity of ∼500 km s{sup −1} and the slower EUV wave has an initial velocity of ∼120 km s{sup −1}. Wemore » report, for the first time, that not only does the slower EUV wave stop at a magnetic separatrix to form bright stationary fronts, but also the faster EUV wave transits a magnetic separatrix, leaving another stationary EUV front behind.« less

Laboratory Study of Wave Generation Near Dipolarization Fronts

NASA Astrophysics Data System (ADS)

Tejero, E. M.; Enloe, C. L.; Amatucci, B.; Crabtree, C. E.; Ganguli, G.; Malaspina, D.

2017-12-01

Experiments conducted in the Space Physics Simulation Chamber at the Naval Research Laboratory (NRL) create plasma equilibria that replicate those found in dipolarization fronts. These experiments were designed to study the dynamics of boundary layers, such as dipolarization fronts, and it was found that there are instabilities generated by highly inhomogeneous plasma flows. It has previously been shown that these highly inhomogeneous flows can generate waves in the lower hybrid frequency range. Analysis of satellite observations indicate that the sheared flows are a plausible explanation for the observed lower hybrid waves at dipolarization fronts since they can generate longer wavelengths compared to the electron gyroradius, which is consistent with observations. Recent experiments at NRL have demonstrated that these flows can also generate electromagnetic waves in the whistler band. These waves are large amplitude, bursty waves that exhibit frequency chirps similar to whistler mode chorus. Recent results from these experiments and comparisons to in situ observations will be presented. * Work supported by the Naval Research Laboratory Base Program and NASA Grant No. NNH17AE70I.

The Effect of Sedimentary Basins on Through-Passing Short-Period Surface Waves

NASA Astrophysics Data System (ADS)

Feng, L.; Ritzwoller, M. H.

2017-12-01

Surface waves propagating through sedimentary basins undergo elastic wave field complications that include multiple scattering, amplification, the formation of secondary wave fronts, and subsequent wave front healing. Unless these effects are accounted for accurately, they may introduce systematic bias to estimates of source characteristics, the inference of the anelastic structure of the Earth, and ground motion predictions for hazard assessment. Most studies of the effects of basins on surface waves have centered on waves inside the basins. In contrast, we investigate wave field effects downstream from sedimentary basins, with particular emphasis on continental basins and propagation paths, elastic structural heterogeneity, and Rayleigh waves at 10 s period. Based on wave field simulations through a recent 3D crustal and upper mantle model of East Asia, we demonstrate significant Rayleigh wave amplification downstream from sedimentary basins in eastern China such that Ms measurements obtained on the simulated wave field vary by more than a magnitude unit. We show that surface wave amplification caused by basins results predominantly from elastic focusing and that amplification effects produced through 3D basin models are reproduced using 2D membrane wave simulations through an appropriately defined phase velocity map. The principal characteristics of elastic focusing in both 2D and 3D simulations include (1) retardation of the wave front inside the basins; (2) deflection of the wave propagation direction; (3) formation of a high amplitude lineation directly downstream from the basin bracketed by two low amplitude zones; and (4) formation of a secondary wave front. Finally, by comparing the impact of elastic focusing with anelastic attenuation, we argue that on-continent sedimentary basins are expected to affect surface wave amplitudes more strongly through elastic focusing than through the anelastic attenuation.

Role of lower hybrid waves in ion heating at dipolarization fronts

NASA Astrophysics Data System (ADS)

Greco, A.; Artemyev, A.; Zimbardo, G.; Angelopoulos, V.; Runov, A.

2017-05-01

One of the important sources of hot ions in the magnetotail is the bursty bulk flows propagating away from the reconnection region and heating the ambient plasma. Charged particles interact with nonlinear magnetic field pulses (dipolarization fronts, DFs) embedded into these flows. The convection electric fields associated with DF propagation are known to reflect and accelerate ambient ions. Moreover, a wide range of waves is observed within/near these fronts, the electric field fluctuations being dominated by the lower hybrid drift (LHD) instability. Here we investigate the potential role of these waves in the further acceleration of ambient ions. We use a LHD wave emission profile superimposed on the leading edge of a two-dimensional model profile of a DF and a test particle approach. We show that LHD waves with realistic amplitudes can significantly increase the upper limit of energies gained by ions. Wave-particle interaction near the front is more effective in producing superthermal ions than in increasing the flux of thermal ions. Comparison of test particle simulations and Time History of Events and Macroscale Interactions during Substorms observations show that ion acceleration by LHD waves is more important for slower DFs.

Measurement of wave-front aberration in a small telescope remote imaging system using scene-based wave-front sensing

DOEpatents

Poyneer, Lisa A; Bauman, Brian J

2015-03-31

Reference-free compensated imaging makes an estimation of the Fourier phase of a series of images of a target. The Fourier magnitude of the series of images is obtained by dividing the power spectral density of the series of images by an estimate of the power spectral density of atmospheric turbulence from a series of scene based wave front sensor (SBWFS) measurements of the target. A high-resolution image of the target is recovered from the Fourier phase and the Fourier magnitude.

Optical observation of shock waves and cavitation bubbles in high intensity laser-induced shock processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marti-Lopez, L.; Ocana, R.; Porro, J. A.

2009-07-01

We report an experimental study of the temporal and spatial dynamics of shock waves, cavitation bubbles, and sound waves generated in water during laser shock processing by single Nd:YAG laser pulses of nanosecond duration. A fast ICCD camera (2 ns gate time) was employed to record false schlieren photographs, schlieren photographs, and Mach-Zehnder interferograms of the zone surrounding the laser spot site on the target, an aluminum alloy sample. We recorded hemispherical shock fronts, cylindrical shock fronts, plane shock fronts, cavitation bubbles, and phase disturbance tracks.

Effect of cross grain on stress waves in lumber

Treesearch

C.C. Gerhards

1980-01-01

An evaluation is made of the effect of cross grain on the transit time of longitudinal compression stress waves in Douglas-fir 2 by 8 lumber. Cross grain causes the stress wave to advance with a front or contour skewed in the direction of the grain angle, rather than to advance with a front normal to the long axis of lumber. Thus, the timing of the stress wave in...

System for the design, manufacture, and testing of custom lenses with known amounts of high-order aberrations.

PubMed

Chernyak, Dimitri A; Campbell, Charles E

2003-11-01

Now that excimer laser systems can be programmed to correct complex aberrations of the eye on the basis of wave-front measurements, a method is needed to test the accuracy of the system from measurement through treatment. A closed-loop test method was developed to ensure that treatment plans generated by a wavefront measuring system were accurately transferred to and executed by the excimer laser. A surface was analytically defined, and a Shack-Hartmann-based wave-front system was used to formulate a treatment plan, which was downloaded to an excimer laser system. A plastic lens was ablated by the laser and then returned to the wave-front device, where it was measured and compared with the analytically defined wave-front surface. The two surfaces agreed up to 6th-order Zernike terms, validating the accuracy of the system.

Characterization and effects of cold fronts in the Colombian Caribbean Coast and their relationship to extreme wave events

NASA Astrophysics Data System (ADS)

Ortiz-Royero, J. C.; Otero, L. J.; Restrepo, J. C.; Ruiz, J.; Cadena, M.

2013-07-01

Extreme ocean waves in the Caribbean Sea are commonly related to the effects of storms and hurricanes during the months of June through November. The collapse of 200 m of the Puerto Colombia pier in March 2009 revealed the effects of meteorological phenomena other than storms and hurricanes that may be influencing the extreme wave regime in the Colombian Caribbean. The marked seasonality of these atmospheric fronts was established by analyzing the meteorological-marine reports of Instituto de Hidrología, Meteorología y Estudios Ambientales of Colombia (IDEAM, based on its initials in Spanish) and Centro de Investigación en Oceanografía y Meteorología of Colombia (CIOH, based on its initials in Spanish). The highest occurrences were observed during the months of January, February, and March, with 6 fronts occurring per year. An annual trend was not observed, although the highest number of fronts occurred in 2010 (20 in total). An annual strong relationship between the maximum average wave values and the cold fronts, in the central zone of the Colombian Caribbean during the first three months of the year was established. In addition, the maximum values of the significant height produced by the passage of cold fronts during the last 16 yr were identified. Although the Colombian Caribbean has been affected by storms and hurricanes in the past, this research allows us to conclude that, there is a strong relationship between cold fronts and the largest waves in the Colombian Caribbean during the last 16 yr, which have caused damage to coastal infrastructure. We verified that the passage of a cold front corresponded to the most significant extreme wave event of the last two decades in the Colombian Caribbean, which caused the structural collapse of the Puerto Colombia pier, located near the city of Barranquilla, between 5 and 10 March 2009. This information is invaluable when evaluating average and extreme wave regimes for the purpose of informing the design of structures in this region of the Caribbean.

Ultrasonic monitoring of spontaneous imbibition experiments: Precursory moisture diffusion effects ahead of water front

NASA Astrophysics Data System (ADS)

David, Christian; Sarout, Joël.; Dautriat, Jérémie; Pimienta, Lucas; Michée, Marie; Desrues, Mathilde; Barnes, Christophe

2017-07-01

Fluid substitution processes have been investigated in the laboratory on 14 carbonate and siliciclastic reservoir rock analogues through spontaneous imbibition experiments on vertical cylindrical specimens with simultaneous ultrasonic monitoring and imaging. The motivation of our study was to identify the seismic attributes of fluid substitution in reservoir rocks and to link them to physical processes. It is shown that (i) the P wave velocity either decreases or increases when the capillary front reaches the Fresnel clearance zone, (ii) the P wave amplitude is systematically impacted earlier than the velocity is, (iii) this precursory amplitude decrease occurs when the imbibition front is located outside of the Fresnel zone, and (iv) the relative variation of the P wave amplitude is always much larger than that of the P wave velocity. These results suggest that moisture diffuses into the pore space ahead of the water front. This postulate is further supported by a quantitative analysis of the time evolution of the observed P wave amplitudes. In a sense, P wave amplitude acts as a precursor of the arrival of the capillary front. This phenomenon is used to estimate the effective diffusivity of moisture in the tested rocks. The effective moisture diffusivity estimated from the ultrasonic data is strongly correlated with permeability: a power law with exponent 0.96 predicts permeability from ultrasonic monitoring within a factor 3 without noticeable bias. When the effective diffusivity is high, moisture diffusion affects ultrasonic P wave attributes even before the imbibition starts and impacts the P wave reflectivity as evidenced by the variations recorded in the waveform coda.

SDO AIA Observations of Large-Scale Coronal Disturbances in the Form of Propagating Fronts

NASA Astrophysics Data System (ADS)

Nitta, Nariaki V.; Schrijver, Carolus J.; Title, Alan M.; Liu, Wei

2013-03-01

One of the most spectacular phenomena detected by SOHO EIT was the large-scale propagating fronts associated with solar eruptions. Initially these 'EIT' waves were thought to be coronal counterparts of chromospheric Moreton waves. However, different spatial and kinematic properties of the fronts seen in H-alpha and EUV images, and far more frequent occurrences of the latter have led to various interpretations that are still actively debated by a number of researchers. A major factor for the lack of closure was the various limitation in EIT data, including the cadence that was typically every 12 minutes. Now we have significantly improved data from SDO AIA, which have revealed some very interesting phenomena associated with EIT waves. However, the studies so far conducted using AIA data have primarily dealt with single or a small number of events, where selection bias and particular observational conditions may prevent us from discovering the general and true nature of EIT waves. Although automated detection of EIT waves was promised for AIA images some time ago, it is still not actually implemented in the data pipeline. Therefore we have manually found nearly 200 examples of large-scale propagating fronts, going through movies of difference images from the AIA 193 A channel up to January 2013. We present our study of the kinematic properties of the fronts in a subset of about 150 well-observed events in relation with other phenomena that can accompany EIT waves. Our emphasis is on the relation of the fronts with the associated coronal eruptions often but not always taking the form of full-blown CMEs, utilizing STEREO data for a subset of more than 80 events that have occurred near the limb as viewed from one of the STEREO spacecraft. In these events, the availability of data from the STEREO inner coronagraph (COR1) as well as from the EUVI allows us to trace eruptions off the solar disk during the times of our propagating fronts. The representative relations between the fronts and CMEs will be discussed in terms of the evolution of EIT waves observed in different channels of AIA, which provide information of the thermal properties of the fronts. Our study will further clarify the variety of solar eruptions and their associated manifestations in the corona.

5-D interpolation with wave-front attributes

NASA Astrophysics Data System (ADS)

Xie, Yujiang; Gajewski, Dirk

2017-11-01

Most 5-D interpolation and regularization techniques reconstruct the missing data in the frequency domain by using mathematical transforms. An alternative type of interpolation methods uses wave-front attributes, that is, quantities with a specific physical meaning like the angle of emergence and wave-front curvatures. In these attributes structural information of subsurface features like dip and strike of a reflector are included. These wave-front attributes work on 5-D data space (e.g. common-midpoint coordinates in x and y, offset, azimuth and time), leading to a 5-D interpolation technique. Since the process is based on stacking next to the interpolation a pre-stack data enhancement is achieved, improving the signal-to-noise ratio (S/N) of interpolated and recorded traces. The wave-front attributes are determined in a data-driven fashion, for example, with the Common Reflection Surface (CRS method). As one of the wave-front-attribute-based interpolation techniques, the 3-D partial CRS method was proposed to enhance the quality of 3-D pre-stack data with low S/N. In the past work on 3-D partial stacks, two potential problems were still unsolved. For high-quality wave-front attributes, we suggest a global optimization strategy instead of the so far used pragmatic search approach. In previous works, the interpolation of 3-D data was performed along a specific azimuth which is acceptable for narrow azimuth acquisition but does not exploit the potential of wide-, rich- or full-azimuth acquisitions. The conventional 3-D partial CRS method is improved in this work and we call it as a wave-front-attribute-based 5-D interpolation (5-D WABI) as the two problems mentioned above are addressed. Data examples demonstrate the improved performance by the 5-D WABI method when compared with the conventional 3-D partial CRS approach. A comparison of the rank-reduction-based 5-D seismic interpolation technique with the proposed 5-D WABI method is given. The comparison reveals that there are significant advantages for steep dipping events using the 5-D WABI method when compared to the rank-reduction-based 5-D interpolation technique. Diffraction tails substantially benefit from this improved performance of the partial CRS stacking approach while the CPU time is comparable to the CPU time consumed by the rank-reduction-based method.

Mesospheric front observations by the OH airglow imager carried out at Ferraz Station on King George Island, Antarctic Peninsula, in 2011

NASA Astrophysics Data System (ADS)

Giongo, Gabriel Augusto; Valentin Bageston, José; Prado Batista, Paulo; Wrasse, Cristiano Max; Dornelles Bittencourt, Gabriela; Paulino, Igo; Paes Leme, Neusa Maria; Fritts, David C.; Janches, Diego; Hocking, Wayne; Schuch, Nelson Jorge

2018-02-01

The main goals of this work are to characterize and investigate the potential wave sources of four mesospheric fronts identified in the hydroxyl near-infrared (OH-NIR) airglow images, obtained with an all-sky airglow imager installed at Comandante Ferraz Antarctic Station (EACF, as per its Portuguese acronym) located on King George Island in the Antarctic Peninsula. We identified and analyzed four mesospheric fronts in 2011 over King George Island. In addition, we investigate the atmospheric background environment between 80 and 100 km altitude and discuss the ducts and propagation conditions for these waves. For that, we used wind data obtained from a meteor radar operated at EACF and temperature data obtained from the TIMED/SABER satellite. The vertical wavenumber squared, m2, was calculated for each of the four waves. Even though no clearly defined duct (indicated by positive values of m2 sandwiched between layers above and below with m2 < 0) was found in any of the events, favorable propagation conditions for horizontal propagation of the fronts were found in three cases. In the fourth case, the wave front did not find any duct support and it appeared to dissipate near the zenith, transferring energy and momentum to the medium and, consequently, accelerating the wind in the wave propagation direction (near to south) above the OH peak (88-92 km). The likely wave sources for these four cases were investigated by using meteorological satellite images and in two cases we could find that strong instabilities were potential sources, i.e., a cyclonic activity and a large convective cloud cell. In the other two cases it was not possible to associate troposphere sources as potential candidates for the generation of such wave fronts observed in the mesosphere and secondary wave sources were attributed to these cases.

Spontaneous Wave Generation from Submesoscale Fronts and Filaments

NASA Astrophysics Data System (ADS)

Shakespeare, C. J.; Hogg, A.

2016-02-01

Submesoscale features such as eddies, fronts, jets and filaments can be significant sources of spontaneous wave generation at the ocean surface. Unlike near-inertial waves forced by winds, these spontaneous waves are typically of higher frequency and can propagate through the thermocline, whereupon they break and drive mixing in the ocean interior. Here we investigate the spontaneous generation, propagation and subsequent breaking of these waves using a combination of theory and submesoscale resolving numerical models. The mechanism of generation is nearly identical to that of lee waves where flow is deflected over a rigid obstacle on the sea floor. Here, very sharp fronts and filaments of order 100m width moving in the submesoscale surface flow generate "surface lee waves" by presenting an obstacle to the surrounding stratified fluid. Using our numerical model we quantify the net downward wave energy flux from the surface, and where it is dissipated in the water column. Our results suggest an alternative to the classical paradigm where the energy associated with mixing in the ocean interior is sourced from bottom-generated lee waves.

Multigrid preconditioned conjugate-gradient method for large-scale wave-front reconstruction.

PubMed

Gilles, Luc; Vogel, Curtis R; Ellerbroek, Brent L

2002-09-01

We introduce a multigrid preconditioned conjugate-gradient (MGCG) iterative scheme for computing open-loop wave-front reconstructors for extreme adaptive optics systems. We present numerical simulations for a 17-m class telescope with n = 48756 sensor measurement grid points within the aperture, which indicate that our MGCG method has a rapid convergence rate for a wide range of subaperture average slope measurement signal-to-noise ratios. The total computational cost is of order n log n. Hence our scheme provides for fast wave-front simulation and control in large-scale adaptive optics systems.

Appearance of wavefront dislocations under interference among beams with simple wavefronts

NASA Astrophysics Data System (ADS)

Angelsky, Oleg V.; Besaha, R. N.; Mokhun, Igor I.

1997-12-01

The appearance of wave front dislocations under interference among beams with simple wave fronts is considered. It is shown, that even two beams with the smooth wave fonts is possible the formation of dislocations screw type. The screw dislocations are formed in cross point of lines of equal amplitude of beams and minimum of an interference pattern.

Traveling waves in a spatially-distributed Wilson-Cowan model of cortex: From fronts to pulses

NASA Astrophysics Data System (ADS)

Harris, Jeremy D.; Ermentrout, Bard

2018-04-01

Wave propagation in excitable media has been studied in various biological, chemical, and physical systems. Waves are among the most common evoked and spontaneous organized activity seen in cortical networks. In this paper, we study traveling fronts and pulses in a spatially-extended version of the Wilson-Cowan equations, a neural firing rate model of sensory cortex having two population types: Excitatory and inhibitory. We are primarily interested in the case when the local or space-clamped dynamics has three fixed points: (1) a stable down state; (2) a saddle point with stable manifold that acts as a threshold for firing; (3) an up state having stability that depends on the time scale of the inhibition. In the case when the up state is stable, we look for wave fronts, which transition the media from a down to up state, and when the up state is unstable, we are interested in pulses, a transient increase in firing that returns to the down state. We explore the behavior of these waves as the time and space scales of the inhibitory population vary. Some interesting findings include bistability between a traveling front and pulse, fronts that join the down state to an oscillation or spatiotemporal pattern, and pulses which go through an oscillatory instability.

The vibration compensation system for ARGOS

NASA Astrophysics Data System (ADS)

Peter, D.; Gaessler, W.; Borelli, J.; Kulas, M.

2011-09-01

For every adaptive optics system telescope vibrations can strongly reduce the performance. This is true for the receiver part of the system i.e. the telescope and wave front sensor part as well as for the transmitter part in the case of a laser guide star system. Especially observations in deep fields observed with a laser guide star system without any tip-tilt star will be greatly spoiled by telescope vibrations. The ARGOS GLAO system actually being built for the LBT aims to implement this kind of mode where wave front correction will rely purely on signals from the laser beacons. To remove the vibrations from the uplink path a vibration compensation system will be installed. This system uses accelerometers to measure the vibrations and corrects their effect with a small fast tip-tilt mirror. The controller of the system is built based on the assumption that the vibrations take place at a few distinct frequencies. Here I present a lab set-up of this system and show first results of the performance.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ro, Stephen; Matzner, Christopher D., E-mail: ro@astro.utoronto.ca

Wave-driven outflows and non-disruptive explosions have been implicated in pre-supernova outbursts, supernova impostors, luminous blue variable eruptions, and some narrow-line and superluminous supernovae. To model these events, we investigate the dynamics of stars set in motion by strong acoustic pulses and wave trains, focusing on nonlinear wave propagation, shock formation, and an early phase of the development of a weak shock. We identify the shock formation radius, showing that a heuristic estimate based on crossing characteristics matches an exact expansion around the wave front and verifying both with numerical experiments. Our general analytical condition for shock formation applies to one-dimensionalmore » motions within any static environment, including both eruptions and implosions. We also consider the early phase of shock energy dissipation. We find that waves of super-Eddington acoustic luminosity always create shocks, rather than damping by radiative diffusion. Therefore, shock formation is integral to super-Eddington outbursts.« less

Storms or cold fronts: what is really responsible for the extreme waves regime in the Colombian Caribbean coastal region?

NASA Astrophysics Data System (ADS)

Otero, L. J.; Ortiz-Royero, J. C.; Ruiz-Merchan, J. K.; Higgins, A. E.; Henriquez, S. A.

2016-02-01

The aim of this study is to determine the contribution and importance of cold fronts and storms to extreme waves in different areas of the Colombian Caribbean in an attempt to determine the extent of the threat posed by the flood processes to which these coastal populations are exposed. Furthermore, the study wishes to establish the actions to which coastal engineering constructions should be subject. In the calculation of maritime constructions, the most important parameter is the height of the wave. For this reason, it is necessary to establish the design wave height to which a coastal engineering structure should be resistant. This wave height varies according to the return period considered. The significant height values for the areas focused on in the study were calculated in accordance with Gumbel's extreme value methodology. The methodology was evaluated using data from the reanalysis of the spectral National Oceanic and Atmospheric Administration (NOAA) WAVEWATCH III® (WW3) model for 15 points along the 1600 km of the Colombian Caribbean coastline (continental and insular) between the years 1979 and 2009. The results demonstrated that the extreme waves caused by tropical cyclones and those caused by cold fronts have different effects along the Colombian Caribbean coast. Storms and hurricanes are of greater importance in the Guajira Peninsula (Alta Guajira). In the central area (consisting of Baja Guajira, and the cities of Santa Marta, Barranquilla, and Cartagena), the strong impact of cold fronts on extreme waves is evident. However, in the southern region of the Colombian Caribbean coast (ranging from the Gulf of Morrosquillo to the Gulf of Urabá), the extreme values of wave heights are lower than in the previously mentioned regions, despite being dominated mainly by the passage of cold fronts. Extreme waves in the San Andrés and Providencia insular region present a different dynamic from that in the continental area due to their geographic location. The wave heights in the extreme regime are similar in magnitude to those found in Alta Guajira, but the extreme waves associated with the passage of cold fronts in this region have lower return periods than those associated with the hurricane season.

Experimentally determining the locations of two astigmatic images for an underwater light source

NASA Astrophysics Data System (ADS)

Yang, Pao-Keng; Liu, Jian-You; Ying, Shang-Ping

2015-05-01

Images formed by an underwater object from light rays refracted in the sagittal and tangential planes are located at different positions for an oblique viewing position. The overlapping of these two images from the observer's perspective will thus prevent the image-splitting astigmatism from being directly observable. In this work, we present a heuristic method to experimentally visualize the astigmatism. A point light source is used as an underwater object and the emerging wave front is recorded using a Shack-Hartmann wave-front sensor. The wave front is found to deform from a circular paraboloid to an elliptic paraboloid as the viewing position changes from normal to oblique. Using geometric optics, we derive an analytical expression for the image position as a function of the rotating angle of an arm used to carry the wave-front sensor in our experimental setup. The measured results are seen to be in good agreement with the theoretical predictions.

Solar tomography adaptive optics.

PubMed

Ren, Deqing; Zhu, Yongtian; Zhang, Xi; Dou, Jiangpei; Zhao, Gang

2014-03-10

Conventional solar adaptive optics uses one deformable mirror (DM) and one guide star for wave-front sensing, which seriously limits high-resolution imaging over a large field of view (FOV). Recent progress toward multiconjugate adaptive optics indicates that atmosphere turbulence induced wave-front distortion at different altitudes can be reconstructed by using multiple guide stars. To maximize the performance over a large FOV, we propose a solar tomography adaptive optics (TAO) system that uses tomographic wave-front information and uses one DM. We show that by fully taking advantage of the knowledge of three-dimensional wave-front distribution, a classical solar adaptive optics with one DM can provide an extra performance gain for high-resolution imaging over a large FOV in the near infrared. The TAO will allow existing one-deformable-mirror solar adaptive optics to deliver better performance over a large FOV for high-resolution magnetic field investigation, where solar activities occur in a two-dimensional field up to 60'', and where the near infrared is superior to the visible in terms of magnetic field sensitivity.

Influence of temperature on linear stability in buoyancy-driven fingering of reaction-diffusion fronts.

PubMed

Levitán, D; D'Onofrio, A

2012-09-01

A vertical Hele-Shaw cell was used to study the influence of temperature on Rayleigh-Taylor instabilities on reaction-diffusion fronts. The propagation of the chemical front can thus be observed, and experimental results can be obtained via image treatment. A chemical front produced by the coupling between molecular diffusion and the auto-catalysis of the chlorite-tetrathionate reaction, descends through the cell, consuming the reactants below while the product is formed above. Buoyancy-driven instabilities are formed due to the density difference between reactants and products, and the front takes a fingering pattern, whose growth rate has temperature dependence. In this study, the effect of temperature on the linear regime of the instability (that is, when the effects of such instability start to appear) was analyzed. To measure the instability, Fourier transform analysis is performed, in order to obtain the different wave numbers and their power as a function of time. Thus, the growth rate for each wave number and the most unstable wave number is obtained for each of the temperatures under study. Based on repeated experiments, a decrease in the growth rate for the most unstable wave number can be observed with the increase of temperature.

Long-distance dispersal suppresses introgression of local alleles during range expansions

PubMed Central

Amorim, C E G; Hofer, T; Ray, N; Foll, M; Ruiz-Linares, A; Excoffier, L

2017-01-01

During range expansions, even low levels of interbreeding can lead to massive introgression of local alleles into an invader's genome. Nonetheless, this pattern is not always observed in human populations. For instance, European Americans in North America are barely introgressed by Amerindian genes in spite of known contact and admixture. With coalescent spatially explicit simulations, we examined the impact of long-distance dispersal (LDD) events on introgression of local alleles into the invading population using a set of different demographic scenarios applicable to a diverse range of natural populations and species. More specifically, we consider two distinct LDD models: one where LDD events originate in the range core and targets only the expansion front and a second one where LDD events can occur from any area to any other. We find that LDD generally prevents introgression, but that LDD events specifically targeting the expansion front are most efficient in suppressing introgression. This is likely due to the fact that LDD allows for the presence of a larger number of invader alleles at the wave front, where effective population size is thus increased and local introgressed alleles are rapidly outnumbered. We postulate that the documented settlement of pioneers directly on the wave front in North America has contributed to low levels of Amerindian admixture observed in European Americans and that this phenomenon may well explain the lack of introgression after a range expansion in natural populations without the need to evoke other mechanisms such as natural selection. PMID:27577693

Variability of tidal signals in the Brent Delta Front: New observations on the Rannoch Formation, northern North Sea

NASA Astrophysics Data System (ADS)

Wei, Xiaojie; Steel, Ronald J.; Ravnås, Rodmar; Jiang, Zaixing; Olariu, Cornel; Li, Zhiyang

2016-04-01

Detailed observations on the Rannoch Formation in several deep Viking Graben wells indicate that the 'classical' wave-dominated Brent delta-front shows coupled storm-tide processes. The tidal signals are of three types: I): alternations of thick cross-laminated sandstone and thin mud-draped sandstone, whereby double mud drapes are prominent but discretely distributed, II): a few tidal bundles within bottomsets and foresets of up to 10 cm-thick sets cross-strata, and III): dm-thick heterolithic lamination showing multiple, well-organized sand-mud couplets. During progradation of the Brent Delta, the Rannoch shoreline system passed upward from 1) a succession dominated by clean-water, storm-event sets and cosets frequently and preferentially interbedded with type I tidal beds, and occasional types II and III tidal deposits, toward 2) very clean storm-event beds less frequently separated by types II and III tidal beds, and then into 3) a thin interval showing muddier storm-event beds mainly alternating with type II tidal beds. It is likely that those variations in preservation bias of storm and tidal beds in each facies succession result from combined effects of 1) the frequency and duration of storms; 2) river discharge; and 3) the absolute and relative strength of tides. Tidal deposits are interpreted as inter-storm, fair-weather deposits, occurred preferentially in longer intermittent fair-weather condition and periods of lower river discharge, and well-pronounced in the distal-reach of delta-front. The formation and preservation of tidal signals between storm beds, indicate that the studied Rannoch Formation was most likely a storm-dominated, tide-influenced delta front 1) near the mouth of a large Brent river, where a significant tidal prism and high tidal range might be expected, and 2) in a setting where there were relatively high sedimentation rates associated with high local subsidence rates, so that the storm waves did not completely rework the inter-storm deposits. The documentation of the unconventional Rannoch Formation contributes to our understanding of mixed-energy coastal systems.

Enhancement of the beam quality of non-uniform output slab laser amplifier with a 39-actuator rectangular piezoelectric deformable mirror.

PubMed

Yang, Ping; Ning, Yu; Lei, Xiang; Xu, Bing; Li, Xinyang; Dong, Lizhi; Yan, Hu; Liu, Wenjing; Jiang, Wenhan; Liu, Lei; Wang, Chao; Liang, Xingbo; Tang, Xiaojun

2010-03-29

We present a slab laser amplifier beam cleanup experimental system based on a 39-actuator rectangular piezoelectric deformable mirror. Rather than use a wave-front sensor to measure distortions in the wave-front and then apply a conjugation wave-front for compensating them, the system uses a Stochastic Parallel Gradient Descent algorithm to maximize the power contained within a far-field designated bucket. Experimental results demonstrate that at the output power of 335W, more than 30% energy concentrates in the 1x diffraction-limited area while the beam quality is enhanced greatly.

Front acceleration by dynamic selection in Fisher population waves

NASA Astrophysics Data System (ADS)

Bénichou, O.; Calvez, V.; Meunier, N.; Voituriez, R.

2012-10-01

We introduce a minimal model of population range expansion in which the phenotypes of individuals present no selective advantage and differ only in their diffusion rate. We show that such neutral phenotypic variability (i.e., that does not modify the growth rate) alone can yield phenotype segregation at the front edge, even in absence of genetic noise, and significantly impact the dynamical properties of the expansion wave. We present an exact asymptotic traveling wave solution and show analytically that phenotype segregation accelerates the front propagation. The results are compatible with field observations such as invasions of cane toads in Australia or bush crickets in Britain.

Automatic low-order aberrations compensator for a conduction-cooled end-pumped solid-state zigzag slab laser

NASA Astrophysics Data System (ADS)

Yu, Xin; Dong, Lizhi; Lai, Boheng; Yang, Ping; Wang, Shuai; Wang, Xun; Liu, Yong; Tang, Guomao; Xu, Bing

2017-11-01

In order to solve the problem of large low-order aberrations with solid-state zigzag slab lasers, an automatic compensator has been developed in this paper. In this compensator, three lenses are mounted on a motorized rail, whose positions can be obtained using ray tracing method based on the beam parameters detected by a wave-front sensor. The initial peak to valley (PV) values of the wave-front range up to several tens of microns. Both simulated and experimental results show that the PV values of the wave-front can be reduced to around 1 . 6 μm with the proposed automatic compensator.

Effect of aberrations in human eye on contrast sensitivity function

NASA Astrophysics Data System (ADS)

Quan, Wei; Wang, Feng-lin; Wang, Zhao-qi

2011-06-01

The quantitative analysis of the effect of aberrations in human eye on vision has important clinical value in the correction of aberrations. The wave-front aberrations of human eyes were measured with the Hartmann-Shack wave-front sensor and modulation transfer function (MTF) was computed from the wave-front aberrations. Contrast sensitivity function (CSF) was obtained from MTF and the retinal aerial image modulation (AIM). It is shown that the 2nd, 3rd, 4th, 5th, 6th Zernike aberrations deteriorate contrast sensitivity function. When the 2nd, 3rd, 4th, 5th, 6th Zernike aberrations are corrected high contrast sensitivity function can be obtained.

Linear quadratic Gaussian control of a deformable mirror adaptive optics system with time-delayed measurements

NASA Astrophysics Data System (ADS)

Paschall, Randall N.; Anderson, David J.

1993-11-01

A linear quadratic Gaussian method is proposed for a deformable mirror adaptive optics system control. Estimates of system states describing the distortion are generated by a Kalman filter based on Hartmann wave front measurements of the wave front gradient.

Maximum likelihood phase-retrieval algorithm: applications.

PubMed

Nahrstedt, D A; Southwell, W H

1984-12-01

The maximum likelihood estimator approach is shown to be effective in determining the wave front aberration in systems involving laser and flow field diagnostics and optical testing. The robustness of the algorithm enables convergence even in cases of severe wave front error and real, nonsymmetrical, obscured amplitude distributions.

Educing the emission mechanism of internal gravity waves in the differentially heat rotating annulus

NASA Astrophysics Data System (ADS)

Rolland, Joran; Hien, Steffen; Achatz, Ulrich; Borchert, Sebastian; Fruman, Mark

2016-04-01

Understanding the lifecycle of gravity waves is fundamental to a good comprehension of the dynamics of the atmosphere. In this lifecycle, the emission mechanisms may be the most elusive. Indeed, while the emission of gravity waves by orography or convection is well understood, the so-called spontaneous emission is still a quite open topic of investigation [1]. This type of emission usually occur very near jet-front systems in the troposphere. In this abstract, we announce our numerical study of the question. Model systems of the atmosphere which can be easily simulated or built in a laboratory have always been an important part of the study of atmospheric dynamics, alongside global simulations, in situ measurements and theory. In the case of the study of the spontaneous emission of gravity waves near jet-front systems, the differentially heated rotating annulus set up has been proposed and extensively used. It comprises of an annular tank containing water: the inner cylinder is kept at a cold temperature while the outer cylinder is kept at a warm temperature. The whole system is rotating. Provided the values of the control parameters (temperature, rotation rate, gap between the cylinders, height of water) are well chosen, the resulting flow mimics the troposphere at midlatitudes: it has a jet stream, and a baroclinic lifecycle develops on top of it. A very reasonable ratio of Brunt-Väisälä frequency over rotation rate of the system can be obtained, so as to be as close to the atmosphere as possible. Recent experiments as well as earlier numerical simulations in our research group have shown that gravity waves are indeed emitted in this set up, in particular near the jet front system of the baroclinic wave [2]. After a first experimental stage of characterising the emitted wavepacket, we focused our work on testing hypotheses on the gravity wave emission mechanism: we have tested and validated the hypothesis of spontaneous imbalance generated by the flow in geostrophic balance. For the first stage of this investigation, we separated the flow between a balance and an imbalanced part at first order in Rossby number: the balanced pressure field was computed through an inversion of the potential vorticity equation [3]. The balanced horizontal velocity field and buoyancy were then computed using the geostrophic and hydrostatic balance conditions. We first checked that this decomposition gave on the one hand a large scaled balanced flow, comprising mostly of the baroclinic wave, and on the other hand a small scale flow comprising mostly of the gravity wave signal. We then proceeded with the central stage of the validation: we simulated the tangent linear dynamics of the imbalanced part of the flow [4]. The equations are linearised about the balanced part, and any imbalances forces the modeled imbalanced part. The output of this simulation compares very well with the actual imbalanced part, thus confirming that the observed gravity waves are indeed generated through spontaneous imbalance. To our knowledge, this is the first demonstration of emission by this mechanism in a flow which is not idealised: a flow which can be obtained as a result of a numerical simulation of primitive equations or actually observed in a laboratory experiment. References [1] R. Plougonven, F. Zhang, Internal gravity waves from atmospheric jets and fronts, Rev. Geophys. 52, 33-76 (2014). [2] S. Borchert, U. Achatz, M.D. Fruman, Spontaneous Gravity wave emission in the differentially heated annulus, J. Fluid Mech. 758, 287-311 (2014). [3] F. Zhang, S.E . Koch, C. A. Davis, M. L. Kaplan, A Survey of unbalanced flow diagnostics and their application, Adv. Atmo. Sci. 17, 165-183 (2000). [4] S. Wang, F. Zhang, Source of gravity waves within a vortex dipole jet revealed by a linear model, J. Atmo. Sci. 67, 1438-1455 (2010).

Shaping Microwave Fields Using Nonlinear Unsolicited Feedback: Application to Enhance Energy Harvesting

NASA Astrophysics Data System (ADS)

del Hougne, Philipp; Fink, Mathias; Lerosey, Geoffroy

2017-12-01

Wave-front shaping has emerged over the past decade as a powerful tool to control wave propagation through complex media, initially in optics and more recently also in the microwave domain with important applications in telecommunication, imaging, and energy transfer. The crux of implementing wave-front shaping concepts in real life is often its need for (direct) feedback, requiring access to the target to focus on. Here, we present the shaping of a microwave field based on indirect, unsolicited, and blind feedback which may be the pivotal step towards practical implementations. With the example of a radio-frequency harvester in a metallic cavity, we demonstrate tenfold enhancement of the harvested power by wave-front shaping based on nonlinear signals detected at an arbitrary position away from the harvesting device.

Holographic nondestructive tests performed on composite samples of ceramic-epoxy-fiberglass sandwich structure

NASA Technical Reports Server (NTRS)

Kurtz, R. L.; Liu, H. K.

1974-01-01

When a hologram storing more than one wave is illuminated with coherent light, the reconstructed wave fronts interfere with each other or with any other phase-related wave front derived from the illuminating source. This multiple wave front comparison is called holographic interferometry, and its application is called holographic nondestructive testing (HNDT). The theoretical aspects of HNDT techniques and the sensitivity of the holographic system to the geometrical placement of the optical components are briefly discussed. A unique HNDT system which is mobile and possesses variable sensitivity to stress amplitude is discribed, the experimental evidence of the application of this system to the testing of the hidden debonds in a ceramic-epoxy-fiberglass structure used for sample testing of the radome of the Pershing missile system is presented.

Traveling wave solutions in a chain of periodically forced coupled nonlinear oscillators

NASA Astrophysics Data System (ADS)

Duanmu, M.; Whitaker, N.; Kevrekidis, P. G.; Vainchtein, A.; Rubin, J. E.

2016-06-01

Motivated by earlier studies of artificial perceptions of light called phosphenes, we analyze traveling wave solutions in a chain of periodically forced coupled nonlinear oscillators modeling this phenomenon. We examine the discrete model problem in its co-traveling frame and systematically obtain the corresponding traveling waves in one spatial dimension. Direct numerical simulations as well as linear stability analysis are employed to reveal the parameter regions where the traveling waves are stable, and these waves are, in turn, connected to the standing waves analyzed in earlier work. We also consider a two-dimensional extension of the model and demonstrate the robust evolution and stability of planar fronts. Our simulations also suggest the radial fronts tend to either annihilate or expand and flatten out, depending on the phase value inside and the parameter regime. Finally, we observe that solutions that initially feature two symmetric fronts with bulged centers evolve in qualitative agreement with experimental observations of phosphenes.

Traveling wave solutions in a chain of periodically forced coupled nonlinear oscillators

DOE PAGES

Duanmu, M.; Whitaker, N.; Kevrekidis, P. G.; ...

2016-02-27

Artificial perceptions of light called phosphenes were motivated by earlier studies. We analyze traveling wave solutions in a chain of periodically forced coupled nonlinear oscillators modeling this phenomenon. We examine the discrete model problem in its co-traveling frame and systematically obtain the corresponding traveling waves in one spatial dimension. Direct numerical simulations as well as linear stability analysis are employed to reveal the parameter regions where the traveling waves are stable, and these waves are, in turn, connected to the standing waves analyzed in earlier work. We also consider a two-dimensional extension of the model and demonstrate the robust evolutionmore » and stability of planar fronts. Moreover, our simulations also suggest the radial fronts tend to either annihilate or expand and flatten out, depending on the phase value inside and the parameter regime. Finally, we observe that solutions that initially feature two symmetric fronts with bulged centers evolve in qualitative agreement with experimental observations of phosphenes.« less

Traveling wave solutions in a chain of periodically forced coupled nonlinear oscillators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duanmu, M.; Whitaker, N.; Kevrekidis, P. G.

Artificial perceptions of light called phosphenes were motivated by earlier studies. We analyze traveling wave solutions in a chain of periodically forced coupled nonlinear oscillators modeling this phenomenon. We examine the discrete model problem in its co-traveling frame and systematically obtain the corresponding traveling waves in one spatial dimension. Direct numerical simulations as well as linear stability analysis are employed to reveal the parameter regions where the traveling waves are stable, and these waves are, in turn, connected to the standing waves analyzed in earlier work. We also consider a two-dimensional extension of the model and demonstrate the robust evolutionmore » and stability of planar fronts. Moreover, our simulations also suggest the radial fronts tend to either annihilate or expand and flatten out, depending on the phase value inside and the parameter regime. Finally, we observe that solutions that initially feature two symmetric fronts with bulged centers evolve in qualitative agreement with experimental observations of phosphenes.« less

Rossby waves, extreme fronts, and wildfires in southeastern Australia

NASA Astrophysics Data System (ADS)

Reeder, Michael J.; Spengler, Thomas; Musgrave, Ruth

2015-03-01

The most catastrophic fires in recent history in southern Australia have been associated with extreme cold fronts. Here an extreme cold front is defined as one for which the maximum temperature at 2 m is at least 17°C lower on the day following the front. An anticyclone, which precedes the cold front, directs very dry northerlies or northwesterlies from the interior of the continent across the region. The passage of the cold front is followed by strong southerlies or southwesterlies. European Centre for Medium-Range Weather Forecasts ERA-Interim Reanalyses show that this regional synoptic pattern common to all strong cold fronts, and hence severe fire conditions, is a consequence of propagating Rossby waves, which grow to large amplitude and eventually irreversibly overturn. The process of overturning produces the low-level anticyclone and dry conditions over southern Australia, while simultaneously producing an upper level trough and often precipitation in northeastern Australia.

Detonative propagation and accelerative expansion of the Crab Nebula shock front.

PubMed

Gao, Yang; Law, Chung K

2011-10-21

The accelerative expansion of the Crab Nebula's outer envelope is a mystery in dynamics, as a conventional expanding blast wave decelerates when bumping into the surrounding interstellar medium. Here we show that the strong relativistic pulsar wind bumping into its surrounding nebula induces energy-generating processes and initiates a detonation wave that propagates outward to form the current outer edge, namely, the shock front, of the nebula. The resulting detonation wave, with a reactive downstream, then provides the needed power to maintain propagation of the shock front. Furthermore, relaxation of the curvature-induced reduction of the propagation velocity from the initial state of formation to the asymptotic, planar state of Chapman-Jouguet propagation explains the observed accelerative expansion. Potential richness in incorporating reactive fronts in the description of various astronomical phenomena is expected. © 2011 American Physical Society

High-gain thompson-scattering X-ray free-electron laser by time-synchronic laterally tilted optical wave

DOEpatents

Chang, Chao; Tang, Chuanxiang; Wu, Juhao

2017-05-09

An improved optical undulator for use in connection with free electron radiation sources is provided. A tilt is introduced between phase fronts of an optical pulse and the pulse front. Two such pulses in a counter-propagating geometry overlap to create a standing wave pattern. A line focus is used to increase the intensity of this standing wave pattern. An electron beam is aligned with the line focus. The relative angle between pulse front and phase fronts is adjusted such that there is a velocity match between the electron beam and the overlapping optical pulses along the line focus. This allows one to provide a long interaction length using short and intense optical pulses, thereby greatly increasing the radiation output from the electron beam as it passes through this optical undulator.

Rapid microscale in-gel processing and digestion of proteins using surface acoustic waves.

PubMed

Kulkarni, Ketav P; Ramarathinam, Sri H; Friend, James; Yeo, Leslie; Purcell, Anthony W; Perlmutter, Patrick

2010-06-21

A new method for in-gel sample processing and tryptic digestion of proteins is described. Sample preparation, rehydration, in situ digestion and peptide extraction from gel slices are dramatically accelerated by treating the gel slice with surface acoustic waves (SAWs). Only 30 minutes total workflow time is required for this new method to produce base peak chromatograms (BPCs) of similar coverage and intensity to those observed for traditional processing and overnight digestion. Simple set up, good reproducibility, excellent peptide recoveries, rapid turnover of samples and high confidence protein identifications put this technology at the fore-front of the next generation of proteomics sample processing tools.

Peculiarity of convergence of shock wave generated by underwater electrical explosion of ring-shaped wire

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shafer, D.; Toker, G. R.; Gurovich, V. Tz.

2013-05-15

Nanosecond timescale underwater electrical wire explosions of ring-shaped Cu wires were investigated using a pulsed generator with a current amplitude up to 50 kA. It was shown that this type of wire explosion results in the generation of a toroidal shock wave (SW). Time- and space-resolved optical diagnostics were used to determine azimuthal uniformity of the shock wave front and its velocity. It was found that the shock wave preserves its circular front shape in the range of radii 50μm

Ionospheric Bow Wave Induced by the Moon Shadow Ship Over the Continent of United States on 21 August 2017

NASA Astrophysics Data System (ADS)

Sun, Yang-Yi; Liu, Jann-Yenq; Lin, Charles Chien-Hung; Lin, Chi-Yen; Shen, Ming-Hsueh; Chen, Chieh-Hung; Chen, Chia-Hung; Chou, Min-Yang

2018-01-01

A moon shadow of the total solar eclipse swept through the continent of United States (CONUS) from west to east on 21 August 2017. Massive total electron content (integration of electron density from 0 km to 20,200 km altitude) observations from 2,255 ground-based Global Navigation Satellite System receivers show that the moon shadow ship generates a great ionospheric bow wave front which extends 1,500 km away from the totality path covering the entire CONUS. The bow wave front consists of the acoustic shock wave due to the supersonic/near-supersonic moon shadow ship and the significant plasma recombination due to the reduction in solar irradiation within the shadow area. The deep bow wave trough (-0.02 total electron content unit (1 TECU = 1016 el m-2) area) nearly coincides with the 100% obscuration moving along the totality path over the CONUS through the entire eclipse period. The supersonic moon shadow ship induces a bow wave crest in front of the ship ( 80% obscuration). It is the first time to find the acoustic shock wave-formed bow wave trough and crest near the totality.

Shock wave and flame front induced detonation in a rapid compression machine

NASA Astrophysics Data System (ADS)

Wang, Y.; Qi, Y.; Xiang, S.; Mével, R.; Wang, Z.

2018-05-01

The present study focuses on one mode of detonation initiation observed in a rapid compression machine (RCM). This mode is referred to as shock wave and flame front-induced detonation (SWFID). Experimental high-speed imaging and two-dimensional numerical simulations with skeletal chemistry are combined to unravel the dominant steps of detonation initiation under SWFID conditions. It is shown that the interaction between the shock wave generated by the end-gas auto-ignition and the spherical flame creates a region of high pressure and temperature which enables the acceleration of the flame front and the detonation onset. The experimental observation lacks adequate spatial and temporal resolution despite good reproducibility of the detonation onset. Based on the numerical results, phenomenological interpretation of the event within the framework of shock wave refraction indicates that the formation of a free-precursor shock wave at the transition between regular and irregular refraction may be responsible for detonation onset. The present results along with previous findings on shock wave reflection-induced detonation in the RCM indicate that super-knock occurs after the interaction of the shock wave generated by end-gas auto-ignition with the RCM walls, preignition flame, or another shock wave.

Longitudinal nonlinear wave propagation through soft tissue.

PubMed

Valdez, M; Balachandran, B

2013-04-01

In this paper, wave propagation through soft tissue is investigated. A primary aim of this investigation is to gain a fundamental understanding of the influence of soft tissue nonlinear material properties on the propagation characteristics of stress waves generated by transient loadings. Here, for computational modeling purposes, the soft tissue is modeled as a nonlinear visco-hyperelastic material, the geometry is assumed to be one-dimensional rod geometry, and uniaxial propagation of longitudinal waves is considered. By using the linearized model, a basic understanding of the characteristics of wave propagation is developed through the dispersion relation and in terms of the propagation speed and attenuation. In addition, it is illustrated as to how the linear system can be used to predict brain tissue material parameters through the use of available experimental ultrasonic attenuation curves. Furthermore, frequency thresholds for wave propagation along internal structures, such as axons in the white matter of the brain, are obtained through the linear analysis. With the nonlinear material model, the authors analyze cases in which one of the ends of the rods is fixed and the other end is subjected to a loading. Two variants of the nonlinear model are analyzed and the associated predictions are compared with the predictions of the corresponding linear model. The numerical results illustrate that one of the imprints of the nonlinearity on the wave propagation phenomenon is the steepening of the wave front, leading to jump-like variations in the stress wave profiles. This phenomenon is a consequence of the dependence of the local wave speed on the local deformation of the material. As per the predictions of the nonlinear material model, compressive waves in the structure travel faster than tensile waves. Furthermore, it is found that wave pulses with large amplitudes and small elapsed times are attenuated over shorter spans. This feature is due to the elevated strain-rates introduced at the end of the structure where the load is applied. In addition, it is shown that when steep wave fronts are generated in the nonlinear viscoelastic material, energy dissipation is focused in those wave fronts implying deposition of energy in a highly localized region of the material. Novel mechanisms for brain tissue damage are proposed based on the results obtained. The first mechanism is related to the dissipation of energy at steep wave fronts, while the second one is related to the interaction of steep wave fronts with axons encountered on its way through the structure. Copyright © 2013 Elsevier Ltd. All rights reserved.

Minimal wave speed for a class of non-cooperative reaction-diffusion systems of three equations

NASA Astrophysics Data System (ADS)

Zhang, Tianran

2017-05-01

In this paper, we study the traveling wave solutions and minimal wave speed for a class of non-cooperative reaction-diffusion systems consisting of three equations. Based on the eigenvalues, a pair of upper-lower solutions connecting only the invasion-free equilibrium are constructed and the Schauder's fixed-point theorem is applied to show the existence of traveling semi-fronts for an auxiliary system. Then the existence of traveling semi-fronts of original system is obtained by limit arguments. The traveling semi-fronts are proved to connect another equilibrium if natural birth and death rates are not considered and to be persistent if these rates are incorporated. Then non-existence of bounded traveling semi-fronts is obtained by two-sided Laplace transform. Then the above results are applied to some disease-transmission models and a predator-prey model.

Subnanosecond measurements of detonation fronts in solid high explosives

NASA Astrophysics Data System (ADS)

Sheffield, S. A.; Bloomquist, D. D.; Tarver, C. M.

1984-04-01

Detonation fronts in solid high explosives have been examined through measurements of particle velocity histories resulting from the interaction of a detonation wave with a thin metal foil backed by a water window. Using a high time resolution velocity-interferometer system, experiments were conducted on three explosives—a TATB (1,3,5-triamino-trinitrobenzene)-based explosive called PBX-9502, TNT (2,4,6-Trinitrotoluene), and CP (2-{5-cyanotetrazolato} pentaamminecobalt {III} perchlorate). In all cases, detonation-front rise times were found to be less than the 300 ps resolution of the interferometer system. The thermodynamic state in the front of the detonation wave was estimated to be near the unreacted state determined from an extrapolation of low-pressure unreacted Hugoniot data for both TNT and PBX-9502 explosives. Computer calculations based on an ignition and growth model of a Zeldovich-von Neumann-Doering (ZND) detonation wave show good agreement with the measurements. By using the unreacted Hugoniot and a JWL equation of state for the reaction products, we estimated the initial reaction rate in the high explosive after the detonation wave front interacted with the foil to be 40 μs-1 for CP, 60 μs-1 for TNT, and 80 μs-1 for PBX-9502. The shape of the profiles indicates the reaction rate decreases as reaction proceeds.

Failure Waves in Glass and Ceramics under Shock Compression

NASA Astrophysics Data System (ADS)

Singh Brar, N.

1999-06-01

The response of various types of glasses (fused silica, borosilicates, soda-lime, and lead filled) to shock wave loading, especially the failure of glass behind the shock wave through the ``so called" failure wave or front has been the subject of intense research among a number of investigators. The variations in material properties across this front include complete loss of tensile (spall) strength, loss in shear strength, reduction in acoustic impedance, and opacity to light. Both the Stress and velocity history from VISAR measurements have shown that the failure front propagates at a speed of 1.5 to 2.5 mm/s, depending on the peak shock stress level. The shear strength [τ = 1/2(σ_x-σ_y)] behind the failure front, determined using embedded transverse gauges, is found to decrease to about 2 GPa for soda-lime, borosilicate, and filled glasses. The optical (high-speed photography) observations also confirm the formation of failure front. There is a general agreement among various researchers on these observations. However, three proposed mechanisms for the formation of failure front are based on totally different formulations. The first, due to Clifton is based on the process of nucleation of local densification due to shock compression followed by shear failure around inhomogeneities resulting in phase boundary between the comminuted from the intact material. The second, proposed by Grady involves the transfer of elastic shear strain energy to dilatant strain energy as a result of severe microcracking originating from impact face. The third, by Espinosa and Brar proposes that the front is created through shear microcracks, which nucleate and propagate from the impact face, as originally suggested by Kanel. This mechanism is incorporated in multiple-plane model and simulations predict the increase in lateral stress and an observed reduction in spall strength behind the failure front. Failure front studies, in terms of loss of shear strength, have been recently extended to alumina and SiC ceramics by Bourne et. al.

Microstructure of wave propagation during combustion synthesis of advanced materials: Experiments and theory

NASA Astrophysics Data System (ADS)

Hwang, Stephen

Combustion synthesis (CS) is an attractive method for producing advanced materials, including ceramics, intermetallics, and composites. In this process, after initiation by an external heat source, a highly exothermic reaction propagates through the sample in a self-sustained combustion wave. The process offers the possibility of producing materials with novel structures and properties. At conventional magnifications and imaging rates, the combustion wave appears to propagate in a planar, steady manner. However, using higher magnifications (>400X) and imaging rates (1000 frames/sec), fluctuations in the shape and propagation of the combustion front were observed. These variations in local conditions (i.e., the microstructure of the combustion wave) can influence the microstructure and properties of materials produced by combustion synthesis. In this work, the microstructure of wave propagation during combustion synthesis is investigated experimentally and theoretically. Using microscopic high-speed imaging, the spatial and temporal fluctuations of the combustion front shape and propagation were investigated. New image analysis methods were developed to characterize the heterogeneity of the combustion front quantitatively. The initial organization of the reaction medium was found to affect the heterogeneity of the combustion wave. Moreover, at the microscopic level, two different regimes of combustion propagation were observed. In the quasihomogeneous mechanism, the microstructure of the combustion wave resembles what is viewed macroscopically, and steady, planar propagation is observed. In the relay-race mechanism, while planar at the macroscopic level, the combustion front profiles are irregularly shaped, with arc-shaped convexities and concavities at the microscopic level. Also, the reaction front propagates as a series of rapid jumps and hesitations. Based on the combustion wave microstructure, new criteria were developed to determine the boundaries between quasihomogeneous and relay-race mechanisms, as functions of the initial organization of the reaction medium (i.e. particle size and porosity). In conjunction with the experiments, a microheterogeneous cell model was developed that simulates the local propagation of the combustion wave. Accounting for the stochastically organized medium with non-uniform properties, calculated results for the microstructural parameters of the combustion wave, and their dependence on density and reactant particle size, were in good qualitative agreement with experimental data.

Using a plenoptic camera to measure distortions in wavefronts affected by atmospheric turbulence

NASA Astrophysics Data System (ADS)

Eslami, Mohammed; Wu, Chensheng; Rzasa, John; Davis, Christopher C.

2012-10-01

Ideally, as planar wave fronts travel through an imaging system, all rays, or vectors pointing in the direction of the propagation of energy are parallel, and thus the wave front is focused to a particular point. If the wave front arrives at an imaging system with energy vectors that point in different directions, each part of the wave front will be focused at a slightly different point on the sensor plane and result in a distorted image. The Hartmann test, which involves the insertion of a series of pinholes between the imaging system and the sensor plane, was developed to sample the wavefront at different locations and measure the distortion angles at different points in the wave front. An adaptive optic system, such as a deformable mirror, is then used to correct for these distortions and allow the planar wave front to focus at the point desired on the sensor plane, thereby correcting the distorted image. The apertures of a pinhole array limit the amount of light that reaches the sensor plane. By replacing the pinholes with a microlens array each bundle of rays is focused to brighten the image. Microlens arrays are making their way into newer imaging technologies, such as "light field" or "plenoptic" cameras. In these cameras, the microlens array is used to recover the ray information of the incoming light by using post processing techniques to focus on objects at different depths. The goal of this paper is to demonstrate the use of these plenoptic cameras to recover the distortions in wavefronts. Taking advantage of the microlens array within the plenoptic camera, CODE-V simulations show that its performance can provide more information than a Shack-Hartmann sensor. Using the microlens array to retrieve the ray information and then backstepping through the imaging system provides information about distortions in the arriving wavefront.

A practical implementation of wave front construction for 3-D isotropic media

NASA Astrophysics Data System (ADS)

Chambers, K.; Kendall, J.-M.

2008-06-01

Wave front construction (WFC) methods are a useful tool for tracking wave fronts and are a natural extension to standard ray shooting methods. Here we describe and implement a simple WFC method that is used to interpolate wavefield properties throughout a 3-D heterogeneous medium. Our approach differs from previous 3-D WFC procedures primarily in the use of a ray interpolation scheme, based on approximating the wave front as a `locally spherical' surface and a `first arrival mode', which reduces computation times, where only first arrivals are required. Both of these features have previously been included in 2-D WFC algorithms; however, until now they have not been extended to 3-D systems. The wave front interpolation scheme allows for rays to be traced from a nearly arbitrary distribution of take-off angles, and the calculation of derivatives with respect to take-off angles is not required for wave front interpolation. However, in regions of steep velocity gradient, the locally spherical approximation is not valid, and it is necessary to backpropagate rays to a sufficiently homogenous region before interpolation of the new ray. Our WFC technique is illustrated using a realistic velocity model, based on a North Sea oil reservoir. We examine wavefield quantities such as traveltimes, ray angles, source take-off angles and geometrical spreading factors, all of which are interpolated on to a regular grid. We compare geometrical spreading factors calculated using two methods: using the ray Jacobian and by taking the ratio of a triangular area of wave front to the corresponding solid angle at the source. The results show that care must be taken when using ray Jacobians to calculate geometrical spreading factors, as the poles of the source coordinate system produce unreliable values, which can be spread over a large area, as only a few initial rays are traced in WFC. We also show that the use of the first arrival mode can reduce computation time by ~65 per cent, with the accuracy of the interpolated traveltimes, ray angles and source take-off angles largely unchanged. However, the first arrival mode does lead to inaccuracies in interpolated angles near caustic surfaces, as well as small variations in geometrical spreading factors for ray tubes that have passed through caustic surfaces.

Polarization and wavelength diversities of Gulf Stream fronts imaged by AIRSAR

NASA Technical Reports Server (NTRS)

Lee, J. S.; Jansen, R. W.; Marmorino, G. O.; Chubb, S. R.

1995-01-01

During the 1990 Gulf Stream Experiment, NASA/JPL AIRSAR imaged the north edge of the Gulf Stream near the coast of Virginia. Simultaneous in-situ measurements of currents, temperatures, salinities, etc. were made for several crossings of the north edge by the R/V Cape Henlopen. Measurements identified two fronts with shearing and converging flows. The polarimetric SAR images from the fronts showed two bright linear features. One of them corresponds to the temperature front, which separated the warm Gulf Stream water to the south from a cool, freshwater filament to the north. The other line, located about 8 km north of the temperature front, is believed to correspond to the velocity front between the filament and the slope water. At these fronts, wave-current interactions produced narrow bands of steep and breaking waves manifesting higher radar returns in polarimetric SAR images. In general, our AIRSAR imagery shows that the signal-to-clutter ratio of radar cross sections for the temperature front is higher than that of the velocity front. In this paper, we study the polarization and wavelength diversities of radar response of these two fronts using the P-, L-, and C-Band Polarimetric SAR data. The north-south flight path of the AIRSAR crossed the temperature front several times and provided valuable data for analysis. Three individual passes are investigated. We found that for the temperature front, the cross-pol (HV) responses are much higher than co-pol responses (VV and HH), and that P-Band HV has the highest signal to clutter ratio. For the velocity front, the ratio is the strongest in P-Band VV, and it is indistinguishable for all polarizations in C-Band. The radar cross sections for all three polarization (HH, HV, and VV) and for all three bands are modelled using an ocean wave model and a composite Bragg scattering model. In our initial investigations, the theoretical model agrees qualitatively with the AIRSAR observations.

A Catalog of Coronal "EIT Wave" Transients

NASA Technical Reports Server (NTRS)

Thompson, B. J.; Myers, D. C.

2009-01-01

Solar and Heliospheric Observatory (SOHO) Extreme ultraviolet Imaging Telescope (EIT) data have been visually searched for coronal "EIT wave" transients over the period beginning from 1997 March 24 and extending through 1998 June 24. The dates covered start at the beginning of regular high-cadence (more than one image every 20 minutes) observations, ending at the four-month interruption of SOHO observations in mid-1998. One hundred and seventy six events are included in this catalog. The observations range from "candidate" events, which were either weak or had insufficient data coverage, to events which were well defined and were clearly distinguishable in the data. Included in the catalog are times of the EIT images in which the events are observed, diagrams indicating the observed locations of the wave fronts and associated active regions, and the speeds of the wave fronts. The measured speeds of the wave fronts varied from less than 50 to over 700 km s(exp -1) with "typical" speeds of 200-400 km s(exp -1).

Nonlinear interaction of strong S-waves with the rupture front in the shallow subsurface

NASA Astrophysics Data System (ADS)

Sleep, N. H.

2017-12-01

Shallow deformation in moderate to large earthquakes is sometimes distributed rather than being concentrated on a single fault plane. Strong high-frequency S-waves interact with the rupture front to produce this effect. For strike-slip faults, the rupture propagation velocity is a fraction of the S-wave velocity. The rupture propagation vector refracts essentially vertically in the low (S-wave) velocity shallow subsurface. So does the propagation direction of S-waves. The shallow rupture front is essentially mode 3 near the surface. Strong S-waves arrive before the rupture front. They continue to arrive for several seconds in a large event. There are simple scaling relationships. The dynamic Coulomb stress ratio of horizontal stress on horizontal planes from S-waves is the normalized acceleration in g's. For fractured rock and gravel, frictional failure occurs when the normalized acceleration exceeds the effective coefficient of friction. Acceleration tends to saturate at that level as the anelastic strain rate increases rapidly with stress. For muddy materials, failure begins at a low normalized acceleration but increases slowly with dynamic stress. Dynamic accelerations sometimes exceed 1 g. In both cases, the rupture tip finds the shallow subsurface already in nonlinear failure down to a few to tens of meters depth. The material does not distinguish between S-wave and rupture tip stresses. Both stresses add to the stress invariant and hence to the anelastic strain rate tensor. Surface anelastic strain from fault slip is thus distributed laterally over a distance scaling to the depth of nonlinearity from S-waves. The environs of the fault anelastically accommodate the fault slip at depth. This process differs from blind faults where the shallow coseismic strain is mostly elastic and interseismic anelastic processes accommodate the long-term shallow deformation.

Cohesive Sedimentary Processes on River-Dominated Deltas: New Perspectives from the Mississippi River Delta Front, Gulf of Mexico

NASA Astrophysics Data System (ADS)

Bentley, S. J.; Keller, G. P.; Obelcz, J.; Maloney, J. M.; Xu, K.; Georgiou, I. Y.; Miner, M. D.

2016-12-01

On river deltas dominated by proximal sediment accumulation (Mississippi, Huang He, others), the delta front region is commonly dominated by rapid accumulation of cohesive fluvial sediments, and mass-wasting processes that remobilize recently deposited sediments. Mass transport is preconditioned in sediments by high water content, biogenic gas production, over steepening, and is commonly triggered by strong wave loading and other processes. This understanding is based on extensive field studies in the 1970's and 80's. Recent studies of the Mississippi River Delta Front are yielding new perspectives on these processes, in a time of anthropogenically reduced sediment loads, rising sea level, and catastrophic deltaic land loss. We have synthesized many industry data sets collected since ca. 1980, and conducted new pilot field and modeling studies of sedimentary and morphodynamic processes. These efforts have yielded several key findings that diverge from historical understanding of this dynamic setting. First, delta distributary mouths have ceased seaward progradation, ending patterns that have been documented since the 18th century. Second, despite reduced sediment supply, offshore mass transport continues, yielding vertical displacements at rates of 1 m/y. This displacement is apparently forced by wave loading from storm events of near-annual return period, rather than major hurricanes that have been the focus of most previous studies. Third, core analysis indicates that this vertical displacement is occurring along failure planes >3 m in the seabed, rather than in more recently deposited sediments closer to the sediment-water interface. These seabed morphodynamics have the potential to destabilize both nearshore navigation infrastructure, and seabed hydrocarbon infrastructure offshore. As well, these findings raise more questions regarding the future seabed evolution offshore of major river deltas, in response to anthropogenic and climatic forcing.

On Emulation of Flueric Devices in Excitable Chemical Medium

PubMed Central

Adamatzky, Andrew

2016-01-01

Flueric devices are fluidic devices without moving parts. Fluidic devices use fluid as a medium for information transfer and computation. A Belousov-Zhabotinsky (BZ) medium is a thin-layer spatially extended excitable chemical medium which exhibits travelling excitation wave-fronts. The excitation wave-fronts transfer information. Flueric devices compute via jets interaction. BZ devices compute via excitation wave-fronts interaction. In numerical model of BZ medium we show that functions of key flueric devices are implemented in the excitable chemical system: signal generator, and, xor, not and nor Boolean gates, delay elements, diodes and sensors. Flueric devices have been widely used in industry since late 1960s and are still employed in automotive and aircraft technologies. Implementation of analog of the flueric devices in the excitable chemical systems opens doors to further applications of excitation wave-based unconventional computing in soft robotics, embedded organic electronics and living technologies. PMID:27997561

On Emulation of Flueric Devices in Excitable Chemical Medium.

PubMed

Adamatzky, Andrew

2016-01-01

Flueric devices are fluidic devices without moving parts. Fluidic devices use fluid as a medium for information transfer and computation. A Belousov-Zhabotinsky (BZ) medium is a thin-layer spatially extended excitable chemical medium which exhibits travelling excitation wave-fronts. The excitation wave-fronts transfer information. Flueric devices compute via jets interaction. BZ devices compute via excitation wave-fronts interaction. In numerical model of BZ medium we show that functions of key flueric devices are implemented in the excitable chemical system: signal generator, and, xor, not and nor Boolean gates, delay elements, diodes and sensors. Flueric devices have been widely used in industry since late 1960s and are still employed in automotive and aircraft technologies. Implementation of analog of the flueric devices in the excitable chemical systems opens doors to further applications of excitation wave-based unconventional computing in soft robotics, embedded organic electronics and living technologies.

How Reflected Wave Fronts Dynamically Establish Hooke's Law in a Spring

ERIC Educational Resources Information Center

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…

Optical analysis of laser systems using interferometry

NASA Astrophysics Data System (ADS)

Viswanathan, V. K.; Liberman, I.; Lawrence, G.; Seery, B. D.

1980-06-01

It is noted that previous approaches of predicting focal spot parameters involved the digitization of interference patterns of the optical components and propagation of the complex amplitude and phase of the wave front throughout the system. The present paper describes an approach in which the computational procedure is extended to produce computer plots of the final emerging wave front. It is shown that this enables direct comparison with the experimentally produced wave front of the total system and makes possible the optical analysis, design, and possible optimization of laser systems. A description is given of the computational procedure and the Twyman-Green and Smartt IR interferometers constructed to verify this approach. Finally, consideration is given to the implications of the results.

Adaptive optics for array telescopes using piston-and-tilt wave-front sensing

NASA Technical Reports Server (NTRS)

Wizinowich, P.; Mcleod, B.; Lloyd-Yhart, M.; Angel, J. R. P.; Colucci, D.; Dekany, R.; Mccarthy, D.; Wittman, D.; Scott-Fleming, I.

1992-01-01

A near-infrared adaptive optics system operating at about 50 Hz has been used to control phase errors adaptively between two mirrors of the Multiple Mirror Telescope by stabilizing the position of the interference fringe in the combined unresolved far-field image. The resultant integrated images have angular resolutions of better than 0.1 arcsec and fringe contrasts of more than 0.6. Measurements of wave-front tilt have confirmed the wavelength independence of image motion. These results show that interferometric sensing of phase errors, when combined with a system for sensing the wave-front tilt of the individual telescopes, will provide a means of achieving a stable diffraction-limited focus with segmented telescopes or arrays of telescopes.

Growth rates of the buoyancy-driven instability of an autocatalytic reaction front in a narrow cell

PubMed

Bockmann; Muller

2000-09-18

Experimental studies were performed on the buoyancy-driven instability of an autocatalytic reaction front in a quasi-2D cell. The unstable density stratification at an ascending front leads to convection that results in a fingerlike front deformation. The growth rates of the spatial modes of the instability are determined at the initial stage. A stabilization is found at higher wave numbers, while the system is unstable against low wave number perturbations. Whereas comparison with a reported model governed by Hele-Shaw flow fails, a two-dimensional Navier-Stokes model yields more satisfactory results. Still, present deviations suggest the presence of an additional mechanism that suppresses the growth.

Charged Particle Distribution near the Shock Front in a Glow Discharge

NASA Astrophysics Data System (ADS)

Baryshnikov, A. S.; Basargin, I. V.; Bezverkhnii, N. O.; Bobashev, S. V.; Monakhov, N. A.; Popov, P. A.; Sakharov, V. A.; Chistyakova, M. V.

2018-02-01

The charged particle distribution near the front of a shock wave propagating in the glow discharge plasma has been investigated. It has been found that the ion concentration before the front varies nonmonotonically. Behind the shock front, the charged particle concentration varies smoothly in contrast to the neutral component density.

Wave refraction in negative-index media: always positive and very inhomogeneous.

PubMed

Valanju, P M; Walser, R M; Valanju, A P

2002-05-06

We present the first treatment of the refraction of physical electromagnetic waves in newly developed negative index media (NIM), also known as left-handed media (LHM). The NIM dispersion relation implies that group fronts refract positively even when phase fronts refract negatively. This difference results in rapidly dispersing, very inhomogeneous waves. In fact, causality and finite signal speed always prevent negative wave signal (not phase) refraction. Earlier interpretations of phase refraction as "negative light refraction" and "light focusing by plane slabs" are therefore incorrect, and published NIM experiments can be explained without invoking negative signal refraction.

Failure Waves in Cylindrical Glass Bars

NASA Astrophysics Data System (ADS)

Cazamias, James U.; Bless, Stephan J.; Marder, Michael P.

1997-07-01

Failure waves, a propagating front separating virgin and comminuted material, have been receiving a fair amount of attention the last couple of years. While most scientists have been looking at failure waves in plate impact geometries, we have conducted a series of experiments on Pyrex bars. In this paper, we present two types of photographic data from a series of tests. A streak camera was used to determine velocities of the failure front as a function of impact stress. A polaroid camera and a flash lamp provide detailed pictures of the actual event. Attempts were made to observe failure waves in amorphous quartz and acrylic.

Shock and Rarefaction Waves in a Heterogeneous Mantle

NASA Astrophysics Data System (ADS)

Jordan, J.; Hesse, M. A.

2012-12-01

We explore the effect of heterogeneities on partial melting and melt migration during active upwelling in the Earth's mantle. We have constructed simple, explicit nonlinear models in one dimension to examine heterogeneity and its dynamic affects on porosity, temperature and the magnesium number in a partially molten, porous medium comprised of olivine. The composition of the melt and solid are defined by a closed, binary phase diagram for a simplified, two-component olivine system. The two-component solid solution is represented by a phase loop where concentrations 0 and 1 to correspond to fayalite and forsterite, respectively. For analysis, we examine an advective system with a Riemann initial condition. Chromatographic tools and theory have primarily been used to track large, rare earth elements as tracers. In our case, we employ these theoretical tools to highlight the importance of the magnesium number, enthalpy and overall heterogeneity in the dynamics of melt migration. We calculate the eigenvectors and eigenvalues in the concentration-enthalpy space in order to glean the characteristics of the waves emerging the Riemann step. Analysis on Riemann problems of this nature shows us that the composition-enthalpy waves can be represented by self-similar solutions. The eigenvalues of the composition-enthalpy system represent the characteristic wave propagation speeds of the compositions and enthalpy through the domain. Furthermore, the corresponding eigenvectors are the directions of variation, or ``pathways," in concentration-enthalpy space that the characteristic waves follow. In the two-component system, the Riemann problem yields two waves connected by an intermediate concentration-enthalpy state determined by the intersections of the integral curves of the eigenvectors emanating from both the initial and boundary states. The first wave, ``slow path," and second wave, ``fast path," follow the aformentioned pathways set by the eigenvectors. The slow path wave has a zero eigenvalue, corresponding to a wave speed of zero, which preserves a residual imprint of the initial condition. Freezing fronts textemdash those that result in a negative change in porositytextemdash feature fast path waves that travel as shocks, whereas the fast path waves of melting fronts travel as spreading, rarefaction waves.

Spatially Localized Chemical Patterns around an A + B → Oscillator Front.

PubMed

Budroni, M A; Lemaigre, L; Escala, D M; Muñuzuri, A P; De Wit, A

2016-02-18

When two gels, each loaded with a different set of reactants A and B of an oscillatory reaction, are brought into contact, reaction-diffusion patterns such as waves or Turing patterns can develop in the reactive contact zone. The initial condition which separates the reactants at the beginning leads to a localization in space of the different dynamical regimes accessible to the chemical oscillator. We study here both numerically and experimentally the composite traveling structures resulting from the interaction between chemical fronts and localized waves in the case in which the reactants of such an A + B → oscillator system are those of the canonical Belousov-Zhabotinsky (BZ) oscillating reaction. A transition between different dynamics is obtained by varying the initial concentration of the organic substrate of the BZ reactants, which is one of the parameters controlling the local excitability. We show that the dynamical regime (excitable or oscillatory) characterizing the BZ oscillator in the initial contact area is the key feature which determines the spatiotemporal evolution of the system. The experimental results are in qualitative agreement with the theoretical predictions.

Wave-front singularities for two-dimensional anisotropic elastic waves.

NASA Technical Reports Server (NTRS)

Payton, R. G.

1972-01-01

Wavefront singularities for the displacement functions, associated with the radiation of linear elastic waves from a point source embedded in a finitely strained two-dimensional elastic solid, are examined in detail. It is found that generally the singularities are of order d to the -1/2 power, where d measures distance away from the front. However, in certain exceptional cases singularities of order d to the -n power, where n = 1/4, 2/3, 3/4, may be encountered.

Ship Shoal as a prospective borrow site for barrier island restoration, coastal south-central Louisiana, Usa: Numerical wave modeling and field measurements of hydrodynamics and sediment transport

USGS Publications Warehouse

Stone, G.W.; Pepper, D.A.; Xu, Jie; Zhang, X.

2004-01-01

Ship Shoal, a transgressive sand body located at the 10 m isobath off south-central Louisiana, is deemed a potential sand source for restoration along the rapidly eroding Isles Dernieres barrier chain and possibly other sites in Louisiana. Through numerical wave modeling we evaluate the potential response of mining Ship Shoal on the wave field. During severe and strong storms, waves break seaward of the western flank of Ship Shoal. Therefore, removal of Ship Shoal (approximately 1.1 billion m3) causes a maximum increase of the significant wave height by 90%-100% and 40%-50% over the shoal and directly adjacent to the lee of the complex for two strong storm scenarios. During weak storms and fair weather conditions, waves do not break over Ship Shoal. The degree of increase in significant wave height due to shoal removal is considerably smaller, only 10%-20% on the west part of the shoal. Within the context of increasing nearshore wave energy levels, removal of the shoal is not significant enough to cause increased erosion along the Isles Dernieres. Wave approach direction exerts significant control on the wave climate leeward of Ship Shoal for stronger storms, but not weak storms or fairweather. Instrumentation deployed at the shoal allowed comparison of measured wave heights with numerically derived wave heights using STWAVE. Correlation coefficients are high in virtually all comparisons indicating the capability of the model to simulate wave behavior satisfactorily at the shoal. Directional waves, currents and sediment transport were measured during winter storms associated with frontal passages using three bottom-mounted arrays deployed on the seaward and landward sides of Ship Shoal (November, 1998-January, 1999). Episodic increases in wave height, mean and oscillatory current speed, shear velocity, and sediment transport rates, associated with recurrent cold front passages, were measured. Dissipation mechanisms included both breaking and bottom friction due to variable depths across the shoal crest and variable wave amplitudes during storms and fair-weather. Arctic surge fronts were associated with southerly storm waves, and southwesterly to westerly currents and sediment transport. Migrating cyclonic fronts generated northerly swell that transformed into southerly sea, and currents and sediment transport that were southeasterly overall. Waves were 36% higher and 9% longer on the seaward side of the shoal, whereas mean currents were 10% stronger landward, where they were directed onshore, in contrast to the offshore site, where seaward currents predominated. Sediment transport initiated by cold fronts was generally directed southeasterly to southwesterly at the offshore site, and southerly to westerly at the nearshore site. The data suggest that both cold fronts and the shoal, exert significant influences on regional hydrodynamics and sediment transport.

Tunable modulation of refracted lamb wave front facilitated by adaptive elastic metasurfaces

NASA Astrophysics Data System (ADS)

Li, Shilong; Xu, Jiawen; Tang, J.

2018-01-01

This letter reports designs of adaptive metasurfaces capable of modulating incoming wave fronts of elastic waves through electromechanical-tuning of their cells. The proposed elastic metasurfaces are composed of arrayed piezoelectric units with individually connected negative capacitance elements that are online tunable. By adjusting the negative capacitances properly, accurately formed, discontinuous phase profiles along the elastic metasurfaces can be achieved. Subsequently, anomalous refraction with various angles can be realized on the transmitted lowest asymmetric mode Lamb wave. Moreover, designs to facilitate planar focal lenses and source illusion devices can also be accomplished. The proposed flexible and versatile strategy to manipulate elastic waves has potential applications ranging from structural fault detection to vibration/noise control.

Fluctuations uncover a distinct class of traveling waves

PubMed Central

Korolev, Kirill S.

2018-01-01

Epidemics, flame propagation, and cardiac rhythms are classic examples of reaction–diffusion waves that describe a switch from one alternative state to another. Only two types of waves are known: pulled, driven by the leading edge, and pushed, driven by the bulk of the wave. Here, we report a distinct class of semipushed waves for which both the bulk and the leading edge contribute to the dynamics. These hybrid waves have the kinetics of pushed waves, but exhibit giant fluctuations similar to pulled waves. The transitions between pulled, semipushed, and fully pushed waves occur at universal ratios of the wave velocity to the Fisher velocity. We derive these results in the context of a species invading a new habitat by examining front diffusion, rate of diversity loss, and fluctuation-induced corrections to the expansion velocity. All three quantities decrease as a power law of the population density with the same exponent. We analytically calculate this exponent, taking into account the fluctuations in the shape of the wave front. For fully pushed waves, the exponent is −1, consistent with the central limit theorem. In semipushed waves, however, the fluctuations average out much more slowly, and the exponent approaches 0 toward the transition to pulled waves. As a result, a rapid loss of genetic diversity and large fluctuations in the position of the front occur, even for populations with cooperative growth and other forms of an Allee effect. The evolutionary outcome of spatial spreading in such populations could therefore be less predictable than previously thought. PMID:29610340

Fluctuations uncover a distinct class of traveling waves.

PubMed

Birzu, Gabriel; Hallatschek, Oskar; Korolev, Kirill S

2018-04-17

Epidemics, flame propagation, and cardiac rhythms are classic examples of reaction-diffusion waves that describe a switch from one alternative state to another. Only two types of waves are known: pulled, driven by the leading edge, and pushed, driven by the bulk of the wave. Here, we report a distinct class of semipushed waves for which both the bulk and the leading edge contribute to the dynamics. These hybrid waves have the kinetics of pushed waves, but exhibit giant fluctuations similar to pulled waves. The transitions between pulled, semipushed, and fully pushed waves occur at universal ratios of the wave velocity to the Fisher velocity. We derive these results in the context of a species invading a new habitat by examining front diffusion, rate of diversity loss, and fluctuation-induced corrections to the expansion velocity. All three quantities decrease as a power law of the population density with the same exponent. We analytically calculate this exponent, taking into account the fluctuations in the shape of the wave front. For fully pushed waves, the exponent is -1, consistent with the central limit theorem. In semipushed waves, however, the fluctuations average out much more slowly, and the exponent approaches 0 toward the transition to pulled waves. As a result, a rapid loss of genetic diversity and large fluctuations in the position of the front occur, even for populations with cooperative growth and other forms of an Allee effect. The evolutionary outcome of spatial spreading in such populations could therefore be less predictable than previously thought. Copyright © 2018 the Author(s). Published by PNAS.

Wavefront sensor for the GAIA Mission

NASA Astrophysics Data System (ADS)

Vosteen, Amir; Draaisma, Folkert; van Werkhoven, Willem; van Riel, Luud; Mol, Margreet; Gielesen, Wim

2017-11-01

TNO has developed, built and tested the Wave Front Sensor (WFS) for ESA's Gaia mission. The WFS will help Gaia create an extraordinarily precise three-dimensional map of more than one billion stars in our Galaxy. Part of ESA's Cosmic Vision programme, Gaia's build is led by EADS Astrium and is scheduled for launch in 2012. The Wave Front Sensor will be used to monitor the wave front errors of the two main telescopes mounted on the GAIA satellite. These mirrors include a 5-degree of freedom (DOF) mechanism that can be used to minimize the wave front errors during operation. The GAIA-WFS will operate over a broad wavelength (450 to 900 nm) and under cryogenic conditions (130 to 200 K operation temperature). The WFS uses an all reflective, a-thermal design and is of the type of Shack-Hartmann. The boundary condition for the design is that the focal plane of the WFS is the same plane as the focal plane of the GAIA telescopes. The spot pattern generated after a micro lens array ( MLA) by a star is compared to the pattern of one of the three calibration sources that is included in the WFS, allowing in flight calibration. We show the robust and lightweight opto mechanical design that is optimised for launch and cryogenic operation. Details are given on its alignment and commissioning. The WFS is able to measure relative wave front distortions in the order of lambda/1000, and can determine the optimum position of the focal plane with an accuracy of 50 μm

Development and Realization of a Shock Wave Test on Expert Flap Qualification Model

NASA Astrophysics Data System (ADS)

De Fruytier, C.; Dell'Orco, F.; Ullio, R.; Gomiero, F.

2012-07-01

This paper presents the methodology and the results of the shock test campaign conducted by TAS-I and TAS ETCA to qualify the EXPERT Flap in regards of shock wave and acoustic load generated by pyrocord detonation at stages 2/3 separation phase of the EXPERT vehicle. The design concept of the open flap (manufactured by MT AEROSPACE) is a fully integral manufactured, four sided control surface, with an additional stiffening rib and flanges to meet the first eigenfrequency and the allowable deformation requirement with a minimum necessary mass. The objectives were to reproduce equivalent loading at test article level in terms of pulse duration, front pressure, front velocity and acoustic emission. The Thales Alenia Space ETCA pyrotechnic shock test device is usually used to produce high level shocks by performing a shock on a test fixture supporting the unit under test. In this case, the facility has been used to produce a shock wave, with different requested physical characteristics, directed to the unit under test. Different configurations have been tried on a dummy of the unit to test, following an empirical process. This unusual work has lead to the definition of a nominal set- up meeting the requested physical parameters. Two blast sensors have been placed to acquire the pressure around the flap. The distance between the two sensors has allowed estimating the front pressure velocity. Then, several locations have been selected to acquire the acceleration responses on the unit when it was submitted to this environment. Additionally, a “standard” shock test has been performed on this model. The qualification of the flap, in regards of shock environment, has been successfully conducted.

Quasi-periodic Fast-mode Wave Trains Within a Global EUV Wave and Sequential Transverse Oscillations Detected by SDO-AIA

NASA Technical Reports Server (NTRS)

Liu, Wei; Ofman, Leon; Nitta, Nariaki; Aschwanden, Markus J.; Schrijver, Carolus J.; Title, Alan M.; Tarbell, Theodore D.

2012-01-01

We present the first unambiguous detection of quasi-periodic wave trains within the broad pulse of a global EUV wave (so-called EIT wave) occurring on the limb. These wave trains, running ahead of the lateral coronal mass ejection (CME) front of 2-4 times slower, coherently travel to distances greater than approximately solar radius/2 along the solar surface, with initial velocities up to 1400 kilometers per second decelerating to approximately 650 kilometers per second. The rapid expansion of the CME initiated at an elevated height of 110 Mm produces a strong downward and lateral compression, which may play an important role in driving the primary EUV wave and shaping its front forwardly inclined toward the solar surface. The wave trains have a dominant 2 minute periodicity that matches the X-ray flare pulsations, suggesting a causal connection. The arrival of the leading EUV wave front at increasing distances produces an uninterrupted chain sequence of deflections and/or transverse (likely fast kink mode) oscillations of local structures, including a flux-rope coronal cavity and its embedded filament with delayed onsets consistent with the wave travel time at an elevated (by approximately 50%) velocity within it. This suggests that the EUV wave penetrates through a topological separatrix surface into the cavity, unexpected from CME-caused magnetic reconfiguration. These observations, when taken together, provide compelling evidence of the fast-mode MHD wave nature of the primary (outer) fast component of a global EUV wave, running ahead of the secondary (inner) slow component of CME-caused restructuring.

Frontal dynamics at the edge of the Columbia River plume

NASA Astrophysics Data System (ADS)

Akan, Çiğdem; McWilliams, James C.; Moghimi, Saeed; Özkan-Haller, H. Tuba

2018-02-01

In the tidal ebb-cycle at the Mouth of the Columbia River, strong density and velocity fronts sometimes form perpendicular to the coast at the edges of the freshwater plume. They are distinct from previously analyzed fronts at the offshore western edge of the plume that evolve as a gravity-wave bore. We present simulation results to demonstrate their occurrence and investigate the mechanisms behind their frontogenesis and evolution. Tidal velocities on average ranged between 1.5 m s-1 in flood and 2.5 m s-1 in ebb during the brief hindcast period. The tidal fronts exhibit strong horizontal velocity and buoyancy gradients on a scale ∼ 100 m in width with normalized relative vorticity (ζz/f) values reaching up to 50. We specifically focus on the front on the northern edge of the plume and examine the evolution in plume characteristics such as its water mass gradients, horizontal and vertical velocity structure, vertical velocity, turbulent vertical mixing, horizontal propagation, cross-front momentum balance, and Lagrangian frontogenetic tendencies in both buoyancy and velocity gradients. Advective frontogenesis leads to a very sharp front where lateral mixing near the grid-resolution limit arrests its further contraction. The negative vorticity within the front is initiated by the positive bottom drag curl on the north side of the Columbia estuary and against the north jetty. Because of the large negative vorticity and horizontal vorticity gradient, centrifugal and lateral shear instability begins to develop along the front, but frontal fragmentation and decay set in only after the turn of the tide because of the briefness of the ebb interval.

Research of centroiding algorithms for extended and elongated spot of sodium laser guide star

NASA Astrophysics Data System (ADS)

Shao, Yayun; Zhang, Yudong; Wei, Kai

2016-10-01

Laser guide stars (LGSs) increase the sky coverage of astronomical adaptive optics systems. But spot array obtained by Shack-Hartmann wave front sensors (WFSs) turns extended and elongated, due to the thickness and size limitation of sodium LGS, which affects the accuracy of the wave front reconstruction algorithm. In this paper, we compared three different centroiding algorithms , the Center-of-Gravity (CoG), weighted CoG (WCoG) and Intensity Weighted Centroid (IWC), as well as those accuracies for various extended and elongated spots. In addition, we compared the reconstructed image data from those three algorithms with theoretical results, and proved that WCoG and IWC are the best wave front reconstruction algorithms for extended and elongated spot among all the algorithms.

BP artificial neural network based wave front correction for sensor-less free space optics communication

NASA Astrophysics Data System (ADS)

Li, Zhaokun; Zhao, Xiaohui

2017-02-01

The sensor-less adaptive optics (AO) is one of the most promising methods to compensate strong wave front disturbance in free space optics communication (FSO). The back propagation (BP) artificial neural network is applied for the sensor-less AO system to design a distortion correction scheme in this study. This method only needs one or a few online measurements to correct the wave front distortion compared with other model-based approaches, by which the real-time capacity of the system is enhanced and the Strehl Ratio (SR) is largely improved. Necessary comparisons in numerical simulation with other model-based and model-free correction methods proposed in Refs. [6,8,9,10] are given to show the validity and advantage of the proposed method.

Generalized self-similar unsteady gas flows behind the strong shock wave front

NASA Astrophysics Data System (ADS)

Bogatko, V. I.; Potekhina, E. A.

2018-05-01

Two-dimensional (plane and axially symmetric) nonstationary gas flows behind the front of a strong shock wave are considered. All the gas parameters are functions of the ratio of Cartesian coordinates to some degree of time tn, where n is a self-similarity index. The problem is solved in Lagrangian variables. It is shown that the resulting system of partial differential equations is suitable for constructing an iterative process. ¢he "thin shock layer" method is used to construct an approximate analytical solution of the problem. The limit solution of the problem is constructed. A formula for determining the path traversed by a gas particle in the shock layer along the front of a shock wave is obtained. A system of equations for determining the first approximation corrections is constructed.

A Photographic Study of Combustion and Knock in a Spark-Ignition Engine

NASA Technical Reports Server (NTRS)

Rothrock, A M; Spencer, R C

1938-01-01

Report presents the results of a photographic study of the combustion in a spark-ignition engine using both Schlieren and flame photographs taken at high rates of speed. Although shock waves are present after knock occurs, there was no evidence of any type of sonic or supersonic compression waves existing in the combustion gases prior to the occurrence of knock. Artificially induced shock waves in the engine did not in themselves cause knock. The photographs also indicate that, although auto-ignition ahead of the flame front may occur in conjunction with knock, it is not necessary for the occurrence of knock. There is also evidence that the reaction is not completed in the flame front but continues for some time after the flame front has passed through the charge.

A downslope propagating thermal front over the continental slope

NASA Astrophysics Data System (ADS)

van Haren, Hans; Hosegood, Phil J.

2017-04-01

In the ocean, internal frontal bores above sloping topography have many appearances, depending on the local density stratification, and on the angle and source of generation of the carrier wave. However, their common characteristics are a backward breaking wave, strong sediment resuspension, and relatively cool (denser) water moving more or less upslope underneath warm (less dense) water. In this paper, we present a rare example of a downslope moving front of cold water moving over near-bottom warm water. Large backscatter is observed in the downslope moving front's trailing edge, rather than the leading edge as is common in upslope moving fronts. Time series observations have been made during a fortnight in summer, using a 101 m long array of high-resolution temperature sensors moored with an acoustic Doppler current profiler at 396 m depth in near-homogeneous waters, near a small canyon in the continental slope off the Malin shelf (West-Scotland, UK). Occurring between fronts that propagate upslope with tidal periodicity, the rare downslope propagating one resembles a gravity current and includes strong convective turbulence coming from the interior rather than the more usual frictionally generated turbulence arising from interaction with the seabed. Its turbulence is 3-10 times larger than that of more common upslope propagating fronts. As the main turbulence is in the interior with a thin stratified layer close to the bottom, little sediment is resuspended by a downslope propagating front. The downslope propagating front is suggested to be generated by oblique propagation of internal (tidal) waves and flow over a nearby upstream promontory.

Broadband high-frequency waves and intermittent energy conversion at dipolarization fronts

NASA Astrophysics Data System (ADS)

Yang, J.; Cao, J.; Fu, H.; Wang, T.; Liu, W.; Yao, Z., Sr.

2017-12-01

Dipolarization front (DF) is a sharp boundary most probably separating the reconnection jet from the background plasma sheet. So far at this boundary, the observed waves are mainly in low-frequency range (e.g., magnetosonic waves and lower hybrid waves). Few high-frequency waves are observed in this region. In this paper, we report the broadband high-frequency wave emissions at the DF. These waves, having frequencies extending from the electron cyclotron frequency fce, up to the electron plasma frequency fpe, could contribute 10% to the in situ measurement of intermittent energy conversion at the DF layer. Their generation may be attributed to electron beams, which are simultaneously observed at the DF as well. Furthermore, we find intermittent energy conversion is primarily to the broadband fluctuations in the lower hybrid frequency range although the net energy conversion is small.

Wave combustors for trans-atmospheric vehicles

NASA Technical Reports Server (NTRS)

Menees, Gene P.; Adelman, Henry G.; Cambier, Jean-Luc; Bowles, Jeffrey V.

1989-01-01

The Wave Combustor is an airbreathing hypersonic propulsion system which utilizes shock and detonation waves to enhance fuel-air mixing and combustion in supersonic flow. In this concept, an oblique shock wave in the combustor can act as a flameholder by increasing the pressure and temperature of the air-fuel mixture and thereby decreasing the ignition delay. If the oblique shock is sufficiently strong, then the combustion front and the shock wave can couple into a detonation wave. In this case, combustion occurs almost instantaneously in a thin zone behind the wave front. The result is a shorter, lighter engine compared to the scramjet. This engine, which is called the Oblique Detonation Wave Engine (ODWE), can then be utilized to provide a smaller, lighter vehicle or to provide a higher payload capability for a given vehicle weight. An analysis of the performance of a conceptual trans-atmospheric vehicle powered by an ODWE is given here.

Link between alginate reaction front propagation and general reaction diffusion theory.

PubMed

Braschler, Thomas; Valero, Ana; Colella, Ludovica; Pataky, Kristopher; Brugger, Jürgen; Renaud, Philippe

2011-03-15

We provide a common theoretical framework reuniting specific models for the Ca(2+)-alginate system and general reaction diffusion theory along with experimental validation on a microfluidic chip. As a starting point, we use a set of nonlinear, partial differential equations that are traditionally solved numerically: the Mikkelsen-Elgsaeter model. Applying the traveling-wave hypothesis as a major simplification, we obtain an analytical solution. The solution indicates that the fundamental properties of the alginate reaction front are governed by a single dimensionless parameter λ. For small λ values, a large depletion zone accompanies the reaction front. For large λ values, the alginate reacts before having the time to diffuse significantly. We show that the λ parameter is of general importance beyond the alginate model system, as it can be used to classify known solutions for second-order reaction diffusion schemes, along with the novel solution presented here. For experimental validation, we develop a microchip model system, in which the alginate gel formation can be carried out in a highly controlled, essentially 1D environment. The use of a filter barrier enables us to rapidly renew the CaCl(2) solution, while maintaining flow speeds lower than 1 μm/s for the alginate compartment. This allows one to impose an exactly known bulk CaCl(2) concentration and diffusion resistance. This experimental model system, taken together with the theoretical development, enables the determination of the entire set of physicochemical parameters governing the alginate reaction front in a single experiment.

Two-zone elastic-plastic single shock waves in solids.

PubMed

Zhakhovsky, Vasily V; Budzevich, Mikalai M; Inogamov, Nail A; Oleynik, Ivan I; White, Carter T

2011-09-23

By decoupling time and length scales in moving window molecular dynamics shock-wave simulations, a new regime of shock-wave propagation is uncovered characterized by a two-zone elastic-plastic shock-wave structure consisting of a leading elastic front followed by a plastic front, both moving with the same average speed and having a fixed net thickness that can extend to microns. The material in the elastic zone is in a metastable state that supports a pressure that can substantially exceed the critical pressure characteristic of the onset of the well-known split-elastic-plastic, two-wave propagation. The two-zone elastic-plastic wave is a general phenomenon observed in simulations of a broad class of crystalline materials and is within the reach of current experimental techniques.

Failure waves in glass and ceramics under shock compression

NASA Astrophysics Data System (ADS)

Brar, N. S.

2000-04-01

The response of various types of glasses (fused silica, borosilicates, soda-lime, and lead filled) to shock wave loading, especially the failure of glass behind the shock wave through the "so called" failure wave or front, has been the subject of intense research among a number of investigators. The variations in material properties across this front include complete loss of tensile (spall) strength, loss in shear strength, reduction in acoustic impedance and opacity to light. Both the Stress and velocity history from VISAR measurements have shown that the failure front propagates at a speed of 1.5 to 2.5 mm/s, depending on the peak shock stress. The shear strength [τ=1/2(σ1-σ2)] behind the failure front, determined using embedded transverse gauges, is found to decrease to about 1 GPa for soda-lime, borosilicate, and filled glasses. Optical (high-speed photography) observations also confirm formation of this failure front. There is a general agreement among various researchers on these failure observations. However, three proposed mechanisms for the formation of failure front are based on totally different formulations. The first, due to Clifton, is based on the hypothesis of densification of glass under shock compression. Densification is followed by shear failure around inhomogeneities resulting in a phase boundary between the comminuted and the intact material. The second, proposed by Grady, involves the transfer of elastic shear strain energy to dilatant strain energy as a result of severe micro-cracking originating from impact. The third, by Espinosa and Brar, proposes that the front is created through shear micro-cracks, which nucleate and propagate from the impact face; as originally suggested by Kanel. This later mechanism is supported by the observed loss of shear strength of glass by Clifton et al. at shock stress above the threshold level. Espinosa has incorporated this mechanism in multiple-plane model and simulations predict the increase in lateral stress and an observed reduction in spall strength behind the failure front. Failure front studies, in terms of loss of shear strength, have been recently extended to alumina and SiC ceramics by Bourne et al.

Weakly and strongly coupled Belousov-Zhabotinsky patterns.

PubMed

Weiss, Stephan; Deegan, Robert D

2017-02-01

We investigate experimentally and numerically the synchronization of two-dimensional spiral wave patterns in the Belousov-Zhabotinsky reaction due to point-to-point coupling of two separate domains. Different synchronization modalities appear depending on the coupling strength and the initial patterns in each domain. The behavior as a function of the coupling strength falls into two qualitatively different regimes. The weakly coupled regime is characterized by inter-domain interactions that distorted but do not break wave fronts. Under weak coupling, spiral cores are pushed around by wave fronts in the other domain, resulting in an effective interaction between cores in opposite domains. In the case where each domain initially contains a single spiral, the cores form a bound pair and orbit each other at quantized distances. When the starting patterns consist of multiple randomly positioned spiral cores, the number of cores decreases with time until all that remains are a few cores that are synchronized with a partner in the other domain. The strongly coupled regime is characterized by interdomain interactions that break wave fronts. As a result, the wave patterns in both domains become identical.

Weakly and strongly coupled Belousov-Zhabotinsky patterns

NASA Astrophysics Data System (ADS)

Weiss, Stephan; Deegan, Robert D.

2017-02-01

We investigate experimentally and numerically the synchronization of two-dimensional spiral wave patterns in the Belousov-Zhabotinsky reaction due to point-to-point coupling of two separate domains. Different synchronization modalities appear depending on the coupling strength and the initial patterns in each domain. The behavior as a function of the coupling strength falls into two qualitatively different regimes. The weakly coupled regime is characterized by inter-domain interactions that distorted but do not break wave fronts. Under weak coupling, spiral cores are pushed around by wave fronts in the other domain, resulting in an effective interaction between cores in opposite domains. In the case where each domain initially contains a single spiral, the cores form a bound pair and orbit each other at quantized distances. When the starting patterns consist of multiple randomly positioned spiral cores, the number of cores decreases with time until all that remains are a few cores that are synchronized with a partner in the other domain. The strongly coupled regime is characterized by interdomain interactions that break wave fronts. As a result, the wave patterns in both domains become identical.

Amplitude-phase characteristics of electromagnetic fields diffracted by a hole in a thin film with realistic optical properties

NASA Astrophysics Data System (ADS)

Dorofeyev, Illarion

2009-03-01

Characteristics of a quasi-spherical wave front of an electromagnetic field diffracted by a subwavelength hole in a thin film with real optical properties are studied. Related diffraction problem is solved in general by use of the scalar and vector Green's theorems and related Green's function of a boundary-value problem. Local phase deviations of a diffracted wave front from an ideal spherical front are calculated. Diffracted patterns are calculated for the coherent incident fields in case of holes array in a screen of perfect conductivity.

Phase-sensitive X-ray imager

DOEpatents

Baker, Kevin Louis

2013-01-08

X-ray phase sensitive wave-front sensor techniques are detailed that are capable of measuring the entire two-dimensional x-ray electric field, both the amplitude and phase, with a single measurement. These Hartmann sensing and 2-D Shear interferometry wave-front sensors do not require a temporally coherent source and are therefore compatible with x-ray tubes and also with laser-produced or x-pinch x-ray sources.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sano, Yukio; Abe, Akihisa; Tokushima, Koji

The aim of this study is to examine the difference between shock temperatures predicted by an equation for temperature inside a steady wave front and the Walsh-Christian equation. Calculations are for yttria-doped tetragonal zirconia, which shows an elastic-plastic and a phase transition: Thus the shock waves treated are multiple structure waves composed of one to three steady wave fronts. The evaluated temperature was 3350K at the minimum specific volume of 0.1175 cm{sup 3}/g (or maximum Hugoniot shock pressure of 140GPa) considered in the present examination, while the temperature predicted by the Walsh-Christian equation under identical conditions was 2657K. The causemore » of the large temperature discrepancy is considered to be that the present model treats nonequilibrium states inside steady waves.« less

Fronts and waves of actin polymerization in a bistability-based mechanism of circular dorsal ruffles

NASA Astrophysics Data System (ADS)

Bernitt, Erik; Döbereiner, Hans-Günther; Gov, Nir S.; Yochelis, Arik

2017-06-01

During macropinocytosis, cells remodel their morphologies for the uptake of extracellular matter. This endocytotic mechanism relies on the collapse and closure of precursory structures, which are propagating actin-based, ring-shaped vertical undulations at the dorsal (top) cell membrane, a.k.a. circular dorsal ruffles (CDRs). As such, CDRs are essential to a range of vital and pathogenic processes alike. Here we show, based on both experimental data and theoretical analysis, that CDRs are propagating fronts of actin polymerization in a bistable system. The theory relies on a novel mass-conserving reaction-diffusion model, which associates the expansion and contraction of waves to distinct counter-propagating front solutions. Moreover, the model predicts that under a change in parameters (for example, biochemical conditions) CDRs may be pinned and fluctuate near the cell boundary or exhibit complex spiral wave dynamics due to a wave instability. We observe both phenomena also in our experiments indicating the conditions for which macropinocytosis is suppressed.

Fronts and waves of actin polymerization in a bistability-based mechanism of circular dorsal ruffles

PubMed Central

Bernitt, Erik; Döbereiner, Hans-Günther; Gov, Nir S.; Yochelis, Arik

2017-01-01

During macropinocytosis, cells remodel their morphologies for the uptake of extracellular matter. This endocytotic mechanism relies on the collapse and closure of precursory structures, which are propagating actin-based, ring-shaped vertical undulations at the dorsal (top) cell membrane, a.k.a. circular dorsal ruffles (CDRs). As such, CDRs are essential to a range of vital and pathogenic processes alike. Here we show, based on both experimental data and theoretical analysis, that CDRs are propagating fronts of actin polymerization in a bistable system. The theory relies on a novel mass-conserving reaction–diffusion model, which associates the expansion and contraction of waves to distinct counter-propagating front solutions. Moreover, the model predicts that under a change in parameters (for example, biochemical conditions) CDRs may be pinned and fluctuate near the cell boundary or exhibit complex spiral wave dynamics due to a wave instability. We observe both phenomena also in our experiments indicating the conditions for which macropinocytosis is suppressed. PMID:28627511

Intracellular signal propagation in a two-dimensional autocatalytic reaction model.

PubMed

Castiglione, F; Bernaschi, M; Succi, S; Heinrich, R; Kirschner, M W

2002-09-01

We study a simple reaction scheme in a two-dimensional lattice of particles or molecules with a refractory state. We analyze the dynamics of the propagating front as a function of physical-chemical properties of the host medium. The anisotropy of the medium significantly affects the smoothness of the wave front. Similarly, if particles or molecules may diffuse slowly to neighboring sites, then the front wave is more likely to be irregular. Both situations affect the ability of the whole system to relax to the original state, which is a required feature in the biological cells. Attempts to map this simple reaction scheme to reactions involved in the intracellular pathways suggest that, in some cases, signal transduction might take both connotation of a random walk and a propagating wave, depending on the local density of the medium. In particular, a sufficient condition for the appearance of waves in high-density regions of the media, is the existence of at least one autocatalytic reaction in the chain of reactions characterizing the pathway.

Determination of wave speed and wave separation in the arteries.

PubMed

Khir, A W; O'Brien, A; Gibbs, J S; Parker, K H

2001-09-01

Considering waves in the arteries as infinitesimal wave fronts rather than sinusoidal wavetrains, the change in pressure across the wave front, dP, is related to the change in velocity, dU, that it induces by the "water hammer" equation, dP=+/-rhocdU, where rho is the density of blood and c is the local wave speed. When only unidirectional waves are present, this relationship corresponds to a straight line when P is plotted against U with slope rhoc. When both forward and backward waves are present, the PU-loop is no longer linear. Measurements in latex tubes and systemic and pulmonary arteries exhibit a linear range during early systole and this provides a way of determining the local wave speed from the slope of the linear portion of the loop. Once the wave speed is known, it is also possible to separate the measured P and U into their forward and backward components. In cases where reflected waves are prominent, this separation of waves can help clarify the pattern of waves in the arteries throughout the cardiac cycle.

Submesoscale features and their interaction with fronts and internal tides in a high-resolution coupled atmosphere-ocean-wave model of the Bay of Bengal

NASA Astrophysics Data System (ADS)

Jensen, Tommy G.; Shulman, Igor; Wijesekera, Hemantha W.; Anderson, Stephanie; Ladner, Sherwin

2018-03-01

Large freshwater fluxes into the Bay of Bengal by rainfall and river discharges result in strong salinity fronts in the bay. In this study, a high-resolution coupled atmosphere-ocean-wave model with comprehensive physics is used to model the weather, ocean circulation, and wave field in the Bay of Bengal. Our objective is to explore the submesoscale activity that occurs in a realistic coupled model that resolves mesoscales and allows part of the submesoscale field. Horizontal resolution in the atmosphere varies from 2 to 6 km and is 13 km for surface waves, while the ocean model is submesoscale permitting with resolutions as high as 1.5 km and a vertical resolution of 0.5 m in the upper 10 m. In this paper, three different cases of oceanic submesoscale features are discussed. In the first case, heavy rainfall and intense downdrafts produced by atmospheric convection are found to force submesoscale currents, temperature, and salinity anomalies in the oceanic mixed layer and impact the mesoscale flow. In a second case, strong solitary-like waves are generated by semidiurnal tides in the Andaman Sea and interact with mesoscale flows and fronts and affect submesoscale features generated along fronts. A third source of submesoscale variability is found further north in the Bay of Bengal where river outflows help maintain strong salinity gradients throughout the year. For that case, a comparison with satellite observations of sea surface height anomalies, sea surface temperature, and chlorophyll shows that the model captures the observed mesoscale eddy features of the flow field, but in addition, submesoscale upwelling and downwelling patterns associated with ageostrophic secondary circulations along density fronts are also captured by the model.

Anti-aliasing Wiener filtering for wave-front reconstruction in the spatial-frequency domain for high-order astronomical adaptive-optics systems.

PubMed

Correia, Carlos M; Teixeira, Joel

2014-12-01

Computationally efficient wave-front reconstruction techniques for astronomical adaptive-optics (AO) systems have seen great development in the past decade. Algorithms developed in the spatial-frequency (Fourier) domain have gathered much attention, especially for high-contrast imaging systems. In this paper we present the Wiener filter (resulting in the maximization of the Strehl ratio) and further develop formulae for the anti-aliasing (AA) Wiener filter that optimally takes into account high-order wave-front terms folded in-band during the sensing (i.e., discrete sampling) process. We employ a continuous spatial-frequency representation for the forward measurement operators and derive the Wiener filter when aliasing is explicitly taken into account. We further investigate and compare to classical estimates using least-squares filters the reconstructed wave-front, measurement noise, and aliasing propagation coefficients as a function of the system order. Regarding high-contrast systems, we provide achievable performance results as a function of an ensemble of forward models for the Shack-Hartmann wave-front sensor (using sparse and nonsparse representations) and compute point-spread-function raw intensities. We find that for a 32×32 single-conjugated AOs system the aliasing propagation coefficient is roughly 60% of the least-squares filters, whereas the noise propagation is around 80%. Contrast improvements of factors of up to 2 are achievable across the field in the H band. For current and next-generation high-contrast imagers, despite better aliasing mitigation, AA Wiener filtering cannot be used as a standalone method and must therefore be used in combination with optical spatial filters deployed before image formation actually takes place.

Control of her1 expression during zebrafish somitogenesis by a Delta-dependent oscillator and an independent wave-front activity

PubMed Central

Holley, Scott A.; Geisler, Robert; Nüsslein-Volhard, Christiane

2000-01-01

Somitogenesis has been linked both to a molecular clock that controls the oscillation of gene expression in the presomitic mesoderm (PSM) and to Notch pathway signaling. The oscillator, or clock, is thought to create a prepattern of stripes of gene expression that regulates the activity of the Notch pathway that subsequently directs somite border formation. Here, we report that the zebrafish gene after eight (aei) that is required for both somitogenesis and neurogenesis encodes the Notch ligand DeltaD. Additional analysis revealed that stripes of her1 expression oscillate within the PSM and that aei/DeltaD signaling is required for this oscillation. aei/DeltaD expression does not oscillate, indicating that the activity of the Notch pathway upstream of her1 may function within the oscillator itself. Moreover, we found that her1 stripes are expressed in the anlage of consecutive somites, indicating that its expression pattern is not pair-rule. Analysis of her1 expression in aei/DeltaD, fused somites (fss), and aei;fss embryos uncovered a wave-front activity that is capable of continually inducing her1 expression de novo in the anterior PSM in the absence of the oscillation of her1. The wave-front activity, in reference to the clock and wave-front model, is defined as such because it interacts with the oscillator-derived pattern in the anterior PSM and is required for somite morphogenesis. This wave-front activity is blocked in embryos mutant for fss but not aei/DeltaD. Thus, our analysis indicates that the smooth sequence of formation, refinement, and fading of her1 stripes in the PSM is governed by two separate activities. PMID:10887161

Millimeter Wave Communications Program: Link Tests of High Speed Digital Radio Set AN/GRC-173 (XW-1)

DTIC Science & Technology

1975-01-01

Terrence Kelly, John Mutty, Edward Rich, James Roche, William J. Smxth, Carson Tsao, and David Trask. Hugh N. Siegel (DCCW) was the RADC...shelter, except for the parabolic dish and front-feed antenna system, which is mast-mounted adjacent to the shelter and connected to an rf input...Equipment: All rf and digital units 8. POWER SUPPLIES Quantity: 1 for rf , 1 for digital Primary Power: 120/240V +10% single phase, 47 - 420 Hz

Space active optics: in flight aberrations correction for the next generation of large space telescopes

NASA Astrophysics Data System (ADS)

Laslandes, M.; Ferrari, M.; Hugot, E.; Lemaitre, G.

2017-11-01

The need for both high quality images and light structures is a constant concern in the conception of space telescopes. In this paper, we present an active optics system as a way to fulfill those two objectives. Indeed, active optics consists in controlling mirrors' deformations in order to improve the images quality [1]. The two main applications of active optics techniques are the in-situ compensation of phase errors in a wave front by using a corrector deformable mirror [2] and the manufacturing of aspherical mirrors by stress polishing or by in-situ stressing [3]. We will focus here on the wave-front correction. Indeed, the next generation of space telescopes will have lightweight primary mirrors; in consequence, they will be sensitive to the environment variations, inducing optical aberrations in the instrument. An active optics system is principally composed of a deformable mirror, a wave front sensor, a set of actuators deforming the mirror and control/command electronics. It is used to correct the wave-front errors due to the optical design, the manufacturing imperfections, the large lightweight primary mirrors' deflection in field gravity, the fixation devices, and the mirrors and structures' thermal distortions due to the local turbulence [4]. Active optics is based on the elasticity theory [5]; forces and/or load are used to deform a mirror. Like in adaptive optics, actuators can simply be placed under the optical surface [1,2], but other configurations have also been studied: a system's simplification, inducing a minimization of the number of actuators can be achieved by working on the mirror design [5]. For instance, in the so called Vase form Multimode Deformable Mirror [6], forces are applied on an external ring clamped on the pupil. With this method, there is no local effect due to the application of forces on the mirror's back face. Furthermore, the number of actuators needed to warp the mirror does not depend on the pupil size; it is a fully scalable configuration. The insertion of a Vase form Multimode Deformable Mirror on the design of an optical instrument will allow correcting the most common low spatial frequency aberrations. This concept could be applied in a space telescope. A Finite Element Analysis of the developed model has been conducted in order to characterize the system's behavior and to validate the concept.

An Optimal Set of Flesh Points on Tongue and Lips for Speech-Movement Classification

PubMed Central

Samal, Ashok; Rong, Panying; Green, Jordan R.

2016-01-01

Purpose The authors sought to determine an optimal set of flesh points on the tongue and lips for classifying speech movements. Method The authors used electromagnetic articulographs (Carstens AG500 and NDI Wave) to record tongue and lip movements from 13 healthy talkers who articulated 8 vowels, 11 consonants, a phonetically balanced set of words, and a set of short phrases during the recording. We used a machine-learning classifier (support-vector machine) to classify the speech stimuli on the basis of articulatory movements. We then compared classification accuracies of the flesh-point combinations to determine an optimal set of sensors. Results When data from the 4 sensors (T1: the vicinity between the tongue tip and tongue blade; T4: the tongue-body back; UL: the upper lip; and LL: the lower lip) were combined, phoneme and word classifications were most accurate and were comparable with the full set (including T2: the tongue-body front; and T3: the tongue-body front). Conclusion We identified a 4-sensor set—that is, T1, T4, UL, LL—that yielded a classification accuracy (91%–95%) equivalent to that using all 6 sensors. These findings provide an empirical basis for selecting sensors and their locations for scientific and emerging clinical applications that incorporate articulatory movements. PMID:26564030

Layer-oriented simulation tool.

PubMed

Arcidiacono, Carmelo; Diolaiti, Emiliano; Tordi, Massimiliano; Ragazzoni, Roberto; Farinato, Jacopo; Vernet, Elise; Marchetti, Enrico

2004-08-01

The Layer-Oriented Simulation Tool (LOST) is a numerical simulation code developed for analysis of the performance of multiconjugate adaptive optics modules following a layer-oriented approach. The LOST code computes the atmospheric layers in terms of phase screens and then propagates the phase delays introduced in the natural guide stars' wave fronts by using geometrical optics approximations. These wave fronts are combined in an optical or numerical way, including the effects of wave-front sensors on measurements in terms of phase noise. The LOST code is described, and two applications to layer-oriented modules are briefly presented. We have focus on the Multiconjugate adaptive optics demonstrator to be mounted upon the Very Large Telescope and on the Near-IR-Visible Adaptive Interferometer for Astronomy (NIRVANA) interferometric system to be installed on the combined focus of the Large Binocular Telescope.

Patterns of spiral wave attenuation by low-frequency periodic planar fronts

NASA Astrophysics Data System (ADS)

de la Casa, Miguel A.; de la Rubia, F. Javier; Ivanov, Plamen Ch.

2007-03-01

There is evidence that spiral waves and their breakup underlie mechanisms related to a wide spectrum of phenomena ranging from spatially extended chemical reactions to fatal cardiac arrhythmias [A. T. Winfree, The Geometry of Biological Time (Springer-Verlag, New York, 2001); J. Schutze, O. Steinbock, and S. C. Muller, Nature 356, 45 (1992); S. Sawai, P. A. Thomason, and E. C. Cox, Nature 433, 323 (2005); L. Glass and M. C. Mackey, From Clocks to Chaos: The Rhythms of Life (Princeton University Press, Princeton, 1988); R. A. Gray et al., Science 270, 1222 (1995); F. X. Witkowski et al., Nature 392, 78 (1998)]. Once initiated, spiral waves cannot be suppressed by periodic planar fronts, since the domains of the spiral waves grow at the expense of the fronts [A. N. Zaikin and A. M. Zhabotinsky, Nature 225, 535 (1970); A. T. Stamp, G. V. Osipov, and J. J. Collins, Chaos 12, 931 (2002); I. Aranson, H. Levine, and L. Tsimring, Phys. Rev. Lett. 76, 1170 (1996); K. J. Lee, Phys. Rev. Lett. 79, 2907 (1997); F. Xie, Z. Qu, J. N. Weiss, and A. Garfinkel, Phys. Rev. E 59, 2203 (1999)]. Here, we show that introducing periodic planar waves with long excitation duration and a period longer than the rotational period of the spiral can lead to spiral attenuation. The attenuation is not due to spiral drift and occurs periodically over cycles of several fronts, forming a variety of complex spatiotemporal patterns, which fall into two distinct general classes. Further, we find that these attenuation patterns only occur at specific phases of the descending fronts relative to the rotational phase of the spiral. We demonstrate these dynamics of phase-dependent spiral attenuation by performing numerical simulations of wave propagation in the excitable medium of myocardial cells. The effect of phase-dependent spiral attenuation we observe can lead to a general approach to spiral control in physical and biological systems with relevance for medical applications.

Wave activity in the neighborhood of the bowshock of Mars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sagdeev, R.Z.; Shapiro, V.D.; Shevchenko, V.I.

Plasma wave activity in the neighborhood of the Martial bow shock were measured for the first time by the Soviet spacecraft Phobos-2 in a wide frequency range from dc to 150 kHz. The wave activity varied in character as the spacecraft moved across different plasma regions: in the neighborhood of the Martian bow shock, inside the magnetosheath and in the tail region. In this paper the authors provide suggestions for the processes responsible for these plasma waves. The most interesting peculiarities of the wave activity around Mars is the sharp increase of wave intensity in the magnetosheath region. This increasemore » is attributed to two different physical mechanisms. High frequency waves are excited at the shock front due to currents flowing along the front; these ion acoustic waves are convected inside by the solar wind. The low frequency waves ({approximately}100 Hz) close to the inside boundary were, they believe, generated by heavy Martian ions diffusing through the planetopause into the magnetosheath.« less

Nitromethane ignition observed with embedded PDV optical fibers

NASA Astrophysics Data System (ADS)

Mercier, P.; Bénier, J.; Frugier, P. A.; Debruyne, M.; Crouzet, B.

For a long time, the nitromethane (NM) ignition has been observed with different means such as high-speed cameras, VISAR or optical pyrometry diagnostics. By 2000, David Goosmann (LLNL) studied solid high-explosive detonation and shock loaded metal plates by measuring velocity (Fabry-Pérot interferometry) in embedded optical fibers. For six years Photonic Doppler Velocimetry (PDV) has become a major tool to better understand the phenomena occurring in shock physics experiments. In 2006, we began to use in turn this technique and studied shock-to-detonation transition in NM. Different kinds of bare optical fibers were set in the liquid; they provided two types of velocity information; those coming from phenomena located in front of the fibers (interface velocity, shock waves, overdriven detonation wave) and those due to phenomena environing the fibers (shock or detonation waves). We achieved several shots; devices were composed of a high explosive plane wave generator ended by a metal barrier followed by a cylindrical vessel containing NM. We present results.

Precision Targeting With a Tracking Adaptive Optics Scanning Laser Ophthalmoscope

DTIC Science & Technology

2006-01-01

automatic high- resolution mosaic generation, and automatic blink detection and tracking re-lock were also tested. The system has the potential to become an...structures can lead to earlier detection of retinal diseases such as age-related macular degeneration (AMD) and diabetic retinopathy (DR). Combined...optics systems sense perturbations in the detected wave-front and apply corrections to an optical element that flatten the wave-front and allow near

Experimental Investigation of Turbojet Thrust Augmentation Using an Ejector

DTIC Science & Technology

2007-03-01

mechanisms in which a particle can exchange energy. Thrust augmenting devices can be divided into two categories: ones that exchange net work or heat and...two categories from the energy equation discussion above. Thrust augmentation is achieved through turbulent entrainment where work and/or heat is...front sustained by compression waves from a trailing reaction zone. A deflagration wave is a subsonic flame front sustained by heat transfer

Microgravity Experiment: The Fate of Confined Shock Waves

NASA Astrophysics Data System (ADS)

Kobel, P.; Obreschkow, D.; Dorsaz, N.; de Bosset, A.; Farhat, M.

2007-11-01

Shockwave induced cavitation is a form of hydrodynamic cavitation generated by the interaction of shock waves with vapor nuclei and microscopic impurities. Both the shock waves and the induced cavitation are known as sources of erosion damage in hydraulic industrial systems and hence represent an important research topic in fluid dynamics. Here we present the first investigation of shock wave induced cavitation inside closed and isolated liquid volumes, which confine the shock wave by reflections and thereby promise a particularly strong coupling with cavitation. A microgravity platform (ESA, 42^nd parabolic flight campaign) was used to produce stable water drops with centimetric diameters. Inside these drops, a fast electrical discharge was generated to release a strong shock wave. This setting results in an amplified form of shockwave induced cavitation, visible in high-speed images as a transient haze of sub-millimetric bubbles synchronized with the shockwave radiation. A comparison between high-speed visualizations and 3D simulations of a shock front inside a liquid sphere reveals that focus zones within the drop lead to a significantly increased density of induced cavitation. Considering shock wave crossing and focusing may hence prove crucially useful to understand the important process of cavitation erosion.

Fundamental performance of transverse wind estimator from Shack-Hartmann wave-front sensor measurements.

PubMed

Li, Zhenghan; Li, Xinyang

2018-04-30

Real time transverse wind estimation contributes to predictive correction which is used to compensate for the time delay error in the control systems of adaptive optics (AO) system. Many methods that apply Shack-Hartmann wave-front sensor to wind profile measurement have been proposed. One of the obvious problems is the lack of a fundamental benchmark to compare the various methods. In this work, we present the fundamental performance limits for transverse wind estimator from Shack-Hartmann wave-front sensor measurements using Cramér-Rao lower bound (CRLB). The bound provides insight into the nature of the transverse wind estimation, thereby suggesting how to design and improve the estimator in the different application scenario. We analyze the theoretical bound and find that factors such as slope measurement noise, wind velocity and atmospheric coherence length r 0 have important influence on the performance. Then, we introduced the non-iterative gradient-based transverse wind estimator. The source of the deterministic bias of the gradient-based transverse wind estimators is analyzed for the first time. Finally, we derived biased CRLB for the gradient-based transverse wind estimators from Shack-Hartmann wave-front sensor measurements and the bound can predict the performance of estimator more accurately.

A case study on dune response to infragravity waves

NASA Astrophysics Data System (ADS)

Li, Wenshan; Wang, Hui; Li, Huan; Wu, Shuangquan; Li, Cheng

2017-08-01

A series of numerical simulations were conducted using the process-based model XBeach to investigate dune response under normal and getting rid of infragravity wave conditions with different slopes. Erosion volume upside the dune toe and dune top recession are set as indicators for dune vulnerability as well as defence capacity for its front-beach. Results show that both dune erosion volume and dune top recession decrease with gentler dune slopes. Of all the simulation cases, dune with a face slope of 1/1 lost most sand and supplied most sand for lower-bed. The presence of infragravity waves is validated to be crucial to dune vulnerability. The dune erosion volume is shown to decrease by 44.5%∼61.5% and the dune top recession decreased by 0%∼45.5% correspondingly, in the case that infragravity motion is not taken into account during simulation for different dune slopes.

Influence of source extension of 26 December 2004 Sumatra earthquake on character of tsunami wave propagation

NASA Astrophysics Data System (ADS)

Mazova, Raissa; Kisel'Man, Broneslav; Baranova, Natalya; Lobkovsky, Leopold

2010-05-01

The analysis of the Indian Ocean earthquake and tsunami on 26 December 2004 carried out in a number of works demonstrates that rupture process in the seismic source was realized during several minutes. In some works, there was suggested that a source probably consists of several segments with width near above hundred of kilometers and with total length more than 1000 km. Such a picture is consistent with subduction keyboard model of tsunamigenic earthquake (see, e.g. [1]) which treats the anomalously long source of Indian Ocean tsunami, caused by oblique subduction, as a multiblock piston mechanism with non-simultaneous realization of each block. Because of existing in literature uncertainty with source structure and movements at all its extent, it is interesting for given event to study in details the dependence of characteristics of surface water wave induced by seismic source on its extent [1,2]. In the work it was studied the influence of submarine seismic source extention to wave field distribution in basin of Bengal bay and central part of Indian ocean. To analyze, it was considered separately the influence of large segment of seismic source for given tsunami. On the basis of keyboard model it is considered the earthquake origin with extension near 1200 km comprises 3 seismic source: Sumatran, Andaman and Nicobar ones, each of which comprises 6, 4 and 3 keyboard blocks, respectively (1, 2 and 3 scenarios). It was calculated the maximal vertical displacement of these segments on 2-5 meters. The velocity of block movement was taken in correspondence with available data on characteristic times in the source. For scenario 1 tsunami source, formed at the ocean surface, generates almost circular wave which, due to bathymetry of given basin, preserve its form and propagates most quickly in west and south-west direction. To north-east, to Indian coast, the wave came with large delay, as compared with records of real mareographs. As follows from the wave field picture for second series of calculations, the wave front, as it was expected, becomes to be more elongated, and the time of approach of the wave front up to east Indian coast is decreased, as compared with the case of wave generation by only Sumatra segment. At turning on of third segment wave field is characterized by else more elongated to north wave front, and time of approach of wave front the south-east Indian coast is more decreased. It's seen that from the source side faced to Bengal bay there are well pronounced three wave fronts in correspondence with marked segments. These fronts evolve then in plane enough united front with bend in the region of Nicobar islands. The change of wave field character for three taken cases is well seen on accounted satellite altimetry. Adequateness of the calculations performed was verified by comparison of mareograms, obtained from real mareographs with records of virtual mareographs placed us in calculating basin and obtained by us for each scenario. The same verification was performed by comparison of real altimetric records of satellite "Yason-1" with virtual altimetric record obtained by us for each scenario. The computations performed explain the complex character of tsunami wave propagation for given earthquake. This work was supported by the Russian Foundation for Basic Research, project no. 08-05-01027 1.Lobkovsky L.I., Mazova R.Kh. The mechanism of source of Indian Ocean tsunami 2004: analysis and numerical simulation // Physics of Earth, v.43, № 7, pp.46-56, 2007. 2.Lobkovsky L.I., Mazova R.Kh., Garagash I.A., Kataeva L.Yu., Nardin I. To analysis of source mechanism of the 26 December 2004 Indian Ocean tsunami, Russ.J.Earth Sci. V.8, ES5001, doi:10.2205/2006ES000208 http://dx.doi.org/ 10.2205/2006ES000208 (2006b).

From the paddle to the beach - A Boussinesq shallow water numerical wave tank based on Madsen and Sørensen's equations

NASA Astrophysics Data System (ADS)

Orszaghova, Jana; Borthwick, Alistair G. L.; Taylor, Paul H.

2012-01-01

This article describes a one-dimensional numerical model of a shallow-water flume with an in-built piston paddle moving boundary wavemaker. The model is based on a set of enhanced Boussinesq equations and the nonlinear shallow water equations. Wave breaking is described approximately, by locally switching to the nonlinear shallow water equations when a critical wave steepness is reached. The moving shoreline is calculated as part of the solution. The piston paddle wavemaker operates on a movable grid, which is Lagrangian on the paddle face and Eulerian away from the paddle. The governing equations are, however, evolved on a fixed mapped grid, and the newly calculated solution is transformed back onto the moving grid via a domain mapping technique. Validation test results are compared against analytical solutions, confirming correct discretisation of the governing equations, wave generation via the numerical paddle, and movement of the wet/dry front. Simulations are presented that reproduce laboratory experiments of wave runup on a plane beach and wave overtopping of a laboratory seawall, involving solitary waves and compact wave groups. In practice, the numerical model is suitable for simulating the propagation of weakly dispersive waves and can additionally model any associated inundation, overtopping or inland flooding within the same simulation.

All-optical dynamic correction of distorted communication signals using a photorefractive polymeric hologram

NASA Astrophysics Data System (ADS)

Li, Guoqiang; Eralp, Muhsin; Thomas, Jayan; Tay, Savaş; Schülzgen, Axel; Norwood, Robert A.; Peyghambarian, N.

2005-04-01

All-optical real-time dynamic correction of wave front aberrations for image transmission is demonstrated using a photorefractive polymeric hologram. The material shows video rate response time with a low power laser. High-fidelity, high-contrast images can be reconstructed when the oil-filled phase plate generating atmospheric-like wave front aberrations is moved at 0.3mm/s. The architecture based on four-wave mixing has potential application in free-space optical communication, remote sensing, and dynamic tracking. The system offers a cost-effective alternative to closed-loop adaptive optics systems.

Nuclear reactions in shock wave front during supernova events

NASA Technical Reports Server (NTRS)

Lavrukhina, A. K.

1985-01-01

The new unique isotopic anomalous coponent of Xe(XeX) was found in the carbonaceous chondrites. It is enriched in light shielded isotopes (124Xe and 126Xe) and in heavy nonshielded isotopes (134Xe and 136Xe. All characteristics of Xe-X can be explained by a model of nucleosynthesis of the Xe isotopes in shock wave front passed through the He envelope during supernova events. The light isotopes are created by p process and the heavy isotopes are created by n process (slow r process). They were captured with high temperature carbon grains condensing by supernova shock waves.

Experimental investigation on the characteristics of supersonic fuel spray and configurations of induced shock waves.

PubMed

Wang, Yong; Yu, Yu-Song; Li, Guo-Xiu; Jia, Tao-Ming

2017-01-05

The macro characteristics and configurations of induced shock waves of the supersonic sprays are investigated by experimental methods. Visualization study of spray shape is carried out with the high-speed camera. The macro characteristics including spray tip penetration, velocity of spray tip and spray angle are analyzed. The configurations of shock waves are investigated by Schlieren technique. For supersonic sprays, the concept of spray front angle is presented. Effects of Mach number of spray on the spray front angle are investigated. The results show that the shape of spray tip is similar to blunt body when fuel spray is at transonic region. If spray entered the supersonic region, the oblique shock waves are induced instead of normal shock wave. With the velocity of spray increasing, the spray front angle and shock wave angle are increased. The tip region of the supersonic fuel spray is commonly formed a cone. Mean droplet diameter of fuel spray is measured using Malvern's Spraytec. Then the mean droplet diameter results are compared with three popular empirical models (Hiroyasu's, Varde's and Merrigton's model). It is found that the Merrigton's model shows a relative good correlation between models and experimental results. Finally, exponent of injection velocity in the Merrigton's model is fitted with experimental results.

Experimental investigation on the characteristics of supersonic fuel spray and configurations of induced shock waves

PubMed Central

Wang, Yong; Yu, Yu-song; Li, Guo-xiu; Jia, Tao-ming

2017-01-01

The macro characteristics and configurations of induced shock waves of the supersonic sprays are investigated by experimental methods. Visualization study of spray shape is carried out with the high-speed camera. The macro characteristics including spray tip penetration, velocity of spray tip and spray angle are analyzed. The configurations of shock waves are investigated by Schlieren technique. For supersonic sprays, the concept of spray front angle is presented. Effects of Mach number of spray on the spray front angle are investigated. The results show that the shape of spray tip is similar to blunt body when fuel spray is at transonic region. If spray entered the supersonic region, the oblique shock waves are induced instead of normal shock wave. With the velocity of spray increasing, the spray front angle and shock wave angle are increased. The tip region of the supersonic fuel spray is commonly formed a cone. Mean droplet diameter of fuel spray is measured using Malvern’s Spraytec. Then the mean droplet diameter results are compared with three popular empirical models (Hiroyasu’s, Varde’s and Merrigton’s model). It is found that the Merrigton’s model shows a relative good correlation between models and experimental results. Finally, exponent of injection velocity in the Merrigton’s model is fitted with experimental results. PMID:28054555

Initiation and structures of gaseous detonation

NASA Astrophysics Data System (ADS)

Vasil'ev, A. A.; Vasiliev, V. A.

2018-03-01

The analysis of the initiation of a detonation wave (DW) and the emergence of a multi-front structure of the DW-front are presented. It is shown that the structure of the DW arises spontaneously at the stage of a strong overdriven of the wave. The hypothesis of the gradual enhancement of small perturbations on an initially smooth initiating blast wave, traditionally used in the numerical simulation of multi-front detonation, does not agree with the experimental data. The instability of the DW is due to the chemical energy release of the combustible mixture Q. A technique for determining the Q-value of mixture was proposed, based on reconstruction of the trajectory of the expanding wave from the position of the strong explosion model. The wave trajectory at the critical initiation of a multifront detonation in a combustible mixture is compared with the trajectory of an explosive wave from the same initiator in an inert mixture whose gas-dynamic parameters are equivalent to the parameters of the combustible mixture. The energy release of a mixture is defined as the difference in the joint energy release of the initiator and the fuel mixture during the critical initiation and energy release of the initiator when the blast wave is excited in an inert mixture. Observable deviations of the experimental profile of Q from existing model representations were found.

Spatially Extended Relativistic Particles Out of Traveling Front Solutions of Sine-Gordon Equation in (1+2) Dimensions

PubMed Central

Zarmi, Yair

2016-01-01

Slower-than-light multi-front solutions of the Sine-Gordon in (1+2) dimensions, constructed through the Hirota algorithm, are mapped onto spatially localized structures, which emulate free, spatially extended, massive relativistic particles. A localized structure is an image of the junctions at which the fronts intersect. It propagates together with the multi-front solution at the velocity of the latter. The profile of the localized structure obeys the linear wave equation in (1+2) dimensions, to which a term that represents interaction with a slower-than-light, Sine-Gordon-multi-front solution has been added. This result can be also formulated in terms of a (1+2)-dimensional Lagrangian system, in which the Sine-Gordon and wave equations are coupled. Expanding the Euler-Lagrange equations in powers of the coupling constant, the zero-order part of the solution reproduces the (1+2)-dimensional Sine-Gordon fronts. The first-order part is the spatially localized structure. PACS: 02.30.Ik, 03.65.Pm, 05.45.Yv, 02.30.Ik. PMID:26930077

Geometric controls of the flexural gravity waves on the Ross Ice Shelf

NASA Astrophysics Data System (ADS)

Sergienko, O. V.

2017-12-01

Long-period ocean waves, formed locally or at distant sources, can reach sub-ice-shelf cavities and excite coupled motion in the cavity and the ice shelf - flexural gravity waves. Three-dimensional numerical simulations of the flexural gravity waves on the Ross Ice Shelf show that propagation of these waves is strongly controlled by the geometry of the system - the cavity shape, its water-column thickness and the ice-shelf thickness. The results of numerical simulations demonstrate that propagation of the waves is spatially organized in beams, whose orientation is determined by the direction of the of the open ocean waves incident on the ice-shelf front. As a result, depending on the beams orientation, parts of the Ross Ice Shelf experience significantly larger flexural stresses compared to other parts where the flexural gravity beams do not propagate. Very long-period waves can propagate farther away from the ice-shelf front exciting flexural stresses in the vicinity of the grounding line.

Sparse aperture differential piston measurements using the pyramid wave-front sensor

NASA Astrophysics Data System (ADS)

Arcidiacono, Carmelo; Chen, Xinyang; Yan, Zhaojun; Zheng, Lixin; Agapito, Guido; Wang, Chaoyan; Zhu, Nenghong; Zhu, Liyun; Cai, Jianqing; Tang, Zhenghong

2016-07-01

In this paper we report on the laboratory experiment we settled in the Shanghai Astronomical Observatory (SHAO) to investigate the pyramid wave-front sensor (WFS) ability to measure the differential piston on a sparse aperture. The ultimate goal is to verify the ability of the pyramid WFS work in close loop to perform the phasing of the primary mirrors of a sparse Fizeau imaging telescope. In the experiment we installed on the optical bench we performed various test checking the ability to flat the wave-front using a deformable mirror and to measure the signal of the differential piston on a two pupils setup. These steps represent the background from which we start to perform full close loop operation on multiple apertures. These steps were also useful to characterize the achromatic double pyramids (double prisms) manufactured in the SHAO optical workshop.

CASOAR - An infrared active wave front sensor for atmospheric turbulence analysis

NASA Astrophysics Data System (ADS)

Cariou, Jean-Pierre; Dolfi, Agnes

1992-12-01

Knowledge of deformation of every point of a wave front over time allows statistical turbulence parameters to be analyzed, and the definition of real time adaptive optics to be designed. An optical instrumentation was built to meet this need. Integrated in a compact enclosure for experiments on outdoor sites, the CASOAR allows the deformations of a wave front to be measured rapidly (100 Hz) and with accuracy (1 deg). The CASOAR is an active system: it includes its own light source (CW CO2 laser), making it self-contained, self-aligned and insensitive to spurious light rays. After being reflected off a mirror located beyond the atmospheric layer to be analyzed (range of several kilometers), the beam is received and detected by coherent mixing. Electronic phase is converted in optical phase and recorded or displayed in real time on a monitor. Experimental results are shown, pointing out the capabilities of this device.

Thermal dephasing in second-harmonic generation of an amplified copper-vapor laser beam in beta barium borate.

PubMed

Prakash, Om; Dixit, Sudhir Kumar; Bhatnagar, Rajiva

2005-03-20

The conversion efficiency in second-harmonic generation of an amplified beam in a master-oscillator power amplifier copper-vapor laser (CVL) is lower than that of the oscillator beam alone. This lower efficiency is often vaguely attributed to wave-front degradation in the amplifier. We investigate the role of wave-front degradation and thermal dephasing in the second-harmonic generation of a CVL from a beta-barium borate crystal. Choosing two beams with constant intrapulse divergence, one from a generalized diffraction filtered resonator master oscillator alone and other obtained by amplifying oscillator by use of a power amplifier, we show that at low flux levels the decrease in efficiency is due to wave-front degradation. At a fundamental power above the critical power for thermal dephasing, the decrease is due to increased UV absorption and consequent thermal dephasing. Thermal dephasing is higher for the beam with the lower coherence width.

An ANN-Based Smart Tomographic Reconstructor in a Dynamic Environment

PubMed Central

de Cos Juez, Francisco J.; Lasheras, Fernando Sánchez; Roqueñí, Nieves; Osborn, James

2012-01-01

In astronomy, the light emitted by an object travels through the vacuum of space and then the turbulent atmosphere before arriving at a ground based telescope. By passing through the atmosphere a series of turbulent layers modify the light's wave-front in such a way that Adaptive Optics reconstruction techniques are needed to improve the image quality. A novel reconstruction technique based in Artificial Neural Networks (ANN) is proposed. The network is designed to use the local tilts of the wave-front measured by a Shack Hartmann Wave-front Sensor (SHWFS) as inputs and estimate the turbulence in terms of Zernike coefficients. The ANN used is a Multi-Layer Perceptron (MLP) trained with simulated data with one turbulent layer changing in altitude. The reconstructor was tested using three different atmospheric profiles and compared with two existing reconstruction techniques: Least Squares type Matrix Vector Multiplication (LS) and Learn and Apply (L + A). PMID:23012524

Experimental Studies on Wave Interactions of Partially Perforated Wall under Obliquely Incident Waves

PubMed Central

Lee, Jong-In; Kim, Young-Taek; Shin, Sungwon

2014-01-01

This study presents wave height distribution in terms of stem wave evolution phenomena on partially perforated wall structures through three-dimensional laboratory experiments. The plain and partially perforated walls were tested to understand their effects on the stem wave evolution under the monochromatic and random wave cases with the various wave conditions, incident angle (from 10 to 40 degrees), and configurations of front and side walls. The partially perforated wall reduced the relative wave heights more effectively compared to the plain wall structure. Partially perforated walls with side walls showed a better performance in terms of wave height reduction compared to the structure without the side wall. Moreover, the relative wave heights along the wall were relatively small when the relative chamber width is large, within the range of the chamber width in this study. The wave spectra showed a frequency dependency of the wave energy dissipation. In most cases, the existence of side wall is a more important factor than the porosity of the front wall in terms of the wave height reduction even if the partially perforated wall was still effective compared to the plain wall. PMID:25254260

Experimental studies on wave interactions of partially perforated wall under obliquely incident waves.

PubMed

Lee, Jong-In; Kim, Young-Taek; Shin, Sungwon

2014-01-01

This study presents wave height distribution in terms of stem wave evolution phenomena on partially perforated wall structures through three-dimensional laboratory experiments. The plain and partially perforated walls were tested to understand their effects on the stem wave evolution under the monochromatic and random wave cases with the various wave conditions, incident angle (from 10 to 40 degrees), and configurations of front and side walls. The partially perforated wall reduced the relative wave heights more effectively compared to the plain wall structure. Partially perforated walls with side walls showed a better performance in terms of wave height reduction compared to the structure without the side wall. Moreover, the relative wave heights along the wall were relatively small when the relative chamber width is large, within the range of the chamber width in this study. The wave spectra showed a frequency dependency of the wave energy dissipation. In most cases, the existence of side wall is a more important factor than the porosity of the front wall in terms of the wave height reduction even if the partially perforated wall was still effective compared to the plain wall.

Analyzing and Post-modelling the High Speed Images of a Wavy Laser Induced Boiling Front

NASA Astrophysics Data System (ADS)

Matti, R. S.; Kaplan, A. F. H.

The boiling front in laser materials processing like remote fusion cutting, keyhole welding or drilling can nowadays be recorded by high speed imaging. It was recently observed that bright waves flow down the front. Several complex physical mechanisms are associated with a stable laser-induced boiling front, like beam absorption, shadowing, heating, ablation pressure, fluid flow, etc. The evidence of dynamic phenomena from high speed imaging is closely linked to these phenomena. As a first step, the directly visible phenomena were classified and analyzed. This has led to the insight that the appearance of steady flow of the bright front peaks is a composition of many short flashing events of 20-50 μs duration, though composing a rather constant melt film flow downwards. Five geometrical front shapes of bright and dark domains were categorized, for example long inclined dark valleys. In addition, the special top and bottom regions of the front are distinguished. As a second step, a new method of post-modelling based on the greyscale variation of the images was applied, to approximately reconstruct the topology of the wavy front and subsequently to calculate the absorption across the front. Despite certain simplifications this kind of analysis provides a variety of additional information, including statistical analysis. In particular, the model could show the sensitivity of front waves to the formation of shadow domains and the robustness of fiber lasers to keep most of an irradiated steel surface in an absorptivity window between 35 to 43%.

Analytical solution of the problem of a shock wave in the collapsing gas in Lagrangian coordinates

NASA Astrophysics Data System (ADS)

Kuropatenko, V. F.; Shestakovskaya, E. S.

2016-10-01

It is proposed the exact solution of the problem of a convergent shock wave and gas dynamic compression in a spherical vessel with an impermeable wall in Lagrangian coordinates. At the initial time the speed of cold ideal gas is equal to zero, and a negative velocity is set on boundary of the sphere. When t > t0 the shock wave spreads from this point into the gas. The boundary of the sphere will move under the certain law correlated with the motion of the shock wave. The trajectories of the gas particles in Lagrangian coordinates are straight lines. The equations determining the structure of the gas flow between the shock front and gas border have been found as a function of time and Lagrangian coordinate. The dependence of the entropy on the velocity of the shock wave has been found too. For Lagrangian coordinates the problem is first solved. It is fundamentally different from previously known formulations of the problem of the self-convergence of the self-similar shock wave to the center of symmetry and its reflection from the center, which was built up for the infinite area in Euler coordinates.

Use of atmospheric backscattering for adaptive formation of the initial wave front of a laser beam by the method of aperture sensing

NASA Astrophysics Data System (ADS)

Gordeev, E. V.; Kuskov, V. V.; Razenkov, I. A.; Shesternin, A. N.

2017-11-01

The quality of adaptive suppression of initial aberrations of the wave front of a main laser beam with the use of the method of aperture sensing by the signal of atmospheric backscattering of the additional (sensing) laser radiation at a different wavelength has been studied experimentally. It is shown that wavefront distortions of the main laser beam were decreased significantly during the setup operation.

Experimental results for correlation-based wavefront sensing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Poyneer, L A; Palmer, D W; LaFortune, K N

2005-07-01

Correlation wave-front sensing can improve Adaptive Optics (AO) system performance in two keys areas. For point-source-based AO systems, Correlation is more accurate, more robust to changing conditions and provides lower noise than a centroiding algorithm. Experimental results from the Lick AO system and the SSHCL laser AO system confirm this. For remote imaging, Correlation enables the use of extended objects for wave-front sensing. Results from short horizontal-path experiments will show algorithm properties and requirements.

Energy-flux characterization of conical and space-time coupled wave packets

NASA Astrophysics Data System (ADS)

Lotti, A.; Couairon, A.; Faccio, D.; Trapani, P. Di

2010-02-01

We introduce the concept of energy density flux as a characterization tool for the propagation of ultrashort laser pulses with spatiotemporal coupling. In contrast with calculations for the Poynting vector, those for energy density flux are derived in the local frame moving at the velocity of the envelope of the wave packet under examination and do not need knowledge of the magnetic field. We show that the energy flux defined from a paraxial propagation equation follows specific geometrical connections with the phase front of the optical wave packet, which demonstrates that the knowledge of the phase fronts amounts to the measurement of the energy flux. We perform a detailed numerical study of the energy density flux in the particular case of conical waves, with special attention paid to stationary-envelope conical waves (X or O waves). A full characterization of linear conical waves is given in terms of their energy flux. We extend the definition of this concept to the case of nonlinear propagation in Kerr media with nonlinear losses.

Robustness of free and pinned spiral waves against breakup by electrical forcing in excitable chemical media.

PubMed

Phantu, Metinee; Sutthiopad, Malee; Luengviriya, Jiraporn; Müller, Stefan C; Luengviriya, Chaiya

2017-04-01

We present an investigation on the breakup of free and pinned spiral waves under an applied electrical current in the Belousov-Zhabotinsky reaction. Spiral fronts propagating towards the negative electrode are decelerated. A breakup of the spiral waves occurs when some segments of the fronts are stopped by a sufficiently strong electrical current. In the absence of obstacles (i.e., free spiral waves), the critical value of the electrical current for the wave breakup increases with the excitability of the medium. For spiral waves pinned to circular obstacles, the critical electrical current increases with the obstacle diameter. Analysis of spiral dynamics shows that the enhancement of the robustness against the breakup of both free and pinned spiral waves is originated by the increment of wave speed when either the excitability is strengthened or the obstacle size is enlarged. The experimental findings are reproduced by numerical simulations using the Oregonator model. In addition, the simulations reveal that the robustness against the forced breakup increases with the activator level in both cases of free and pinned spiral waves.

Coronal "wave": Magnetic Footprint Of A Cme?

NASA Astrophysics Data System (ADS)

Attrill, Gemma; Harra, L. K.; van Driel-Gesztelyi, L.; Demoulin, P.; Wuelser, J.

2007-05-01

We propose a new mechanism for the generation of "EUV coronal waves". This work is based on new analysis of data from SOHO/EIT, SOHO/MDI & STEREO/EUVI. Although first observed in 1997, the interpretation of coronal waves as flare-induced or CME-driven remains a debated topic. We investigate the properties of two "classical" SOHO/EIT coronal waves in detail. The source regions of the associated CMEs possess opposite helicities & the coronal waves display rotations in opposite senses. We observe deep dimmings near the flare site & also widespread diffuse dimming, accompanying the expansion of the EIT wave. We report a new property of these EIT waves, namely, that they display dual brightenings: persistent ones at the outermost edge of the core dimming regions & simultaneously diffuse brightenings constituting the leading edge of the coronal wave, surrounding the expanding diffuse dimmings. We show that such behaviour is consistent with a diffuse EIT wave being the magnetic footprint of a CME. We propose a new mechanism where driven magnetic reconnections between the skirt of the expanding CME & quiet-Sun magnetic loops generate the observed bright diffuse front. The dual brightenings & widespread diffuse dimming are identified as innate characteristics of this process. In addition we present some of the first analysis of a STEREO/EUVI limb coronal wave. We show how the evolution of the diffuse bright front & dimmings can be understood in terms of the model described above. We show that an apparently stationary part of the bright front can be understood in terms of magnetic interchange reconnections between the expanding CME & the "open" magnetic field of a low-latitude coronal hole. We use both the SOHO/EIT & STEREO/EUVI events to demonstrate that through successive reconnections, this new model provides a natural mechanism via which CMEs can become large-scale in the lower corona.

Evans functions and bifurcations of nonlinear waves of some nonlinear reaction diffusion equations

NASA Astrophysics Data System (ADS)

Zhang, Linghai

2017-10-01

The main purposes of this paper are to accomplish the existence, stability, instability and bifurcation of the nonlinear waves of the nonlinear system of reaction diffusion equations ut =uxx + α [ βH (u - θ) - u ] - w, wt = ε (u - γw) and to establish the existence, stability, instability and bifurcation of the nonlinear waves of the nonlinear scalar reaction diffusion equation ut =uxx + α [ βH (u - θ) - u ], under different conditions on the model constants. To establish the bifurcation for the system, we will study the existence and instability of a standing pulse solution if 0 < 2 (1 + αγ) θ < αβγ; the existence and stability of two standing wave fronts if 2 (1 + αγ) θ = αβγ and γ2 ε > 1; the existence and instability of two standing wave fronts if 2 (1 + αγ) θ = αβγ and 0 <γ2 ε < 1; the existence and instability of an upside down standing pulse solution if 0 < (1 + αγ) θ < αβγ < 2 (1 + αγ) θ. To establish the bifurcation for the scalar equation, we will study the existence and stability of a traveling wave front as well as the existence and instability of a standing pulse solution if 0 < 2 θ < β; the existence and stability of two standing wave fronts if 2 θ = β; the existence and stability of a traveling wave front as well as the existence and instability of an upside down standing pulse solution if 0 < θ < β < 2 θ. By the way, we will also study the existence and stability of a traveling wave back of the nonlinear scalar reaction diffusion equation ut =uxx + α [ βH (u - θ) - u ] -w0, where w0 = α (β - 2 θ) > 0 is a positive constant, if 0 < 2 θ < β. To achieve the main goals, we will make complete use of the special structures of the model equations and we will construct Evans functions and apply them to study the eigenvalues and eigenfunctions of several eigenvalue problems associated with several linear differential operators. It turns out that a complex number λ0 is an eigenvalue of the linear differential operator, if and only if λ0 is a zero of the Evans function. The stability, instability and bifurcations of the nonlinear waves follow from the zeros of the Evans functions. A very important motivation to study the existence, stability, instability and bifurcations of the nonlinear waves is to study the existence and stability/instability of infinitely many fast/slow multiple traveling pulse solutions of the nonlinear system of reaction diffusion equations. The existence and stability of infinitely many fast multiple traveling pulse solutions are of great interests in mathematical neuroscience.

A Census of Plasma Waves and Structures Associated With an Injection Front in the Inner Magnetosphere

NASA Astrophysics Data System (ADS)

Malaspina, David M.; Ukhorskiy, Aleksandr; Chu, Xiangning; Wygant, John

2018-04-01

Now that observations have conclusively established that the inner magnetosphere is abundantly populated with kinetic electric field structures and nonlinear waves, attention has turned to quantifying the ability of these structures and waves to scatter and accelerate inner magnetospheric plasma populations. A necessary step in that quantification is determining the distribution of observed structure and wave properties (e.g., occurrence rates, amplitudes, and spatial scales). Kinetic structures and nonlinear waves have broadband signatures in frequency space, and consequently, high-resolution time domain electric and magnetic field data are required to uniquely identify such structures and waves as well as determine their properties. However, most high-resolution fields data are collected with a strong bias toward high-amplitude signals in a preselected frequency range, strongly biasing observations of structure and wave properties. In this study, an ˜45 min unbroken interval of 16,384 samples/s field burst data, encompassing an electron injection event, is examined. This data set enables an unbiased census of the kinetic structures and nonlinear waves driven by this electron injection, as well as determination of their "typical" properties. It is found that the properties determined using this unbiased burst data are considerably different than those inferred from amplitude-biased burst data, with significant implications for wave-particle interactions due to kinetic structures and nonlinear waves in the inner magnetosphere.

Nonlinear self-sustained structures and fronts in spatially developing wake flows

NASA Astrophysics Data System (ADS)

Pier, Benoît; Huerre, Patrick

2001-05-01

A family of slowly spatially developing wakes with variable pressure gradient is numerically demonstrated to sustain a synchronized finite-amplitude vortex street tuned at a well-defined frequency. This oscillating state is shown to be described by a steep global mode exhibiting a sharp Dee Langer-type front at the streamwise station of marginal absolute instability. The front acts as a wavemaker which sends out nonlinear travelling waves in the downstream direction, the global frequency being imposed by the real absolute frequency prevailing at the front station. The nonlinear travelling waves are determined to be governed by the local nonlinear dispersion relation resulting from a temporal evolution problem on a local wake profile considered as parallel. Although the vortex street is fully nonlinear, its frequency is dictated by a purely linear marginal absolute instability criterion applied to the local linear dispersion relation.

Parameterization of synoptic weather systems in the South Atlantic Bight for modeling applications

NASA Astrophysics Data System (ADS)

Wu, Xiaodong; Voulgaris, George; Kumar, Nirnimesh

2017-10-01

An event based, long-term, climatological analysis is presented that allows the creation of coastal ocean atmospheric forcing on the coastal ocean that preserves both frequency of occurrence and event time history. An algorithm is developed that identifies individual storm event (cold fronts, warm fronts, and tropical storms) from meteorological records. The algorithm has been applied to a location along the South Atlantic Bight, off South Carolina, an area prone to cyclogenesis occurrence and passages of atmospheric fronts. Comparison against daily weather maps confirms that the algorithm is efficient in identifying cold fronts and warm fronts, while the identification of tropical storms is less successful. The average state of the storm events and their variability are represented by the temporal evolution of atmospheric pressure, air temperature, wind velocity, and wave directional spectral energy. The use of uncorrected algorithm-detected events provides climatologies that show a little deviation from those derived using corrected events. The effectiveness of this analysis method is further verified by numerically simulating the wave conditions driven by the characteristic wind forcing and comparing the results with the wave climatology that corresponds to each storm type. A high level of consistency found in the comparison indicates that this analysis method can be used for accurately characterizing event-based oceanic processes and long-term storm-induced morphodynamic processes on wind-dominated coasts.

Close range fault tolerant noncontacting position sensor

DOEpatents

Bingham, D.N.; Anderson, A.A.

1996-02-20

A method and system are disclosed for locating the three dimensional coordinates of a moving or stationary object in real time. The three dimensional coordinates of an object in half space or full space are determined based upon the time of arrival or phase of the wave front measured by a plurality of receiver elements and an established vector magnitudes proportional to the measured time of arrival or phase at each receiver element. The coordinates of the object are calculated by solving a matrix equation or a set of closed form algebraic equations. 3 figs.

On impact by a hard cone on elasto-viscoplastic material, leading to the generation of a conical crack

NASA Astrophysics Data System (ADS)

Verveiko, N. D.; Shashkin, A. I.; Krupenko, S. E.

2018-03-01

The destruction of solid physical objects is a complex process in which mechanical, chemical, thermobaric and other matter transformations take place. Under mechanical destruction is understood the violation of the integrity of the object due to the occurrence of cracks. High-speed impact of a solid body on deformable materials is accompanied by the spread of cracks and is of a wave nature. This article presents an analysis of the dynamic stress-strain state in an elastoviscoplastic (EVP) material near the leading edge of a moving crack, approximated by a zone of continuous deformation. An analysis of the distribution of the intensity of tangential stresses and plastic deformations that occur behind the front of the longitudinal and shear head waves of a spherical shape generated by the impact of the vertex of the solid cone is carried out on the model EVP of the medium by the ray method. It is shown that the presence of a maximum of the jump of the tangential velocity component on the shear wave leads to a development with time of a jump in the displacements of the tangents to the front of the shear wave. This can be interpreted as the moment of initiation of the head part of a crack running along with the front of the elastic wave with the velocity of shear waves.

Propagation of transition fronts in nonlinear chains with non-degenerate on-site potentials

NASA Astrophysics Data System (ADS)

Shiroky, I. B.; Gendelman, O. V.

2018-02-01

We address the problem of transition front propagation in chains with a bi-stable nondegenerate on-site potential and a nonlinear gradient coupling. For generic nonlinear coupling, one encounters a special regime of transitions, characterized by extremely narrow fronts, far supersonic velocities of the front propagation, and long waves in the oscillatory tail. This regime can be qualitatively associated with a shock wave. The front propagation can be described with the help of a simple reduced-order model; the latter delivers a kinetic law, which is almost not sensitive to the fine details of the on-site potential. Besides, it is possible to predict all main characteristics of the transition front, including its velocity, as well as the frequency and the amplitude of the oscillatory tail. Numerical results are in good agreement with the analytical predictions. The suggested approach allows one to consider the effects of an external pre-load, the next-nearest-neighbor coupling and the on-site damping. When the damping is moderate, it is possible to consider the shock propagation in the damped chain as a perturbation of the undamped dynamics. This approach yields reasonable predictions. When the damping is high, the transition front enters a completely different asymptotic regime of a subsonic kink. The gradient nonlinearity generically turns negligible, and the propagating front converges to the regime described by a simple exact solution for a continuous model with linear coupling.

Cross-shore transport of nearshore sediment by river plume frontal pumping

NASA Astrophysics Data System (ADS)

Horner-Devine, Alexander R.; Pietrzak, Julie D.; Souza, Alejandro J.; McKeon, Margaret A.; Meirelles, Saulo; Henriquez, Martijn; Flores, Raúl P.; Rijnsburger, Sabine

2017-06-01

We present a new mechanism for cross-shore transport of fine sediment from the nearshore to the inner shelf resulting from the onshore propagation of river plume fronts. Onshore frontal propagation is observed in moorings and radar images, which show that fronts penetrate onshore through the nearshore and surf zone, almost to the waterline. During frontal passage a two-layer counterrotating velocity field characteristic of tidal straining is immediately set up, generating a net offshore flow beneath the plume. The seaward flow at depth carries with it high suspended sediment concentrations, which appear to have been generated by wave resuspension in the nearshore region. These observations describe a mechanism by which vertical density stratification can drive exchange of material between the nearshore region and the inner shelf. To our knowledge these are the first observations of this frontal pumping mechanism, which is expected to play an important role in sediment transport near river mouths.

Front-form spinors in the Weinberg-Soper formalism and generalized Melosh transformations for any spin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahluwalia, D.V.; Sawicki, M.

Using the Weinberg-Soper formalism we construct the front-form ([ital j],0)[direct sum](0,[ital j]) spinors. Explicit expressions for the generalized Melosh transformations up to spin two are obtained. The formalism, without explicitly invoking any wave equations, reproduces the spin-1/2 front-form results of Melosh, Lepage and Brodsky, and Dziembowski.

Numerical investigation of interactions of multiple spherical shock waves between themselves and with the underlying surface

NASA Astrophysics Data System (ADS)

Andrushchenko, V. A.; Murashkin, I. V.; Shevelev, Yu. D.

2016-06-01

Within the investigation of various aspects of asteroid and comet danger and, in particular, the explosion of several fragments of meteoroids in the atmosphere above the Earth surface, the toy problem about four point explosions in the case of their special arrangement above the underlying surface is numerically solved. Complex interactions of primary and secondary shock waves between themselves, with the hard surface, and with tangential discontinuities are examined. The structure of flow inside gas regions disturbed by the explosions—the occurrence of eddy structures in them and the influence of reflected shocks waves on them—are investigated. The tendency of the external wave fronts of each explosion to form a unified front and the tendency of their internal hot domains to merge into a joined configuration (where the second process proceeds a little later than the first one) is revealed. This unified front and joined configuration are qualitatively identical to the external internal structure for the solitary explosion. The specially arranged explosions are chosen because the effects of multiple diffraction, interference, and, the main thing, cumulation of spherical waves are manifested more clearly in this caseTwo variants with different altitude of the explosions above the surface are calculated.

Vibration waveform effects on dynamic stabilization of ablative Rayleigh-Taylor instability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Piriz, A. R.; Lucchio, L. Di; Rodriguez Prieto, G.

2011-08-15

An analysis of dynamic stabilization of Rayleigh-Taylor instability in an ablation front is performed by considering a general square wave for modulating the vertical acceleration of the front. Such a kind of modulation allows for clarifying the role of thermal conduction in the mechanism of dynamic stabilization. In addition, the study of the effect of different modulations by varying the duration and amplitude of the square wave in each half-period provides insight on the optimum performance of dynamic stabilization.

Scanning Shack-Hartmann wavefront sensor

NASA Astrophysics Data System (ADS)

Molebny, Vasyl V.

2004-09-01

Criss-crossing of focal images is the cause of a narrow dynamic range in Shack-Hartmann sensors. Practically, aberration range wider than +/-3 diopters can not be measured. A method has been proposed for ophthalmologic applications using a rarefied lenslet array through which a wave front is projected with the successive step-by-step changing of the global tilt. The data acquired in each step are accumulated and processed. In experimental setup, a doubled dynamic range was achieved with four steps of wave front tilting.

Diffractive Alvarez lens

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barton, Ian M.; Dixit, Sham N.; Summers, Leslie J.

2000-01-01

A diffractive Alvarez lens is demonstrated that consists of two separate phase plates, each having complementary 16-level surface-relief profiles that contain cubic phase delays. Translation of these two components in the plane of the phase plates is shown to produce a variable astigmatic focus. Both spherical and cylindrical phase profiles are demonstrated with good accuracy, and the discrete surface-relief features are shown to cause less than {lambda}/10 wave-front aberration in the transmitted wave front over a 40 mmx80 mm region. (c) 2000 Optical Society of America.

High power water load for microwave and millimeter-wave radio frequency sources

DOEpatents

Ives, R. Lawrence; Mizuhara, Yosuke M.; Schumacher, Richard V.; Pendleton, Rand P.

1999-01-01

A high power water load for microwave and millimeter wave radio frequency sources has a front wall including an input port for the application of RF power, a cylindrical dissipation cavity lined with a dissipating material having a thickness which varies with depth, and a rear wall including a rotating reflector for the reflection of wave energy inside the cylindrical cavity. The dissipation cavity includes a water jacket for removal of heat generated by the absorptive material coating the dissipation cavity, and this absorptive material has a thickness which is greater near the front wall than near the rear wall. Waves entering the cavity reflect from the rotating reflector, impinging and reflecting multiple times on the absorptive coating of the dissipation cavity, dissipating equal amounts of power on each internal reflection.

The wave-field from an array of periodic emitters driven simultaneously by a broadband pulse.

PubMed

Dixon, Steve; Hill, Samuel; Fan, Yichao; Rowlands, George

2013-06-01

The use of phased array methods are commonplace in ultrasonic applications, where controlling the variation of the phase between the narrowband emitters in an array facilitates beam steering and focusing of ultrasonic waves. An approach is presented here whereby emitters of alternating polarity arranged in a one-dimensional array are pulsed simultaneously, and have sufficiently wide, controlled bandwidth to emit a two-dimensional wave. This pulsed approach provides a rapid means of simultaneously covering a region of space with a wave-front, whereby any wave that scatters or reflects off a body to a detector will have a distinct arrival time and frequency. This is a general wave phenomenon with a potential application in radar, sonar, and ultrasound. The key result is that one can obtain a smooth, continuous wave-front emitted from the array, over a large solid angle, whose frequency varies as a function of angle to the array. Analytic and finite element models created to describe this phenomenon have been validated with experimental results using ultrasonic waves in metal samples.

Wave combustors for trans-atmospheric vehicles

NASA Technical Reports Server (NTRS)

Menees, Gene P.; Bowles, Jeffrey V.; Adelman, Henry G.; Cambier, Jean-Luc

1989-01-01

A performance analysis is given of a conceptual transatmospheric vehicle (TAV). The TAV is powered by a an oblique detonation wave engine (ODWE). The ODWE is an airbreathing hypersonic propulsion system which utilizes shock and detonation waves to enhance fuel-air mixing and combustion in supersonic flow. In this wave combustor concept, an oblique shock wave in the combustor can act as a flameholder by increasing the pressure and temperature of the air-fuel mixture, thereby decreasing the ignition delay. If the oblique shock is sufficiently strong, then the combustion front and the shock wave can couple into a detonation wave. In this case, combustion occurs almost instantaneously in a thin zone behind the wave front. The result is a shorter lighter engine compared to the scramjet. The ODWE-powered hypersonic vehicle performance is compared to that of a scramjet-powered vehicle. Among the results outlined, it is found that the ODWE trades a better engine performance above Mach 15 for a lower performance below Mach 15. The overall higher performance of the ODWE results in a 51,000-lb weight savings and a higher payload weight fraction of approximately 12 percent.

Shock wave interaction with L-shaped structures

NASA Astrophysics Data System (ADS)

Miller, Richard C.

1993-12-01

This study investigated the interaction of shock waves with L-shaped structures using the CTH hydrodynamics code developed by Sandia National Laboratories. Computer models of shock waves traveling through air were developed using techniques similar to shock tube experiments. Models of L-shaped buildings were used to determine overpressures achieved by the reflecting shock versus angle of incidence of the shock front. An L-shaped building model rotated 45 degrees to the planar shock front produced the highest reflected overpressure of 9.73 atmospheres in the corner joining the two wings, a value 9.5 times the incident overpressure of 1.02 atmospheres. The same L-shaped building was modeled with the two wings separated by 4.24 meters to simulate an open courtyard. This open area provided a relief path for the incident shock wave, creating a peak overpressure of only 4.86 atmospheres on the building's wall surfaces from the same 1.02 atmosphere overpressure incident shock wave.

Transmission and reflection of charge-density wave packets in a quantum Hall edge controlled by a metal gate

NASA Astrophysics Data System (ADS)

Matsuura, Masahiro; Mano, Takaaki; Noda, Takeshi; Shibata, Naokazu; Hotta, Masahiro; Yusa, Go

2018-02-01

Quantum energy teleportation (QET) is a proposed protocol related to quantum vacuum. The edge channels in a quantum Hall system are well suited for the experimental verification of QET. For this purpose, we examine a charge-density wave packet excited and detected by capacitively coupled front gate electrodes. We observe the waveform of the charge packet, which is proportional to the time derivative of the applied square voltage wave. Further, we study the transmission and reflection behaviors of the charge-density wave packet by applying a voltage to another front gate electrode to control the path of the edge state. We show that the threshold voltages where the dominant direction is switched in either transmission or reflection for dense and sparse wave packets are different from the threshold voltage where the current stops flowing in an equilibrium state.

Gene surfing in expanding populations.

PubMed

Hallatschek, Oskar; Nelson, David R

2008-02-01

Large scale genomic surveys are partly motivated by the idea that the neutral genetic variation of a population may be used to reconstruct its migration history. However, our ability to trace back the colonization pathways of a species from their genetic footprints is limited by our understanding of the genetic consequences of a range expansion. Here, we study, by means of simulations and analytical methods, the neutral dynamics of gene frequencies in an asexual population undergoing a continual range expansion in one dimension. During such a colonization period, lineages can fix at the wave front by means of a "surfing" mechanism [Edmonds, C.A., Lillie, A.S., Cavalli-Sforza, L.L., 2004. Mutations arising in the wave front of an expanding population. Proc. Natl. Acad. Sci. 101, 975-979]. We quantify this phenomenon in terms of (i) the spatial distribution of lineages that reach fixation and, closely related, (ii) the continual loss of genetic diversity (heterozygosity) at the wave front, characterizing the approach to fixation. Our stochastic simulations show that an effective population size can be assigned to the wave that controls the (observable) gradient in heterozygosity left behind the colonization process. This effective population size is markedly higher in the presence of cooperation between individuals ("pushed waves") than when individuals proliferate independently ("pulled waves"), and increases only sub-linearly with deme size. To explain these and other findings, we develop a versatile analytical approach, based on the physics of reaction-diffusion systems, that yields simple predictions for any deterministic population dynamics. Our analytical theory compares well with the simulation results for pushed waves, but is less accurate in the case of pulled waves when stochastic fluctuations in the tip of the wave are important.

North Atlantic storm driving of extreme wave heights in the North Sea

NASA Astrophysics Data System (ADS)

Bell, R. J.; Gray, S. L.; Jones, O. P.

2017-04-01

The relationship between storms and extreme ocean waves in the North Sea is assessed using a long-period wave data set and storms identified in the Interim ECMWF Re-Analysis (ERA-Interim). An ensemble sensitivity analysis is used to provide information on the spatial and temporal forcing from mean sea-level pressure and surface wind associated with extreme ocean wave height responses. Extreme ocean waves in the central North Sea arise due to intense extratropical cyclone winds from either the cold conveyor belt (northerly-wind events) or the warm conveyor belt (southerly-wind events). The largest wave heights are associated with northerly-wind events which tend to have stronger wind speeds and occur as the cold conveyor belt wraps rearward round the cyclone to the cold side of the warm front. The northerly-wind events provide a larger fetch to the central North Sea to aid wave growth. Southerly-wind events are associated with the warm conveyor belts of intense extratropical cyclones that develop in the left upper tropospheric jet exit region. Ensemble sensitivity analysis can provide early warning of extreme wave events by demonstrating a relationship between wave height and high pressure to the west of the British Isles for northerly-wind events 48 h prior. Southerly-wind extreme events demonstrate sensitivity to low pressure to the west of the British Isles 36 h prior.

Revisiting the Rossby Haurwitz wave test case with contour advection

NASA Astrophysics Data System (ADS)

Smith, Robert K.; Dritschel, David G.

2006-09-01

This paper re-examines a basic test case used for spherical shallow-water numerical models, and underscores the need for accurate, high resolution models of atmospheric and ocean dynamics. The Rossby-Haurwitz test case, first proposed by Williamson et al. [D.L. Williamson, J.B. Drake, J.J. Hack, R. Jakob, P.N. Swarztrauber, A standard test set for numerical approximations to the shallow-water equations on the sphere, J. Comput. Phys. (1992) 221-224], has been examined using a wide variety of shallow-water models in previous papers. Here, two contour-advective semi-Lagrangian (CASL) models are considered, and results are compared with previous test results. We go further by modifying this test case in a simple way to initiate a rapid breakdown of the basic wave state. This breakdown is accompanied by the formation of sharp potential vorticity gradients (fronts), placing far greater demands on the numerics than the original test case does. We also go further by examining other dynamical fields besides the height and potential vorticity, to assess how well the models deal with gravity waves. Such waves are sensitive to the presence or not of sharp potential vorticity gradients, as well as to numerical parameter settings. In particular, large time steps (convenient for semi-Lagrangian schemes) can seriously affect gravity waves but can also have an adverse impact on the primary fields of height and velocity. These problems are exacerbated by a poor resolution of potential vorticity gradients.

Amplitude and Wavelength Measurement of Sound Waves in Free Space using a Sound Wave Phase Meter

NASA Astrophysics Data System (ADS)

Ham, Sounggil; Lee, Kiwon

2018-05-01

We developed a sound wave phase meter (SWPM) and measured the amplitude and wavelength of sound waves in free space. The SWPM consists of two parallel metal plates, where the front plate was operated as a diaphragm. An aluminum perforated plate was additionally installed in front of the diaphragm, and the same signal as that applied to the sound source was applied to the perforated plate. The SWPM measures both the sound wave signal due to the diaphragm vibration and the induction signal due to the electric field of the aluminum perforated plate. Therefore, the two measurement signals interfere with each other due to the phase difference according to the distance between the sound source and the SWPM, and the amplitude of the composite signal that is output as a result is periodically changed. We obtained the wavelength of the sound wave from this periodic amplitude change measured in the free space and compared it with the theoretically calculated values.

Co-evolution of upstream waves and accelerated ions at parallel shocks

NASA Astrophysics Data System (ADS)

Fujimoto, M.; Sugiyama, T.

2016-12-01

Shock waves in space plasmas have been considered as the agents for various particle acceleration phenomena. The basic idea behind shock acceleration is that particles are accelerated as they move back-and-forth across a shock front. Detailed studies of ion acceleration at the terrestrial bow shock have been performed, however, the restricted maximum energies attained prevent a straight-forward application of obtained knowledge to more energetic astrophysical situations. Here we show by a large-scale self-consistent particle simulation that the co-evolution of magnetic turbulence and accelerated ion population is the foundation for continuous operation of shock acceleration to ever higher energies. Magnetic turbulence is created by ions reflected back upstream of a parallel shock front. The co-evolution arises because more energetic ions excite waves of longer wavelengths, and because longer wavelength modes are capable of scattering (in the upstream) and reflecting (at the shock front) more energetic ions. Via carefully designed numerical experiments, we show very clearly that this picture is true.

Resent Status of ITER Equatorial Launcher Development

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takahashi, K.; Kajiwara, K.; Kasugai, A.

2009-11-26

The ITER equatorial launcher is divided into a front shield and a port plug. The front shield is composed of fourteen blanket shield modules so as to form three openings for the injection of mm-wave beams into plasma. Twenty-four waveguide transmission lines, internal shields, cooling pipes and so on are installed in the port plug. The transmission lines consist of the corrugated waveguides, miter bends and the free space propagation region utilizing two mirrors in front of the waveguide outlet. The analysis of mm-wave beam propagation in the region shows that the transmission efficiency more than 99.5% is attained. Themore » high power experiments of the launcher mock-up have been carried out and the measured field patterns at each mirror and the outlet of the launcher are agreed with the calculations. It is concluded that the transmission line components in the launcher mock-up are fabricated as designed and the present mm-wave design in the launcher is feasible.« less

Application of dynamic displacement current for diagnostics of subnanosecond breakdowns in an inhomogeneous electric field

NASA Astrophysics Data System (ADS)

Shao, Tao; Tarasenko, Victor F.; Zhang, Cheng; Burachenko, Alexandr G.; Rybka, Dmitry V.; Kostyrya, Igor'D.; Lomaev, Mikhail I.; Baksht, Evgeni Kh.; Yan, Ping

2013-05-01

The breakdown of different air gaps at high overvoltages in an inhomogeneous electric field was investigated with a time resolution of up to 100 ps. Dynamic displacement current was used for diagnostics of ionization processes between the ionization wave front and a plane anode. It is demonstrated that during the generation of a supershort avalanche electron beam (SAEB) with amplitudes of ˜10 A and more, conductivity in the air gaps at the breakdown stage is ensured by the ionization wave, whose front propagates from the electrode of small curvature radius, and by the dynamic displacement current between the ionization wave front and the plane electrode. The amplitude of the dynamic displacement current measured by a current shunt is 100 times greater than the SAEB. It is shown that with small gaps and with a large cathode diameter, the amplitude of the dynamic displacement current during a subnanosecond rise time of applied pulse voltage can be higher than 4 kA.

Millimeter wave front-end figure of merit, part 2

NASA Astrophysics Data System (ADS)

Silberman, Gabriel G.

1995-09-01

This report presents a practical approach for defining and calculating a meaningful figure of merit for frequency modulated continuous wave radar systems with separate receive and transmit (bistatic) antennas.

RF to millimeter wave integration and module technologies

NASA Astrophysics Data System (ADS)

Vähä-Heikkilä, T.

2015-04-01

Radio Frequency (RF) consumer applications have boosted silicon integrated circuits (IC) and corresponding technologies. More and more functions are integrated to ICs and their performance is also increasing. However, RF front-end modules with filters and switches as well as antennas still need other way of integration. This paper focuses to RF front-end module and antenna developments as well as to the integration of millimeter wave radios. VTT Technical Research Centre of Finland has developed both Low Temperature Co-fired Ceramics (LTCC) and Integrated Passive Devices (IPD) integration platforms for RF and millimeter wave integrated modules. In addition to in-house technologies, VTT is using module and component technologies from other commercial sources.

Non-LTE radiating acoustic shocks and Ca II K2V bright points

NASA Technical Reports Server (NTRS)

Carlsson, Mats; Stein, Robert F.

1992-01-01

We present, for the first time, a self-consistent solution of the time-dependent 1D equations of non-LTE radiation hydrodynamics in solar chromospheric conditions. The vertical propagation of sinusoidal acoustic waves with periods of 30, 180, and 300 s is calculated. We find that departures from LTE and ionization recombination determine the temperature profiles of the shocks that develop. In LTE almost all the thermal energy goes into ionization, so the temperature rise is very small. In non-LTE, the finite transition rates delay the ionization to behind the shock front. The compression thus goes into thermal energy at the shock front leading to a high temperature amplitude. Further behind the shock front, the delayed ionization removes energy from the thermal pool, which reduces the temperature, producing a temperature spike. The 180 s waves reproduce the observed temporal changes in the calcium K line profiles quite well. The observed wing brightening pattern, the violet/red peak asymmetry and the observed line center behavior are all well reproduced. The short-period waves and the 5 minute period waves fail especially in reproducing the observed behavior of the wings.

Collective cell migration without proliferation: density determines cell velocity and wave velocity

NASA Astrophysics Data System (ADS)

Tlili, Sham; Gauquelin, Estelle; Li, Brigitte; Cardoso, Olivier; Ladoux, Benoît; Delanoë-Ayari, Hélène; Graner, François

2018-05-01

Collective cell migration contributes to embryogenesis, wound healing and tumour metastasis. Cell monolayer migration experiments help in understanding what determines the movement of cells far from the leading edge. Inhibiting cell proliferation limits cell density increase and prevents jamming; we observe long-duration migration and quantify space-time characteristics of the velocity profile over large length scales and time scales. Velocity waves propagate backwards and their frequency depends only on cell density at the moving front. Both cell average velocity and wave velocity increase linearly with the cell effective radius regardless of the distance to the front. Inhibiting lamellipodia decreases cell velocity while waves either disappear or have a lower frequency. Our model combines conservation laws, monolayer mechanical properties and a phenomenological coupling between strain and polarity: advancing cells pull on their followers, which then become polarized. With reasonable values of parameters, this model agrees with several of our experimental observations. Together, our experiments and model disantangle the respective contributions of active velocity and of proliferation in monolayer migration, explain how cells maintain their polarity far from the moving front, and highlight the importance of strain-polarity coupling and density in long-range information propagation.

Oxy-acetylene driven laboratory scale shock tubes for studying blast wave effects

NASA Astrophysics Data System (ADS)

Courtney, Amy C.; Andrusiv, Lubov P.; Courtney, Michael W.

2012-04-01

This paper describes the development and characterization of modular, oxy-acetylene driven laboratory scale shock tubes. Such tools are needed to produce realistic blast waves in a laboratory setting. The pressure-time profiles measured at 1 MHz using high-speed piezoelectric pressure sensors have relevant durations and show a true shock front and exponential decay characteristic of free-field blast waves. Descriptions are included for shock tube diameters of 27-79 mm. A range of peak pressures from 204 kPa to 1187 kPa (with 0.5-5.6% standard error of the mean) were produced by selection of the driver section diameter and distance from the shock tube opening. The peak pressures varied predictably with distance from the shock tube opening while maintaining both a true blast wave profile and relevant pulse duration for distances up to about one diameter from the shock tube opening. This shock tube design provides a more realistic blast profile than current compression-driven shock tubes, and it does not have a large jet effect. In addition, operation does not require specialized personnel or facilities like most blast-driven shock tubes, which reduces operating costs and effort and permits greater throughput and accessibility. It is expected to be useful in assessing the response of various sensors to shock wave loading; assessing the reflection, transmission, and absorption properties of candidate armor materials; assessing material properties at high rates of loading; assessing the response of biological materials to shock wave exposure; and providing a means to validate numerical models of the interaction of shock waves with structures. All of these activities have been difficult to pursue in a laboratory setting due in part to lack of appropriate means to produce a realistic blast loading profile.

Converging Oceaniac Internal Waves, Somalia, Africa

NASA Image and Video Library

1988-10-03

The arculate fronts of these apparently converging internal waves off the northeast coast of Somalia (11.5N, 51.5E) probably were produced by interaction with two parallel submarine canyons off the Horn of Africa. Internal waves are packets of tidally generated waves traveling within the ocean at varying depths and are not detectable by any surface disturbance.

Observation of Wave Packet Distortion during a Negative-Group-Velocity Transmission

PubMed Central

Ye, Dexin; Salamin, Yannick; Huangfu, Jiangtao; Qiao, Shan; Zheng, Guoan; Ran, Lixin

2015-01-01

In Physics, causality is a fundamental postulation arising from the second law of thermodynamics. It states that, the cause of an event precedes its effect. In the context of Electromagnetics, the relativistic causality limits the upper bound of the velocity of information, which is carried by electromagnetic wave packets, to the speed of light in free space (c). In anomalously dispersive media (ADM), it has been shown that, wave packets appear to propagate with a superluminal or even negative group velocity. However, Sommerfeld and Brillouin pointed out that the “front” of such wave packets, known as the initial point of the Sommerfeld precursor, always travels at c. In this work, we investigate the negative-group-velocity transmission of half-sine wave packets. We experimentally observe the wave front and the distortion of modulated wave packets propagating with a negative group velocity in a passive artificial ADM in microwave regime. Different from previous literature on the propagation of superluminal Gaussian packets, strongly distorted sinusoidal packets with non-superluminal wave fronts were observed. This result agrees with Brillouin's assertion, i.e., the severe distortion of seemingly superluminal wave packets makes the definition of group velocity physically meaningless in the anomalously dispersive region. PMID:25631746

Numerical investigation of internal high-speed viscous flows using a parabolic technique

NASA Technical Reports Server (NTRS)

Anderson, O. L.; Power, G. D.

1985-01-01

A feasibility study has been conducted to assess the applicability of an existing parabolic analysis (ADD-Axisymmetric Diffuser Duct), developed previously for subsonic viscous internal flows, to mixed supersonic/subsonic flows with heat addition simulating a SCRAMJET combustor. A study was conducted with the ADD code modified to include additional convection effects in the normal momentum equation when supersonic expansion and compression waves are present. A set of test problems with weak shock and expansion waves have been analyzed with this modified ADD method and stable and accurate solutions were demonstrated provided the streamwise step size was maintained at levels larger than the boundary layer displacement thickness. Calculations made with further reductions in step size encountered departure solutions consistent with strong interaction theory. Calculations were also performed for a flow field with a flame front in which a specific heat release was imposed to simulate a SCRAMJET combustor. In this case the flame front generated relatively thick shear layers which aggravated the departure solution problem. Qualitatively correct results were obtained for these cases using a marching technique with the convective terms in the normal momentum equation suppressed. It is concluded from the present study that for the class of problems where strong viscous/inviscid interactions are present a global iteration procedure is required.

Attenuation of the dynamic yield point of shocked aluminum using elastodynamic simulations of dislocation dynamics.

PubMed

Gurrutxaga-Lerma, Beñat; Balint, Daniel S; Dini, Daniele; Eakins, Daniel E; Sutton, Adrian P

2015-05-01

When a metal is subjected to extremely rapid compression, a shock wave is launched that generates dislocations as it propagates. The shock wave evolves into a characteristic two-wave structure, with an elastic wave preceding a plastic front. It has been known for more than six decades that the amplitude of the elastic wave decays the farther it travels into the metal: this is known as "the decay of the elastic precursor." The amplitude of the elastic precursor is a dynamic yield point because it marks the transition from elastic to plastic behavior. In this Letter we provide a full explanation of this attenuation using the first method of dislocation dynamics to treat the time dependence of the elastic fields of dislocations explicitly. We show that the decay of the elastic precursor is a result of the interference of the elastic shock wave with elastic waves emanating from dislocations nucleated in the shock front. Our simulations reproduce quantitatively recent experiments on the decay of the elastic precursor in aluminum and its dependence on strain rate.

Photographic laboratory studies of explosions.

NASA Technical Reports Server (NTRS)

Kamel, M. M.; Oppenheim, A. K.

1973-01-01

Description of a series of cinematographic studies of explosions made with a high-speed rotating-mirror streak camera which uses a high-frequency stroboscopic ruby laser as the light source. The results obtained mainly concern explosions initiated by focused laser irradiation from a pulsed neodymium laser in a detonating gas consisting essentially of an equimolar mixture of acetylene and oxygen at an initial pressure of 100 torr at room temperature. Among the most significant observations were observations of a spherical blast wave preceded by a Chapman-Jouguet detonation which is stabilized immediately after initiation, the merging of a spherical flame with a shock front of the blast wave in which the flame is propagating, the division of a spherical detonation front into a shock wave and flame, and the generation of shock waves by a network of spherical flames.

Turbulent premixed combustion in V-shaped flames: Characteristics of flame front

NASA Astrophysics Data System (ADS)

Kheirkhah, S.; Gülder, Ö. L.

2013-05-01

Flame front characteristics of turbulent premixed V-shaped flames were investigated experimentally using the Mie scattering and the particle image velocimetry techniques. The experiments were performed at mean streamwise exit velocities of 4.0, 6.2, and 8.6 m/s, along with fuel-air equivalence ratios of 0.7, 0.8, and 0.9. Effects of vertical distance from the flame-holder, mean streamwise exit velocity, and fuel-air equivalence ratio on statistics of the distance between the flame front and the vertical axis, flame brush thickness, flame front curvature, and angle between tangent to the flame front and the horizontal axis were studied. The results show that increasing the vertical distance from the flame-holder and the fuel-air equivalence ratio increase the mean and root-mean-square (RMS) of the distance between the flame front and the vertical axis; however, increasing the mean streamwise exit velocity decreases these statistics. Spectral analysis of the fluctuations of the flame front position depicts that the normalized and averaged power-spectrum-densities collapse and show a power-law relation with the normalized wave number. The flame brush thickness is linearly correlated with RMS of the distance between the flame front and the vertical axis. Analysis of the curvature of the flame front data shows that the mean curvature is independent of the experimental conditions tested and equals to zero. Values of the inverse of the RMS of flame front curvature are similar to those of the integral length scale, suggesting that the large eddies in the flow make a significant contribution in wrinkling of the flame front. Spectral analyses of the flame front curvature as well as the angle between tangent to the flame front and the horizontal axis show that the power-spectrum-densities feature a peak. Value of the inverse of the wave number pertaining to the peak is larger than that of the integral length scale.

The Formation and Early Evolution of a Coronal Mass Ejection and its Associated Shock Wave on 2014 January 8

NASA Astrophysics Data System (ADS)

Wan, Linfeng; Cheng, Xin; Shi, Tong; Su, Wei; Ding, M. D.

2016-08-01

In this paper, we study the formation and early evolution of a limb coronal mass ejection (CME) and its associated shock wave that occurred on 2014 January 8. The extreme ultraviolet (EUV) images provided by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory disclose that the CME first appears as a bubble-like structure. Subsequently, its expansion forms the CME and causes a quasi-circular EUV wave. Interestingly, both the CME and the wave front are clearly visible at all of the AIA EUV passbands. Through a detailed kinematical analysis, it is found that the expansion of the CME undergoes two phases: a first phase with a strong but transient lateral over-expansion followed by a second phase with a self-similar expansion. The temporal evolution of the expansion velocity coincides very well with the variation of the 25-50 keV hard X-ray flux of the associated flare, which indicates that magnetic reconnection most likely plays an important role in driving the expansion. Moreover, we find that, when the velocity of the CME reaches ˜600 km s-1, the EUV wave starts to evolve into a shock wave, which is evidenced by the appearance of a type II radio burst. The shock’s formation height is estimated to be ˜0.2 R sun, which is much lower than the height derived previously. Finally, we also study the thermal properties of the CME and the EUV wave. We find that the plasma in the CME leading front and the wave front has a temperature of ˜2 MK, while that in the CME core region and the flare region has a much higher temperature of ≥8 MK.

Optical mapping of Langendorff-perfused human hearts: establishing a model for the study of ventricular fibrillation in humans.

PubMed

Nanthakumar, Kumaraswamy; Jalife, José; Massé, Stéphane; Downar, Eugene; Pop, Mihaela; Asta, John; Ross, Heather; Rao, Vivek; Mironov, Sergey; Sevaptsidis, Elias; Rogers, Jack; Wright, Graham; Dhopeshwarkar, Rajesh

2007-07-01

Our objective was to establish a novel model for the study of ventricular fibrillation (VF) in humans. We adopted the established techniques of optical mapping to human ventricles for the first time to determine whether human VF is the result of wave breaks and singularity point formation and is maintained by high-frequency rotors and fibrillatory conduction. We describe the technique of acquiring optical signals in human hearts during VF, their characteristics, and the feasibility of possible analyses that could be performed to elucidate mechanisms of human VF. We used explanted hearts from five cardiomyopathic patients who underwent transplantation. The hearts were Langendorff perfused with Tyrode solution (95% O(2)-5% CO(2)), and the potentiometric dye di-4-ANEPPS was injected as a bolus into the coronary circulation. Fluorescence was excited at 531 +/- 20 nm with a 150-W halogen light source; the emission signal was long-pass filtered at 610 nm and recorded with a mapping camera. Fractional change of fluorescence varied between 2% and 12%. Average signal-to-noise ratio was 40 dB. The mean velocity of VF wave fronts was 0.25 +/- 0.04 m/s. Submillimetric spatial resolution (0.65-0.85 mm), activation mapping, and transformation of the data to phase-based analysis revealed reentrant, colliding, and fractionating wave fronts in human VF. On many occasions the VF wave fronts were as large as the entire vertical length (8 cm) of the mapping field, suggesting that there are a limited number of wave fronts on the human heart during VF. Phase transformation of the optical signals allowed the first demonstration ever of phase singularity point, wave breaks, and rotor formation in human VF. This method provides opportunities for potential analyses toward elucidation of the mechanisms of VF and defibrillation in humans.

Experimental investigation of detonation waves instabilities in liquid high explosives

NASA Astrophysics Data System (ADS)

Sosikov, V. A.; Torunov, S. I.; Utkin, A. V.; Mochalova, V. M.; Rapota, D. Yu

2018-01-01

Experimental investigation of unstable detonation front structure in mixtures of liquid high explosives (nitromethane and FEFO—bis-(2-fluor-2.2-dinitroethyl)-formal) with inert diluents (acetone, methanol, DETA—diethylene triamine) has been carried out. Inhomogeneities have been registered by electro-optical camera NANOGATE 4BP allowing to make 4 frames with the exposure time 10 ns. According to experimental results the detonation front in nitromethane-acetone mixture is unstable. It is evident that pulsations on detonation front do not form spatial periodic structure and their dimensions differ several times. But mean longitudinal size of pulsation is about 500 μm at 20 wt% of acetone concentration. This means that the typical size of cell equals to reaction zone width. The same structure of cellular front have been registered in 70/30 FEFO-methanol mixture. Second kind of instability, failure waves, was observed in neat nitromethane at the free surface. In this case the stability loss result in turbulent flow which is clearly detected in the shots obtained. Adding small amount of DETA (0.5 wt%) results in disappearance of the failure waves and flow stabilization. The effect is caused by the fact that DETA sharply accelerates initial rate of chemical reaction because it is sensitizer for nitromethane.

Comparison of geometrical shock dynamics and kinematic models for shock-wave propagation

NASA Astrophysics Data System (ADS)

Ridoux, J.; Lardjane, N.; Monasse, L.; Coulouvrat, F.

2018-03-01

Geometrical shock dynamics (GSD) is a simplified model for nonlinear shock-wave propagation, based on the decomposition of the shock front into elementary ray tubes. Assuming small changes in the ray tube area, and neglecting the effect of the post-shock flow, a simple relation linking the local curvature and velocity of the front, known as the A{-}M rule, is obtained. More recently, a new simplified model, referred to as the kinematic model, was proposed. This model is obtained by combining the three-dimensional Euler equations and the Rankine-Hugoniot relations at the front, which leads to an equation for the normal variation of the shock Mach number at the wave front. In the same way as GSD, the kinematic model is closed by neglecting the post-shock flow effects. Although each model's approach is different, we prove their structural equivalence: the kinematic model can be rewritten under the form of GSD with a specific A{-}M relation. Both models are then compared through a wide variety of examples including experimental data or Eulerian simulation results when available. Attention is drawn to the simple cases of compression ramps and diffraction over convex corners. The analysis is completed by the more complex cases of the diffraction over a cylinder, a sphere, a mound, and a trough.

Determination and Control of Optical and X-Ray Wave Fronts

NASA Technical Reports Server (NTRS)

Kim, Young K.

1997-01-01

A successful design of a space-based or ground optical system requires an iterative procedure which includes the kinematics and dynamics of the system in operating environment, control synthesis and verification. To facilitate the task of designing optical wave front control systems being developed at NASA/MSFC, a multi-discipline dynamics and control tool has been developed by utilizing TREETOPS, a multi-body dynamics and control simulation, NASTRAN and MATLAB. Dynamics and control models of STABLE and ARIS were developed for TREETOPS simulation, and their simulation results are documented in this report.

Sandia technology & entrepreneurs improve Lasik

ScienceCinema

Neal, Dan; Turner, Tim

2018-05-11

Former Sandian Dan Neal started his company, WaveFront Sciences, based on wavefront sensing metrology technologies licensed from Sandia National Laboratories and by taking advantage of its Entrepreneurial Separation to Transfer Technology (ESTT) program. Abbott Medical Optics since acquired WaveFront and estimates that one million patients have improved the quality of their vision thanks to its products. ESTT is a valuable tool which allows Sandia to transfer technology to the private sector and Sandia employees to leave the Labs in order to start up new technology companies or help expand existing companies.

Applications of variable focus liquid lenses for curvature wave-front sensors in astronomy

NASA Astrophysics Data System (ADS)

Fuentes-Fernández, J.; Cuevas, S.; Alvarez-Nuñez, L. C.; Watson, A. M.

2014-08-01

Curvature wavefront sensors obtain the wave-front aberrations from two defocused intensity images at each side of the pupil plane. Typically, when high modulation speeds are required, as it is the case with Adaptive Optics, that defocusing is done with a fast vibrating membrane mirror. We propose an alternative defocusing mechanism based on an electrowetting variable focus liquid lens. The use of such lenses may perform the required focus modulation without the need of extra moving parts, reducing the overall size of the system.

Microwave interferometry technique for obtaining gas interface velocity measurements in an expansion tube facility

NASA Technical Reports Server (NTRS)

Laney, C. C., Jr.

1974-01-01

A microwave interferometer technique to determine the front interface velocity of a high enthalpy gas flow, is described. The system is designed to excite a standing wave in an expansion tube, and to measure the shift in this standing wave as it is moved by the test gas front. Data, in the form of a varying sinusoidal signal, is recorded on a high-speed drum camera-oscilloscope combination. Measurements of average and incremental velocities in excess of 6,000 meters per second were made.

Sandia technology & entrepreneurs improve Lasik

DOE Office of Scientific and Technical Information (OSTI.GOV)

Neal, Dan; Turner, Tim

2013-11-21

Former Sandian Dan Neal started his company, WaveFront Sciences, based on wavefront sensing metrology technologies licensed from Sandia National Laboratories and by taking advantage of its Entrepreneurial Separation to Transfer Technology (ESTT) program. Abbott Medical Optics since acquired WaveFront and estimates that one million patients have improved the quality of their vision thanks to its products. ESTT is a valuable tool which allows Sandia to transfer technology to the private sector and Sandia employees to leave the Labs in order to start up new technology companies or help expand existing companies.

Optical emission from a fast shock wave - The remnants of Tycho's supernova and SN 1006

NASA Technical Reports Server (NTRS)

Chevalier, R. A.; Raymond, J. C.

1978-01-01

The faint optical filaments in Tycho's supernova remnant appear to be emission from a shock front moving at 5600 km/s. The intensity of the hydrogen lines, the absence of forbidden lines of heavy elements in the spectrum, and the width of the filaments are explained by a model in which a collisionless shock wave is moving into partially neutral gas. The presence of the neutral gas can be used to set an upper limit of approximately 5 x 10 to the 47th power ergs to the energy in ionizing radiation emitted by a Type I supernova. The patchy neutral gas is probably part of the warm neutral component of the interstellar medium. The existing information on the remnant of SN 1006 indicates that its emission is similar in nature to that from Tycho's remnant.

Heavy and Heavy-Light Mesons in the Covariant Spectator Theory

NASA Astrophysics Data System (ADS)

Stadler, Alfred; Leitão, Sofia; Peña, M. T.; Biernat, Elmar P.

2018-05-01

The masses and vertex functions of heavy and heavy-light mesons, described as quark-antiquark bound states, are calculated with the Covariant Spectator Theory (CST). We use a kernel with an adjustable mixture of Lorentz scalar, pseudoscalar, and vector linear confining interaction, together with a one-gluon-exchange kernel. A series of fits to the heavy and heavy-light meson spectrum were calculated, and we discuss what conclusions can be drawn from it, especially about the Lorentz structure of the kernel. We also apply the Brodsky-Huang-Lepage prescription to express the CST wave functions for heavy quarkonia in terms of light-front variables. They agree remarkably well with light-front wave functions obtained in the Hamiltonian basis light-front quantization approach, even in excited states.

pH Wave-Front Propagation in the Urea-Urease Reaction

PubMed Central

Wrobel, Magdalena M.; Bánsági, Tamás; Scott, Stephen K.; Taylor, Annette F.; Bounds, Chris O.; Carranza, Arturo; Pojman, John A.

2012-01-01

The urease-catalyzed hydrolysis of urea displays feedback that results in a switch from acid (pH ∼3) to base (pH ∼9) after a controllable period of time (from 10 to >5000 s). Here we show that the spatially distributed reaction can support pH wave fronts propagating with a speed of the order of 0.1−1 mm min−1. The experimental results were reproduced qualitatively in reaction-diffusion simulations including a Michaelis-Menten expression for the urease reaction with a bell-shaped rate-pH dependence. However, this model fails to predict that at lower enzyme concentrations, the unstirred reaction does not always support fronts when the well-stirred reaction still rapidly switches to high pH. PMID:22947878

Storm-induced inner-continental shelf circulation and sediment transport: Long Bay, South Carolina

USGS Publications Warehouse

Warner, John C.; Armstrong, Brandy N.; Sylvester, Charlene S.; Voulgaris, George; Nelson, Tim; Schwab, William C.; Denny, Jane F.

2012-01-01

Long Bay is a sediment-starved, arcuate embayment located along the US East Coast connecting both South and North Carolina. In this region the rates and pathways of sediment transport are important because they determine the availability of sediments for beach nourishment, seafloor habitat, and navigation. The impact of storms on sediment transport magnitude and direction were investigated during the period October 2003–April 2004 using bottom mounted flow meters, acoustic backscatter sensors and rotary sonars deployed at eight sites offshore of Myrtle Beach, SC, to measure currents, water levels, surface waves, salinity, temperature, suspended sediment concentrations, and bedform morphology. Measurements identify that sediment mobility is caused by waves and wind driven currents from three predominant types of storm patterns that pass through this region: (1) cold fronts, (2) warm fronts and (3) low-pressure storms. The passage of a cold front is accompanied by a rapid change in wind direction from primarily northeastward to southwestward. The passage of a warm front is accompanied by an opposite change in wind direction from mainly southwestward to northeastward. Low-pressure systems passing offshore are accompanied by a change in wind direction from southwestward to southeastward as the offshore storm moves from south to north.During the passage of cold fronts more sediment is transported when winds are northeastward and directed onshore than when the winds are directed offshore, creating a net sediment flux to the north–east. Likewise, even though the warm front has an opposite wind pattern, net sediment flux is typically to the north–east due to the larger fetch when the winds are northeastward and directed onshore. During the passage of low-pressure systems strong winds, waves, and currents to the south are sustained creating a net sediment flux southwestward. During the 3-month deployment a total of 8 cold fronts, 10 warm fronts, and 10 low-pressure systems drove a net sediment flux southwestward. Analysis of a 12-year data record from a local buoy shows an average of 41 cold fronts, 32 warm fronts, and 26 low-pressure systems per year. The culmination of these events would yield a cumulative net inner-continental shelf transport to the south–west, a trend that is further verified by sediment textural analysis and bedform morphology on the inner-continental shelf.

Formation of temperature front in stably stratified turbulence

NASA Astrophysics Data System (ADS)

Kimura, Yoshifumi; Sullivan, Peter; Herring, Jackson

2016-11-01

An important feature of stably stratified turbulence is the significant influence of internal gravity waves which makes stably stratified turbulence unique compared to homogeneous isotropic turbulence. In this paper, we investigate the genesis of temperature fronts-a crucial subject both practically and fundamentally-in stably stratified turbulence using Direct Numerical Simulations (DNS) of the Navier-Stokes equation under the Boussinesq approximation with 10243 grid points. Vertical profiles of temperature fluctuations show almost vertically periodic sawtooth wavy structures with negative and positive layers stacked together with clear boundaries implying a sharp temperature fronts. The sawtooth waves consist of gradual decreasing temperature fluctuations with rapid recovery to a positive value as the frontal boundary is crossed vertically. This asymmetry of gradients comes from the structure that warm temperature region lies on top of cool temperature region, and can be verified in the skewed probability density function (PDF) of vertical temperature gradient. We try to extract the flow structures and mechanism for the formation and maintenance of the strong temperature front numerically.

Light-front holographic QCD and emerging confinement

DOE PAGES

Brodsky, Stanley J.; de Téramond, Guy F.; Dosch, Hans Günter; ...

2015-05-21

In this study we explore the remarkable connections between light-front dynamics, its holographic mapping to gravity in a higher-dimensional anti-de Sitter (AdS) space, and conformal quantum mechanics. This approach provides new insights into the origin of a fundamental mass scale and the physics underlying confinement dynamics in QCD in the limit of massless quarks. The result is a relativistic light-front wave equation for arbitrary spin with an effective confinement potential derived from a conformal action and its embedding in AdS space. This equation allows for the computation of essential features of hadron spectra in terms of a single scale. Themore » light-front holographic methods described here give a precise interpretation of holographic variables and quantities in AdS space in terms of light-front variables and quantum numbers. This leads to a relation between the AdS wave functions and the boost-invariant light-front wave functions describing the internal structure of hadronic bound-states in physical spacetime. The pion is massless in the chiral limit and the excitation spectra of relativistic light-quark meson and baryon bound states lie on linear Regge trajectories with identical slopes in the radial and orbital quantum numbers. In the light-front holographic approach described here currents are expressed as an infinite sum of poles, and form factors as a product of poles. At large q 2 the form factor incorporates the correct power-law fall-off for hard scattering independent of the specific dynamics and is dictated by the twist. At low q 2 the form factor leads to vector dominance. The approach is also extended to include small quark masses. We briefly review in this report other holographic approaches to QCD, in particular top-down and bottom-up models based on chiral symmetry breaking. We also include a discussion of open problems and future applications.« less

PLASMA DIAGNOSTICS OF AN EIT WAVE OBSERVED BY HINODE/EIS AND SDO/AIA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Veronig, A. M.; Kienreich, I. W.; Muhr, N.

2011-12-10

We present plasma diagnostics of an Extreme-Ultraviolet Imaging Telescope (EIT) wave observed with high cadence in Hinode/Extreme-Ultraviolet Imaging Spectrometer (EIS) sit-and-stare spectroscopy and Solar Dynamics Observatory/Atmospheric Imaging Assembly imagery obtained during the HOP-180 observing campaign on 2011 February 16. At the propagating EIT wave front, we observe downward plasma flows in the EIS Fe XII, Fe XIII, and Fe XVI spectral lines (log T Almost-Equal-To 6.1-6.4) with line-of-sight (LOS) velocities up to 20 km s{sup -1}. These redshifts are followed by blueshifts with upward velocities up to -5 km s{sup -1} indicating relaxation of the plasma behind the wave front.more » During the wave evolution, the downward velocity pulse steepens from a few km s{sup -1} up to 20 km s{sup -1} and subsequently decays, correlated with the relative changes of the line intensities. The expected increase of the plasma densities at the EIT wave front estimated from the observed intensity increase lies within the noise level of our density diagnostics from EIS Fe XIII 202/203 A line ratios. No significant LOS plasma motions are observed in the He II line, suggesting that the wave pulse was not strong enough to perturb the underlying chromosphere. This is consistent with the finding that no H{alpha} Moreton wave was associated with the event. The EIT wave propagating along the EIS slit reveals a strong deceleration of a Almost-Equal-To -540 m s{sup -2} and a start velocity of v{sub 0} Almost-Equal-To 590 km s{sup -1}. These findings are consistent with the passage of a coronal fast-mode MHD wave, pushing the plasma downward and compressing it at the coronal base.« less

Unusual spiral wave dynamics in the Kessler-Levine model of an excitable medium.

PubMed

Oikawa, N; Bodenschatz, E; Zykov, V S

2015-05-01

The Kessler-Levine model is a two-component reaction-diffusion system that describes spatiotemporal dynamics of the messenger molecules in a cell-to-cell signaling process during the aggregation of social amoeba cells. An excitation wave arising in the model has a phase wave at the wave back, which simply follows the wave front after a fixed time interval with the same propagation velocity. Generally speaking, the medium excitability and the refractoriness are two important factors which determine the spiral wave dynamics in any excitable media. The model allows us to separate these two factors relatively easily since the medium refractoriness can be changed independently of the medium excitability. For rigidly rotating waves, the universal relationship has been established by using a modified free-boundary approach, which assumes that the front and the back of a propagating wave are thin in comparison to the wave plateau. By taking a finite thickness of the domain boundary into consideration, the validity of the proposed excitability measure has been essentially improved. A novel method of numerical simulation to suppress the spiral wave instabilities is introduced. The trajectories of the spiral tip observed for a long refractory period have been investigated under a systematic variation of the medium refractoriness.

Unusual spiral wave dynamics in the Kessler-Levine model of an excitable medium

NASA Astrophysics Data System (ADS)

Oikawa, N.; Bodenschatz, E.; Zykov, V. S.

2015-05-01

The Kessler-Levine model is a two-component reaction-diffusion system that describes spatiotemporal dynamics of the messenger molecules in a cell-to-cell signaling process during the aggregation of social amoeba cells. An excitation wave arising in the model has a phase wave at the wave back, which simply follows the wave front after a fixed time interval with the same propagation velocity. Generally speaking, the medium excitability and the refractoriness are two important factors which determine the spiral wave dynamics in any excitable media. The model allows us to separate these two factors relatively easily since the medium refractoriness can be changed independently of the medium excitability. For rigidly rotating waves, the universal relationship has been established by using a modified free-boundary approach, which assumes that the front and the back of a propagating wave are thin in comparison to the wave plateau. By taking a finite thickness of the domain boundary into consideration, the validity of the proposed excitability measure has been essentially improved. A novel method of numerical simulation to suppress the spiral wave instabilities is introduced. The trajectories of the spiral tip observed for a long refractory period have been investigated under a systematic variation of the medium refractoriness.

Ocean Wave-to-Ice Energy Transfer Determined from Seafloor Pressure and Ice Shelf Seismic Observations

NASA Astrophysics Data System (ADS)

Chen, Z.; Bromirski, P. D.; Gerstoft, P.; Stephen, R. A.; Wiens, D.; Aster, R. C.; Nyblade, A.

2017-12-01

Ice shelves play an important role in buttressing land ice from reaching the sea, thus restraining the rate of sea level rise. Long-period gravity wave impacts excite vibrations in ice shelves that may trigger tabular iceberg calving and/or ice shelf collapse events. Three kinds of seismic plate waves were continuously observed by broadband seismic arrays on the Ross Ice Shelf (RIS) and on the Pine Island Glacier (PIG) ice shelf: (1) flexural-gravity waves, (2) flexural waves, and (3) extensional Lamb waves, suggesting that all West Antarctic ice shelves are subjected to similar gravity wave excitation. Ocean gravity wave heights were estimated from pressure perturbations recorded by an ocean bottom differential pressure gauge at the RIS front, water depth 741 m, about 8 km north of an on-ice seismic station that is 2 km from the shelf front. Combining the plate wave spectrum, the frequency-dependent energy transmission and reflection at the ice-water interface were determined. In addition, Young's modulus and Poisson's ratio of the RIS are estimated from the plate wave motions, and compared with the widely used values. Quantifying these ice shelf parameters from observations will improve modeling of ice shelf response to ocean forcing, and ice shelf evolution.

Shock Wave Dynamics in Weakly Ionized Plasmas

NASA Technical Reports Server (NTRS)

Johnson, Joseph A., III

1999-01-01

An investigation of the dynamics of shock waves in weakly ionized argon plasmas has been performed using a pressure ruptured shock tube. The velocity of the shock is observed to increase when the shock traverses the plasma. The observed increases cannot be accounted for by thermal effects alone. Possible mechanisms that could explain the anomalous behavior include a vibrational/translational relaxation in the nonequilibrium plasma, electron diffusion across the shock front resulting from high electron mobility, and the propagation of ion-acoustic waves generated at the shock front. Using a turbulence model based on reduced kinetic theory, analysis of the observed results suggest a role for turbulence in anomalous shock dynamics in weakly ionized media and plasma-induced hypersonic drag reduction.

Numerical techniques for solving nonlinear instability problems in smokeless tactical solid rocket motors. [finite difference technique

NASA Technical Reports Server (NTRS)

Baum, J. D.; Levine, J. N.

1980-01-01

The selection of a satisfactory numerical method for calculating the propagation of steep fronted shock life waveforms in a solid rocket motor combustion chamber is discussed. A number of different numerical schemes were evaluated by comparing the results obtained for three problems: the shock tube problems; the linear wave equation, and nonlinear wave propagation in a closed tube. The most promising method--a combination of the Lax-Wendroff, Hybrid and Artificial Compression techniques, was incorporated into an existing nonlinear instability program. The capability of the modified program to treat steep fronted wave instabilities in low smoke tactical motors was verified by solving a number of motor test cases with disturbance amplitudes as high as 80% of the mean pressure.

High Data Density Temperature Measurement for Quasi Steady-State Flows

NASA Technical Reports Server (NTRS)

Mercer, C. R.; Rashidnia, N.; Creath, K.

1996-01-01

A new optical instrument, the liquid crystal point diffraction interferometer (LCPDI), is used to measure the temperature distribution across a heated chamber filled with silicone oil. Data taken using the LCPDI are compared to equivalent measurements made with a traversing thermo-couple and the two data sets show excellent agreement. This instrument maintains the compact, robust design of Linniks point diffraction interferometer and adds to it phase stepping capability for quantitative interferogram analysis. The result is a compact, simple to align, environmentally insensitive interferometer capable of accurately measuring optical wave-fronts with very high data density and with automated data reduction.

The role of conductivity discontinuities in design of cardiac defibrillation

NASA Astrophysics Data System (ADS)

Lim, Hyunkyung; Cun, Wenjing; Wang, Yue; Gray, Richard A.; Glimm, James

2018-01-01

Fibrillation is an erratic electrical state of the heart, of rapid twitching rather than organized contractions. Ventricular fibrillation is fatal if not treated promptly. The standard treatment, defibrillation, is a strong electrical shock to reinitialize the electrical dynamics and allow a normal heart beat. Both the normal and the fibrillatory electrical dynamics of the heart are organized into moving wave fronts of changing electrical signals, especially in the transmembrane voltage, which is the potential difference between the cardiac cellular interior and the intracellular region of the heart. In a normal heart beat, the wave front motion is from bottom to top and is accompanied by the release of Ca ions to induce contractions and pump the blood. In a fibrillatory state, these wave fronts are organized into rotating scroll waves, with a centerline known as a filament. Treatment requires altering the electrical state of the heart through an externally applied electrical shock, in a manner that precludes the existence of the filaments and scroll waves. Detailed mechanisms for the success of this treatment are partially understood, and involve local shock-induced changes in the transmembrane potential, known as virtual electrode alterations. These transmembrane alterations are located at boundaries of the cardiac tissue, including blood vessels and the heart chamber wall, where discontinuities in electrical conductivity occur. The primary focus of this paper is the defibrillation shock and the subsequent electrical phenomena it induces. Six partially overlapping causal factors for defibrillation success are identified from the literature. We present evidence in favor of five of these and against one of them. A major conclusion is that a dynamically growing wave front starting at the heart surface appears to play a primary role during defibrillation by critically reducing the volume available to sustain the dynamic motion of scroll waves; in contrast, virtual electrodes occurring at the boundaries of small, isolated blood vessels only cause minor effects. As a consequence, we suggest that the size of the heart (specifically, the surface to volume ratio) is an important defibrillation variable.

Areal Mass Oscillations in Planar Targets Due to Feedout: Theory and Simulations.

NASA Astrophysics Data System (ADS)

Velikovich, A. L.; Schmitt, A. J.; Karasik, M.; Obenschain, S. P.; Serlin, V.; Pawley, C. J.; Gardner, J. H.; Aglitskiy, Y.; Metzler, N.

2001-10-01

When a planar shock wave breaks out at a rippled rear surface of a laser-driven target, the lateral pressure gradient in a rippled rarefaction wave propagating back to the front surface causes a lateral mass redistribution that reverses the phase of mass variation. If the driving laser pulse has no foot, then the RT growth, starting when the rarefaction wave reaches the front surface, causes the second phase reversal of mass variation, and continues at the initial phase, as consistently observed in feedout experiments on Nike. A foot of the laser pulse can cause an early phase reversal of mass variation, making the strong shock wave driven by the main pulse interact with a density variation in a rippled rarefaction wave rather than with static rear surface ripples. Theory and simulations predict that this interaction can make the phase of mass variation reverse one or three times. Then the phase of the RT growing mode would be opposite to that of the initial mass variation.

Passive front-ends for wideband millimeter wave electronic warfare

NASA Astrophysics Data System (ADS)

Jastram, Nathan Joseph

This thesis presents the analysis, design and measurements of novel passive front ends of interest to millimeter wave electronic warfare systems. However, emerging threats in the millimeter waves (18 GHz and above) has led to a push for new systems capable of addressing these threats. At these frequencies, traditional techniques of design and fabrication are challenging due to small size, limited bandwidth and losses. The use of surface micromachining technology for wideband direction finding with multiple element antenna arrays for electronic support is demonstrated. A wideband tapered slot antenna is first designed and measured as an array element for the subsequent arrays. Both 18--36 GHz and 75--110 GHz amplitude only and amplitude/phase two element direction finding front ends are designed and measured. The design of arrays using Butler matrix and Rotman lens beamformers for greater than two element direction finding over W band and beyond using is also presented. The design of a dual polarized high power capable front end for electronic attack over an 18--45 GHz band is presented. To combine two polarizations into the same radiating aperture, an orthomode transducer (OMT) based upon a new double ridge waveguide cross section is developed. To provide greater flexibility in needed performance characteristics, several different turnstile junction matching sections are tested. A modular horn section is proposed to address flexible and ever changing operational requirements, and is designed for performance criteria such as constant gain, beamwidth, etc. A multi-section branch guide coupler and low loss Rotman lens based upon the proposed cross section are also developed. Prototyping methods for the herein designed millimeter wave electronic warfare front ends are investigated. Specifically, both printed circuit board (PCB) prototyping of micromachined systems and 3D printing of conventionally machined horns are presented. A 4--8 GHz two element array with integrated beamformer fabricated using the stacking of PCB boards is shown, and measured results compare favorably with the micromachined front ends. A 3D printed small aperture horn is compared with a conventionally machined horn, and measured results show similar performance with a ten-fold reduction in cost and weight.

Using the analysis of stress waves to build research for experimentation on ultrasonic film measurement

NASA Astrophysics Data System (ADS)

Chang, Shi-Shing; Wu, John H.

1993-09-01

After the 2th world war, although the application of ultrasonic wave in industries is becoming more and more popular. But due to the restriction of the precise equivelent , experimental method and the support of the basic theoremsetc. Ultrasonic wave is not applied in precise measurement. Nowadays due to many conditions - the improvement in the production technic, the precise of the equivelent, causes to increase the application of ultrasonic wave. But it's still limited due to the lack of measurement and analysis theorem. In this paper, first we caculate translation of the stress wave (elastic wave) in material for the free surface of material by a normal impulse load. as the theorem analysis base in real application. It is applied to an experiment of film measurement. We can find the partical motion in material and the arriving time of wave front. Then we can estimate the thickness of layers and can prove the actual condition with the result of experiment. This resarch is not only in the theoretical investigation but also in setting overall the measurement system, and excutes the following three experiments: the thickness measurement of two layers, the thickness measurement of film material. the thickness measurement of air propagation. About the data processing, we relied on the frequency analysis to evalute the time difference of two overlapped ultrasonic wave signal. in the meanwhile. we also designed several computer programs to assist the sonic wave identification and signal analysis.

Dynamic properties of ceramic materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grady, D.E.

1995-02-01

The present study offers new data and analysis on the transient shock strength and equation-of-state properties of ceramics. Various dynamic data on nine high strength ceramics are provided with wave profile measurements, through velocity interferometry techniques, the principal observable. Compressive failure in the shock wave front, with emphasis on brittle versus ductile mechanisms of deformation, is examined in some detail. Extensive spall strength data are provided and related to the theoretical spall strength, and to energy-based theories of the spall process. Failure waves, as a mechanism of deformation in the transient shock process, are examined. Strength and equation-of-state analysis ofmore » shock data on silicon carbide, boron carbide, tungsten carbide, silicon dioxide and aluminum nitride is presented with particular emphasis on phase transition properties for the latter two. Wave profile measurements on selected ceramics are investigated for evidence of rate sensitive elastic precursor decay in the shock front failure process.« less

Second sound shock waves and critical velocities in liquid helium 2. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Turner, T. N.

1979-01-01

Large amplitude second-sound shock waves were generated and the experimental results compared to the theory of nonlinear second-sound. The structure and thickness of second-sound shock fronts are calculated and compared to experimental data. Theoretically it is shown that at T = 1.88 K, where the nonlinear wave steepening vanishes, the thickness of a very weak shock must diverge. In a region near this temperature, a finite-amplitude shock pulse evolves into an unusual double-shock configuration consisting of a front steepened, temperature raising shock followed by a temperature lowering shock. Double-shocks are experimentally verified. It is experimentally shown that very large second-sound shock waves initiate a breakdown in the superfluidity of helium 2, which is dramatically displayed as a limit to the maximum attainable shock strength. The value of the maximum shock-induced relative velocity represents a significant lower bound to the intrinsic critical velocity of helium 2.

Quick reproduction of blast-wave flow-field properties of nuclear, TNT, and ANFO explosions

NASA Astrophysics Data System (ADS)

Groth, C. P. T.

1986-04-01

In many instances, extensive blast-wave flow-field properties are required in gasdynamics research studies of blast-wave loading and structure response, and in evaluating the effects of explosions on their environment. This report provides a very useful computer code, which can be used in conjunction with the DNA Nuclear Blast Standard subroutines and code, to quickly reconstruct complete and fairly accurate blast-wave data for almost any free-air (spherical) and surface-burst (hemispherical) nuclear, trinitrotoluene (TNT), or ammonium nitrate-fuel oil (ANFO) explosion. This code is capable of computing all of the main flow properties as functions of radius and time, as well as providing additional information regarding air viscosity, reflected shock-wave properties, and the initial decay of the flow properties just behind the shock front. Both spatial and temporal distributions of the major blast-wave flow properties are also made readily available. Finally, provisions are also included in the code to provide additional information regarding the peak or shock-front flow properties over a range of radii, for a specific explosion of interest.

Detonation suppression in hydrogen-air mixtures using porous coatings on the walls

NASA Astrophysics Data System (ADS)

Bivol, G. Yu.; Golovastov, S. V.; Golub, V. V.

2018-05-01

We considered the problem of detonation suppression and weakening of blast wave effects occurring during the combustion of hydrogen-air mixtures in confined spaces. The gasdynamic processes during combustion of hydrogen, an alternative environmentally friendly fuel, were also considered. Detonation decay and flame propagation in hydrogen-air mixtures were experimentally investigated in rectangular cross-section channels with solid walls and two types of porous coatings: steel wool and polyurethane foam. Shock wave pressure dynamics inside the section with porous coating were studied using pressure sensors; flame front propagation was studied using photodiodes and high-speed camera visualization. For all mixtures, the detonation wave formed before entering the section with porous coating. For both porous materials, the steady detonation wave decoupled in the porous section of the channel into a shock wave and flame front propagating with a velocity around the Chapman-Jouguet acoustic velocity. By the end of the porous section, shock wave pressure reductions of 70 and 85% were achieved for the polyurethane foam and steel wool, respectively. The dependence of the flame velocity on the mixture composition (equivalence ratio) is presented.

Non-filamentated ultra-intense and ultra-short pulse fronts in three-dimensional Raman seed amplification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lehmann, G.; Spatschek, K. H.

Ultra-intense and ultra-short laser pulses may be generated up to the exawatt-zetawatt regime due to parametric processes in plasmas. The minimization of unwanted plasma processes leads to operational limits which are discussed here with respect to filamentation. Transverse filamentation, which originally was derived for plane waves, is being investigated for seed pulse propagation in the so called π-pulse limit. A three-dimensional (3D) three-wave-interaction model is the basis of the present investigation. To demonstrate the applicability of the three-wave-interaction model, the 1D pulse forms are compared with those obtained from 1D particle in cell and Vlasov simulations. Although wave-breaking may occur,more » the kinetic simulations show that the leading pumped pulse develops a form similar to that obtained from the three-wave-interaction model. In the main part, 2D and 3D filamentation processes of (localized) pulses are investigated with the three-wave-interaction model. It is shown that the leading pulse front can stay filamentation-free, whereas the rear parts show transverse modulations.« less

Sivers and cos 2 ϕ asymmetries in semi-inclusive deep inelastic scattering in light-front holographic model

NASA Astrophysics Data System (ADS)

Maji, Tanmay; Chakrabarti, Dipankar; Mukherjee, Asmita

2018-01-01

The spin asymmetries in SIDIS associated with T -odd TMDs are presented in a light-front quark-diquark model of a proton. To incorporate the effects of the final-state interaction, the light front wave functions are modified to have a phase factor which is essential to have Sivers or Boer-Mulders functions. The Sivers and Boer-Mulder asymmetries are compared with HERMES and COMPASS data.

Generation of Wind Waves in the Persian Gulf: A Numerical Investigation

NASA Astrophysics Data System (ADS)

Liao, Y.; Kaihatu, J. M.

2010-12-01

The Persian Gulf is a long shallow basin located between the Arabian Peninsula and Iran. Wind-wave generation processes in the region are often affected by the shamal, a strong wind caused by the passage of cold fronts over the mountains of Turkey and Kurdistan. This can set up sudden energetic wind seas, hampering marine traffic. It is not immediately clear whether present wind-wave models can predict this intense, short-term growth and evolution under these conditions. Furthermore, few wave measurements or models studies have been performed in this area. In advance of a wind-wave generation experiment to be conducted off the Qatar coast, we performed a climatological study of the wind wave environment in the Persian Gulf. Using the SWAN wave model as a baseline of the state of the art, five years (2004-2008)of wind field model hindcasts from COAMPS are used as forcing.To investigate the sensitivity of the results to bathymetry, the climatological analysis was run twice more, with refraction or wave breaking deactivated, in turn. The results do not show significant differences with and without refraction, which implies the wind-wave process in Persian Gulf is less dominated by the variation of bathymetry. However the results show that a large amount of wave is dissipated by wave breaking. Wide, flat and shallow bathymetry in Persian Gulf results in a long-fetch scenario, particularly for waves arriving from the northwest. It implies that long period wind-generated waves can be fully generated in this region. Wave height is therefore fully grown by the long-fetch condition, so as to lead in higher possibility of wave breaking and energy dissipation.

Subduction beneath Laurentia modified the eastern North American cratonic edge: Evidence from P wave and S wave tomography

NASA Astrophysics Data System (ADS)

Boyce, A.; Bastow, I. D.; Darbyshire, F. A.; Ellwood, A. G.; Gilligan, A.; Levin, V.; Menke, W.

2016-07-01

The cratonic cores of the continents are remarkably stable and long-lived features. Their ability to resist destructive tectonic processes is associated with their thick (˜250 km), cold, chemically depleted, buoyant lithospheric keels that isolate the cratons from the convecting mantle. The formation mechanism and tectonic stability of cratonic keels remains under debate. To address this issue, we use P wave and S wave relative arrival-time tomography to constrain upper mantle structure beneath southeast Canada and the northeast USA, a region spanning three quarters of Earth's geological history. Our models show three distinct, broad zones: Seismic wave speeds increase systematically from the Phanerozoic coastal domains, through the Proterozoic Grenville Province, and to the Archean Superior craton in central Québec. We also recover the NW-SE trending track of the Great Meteor hot spot that crosscuts the major tectonic domains. The decrease in seismic wave speed from Archean to Proterozoic domains across the Grenville Front is consistent with predictions from models of two-stage keel formation, supporting the idea that keel growth may not have been restricted to Archean times. However, while crustal structure studies suggest that Archean Superior material underlies Grenvillian age rocks up to ˜300 km SE of the Grenville Front, our tomographic models show a near-vertical boundary in mantle wave speed directly beneath the Grenville Front. We interpret this as evidence for subduction-driven metasomatic enrichment of the Laurentian cratonic margin, prior to keel stabilization. Variable chemical depletion levels across Archean-Proterozoic boundaries worldwide may thus be better explained by metasomatic enrichment than inherently less depleted Proterozoic composition at formation.

Thermodynamic and Optical Response of Multiply Shocked Liquid Nitromethane

NASA Astrophysics Data System (ADS)

Flanders, B. M.; Winey, J. M.; Gupta, Y. M.

2015-06-01

To investigate the thermodynamic and optical response of multiply shocked liquids, particle velocity profiles were measured for liquid nitromethane (NM) subjected to stepwise loading to a peak pressure of 10 GPa. Using a multi-point velocity interferometer (VISAR), wave profiles were obtained at both the front and rear interfaces of the thin (200 μm) liquid sample to obtain data regarding the thermodynamic response and the refractive index at the intermediate stepwise loading states, in addition to the peak state. Changes in the apparent velocity at the front sample interface were well accounted for by using a Gladstone-Dale relationship to describe the NM index of refraction. The thermodynamic states of multiply shocked NM were examined by comparing the measured wave profiles to those calculated using a published NM equation of state. Although the calculated and measured particle velocity states are in good overall agreement, comparison of the calculated shock wave reverberation times at the front and rear sample interfaces with the measured values suggests that the published NM equation of state can be improved. Work supported by DOE/NNSA.

Implementation of the pyramid wavefront sensor as a direct phase detector for large amplitude aberrations

NASA Astrophysics Data System (ADS)

Kupke, Renate; Gavel, Don; Johnson, Jess; Reinig, Marc

2008-07-01

We investigate the non-modulating pyramid wave-front sensor's (P-WFS) implementation in the context of Lick Observatory's Villages visible light AO system on the Nickel 1-meter telescope. A complete adaptive optics correction, using a non-modulated P-WFS in slope sensing mode as a boot-strap to a regime in which the P-WFS can act as a direct phase sensor is explored. An iterative approach to reconstructing the wave-front phase, given the pyramid wave-front sensor's non-linear signal, is developed. Using Monte Carlo simulations, the iterative reconstruction method's photon noise propagation behavior is compared to both the pyramid sensor used in slope-sensing mode, and the traditional Shack Hartmann sensor's theoretical performance limits. We determine that bootstrapping using the P-WFS as a slope sensor does not offer enough correction to bring the phase residuals into a regime in which the iterative algorithm can provide much improvement in phase measurement. It is found that both the iterative phase reconstructor and the slope reconstruction methods offer an advantage in noise propagation over Shack Hartmann sensors.

Speed hysteresis and noise shaping of traveling fronts in neural fields: role of local circuitry and nonlocal connectivity

NASA Astrophysics Data System (ADS)

Capone, Cristiano; Mattia, Maurizio

2017-01-01

Neural field models are powerful tools to investigate the richness of spatiotemporal activity patterns like waves and bumps, emerging from the cerebral cortex. Understanding how spontaneous and evoked activity is related to the structure of underlying networks is of central interest to unfold how information is processed by these systems. Here we focus on the interplay between local properties like input-output gain function and recurrent synaptic self-excitation of cortical modules, and nonlocal intermodular synaptic couplings yielding to define a multiscale neural field. In this framework, we work out analytic expressions for the wave speed and the stochastic diffusion of propagating fronts uncovering the existence of an optimal balance between local and nonlocal connectivity which minimizes the fluctuations of the activation front propagation. Incorporating an activity-dependent adaptation of local excitability further highlights the independent role that local and nonlocal connectivity play in modulating the speed of propagation of the activation and silencing wavefronts, respectively. Inhomogeneities in space of local excitability give raise to a novel hysteresis phenomenon such that the speed of waves traveling in opposite directions display different velocities in the same location. Taken together these results provide insights on the multiscale organization of brain slow-waves measured during deep sleep and anesthesia.

Longshore Sediment Transport Rate Calculated Incorporating Wave Orbital Velocity Fluctuations

DTIC Science & Technology

2006-09-01

distribution of longshore sediment transport in the surf zone is necessary in the design and planning of groins, jetties, weirs and pipeline landfalls...transported by any current. Breaker height is defined as the vertical distance between the wave crest and the preceding wave trough at incipient...terminology; spilling breakers occur if the wave crest becomes unstable and flows down the front face of the wave producing a foamy water surface; plunging

On the relationship between satellite-retrieved surface temperature fronts and chlorophyll a in the western South Atlantic

NASA Astrophysics Data System (ADS)

Saraceno, Martin; Provost, Christine; Piola, Alberto R.

2005-11-01

The time-space distribution of chlorophyll a in the southwestern Atlantic is examined using 6 years (1998-2003) of sea surface color images from Sea-viewing Wide Field of View Sensor (SeaWiFS). Chlorophyll a (chl a) distribution is confronted with sea surface temperature (SST) fronts retrieved from satellite imagery. Histogram analysis of the color, SST, and SST gradient data sets provides a simple procedure for pixel classification from which eight biophysical regions in the SWA are identified, including three new regions with regard to Longhurst (1998) work: Patagonian Shelf Break (PSB), Brazil Current Overshoot, and Zapiola Rise region. In the PSB region, coastal-trapped waves are suggested as a possible mechanism leading to the intraseasonal frequencies observed in SST and chl a. Mesoscale activity associated with the Brazil Current Front and, in particular, eddies drifting southward is probably responsible for the high chl a values observed throughout the Brazil Current Overshoot region. The Zapiola Rise is characterized by a local minimum in SST gradient magnitudes and shows chl a maximum values in February, 3 months later than the austral spring bloom of the surroundings. Significant interannual variability is present in the color imagery. In the PSB, springs and summers with high chl a concentrations seem associated with stronger local northerly wind speed, and possible mechanisms are discussed. Finally, the Brazil-Malvinas front is detected using both SST gradient and SeaWiFS images. The time-averaged position of the front at 54.2°W is estimated at 38.9°S and its alongshore migration of about 300 km.

Quadrupedal gaits in hexapod animals - inter-leg coordination in free-walking adult stick insects.

PubMed

Grabowska, Martyna; Godlewska, Elzbieta; Schmidt, Joachim; Daun-Gruhn, Silvia

2012-12-15

The analysis of inter-leg coordination in insect walking is generally a study of six-legged locomotion. For decades, the stick insect Carausius morosus has been instrumental for unravelling the rules and mechanisms that control leg coordination in hexapeds. We analysed inter-leg coordination in C. morosus that freely walked on straight paths on plane surfaces with different slopes. Consecutive 1.7 s sections were assigned inter-leg coordination patterns (which we call gaits) based on footfall patterns. Regular gaits, i.e. wave, tetrapod or tripod gaits, occurred in different proportions depending on surface slopes. Tetrapod gaits were observed most frequently, wave gaits only occurred on 90 deg inclining slopes and tripod gaits occurred most often on 15 deg declining slopes, i.e. in 40% of the sections. Depending on the slope, 36-66% of the sections were assigned irregular gaits. Irregular gaits were mostly due to multiple stepping by the front legs, which is perhaps probing behaviour, not phase coupled to the middle legs' cycles. In irregular gaits, middle leg and hindleg coordination was regular, related to quadrupedal walk and wave gaits. Apparently, front legs uncouple from and couple to the walking system without compromising middle leg and hindleg coordination. In front leg amputees, the remaining legs were strictly coordinated. In hindleg and middle leg amputees, the front legs continued multiple stepping. The coordination of middle leg amputees was maladapted, with front legs and hindlegs performing multiple steps or ipsilateral legs being in simultaneous swing. Thus, afferent information from middle legs might be necessary for a regular hindleg stepping pattern.

Binary full adder, made of fusion gates, in a subexcitable Belousov-Zhabotinsky system

NASA Astrophysics Data System (ADS)

Adamatzky, Andrew

2015-09-01

In an excitable thin-layer Belousov-Zhabotinsky (BZ) medium a localized perturbation leads to the formation of omnidirectional target or spiral waves of excitation. A subexcitable BZ medium responds to asymmetric local perturbation by producing traveling localized excitation wave-fragments, distant relatives of dissipative solitons. The size and life span of an excitation wave-fragment depend on the illumination level of the medium. Under the right conditions the wave-fragments conserve their shape and velocity vectors for extended time periods. I interpret the wave-fragments as values of Boolean variables. When two or more wave-fragments collide they annihilate or merge into a new wave-fragment. States of the logic variables, represented by the wave-fragments, are changed in the result of the collision between the wave-fragments. Thus, a logical gate is implemented. Several theoretical designs and experimental laboratory implementations of Boolean logic gates have been proposed in the past but little has been done cascading the gates into binary arithmetical circuits. I propose a unique design of a binary one-bit full adder based on a fusion gate. A fusion gate is a two-input three-output logical device which calculates the conjunction of the input variables and the conjunction of one input variable with the negation of another input variable. The gate is made of three channels: two channels cross each other at an angle, a third channel starts at the junction. The channels contain a BZ medium. When two excitation wave-fragments, traveling towards each other along input channels, collide at the junction they merge into a single wave-front traveling along the third channel. If there is just one wave-front in the input channel, the front continues its propagation undisturbed. I make a one-bit full adder by cascading two fusion gates. I show how to cascade the adder blocks into a many-bit full adder. I evaluate the feasibility of my designs by simulating the evolution of excitation in the gates and adders using the numerical integration of Oregonator equations.

The formation and evolution of reconnection-driven, slow-mode shocks in a partially ionised plasma

NASA Astrophysics Data System (ADS)

Hillier, A.; Takasao, S.; Nakamura, N.

2016-06-01

The role of slow-mode magnetohydrodynamic (MHD) shocks in magnetic reconnection is of great importance for energy conversion and transport, but in many astrophysical plasmas the plasma is not fully ionised. In this paper, we use numerical simulations to investigate the role of collisional coupling between a proton-electron, charge-neutral fluid and a neutral hydrogen fluid for the one-dimensional (1D) Riemann problem initiated in a constant pressure and density background state by a discontinuity in the magnetic field. This system, in the MHD limit, is characterised by two waves. The first is a fast-mode rarefaction wave that drives a flow towards a slow-mode MHD shock wave. The system evolves through four stages: initiation, weak coupling, intermediate coupling, and a quasi-steady state. The initial stages are characterised by an over-pressured neutral region that expands with characteristics of a blast wave. In the later stages, the system tends towards a self-similar solution where the main drift velocity is concentrated in the thin region of the shock front. Because of the nature of the system, the neutral fluid is overpressured by the shock when compared to a purely hydrodynamic shock, which results in the neutral fluid expanding to form the shock precursor. Once it has formed, the thickness of the shock front is proportional to ξ I-1.2 , which is a smaller exponent than would be naively expected from simple scaling arguments. One interesting result is that the shock front is a continuous transition of the physical variables of subsonic velocity upstream of the shock front (a c-shock) to a sharp jump in the physical variables followed by a relaxation to the downstream values for supersonic upstream velocity (a j-shock). The frictional heating that results from the velocity drift across the shock front can amount to ~2 per cent of the reference magnetic energy.

Monochromatic plane-fronted waves in conformal gravity are pure gauge

NASA Astrophysics Data System (ADS)

Fabbri, Luca; Paranjape, M. B.

2011-05-01

We consider plane-fronted, monochromatic gravitational waves on a Minkowski background, in a conformally invariant theory of general relativity. By this we mean waves of the form: gμν=ημν+γμνF(k·x), where γμν is a constant polarization tensor, and kμ is a lightlike vector. We also assume the coordinate gauge condition |g|-1/4∂τ(|g|1/4gστ)=0 which is the conformal analog of the harmonic gauge condition gμνΓμνσ=-|g|-1/2∂τ(|g|1/2gστ)=0, where det⁡[gμν]≡g. Requiring additionally the conformal gauge condition g=-1 surprisingly implies that the waves are both transverse and traceless. Although the ansatz for the metric is eminently reasonable when considering perturbative gravitational waves, we show that the metric is reducible to the metric of Minkowski space-time via a sequence of coordinate transformations which respect the gauge conditions, without any perturbative approximation that γμν be small. This implies that we have, in fact, exact plane-wave solutions; however, they are simply coordinate/conformal artifacts. As a consequence, they carry no energy. Our result does not imply that conformal gravity does not have gravitational wave phenomena. A different, more generalized ansatz for the deviation, taking into account the fourth-order nature of the field equation, which has the form gμν=ημν+Bμν(n·x)G(k·x), indeed yields waves which carry energy and momentum [P. D. Mannheim, Gen. Relativ. Gravit.GRGVA80001-7701 43, 703 (2010)10.1007/s10714-010-1088-z]. It is just surprising that transverse, traceless, plane-fronted gravitational waves, those that would be used in any standard, perturbative, quantum analysis of the theory, simply do not exist.

Jet-front systems nearing strongly stratified region in differentially heated, rotating stratified annulus

NASA Astrophysics Data System (ADS)

Rolland, Joran; Achatz, Ulrich

2017-04-01

The differentially heated, rotating annulus configuration has been used for a long time as a model system of the earth troposphere. It can easily reproduce thermal wind and baroclinic waves in the laboratory. It has recently been shown numerically that provided the Rossby number, the rotation rate and the Brunt-Väisälä frequency were well chosen, this configuration also reproduces the spontaneous emission of gravity waves by jet front systems [1]. This offers a very practical configuration in which to study an important process of emission of atmospheric gravity waves. It has also been shown experimentally that this configuration can be modified in order to add the possibility for the emitted wave to reach a strongly stratified region [2]. It thus creates a system containing a model troposphere where gravity waves are spontaneously emitted and can propagate to a model stratosphere. For this matter a stratification was created using a salinity gradient in the experimental apparatus. Through double diffusion, this generates a strongly stratified layer in the middle of the flow (the model stratosphere) and two weakly stratified region in the top and bottom layers (the model troposphere). In this poster, we present simulations of this configuration displaying baroclinic waves in the top and bottom layers. We aim at creating jet front systems strong enough that gravity waves can be spontaneously emitted. This will thus offer the possibility of studying the wave characteristic and mechanisms in emission and propagation in details. References [1] S. Borchert, U. Achatz, M.D. Fruman, Spontaneous Gravity wave emission in the differentially heated annulus, J. Fluid Mech. 758, 287-311 (2014). [2] M. Vincze, I. Borcia, U. Harlander, P. Le Gal, Double-diffusive convection convection and baroclinic instability in a differentially heated and initially stratified rotating system: the barostrat instability, Fluid Dyn. Res. 48, 061414 (2016).

Analysis of the dependence of surfatron acceleration of electrons by an electromagnetic wave in space plasma on the particle momentum along the wave front

DOE Office of Scientific and Technical Information (OSTI.GOV)

Erokhin, A. N., E-mail: nerokhin@mx.iki.rssi.ru; Zol’nikova, N. N.; Erokhin, N. S.

Based on the numerical solution of the nonlinear nonstationary second-order equation for the wave phase on the particle trajectory, the dynamics of surfatron acceleration of electrons by an electromagnetic wave propagating across the external magnetic field in space plasma is analyzed as a function of the electron momentum along the wave front. Numerical calculations show that, for strongly relativistic initial values of the electron momentum component along the wave front g{sub y}(0) (the other parameters of the problem being the same), electrons are trapped into the regime of ultrarelativistic surfatron acceleration within a certain interval of the initial wave phasemore » Ψ(0) on the particle trajectory. It is assumed in the calculations that vertical bar Ψ(0) vertical bar ≤ π. For strongly relativistic values of g{sub y}(0), electrons are immediately trapped by the wave for 19% of the initial values of the phase Ψ(0) (favorable phases). For the rest of the values of Ψ(0), trapping does not occur even at long times. This circumstance substantially simplifies estimations of the wave damping due to particle acceleration in subsequent calculations. The dynamics of the relativistic factor and the components of the electron velocity and momentum under surfatron acceleration is also analyzed. The obtained results are of interest for the development of modern concepts of possible mechanisms of generation of ultrarelativistic particle fluxes in relatively calm space plasma, as well as for correct interpretation of observational data on the fluxes of such particles and explanation of possible reasons for the deviation of ultrarelativistic particle spectra detected in the heliosphere from the standard power-law scalings and the relation of these variations to space weather and large-scale atmospheric processes similar to tropical cyclones.« less

RELATIVISTIC MAGNETOHYDRODYNAMICS: RENORMALIZED EIGENVECTORS AND FULL WAVE DECOMPOSITION RIEMANN SOLVER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anton, Luis; MartI, Jose M; Ibanez, Jose M

2010-05-01

We obtain renormalized sets of right and left eigenvectors of the flux vector Jacobians of the relativistic MHD equations, which are regular and span a complete basis in any physical state including degenerate ones. The renormalization procedure relies on the characterization of the degeneracy types in terms of the normal and tangential components of the magnetic field to the wave front in the fluid rest frame. Proper expressions of the renormalized eigenvectors in conserved variables are obtained through the corresponding matrix transformations. Our work completes previous analysis that present different sets of right eigenvectors for non-degenerate and degenerate states, andmore » can be seen as a relativistic generalization of earlier work performed in classical MHD. Based on the full wave decomposition (FWD) provided by the renormalized set of eigenvectors in conserved variables, we have also developed a linearized (Roe-type) Riemann solver. Extensive testing against one- and two-dimensional standard numerical problems allows us to conclude that our solver is very robust. When compared with a family of simpler solvers that avoid the knowledge of the full characteristic structure of the equations in the computation of the numerical fluxes, our solver turns out to be less diffusive than HLL and HLLC, and comparable in accuracy to the HLLD solver. The amount of operations needed by the FWD solver makes it less efficient computationally than those of the HLL family in one-dimensional problems. However, its relative efficiency increases in multidimensional simulations.« less

Schwarzschild camera

NASA Technical Reports Server (NTRS)

1980-01-01

The fabrication procedures for the primary and secondary mirrors for a Schwarzschild camera are summarized. The achieved wave front for the telescope was 1/2 wave at .63 microns. Interferograms of the two mirrors as a system are given and the mounting procedures are outlined.

Liquid-Crystal Point-Diffraction Interferometer for Wave-Front Measurements

NASA Technical Reports Server (NTRS)

Mercer, Carolyn R.; Creath, Katherine

1996-01-01

A new instrument, the liquid-crystal point-diffraction interferometer (LCPDI), is developed for the measurement of phase objects. This instrument maintains the compact, robust design of Linnik's point-diffraction interferometer and adds to it a phase-stepping capability for quantitative interferogram analysis. The result is a compact, simple to align, environmentally insensitive interferometer capable of accurately measuring optical wave fronts with very high data density and with automated data reduction. We describe the theory and design of the LCPDI. A focus shift was measured with the LCPDI, and the results are compared with theoretical results,

Modularization of gradient-index optical design using wavefront matching enabled optimization.

PubMed

Nagar, Jogender; Brocker, Donovan E; Campbell, Sawyer D; Easum, John A; Werner, Douglas H

2016-05-02

This paper proposes a new design paradigm which allows for a modular approach to replacing a homogeneous optical lens system with a higher-performance GRadient-INdex (GRIN) lens system using a WaveFront Matching (WFM) method. In multi-lens GRIN systems, a full-system-optimization approach can be challenging due to the large number of design variables. The proposed WFM design paradigm enables optimization of each component independently by explicitly matching the WaveFront Error (WFE) of the original homogeneous component at the exit pupil, resulting in an efficient design procedure for complex multi-lens systems.

Combined approach to the Hubble Space Telescope wave-front distortion analysis

NASA Astrophysics Data System (ADS)

Roddier, Claude; Roddier, Francois

1993-06-01

Stellar images taken by the HST at various focus positions have been analyzed to estimate wave-front distortion. Rather than using a single algorithm, we found that better results were obtained by combining the advantages of various algorithms. For the planetary camera, the most accurate algorithms consistently gave a spherical aberration of -0.290-micron rms with a maximum deviation of 0.005 micron. Evidence was found that the spherical aberration is essentially produced by the primary mirror. The illumination in the telescope pupil plane was reconstructed and evidence was found for a slight camera misalignment.

Numerical Modeling of Infragravity Wave Runup on Steep and Mildly Sloping Natural Beaches

NASA Astrophysics Data System (ADS)

Fiedler, J. W.; Smit, P.; Brodie, K. L.; McNinch, J.; Guza, R. T.; Gallien, T.

2016-12-01

We present ongoing work which aims to validate the non-hydrostatic model SWASH for wave runup and infragravity waves generated by a range of different incident wave spectra at the offshore boundary, including the effect of finite directional spread. Flume studies of wave runup are limited to normally incident (1D) sea and infragravity waves, but natural waves are directionally spread (2D), with substantially different dynamics from 1D. For example, refractive trapping (edge waves) is only possible with 2D waves, and the bound infragravity wave response to short wave groups is highly amplified for the special case of normal incidence. Selected case studies are modeled at Agate Beach, Oregon, a low slope (1:80) beach with maximum offshore wave heights greater than 7m, and Cardiff, California, a steep (1:8) beach with maximum wave heights of 2m. Peak periods ranged between 5-20 s at both sites. On both beaches, waves were measured on a transect from approximately 10m depth to the runup, using pressure sensors, current meters, and a scanning lidar. Bulk short wave quantities, wave runup, infragravity frequency spectra and energy fluxes are compared with SWASH. On the low slope beach with energetic incident waves, the observed horizontal runup excursions reach 140m ( 100s periods). Swash front velocities reached up to several m/s, causing short waves to stack up during runup drawdown. On reversal of the infragravity phase, the stacked short waves are swept onshore with the long wave front, effectively enhancing runup by phase coupling long and short waves. Statistical variability and nonlinearity in swash generation lead to time-varying runup heights. Here, we test these observations with 2D SWASH, as well as the sensitivity of modeled runup to the parameterization of bottom friction.

Production of confluent hypergeometric beam by computer-generated hologram

NASA Astrophysics Data System (ADS)

Chen, Jiannong; Wang, Gang; Xu, Qinfeng

2011-02-01

Because of their spiral wave front, phase singularity, zero-intensity center and orbital angular momentum, dark hollow vortex beams have been found many applications in the field of atom optics such as atom cooling, atom transport and atom guiding. In this paper, a method for generating confluent hypergeometric beam by computer-generated hologram displayed on the spatial light modulator is presented. The hologram is formed by interference between a single ring Laguerre-Gaussian beam and a plane wave. The far-field Fraunhofer diffraction of this optical field transmitted from the hologram is the confluent hypergeometric beam. This beam is a circular symmetric beam which has a phase singularity, spiral wave front, zero-intensity center, and intrinsic orbital angular momentum. It is a new dark hollow vortex beam.

Transient response of a liquid injector to a steep-fronted transverse pressure wave

NASA Astrophysics Data System (ADS)

Lim, D.; Heister, S.; Stechmann, D.; Kan, B.

2017-12-01

Motivated by the dynamic injection environment posed by unsteady pressure gain combustion processes, an experimental apparatus was developed to visualize the dynamic response of a transparent liquid injector subjected to a single steep-fronted transverse pressure wave. Experiments were conducted at atmospheric pressure with a variety of acrylic injector passage designs using water as the working fluid. High-speed visual observations were made of the injector exit near field, and the extent of backflow and the time to refill the orifice passage were characterized over a range of injection pressures. A companion transient one-dimensional model was developed for interpretation of the results and to elucidate the trends with regard to the strength of the transverse pressure wave. Results from the model were compared with the experimental observations.

Ionization waves of arbitrary velocity driven by a flying focus

NASA Astrophysics Data System (ADS)

Palastro, J. P.; Turnbull, D.; Bahk, S.-W.; Follett, R. K.; Shaw, J. L.; Haberberger, D.; Bromage, J.; Froula, D. H.

2018-03-01

A chirped laser pulse focused by a chromatic lens exhibits a dynamic, or flying, focus in which the trajectory of the peak intensity decouples from the group velocity. In a medium, the flying focus can trigger an ionization front that follows this trajectory. By adjusting the chirp, the ionization front can be made to travel at an arbitrary velocity along the optical axis. We present analytical calculations and simulations describing the propagation of the flying focus pulse, the self-similar form of its intensity profile, and ionization wave formation. The ability to control the speed of the ionization wave and, in conjunction, mitigate plasma refraction has the potential to advance several laser-based applications, including Raman amplification, photon acceleration, high-order-harmonic generation, and THz generation.

Transient response of a liquid injector to a steep-fronted transverse pressure wave

NASA Astrophysics Data System (ADS)

Lim, D.; Heister, S.; Stechmann, D.; Kan, B.

2018-07-01

Motivated by the dynamic injection environment posed by unsteady pressure gain combustion processes, an experimental apparatus was developed to visualize the dynamic response of a transparent liquid injector subjected to a single steep-fronted transverse pressure wave. Experiments were conducted at atmospheric pressure with a variety of acrylic injector passage designs using water as the working fluid. High-speed visual observations were made of the injector exit near field, and the extent of backflow and the time to refill the orifice passage were characterized over a range of injection pressures. A companion transient one-dimensional model was developed for interpretation of the results and to elucidate the trends with regard to the strength of the transverse pressure wave. Results from the model were compared with the experimental observations.

Well-defined EUV wave associated with a CME-driven shock

NASA Astrophysics Data System (ADS)

Cunha-Silva, R. D.; Selhorst, C. L.; Fernandes, F. C. R.; Oliveira e Silva, A. J.

2018-05-01

Aims: We report on a well-defined EUV wave observed by the Extreme Ultraviolet Imager (EUVI) on board the Solar Terrestrial Relations Observatory (STEREO) and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). The event was accompanied by a shock wave driven by a halo CME observed by the Large Angle and Spectrometric Coronagraph (LASCO-C2/C3) on board the Solar and Heliospheric Observatory (SOHO), as evidenced by the occurrence of type II bursts in the metric and dekameter-hectometric wavelength ranges. We investigated the kinematics of the EUV wave front and the radio source with the purpose of verifying the association between the EUV wave and the shock wave. Methods: The EUV wave fronts were determined from the SDO/AIA images by means of two appropriate directions (slices). The heights (radial propagation) of the EUV wave observed by STEREO/EUVI and of the radio source associated with the shock wave were compared considering the whole bandwidth of the harmonic lane of the radio emission, whereas the speed of the shock was estimated using the lowest frequencies of the harmonic lane associated with the undisturbed corona, using an appropriate multiple of the Newkirk (1961, ApJ, 133, 983) density model and taking into account the H/F frequency ratio fH/fF = 2. The speed of the radio source associated with the interplanetary shock was determined using the Mann et al. (1999, A&A, 348, 614) density model. Results: The EUV wave fronts determined from the SDO/AIA images revealed the coexistence of two types of EUV waves, a fast one with a speed of 560 km s-1, and a slower one with a speed of 250 km s-1, which corresponds approximately to one-third of the average speed of the radio source ( 680 km s-1). The radio signature of the interplanetary shock revealed an almost constant speed of 930 km s-1, consistent with the linear speed of the halo CME (950 km s-1) and with the values found for the accelerating coronal shock ( 535-823 km s-1), taking into account the gap between the radio emissions.

Digital Data Acquisition for Laser Radar for Vibration Analysis

DTIC Science & Technology

1998-06-01

and the resulting signal is a function of the relative phase of the two waves , which changes as the target vibrates. The relative phase is inversely...light crosses the medium in a direction perpendicular to the acoustic waves , a modulated optical wave front will result. A standing acoustic wave in the...mean that the frequency can be up or down-shifted, depending on the orientation of the AOM, or the direction of the traveling acoustic waves . An

Modeling deflagration waves out of hot spots

NASA Astrophysics Data System (ADS)

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.

Fisher waves and front roughening in a two-species invasion model with preemptive competition.

PubMed

O'Malley, L; Kozma, B; Korniss, G; Rácz, Z; Caraco, T

2006-10-01

We study front propagation when an invading species competes with a resident; we assume nearest-neighbor preemptive competition for resources in an individual-based, two-dimensional lattice model. The asymptotic front velocity exhibits an effective power-law dependence on the difference between the two species' clonal propagation rates (key ecological parameters). The mean-field approximation behaves similarly, but the power law's exponent slightly differs from the individual-based model's result. We also study roughening of the front, using the framework of nonequilibrium interface growth. Our analysis indicates that initially flat, linear invading fronts exhibit Kardar-Parisi-Zhang (KPZ) roughening in one transverse dimension. Further, this finding implies, and is also confirmed by simulations, that the temporal correction to the asymptotic front velocity is of O(t(-2/3)).

The Rate of Beneficial Mutations Surfing on the Wave of a Range Expansion

PubMed Central

Lehe, Rémi; Hallatschek, Oskar; Peliti, Luca

2012-01-01

Many theoretical and experimental studies suggest that range expansions can have severe consequences for the gene pool of the expanding population. Due to strongly enhanced genetic drift at the advancing frontier, neutral and weakly deleterious mutations can reach large frequencies in the newly colonized regions, as if they were surfing the front of the range expansion. These findings raise the question of how frequently beneficial mutations successfully surf at shifting range margins, thereby promoting adaptation towards a range-expansion phenotype. Here, we use individual-based simulations to study the surfing statistics of recurrent beneficial mutations on wave-like range expansions in linear habitats. We show that the rate of surfing depends on two strongly antagonistic factors, the probability of surfing given the spatial location of a novel mutation and the rate of occurrence of mutations at that location. The surfing probability strongly increases towards the tip of the wave. Novel mutations are unlikely to surf unless they enjoy a spatial head start compared to the bulk of the population. The needed head start is shown to be proportional to the inverse fitness of the mutant type, and only weakly dependent on the carrying capacity. The precise location dependence of surfing probabilities is derived from the non-extinction probability of a branching process within a moving field of growth rates. The second factor is the mutation occurrence which strongly decreases towards the tip of the wave. Thus, most successful mutations arise at an intermediate position in the front of the wave. We present an analytic theory for the tradeoff between these factors that allows to predict how frequently substitutions by beneficial mutations occur at invasion fronts. We find that small amounts of genetic drift increase the fixation rate of beneficial mutations at the advancing front, and thus could be important for adaptation during species invasions. PMID:22479175

A FAST PROPAGATING EXTREME-ULTRAVIOLET WAVE ASSOCIATED WITH A MINI-FILAMENT ERUPTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng Ruisheng; Jiang Yunchun; Yang Jiayan

The fast extreme-ultraviolet (EUV) waves (>1000 km s{sup -1}) in the solar corona were very rare in the past. Taking advantage of the high temporal and spatial resolution of the Solar Dynamics Observatory observations, we present a fast EUV wave associated with a mini-filament eruption, a C1.0 flare, and a coronal mass ejection (CME) on 2011 September 30. The event took place at the periphery between two active regions (ARs). The mini-filament rapidly erupted as a blowout jet associated with a flare and a CME. The CME front was likely developed from the large-scale overlying loops. The wave onset wasmore » nearly simultaneous with the start of the jet and the flare. The wave departed far from the flare center and showed a close location relative to the rapid jet. The wave had an initial speed of about 1100 km s{sup -1} and a slight deceleration in the last phase, and the velocity decreased to about 500 km s{sup -1}. The wave propagated in a narrow angle extent, likely to avoid the ARs on both sides. All the results provide evidence that the fast EUV wave was a fast-mode MHD wave. The wave resisted being driven by the CME, because it opened up the large-scale loops and its front likely formed later than the wave. The wave was most likely triggered by the jet, due to their close timing and location relations.« less

Pseudo-incompressible, finite-amplitude gravity waves: wave trains and stability

NASA Astrophysics Data System (ADS)

Schlutow, Mark; Klein, Rupert

2017-04-01

Based on weak asymptotic WKB-like solutions for two-dimensional atmospheric gravity waves (GWs) traveling wave solutions (wave trains) are derived and analyzed with respect to stability. A systematic multiple-scale analysis using the ratio of the dominant wavelength and the scale height as a scale separation parameter is applied on the fully compressible Euler equations. A distinguished limit favorable for GWs close to static instability, reveals that pseudo-incompressible rather than Boussinesq theory applies. A spectral expansion including a mean flow, combined with the additional WKB assumption of slowly varying phases and amplitudes, is used to find general weak asymptotic solutions. This ansatz allows for arbitrarily strong, non-uniform stratification and holds even for finite-amplitude waves. It is deduced that wave trains as leading order solutions can only exist if either some non-uniform background stratification is given but the wave train propagates only horizontally or if the wave train velocity vector is given but the background is isothermal. For the first case, general analytical solutions are obtained that may be used to model mountain lee waves. For the second case with the additional assumption of horizontal periodicity, upward propagating wave train fronts were found. These wave train fronts modify the mean flow beyond the non-acceleration theorem. Stability analysis reveal that they are intrinsically modulationally unstable. The range of validity for the scale separation parameter was tested with fully nonlinear simulations. Even for large values an excellent agreement with the theory was found.

Image registration for daylight adaptive optics.

PubMed

Hart, Michael

2018-03-15

Daytime use of adaptive optics (AO) at large telescopes is hampered by shot noise from the bright sky background. Wave-front sensing may use a sodium laser guide star observed through a magneto-optical filter to suppress the background, but the laser beacon is not sensitive to overall image motion. To estimate that, laser-guided AO systems generally rely on light from the object itself, collected through the full aperture of the telescope. Daylight sets a lower limit to the brightness of an object that may be tracked at rates sufficient to overcome the image jitter. Below that limit, wave-front correction on the basis of the laser alone will yield an image that is approximately diffraction limited but that moves randomly. I describe an iterative registration algorithm that recovers high-resolution long-exposure images in this regime from a rapid series of short exposures with very low signal-to-noise ratio. The technique takes advantage of the fact that in the photon noise limit there is negligible penalty in taking short exposures, and also that once the images are recorded, it is not necessary, as in the case of an AO tracker loop, to estimate the image motion correctly and quickly on every cycle. The algorithm is likely to find application in space situational awareness, where high-resolution daytime imaging of artificial satellites is important.

Integrated Arrays on Silicon at Terahertz Frequencies

NASA Technical Reports Server (NTRS)

Chattopadhayay, Goutam; Lee, Choonsup; Jung, Cecil; Lin, Robert; Peralta, Alessandro; Mehdi, Imran; Llombert, Nuria; Thomas, Bertrand

2011-01-01

In this paper we explore various receiver font-end and antenna architecture for use in integrated arrays at terahertz frequencies. Development of wafer-level integrated terahertz receiver front-end by using advanced semiconductor fabrication technologies and use of novel integrated antennas with silicon micromachining are reported. We report novel stacking of micromachined silicon wafers which allows for the 3-dimensional integration of various terahertz receiver components in extremely small packages which easily leads to the development of 2- dimensioanl multi-pixel receiver front-ends in the terahertz frequency range. We also report an integrated micro-lens antenna that goes with the silicon micro-machined front-end. The micro-lens antenna is fed by a waveguide that excites a silicon lens antenna through a leaky-wave or electromagnetic band gap (EBG) resonant cavity. We utilized advanced semiconductor nanofabrication techniques to design, fabricate, and demonstrate a super-compact, low-mass submillimeter-wave heterodyne frontend. When the micro-lens antenna is integrated with the receiver front-end we will be able to assemble integrated heterodyne array receivers for various applications such as multi-pixel high resolution spectrometer and imaging radar at terahertz frequencies.

A Simplified Approach for Simultaneous Measurements of Wavefront Velocity and Curvature in the Heart Using Activation Times.

PubMed

Mazeh, Nachaat; Haines, David E; Kay, Matthew W; Roth, Bradley J

2013-12-01

The velocity and curvature of a wave front are important factors governing the propagation of electrical activity through cardiac tissue, particularly during heart arrhythmias of clinical importance such as fibrillation. Presently, no simple computational model exists to determine these values simultaneously. The proposed model uses the arrival times at four or five sites to determine the wave front speed ( v ), direction (θ), and radius of curvature (ROC) ( r 0 ). If the arrival times are measured, then v , θ, and r 0 can be found from differences in arrival times and the distance between these sites. During isotropic conduction, we found good correlation between measured values of the ROC r 0 and the distance from the unipolar stimulus ( r = 0.9043 and p < 0.0001). The conduction velocity (m/s) was correlated ( r = 0.998, p < 0.0001) using our method (mean = 0.2403, SD = 0.0533) and an empirical method (mean = 0.2352, SD = 0.0560). The model was applied to a condition of anisotropy and a complex case of reentry with a high voltage extra stimulus. Again, results show good correlation between our simplified approach and established methods for multiple wavefront morphologies. In conclusion, insignificant measurement errors were observed between this simplified approach and an approach that was more computationally demanding. Accuracy was maintained when the requirement that ε (ε = b/r 0 , ratio of recording site spacing over wave fronts ROC) was between 0.001 and 0.5. The present simplified model can be applied to a variety of clinical conditions to predict behavior of planar, elliptical, and reentrant wave fronts. It may be used to study the genesis and propagation of rotors in human arrhythmias and could lead to rotor mapping using low density endocardial recording electrodes.

THE FORMATION AND EARLY EVOLUTION OF A CORONAL MASS EJECTION AND ITS ASSOCIATED SHOCK WAVE ON 2014 JANUARY 8

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wan Linfeng; Cheng, Xin; Shi, Tong

2016-08-01

In this paper, we study the formation and early evolution of a limb coronal mass ejection (CME) and its associated shock wave that occurred on 2014 January 8. The extreme ultraviolet (EUV) images provided by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory disclose that the CME first appears as a bubble-like structure. Subsequently, its expansion forms the CME and causes a quasi-circular EUV wave. Interestingly, both the CME and the wave front are clearly visible at all of the AIA EUV passbands. Through a detailed kinematical analysis, it is found that the expansion of the CMEmore » undergoes two phases: a first phase with a strong but transient lateral over-expansion followed by a second phase with a self-similar expansion. The temporal evolution of the expansion velocity coincides very well with the variation of the 25–50 keV hard X-ray flux of the associated flare, which indicates that magnetic reconnection most likely plays an important role in driving the expansion. Moreover, we find that, when the velocity of the CME reaches ∼600 km s{sup −1}, the EUV wave starts to evolve into a shock wave, which is evidenced by the appearance of a type II radio burst. The shock’s formation height is estimated to be ∼0.2 R {sub sun}, which is much lower than the height derived previously. Finally, we also study the thermal properties of the CME and the EUV wave. We find that the plasma in the CME leading front and the wave front has a temperature of ∼2 MK, while that in the CME core region and the flare region has a much higher temperature of ≥8 MK.« less

Dynamics and management of infectious disease in colonizing populations.

PubMed

Bar-David, Shirli; Lloyd-Smith, James O; Getz, Wayne M

2006-05-01

The introduction of chronic, infectious diseases by colonizing populations (invasive or reintroduced) is a serious hazard in conservation biology, threatening the original host and other spillover species. Most research on spatial invasion of diseases has pertained to established host populations, either at steady state or fluctuating through time. Within a colonizing population, however, the spread of disease may be influenced by the expansion process of the population itself. Here we explore the simultaneous expansion of a colonizing population and a chronic, nonlethal disease introduced with it, describing basic patterns in homogeneous and structured landscapes and discussing implications for disease management. We describe expected outcomes of such introductions for three qualitatively distinct cases, depending on the relative velocities at which the population and epidemic expand. (1) If transmissibility is low the disease cannot be sustained, although it may first expand its range somewhat around the point of introduction. (2) If transmissibility is moderate but the wave-front velocity for the population, vp, is higher than that for the disease, vd, the disease wave front lags behind that of the population. (3) A highly transmissible disease, with vd > vp, will invade sufficiently rapidly to track the spread of the host. To test these elementary theoretical predictions, we simulated disease outbreaks in a spatially structured host population occupying a real landscape. We used a spatially explicit, individual-based model of Persian fallow deer (Dama mesopotamica) reintroduced in northern Israel, considering a hypothetical introduction of bovine tuberculosis. Basic patterns of disease expansion in this realistic setting were similar to our conceptual predictions for homogeneous landscapes. Landscape heterogeneity, however, induced the establishment of population activity centers and disease foci within them, leading to jagged wave fronts and causing local variation in the relative velocities at which the population and epidemic expanded. Based on predictions from simple theory and simulations of managed outbreaks, we suggest that the relative velocities at which the population and epidemic expand have important implications for the impact of different management strategies. Recognizing which of our three general cases best describes a particular outbreak will aid in planning an efficient strategy to contain the disease.

Formation events of shoreline sand waves on a gravel beach

NASA Astrophysics Data System (ADS)

Arriaga, Jaime; Falqués, Albert; Ribas, Francesca; Crews, Eddie

2018-06-01

Kilometric-scale shoreline sand waves (KSSW) have been observed in the north-east flank of the Dungeness Cuspate Foreland (southeastern coast of the UK). They consist of two bumps separated by embayments with a 350-450-m spacing. We have analysed 36 shoreline surveys of 2-km length using the Discrete Fourier Transformation (DFT), from 2005 to 2016, and seven topographic surveys encompassing the intertidal zone, from 2010 to 2016. The data set shows two clear formation events. In order to test the role of high-angle waves on the KSSW formation, the 10-year wave series is propagated from the wave buoy located at 43 m depth up to a location in front of the undulations at 4 m depth using the SWAN wave model. The dominating SW waves arrive with a very high incidence angle (˜ 80°) while the NE waves arrive almost shore normal. The ratio R, which measures the degree of dominance of high-angle waves with respect to low-angle waves, correlates well with the shoreline DFT magnitude values of the observed wavelength undulations. In particular, the highest R values coincide with the formation events. Finally, a linear stability model based on the one-line approximation is applied to the Dungeness profile and the 10-year propagated wave series. It predicts accurately the formation moments, with positive growth rates in the correct order of magnitude for wavelengths similar to the observed ones. All these results confirm that the shoreline undulations in Dungeness are self-organized and that the underlying formation mechanism is the high-angle wave instability. The two detected formation events provide a unique opportunity to validate the existing morphodynamic models that include such instability.

Formation events of shoreline sand waves on a gravel beach

NASA Astrophysics Data System (ADS)

Arriaga, Jaime; Falqués, Albert; Ribas, Francesca; Crews, Eddie

2018-05-01

Kilometric-scale shoreline sand waves (KSSW) have been observed in the north-east flank of the Dungeness Cuspate Foreland (southeastern coast of the UK). They consist of two bumps separated by embayments with a 350-450-m spacing. We have analysed 36 shoreline surveys of 2-km length using the Discrete Fourier Transformation (DFT), from 2005 to 2016, and seven topographic surveys encompassing the intertidal zone, from 2010 to 2016. The data set shows two clear formation events. In order to test the role of high-angle waves on the KSSW formation, the 10-year wave series is propagated from the wave buoy located at 43 m depth up to a location in front of the undulations at 4 m depth using the SWAN wave model. The dominating SW waves arrive with a very high incidence angle (˜ 80°) while the NE waves arrive almost shore normal. The ratio R, which measures the degree of dominance of high-angle waves with respect to low-angle waves, correlates well with the shoreline DFT magnitude values of the observed wavelength undulations. In particular, the highest R values coincide with the formation events. Finally, a linear stability model based on the one-line approximation is applied to the Dungeness profile and the 10-year propagated wave series. It predicts accurately the formation moments, with positive growth rates in the correct order of magnitude for wavelengths similar to the observed ones. All these results confirm that the shoreline undulations in Dungeness are self-organized and that the underlying formation mechanism is the high-angle wave instability. The two detected formation events provide a unique opportunity to validate the existing morphodynamic models that include such instability.

Langevin approach to a chemical wave front: Selection of the propagation velocity in the presence of internal noise

NASA Astrophysics Data System (ADS)

Lemarchand, A.; Lesne, A.; Mareschal, M.

1995-05-01

The reaction-diffusion equation associated with the Fisher chemical model A+B-->2A admits wave-front solutions by replacing an unstable stationary state with a stable one. The deterministic analysis concludes that their propagation velocity is not prescribed by the dynamics. For a large class of initial conditions the velocity which is spontaneously selected is equal to the minimum allowed velocity vmin, as predicted by the marginal stability criterion. In order to test the relevance of this deterministic description we investigate the macroscopic consequences, on the velocity and the width of the front, of the intrinsic stochasticity due to the underlying microscopic dynamics. We solve numerically the Langevin equations, deduced analytically from the master equation within a system size expansion procedure. We show that the mean profile associated with the stochastic solution propagates faster than the deterministic solution at a velocity up to 25% greater than vmin.

Blast waves from violent explosive activity at Yasur Volcano, Vanuatu

NASA Astrophysics Data System (ADS)

Marchetti, E.; Ripepe, M.; Delle Donne, D.; Genco, R.; Finizola, A.; Garaebiti, E.

2013-11-01

and seismic waveforms were collected during violent strombolian activity at Yasur Volcano (Vanuatu). Averaging ~3000 seismic events showed stable waveforms, evidencing a low-frequency (0.1-0.3 Hz) signal preceding ~5-6 s the explosion. Infrasonic waveforms were mostly asymmetric with a sharp compressive (5-106 Pa) onset, followed by a small long-lasting rarefaction phase. Regardless of the pressure amplitude, the ratio between the positive and negative phases was constant. These waveform characteristics closely resembled blast waves. Infrared imagery showed an apparent cold spherical front ~20 m thick, which moved between 342 and 405 m/s before the explosive hot gas/fragments cloud. We interpret this cold front as that produced by the vapor condensation induced by the passage of the shock front. We suggest that violent strombolian activity at Yasur was driven by supersonic dynamics with gas expanding at 1.1 Mach number inside the conduit.

Two-Dimensional Failure Waves and Ignition Fronts in Premixed Combustion

NASA Technical Reports Server (NTRS)

Vedarajan, T. G.; Buckmaster J.; Ronney, P.

1998-01-01

This paper is a continuation of our work on edge-flames in premixed combustion. An edge-flame is a two-dimensional structure constructed from a one-dimensional configuration that has two stable solutions (bistable equilibrium). Edge-flames can display wavelike behavior, advancing as ignition fronts or retreating as failure waves. Here we consider two one-dimensional configurations: twin deflagrations in a straining flow generated by the counterflow of fresh streams of mixture: and a single deflagration subject to radiation losses. The edge-flames constructed from the first configuration have positive or negative speeds, according to the value of the strain rate. But our numerical solutions strongly suggest that only positive speeds (corresponding to ignition fronts) can exist for the second configuration. We show that this phenomenon can also occur in diffusion flames when the Lewis numbers are small. And we discuss the asymptotics of the one-dimensional twin deflagration configuration. an overlooked problem from the 70s.

Soliton interactions and the formation of solitonic patterns

NASA Astrophysics Data System (ADS)

Sears, Suzanne M.

From the stripes of a zebra, to the spirals of cream in a hot cup of coffee, we are surrounded by patterns in the natural world. But why are there patterns? Why drives their formation? In this thesis we study some of the diverse ways patterns can arise due to the interactions between solitary waves in nonlinear systems, sometimes starting from nothing more than random noise. What follows is a set of three studies. In the first, we show how a nonlinear system that supports solitons can be driven to generate exact (regular) Cantor set fractals. As an example, we use numerical simulations to demonstrate the formation of Cantor set fractals by temporal optical solitons. This fractal formation occurs in a cascade of nonlinear optical fibers through the dynamical evolution of a single input soliton. In the second study, we investigate pattern formation initiated by modulation instability in nonlinear partially coherent wave fronts and show that anisotropic noise and/or anisotropic correlation statistics can lead to ordered patterns such as grids and stripes. For the final study, we demonstrate the spontaneous clustering of solitons in partially coherent wavefronts during the final stages of pattern formation initiated by modulation instability and noise. Experimental observations are in agreement with theoretical predictions and are confirmed using numerical simulations.

Rupture Dynamics along Thrust Dipping Fault: Inertia Effects due to Free Surface Wave Interactions

NASA Astrophysics Data System (ADS)

Vilotte, J. P.; Scala, A.; Festa, G.

2017-12-01

We numerically investigate the dynamic interaction between free surface and up-dip, in-plane rupture propagation along thrust faults, under linear slip-weakening friction. With reference to shallow along-dip rupture propagation during large subduction earthquakes, we consider here low dip-angle fault configurations with fixed strength excess and depth-increasing initial stress. In this configuration, the rupture undergoes a break of symmetry with slip-induced normal stress perturbations triggered by the interaction with reflected waves from the free surface. We found that both body-waves - behind the crack front - and surface waves - at the crack front - can trigger inertial effects. When waves interact with the rupture before this latter reaches its asymptotic speed, the rupture can accelerate toward the asymptotic speed faster than in the unbounded symmetric case, as a result of these inertial effects. Moreover, wave interaction at the crack front also affects the slip rate generating large ground motion on the hanging wall. Imposing the same initial normal stress, frictional strength and stress drop while varying the static friction coefficient we found that the break of symmetry makes the rupture dynamics dependent on the absolute value of friction. The higher the friction the stronger the inertial effect both in terms of rupture acceleration and slip amount. When the contact condition allows the fault interface to open close to the free surface, the length of the opening zone is shown to depend on the propagation length, the initial normal stress and the static friction coefficient. These new results are shown to agree with analytical results of rupture propagation in bounded media, and open new perspectives for understanding the shallow rupture of large subduction earthquakes and tsunami sources.

Burnett-Cattaneo continuum theory for shock waves.

PubMed

Holian, Brad Lee; Mareschal, Michel; Ravelo, Ramon

2011-02-01

We model strong shock-wave propagation, both in the ideal gas and in the dense Lennard-Jones fluid, using a refinement of earlier work, which accounts for the cold compression in the early stages of the shock rise by a nonlinear, Burnett-like, strain-rate dependence of the thermal conductivity, and relaxation of kinetic-temperature components on the hot, compressed side of the shock front. The relaxation of the disequilibrium among the three components of the kinetic temperature, namely, the difference between the component in the direction of a planar shock wave and those in the transverse directions, particularly in the region near the shock front, is accomplished at a much more quantitative level by a rigorous application of the Cattaneo-Maxwell relaxation equation to a reference solution, namely, the steady shock-wave solution of linear Navier-Stokes-Fourier theory, along with the nonlinear Burnett heat-flux term. Our new continuum theory is in nearly quantitative agreement with nonequilibrium molecular-dynamics simulations under strong shock-wave conditions, using relaxation parameters obtained from the reference solution. ©2011 American Physical Society

Fourth-power law structure of the shock wave fronts in metals and ceramics

NASA Astrophysics Data System (ADS)

Bayandin, Yuriy; Naimark, Oleg; Saveleva, Natalia

2017-06-01

The plate impact experiments were performed for solids during last fifty years. It was established that the dependence between the strain rate and the shock wave amplitude for metals and ceramics expressed by a fourth-power law. Present study is focused on the theoretical investigation and numerical simulation of plane shock wave propagation in metals and ceramics. Statistically based constitutive model of solid with defects (microcracks and microshears) was developed to provide the relation between damage induced mechanisms of structural relaxation, thermally activated plastic flow and material reactions for extreme loading conditions. Original approach based on the wide range constitutive equations was proposed for the numerical simulation of multiscale damage-failure transition mechanisms and plane shock wave propagation in solids with defects in the range of strain rate 103 -108s-1 . It was shown that mechanisms of plastic relaxation and damage-failure transitions are linked to the multiscale kinetics of defects leading to the self-similar nature of shock wave fronts in metals and ceramics. The work was supported by the Russian Science Foundation (Project No. 14-19-01173).

Shock-wave-like structures induced by an exothermic neutralization reaction in miscible fluids

NASA Astrophysics Data System (ADS)

Bratsun, Dmitry; Mizev, Alexey; Mosheva, Elena; Kostarev, Konstantin

2017-11-01

We report shock-wave-like structures that are strikingly different from previously observed fingering instabilities, which occur in a two-layer system of miscible fluids reacting by a second-order reaction A +B →S in a vertical Hele-Shaw cell. While the traditional analysis expects the occurrence of a diffusion-controlled convection, we show both experimentally and theoretically that the exothermic neutralization reaction can also trigger a wave with a perfectly planar front and nearly discontinuous change in density across the front. This wave propagates fast compared with the characteristic diffusion times and separates the motionless fluid and the area with anomalously intense convective mixing. We explain its mechanism and introduce a new dimensionless parameter, which allows to predict the appearance of such a pattern in other systems. Moreover, we show that our governing equations, taken in the inviscid limit, are formally analogous to well-known shallow-water equations and adiabatic gas flow equations. Based on this analogy, we define the critical velocity for the onset of the shock wave which is found to be in the perfect agreement with the experiments.

Stress Wave Propagation in Larch Plantation Trees-Numerical Simulation

Treesearch

Fenglu Liu; Fang Jiang; Xiping Wang; Houjiang Zhang; Wenhua Yu

2015-01-01

In this paper, we attempted to simulate stress wave propagation in virtual tree trunks and construct two dimensional (2D) wave-front maps in the longitudinal-radial section of the trunk. A tree trunk was modeled as an orthotropic cylinder in which wood properties along the fiber and in each of the two perpendicular directions were different. We used the COMSOL...

Features in the Behavior of the Solar Wind behind the Bow Shock Front near the Boundary of the Earth's Magnetosphere

NASA Astrophysics Data System (ADS)

Grib, S. A.; Leora, S. N.

2017-12-01

Macroscopic discontinuous structures observed in the solar wind are considered in the framework of magnetic hydrodynamics. The interaction of strong discontinuities is studied based on the solution of the generalized Riemann-Kochin problem. The appearance of discontinuities inside the magnetosheath after the collision of the solar wind shock wave with the bow shock front is taken into account. The propagation of secondary waves appearing in the magnetosheath is considered in the approximation of one-dimensional ideal magnetohydrodynamics. The appearance of a compression wave reflected from the magnetopause is indicated. The wave can nonlinearly break with the formation of a backward shock wave and cause the motion of the bow shock towards the Sun. The interaction between shock waves is considered with the well-known trial calculation method. It is assumed that the velocity of discontinuities in the magnetosheath in the first approximation is constant on the average. All reasonings and calculations correspond to consideration of a flow region with a velocity less than the magnetosonic speed near the Earth-Sun line. It is indicated that the results agree with the data from observations carried out on the WIND and Cluster spacecrafts.

Influence of radiation absorption by microparticles on the flame velocity and combustion regimes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ivanov, M. F., E-mail: ivanov-mf@mail.ru; Kiverin, A. D.; Liberman, M. A., E-mail: michael.liberman@nordita.org

Thermal radiation from hot combustion products has virtually no effect on the flame propagation in a gas medium. We consider a different situation when even a small concentration of microparticles suspended in a gas absorbs the thermal radiation and heats the gas mixture ahead of the combustion wave front by transferring it to the gas. The mixture heating ahead of the flame front can lead either to a moderate increase in the combustion wave velocity for a fast flame or to its significant increase for a slow flame, depending on the gas mixture reactivity and the normal laminar flame velocity.more » For a slow flame, the heat transfer by radiation from the combustion products can become the dominant mechanism compared to the ordinary molecular thermal conduction that determines the combustion wave structure and velocity. The radiative heating for a spatially nonuniform distribution of particles ahead of the flame front is shown to give rise to a temperature gradient that, in turn, can lead to the ignition of different combustion regimes, depending on the radiation absorption length. In accordance with the Zeldovich gradient mechanism, both deflagration and detonation regimes can be formed in this case. A hydrogen–oxygen flame is used as an example to illustrate the ignition of different combustion wave propagation regimes, depending on the radiation absorption length.« less

An ignition-temperature model with two free interfaces in premixed flames

NASA Astrophysics Data System (ADS)

Brauner, Claude-Michel; Gordon, Peter V.; Zhang, Wen

2016-11-01

In this paper we consider an ignition-temperature zero-order reaction model of thermo-diffusive combustion. This model describes the dynamics of thick flames, which have recently received considerable attention in the physical and engineering literature. The model admits a unique (up to translations) planar travelling wave solution. This travelling wave solution is quite different from those usually studied in combustion theory. The main qualitative feature of this travelling wave is that it has two interfaces: the ignition interface where the ignition temperature is attained and the trailing interface where the concentration of deficient reactants reaches zero. We give a new mathematical framework for studying the cellular instability of such travelling front solutions. Our approach allows the analysis of a free boundary problem to be converted into the analysis of a boundary value problem having a fully nonlinear system of parabolic equations. The latter is very suitable for both mathematical and numerical analysis. We prove the existence of a critical Lewis number such that the travelling wave solution is stable for values of Lewis number below the critical one and is unstable for Lewis numbers that exceed this critical value. Finally, we discuss the results of numerical simulations of a fully nonlinear system that describes the perturbation dynamics of planar fronts. These simulations reveal, in particular, some very interesting 'two-cell' steady patterns of curved combustion fronts.

A study of the adequacy of quasi-geostrophic dynamics for modeling the effect of frontal cyclones on the larger scale flow

NASA Technical Reports Server (NTRS)

Mudrick, Stephen

1987-01-01

The evolution of individual cyclone waves is studied in order to see how well quasi-geostrophic (QG) dynamics can simulate the behavior of primitive equations (PE) dynamics. This work is an extension of a similar study (Mudrick, 1982); emphasis is placed here on adding a frontal zone and other more diverse features to the basic states used. In addition, sets of PE integrations, with and without friction, are used to study the formation of surface occluded fronts within the evolving cyclones. Results of the study are summarized at the beginning of the report.

Time-resolved acoustic emission tomography in the laboratory: tracking localised damage in rocks

NASA Astrophysics Data System (ADS)

Brantut, N.

2017-12-01

Over the past three decades, there has been tremendous technological developments of laboratory equipment and studies using acoustic emission and ultrasonic monitoring of rock samples during deformation. Using relatively standard seismological techniques, acoustic emissions can be detected, located in space and time, and source mechanisms can be obtained. In parallel, ultrasonic velocities can be measured routinely using standard pulse-receiver techniques.Despite these major developments, current acoustic emission and ultrasonic monitoring systems are typically used separately, and the poor spatial coverage of acoustic transducers precludes performing active 3D tomography in typical laboratory settings.Here, I present an algorithm and software package that uses both passive acoustic emission data and active ultrasonic measurements to determine acoustic emission locations together with the 3D, anisotropic P-wave structure of rock samples during deformation. The technique is analogous to local earthquake tomography, but tailored to the specificities of small scale laboratory tests. The fast marching method is employed to compute the forward problem. The acoustic emission locations and the anisotropic P-wave field are jointly inverted using the Quasi-Newton method.The method is used to track the propagation of compaction bands in a porous sandstone deformed in the ductile, cataclastic flow regime under triaxial stress conditions. Near the yield point, a compaction front forms at one end of the sample, and slowly progresses towards the other end. The front is illuminated by clusters of Acoustic Emissions, and leaves behind a heavily damaged material where the P-wave speed has dropped by up to 20%.The technique opens new possibilities to track in-situ strain localisation and damage around laboratory faults, and preliminary results on quasi-static rupture in granite will be presented.

Numerical simulation of detonation reignition in H 2-O 2 mixtures in area expansions

NASA Astrophysics Data System (ADS)

Jones, D. A.; Kemister, G.; Tonello, N. A.; Oran, E. S.; Sichel, M.

Time-dependent, two-dimensional, numerical simulations of a transmitted detonation show reignition occuring by one of two mechanisms. The first mechanism involves the collision of triple points as they expand along a decaying shock front. In the second mechanism ignition results from the coalescence of a number of small, relatively high pressure regions left over from the decay of weakened transverse waves. The simulations were performed using an improved chemical kinetic model for stoichiometric H 2-O 2 mixtures. The initial conditions were a propagating, two-dimensional detonation resolved enough to show transverse wave structure. The calculations provide clarification of the reignition mechanism seen in previous H 2-O 2-Ar simulations, and again demonstrate that the transverse wave structure of the detonation front is critical to the reignition process.

Ionization waves of arbitrary velocity driven by a flying focus

DOE Office of Scientific and Technical Information (OSTI.GOV)

Palastro, J. P.; Turnbull, D.; Bahk, S. -W.

A chirped laser pulse focused by a chromatic lens exhibits a dynamic, or flying, focus in which the trajectory of the peak intensity decouples from the group velocity. In a medium, the flying focus can trigger an ionization front that follows this trajectory. By adjusting the chirp, the ionization front can be made to travel at an arbitrary velocity along the optical axis. For this study, we present analytical calculations and simulations describing the propagation of the flying focus pulse, the self-similar form of its intensity profile, and ionization wave formation. The ability to control the speed of the ionizationmore » wave and, in conjunction, mitigate plasma refraction has the potential to advance several laser-based applications, including Raman amplification, photon acceleration, high-order-harmonic generation, and THz generation.« less

Hot spot formation from shock reflections

NASA Astrophysics Data System (ADS)

Menikoff, R.

2011-04-01

Heterogeneities sensitize an explosive to shock initiation. This is due to hot-spot formation and the sensitivity of chemical reaction rates to temperature. Here, we describe a numerical experiment aimed at elucidating a mechanism for hot-spot formation that occurs when a shock wave passes over a high-density impurity. The simulation performed is motivated by a physical experiment in which glass beads are added to liquid nitromethane. The impedance mismatch between the beads and the nitromethane results in shock reflections. These, in turn, give rise to transverse waves along the lead shock front. Hot spots arise on local portions of the lead front with a higher shock strength, rather than on the reflected shocks behind the beads. Moreover, the interactions generated by reflected waves from neighboring beads can significantly increase the peak hot-spot temperature when the beads are suitably spaced.

Adaptive elastic metasurfaces for wave front manipulation

NASA Astrophysics Data System (ADS)

Li, Shilong; Xu, Jiawen; Tang, Jiong

2018-04-01

In this research, by combining the concept of elastic metasurfaces with piezoelectric transducer with shunted circuitry, we investigate the designs of elastic metasurfaces, consisting of an array of piezoelectric transducers shunted with negative capacitance, which is capable of modulating wave fronts adaptively. In order to construct different adaptive elastic metasurfaces, different phase profiles along the interface can be framed through properly adjusting the negative capacitance values. Flat planar lenses for focusing transmitted A0 Lamb waves are achieved, and possess the flexibility of changing focal locations through electromechanical tunings. Additionally, nonparaxial self-bending beams with arbitrary trajectories and source illusion devices can also be accomplished owing to the free manipulation of phase shifts. With their versatility and tunability, the adaptive elastic metasurfaces could pave new avenues to a wide variety of potential applications, such as nondestructive testing, ultrasound imaging, and caustic engineering.

Ionization waves of arbitrary velocity driven by a flying focus

DOE PAGES

Palastro, J. P.; Turnbull, D.; Bahk, S. -W.; ...

2018-03-01

A chirped laser pulse focused by a chromatic lens exhibits a dynamic, or flying, focus in which the trajectory of the peak intensity decouples from the group velocity. In a medium, the flying focus can trigger an ionization front that follows this trajectory. By adjusting the chirp, the ionization front can be made to travel at an arbitrary velocity along the optical axis. For this study, we present analytical calculations and simulations describing the propagation of the flying focus pulse, the self-similar form of its intensity profile, and ionization wave formation. The ability to control the speed of the ionizationmore » wave and, in conjunction, mitigate plasma refraction has the potential to advance several laser-based applications, including Raman amplification, photon acceleration, high-order-harmonic generation, and THz generation.« less

Fast gradient-based algorithm on extended landscapes for wave-front reconstruction of Earth observation satellite

NASA Astrophysics Data System (ADS)

Thiebaut, C.; Perraud, L.; Delvit, J. M.; Latry, C.

2016-07-01

We present an on-board satellite implementation of a gradient-based (optical flows) algorithm for the shifts estimation between images of a Shack-Hartmann wave-front sensor on extended landscapes. The proposed algorithm has low complexity in comparison with classical correlation methods which is a big advantage for being used on-board a satellite at high instrument data rate and in real-time. The electronic board used for this implementation is designed for space applications and is composed of radiation-hardened software and hardware. Processing times of both shift estimations and pre-processing steps are compatible of on-board real-time computation.

Thermal waves or beam heating in the 1980, November 5 flare

NASA Technical Reports Server (NTRS)

Smith, Dean F.

1986-01-01

Observations of the temporal evolution of loop BC in soft X rays in the November 5, 1980 flare are reviewed. Calculations are performed to model this evolution. The most consistent interpretation involving a minimum account of energy is the following. Thermal heating near B gives rise to a conduction front which moves out along the loop uninhibited for about 27 s. Beam heating near C gives rise to a second conduction front which moves in the opposite direction and prevents any energy reaching C by thermal conduction from B. Thus both thermal waves and beam heating are required to explain the observed evolution.

Retina imaging system with adaptive optics for the eye with or without myopia

NASA Astrophysics Data System (ADS)

Li, Chao; Xia, Mingliang; Jiang, Baoguang; Mu, Quanquan; Chen, Shaoyuan; Xuan, Li

2009-04-01

An adaptive optics system for the retina imaging is introduced in the paper. It can be applied to the eye with myopia from 0 to 6 diopters without any adjustment of the system. A high-resolution liquid crystal on silicon (LCOS) device is used as the wave-front corrector. The aberration is detected by a Shack-Harmann wave-front sensor (HASO) that has a Root Mean Square (RMS) measurement accuracy of λ/100 ( λ = 0.633 μm). And an equivalent scale model eye is constructed with a short focal length lens (˜18 mm) and a diffuse reflection object (paper screen) as the retina. By changing the distance between the paper screen and the lens, we simulate the eye with larger diopters than 5 and the depth of field. The RMS value both before and after correction is obtained by the wave-front sensor. After correction, the system reaches the diffraction-limited resolution approximately 230 cycles/mm at the object space. It is proved that if the myopia is smaller than 6 diopters and the depth of field is between -40 and +50 mm, the system can correct the aberration very well.

SPECKLE NOISE SUBTRACTION AND SUPPRESSION WITH ADAPTIVE OPTICS CORONAGRAPHIC IMAGING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ren Deqing; Dou Jiangpei; Zhang Xi

2012-07-10

Future ground-based direct imaging of exoplanets depends critically on high-contrast coronagraph and wave-front manipulation. A coronagraph is designed to remove most of the unaberrated starlight. Because of the wave-front error, which is inherit from the atmospheric turbulence from ground observations, a coronagraph cannot deliver its theoretical performance, and speckle noise will limit the high-contrast imaging performance. Recently, extreme adaptive optics, which can deliver an extremely high Strehl ratio, is being developed for such a challenging mission. In this publication, we show that barely taking a long-exposure image does not provide much gain for coronagraphic imaging with adaptive optics. We furthermore » discuss a speckle subtraction and suppression technique that fully takes advantage of the high contrast provided by the coronagraph, as well as the wave front corrected by the adaptive optics. This technique works well for coronagraphic imaging with conventional adaptive optics with a moderate Strehl ratio, as well as for extreme adaptive optics with a high Strehl ratio. We show how to substrate and suppress speckle noise efficiently up to the third order, which is critical for future ground-based high-contrast imaging. Numerical simulations are conducted to fully demonstrate this technique.« less

Electric generator

DOEpatents

Foster, Jr., John S.; Wilson, James R.; McDonald, Jr., Charles A.

1983-01-01

1. In an electrical energy generator, the combination comprising a first elongated annular electrical current conductor having at least one bare surface extending longitudinally and facing radially inwards therein, a second elongated annular electrical current conductor disposed coaxially within said first conductor and having an outer bare surface area extending longitudinally and facing said bare surface of said first conductor, the contiguous coaxial areas of said first and second conductors defining an inductive element, means for applying an electrical current to at least one of said conductors for generating a magnetic field encompassing said inductive element, and explosive charge means disposed concentrically with respect to said conductors including at least the area of said inductive element, said explosive charge means including means disposed to initiate an explosive wave front in said explosive advancing longitudinally along said inductive element, said wave front being effective to progressively deform at least one of said conductors to bring said bare surfaces thereof into electrically conductive contact to progressively reduce the inductance of the inductive element defined by said conductors and transferring explosive energy to said magnetic field effective to generate an electrical potential between undeformed portions of said conductors ahead of said explosive wave front.

Study of Pressure Oscillations in Supersonic Parachute

NASA Astrophysics Data System (ADS)

Dahal, Nimesh; Fukiba, Katsuyoshi; Mizuta, Kazuki; Maru, Yusuke

2018-04-01

Supersonic parachutes are a critical element of planetary mission whose simple structure, light-weight characteristics together with high ratio of aerodynamic drag makes them the most suitable aerodynamic decelerators. The use of parachute in supersonic flow produces complex shock/shock and wake/shock interaction giving rise to dynamic pressure oscillations. The study of supersonic parachute is difficult, because parachute has very flexible structure which makes obtaining experimental pressure data difficult. In this study, a supersonic wind tunnel test using two rigid bodies is done. The wind tunnel test was done at Mach number 3 by varying the distance between the front and rear objects, and the distance of a bundle point which divides suspension lines and a riser. The analysis of Schlieren movies revealed shock wave oscillation which was repetitive and had large pressure variation. The pressure variation differed in each case of change in distance between the front and rear objects, and the change in distance between riser and the rear object. The causes of pressure oscillation are: interaction of wake caused by front object with the shock wave, fundamental harmonic vibration of suspension lines, interference between shock waves, and the boundary layer of suspension lines.

Analyses of electron runaway in front of the negative streamer channel

NASA Astrophysics Data System (ADS)

Babich, L. P.; Bochkov, E. I.; Kutsyk, I. M.; Neubert, T.; Chanrion, O.

2017-08-01

X-ray and γ-ray emissions, observed in correlation with negative leaders of lightning and long sparks of high-voltage laboratory experiments, are conventionally connected with the bremsstrahlung of high-energy runaway electrons (REs). Here we extend a focusing mechanism, analyzed in our previous paper, which allows the electric field to reach magnitudes, required for a generation of significant RE fluxes and associated bremsstrahlung, when the ionization wave propagates in a narrow, ionized channel created by a previous streamer. Under such conditions we compute the production rate of REs per unit streamer length as a function of the streamer velocity and predict that, once a streamer is formed with the electric field capable of producing REs ahead of the streamer front, the ionization induced by the REs is capable of creating an ionized channel that allows for self-sustained propagation of the RE-emitting ionization wave independent of the initial electron concentration. Thus, the streamer coronas of the leaders are probable sources of REs producing the observed high-energy radiation. To prove these predictions, new simulations are planned, which would show explicitly that the preionization in front of the channel via REs will lead to the ionization wave propagation self-consistent with RE generation.

Direct numerical simulation of two-dimensional wall-bounded turbulent flows from receptivity stage.

PubMed

Sengupta, T K; Bhaumik, S; Bhumkar, Y G

2012-02-01

Deterministic route to turbulence creation in 2D wall boundary layer is shown here by solving full Navier-Stokes equation by dispersion relation preserving (DRP) numerical methods for flow over a flat plate excited by wall and free stream excitations. Present results show the transition caused by wall excitation is predominantly due to nonlinear growth of the spatiotemporal wave front, even in the presence of Tollmien-Schlichting (TS) waves. The existence and linear mechanism of creating the spatiotemporal wave front was established in Sengupta, Rao and Venkatasubbaiah [Phys. Rev. Lett. 96, 224504 (2006)] via the solution of Orr-Sommerfeld equation. Effects of spatiotemporal front(s) in the nonlinear phase of disturbance evolution have been documented by Sengupta and Bhaumik [Phys. Rev. Lett. 107, 154501 (2011)], where a flow is taken from the receptivity stage to the fully developed 2D turbulent state exhibiting a k(-3) energy spectrum by solving the Navier-Stokes equation without any artifice. The details of this mechanism are presented here for the first time, along with another problem of forced excitation of the boundary layer by convecting free stream vortices. Thus, the excitations considered here are for a zero pressure gradient (ZPG) boundary layer by (i) monochromatic time-harmonic wall excitation and (ii) free stream excitation by convecting train of vortices at a constant height. The latter case demonstrates neither monochromatic TS wave, nor the spatiotemporal wave front, yet both the cases eventually show the presence of k(-3) energy spectrum, which has been shown experimentally for atmospheric dynamics in Nastrom, Gage and Jasperson [Nature 310, 36 (1984)]. Transition by a nonlinear mechanism of the Navier-Stokes equation leading to k(-3) energy spectrum in the inertial subrange is the typical characteristic feature of all 2D turbulent flows. Reproduction of the spectrum noted in atmospheric data (showing dominance of the k(-3) spectrum over the k(-5/3) spectrum in Nastrom et al.) in laboratory scale indicates universality of this spectrum for all 2D turbulent flows. Creation of universal features of 2D turbulence by a deterministic route has been established here for the first time by solving the Navier-Stokes equation without any modeling, as has been reported earlier in the literature by other researchers.

An Intense Traveling Airglow Front in the Upper Mesosphere-Lower Thermosphere with Characteristic of a Turbulent Bore Observed over Alice Springs, Australia

NASA Astrophysics Data System (ADS)

Walterscheid, R. L.; Hecht, J. H.; Hickey, M. P.; Gelinas, L. J.; Vincent, R. A.; Reid, I. M.; Woithe, J.

2010-12-01

The Aerospace Corporation’s Nightglow Imager observed a large step-function change in airglow in the form of a traveling front in the OH and O2 airglow emissions over Alice Springs Australia on February 2, 2003. The front exhibited a stepwise increase of nearly a factor two in the OH brightness and a stepwise decrease in the O2 brightness. The change in brightness in each layer was associated with a strong leading disturbance followed by a train of weak barely visible waves. The OH airglow brightness behind the front was the brightness night for 02 at Alice Springs that we have measured in seven years of observations. The OH brightness was among the five brightest. The event was associated with a strong phase-locked two-day wave (TDW).We have analyzed the stability conditions for the upper mesosphere and lower thermosphere and found that the airglow layers were found in a region of strong ducting. The thermal structure was obtained from combining data from the SABER instrument on the TIMED satellite and the NRLMSISE-00 model. The wind profile was obtained by combining the HWM07 model and MF radar winds from Buckland Park Australia. We found that the TDW-disturbed profile was significantly more effective in supporting a high degree of ducting than a profile based only on HWM07 winds. Dramatic wall events have been interpreted as manifestations of undular bores (e.g., Smith et al. [2003]). Undular bores are nonlinear high Froude number events that must generate an ever increasing train of waves to carry the excess energy away from the bore front. Only a very weak wave train behind the initial disturbance was seen for the Alice Springs event. The form of the amplitude ordering was not typical of a nonlinear wave train. Therefore a bore interpretation requires another means of energy dissipation, namely turbulent dissipation. We suggest that a reasonable interpretation of the observed event is a turbulent bore. We are unaware of any previous event having characteristics of a turbulent bore. Smith, S. M., et al., A multidiagnostic investigation of the mesospheric bore phenomenon, J. Geophys. Res., 108, 2003

Image formation in microwave holography

NASA Technical Reports Server (NTRS)

Cribbs, R. W.; Lamb, B. L.

1973-01-01

Microwave holograms are made without offset reference beam, but it has been found that Van der Lugt filter can be used to produce image offset. Also, filter permits "decoding" of holograms in contrast with usual practice of reconstructing visible-light analogs of original micro-wave wave fronts.

A terahertz in-line polarization converter based on through-via connected double layer slot structures

PubMed Central

Woo, Jeong Min; Hussain, Sajid; Jang, Jae-Hyung

2017-01-01

A terahertz (THz) in-line polarization converter that yields a polarization conversion ratio as high as 99.9% is demonstrated at 1 THz. It has double-layer slot structures oriented in orthogonal directions that are electrically connected by 1/8-wavelngth-long through-via holes beside the slot structures. The slots on the front metal-plane respond to the incident THz wave with polarization orthogonal to the slots and generates a circulating surface current around the slots. The surface current propagates along a pair of through-via holes that function as a two-wire transmission line. The propagating current generates a surface current around the backside slot structures oriented orthogonal to the slot structures on the front metal layer. The circulating current generates a terahertz wave polarized orthogonal to the backside slot structures and the 90° polarization conversion is completed. The re-radiating THz wave with 90° converted polarization propagates in the same direction as the incident THz wave. PMID:28211498

Deformation and deceleration of coronal wave

NASA Astrophysics Data System (ADS)

Xue, Z. K.; Qu, Z. Q.; Yan, X. L.; Zhao, L.; Ma, L.

2013-08-01

Aims: We studied the kinematics and morphology of two coronal waves to better understand the nature and origin of coronal waves. Methods: Using multi-wavelength observations of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) and the Extreme Ultraviolet Imager (EUVI) on board the twin spacecraft Solar-TErrestrial RElations Observatory (STEREO), we present morphological and dynamic characteristics of consecutive coronal waves on 2011 March 24. We also show the coronal magnetic field based on the potential field source surface model. Results: This event contains several interesting aspects. The first coronal wave initially appeared after a surge-like eruption. Its front was changed and deformed significantly from a convex shape to a line-shaped appearance, and then to a concave configuration during its propagation to the northwest. The initial speeds ranged from 947 km s-1 to 560 km s-1. The first wave decelerated significantly after it passed through a filament channel. After the deceleration, the final propagation speeds of the wave were from 430 km s-1 to 312 km s-1. The second wave was found to appear after the first wave in the northwest side of the filament channel. Its wave front was more diffused and the speed was around 250 km s-1, much slower than that of the first wave. Conclusions: The deformation of the first coronal wave was caused by the different speeds along different paths. The sudden deceleration implies that the refraction of the first wave took place at the boundary of the filament channel. The event provides evidence that the first coronal wave may be a coronal MHD shock wave, and the second wave may be the apparent propagation of the brightenings caused by successive stretching of the magnetic field lines.

Hybrid Simulations for the Turbulence and the Wave-Particle Interaction in the Inner and the Outer Heliopause.

NASA Astrophysics Data System (ADS)

Kucharek, H.; Pogorelov, N. V.; Mueller, H. R.; Gamayunov, K. V.

2014-12-01

IBEX and the Voyager spacecraft provide unique data sets that enable us to study plasma conditions in the key regions of the heliosphere: the termination shock (TS), at the heliospause and beyond. Whereas Voyager provides in-situ plasma data IBEX uses neutral atoms to remote sense the plasma conditions in interstellar space, the heliopause, and the termination shock. The IBEX data sets revealed a ribbon feature which was unexpected and which formation mechanism is still unknown. Even the location of the source is not known considering the fact that IBEX measures neutral along a line of sight. Aside from the ribbon feature the distributed ENA flux shows temporal variations that are unexplained, in particular at solar wind energies. Furthermore, Voyager observations questioned the role of the termination shock being the main accelerator for high-energetic ions. All of these outstanding science questions are associated with wave-particle interaction and turbulence in most likely different key regions of the heliosphere. Hybrid simulations, which included all kinetic processes self-consistently on the ion level, are a proven to be a very powerful tool to investigate wave-particle interaction, turbulence, and phase-space evolution of pickup and solar wind ions. We performed 3D multi-species hybrid simulations for an ion/ion beam instability to study the temporal evolution of ion distributions, their stability, and the associated ENA generation under the influence of self-generated waves in the heliosheath. We investigated the energetization of ions downstream of the TS, the turbulence, and growth rate of instabilities in the heliosheath. The simulations show that ions can be accelerated downstream of the TS by trapping ions in coherent wave fronts.

Highly Efficient Broadband Multiplexed Millimeter-Wave Vortices from Metasurface-Enabled Transmit-Arrays of Subwavelength Thickness

NASA Astrophysics Data System (ADS)

Jiang, Zhi Hao; Kang, Lei; Hong, Wei; Werner, Douglas H.

2018-06-01

Structured electromagnetic waves carrying nonvanishing orbital angular momentum (OAM) have recently opened up alternative frontiers in the field of wave physics, holding great promise for a wide range of potential applications. By leveraging geometric phases originating from spin-to-orbital interactions, spin-dependent wave phenomena can be created, leading to a more versatile realm of dispersionless wave-front manipulation. However, the currently available transmissive vortex-beam generators suffer from a narrow bandwidth, require an optically thick device profile, or are limited by a low efficiency, severely restricting their integration into systems and/or widespread usage for practical applications. We present the design methodology and a physical analysis and complete experimental characterization of a class of millimeter-wave Pancharatnam-Berry transmit-arrays with a thickness of about λ0/3 , which enables highly efficient generation and separation of spin-controlled vortex beams over a broad bandwidth, achieving an unprecedented peak efficiency of 88% for a single vortex beam and 71% for dual vortex beams. The proposed transmit-array, which is capable of providing two-dimensional OAM multiplexing and demultiplexing without normal-mode background interference, overcomes all previous roadblocks and paves the way for high-efficiency electromagnetic vortex-beam generation as well as other wave-front-shaping devices from microwave frequencies to optical wavelengths.

Magnetic antenna excitation of whistler modes. III. Group and phase velocities of wave packets

NASA Astrophysics Data System (ADS)

Urrutia, J. M.; Stenzel, R. L.

2015-07-01

The properties of whistler modes excited by single and multiple magnetic loop antennas have been investigated in a large laboratory plasma. A single loop excites a wavepacket, but an array of loops across the ambient magnetic field B0 excites approximate plane whistler modes. The single loop data are measured. The array patterns are obtained by linear superposition of experimental data shifted in space and time, which is valid in a uniform plasma and magnetic field for small amplitude waves. Phasing the array changes the angle of wave propagation. The antennas are excited by an rf tone burst whose propagating envelope and oscillations yield group and phase velocities. A single loop antenna with dipole moment across B0 excites wave packets whose topology resembles m = 1 helicon modes, but without radial boundaries. The phase surfaces are conical with propagation characteristics of Gendrin modes. The cones form near the antenna with comparable parallel and perpendicular phase velocities. A physical model for the wave excitation is given. When a wave burst is applied to a phased antenna array, the wave front propagates both along the array and into the plasma forming a "whistler wing" at the front. These laboratory observations may be relevant for excitation and detection of whistler modes in space plasmas.

Shock wave polarizations and optical metrics in the Born and the Born–Infeld electrodynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Minz, Christoph, E-mail: christoph.minz@alumni.tu-berlin.de; Borzeszkowski, Horst-Heino von, E-mail: borzeszk@mailbox.tu-berlin.de; Chrobok, Thoralf, E-mail: tchrobok@mailbox.tu-berlin.de

We analyze the behavior of shock waves in nonlinear theories of electrodynamics. For this, by use of generalized Hadamard step functions of increasing order, the electromagnetic potential is developed in a series expansion near the shock wave front. This brings about a corresponding expansion of the respective electromagnetic field equations which allows for deriving relations that determine the jump coefficients in the expansion series of the potential. We compute the components of a suitable gauge-normalized version of the jump coefficients given for a prescribed tetrad compatible with the shock front foliation. The solution of the first-order jump relations shows that,more » in contrast to linear Maxwell’s electrodynamics, in general the propagation of shock waves in nonlinear theories is governed by optical metrics and polarization conditions describing the propagation of two differently polarized waves (leading to a possible appearance of birefringence). In detail, shock waves are analyzed in the Born and Born–Infeld theories verifying that the Born–Infeld model exhibits no birefringence and the Born model does. The obtained results are compared to those ones found in literature. New results for the polarization of the two different waves are derived for Born-type electrodynamics.« less

Ultrasonic monitoring of spontaneous imbibition experiments: Acoustic signature of fluid migration

NASA Astrophysics Data System (ADS)

David, Christian; Barnes, Christophe; Desrues, Mathilde; Pimienta, Lucas; Sarout, Joël.; Dautriat, Jérémie

2017-07-01

Capillary rise experiments (spontaneous imbibition tests) were conducted in the laboratory with ultrasonic and X-ray monitoring on the Sherwood sandstone and the Majella grainstone. The aim was to provide a direct comparison between the variation in seismic attributes (amplitude, velocity, spectral content, and energy) and the actual fluid distribution in the rock. Two pairs of ultrasonic P wave sensors located at different heights on a cylindrical rock specimen recorded every 5 s the waveforms when capillary forces make water rise up into the rock from the bottom in contact with a water tank. Simultaneously, computerized tomography scan images of a vertical cross section were also recorded. Two important results were found. (i) The amplitude of the first P wave arrival is impacted by the upward moving fluid front before the P wave velocity is, while the fluid front has not yet reached the sensors level. In contrast, the P wave velocity decreases when the fluid front reaches the Fresnel clearance zone. The spectral analysis of the waveforms shows that the peak frequency amplitude is continuously decreasing without noticeable frequency shift. (ii) A methodology based on the calculation of the analytical signal and instantaneous phase was designed to decompose each waveform into discrete wavelets associated with direct or reflected waves. The energy carried by the wavelets is very sensitive to the fluid substitution process: the coda wavelets related to reflections on the bottom end face of the specimen are impacted as soon as imbibition starts and can be used as a precursor for the arriving fluid.

Moreton wave, "EIT wave", and type II radio burst as manifestations of a single wave front

NASA Astrophysics Data System (ADS)

Kuzmenko, I. V.; Grechnev, V. V.; Uralov, A. M.

2011-12-01

We show that a Moreton wave, an "EIT wave," and a type II radio burst observed during a solar flare of July 13, 2004, might have been a manifestation of a single front of a decelerating shock wave, which appeared in an active region (AR) during a filament eruption. We propose describing a quasi-spheroidal wave propagating upward and along the solar surface by using relations known from a theory of a point-like explosion in a gas whose density changes along the radius according to a power law. By applying this law to fit the drop in density of the coronal plasma enveloping the solar active region, we first managed to bring the measured positions and velocities of surface Moreton wave and "EIT wave" into correspondence with the observed frequency drift rate of the meter type II radio burst. The exponent of the vertical coronal density falloff is selected by fitting the power law to the Newkirk and Saito empirical distributions in the height range of interest. Formal use of such a dependence in the horizontal direction with a different exponent appears to be reasonable up to distances of less than 200 Mm around the eruption center. It is possible to assume that the near-surface shock wave weakens when leaving this radius and finally the active region, entering the region of the quiet Sun where the coronal plasma density and the fast-mode speed are almost constant along the horizontal.

Shear wave speed recovery in transient elastography and supersonic imaging using propagating fronts

NASA Astrophysics Data System (ADS)

McLaughlin, Joyce; Renzi, Daniel

2006-04-01

Transient elastography and supersonic imaging are promising new techniques for characterizing the elasticity of soft tissues. Using this method, an 'ultrafast imaging' system (up to 10 000 frames s-1) follows in real time the propagation of a low frequency shear wave. The displacement of the propagating shear wave is measured as a function of time and space. The objective of this paper is to develop and test algorithms whose ultimate product is images of the shear wave speed of tissue mimicking phantoms. The data used in the algorithms are the front of the propagating shear wave. Here, we first develop techniques to find the arrival time surface given the displacement data from a transient elastography experiment. The arrival time surface satisfies the Eikonal equation. We then propose a family of methods, called distance methods, to solve the inverse Eikonal equation: given the arrival times of a propagating wave, find the wave speed. Lastly, we explain why simple inversion schemes for the inverse Eikonal equation lead to large outliers in the wave speed and numerically demonstrate that the new scheme presented here does not have any large outliers. We exhibit two recoveries using these methods: one is with synthetic data; the other is with laboratory data obtained by Mathias Fink's group (the Laboratoire Ondes et Acoustique, ESPCI, Université Paris VII).

Breaking Wave Impact on a Partially Submerged Rigid Cube in Deep Water

NASA Astrophysics Data System (ADS)

Ikeda, C. M.; Choquette, M.; Duncan, J. H.

2011-11-01

The impact of a plunging breaking wave on a partially submerged cube is studied experimentally. The experiments are performed in a wave tank that is 14.8 m long, 1.15 m wide and 2.2 m high with a water depth of 0.91 m. A single repeatable plunging breaker is generated from a dispersively focused wave packet (average frequency of 1.4 Hz) that is created with a programmable wave maker. The rigid (L = 30 . 5 cm) cube is centered in the width of the tank and mounted from above with one face oriented normal to the oncoming wave. The position of the center of the front face of the cube is varied from the breaker location (xb ~ 6 . 35 m) to xb + 0 . 05 m in the streamwise direction and from - 0 . 25 L to 0 . 25 L vertically relative to the mean water level. A high-speed digital camera is used to record both white-light and laser-induced fluorescence (LIF) movies of the free surface shape in front of the cube before and after the wave impact. When the wave hits the cube just as the plunging jet is formed, a high-velocity vertical jet is created and the trajectory and maximum height of the jet are strongly influenced by the vertical position of the cube. Supported by the Office of Naval Research, Contract Monitor R. D. Joslin.

Traveling-wave synchronous coil gun

NASA Technical Reports Server (NTRS)

Elliott, David G.

1991-01-01

An outline is presented of the coilgun concept, excitation, switching, brush commutation, power supply, and performance. It is shown that a traveling-wave synchronous coilgun permits independent adjustment of the magnetic field and armature current for high velocity at low armature mass fraction. Magnetic field energy is transferred from the rear of the wave to the front without passing through the power supply. Elaborate switching is required.

Integration of an Acoustic Modem onto a Wave Glider Unmanned Surface Vehicle

DTIC Science & Technology

2012-06-01

of the wave and ωτ represents the phase of the wave. After some amount of math and taking the limit as ω →∞ , we arrive at a form of the eikonal ...the phase front. (5.5) 22 0A Aτ τ∇ ⋅∇ + ∇ = The transport equation and the eikonal equation can be solved by using multiple methods to give

Al 1s-2p absorption spectroscopy of shock-wave heating and compression in laser-driven planar foil

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sawada, H.; Regan, S. P.; Radha, P. B.

Time-resolved Al 1s-2p absorption spectroscopy is used to diagnose direct-drive, shock-wave heating and compression of planar targets having nearly Fermi-degenerate plasma conditions (T{sub e}{approx}10-40 eV, {rho}{approx}3-11 g/cm{sup 3}) on the OMEGA Laser System [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. A planar plastic foil with a buried Al tracer layer was irradiated with peak intensities of 10{sup 14}-10{sup 15} W/cm{sup 2} and probed with the pseudocontinuum M-band emission from a point-source Sm backlighter in the range of 1.4-1.7 keV. The laser ablation process launches 10-70 Mbar shock waves into the CH/Al/CH target. The Al 1s-2p absorption spectramore » were analyzed using the atomic physic code PRISMSPECT to infer T{sub e} and {rho} in the Al layer, assuming uniform plasma conditions during shock-wave heating, and to determine when the heat front penetrated the Al layer. The drive foils were simulated with the one-dimensional hydrodynamics code LILAC using a flux-limited (f=0.06 and f=0.1) and nonlocal thermal-transport model [V. N. Goncharov et al., Phys. Plasmas 13, 012702 (2006)]. The predictions of simulated shock-wave heating and the timing of heat-front penetration are compared to the observations. The experimental results for a wide variety of laser-drive conditions and buried depths have shown that the LILAC predictions using f=0.06 and the nonlocal model accurately model the shock-wave heating and timing of the heat-front penetration while the shock is transiting the target. The observed discrepancy between the measured and simulated shock-wave heating at late times of the drive can be explained by the reduced radiative heating due to lateral heat flow in the corona.« less

Al 1s-2p Absorption Spectroscopy of Shock-Wave Heating and Compression in Laser-Driven Planar Foil

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sawada, H.; Regan, S.P.; Radha, P.B.

Time-resolved Al 1s-2p absorption spectroscopy is used to diagnose direct-drive, shock-wave heating and compression of planar targets having nearly Fermi-degenerate plasma conditions (Te ~ 10–40 eV, rho ~ 3–11 g/cm^3) on the OMEGA Laser System [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. A planar plastic foil with a buried Al tracer layer was irradiated with peak intensities of 10^14–10^15 W/cm^2 and probed with the pseudocontinuum M-band emission from a point-source Sm backlighter in the range of 1.4–1.7 keV. The laser ablation process launches 10–70 Mbar shock waves into the CH/Al/CH target. The Al 1s-2p absorption spectra weremore » analyzed using the atomic physic code PRISMSPECT to infer Te and rho in the Al layer, assuming uniform plasma conditions during shock-wave heating, and to determine when the heat front penetrated the Al layer. The drive foils were simulated with the one-dimensional hydrodynamics code LILAC using a flux-limited (f =0.06 and f =0.1) and nonlocal thermal-transport model [V. N. Goncharov et al., Phys. Plasmas 13, 012702 (2006)]. The predictions of simulated shock-wave heating and the timing of heat-front penetration are compared to the observations. The experimental results for a wide variety of laser-drive conditions and buried depths have shown that the LILAC predictions using f = 0.06 and the nonlocal model accurately model the shock-wave heating and timing of the heat-front penetration while the shock is transiting the target. The observed discrepancy between the measured and simulated shock-wave heating at late times of the drive can be explained by the reduced radiative heating due to lateral heat flow in the corona.« less

Slide-induced waves, seiching and ground fracturing caused by the earthquake of March 27, 1964 at Kenai Lake, Alaska: Chapter A in The Alaska earthquake, March 27, 1964: regional effects

USGS Publications Warehouse

McCulloch, David S.

1966-01-01

The March 27, 1964, earthquake dislodged slides from nine deltas in Kenai Lake, south-central Alaska. Sliding removed protruding parts of deltas-often the youngest parts-and steepened delta fronts, increasing the chances of further sliding. Fathograms show that debris from large slides spread widely over the lake floor, some reaching the toe of the opposite shore; at one place debris traveled 5,000 feet over the horizontal lake floor. Slides generated two kinds of local waves: a backfill and far-shore wave. Backfill waves were formed by water that rushed toward the delta to fill the void left by the sinking slide mass, overtopped the slide scrap, and came ashore over the delta. Some backfill waves had runup heights of 30 feet and ran inland more than 300 feet, uprooting and breaking off large trees. Far-shore waves hit the shore opposite the slides. They were formed by slide debris that crossed the lake floor and forced water ahead of it, which then ran up the opposite slope, burst above the lake surface, and struck the shore. One far-shore wave had a runup height of 72 feet. Kenai Lake was tilted and seiched; a power spectrum analysis of a limnogram shows a wave having the period of the calculated uninodal seiche (36 minutes) and several shorter period waves. In constricted and shallow reaches, waves caused by seiching had 20- and 30-foot runup heights. Deep lateral spreading of sediments toward delta margins displaced deeply driven railroad-bridge piles, and set up stress fields in the surface sediments which resulted in the formation of many shear and some tension fractures on the surface of two deltas.

Spatial structure of directional wave spectra in hurricanes

NASA Astrophysics Data System (ADS)

Esquivel-Trava, Bernardo; Ocampo-Torres, Francisco J.; Osuna, Pedro

2015-01-01

The spatial structure of the wave field during hurricane conditions is studied using the National Data Buoy Center directional wave buoy data set from the Caribbean Sea and the Gulf of Mexico. The buoy information, comprising the directional wave spectra during the passage of several hurricanes, was referenced to the center of the hurricane using the path of the hurricane, the propagation velocity, and the radius of the maximum winds. The directional wave spectra were partitioned into their main components to quantify the energy corresponding to the observed wave systems and to distinguish between wind-sea and swell. The findings are consistent with those found using remote sensing data (e.g., Scanning Radar Altimeter data). Based on the previous work, the highest waves are found in the right forward quadrant of the hurricane, where the spectral shape tends to become uni-modal, in the vicinity of the region of maximum winds. More complex spectral shapes are observed in distant regions at the front of and in the rear quadrants of the hurricane, where there is a tendency of the spectra to become bi- and tri-modal. The dominant waves generally propagate at significant angles to the wind direction, except in the regions next to the maximum winds of the right quadrants. Evidence of waves generated by concentric eyewalls associated with secondary maximum winds was also found. The frequency spectra display some of the characteristics of the JONSWAP spectrum adjusted by Young (J Geophys Res 111:8020, 2006); however, at the spectral peak, the similarity with the Pierson-Moskowitz spectrum is clear. These results establish the basis for the use in assessing the ability of numerical models to simulate the wave field in hurricanes.

Nonperturbative light-front Hamiltonian methods

NASA Astrophysics Data System (ADS)

Hiller, J. R.

2016-09-01

We examine the current state-of-the-art in nonperturbative calculations done with Hamiltonians constructed in light-front quantization of various field theories. The language of light-front quantization is introduced, and important (numerical) techniques, such as Pauli-Villars regularization, discrete light-cone quantization, basis light-front quantization, the light-front coupled-cluster method, the renormalization group procedure for effective particles, sector-dependent renormalization, and the Lanczos diagonalization method, are surveyed. Specific applications are discussed for quenched scalar Yukawa theory, ϕ4 theory, ordinary Yukawa theory, supersymmetric Yang-Mills theory, quantum electrodynamics, and quantum chromodynamics. The content should serve as an introduction to these methods for anyone interested in doing such calculations and as a rallying point for those who wish to solve quantum chromodynamics in terms of wave functions rather than random samplings of Euclidean field configurations.

Modelling of Charles Darwin's tsunami reports

NASA Astrophysics Data System (ADS)

Galiev, Shamil

2010-05-01

Darwin landed at Valdivia and Concepcion, Chile, just before, during, and after a great 1835 earthquake. He described his impressions and results of the earthquake-induced natural catastrophe in The Voyage of the Beagle. His description of the tsunami could easily be read as a report from Indonesia or Sri Lanka, after the catastrophic tsunami of 26 December 2004. In particular, Darwin emphasised the dependence of earthquake-induced waves on a form of the coast and the coastal depth: ‘… Talcuhano and Callao are situated at the head of great shoaling bays, and they have always suffered from this phenomenon; whereas, the town of Valparaiso, which is seated close on the border of a profound ocean... has never been overwhelmed by one of these terrific deluges…' . He reports also, that ‘… the whole body of the sea retires from the coast, and then returns in great waves of overwhelming force ...' (we cite the Darwin's sentences following researchspace. auckland. ac. nz/handle/2292/4474). The coastal evolution of a tsunami was analytically studied in many publications (see, for example, Synolakis, C.E., Bernard, E.N., 2006. Philos. Trans. R. Soc., Ser. A, 364, 2231-2265; Tinti, S., Tonini, R. 205. J.Fluid Mech., 535, 11-21). However, the Darwin's reports and the influence of the coastal depth on the formation and the evolution of the steep front and the profile of tsunami did not practically discuss. Recently, a mathematical theory of these phenomena was presented in researchspace. auckland. ac. nz/handle/2292/4474. The theory describes the waves which are excited due to nonlinear effects within a shallow coastal zone. The tsunami elevation is described by two components: . Here is the linear (prime) component. It describes the wave coming from the deep ocean. is the nonlinear component. This component may become very important near the coastal line. After that the theory of the shallow waves is used. This theory yields the linear equation for and the weakly-nonlinear equation for . The last equation contains the forcing term which is generated by nonlinearity and depends on . The nonlinear shock-like solution for is constructed which is valid within the narrow coastal zone. Then the tsunami evolution near a coast is studied. It is found that the coastal evolution strongly depends on the profile of the bottom and the distance from the coastline. Far from this the wave surface is smooth and the wave is long enough. The wave profile begins to change quickly, if the coastal water is shallow. The steep (discontinuous) front of the tsunami can be generated. The water level reduces ahead of the front, or the ebb can appear there. Then this front begins to move away from the coast - into the ocean. This direction is opposite to the motion of the whole wave. The amplitude of the front is increased. The water wall is formed. This process explains the catastrophic effect of a tsunami, when a water-wall appears instantly. The wave, having two steep peaks, may be generated in the case of very shallow water. In contrast with this, the tsunami, practically, does not change, if the coastal water is deep. On the whole, the conclusions agree with the Darwin's reports.

Stochastic Ion Heating by the Lower-Hybrid Waves

NASA Technical Reports Server (NTRS)

Khazanov, G.; Tel'nikhin, A.; Krotov, A.

2011-01-01

The resonance lower-hybrid wave-ion interaction is described by a group (differentiable map) of transformations of phase space of the system. All solutions to the map belong to a strange attractor, and chaotic motion of the attractor manifests itself in a number of macroscopic effects, such as the energy spectrum and particle heating. The applicability of the model to the problem of ion heating by waves at the front of collisionless shock as well as ion acceleration by a spectrum of waves is discussed. Keywords: plasma; ion-cyclotron heating; shocks; beat-wave accelerator.

Sedimentary structures formed under water surface waves: examples from a sediment-laden flash flood observed by remote camer

NASA Astrophysics Data System (ADS)

Froude, Melanie; Alexander, Jan; Cole, Paul; Barclay, Jenni

2014-05-01

On 13-14 October 2012, Tropical Storm Rafael triggered sediment-laden flash floods in the Belham Valley on Montserrat, West Indies. Rainfall was continuous for ~38 hours and intensity peaked at 48 mm/hr. Flow was strongly unsteady, turbulent with sediment concentrations varying up to hyperconcentrated. Time-lapse images captured at >1 frame per second by remote camera overlooking a surveyed valley section show the development of trains of water surface waves at multiple channel locations during different flow stages. Waves grew and diminished in height and remained stationary or migrated upstream. Trains of waves persisted for <5 minutes, until a single wave broke, sometimes initiating the breaking of adjacent waves within the train. Channel-wide surges (bores) propagating downstream with distinct turbulent flow fronts, were observed at irregular intervals during and up to 7 hours after peak stage. These bores are mechanically similar to breaking front tidal bores and arid flood bores, and resulted in a sudden increase in flow depth and velocity. When a bore front came into close proximity (within ~10 m) upstream of a train of water surface waves, the waves appeared to break simultaneously generating a localised surge of water upstream, that was covered by the bore travelling downstream. Those trains in which waves did not break during the passage of a bore temporarily reduced in height. In both cases, water surface waves reformed immediately after the surge in the same location. Deposits from the event, were examined in <4 m deep trenches ~0.5 km downstream of the remote camera. These contained laterally extensive lenticular and sheet-like units comprised of varying admixtures of sand and gravel that are attributed to antidunes, and associated transitions from upper-stage-plane-beds. Some of the structures are organised within concave upward sequences which contain downflow shifts between foreset and backset laminae; interpreted as trough fills from chute-and-pools or water surface wave breaking. At least 90% of the deposit is interpreted upper flow regime origin. The sequence, geometry and lamina-scale texture of the sedimentary structures will be discussed with reference to remote camera images of rapidly varying, unsteady and pulsatory flow behaviour.

Gravity wave generation from jets and fronts: idealized and real-case simulations

NASA Astrophysics Data System (ADS)

Plougonven, Riwal; Arsac, Antonin; Hertzog, Albert; Guez, Lionel; Vial, François

2010-05-01

The generation of gravity waves from jets and fronts remains an outstanding issue in the dynamics of the atmosphere. It is important to explain and quantify this emission because of the several impacts of these waves, in particular the induced momentum fluxes towards the middle atmosphere, and their contribution to turbulence and mixing, e.g. in the region of the tropopause. Yet, the mechanisms at the origin of these waves have been difficult to identify, the fundamental reason for this being the separation between the time scales of balanced motions and gravity waves. Recent simulations of idealized baroclinic life cycles and of dipoles have provided insights into the mechanisms determining the characteristics and the amplitude of gravity waves emitted by jets. It has been shown in particular that the environmental strain and shear play a crucial role in determining the characteristics and location of the emitted waves, emphasizing jet exit regions for the appearance of coherent low-frequency waves. It has also been shown how advection of relatively small-scales allow to overcome the separation of time scales alluded to above. Recent results, remaining open questions and ongoing work on these idealized simulations will be briefly summarized. Nevertheless, unavoidable shortcomings of such idealized simulations include the sensitivity of the emitted waves to model setup (resolution, diffusion, parameterizations) and uncertainty regarding the realism of this aspect of the simulations. Hence, it is necessary to compare simulations with observations in order to assess their relevance. Such comparison has been undertaken using the dataset from the Vorcore campaign (Sept. 2005 - Feb. 2006, Hertzog, J. Atmos. Ocean. Techno. 2007) during which 27 superpressure balloons drifted as quasi-Lagrangian tracers in the lower stratosphere above Antarctica and the Southern Ocean. High-resolution simulations (dx = 20 km) have been carried out using the Weather Research and Forecast model for nearly two months. The realism of the simulated gravity waves is established based on systematic comparison with the observations and on case studies. The simulations are then used to quantify the importance and characteristics of gravity waves emitted from jets and fronts above the Southern Ocean. In particular, application of results from the idealized simulations to real cases, with a check provided by observations, will be discussed.

MAVEN Observations of Solar Wind-Driven Magnetosonic Waves Heating the Martian Dayside Ionosphere

NASA Astrophysics Data System (ADS)

Fowler, C. M.; Andersson, L.; Ergun, R. E.; Harada, Y.; Hara, T.; Collinson, G.; Peterson, W. K.; Espley, J.; Halekas, J.; Mcfadden, J.; Mitchell, D. L.; Mazelle, C.; Benna, M.; Jakosky, B. M.

2018-05-01

We present Mars Atmosphere and Volatile EvolutioN observations of large-amplitude magnetosonic waves propagating through the magnetosheath into the Martian ionosphere near the subsolar point on the dayside of the planet. The observed waves grow in amplitude as predicted for a wave propagating into a denser, charged medium, with wave amplitudes reaching 25 nT, equivalent to ˜40% of the background field strength. These waves drive significant density and temperature variations (˜20% to 100% in amplitude) in the suprathermal electrons and light ion species (H+) that correlate with compressional fronts of the magnetosonic waves. Density and temperature variations are also observed for the ionospheric electrons, and heavy ion species (O+ and O2+); however, these variations are not in phase with the magnetic field variations. Whistler waves are observed at compressional wave fronts and are thought to be produced by unstable, anistropic suprathermal electrons. The magnetosonic waves drive significant ion and electron heating down to just above the exobase region. Ion heating rates are estimated to be between 0.03 and 0.2 eVs-1 per ion, and heavier ions could thus gain escape energy if located in this heating region for ˜10-70 s. The measured ionospheric density profile indicates severe ionospheric erosion above the exobase region, and this is likely caused by substantial ion outflow that is driven by the observed heating. The effectiveness of these magnetosonic waves to energize the plasma close to the exobase could have important implications for the long-term climate evolution for unmagnetized bodies that are exposed to the solar wind.

Deleterious mutations can surf to high densities on the wave front of an expanding population.

PubMed

Travis, Justin M J; Münkemüller, Tamara; Burton, Olivia J; Best, Alex; Dytham, Calvin; Johst, Karin

2007-10-01

There is an increasing recognition that evolutionary processes play a key role in determining the dynamics of range expansion. Recent work demonstrates that neutral mutations arising near the edge of a range expansion sometimes surf on the expanding front leading them rather than that leads to reach much greater spatial distribution and frequency than expected in stationary populations. Here, we extend this work and examine the surfing behavior of nonneutral mutations. Using an individual-based coupled-map lattice model, we confirm that, regardless of its fitness effects, the probability of survival of a new mutation depends strongly upon where it arises in relation to the expanding wave front. We demonstrate that the surfing effect can lead to deleterious mutations reaching high densities at an expanding front, even when they have substantial negative effects on fitness. Additionally, we highlight that this surfing phenomenon can occur for mutations that impact reproductive rate (i.e., number of offspring produced) as well as mutations that modify juvenile competitive ability. We suggest that these effects are likely to have important consequences for rates of spread and the evolution of spatially expanding populations.

Shock front distortion and Richtmyer-Meshkov-type growth caused by a small preshock nonuniformity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Velikovich, A. L.; Wouchuk, J. G.; Huete Ruiz de Lira, C.

The response of a shock front to small preshock nonuniformities of density, pressure, and velocity is studied theoretically and numerically. These preshock nonuniformities emulate imperfections of a laser target, due either to its manufacturing, like joints or feeding tubes, or to preshock perturbation seeding/growth, as well as density fluctuations in foam targets, ''thermal layers'' near heated surfaces, etc. Similarly to the shock-wave interaction with a small nonuniformity localized at a material interface, which triggers a classical Richtmyer-Meshkov (RM) instability, interaction of a shock wave with periodic or localized preshock perturbations distributed in the volume distorts the shape of the shockmore » front and can cause a RM-type instability growth. Explicit asymptotic formulas describing distortion of the shock front and the rate of RM-type growth are presented. These formulas are favorably compared both to the exact solutions of the corresponding initial-boundary-value problem and to numerical simulations. It is demonstrated that a small density modulation localized sufficiently close to a flat target surface produces the same perturbation growth as an 'equivalent' ripple on the surface of a uniform target, characterized by the same initial areal mass modulation amplitude.« less

CORONAL AND CHROMOSPHERIC SIGNATURES OF LARGE-SCALE DISTURBANCES ASSOCIATED WITH A MAJOR SOLAR ERUPTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zong, Weiguo; Dai, Yu, E-mail: ydai@nju.edu.cn

We present both coronal and chromospheric observations of large-scale disturbances associated with a major solar eruption on 2005 September 7. In the Geostationary Operational Environmental Satellites/Solar X-ray Imager (SXI), arclike coronal brightenings are recorded propagating in the southern hemisphere. The SXI front shows an initially constant speed of 730 km s{sup −1} and decelerates later on, and its center is near the central position angle of the associated coronal mass ejection (CME) but away from the flare site. Chromospheric signatures of the disturbances are observed in both Mauna Loa Solar Observatory (MLSO)/Polarimeter for Inner Coronal Studies Hα and MLSO/Chromospheric Helium Imore » Imaging Photometer He i λ10830 and can be divided into two parts. The southern signatures occur in regions where the SXI front sweeps over, with the Hα bright front coincident with the SXI front, while the He i dark front lags the SXI front but shows a similar kinematics. Ahead of the path of the southern signatures, oscillations of a filament are observed. The northern signatures occur near the equator, with the Hα and He i fronts coincident with each other. They first propagate westward and then deflect to the north at the boundary of an equatorial coronal hole. Based on these observational facts, we suggest that the global disturbances are associated with the CME lift-off and show a hybrid nature: a mainly non-wave CME flank nature for the SXI signatures and the corresponding southern chromospheric signatures, and a shocked fast-mode coronal MHD wave nature for the northern chromospheric signatures.« less

Kelvin-Mach Wake in a Two-Dimensional Fermi Sea

NASA Astrophysics Data System (ADS)

Kolomeisky, Eugene B.; Straley, Joseph P.

2018-06-01

The dispersion law for plasma oscillations in a two-dimensional electron gas in the hydrodynamic approximation interpolates between Ω ∝√{q } and Ω ∝q dependences as the wave vector q increases. As a result, downstream of a charged impurity in the presence of a uniform supersonic electric current flow, a wake pattern of induced charge density and potential is formed whose geometry is controlled by the Mach number M . For 1 √{2 }. These wakes also trail an external charge, traveling supersonically, a fixed distance away from the electron gas.

Optical pin apparatus for measuring the arrival time and velocity of shock waves and particles

DOEpatents

Benjamin, R.F.

1983-10-18

An apparatus for the detection of the arrival and for the determination of the velocity of disturbances such as shock-wave fronts and/or projectiles. Optical pins using fluid-filled microballoons as the light source and an optical fiber as a link to a photodetector have been used to investigate shock-waves and projectiles. A microballoon filled with a noble gas is affixed to one end of a fiber-optic cable, and the other end of the cable is attached to a high-speed streak camera. As the shock-front or projectile compresses the microballoon, the gas inside is heated and compressed producing a bright flash of light. The flash of light is transmitted via the optic cable to the streak camera where it is recorded. One image-converter streak camera is capable of recording information from more than 100 microballoon-cable combinations simultaneously.

Optical pin apparatus for measuring the arrival time and velocity of shock waves and particles

DOEpatents

Benjamin, Robert F.

1987-01-01

An apparatus for the detection of the arrival and for the determination of the velocity of disturbances such as shock-wave fronts and/or projectiles. Optical pins using fluid-filled microballoons as the light source and an optical fiber as a link to a photodetector have been used to investigate shock-waves and projectiles. A microballoon filled with a noble gas is affixed to one end of a fiber-optic cable, and the other end of the cable is attached to a high-speed streak camera. As the shock-front or projectile compresses the microballoon, the gas inside is heated and compressed producing a bright flash of light. The flash of light is transmitted via the optic cable to the streak camera where it is recorded. One image-converter streak camera is capable of recording information from more than 100 microballoon-cable combinations simultaneously.

Optical pin apparatus for measuring the arrival time and velocity of shock waves and particles

DOEpatents

Benjamin, R.F.

1987-03-10

An apparatus is disclosed for the detection of the arrival and for the determination of the velocity of disturbances such as shock-wave fronts and/or projectiles. Optical pins using fluid-filled microballoons as the light source and an optical fiber as a link to a photodetector have been used to investigate shock-waves and projectiles. A microballoon filled with a noble gas is affixed to one end of a fiber-optic cable, and the other end of the cable is attached to a high-speed streak camera. As the shock-front or projectile compresses the microballoon, the gas inside is heated and compressed producing a bright flash of light. The flash of light is transmitted via the optic cable to the streak camera where it is recorded. One image-converter streak camera is capable of recording information from more than 100 microballoon-cable combinations simultaneously. 3 figs.

Relativistic shock waves in an electron-positron plasma

NASA Astrophysics Data System (ADS)

Tsintsadze, Levan N.

1995-12-01

The equations describing the detailed structure of radiation electromagnetic hydrodynamics for a relativistically hot electron-positron plasma are derived. Various discontinuities are studied by these equations. It is shown that the dependence of the electron (positron) mass on the temperature changes the structure of discontinuities, including shock waves, both qualitatively and quantitatively. Steady radiative shocks are considered, which can arise in steady flows, and which also can be used to describe the propagation of shocks when the shock thickness is very small as compared to the characteristic length over which the ambient medium changes significantly. First, the magnetohydrodynamic shock wave is treated as a discontinuity and jump relations, which relate the equilibrium states of the upstream and downstream plasma far from the front, are derived. Then the structure of the front itself is considered and tangential, contact (or entropy) and rotational discontinuities are investigated.

The reflection of an ionized shock wave

NASA Astrophysics Data System (ADS)

Asakura, Fumioki; Corli, Andrea

2018-03-01

In a previous paper, we studied the thermodynamic and kinetic theory for an ionized gas, in one space dimension; in this paper, we provide an application of those results to the reflection of a shock wave in an electromagnetic shock tube. Under some reasonable limitations, which fully agree with experimental data, we prove that both the incident and the reflected shock waves satisfy the Lax entropy conditions; this result holds even outside genuinely nonlinear regions, which are present in the model. We show that the temperature increases in a significant way behind the incident shock front but the degree of ionization does not undergo a similar growth. On the contrary, the degree of ionization increases substantially behind the reflected shock front. We explain these phenomena by means of the concavity of the Hugoniot loci. Therefore, our results not only fit perfectly but explain what was remarked in experiments.

Light-front spin-dependent spectral function and nucleon momentum distributions for a three-body system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Del Dotto, Alessio; Pace, Emanuele; Salme, Giovanni

Poincare covariant definitions for the spin-dependent spectral function and for the momentum distributions within the light-front Hamiltonian dynamics are proposed for a three-fermion bound system, starting from the light-front wave function of the system. The adopted approach is based on the Bakamjian–Thomas construction of the Poincaré generators, which allows one to easily import the familiar and wide knowledge on the nuclear interaction into a light-front framework. The proposed formalism can find useful applications in refined nuclear calculations, such as those needed for evaluating the European Muon Collaboration effect or the semi-inclusive deep inelastic cross sections with polarized nuclear targets, sincemore » remarkably the light-front unpolarized momentum distribution by definition fulfills both normalization and momentum sum rules. As a result, also shown is a straightforward generalization of the definition of the light-front spectral function to an A-nucleon system.« less

Light-front spin-dependent spectral function and nucleon momentum distributions for a three-body system

DOE PAGES

Del Dotto, Alessio; Pace, Emanuele; Salme, Giovanni; ...

2017-01-10

Poincare covariant definitions for the spin-dependent spectral function and for the momentum distributions within the light-front Hamiltonian dynamics are proposed for a three-fermion bound system, starting from the light-front wave function of the system. The adopted approach is based on the Bakamjian–Thomas construction of the Poincaré generators, which allows one to easily import the familiar and wide knowledge on the nuclear interaction into a light-front framework. The proposed formalism can find useful applications in refined nuclear calculations, such as those needed for evaluating the European Muon Collaboration effect or the semi-inclusive deep inelastic cross sections with polarized nuclear targets, sincemore » remarkably the light-front unpolarized momentum distribution by definition fulfills both normalization and momentum sum rules. As a result, also shown is a straightforward generalization of the definition of the light-front spectral function to an A-nucleon system.« less

A Review of Alfvénic Turbulence in High-Speed Solar Wind Streams: Hints From Cometary Plasma Turbulence

NASA Astrophysics Data System (ADS)

Tsurutani, Bruce T.; Lakhina, Gurbax S.; Sen, Abhijit; Hellinger, Petr; Glassmeier, Karl-Heinz; Mannucci, Anthony J.

2018-04-01

Solar wind turbulence within high-speed streams is reviewed from the point of view of embedded single nonlinear Alfvén wave cycles, discontinuities, magnetic decreases (MDs), and shocks. For comparison and guidance, cometary plasma turbulence is also briefly reviewed. It is demonstrated that cometary nonlinear magnetosonic waves phase-steepen, with a right-hand circular polarized foreshortened front and an elongated, compressive trailing edge. The former part is a form of "wave breaking" and the latter that of "period doubling." Interplanetary nonlinear Alfvén waves, which are arc polarized, have a 180° foreshortened front and with an elongated trailing edge. Alfvén waves have polarizations different from those of cometary magnetosonic waves, indicating that helicity is a durable feature of plasma turbulence. Interplanetary Alfvén waves are noted to be spherical waves, suggesting the possibility of additional local generation. They kinetically dissipate, forming MDs, indicating that the solar wind is partially "compressive" and static. The 2 MeV protons can nonresonantly interact with MDs leading to rapid cross-field ( 5.5% Bohm) diffusion. The possibility of local ( 1 AU) generation of Alfvén waves may make it difficult to forecast High-Intensity, Long-Duration AE Activity and relativistic magnetospheric electrons with great accuracy. The future Solar Orbiter and Solar Probe Plus missions should be able to not only test these ideas but to also extend our knowledge of plasma turbulence evolution.

Case study of convective instability observed in airglow images over the Northeast of Brazil

NASA Astrophysics Data System (ADS)

Carvalho, A. J. A.; Paulino, I.; Medeiros, A. F.; Lima, L. M.; Buriti, R. A.; Paulino, A. R.; Wrasse, C. M.; Takahashi, H.

2017-02-01

An intense activity of ripples during the nighttime was observed in airglow images over São João do Cariri (36.5° W, 7.4° S) on 10 October 2004 which lasted for two hours. Those ripples appeared simultaneously with the crossing of a mesospheric front and medium scale gravity waves. The ripples occurred ahead of the mesospheric front and their phase front were almost parallel to the phase of the mesospheric front and were almost perpendicular to the phase front of the gravity wave. Using wind measurements from a meteor radar located at São João do Cariri and simultaneous vertical temperature profiles from the TIMED/SABER satellite, on the night of the events and within the imager field of view, the atmospheric background environment in the mesosphere and lower thermosphere (MLT) was investigated in order to understand the instability process that caused the appearance of the ripples. Dynamic and convective instabilities have been pointed out as responsible for creation of ripples in the MLT. The observed ripples were advected by the neutral wind, they occurred into a region with negative lapse rate of the potential temperature and the Richardson number was negative as well. According to these characteristics, the ripple structures could be generated in the MLT region due to the predominance of convective instability.

Numerical modeling of a multiscale gravity wave event and its airglow signatures over Mount Cook, New Zealand, during the DEEPWAVE campaign

NASA Astrophysics Data System (ADS)

Heale, C. J.; Bossert, K.; Snively, J. B.; Fritts, D. C.; Pautet, P.-D.; Taylor, M. J.

2017-01-01

A 2-D nonlinear compressible model is used to simulate a large-amplitude, multiscale mountain wave event over Mount Cook, NZ, observed as part of the Deep Propagating Gravity Wave Experiment (DEEPWAVE) campaign and to investigate its observable signatures in the hydroxyl (OH) layer. The campaign observed the presence of a λx=200 km mountain wave as part of the 22nd research flight with amplitudes of >20 K in the upper stratosphere that decayed rapidly at airglow heights. Advanced Mesospheric Temperature Mapper (AMTM) showed the presence of small-scale (25-28 km) waves within the warm phase of the large mountain wave. The simulation results show rapid breaking above 70 km altitude, with the preferential formation of almost-stationary vortical instabilities within the warm phase front of the mountain wave. An OH airglow model is used to identify the presence of small-scale wave-like structures generated in situ by the breaking of the mountain wave that are consistent with those seen in the observations. While it is easy to interpret these feature as waves in OH airglow data, a considerable fraction of the features are in fact instabilities and vortex structures. Simulations suggest that a combination of a large westward perturbation velocity and shear, in combination with strong perturbation temperature gradients, causes both dynamic and convective instability conditions to be met particularly where the wave wind is maximized and the temperature gradient is simultaneously minimized. This leads to the inevitable breaking and subsequent generation of smaller-scale waves and instabilities which appear most prominent within the warm phase front of the mountain wave.

Suspended liquid particle disturbance on laser-induced blast wave and low density distribution

NASA Astrophysics Data System (ADS)

Ukai, Takahiro; Zare-Behtash, Hossein; Kontis, Konstantinos

2017-12-01

The impurity effect of suspended liquid particles on the laser-induced gas breakdown was experimentally investigated in quiescent gas. The focus of this study is the investigation of the influence of the impurities on the shock wave structure as well as the low density distribution. A 532 nm Nd:YAG laser beam with an 188 mJ/pulse was focused on the chamber filled with suspended liquid particles 0.9 ± 0.63 μm in diameter. Several shock waves are generated by multiple gas breakdowns along the beam path in the breakdown with particles. Four types of shock wave structures can be observed: (1) the dual blast waves with a similar shock radius, (2) the dual blast waves with a large shock radius at the lower breakdown, (3) the dual blast waves with a large shock radius at the upper breakdown, and (4) the triple blast waves. The independent blast waves interact with each other and enhance the shock strength behind the shock front in the lateral direction. The triple blast waves lead to the strongest shock wave in all cases. The shock wave front that propagates toward the opposite laser focal spot impinges on one another, and thereafter a transmitted shock wave (TSW) appears. The TSW interacts with the low density core called a kernel; the kernel then longitudinally expands quickly due to a Richtmyer-Meshkov-like instability. The laser-particle interaction causes an increase in the kernel volume which is approximately five times as large as that in the gas breakdown without particles. In addition, the laser-particle interaction can improve the laser energy efficiency.

Stationary Shock Waves with Oscillating Front in Dislocation Systems of Semiconductors

NASA Astrophysics Data System (ADS)

Gestrin, S. G.; Shchukina, E. V.

2018-05-01

The paper presents a study of weakly nonlinear wave processes in the cylindrical region of a hole gas surrounding a negatively charged dislocation in an n-type semiconductor crystal. It is shown that shock waves propagating along the dislocation are the solutions of the Korteweg-de Vries-Burgers equation when the dispersion and dissipation of medium are taken into account. Estimates are obtained for the basic physical parameters characterizing the shock wave and the region inside the Reed cylinder.

Understanding Effects of Traumatic Insults on Brain Structure and Function

DTIC Science & Technology

2016-08-01

42 Fig. 33 The supersonic shock wave at the various distances from its launch. The liposome is located at 117.4 nm. The...For instance, although the pressure front of a shock wave travels at supersonic speeds (the speed of sound in water is 1,497 m/s), the shock wave... supersonic shock wave at the various distances from its launch. The liposome is located at 117.4 nm. The Mach number is 1.49. b) The pressure profile at t

Modeling wildland fire propagation with level set methods

Treesearch

V. Mallet; D.E Keyes; F.E. Fendell

2009-01-01

Level set methods are versatile and extensible techniques for general front tracking problems, including the practically important problem of predicting the advance of a fire front across expanses of surface vegetation. Given a rule, empirical or otherwise, to specify the rate of advance of an infinitesimal segment of fire front arc normal to itself (i.e., given the...

Observation of laser-driven shock propagation by nanosecond time-resolved Raman spectroscopy

NASA Astrophysics Data System (ADS)

Yu, Guoyang; Zheng, Xianxu; Song, Yunfei; Zeng, Yangyang; Guo, Wencan; Zhao, Jun; Yang, Yanqiang

2015-01-01

An improved nanosecond time-resolved Raman spectroscopy is performed to observe laser-driven shock propagation in the anthracene/epoxy glue layer. The digital delay instead of optical delay line is introduced for sake of unlimited time range of detection, which enables the ability to observe both shock loading and shock unloading that always lasts several hundred nanoseconds. In this experiment, the peak pressure of shock wave, the pressure distribution, and the position of shock front in gauge layer were determined by fitting Raman spectra of anthracene using the Raman peak shift simulation. And, the velocity of shock wave was calculated by the time-dependent position of shock front.

The stabilization of unstable detonation waves for the mixture of nitromethane/methanol

NASA Astrophysics Data System (ADS)

Utkin, A. V.; Koldunov, S. A.; Mochalova, V. M.; Torunov, S. I.; Lapin, S. M.

2015-11-01

Using a laser interferometer VISAR the measurements of the particle velocity profiles in detonation waves for nitromethane/methanol mixtures with additions of a sensitizer diethylenetriamine were conducted. It is shown that the detonation front in a mixture of nitromethane/methanol is unstable and sensitizer is an effective method for the flow stabilization. If the diluent concentration is less than 10%, the detonation front is stabilized by adding of 1% diethylenetriamine. At higher concentrations of methanol, the sensitizer does not reject instability, but the amplitude of oscillations decreases in several times. An increase of the limit concentration of methanol at the addition of diethylenetriamine to the mixture was found.

On the effect of conductivity of a shock-compressed gas on interferometric recording of parameters of motion of a liner

NASA Astrophysics Data System (ADS)

Ogorodnikov, V. A.; Mikhailov, A. L.; Peshkov, V. V.; Bogdanov, E. N.; Rodionov, A. V.; Sedov, A. A.; Fedorov, A. V.; Nazarov, D. V.; Finyushin, S. A.; Dudoladov, V. I.; Erunov, S. V.; Blikov, A. O.

2012-01-01

We report on the results of a study of the acceleration dynamics of an aluminum liner to a velocity of 5.5 km/s using continuous recording of velocity (velocity interferometer system for any reflector (VISAR) and Fabry-Perot interferometer) and motion trajectory (radiointerferometer and resistive transducer) in air and in a helium atmosphere. It is found that for liner velocities exceeding 4.0 and 5.0 km/s, the displacement of the shock wave front is recorded by the radiointerferometer in air and helium, respectively. At these velocities, the conductivities of air and helium behind the shock wave front are estimated.

Performance of synchronous optical receivers using atmospheric compensation techniques.

PubMed

Belmonte, Aniceto; Khan, Joseph

2008-09-01

We model the impact of atmospheric turbulence-induced phase and amplitude fluctuations on free-space optical links using synchronous detection. We derive exact expressions for the probability density function of the signal-to-noise ratio in the presence of turbulence. We consider the effects of log-normal amplitude fluctuations and Gaussian phase fluctuations, in addition to local oscillator shot noise, for both passive receivers and those employing active modal compensation of wave-front phase distortion. We compute error probabilities for M-ary phase-shift keying, and evaluate the impact of various parameters, including the ratio of receiver aperture diameter to the wave-front coherence diameter, and the number of modes compensated.

Intense deformation field at oceanic front inferred from directional sea surface roughness observations

NASA Astrophysics Data System (ADS)

Rascle, Nicolas; Molemaker, Jeroen; Marié, Louis; Nouguier, Frédéric; Chapron, Bertrand; Lund, Björn; Mouche, Alexis

2017-06-01

Fine-scale current gradients at the ocean surface can be observed by sea surface roughness. More specifically, directional surface roughness anomalies are related to the different horizontal current gradient components. This paper reports results from a dedicated experiment during the Lagrangian Submesoscale Experiment (LASER) drifter deployment. A very sharp front, 50 m wide, is detected simultaneously in drifter trajectories, sea surface temperature, and sea surface roughness. A new observational method is applied, using Sun glitter reflections during multiple airplane passes to reconstruct the multiangle roughness anomaly. This multiangle anomaly is consistent with wave-current interactions over a front, including both cross-front convergence and along-front shear with cyclonic vorticity. Qualitatively, results agree with drifters and X-band radar observations. Quantitatively, the sharpness of roughness anomaly suggests intense current gradients, 0.3 m s-1 over the 50 m wide front. This work opens new perspectives for monitoring intense oceanic fronts using drones or satellite constellations.

SAR Observation and Numerical Simulation of Internal Solitary Wave Refraction and Reconnection Behind the Dongsha Atoll

NASA Astrophysics Data System (ADS)

Jia, T.; Liang, J. J.; Li, X.-M.; Sha, J.

2018-01-01

The refraction and reconnection of internal solitary waves (ISWs) around the Dongsha Atoll (DSA) in the northern South China Sea (SCS) are investigated based on spaceborne synthetic aperture radar (SAR) observations and numerical simulations. In general, a long ISW front propagating from the deep basin of the northern SCS splits into northern and southern branches when it passes the DSA. In this study, the statistics of Envisat Advanced SAR (ASAR) images show that the northern and southern wave branches can reconnect behind the DSA, but the reconnection location varies. A previously developed nonlinear refraction model is set up to simulate the refraction and reconnection of the ISWs behind the DSA, and the model is used to evaluate the effects of ocean stratification, background currents, and incoming ISW characteristics at the DSA on the variation in reconnection locations. The results of the first realistic simulation agree with consecutive TerraSAR-X (TSX) images captured within 12 h of each other. Further sensitivity simulations show that ocean stratification, background currents, and initial wave amplitudes all affect the phase speeds of wave branches and therefore shift their reconnection locations while shapes and locations of incoming wave branches upstream of the DSA profoundly influence the subsequent propagation paths. This study clarifies the variation in reconnection locations of ISWs downstream of the DSA and reveals the important mechanisms governing the reconnection process, which can improve our understanding of the propagation of ISWs near the DSA.

Picosecond phase-velocity dispersion of hypersonic phonons imaged with ultrafast electron microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cremons, Daniel R.; Du, Daniel X.; Flannigan, David J.

We describe the direct imaging—with four-dimensional ultrafast electron microscopy—of the emergence, evolution, dispersion, and decay of photoexcited, hypersonic coherent acoustic phonons in nanoscale germanium wedges. Coherent strain waves generated via ultrafast in situ photoexcitation were imaged propagating with initial phase velocities of up to 35 km/s across discrete micrometer-scale crystal regions. We then observe that, while each wave front travels at a constant velocity, the entire wave train evolves with a time-varying phase-velocity dispersion, displaying a single-exponential decay to the longitudinal speed of sound (5 km/s) and with a mean lifetime of 280 ps. We also find that the wavemore » trains propagate along a single in-plane direction oriented parallel to striations introduced during specimen preparation, independent of crystallographic direction. Elastic-plate modeling indicates the dynamics arise from excitation of a single, symmetric (dilatational) guided acoustic mode. Further, by precisely determining the experiment time-zero position with a plasma-lensing method, we find that wave-front emergence occurs approximately 100 ps after femtosecond photoexcitation, which matches well with Auger recombination times in germanium. We conclude by discussing the similarities between the imaged hypersonic strain-wave dynamics and electron/hole plasma-wave dynamics in strongly photoexcited semiconductors.« less

Picosecond phase-velocity dispersion of hypersonic phonons imaged with ultrafast electron microscopy

DOE PAGES

Cremons, Daniel R.; Du, Daniel X.; Flannigan, David J.

2017-12-05

We describe the direct imaging—with four-dimensional ultrafast electron microscopy—of the emergence, evolution, dispersion, and decay of photoexcited, hypersonic coherent acoustic phonons in nanoscale germanium wedges. Coherent strain waves generated via ultrafast in situ photoexcitation were imaged propagating with initial phase velocities of up to 35 km/s across discrete micrometer-scale crystal regions. We then observe that, while each wave front travels at a constant velocity, the entire wave train evolves with a time-varying phase-velocity dispersion, displaying a single-exponential decay to the longitudinal speed of sound (5 km/s) and with a mean lifetime of 280 ps. We also find that the wavemore » trains propagate along a single in-plane direction oriented parallel to striations introduced during specimen preparation, independent of crystallographic direction. Elastic-plate modeling indicates the dynamics arise from excitation of a single, symmetric (dilatational) guided acoustic mode. Further, by precisely determining the experiment time-zero position with a plasma-lensing method, we find that wave-front emergence occurs approximately 100 ps after femtosecond photoexcitation, which matches well with Auger recombination times in germanium. We conclude by discussing the similarities between the imaged hypersonic strain-wave dynamics and electron/hole plasma-wave dynamics in strongly photoexcited semiconductors.« less

Deflagration Wave Profiles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Menikoff, Ralph

2012-04-03

Shock initiation in a plastic-bonded explosives (PBX) is due to hot spots. Current reactive burn models are based, at least heuristically, on the ignition and growth concept. The ignition phase occurs when a small localized region of high temperature (or hot spot) burns on a fast time scale. This is followed by a growth phase in which a reactive front spreads out from the hot spot. Propagating reactive fronts are deflagration waves. A key question is the deflagration speed in a PBX compressed and heated by a shock wave that generated the hot spot. Here, the ODEs for a steadymore » deflagration wave profile in a compressible fluid are derived, along with the needed thermodynamic quantities of realistic equations of state corresponding to the reactants and products of a PBX. The properties of the wave profile equations are analyzed and an algorithm is derived for computing the deflagration speed. As an illustrative example, the algorithm is applied to compute the deflagration speed in shock compressed PBX 9501 as a function of shock pressure. The calculated deflagration speed, even at the CJ pressure, is low compared to the detonation speed. The implication of this are briefly discussed.« less

Gravity wave characteristics in the middle atmosphere during the CESAR campaign at Palma de Mallorca in 2011/2012: Impact of extratropical cyclones and cold fronts

NASA Astrophysics Data System (ADS)

Kramer, R.; Wüst, S.; Schmidt, C.; Bittner, M.

2015-06-01

Based on a measuring campaign which was carried out at Mallorca (39.6°N, 2.7°E) as cooperation between Agència Estatal de Meteorologia (AEMET) and Deutsches Zentrum für Luft- und Raumfahrt, engl. 'German Aerospace Center' (DLR) in 2011/2012 (September-January), 143 radiosondes (day and night) providing vertical temperature and wind profiles were released. Additionally, nocturnal mesopause temperature measurements with a temporal resolution of about 1 min were conducted by the infrared (IR) - Ground-based Infrared P-branch Spectrometer (GRIPS) during the campaign period. Strongly enhanced gravity wave activity in the lower stratosphere is observed which can be attributed to a hurricane-like storm (so-called Medicane) and to passing by cold fronts. Statistical features of gravity wave parameters including energy densitiy and momentum fluxes are calculated. Gravity wave momentum fluxes turned out being up to five times larger during severe weather. Moreover, gravity wave horizontal propagation characteristics are derived applying hodograph and Stokes parameter analysis. Preferred directions are of southeast and northwest due to prevailing wind directions at Mallorca.

Density-wave fronts on the brink of wet granular condensation

NASA Astrophysics Data System (ADS)

Huang, Kai; Zippelius, Andreas; Sand lab @ University of Bayreuth Team

2017-11-01

From sand dunes to Faraday heaping, driven granular matter, i.e., large agglomeration of macroscopic particles, is rich pattern forming system. When a granular material is partially wet (e.g., wet sand on the beach), a different pattern forming scenario arises due to the cohesive particle-particle interactions. Here, we focus on the formation of density-wave fronts in an oscillated wet granular layer undergoing a gas-liquid-like transition. The threshold of the instability is governed by the amplitude of the vertical vibrations. Fronts, which are curved into a spiral shape, propagate coherently along the circular rim of the container with leading edges. They are stable beyond a critical distance from the container center. Based on the measurement of the critical distance and the rotation frequency, we propose a model for the pattern formation by considering the competition between the time scale for the collapse of cohesive particles and that of the energy injection resisting this process. Deutsche Forschungsgemeinschaft (Grant No. HU1939 4-1).

The effects of noise on binocular rivalry waves: a stochastic neural field model

NASA Astrophysics Data System (ADS)

Webber, Matthew A.; Bressloff, Paul C.

2013-03-01

We analyze the effects of extrinsic noise on traveling waves of visual perception in a competitive neural field model of binocular rivalry. The model consists of two one-dimensional excitatory neural fields, whose activity variables represent the responses to left-eye and right-eye stimuli, respectively. The two networks mutually inhibit each other, and slow adaptation is incorporated into the model by taking the network connections to exhibit synaptic depression. We first show how, in the absence of any noise, the system supports a propagating composite wave consisting of an invading activity front in one network co-moving with a retreating front in the other network. Using a separation of time scales and perturbation methods previously developed for stochastic reaction-diffusion equations, we then show how extrinsic noise in the activity variables leads to a diffusive-like displacement (wandering) of the composite wave from its uniformly translating position at long time scales, and fluctuations in the wave profile around its instantaneous position at short time scales. We use our analysis to calculate the first-passage-time distribution for a stochastic rivalry wave to travel a fixed distance, which we find to be given by an inverse Gaussian. Finally, we investigate the effects of noise in the depression variables, which under an adiabatic approximation lead to quenched disorder in the neural fields during propagation of a wave.

Impact of plunging breaking waves on a partially submerged cube

NASA Astrophysics Data System (ADS)

Wang, A.; Ikeda, C.; Duncan, J. H.

2013-11-01

The impact of a deep-water plunging breaking wave on a partially submerged cube is studied experimentally in a tank that is 14.8 m long and 1.2 m wide with a water depth of 0.91 m. The breakers are created from dispersively focused wave packets generated by a programmable wave maker. The water surface profile in the vertical center plane of the cube is measured using a cinematic laser-induced fluorescence technique with movie frame rates ranging from 300 to 4,500 Hz. The pressure distribution on the front face of the cube is measured with 24 fast-response sensors simultaneously with the wave profile measurements. The cube is positioned vertically at three heights relative to the mean water level and horizontally at a distance from the wave maker where a strong vertical water jet is formed. The portion of the water surface between the contact point on the front face of the cube and the wave crest is fitted with a circular arc and the radius and vertical position of the fitted circle is tracked during the impact. The vertical acceleration of the contact point reaches more than 50 times the acceleration of gravity and the pressure distribution just below the free surface shows a localized high-pressure region with a very high vertical pressure gradient. This work is supported by the Office of Naval Research under grant N000141110095.

On the Traversal Time of Barriers

NASA Astrophysics Data System (ADS)

Aichmann, Horst; Nimtz, Günter

2014-06-01

Fifty years ago Hartman studied the barrier transmission time of wave packets (J Appl Phys 33:3427-3433, 1962). He was inspired by the tunneling experiments across thin insulating layers at that time. For opaque barriers he calculated faster than light propagation and a transmission time independent of barrier length, which is called the Hartman effect. A faster than light (FTL or superluminal) wave packet velocity was deduced in analog tunneling experiments with microwaves and with infrared light thirty years later. Recently, the conjectured zero time of electron tunneling was claimed to have been observed in ionizing helium inside the barrier. The calculated and measured short tunneling time arises at the barrier front. This tunneling time was found to be universal for elastic fields as well as for electromagnetic fields. Remarkable is that the delay time is the same for the reflected and the transmitted waves in the case of symmetric barriers. Several theoretical physicists predicted this strange nature of the tunneling process. However, even with this background many members of the physics community do not accept a FTL signal velocity interpretation of the experimental tunneling results. Instead a luminal front velocity was calculated to explain the FTL experimental results frequently. However, Brillouin stated in his book on wave propagation and group velocity that the front velocity is given by the group velocity of wave packets in the case of physical signals, which have only finite frequency bandwidths. Some studies assumed barriers to be cavities and the observed tunneling time does represent the cavity lifetime. We are going to discus these continuing misleading interpretations, which are found in journals and in textbooks till today.

The Coronal Analysis of SHocks and Waves (CASHeW) framework

NASA Astrophysics Data System (ADS)

Kozarev, Kamen A.; Davey, Alisdair; Kendrick, Alexander; Hammer, Michael; Keith, Celeste

2017-11-01

Coronal bright fronts (CBF) are large-scale wavelike disturbances in the solar corona, related to solar eruptions. They are observed (mostly in extreme ultraviolet (EUV) light) as transient bright fronts of finite width, propagating away from the eruption source location. Recent studies of individual solar eruptive events have used EUV observations of CBFs and metric radio type II burst observations to show the intimate connection between waves in the low corona and coronal mass ejection (CME)-driven shocks. EUV imaging with the atmospheric imaging assembly instrument on the solar dynamics observatory has proven particularly useful for detecting large-scale short-lived CBFs, which, combined with radio and in situ observations, holds great promise for early CME-driven shock characterization capability. This characterization can further be automated, and related to models of particle acceleration to produce estimates of particle fluxes in the corona and in the near Earth environment early in events. We present a framework for the coronal analysis of shocks and waves (CASHeW). It combines analysis of NASA Heliophysics System Observatory data products and relevant data-driven models, into an automated system for the characterization of off-limb coronal waves and shocks and the evaluation of their capability to accelerate solar energetic particles (SEPs). The system utilizes EUV observations and models written in the interactive data language. In addition, it leverages analysis tools from the SolarSoft package of libraries, as well as third party libraries. We have tested the CASHeW framework on a representative list of coronal bright front events. Here we present its features, as well as initial results. With this framework, we hope to contribute to the overall understanding of coronal shock waves, their importance for energetic particle acceleration, as well as to the better ability to forecast SEP events fluxes.

A miniature bidirectional telemetry system for in vivo gastric slow wave recordings.

PubMed

Farajidavar, Aydin; O'Grady, Gregory; Rao, Smitha M N; Cheng, Leo K; Abell, Thomas; Chiao, J-C

2012-06-01

Stomach contractions are initiated and coordinated by an underlying electrical activity (slow waves), and electrical dysrhythmias accompany motility diseases. Electrical recordings taken directly from the stomach provide the most valuable data, but face technical constraints. Serosal or mucosal electrodes have cables that traverse the abdominal wall, or a natural orifice, causing discomfort and possible infection, and restricting mobility. These problems motivated the development of a wireless system. The bidirectional telemetric system constitutes a front-end transponder, a back-end receiver and a graphical userinter face. The front-end module conditions the analogue signals, then digitizes and loads the data into a radio for transmission. Data receipt at the backend is acknowledged via a transceiver function. The system was validated in a bench-top study, then validated in vivo using serosal electrodes connected simultaneously to a commercial wired system. The front-end module was 35 × 35 × 27 mm3 and weighed 20 g. Bench-top tests demonstrated reliable communication within a distance range of 30 m, power consumption of 13.5 mW, and 124 h operation when utilizing a 560 mAh, 3 V battery. In vivo,slow wave frequencies were recorded identically with the wireless and wired reference systems (2.4 cycles min−1), automated activation time detection was modestly better for the wireless system (5% versus 14% FP rate), and signal amplitudes were modestly higher via the wireless system (462 versus 3 86μV; p<0.001). This telemetric system for slow wave acquisition is reliable,power efficient, readily portable and potentially implantable. The device will enable chronic monitoring and evaluation of slow wave patterns in animals and patients.0967-3334/

A miniature bidirectional telemetry system for in-vivo gastric slow wave recordings

PubMed Central

Farajidavar, Aydin; O’Grady, Gregory; Rao, Smitha M.N.; Cheng, Leo K; Abell, Thomas; Chiao, J.-C.

2012-01-01

Stomach contractions are initiated and coordinated by an underlying electrical activity (slow waves), and electrical dysrhythmias accompany motility diseases. Electrical recordings taken directly from the stomach provide the most valuable data, but face technical constraints. Serosal or mucosal electrodes have cables that traverse the abdominal wall, or a natural orifice, causing discomfort and possible infection, and restricting mobility. These problems motivated the development of a wireless system. The bidirectional telemetric system constitutes a front-end transponder, a back-end receiver and a graphical user interface. The front-end module conditions the analog signals, then digitizes and loads the data into a radio for transmission. Data receipt at the back-end is acknowledged via a transceiver function. The system was validated in a bench-top study, then validated in-vivo using serosal electrodes connected simultaneously to a commercial wired system. The front-end module was 35×35×27 mm3 and weighed 20 g. Bench-top tests demonstrated reliable communication within a distance range of 30 m, power consumption of 13.5 mW, and 124-hour operation when utilizing a 560-mAh, 3-V battery. In-vivo, slow wave frequencies were recorded identically with the wireless and wired reference systems (2.4 cycles/min), automated activation time detection was modestly better for the wireless system (5% vs 14% false positive rate), and signal amplitudes were modestly higher via the wireless system (462 vs 386 μV; p<0.001). This telemetric system for slow wave acquisition is reliable, power efficient, readily portable and potentially implantable. The device will enable chronic monitoring and evaluation of slow wave patterns in animals and patients. PMID:22635054

Off-equatorial current-driven instabilities ahead of approaching dipolarization fronts

NASA Astrophysics Data System (ADS)

Zhang, Xu; Angelopoulos, V.; Pritchett, P. L.; Liu, Jiang

2017-05-01

Recent kinetic simulations have revealed that electromagnetic instabilities near the ion gyrofrequency and slightly away from the equatorial plane can be driven by a current parallel to the magnetic field prior to the arrival of dipolarization fronts. Such instabilities are important because of their potential contribution to global electromagnetic energy conversion near dipolarization fronts. Of the several instabilities that may be consistent with such waves, the most notable are the current-driven electromagnetic ion cyclotron instability and the current-driven kink-like instability. To confirm the existence and characteristics of these instabilities, we used observations by two Time History of Events and Macroscale Interactions during Substorms satellites, one near the neutral sheet observing dipolarization fronts and the other at the boundary layer observing precursor waves and currents. We found that such instabilities with monochromatic signatures are rare, but one of the few cases was selected for further study. Two different instabilities, one at about 0.3 Hz and the other at a much lower frequency, 0.02 Hz, were seen in the data from the off-equatorial spacecraft. A parallel current attributed to an electron beam coexisted with the waves. Our instability analysis attributes the higher-frequency instability to a current-driven ion cyclotron instability and the lower frequency instability to a kink-like instability. The current-driven kink-like instability we observed is consistent with the instabilities observed in the simulation. We suggest that the currents needed to excite these low-frequency instabilities are so intense that the associated electron beams are easily thermalized and hence difficult to observe.

Experimental particle acceleration by water evaporation induced by shock waves

NASA Astrophysics Data System (ADS)

Scolamacchia, T.; Alatorre Ibarguengoitia, M.; Scheu, B.; Dingwell, D. B.; Cimarelli, C.

2010-12-01

Shock waves are commonly generated during volcanic eruptions. They induce sudden changes in pressure and temperature causing phase changes. Nevertheless, their effects on flowfield properties are not well understood. Here we investigate the role of gas expansion generated by shock wave propagation in the acceleration of ash particles. We used a shock tube facility consisting of a high-pressure (HP) steel autoclave (450 mm long, 28 mm in internal diameter), pressurized with Ar gas, and a low-pressure tank at atmospheric conditions (LP). A copper diaphragm separated the HP autoclave from a 180 mm tube (PVC or acrylic glass) at ambient P, with the same internal diameter of the HP reservoir. Around the tube, a 30 cm-high acrylic glass cylinder, with the same section of the LP tank (40 cm), allowed the observation of the processes occurring downstream from the nozzle throat, and was large enough to act as an unconfined volume in which the initial diffracting shock and gas jet expand. All experiments were performed at Pres/Pamb ratios of 150:1. Two ambient conditions were used: dry air and air saturated with steam. Carbon fibers and glass spheres in a size range between 150 and 210 μm, were placed on a metal wire at the exit of the PVC tube. The sudden decompression of the Ar gas, due to the failure of the diaphragm, generated an initial air shock wave. A high-speed camera recorded the processes between the first 100 μsec and several ms after the diaphragm failure at frame rates ranging between 30,000 and 50,000 fps. In the experiments with ambient air saturated with steam, the high-speed camera allowed to visualize the condensation front associated with the initial air shock; a maximum velocity of 788 m/s was recorded, which decreases to 524 m/s at distance of 0.5 ±0.2 cm, 1.1 ms after the diaphragm rupture. The condensation front preceded the Ar jet front exhausting from the reservoir, by 0.2-0.5 ms. In all experiments particles velocities following the initial condensation front exhibited large accelerations, with velocity varying from few tens of m/s up to 479 (±0.5) m/s, at distances of 1.5 (±0.3) cm and in times of 0.1 ms. This process preceded the appearance of the Ar front. Our first results suggest that the evaporation of moisture induced by compression waves associated with the air shock is able to accelerate particles (ca.100s microns in size) efficiently, at short distances. This process could have broader implications in active volcanic areas where shock waves are generated, for the damage that may follow.

Adapting wave-front algorithms to efficiently utilize systems with deep communication hierarchies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kerbyson, Darren J; Lang, Michael; Pakin, Scott

2009-01-01

Large-scale systems increasingly exhibit a differential between intra-chip and inter-chip communication performance. Processor-cores on the same socket are able to communicate at lower latencies, and with higher bandwidths, than cores on different sockets either within the same node or between nodes. A key challenge is to efficiently use this communication hierarchy and hence optimize performance. We consider here the class of applications that contain wave-front processing. In these applications data can only be processed after their upstream neighbors have been processed. Similar dependencies result between processors in which communication is required to pass boundary data downstream and whose cost ismore » typically impacted by the slowest communication channel in use. In this work we develop a novel hierarchical wave-front approach that reduces the use of slower communications in the hierarchy but at the cost of additional computation and higher use of on-chip communications. This tradeoff is explored using a performance model and an implementation on the Petascale Roadrunner system demonstrates a 27% performance improvement at full system-scale on a kernel application. The approach is generally applicable to large-scale multi-core and accelerated systems where a differential in system communication performance exists.« less

An Analysis of Fundamental Waffle Mode in Early AEOS Adaptive Optics Images

NASA Astrophysics Data System (ADS)

Makidon, Russell B.; Sivaramakrishnan, Anand; Perrin, Marshall D.; Roberts, Lewis C., Jr.; Oppenheimer, Ben R.; Soummer, Rémi; Graham, James R.

2005-08-01

Adaptive optics (AO) systems have significantly improved astronomical imaging capabilities over the last decade and are revolutionizing the kinds of science possible with 4-5 m class ground-based telescopes. A thorough understanding of AO system performance at the telescope can enable new frontiers of science as observations push AO systems to their performance limits. We look at recent advances with wave-front reconstruction (WFR) on the Advanced Electro-Optical System (AEOS) 3.6 m telescope to show how progress made in improving WFR can be measured directly in improved science images. We describe how a ``waffle mode'' wave-front error (which is not sensed by a Fried geometry Shack-Hartmann wave-front sensor) affects the AO point-spread function. We model details of AEOS AO to simulate a PSF that matches the actual AO PSF in the I band and show that while the older observed AEOS PSF contained several times more waffle error than expected, improved WFR techniques noticeably improve AEOS AO performance. We estimate the impact of these improved WFRs on H-band imaging at AEOS, chosen based on the optimization of the Lyot Project near-infrared coronagraph at this bandpass. Based on observations made at the Maui Space Surveillance System, operated by Detachment 15 of the US Air Force Research Laboratory's Directed Energy Directorate.

Wave-front propagation of rinsing flows on rotating semiconductor wafers

NASA Astrophysics Data System (ADS)

Frostad, John M.; Ylitalo, Andy; Walls, Daniel J.; Mui, David S. L.; Fuller, Gerald G.

2016-11-01

The semiconductor manufacturing industry is migrating to a cleaning technology that involves dispersing cleaning solutions onto a rotating wafer, similar to spin-coating. Advantages include a more continuous overall fabrication process, lower particle level, no cross contamination from the back side of a wafer, and less usage of harsh chemicals for a lower environmental impact. Rapid rotation of the wafer during rinsing can be more effective, but centrifugal forces can pull spiral-like ribbons of liquid radially outward from the advancing wave-front where particles can build up, causing higher instances of device failure at these locations. A better understanding of the rinsing flow is essential for reducing yield losses while taking advantage of the benefits of rotation. In the present work, high-speed video and image processing are used to study the dynamics of the advancing wave-front from an impinging jet on a rotating substrate. The flow-rate and rotation-speed are varied for substrates coated with a thin layer of a second liquid that has a different surface tension than the jet liquid. The difference in surface tension of the two fluids gives rise to Marangoni stresses at the interface that have a significant impact on the rinsing process, despite the extremely short time-scales involved.

Mechanical signaling coordinates the embryonic heartbeat.

PubMed

Chiou, Kevin K; Rocks, Jason W; Chen, Christina Yingxian; Cho, Sangkyun; Merkus, Koen E; Rajaratnam, Anjali; Robison, Patrick; Tewari, Manorama; Vogel, Kenneth; Majkut, Stephanie F; Prosser, Benjamin L; Discher, Dennis E; Liu, Andrea J

2016-08-09

In the beating heart, cardiac myocytes (CMs) contract in a coordinated fashion, generating contractile wave fronts that propagate through the heart with each beat. Coordinating this wave front requires fast and robust signaling mechanisms between CMs. The primary signaling mechanism has long been identified as electrical: gap junctions conduct ions between CMs, triggering membrane depolarization, intracellular calcium release, and actomyosin contraction. In contrast, we propose here that, in the early embryonic heart tube, the signaling mechanism coordinating beats is mechanical rather than electrical. We present a simple biophysical model in which CMs are mechanically excitable inclusions embedded within the extracellular matrix (ECM), modeled as an elastic-fluid biphasic material. Our model predicts strong stiffness dependence in both the heartbeat velocity and strain in isolated hearts, as well as the strain for a hydrogel-cultured CM, in quantitative agreement with recent experiments. We challenge our model with experiments disrupting electrical conduction by perfusing intact adult and embryonic hearts with a gap junction blocker, β-glycyrrhetinic acid (BGA). We find this treatment causes rapid failure in adult hearts but not embryonic hearts-consistent with our hypothesis. Last, our model predicts a minimum matrix stiffness necessary to propagate a mechanically coordinated wave front. The predicted value is in accord with our stiffness measurements at the onset of beating, suggesting that mechanical signaling may initiate the very first heartbeats.

Statistical anisotropy in free turbulence for mixing layers at high Reynolds numbers

NASA Astrophysics Data System (ADS)

Gardner, Patrick J.; Roggemann, Michael C.; Welsh, Byron M.; Bowersox, Rodney D.; Luke, Theodore E.

1996-08-01

A lateral shearing interferometer was used to measure the slope of perturbed wave fronts after propagating through free turbulent mixing layers. Shearing interferometers provide a two-dimensional flow visualization that is nonintrusive. Slope measurements were used to reconstruct the phase of the turbulence-corrupted wave front. The random phase fluctuations induced by the mixing layer were captured in a large ensemble of wave-front measurements. Experiments were performed on an unbounded, plane shear mixing layer of helium and nitrogen gas at fixed velocities and high Reynolds numbers for six locations in the flow development. Statistical autocorrelation functions and structure functions were computed on the reconstructed phase maps. The autocorrelation function results indicated that the turbulence-induced phase fluctuations were not wide-sense stationary. The structure functions exhibited statistical homogeneity, indicating that the phase fluctuations were stationary in first increments. However, the turbulence-corrupted phase was not isotropic. A five-thirds power law is shown to fit orthogonal slices of the structure function, analogous to the Kolmogorov model for isotropic turbulence. Strehl ratios were computed from the phase structure functions and compared with classical estimates that assume isotropy. The isotropic models are shown to overestimate the optical degradation by nearly 3 orders of magnitude compared with the structure function calculations.

Comparison of measured and computed Strehl ratios for light propagated through a channel flow of a He N 2 mixing layer at high Reynolds numbers

NASA Astrophysics Data System (ADS)

Gardner, Patrick J.; Roggemann, Michael C.; Welsh, Byron M.; Bowersox, Rodney D.; Luke, Theodore E.

1997-04-01

A lateral shearing interferometer was used to measure the slope of perturbed wave fronts after they propagated through a He N 2 mixing layer in a rectangular channel. Slope measurements were used to reconstruct the phase of the turbulence-corrupted wave front. The random phase fluctuations induced by the mixing layer were captured in a large ensemble of wave-front measurements. Phase structure functions, computed from the reconstructed phase surfaces, were stationary in first increments. A five-thirds power law is shown to fit streamwise and cross-stream slices of the structure function, analogous to the Kolmogorov model for isotropic turbulence, which describes the structure function with a single parameter. Strehl ratios were computed from the phase structure functions and compared with a measured experiment obtained from simultaneous point-spread function measurements. Two additional Strehl ratios were calculated by using classical estimates that assume statistical isotropy throughout the flow. The isotropic models are a reasonable estimate of the optical degradation only within a few centimeters of the initial mixing, where the Reynolds number is low. At higher Reynolds numbers, Strehl ratios calculated from the structure functions match the experiment much better than Strehl ratio calculations that assume isotropic flow.

External front instabilities induced by a shocked particle ring.

PubMed

Rodriguez, V; Saurel, R; Jourdan, G; Houas, L

2014-10-01

The dispersion of a cylindrical particle ring by a blast or shock wave induces the formation of coherent structures which take the form of particle jets. A blast wave, issuing from the discharge of a planar shock wave at the exit of a conventional shock tube, is generated in the center of a granular medium ring initially confined inside a Hele-Shaw cell. With the present experimental setup, under impulsive acceleration, a solid particle-jet formation is observed in a quasi-two-dimensional configuration. The aim of the present investigation is to observe in detail the formation of very thin perturbations created around the external surface of the dispersed particle layer. By means of fast flow visualization with an appropriate recording window, we focus solely on the first instants during which the external particle ring becomes unstable. We find that the critical area of the destabilization of the external ring surface is constant regardless of the acceleration of the initial layer. Moreover, we observe in detail the external front perturbation wavelength, rendered dimensionless by the initial ring perimeter, and follow its evolution with the initial particle layer acceleration. We report this quantity to be constant regardless of the evolution of the initial particle layer acceleration. Finally, we can reasonably assert that external front perturbations depend solely on the material of the particles.

Concentric circular focusing reflector realized using high index contrast gratings

NASA Astrophysics Data System (ADS)

Fang, Wenjing; Huang, Yongqing; Fei, Jiarui; Duan, Xiaofeng; Liu, Kai; Ren, Xiaomin

2017-11-01

A non-periodic concentric circular high index contrast grating (CC-HCG) focusing reflector on 500 nm silicon-on-insulator (SOI) platform is fabricated and experimentally demonstrated. The proposed mirror is realized with phase modulation of wave front in a high reflectivity region. The circular structure based HCG focusing reflector has a spot of high concentration at the 10.87 mm with normal incidence for radially polarization, along with the center wavelength set at 1550 nm. The FWHM spot size of the focusing beam decreases to 260 μm, and the intensity increases to 1.26 compared with the incident beam. The focusing efficiency of about 80% is observed at 1550 nm in the experimental measurement.

Identifying the Development in Phase and Amplitude of Dipole and Multipole Radiation

ERIC Educational Resources Information Center

Rice, E. M.; Bradshaw, D. S.; Saadi, K.; Andrews, D. L.

2012-01-01

The spatial variation in phase and the propagating wave-front of plane wave electromagnetic radiation are widely familiar text-book territory. In contrast, the developing amplitude and phase of radiation emitted by a dipole or multipole source generally receive less attention, despite the prevalence of these systems. There is additional complexity…

Focus expansion and stability of the spread parameter estimate of the power law model for dispersal gradients

USDA-ARS?s Scientific Manuscript database

Empirical and mechanistic modeling indicate that aerially transmitted pathogens follow a power law, resulting in dispersive epidemic waves. The spread parameter (b) of the power law model, which defines the distance travelled by the epidemic wave front, has been found to be approximately 2 for sever...

Vibrational Responses Of Structures To Impulses

NASA Technical Reports Server (NTRS)

Zak, Michail A.

1990-01-01

Report discusses propagation of vibrations in structure in response to impulsive and/or concentrated loads. Effects of pulsed loads treated by analyzing propagation of characteristic vibrational waves explicitly through each member of structure. This wave-front analysis used in combination with usual finite-element modal analysis to obtain more accurate representation of overall vibrational behavior.

Trajectory Control of Small Rotating Projectiles by Laser Sparks

NASA Astrophysics Data System (ADS)

Starikovskiy, Andrey; Limbach, Christopher; Miles, Richard

2015-09-01

The possibility of controlling the trajectory of the supersonic motion of a rotating axisymmetric projectile using a remotely generated laser spark was investigated. The dynamic images of the interaction of thermal inhomogeneity created by the laser spark with the bow shock in front of the projectile were obtained. The criterion for a strong shock wave interaction with the thermal inhomogeneity at different angles of a shock wave was derived. Significant changes in the configuration of the bow shock wave and changes in the pressure distribution over the surface of the rotating projectile can appear for laser spark temperature of T' = 2500-3000 K. The experiment showed that strong interaction takes place for both plane and oblique shock waves. The measurement of the velocity of the precession of the rotating projectile axis from the initial position in time showed that the angle of attack of the projectile deviates with a typical time of perturbation propagation along the projectile's surface. Thus the laser spark can change the trajectory of the rotating projectile, moving at supersonic speed, through the creation of thermal heterogeneity in front of it.

Observations of thunderstorm-related 630 nm airglow depletions

NASA Astrophysics Data System (ADS)

Kendall, E. A.; Bhatt, A.

2015-12-01

The Midlatitude All-sky imaging Network for Geophysical Observations (MANGO) is an NSF-funded network of 630 nm all-sky imagers in the continental United States. MANGO will be used to observe the generation, propagation, and dissipation of medium and large-scale wave activity in the subauroral, mid and low-latitude thermosphere. This network is actively being deployed and will ultimately consist of nine all-sky imagers. These imagers form a network providing continuous coverage over the western United States, including California, Oregon, Washington, Utah, Arizona and Texas extending south into Mexico. This network sees high levels of both medium and large scale wave activity. Apart from the widely reported northeast to southwest propagating wave fronts resulting from the so called Perkins mechanism, this network observes wave fronts propagating to the west, north and northeast. At least three of these anomalous events have been associated with thunderstorm activity. Imager data has been correlated with both GPS data and data from the AIRS (Atmospheric Infrared Sounder) instrument on board NASA's Earth Observing System Aqua satellite. We will present a comprehensive analysis of these events and discuss the potential thunderstorm source mechanism.

Fast penetration of megagauss fields into metallic conductors

NASA Astrophysics Data System (ADS)

Schnitzer, Ory

2014-08-01

Megagauss magnetic-field penetration into a conducting material is studied via a simplified but representative model, wherein the magnetic-diffusion equation is coupled with a thermal-energy balance. The specific scenario considered is that of a prescribed magnetic field rising (in proportion to an arbitrary power r of time) at the surface of a conducting half-space whose electric conductivity is assumed proportional to an arbitrary inverse power γ of temperature. We employ a systematic asymptotic scheme in which the case of a strong surface field corresponds to a singular asymptotic limit. In this limit, the highly magnetized and hot "skin" terminates at a distinct propagating wave-front. Employing the method of matched asymptotic expansions, we find self-similar solutions of the magnetized region which match a narrow boundary-layer region about the advancing wave front. The rapidly decaying magnetic-field profile in the latter region is also self similar; when scaled by the instantaneous propagation speed, its shape is time-invariant, depending only on the parameter γ. The analysis furnishes a simple asymptotic formula for the skin-depth (i.e., the wave-front position), which substantially generalizes existing approximations. It scales with the power γr + 1/2 of time and the power γ of field strength, and is much larger than the field-independent skin depth predicted by an athermal model. The formula further involves a dimensionless O(1) pre-factor which depends on r and γ. It is determined by solving a nonlinear eigenvalue problem governing the magnetized region. Another main result of the analysis, apparently unprecedented, is an asymptotic formula for the magnitude of the current-density peak characterizing the wave-front region. Complementary to these systematic results, we provide a closed-form but ad hoc generalization of the theory approximately applicable to arbitrary monotonically rising surface fields. Our results are in excellent agreement with numerical simulations of the model, and compare favourably with detailed magnetohydrodynamic simulations reported in the literature.

Wave interactions with multiple semi-immersed Jarlan-type perforated breakwaters

NASA Astrophysics Data System (ADS)

Elbisy, Moussa S.

2017-06-01

This study examines wave interactions with multiple semi-immersed Jarlan-type perforated breakwaters. A numerical model based on linear wave theory and an eigenfunction expansion method has been developed to study the hydrodynamic characteristics of breakwaters. The numerical results show a good agreement with previous analytical results and experimental data for limiting cases of double partially immersed impermeable walls and double and triple Jarlan-type breakwaters. The wave transmission coefficient C T; reflection coefficient C R, and energy dissipation coefficient C E coefficients and the horizontal wave force exerted on the front and rear walls are examined. The results show that C R reaches the maximum value when B/L = 0.46 n while it is smallest when B/L=0.46 n+0.24 ( n=0, 1, 2,...). An economical triple semi-immersed Jarlan-type perforated breakwater can be designed with B/L = 0.25 and C R and C T ranging from 0.25 to 0.32 by choosing a relative draft d/h of 0.35 and a permeability parameter of the perforated front walls being 0.5 for an incident wave number kh nearly equal to 2.0. The triple semi-immersed Jarlan-type perforated breakwaters with significantly reduced C R, will enhance the structure's wave absorption ability, and lead to smaller wave forces compared with the double one. The proposed model may be used to predict the response of a structure in the preliminary design stage for practical engineering.

Processes affecting suspended sediment transport in the mid-field plume region of the Rhine River, Netherlands.

NASA Astrophysics Data System (ADS)

Flores, R. P.; Rijnsburger, S.; Horner-Devine, A.; Souza, A. J.; Pietrzak, J.

2016-02-01

This work will describe dominant processes affecting suspended sediment transport along the Dutch coast, in the mid-field plume region of the Rhine River. We will present field observations from two long-term deployments conducted in the vicinity of the Sand Engine, a mega-nourishment experiment located 10 km north of the Rhine river mouth. To investigate the role of density stratification, winds, tides, waves and river plume processes on sediment transport, frames and moorings were deployed within the excursion of the tidal plume front generated by the freshwater outflow from the Rhine River for 4 and 6 weeks during years 2013 and 2014, respectively. The moorings were designed to measure vertical profiles of suspended sediment concentration (SSC) and salinity, using arrays of CTDs and OBS sensors. Mean tidal velocities were measured using bottom-mounted ADCPs. The near-bed dynamics and the near-bottom sediment concentrations were measured as well using a set of synchronized ADVs and OBSs. By combining the two deployments we observe hydrodynamics and suspended sediment dynamics under a wide range of forcing conditions. Preliminary observations indicate that stratification is highly dependent on wind magnitude and direction, and its role is primarily identified as to induce significant cross-shore sediment transport product of the generation of cross-shore velocities due to the modification of the tidal ellipses and the passage of the surface plume front. The passage of the surface plume front generates strong offshore currents near the bottom, producing transport events that can be similar in magnitude to the dominant alongshore transport. Preliminary results also indicate that storms play an important role in alongshore transport primarily by wave-induced sediment resuspension, but as stratification is suppressed due to the enhancement of mixing processes, no significant cross-shore transport is observed during very energetic conditions.

The analytical solution of the problem of a shock focusing in a gas for one-dimensional case

NASA Astrophysics Data System (ADS)

Shestakovskaya, E. S.; Magazov, F. G.

2018-03-01

The analytical solution of the problem of an imploding shock wave in the vessel with an impermeable wall is constructed for the cases of planar, cylindrical and spherical symmetry. The negative velocity is set at the vessel boundary. The velocity of cold ideal gas is zero. At the initial time the shock spreads from this point into the center of symmetry. The boundary moves under the particular law which conforms to the movement of the shock. In Euler variables it moves but in Lagrangian variables its trajectory is a vertical line. Equations that determine the structure of the gas flow between the shock front and the boundary as a function of time and the Lagrangian coordinate as well as the dependence of the entropy on the shock wave velocity are obtained. Self-similar coefficients and corresponding critical values of self-similar coordinates were found for a wide range of adiabatic index. The problem is solved for Lagrangian coordinates.

Quasi-optical antenna-mixer-array design for terahertz frequencies

NASA Technical Reports Server (NTRS)

Guo, Yong; Potter, Kent A.; Rutledge, David B.

1992-01-01

A new quasi-optical antenna-mixer-array design for terahertz frequencies is presented. In the design, antenna and mixer are combined into an entity, based on the technology in which millimeter-wave horn antenna arrays have been fabricated in silicon wafers. It consists of a set of forward- and backward-looking horns made with a set of silicon wafers. The front side is used to receive incoming signal, and the back side is used to feed local oscillator signal. Intermediate frequency is led out from the side of the array. Signal received by the horn array is picked up by antenna probes suspended on thin silicon-oxynitride membranes inside the horns. Mixer diodes will be located on the membranes inside the horns. Modeling of such an antenna-mixer-array design is done on a scaled model at microwave frequencies. The impedance matching, RF and LO isolation, and patterns of the array have been tested and analyzed.

Laser-induced damage of fused silica optics at 355 nm due to backward stimulated Brillouin scattering: experimental and theoretical results.

PubMed

Lamaignère, Laurent; Gaudfrin, Kévin; Donval, Thierry; Natoli, Jeanyves; Sajer, Jean-Michel; Penninckx, Denis; Courchinoux, Roger; Diaz, Romain

2018-04-30

Forward pump pulses with nanosecond duration are able to generate an acoustic wave via electrostriction through a few centimeters of bulk silica. Part of the incident energy is then scattered back on this sound wave, creating a backward Stokes pulse. This phenomenon known as stimulated Brillouin scattering (SBS) might induce first energy-loss, variable change of the temporal waveform depending on the location in the spatial profile making accurate metrology impossible, and moreover it might also initiate front surface damage making the optics unusable. Experiments performed on thick fused silica optics at 355 nm with single longitudinal mode pulses allowed us to detect, observe and quantify these backward pulses. Experimental results are first compared to theoretical calculations in order to strengthen our confidence in metrology. On this basis a phase-modulator has been implemented on the continuous-wave seeders of the lasers leading to pulses with a wide spectrum that suppress SBS and do not exhibit temporal overshoots that also reduce Kerr effects. The developed set-ups are used to check the reduction of the backward stimulated Brillouin scattering and they allow measuring with accuracy the rear surface damage of thick fused silica optics.

Detail of front entry stairs showing original boot scrape set ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Detail of front entry stairs showing original boot scrape set in concrete, facing northwest. - Albrook Air Force Station, Company Officer's Quarters, East side of Canfield Avenue, Balboa, Former Panama Canal Zone, CZ

Semileptonic decays of B and D mesons in the light-front formalism

NASA Astrophysics Data System (ADS)

Jaus, W.

1990-06-01

The light-front formalism is used to present a relativistic calculation of form factors for semileptonic D and B decays in the constituent quark model. The quark-antiquark wave functions of the mesons can be obtained, in principle, from an analysis of the meson spectrum, but are approximated in this work by harmonic-oscillator wave functions. The predictions of the model are consistent with the experimental data for B decays. The Kobayashi-Maskawa (KM) matrix element ||Vcs|| is determined by a comparison of the experimental and theoretical rates for D0-->K-e+ν, and is consistent with a unitary KM matrix for three families. The predictions for D-->K* transitions are in conflict with the data.

Perturbing laser field dependent high harmonic phase modulations

NASA Astrophysics Data System (ADS)

Li, Zhengyan; Kong, Fanqi; Brown, Graham; Hammond, TJ; Ko, Dong-Hyuk; Zhang, Chunmei; Corkum, P. B.

2018-06-01

A perturbing laser pulse modulates and controls the phase of the high harmonic radiation driven by an intense fundamental pulse. Thus, a structured wave front can impress a specific spatial phase onto the generated high harmonic wave front. This modulation procedure leads to all-optical spatial light modulators for VUV or XUV radiation created by high harmonic generation. Here, through theoretical analysis and experiment, we study the correlation between the high harmonic phase modulations and the perturbing laser field amplitude and phase, providing guidelines for practical high harmonic spatial light modulators. In addition, we show that the petahertz optical oscilloscope for measuring electric fields of a perturbing beam is most robust using low order harmonics, far from the cut-off.

Pareto fronts for multiobjective optimization design on materials data

NASA Astrophysics Data System (ADS)

Gopakumar, Abhijith; Balachandran, Prasanna; Gubernatis, James E.; Lookman, Turab

Optimizing multiple properties simultaneously is vital in materials design. Here we apply infor- mation driven, statistical optimization strategies blended with machine learning methods, to address multi-objective optimization tasks on materials data. These strategies aim to find the Pareto front consisting of non-dominated data points from a set of candidate compounds with known character- istics. The objective is to find the pareto front in as few additional measurements or calculations as possible. We show how exploration of the data space to find the front is achieved by using uncer- tainties in predictions from regression models. We test our proposed design strategies on multiple, independent data sets including those from computations as well as experiments. These include data sets for Max phases, piezoelectrics and multicomponent alloys.

Instability of isolated planar shock waves

DTIC Science & Technology

2007-06-07

Note that multi-mode perturbations can be treated by the inclusion of additional terms in Eq. (4), but owing to the linear independence of the... Volterra equation Figure 4 shows five examples of the evolution of the amplitude of a linear sinusoidal perturbation on a shock front obtained by...showing the evolution of the amplitude of a linear sinusoidal perturbation on a shock front obtained by numerically solving the Volterra equation in

Subsurface control on seafloor erosional processes offshore of the Chandeleur Islands, Louisiana

NASA Astrophysics Data System (ADS)

Twichell, David; Pendleton, Elizabeth; Baldwin, Wayne; Flocks, James

2009-12-01

The Chandeleur Islands lie on the eastern side of the modern Mississippi River delta plain, near the edge of the St. Bernard Delta complex. Since abandonment approximately 2,000 years b.p., this delta complex has undergone subsidence and ravinement as the shoreline has transgressed across it. High-resolution seismic-reflection, sidescan-sonar, and bathymetry data show that seafloor erosion is influenced by locally variable shallow stratigraphy. The data reveal two general populations of shallow erosional depressions, either linear or subcircular in shape. Linear depressions occur primarily where sandy distributary-channel deposits are exposed on the seafloor. The subcircular pits are concentrated in areas where delta-front deposits crop out, and occasional seismic blanking indicates that gas is present. The difference in erosional patterns suggests that delta-front and distributary-channel deposits respond uniquely to wave and current energy expended on the inner shelf, particularly during stormy periods. Linear depressions may be the result of the sandy distributary-channel deposits eroding more readily by waves and coastal currents than the surrounding delta-front deposits. Pits may develop as gas discharge or liquefaction occurs within fine-grained delta-front deposits, causing seafloor collapse. These detailed observations suggest that ravinement of this inner shelf surface may be ongoing, is controlled by the underlying stratigraphy, and has varied morphologic expression.

Subsurface control on seafloor erosional processes offshore of the Chandeleur Islands, Louisiana

USGS Publications Warehouse

Twichell, David; Pendleton, Elizabeth A.; Baldwin, Wayne E.; Flocks, James G.

2009-01-01

The Chandeleur Islands lie on the eastern side of the modern Mississippi River delta plain, near the edge of the St. Bernard Delta complex. Since abandonment approximately 2,000 years b.p., this delta complex has undergone subsidence and ravinement as the shoreline has transgressed across it. High-resolution seismic-reflection, sidescan-sonar, and bathymetry data show that seafloor erosion is influenced by locally variable shallow stratigraphy. The data reveal two general populations of shallow erosional depressions, either linear or subcircular in shape. Linear depressions occur primarily where sandy distributary-channel deposits are exposed on the seafloor. The subcircular pits are concentrated in areas where delta-front deposits crop out, and occasional seismic blanking indicates that gas is present. The difference in erosional patterns suggests that delta-front and distributary-channel deposits respond uniquely to wave and current energy expended on the inner shelf, particularly during stormy periods. Linear depressions may be the result of the sandy distributary-channel deposits eroding more readily by waves and coastal currents than the surrounding delta-front deposits. Pits may develop as gas discharge or liquefaction occurs within fine-grained delta-front deposits, causing seafloor collapse. These detailed observations suggest that ravinement of this inner shelf surface may be ongoing, is controlled by the underlying stratigraphy, and has varied morphologic expression.

Generation of large-scale intrusions at baroclinic fronts: an analytical consideration with a reference to the Arctic Ocean

NASA Astrophysics Data System (ADS)

Kuzmina, Natalia

2016-12-01

Analytical solutions are found for the problem of instability of a weak geostrophic flow with linear velocity shear accounting for vertical diffusion of buoyancy. The analysis is based on the potential-vorticity equation in a long-wave approximation when the horizontal scale of disturbances is considered much larger than the local baroclinic Rossby radius. It is hypothesized that the solutions found can be applied to describe stable and unstable disturbances of the planetary scale with respect, in particular, to the Arctic Ocean, where weak baroclinic fronts with typical temporal variability periods on the order of several years or more have been observed and the β effect is negligible. Stable (decaying with time) solutions describe disturbances that, in contrast to the Rossby waves, can propagate to both the west and east, depending on the sign of the linear shear of geostrophic velocity. The unstable (growing with time) solutions are applied to explain the formation of large-scale intrusions at baroclinic fronts under the stable-stable thermohaline stratification observed in the upper layer of the Polar Deep Water in the Eurasian Basin. The suggested mechanism of formation of intrusions can be considered a possible alternative to the mechanism of interleaving at the baroclinic fronts due to the differential mixing.

GYROSURFING ACCELERATION OF IONS IN FRONT OF EARTH's QUASI-PARALLEL BOW SHOCK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kis, Arpad; Lemperger, Istvan; Wesztergom, Viktor

2013-07-01

It is well known that shocks in space plasmas can accelerate particles to high energies. However, many details of the shock acceleration mechanism are still unknown. A critical element of shock acceleration is the injection problem; i.e., the presence of the so called seed particle population that is needed for the acceleration to work efficiently. In our case study, we present for the first time observational evidence of gyroresonant surfing acceleration in front of Earth's quasi-parallel bow shock resulting in the appearance of the long-suspected seed particle population. For our analysis, we use simultaneous multi-spacecraft measurements provided by the Clustermore » spacecraft ion (CIS), magnetic (FGM), and electric field and wave instrument (EFW) during a time period of large inter-spacecraft separation distance. The spacecraft were moving toward the bow shock and were situated in the foreshock region. The results show that the gyroresonance surfing acceleration takes place as a consequence of interaction between circularly polarized monochromatic (or quasi-monochromatic) transversal electromagnetic plasma waves and short large amplitude magnetic structures (SLAMSs). The magnetic mirror force of the SLAMS provides the resonant conditions for the ions trapped by the waves and results in the acceleration of ions. Since wave packets with circular polarization and different kinds of magnetic structures are very commonly observed in front of Earth's quasi-parallel bow shock, the gyroresonant surfing acceleration proves to be an important particle injection mechanism. We also show that seed ions are accelerated directly from the solar wind ion population.« less

Solitary waves in morphogenesis: Determination fronts as strain-cued strain transformations among automatous cells

NASA Astrophysics Data System (ADS)

Cox, Brian N.; Landis, Chad M.

2018-02-01

We present a simple theory of a strain pulse propagating as a solitary wave through a continuous two-dimensional population of cells. A critical strain is assumed to trigger a strain transformation, while, simultaneously, cells move as automata to tend to restore a preferred cell density. We consider systems in which the strain transformation is a shape change, a burst of proliferation, or the commencement of growth (which changes the shape of the population sheet), and demonstrate isomorphism among these cases. Numerical and analytical solutions describe a strain pulse whose height does not depend on how the strain disturbance was first launched, or the rate at which the strain transformation is achieved, or the rate constant in the rule for the restorative cell motion. The strain pulse is therefore very stable, surviving the imposition of strong perturbations: it would serve well as a timing signal in development. The automatous wave formulation is simple, with few model parameters. A strong case exists for the presence of a strain pulse during amelogenesis. Quantitative analysis reveals a simple relationship between the velocity of the leading edge of the pulse in amelogenesis and the known speed of migration of ameloblast cells. This result and energy arguments support the depiction of wave motion as an automatous cell response to strain, rather than as a response to an elastic energy gradient. The theory may also contribute to understanding the determination front in somitogenesis, moving fronts of convergent-extension transformation, and mitotic wavefronts in the syncytial drosophila embryo.

Demonstrating Sound Wave Propagation with Candle Flame and Loudspeaker

ERIC Educational Resources Information Center

Hrepic, Zdeslav; Nettles, Corey; Bonilla, Chelsea

2013-01-01

The motion of a candle flame in front of a loudspeaker has been suggested as a productive demonstration of the longitudinal wave nature of sound. The demonstration has been used also as a research tool to investigate students' understanding about sound. The underpinning of both applications is the expectation of a horizontal, back-and-forth…

Facilitation of cytosolic calcium wave propagation by local calcium uptake into the sarcoplasmic reticulum in cardiac myocytes.

PubMed

Maxwell, Joshua T; Blatter, Lothar A

2012-12-01

The widely accepted paradigm for cytosolic Ca(2+) wave propagation postulates a 'fire-diffuse-fire' mechanism where local Ca(2+)-induced Ca(2+) release (CICR) from the sarcoplasmic reticulum (SR) via ryanodine receptor (RyR) Ca(2+) release channels diffuses towards and activates neighbouring release sites, resulting in a propagating Ca(2+) wave. A recent challenge to this paradigm proposed the requirement for an intra-SR 'sensitization' Ca(2+) wave that precedes the cytosolic Ca(2+) wave and primes RyRs from the luminal side to CICR. Here, we tested this hypothesis experimentally with direct simultaneous measurements of cytosolic ([Ca(2+)](i); rhod-2) and intra-SR ([Ca(2+)](SR); fluo-5N) calcium signals during wave propagation in rabbit ventricular myocytes, using high resolution fluorescence confocal imaging. The increase in [Ca(2+)](i) at the wave front preceded depletion of the SR at each point along the calcium wave front, while during this latency period a transient increase of [Ca(2+)](SR) was observed. This transient elevation of [Ca(2+)](SR) could be identified at individual release junctions and depended on the activity of the sarco-endoplasmic reticulum Ca(2+)-ATPase (SERCA). Increased SERCA activity (β-adrenergic stimulation with 1 μM isoproterenol (isoprenaline)) decreased the latency period and increased the amplitude of the transient elevation of [Ca(2+)](SR), whereas inhibition of SERCA (3 μM cyclopiazonic acid) had the opposite effect. In conclusion, the data provide experimental evidence that local Ca(2+) uptake by SERCA into the SR facilitates the propagation of cytosolic Ca(2+) waves via luminal sensitization of the RyR, and supports a novel paradigm of a 'fire-diffuse-uptake-fire' mechanism for Ca(2+) wave propagation in cardiac myocytes.

Facilitation of cytosolic calcium wave propagation by local calcium uptake into the sarcoplasmic reticulum in cardiac myocytes

PubMed Central

Maxwell, Joshua T; Blatter, Lothar A

2012-01-01

The widely accepted paradigm for cytosolic Ca2+ wave propagation postulates a ‘fire-diffuse-fire’ mechanism where local Ca2+-induced Ca2+ release (CICR) from the sarcoplasmic reticulum (SR) via ryanodine receptor (RyR) Ca2+ release channels diffuses towards and activates neighbouring release sites, resulting in a propagating Ca2+ wave. A recent challenge to this paradigm proposed the requirement for an intra-SR ‘sensitization’ Ca2+ wave that precedes the cytosolic Ca2+ wave and primes RyRs from the luminal side to CICR. Here, we tested this hypothesis experimentally with direct simultaneous measurements of cytosolic ([Ca2+]i; rhod-2) and intra-SR ([Ca2+]SR; fluo-5N) calcium signals during wave propagation in rabbit ventricular myocytes, using high resolution fluorescence confocal imaging. The increase in [Ca2+]i at the wave front preceded depletion of the SR at each point along the calcium wave front, while during this latency period a transient increase of [Ca2+]SR was observed. This transient elevation of [Ca2+]SR could be identified at individual release junctions and depended on the activity of the sarco-endoplasmic reticulum Ca2+-ATPase (SERCA). Increased SERCA activity (β-adrenergic stimulation with 1 μm isoproterenol (isoprenaline)) decreased the latency period and increased the amplitude of the transient elevation of [Ca2+]SR, whereas inhibition of SERCA (3 μm cyclopiazonic acid) had the opposite effect. In conclusion, the data provide experimental evidence that local Ca2+ uptake by SERCA into the SR facilitates the propagation of cytosolic Ca2+ waves via luminal sensitization of the RyR, and supports a novel paradigm of a ‘fire-diffuse-uptake-fire’ mechanism for Ca2+ wave propagation in cardiac myocytes. PMID:22988145

A Relation Between the Eikonal Equation Associated to a Potential Energy Surface and a Hyperbolic Wave Equation.

PubMed

Bofill, Josep Maria; Quapp, Wolfgang; Caballero, Marc

2012-12-11

The potential energy surface (PES) of a molecule can be decomposed into equipotential hypersurfaces. We show in this article that the hypersurfaces are the wave fronts of a certain hyperbolic partial differential equation, a wave equation. It is connected with the gradient lines, or the steepest descent, or the steepest ascent lines of the PES. The energy seen as a reaction coordinate plays the central role in this treatment.

Point Judith, Rhode Island, Breakwater Risk Assessment

DTIC Science & Technology

2015-08-01

output stations. Beach zones considered included the sandy beach to the west side of the HoR, which had significant dune features and was fronting...time dependency for crest height and wave parameters is assumed, hc = total damaged crest height of structure from toe , Lp is the local wave length...computed using linear wave theory and Tp, h is the toe depth, hc’ = total undamaged crest height of structure from toe , At = area of structure enclosed

Long waves in the eastern equatorial pacific ocean: a view from a geostationary satellite.

PubMed

Legeckis, R

1977-09-16

During 1975, westward-moving long waves with a period of about 25 days and a wavelength of 1000 kilometers were observed at a sea surface temperature front in the equatorial Pacific on infrared images obtained by a geostationary environmental satellite system. The absence of these waves during 1976, and the above-average equatorial sea surface temperatures during 1976, may be related to a decrease in the southeasterly trade winds during that year.

Research into Surface Wave Phenomena in Sedimentary Basins.

DTIC Science & Technology

1981-12-31

150 km of the southerly extension of the Overthrust Belt, 350 km of the Green River Basin paralleling the Uinta Mountains and 150 km across the Front...WEIDLINGER ASSOCIATES O300 SAND HiLL ROAD BUILDING 4, SUITE 245 MENLO PARK, CALIFORNIA 9462 RESEARCH INTO SURFACE WAVE PHENOMENA IN SEDIMENTARY BASINS BY...PARK, CALIFORNIA 94025 ! I RESEARCH INTO SURFACE WAVE PHENOMENA IN SEDIMENTARY BASINS I Dy G.L. Wojcik J. Isenberg F. Ma E. Richardson Prepared for

Excitation of slow waves in front of an ICRF antenna in a basic plasma experiment

NASA Astrophysics Data System (ADS)

Soni, Kunal; van Compernolle, Bart; Crombe, Kristel; van Eester, Dirk

2017-10-01

Recent results of ICRF experiments at the Large Plasma Device (LAPD) indicate parasitic coupling to the slow wave by the fast wave antenna. Plasma parameters in LAPD are similar to the scrape-off layer of current fusion devices. The machine has a 17 m long, 60 cm diameter magnetized plasma column with typical plasma parameters ne 1012 -1013 cm-3, Te 1 - 10 eV and B0 1000 G. It was found that coupling to the slow mode occurs when the plasma density in front of the antenna is low enough such that the lower hybrid resonance is present in the plasma. The radial density profile is tailored to allow for fast mode propagation in the high density core and slow mode propagation in the low density edge region. Measurements of the wave fields clearly show two distinct modes, one long wavelength m=1 fast wave mode in the core and a short wavelength backward propagating mode in the edge. Perpendicular wave numbers compare favorably to the predicted values. The experiment was done for varying frequencies, ω /Ωi = 25 , 6 and 1.5. Future experiments will investigate the dependence on antenna tilt angle with respect to the magnetic field, with and without Faraday screen. This work is performed at the Basic Plasma Science Facility, sponsored jointly by DOE and NSF.

Alignment error of mirror modules of advanced telescope for high-energy astrophysics due to wavefront aberrations

NASA Astrophysics Data System (ADS)

Zocchi, Fabio E.

2017-10-01

One of the approaches that is being tested for the integration of the mirror modules of the advanced telescope for high-energy astrophysics x-ray mission of the European Space Agency consists in aligning each module on an optical bench operated at an ultraviolet wavelength. The mirror module is illuminated by a plane wave and, in order to overcome diffraction effects, the centroid of the image produced by the module is used as a reference to assess the accuracy of the optical alignment of the mirror module itself. Among other sources of uncertainty, the wave-front error of the plane wave also introduces an error in the position of the centroid, thus affecting the quality of the mirror module alignment. The power spectral density of the position of the point spread function centroid is here derived from the power spectral density of the wave-front error of the plane wave in the framework of the scalar theory of Fourier diffraction. This allows the defining of a specification on the collimator quality used for generating the plane wave starting from the contribution to the error budget allocated for the uncertainty of the centroid position. The theory generally applies whenever Fourier diffraction is a valid approximation, in which case the obtained result is identical to that derived by geometrical optics considerations.

Ocean wave generation by collapsing ice shelves

NASA Astrophysics Data System (ADS)

Macayeal, D. R.; Bassis, J. N.; Okal, E. A.; Aster, R. C.; Cathles, L. M.

2008-12-01

The 28-29 February, 2008, break-up of the Wilkins Ice Shelf, Antarctica, exemplifies the now-familiar, yet largely unexplained pattern of explosive ice-shelf break-up. While environmental warming is a likely ultimate cause of explosive break-up, several key aspects of their short-term behavior need to be explained: (1) The abrupt, near-simultaneous onset of iceberg calving across long spans of the ice front margin; (2) High outward drift velocity (about 0.3 m/s) of a leading phalanx of tabular icebergs that originate from the seaward edge of the intact ice shelf prior to break-up; (3) Rapid coverage of the ocean surface in the wake of this leading phalanx by small, capsized and dismembered tabular icebergs; (4) Extremely large gravitational potential energy release rates, e.g., up to 3 × 1010 W; (5) Lack of proximal iceberg-calving triggers that control the timing of break-up onset and that maintain the high break-up calving rates through to the conclusion of the event. Motivated by seismic records obtained from icebergs and the Ross Ice Shelf that show hundreds of micro- tsunamis emanating from near the ice shelf front, we re-examine the basic dynamic features of ice- shelf/ocean-wave interaction and, in particular, examine the possibility that collapsing ice shelves themselves are a source of waves that stimulate the disintegration process. We propose that ice-shelf generated surface-gravity waves associated with initial calving at an arbitrary seed location produce stress perturbations capable of triggering the onset of calving on the entire ice front. Waves generated by parting detachment rifts, iceberg capsize and break-up act next to stimulate an inverted submarine landslide (ice- slide) process, where gravitational potential energy released by upward movement of buoyant ice is radiated as surface gravity waves in the wake of the advancing phalanx of tabular icebergs. We conclude by describing how field research and remote sensing can be used to test the various conjectures about ice- shelf/wave interaction that appear to be at play during ice-shelf disintegration.

Optimization and experimental validation of stiff porous phononic plates for widest complete bandgap of mixed fundamental guided wave modes

NASA Astrophysics Data System (ADS)

Hedayatrasa, Saeid; Kersemans, Mathias; Abhary, Kazem; Uddin, Mohammad; Van Paepegem, Wim

2018-01-01

Phononic crystal plates (PhPs) have promising application in manipulation of guided waves for design of low-loss acoustic devices and built-in acoustic metamaterial lenses in plate structures. The prominent feature of phononic crystals is the existence of frequency bandgaps over which the waves are stopped, or are resonated and guided within appropriate defects. Therefore, maximized bandgaps of PhPs are desirable to enhance their phononic controllability. Porous PhPs produced through perforation of a uniform background plate, in which the porous interfaces act as strong reflectors of wave energy, are relatively easy to produce. However, the research in optimization of porous PhPs and experimental validation of achieved topologies has been very limited and particularly focused on bandgaps of flexural (asymmetric) wave modes. In this paper, porous PhPs are optimized through an efficient multiobjective genetic algorithm for widest complete bandgap of mixed fundamental guided wave modes (symmetric and asymmetric) and maximized stiffness. The Pareto front of optimization is analyzed and variation of bandgap efficiency with respect to stiffness is presented for various optimized topologies. Selected optimized topologies from the stiff and compliant regimes of Pareto front are manufactured by water-jetting an aluminum plate and their promising bandgap efficiency is experimentally observed. An optimized Pareto topology is also chosen and manufactured by laser cutting a Plexiglas (PMMA) plate, and its performance in self-collimation and focusing of guided waves is verified as compared to calculated dispersion properties.

Statistics of peak overpressure and shock steepness for linear and nonlinear N-wave propagation in a kinematic turbulence.

PubMed

Yuldashev, Petr V; Ollivier, Sébastien; Karzova, Maria M; Khokhlova, Vera A; Blanc-Benon, Philippe

2017-12-01

Linear and nonlinear propagation of high amplitude acoustic pulses through a turbulent layer in air is investigated using a two-dimensional KZK-type (Khokhlov-Zabolotskaya-Kuznetsov) equation. Initial waves are symmetrical N-waves with shock fronts of finite width. A modified von Kármán spectrum model is used to generate random wind velocity fluctuations associated with the turbulence. Physical parameters in simulations correspond to previous laboratory scale experiments where N-waves with 1.4 cm wavelength propagated through a turbulence layer with the outer scale of about 16 cm. Mean value and standard deviation of peak overpressure and shock steepness, as well as cumulative probabilities to observe amplified peak overpressure and shock steepness, are analyzed. Nonlinear propagation effects are shown to enhance pressure level in random foci for moderate initial amplitudes of N-waves thus increasing the probability to observe highly peaked waveforms. Saturation of the pressure level is observed for stronger nonlinear effects. It is shown that in the linear propagation regime, the turbulence mainly leads to the smearing of shock fronts, thus decreasing the probability to observe high values of steepness, whereas nonlinear effects dramatically increase the probability to observe steep shocks.

Supporting Structure of the LSD Wave in an Energy Absorption Perspective

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fukui, Akihiro; Hatai, Keigo; Cho, Shinatora

In Repetitively Pulsed (RP) Laser Propulsion, laser energy irradiated to a vehicle is converted to blast wave enthalpy during the Laser Supported Detonation (LSD) regime. Based on the measured post-LSD electron number density profiles by two-wavelength Mach Zehnder interferometer in a line-focusing optics, electron temperature and absorption coefficient were estimated assuming Local Thermal Equilibrium. A 10J/pulse CO{sub 2} laser was used. As a result, laser absorption was found completed in the layer between the shock wave and the electron density peak. Although the LSD-termination timing was not clear from the shock-front/ionization-front separation in the shadowgraph images, there observed drastic changesmore » in the absorption layer thickness from 0.2 mm to 0.5 mm and in the peak heating rate from 12-17x10{sup 13} kW/m{sup 3} to 5x10{sup 13} kW/m{sup 3} at the termination.« less

Parametric excitation of multiple resonant radiations from localized wavepackets

PubMed Central

Conforti, Matteo; Trillo, Stefano; Mussot, Arnaud; Kudlinski, Alexandre

2015-01-01

Fundamental physical phenomena such as laser-induced ionization, driven quantum tunneling, Faraday waves, Bogoliubov quasiparticle excitations, and the control of new states of matter rely on time-periodic driving of the system. A remarkable property of such driving is that it can induce the localized (bound) states to resonantly couple to the continuum. Therefore experiments that allow for enlightening and controlling the mechanisms underlying such coupling are of paramount importance. We implement such an experiment in a special optical fiber characterized by a dispersion oscillating along the propagation coordinate, which mimics “time”. The quasi-momentum associated with such periodic perturbation is responsible for the efficient coupling of energy from the localized wave-packets (solitons in anomalous dispersion and shock fronts in normal dispersion) sustained by the fiber nonlinearity, into free-running linear dispersive waves (continuum) at multiple resonant frequencies. Remarkably, the observed resonances can be explained by means of a unified approach, regardless of the fact that the localized state is a soliton-like pulse or a shock front. PMID:25801054

Modulation of Polarization for Phase Extraction in Holographic Interferometry with Two References

NASA Astrophysics Data System (ADS)

Rodriguez-Zurita, G.; Vázquez-Castillo, J.-F.; Toto-Arellano, N.-I.; Meneses-Fabian, C.; Jiménez-Montero, L.-E.

2010-04-01

Heterodyne holographic interferometry allows high accuracy for phase-difference extraction between two wave fronts, especially when they are previously recorded in the same recording medium. In part, this is because the wave fronts can be affected by the recording process in a very similar way. The double reconstruction of a double-exposure hologram with two independent references results in a two-beam holographic interferometer with an arm conveying a wave modulated in frequency when using heterodyne techniques. The heterodyne frequency has been usually introduced with a plane mirror attached to a piezo-electric stack driven with a suitable variable power supply. For holographic interferometry, however, less attention has been devoted to alternative phase retrieval variants as, for example, phase-shifting with modulation of polarization or Fourier methods. In this work, we propose and demonstrate the basic capabilities of modulation of polarization performing as a phase-shifting technique for holographic interferometry with two references in a phase-stepping scheme. Experimental results are provided.

Wavespace-Based Coherent Deconvolution

NASA Technical Reports Server (NTRS)

Bahr, Christopher J.; Cattafesta, Louis N., III

2012-01-01

Array deconvolution is commonly used in aeroacoustic analysis to remove the influence of a microphone array's point spread function from a conventional beamforming map. Unfortunately, the majority of deconvolution algorithms assume that the acoustic sources in a measurement are incoherent, which can be problematic for some aeroacoustic phenomena with coherent, spatially-distributed characteristics. While several algorithms have been proposed to handle coherent sources, some are computationally intractable for many problems while others require restrictive assumptions about the source field. Newer generalized inverse techniques hold promise, but are still under investigation for general use. An alternate coherent deconvolution method is proposed based on a wavespace transformation of the array data. Wavespace analysis offers advantages over curved-wave array processing, such as providing an explicit shift-invariance in the convolution of the array sampling function with the acoustic wave field. However, usage of the wavespace transformation assumes the acoustic wave field is accurately approximated as a superposition of plane wave fields, regardless of true wavefront curvature. The wavespace technique leverages Fourier transforms to quickly evaluate a shift-invariant convolution. The method is derived for and applied to ideal incoherent and coherent plane wave fields to demonstrate its ability to determine magnitude and relative phase of multiple coherent sources. Multi-scale processing is explored as a means of accelerating solution convergence. A case with a spherical wave front is evaluated. Finally, a trailing edge noise experiment case is considered. Results show the method successfully deconvolves incoherent, partially-coherent, and coherent plane wave fields to a degree necessary for quantitative evaluation. Curved wave front cases warrant further investigation. A potential extension to nearfield beamforming is proposed.

Mechanical signaling coordinates the embryonic heartbeat

PubMed Central

Chiou, Kevin K.; Rocks, Jason W.; Chen, Christina Yingxian; Cho, Sangkyun; Merkus, Koen E.; Rajaratnam, Anjali; Robison, Patrick; Tewari, Manorama; Vogel, Kenneth; Majkut, Stephanie F.; Prosser, Benjamin L.; Discher, Dennis E.; Liu, Andrea J.

2016-01-01

In the beating heart, cardiac myocytes (CMs) contract in a coordinated fashion, generating contractile wave fronts that propagate through the heart with each beat. Coordinating this wave front requires fast and robust signaling mechanisms between CMs. The primary signaling mechanism has long been identified as electrical: gap junctions conduct ions between CMs, triggering membrane depolarization, intracellular calcium release, and actomyosin contraction. In contrast, we propose here that, in the early embryonic heart tube, the signaling mechanism coordinating beats is mechanical rather than electrical. We present a simple biophysical model in which CMs are mechanically excitable inclusions embedded within the extracellular matrix (ECM), modeled as an elastic-fluid biphasic material. Our model predicts strong stiffness dependence in both the heartbeat velocity and strain in isolated hearts, as well as the strain for a hydrogel-cultured CM, in quantitative agreement with recent experiments. We challenge our model with experiments disrupting electrical conduction by perfusing intact adult and embryonic hearts with a gap junction blocker, β-glycyrrhetinic acid (BGA). We find this treatment causes rapid failure in adult hearts but not embryonic hearts—consistent with our hypothesis. Last, our model predicts a minimum matrix stiffness necessary to propagate a mechanically coordinated wave front. The predicted value is in accord with our stiffness measurements at the onset of beating, suggesting that mechanical signaling may initiate the very first heartbeats. PMID:27457951

Fundamental properties of cooperative contagion processes

NASA Astrophysics Data System (ADS)

Chen, Li; Ghanbarnejad, Fakhteh; Brockmann, Dirk

2017-10-01

We investigate the effects of cooperativity between contagion processes that spread and persist in a host population. We propose and analyze a dynamical model in which individuals that are affected by one transmissible agent A exhibit a higher than baseline propensity of being affected by a second agent B and vice versa. The model is a natural extension of the traditional susceptible-infected-susceptible model used for modeling single contagion processes. We show that cooperativity changes the dynamics of the system considerably when cooperativity is strong. The system exhibits discontinuous phase transitions not observed in single agent contagion, multi-stability, a separation of the traditional epidemic threshold into different thresholds for inception and extinction as well as hysteresis. These properties are robust and are corroborated by stochastic simulations on lattices and generic network topologies. Finally, we investigate wave propagation and transients in a spatially extended version of the model and show that especially for intermediate values of baseline reproduction ratios the system is characterized by various types of wave-front speeds. The system can exhibit spatially heterogeneous stationary states for some parameters and negative front speeds (receding wave fronts). The two agent model can be employed as a starting point for more complex contagion processes, involving several interacting agents, a model framework particularly suitable for modeling the spread and dynamics of microbiological ecosystems in host populations.

Existence and exponential stability of traveling waves for delayed reaction-diffusion systems

NASA Astrophysics Data System (ADS)

Hsu, Cheng-Hsiung; Yang, Tzi-Sheng; Yu, Zhixian

2018-03-01

The purpose of this work is to investigate the existence and exponential stability of traveling wave solutions for general delayed multi-component reaction-diffusion systems. Following the monotone iteration scheme via an explicit construction of a pair of upper and lower solutions, we first obtain the existence of monostable traveling wave solutions connecting two different equilibria. Then, applying the techniques of weighted energy method and comparison principle, we show that all solutions of the Cauchy problem for the considered systems converge exponentially to traveling wave solutions provided that the initial perturbations around the traveling wave fronts belong to a suitable weighted Sobolev space.

Deuteron electromagnetic form factors with the light-front approach

NASA Astrophysics Data System (ADS)

Sun, Bao-dong; Dong, Yu-bing

2017-01-01

The electromagnetic form factors and low-energy observables of the deuteron are studied with the help of the light-front approach, where the deuteron is regarded as a weakly bound state of a proton and a neutron. Both the S and D wave interacting vertexes among the deuteron, proton, and neutron are taken into account. Moreover, the regularization functions are also introduced. In our calculations, the vertex and the regularization functions are employed to simulate the momentum distribution inside the deuteron. Our numerical results show that the light-front approach can roughly reproduce the deuteron electromagnetic form factors, like charge G 0, magnetic G 1, and quadrupole G 2, in the low Q 2 region. The important effect of the D wave vertex on G 2 is also addressed. Supported by National Natural Science Foundation of China (10975146, 11475192), The fund provided by the Sino-German CRC 110 “Symmetries and the Emergence of Structure in QCD" project is also appreciated, YBD thanks FAPESP grant 2011/11973-4 for funding his visit to ICTP-SAIFR

Light-front holographic distribution amplitudes of pseudoscalar mesons and their application to B -meson decays

DOE PAGES

Chang, Qin; Brodsky, Stanley J.; Li, Xin-Qiang

2017-05-30

In this article the dynamical spin effects of the light-front holographic wave functions for light pseudoscalar mesons are studied. These improved wave functions are then confronted with a number of hadronic observables: the decay constants of π and K mesons, their ξ -moments, the pion-to-photon transition form factor, and the pure annihilationmore » $$\\bar{B}_s$$ → π + π - and $$\\bar{B}_d$$ → K + K - decays. Taking f π , fK , and their ratio fK / f π as constraints, we perform a χ 2 analysis for the holographic parameters, including the mass scale parameter $$\\sqrtλ$$ and the effective quark masses, and find that the fitted results are quite consistent with the ones obtained from the light-quark hadronic Regge trajectories. In addition, we also show that the end point divergence appearing in the pure annihilation $$\\bar{B}_s$$ → π + π - and $$\\bar{B}_d$$ → K + K - decays can be controlled well by using these improved light-front holographic distribution amplitudes.« less

Upstream waves and particles /Tutorial Lecture/. [from shocks in interplanetary space

NASA Technical Reports Server (NTRS)

Russell, C. T.; Hoppe, M. M.

1983-01-01

The plasma waves, MHD waves, energetic electrons and ions associated with the proximity of the region upstream from terrestrial, planetary and interplanetary shocks are discussed in view of observations and current theories concerning their origin. These waves cannot be separated from the study of shock structure. Since the shocks are supersonic, they continually overtake any ULF waves created in the plasma in front of the shock. The upstream particles and waves are also of intrinsic interest because they provide a plasma laboratory for the study of wave-particle interactions in a plasma which, at least at the earth, is accessible to sophisticated probing. Insight may be gained into interstellar medium cosmic ray acceleration through the study of these phenomena.

Propagation of finite amplitude sound through turbulence: Modeling with geometrical acoustics and the parabolic approximation

NASA Astrophysics Data System (ADS)

Blanc-Benon, Philippe; Lipkens, Bart; Dallois, Laurent; Hamilton, Mark F.; Blackstock, David T.

2002-01-01

Sonic boom propagation can be affected by atmospheric turbulence. It has been shown that turbulence affects the perceived loudness of sonic booms, mainly by changing its peak pressure and rise time. The models reported here describe the nonlinear propagation of sound through turbulence. Turbulence is modeled as a set of individual realizations of a random temperature or velocity field. In the first model, linear geometrical acoustics is used to trace rays through each realization of the turbulent field. A nonlinear transport equation is then derived along each eigenray connecting the source and receiver. The transport equation is solved by a Pestorius algorithm. In the second model, the KZK equation is modified to account for the effect of a random temperature field and it is then solved numerically. Results from numerical experiments that simulate the propagation of spark-produced N waves through turbulence are presented. It is observed that turbulence decreases, on average, the peak pressure of the N waves and increases the rise time. Nonlinear distortion is less when turbulence is present than without it. The effects of random vector fields are stronger than those of random temperature fields. The location of the caustics and the deformation of the wave front are also presented. These observations confirm the results from the model experiment in which spark-produced N waves are used to simulate sonic boom propagation through a turbulent atmosphere.

Propagation of finite amplitude sound through turbulence: modeling with geometrical acoustics and the parabolic approximation.

PubMed

Blanc-Benon, Philippe; Lipkens, Bart; Dallois, Laurent; Hamilton, Mark F; Blackstock, David T

2002-01-01

Sonic boom propagation can be affected by atmospheric turbulence. It has been shown that turbulence affects the perceived loudness of sonic booms, mainly by changing its peak pressure and rise time. The models reported here describe the nonlinear propagation of sound through turbulence. Turbulence is modeled as a set of individual realizations of a random temperature or velocity field. In the first model, linear geometrical acoustics is used to trace rays through each realization of the turbulent field. A nonlinear transport equation is then derived along each eigenray connecting the source and receiver. The transport equation is solved by a Pestorius algorithm. In the second model, the KZK equation is modified to account for the effect of a random temperature field and it is then solved numerically. Results from numerical experiments that simulate the propagation of spark-produced N waves through turbulence are presented. It is observed that turbulence decreases, on average, the peak pressure of the N waves and increases the rise time. Nonlinear distortion is less when turbulence is present than without it. The effects of random vector fields are stronger than those of random temperature fields. The location of the caustics and the deformation of the wave front are also presented. These observations confirm the results from the model experiment in which spark-produced N waves are used to simulate sonic boom propagation through a turbulent atmosphere.

Rigorous results for the minimal speed of Kolmogorov-Petrovskii-Piscounov monotonic fronts with a cutoffa)

NASA Astrophysics Data System (ADS)

Benguria, Rafael D.; Depassier, M. Cristina; Loss, Michael

2012-12-01

We study the effect of a cutoff on the speed of pulled fronts of the one-dimensional reaction diffusion equation. To accomplish this, we first use variational techniques to prove the existence of a heteroclinic orbit in phase space for traveling wave solutions of the corresponding reaction diffusion equation under conditions that include discontinuous reaction profiles. This existence result allows us to prove rigorous upper and lower bounds on the minimal speed of monotonic fronts in terms of the cut-off parameter ɛ. From these bounds we estimate the range of validity of the Brunet-Derrida formula for a general class of reaction terms.

Periodic waves in the lower thermosphere observed by OI630 nm airglow images

NASA Astrophysics Data System (ADS)

Paulino, I.; Medeiros, A. F.; Vadas, S. L.; Wrasse, C. M.; Takahashi, H.; Buriti, R. A.; Leite, D.; Filgueira, S.; Bageston, J. V.; Sobral, J. H. A.; Gobbi, D.

2016-02-01

Periodic wave structures in the thermosphere have been observed at São João do Cariri (geographic coordinates: 36.5° W, 7.4° S; geomagnetic coordinates based on IGRF model to 2015: 35.8° E, 0.48° N) from September 2000 to November 2010 using OI630.0 nm airglow images. During this period, which corresponds to almost one solar cycle, characteristics of 98 waves were studied. Similarities between the characteristics of these events and observations at other places around the world were noted, primarily the spectral parameters. The observed periods were mostly found between 10 and 35 min; horizontal wavelengths ranged from 100 to 200 km, and phase speed from 30 to 180 m s-1. These parameters indicated that some of the waves, presented here, are slightly faster than those observed previously at low and middle latitudes (Indonesia, Carib and Japan), indicating that the characteristics of these waves may change at different places. Most of observed waves have appeared during magnetically quiet nights, and the occurrence of those waves followed the solar activity. Another important characteristic is the quasi-monochromatic periodicity that distinguish them from the single-front medium-scale traveling ionospheric disturbances (MSTIDs) that have been observed previously over the Brazilian region. Moreover, most of the observed waves did not present a phase front parallel to the northeast-southwest direction, which is predicted by the Perkins instability process. It strongly suggests that most of these waves must have had different generation mechanisms from the Perkins instability, which have been pointed out as being a very important mechanism for the generation of MSTIDs in the lower thermosphere.

Miscellaneous High-Resolution Seismic Imaging Investigations in Salt Lake and Utah Valleys for Earthquake Hazards

USGS Publications Warehouse

Stephenson, W.J.; Williams, R.A.; Odum, J.K.; Worley, D.M.

2007-01-01

Introduction In support of earthquake hazards and ground motion studies by researchers at the Utah Geological Survey, University of Utah, Utah State University, Brigham Young University, and San Diego State University, the U.S. Geological Survey Geologic Hazards Team Intermountain West Project conducted three high-resolution seismic imaging investigations along the Wasatch Front between September 2003 and September 2005. These three investigations include: (1) a proof-of-concept P-wave minivib reflection imaging profile in south-central Salt Lake Valley, (2) a series of seven deep (as deep as 400 m) S-wave reflection/refraction soundings using an S-wave minivib in both Salt Lake and Utah Valleys, and (3) an S-wave (and P-wave) investigation to 30 m at four sites in Utah Valley and at two previously investigated S-wave (Vs) minivib sites. In addition, we present results from a previously unpublished downhole S-wave investigation conducted at four sites in Utah Valley. The locations for each of these investigations are shown in figure 1. Coordinates for the investigation sites are listed in Table 1. With the exception of the P-wave common mid-point (CMP) reflection profile, whose end points are listed, these coordinates are for the midpoint of each velocity sounding. Vs30 and Vs100, also shown in Table 1, are defined as the average shear-wave velocities to depths of 30 and 100 m, respectively, and details of their calculation can be found in Stephenson and others (2005). The information from these studies will be incorporated into components of the urban hazards maps along the Wasatch Front being developed by the U.S. Geological Survey, Utah Geological Survey, and numerous collaborating research institutions.

Underwater glider observations of the ongoing El Niño

NASA Astrophysics Data System (ADS)

Rudnick, D. L.; Owens, B.; Johnston, S.; Karnauskas, K.

2016-02-01

We report on observations by underwater gliders in the equatorial current system along 93°W and 95°W between 2°S and 2°N starting in October 2013 and continuing through the present. The project Repeat Observations by Gliders in the Equatorial Region (ROGER) was conceived with the intention of using underwater gliders to make repeat sections across equatorial system to quantify the location and strength of the Equatorial Undercurrent (EUC) and the equatorial front. ROGER serendipitously started near the beginning of a series of events that have led to the El Niño currently ongoing. We use Spray underwater gliders equipped with CTDs and ADCPs to measure pressure, temperature, salinity, velocity and chlorophyll fluorescence in a series of deployments from the Galapagos Islands. At the time of writing of this abstract, we have completed 15 glider missions, with 3 currently underway. Gliders have completed 7300 dives to as deep as 1000 m, traveling 27,000 km in 1600 glider-days. To our knowledge, this is the most extensive glider data set ever collected in the equatorial current system. With 6-km horizontal spacing between profiles, these more than 30 sections across the equator allow a finely-resolved look at the passage of Kelvin waves that establish El Niño. The Kelvin waves are manifest as deepening of the thermocline, warming of the surface, strengthening of the EUC, and northward migration of the equatorial front. We will present an up-to-date account of the continuing glider observations of El Niño.

Synchro-ballistic recording of detonation phenomena

NASA Astrophysics Data System (ADS)

Critchfield, Robert R.; Asay, Blaine W.; Bdzil, John B.; Davis, William C.; Ferm, Eric N.; Idar, Deanne J.

1997-12-01

Synchro-ballistic use of rotating-mirror streak cameras allows for detailed recording of high-speed events of known velocity and direction. After an introduction to the synchro-ballistic technique, this paper details two diverse applications of the technique as applied in the field of high-explosives research. In the first series of experiments detonation-front shape is recorded as the arriving detonation shock wave tilts an obliquely mounted mirror, causing reflected light to be deflected from the imaging lens. These tests were conducted for the purpose of calibrating and confirming the asymptotic detonation shock dynamics (DSD) theory of Bdzil and Stewart. The phase velocities of the events range from ten to thirty millimeters per microsecond. Optical magnification is set for optimal use of the film's spatial dimension and the phase velocity is adjusted to provide synchronization at the camera's maximum writing speed. Initial calibration of the technique is undertaken using a cylindrical HE geometry over a range of charge diameters and of sufficient length-to- diameter ratio to insure a stable detonation wave. The final experiment utilizes an arc-shaped explosive charge, resulting in an asymmetric denotation-front record. The second series of experiments consists of photographing a shaped-charge jet having a velocity range of two to nine millimeters per microsecond. To accommodate the range of velocities it is necessary to fire several tests, each synchronized to a different section of the jet. The experimental apparatus consists of a vacuum chamber to preclude atmospheric ablation of the jet tip with shocked-argon back lighting to produce a shadow-graph image.

Synchro-ballistic recording of detonation phenomena

DOE Office of Scientific and Technical Information (OSTI.GOV)

Critchfield, R.R.; Asay, B.W.; Bdzil, J.B.

1997-09-01

Synchro-ballistic use of rotating-mirror streak cameras allows for detailed recording of high-speed events of known velocity and direction. After an introduction to the synchro-ballistic technique, this paper details two diverse applications of the technique as applied in the field of high-explosives research. In the first series of experiments detonation-front shape is recorded as the arriving detonation shock wave tilts an obliquely mounted mirror, causing reflected light to be deflected from the imaging lens. These tests were conducted for the purpose of calibrating and confirming the asymptotic Detonation Shock Dynamics (DSD) theory of Bdzil and Stewart. The phase velocities of themore » events range from ten to thirty millimeters per microsecond. Optical magnification is set for optimal use of the film`s spatial dimension and the phase velocity is adjusted to provide synchronization at the camera`s maximum writing speed. Initial calibration of the technique is undertaken using a cylindrical HE geometry over a range of charge diameters and of sufficient length-to-diameter ratio to insure a stable detonation wave. The final experiment utilizes an arc-shaped explosive charge, resulting in an asymmetric detonation-front record. The second series of experiments consists of photographing a shaped-charge jet having a velocity range of two to nine millimeters per microsecond. To accommodate the range of velocities it is necessary to fire several tests, each synchronized to a different section of the jet. The experimental apparatus consists of a vacuum chamber to preclude atmospheric ablation of the jet tip with shocked-argon back lighting to produce a shadow-graph image.« less

The LAM space active optics facility

NASA Astrophysics Data System (ADS)

Engel, C.; Ferrari, M.; Hugot, E.; Escolle, C.; Bonnefois, A.; Bernot, M.; Bret-Dibat, T.; Carlavan, M.; Falzon, F.; Fusco, T.; Laubier, D.; Liotard, A.; Michau, V.; Mugnier, L.

2017-11-01

The next generation of large lightweight space telescopes will require the use of active optics systems to enhance the performance and increase the spatial resolution. Since almost 10 years now, LAM, CNES, THALES and ONERA conjugate their experience and efforts for the development of space active optics through the validation of key technological building blocks: correcting devices, metrology components and control strategies. This article presents the work done so far on active correcting mirrors and wave front sensing, as well as all the facilities implemented. The last part of this paper focuses on the merging of the MADRAS and RASCASSE test-set up. This unique combination will provide to the active optics community an automated, flexible and versatile facility able to feed and characterise space active optics components.

Shock wave structure in a strongly nonlinear lattice with viscous dissipation.

PubMed

Herbold, E B; Nesterenko, V F

2007-02-01

The shock wave structure in a one-dimensional lattice (e.g., granular chain of elastic particles) with a power law dependence of force on displacement between particles (F proportional to delta(n)) with viscous dissipation is considered and compared to the corresponding long wave approximation. A dissipative term depending on the relative velocity between neighboring particles is included to investigate its influence on the shape of a steady shock. The critical viscosity coefficient p(c), defining the transition from an oscillatory to a monotonic shock profile in strongly nonlinear systems, is obtained from the long-wave approximation for arbitrary values of the exponent n. The expression for the critical viscosity is comparable to the value obtained in the numerical analysis of a discrete system with a Hertzian contact interaction (n=3/2) . The expression for p(c) in the weakly nonlinear case converges to the known equation for the critical viscosity. An initial disturbance in a discrete system approaches a stationary shock profile after traveling a short distance that is comparable to the width of the leading pulse of a stationary shock front. The shock front width is minimized when the viscosity is equal to its critical value.

Electron acceleration and radiation signatures in loop coronal transients

NASA Technical Reports Server (NTRS)

Vlahos, L.; Gergely, T. E.; Papadopoulos, K.

1982-01-01

It is proposed that in loop coronal transients an erupting loop moves away from the solar surface, with a velocity exceeding the local Alfven speed, pushing against the overlying magnetic fields and driving a shock in the front of the moving part of the loop. Lower hybrid waves are excited at the shock front and propagate radially toward the center of the loop with phase velocity along the magnetic field that exceeds the thermal velocity. The lower hybrid waves stochastically accelerate the tail of the electron distribution inside the loop. The manner in which the accelerated electrons are trapped in the moving loop are discussed, and their radiation signature is estimated. It is suggested that plasma radiation can explain the power observed in stationary and moving type IV bursts.

Dynamic stabilization of Rayleigh-Taylor instability in an ablation front

DOE Office of Scientific and Technical Information (OSTI.GOV)

Piriz, A. R.; Di Lucchio, L.; Rodriguez Prieto, G.

2011-01-15

Dynamic stabilization of Rayleigh-Taylor instability in an ablation front is studied by considering a modulation in the acceleration that consists of sequences of Dirac deltas. This allows obtaining explicit analytical expressions for the instability growth rate as well as for the boundaries of the stability region. As a general rule, it is found that it is possible to stabilize all wave numbers above a certain minimum value k{sub m}, but the requirements in the modulation amplitude and frequency become more exigent with smaller k{sub m}. The essential role of compressibility is phenomenologically addressed in order to find the constraint itmore » imposes on the stability region. The results for some different wave forms of the acceleration modulation are also presented.« less

Measuring seeing with a Shack-Hartmann wave-front sensor during an active-optics experiment.

PubMed

Zhang, Yong; Yang, Dehua; Cui, Xiangqun

2004-02-01

We describe the measurement of atmospheric enclosure seeing along a 120-m light path by use of a Shack-Hartmann wave-front sensor (S-H WFS) for the first time to our knowledge in the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) outdoor active-optics experiment system, based on the differential image motion method and a S-H WFS. Seeing estimates that were gained with the S-H WFS were analyzed and found to be in close agreement with the actual seeing conditions, the estimates of refractive-index structure constant, and the thin-mirror active optics results, which usually include the shape sensing precision and the active correction precision of the experimental system. Finally, some countermeasures against poor seeing conditions were considered and adopted.

The role of luminal Ca2+ in the generation of Ca2+ waves in rat ventricular myocytes

PubMed Central

Lukyanenko, Valeriy; Subramanian, Saisunder; Györke, Inna; Wiesner, Theodore F; Györke, Sandor

1999-01-01

We used confocal Ca2+ imaging and fluo-3 to investigate the transition of localized Ca2+ releases induced by focal caffeine stimulation into propagating Ca2+ waves in isolated rat ventricular myocytes. Self-sustaining Ca2+ waves could be initiated when the cellular Ca2+ load was increased by elevating the extracellular [Ca2+] ([Ca2+]o) and they could also be initiated at normal Ca2+ loads when the sensitivity of the release sites to cytosolic Ca2+ was enhanced by low doses of caffeine. When we prevented the accumulation of extra Ca2+ in the luminal compartment of the sarcoplasmic reticulum (SR) with thapsigargin, focal caffeine pulses failed to trigger self-sustaining Ca2+ waves on elevation of [Ca2+]o. Inhibition of SR Ca2+ uptake by thapsigargin in cells already preloaded with Ca2+ above normal levels did not prevent local Ca2+ elevations from triggering propagating waves. Moreover, wave velocity increased by 20 %. Tetracaine (0·75 mM) caused transient complete inhibition of both local and propagating Ca2+ signals, followed by full recovery of the responses due to increased SR Ca2+ accumulation. Computer simulations using a numerical model with spatially distinct Ca2+ release sites suggested that increased amounts of releasable Ca2+ might not be sufficient to generate self-sustaining Ca2+ waves under conditions of Ca2+ overload unless the threshold of release site Ca2+ activation was set at relatively low levels (< 1·5 μM). We conclude that the potentiation of SR Ca2+ release channels by luminal Ca2+ is an important factor in Ca2+ wave generation. Wave propagation does not require the translocation of Ca2+ from the spreading wave front into the SR. Instead, it relies on luminal Ca2+ sensitizing Ca2+ release channels to cytosolic Ca2+. PMID:10373699

3D level set methods for evolving fronts on tetrahedral meshes with adaptive mesh refinement

DOE PAGES

Morgan, Nathaniel Ray; Waltz, Jacob I.

2017-03-02

The level set method is commonly used to model dynamically evolving fronts and interfaces. In this work, we present new methods for evolving fronts with a specified velocity field or in the surface normal direction on 3D unstructured tetrahedral meshes with adaptive mesh refinement (AMR). The level set field is located at the nodes of the tetrahedral cells and is evolved using new upwind discretizations of Hamilton–Jacobi equations combined with a Runge–Kutta method for temporal integration. The level set field is periodically reinitialized to a signed distance function using an iterative approach with a new upwind gradient. We discuss themore » details of these level set and reinitialization methods. Results from a range of numerical test problems are presented.« less

CYLINDRICAL WAVES OF FINITE AMPLITUDE IN DISSIPATIVE MEDIUM (in Russian)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Naugol'nykh, K.A.; Soluyan, S.I.; Khokhlov, R.V.

1962-07-01

Propagation of diverging and converging cylindrical waves in a nonlinear, viscous, heat conducting medium is analyzed using approximation methods. The KrylovBogolyubov method was used for small Raynold's numbers, and the method of S. I. Soluyan et al. (Vest. Mosk. Univ. ser. phys. and astronomy 3, 52-81, 1981), was used for large Raynold's numbers. The formation and dissipation of shock fronts and spatial dimensions of shock phenomena were analyzed. It is shown that the problem of finiteamplitude cylindrical wave propagation is identical to the problem of plane wave propagations in a medium with variable viscosity. (tr-auth)

Wave and particle evolution downstream of quasi-perpendicular shocks

NASA Technical Reports Server (NTRS)

Mckean, M. E.; Omidi, N.; Krauss-Varban, D.; Karimabadi, H.

1995-01-01

Distributions of ions heated in quasi-perpendicular bow shocks have large perpendicular temperature anisotropies that provide free energy for the growth of Alfven ion cyclotron (AIC) and mirror waves. These modes are often obsreved in the Earth's magnetosheath. Using two-dimensional hybrid simulations, we show that these waves are produced near the shock front and convected downstream rather than being produced locally downstream. The wave activity reduces the proton anisotropy to magnetosheath levels within a few tens of gyroradii of the shock but takes significantly longer to reduce the anisotropy of He(++) ions. The waves are primarily driven by proton anisotropy and the dynamics of the helium ions is controlled by the proton waves. Downstream of high Mach number shocks, mirror waves compete effectively with AIC waves. Downstream of low Mach number shocks, AIC waves dominate.

Planar Reflection of Gaseous Detonations

NASA Astrophysics Data System (ADS)

Damazo, Jason Scott

Pipes containing flammable gaseous mixtures may be subjected to internal detonation. When the detonation normally impinges on a closed end, a reflected shock wave is created to bring the flow back to rest. This study built on the work of Karnesky (2010) and examined deformation of thin-walled stainless steel tubes subjected to internal reflected gaseous detonations. A ripple pattern was observed in the tube wall for certain fill pressures, and a criterion was developed that predicted when the ripple pattern would form. A two-dimensional finite element analysis was performed using Johnson-Cook material properties; the pressure loading created by reflected gaseous detonations was accounted for with a previously developed pressure model. The residual plastic strain between experiments and computations was in good agreement. During the examination of detonation-driven deformation, discrepancies were discovered in our understanding of reflected gaseous detonation behavior. Previous models did not accurately describe the nature of the reflected shock wave, which motivated further experiments in a detonation tube with optical access. Pressure sensors and schlieren images were used to examine reflected shock behavior, and it was determined that the discrepancies were related to the reaction zone thickness extant behind the detonation front. During these experiments reflected shock bifurcation did not appear to occur, but the unfocused visualization system made certainty impossible. This prompted construction of a focused schlieren system that investigated possible shock wave-boundary layer interaction, and heat-flux gauges analyzed the boundary layer behind the detonation front. Using these data with an analytical boundary layer solution, it was determined that the strong thermal boundary layer present behind the detonation front inhibits the development of reflected shock wave bifurcation.

Semiempirical models for description of shear modulus in wide ranges of temperatures and pressures of shock compression

NASA Astrophysics Data System (ADS)

El'Kin, V. M.; Mikhailov, V. N.; Mikhailova, T. Yu.

2011-12-01

In this paper, we discuss the potentials of the Steinberg-Cochran-Guinan (SCG) and Burakovsky-Preston (BP) models for the description of the shear-modulus behavior at temperatures and pressures that arise behind the shock-wave front. A modernized variant of the SCG model is suggested, which reduces to the introduction of a free parameter and the representation of the model in the volume-temperature coordinates (( V, T) model). A systematic comparison is performed of all three models of shear modulus with experimental data and data of ab initio calculations for metals such as Al, Be, Cu, K, Na, Mg, Mo, W, and Ta in a wide range of pressures. In addition, for Al, Cu, Mo, W, and Ta there is performed a comparison with the known temperature dependences of the shear modulus and with the results of measurements of the velocities of longitudinal sound behind the shock-wave front. It is shown that in the original form the SCG and BP models give overestimated values of the shear modulus as compared to the data of ab initio calculations and shock-wave experiments. The ( V, T) model, due to the use of a free parameter, makes it possible to optimally describe the totality of experimental and calculated data. The same result is achieved in the case of the BP model after a redefining of its initial parameters. The adequate description of the shear modulus in the range of high intermediate pressures characteristic of the solid-phase states behind the shock-wave front is accompanied in both cases by the violation of the correct asymptotic behavior of the shear modulus at ultrahigh compressions which is originally laid into the SCG and BP models.

Reflection and Refraction of Acoustic Waves by a Shock Wave

NASA Technical Reports Server (NTRS)

Brillouin, J.

1957-01-01

The presence of sound waves in one or the other of the fluid regions on either side of a shock wave is made apparent, in the region under superpressure, by acoustic waves (reflected or refracted according to whether the incident waves lie in the region of superpressure or of subpressure) and by thermal waves. The characteristics of these waves are calculated for a plane, progressive, and uniform incident wave. In the case of refraction, the refracted acoustic wave can, according to the incidence, be plane, progressive, and uniform or take the form of an 'accompanying wave' which remains attached to the front of the shock while sliding parallel to it. In all cases, geometrical constructions permit determination of the kinematic characteristics of the reflected or refractive acoustic waves. The dynamic relationships show that the amplitude of the reflected wave is always less than that of the incident wave. The amplitude of the refracted wave, whatever its type, may in certain cases be greater than that of the incident wave.

Dynamics of ionization processes in high-pressure nitrogen, air, and SF{sub 6} during a subnanosecond breakdown initiated by runaway electrons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tarasenko, V. F., E-mail: vft@loi.hcei.tsc.ru; Beloplotov, D. V.; Lomaev, M. I.

2015-10-15

The dynamics of ionization processes in high-pressure nitrogen, air, and SF{sub 6} during breakdown of a gap with a nonuniform distribution of the electric field by nanosecond high-voltage pulses was studied experimentally. Measurements of the amplitude and temporal characteristics of a diffuse discharge and its radiation with a subnanosecond time resolution have shown that, at any polarity of the electrode with a small curvature radius, breakdown of the gap occurs via two ionization waves, the first of which is initiated by runaway electrons. For a voltage pulse with an ∼500-ps front, UV radiation from different zones of a diffuse dischargemore » is measured with a subnanosecond time resolution. It is shown that the propagation velocity of the first ionization wave increases after its front has passed one-half of the gap, as well as when the pressure in the discharge chamber is reduced and/or when SF{sub 6} is replaced with air or nitrogen. It is found that, at nitrogen pressures of 0.4 and 0.7 MPa and the positive polarity of the high-voltage electrode with a small curvature radius, the ionization wave forms with a larger (∼30 ps) time delay with respect to applying the voltage pulse to the gap than at the negative polarity. The velocity of the second ionization wave propagating from the plane electrode is measured. In a discharge in nitrogen at a pressure of 0.7 MPa, this velocity is found to be ∼10 cm/ns. It is shown that, as the nitrogen pressure increases to 0.7 MPa, the propagation velocity of the front of the first ionization wave at the positive polarity of the electrode with a small curvature radius becomes lower than that at the negative polarity.« less

Gas dynamic and force effects of a solid particle in a shock wave in air

NASA Astrophysics Data System (ADS)

Obruchkova, L. R.; Baldina, E. G.; Efremov, V. P.

2017-03-01

Shock wave interaction with an adiabatic solid microparticle is numerically simulated. In the simulation, the shock wave is initiated by the Riemann problem with instantaneous removal of a diaphragm between the high- and low-pressure chambers. The calculation is performed in the two-dimensional formulation using the ideal gas equation of state. The left end of the tube is impermeable, while outflow from the right end is permitted. The particle is assumed to be motionless, impermeable, and adiabatic, and the simulation is performed for time intervals shorted than the time of velocity and temperature relaxation of the particle. The numerical grid is chosen for each particle size to ensure convergence. For each particle size, the calculated hydraulic resistance coefficient describing the particle force impact on the flow is compared with that obtained from the analytical Stokes formula. It is discovered that the Stokes formula can be used for calculation of hydraulic resistance of a motionless particle in a shock wave flow. The influence of the particle diameter on the flow perturbation behind the shock front is studied. Specific heating of the flow in front of the particle is calculated and a simple estimate is proposed. The whole heated region is divided by the acoustic line into the subsonic and supersonic regions. It is demonstrated that the main heat generated by the particle in the flow is concentrated in the subsonic region. The calculations are performed using two different 2D hydro codes. The energy release in the flow induced by the particle is compared with the maximum possible heating at complete termination of the flow. The results can be used for estimating the possibility of gas ignition in front of the particle by a shock wave whose amplitude is insufficient for initiating detonation in the absence of a particle.

Wave Front Sensor for Solar Concentrator Control

DTIC Science & Technology

2009-10-01

terrestrial-based and space-based. Both types of concentrator can be either imaging or nonimaging and they can be rigid or inflatable. Other...and T is the temperature of the absorber and propellant. In (5), Iin is input intensity with effects of the optical path through the concentrator acting...Hartmann in 1900 and was used for checking optical telescopes for aberrations. It was an array of holes in a plate placed in front of the mirror of

Method and apparatus for generating radiation utilizing DC to AC conversion with a conductive front

DOEpatents

Dawson, John M.; Mori, Warren B.; Lai, Chih-Hsiang; Katsouleas, Thomas C.

1998-01-01

Method and apparatus for generating radiation of high power, variable duration and broad tunability over several orders of magnitude from a laser-ionized gas-filled capacitor array. The method and apparatus convert a DC electric field pattern into a coherent electromagnetic wave train when a relativistic ionization front passes between the capacitor plates. The frequency and duration of the radiation is controlled by the gas pressure and capacitor spacing.

Active Stabilization of Aeromechanical Systems

DTIC Science & Technology

1993-01-05

rotatingUsing the linearized forms of the equations of motion in the stall the compressed reverse flow comes from the annular space upstream and...and temperatures of the two opposite flows, I tential. This is a baroclinic instability deforms the ring into a wavy motion . I~dol)_ This front was...1989. Fig. 14, and 1990a, Fig, 17). The wavy motion of the S (2+ () front is then developed into Rossby waves, the velocity field If we define of which

Detailed study of upper mantle anisotropy in the upper mantle of eastern North America

NASA Astrophysics Data System (ADS)

Chen, X.; Levin, V. L.; Li, Y.

2016-12-01

We collected observations of core-refracted shear waves on a 1300 km long array crossing the eastern part of the North American continent from James Bay to the Fundy Basin. We combine data from the Earthscope Transportable Array, Canadian and US permanent observatories, and the recently completed Earthscope FlexArray QMIII.Past studies found ample evidence for directional dependence (anisotropy) of seismic wave speed in the upper mantle of this region. However, to date the lateral spacing of seismic observatories made direct comparisons between anisotropic structure and tectonic divisions evident on the surface challenging. With instruments spacing 50 km, and less near major tectonic boundaries such as the Grenville Front and the Appalachian Front, we can discriminate between gradual changes in anisotropic properties due to asthenospheric flow variations, and abrupt and localized changes likely to arise from juxtaposition of distinct lithospheric blocks.To insure lateral consistency of measurements we selected core-refracted shear waves that were observed over the entire length of our array. Also, since directional dependence of splitting parameters is a well recognized signature of vertical changes in anisotropic properties we examine observations from different directions, and look for systematic changes.Most locations show evidence for some degree of splitting in observed shear waves. Delays between fast and slow components estimated using rotation-correlation method range from 0.3 to 1.5 s. At most sites delay values vary considerably between individual phases measured. Fast polarizations are predominantly NE-SW, which agrees with numerous past studies of the region. Systematic directional dependence of fast polarization is seen at all sites we studied. Furthermore, the values of fast polarization appear to be similar along the entire array for individual events but vary from event to event. Both of these observations are consistent with the previously proposed notion of layered anisotropy in the upper mantle of the North American continent. We find localized changes in splitting parameters at the Grenville Front. The Appalachian Front, or the internal divisions of the Appalachian Orogen do not have obvious changes in splitting parameters associated with them.

A diffusion-limited reaction model for self-propagating Al/Pt multilayers with quench limits

NASA Astrophysics Data System (ADS)

Kittell, D. E.; Yarrington, C. D.; Hobbs, M. L.; Abere, M. J.; Adams, D. P.

2018-04-01

A diffusion-limited reaction model was calibrated for Al/Pt multilayers ignited on oxidized silicon, sapphire, and tungsten substrates, as well as for some Al/Pt multilayers ignited as free-standing foils. The model was implemented in a finite element analysis code and used to match experimental burn front velocity data collected from several years of testing at Sandia National Laboratories. Moreover, both the simulations and experiments reveal well-defined quench limits in the total Al + Pt layer (i.e., bilayer) thickness. At these limits, the heat generated from atomic diffusion is insufficient to support a self-propagating wave front on top of the substrates. Quench limits for reactive multilayers are seldom reported and are found to depend on the thermal properties of the individual layers. Here, the diffusion-limited reaction model is generalized to allow for temperature- and composition-dependent material properties, phase change, and anisotropic thermal conductivity. Utilizing this increase in model fidelity, excellent overall agreement is shown between the simulations and experimental results with a single calibrated parameter set. However, the burn front velocities of Al/Pt multilayers ignited on tungsten substrates are over-predicted. Possible sources of error are discussed and a higher activation energy (from 41.9 kJ/mol.at. to 47.5 kJ/mol.at.) is shown to bring the simulations into agreement with the velocity data observed on tungsten substrates. This higher activation energy suggests an inhibited diffusion mechanism present at lower heating rates.

Retrograde accretion of a Caribbean fringing reef controlled by hurricanes and sea-level rise

NASA Astrophysics Data System (ADS)

Blanchon, Paul; Richards, Simon; Bernal, Juan Pablo; Cerdeira-Estrada, Sergio; Ibarra, M. Socrates; Corona-Martínez, Liliana; Martell-Dubois, Raúl

2017-10-01

Predicting the impact of sea-level (SL) rise on coral reefs requires reliable models of reef accretion. Most assume that accretion results from vertical growth of coralgal framework, but recent studies show that reefs exposed to hurricanes consist of layers of coral gravel rather than in-place corals. New models are therefore needed to account for hurricane impact on reef accretion over geological timescales. To investigate this geological impact, we report the configuration and development of a 4-km-long fringing reef at Punta Maroma along the northeast Yucatan Peninsula. Satellite-derived bathymetry shows the crest is set-back a uniform distance of 315 ±15 m from a mid-shelf slope break, and the reef-front decreases 50% in width and depth along its length. A 12-core drill transect constrained by multiple 230Th ages shows the reef is composed of an 2-m thick layer of coral clasts that has retrograded 100 m over its back-reef during the last 5.5 ka. These findings are consistent with a hurricane-control model of reef development where large waves trip and break over the mid-shelf slope break, triggering rapid energy dissipation and thus limiting how far upslope individual waves can fragment corals and redistribute clasts. As SL rises and water depth increases, energy dissipation during wave-breaking is reduced, extending the clast-transport limit, thus leading to reef retrogradation. This hurricane model may be applicable to a large sub-set of fringing reefs in the tropical Western-Atlantic necessitating a reappraisal of their accretion rates and response to future SL rise.

Seismic shear waves as Foucault pendulum

NASA Astrophysics Data System (ADS)

Snieder, Roel; Sens-Schönfelder, Christoph; Ruigrok, Elmer; Shiomi, Katsuhiko

2016-03-01

Earth's rotation causes splitting of normal modes. Wave fronts and rays are, however, not affected by Earth's rotation, as we show theoretically and with observations made with USArray. We derive that the Coriolis force causes a small transverse component for P waves and a small longitudinal component for S waves. More importantly, Earth's rotation leads to a slow rotation of the transverse polarization of S waves; during the propagation of S waves the particle motion behaves just like a Foucault pendulum. The polarization plane of shear waves counteracts Earth's rotation and rotates clockwise in the Northern Hemisphere. The rotation rate is independent of the wave frequency and is purely geometric, like the Berry phase. Using the polarization of ScS and ScS2 waves, we show that the Foucault-like rotation of the S wave polarization can be observed. This can affect the determination of source mechanisms and the interpretation of observed SKS splitting.

Export of Ice-Cavity Water from Pine Island Ice Shelf, West Antarctica

NASA Astrophysics Data System (ADS)

Thurnherr, Andreas; Jacobs, Stanley; Dutrieux, Pierre

2013-04-01

Stability of the West Antarctic Ice Sheet is sensitive to changes in melting at the bottom of floating ice shelves that form the seaward extensions of Antarctic glaciers flowing into the ocean. Not least because observations in the cavities beneath ice shelves are difficult, heat fluxes and melt rates have been inferred from oceanographic measurements obtained near the ice edge (calving fronts). Here, we report on a set of hydrographic and velocity data collected in early 2009 near the calving front of the Amundsen Sea's fast-moving and (until recently) accelerating Pine Island Glacier and its associated ice shelf. CTD profiles collected along the southern half of the meridionally-trending ice front show clear evidence for export of ice-cavity water. That water was carried in the upper ocean along the ice front by a southward current that is possibly related to a striking clockwise gyre that dominated the (summertime) upper-ocean circulation in Pine Island Bay. Signatures of ice-cavity water appear unrelated to current direction along most of the ice front, suggesting that cross-frontal exchange is dominated by temporal variability. However, repeated hydrographic and velocity measurements in a small "ice cove" at the southern end of the calving front show a persistent strong (mean velocity peaking near 0.5 ms-1) outflow of ice-cavity water in the upper 500 m. While surface features (boils) suggested upwelling from deep below the ice shelf, vertical velocity measurements reveal 1) that the mean upwelling within the confines of the cove was too weak to feed the observed outflow, and 2) that large high-frequency internal waves dominated the vertical motion of water inside the cove. These observations indicate that water exchange between the Pine Island Ice Shelf cavity and the Amundsen sea is strongly asymmetric with weak broad inflow at depth and concentrated surface-intensified outflow of melt-laden deep water at the southern edge of the calving front. The lack of significant mean upward motion within the cove strongly suggests that the upwelling takes place within the highly fractured ice along the southern shear margin of the ice shelf. If so, the upwelling water is likely to contribute to both the volume of apparent "basal" melting and to the weakness of that shear margin.

Control of wave propagation in a biological excitable medium by an external electric field.

PubMed

Sebestikova, Lenka; Slamova, Elena; Sevcikova, Hana

2005-03-01

We present an experimental evidence of effects of external electric fields (EFs) on the velocity of pulse waves propagating in a biological excitable medium. The excitable medium used is formed by a layer of starving cells of Dictyostelium discoideum through which the waves of increased concentration of cAMP propagate by reaction-diffusion mechanism. External dc EFs of low intensities (up to 5 V/cm) are shown to speed up the propagation of cAMP waves towards the positive electrode and slow it down towards the negative electrode. Electric fields were also found to support an emergence of new centers, emitting cAMP waves, in front of cAMP waves propagating towards the negative electrode.

Intermittent large amplitude internal waves observed in Port Susan, Puget Sound

NASA Astrophysics Data System (ADS)

Harris, J. C.; Decker, L.

2017-07-01

A previously unreported internal tidal bore, which evolves into solitary internal wave packets, was observed in Port Susan, Puget Sound, and the timing, speed, and amplitude of the waves were measured by CTD and visual observation. Acoustic Doppler current profiler (ADCP) measurements were attempted, but unsuccessful. The waves appear to be generated with the ebb flow along the tidal flats of the Stillaguamish River, and the speed and width of the resulting waves can be predicted from second-order KdV theory. Their eventual dissipation may contribute significantly to surface mixing locally, particularly in comparison with the local dissipation due to the tides. Visually the waves appear in fair weather as a strong foam front, which is less visible the farther they propagate.

Advances in directional borehole radar data analysis and visualization

USGS Publications Warehouse

Smith, D.V.G.; Brown, P.J.

2002-01-01

The U.S. Geological Survey is developing a directional borehole radar (DBOR) tool for mapping fractures, lithologic changes, and underground utility and void detection. An important part of the development of the DBOR tool is data analysis and visualization, with the aim of making the software graphical user interface (GUI) intuitive and easy to use. The DBOR software system consists of a suite of signal and image processing routines written in Research Systems' Interactive Data Language (IDL). The software also serves as a front-end to many widely accepted Colorado School of Mines Center for Wave Phenomena (CWP) Seismic UNIX (SU) algorithms (Cohen and Stockwell, 2001). Although the SU collection runs natively in a UNIX environment, our system seamlessly emulates a UNIX session within a widely used PC operating system (MicroSoft Windows) using GNU tools (Noer, 1998). Examples are presented of laboratory data acquired with the prototype tool from two different experimental settings. The first experiment imaged plastic pipes in a macro-scale sand tank. The second experiment monitored the progress of an invasion front resulting from oil injection. Finally, challenges to further development and planned future work are discussed.

Spreading of correlations in the XXZ chain at finite temperatures

NASA Astrophysics Data System (ADS)

Bonnes, Lars; Läuchli, Andreas

2014-03-01

In a quantum quench, for instance by abruptly changing the interaction parameter in a spin chain, correlations can spread across the system but have to obey a speed limit set by the Lieb-Robinson bound. This results into a causal structure where the propagation front resembles a light-cone. One can ask how fast a correlation front actually propagates and how its velocity depends on the nature of the quench. This question is addressed by performing global quenches in the XXZ chain initially prepared in a finite-temperature state using minimally entangled typical thermal states (METTS). We provide numerical evidence that the spreading velocity of the spin correlation functions for the quench into the gapless phase is solely determined by the value of the final interaction and the amount of excess energy of the system. This is quite surprising as the XXZ model is integrable and its dynamics is constrained by a large amount of conserved quantities. In particular, the spreading velocity seems to interpolate linearly from a universal value at T = ∞ to the spin wave velocity of the final Hamiltonian in the limit of zero excess energy for Δfinal > 0 .

Experimental Study on Tsunami Risk Reduction on Coastal Building Fronted by Sea Wall

PubMed Central

Khan, M. T. R.; Shirazi, S. M.

2014-01-01

This experimental study was conducted to idealize the efficacy of sea wall in controlling the tsunami forces on onshore structures. Different types of sea walls were placed in front of the building model. The tsunami forces and the wave heights were measured with and without the sea wall conditions. Types of sea wall, wall height, and wall positions were varied simultaneously to quantify the force reductions. Maximum of 41% forces was reduced by higher sea wall, positioned closer proximity to the model whereas this reduction was about 27% when the wall height was half of the high wall. Experimental investigations revealed that wall with adequate height and placed closer to the structures enables a satisfactory predictor of the force reduction on onshore structures. Another set of tests were performed with perforated wall placing near the building model. Less construction cost makes the provision of perforated sea wall interesting. The overall results showed that the efficacy of perforated wall is almost similar to solid wall. Hence, it can be efficiently used instead of solid wall. Moreover, overtopped water that is stuck behind the wall is readily gone back to the sea through perforations releasing additional forces on the nearby structures. PMID:24790578

Signatures of Nonlinear Waves in Coronal Plumes and Holes

NASA Technical Reports Server (NTRS)

Ofman, Leon

1999-01-01

In recent Ultraviolet Coronagraph Spectrometer/Solar and Heliospheric Observatory (UVCS/SOHO) White Light Channel (WLC) observations we found quasi-periodic variations in the polarized brightness (pB) in the polar coronal holes at heliocentric distances of 1.9-2.45 solar radii. The motivation for the observation is the 2.5D Magnetohydrodynamics (MHD) model of solar wind acceleration by nonlinear waves, that predicts compressive fluctuations in coronal holes. To help identify the waves observed with the UVCS/WLC we model the propagation and dissipation of slow magnetosonic waves in polar plumes using 1D MHD code in spherical geometry, We find that the slow waves nonlinearly steepen in the gravitationally stratified plumes. The nonlinear steepening of the waves leads to enhanced dissipation due to compressive viscosity at the wave-fronts.

Macro-mechanical modeling of blast-wave mitigation in foams. Part II: reliability of pressure measurements

NASA Astrophysics Data System (ADS)

Britan, A.; Liverts, M.; Shapiro, H.; Ben-Dor, G.

2013-02-01

A phenomenological study of the process occurring when a plane shock wave reflected off an aqueous foam column filling the test section of a vertical shock tube has been undertaken. The experiments were conducted with initial shock wave Mach numbers in the range 1.25le {M}_s le 1.7 and foam column heights in the range 100-450 mm. Miniature piezotrone circuit electronic pressure transducers were used to record the pressure histories upstream and alongside the foam column. The aim of these experiments was to find a simple way to eliminate a spatial averaging as an artifact of the pressure history recorded by the side-on transducer. For this purpose, we discuss first the common behaviors of the pressure traces in extended time scales. These observations evidently quantify the low frequency variations of the pressure field within the different flow domains of the shock tube. Thereafter, we focus on the fronts of the pressure signals, which, in turn, characterize the high-frequency response of the foam column to the shock wave impact. Since the front shape and the amplitude of the pressure signal most likely play a significant role in the foam destruction, phase changes and/or other physical factors, such as high capacity, viscosity, etc., the common practice of the data processing is revised and discussed in detail. Generally, side-on pressure measurements must be used with great caution when performed in wet aqueous foams, because the low sound speed is especially prone to this effect. Since the spatial averaged recorded pressure signals do not reproduce well the real behaviors of the pressure rise, the recorded shape of the shock wave front in the foam appears much thicker. It is also found that when a thin liquid film wet the sensing membrane, the transducer sensitivity was changed. As a result, the pressure recorded in the foam could exceed the real amplitude of the post-shock wave flow. A simple procedure, which allows correcting this imperfection, is discussed in detail.

Wideband monolithically integrated front-end subsystems and components

NASA Astrophysics Data System (ADS)

Mruk, Joseph Rene

This thesis presents the analysis, design, and measurements of passive, monolithically integrated, wideband recta-coax and printed circuit board front-end components. Monolithic fabrication of antennas, impedance transformers, filters, and transitions lowers manufacturing costs by reducing assembly time and enhances performance by removing connectors and cabling between the devices. Computational design, fabrication, and measurements are used to demonstrate the capabilities of these front-end assemblies. Two-arm wideband planar log-periodic antennas fed using a horizontal feed that allows for filters and impedance transformers to be readily fabricated within the radiating region of the antenna are demonstrated. At microwave frequencies, low-cost printed circuit board processes are typically used to produce planar devices. A 1.8 to 11 GHz two-arm planar log-periodic antenna is designed with a monolithically integrated impedance transformer. Band rejection methods based on modifying the antenna aperture, use of an integrated filter, and the application of both methods are investigated with realized gain suppressions of over 25 dB achieved. The ability of standard circuit board technology to fabricate millimeter-wave devices up to 110 GHz is severely limited. Thin dielectrics are required to prevent the excitation of higher order modes in the microstrip substrate. Fabricating the thin line widths required for the antenna aperture also becomes prohibitively challenging. Surface micro-machining typically used in the fabrication of MEMS devices is capable of producing the extremely small features that can be used to fabricate antennas extending through W-band. A directly RF fed 18 to 110 GHz planar log-periodic antenna is developed. The antenna is fabricated with an integrated impedance transformer and additional transitions for measurement characterization. Singly terminated low-loss wideband millimeter-wave filters operating over V- and W- band are developed. High quality performance of an 18 to 100 GHz front-end is realized by dividing the single instantaneous antenna into two apertures operating from 18 to 50 and 50 to 100 GHz. Each channel features an impedance transformer, low-pass (low-frequency) or band-pass (high-frequency) filter, and grounded CPW launch. This dual-aperture front-end demonstrates that micromachining technology is now capable of fabricating broadband millimeter-wave components with a high degree of integration.

Facies-dependent variations in sediment physical properties on the Mississippi River Delta Front, USA: evidence for depositional and post-depositional processes

NASA Astrophysics Data System (ADS)

Smith, J. E., IV; Bentley, S. J.; Courtois, A. J.; Obelcz, J.; Chaytor, J. D.; Maloney, J. M.; Georgiou, I. Y.; Xu, K.; Miner, M. D.

2017-12-01

Recent studies on Mississippi River Delta have documented sub-aerial land loss, driven in part by declining sediment load over the past century. Impacts of changing sediment load on the subaqueous delta are less well known. The subaqueous Mississippi River Delta Front is known to be shaped by extensive submarine mudflows operating at a range of temporal and spatial scales, however impacts of changing sediment delivery on mudflow deposits have not been investigated. To better understand seabed morphology and stratigraphy as impacted by plume sedimentation and mudflows, an integrated geological/geophysical study was undertaken in delta front regions offshore the three main passes of the Mississippi River Delta. This study focuses on stratigraphy and physical properties of 30 piston cores (5-9 m length) collected in June 2017. Coring locations were selected in gully, lobe and prodelta settings based on multibeam bathymetry and seismic profiles collected in mid-May 2017. Cores were analyzed for density, magnetic susceptibility, P-wave speed, and resistivity using a Geotek multi sensor core logger; here, we focus on density data. Core density profiles generally vary systematically across facies. Density profiles of gully cores are nearly invariant with some downward stepwise increases delineating units meters thick, and abundant gaps likely caused by gas expansion. Lobe cores generally have subtle downward increases in density, some stepwise density increases, and fewer gaps. Prodelta cores show more pronounced downward density increases, decimeter-scale peaks and valleys in density profiles, but stepwise increases are less evident. We hypothesize that density profiles in gully and lobe settings (uniform profiles except for stepwise increases) reflect remolding by mudflows, whereas density variations in prodelta settings instead reflect grain size variations (decimeter-scale) and more advanced consolidation (overall downward density increase) consistent with slower sediment deposition. These hypotheses will be evaluated by a more detailed study of seismic stratigraphy and core properties, including geochronology, grain size distribution and X-radiographic imaging, to further relate important sedimentary processes with resulting deposits.

Surface layer motion in planetary atmosphere containing fog of condensed gases

NASA Astrophysics Data System (ADS)

Datsenko, E. N.; Vasiliev, N. I.; Orlova, I. O.; Avakimyan, N. N.

2017-11-01

The article contains a simplified model of a wave motion of the atmospheric surface of planets containing finely dispersed particles of condensed gases, it is assumed that the surface of planets is heated above the saturation temperature of gas condensate, and the surface layers of the foggy atmosphere are strongly cooled. The mechanism of formation and growth of such waves is proposed and justified. It was found that the existence of growing waves on the surface of such an atmosphere is possible, as well as, in the course of time, the formation of a vortex in the atmosphere around the planet. Perturbations of the atmosphere thickness lead to the formation of gravitational waves propagating along its surface. The thickness of the atmosphere at the crest of the wave is greater than that in the trough. While the temperature of the atmosphere under the ridge increases, it decreases under the trough due to shielding of the thermal radiation of the planet. When the crest of a gravitational wave moves, the atmosphere under the trailing edge of the crest has a temperature higher than that under the front edge, since the trailing edge of the crest is heated more intensively by radiation from the surface of the planet. The partial pressure of the vapor of the condensed gases at the rear edge of the ridge is higher than that at the front edge; the work of the pressure difference during the motion of the ridge increases its energy and height. The authors demonstrate the analogy between the mechanisms of wave growth in a foggy atmosphere of planets and the mechanism of wave growth in a thin vapor layer between a strongly heated solid surface or a metal melt and a volatile liquid.

The Role of Secondary Frontal Waves in Causing Missed or False Alarm Flood Forecasts During Landfalling Atmospheric Rivers

NASA Astrophysics Data System (ADS)

Martin, A.; Ralph, F. M.; Lavers, D. A.; Kalansky, J.; Kawzenuk, B.

2015-12-01

The previous ten years has seen an explosion in research devoted to the Atmospheric River (AR) phenomena, features of the midlatitude circulation responsible for large horizontal water vapor transport. Upon landfall, ARs can be associated with 30-50% of annual precipitation in some regions, while also causing the largest flooding events in places such as coastal California. Little discussed is the role secondary frontal waves play in modulating precipitation during a landfalling AR. Secondary frontal waves develop along an existing cold front in response to baroclinic frontogenesis, often coinciding with a strong upper-tropospheric jet. If the secondary wave develops along a front associated with a landfalling AR, the resulting precipitation may be much greater or much less than originally forecasted - especially in regions where orographic uplift of horizontally transported water vapor is responsible for a large portion of precipitation. In this study, we present several cases of secondary frontal waves that have occurred in conjunction with a landfalling AR on the US West Coast. We put the impact of these cases in historical perspective using quantitative precipitation forecasts, satellite data, reanalyses, and estimates of damage related to flooding. We also discuss the dynamical mechanisms behind secondary frontal wave development and relate these mechanisms to the high spatiotemporal variability in precipitation observed during ARs with secondary frontal waves. Finally, we demonstrate that even at lead times less than 24 hours, current quantitative precipitation forecasting methods have difficulty accurately predicting the rainfall in the area near the secondary wave landfall, in some cases leading to missed or false alarm flood warnings, and suggest methods which may improve quantitative precipitation forecasts for this type of system in the future.

Wave induced coastal cliff top ground motions and infragravity wave dissipation under high energy wave conditions.

NASA Astrophysics Data System (ADS)

Earlie, C. S.; le Dantec, N.; Young, A.

2016-12-01

Coastal cliff erosion is a widespread problem that threatens property and infrastructure globally. The prediction of this risk calls for robust understanding of the processes and mechanisms involved in causing coastal cliff failure. Over the last decade, a number of geomorphological studies have highlighted the importance of the relationship between the offshore wave climate and cliff-toe water levels, and the resultant coastal response in terms of cliff-top ground motion and erosion. Field-based studies of instantaneous cliff response to direct wave impact have shown that wave-induced loading of the foreshore leads to cliff-top ground motions that may have the potential to weaken the integrity of the rocks and prepare them for failure. In order to understand wave-cliff interaction and how beach morphodynamics influences cliff-top ground motion and cliff erosion, two field experiments were carried out simultaneously at two locations in Northern Brittany (France). This three-month long winter field campaign (Jan-Mar 2016) included, for the first time, a comparison of cliff-top ground motion and cliff erosion at sites fronted by different beach morphologies (reflective/dissipative), along with monitoring of hydrodynamic forcing and beach topography. The magnitude of cliff-top displacements at both sites were dependent on tidal stage and free water surface elevation at the cliff toe, with the greatest contributions of cliff-top ground motions found at infragravity frequencies (0.05-0.005 Hz). Vertical displacements at infragravity and incident sea-swell (0.1-0.5 Hz) frequencies were greater at the dissipative site, apart from during spring high tide and energetic wave conditions, where displacements were two times that at the reflective site. Combining these wave-cliff interaction data with beach morphology and nearshore bathymetry will be key to understanding the spatial variability in cliff erosion under a variety of environmental settings and forcing conditions.

The structure and evolution of galacto-detonation waves - Some analytic results in sequential star formation models of spiral galaxies

NASA Technical Reports Server (NTRS)

Cowie, L. L.; Rybicki, G. B.

1982-01-01

Waves of star formation in a uniform, differentially rotating disk galaxy are treated analytically as a propagating detonation wave front. It is shown, that if single solitary waves could be excited, they would evolve asymptotically to one of two stable spiral forms, each of which rotates with a fixed pattern speed. Simple numerical solutions confirm these results. However, the pattern of waves that develop naturally from an initially localized disturbance is more complex and dies out within a few rotation periods. These results suggest a conclusive observational test for deciding whether sequential star formation is an important determinant of spiral structure in some class of galaxies.

Simulation and scaling analysis of a spherical particle-laden blast wave

NASA Astrophysics Data System (ADS)

Ling, Y.; Balachandar, S.

2018-02-01

A spherical particle-laden blast wave, generated by a sudden release of a sphere of compressed gas-particle mixture, is investigated by numerical simulation. The present problem is a multiphase extension of the classic finite-source spherical blast-wave problem. The gas-particle flow can be fully determined by the initial radius of the spherical mixture and the properties of gas and particles. In many applications, the key dimensionless parameters, such as the initial pressure and density ratios between the compressed gas and the ambient air, can vary over a wide range. Parametric studies are thus performed to investigate the effects of these parameters on the characteristic time and spatial scales of the particle-laden blast wave, such as the maximum radius the contact discontinuity can reach and the time when the particle front crosses the contact discontinuity. A scaling analysis is conducted to establish a scaling relation between the characteristic scales and the controlling parameters. A length scale that incorporates the initial pressure ratio is proposed, which is able to approximately collapse the simulation results for the gas flow for a wide range of initial pressure ratios. This indicates that an approximate similarity solution for a spherical blast wave exists, which is independent of the initial pressure ratio. The approximate scaling is also valid for the particle front if the particles are small and closely follow the surrounding gas.

Simulation and scaling analysis of a spherical particle-laden blast wave

NASA Astrophysics Data System (ADS)

Ling, Y.; Balachandar, S.

2018-05-01

A spherical particle-laden blast wave, generated by a sudden release of a sphere of compressed gas-particle mixture, is investigated by numerical simulation. The present problem is a multiphase extension of the classic finite-source spherical blast-wave problem. The gas-particle flow can be fully determined by the initial radius of the spherical mixture and the properties of gas and particles. In many applications, the key dimensionless parameters, such as the initial pressure and density ratios between the compressed gas and the ambient air, can vary over a wide range. Parametric studies are thus performed to investigate the effects of these parameters on the characteristic time and spatial scales of the particle-laden blast wave, such as the maximum radius the contact discontinuity can reach and the time when the particle front crosses the contact discontinuity. A scaling analysis is conducted to establish a scaling relation between the characteristic scales and the controlling parameters. A length scale that incorporates the initial pressure ratio is proposed, which is able to approximately collapse the simulation results for the gas flow for a wide range of initial pressure ratios. This indicates that an approximate similarity solution for a spherical blast wave exists, which is independent of the initial pressure ratio. The approximate scaling is also valid for the particle front if the particles are small and closely follow the surrounding gas.

Exploring dynamic events in the solar corona

NASA Astrophysics Data System (ADS)

Downs, Cooper James

With the advent of modern computational technology it is now becoming the norm to employ detailed 3D computer models as empirical tools that directly account for the inhomogeneous nature of the Sun-Heliosphere environment. The key advantage of this approach lies in the ability to compare model results directly to observational data and to use a successful comparison (or lack thereof) to glean information on the underlying physical processes. Using extreme ultraviolet waves (EUV waves) as the overarching scientific driver, we apply this observation modeling approach to study the complex dynamics of the magnetic and thermodynamic structures that are observed in the low solar corona. Representing a highly non-trivial effort, this work includes three main scientific thrusts: an initial modeling effort and two EUV wave case-studies. First we document the development of the new Low Corona (LC) model, a 3D time-dependent thermodynamic magnetohydrodynamic (MHD) model implemented within the Space Weather Modeling Framework (SWMF). Observation synthesis methods are integrated within the LC model, which provides the ability to compare model results directly to EUV imaging observations taken by spacecraft. The new model is then used to explore the dynamic interplay between magnetic structures and thermodynamic energy balance in the corona that is caused by coronal heating mechanisms. With the model development complete, we investigate the nature of EUV waves in detail through two case-studies. Starting with the 2008 March 25 event, we conduct a series of numerical simulations that independently vary fundamental parameters thought to govern the physical mechanisms behind EUV waves. Through the subsequent analysis of the 3D data and comparison to observations we find evidence for both wave and non-wave mechanisms contributing to the EUV wave signal. We conclude with a comprehensive observation and modeling analysis of the 2010 June 13 EUV wave event, which was observed by the recently launched Solar Dynamics Observatory. We use a high resolution simulation of the transient to unambiguously characterize the globally propagating front of EUV wave as a fast-mode magnetosonic wave, and use the rich set of observations to place the many other facets of the EUV transient within a unified scenario involving wave and non-wave components.

Stability of nonlinear waves and patterns and related topics

NASA Astrophysics Data System (ADS)

Ghazaryan, Anna; Lafortune, Stephane; Manukian, Vahagn

2018-04-01

Periodic and localized travelling waves such as wave trains, pulses, fronts and patterns of more complex structure often occur in natural and experimentally built systems. In mathematics, these objects are realized as solutions of nonlinear partial differential equations. The existence, dynamic properties and bifurcations of those solutions are of interest. In particular, their stability is important for applications, as the waves that are observable are usually stable. When the waves are unstable, further investigation is warranted of the way the instability is exhibited, i.e. the nature of the instability, and also coherent structures that appear as a result of an instability of travelling waves. A variety of analytical, numerical and hybrid techniques are used to study travelling waves and their properties. This article is part of the theme issue `Stability of nonlinear waves and patterns and related topics'.

Front-end multiplexing—applied to SQUID multiplexing: Athena X-IFU and QUBIC experiments

NASA Astrophysics Data System (ADS)

Prele, D.

2015-08-01

As we have seen for digital camera market and a sensor resolution increasing to "megapixels", all the scientific and high-tech imagers (whatever the wave length - from radio to X-ray range) tends also to always increases the pixels number. So the constraints on front-end signals transmission increase too. An almost unavoidable solution to simplify integration of large arrays of pixels is front-end multiplexing. Moreover, "simple" and "efficient" techniques allow integration of read-out multiplexers in the focal plane itself. For instance, CCD (Charge Coupled Device) technology has boost number of pixels in digital camera. Indeed, this is exactly a planar technology which integrates both the sensors and a front-end multiplexed readout. In this context, front-end multiplexing techniques will be discussed for a better understanding of their advantages and their limits. Finally, the cases of astronomical instruments in the millimeter and in the X-ray ranges using SQUID (Superconducting QUantum Interference Device) will be described.

Tracking fronts in solutions of the shallow-water equations

NASA Astrophysics Data System (ADS)

Bennett, Andrew F.; Cummins, Patrick F.

1988-02-01

A front-tracking algorithm of Chern et al. (1986) is tested on the shallow-water equations, using the Parrett and Cullen (1984) and Williams and Hori (1970) initial state, consisting of smooth finite amplitude waves depending on one space dimension alone. At high resolution the solution is almost indistinguishable from that obtained with the Glimm algorithm. The latter is known to converge to the true frontal solution, but is 20 times less efficient at the same resolution. The solutions obtained using the front-tracking algorithm at 8 times coarser resolution are quite acceptable, indicating a very substantial gain in efficiency, which encourages application in realistic ocean models possessing two or three space dimensions.

Phase-front measurements of an injection-locked AlGaAs laser-diode array

NASA Technical Reports Server (NTRS)

Cornwell, Donald M., Jr.; Rall, Jonathan A. R.; Abshire, James B.

1989-01-01

The phase-front quality of the primary spatial lobe emitted from an injection-locked gain-guided AlGaAs laser-diode array is measured by using an equal-path, phase-shifting Mach-Zehnder interferometer. Root-mean-square phase errors of 0.037 + or - 0.003 wave are measured for the single spatial lobe, which contained 240-mW cw output power in a single longitudinal mode. This phase-front quality corresponds to a Strehl ratio of S = 0.947, which results in a 0.23-dB power loss from the single lobe's ideal diffraction-limited power. These values are comparable with those measured for single-stripe index-guided AlGaAs lasers.

Light-front Ward-Takahashi identity for two-fermion systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marinho, J. A. O.; Frederico, T.; Pace, E.

We propose a three-dimensional electromagnetic current operator within light-front dynamics that satisfies a light-front Ward-Takahashi identity for two-fermion systems. The light-front current operator is obtained by a quasipotential reduction of the four-dimensional current operator and acts on the light-front valence component of bound or scattering states. A relation between the light-front valence wave function and the four-dimensional Bethe-Salpeter amplitude both for bound or scattering states is also derived, such that the matrix elements of the four-dimensional current operator can be fully recovered from the corresponding light-front ones. The light-front current operator can be perturbatively calculated through a quasipotential expansion, andmore » the divergence of the proposed current satisfies a Ward-Takahashi identity at any given order of the expansion. In the quasipotential expansion the instantaneous terms of the fermion propagator are accounted for by the effective interaction and two-body currents. We exemplify our theoretical construction in the Yukawa model in the ladder approximation, investigating in detail the current operator at the lowest nontrivial order of the quasipotential expansion of the Bethe-Salpeter equation. The explicit realization of the light-front form of the Ward-Takahashi identity is verified. We also show the relevance of instantaneous terms and of the pair contribution to the two-body current and the Ward-Takahashi identity.« less

Ionospheric research opportunity

NASA Astrophysics Data System (ADS)

Rickel, Dwight

1985-05-01

Ground-based explosions have been exploited successfully in the past as a relatively controlled source for producing ionospheric disturbances. On June 25, the Defense Nuclear Agency will conduct a high explosives test on the northern section of the White Sands Missile Range. Approximately 4,800 tons of ammonium nitrate and fuel oil (ANFO) will be detonated at ground level, producing an acoustic shock wave with a surface pressure change of approximately 20 mbar at a 6 km range. This shock front will have sufficient strength to propagate into the ionosphere with at least a 10% change in the ambient pressure across the disturbance front in the lower F region. Such an ionospheric perturbation will give ionospheric researchers an excellent opportunity to investigate acoustic propagation at ionospheric heights, shock dissipation effect, the ion-neutral coupling process, acoustic-gravity wave (traveling ionospheric disturbance) generation mechanisms, and associated RF phenomena.

Impact of Shock Front Rippling and Self-reformation on the Electron Dynamics at Low-Mach-number Shocks

NASA Astrophysics Data System (ADS)

Yang, Zhongwei; Lu, Quanming; Liu, Ying D.; Wang, Rui

2018-04-01

Electron dynamics at low-Mach-number collisionless shocks are investigated by using two-dimensional electromagnetic particle-in-cell simulations with various shock normal angles. We found: (1) The reflected ions and incident electrons at the shock front provide an effective mechanism for the quasi-electrostatic wave generation due to the charge-separation. A fraction of incident electrons can be effectively trapped and accelerated at the leading edge of the shock foot. (2) At quasi-perpendicular shocks, the electron trapping and reflection is nonuniform due to the shock rippling along the shock surface and is more likely to take place at some locations accompanied by intense reflected ion-beams. The electron trapping process has a periodical evolution over time due to the shock front self-reformation, which is controlled by ion dynamics. Thus, this is a cross-scale coupling phenomenon. (3) At quasi-parallel shocks, reflected ions can travel far back upstream. Consequently, quasi-electrostatic waves can be excited in the shock transition and the foreshock region. The electron trajectory analysis shows these waves can trap electrons at the foot region and reflect a fraction of them far back upstream. Simulation runs in this paper indicate that the micro-turbulence at the shock foot can provide a possible scenario for producing the reflected electron beam, which is a basic condition for the type II radio burst emission at low-Mach-number interplanetary shocks driven by Coronal Mass Ejections (CMEs).

A Study of Mesoscale Gravity Waves over the North Atlantic with Satellite Observations and a Mesoscale Model

NASA Technical Reports Server (NTRS)

Wu, Dong L.; Zhang, Fuqing

2004-01-01

Satellite microwave data are used to study gravity wave properties and variabilities over the northeastern United States and the North Atlantic in the December-January periods. The gravity waves in this region, found in many winters, can reach the stratopause with growing amplitude. The Advanced Microwave Sounding Unit-A (AMSU-A) observations show that the wave occurrences are correlated well with the intensity and location of the tropospheric baroclinic jet front systems. To further investigate the cause(s) and properties of the North Atlantic gravity waves, we focus on a series of wave events during 19-21 January 2003 and compare AMSU-A observations to simulations from a mesoscale model (MM5). The simulated gravity waves compare qualitatively well with the satellite observations in terms of wave structures, timing, and overall morphology. Excitation mechanisms of these large-amplitude waves in the troposphere are complex and subject to further investigations.

Nonlinear hyperbolic theory of thermal waves in metals

NASA Technical Reports Server (NTRS)

Wilhelm, H. E.; Choi, S. H.

1975-01-01

A closed-form solution for cylindrical thermal waves in metals is given based on the nonlinear hyperbolic system of energy-conservation and heat-flux relaxation equations. It is shown that heat released from a line source propagates radially outward with finite speed in the form of a thermal wave which exhibits a discontinuous wave front. Unique nonlinear thermal-wave solutions exist up to a critical amount of driving energy, i.e., for larger energy releases, the thermal flow becomes multivalued (occurrence of shock waves). By comparison, it is demonstrated that the parabolic thermal-wave theory gives, in general, a misleading picture of the profile and propagation of thermal waves and leads to physical (infinite speed of heat propagation) and mathematical (divergent energy integrals) difficulties. Attention is drawn to the importance of temporal heat-flux relaxation for the physical understanding of fast transient processes such as thermal waves and more general explosions and implosions.

Generation of internal solitary waves by frontally forced intrusions in geophysical flows.

PubMed

Bourgault, Daniel; Galbraith, Peter S; Chavanne, Cédric

2016-12-06

Internal solitary waves are hump-shaped, large-amplitude waves that are physically analogous to surface waves except that they propagate within the fluid, along density steps that typically characterize the layered vertical structure of lakes, oceans and the atmosphere. As do surface waves, internal solitary waves may overturn and break, and the process is thought to provide a globally significant source of turbulent mixing and energy dissipation. Although commonly observed in geophysical fluids, the origins of internal solitary waves remain unclear. Here we report a rarely observed natural case of the birth of internal solitary waves from a frontally forced interfacial gravity current intruding into a two-layer and vertically sheared background environment. The results of the analysis carried out suggest that fronts may represent additional and unexpected sources of internal solitary waves in regions of lakes, oceans and atmospheres that are dynamically similar to the situation examined here in the Saguenay Fjord, Canada.

On the Unsteady Response of an Oceanic Front to Local Atmospheric Forcing.

DTIC Science & Technology

1983-06-01

fluxes, mass and momentum transport, inertial-internal wave activity and mix- ing all can occur. Oceanic frontal areas are areas of sound 11 speed...in the Sargasso Sea in May. He found the front to be a separaticn cf two distinct water masses , with a tran- sitin zone cf only a few meters in the...presence of an eddy. If the water masses had been of similar types, it would have been indicative cf downwelling. With regard tc one-dimensional mixing

Method and apparatus for generating radiation utilizing DC to AC conversion with a conductive front

DOEpatents

Dawson, J.M.; Mori, W.B.; Lai, C.H.; Katsouleas, T.C.

1998-07-14

Method and apparatus ar disclosed for generating radiation of high power, variable duration and broad tunability over several orders of magnitude from a laser-ionized gas-filled capacitor array. The method and apparatus convert a DC electric field pattern into a coherent electromagnetic wave train when a relativistic ionization front passes between the capacitor plates. The frequency and duration of the radiation is controlled by the gas pressure and capacitor spacing. 4 figs.

Measurement of Electron Beam Emittance Using Optical Transition Radiation and Development of a Diffuse Screen Electron Beam Monitor

DTIC Science & Technology

1990-12-01

Zerodur ,irror, 2" relfects light. 1OZ20BD.1; 20th wave zerodur mirror , 1" reflects light. LS-35; 3’ x 5’ optical breadboard; for mounting components...profile measurements using the diffuse screen were compared with measurements using a front surface mirror and a fluorescent screen. The 20 DISTRIBUTION...Beam current and profile measurements using the diffuse screen were compared with measurements using a front surface mirror and a fluorescent screen

Electromagnetically driven radiative shocks and their measurements

NASA Astrophysics Data System (ADS)

Kondo, K.; Nakajima, M.; Kawamura, T.; Horioka, K.

2006-06-01

Experimental results on a generation of strong shocks in a compact pulse power device are reported. To make a strong and plain shock wave, electrodes are tapered and an acrylic guiding tube is located on the top of the electrodes. It drives a quasi-one-dimensional strong shock in the guiding tube. When the front speed is more than the critical speed Drad, an interesting structure is confirmed at the shock front, which indicate a phenomenon proceeded by the radiative transport.

THz semiconductor-based front-end receiver technology for space applications

NASA Technical Reports Server (NTRS)

Mehdi, Imran; Siegel, Peter

2004-01-01

Advances in the design and fabrication of very low capacitance planar Schottky diodes and millimeter-wave power amplifiers, more accurate device and circuit models for commercial 3-D electromagnetic simulators, and the availability of both MEMS and high precision metal machining, have enabled RF engineers to extend traditional waveguide-based sensor and source technologies well into the TI-Iz frequency regime. This short paper will highlight recent progress in realizing THz space-qualified receiver front-ends based on room temperature semiconductor devices.

Order parameter description of walk-off effect on pattern selection in degenerate optical parametric oscillators

NASA Astrophysics Data System (ADS)

Taki, Majid; San Miguel, Maxi; Santagiustina, Marco

2000-02-01

Degenerate optical parametric oscillators can exhibit both uniformly translating fronts and nonuniformly translating envelope fronts under the walk-off effect. The nonlinear dynamics near threshold is shown to be described by a real convective Swift-Hohenberg equation, which provides the main characteristics of the walk-off effect on pattern selection. The predictions of the selected wave vector and the absolute instability threshold are in very good quantitative agreement with numerical solutions found from the equations describing the optical parametric oscillator.

A Numerical Simulation of the Energy Conversion Process in Microwave Rocket

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shibata, Teppei; Oda, Yasuhisa; Komurasaki, Kimiya

2008-04-28

In Microwave Rocket, a high power microwave beam ionizes atmospheric air inside of the thruster and the ionization front drives a shock wave. In this paper, CFD simulation was conducted using measured propagation velocity of the ionization front to evaluate the engine performance. As a result, maximum cycle efficiency was obtained at the power density of about 200 kW/m{sup 2} which is the transitional beam power condition between Microwave Supported Combustion and Microwave Supported Detonation regimes.

General method for designing wave shape transformers.

PubMed

Ma, Hua; Qu, Shaobo; Xu, Zhuo; Wang, Jiafu

2008-12-22

An effective method for designing wave shape transformers (WSTs) is investigated by adopting the coordinate transformation theory. Following this method, the devices employed to transform electromagnetic (EM) wave fronts from one style with arbitrary shape and size to another style, can be designed. To verify this method, three examples in 2D spaces are also presented. Compared with the methods proposed in other literatures, this method offers the general procedure in designing WSTs, and thus is of great importance for the potential and practical applications possessed by such kinds of devices.