Dynamic stabilization of Rayleigh-Taylor instability in ablation fronts
Piriz A.R.
2013-11-01
Full Text Available Dynamic stabilization of Rayleigh-Taylor instability in an ablation front is studied by considering the simplest possible modulations in the acceleration. Explicit analytical expressions for the instability growth rate and for the boundaries of the stability region are obtained by considering a sequence of Dirac deltas. Besides, general square waves allow for studying the effect of the driving asymmetries on the stability region as well as the optimization process. The essential role of compressibility is phenomenologically addressed in order to find the constraints it imposes on the stability region.
Ablation Front Rayleigh-Taylor Growth Experiments in Spherically Convergent Geometry
Glendinning, S.G.; Cherfils, C.; Colvin, J.; Divol, L.; Galmiche, D.; Haan, S.; Marinak, M.M.; Remington, B.A.; Richard, A.L.; Wallace, R.
1999-11-03
Experiments were performed on the Nova laser, using indirectly driven capsules mounted in cylindrical gold hohlraums, to measure the Rayleigh-Taylor growth at the ablation front by time-resolved radiography. Modulations were preformed on the surface of Ge-doped plastic capsules. With initial modulations of 4 {micro}m, growth factors of about 6 in optical depth were seen, in agreement with simulations using the radiation hydrocode FCI2. With initial modulations of 1 {micro}m, growth factors of about 100-150 in optical depth were seen. The Rayleigh-Taylor (RT) instability at the ablation front in an inertial confinement fusion capsule has been the subject of considerable investigation. Much of this research has been concentrated on planar experiments, in which RT growth is inferred from radiography. The evolution is somewhat different in a converging geometry; the spatial wavelength decreases (affecting the onset of nonlinear saturation), and the shell thickens and compresses rather than decompressing as in a planar geometry. In a cylindrically convergent geometry, the latter effect is proportional to the radius, while in spherically convergent geometry, the latter effect is proportional to the radius squared. Experiments were performed on the Nova and Omega lasers in cylindrical geometry (using both direct and indirect drive) and have been performed in spherical geometry using direct drive.
Plasma transport driven by the Rayleigh-Taylor instability
Ma, X.; Delamere, P. A.; Otto, A.
2016-06-01
Two important differences between the giant magnetospheres (i.e., Jupiter's and Saturn's magnetospheres) and the terrestrial magnetosphere are the internal plasma sources and the fast planetary rotation. Thus, there must be a radially outward flow to transport the plasma to avoid infinite accumulation of plasma. This radial outflow also carries the magnetic flux away from the inner magnetosphere due to the frozen-in condition. As such, there also must be a radial inward flow to refill the magnetic flux in the inner magnetosphere. Due to the similarity between Rayleigh-Taylor (RT) instability and the centrifugal instability, we use a three-dimensional RT instability to demonstrate that an interchange instability can form a convection flow pattern, locally twisting the magnetic flux, consequently forming a pair of high-latitude reconnection sites. This process exchanges a part of the flux tube, thereby transporting the plasma radially outward without requiring significant latitudinal convection of magnetic flux in the ionosphere.
Similar Rayleigh-Taylor Instability of Shock Fronts Perturbed by Corrugated Interfaces
HE Yong; HU Xi-Wei; JIANG Zhong-He
2011-01-01
@@ Instability of a planar shock front perturbed by a corrugated interface is analyzed,where the perturbation wavelength is along the shock front plane.The presented analysis involves the effects of the features on the shock front,which is different from a general method presented by D'yakov and Kontorovich,where the shock front is taken as an infinitely discontinuity.The growth rate of the instability of the perturbed shock front is obtained and compared with the growth rate of the Rayleigh-Taylor instability(RTI) of an interface,on which the density gradient and the initial conditions are similar to the perturbed shock front.The analysis and comparisons of the growth rate of the instability indicate that the features of the shock front should be considered seriously in the shock interface interactions.%Instability of a planar shock front perturbed by a corrugated interface is analyzed, where the perturbation wavelength is along the shock front plane. The presented analysis involves the effects of the features on the shock front, which is different from a general method presented by D'yakov and Kontorovich, where the shock front is taken as an infinitely discontinuity. The growth rate of the instability of the perturbed shock front is obtained and compared with the growth rate of the Rayleigh-Taylor instability (RTI) of an interface, on which the density gradient and the initial conditions are similar to the perturbed shock front. The analysis and comparisons of the growth rate of the instability indicate that the features of the shock front should be considered seriously in the shock interface interactions.
Particle drift model for Z-pinch-driven magneto-Rayleigh-Taylor instability
Dan, Jia Kun; Xu, Qiang; Wang, Kun Lun; Ren, Xiao Dong; Huang, Xian Bin
2016-09-01
A theoretical model of Z-pinch driven magneto-Rayleigh-Taylor instability is proposed based on the particle drift point of view, which can explain the helical instability structure observed in premagnetized imploding liner experiments. It is demonstrated that all possible drift motions, including polarization drift, gradient drift, and curvature drift, which can lead to charge separations, each will attribute to an effective gravity acceleration. Theoretical predictions given by this model are dramatically different from those given by previous theories which have been readily recovered in the theory presented here as a limiting case. The theory shows qualitative agreement with available experimental data of the pitch angle and provides certain predictions to be verified.
Rayleigh Taylor growth at an embedded interface driven by a radiative shock
Huntington, Channing
2016-10-01
Radiative shocks are those where the radiation generated by the shock influences the hydrodynamics of the matter in the system. Radiative shocks are common in astrophysics, including during type II supernovae, and have also been observed in the rebound phase of a compressed inertial confinement fusion (ICF) capsule. It is predicted that the radiative heating serves to stabilize hydrodynamic instabilities in these systems, but studying the effect is challenging. Only in recent experiments at the National Ignition Facility has the energy been available to drive a radiative shock across a planar, Rayleigh-Taylor unstable interface in solid-density materials. Because the generation of radiation at the shock front is a strong function of shock velocity (v8) , the RT growth rates in the presence of fast and slow shockas were directly compared. We observe reduced RT spike development when the driving shock is expected to be radiative. Both low drive (225 eV) hydrodynamic RT growth and high drive (325 eV), radiatively-stabilized growth rates are in good agreement with 2D models. This NIF Discovery Science result has important implications for our understanding of astrophysical radiative shocks, as well as the dynamics of ICF capsules. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Martinez, D A; Smalyuk, V A; Kane, J O; Casner, A; Liberatore, S; Masse, L P
2015-05-29
We investigate on the National Ignition Facility the ablative Rayleigh-Taylor instability in the transition from weakly nonlinear to highly nonlinear regimes. A planar plastic package with preimposed two-dimensional broadband modulations is accelerated for up to 12 ns by the x-ray drive of a gas-filled Au radiation cavity with a radiative temperature plateau at 175 eV. This extended tailored drive allows a distance traveled in excess of 1 mm for a 130 μm thick foil. Measurements of the modulation optical density performed by x-ray radiography show that a bubble-merger regime for the Rayleigh-Taylor instability at an ablation front is achieved for the first time in indirect drive. The mutimode modulation amplitudes are in the nonlinear regime, grow beyond the Haan multimode saturation level, evolve toward the longer wavelengths, and show insensitivity to the initial conditions.
Study of Rayleigh-Taylor growth in directly driven cryogenic-deuterium targets
Hager, J. D.; Hu, S. X.; Knauer, J. P.; Meyerhofer, D. D.; Sangster, T. C. [Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623-1299 (United States); Smalyuk, V. A. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)
2012-07-15
Direct-drive, Rayleigh-Taylor growth experiments in liquid deuterium (D{sub 2}) were performed on the OMEGA laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] using planar cryogenic targets at a laser intensity of {approx}4 Multiplication-Sign 10{sup 14} W/cm{sup 2}. These are the first Rayleigh-Taylor measurements in deuterium at conditions relevant to inertial confinement fusion using a mass preimposed initial modulation. The measured modulation optical depths are in agreement with the 2D hydrodynamics code DRACO using flux-limited local thermal transport, providing an important step in the experimental validation of simulations for direct-drive ignition.
Ripesi, P; Schifano, S F; Tripiccione, R
2014-01-01
We study the turbulent evolution originated from a system subjected to a Rayleigh-Taylor instability with a double density at high resolution in a 2 dimensional geometry using a highly optimized thermal Lattice Boltzmann code for GPUs. The novelty of our investigation stems from the initial condition, given by the superposition of three layers with three different densities, leading to the development of two Rayleigh-Taylor fronts that expand upward and downward and collide in the middle of the cell. By using high resolution numerical data we highlight the effects induced by the collision of the two turbulent fronts in the long time asymptotic regime. We also provide details on the optimized Lattice-Boltzmann code that we have run on a cluster of GPUs
Casner, A.; Liberatore, S.; Masse, L.; Martinez, D.; Haan, S. W.; Kane, J.; Moore, A. S.; Seugling, R.; Farrell, M.; Giraldez, E.; Nikroo, A.; Smalyuk, V. A.; Remington, B. A.
2016-05-01
Under the Discovery Science program, the longer pulses and higher laser energies provided by the National Ignition Facility (NIF) have been harnessed to study, first time in indirect-drive, the highly nonlinear stage of the Rayleigh-Taylor Instability (RTI) at the ablation front. A planar plastic package with pre-imposed two-dimensional broadband modulations is accelerated for up to 12 ns by the x-ray drive of a gas-filled gold radiation cavity with a radiative temperature plateau at 175 eV. This extended tailored drive allows a distance traveled in excess of 1 mm for a 130 μm thick foil, a factor 3x larger than previously achieved on other laser facilities. As a consequence, we have measured the ablative RTI in transition from the weakly nonlinear stage up to the deep nonlinear stage for various initial conditions. A bubble merger regime has been observed and the ablative stabilization strength varied by changing the plastic dopant from iodine to germanium.
Understanding the impact of initial condition on low Atwood number Rayleigh-Taylor driven flows
Kuchibhatla, Sarat Chandra; Ranjan, Devesh
2012-11-01
Experimental investigation of the effects of initial conditions on Rayleigh-Taylor instability was performed using the Water Channel facility at Texas A&M University. Hot and cold water (with a temperature difference of ~7-8 degrees C) selected as working fluids were unstably stratified using a splitter plate resulting in a low Atwood number of ~0.0015. Using a servo controlled flapper system the effect of initial conditions is studied using different diagnostics such as optical imaging, thermocouples and hot-wire anemometry. A parametric study comprising of up to 10 modes of the initial condition was performed by varying the number of modes as well as modal composition (i . e . ratio of wavenumbers and phase differences). Variation of density, temperature and velocity field in the linear and non-linear stages of RT growth was recorded and analyzed. At non-dimensional time, t* = t (At g /H)0.5= 1.3, where t is the time, H is the width of the Channel, and g is the acceleration due to gravity, power spectra of the non-dimensional density showed fine-scale components that are dependent upon the initial condition. Plots of scalar dissipation and mixing rate indicate greater dissipation rate at early times that tends to asymptote to the order of kinematic viscosity at late times.
Direct numerical simulation of a small Atwood number Rayleigh-Taylor instability-driven mixing layer
Mueschke, Nicholas; Schilling, Oleg; Andrews, Malcolm
2005-11-01
A direct numerical simulation (DNS) of a small Atwood number Rayleigh-Taylor mixing layer was performed using a spectral/compact-difference scheme. The initial conditions were parameterized from interfacial and velocity perturbations measured from water channel experiments at Texas A&M University. Turbulence and mixing statistics, as well as energy spectra, obtained from experimental measurements are compared with those from the DNS to validate the use of experimental measurements as computational initial conditions. The experimental and numerical data are used to examine the transitional dynamics of the mixing layer. The DNS results indicate that initial conditions including both interfacial and velocity perturbations are required to accurately simulate the flow. This research was sponsored by the U.S. DOE National Nuclear Security Administration under the Stewardship Science Academic Alliances program through DOE Research Grant #DE-FG03- 02NA00060. This work was also performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W- 7405-Eng-48. UCRL-ABS-214352.
Sengupta, Tapan K.; Sengupta, Aditi; Sharma, Nidhi; Sengupta, Soumyo; Bhole, Ashish; Shruti, K. S.
2016-09-01
Direct numerical simulations of Rayleigh-Taylor instability (RTI) between two air masses with a temperature difference of 70 K is presented using compressible Navier-Stokes formulation in a non-equilibrium thermodynamic framework. The two-dimensional flow is studied in an isolated box with non-periodic walls in both vertical and horizontal directions. The non-conducting interface separating the two air masses is impulsively removed at t = 0 (depicting a heaviside function). No external perturbation has been used at the interface to instigate the instability at the onset. Computations have been carried out for rectangular and square cross sections. The formulation is free of Boussinesq approximation commonly used in many Navier-Stokes formulations for RTI. Effect of Stokes' hypothesis is quantified, by using models from acoustic attenuation measurement for the second coefficient of viscosity from two experiments. Effects of Stokes' hypothesis on growth of mixing layer and evolution of total entropy for the Rayleigh-Taylor system are reported. The initial rate of growth is observed to be independent of Stokes' hypothesis and the geometry of the box. Following this stage, growth rate is dependent on the geometry of the box and is sensitive to the model used. As a consequence of compressible formulation, we capture pressure wave-packets with associated reflection and rarefaction from the non-periodic walls. The pattern and frequency of reflections of pressure waves noted specifically at the initial stages are reflected in entropy variation of the system.
Sengupta, Tapan K., E-mail: tksen@iitk.ac.in; Bhole, Ashish; Shruti, K. S. [HPCL, Department of Aerospace Engineering, IIT Kanpur, Kanpur, UP (India); Sengupta, Aditi [Department of Engineering, University of Cambridge, Cambridge (United Kingdom); Sharma, Nidhi [Graduate Student, HPCL, Department of Aerospace Engineering, IIT Kanpur, Kanpur, UP (India); Sengupta, Soumyo [Department of Mechanical and Aerospace Engineering, Ohio State University, Columbus, Ohio 43210 (United States)
2016-09-15
Direct numerical simulations of Rayleigh-Taylor instability (RTI) between two air masses with a temperature difference of 70 K is presented using compressible Navier-Stokes formulation in a non-equilibrium thermodynamic framework. The two-dimensional flow is studied in an isolated box with non-periodic walls in both vertical and horizontal directions. The non-conducting interface separating the two air masses is impulsively removed at t = 0 (depicting a heaviside function). No external perturbation has been used at the interface to instigate the instability at the onset. Computations have been carried out for rectangular and square cross sections. The formulation is free of Boussinesq approximation commonly used in many Navier-Stokes formulations for RTI. Effect of Stokes’ hypothesis is quantified, by using models from acoustic attenuation measurement for the second coefficient of viscosity from two experiments. Effects of Stokes’ hypothesis on growth of mixing layer and evolution of total entropy for the Rayleigh-Taylor system are reported. The initial rate of growth is observed to be independent of Stokes’ hypothesis and the geometry of the box. Following this stage, growth rate is dependent on the geometry of the box and is sensitive to the model used. As a consequence of compressible formulation, we capture pressure wave-packets with associated reflection and rarefaction from the non-periodic walls. The pattern and frequency of reflections of pressure waves noted specifically at the initial stages are reflected in entropy variation of the system.
THE RAYLEIGH-TAYLOR INSTABILITY IN SMALL ASPECT RATIO CONTAINERS
RIVERA, MICHAEL K. [Los Alamos National Laboratory; ECKE, ROBERT E. [Los Alamos National Laboratory
2007-01-22
We present experimental measurements of density and velocity obtained from the mixing zone of buoyancy driven turbulence initiated by the Rayleigh-Taylor instability in a small aspect ration chamber (a chamber who's vertical height is significantly larger than its lateral dimesion). The mixing front propogates at a slightly slower rate than the expected t{sup 2} behavior obtained from earlier experiments and numerics. Once the front has propogated significantly far away, we observe that the mixing zone develops to a statistically stationary state. In this stationary state, the spectral distributions of energy and density deviate from the familiar k{sup -5/3} ubiquitous to turbulence in three dimensions.
Rotating Rayleigh-Taylor turbulence
Boffetta, G.; Mazzino, A.; Musacchio, S.
2016-09-01
The turbulent Rayleigh-Taylor system in a rotating reference frame is investigated by direct numerical simulations within the Oberbeck-Boussinesq approximation. On the basis of theoretical arguments, supported by our simulations, we show that the Rossby number decreases in time, and therefore the Coriolis force becomes more important as the system evolves and produces many effects on Rayleigh-Taylor turbulence. We find that rotation reduces the intensity of turbulent velocity fluctuations and therefore the growth rate of the temperature mixing layer. Moreover, in the presence of rotation the conversion of potential energy into turbulent kinetic energy is found to be less effective, and the efficiency of the heat transfer is reduced. Finally, during the evolution of the mixing layer we observe the development of a cyclone-anticyclone asymmetry.
Overview of Rayleigh-Taylor instability
Sharp, D.H.
1983-01-01
The aim of this talk is to survey Rayleigh-Taylor instability, describing the phenomenology that occurs at a Taylor unstable interface, and reviewing attempts to understand these phenomena quantitatively.
Rayleigh-Taylor Instability in a Relativistic Fireball on a Moving Computational Grid
Duffell, Paul C
2013-01-01
We numerically calculate the growth and saturation of the Rayleigh-Taylor instability caused by the deceleration of relativistic outflows with Lorentz factor \\Gamma = 10, 30, and 100. The instability generates turbulence whose scale exhibits strong dependence on Lorentz factor, as only modes within the causality scale \\Delta \\theta ~ 1/\\Gamma can grow. We develop a simple diagnostic to measure the fraction of energy in turbulent eddies and use it to estimate magnetic field amplification by the instability. We estimate a magnetic energy fraction ~ 0.01 due to Rayleigh-Taylor turbulence in a shock-heated region behind the forward shock. The instability completely disrupts the contact discontinuity between the ejecta and the swept up circumburst medium. The reverse shock is stable, but is impacted by the Rayleigh-Taylor instability, which strengthens the reverse shock and pushes it away from the forward shock. The forward shock front is unaffected by the instability, but Rayleigh-Taylor fingers can penetrate abo...
Rayleigh-Taylor mixing in supernova experiments
Swisher, N. C.; Abarzhi, S. I., E-mail: snezhana.abarzhi@gmail.com [Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 (United States); Kuranz, C. C. [University of Michigan, Ann Arbor, Michigan 48109 (United States); Arnett, D. [University of Arizona, Tucson, Arizona 85721 (United States); Hurricane, O.; Remington, B. A.; Robey, H. F. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)
2015-10-15
We report a scrupulous analysis of data in supernova experiments that are conducted at high power laser facilities in order to study core-collapse supernova SN1987A. Parameters of the experimental system are properly scaled to investigate the interaction of a blast-wave with helium-hydrogen interface, and the induced Rayleigh-Taylor instability and Rayleigh-Taylor mixing of the denser and lighter fluids with time-dependent acceleration. We analyze all available experimental images of the Rayleigh-Taylor flow in supernova experiments and measure delicate features of the interfacial dynamics. A new scaling is identified for calibration of experimental data to enable their accurate analysis and comparisons. By properly accounting for the imprint of the experimental conditions, the data set size and statistics are substantially increased. New theoretical solutions are reported to describe asymptotic dynamics of Rayleigh-Taylor flow with time-dependent acceleration by applying theoretical analysis that considers symmetries and momentum transport. Good qualitative and quantitative agreement is achieved of the experimental data with the theory and simulations. Our study indicates that in supernova experiments Rayleigh-Taylor flow is in the mixing regime, the interface amplitude contributes substantially to the characteristic length scale for energy dissipation; Rayleigh-Taylor mixing keeps order.
Rayleigh--Taylor spike evaporation
Schappert, G. T.; Batha, S. H.; Klare, K. A.; Hollowell, D. E.; Mason, R. J.
2001-09-01
Laser-based experiments have shown that Rayleigh--Taylor (RT) growth in thin, perturbed copper foils leads to a phase dominated by narrow spikes between thin bubbles. These experiments were well modeled and diagnosed until this '' spike'' phase, but not into this spike phase. Experiments were designed, modeled, and performed on the OMEGA laser [T. R. Boehly, D. L. Brown, R. S. Craxton , Opt. Commun. 133, 495 (1997)] to study the late-time spike phase. To simulate the conditions and evolution of late time RT, a copper target was fabricated consisting of a series of thin ridges (spikes in cross section) 150 {mu}m apart on a thin flat copper backing. The target was placed on the side of a scale-1.2 hohlraum with the ridges pointing into the hohlraum, which was heated to 190 eV. Side-on radiography imaged the evolution of the ridges and flat copper backing into the typical RT bubble and spike structure including the '' mushroom-like feet'' on the tips of the spikes. RAGE computer models [R. M. Baltrusaitis, M. L. Gittings, R. P. Weaver, R. F. Benjamin, and J. M. Budzinski, Phys. Fluids 8, 2471 (1996)] show the formation of the '' mushrooms,'' as well as how the backing material converges to lengthen the spike. The computer predictions of evolving spike and bubble lengths match measurements fairly well for the thicker backing targets but not for the thinner backings.
Aglitskiy, Y. [Science Applications International Corporation, McLean, Virginia 22150 (United States); Karasik, M.; Velikovich, A. L.; Serlin, V.; Weaver, J. L.; Kessler, T. J.; Schmitt, A. J.; Obenschain, S. P. [Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375 (United States); Nikitin, S. P.; Oh, J. [Research Support Instruments, Lanham, Maryland 20706 (United States); Metzler, N. [Research Support Instruments, Lanham, Maryland 20706 (United States); Ben Gurion University, Beer Sheva (Israel)
2012-10-15
Experimental study of hydrodynamic perturbation evolution triggered by a laser-driven shock wave breakout at the free rippled rear surface of a plastic target is reported. At sub-megabar shock pressure, planar jets manifesting the development of the Richtmyer-Meshkov-type instability in a non-accelerated target are observed. As the shock pressure exceeds 1 Mbar, an oscillatory rippled expansion wave is observed, followed by the 'feedout' of the rear-surface perturbations to the ablation front and the development of the Rayleigh-Taylor instability, which breaks up the accelerated target.
Theoretical and Experimental Studies of Magneto-Rayleigh-Taylor Instabilities
Lau, Yue Ying [University of Michigan, Ann Arbor, MI (United States); Gilgenbach, Ronald [University of Michigan, Ann Arbor, MI (United States)
2013-07-07
Magneto-Rayleigh-Taylor instability (MRT) is important to magnetized target fusion, wire-array z-pinches, and equation-of-state studies using flyer plates or isentropic compression. It is also important to the study of the crab nebula. The investigators performed MRT experiments on thin foils, driven by the mega-ampere linear transformer driver (LTD) facility completed in their laboratory. This is the first 1-MA LTD in the USA. Initial experiments on the seeding of MRT were performed. Also completed was an analytic study of MRT for a finite plasma slab with arbitrary magnetic fields tangential to the interfaces. The effects of magnetic shear and feedthrough were analyzed.
ALE simulation of Rayleigh-Taylor instability
Anbarlooei, H.R. [Univ. of Science and Technology, Dept. of Mechanical Engineering, Tehran (Iran, Islamic Republic of); Mazaheri, K. [Univ. of Tarbiyat Modares, Dept. of Mechanical Engineering, Tehran, (Iran, Islamic Republic of)]. E-mail: Kiumars@modares.ac.ir; Bidabadi, M. [Univ. of Science and Technology, Dept. of Mechanical Engineering, Tehran (Iran, Islamic Republic of)
2004-07-01
This paper investigates the use of an Arbitrary Lagrangian-Eulerian (ALE) technique for the simulation of a single mode Rayleigh-Taylor instability. A compatible Lagrangian algorithm is used on a simply connected quadrilateral grid in Lagrangian Phase. This algorithm includes subzonal pressures, which are used to control spurious grid motion, and an edge centered artificial viscosity. We use Reference Jacobians optimization based rezone algorithm in the rezoning phase of ALE method. Also a second order sign preserving method is used for remapping. To force monotonocity in remapping phase a Repair algorithm is used. Finally, for remapping of nodal variables we used a second order transformer to transfer these data to cell centers. It is shown that the usage of these algorithms for an ALE method can improve the simulation of a single mode Rayleigh-Taylor Instability. (author)
Large-eddy-simulation of 3-dimensional Rayleigh-Taylor instability in incompressible fluids
WANG; Lili
2002-01-01
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Compressible, inviscid Rayleigh-Taylor instability
Guo, Yan
2009-01-01
We consider the Rayleigh-Taylor problem for two compressible, immiscible, inviscid, barotropic fluids evolving with a free interface in the presence of a uniform gravitational field. After constructing Rayleigh-Taylor steady-state solutions with a denser fluid lying above the free interface with the second fluid, we turn to an analysis of the equations obtained from linearizing around such a steady state. By a natural variational approach, we construct normal mode solutions that grow exponentially in time with rate like $e^{t \\sqrt{\\abs{\\xi}}}$, where $\\xi$ is the spatial frequency of the normal mode. A Fourier synthesis of these normal mode solutions allows us to construct solutions that grow arbitrarily quickly in the Sobolev space $H^k$, which leads to an ill-posedness result for the linearized problem. Using these pathological solutions, we then demonstrate ill-posedness for the original non-linear problem in an appropriate sense. More precisely, we use a contradiction argument to show that the non-linear...
Anelastic Rayleigh-Taylor mixing layers
Schneider, N.; Gauthier, S.
2016-07-01
Anelastic Rayleigh-Taylor mixing layers for miscible fluids are investigated with a recently built model (Schneider and Gauthier 2015 J. Eng. Math. 92 55-71). Four Chebyshev-Fourier-Fourier direct numerical simulations are analyzed. They use different values for the compressibility parameters: Atwood number (the dimensionless difference of the heavy and light fluid densities) and stratification (accounts for the vertical variation of density due to gravity). For intermediate Atwood numbers and finite stratification, compressibility effects quickly occurs. As a result only nonlinear behaviours are reached. The influence of the compressibility parameters on the growth speed of the RTI is discussed. The 0.1—Atwood number/0.4—stratification configuration reaches a turbulent regime. This turbulent mixing layer is analyzed with statistical tools such as moments, PDFs, anisotropy indicators and spectra.
Planar and cylindrical Rayleigh-Taylor experiments on Nova (HEP2)
Remington, B.A.; Weber, S.V.; Marinak, M.M. [and others
1996-06-01
A high-density fluid on top of a low-density fluid is Rayleigh-Taylor (RT) unstable. Driven by gravity, random perturbations at the interface between the two fluids will grow: fingers ({open_quotes}spikes{close_quotes}) of the heavier fluid will poke through the lighter fluid, and bubbles of the lighter fluid will rise into the heavier fluid. The RT instability and its shock-driven analog, the Richtmyer-Meshkov (RM) instability, have been a focus of research in inertial confinement fusion (ICF) for some time. In ICF, the driver - laser light, x rays, or ions - heats the outer layer of the capsule wall, causing it to ionize and expand rapidly. The result is a low-density ablated plasma accelerating the high-density capsule wall ({open_quotes}Pusher{close_quotes}). The ablation front is RT unstable, and outer-surface imperfections grow. This growth can seed perturbations at the pusher inner wall, which in turn become RT unstable during deceleration and stagnation. Ultimately, pusher material can mix into the fuel, degrading performance.
Stability of Rayleigh-Taylor Vortices in Dusty Plasma
MA Jun; CHEN Yin-Hua; GAN Bao-Xia; WANG Fei-Hu; WANG Dong
2006-01-01
@@ The evolution of Rayleigh-Taylor mode in dusty plasma with vortex-flow is investigated. Based on fluid theory and Bayly's method, we derive the coupling equations describing the Rayleigh-Taylor mode in the core of vortex,and research the evolution characteristics of the perturbation amplitude with time numerically. It is shown that the eccentric of vortex and the content of dust have considerable effects on the amplitude evolutions.
Rayleigh-Taylor instability simulations with CRASH
Chou, C.-C.; Fryxell, B.; Drake, R. P.
2012-03-01
CRASH is a code package developed for the predictive study of radiative shocks. It is based on the BATSRUS MHD code used extensively for space-weather research. We desire to extend the applications of this code to the study of hydrodynamically unstable systems. We report here the results of Rayleigh-Taylor instability (RTI) simulations with CRASH, as a necessary step toward the study of such systems. Our goal, motivated by the previous comparison of simulations and experiment, is to be able to simulate the magnetic RTI with self-generated magnetic fields produced by the Biermann Battery effect. Here we show results for hydrodynamic RTI, comparing the effects of different solvers and numerical parameters. We find that the early-time behavior converges to the analytical result of the linear theory. We observe that the late-time morphology is sensitive to the numerical scheme and limiter beta. At low-resolution limit, the growth of RTI is highly dependent on the setup and resolution, which we attribute to the large numerical viscosity at low resolution.
Kinetic Simulations of Rayleigh-Taylor Instabilities
Sagert, Irina; Colbry, Dirk; Howell, Jim; Staber, Alec; Strother, Terrance
2014-01-01
We report on an ongoing project to develop a large scale Direct Simulation Monte Carlo code. The code is primarily aimed towards applications in astrophysics such as simulations of core-collapse supernovae. It has been tested on shock wave phenomena in the continuum limit and for matter out of equilibrium. In the current work we focus on the study of fluid instabilities. Like shock waves these are routinely used as test-cases for hydrodynamic codes and are discussed to play an important role in the explosion mechanism of core-collapse supernovae. As a first test we study the evolution of a single-mode Rayleigh-Taylor instability at the interface of a light and a heavy fluid in the presence of a gravitational acceleration. To suppress small-wavelength instabilities caused by the irregularity in the separation layer we use a large particle mean free path. The latter leads to the development of a diffusion layer as particles propagate from one fluid into the other. For small amplitudes, when the instability is i...
Reynolds and Atwood Numbers Effects on Homogeneous Rayleigh Taylor Instability
Aslangil, Denis; Livescu, Daniel; Banerjee, Arindam
2015-11-01
The effects of Reynolds and Atwood numbers on turbulent mixing of a heterogeneous mixture of two incompressible, miscible fluids with different densities are investigated by using high-resolution Direct Numerical Simulations (DNS). The flow occurs in a triply periodic 3D domain, with the two fluids initially segregated in random patches, and turbulence is generated in response to buoyancy. In turn, stirring produced by turbulence breaks down the scalar structures, accelerating the molecular mixing. Statistically homogeneous variable-density (VD) mixing, with density variations due to compositional changes, is a basic mixing problem and aims to mimic the core of the mixing layer of acceleration driven Rayleigh Taylor Instability (RTI). We present results covering a large range of kinematic viscosity values for density contrasts including small (A =0.04), moderate (A =0.5), and high (A =0.75 and 0.9) Atwood numbers. Particular interest will be given to the structure of the turbulence and mixing process, including the alignment between various turbulence and scalar quantities, as well as providing fidelity data for verification and validation of mix models. Arindam Banerjee acknowledges support from NSF CAREER award # 1453056.
Non-equilibrium Thermodynamics of Rayleigh-Taylor instability
Sengupta, Tapan K.; Sengupta, Aditi; Shruti, K. S.; Sengupta, Soumyo; Bhole, Ashish
2016-10-01
Rayleigh-Taylor instability (RTI) has been studied here as a non-equilibrium thermodynamics problem. Air masses with temperature difference of 70K, initially with heavier air resting on lighter air isolated by a partition, are allowed to mix by impulsively removing the partition. This results in interface instabilities, which are traced here by solving two dimensional (2D) compressible Navier-Stokes equation (NSE), without using Boussinesq approximation (BA henceforth). The non-periodic isolated system is studied by solving NSE by high accuracy, dispersion relation preserving (DRP) numerical methods described in Sengupta T.K.: High Accuracy Computing Method (Camb. Univ. Press, USA, 2013). The instability onset is due to misaligned pressure and density gradients and is evident via creation and evolution of spikes and bubbles (when lighter fluid penetrates heavier fluid and vice versa, associated with pressure waves). Assumptions inherent in compressible formulation are: (i) Stokes' hypothesis that uses zero bulk viscosity assumption and (ii) the equation of state for perfect gas which is a consequence of equilibrium thermodynamics. Present computations for a non-equilibrium thermodynamic process do not show monotonic rise of entropy with time, as one expects from equilibrium thermodynamics. This is investigated with respect to the thought-experiment. First, we replace Stokes' hypothesis, with another approach where non-zero bulk viscosity of air is taken from an experiment. Entropy of the isolated system is traced, with and without the use of Stokes' hypothesis. Without Stokes' hypothesis, one notes the rate of increase in entropy to be higher as compared to results with Stokes' hypothesis. We show this using the total entropy production for the thermodynamically isolated system. The entropy increase from the zero datum is due to mixing in general; punctuated by fluctuating entropy due to creation of compression and rarefaction fronts originating at the interface
Very-high-growth-factor Planar Ablative Rayleigh Taylor Experiments
Bradley, D K; Braun, D G; Glendinning, S G; Edwards, M J; Milovich, J L; Sorce, C M; Collins, G W; Haan, S W; Page, R H
2006-10-30
The Rayleigh-Taylor (RT) instability is an important factor in bounding the performance envelope of ignition targets. This paper describes an experiment for ablative RT instability that for the first time achieves growth factors close to those expected to occur in ignition targets at the National Ignition Facility (NIF). The large growth allows small seed perturbations to be detected and can be used to place an upper bound on perturbation growth at the ablation front resulting from microstructure in the preferred Be ablator. The experiments were performed on the Omega laser using a halfraum 1.2 mm long by 2 mm diameter with a 75% laser entrance hole. The halfraum was filled with {approx} 1 atm of neopentane to delay gold plasma from closing the diagnostic line of sight down the axis of the halfraum. The ablator was mounted at the base of the halfraum, and was accelerated by a two stepped X-ray pulse consisting of an early time section {approx} 100 eV to emulate the NIF foot followed by an approximately constant {approx} 150 eV drive sustained over an additional 5-7ns. It is this long pulse duration and late time observation that distinguishes the present work from previous experiments, and is responsible for the large growth that is achieved. The growth of a 2D sinusoidal perturbation machined on the drive side of the ablator was measured using face-on radiography. The diagnostic view remained open until {approx} 11 ns with maximum growth factors measured to be {approx} 200. The trajectory of the ablator was measured using streaked backlit radiography. The design and analysis of the experiments is described, and implications for experiments on ignition target ablators are discussed.
Effect of noise on Rayleigh-Taylor mixing with time-dependent acceleration
Swisher, Nora; Pandian, Arun; Abarzhi, Snezhana
2016-11-01
We perform a detailed stochastic study of Rayleigh-Taylor (RT) mixing with time-dependent acceleration. A set of nonlinear stochastic differential equations with multiplicative noise is derived on the basis of momentum model and group theory analysis. A broad range of parameters is investigated, and self-similar asymptotic solutions are found. The existence is shown of two sub-regimes of RT mixing dynamics - the acceleration-driven and the dissipation-driven mixing. In each sub-regime, statistic properties of the solutions are investigated, and dynamic invariants are found. Transition between the sub-regimes is studied. The work is supported by the US National Science Foundation.
Nonlinear diffusion model for Rayleigh-Taylor mixing.
Boffetta, G; De Lillo, F; Musacchio, S
2010-01-22
The complex evolution of turbulent mixing in Rayleigh-Taylor convection is studied in terms of eddy diffusivity models for the mean temperature profile. It is found that a nonlinear model, derived within the general framework of Prandtl mixing theory, reproduces accurately the evolution of turbulent profiles obtained from numerical simulations. Our model allows us to give very precise predictions for the turbulent heat flux and for the Nusselt number in the ultimate state regime of thermal convection.
Nonlinear diffusion model for Rayleigh-Taylor mixing
Boffetta, G; Musacchio, S
2010-01-01
The complex evolution of turbulent mixing in Rayleigh-Taylor convection is studied in terms of eddy diffusiviy models for the mean temperature profile. It is found that a non-linear model, derived within the general framework of Prandtl mixing theory, reproduces accurately the evolution of turbulent profiles obtained from numerical simulations. Our model allows to give very precise predictions for the turbulent heat flux and for the Nusselt number in the ultimate state regime of thermal convection.
Belof, J L; Cavallo, R M; Olson, R T; King, R S; Gray, G T; Holtkamp, D B; Chen, S R; Rudd, R E; Barton, N R; Arsenlis, A; Remington, B A; Park, H; Prisbrey, S T; Vitello, P A; Bazan, G; Mikaelian, K O; Comley, A J; Maddox, B R; May, M J
2011-08-10
We present here the first dynamic Rayleigh-Taylor (RT) strength measurement of a material undergoing solid-solid phase transition. Iron is quasi-isentropically driven across the pressure-induced bcc ({alpha}-Fe) {yields} hcp ({var_epsilon}-Fe) phase transition and the dynamic strength of the {alpha}, {var_epsilon} and reverted {alpha}{prime} phases have been determined via proton radiography of the resulting Rayleigh-Taylor unstable interface between the iron target and high-explosive products. Simultaneous velocimetry measurements of the iron free surface yield the phase transition dynamics and, in conjunction with detailed hydrodynamic simulations, allow for determination of the strength of the distinct phases of iron. Forward analysis of the experiment via hydrodynamic simulations reveals significant strength enhancement of the dynamically-generated {var_epsilon}-Fe and reverted {alpha}{prime}-Fe, comparable in magnitude to the strength of austenitic stainless steels.
Mokler, Matthew; Roberts, Michael; Jacobs, Jeffrey
2011-11-01
Incompressible Rayleigh-Taylor instability experiments are presented in which two stratified miscible liquids having Atwood number of 0.2 are accelerated in a vertical linear induction motor driven drop tower. A test sled having only vertical freedom of motion contains the experiment tank and visualization equipment. The sled is positioned at the top of the tower within the linear motors and accelerated downward causing the initially stable interface to be unstable and allowing the Rayleigh-Taylor instability to develop. Experiments are presented with and without forced initial perturbations produced by vertically oscillating the test sled prior to the start of acceleration. The interface is visualized using a 445nm laser light source that illuminates a fluorescent dye mixed in one of the fluids. The resulting fluorescent images are recorded using a monochromatic high speed video camera. The laser beam is synchronously swept across the fluorescent fluid, at the frame rate of the camera, exposing a single plane of the interface allowing for the measurement of spike and bubble mixing layer growth rates.
Mokler, Matthew; Roberts, Michael; Jacobs, Jeffrey
2013-11-01
Incompressible Rayleigh-Taylor instability experiments are presented in which two stratified liquids having Atwood number of 0.2 are accelerated in a vertical linear induction motor driven drop tower. A test sled having only vertical freedom of motion contains the experiment tank and visualization equipment. The sled is positioned at the top of the tower within the linear induction motors and accelerated downward causing the initially stable interface to be unstable and allowing the Rayleigh-Taylor instability to develop. Forced and unforced experiments are conducted using both immiscible and miscible liquid combinations. Forced initial perturbations are produced by vertically oscillating the test sled prior to the start of acceleration. The interface is visualized using a 445 nm laser light source that illuminates a fluorescent dye mixed in one of the fluids. The resulting fluorescent images are recorded using a monochromatic high speed video camera. The laser beam is synchronously swept across the fluorescent fluid, at the frame rate of the camera, exposing a single plane of the interface allowing for the measurement of spike and bubble growth. Comparisons between miscible and immiscible mixing layer distributions are made from the resulting interface concentration profiles.
Three-Dimensional Single-Mode Nonlinear Ablative Rayleigh-Taylor Instability
Yan, R.; Betti, R.; Sanz, J.; Liu, B.; Frank, A.
2015-11-01
The nonlinear evolution of the ablative Rayleigh-Taylor (ART) instability is studied in three dimensions for conditions relevant to inertial confinement fusion targets. The simulations are performed using our newly developed code ART3D and an astrophysical code AstroBEAR. The laser ablation can suppress the growth of the short-wavelength modes in the linear phase but may enhance their growth in the nonlinear phase because of the vortex-acceleration mechanism. As the mode wavelength approaches the cutoff of the linear spectrum (short-wavelength modes), it is found that the bubble velocity grows faster than predicted in the classical 3-D theory. When compared to 2-D results, 3-D short-wavelength bubbles grow faster and do not reach saturation. The unbounded 3-D bubble acceleration is driven by the unbounded accumulation of vorticity inside the bubble. The vorticity is transferred by mass ablation from the Rayleigh-Taylor spikes into the ablated plasma filling the bubble volume. A density plateau is observed inside a nonlinear ART bubble and the plateau density is higher for shorter-wavelength modes. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.
A generalised Rayleigh-Taylor condition for the Muskat problem
Escher, Joachim; Matioc, Bogdan-Vasile
2010-01-01
In this paper we consider the evolution of two fluid phases in a porous medium. The fluids are separated from each other and also the wetting phase from air by interfaces which evolve in time. We reduce the problem to an abstract evolution equation. A generalised Rayleigh-Taylor condition characterizes the parabolicity regime of the problem and allows us to establish a general well-posedness result and to study stability properties of flat steady-states. When considering surface tension effects at the interface between the fluids and if the more dense fluid lies above, we find bifurcating finger-shaped equilibria which are all unstable.
Experimental Study of Rayleigh-Taylor Instability Using Paramagnetic Fluids
Tsiklashvili, Vladimer; Likhachev, Oleg; Jacobs, Jeffry
2009-11-01
Experiments that take advantage of the properties of paramagnetic liquids are used to study Rayleigh-Taylor instability. A gravitationally unstable combination of a paramagnetic salt solution and a nonmagnetic solution is initially stabilized by a magnetic field gradient that is produced by the contoured pole-caps of a large electromagnet. Rayleigh-Taylor instability originates with the rapid removal of current from the electromagnet, which results in the heavy liquid falling into the light liquid due to gravity and, thus, mixing with it. The mixing zone is visualized by back-lit photography and is recorded with a digital video camera. For visualization purposes, a blue-green dye is added to the magnetic fluid. The mixing rate of the two liquids is determined from an averaged dye concentration across the mixing layer by means of the Beer-Lambert law. After removal of the suspending magnetic field, the initially flat interface between the two liquids develops a random surface pattern with the dominant length scale well approximated by the fastest growing wavelength in accordance with the viscous linear stability theory. Several combinations of paramagnetic and nonmagnetic solutions have been considered during the course of the research. A functional dependence of the mixing layer growth constant, α, on the properties of the liquids is a primary subject of the present study.
Rayleigh-Taylor instability of viscous fluids with phase change
Kim, Byoung Jae; Kim, Kyung Doo
2016-04-01
Film boiling on a horizontal surface is a typical example of the Rayleigh-Taylor instability. During the film boiling, phase changes take place at the interface, and thus heat and mass transfer must be taken into consideration in the stability analysis. Moreover, since the vapor layer is not quite thick, a viscous flow must be analyzed. Existing studies assumed equal kinematic viscosities of two fluids, and/or considered thin viscous fluids. The purpose of this study is to derive the analytical dispersion relation of the Rayleigh-Taylor instability for more general conditions. The two fluids have different properties. The thickness of the vapor layer is finite, but the liquid layer is thick enough to be nearly semi-infinite in view of perturbation. Initially, the vapor is in equilibrium with the liquid at the interface, and the direction of heat transfer is from the vapor side to the liquid side. In this case, the phase change has a stabilizing effect on the growth rate of the interface. When the vapor layer is thin, there is a coupled effect of the vapor viscosity, phase change, and vapor thickness on the critical wave number. For the other limit of a thick vapor, both the liquid and vapor viscosities influence the critical wave number. Finally, the most unstable wavelength is investigated. When the vapor layer is thin, the most unstable wavelength is not affected by phase change. When the vapor layer is thick, however, it increases with the increasing rate of phase change.
HUANG Lin; JIAN Guang-de; QIU Xiao-ming
2007-01-01
The synergistic stabilizing effect of gyroviscosity and sheared axial flow on the Rayleigh-Taylor instability in Z-pinch implosions is studied by means of the incompressible viscid magneto-hydrodynamic equations. The gyroviscosity (or finite Larmor radius) effects are introduced in the momentum equation through an anisotropic ion stress tensor. Dispersion relation with the effect of a density discontinuity is derived. The results indicate that the short-wavelength modes of the Rayleigh-Taylor instability are easily stabilized by the gyroviscosity effects. The long wavelength modes are stabilized by the sufficient sheared axial flow. However, the synergistic effects of the finite Larmor radius and sheared axial flow can heavily mitigate the Rayleigh-Taylor instability. This synergistic effect can compress the Rayleigh-Taylor instability to a narrow wave number region. Even with a sufficient gyroviscosity and large enough flow velocity, the synergistic effect can completely suppressed the Rayleigh-Taylor instability in whole wave number region.
Henry de Frahan, M. T., E-mail: marchdf@umich.edu; Johnsen, E. [Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109 (United States); Belof, J. L.; Cavallo, R. M.; Ancheta, D. S.; El-dasher, B. S.; Florando, J. N.; Gallegos, G. F.; LeBlanc, M. M. [Lawrence Livermore National Laboratory Livermore, California 94551-0808 (United States); Raevsky, V. A.; Ignatova, O. N.; Lebedev, A. [Russian Federal Nuclear Center-VNIIEF, Sarov 607188 (Russian Federation)
2015-06-14
We present a set of high explosive driven Rayleigh-Taylor strength experiments for beryllium to produce data to distinguish predictions by various strength models. Design simulations using existing strength model parameterizations from Steinberg-Lund and Preston-Tonks-Wallace (PTW) suggested an optimal design that would delineate between not just different strength models, but different parameters sets of the PTW model. Application of the models to the post-shot results, however, suggests growth consistent with little material strength. We focus mostly on efforts to simulate the data using published strength models as well as the more recent RING relaxation model developed at VNIIEF. The results of the strength experiments indicate weak influence of strength in mitigating the growth with the RING model coming closest to predicting the material behavior. Finally, we present shock and ramp-loading recovery experiments.
Lecoanet, Daniel; Quataert, Eliot
2012-01-01
We study the effects of anisotropic thermal conduction along magnetic field lines on an accelerated contact discontinuity in a weakly collisional plasma. We first perform a linear stability analysis similar to that used to derive the Rayleigh-Taylor instability (RTI) dispersion relation. We find that anisotropic conduction is only important for compressible modes, as incompressible modes are isothermal. Modes grow faster in the presence of anisotropic conduction, but growth rates do not change by more than a factor of order unity. We next run fully non-linear numerical simulations of a contact discontinuity with anisotropic conduction. The non-linear evolution can be thought of as a superposition of three physical effects: temperature diffusion due to vertical conduction, the RTI, and the heat flux driven buoyancy instability (HBI). In simulations with RTI-stable contact discontinuities, the temperature discontinuity spreads due to vertical heat conduction. This occurs even for initially horizontal magnetic f...
Henry de Frahan, M. T. [Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA; Belof, J. L. [Lawrence Livermore National Laboratory Livermore, California 94551-0808, USA; Cavallo, R. M. [Lawrence Livermore National Laboratory Livermore, California 94551-0808, USA; Raevsky, V. A. [Russian Federal Nuclear Center-VNIIEF, Sarov 607188, Russia; Ignatova, O. N. [Russian Federal Nuclear Center-VNIIEF, Sarov 607188, Russia; Lebedev, A. [Russian Federal Nuclear Center-VNIIEF, Sarov 607188, Russia; Ancheta, D. S. [Lawrence Livermore National Laboratory Livermore, California 94551-0808, USA; El-dasher, B. S. [Lawrence Livermore National Laboratory Livermore, California 94551-0808, USA; Florando, J. N. [Lawrence Livermore National Laboratory Livermore, California 94551-0808, USA; Gallegos, G. F. [Lawrence Livermore National Laboratory Livermore, California 94551-0808, USA; Johnsen, E. [Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA; LeBlanc, M. M. [Lawrence Livermore National Laboratory Livermore, California 94551-0808, USA
2015-06-14
A recent collaboration between LLNL and VNIIEF has produced a set of high explosive driven Rayleigh-Taylor strength data for beryllium. Design simulations using legacy strength models from Steinberg-Lund and Preston-Tonks-Wallace (PTW) suggested an optimal design that would delineate between not just different strength models, but different parameters sets of the PTW model. Application of the models to the post-shot results, however, shows close to classical growth. We characterize the material properties of the beryllium tested in the experiments. We also discuss recent efforts to simulate the data using the legacy strength models as well as the more recent RING relaxation model developed at VNIIEF. Finally, we present shock and ramp-loading recovery experiments conducted as part of the collaboration.
Measurements of Molecular Mixing in a High Schmidt Number Rayleigh-Taylor Mixing Layer
Mueschke, N J; Schilling, O; Youngs, D L; Andrews, M
2007-12-03
Molecular mixing measurements are performed for a high Schmidt number (Sc {approx} 10{sup 3}), small Atwood number (A {approx} 7.5 x 10{sup -4}) buoyancy-driven turbulent Rayleigh-Taylor mixing layer in a water channel facility. Salt was added to the top stream to create the desired density difference. The degree of molecular mixing was measured as a function of time by monitoring a diffusion-limited chemical reaction between the two fluid streams. The pH of each stream was modified by the addition of acid or alkali such that a local neutralization reaction occurred as the two fluids molecularly mixed. The progress of this neutralization reaction was tracked by the addition of phenolphthalein - a pH-sensitive chemical indicator - to the acidic stream. Accurately calibrated backlit optical techniques were used to measure the average concentration of the colored chemical indicator. Comparisons of chemical product formation for pre-transitional buoyancy- and shear-driven mixing layers are given. It is also shown that experiments performed at different equivalence ratios (acid/alkali concentration) can be combined to obtain a mathematical relationship between the colored product formed and the density variance. This relationship was used to obtain high-fidelity, quantitative measures of the degree of molecular mixing which are independent of probe resolution constraints. The dependence of such mixing parameters on the Schmidt and Reynolds numbers is examined by comparing the current Sc {approx} 10{sup 3} measurements with Sc = 0.7 gas-phase and Pr = 7 liquid-phase measurements. This comparison indicates that the Schmidt number has a large effect on the bulk quantity of mixed fluid at small Reynolds numbers Re{sub h} < 10{sup 3}. At late times, all mixing parameters indicated a greater degree of molecular mixing and a decreased Schmidt number dependence. Implications for the development and quantitative assessment of turbulent transport and mixing models appropriate for
Statistically steady measurements of Rayleigh-Taylor mixing in a gas channel
Banerjee, Arindam
A novel gas channel experiment was constructed to study the development of high Atwood number Rayleigh-Taylor mixing. Two gas streams, one containing air and the other containing helium-air mixture, flow parallel to each other separated by a thin splitter plate. The streams meet at the end of a splitter plate leading to the formation of an unstable interface and of buoyancy driven mixing. This buoyancy driven mixing experiment allows for long data collection times, short transients and was statistically steady. The facility was designed to be capable of large Atwood number studies of At ˜ 0.75. We describe work to measure the self similar evolution of mixing at density differences corresponding to 0.035 hot-wire anemometer, and high resolution digital image analysis. The hot-wire probe gives velocity, density and velocity-density statistics of the mixing layer. Two different multi-position single-wire techniques were used to measure the velocity fluctuations in three mutually perpendicular directions. Analysis of the measured data was used to explain the mixing as it develops to a self-similar regime in this flow. These measurements are to our knowledge, the first use of hot-wire anemometry in the Rayleigh-Taylor community. Since the measurement involved extensive calibration of the probes in a binary gas mixture of air and helium, a new convective heat transfer correlation was formulated to account for variable-density low Reynolds number flows past a heated cylinder. In addition to the hot-wire measurements, a digital image analysis procedure was used to characterize various properties of the flow and also to validate the hot-wire measurements. A test of statistical convergence was performed and the study revealed that the statistical convergence was a direct consequence of the number of different large three-dimensional structures that were averaged over the duration of the run.
Late-time quadratic growth in single-mode Rayleigh-Taylor instability.
Wei, Tie; Livescu, Daniel
2012-10-01
The growth of the two-dimensional single-mode Rayleigh-Taylor instability (RTI) at low Atwood number (A=0.04) is investigated using Direct Numerical Simulations. The main result of the paper is that, at long times and sufficiently high Reynolds numbers, the bubble acceleration becomes stationary, indicating mean quadratic growth. This is contrary to the general belief that single-mode Rayleigh-Taylor instability reaches a constant bubble velocity at long times. At unity Schmidt number, the development of the instability is strongly influenced by the perturbation Reynolds number, defined as Rep≡λsqrt[Agλ/(1+A)]/ν. Thus, the instability undergoes different growth stages at low and high Rep. A new stage, chaotic development, was found at sufficiently high Rep values, after the reacceleration stage. During the chaotic stage, the instability experiences seemingly random acceleration and deceleration phases, as a result of complex vortical motions, with strong dependence on the initial perturbation shape (i.e., wavelength, amplitude, and diffusion thickness). Nevertheless, our results show that the mean acceleration of the bubble front becomes constant at late times, with little influence from the initial shape of the interface. As Rep is lowered to small values, the later instability stages, chaotic development, reacceleration, potential flow growth, and even the exponential growth described by linear stability theory, are subsequently no longer reached. Therefore, the results suggest a minimum Reynolds number and a minimum development time necessary to achieve all stages of single-mode RTI development, requirements which were not satisfied in the previous studies of single-mode RTI.
The magnetic Rayleigh-Taylor instability in astrophysical discs
Contopoulos, I.; Kazanas, D.; Papadopoulos, D. B.
2016-10-01
This is our first study of the magnetic Rayleigh-Taylor instability at the inner edge of an astrophysical disc around a central back hole. We derive the equations governing small-amplitude oscillations in general relativistic ideal magnetodydrodynamics and obtain a criterion for the onset of the instability. We suggest that static disc configurations where magnetic field is held by the disc material are unstable around a Schwarzschild black hole. On the other hand, we find that such configurations are stabilized by the space-time rotation around a Kerr black hole. We obtain a crude estimate of the maximum amount of poloidal magnetic flux that can be accumulated around the centre, and suggest that it is proportional to the black hole spin. Finally, we discuss the astrophysical implications of our result for the theoretical and observational estimations of the black hole jet power.
Rayleigh-Taylor instability in accelerated solid media
Piriz, A. R.; Sun, Y. B.; Tahir, N. A.
2017-01-01
A linear study of the Rayleigh-Taylor instability based on momentum conservation and the consideration of an irrotational velocity field for incompressible perturbations is discussed. The theory allows for a very appealing physical picture and for a relatively simple description of the main features of the instability. As a result, it is suitable for the study of the very complex problem of the instability of accelerated solids with non-linear elastic-plastic constitutive properties, which cannot be studied by the usual normal modes approach. The elastic to plastic transition occurring early in the instability process determines the entire evolution and makes the instability exhibit behavior that cannot be captured by an asymptotic analysis.
Rayleigh-Taylor instability in soft elastic layers
Riccobelli, D.; Ciarletta, P.
2017-04-01
This work investigates the morphological stability of a soft body composed of two heavy elastic layers attached to a rigid surface and subjected only to the bulk gravity force. Using theoretical and computational tools, we characterize the selection of different patterns as well as their nonlinear evolution, unveiling the interplay between elastic and geometric effects for their formation. Unlike similar gravity-induced shape transitions in fluids, such as the Rayleigh-Taylor instability, we prove that the nonlinear elastic effects saturate the dynamic instability of the bifurcated solutions, displaying a rich morphological diagram where both digitations and stable wrinkling can emerge. The results of this work provide important guidelines for the design of novel soft systems with tunable shapes, with several applications in engineering sciences. This article is part of the themed issue 'Patterning through instabilities in complex media: theory and applications.'
Non-stationary Rayleigh-Taylor instability in supernovae ejecta
Ribeyre, X; Tikhonchuk, V T; Bouquet, S; Sanz, J; Ribeyre, Xavier; Hallo, Ludovic; Tikhonchuk, Vladimir; Bouquet, Serge; Sanz, Javier
2005-01-01
The Rayleigh-Taylor instability plays an important role in the dynamics of several astronomical objects, in particular, in supernovae (SN) evolution. In this paper we develop an analytical approach to study the stability analysis of spherical expansion of the SN ejecta by using a special transformation in the co-moving coordinate frame. We first study a non-stationary spherical expansion of a gas shell under the pressure of a central source. Then we analyze its stability with respect to a no radial, non spherically symmetric perturbation of the of the shell. We consider the case where the polytropic constant of the SN shell is $\\gamma=5/3$ and we examine the evolution of a arbitrary shell perturbation. The dispersion relation is derived. The growth rate of the perturbation is found and its temporal and spatial evolution is discussed. The stability domain depends on the ejecta shell thickness, its acceleration, and the perturbation wavelength.
Rayleigh-Taylor instability in partially ionized prominence plasma
Khomenko, E; de Vicente, A; Collados, M; Luna, M
2013-01-01
We study Rayleigh-Taylor instability (RTI) at the coronal-prominence boundary by means of 2.5D numerical simulations in a single-fluid MHD approach including a generalized Ohm's law. The initial configuration includes a homogeneous magnetic field forming an angle with the direction in which the plasma is perturbed. For each field inclination we compare two simulations, one for the pure MHD case, and one including the ambipolar diffusion in the Ohm's law, otherwise identical. We find that the configuration containing neutral atoms is always unstable. The growth rate of the small-scale modes in the non-linear regime is larger than in the purely MHD case.
The cylindrical magnetic Rayleigh-Taylor instability for viscous fluids
Chambers, K.; Forbes, L. K. [School of Mathematics and Physics, University of Tasmania, Private Bag 37-Hobart, Tasmania 7005 (Australia)
2012-10-15
This paper considers a cylindrical Rayleigh-Taylor instability, in which a heavy fluid surrounds a light fluid, and gravity is directed radially inwards. A massive object is located at the centre of the light fluid, and it behaves like a line dipole both for fluid flow and magnetic field strength. The initially circular interface between the two conducting fluids evolves into plumes, dependent on the magnetic and fluid dipole strengths and the nature of the initial disturbance to the interface. A spectral method is presented to solve the time-dependent interface shapes, and results are presented and discussed. Bipolar solutions are possible, and these are of particular relevance to astrophysics. The solutions obtained resemble structures of some HII regions and nebulae.
Rayleigh-Taylor stabilization by material strength at Mbar pressures
Remington, Bruce; Park, Hye-Sook; Lorenz, Thomas; Cavallo, Robert; Pollaine, Stephen; Prisbrey, Shon; Rudd, Robert; Becker, Richard; Bernier, Joel
2009-11-01
We present experiments on the Rayleigh-Taylor (RT) instability in the plastic flow regime of solid-state vanadium (V) foils at 1 Mbar pressures and strain rates of 1.e6-1.e8 1/s, using a laser based, ramped-pressure acceleration technique. High pressure material strength causes strong stabilization of the RT instability at short wavelengths. Comparisons with 2D simulations utilizing models of high pressure strength show that the V strength increases by factors of 3-4 at peak pressure, compared to its ambient strength. An effective lattice viscosity of 400 poise would have a similar effect. [1] Constitutive models, and theoretical implications of these experiments will be discussed. [1] H.S. Park, B.A. Remington et al., submitted for publication (July, 2009).
Magneto-Rayleigh-Taylor growth and feedthrough in cylindrical liners
Weis, Matthew; Lau, Y. Y.; Gilgenbach, Ronald; Peterson, Kyle; Hess, Mark
2013-10-01
Cylindrical liner implosions in the MagLIF concept are susceptible to the magneto-Rayleigh-Taylor instability (MRT). The linearized ideal MHD equations are solved, including the presence of an axial magnetic field and the effects of sausage and kink modes. The eigenmode solution, using appropriate equilibrium profiles, allows an assessment of the local MRT growth rate and of the instantaneous feedthrough factor during the entire implosion process. Of particular interest will be the high convergence/stagnation phase, which is difficult to image experimentally. Strong axial magnetic fields can mitigate feedthrough and MRT growth, which may be useful at the fuel/liner interface during this phase of the MagLIF implosion. For the MRT growth rate and feedthrough factors, the LLNL code, HYDRA, is used to benchmark with the analytic theory, and with experiments on the Z-machine. This work was supported by DoE and NSF.
The Magnetic Rayleigh-Taylor Instability in Astrophysical Discs
Contopoulos, I.; Kazanas, D.; Papadopoulos, D. B.
2016-01-01
This is our first study of the magnetic Rayleigh-Taylor instability at the inner edge of an astrophysical disc around a central back hole. We derive the equations governing small-amplitude oscillations in general relativistic ideal magnetodydrodynamics and obtain a criterion for the onset of the instability. We suggest that static disc configurations where magnetic field is held by the disc material are unstable around a Schwarzschild black hole. On the other hand, we find that such configurations are stabilized by the space-time rotation around a Kerr black hole. We obtain a crude estimate of the maximum amount of poloidal magnetic flux that can be accumulated around the centre, and suggest that it is proportional to the black hole spin. Finally, we discuss the astrophysical implications of our result for the theoretical and observational estimations of the black hole jet power.
Qualitative and quantitative features of Rayleigh-Taylor mixing dynamics
Ramaprabhu, Praveen; Karkhanis, Varad; Lawrie, Andrew; Bhowmick, Aklant; Abarzhi, Snezhana; RTI Collaboration
2015-11-01
We consider dynamics of Rayleigh-Taylor (RT) flow in a large aspect ratio three-dimensional domain with square symmetry in the plane for fluids with contrasting densities. In order to quantify the interface evolution from a small amplitude single-mode initial perturbation to advanced stage of RT mixing, we apply numerical simulations using the MOBILE code, theoretical analyses, including group theory and momentum model, as well as parameters describing the interplay between acceleration and turbulence. We find: In RT flow, the fluid motion is intense near the interface and is negligible far from the interface. At late times the growth rates of RT bubbles and spikes may increase without a corresponding increase of length-scales in the direction normal to acceleration. The parameters describing the interplay between acceleration and turbulence in RT mixing are shown to scale well with the flow Reynolds number and Froude number.
Collisional effects on Rayleigh-Taylor-induced magnetic fields
Manuel, M. J.-E. [University of Michigan, Ann Arbor, Michigan 48109 (United States); Flaig, M.; Plewa, T. [Florida State University, Tallahassee, Florida 32306 (United States); Li, C. K.; Séguin, F. H.; Frenje, J. A.; Casey, D. T.; Petrasso, R. D. [Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Hu, S. X.; Betti, R.; Hager, J.; Meyerhofer, D. D.; Smalyuk, V. [Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623 (United States)
2015-05-15
Magnetic-field generation from the Rayleigh-Taylor (RT) instability was predicted more than 30 years ago, though experimental measurements of this phenomenon have only occurred in the past few years. These pioneering observations demonstrated that collisional effects are important to B-field evolution. To produce fields of a measurable strength, high-intensity lasers irradiate solid targets to generate the nonaligned temperature and density gradients required for B-field generation. The ablation process naturally generates an unstable system where RT-induced magnetic fields form. Field strengths inferred from monoenergetic-proton radiographs indicate that in the ablation region diffusive effects caused by finite plasma resistivity are not negligible. Results from the first proof-of-existence experiments are reviewed and the role of collisional effects on B-field evolution is discussed in detail.
Roberts, Michael Scott
The Rayleigh-Taylor instability is a buoyancy driven instability that takes place in a stratified fluid system with a constant acceleration directed from the heavy fluid into the light fluid. In this study, both experimental data and numerical simulations are presented. Experiments are performed primarily using a lithium-tungstate aqueous solution as the heavy liquid, but sometimes a calcium nitrate aqueous solution is used for comparison purposes. Experimental data is obtained for both miscible and immiscible fluid combinations. For the miscible experiments the light liquid is either ethanol or isopropanol, and for the immiscible experiments either silicone oil or trans-anethole is used. The resulting Atwood number is either 0.5 when the lithium-tungstate solution is used or 0.2 when the calcium nitrate solution is used. These fluid combinations are either forced or left unforced. The forced experiments have an initial perturbation imposed by vertically oscillating the liquid containing tank to produce Faraday waves at the interface. The unforced experiments rely on random interfacial fluctuations, due to background noise, to seed the instability. The liquid combination is partially enclosed in a test section that is accelerated downward along a vertical rail system causing the Rayleigh-Taylor instability. Accelerations of approximately 1g (with a weight and pulley system) or 10g (with a linear induction motor system) are experienced by the liquids. The tank is backlit and digitally recorded with high speed video cameras. These experiments are then simulated with the incompressible, Navier-Stokes code Miranda. The main focus of this study is the growth parameter (α) of the mixing region produced by the instability after it has become apparently self-similar and turbulent. The measured growth parameters are compared to determine the effects of miscibility and initial perturbations (of the small wavelength, finite bandwidth type used here). It is found that while
Direct Numerical Simulation of the Rayleigh-Taylor Instability with the Spectral Element Method
ZHANG Xu; TAN Duo-Wang
2009-01-01
A novel method is proposed to simulate Rayleigh-Taylor instabilities using a specially-developed unsteady threedimensional high-order spectral element method code.The numerical model used consists of Navier-Stokes equations and a transport-diffusive equation.The code is first validated with the results of linear stability perturbation theory.Then several characteristics of the Rayleigh-Taylor instabjJjties are studied using this three-dimensional unsteady code,inducling instantaneous turbulent structures and statistical turbulent mixing heights under different initial wave numbers.These results indicate that turbulent structures ofRayleigh-Taylor instabilities are strongly dependent on the initial conditions.The results also suggest that a high-order numerical method should provide the capability of sir.ulating small scale fluctuations of Rayleigh-Taylor instabilities of turbulent flows.
Linear Rayleigh-Taylor instability for viscous, compressible fluids
Guo, Yan
2009-01-01
We study the equations obtained from linearizing the compressible Navier-Stokes equations around a steady-state profile with a heavier fluid lying above a lighter fluid along a planar interface, i.e. a Rayleigh-Taylor instability. We consider the equations with or without surface tension, with the viscosity allowed to depend on the density, and in both periodic and non-periodic settings. In the presence of viscosity there is no natural variational framework for constructing growing mode solutions to the linearized problem. We develop a general method of studying a family of modified variational problems in order to produce maximal growing modes. Using these growing modes, we construct smooth (when restricted to each fluid domain) solutions to the linear equations that grow exponentially in time in Sobolev spaces. We then prove an estimate for arbitrary solutions to the linearized equations in terms of the fastest possible growth rate for the growing modes. In the periodic setting, we show that sufficiently sm...
Critical Magnetic Number in the MHD Rayleigh-Taylor instability
Wang, Yanjin
2010-01-01
We reformulate in Lagrangian coordinates the two-phase free boundary problem for the equations of Magnetohydrodynamics in a infinite slab, which is incompressible, viscous and of zero resistivity, as one for the Navier-Stokes equations with a force term induced by the fluid flow map. We study the stabilized effect of the magnetic field for the linearized equations around the steady-state solution by assuming that the upper fluid is heavier than the lower fluid, $i. e.$, the linear Rayleigh-Taylor instability. We identity the critical magnetic number $|B|_c$ by a variational problem. For the cases $(i)$ the magnetic number $\\bar{B}$ is vertical in 2D or 3D; $(ii)$ $\\bar{B}$ is horizontal in 2D, we prove that the linear system is stable when $|\\bar{B}|\\ge |B|_c$ and is unstable when $|\\bar{B}|<|B|_c$. Moreover, for $|\\bar{B}|<|B|_c$ the vertical $\\bar{B}$ stabilizes the low frequency interval while the horizontal $\\bar{B}$ stabilizes the high frequency interval, and the growth rate of growing modes is bou...
DSMC Simulations of the Rayleigh-Taylor Instability in Gases
Gallis, Michael; Koehler, Timothy; Torczynski, John; Plimpton, Steven
2015-11-01
The Direct Simulation Monte Carlo (DSMC) method of molecular gas dynamics is applied to simulate the Rayleigh-Taylor instability (RTI) in atmospheric-pressure monatomic gases (e.g., argon and helium). The computational domain is a 1 mm × 4 mm rectangle divided into 50-nm square cells. Each cell is populated with 1000 computational molecules, and time steps of 0.1 ns are used. Simulations are performed to quantify the growth of a single-mode perturbation on the interface as a function of the Atwood number and the gravitational acceleration. The DSMC results qualitatively reproduce all observed features of the RTI and are in reasonable quantitative agreement with existing theoretical and empirical models. Consistent with previous work in this field, the DSMC simulations indicate that the growth of the RTI follows a universal behavior. For cases with multiple-mode perturbations, the numbers of bubble-spike pairs that eventually appear are found to be in agreement with theoretical results for the most unstable wavelength. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Magneto-Rayleigh-Taylor instability in solid media
Sun, Y. B. [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); School of Physical Science and Technology, Lanzhou University, Lanzhou 73000 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Piriz, A. R., E-mail: roberto.piriz@uclm.es [E.T.S.I. Industriales (Spain); CYTEMA (Spain); Instituto de Investigaciones Energéticas, Universidad de Castilla-La Mancha, 13071 Ciudad Real (Spain)
2014-07-15
A linear analysis of the magneto-Rayleigh-Taylor instability at the interface between a Newtonian fluid and an elastic-plastic solid is performed by considering a uniform magnetic B{sup →}, parallel to the interface, which has diffused into the fluid but not into the solid. It is found that the magnetic field attributes elastic properties to the viscous fluid which enhance the stability region by stabilizing all the perturbation wavelengths shorter than λ{sub 0}∝B{sup 2} for any initial perturbation amplitude. Longer wavelengths are stabilized by the mechanical properties of the solid provided that the initial perturbation wavelength is smaller than a threshold value determined by the yield strength and the shear modulus of the solid. Beyond this threshold, the amplitude grows initially with a growth rate reduced by the solid strength properties. However, such properties do not affect the asymptotic growth rate which is only determined by the magnetic field and the fluid viscosity. The described physical situation intends to resemble some of the features present in recent experiments involving the magnetic shockless acceleration of flyers plates.
Cylindrical Effects on Magneto-Rayleigh-Taylor Instability
Weis, Matthew; Lau, Yue Ying; Gilgenbach, Ronald; Jennings, Christopher; Hess, Mark
2012-10-01
This paper concentrates on the effects of cylindrical geometry on the magneto-Rayleigh-Taylor instability (MRT), a major concern in the magnetized liner inertial fusion concept (MagLIF) [1]. Several issues are being studied, such as the Bell-Plesset effect [2], the effects of magnetic shear and feedthrough [3], and the nonzero MRT growth rate that remains (but was hardly noticed) in the k = m = 0 limit in Harris' seminal paper on a cylindrical liner [4], where k and m are respectively the azimuthal and axial wavenumber. We shall use simulation and direct integration of the eigenvalue equation to investigate the importance of the cylindrical geometry, which is particularly relevant in the final stage of compression in the MagLIF concept. [4pt] [1] S. A. Slutz, et. al, Phys. Plasmas 17, 056303 (2010). [0pt] [2] G. I. Bell, Los Alamos Scientific Laboratory, Report LA-1321 (1951); M. S. Plesset, J. Appl. Phys. 25, 96 (1954).[0pt] [3] P. Zhang et al., Phys. Plasmas 19, 200703 (2012); Y. Y. Lau et al., Phys. Rev. E 83, 006405 (2011). [0pt] [4] E. G. Harris, Phys. Fluids 5, 1057 (1962).
The role of Rayleigh-Taylor instabilities in filament threads
Terradas, J; Ballester, J L
2012-01-01
Many solar filaments and prominences show short-lived horizontal threads lying parallel to the photosphere. In this work the possible link between Rayleigh-Taylor instabilities and thread lifetimes is investigated. This is done by calculating the eigenmodes of a thread modelled as a Cartesian slab under the presence of gravity. An analytical dispersion relation is derived using the incompressible assumption for the magnetohydrodynamic (MHD) perturbations. The system allows a mode that is always stable, independently of the value of the Alfv\\'en speed in the thread. The character of this mode varies from being localised at the upper interface of the slab when the magnetic field is weak, to having a global nature and resembling the transverse kink mode when the magnetic field is strong. On the contrary, the slab model permits another mode that is unstable and localised at the lower interface when the magnetic field is weak. The growth rates of this mode can be very short, of the order of minutes for typical thr...
Shvarts, D.; Oron, D.; Kartoon, D.; Rikanati, A.; Sadot, O.; Srebro, Y.; Yedvab, Y.; Ofer, D.; Levin, A.; Sarid, E.; Ben-Dor, G.; Erez, L.; Erez, G.; Yosef-Hai, A.; Alon, U.; Arazi, L.
2016-10-01
The late-time nonlinear evolution of the Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) instabilities for random initial perturbations is investigated using a statistical mechanics model based on single-mode and bubble-competition physics at all Atwood numbers (A) and full numerical simulations in two and three dimensions. It is shown that the RT mixing zone bubble and spike fronts evolve as h ~ α · A · gt2 with different values of a for the bubble and spike fronts. The RM mixing zone fronts evolve as h ~ tθ with different values of θ for bubbles and spikes. Similar analysis yields a linear growth with time of the Kelvin-Helmholtz mixing zone. The dependence of the RT and RM scaling parameters on A and the dimensionality will be discussed. The 3D predictions are found to be in good agreement with recent Linear Electric Motor (LEM) experiments.
Effect of noise on Rayleigh-Taylor mixing with space-dependent acceleration
Pandian, Arun; Abarzhi, Snezhana
2016-11-01
We analyze, for the first time by our knowledge, the effect of noise on Rayleigh-Taylor (RT) mixing with space-dependent acceleration by applying the stochastic model. In these conditions, the RT mixing is a statistically unsteady process where the means values of the flow quantities vary in space and time, and there are also the space and time dependent fluctuations around these mean values. The stochastic model is derived from the momentum model and is represented by a set of nonlinear differential equations with multiplicative noise. The models equations are solved theoretically and numerically. Investigating a broad range of values of acceleration, self-similar asymptotic solutions are found in the mixing regime. There are two types of mixing sub-regimes (acceleration-driven and dissipation-driven respectively), each of which has its own types of solutions and characteristic values with the latter saturating to a value on the order of one. It is also observed that the representation of the dynamics in an implicit form is noisier as compared to the case of an explicit time-dependent form. The work is supported by the US National Science Foundation.
Mokler, Matthew; Roberts, Michael; Jacobs, Jeffrey
2012-11-01
Incompressible Rayleigh-Taylor instability experiments are presented in which two stratified liquids having Atwood number of 0.2 are accelerated in a vertical linear induction motor driven drop tower. A test sled having only vertical freedom of motion contains the experiment tank and visualization equipment. The sled is positioned at the top of the tower within the linear motors and accelerated downward causing the initially stable interface to be unstable and allowing the Rayleigh-Taylor instability to develop. Experiments are presented with and without forced initial perturbations produced by vertically oscillating the test sled prior to the start of acceleration. Half of the experimental tank is visualized using a 445nm laser light source that illuminates a fluorescent dye mixed in one of the fluids. The other half is illuminated with a white backlight. The resulting images are recorded using a monochromatic high speed video camera allowing for the measurement of spike and bubble mixing layer growth rates for both visualization techniques in a single experiment.
Mokler, Matthew; Jacobs, Jeffrey
2014-11-01
Incompressible Rayleigh-Taylor instability experiments are presented in which two stratified liquids having Atwood number of 0.2 are accelerated in a vertical linear induction motor driven drop tower. A test sled having only vertical freedom of motion contains the experiment tank and visualization equipment. The sled is positioned at the top of the tower within the linear induction motors and accelerated downward causing the initially stable interface to be unstable and allowing the Rayleigh-Taylor instability to develop. Forced and unforced experiments are conducted using an immiscible liquid combination. Forced initial perturbations are produced by vertically oscillating the test sled prior to the start of acceleration. The interface is visualized using a 445 nm laser light source that illuminates a fluorescent dye mixed in one of the fluids and aluminum oxide particles dispersed in both fluids. The laser beam is synchronously swept across the fluorescent fluid, at the frame rate of the camera, exposing a single plane of the interface. The resulting images are recorded using a monochromatic high speed video camera. Time dependent velocity and density fields are obtained from the recorded images allowing for 2D full field measurements of turbulent kinetic energy and turbulent mass transport.
Mueschke, N J; Andrews, M J; Schilling, O
2006-03-24
The initial multi-mode interfacial velocity and density perturbations present at the onset of a small Atwood number, incompressible, miscible, Rayleigh-Taylor instability-driven mixing layer have been quantified using a combination of experimental techniques. The streamwise interfacial and spanwise interfacial perturbations were measured using high-resolution thermocouples and planar laser-induced fluorescence (PLIF), respectively. The initial multi-mode streamwise velocity perturbations at the two-fluid density interface were measured using particle-image velocimetry (PIV). It was found that the measured initial conditions describe an initially anisotropic state, in which the perturbations in the streamwise and spanwise directions are independent of one another. The evolution of various fluctuating velocity and density statistics, together with velocity and density variance spectra, were measured using PIV and high-resolution thermocouple data. The evolution of the velocity and density statistics is used to investigate the early-time evolution and the onset of strongly-nonlinear, transitional dynamics within the mixing layer. The early-time evolution of the density and vertical velocity variance spectra indicate that velocity fluctuations are the dominant mechanism driving the instability development. The implications of the present experimental measurements on the initialization of Reynolds-averaged turbulent transport and mixing models and of direct and large-eddy simulations of Rayleigh-Taylor instability-induced turbulence are discussed.
Mueschke, N J; Andrews, M J; Schilling, O
2005-09-26
The initial multi-mode interfacial velocity and density perturbations present at the onset of a small Atwood number, incompressible, miscible, Rayleigh-Taylor instability-driven mixing layer have been quantified using a combination of experimental techniques. The streamwise interfacial and spanwise interfacial perturbations were measured using high-resolution thermocouples and planar laser-induced fluorescence (PLIF), respectively. The initial multi-mode streamwise velocity perturbations at the two-fluid density interface were measured using particle-image velocimetry (PIV). It was found that the measured initial conditions describe an initially anisotropic state, in which the perturbations in the streamwise and spanwise directions are independent of one another. The evolution of various fluctuating velocity and density statistics, together with velocity and density variance spectra, were measured using PIV and high-resolution thermocouple data. The evolution of the velocity and density statistics is used to investigate the early-time evolution and the onset of strongly-nonlinear, transitional dynamics within the mixing layer. The early-time evolution of the density and vertical velocity variance spectra indicate that velocity fluctuations are the dominant mechanism driving the instability development. The implications of the present experimental measurements on the initialization of Reynolds-averaged turbulent transport and mixing models and of direct and large-eddy simulations of Rayleigh-Taylor instability-induced turbulence are discussed.
Schilling, Oleg; Mueschke, Nicholas; Latini, Marco; Don, Wai Sun; Andrews, Malcolm
2006-11-01
Gradient-diffusion models of turbulent transport in Rayleigh- Taylor and Richtmyer-Meshkov instability-induced mixing are assessed using direct numerical simulation (DNS) and implicit large-eddy simulation (ILES) data. Mean and fluctuating fields, defined from spatial averages over the periodic directions of the DNS, are used to construct the unclosed terms in the turbulent kinetic energy transport equation. These terms are then compared a priori with the corresponding terms modeled using the gradient-diffusion approximation to assess the validity of this approximation for these buoyancy- and shock- driven flows. Implications for two-equation turbulence modeling of Rayleigh-Taylor and Richtmyer-Meshkov instability-induced mixing are discussed. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48. This research was also sponsored by the National Nuclear Security Administration under the Stewardship Science Academic Alliances Program through DOE Research Grant No. DE-FG03- 02NA00060. UCRL-ABS-223369
Stabilization of the Rayleigh-Taylor instability in quantum magnetized plasmas
Wang, L. F.; Ye, W. H.; He, X. T. [HEDPS and CAPT, Peking University, Beijing 100871 (China); Institute of Applied Physics and Computational Mathematics, Beijing 100088 (China); Yang, B. L. [Institute of Applied Physics and Computational Mathematics, Beijing 100088 (China); Graduate School, China Academy of Engineering Physics, Beijing 100088 (China)
2012-07-15
In this research, stabilization of the Rayleigh-Taylor instability (RTI) due to density gradients, magnetic fields, and quantum effects, in an ideal incompressible plasma, is studied analytically and numerically. A second-order ordinary differential equation (ODE) for the RTI including quantum corrections, with a continuous density profile, in a uniform external magnetic field, is obtained. Analytic expressions of the linear growth rate of the RTI, considering modifications of density gradients, magnetic fields, and quantum effects, are presented. Numerical approaches are performed to solve the second-order ODE. The analytical model proposed here agrees with the numerical calculation. It is found that the density gradients, the magnetic fields, and the quantum effects, respectively, have a stabilizing effect on the RTI (reduce the linear growth of the RTI). The RTI can be completely quenched by the magnetic field stabilization and/or the quantum effect stabilization in proper circumstances leading to a cutoff wavelength. The quantum effect stabilization plays a central role in systems with large Atwood number and small normalized density gradient scale length. The presence of external transverse magnetic fields beside the quantum effects will bring about more stability on the RTI. The stabilization of the linear growth of the RTI, for parameters closely related to inertial confinement fusion and white dwarfs, is discussed. Results could potentially be valuable for the RTI treatment to analyze the mixing in supernovas and other RTI-driven objects.
The Experimental Study of Rayleigh-Taylor Instability using a Linear Induction Motor Accelerator
Yamashita, Nicholas; Jacobs, Jeffrey
2009-11-01
The experiments to be presented utilize an incompressible system of two stratified miscible liquids of different densities that are accelerated in order to produce the Rayleigh-Taylor instability. Three liquid combinations are used: isopropyl alcohol with water, a calcium nitrate solution or a lithium polytungstate solution, giving Atwood numbers of 0.11, 0.22 and 0.57, respectively. The acceleration required to drive the instability is produced by two high-speed linear induction motors mounted to an 8 m tall drop tower. The motors are mounted in parallel and have an effective acceleration length of 1.7 m and are each capable of producing 15 kN of thrust. The liquid system is contained within a square acrylic tank with inside dimensions 76 x76x184 mm. The tank is mounted to an aluminum plate, which is driven by the motors to create constant accelerations in the range of 1-20 g's, though the potential exists for higher accelerations. Also attached to the plate are a high-speed camera and an LED backlight to provide continuous video of the instability. In addition, an accelerometer is used to provide acceleration measurements during each experiment. Experimental image sequences will be presented which show the development of a random three-dimensional instability from an unforced initial perturbation. Measurements of the mixing zone width will be compared with traditional growth models.
Investigating iron material strength up to 1 Mbar using Rayleigh-Taylor growth measurements
Huntington, C. M.; Belof, J. L.; Blobaum, K. J. M.; Cavallo, R. M.; Kostinski, N. B.; Maddox, B. R.; Park, H.-S.; Plechaty, C.; Prisbrey, S. T.; Rudd, R.; Swift, D. W.; Wallace, R. J.; Weber, S. V.; Wehrenberg, C.; Wilson, M. J.; Remington, B. A.
2017-01-01
The solid-solid phase transition between the bcc (α) and hcp (ɛ) lattice structures in iron is known to occur as the material is compressed. When kept below its melting point, an effective increase in the macroscopic strength of the material accompanies this phase transition. Understanding the material strength of iron throughout the deformation process presents a significant computational challenge, but is important for improving models of planetary structure, including interpretation of seismic measurements taken through our own Earth's core. To explore the strength of iron at high pressures and strain rates, we have developed the IronRT campaign at the OMEGA laser [1]. This laser-driven platform produces pressure greater than 1 Mbar on a thin Fe disk with a sinusoidal ripple pattern imposed on its face. These ripples seed the Rayleigh-Taylor (RT) instability, the growth of which is suppressed by the material strength of the sample. The amplitude of the ripples is diagnosed with high-energy x-ray radiography, and the measured growth is compared to simulations performed with different strength models. By matching the simulations to the low level of growth measured, we infer an average flow stress of greater than 40 GPa over the course of the experiment. This value is in agreement with other dynamic iron strength experiments at pressures greater than 1 Mbar [2].
On hot-wire diagnostics in Rayleigh-Taylor mixing layers
Kraft, Wayne N. [Texas A and M University, Department of Mechanical Engineering, College Station, TX (United States); Banerjee, Arindam [Missouri University of Science and Technology, Department of Mechanical and Aerospace Engineering, Rolla, MO (United States); Andrews, Malcolm J. [Texas A and M University, Department of Mechanical Engineering, College Station, TX (United States); Los Alamos National Laboratory, NM (United States)
2009-07-15
Two hot-wire flow diagnostics have been developed to measure a variety of turbulence statistics in the buoyancy driven, air-helium Rayleigh-Taylor mixing layer. The first diagnostic uses a multi-position, multi-overheat (MPMO) single wire technique that is based on evaluating the wire response function to variations in density, velocity and orientation, and gives time-averaged statistics inside the mixing layer. The second diagnostic utilizes the concept of temperature as a fluid marker, and employs a simultaneous three-wire/cold-wire anemometry technique (S3WCA) to measure instantaneous statistics. Both of these diagnostics have been validated in a low Atwood number (A{sub t}{<=} 0.04), small density difference regime, that allowed validation of the diagnostics with similar experiments done in a hot-water/cold-water water channel facility. Good agreement is found for the measured growth parameters for the mixing layer, velocity fluctuation anisotropy, velocity fluctuation p.d.f behavior, and measurements of molecular mixing. We describe in detail the MPMO and S3WCA diagnostics, and the validation measurements in the low Atwood number regime (A{sub t}{<=} 0.04). We also outline the advantages of each technique for measurement of turbulence statistics in fluid mixtures with large density differences. (orig.)
Rayleigh-Taylor finger instability mixing in hydrodynamic shell convection models
Mocak, Miroslav
2010-01-01
Mixing processes in stars driven by composition gradients as a result of the Rayleigh-Taylor instability are not anticipated. They are supported only by hydrodynamic studies of stellar convection. We find that such mixing occurs below the bottom edge of convection zones in our multidimensional hydrodynamic shell convection models. It operates at interfaces created by off-center nuclear burning, where less dense gas with higher mean molecular weight is located above denser gas with a lower mean molecular weight. We discuss the mixing under various conditions with hydrodynamic convection models based on stellar evolutionary calculations of the core helium flash in a 1.25 Msun star, the core carbon flash in a 9.3 Msun star, and of oxygen burning shell in a star with a mass of 23 Msun. We simulate the hydrodynamic behavior of shell convection during various phases of stellar evolution with the Eulerian hydrodynamics code HERAKLES in two and three spatial dimensions. Initial models for this purpose are obtained by...
Large eddy simulation of Rayleigh-Taylor instability using the arbitrary Lagrangian-Eulerian method
Darlington, R
1999-12-01
This research addresses the application of a large eddy simulation (LES) to Arbitrary Lagrangian Eulerian (ALE) simulations of Rayleigh-Taylor instability. First, ALE simulations of simplified Rayleigh-Taylor instability are studied. The advantages of ALE over Eulerian simulations are shown. Next, the behavior of the LES is examined in a more complicated ALE simulation of Rayleigh-Taylor instability. The effects of eddy viscosity and stochastic backscatter are examined. The LES is also coupled with ALE to increase grid resolution in areas where it is needed. Finally, the methods studied above are applied to two sets of experimental simulations. In these simulations, ALE allows the mesh to follow expanding experimental targets, while LES can be used to mimic the effect of unresolved instability modes.
Ducros, F.
1996-06-12
Here is a study about fluid flows (the hydrodynamic part of codes modeling the plasma dynamics) showing great gradients and unsteady flows (Rayleigh-Taylor, Richtmyer-Meshkov). The numerical resolution of these problems needs codes able to simulate the transition at the turbulence. The code exposed here (NSMP), tries to answer to these demands by the resolution of Navier-Stokes equations. After the resolution of these equations are presented the consequences of the discretization of continuous equations of fluids mechanics and then a modeling of turbulence is introduced. The two last chapters are devoted to the simulation of Rayleigh-Taylor instabilities. (N.C.). 34 refs., 39 figs., 8 colour plates.
Three-dimensional Rayleigh-Taylor instability analysis of implosion system with scientific animation
Sakagami, Hitoshi [Himeji Inst. of Tech., Hyogo (Japan)
1999-05-01
A fully three-dimensional Rayleigh-Taylor instability taking place at the pusher-fuel contact surface in spherically stagnating systems has been investigated. Scientific color animations were rendered and constructed from the simulation results. At first, the rendering algorithm for an isovalue surface is discussed, and then the construction methods for scientific color animation are summarized by comparing analog based animation systems and digital ones. It is showed that the nonlinear dynamics of the Rayleigh-Taylor instability are characterized by vortex rings that are induced in bubble-spike structures with the use of scientific animation analysis. (author)
Toward analytic theory of the Rayleigh-Taylor instability: lessons from a toy model
Mailybaev, Alexei A
2016-01-01
In this work we suggest that a turbulent phase of the Rayleigh-Taylor instability can be explained as a universal stochastic wave traveling with constant speed in a properly renormalized system. This wave, originating from ordinary deterministic chaos in a renormalized time, has two constant limiting states at both sides. These states are related to the initial discontinuity at large scales and to stationary turbulence at small scales. The theoretical analysis is confirmed with extensive numerical simulations made for a new shell model, which features all basic properties of the phenomenological theory for the Rayleigh-Taylor instability.
Smalyuk, V A
2012-06-07
Rayleigh-Taylor (RT) instability is one of the major concerns in inertial confinement fusion (ICF) because it amplifies target modulations in both acceleration and deceleration phases of implosion, which leads to shell disruption and performance degradation of imploding targets. This article reviews experimental results of the RT growth experiments performed on OMEGA laser system, where targets were driven directly with laser light. RT instability was studied in the linear and nonlinear regimes. The experiments were performed in acceleration phase, using planar and spherical targets, and in deceleration phase of spherical implosions, using spherical shells. Initial target modulations consisted of 2-D pre-imposed modulations, and 2-D and 3-D modulations imprinted on targets by the non-uniformities in laser drive. In planar geometry, the nonlinear regime was studied using 3-D modulations with broadband spectra near nonlinear saturation levels. In acceleration-phase, the measured modulation Fourier spectra and nonlinear growth velocities are in good agreement with those predicted by Haan's model [Haan S W 1989 Phys. Rev. A 39 5812]. In a real-space analysis, the bubble merger was quantified by a self-similar evolution of bubble size distributions [Oron D et al 2001 Phys. Plasmas 8, 2883]. The 3-D, inner-surface modulations were measured to grow throughout the deceleration phase of spherical implosions. RT growth rates are very sensitive to the drive conditions, therefore they can be used to test and validate drive physics in hydrodynamic codes used to design ICF implosions. Measured growth rates of pre-imposed 2-D target modulations below nonlinear saturation levels were used to validate non-local thermal electron transport model in laser-driven experiments.
Indirect drive ablative Rayleigh-Taylor experiments with rugby hohlraums on OMEGA
Casner, A.; Galmiche, D.; Huser, G.; Jadaud, J.-P.; Liberatore, S.; Vandenboomgaerde, M.
2009-09-01
Results of ablative Rayleigh-Taylor instability growth experiments performed in indirect drive on the OMEGA laser facility [T. R. Boehly, D. L. Brown, S. Craxton et al., Opt. Commun. 133, 495 (1997)] are reported. These experiments aim at benchmarking hydrocodes simulations and ablator instabilities growth in conditions relevant to ignition in the framework of the Laser MégaJoule [C. Cavailler, Plasma Phys. Controlled Fusion 47, 389 (2005)]. The modulated samples under study were made of germanium-doped plastic (CHGe), which is the nominal ablator for future ignition experiments. The incident x-ray drive was provided using rugby-shaped hohlraums [M. Vandenboomgaerde, J. Bastian, A. Casner et al., Phys. Rev. Lett. 99, 065004 (2007)] and was characterized by means of absolute time-resolved soft x-ray power measurements through a dedicated diagnostic hole, shock breakout data and one-dimensional and two-dimensional (2D) side-on radiographies. All these independent x-ray drive diagnostics lead to an actual on-foil flux that is about 50% smaller than laser-entrance-hole measurements. The experimentally inferred flux is used to simulate experimental optical depths obtained from face-on radiographies for an extensive set of initial conditions: front-side single-mode (wavelength λ =35, 50, and 70 μm) and two-mode perturbations (wavelength λ =35 and 70 μm, in phase or in opposite phase). Three-dimensional pattern growth is also compared with the 2D case. Finally the case of the feedthrough mechanism is addressed with rear-side modulated foils.
Lattice Boltzmann simulation of three-dimensional Rayleigh-Taylor instability
Liang, H.; Li, Q. X.; Shi, B. C.; Chai, Z. H.
2016-03-01
In this paper, the three-dimensional (3D) Rayleigh-Taylor instability (RTI) with low Atwood number (At=0.15 ) in a long square duct (12 W ×W ×W ) is studied by using a multiple-relaxation-time lattice Boltzmann (LB) multiphase model. The effect of the Reynolds number on the interfacial dynamics and bubble and spike amplitudes at late time is investigated in detail. The numerical results show that at sufficiently large Reynolds numbers, a sequence of stages in the 3D immiscible RTI can be observed, which includes the linear growth, terminal velocity growth, reacceleration, and chaotic development stages. At late stage, the RTI induces a very complicated topology structure of the interface, and an abundance of dissociative drops are also observed in the system. The bubble and spike velocities at late stage are unstable and their values have exceeded the predictions of the potential flow theory [V. N. Goncharov, Phys. Rev. Lett. 88, 134502 (2002), 10.1103/PhysRevLett.88.134502]. The acceleration of the bubble front is also measured and it is found that the normalized acceleration at late time fluctuates around a constant value of 0.16. When the Reynolds number is reduced to small values, some later stages cannot be reached sequentially. The interface becomes relatively smoothed and the bubble velocity at late time is approximate to a constant value, which coincides with the results of the extended Layzer model [S.-I. Sohn, Phys. Rev. E 80, 055302(R) (2009), 10.1103/PhysRevE.80.055302] and the modified potential theory [R. Banerjee, L. Mandal, S. Roy, M. Khan, and M. R. Guptae, Phys. Plasmas 18, 022109 (2011), 10.1063/1.3555523]. In our simulations, the Graphics Processing Unit (GPU) parallel computing is also used to relieve the massive computational cost.
Ivanov, A.A
2001-06-01
The instabilities of Rayleigh-Taylor type are considered in the thesis. The topic of the thesis was inspired by recent advances in the physics of plasma compression, especially with the aid of systems like Z-pinch. Rayleigh-Taylor instability (RTI) plays an important role in the evolution of magnetized plasmas in these experiments, as well as in stellar plasmas and classic fluids. For the phenomena concerning the nuclear fusion the RTI is very often the factor limiting the possibility of compression. In the current work we try to examine in detail the characteristic features of the instabilities of this type in order to eliminate their detrimental influence. In this thesis we are studying both the general case of the 'classic' Rayleigh-Taylor instability (in incompressible fluids) and more specific cases of the instabilities of Rayleigh-Taylor type in magnetized plasmas, in the liners or wire array implosions etc. We have studied the influence of the Hall diffusion of magnetic field on the growth rate of the instability. We have obtained in this work a self-similar solution for the widening of the initial profile of the magnetic field and for the wave of the penetration of magnetic field. After that the subsequent evolution of the magnetic field in plasma opening switches (POS) has been examined. We have shown the possibility of the existence of a strong rarefaction wave for collisional and non-collisional cases. This wave can explain the phenomenon of the opening of POS. The effect of the suppression of Rayleigh-Taylor instability by forced oscillations of the boundary between two fluids permits us to propose some ideas for the experiments of inertial fusion. We have considered the general case of the instability, in other words, two incompressible viscous superposed fluids in a gravitational field. We have obtained an exact analytical expression for the growth rate and then we have analyzed the influence of the parameters of external &apos
Wu, Dong; Qiao, B; Zhou, C T; Yan, X Q; Yu, M Y; He, X T
2014-01-01
It is shown that the transverse Rayleigh-Taylor-like (RT) instability in the hole boring radiation pressure acceleration can be suppressed by using elliptically polarized (EP) laser. A moderate ${J}\\times{B}$ heating of the EP laser will thermalize the local electrons, which leads to the transverse diffusion of ions, suppressing the short wavelength perturbations of RT instability. A proper condition of polarization ratio is obtained analytically for the given laser intensity and plasma density. The idea is confirmed by two dimensional Particle-in-Cell simulations, showing that the ion beam driven by the EP laser is more concentrated and intense compared with that of the circularly polarized laser.
Egly, H
2007-10-15
This thesis deals with the dynamics of accelerated ablative front spreading in Inertial Confinement Fusion experiments. ICF is designed for the implosion of a deuterium-tritium spherical target. The outer shell, the ablator, is irradiated providing a high level pressure inside the target. During this first stage, the ablation front propagating inwards is perturbed by hydrodynamics instabilities, which can prevent the fusion reaction in the decelerated stage. We propose here a study on Rayleigh-Taylor instabilities during ablation process, in the two dimensional case. In order to obtain a numerical solution, we perform an asymptotic analysis in the limit of a high temperature ratio, between the remaining cold ablator and the hot ablated plasma. This study is divided in two steps. First, the thermo-diffusive part of the set of equations is approximated by a Hele-Shaw model, which is then perturbed by the hydrodynamics part. Using a vortex method, we have to solve the advection of a vortical sheet moving with the ablation front. We compute the numerical solution on an Eulerian mesh coupled with a marker method. The thermal part is computed by implementing the Fat Boundary Method, recently developed. The hydrodynamic part is obtained from a Finite Volume scheme. (author)
Andrei, A. Ivanov
2001-06-15
In this thesis we're studying both the general case of the 'classic' Rayleigh-Taylor instability (in incompressible fluids) and more specific cases of the instabilities of Rayleigh-Taylor type in magnetized plasmas, in the liners or wire array implosions etc. We have studied the influence of the Hall diffusion of magnetic field on the growth rate of the instability. We have obtained in this work a self-similar solution for the widening of the initial profile of the magnetic field and for the wave of the penetration of magnetic field. After that the subsequent evolution of the magnetic field in plasma opening switches (POS) has been examined. We have shown the possibility of the existence of a strong rarefaction wave for collisional and non-collisional cases. This wave can explain the phenomenon of the opening of POS. The effect of the suppression of Rayleigh-Taylor instability by forced oscillations of the boundary between two fluids permits us to propose some ideas for the experiments of inertial fusion. We have considered the general case of the instability, in other words - two incompressible viscous superposed fluids in a gravitational field. We have obtained an exact analytical expression for the growth rate and then we have analyzed the influence of the parameters of external 'pumping' on the instability. These results can be applied to a wide range of systems, starting from classic hydrodynamics and up to astrophysical plasmas. The scheme of wire arrays has become recently a very popular method to obtain a high power X-radiation or for a high quality implosion in Z-pinches. The experimental studies have demonstrated that the results of implosion are much better for the case of multiple thin wires situated cylindrically than in a usual liner scheme. We have examined the problem modeling the stabilization of Rayleigh-Taylor instability for a wire array system. The reason for instability suppression is the regular spatial modulation of
Mueschke, N; Schilling, O
2008-07-23
A 1152 x 760 x 1280 direct numerical simulation (DNS) using initial conditions, geometry, and physical parameters chosen to approximate those of a transitional, small Atwood number Rayleigh-Taylor mixing experiment [Mueschke, Andrews and Schilling, J. Fluid Mech. 567, 27 (2006)] is presented. The density and velocity fluctuations measured just off of the splitter plate in this buoyantly unstable water channel experiment were parameterized to provide physically-realistic, anisotropic initial conditions for the DNS. The methodology for parameterizing the measured data and numerically implementing the resulting perturbation spectra in the simulation is discussed in detail. The DNS model of the experiment is then validated by comparing quantities from the simulation to experimental measurements. In particular, large-scale quantities (such as the bubble front penetration hb and the mixing layer growth parameter {alpha}{sub b}), higher-order statistics (such as velocity variances and the molecular mixing parameter {theta}), and vertical velocity and density variance spectra from the DNS are shown to be in favorable agreement with the experimental data. Differences between the quantities obtained from the DNS and from experimental measurements are related to limitations in the dynamic range of scales resolved in the simulation and other idealizations of the simulation model. This work demonstrates that a parameterization of experimentally-measured initial conditions can yield simulation data that quantitatively agrees well with experimentally-measured low- and higher-order statistics in a Rayleigh-Taylor mixing layer. This study also provides resolution and initial conditions implementation requirements needed to simulate a physical Rayleigh-Taylor mixing experiment. In Part II [Mueschke and Schilling, Phys. Fluids (2008)], other quantities not measured in the experiment are obtained from the DNS and discussed, such as the integral- and Taylor-scale Reynolds numbers
LI Zhang-Guo; LIU Qiu-Sheng; LIU Rong; HU Wei; DENG Xin-Yu
2009-01-01
A computational simulation is conducted to investigate the influence of Rayleigh-Taylor instability on liquid propellant reorientation flow dynamics for the tank of CZ-3A launch vehicle series fuel tanks in a low-gravity environment. The volume-of-fluid (VOF) method is used to simulate the free surface flow of gas-liquid. The process of the liquid propellant reorientation started from initially fiat and curved interfaces are numerically studied. These two different initial conditions of the gas-liquid interface result in two modes of liquid flow. It is found that the Rayleigh-Taylor instability can be reduced evidently at the initial gas-liquid interface with a high curve during the process of liquid reorientation in a low-gravity environment.
Large-eddy-simulation of 3-dimensional Rayleigh-Taylor instability in incompressible fluids
无
2002-01-01
The 3-dimensional incompressible Rayleigh-Taylor instability is numerically studied through the large-eddy-simulation (LES) approach based on the passive scalar transport model. Both the instantaneous velocity and the passive scalar fields excited by sinusoidal perturbation and random perturbation are simulated. A full treatment of the whole evolution process of the instability is addressed. To verify the reliability of the LES code, the averaged turbulent energy as well as the flux of passive scalar are calculated at both the resolved scale and the subgrid scale. Our results show good agreement with the experimental and other numerical work. The LES method has proved to be an effective approach to the Rayleigh-Taylor instability.
Mitigation Effect of Finite Larmor Radius on Rayleigh-Taylor Instability in Z-Pinch Implosions
邱孝明; 黄林; 简广德
2002-01-01
Based on the framework of magnetohydrodynamic theory, a simple model is proposed to study the mitigation effect of finite Larmor radius on the Rayleigh-Taylor instability in Z-pinch implosions. In this model, taking account of Ti ≥ Te in Z-pinch implosions we believe that the magnetohydrodynamic plasma responds to a perturbation (～ exp [i (k. x - ωt)]) at frequency (ω + ik2⊥ρ2iΩi) instead of frequency ω, where k2⊥ρ2i is due to the finite Larmor radius effects expressed from the generalkinetic theory of magnetized plasma. Therefore the linearized continuity and momentum equations for the perturbed mass-density and velocity include the finite Larmor radius effects. The calculations indicate that, in the wavenumber region of interest, the finite Larmor radius effects can mitigate the Rayleigh-Taylor instability in Z-pinch implosions.
Study on Electrohydrodynamic Rayleigh-Taylor Instability with Heat and Mass Transfer
Mukesh Kumar Awasthi
2014-01-01
Full Text Available The linear analysis of Rayleigh-Taylor instability of the interface between two viscous and dielectric fluids in the presence of a tangential electric field has been carried out when there is heat and mass transfer across the interface. In our earlier work, the viscous potential flow analysis of Rayleigh-Taylor instability in presence of tangential electric field was studied. Here, we use another irrotational theory in which the discontinuities in the irrotational tangential velocity and shear stress are eliminated in the global energy balance. Stability criterion is given by critical value of applied electric field as well as critical wave number. Various graphs have been drawn to show the effect of various physical parameters such as electric field, heat transfer coefficient, and vapour fraction on the stability of the system. It has been observed that heat transfer and electric field both have stabilizing effect on the stability of the system.
Ablative Stabilization of the Deceleration-Phase Rayleigh-Taylor Instability, control No. 2000-107
Lobatchev, V.; Betti, R.
2000-10-01
The growth rates of the deceleration-phase Rayleigh-Taylor instability for imploding inertial confinement fusion capsules are calculated and compared with the results of numerical simulations. It is found that the unstable spectrum and the growth rates are significantly reduced by the finite ablation flow at the shell's inner surface. For typical direct-drive capsules designed for the National Ignition Facility, the unstable spectrum exhibits a cutoff for {ell} {approx} 90.
Nonlinear Rayleigh--Taylor instability of the cylindrical fluid flow with mass and heat transfer
ALY R SEADAWY; K EL-RASHIDY
2016-08-01
The nonlinear Rayleigh--Taylor stability of the cylindrical interface between the vapour and liquid phases of a fluid is studied. The phases enclosed between two cylindrical surfaces coaxial with mass and heat transfer is derived from nonlinear Ginzburg--Landau equation. The F-expansion method is used to get exactsolutions for a nonlinear Ginzburg--Landau equation. The region of solutions is displayed graphically.
Numerical simulations of compressible Rayleigh-Taylor turbulence in stratified fluids
Scagliarini, A; Sbragaglia, M; Sugiyama, K; Toschi, F
2010-01-01
We present results from numerical simulations of Rayleigh-Taylor turbulence, performed using a recently proposed lattice Boltzmann method able to describe consistently a thermal compressible flow subject to an external forcing. The method allowed us to study the system both in the nearly-Boussinesq and strongly compressible regimes. Moreover, we show that when the stratification is important, the presence of the adiabatic gradient causes the arrest of the mixing process.
A new approach to Rayleigh-Taylor instability: Application to accelerated elastic solids
Piriz, A.R. [E.T.S.I. Industriales, Universidad de Castilla - La Mancha, 13071 Ciudad Real (Spain)]. E-mail: roberto.piriz@uclm.es; Lopez Cela, J.J. [E.T.S.I. Industriales, Universidad de Castilla - La Mancha, 13071 Ciudad Real (Spain); Serna Moreno, M.C. [E.T.S.I. Industriales, Universidad de Castilla - La Mancha, 13071 Ciudad Real (Spain); Cortazar, O.D. [E.T.S.I. Industriales, Universidad de Castilla - La Mancha, 13071 Ciudad Real (Spain); Tahir, N.A. [Gesellschaft fuer Schwerionenforschung, 64291 Darmstadt (Germany); Hoffmann, D.H.H. [Gesellschaft fuer Schwerionenforschung, 64291 Darmstadt (Germany); Institut fuer Kernephysik, Technische Universitaet of Darmstadt, 64289 Darmstadt (Germany)
2007-07-01
A new approach to Rayleigh-Taylor instability based on the Newton second law is presented. The model is applied to the instability analysis of elastic solid/viscous fluid interfaces. The effect of the thickness of the elastic medium is studied by considering a thin elastic plate. The importance of the initial transient phase that takes place before reaching the asymptotic regime is also shown.
Direct numerical simulations of type Ia supernovae flames II: The Rayleigh-Taylor instability
Bell, J.B.; Day, M.S.; Rendleman, C.A.; Woosley, S.E.; Zingale, M.
2004-01-12
A Type Ia supernova explosion likely begins as a nuclear runaway near the center of a carbon-oxygen white dwarf. The outward propagating flame is unstable to the Landau-Darrieus, Rayleigh-Taylor, and Kelvin-Helmholtz instabilities, which serve to accelerate it to a large fraction of the speed of sound. We investigate the Rayleigh-Taylor unstable flame at the transition from the flamelet regime to the distributed-burning regime, around densities of 10e7 gm/cc, through detailed, fully resolved simulations. A low Mach number, adaptive mesh hydrodynamics code is used to achieve the necessary resolution and long time scales. As the density is varied, we see a fundamental change in the character of the burning--at the low end of the density range the Rayleigh-Taylor instability dominates the burning, whereas at the high end the burning suppresses the instability. In all cases, significant acceleration of the flame is observed, limited only by the size of the domain we are able to study. We discuss the implications of these results on the potential for a deflagration to detonation transition.
无
2003-01-01
A hybrid model of MHD and kinetic theory is proposed to investigate the synergetic stabilizing effects of sheared axial flow and finite Larmor radius on the Rayleigh-Taylor instability in Z-pinch implosions.In our model the MHD plasma is considered to respond to a perturbation with exp[i(k*x-ωt)] at frequency ω+ik2⊥ρ2iΩi instead of frequency ω,where k2⊥ρ2i is the finite Larmor radius effects given from the general kinetic theory of magnetized plasma.Therefore linearized continuity and momentum equations include automatically the finite Larmor radius effects.Dispersion relation is derived,which includes the effects of a density discontinuity and the finite Larmor radius as well as a sheared flow that produces the Kelvin-Helmholtz instability.The dispersion equation is examined in three cases.The results indicate that the synergetic effect of sheared axial flow and the finite Larmor radius can mitigate both the Rayleigh-Taylor instability and the hybrid Rayleigh-Taylor/Kelvin-Helmholtz instability.Moreover,the synergetic mitigation effect is stronger than either of them acting separately.
Adams, Colin Stuart [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Univ. of New Mexico, Albuquerque, NM (United States)
2015-01-15
The Rayleigh-Taylor instability causes mixing in plasmas throughout the universe, from micron-scale plasmas in inertial confinement fusion implosions to parsec-scale supernova remnants. The evolution of this interchange instability in a plasma is influenced by the presence of viscosity and magnetic fields, both of which have the potential to stabilize short-wavelength modes. Very few experimental observations of Rayleigh-Taylor growth in plasmas with stabilizing mechanisms are reported in the literature, and those that are reported are in sub-millimeter scale plasmas that are difficult to diagnose. Experimental observations in well-characterized plasmas are important for validation of computational models used to make design predictions for inertial confinement fusion efforts. This dissertation presents observations of instability growth during the interaction between a high Mach-number, initially un-magnetized plasma jet and a stagnated, magnetized plasma. A multi-frame fast camera captures Rayleigh-Taylor-instability growth while interferometry, spectroscopy, photodiode, and magnetic probe diagnostics are employed to estimate plasma parameters in the vicinity of the collision. As the instability grows, an evolution to longer mode wavelength is observed. Comparisons of experimental data with idealized magnetohydrodynamic simulations including a physical viscosity model suggest that the observed instability evolution is consistent with both magnetic and viscous stabilization. These data provide the opportunity to benchmark computational models used in astrophysics and fusion research.
Adams, Colin Stuart [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Univ. of New Mexico, Albuquerque, NM (United States); Univ. of Washington, Seattle, WA (United States)
2015-01-15
The Rayleigh-Taylor instability causes mixing in plasmas throughout the universe, from micron-scale plasmas in inertial confinement fusion implosions to parsec-scale supernova remnants. The evolution of this interchange instability in a plasma is influenced by the presence of viscosity and magnetic fields, both of which have the potential to stabilize short-wavelength modes. Very few experimental observations of Rayleigh-Taylor growth in plasmas with stabilizing mechanisms are reported in the literature, and those that are reported are in sub-millimeter scale plasmas that are difficult to diagnose. Experimental observations in well-characterized plasmas are important for validation of computational models used to make design predictions for inertial confinement fusion efforts. This dissertation presents observations of instability growth during the interaction between a high Mach-number, initially un-magnetized plasma jet and a stagnated, magnetized plasma. A multi-frame fast camera captures Rayleigh-Taylor-instability growth while interferometry, spectroscopy, photodiode, and magnetic probe diagnostics are employed to estimate plasma parameters in the vicinity of the collision. As the instability grows, an evolution to longer mode wavelength is observed. Comparisons of experimental data with idealized magnetohydrodynamic simulations including a physical viscosity model suggest that the observed instability evolution is consistent with both magnetic and viscous stabilization. These data provide the opportunity to benchmark computational models used in astrophysics and fusion research.
Rayleigh-Taylor-Induced Electromagnetic Fields in Laser-Produced Plasmas
Manuel, Mario J.-E.
Spontaneous electromagnetic fields can be important to the dynamic evolution of a plasma by directing heat flow as well as providing additional pressures on the conducting fluids through the Lorentz force. Electromagnetic fields are predicted to affect fluid behavior during the core-collapse of supernovae through generation of fields due to hydrodynamic instabilities. In the coronae of stars, self-generated magnetic fields lead to filamentary structure in the hot plasma. Recent experiments by Gregori et al. investigated sources of protogalactic magnetic fields generated by laser-produced shock waves. In inertial confinement fusion experiments, self-generated electromagnetic fields can also play a role and have recently become of great interest to the community. Present day laser facilities provide a unique opportunity to study spontaneous field-generation in these extreme environments under controlled conditions. Instability-induced electromagnetic fields were investigated using a novel monoenergetic-proton radiography system. Fusion protons generated by an 'exploding-pusher' implosion were used to probe laser-irradiated plastic foils with various preimposed surface perturbations. Imaging protons are sensitive to electromagnetic fields and density modulations in the plasma through the Lorentz force and Coulomb collisions, respectively. Corresponding x-ray radiographs of these targets provided mass density distributions and Coulomb effects on protons were assessed using a Monte Carlo code written using the Geant4 framework. Proton fluence distributions were recorded on CR-39 detectors and Fourier analyzed to infer path-integrated field strengths. Rayleigh-Taylor (RT) growth of preimposed surface perturbations generated magnetic fields by the RT-induced Biermann battery and were measured for the first time. Good data were obtained during linear growth and when compared to ideal calculations, demonstrated that field diffusion near the source played an important role
Weis, Matthew R.
Cylindrical liner implosions in the Magnetized Liner Inertial Fusion (MagLIF) concept are susceptible to the magneto-Rayleigh-Taylor instability (MRT). The danger of MRT enters in two phases, (1) during the main implosion, the outer surface of the liner is MRT unstable, and (2) during the short time period when the liner decelerates onto hot fuel, the inner surface becomes unstable. Growth of MRT on the outer surface may also feedthrough, which may seed the inner surface leading to high MRT growth in the second phase. If MRT growth becomes large enough, confinement of the fuel is lost. To characterize MRT we solve the linearized, ideal MHD equations in both planar and cylindrical geometries, including the presence of an axial magnetic field and the effects of sausage and kink modes (present in cylindrical coordinates only). In general, the total instability growth rates in cylindrical geometry are found to be larger than those in planar geometry. MRT and feedthrough is shown to be suppressed by strong magnetic field line bending (tension). However, for the same amount of field line bending, feedthrough is the most stabilized. Application of the planar and the cylindrical model to results from the Z-machine at Sandia National Laboratories is presented. Analytic MRT growth rates for a typical magnetized MagLIF-like implosion show the kink mode to be the fastest growing early and very late in the liner implosion (during deceleration). 1D HYDRA MHD simulations are used to generate realistic, evolving profiles (in density, pressure, and magnetic field) during the implosion from which instantaneous growth rates can be computed exactly, using either the planar or cylindrical analytic formulae developed in this thesis. Sophisticated 2D HYDRA MHD simulations were also performed to compare with the analytic theory and experimental results. In 2D, highly compressed axial magnetic fields can reduce the growth of perturbations at the fuel/liner interface during the implosion
Pandian, Arun; Swisher, Nora C.; Abarzhi, S. I.
2017-01-01
Rayleigh-Taylor (RT) mixing occurs in a variety of natural and man-made phenomena in fluids, plasmas and materials, from celestial event to atoms. In many circumstances, RT flows are driven by variable acceleration, whereas majority of existing studies have considered only sustained acceleration. In this work we perform detailed analytical and numerical study of RT mixing with a power-law time-dependent acceleration. A set of deterministic nonlinear non-homogeneous ordinary differential equations and nonlinear stochastic differential equations with multiplicative noise are derived on the basis of momentum model. For a broad range of parameters, self-similar asymptotic solutions are found analytically, and their statistical properties are studied numerically. We identify two sub-regimes of RT mixing dynamics depending on the acceleration exponent—the acceleration-driven mixing and dissipation-driven mixing. Transition between the sub-regimes is studied, and it is found that each sub-regime has its own characteristic dimensionless invariant quantity.
Casner, A.; Galmiche, D.; Huser, G.; Jadaud, J.P.; Richard, A.; Liberatore, S.; Vandenboomgaerde, M. [CEA Bruyeres-le-Chatel, 91 (France)
2009-07-01
The mastering of the development of hydrodynamic instabilities like Rayleigh-Taylor instabilities is an important milestone on the way to perform efficient laser implosions. The complexity of these instabilities implies an experimental validation of the theoretical models and their computer simulations. An experimental platform involving the Omega laser has allowed us to perform indirect drive with rugby-shaped hohlraums. The experiments have validated the growth of 2- and 3-dimensional initial defects as predicted by theory. We have shown that the 3-dimensional defect saturates for an higher amplitude than the 2-dimensional one does. The experiments have been made by using a plastic shell doped with Germanium (CH:Ge). (A.C.)
The viscous surface-internal wave problem: nonlinear Rayleigh-Taylor instability
Wang, Yanjin
2011-01-01
We consider the free boundary problem for two layers of immiscible, viscous, incompressible fluid in a uniform gravitational field, lying above a rigid bottom in a three-dimensional horizontally periodic setting. The effect of surface tension is either taken into account at both free boundaries or neglected at both. We are concerned with the Rayleigh-Taylor instability, so we assume that the upper fluid is heavier than the lower fluid. When the surface tension at the free internal interface is below a critical value, which we identify, we establish that the problem under consideration is nonlinearly unstable.
Combined effect of horizontal magnetic field and vorticity on Rayleigh Taylor instability
Banerjee, Rahul
2016-01-01
In this research, the height, curvature and velocity of the bubble tip in Rayleigh-Taylor instability at arbitrary Atwood number with horizontal magnetic field are investigated. To support the earlier simulation and experimental results, the vorticity generation inside the bubble is introduced. It is found that, in early nonlinear stage, the temporal evolution of the bubble tip parameters depend essentially on the strength and initial perturbation of the magnetic field, although the asymptotic nature coincides with the non magnetic case. The model proposed here agrees with the previous linear, nonlinear and simulation observations.
Proton Beam Fast Ignition Fusion: Synergy of Weibel and Rayleigh-Taylor Instabilities
Stefan, V. Alexander
2011-04-01
The proton beam generation and focusing in fast ignition inertial confinement fusion is studied. The spatial and energy spread of the proton beam generated in a laser-solid interaction is increased due to the synergy of Weibel and Rayleigh-Taylor instabilities. The focal spot radius can reach 100 μm, which is nearly an order of magnitude larger than the optimal value. The energy spread decreases the beam deposition energy in the focal spot. Under these conditions, ignition of a precompressed DT fuel is achieved with the beam powers much higher than the values presently in consideration. Work supported in part by NIKOLA TESLA Laboratories (Stefan University), La Jolla, CA.
Quantum Effects on Rayleigh-Taylor Instability of Incompressible Plasma in a Vertical Magnetic Field
G.A.Hoshoudy
2010-01-01
@@ Quantum effects on Rayleigh-Taylor instability of a stratified incompressible plasmas layer under the influence of vertical magnetic field are investigated.The solutions of the linearized equations of motion together with the boundary conditions lead to deriving the relation between square normalized growth rate and square normalized wawe number in two algebraic equations and are numerically analyzed.In the case of the real solution of these two equations,they can be combined to generate a single equation.The results show that the presence of vertical magnetic field beside the quantum effect will bring about more stability on the growth rate of unstable configuration.
Strong stabilization of the Rayleigh-Taylor instability by material strength at Mbar pressures
Park, H S; Lorenz, K T; Cavallo, R M; Pollaine, S M; Prisbrey, S T; Rudd, R E; Becker, R C; Bernier, J V; Remington, B A
2009-11-19
Experimental results showing significant reductions from classical in the Rayleigh-Taylor (RT) instability growth rate due to high pressure effective lattice viscosity are presented. Using a laser created ramped drive, vanadium samples are compressed and accelerated quasi-isentropically at {approx}1 Mbar pressures, while maintaining the sample in the solid-state. Comparisons with simulations and theory indicate that the high pressure, high strain rate conditions trigger a phonon drag mechanism, resulting in the observed high effective lattice viscosity and strong stabilization of the RT instability.
Reckinger, Scott James [Montana State Univ., Bozeman, MT (United States); Livescu, Daniel [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Vasilyev, Oleg V. [Univ. of Colorado, Boulder, CO (United States)
2016-09-02
A comprehensive numerical methodology has been developed that handles the challenges introduced by considering the compressive nature of Rayleigh-Taylor instability (RTI) systems, which include sharp interfacial density gradients on strongly stratified background states, acoustic wave generation and removal at computational boundaries, and stratification-dependent vorticity production. The computational framework is used to simulate two-dimensional single-mode RTI to extreme late-times for a wide range of flow compressibility and variable density effects. The results show that flow compressibility acts to reduce the growth of RTI for low Atwood numbers, as predicted from linear stability analysis.
Measurements of Magneto-Rayleigh-Taylor instability growth in solid liners on the 20 MA Z facility.
Bigman, Verle; Vesey, Roger Alan; Shores, Jonathon; Herrmann, Mark C.; Stamm, Robert (General Atomics, San Diego, CA); Killebrew, Korbie (General Atomics, San Diego, CA); Holt, Randy (General Atomics, San Diego, CA); Blue, Brent (General Atomics, San Diego, CA); Nakhleh, Charlie; McBride, Ryan D.; Leifeste, Gordon T.; Smith, Ian Craig; Stygar, William A.; Porter, John Larry, Jr.; Cuneo, Michael Edward; Bennett, Guy R.; Schroen, Diana Grace (General Atomics, San Diego, CA); Sinars, Daniel Brian; Lopez, Mike R.; Slutz, Stephen A.; Atherton, Briggs W.; Tomlinson, Kurt; Edens, Aaron D.; Savage, Mark Edward; Peterson, Kyle J.
2010-07-01
The magneto-Rayleigh-Taylor (MRT) instability is the most important instability for determining whether a cylindrical liner can be compressed to its axis in a relatively intact form, a requirement for achieving the high pressures needed for inertial confinement fusion (ICF) and other high energy-density physics applications. While there are many published RT studies, there are a handful of well-characterized MRT experiments at time scales >1 {micro}s and none for 100 ns z-pinch implosions. Experiments used solid Al liners with outer radii of 3.16 mm and thicknesses of 292 {micro}m, dimensions similar to magnetically-driven ICF target designs [1]. In most tests the MRT instability was seeded with sinusoidal perturbations ({lambda} = 200, 400 {micro}m, peak-to-valley amplitudes of 10, 20 {micro}m, respectively), wavelengths similar to those predicted to dominate near stagnation. Radiographs show the evolution of the MRT instability and the effects of current-induced ablation of mass from the liner surface. Additional Al liner tests used 25-200 {micro}m wavelengths and flat surfaces. Codes being used to design magnetized liner ICF loads [1] match the features seen except at the smallest scales (<50 {micro}m). Recent experiments used Be liners to enable penetrating radiography using the same 6.151 keV diagnostics and provide an in-flight measurement of the liner density profile.
Dan, Jia Kun; Huang, Xian Bin; Ren, Xiao Dong; Wei, Bing
2017-08-01
A theoretical model referring to mode selection of Z-pinch-driven magneto-Rayleigh-Taylor (MRT) instability, which explains the generation of fundamental instability mode and evolution of fundamental wavelength in experiments, is proposed on the basis of the Landau theory of phase transition. The basic idea of this phase transition model lies in that the appearance of MRT instability pattern can be considered as a consequence of the spontaneous generation of interfacial structure like the spontaneous magnetization in a ferromagnetic system. It is demonstrated that the amplitude of instability is responsible for the order parameter in the Landau theory of phase transition and the fundamental wavelength appears to play a role analogous to inverse temperature in thermodynamics. Further analysis indicates that the MRT instability is characterized by first order phase transition and the fundamental wavelength is proportional to the square root of energy entering into the system from the driving source. The theory predicts that the fundamental wavelength grows rapidly and saturates reaching a limiting wavelength of the order of the liner's final outer radius. The results given by this theory show qualitative agreement with the available experimental data of MRT instability of liner implosions conducted on the Sandia Z machine as well as Primary Test Stand facility at the Institute of Fluid Physics.
Fraschetti, Federico; Ballet, Jean; Decourchelle, Anne
2010-01-01
Context: The Rayleigh-Taylor instabilities generated by the deceleration of a supernova remnant during the ejecta-dominated phase are known to produce finger-like structures in the matter distribution which modify the geometry of the remnant. The morphology of supernova remnants is also expected to be modified when efficient particle acceleration occurs at their shocks. Aims: The impact of the Rayleigh-Taylor instabilities from the ejecta-dominated to the Sedov-Taylor phase is investigated over one octant of the supernova remnant. We also study the effect of efficient particle acceleration at the forward shock on the growth of the Rayleigh-Taylor instabilities. Methods: We modified the Adaptive Mesh Refinement code RAMSES to study with hydrodynamic numerical simulations the evolution of supernova remnants in the framework of an expanding reference frame. The adiabatic index of a relativistic gas between the forward shock and the contact discontinuity mimics the presence of accelerated particles. Results: The ...
Jian Guangde; Huang Lin; Qiu Xiaoming
2005-01-01
The assembling stabilizing effect of the finite Larmor radius (FLR) and the sheared axial flow (SAF) on the Rayleigh-Taylor instability in Z-pinch implosions is studied by means of the incompressible finite Larmor radius magnetohydrodynamic (MHD) equations. The finite Larmor radius effects are introduced in the momentum equation with the sheared axial flow through an anisotropic ion stress tensor. In this paper a linear mode equation is derived that is valid for arbitrary kL, where k is the wave number and L is the plasma shell thickness. Numerical solutions are presented. The results indicate that the short-wavelength modes of the RayleighTaylor instability are easily stabilized by the individual effect of the finite Larmor radius or the sheared axial flow. The assembling effects of the finite Larmor radius and sheared axial flow can heavily mitigate the Rayleigh-Taylor instability, and the unstable region can be compressed considerably.
Simulations of Rayleigh Taylor Instabilities in the presence of a Strong Radiative shock
Trantham, Matthew; Kuranz, Carolyn; Shvarts, Dov; Drake, R. P.
2016-10-01
Recent Supernova Rayleigh Taylor experiments on the National Ignition Facility (NIF) are relevant to the evolution of core-collapse supernovae in which red supergiant stars explode. Here we report simulations of these experiments using the CRASH code. The CRASH code, developed at the University of Michigan to design and analyze high-energy-density experiments, is an Eulerian code with block-adaptive mesh refinement, multigroup diffusive radiation transport, and electron heat conduction. We explore two cases, one in which the shock is strongly radiative, and another with negligible radiation. The experiments in all cases produced structures at embedded interfaces by the Rayleigh Taylor instability. The weaker shocked environment is cooler and the instability grows classically. The strongly radiative shock produces a warm environment near the instability, ablates the interface, and alters the growth. We compare the simulated results with the experimental data and attempt to explain the differences. This work is funded by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, Grant Number DE-NA0002956.
Analytical modeling of magnetic Rayleigh-Taylor instabilities in compressible fluids
Liberatore, Stéphane; Bouquet, Serge
2008-11-01
The magnetic Rayleigh-Taylor instability (MRTI) is investigated in the case of compressible plasmas. The goal of this work is highlighting the influence of both the magnetic field and the compressibility of the material on the growth rate of the Rayleigh-Taylor instability, compared to the classical growth rate derived for incompressible fluids. Our analytical linear models are derived in the framework of the ideal magnetohydrodynamics theory. Three general dispersion relations are obtained: (1) Two for stratified fluids, including compressible (denoted CS∥ when the wave vector k is parallel to the equilibrium magnetic field B0 and CS⊥ when k ⊥B0) and incompressible (denoted IS∥ and IS⊥) and (2) one for incompressible uniform density fluids, including finite mass (denoted Ifm) and infinite (denoted IU). For k ⊥B0, Ifm, IU, and IS⊥ are unmagnetized cases. Comparisons of those various configurations are performed and several differences are pointed out. The main results are as follows: Stratification weakens the MRTI while compressibility has a destabilizing effect. The magnetic field enhances these phenomena. The CS∥ and IU configurations have an identical cutoff wave number. The upper fluid (also called heavy fluid) is more sensitive to compressibility than the light one when k ∥B0. Finally, the CS∥ case is more sensitive than the CS⊥ one to physical variations.
Experimental study of 3D Rayleigh-Taylor convection between miscible fluids in a porous medium
Nakanishi, Yuji; Hyodo, Akimitsu; Wang, Lei; Suekane, Tetsuya
2016-11-01
The natural convection of miscible fluids in porous media has applications in several fields, such as geoscience and geoengineering, and can be employed for the geological storage of CO2. In this study, we used X-ray computer tomography to visualize 3D fingering structures associated with the Rayleigh-Taylor instability between miscible fluids in a porous medium. In the early stages of the onset of the Rayleigh-Taylor instability, a fine crinkling pattern gradually appeared at the interface. As the wavelength and amplitude increased, descending fingers formed on the interface and extended vertically downward; in addition, ascending and highly symmetric fingers formed. The adjacent fingers were cylindrical in shape and coalesced to form large fingers. The fingers appearing on the interface tended to become finer with increasing Rayleigh number, which is consistent with linear perturbation theory. When the Péclet number exceeded 10, transverse dispersion increased the finger diameter and enhanced the finger coalescence, strongly impacting the decrease in finger number density. When mechanical dispersion was negligible, the finger-extension velocity and the dimensionless mass-transfer rate scaled with the characteristic velocity and the Rayleigh number with an appropriate length scale. Mechanical dispersion not only reduced the onset time but also enhanced the mass transport.
Kilkenny, J.D.
1994-08-04
As shown elsewhere an ablatively imploded shell is hydrodynamically unstable, the dominant instability being the well known Rayleigh-Taylor instability with growth rate {gamma} = {radical}Akg where k = 2{pi}/{lambda} is the wave number, g is the acceleration and A the Attwood number ({rho}{sub hi} {minus} {rho}{sub lo})/({rho}{sub hi} + {rho}{sub lo}) where {rho}{sub hi} is the density of the heavier fluid and {rho}{sub lo} is the density of the lighter fluid. A theoretical understanding of ablative stabilization has gradually evolved, confirmed over the last five years by experiments. The linear growth is very well understood with excellent agreement between experiment and simulation for planar geometry with wavelengths in the region of 30--100{mu}m. There is an accurate, albeit phenomenological dispersion relation. The non-linear growth has been measured and agrees with calculations. In this lecture, the authors go into the fundamentals of the Rayleigh-Taylor instability and the experimental measurements that show it is stabilized sufficiently by ablation in regimes relevant to ICF.
Wu, D; Zheng, C Y; Qiao, B; Zhou, C T; Yan, X Q; Yu, M Y; He, X T
2014-08-01
It is shown that the transverse Rayleigh-Taylor-like (RT) instability in the hole-boring radiation pressure acceleration can be suppressed by using an elliptically polarized (EP) laser. A moderate J×B heating of the EP laser will thermalize the local electrons, which leads to the transverse diffusion of ions, suppressing the short wavelength perturbations of RT instability. A proper condition of polarization ratio is obtained analytically for the given laser intensity and plasma density. The idea is confirmed by two-dimensional particle-in-cell simulations, showing that the ion beam driven by the EP laser is more concentrated and intense compared with that of the circularly polarized laser.
The effect of normal electric field on the evolution of immiscible Rayleigh-Taylor instability
Tofighi, Nima; Ozbulut, Murat; Feng, James J.; Yildiz, Mehmet
2016-10-01
Manipulation of the Rayleigh-Taylor instability using an external electric field has been the subject of many studies. However, most of these studies are focused on early stages of the evolution. In this work, the long-term evolution of the instability is investigated, focusing on the forces acting on the interface between the two fluids. To this end, numerical simulations are carried out at various electric permittivity and conductivity ratios as well as electric field intensities using Smoothed Particle Hydrodynamics method. The electric field is applied in parallel to gravity to maintain unstable evolution. The results show that increasing top-to-bottom permittivity ratio increases the rising velocity of the bubble while hindering the spike descent. The opposite trend is observed for increasing top-to-bottom conductivity ratio. These effects are amplified at larger electric field intensities, resulting in narrower structures as the response to the excitation is non-uniform along the interface.
Effect of enhanced thermal dissipation on the Rayleigh-Taylor instability in emulsion-like media
Toor, A.; Ryutov, D.
1997-07-01
Rayleigh-Taylor instability in a finely structured emulsion-like medium consisting of the two components of different compressibility is considered. Although the term ``emulsion`` is used to describe the structure of the medium, under typical fast Z-pinch conditions both components behave as gases. The two components are chosen in such a way that their densities in the unperturbed state are approximately equal. Specific emphasis has been made on the analysis of perturbations with the scale {lambda} considerably exceeding the size of the grains a. Averaged equations describing such perturbations am derived. The difference in compressibility of the two components leads to the formation of temperature variations at the scale a, and increases the rate of the thermal dissipation by a factor ({lambda}/a){sup 2}. The strongest stabilizing effect of the thermal dissipation takes place when the thermal relaxation time is comparable with the instability growth rate.
Non-linear Evolution of Rayleigh-Taylor Instability in a Radiation Supported Atmosphere
Jiang, Yan-Fei; Stone, James
2012-01-01
The non-linear regime of Rayleigh-Taylor instability (RTI) in a radiation supported atmosphere, consisting of two uniform fluids with different densities, is studied numerically. We perform simulations using our recently developed numerical algorithm for multi-dimensional radiation hydrodynamics based on a variable Eddington tensor as implemented in Athena, focusing on the regime where scattering opacity greatly exceeds absorption opacity. We find that the radiation field can reduce the growth and mixing rate of RTI, but this reduction is only significant when radiation pressure significantly exceeds gas pressure. Small scale structures are also suppressed in this case. In the non-linear regime, dense fingers sink faster than rarefied bubbles can rise, leading to asymmetric structures about the interface. By comparing the calculations that use a variable Eddington tensor (VET) versus the Eddington approximation, we demonstrate that anisotropy in the radiation field can affect the non-linear development of RTI...
Development of Richtmyer-Meshkov and Rayleigh-Taylor Instability in presence of magnetic field
Khan, Manoranjan; Banerjee, Rahul; Roy, Sourav; Gupta, M R
2011-01-01
Fluid instabilities like Rayleigh-Taylor,Richtmyer-Meshkov and Kelvin-Helmholtz instability can occur in a wide range of physical phenomenon from astrophysical context to Inertial Confinement Fusion(ICF).Using Layzer's potential flow model, we derive the analytical expressions of growth rate of bubble and spike for ideal magnetized fluid in R-T and R-M cases. In presence of transverse magnetic field the R-M and R-T instability are suppressed or enhanced depending on the direction of magnetic pressure and hydrodynamic pressure. Again the interface of two fluid may oscillate if both the fluids are conducting. However the magnetic field has no effect in linear case.
Miscible and immiscible, forced and unforced experiments on the Rayleigh-Taylor instability
Roberts, Michael; Mokler, Matthew; Jacobs, Jeffrey
2012-11-01
Experiments are presented in which an incompressible system of two liquids is accelerated to produce the Rayleigh-Taylor instability. In these experiments, the initially stable, stratified liquid combination is accelerated downward on a vertical rail system in one of two experimental apparatuses: an apparatus in which a system of weights and pulleys accelerates the liquid filled tank, or a new apparatus which uses linear induction motors to accelerate the tank to produce much greater acceleration levels. Both miscible and immiscible liquid combinations are used. In both apparatuses the resulting fluid flows are visualized with backlit imaging using LED backlights in conjunction with monochrome high-speed video cameras, both of which travel with the moving fluid filled containers. Initial perturbations are either unforced and allowed to progress from background noise or forced by vertically oscillating the liquid combination to produce parametric internal waves. The mixing layer growth rate α is determined for all cases and compared to numerical simulations and past experiments.
Kulkarni, Akshay K
2008-01-01
We present results of 3D simulations of MHD instabilities at the accretion disk-magnetosphere boundary. The instability is Rayleigh-Taylor, and develops for a fairly broad range of accretion rates and stellar rotation rates and magnetic fields. It produces tall, thin tongues of plasma that penetrate the magnetosphere in the equatorial plane. The shape and number of the tongues changes with time on the inner-disk dynamical timescale. In contrast with funnel flows, which deposit matter mainly in the polar region, the tongues deposit matter much closer to the stellar equator. The instability appears for relatively small misalignment angles, $\\Theta\\lesssim30^\\circ$, between the star's rotation and magnetic axes, and is associated with higher accretion rates. The hot spots and light curves during accretion through instability are generally much more chaotic than during stable accretion. The unstable state of accretion has possible implications for quasi-periodic oscillations and intermittent pulsations from accre...
Kulkarni, Akshay K
2008-01-01
We present results of 3D simulations of MHD instabilities at the accretion disk-magnetosphere boundary. The instability is Rayleigh-Taylor, and develops for a fairly broad range of accretion rates and stellar rotation rates and magnetic fields. It manifests itself in the form of tall, thin tongues of plasma that penetrate the magnetosphere in the equatorial plane. The shape and number of the tongues changes with time on the inner-disk dynamical timescale. In contrast with funnel flows, which deposit matter mainly in the polar region, the tongues deposit matter much closer to the stellar equator. The instability appears for relatively small misalignment angles, $\\Theta\\lesssim30^\\circ$, between the star's rotation and magnetic axes, and is associated with higher accretion rates. The hot spots and light curves during accretion through instability are generally much more chaotic than during stable accretion. The unstable state of accretion has possible implications for quasi-periodic oscillations and intermitten...
The Rayleigh-Taylor instability for a thin film on the inside of a horizontal cylinder
Hammoud, Naima; Trinh, Philippe; Howell, Peter; Chapman, Jonathan; Stone, Howard
2013-11-01
Thin films on curved surfaces are widely observed in coating and painting processes and wetting problems. We consider a thin film on a curved substrate under the effect of gravitational, viscous, and surface tension forces. When the film is on the underside of the substrate, gravity works as a destabilizing force, and a Rayleigh-Taylor type instability is expected. We consider the stability of a uniform thin film coating the inside of a horizontal circular cylinder. Using asymptotic methods, we find that instabilities are of a transient nature, thus showing that curvature helps stabilize the film. We also find that these ``instabilities'' occur primarily in the angular direction with the axial perturbations only appearing as higher-order corrections. These results seem to agree well with experiments (H. Kim et al., this conference).
Nonequilibrium thermohydrodynamic effects on the Rayleigh-Taylor instability in compressible flows
Lai, Huilin; Xu, Aiguo; Zhang, Guangcai; Gan, Yanbiao; Ying, Yangjun; Succi, Sauro
2016-08-01
The effects of compressibility on Rayleigh-Taylor instability (RTI) are investigated by inspecting the interplay between thermodynamic and hydrodynamic nonequilibrium phenomena (TNE, HNE, respectively) via a discrete Boltzmann model. Two effective approaches are presented, one tracking the evolution of the local TNE effects and the other focusing on the evolution of the mean temperature of the fluid, to track the complex interfaces separating the bubble and the spike regions of the flow. It is found that both the compressibility effects and the global TNE intensity show opposite trends in the initial and the later stages of the RTI. Compressibility delays the initial stage of RTI and accelerates the later stage. Meanwhile, the TNE characteristics are generally enhanced by the compressibility, especially in the later stage. The global or mean thermodynamic nonequilibrium indicators provide physical criteria to discriminate between the two stages of the RTI.
Direct simulation Monte Carlo investigation of the Rayleigh-Taylor instability
Gallis, M. A.; Koehler, T. P.; Torczynski, J. R.; Plimpton, S. J.
2016-08-01
The Rayleigh-Taylor instability (RTI) is investigated using the direct simulation Monte Carlo (DSMC) method of molecular gas dynamics. Here, fully resolved two-dimensional DSMC RTI simulations are performed to quantify the growth of flat and single-mode perturbed interfaces between two atmospheric-pressure monatomic gases as a function of the Atwood number and the gravitational acceleration. The DSMC simulations reproduce many qualitative features of the growth of the mixing layer and are in reasonable quantitative agreement with theoretical and empirical models in the linear, nonlinear, and self-similar regimes. In some of the simulations at late times, the instability enters the self-similar regime, in agreement with experimental observations. For the conditions simulated, diffusion can influence the initial instability growth significantly.
Experimental investigation of late time Rayleigh-Taylor mixing at high Atwood number
Suchandra, Prasoon; Mikhaeil, Mark; Ranjan, Devesh
2016-11-01
Dynamics of late time, high Reynolds number (Re >20000) Rayleigh-Taylor (RT) mixing is studied using statistically steady experiments performed in a multi-layer gas tunnel. The density ratio of air and air-Helium mixture used in the present experiment results in an Atwood number 0.73. Three types of diagnostics - back-lit visualization, hot-wire anemometry and stereo particle image velocimetry (S-PIV) - are employed to obtain mixing width, velocity and density fields, with S-PIV employed for the first time for such experimental conditions. Velocity and density statistics, and their correlations (u', v', w',ρ' ,ρ'v') are presented. Calculations of probability density functions (p.d.f.s) and energy spectra are made to provide further insight into the flow physics. Energy budget of the flow is also discussed.
On the Rayleigh-Taylor instability for incompressible viscous magnetohydrodynamic equations
Jiang, Fei; Wang, Yanjin
2012-01-01
We study the Rayleigh-Taylor problem for two incompressible, immiscible, viscous magnetohydrodynamic (MHD) flows, with zero resistivity, surface tension (or without surface tenstion) and special initial magnetic field, evolving with a free interface in the presence of a uniform gravitational field. First, we reformulate in Lagrangian coordinates MHD equations in a infinite slab as one for the Navier-Stokes equations with a force term induced by the fluid flow map. Then we analyze the linearized problem around the steady state which describes a denser immiscible fluid lying above a light one with an free interface separating the two fluids, and both fluids being in (unstable) equilibrium. By a general method of studying a family of modified variational problems, we construct smooth (when restricted to each fluid domain) solutions to the linearized problem that grow exponentially fast in time in Sobolev spaces, thus leading to an global instability result for the linearized problem. Finally, using these patholo...
The Rayleigh-Taylor instability of Newtonian and non-Newtonian fluids
Doludenko, A. N.; Fortova, S. V.; Son, E. E.
2016-10-01
Along with Newtonian fluids (for example, water), fluids with non-Newtonian rheology are widespread in nature and industry. The characteristic feature of a non-Newtonian fluid is the non-linear dependence between the shear stress and shear rate tensors. The form of this relation defines the types of non-Newtonian behavior: viscoplastic, pseudoplastic, dilatant and viscoelastic. The present work is devoted to the study of the Rayleigh-Taylor instability in pseudoplastic fluids. The main aim of the work is to undertake a direct three-dimensional numerical simulation of the mixing of two media with various rheologies and obtain the width of the mixing layer and the kinetic energy spectra, depending on the basic properties of the shear thinning liquids and the Atwood number. A theoretical study is carried out on the basis of the Navier-Stokes equation system for weakly compressible media.
Gauglitz, Phillip A.; Wells, Beric E.; Buchmiller, William C.; Rassat, Scot D.
2013-03-21
In Hanford underground waste storage tanks, a typical waste configuration is settled beds of waste particles beneath liquid layers. The settled beds are typically composed of layers, and these layers can have different physical and chemical properties. One postulated configuration within the settled bed is a less-dense layer beneath a more-dense layer. The different densities can be a result of different gas retention in the layers or different degrees of settling and compaction in the layers. This configuration can experience a Rayleigh-Taylor (RT) instability where the less dense lower layer rises into the upper layer. Previous studies of gas retention and release have not considered potential buoyant motion within a settle bed of solids. The purpose of this report is to provide a review of RT instabilities, discuss predictions of RT behavior for sediment layers, and summarize preliminary experimental observations of RT instabilities in simulant experiments.
Rayleigh-Taylor instability in Magnetohydrodynamic Simulations of the Crab Nebula
Porth, Oliver; Keppens, Rony
2014-01-01
In this paper we discuss the development of Rayleigh-Taylor filaments in axisymmetric simulations of Pulsar wind nebulae (PWN). High-resolution adaptive mesh refinement magnetohydrodynamic (MHD) simulations are used to resolve the non-linear evolution of the instability. The typical separation of filaments is mediated by the turbulent flow in the nebula and hierarchical growth of the filaments. The strong magnetic dissipation and field-randomization found in recent global three-dimensional simulations of PWN suggests that magnetic tension is not strong enough to suppress the growth of RT filaments, in agreement with the observations of prominent filaments in the Crab nebula. The long-term axisymmetric results presented here confirm this finding.
2D HYDRA Calculations of Magneto-Rayleigh-Taylor Growth and Feedthrough in Cylindrical Liners
Weis, Matthew; Zhang, Peng; Lau, Y. Y.; Gilgenbach, Ronald; Peterson, Kyle; Hess, Mark
2014-10-01
Cylindrical liner implosions are susceptible to the magneto-Rayleigh-Taylor instability (MRT), along with the azimuthal current-carrying modes (sausage, kink, etc). ``Feedthrough'' of these instabilities has a strong influence on the integrity of the liner/fuel interface in the magnetized liner inertial fusion concept (MagLIF). The linearized ideal MHD equations can be solved to quantify these effects, including the presence of an effective gravity and an axial magnetic field. We investigate the potential of this field to mitigate feedthrough, due to MRT growth from various initial surface finishes (seeded, rough), throughout the implosion using our analytic results and the LLNL code, HYDRA. We will present both low and high convergence cases. Lastly, we illustrate the effect shock compression can have on feedthrough in seeded liners for various fill gases (cold and pre-heated) and magnetic field configurations. M. R. Weis was supported by the Sandia National Laboratories.
Magneto-Rayleigh-Taylor, Sausage And Kink Mode In Cylindrical Liners
Lau, Y. Y.; Zhang, Peng; Weis, Matthew; Gilgenbach, Ronald; Hess, Mark; Peterson, Kyle
2014-10-01
This paper analyzes the coupling of magneto-Rayleigh-Taylor (MRT), sausage (azimuthal mode number m = 0) and kink mode (m = 1) in an imploding cylindrical liner, using ideal MHD. A uniform axial magnetic field of arbitrary value is included in each region: liner, its interior, and its exterior. The dispersion relation, the feedthrough factor, and the temporal evolution of perturbations were solved exactly, for arbitrary values of g (= gravity), k (= axial wavenumber), m, aspect ratio, and equilibrium quantities in each region. For small k, a positive g (inward radial acceleration in the lab frame) tends to stabilize the sausage mode, but destabilize the kink mode. For large k, a positive g destabilizes both the kink and sausage mode. This analysis might shed lights into some puzzling features in Harris' classic paper, and in the recent cylindrical liner experiments on MRT. M. R. Weis was supported by the Sandia National Laboratories.
Revisiting the Effects of Compressibility on the Rayleigh-Taylor Instability
ZHOU Qianhong; LI Ding
2007-01-01
The effects of compressibility on the Rayleigh-Taylor instability(RTI)are investigated.It is shown that the controversy over compressibility effects in the previous studies is due to improper comparison,in which the density varying effect obscures the real role of compressibility.After eliminating the density varying effect,it is found that the compressibility destabilizes RTI in both the cases of constant density and exponentially varying density when M<1.This destabilizing effect is more important at smaller values of the Atwood number AT or greater values of gravity g,and the increment in the growth rate produced by compressibility depends inversely on the pressure p or the ratio of specific heat I.
Comparison of two- and three-dimensional simulations of miscible Rayleigh-Taylor instability
Cabot, W
2006-02-23
A comparison of two-dimensional and three-dimensional high-resolution numerical large-eddy simulations of planar, miscible Rayleigh-Taylor instability flows are presented. The resolution of the three-dimensional simulation is sufficient to attain a fully turbulent state. A number of different statistics from the mixing region (e.g., growth rates, PDFs, mixedness measures, and spectra) are used to demonstrate that two-dimensional flow simulations differ substantially from the three-dimensional one. It is found that the two-dimensional flow grows more quickly than its three-dimensional counterpart at late times, develops larger structures, and is much less well mixed. These findings are consistent with the concept of inverse cascade in two-dimensional flow, as well as the influence of a reduced effective Atwood number on miscible flow.
The effect of a magnetic field on the development of Rayleigh Taylor type instability
Syusyukin, A.I.
1984-01-01
The results are presented of an experimental study of magnetohydrodynamic (MGD) instability of the Rayleigh Taylor type. The effect of a magnetic field on the development of magnetohydrodynamic instability was studied in the free surfaces of an accelerating electricity conducting piston. The tests were conducted with a liquid metallic piston and with a piston which is made up of a liquid which does not conduct electricity and one which does. It is shown that a rise in the magnetic induction leads to a more intense development of the instability which is accompanied by a more rapid destruction of the dense structure of the piston. The mechanism of destruction of a free surface under the effects of bulk forces is discussed.
Retarding viscous Rayleigh-Taylor mixing by an optimized additional mode
Xie, C. Y.; Tao, J. J.; Sun, Z. L.; Li, J.
2017-02-01
The Rayleigh-Taylor (RT) mixing induced by random interface disturbances between two incompressible viscous fluids is simulated numerically. The ensemble averaged spike velocity is found to be remarkably retarded when the random interface disturbances are superimposed with an optimized additional mode. The mode's wavenumber is selected to be large enough to avoid enhancing the dominance of long-wavelength modes, but not so large that its saturated spike and bubble velocities are too small to stimulate a growing effective density-gradient layer suppressing the long-wavelength modes. Such an optimized suppressing mode is expected to be found in the RT mixing including other diffusion processes, e.g., concentration diffusion and thermal diffusion.
Compressibility Effect on the Rayleigh-Taylor Instability with Sheared Magnetic Fields
Ruderman, M. S.
2017-04-01
We study the effect of plasma compressibility on the Rayleigh-Taylor instability of a magnetic interface with a sheared magnetic field. We assume that the plasma is ideal and the equilibrium quantities are constant above and below the interface. We derive the dispersion equation. Written in dimensionless variables, it contains seven dimensionless parameters: the ratio of plasma densities above and below the interface ζ, the ratio of magnetic field magnitude squared χ, the shear angle α, the plasma beta above and below the interface, β2 and β1, the angle between the perturbation wave number and the magnetic field direction above the interface φ, and the dimensionless wave number κ. Only six of these parameters are independent because χ, β1, and β2 are related by the condition of total pressure continuity at the interface. Only perturbations with the wave number smaller than the critical wave number are unstable. The critical wave number depends on φ, but it is independent of β1 and β2, and is the same as that in the incompressible plasma approximation. The dispersion equation is solved numerically with ζ= 100, χ= 1, and β1 = β2 = β. We obtain the following results. When β decreases, so does the maximum instability increment. However, the effect is very moderate. It is more pronounced for high values of α. We also calculate the dependence on φ of the maximum instability increment with respect to κ. The instability increment takes its maximum at φ= φm. Again, the decrease of β results in the reduction of the instability increment. This reduction is more pronounced for high values of |φ- φm|. When both α and |φ- φm| are small, the reduction effect is practically negligible. The theoretical results are applied to the magnetic Rayleigh-Taylor instability of prominence threads in the solar atmosphere.
Adams, Colin S; Hsu, Scott C
2014-01-01
We present time-resolved observations of Rayleigh-Taylor-instability growth at the interface between an unmagnetized plasma jet colliding with a stagnated, magnetized plasma. The observed instability growth time ($\\sim 10$ $\\mu$s) is consistent with the estimated linear Rayleigh-Taylor growth rate calculated using experimentally inferred values of density ($\\sim 10^{14}$ cm$^{-3}$) and acceleration ($10^9$ m/s$^2$). The observed instability wavelengths ($\\gtrsim 1$ cm) are consistent with stabilization of short wavelengths by a magnetic field of the experimentally measured magnitude ($\\sim 15$ G) and direction. Comparisons of data with idealized magnetohydrodynamic simulations including a physical viscosity model suggest that the observed instability evolution is consistent with both magnetic and viscous stabilization.
Hydrodynamic Instability of Ionization Fronts in HII Regions
Mizuta, A; Kane, J; Ryutov, D; Remington, B; Takabe, H; Pound, M
2003-08-21
The authors investigate hydrodynamic instability of accelerating ionization fronts with two dimensional hydrodynamic simulations. When recombination in the ionized region is turned off, Rayleigh-Taylor instability is effective. Perturbation grows up with classical Rayleigh-Taylor growth rate. In the case with recombination, the local difference of absorption profile works to smooth the surface. The perturbation does not grow and the amplitude follows a damped oscillations with time.
Numerical study on Rayleigh-Taylor instabilities in the lightning return stroke
Chen, Qiang, E-mail: cq0405@126.com [National Key Laboratory of Electromagnetic Environment and Electro-optical Engineering, PLA University of Science and Technology, Nanjing 210007 (China); Luoyang Electronic Equipment Testing Center, Luoyang 471000 (China); Chen, Bin, E-mail: emcchen@163.com; Shi, Lihua; Yi, Yun [National Key Laboratory of Electromagnetic Environment and Electro-optical Engineering, PLA University of Science and Technology, Nanjing 210007 (China); Wang, Yangyang [Department of Electro-optical Engineering, Electronic Engineering Institute of PLA, Hefei 230037 (China)
2015-09-15
The Rayleigh-Taylor (R-T) instabilities are important hydrodynamics and magnetohydrodynamics (MHD) phenomena that are found in systems in high energy density physics and normal fluids. The formation and evolution of the R-T instability at channel boundary during back-flow of the lightning return stroke are analyzed using the linear perturbation theory and normal mode analysis methods, and the linear growth rate of the R-T instability in typical condition for lightning return stroke channel is obtained. Then, the R-T instability phenomena of lightning return stroke are simulated using a two-dimensional Eulerian finite volumes resistive radiation MHD code. The numerical results show that the evolution characteristics of the R-T instability in the early stage of back-flow are consistent with theoretical predictions obtained by linear analysis. The simulation also yields more evolution characteristics for the R-T instability beyond the linear theory. The results of this work apply to some observed features of the return stroke channel and further advance previous theoretical and experimental work.
Numerical study on Rayleigh-Taylor instabilities in the lightning return stroke
Chen, Qiang; Chen, Bin; Shi, Lihua; Yi, Yun; Wang, Yangyang
2015-09-01
The Rayleigh-Taylor (R-T) instabilities are important hydrodynamics and magnetohydrodynamics (MHD) phenomena that are found in systems in high energy density physics and normal fluids. The formation and evolution of the R-T instability at channel boundary during back-flow of the lightning return stroke are analyzed using the linear perturbation theory and normal mode analysis methods, and the linear growth rate of the R-T instability in typical condition for lightning return stroke channel is obtained. Then, the R-T instability phenomena of lightning return stroke are simulated using a two-dimensional Eulerian finite volumes resistive radiation MHD code. The numerical results show that the evolution characteristics of the R-T instability in the early stage of back-flow are consistent with theoretical predictions obtained by linear analysis. The simulation also yields more evolution characteristics for the R-T instability beyond the linear theory. The results of this work apply to some observed features of the return stroke channel and further advance previous theoretical and experimental work.
Zaitsev, V. V.; Kronshtadtov, P. V.; Stepanov, A. V.
2016-11-01
Within the framework of the long-standing so-called "number problem" in the physics of solar flares, we consider the excitation of a super-Dreicer electric field at the leading edge of the electric current pulse that occurs at the chromospheric legs of a coronal magnetic loop as a result of the magnetic Rayleigh-Taylor instability. It is shown that for a sufficiently strong electric current, I0 ≥ 10^{10} A, the current pulse propagates in the non-linear mode and generates a strong longitudinal electric field Ez, which strongly depends on the current (Ez ∝ I03) and can exceed the Dreicer field (Ez > ED). In this case, the bulk of electrons in the site of the current pulse is in a runaway mode, and the energy release rate in the chromosphere increases significantly. Super-Dreicer electric fields also provide injection of protons into the regime of acceleration by Langmuir turbulence generated by fast electrons at the leading edge of the electric current pulse. The electric field at the pulse edge can exceed the Dreicer field starting from the chromosphere level with the number density n ≈ 10^{13} cm^{-3}. At a lower current I0 < 10^{10} A, a super-Dreicer mode at the higher levels of the chromosphere with n < 10^{12} cm^{-3} occurs.
Solar effect on the Rayleigh-Taylor instability growth rate as simulated by the NCAR TIEGCM
Wu, Qian
2017-04-01
The TIEGCM (Thermosphere Ionosphere Electrodynamics General Circulation Model) is used to investigate the solar effect on the equatorial ionospheric Rayleigh-Taylor (R-T) instability growth rate, which is responsible for the occurrence of the plasma bubbles. The R-T growth rate is calculated for the solar maximum year 2003 and minimum 2009. The growth rate is strongly dependent on the solar activity. During solar maximum, the pre-reversal enhancement is much stronger leading to higher R-T growth rate. The R-T growth rates from the TIEGCM follow the same solar dependence as the observed occurrence of equatorial plasma bubbles by DMSP satellites. The R-T growth rate also enhances when the day/night terminator is parallel to the magnetic field line near the equator. The R-T growth rate does not correlate well with the solar F10.7 index on a short time scale ( 10 days) because the field-line integrated electron content gradient cancels out the positive correlation between the vertical ion drift with the F10.7 index. The TIEGCM result shows the importance of the electron content gradient to the R-T growth rate and the plasma bubble occurrence. The bubble occurrence rates were estimated based on the vertical ion drift simulation results.
Reckinger, Scott J.; Livescu, Daniel; Vasilyev, Oleg V.
2016-05-01
An investigation of compressible Rayleigh-Taylor instability (RTI) using Direct Numerical Simulations (DNS) requires efficient numerical methods, advanced boundary conditions, and consistent initialization in order to capture the wide range of scales and vortex dynamics present in the system, while reducing the computational impact associated with acoustic wave generation and the subsequent interaction with the flow. An advanced computational framework is presented that handles the challenges introduced by considering the compressive nature of RTI systems, which include sharp interfacial density gradients on strongly stratified background states, acoustic wave generation and removal at computational boundaries, and stratification dependent vorticity production. The foundation of the numerical methodology described here is the wavelet-based grid adaptivity of the Parallel Adaptive Wavelet Collocation Method (PAWCM) that maintains symmetry in single-mode RTI systems to extreme late-times. PAWCM is combined with a consistent initialization, which reduces the generation of acoustic disturbances, and effective boundary treatments, which prevent acoustic reflections. A dynamic time integration scheme that can handle highly nonlinear and potentially stiff systems, such as compressible RTI, completes the computational framework. The numerical methodology is used to simulate two-dimensional single-mode RTI to extreme late-times for a wide range of flow compressibility and variable density effects. The results show that flow compressibility acts to reduce the growth of RTI for low Atwood numbers, as predicted from linear stability analysis.
Phase-field model for the Rayleigh--Taylor instability of immiscible fluids
Celani, Antonio; Muratore-Ginanneschi, Paolo; Vozella, Lara
2008-01-01
The Rayleigh--Taylor instability of two immiscible fluids in the limit of small Atwood numbers is studied by means of a phase-field description. In this method the sharp fluid interface is replaced by a thin, yet finite, transition layer where the interfacial forces vary smoothly. This is achieved by introducing an order parameter (the phase field) whose variation is continuous across the interfacial layers and is uniform in the bulk region. The phase field model obeys a Cahn--Hilliard equation and is two-way coupled to the standard Navier--Stokes equations. Starting from this system of equations we have first performed a linear analysis from which we have analytically rederived the known gravity-capillary dispersion relation in the limit of vanishing mixing energy density and capillary width. We have performed numerical simulations and identified a region of parameters in which the known properties of the linear phase (both stable and unstable) are reproduced in a very accurate way. This has been done both i...
Application of monotone integrated large eddy simulation to Rayleigh-Taylor mixing.
Youngs, David L
2009-07-28
Rayleigh-Taylor (RT) instability occurs when a dense fluid rests on top of a light fluid in a gravitational field. It also occurs in an equivalent situation (in the absence of gravity) when an interface between fluids of different density is accelerated by a pressure gradient, e.g. in inertial confinement fusion implosions. Engineering models (Reynolds-averaged Navier-Stokes models) are needed to represent the effect of mixing in complex applications. However, large eddy simulation (LES) currently makes an essential contribution to understanding the mixing process and calibration or validation of the engineering models. In this paper, three cases are used to illustrate the current role of LES: (i) mixing at a plane boundary, (ii) break-up of a layer of dense fluid due to RT instability, and (iii) mixing in a simple spherical implosion. A monotone integrated LES approach is preferred because of the need to treat discontinuities in the flow, i.e. the initial density discontinuities or shock waves. Of particular interest is the influence of initial conditions and how this needs to be allowed for in engineering modelling. It is argued that loss of memory of the initial conditions is unlikely to occur in practical applications.
Miscible and immiscible liquid experiments and simulations on the Rayleigh-Taylor instability
Roberts, Michael; Mokler, Matthew; Cabot, William; Jacobs, Jeffrey
2011-11-01
Experiments and numerical simulations are presented in which an incompressible system of two liquids is accelerated to produce the Rayleigh-Taylor instability. In these experiments, the initially stable, stratified liquid combination is accelerated downward on a vertical rail system in one of two experimental apparatuses: an apparatus in which a system of weights and pulleys accelerates the liquid filled tank (which is affixed to a test sled), or a new apparatus which uses linear induction motors to accelerate the tank (which is attached to an aluminum plate) to produce much greater acceleration levels. Both miscible and immiscible liquid combinations are used. In both apparatuses the resulting fluid flows are visualized with backlit imaging using LED backlights in conjunction with monochrome high-speed video cameras, both of which travel with the moving fluid filled containers. Initial perturbations are either unforced and allowed to progress from background noise or forced by vertically oscillating the liquid combination to produce parametric internal waves. The results of these experiments are compared to numerical simulations performed using the CFD code Miranda.
Bhowmick, Aklant K.; Abarzhi, Snezhana
2016-10-01
Rayleigh Taylor instability in a power-law time dependent acceleration field is investigated for a flow with the symmetry group p6mm (hexagonal) in the plane normal to acceleration. The Regular asymptotic solutions form a one-parameter family and the physically significant solution is identified with the one having the fastest growth and being stable (bubble tip velocity). Two distinct regimes are identified dependent on the acceleration exponent, the RM-type regime, where the dynamics is identical to conventional RM instability and is dominated by initial conditions, and the RT-type regime where the dynamics is dominated by the acceleration term. For the latter, the time dependence has profound effects on the dynamics. In the RT non-linear regime, the time dependence has no consequence on the morphology of the bubbles but the growth rate (bubble tip velocity) evolves as power law with the exponent set by the acceleration. The solutions for a one-parameter family, and are convergent with exponential decay of Fourier amplitudes close to the physical solution. The solutions are stable at maximum tip velocity and flat bubbles are unstable, and the growth/decay of perturbations is no longer purely exponential and depends on the acceleration exponent. The work is supported by the US National Science Foundation.
Bhowmick, Aklant K.; Abarzhi, Snezhana
2016-11-01
Rayleigh Taylor instability in a power-law time dependent acceleration field is investigated theoretically for a flow with the symmetry group p6mm (hexagon) in the plane normal to acceleration. In the nonlinear regime, regular asymptotic solutions form a one-parameter family. The physically significant solution is identified with the one having the fastest growth and being stable (bubble tip velocity). Two distinct regimes are identified depending on the acceleration exponent. Particularly, the RM-type regime, where the dynamics is identical to conventional RM instability and is dominated by initial conditions, and the RT-type regime where the dynamics is dominated by the acceleration term. For the latter, the time dependence has profound effects on the dynamics. In the RT non-linear regime, the time dependence has no consequence on the morphology of the bubbles; the growth rate (bubble tip velocity) evolves as power law with the exponent set by the acceleration. The solutions for a one-parameter family, and are convergent with exponential decay of Fourier amplitudes. The solutions are stable at maximum tip velocity, whereas flat bubbles are unstable, and the growth/decay of perturbations is no longer purely exponential and depends on the acceleration exponent. The work is supported by the US National Science Foundation.
Zaitsev, V. V.; Kronshtadtov, P. V.; Stepanov, A. V.
2016-09-01
Within the framework of the long-standing so-called "number problem" in the physics of solar flares, we consider the excitation of a super-Dreicer electric field at the leading edge of the electric current pulse that occurs at the chromospheric legs of a coronal magnetic loop as a result of the magnetic Rayleigh-Taylor instability. It is shown that for a sufficiently strong electric current, I0 ≥ 10^{10} A, the current pulse propagates in the non-linear mode and generates a strong longitudinal electric field Ez, which strongly depends on the current ( Ez ∝ I03) and can exceed the Dreicer field ( Ez > ED). In this case, the bulk of electrons in the site of the current pulse is in a runaway mode, and the energy release rate in the chromosphere increases significantly. Super-Dreicer electric fields also provide injection of protons into the regime of acceleration by Langmuir turbulence generated by fast electrons at the leading edge of the electric current pulse. The electric field at the pulse edge can exceed the Dreicer field starting from the chromosphere level with the number density n ≈ 10^{13} cm^{-3}. At a lower current I0 < 10^{10} A, a super-Dreicer mode at the higher levels of the chromosphere with n < 10^{12} cm^{-3} occurs.
The Destruction of 3He by Rayleigh-Taylor Instability on the First Giant Branch
Eggleton, P P; Lattanzio, J C
2006-01-01
Low-mass stars, ~1-2 solar masses, near the Main Sequence are efficient at producing 3He, which they mix into the convective envelope on the giant branch and distribute into the Galaxy by way of envelope loss. This process is so efficient that it is difficult to reconcile the observed cosmic abundance of 3He with the predictions of Big Bang nucleosynthesis. In this paper we find, by modeling a red giant with a fully three-dimensional hydrodynamic code and a full nucleosynthetic network, that mixing arises in the supposedly stable and radiative zone between the hydrogen-burning shell and the base of the convective envelope. This mixing is due to Rayleigh-Taylor instability within a zone just above the hydrogen-burning shell. In this zone the burning of the 3He left behind by the retreating convective envelope is predominantly by the reaction 3He + 3He -> 4He + 2p, a reaction which, untypically for stellar nuclear reactions, {\\it lowers} the mean molecular weight, leading to a local minimum. This local minimum ...
Rayleigh-Taylor instability under curved substrates: An optimal transient growth analysis
Balestra, Gioele; Brun, P.-T.; Gallaire, François
2016-12-01
We investigate the stability of thin viscous films coated on the inside of a horizontal cylindrical substrate. In such a case, gravity acts both as a stabilizing force through the progressive drainage of the film and as a destabilizing force prone to form droplets via the Rayleigh-Taylor instability. The drainage solution, derived from lubrication equations, is found asymptotically stable with respect to infinitesimally small perturbations, although in reality, droplets often form. To resolve this paradox, we perform an optimal transient growth analysis for the first-order perturbations of the liquid's interface, generalizing the results of Trinh et al. [Phys. Fluids 26, 051704 (2014), 10.1063/1.4876476]. We find that the system displays a linear transient growth potential that gives rise to two different scenarios depending on the value of the Bond number (prescribing the relative importance of gravity and surface tension forces). At low Bond numbers, the optimal perturbation of the interface does not generate droplets. In contrast, for higher Bond numbers, perturbations on the upper hemicircle yield gains large enough to potentially form droplets. The gain increases exponentially with the Bond number. In particular, depending on the amplitude of the initial perturbation, we find a critical Bond number above which the short-time linear growth is sufficient to trigger the nonlinear effects required to form dripping droplets. We conclude that the transition to droplets detaching from the substrate is noise and perturbation dependent.
Algorithm and exploratory study of the Hall MHD Rayleigh-Taylor instability.
Gardiner, Thomas Anthony
2010-09-01
This report is concerned with the influence of the Hall term on the nonlinear evolution of the Rayleigh-Taylor (RT) instability. This begins with a review of the magnetohydrodynamic (MHD) equations including the Hall term and the wave modes which are present in the system on time scales short enough that the plasma can be approximated as being stationary. In this limit one obtains what are known as the electron MHD (EMHD) equations which support two characteristic wave modes known as the whistler and Hall drift modes. Each of these modes is considered in some detail in order to draw attention to their key features. This analysis also serves to provide a background for testing the numerical algorithms used in this work. The numerical methods are briefly described and the EMHD solver is then tested for the evolution of whistler and Hall drift modes. These methods are then applied to study the nonlinear evolution of the MHD RT instability with and without the Hall term for two different configurations. The influence of the Hall term on the mixing and bubble growth rate are analyzed.
An Investigation of the Influence of Initial Conditions on Rayleigh-Taylor Mixing
Mueschke, Nicholas J. [Texas A & M Univ., College Station, TX (United States)
2004-12-01
Experiments and direct numerical simulations (DNS) have been performed to examine the effects of initial conditions on the dynamics of a Rayleigh-Taylor unstable mixing layer. Experiments were performed on a water channel facility to measure the interfacial and velocity perturbations initially present at the two-fluid interface in a small Atwood number mixing layer. The experimental measurements have been parameterized for use in numerical simulations of the experiment. Two- and three-dimensional DNS of the experiment have been performed using the parameterized initial conditions. It is shown that simulations implemented with initial velocity and density perturbations, rather than density perturbations alone, are required to match experimentally-measured statistics and spectra. Data acquired from both the experiment and numerical simulations are used to examine the role of initial conditions on the evolution of integral-scale, turbulence, and mixing statistics. Early-time turbulence and mixing statistics are shown to be strongly-dependent upon the early-time transition of the initial perturbation from a weakly-nonlinear to a strongly-nonlinear flow.
Effects of acceleration rate on Rayleigh-Taylor instability in elastic-plastic materials
Banerjee, Arindam; Polavarapu, Rinosh
2016-11-01
The effect of acceleration rate in the elastic-plastic transition stage of Rayleigh-Taylor instability in an accelerated non-Newtonian material is investigated experimentally using a rotating wheel experiment. A non-Newtonian material (mayonnaise) was accelerated at different rates by varying the angular acceleration of a rotating wheel and growth patterns of single mode perturbations with different combinations of amplitude and wavelength were analyzed. Experiments were run at two different acceleration rates to compare with experiments presented in prior years at APS DFD meetings and the peak amplitude responses are captured using a high-speed camera. Similar to the instability acceleration, the elastic-plastic transition acceleration is found to be increasing with increase in acceleration rate for a given amplitude and wavelength. The experimental results will be compared to various analytical strength models and prior experimental studies using Newtonian fluids. Authors acknowledge funding support from Los Alamos National Lab subcontract(370333) and DOE-SSAA Grant (DE-NA0001975).
Viscous effects on the Rayleigh-Taylor instability with background temperature gradient
Gerashchenko, S
2016-01-01
The growth rate of the compressible Rayleigh-Taylor instability is studied in the presence of a background temperature gradient, $\\Theta$, using a normal mode analysis. The effect of $\\Theta$ variation is examined for three interface types corresponding to combinations of the viscous properties of the fluids (inviscid-inviscid, viscous-viscous and viscous-inviscid) at different Atwood numbers, $At$, and, when at least one of the fluids' viscosity is non-zero, as a function of the Grashof number. For the general case, the resulting ordinary differential equations are solved numerically; however, dispersion relations for the growth rate are presented for several limiting cases. An analytical solution is found for the inviscid-inviscid interface and the corresponding dispersion equation for the growth rate is obtained in the limit of a large $\\Theta$. For the viscous-inviscid case, a dispersion relation is derived in the incompressible limit and $\\Theta=0$. Compared to $\\Theta=0$ case, the role of $\\Theta0$ (col...
Numerical Experiments with a Turbulent Single-Mode Rayleigh-Taylor Instability
Cloutman, L.D.
2000-04-01
Direct numerical simulation is a powerful tool for studying turbulent flows. Unfortunately, it is also computationally expensive and often beyond the reach of the largest, fastest computers. Consequently, a variety of turbulence models have been devised to allow tractable and affordable simulations of averaged flow fields. Unfortunately, these present a variety of practical difficulties, including the incorporation of varying degrees of empiricism and phenomenology, which leads to a lack of universality. This unsatisfactory state of affairs has led to the speculation that one can avoid the expense and bother of using a turbulence model by relying on the grid and numerical diffusion of the computational fluid dynamics algorithm to introduce a spectral cutoff on the flow field and to provide dissipation at the grid scale, thereby mimicking two main effects of a large eddy simulation model. This paper shows numerical examples of a single-mode Rayleigh-Taylor instability in which this procedure produces questionable results. We then show a dramatic improvement when two simple subgrid-scale models are employed. This study also illustrates the extreme sensitivity to initial conditions that is a common feature of turbulent flows.
Khomenko, E; de Vicente, A; Collados, M; Luna, M
2014-01-01
We study the Rayleigh-Taylor instability (RTI) at a prominence-corona transition region in a non-linear regime. Our aim is to understand how the presence of neutral atoms in the prominence plasma influences the instability growth rate, and the evolution of velocity, magnetic field vector and thermodynamic parameters of turbulent drops. We perform 2.5D numerical simulations of the instability initiated by a multi-mode perturbation at the corona-prominence interface using a single-fluid MHD approach including a generalized Ohm's law. The initial equilibrium configuration is purely hydrostatic and contains a homogeneous horizontal magnetic field forming an angle with the direction in which the plasma is perturbed. We analyze simulations with two different orientations of the magnetic field. For each field orientation we compare two simulations, one for the pure MHD case, and one including the ambipolar diffusion in the Ohm's law (AD case). Other than that, both simulations for each field orientation are identica...
Rayleigh-Taylor instability in partially ionized compressible plasmas: one fluid approach
Diaz, A J; Collados, M
2014-01-01
We study the modification of the classical criterion for the linear onset and growth rate of the Rayleigh-Taylor instability (RTI) in a partially ionized (PI) plasma in the one-fluid description, considering a generalized induction equation. The governing linear equations and appropriate boundary conditions, including gravitational terms, are derived and applied to the case of the RTI in a single interface between two partially ionized plasmas. The boundary conditions lead to an equation for the frequencies in which some of them have positive complex parts, marking the appearance of the RTI. We study the ambipolar term alone first, extending the result to the full induction equation later. We find that the configuration is always unstable because of the presence of a neutral species. In the classical stability regime the growth rate is small, since the collisions prevent the neutral fluid to fully develop the RTI. For parameters in the classical instability regime the growth rate is lowered, but for the consi...
Fully-kinetic simulations of the Rayleigh-Taylor instability in high-energy-density plasmas
Alves, E. Paulo; Mori, Warren B.; Fiuza, Frederico
2016-10-01
The Rayleigh-Taylor instability (RTI) in high-energy-density (HED) plasmas is a central problem in a wide range of scenarios. It dictates, for instance, the dynamics of supernovae in astrophysical plasmas, and is also recognized as a critical challenge to achieving ignition in inertial confinement fusion. In some of these conditions the Larmor radius or Coulomb mean free path (m.f.p.) is finite, allowing kinetic effects to become important, and it is not fully clear how the development of the RTI deviates from standard hydrodynamic behavior. In order to obtain an accurate description of the RTI in these HED conditions it is essential to capture the self-consistent interplay between collisional and collisionless plasma processes, and the role of self-generated electric and magnetic fields. We have explored the dynamics of the RTI in HED plasma conditions using first-principles particle-in-cell simulations combined with Monte Carlo binary collisions. Our simulations capture the role of kinetic diffusion as well as the self-generated electric (e.g. space-charge) and magnetic (e.g. Biermann battery) fields on the growth rate and nonlinear evolution of the RTI for different plasma conditions. We will discuss how different collisional m.f.p. relative to the collisionless plasma skin depth affect the RTI development. This work was supported by the DOE Office of Science, Fusion Energy Science (FWP 100182).
Adjoint-based approach to Enhancing Mixing in Rayleigh-Taylor Turbulence
Kord, Ali; Capecelatro, Jesse
2016-11-01
A recently developed adjoint method for multi-component compressible flow is used to measure sensitivity of the mixing rate to initial perturbations in Rayleigh-Taylor (RT) turbulence. Direct numerical simulations (DNS) of RT instabilities are performed at moderate Reynolds numbers. The DNS are used to provide an initial prediction, and the corresponding space-time discrete-exact adjoint provides a sensitivity gradient for a specific quantity of interest (QoI). In this work, a QoI is defined based on the time-integrated scalar field to quantify the mixing rate. Therefore, the adjoint solution is used to measure sensitivity of this QoI to a set of initial perturbations, and inform a gradient-based line search to optimize mixing. We first demonstrate the adjoint approach in the linear regime and compare the optimized initial conditions to the expected values from linear stability analysis. The adjoint method is then used in the high Reynolds number limit where theory is no longer valid. Finally, chaos is known to contaminate the accuracy of the adjoint gradient in turbulent flows when integrated over long time horizons. We assess the influence of chaos on the accuracy of the adjoint gradient to guide the work of future studies on adjoint-based sensitivity of turbulent mixing. PhD Student, Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI.
Three-Dimensional DSMC Simulations of the Rayleigh-Taylor Instability in Gases
Koehler, T. P.; Gallis, M. A.; Torczynski, J. R.; Plimpton, S. J.
2016-11-01
The Direct Simulation Monte Carlo (DSMC) method of molecular gas dynamics is applied to simulate the Rayleigh-Taylor instability (RTI) in atmospheric-pressure monatomic gases (e.g., argon and helium). The computational domain is a 1-mm by 1-mm by 4-mm cuboid uniformly divided into 62.5 billion cubical cells. A total of 1 trillion computational molecules are used, and time steps of 0.1 ns are used. Simulations are performed to quantify the growth of perturbations on an initially flat interface as a function of the Atwood number. The DSMC results reproduce many features of the RTI and are in reasonable agreement with theoretical and empirical models. Consistent with previous work, the DSMC simulations indicate that the growth of the RTI follows a universal behavior. The numbers of bubble-spike pairs that eventually appear agree with theoretical values based on the most unstable wavelength and are independent of the statistical representation of the gas. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Simulating the Rayleigh-Taylor instability in polymer fluids with dissipative particle dynamics
Li, Yanggui; Geng, Xingguo; Zhuang, Xin; Wang, Lihua; Ouyang, Jie
2016-04-01
The Rayleigh-Taylor (RT) instability that occurs in the flow of polymer fluids is numerically investigated with dissipative particle dynamics (DPD) method at the mesoscale particle level. For modeling two-phase flow, the Flory-Huggins parameter is introduced to model binary fluids. And the polymer chains in fluids are described by the modified FENE model that depicts both the elastic tension and the elastic repulsion between the adjacent beads with bond length as the equilibrium length of one segment. Besides, a bead repulsive potential is employed to capture entanglements between polymer chains. Through our model and numerical simulation, we research the dynamics behaviors of the RT instability in polymer fluid medium. Furthermore, we also explore the effects of polymer volume concentration, chain length, and extensibility on the evolution of RT instability. These simulation results show that increasing any of the parameters, concentration, chain length, and extensibility, the saturation length of spikes becomes longer, and the two polymer fluids have less mixture. On the contrary, for the case of low concentration, or short chain, or small extensibility, the spikes easily split and break up, and the RT instability pattern evolves into chaotic structure. These observations indicate that the polymer and its properties drastically modify the RT instability pattern.
3-D simulations to investigate initial condition effects on the growth of Rayleigh-Taylor mixing
Andrews, Malcolm J [Los Alamos National Laboratory
2008-01-01
The effect of initial conditions on the growth rate of turbulent Rayleigh-Taylor (RT) mixing has been studied using carefully formulated numerical simulations. An integrated large-eddy simulation (ILES) that uses a finite-volume technique was employed to solve the three-dimensional incompressible Euler equations with numerical dissipation. The initial conditions were chosen to test the dependence of the RT growth parameters ({alpha}{sub b}, {alpha}{sub s}) on variations in (a) the spectral bandwidth, (b) the spectral shape, and (c) discrete banded spectra. Our findings support the notion that the overall growth of the RT mixing is strongly dependent on initial conditions. Variation in spectral shapes and bandwidths are found to have a complex effect of the late time development of the RT mixing layer, and raise the question of whether we can design RT transition and turbulence based on our choice of initial conditions. In addition, our results provide a useful database for the initialization and development of closures describing RT transition and turbulence.
Beryllium liner z-pinches for magneto-Rayleigh-Taylor studies on Z
McBride, R. D.; Slutz, S. A.; Sinars, D. B.; Lemke, R. W.; Martin, M. R.; Jennings, C. A.; Cuneo, M. E.; Herrmann, M. C.; Blue, B. E.
2011-10-01
Magnetized Liner Inertial Fusion (MagLIF) [S. A. Slutz, et al., Phys. Plasmas 17, 056303 (2010)] is a promising new concept for achieving >100 kJ of fusion yield on Z. The greatest threat to this concept is the magneto-Rayleigh-Taylor (MRT) instability. Thus experimental campaigns have been initiated to study MRT growth in fast imploding (<100 ns) cylindrical liners. This talk will present results from experiments that used 6.151-keV radiography to study the implosions of unperturbed (surface roughness only) beryllium (Be) liners. The high transmission efficiency of 6.151-keV photons through Be allowed us to obtain radiographs with finite transmission throughout the radial extent of the imploding liners. The data from these experiments will be shown and compared to simulation data from several magneto-hydrodynamic codes. These data are allowing us to evaluate the integrity of the inside (fuel-confining) surface of the imploding liner as it approaches stagnation. Sandia is a multi-program laboratory operated by Sandia Corp, a Lockheed-Martin company, for the US Dept of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.
Steiner, Adam; Yager-Elorriaga, David; Patel, Sonal; Jordan, Nicholas; Gilgenbach, Ronald; Lau, Y. Y.
2015-11-01
The electrothermal instability (ETI) and magneto-Rayleigh Taylor instability (MRT) are important in the implosion of metallic liners, such as magnetized liner implosion fusion (MagLIF). The MAIZE linear transformer driver (LTD) at the University of Michigan generates 200 ns risetime-current pulses of 500 to 600 kA into Al foil liners to study plasma instabilities and implosion dynamics, most recently MRT growth on imploding cylindrical liners. A full circuit model of MAIZE, along with I-V measurements, yields time-resolved load inductance. This has enabled measurements of an effective current-carrying radius to determine implosion velocity and plasma-vacuum interface acceleration. Measurements are also compared to implosion data from 4-time-frame laser shadowgraphy. Improved resolution measurements on the laser shadowgraph system have been used to examine the liner interface early in the shot to examine surface perturbations resulting from ETI for various seeding conditions. Fourier analysis examines the growth rates of wavelength bands of these structures to examine the transition from ETI to MRT. This work was supported by the U.S. DoE through award DE-SC0012328. S.G. Patel is supported by Sandia National Labs. D.A. Yager is supported by NSF fellowship grant DGE 1256260.
Coupling of sausage, kink, and magneto-Rayleigh-Taylor instabilities in a cylindrical liner
Weis, M. R.; Zhang, P.; Lau, Y. Y., E-mail: yylau@umich.edu; Gilgenbach, R. M. [Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, Michigan 48109-2104 (United States); Schmit, P. F.; Peterson, K. J.; Hess, M. [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)
2015-03-15
This paper analyzes the coupling of magneto-Rayleigh-Taylor (MRT), sausage, and kink modes in an imploding cylindrical liner, using ideal MHD. A uniform axial magnetic field of arbitrary value is included in each region: liner, its interior, and its exterior. The dispersion relation is solved exactly, for arbitrary radial acceleration (-g), axial wavenumber (k), azimuthal mode number (m), liner aspect ratio, and equilibrium quantities in each region. For small k, a positive g (inward radial acceleration in the lab frame) tends to stabilize the sausage mode, but destabilize the kink mode. For large k, a positive g destabilizes both the kink and sausage mode. Using the 1D-HYDRA simulation results for an equilibrium model that includes a pre-existing axial magnetic field and a preheated fuel, we identify several stages of MRT-sausage-kink mode evolution. We find that the m = 1 kink-MRT mode has a higher growth rate at the initial stage and stagnation stage of the implosion, and that the m = 0 sausage-MRT mode dominates at the main part of implosion. This analysis also sheds light on a puzzling feature in Harris' classic paper of MRT [E. G. Harris, Phys. Fluids 5, 1057 (1962)]. An attempt is made to interpret the persistence of the observed helical structures [Awe et al., Phys. Rev. Lett. 111, 235005 (2013)] in terms of non-axisymmetric eigenmode.
Coupling of sausage, kink, and magneto-Rayleigh-Taylor instabilities in a cylindrical liner
Weis, M. R.; Zhang, P.; Lau, Y. Y.; Schmit, P. F.; Peterson, K. J.; Hess, M.; Gilgenbach, R. M.
2015-03-01
This paper analyzes the coupling of magneto-Rayleigh-Taylor (MRT), sausage, and kink modes in an imploding cylindrical liner, using ideal MHD. A uniform axial magnetic field of arbitrary value is included in each region: liner, its interior, and its exterior. The dispersion relation is solved exactly, for arbitrary radial acceleration (-g), axial wavenumber (k), azimuthal mode number (m), liner aspect ratio, and equilibrium quantities in each region. For small k, a positive g (inward radial acceleration in the lab frame) tends to stabilize the sausage mode, but destabilize the kink mode. For large k, a positive g destabilizes both the kink and sausage mode. Using the 1D-HYDRA simulation results for an equilibrium model that includes a pre-existing axial magnetic field and a preheated fuel, we identify several stages of MRT-sausage-kink mode evolution. We find that the m = 1 kink-MRT mode has a higher growth rate at the initial stage and stagnation stage of the implosion, and that the m = 0 sausage-MRT mode dominates at the main part of implosion. This analysis also sheds light on a puzzling feature in Harris' classic paper of MRT [E. G. Harris, Phys. Fluids 5, 1057 (1962)]. An attempt is made to interpret the persistence of the observed helical structures [Awe et al., Phys. Rev. Lett. 111, 235005 (2013)] in terms of non-axisymmetric eigenmode.
Controlling Rayleigh-Taylor instabilities in solid liner implosions with rotating magnetic fields
Schmit, P. F.; McBride, R. D.; Robertson, G. K.; Velikovich, A. L.
2016-10-01
We report calculations demonstrating that a remarkable reduction in the growth of the magneto-Rayleigh-Taylor instability (MRTI) in initially solid, cylindrical metal shells can be achieved by applying a magnetic drive with a tilted, dynamic polarization, forming a solid-liner dynamic screw pinch (SLDSP). Using a self-consistent analytic framework, we demonstrate that MRTI growth factors of the most detrimental modes may be reduced by up to two orders of magnitude relative to conventional z-pinch implosions. One key application of this technique is to enable increasingly stable, higher performance liner implosions to achieve fusion. We weigh the potentially dramatic benefits of the SLDSP against the practical tradeoffs required to achieve the desired drive field history and identify promising target designs for future experimental and computational investigations. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. DoE's National Nuclear Security Administration under contract DE-AC04-94AL85000.
A new data processing technique for Rayleigh-Taylor instability growth experiments
Yuan, Yongteng; Tu, Shaoyong; Miao, Wenyong; Yin, Chuansheng; Hao, Yidan; Ding, Yongkun; Jiang, Shaoen, E-mail: jiangshn@vip.sina.com [Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang, Sichuan 621900 (China); Wu, Junfeng; Wang, Lifeng; Ye, Wenhua [Institute of Applied Physics and Computational Mathematics, Beijing 100094 (China)
2016-06-15
Typical face-on experiments for Rayleigh-Taylor instability study involve the time-resolved radiography of an accelerated foil with line-of-sight of the radiography along the direction of motion. The usual method which derives perturbation amplitudes from the face-on images reverses the actual image transmission procedure, so the obtained results will have a large error in the case of large optical depth. In order to improve the accuracy of data processing, a new data processing technique has been developed to process the face-on images. This technique based on convolution theorem, refined solutions of optical depth can be achieved by solving equations. Furthermore, we discuss both techniques for image processing, including the influence of modulation transfer function of imaging system and the backlighter spatial profile. Besides, we use the two methods to the process the experimental results in Shenguang-II laser facility and the comparison shows that the new method effectively improve the accuracy of data processing.
A new data processing technique for Rayleigh-Taylor instability growth experiments
Yongteng Yuan
2016-06-01
Full Text Available Typical face-on experiments for Rayleigh-Taylor instability study involve the time-resolved radiography of an accelerated foil with line-of-sight of the radiography along the direction of motion. The usual method which derives perturbation amplitudes from the face-on images reverses the actual image transmission procedure, so the obtained results will have a large error in the case of large optical depth. In order to improve the accuracy of data processing, a new data processing technique has been developed to process the face-on images. This technique based on convolution theorem, refined solutions of optical depth can be achieved by solving equations. Furthermore, we discuss both techniques for image processing, including the influence of modulation transfer function of imaging system and the backlighter spatial profile. Besides, we use the two methods to the process the experimental results in Shenguang-II laser facility and the comparison shows that the new method effectively improve the accuracy of data processing.
A new data processing technique for Rayleigh-Taylor instability growth experiments
Yuan, Yongteng; Tu, Shaoyong; Miao, Wenyong; Wu, Junfeng; Wang, Lifeng; Yin, Chuansheng; Hao, Yidan; Ye, Wenhua; Ding, Yongkun; Jiang, Shaoen
2016-06-01
Typical face-on experiments for Rayleigh-Taylor instability study involve the time-resolved radiography of an accelerated foil with line-of-sight of the radiography along the direction of motion. The usual method which derives perturbation amplitudes from the face-on images reverses the actual image transmission procedure, so the obtained results will have a large error in the case of large optical depth. In order to improve the accuracy of data processing, a new data processing technique has been developed to process the face-on images. This technique based on convolution theorem, refined solutions of optical depth can be achieved by solving equations. Furthermore, we discuss both techniques for image processing, including the influence of modulation transfer function of imaging system and the backlighter spatial profile. Besides, we use the two methods to the process the experimental results in Shenguang-II laser facility and the comparison shows that the new method effectively improve the accuracy of data processing.
Casner, A., E-mail: alexis.casner@cea.fr; Masse, L.; Liberatore, S.; Loiseau, P.; Masson-Laborde, P. E.; Jacquet, L. [CEA, DAM, DIF, F-91297 Arpajon (France); Martinez, D.; Moore, A. S.; Seugling, R.; Felker, S.; Haan, S. W.; Remington, B. A.; Smalyuk, V. A. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Farrell, M.; Giraldez, E.; Nikroo, A. [General Atomics, San Diego, California 92121 (United States)
2015-05-15
Academic tests in physical regimes not encountered in Inertial Confinement Fusion will help to build a better understanding of hydrodynamic instabilities and constitute the scientifically grounded validation complementary to fully integrated experiments. Under the National Ignition Facility (NIF) Discovery Science program, recent indirect drive experiments have been carried out to study the ablative Rayleigh-Taylor Instability (RTI) in transition from weakly nonlinear to highly nonlinear regime [A. Casner et al., Phys. Plasmas 19, 082708 (2012)]. In these experiments, a modulated package is accelerated by a 175 eV radiative temperature plateau created by a room temperature gas-filled platform irradiated by 60 NIF laser beams. The unique capabilities of the NIF are harnessed to accelerate this planar sample over much larger distances (≃1.4 mm) and longer time periods (≃12 ns) than previously achieved. This extended acceleration could eventually allow entering into a turbulent-like regime not precluded by the theory for the RTI at the ablation front. Simultaneous measurements of the foil trajectory and the subsequent RTI growth are performed and compared with radiative hydrodynamics simulations. We present RTI growth measurements for two-dimensional single-mode and broadband multimode modulations. The dependence of RTI growth on initial conditions and ablative stabilization is emphasized, and we demonstrate for the first time in indirect-drive a bubble-competition, bubble-merger regime for the RTI at ablation front.
Martinez, David
2015-11-01
We investigate on the National Ignition Facility (NIF) the ablative Rayleigh-Taylor (RT) instability in the transition from linear to highly nonlinear regimes. This work is part of the Discovery Science Program on NIF and of particular importance to indirect-drive inertial confinement fusion (ICF) where careful attention to the form of the rise to final peak drive is calculated to prevent the RT instability from shredding the ablator in-flight and leading to ablator mixing into the cold fuel. The growth of the ablative RT instability was investigated using a planar plastic foil with pre-imposed two-dimensional broadband modulations and diagnosed using x-ray radiography. The foil was accelerated for 12ns by the x-ray drive created in a gas-filled Au radiation cavity with a radiative temperature plateau at 175 eV. The dependence on initial conditions was investigated by systematically changing the modulation amplitude, ablator material and the modulation pattern. For each of these cases bubble mergers were observed and the nonlinear evolution of the RT instability showed insensitivity to the initial conditions. This experiment provides critical data needed to validate current theories on the ablative RT instability for indirect drive that relies on the ablative stabilization of short-scale modulations for ICF ignition. This paper will compare the experimental data to the current nonlinear theories. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC.
Analysis of Rayleigh-Taylor Instability Part I: Bubble and Spike Count
Kamath, C; Gezahegne, A; Miller, P
2006-08-08
The use of high-performance computers to simulate hydrodynamic instabilities has resulted in the generation of massive amounts of data. One aspect of the analysis of this data involves the identification and characterization of coherent structures known as ''bubbles'' and ''spikes''. This can be a challenge as there is no precise definition of these structures, and the large size of the data, as well as its distributed nature, precludes any extensive experimentation with different definitions and analysis algorithms. In this report, we describe the use of image processing techniques to identify and count bubbles and spikes in the Rayleigh-Taylor instability, which occurs when an initially perturbed interface between a heavier fluid and a lighter fluid is allowed to grow under the influence of gravity. We analyze data from two simulations, one a large-eddy simulation with 30 terabytes of analysis data, and the other a direct numerical simulation with 80 terabytes of analysis data. We consider different techniques to first convert the three-dimensional data to two dimensions and then count the structures of interest in the two-dimensional data. Our analysis of the bubble and spike counts over time indicates that there are four distinct regimes in the process of the mixing of the two fluids, starting from the initial linear stage, followed by the non-linear stage with weak turbulence, the mixing transition stage, and the final stage of strong turbulence. We also show that our results are relatively insensitive to the parameters used in our algorithms.
Detailed Measurements of Turbulent Rayleigh-Taylor Mixing at Large and Small Atwood Numbers
Malcolm J. Andrews, Ph.D.
2004-12-14
This project has two major tasks: Task 1. The construction of a new air/helium facility to collect detailed measurements of Rayleigh-Taylor (RT) mixing at high Atwood number, and the distribution of these data to LLNL, LANL, and Alliance members for code validation and design purposes. Task 2. The collection of initial condition data from the new Air/Helium facility, for use with validation of RT simulation codes at LLNL and LANL. Also, studies of multi-layer mixing with the existing water channel facility. Over the last twelve (12) months there has been excellent progress, detailed in this report, with both tasks. As of December 10, 2004, the air/helium facility is now complete and extensive testing and validation of diagnostics has been performed. Currently experiments with air/helium up to Atwood numbers of 0.25 (the maximum is 0.75, but the highest Reynolds numbers are at 0.25) are being performed. The progress matches the project plan, as does the budget, and we expect this to continue for 2005. With interest expressed from LLNL we have continued with initial condition studies using the water channel. This work has also progressed well, with one of the graduate Research Assistants (Mr. Nick Mueschke) visiting LLNL the past two summers to work with Dr. O. Schilling. Several journal papers are in preparation that describe the work. Two MSc.'s have been completed (Mr. Nick Mueschke, and Mr. Wayne Kraft, 12/1/03). Nick and Wayne are both pursuing Ph.D.s' funded by this DOE Alliances project. Presently three (3) Ph.D. graduate Research Assistants are supported on the project, and two (2) undergraduate Research Assistants. During the year two (2) journal papers and two (2) conference papers have been published, ten (10) presentations made at conferences, and three (3) invited presentations.
Gopalakrishnan, S. S.; Carballido-Landeira, J.; De Wit, A.; Knaepen, B.
2017-01-01
The relative role of convection and diffusion is characterized both numerically and experimentally for porous media flows due to a Rayleigh-Taylor instability of a horizontal interface between two miscible solutions in the gravity field. We show that, though globally convection dominates over diffusion during the nonlinear regime, diffusion can locally be as important as convection and even dominates over lateral convection far away from the fingertips. Our experimental and numerical computations of the temporal evolution of the mixing length, the width of the fingers, and their wavelength are in good agreement and show that the lateral evolution of fingers is governed by diffusion.
Y.G. Cao; W.K. Chow; N.K. Fong
2011-01-01
With a self-similar parameter b（At） = Hi/λi, where At is the Atwood number, Hi and λi are the a.mplluae and wavelength of bubble （i = 1） and spike （i = 2） respectively, we derive analytically the solutions to the buoyancy-drag equation recently proposed for dynamical evolution of Rayleigh-Taylor and Richtmyer-Meshkov mixing zone. Numerical solutions are obtained with a simple form ofb（At）--- 1/（1 ＋ At） and comparisons with recent LEM （linear electric motor） experiments are made, and an agreement is found with properly chosen initial conditions.
Nagel, S. R.; Raman, K. S.; Huntington, C. M.; MacLaren, S. A.; Wang, P.; Barrios, M. A.; Baumann, T.; Bender, J. D.; Benedetti, L. R.; Doane, D. M.; Felker, S.; Fitzsimmons, P.; Flippo, K. A.; Holder, J. P.; Kaczala, D. N.; Perry, T. S.; Seugling, R. M.; Savage, L.; Zhou, Y.
2017-07-01
A new experimental platform has been developed at the National Ignition Facility (NIF) for studying the Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) instabilities in a planar geometry at high-energy-densities. The platform uses 60 beams of the NIF laser to drive an initially solid shock tube containing a pre-machined interface between dense and light materials. The strong shock turns the initially solid target into a plasma and the material boundary into a fluid interface with the imprinted initial condition. The interface evolves by action of the RT and RM instabilities, and the growth is imaged with backlit x-ray radiography. We present our first data involving sinusoidal interface perturbations driven from the heavy side to the light side. Late-time radiographic images show the initial conditions reaching the deeply nonlinear regime, and an evolution of fine structure consistent with a transition to turbulence. We show preliminary comparisons with post-shot numerical simulations and discuss the implications for future campaigns.
Velikovich, A. L.; Giuliani, J. L.; Clark, R. W.; Mikitchuk, D.; Kroupp, E.; Maron, Y.; Fisher, A.; Schmit, P. F.
2014-10-01
Recent progress in developing the MagLIF approach to pulsed-power driven inertial confinement fusion has stimulated the interest in observation and mitigation of the magnetic Rayleigh-Taylor instability (MRTI) of liners and Z-pinches imploded in an axial magnetic field. Theoretical analysis of these issues is particularly important because direct numerical simulation of the MRTI development is challenging due to intrinsically 3D helical structure of the fastest-growing modes. We review the analytical small-amplitude theory of the MRTI perturbation development and the weakly nonlinear theory of MRTI mode interaction, emphasizing basic physics, opportunity for 3D code verification against exact analytical solutions, and stabilization criteria. The theory is compared to the experimental results obtained at Weizmann Institute with gas-puff Z pinches and on the Z facility at Sandia with solid liners imploded in an axial magnetic field. Work supported by the US DOE/NNSA, and by the US-Israel Binational Science Foundation. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.
Hillier, Andrew; Isobe, Hiroaki; Shibata, Kazunari [Kwasan and Hida Observatories, Kyoto University, Kyoto (Japan); Berger, Thomas [Lockheed Martin Solar and Astrophysics Laboratory, Palo Alto, CA (United States)
2012-09-10
The launch of the Hinode satellite has allowed high-resolution observations of supersonic bright downflows in quiescent prominences, known as prominence knots. We present observations in the Ca II H spectral line using the Solar Optical Telescope on board the Hinode satellite of a descending plasma knot of size {approx}900 km. The knot initially undergoes ballistic motion before undergoing impulsive accelerations at the same time as experiencing increases in intensity. We also present a subset of our three-dimensional magnetohydrodynamic simulations, performed to investigate the nonlinear stability of the Kippenhahn-Shlueter prominence model to the magnetic Rayleigh-Taylor instability in which interchange reconnection occurs. The interchange reconnection in the model breaks the force balance along the field lines which initiates the downflows. The downflows propagate with a downward fluid velocity of {approx}15 km s{sup -1} and a characteristic size of {approx}700 km. We conclude that the observed plasma blob and the simulated downflow are driven by the breaking of the force balance along the magnetic field as a result of a change in magnetic topology caused by reconnection of the magnetic field.
Rayleigh-Taylor Gravity Waves and Quasiperiodic Oscillation Phenomenon in X-ray Binaries
Titarchuk, Lev
2002-01-01
Accretion onto compact objects in X-ray binaries (black hole, neutron star (NS), white dwarf) is characterized by non-uniform flow density profiles. Such an effect of heterogeneity in presence of gravitational forces and pressure gradients exhibits Rayleigh-Taylor gravity waves (RTGW). They should be seen as quasiperiodic wave oscillations (QPO) of the accretion flow in the transition (boundary) layer between the Keplerian disk and the central object. In this paper the author shows that the main QPO frequency, which is very close to the Keplerian frequency, is split into separate frequencies (hybrid and low branch) under the influence of the gravitational forces in the rotational frame of reference. The RTGWs must be present and the related QPOs should be detected in any system where the gravity, buoyancy and Coriolis force effects cannot be excluded (even in the Earth and solar environments). The observed low and high QPO frequencies are an intrinsic signature of the RTGW. The author elaborates the conditions for the density profile when the RTGW oscillations are stable. A comparison of the inferred QPO frequencies with QPO observations is presented. The author finds that hectohertz frequencies detected from NS binaries can be identified as the RTGW low branch frequencies. The author also predicts that an observer can see the double NS spin frequency during the NS long (super) burst events when the pressure gradients and buoyant forces are suppressed. The Coriolis force is the only force which acts in the rotational frame of reference and its presence causes perfect coherent pulsations with a frequency twice of the NS spin. The QPO observations of neutron binaries have established that the high QPO frequencies do not go beyond of the certain upper limit. The author explains this observational effect as a result of the density profile inversions. Also the author demonstrates that a particular problem of the gravity waves in the rotational frame of reference in the
Generalized Rayleigh-Taylor instability in the presence of time-dependent equilibrium
Basu, B.
1997-08-01
Plasma instability under the combined influence of the gravity and an eastward electric field, commonly referred to as the generalized Rayleigh-Taylor instability, is considered for a time-dependent equilibrium situation. In the nighttime equatorial ionosphere the time-dependent equilibrium situation arises because of the vertically upward E0×B0 drift of the plasma in conjunction with the altitude-dependent recombination process and the collisional diffusion process. After determining the time-dependent equilibrium density and, in particular, the inverse density gradient scale length L-1, which determines the growth rate of the instability, the stability of small-amplitude perturbations is analyzed. The general solution of the problem, where the effects of all of the above-mentioned processes are included simultaneously, requires numerical analysis. In this paper the effects are studied in limiting situations for which useful analytic solutions can be obtained. The effect of diffusion on L-1 is studied by neglecting both the upward plasma drift and the altitude variation of the recombination frequency νR, and it is verified that the effect is negligible for typical values of the ionospheric parameters. The effects of the other two processes on L-1 are studied by neglecting diffusion. The effect of the altitude variation of νR on the linear growth of the perturbations is studied by adopting the so-called local approximation. It is found that the value of L-1 and hence the value of the growth rate are enhanced by the altitude variation of νR. The enhancements rapidly increase with time to large values at lower altitudes and to significant values at higher altitudes when compared with the values for the spatially uniform νR case. Consequently, the time evolution of the instability and, more importantly, the level of fluctuations at saturation will be significantly affected by the enhancements. The nonlocal aspect of the instability in the upward drifting plasma
Rarefaction-undercompressive fronts in driven films
Münch, A.; Bertozzi, A. L.
1999-10-01
We consider experiments by Ludviksson and Lightfoot [AIChE J. 17, 1166 (1971)] on thin liquid films driven up a vertical plate by a thermally induced surface tension gradient with a counteracting gravitational force, and revisit their theoretical analysis, which neglects the effects of curvature, for predicting the climbing rate of the front. We present a new theory for the lubrication model with curvature effects, and get rising rates that depend on the microscopic length scale at the contact line. The predictions are, in general, in better agreement with the experiment.
Prajapati, Ramprasad
2016-07-01
The Rayleigh-Taylor (R-T) instability is recently investigated is strongly coupled plasma looking to its importance in dense stellar systems and Inertial Confinement Fusion [1-3]. In the present work, the effect of quantum corrections are studied on Rayleigh-Taylor (R-T) instability and internal wave propagation in a strongly coupled, magnetized, viscoelastic fluid. The modified generalized hydrodynamic model is used to derive the analytical dispersion relation. The internal wave mode and dispersion relation are modified due to the presence of quantum corrections and viscoelastic effects. We observe that strong coupling effects and quantum corrections significantly modifies the dispersion characteristics. The dispersion relation is also discussed in weakly coupled (hydrodynamic) and strongly coupled (kinetic) limits. The explicit expression of R-T instability criterion is derived which is influenced by shear velocity and quantum corrections. Numerical calculations are performed in astrophysical and experimental relevance and it is examined that both the shear and quantum effects suppresses the growth rate of R-T instability. The possible application of the work is discussed in Inertial Confinement Fusion (ICF) to discuss the suppression of R-T instability under considered situation. References: [1] R. P. Prajapati, Phys. Plasmas 23, 022106 (2016). [2] K. Avinash and A. Sen, Phys. Plasmas 22, 083707 (2015). [3] A. Das and P. Kaw, Phys. Plasmas 21 (2014) 062102.
Wang, H.; Currie, C. A.
2013-12-01
For many continental plates, significant vertical motion of Earth's surface has occurred within the plate interior which can not be clearly linked to plate tectonic processes. For example, several craton areas exhibit anomalous basins, e.g., the Williston basin, Illinois basin and Michigan basin in North America. In orogenic belts, there are examples of local areas (~100 km wide) where the surface has undergone subsidence and then uplift of >1 km, such as the Arizaro basin (central Andes) and Wallowa Mountains (northeast Oregon). Given the near-circular shape of the surface deflection, it has been suggested that they may be related to gravitational foundering of dense lower lithosphere, i.e., Rayleigh-Taylor instability (or 'RT drip'). In order to investigate the surface effects of an RT drip, we use two methods: (1) 2D thermal-mechanical numerical models to study links between drip dynamics and crustal deformation and (2) a theoretical analysis of the crustal deformation induced by stresses from the RT drip. The numerical models consist of a continental lithosphere overlying a sublithospheric mantle. A high-density material is placed in the mantle lithosphere or lower crust to initiate a drip event, and a stress-free boundary condition allows the development of surface topography during model evolution. A reasonable range of crustal viscosity and thickness is tested to study the RT drip in different tectonic settings, from a cold craton to a hot orogen with thick crust. Four types of surface deflection are observed: (1) subsidence; (2) subsidence followed by uplift; (3) uplift; and (4) little deflection. When the crust is relatively strong or thin, the surface has a negative elevation, forming a basin. For a weak or thick crust, the RT drip induces crustal flow, leading to crustal thickening that can uplift the surface; an extremely weak crust decouples the surface and RT drip and the surface is unperturbed. Our theoretical analysis considers the surface
Zhou, M. L.; Liu, B.; Hu, R. H.; Shou, Y. R.; Lin, C.; Lu, H. Y.; Lu, Y. R.; Gu, Y. Q.; Ma, W. J.; Yan, X. Q.
2016-08-01
In the case of a thin plasma slab accelerated by the radiation pressure of an ultra-intense laser pulse, the development of Rayleigh-Taylor instability (RTI) will destroy the acceleration structure and terminate the acceleration process much sooner than theoretical limit. In this paper, a new scheme using multiple Gaussian pulses for ion acceleration in a radiation pressure acceleration regime is investigated with particle-in-cell simulation. We found that with multiple Gaussian pulses, the instability could be efficiently suppressed and the divergence of the ion bunch is greatly reduced, resulting in a longer acceleration time and much more collimated ion bunch with higher energy than using a single Gaussian pulse. An analytical model is developed to describe the suppression of RTI at the laser-plasma interface. The model shows that the suppression of RTI is due to the introduction of the long wavelength mode RTI by the multiple Gaussian pulses.
A comparative study of Rayleigh-Taylor and Richtmyer-Meshkov instabilities in 2D and 3D in tantalum
Sternberger, Z.; Maddox, B. R.; Opachich, Y. P.; Wehrenberg, C. E.; Kraus, R. G.; Remington, B. A.; Randall, G. C.; Farrell, M.; Ravichandran, G.
2017-01-01
Driving a shock wave through the interface between two materials with different densities can result in the Richtmyer-Meshkov or Rayleigh-Taylor instability and initial perturbations at the interface will grow. If the shock wave is sufficiently strong, the instability will lead to plastic flow at the interface. Material strength will reduce the amount of plastic flow and suppress growth. While such instabilities have been investigated in 2D, no studies of this phenomena have been performed in 3D on materials with strength. Initial perturbations to seed the hydrodynamic instability were coined into tantalum recovery targets. Two types of perturbations were used, two dimensional (2D) perturbations (hill and valley) and three-dimensional (3D) perturbations (egg crate pattern). The targets were subjected to dynamic loading using the Janus laser at the Jupiter Laser Facility. Shock pressures ranged from 50 GPa up to 150 GPa and were calibrated using VISAR drive targets.
Wang, Y.-M.; Nepveu, M.; Robertson, J. A.
1984-06-01
An earlier investigation of the nonlinear Rayleigh-Taylor instability for accreting X-ray sources is extended to allow for more realistic initial conditions. The two-dimensional computations show the heavy and light fluids undergoing complementary circulatory motions which result in the formation of alternating inverted and upright 'mushroom' structures along the interface. The structures develop independently of the shape of the initial perturbation. Short wavelength modes have a strong tendency to dominate long ones, with the lower bound being set by viscous damping. A relatively modest vertical magnetic field will act to suppress the vortex motions and produce a 'bubble and spike' structure. A crude simulation of the instability occurring in a radiation-supported accretion column is presented; after a slow start, the magnetically constrained plasma drips down into the photon medium in the form of long narrow fingers, the dominant scale-length being determined by radiative viscosity.
Jiang, Fei
2016-11-01
In this article, we investigate the effect of viscosity on the largest growth rate in the linear Rayleigh-Taylor (RT) instability of a three-dimensional nonhomogeneous incompressible viscous flow in a bounded domain. By adapting a modified variational approach and careful analysis, we show that the largest growth rate in linear RT instability tends to zero as the viscosity coefficient goes to infinity. Moreover, the largest growth rate increasingly converges to one of the corresponding inviscid fluids as the viscosity coefficient goes to zero. Applying these analysis techniques to the corresponding viscous magnetohydrodynamic fluids, we can also show that the largest growth rate in linear magnetic RT instability tends to zero as the strength of horizontal (or vertical) magnetic field increasingly goes to a critical value.
Hillier, Andrew
2016-01-01
The magnetic Rayleigh-Taylor instability has been shown to play a key role in many astrophysical systems. The equation for the growth rate of this instability in the incompressible limit, and the most-unstable mode that can be derived from it, are often used to estimate the strength of the magnetic field that is associated with the observed dynamics. However, there are some issues with the interpretations given. Here we show that the class of most unstable modes $k_u$ for a given $\\theta$, the class of modes often used to estimate the strength of the magnetic field from observations, for the system leads to the instability growing as $\\sigma^2=1/2 A g k_u$, a growth rate which is independent of the strength of the magnetic field and which highlights that small scales are preferred by the system, but not does not give the fastest growing mode for that given $k$. We also highlight that outside of the interchange ($\\mathbf{k}\\cdot\\mathbf{B}=0$) and undular ($\\mathbf{k}$ parallel to $\\mathbf{B}$) modes, all the o...
Morgan, Brandon; Olson, Britton; White, Justin; McFarland, Jacob
2016-11-01
High-fidelity large eddy simulation (LES) of a low-Atwood number (A = 0.05) Rayleigh-Taylor mixing layer is performed using the tenth-order compact difference code Miranda. An initial multimode perturbation spectrum is specified in Fourier space as a function of mesh resolution such that a database of results is obtained in which each successive level of increased grid resolution corresponds approximately to one additional doubling of the mixing layer width, or generation. The database is then analyzed to determine approximate requirements for self-similarity, and a new metric is proposed to quantify how far a given simulation is from the limit of self-similarity. It is determined that the present database reaches a high degree of self-similarity after approximately 4.5 generations. Finally, self-similar turbulence profiles from the LES database are compared with one-dimensional simulations using the k- L- a and BHR-2 Reynolds-averaged Navier-Stokes (RANS) models. The k- L- a model, which is calibrated to reproduce a quadratic turbulence kinetic energy profile for a self-similar mixing layer, is found to be in better agreement with the LES than BHR-2 results. This work was preformed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.
Yager-Elorriaga, D. A.; Steiner, A. M.; Patel, S. G.; Jordan, N. M.; Gilgenbach, R. M.; Lau, Y. Y.; Weis, M. R.; Zhang, P.
2015-11-01
At the Michigan Accelerator for Inductive Z-Pinch Experiments (MAIZE) facility, a 1-MA Linear Transformer Driver (LTD) is being used to deliver 500-600 kA to cylindrical liners in order to study the magneto Rayleigh-Taylor (MRT), sausage, and kink instabilities in imploding and exploding Al plasmas. The liners studied in this experiment had thicknesses of 400 nm to 30 μm, heights of 1-2 cm, and diameters of 1-6 mm. The plasmas were imaged using 4-time-frame, laser shadowgraphy and shearing-interferometry at 532 nm. For imploding liners, the measured acceleration was found to be less than predicted from the current pulse, indicating significant diffusion of the azimuthal magnetic field. A simple experimental configuration is presented for ``end-on'' laser probing in the r- θ plane in order to study the interior of the liner. Finally, the effects of axial magnetic fields are determined by modifying the return current posts and incorporating external coils. Experimental growth rates are determined and discussed. This work was supported by DOE award DE-SC0012328. S.G. Patel supported by Sandia National Labs. D.A. Yager was supported by NSF fellowship grant DGE 1256260.
HIGH-MODE RAYLEIGH-TAYLOR GROWTH IN NIF IGNITION CAPSULES
Hammel, B A; Haan, S W; Clark, D; Edwards, M J; Langer, S H; Marinak, M; Patel, M; Salmonson, J; Scott, H A
2009-08-04
An assessment of short wavelength hydrodynamic stability is an essential component in the optimization of NIF ignition target designs. Using highly-resolved massively-parallel 2-D Hydra simulations, we routinely evaluate target designs up to mode numbers of 2000 ({lambda} {approx} 2 {micro}m). On the outer ablator surface, mode numbers up to {approx}300 ({lambda} {approx} 20 {micro}m) can have significant growth in CH capsule designs. At the internal fuel:ablator interface mode numbers up to {approx}2000 are important for both CH and Be designs. In addition, 'isolated features' on the capsule, such as the 'fill-tube' ({approx} 5 {micro}m scale-length) and defects, can seed short wavelength growth at the ablation front and the fuel:ablator interface, leading to the injection of {approx} 10's ng of ablator material into the central hot-spot. We are developing methods to measure high-mode mix on NIF implosion experiments. X-ray spectroscopic methods are appealing since mix into the hot-spot will result in x-ray emission from the high-Z dopant (Cu or Ge) in the ablator material (Be or CH).
Hillier, Andrew S.
2016-10-01
The magnetic Rayleigh-Taylor instability has been shown to play a key role in many astrophysical systems. The equation for the growth rate of this instability in the incompressible limit, and the most-unstable mode that can be derived from it, are often used to estimate the strength of the magnetic field that is associated with the observed dynamics. However, there are some issues with the interpretations given. Here, we show that the class of most unstable modes ku for a given θ, the class of modes often used to estimate the strength of the magnetic field from observations, for the system leads to the instability growing as σ2 = 1/2Agku, a growth rate which is independent of the strength of the magnetic field and which highlights that small scales are preferred by the system, but not does not give the fastest growing mode for that given k. We also highlight that outside of the interchange (k ṡ B = 0) and undular (k parallel to B) modes, all the other modes have a perturbation pair of the same wavenumber and growth rate that when excited in the linear regime can result in an interference pattern that gives field aligned filamentary structure often seen in 3D simulations. The analysis was extended to a sheared magnetic field, where it was found that it was possible to extend the results for a non-sheared field to this case. We suggest that without magnetic shear it is too simplistic to be used to infer magnetic field strengths in astrophysical systems.
Fiksel, G.; Hu, S. X.; Epstein, R.; Goncharov, V. N.; Meyerhofer, D. D.; Sangster, T. C.; Yaakobi, B.; Bonino, M. J.; Jungquist, R. K.; Smalyuk, V. A.
2012-10-01
The effect of medium-Z doping of plastic ablators on laser imprinting and Rayleigh-- Taylor (RT) instability growth was studied using spherical direct-drive implosions on the OMEGA Laser System. The targets were spherical plastic (CH) shells, with an outer diameter of 860 μm and a thickness of 22 μm, doped with a varied concentration of Si (4.3% and 7.4%) and Ge (3.9%). The targets were imploded with 48 beams with a low-adiabat, triple-picket laser shape pulse with a peak intensity of 4 x 10^14 W/cm^2 and a pulse duration of 2.5 ns. The shells were x-ray radiographed through a 400-μm opening in the side of the target. The results show that impurity doping strongly reduces the shell-density modulation and the instability growth rate. The amplitude of the initial imprint is reduced by a factor of 2.5±0.5 for CH[4.3% Si] targets and a factor of 3±0.5 for CH[7.4% Si] and CH[3.9% Ge] targets. At the end of the acceleration phase, the reduction factor becomes 3±0.5 and 5±0.5, correspondingly. The RT instability growth rate in doped targets is reduced by a factor of 1.5 compared to undoped ones. Simulations using the 2-D radiation--hydrodynamics code DRACO show good agreement with the measurements. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302.
Fiksel, G.; Hu, S. X.; Goncharov, V. A.; Meyerhofer, D. D.; Sangster, T. C.; Smalyuk, V. A.; Yaakobi, B.; Bonino, M. J.; Jungquist, R.
2012-06-01
The effect of medium-Z doping of plastic ablators on laser imprinting and Rayleigh-Taylor (RT) instability growth was studied using spherical direct-drive implosions on the OMEGA Laser System [T. R. Boehly et al., Opt. Commun. 133, 495 (1977)]. The targets were spherical plastic (CH) shells, with an outer diameter of 860 μm and a thickness of 22 μm, volume doped with a varied concentration of Si (4.3% and 7.4%) and Ge (3.9%). The targets were imploded with 48 beams with a low-adiabat, triple-picket laser shape pulse with a peak intensity of 4×1014W/cm2, and a pulse duration of 2.5 ns. The shells were x-ray radiographed through a 400 -μm opening in the side of the target. The results show that volumetric impurity doping strongly reduces the shell density modulation and the instability growth rate. The amplitude of the initial imprint is reduced by a factor of 2.5 ± 0.5 for CH[4.3% Si] targets and by a factor of 3 ± 0.5 for CH[7.4% Si] and CH[3.9% Ge] targets. At the end of the acceleration phase, the reduction factor becomes 3 ± 0.5 and 5 ± 0.5, correspondingly. The RT instability growth rate in doped targets is reduced by a factor of 1.5 compared to undoped ones. Simulations using the two-dimensional, radiation-hydrodynamics code draco show good agreement with the measurements.
Fiksel, G.; Hu, S. X.; Goncharov, V. A.; Meyerhofer, D. D.; Sangster, T. C.; Yaakobi, B.; Bonino, M. J.; Jungquist, R. [Laboratory for Laser Energetics, University of Rochester, 250 East River Rd., Rochester, New York 14623-1299 (United States); Smalyuk, V. A. [Lawrence Livermore National Laboratory, Livermore, California 94551 (United States)
2012-06-15
The effect of medium-Z doping of plastic ablators on laser imprinting and Rayleigh-Taylor (RT) instability growth was studied using spherical direct-drive implosions on the OMEGA Laser System [T. R. Boehly et al., Opt. Commun. 133, 495 (1977)]. The targets were spherical plastic (CH) shells, with an outer diameter of 860 {mu}m and a thickness of 22 {mu}m, volume doped with a varied concentration of Si (4.3% and 7.4%) and Ge (3.9%). The targets were imploded with 48 beams with a low-adiabat, triple-picket laser shape pulse with a peak intensity of 4 Multiplication-Sign 10{sup 14}W/cm{sup 2}, and a pulse duration of 2.5 ns. The shells were x-ray radiographed through a 400 -{mu}m opening in the side of the target. The results show that volumetric impurity doping strongly reduces the shell density modulation and the instability growth rate. The amplitude of the initial imprint is reduced by a factor of 2.5 {+-} 0.5 for CH[4.3% Si] targets and by a factor of 3 {+-} 0.5 for CH[7.4% Si] and CH[3.9% Ge] targets. At the end of the acceleration phase, the reduction factor becomes 3 {+-} 0.5 and 5 {+-} 0.5, correspondingly. The RT instability growth rate in doped targets is reduced by a factor of 1.5 compared to undoped ones. Simulations using the two-dimensional, radiation-hydrodynamics code draco show good agreement with the measurements.
Hillier, Andrew; Isobe, Hiroaki; Shibata, Kazunari [Kwasan and Hida Observatories, Kyoto University, Kyoto (Japan); Berger, Thomas, E-mail: andrew@kwasan.kyoto-u.ac.jp [Lockheed Martin Solar and Astrophysics Laboratory, Palo Alto, CA (United States)
2012-02-20
The launch of the Hinode satellite led to the discovery of rising plumes, dark in chromospheric lines, that propagate from large ({approx}10 Mm) bubbles that form at the base of quiescent prominences. The plumes move through a height of approximately 10 Mm while developing highly turbulent profiles. The magnetic Rayleigh-Taylor instability was hypothesized to be the mechanism that drives these flows. In this study, using three-dimensional (3D) MHD simulations, we investigate the nonlinear stability of the Kippenhahn-Schlueter prominence model for the interchange mode of the magnetic Rayleigh-Taylor instability. The model simulates the rise of a buoyant tube inside the quiescent prominence model, where the interchange of magnetic field lines becomes possible at the boundary between the buoyant tube and the prominence. Hillier et al. presented the initial results of this study, where upflows of constant velocity (maximum found 6 km s{sup -1}) and a maximum plume width Almost-Equal-To 1.5 Mm which propagate through a height of approximately 6 Mm were found. Nonlinear interaction between plumes was found to be important for determining the plume dynamics. In this paper, using the results of ideal MHD simulations, we determine how the initial parameters for the model and buoyant tube affect the evolution of instability. We find that the 3D mode of the magnetic Rayleigh-Taylor instability grows, creating upflows aligned with the magnetic field of constant velocity (maximum found 7.3 km s{sup -1}). The width of the upflows is dependent on the initial conditions, with a range of 0.5-4 Mm which propagate through heights of 3-6 Mm. These results are in general agreement with the observations of the rising plumes.
Integrated code development for studying laser driven plasmas
Takabe, Hideaki; Nagatomo, Hideo; Sunahara, Atsusi; Ohnishi, Naofumi; Naruo, Syuji; Mima, Kunioki [Osaka Univ., Suita (Japan). Inst. of Laser Engineering
1998-03-01
Present status and plan for developing an integrated implosion code are briefly explained by focusing on motivation, numerical scheme and issues to be developed more. Highly nonlinear stage of Rayleigh-Taylor instability of ablation front by laser irradiation has been simulated so as to be compared with model experiments. Improvement in transport and rezoning/remapping algorithms in ILESTA code is described. (author)
Liu, Wanhai; Yu, Changping; Jiang, Hongbin; Li, Xinliang
2017-02-01
Based on the harmonic analysis [Liu et al., Phys. Plasmas 22, 112112 (2015)], the analytical investigation on the harmonic evolution in Rayleigh-Taylor instability (RTI) at a spherical interface has been extended to the general case of arbitrary Atwood numbers by using the method of the formal perturbation up to the third order in a small parameter. Our results show that the radius of the initial interface [i.e., Bell-Plessett (BP) effect] dramatically influences the harmonic evolution for arbitrary Atwood numbers. When the initial radius approaches infinity compared against the initial perturbation wavelength, the amplitudes of the first four harmonics will recover those in planar RTI. The BP effect makes the amplitudes of the zeroth, second, and third harmonics increase faster for a larger Atwood number than smaller one. The BP effect reduces the third-order negative feedback to the fundamental mode for a smaller Atwood number, and strengthens it for a larger one. Hence, the BP effect helps the fundamental mode grow faster for a smaller Atwood number.
邱孝明; 黄林; 简广德
2002-01-01
A magnetohydrodynamic (MHD) formulation is derived to investigate and compare the mitigation effects of both the sheared axial flow and finite Larmor radius (FLR) on the Rayleigh-Taylor (RT) instability in Z-pinch implosions. The sheared axial flow is introduced into MHD equations in a conventional way and the FLR effect into the equations via а/аt → -i(ω + ik2⊥ρi2Ωi), as proposed in our previous paper [Chin. Phys. Lett. 2002, 19:217] , where k2⊥ρ2i is referred to FLR effect from the general kinetic theory of magnetized plasma. Therefore the linearized continuity and momentum equations for the perturbed massdensity and velocity include both the sheared axial flow and the FLR effect. It is found that the effect of sheared axial flow with a lower peak velocity can mitigate RT instability in the whole wavenumber region and the effect of sheared axial flow with a higher one can mitigate RT instability only in the large wavenumber region (for normalized wavenumber κ＞ 2.4); The effect of FLR can mitigate RT instability in the whole wavenumber region and the mitigation effect is stronger than that of the sheared axial flow with a lower peak velocity in the almost whole wavenumber region.
Schilling, Oleg
2016-11-01
Two-, three- and four-equation, single-velocity, multicomponent Reynolds-averaged Navier-Stokes (RANS) models, based on the turbulent kinetic energy dissipation rate or lengthscale, are used to simulate At = 0 . 5 Rayleigh-Taylor turbulent mixing with constant and complex accelerations. The constant acceleration case is inspired by the Cabot and Cook (2006) DNS, and the complex acceleration cases are inspired by the unstable/stable and unstable/neutral cases simulated using DNS (Livescu, Wei & Petersen 2011) and the unstable/stable/unstable case simulated using ILES (Ramaprabhu, Karkhanis & Lawrie 2013). The four-equation models couple equations for the mass flux a and negative density-specific volume correlation b to the K- ɛ or K- L equations, while the three-equation models use a two-fluid algebraic closure for b. The lengthscale-based models are also applied with no buoyancy production in the L equation to explore the consequences of neglecting this term. Predicted mixing widths, turbulence statistics, fields, and turbulent transport equation budgets are compared among these models to identify similarities and differences in the turbulence production, dissipation and diffusion physics represented by the closures used in these models. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Stabilizing the Advancing Front of Thermally Driven Climbing Films.
Kataoka; Troian
1998-07-15
As known from thermodynamic principles, the surface tension of a liquid decreases with increasing temperature. This property can be used to force a liquid film to climb a vertical substrate whose lower end is held warmer than the top. The vertical gradient in surface tension generates a surface shear stress that causes the liquid film to spread upward spontaneously in the direction of higher surface tension. Experimental investigations have shown that the application of a large temperature gradient produces a thin climbing film whose leading edge develops a pronounced capillary rim which breaks up into vertical rivulets. In contrast, smaller temperature gradients produce thicker films whose profiles decrease monotonically toward the substrate with no evidence of a rim or subsequent film breakup. We have previously shown within linear stability analysis that a climbing film can undergo a fingering instability at the leading edge when the film is sufficiently thin or the shear stress sufficiently large for gravitational effects to be negligible. In this work we show that thicker films which experience significant drainage cannot form a capillary rim and spread in stable fashion. Gravitational drainage helps promote a straight advancing front and complete surface coverage. Our numerical predictions for the entire shape and stability of the climbing film are in good agreement with extensive experiments published years ago by Ludviksson and Lightfoot (AIChE J. 17, 1166 (1971)). We propose that the presence of a counterflow which eliminates the capillary rim can provide a simple and general technique for stabilizing thermally driven films in other geometries. Copyright 1998 Academic Press.
Dutta, Urmi; Baruah, Amiya; Mandal, Nibir
2016-09-01
In many geological systems, inversion of density stratification sets in Rayleigh-Taylor (RT) instabilities, leading to an ascent of relatively low-density materials through the high-density overburden in the form of diapirs. These diapirs often originate from dipping low-density layers. This study aims to show how the initial tilt of such source layers can control the ascent behaviour of diapirs initiated by RT instabilities. Using two-layer viscous models we produced RT instabilities in physical experiments, and investigated the effects of source-layer tilts (beta;). Our experiments suggest that these diapirs ascend with contrasting lateral spreading rates in the up and down slope directions, resulting in their axi-asymmetric geometry. However, their heads retain a circular outline on the horizontal top surface, where the upwelling axis is located away from their geometric centre in the upslope direction. In this paper, we present a series of experimental models to demonstrate the spectrum of axi-symmetric to -asymmetric geometrical transitions with increasing beta;. Our experiments also reveal that when beta; is large (>4°) the diapirs become unstable, resulting in a continuous migration of their stems in the upslope direction. Using the volume of fluid method we ran computational fluid dynamic (CFD) simulations to study the underlying hydrodynamics of axi-asymmetric diapiric growth. The CFD simulations show that beta; > 0° conditions develop stronger flow vortices on the downslope side of an ascending diapir, leading to a pressure difference between the up- and downslope flanks. Such a differential pressure causes the diapir head to spread at a faster rate in the tilt direction. An estimate of the asymmetric spreading rates is given as a function of beta;. Our present study provides a fundamental understanding of the hydrodynamic flow structure responsible for the asymmetric growth of RT instabilities on tilted source layers, as applicable to a wide range of
Kuranz, Carolyn C.; Drake, R. Paul; Park, Hye Sook; Huntington, Channing; Miles, Aaron R.; Remington, Bruce A.; Plewa, Tomek; Trantham, Matt; Shvarts, Dov; Raman, Kumar; MacLaren, Steven; Wan, Wesley; Doss, Forrest; Kline, John; Flippos, Kirk; Malamud, Guy; Handy, Timothy; Prisbey, Shon; Grosskopf, Michael; Krauland, Christine; Klein, Sallee; Harding, Eric; Wallace, Russell; Marion, Donna; Kalantar, Dan
2017-06-01
Energy-transport effects can alter the structure that develops as a supernova evolves into a supernova remnant. The Rayleigh Taylor (RT) instability is thought to produce structure at the interface between the stellar ejecta and the circumstellar matter (CSM), based on simple models and hydrodynamic simulations. When a blast wave emerges from an exploding star, it drives a forward shock into the CSM and a reverse shock forms in the expanding stellar ejecta, creating a young supernova remnant (SNR). As mass accumulates in the shocked layers, the interface between these two shocks decelerates, becoming unstable to the RT instability. Simulations predict that RT produces structures at this interface, having a range of spatial scales. When the CSM is dense enough, as in the case of SN 1993J, the hot shocked matter can produce significant radiative fluxes that affect the emission from the SNR. Here we report experimental results from the National Ignition Facility (NIF) to explore how large energy fluxes, which are present in supernovae such as SN 1993J, might affect this structure. The experiment used NIF to create a RT unstable interface subject to a high energy flux by the emergence of a blast wave into lower-density matter, in analogy to the SNR. We also preformed and with a low energy flux to compare the affect of the energy flux on the instability growth. We found that the RT growth was reduced in the experiments with a high energy flux. In analyzing the comparison with SN 1993J, we discovered that the energy fluxes produced by heat conduction appear to be larger than the radiative energy fluxes, and large enough to have dramatic consequences. No reported astrophysical simulations have included radiation and heat conduction self-consistently in modeling SNRs.
Bates, J. W.; Schmitt, A. J.; Karasik, M.; Zalesak, S. T.
2016-12-01
The ablative Rayleigh-Taylor (RT) instability is a central issue in the performance of laser-accelerated inertial-confinement-fusion targets. Historically, the accurate numerical simulation of this instability has been a challenging task for many radiation hydrodynamics codes, particularly when it comes to capturing the ablatively stabilized region of the linear dispersion spectrum and modeling ab initio perturbations. Here, we present recent results from two-dimensional numerical simulations of the ablative RT instability in planar laser-ablated foils that were performed using the Eulerian code FastRad3D. Our study considers polystyrene, (cryogenic) deuterium-tritium, and beryllium target materials, quarter- and third-micron laser light, and low and high laser intensities. An initial single-mode surface perturbation is modeled in our simulations as a small modulation to the target mass density and the ablative RT growth-rate is calculated from the time history of areal-mass variations once the target reaches a steady-state acceleration. By performing a sequence of such simulations with different perturbation wavelengths, we generate a discrete dispersion spectrum for each of our examples and find that in all cases the linear RT growth-rate γ is well described by an expression of the form γ = α [ k g / ( 1 + ɛ k L m ) ] 1 / 2 - β k V a , where k is the perturbation wavenumber, g is the acceleration of the target, Lm is the minimum density scale-length, Va is the ablation velocity, and ɛ is either one or zero. The dimensionless coefficients α and β in the above formula depend on the particular target and laser parameters and are determined from two-dimensional simulation results through the use of a nonlinear curve-fitting procedure. While our findings are generally consistent with those of Betti et al. (Phys. Plasmas 5, 1446 (1998)), the ablative RT growth-rates predicted in this investigation are somewhat smaller than the values previously reported for the
Parker, E. N.
1987-01-01
The dynamics of thermal shadows which develop in the convective zone of a star around an insulating obstacle such as a horizontal band in intense magnetic field are studied. The depth of the shadow on the cool side of the obstacle is found to depend largely on the width of the obstacle multiplied by the temperature gradient. Thermal shadows pressing fields up to 10,000 G downward against the bottom of the convective zone are produced by the broad bands of the azimuthal field in the sun's convective zone. In the third part, the time-dependent accumulation of heat beneath a thermal barrier simulating such a band in the lower convective zone of the sun is considered. The resulting Rayleigh-Taylor instability is shown to cause tongues of heated gas to penetrate upward through the field, providing the emerging magnetic fields that give rise to the activity of the sun.
Laboratory blast wave driven instabilities
Kuranz, Carolyn
2008-11-01
This presentation discusses experiments involving the evolution of hydrodynamic instabilities in the laboratory under high-energy-density (HED) conditions. These instabilities are driven by blast waves, which occur following a sudden, finite release of energy, and consist of a shock front followed by a rarefaction wave. When a blast wave crosses an interface with a decrease in density, hydrodynamic instabilities will develop. Instabilities evolving under HED conditions are relevant to astrophysics. These experiments include target materials scaled in density to the He/H layer in SN1987A. About 5 kJ of laser energy from the Omega Laser facility irradiates a 150 μm plastic layer that is followed by a low-density foam layer. A blast wave structure similar to those in supernovae is created in the plastic layer. The blast wave crosses an interface having a 2D or 3D sinusoidal structure that serves as a seed perturbation for hydrodynamic instabilities. This produces unstable growth dominated by the Rayleigh-Taylor (RT) instability in the nonlinear regime. We have detected the interface structure under these conditions using x-ray backlighting. Recent advances in our diagnostic techniques have greatly improved the resolution of our x-ray radiographic images. Under certain conditions, the improved images show some mass extending beyond the RT spike and penetrating further than previously observed or predicted by current simulations. The observed effect is potentially of great importance as a source of mass transport to places not anticipated by current theory and simulation. I will discuss the amount of mass in these spike extensions, the associated uncertainties, and hypotheses regarding their origin We also plan to show comparisons of experiments using single mode and multimode as well as 2D and 3D initial conditions. This work is sponsored by DOE/NNSA Research Grants DE-FG52-07NA28058 (Stewardship Sciences Academic Alliances) and DE-FG52-04NA00064 (National Laser User
Buoyancy-driven convection around chemical fronts traveling in covered horizontal solution layers.
Rongy, L; Goyal, N; Meiburg, E; De Wit, A
2007-09-21
Density differences across an autocatalytic chemical front traveling horizontally in covered thin layers of solution trigger hydrodynamic flows which can alter the concentration profile. We theoretically investigate the spatiotemporal evolution and asymptotic dynamics resulting from such an interplay between isothermal chemical reactions, diffusion, and buoyancy-driven convection. The studied model couples the reaction-diffusion-convection evolution equation for the concentration of an autocatalytic species to the incompressible Stokes equations ruling the evolution of the flow velocity in a two-dimensional geometry. The dimensionless parameter of the problem is a solutal Rayleigh number constructed upon the characteristic reaction-diffusion length scale. We show numerically that the asymptotic dynamics is one steady vortex surrounding, deforming, and accelerating the chemical front. This chemohydrodynamic structure propagating at a constant speed is quite different from the one obtained in the case of a pure hydrodynamic flow resulting from the contact between two solutions of different density or from the pure reaction-diffusion planar traveling front. The dynamics is symmetric with regard to the middle of the layer thickness for positive and negative Rayleigh numbers corresponding to products, respectively, lighter or heavier than the reactants. A parametric study shows that the intensity of the flow, the propagation speed, and the deformation of the front are increasing functions of the Rayleigh number and of the layer thickness. In particular, the asymptotic mixing length and reaction-diffusion-convection speed both scale as square root Ra for Ra>5. The velocity and concentration fields in the asymptotic dynamics are also found to exhibit self-similar properties with Ra. A comparison of the dynamics in the case of a monostable versus bistable kinetics is provided. Good agreement is obtained with experimental data on the speed of iodate-arsenous acid fronts
Design of Laboratory Experiments to Study Photoionization Fronts Driven by Thermal Sources
Drake, R. P.; Hazak, G.; Keiter, P. A.; Davis, J. S.; Patterson, C. R.; Frank, A.; Blackman, E. G.; Busquet, Michel
2016-12-01
This paper analyzes the requirements of a photoionization-front experiment that could be driven in the laboratory, using thermal sources to produce the necessary flux of ionizing photons. It reports several associated conclusions. Such experiments will need to employ the largest available facilities, capable of delivering many kJ to MJ of energy to an X-ray source. They will use this source to irradiate a volume of neutral gas, likely of N, on a scale of a few mm to a few cm, increasing with source energy. For a gas pressure of several to ten atmospheres at room temperature, and a source temperature near 100 eV, one will be able to drive a photoionization front through a system of tens to hundreds of photon mean free paths. The front should make the familiar transition from the so-called R-Type to D-Type as the radiation flux diminishes with distance. The N is likely to reach the He-like state. Preheating from the energetic photons appears unlikely to become large enough to alter the essential dynamics of the front beyond some layer near the surface. For well-chosen experimental conditions, competing energy transport mechanisms are small.
Does laser-driven heat front propagation depend on material microstructure?
Colvin, J. D.; Matsukuma, H.; Fournier, K. B.; Yoga, A.; Kemp, G. E.; Tanaka, N.; Zhang, Z.; Kota, K.; Tosaki, S.; Ikenouchi, T.; Nishimura, H.
2016-10-01
We showed earlier that the laser-driven heat front propagation velocity in low-density Ti-silica aerogel and TiO2 foam targets was slower than that simulated with a 2D radiation-hydrodynamics code incorporating an atomic kinetics model in non-LTE and assuming initially homogeneous material. Some theoretical models suggest that the heat front is slowed over what it would be in a homogeneous medium by the microstructure of the foam. In order to test this hypothesis we designed and conducted a comparison experiment on the GEKKO laser to measure heat front propagation velocity in two targets, one an Ar/CO2 gas mixture and the other a TiO2 foam, that had identical initial densities and average ionization states. We found that the heat front traveled about ten times faster in the gas than in the foam. We present the details of the experiment design and a comparison of the data with the simulations. This work was performed under the auspices of the U.S. Department of Energy by LLNL under Contract No. DE-AC52-07NA27344, and the joint research project of ILE Osaka U. (contract Nos. 2014A1-04 and 2015A1-02).
Buoyancy-driven instabilities of acid-base fronts: the case of a color indicator
Riolfo, L. A.; Kuster, S.; Trevelyan, P. M. J.; El Hasi, C.; Zalts, A.; Almarcha, C.; D'Onofrio, A.; de Wit, A.
2011-11-01
Buoyancy-driven hydrodynamic instabilities of acid-base fronts are studied both experimentally and theoretically in the case where an aqueous solution of a strong acid is put above a denser aqueous solution of a color indicator in the gravity field. The neutralization reaction between the acid and the color indicator as well as their differential diffusion modifies the initially stable density profile in the system and can trigger convective motion both above and below the initial contact line. The type of patterns observed as well as their wavelength and the speed of the reaction front are shown to depend on the value of the initial concentrations of the acid and of the color indicator and on their ratio. A reaction-diffusion model explains how the hydrodynamic instability scenarios change when the concentration of the reactants are varied.
T. A. Scambos
2014-06-01
Full Text Available The northern Antarctic Peninsula (nAP, 3 a−1 and 24.9 ± 7.8 Gt a−1. This mass loss is compatible with recent gravimetric assessments, but it implies that almost all the gravimetry-inferred loss lies in the nAP sector. Mass loss is highest for eastern glaciers affected by major ice shelf collapses in 1995 and 2002, where twelve glaciers account for 60% of the total imbalance. However, losses at smaller rates occur throughout the nAP, and at high and low elevation, despite increased snow accumulation along the western coast and at high elevations. We interpret the widespread mass loss to be driven by decades of ice front retreats on both sides of the nAP, and by the propagation of kinematic waves triggered at the fronts into the interior.
Thomas, Leif N.
2008-08-01
A mechanism for the generation of intrathermocline eddies (ITEs) at wind-forced fronts is examined using a high resolution numerical simulation. Favorable conditions for ITE formation result at fronts forced by "down-front" winds, i.e. winds blowing in the direction of the frontal jet. Down-front winds exert frictional forces that reduce the potential vorticity (PV) within the surface boundary in the frontal outcrop, providing a source for the low-PV water that is the materia prima of ITEs. Meandering of the front drives vertical motions that subduct the low-PV water into the pycnocline, pooling it into the coherent anticyclonic vortex of a submesoscale ITE. As the fluid is subducted along the outcropping frontal isopycnal, the low-PV water, which at the surface is associated with strongly baroclinic flow, re-expresses itself as water with nearly zero absolute vorticity. This generation of strong anticyclonic vorticity results from the tilting of the horizontal vorticity of the frontal jet, not from vortex squashing. During the formation of the ITE, high-PV water from the pycnocline is upwelled alongside the subducting low-PV surface water. The positive correlation between the ITE's velocity and PV fields results in an upward, along-isopycnal eddy PV flux that scales with the surface frictional PV flux driven by the wind. The relationship between the eddy and wind-induced frictional PV flux is nonlocal in time, as the eddy PV flux persists long after the wind forcing is shut off. The ITE's PV flux affects the large-scale flow by driving an eddy-induced transport or bolus velocity down the outcropping isopycnal layer with a magnitude that scales with the Ekman velocity.
Lapenta, Giovanni; Goldman, Martin; Newman, David; olshevskyi, Vyacheslav; Markidis, Stefano
2016-04-01
Dipolarization fronts (DF) are formed by reconnection outflows interacting with the pre-existing environment. These regions are host of important energy exchanges [1], particle acceleration [2] and a complex structure and evolution [3]. Our recent work has investigated these regions via fully kinetic 3D simulations [4]. As reported recently on Nature Physics [3], based on 3D fully kinetic simulations started with a well defined x-line, we observe that in the DF reconnection transitions towards a more chaotic regime. In the fronts an instability devel- ops caused by the local gradients of the density and by the unfavourable acceleration and field line curvature. The consequence is the break up of the fronts in a fashion similar to the classical fluid Rayleigh-Taylor instability with the formation of "fingers" of plasma and embedded magnetic fields. These fingers interact and produce secondary reconnection sites. We present several different diagnostics that prove the existence of these secondary reconnection sites. Each site is surrounded by its own electron diffusion region. At the fronts the ions are generally not magnetized and considerable ion slippage is present. The discovery we present is that electrons are also slipping, forming localized diffusion regions near secondary reconnection sites [1]. The consequence of this discovery is twofold. First, the instability in the fronts has strong energetic implications. We observe that the energy transfer locally is very strong, an order of magnitude stronger than in the "X" line. However, this energy transfer is of both signs as it is natural for a wavy rippling with regions of magnetic to kinetic and regions of kinetic to magnetic energy conversion. Second, and most important for this session, is that MMS should not limit the search for electron diffusion regions to the location marked with X in all reconnection cartoons. Our simulations predict more numerous and perhaps more easily measurable electron diffusion
Meng, Xuhui; Yang, Xiaofan; Guo, Zhaoli
2016-11-01
Geological storage of the CO2 in subsurface saline aquifers is a promising way to reduce CO2 emissions. During this process, CO2 first dissolves into pure brine. Then the acidic and denser mixture falls down under the gravity and reacts with the rock. In the present work, a microfluidic experiment is conducted to investigate the density-driven convection with dissolution in porous media. Moreover, the linear stability analysis and numerical simulations are further performed to investigate the interfacial instability. The results demonstrate that front instability can be triggered by the density contrast between the two miscible fluids, leading to the Rayleigh-Taylor instability. While this type of instability can be suppressed by the surface reaction between the fluid and solid phases, which prevents the transport of the denser fluid to the deeper region at the beginning. Over the long term, it is found that the interfacial instability can be influenced by the evolution of the porosity due to the dissolution, which will drive the transport of denser fluid further down. Our investigation shows that the transport of the reactive fluid in porous media depends on the competition among the density contrast, the chemical reaction rate and the evolution of the porosity/permeability.
Malcolm J. Andrews
2006-04-14
This project had two major tasks: Task 1. The construction of a new air/helium facility to collect detailed measurements of Rayleigh-Taylor (RT) mixing at high Atwood number, and the distribution of these data to LLNL, LANL, and Alliance members for code validation and design purposes. Task 2. The collection of initial condition data from the new Air/Helium facility, for use with validation of RT simulation codes at LLNL and LANL. This report describes work done in the last twelve (12) months of the project, and also contains a summary of the complete work done over the three (3) life of the project. As of April 1, 2006, the air/helium facility (Task 1) is now complete and extensive testing and validation of diagnostics has been performed. Initial condition studies (Task 2) is also comp lete. Detailed experiments with air/helium with Atwood numbers up to 0.1 have been completed, and Atwood numbers of 0.25. Within the last three (3) months we have been able to successfully run the facility at Atwood numbers of 0.5. The progress matches the project plan, as does the budget. We have finished the initial condition studies using the water channel, and this work has been accepted for publication on the Journal of Fluid Mechanics (the top fluid mechanics journal). Mr. Nick Mueschke and Mr. Wayne Kraft are continuing with their studies to obtain PhDs in the same field, and will also continue their collaboration visits to LANL and LLNL. Over its three (3) year life the project has supported two(2) Ph.D.’s and three (3) MSc’s, and produced nine (9) international journal publications, twenty four (24) conference publications, and numerous other reports. The highlight of the project has been our close collaboration with LLNL (Dr. Oleg Schilling) and LANL (Drs. Dimonte, Ristorcelli, Gore, and Harlow).
Martinez-Pedrero, Fernando; Tierno, Pietro; Johansen, Tom H; Straube, Arthur V
2016-02-03
The emergence of wave fronts in dissipative driven systems is a fascinating phenomenon which can be found in a broad range of physical and biological disciplines. Here we report the direct experimental observation of discrete fronts propagating along chains of paramagnetic colloidal particles, the latter propelled above a traveling wave potential generated by a structured magnetic substrate. We develop a rigorously reduced theoretical framework and describe the dynamics of the system in terms of a generalized one-dimensional dissipative Frenkel-Kontorova model. The front dynamics is explored in a wide range of field parameters close to and far from depinning, where the discrete and continuum limits apply. We show how symmetry breaking and finite size of chains are used to control the direction of front propagation, a universal feature relevant to different systems and important for real applications.
Experimental, Numerical and Analytical Studies of the MHD-driven plasma jet, instabilities and waves
Zhai, Xiang
This thesis describes a series of experimental, numerical, and analytical studies involving the Caltech magnetohydrodynamically (MHD)-driven plasma jet experiment. The plasma jet is created via a capacitor discharge that powers a magnetized coaxial planar electrodes system. The jet is collimated and accelerated by the MHD forces. We present three-dimensional ideal MHD finite-volume simulations of the plasma jet experiment using an astrophysical magnetic tower as the baseline model. A compact magnetic energy/helicity injection is exploited in the simulation analogous to both the experiment and to astrophysical situations. Detailed analysis provides a comprehensive description of the interplay of magnetic force, pressure, and flow effects. We delineate both the jet structure and the transition process that converts the injected magnetic energy to other forms. When the experimental jet is sufficiently long, it undergoes a global kink instability and then a secondary local Rayleigh-Taylor instability caused by lateral acceleration of the kink instability. We present an MHD theory of the Rayleigh-Taylor instability on the cylindrical surface of a plasma flux rope in the presence of a lateral external gravity. The Rayleigh-Taylor instability is found to couple to the classic current-driven instability, resulting in a new type of hybrid instability. The coupled instability, produced by combination of helical magnetic field, curvature of the cylindrical geometry, and lateral gravity, is fundamentally different from the classic magnetic Rayleigh-Taylor instability occurring at a two-dimensional planar interface. In the experiment, this instability cascade from macro-scale to micro-scale eventually leads to the failure of MHD. When the Rayleigh-Taylor instability becomes nonlinear, it compresses and pinches the plasma jet to a scale smaller than the ion skin depth and triggers a fast magnetic reconnection. We built a specially designed high-speed 3D magnetic probe and
Transient effects in unstable ablation fronts and mixing layers in HEDP
Clarisse, J.-M.; Gauthier, S.; Dastugue, L.; Vallet, A.; Schneider, N.
2016-07-01
We report results obtained for two elementary unstable flow configurations relevant to high energy density physics: the ablation front instability and the Rayleigh-Taylor -instability induced mixing layer. These two flows are characterized by a transience of their perturbation dynamics. In the ablative flow case, this perturbation dynamics transience takes the form of finite-durations of successive linear-perturbation evolution phases until reaching regimes of decaying oscillations. This behaviour is observed in various regimes: weakly or strongly accelerated ablation fronts, irradiation asymmetries or initial external-surface defects, and is a result of the mean-flow unsteadiness and stretching. In the case of the Rayleigh-Taylor-instability induced mixing layer, perturbation dynamics transience manifests itself through the extinction of turbulence and mixing as the flow reaches a stable state made of two stably stratified layers of pure fluids separated by an unstratified mixing layer. A second feature, also due to compressibility, takes the form of an intense acoustic wave production, mainly localized in the heavy fluid. Finally, we point out that a systematic short-term linear-perturbation dynamics analysis should be undertaken within the framework of non-normal stability theory.
WANG Jing-yi; ZOU Jian-feng; ZHENG Yao; REN An-lu
2011-01-01
A front tracking method based on a marching cubes isosurface extractor,which is related filter generating isosurfaces from a structured point set,is provided to achieve sharp resolution for the simulation of non-diffusive interfacial flow.Compared with the traditional topology processing procedure,the current front tracking method is easier to be implemented and presents high performance in terms of computational resources.The numerical tests for 2-D highly-shearing flows and 3-D bubbles merging process are conducted to numerically examine the performance of the current methodology for tracking interfaces between two immiscible fluids.The Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) instability problems are successfully investigated with the present marching cubes based front tracking method.
Nonlinear Dynamics of Ionization Fronts in HII Regions
Mizuta, A; Kane, J O; Pound, M W; Remington, B A; Ryutov, D D; Takabe, H
2006-04-20
Hydrodynamic instability of an accelerating ionization front (IF) is investigated with 2D hydrodynamic simulations, including absorption of incident photoionizing photons, recombination in the HII region, and radiative molecular cooling. When the amplitude of the perturbation is large enough, nonlinear dynamics of the IF triggered by the separation of the IF from the cloud surface is observed. This causes the second harmonic of the imposed perturbation to appear on the cloud surfaces, whereas the perturbation in density of ablated gas in the HII region remains largely single mode. This mismatch of modes between the IF and the density perturbation in the HII region prevents the strong stabilization effect seen in the linear regime. Large growth of the perturbation caused by Rayleigh-Taylor-like instability is observed late in time.
Zamon, Jeannette E.; Phillips, Elizabeth M.; Guy, Troy J.
2014-09-01
Freshwater discharge from large rivers into the coastal ocean creates tidally-driven frontal systems known to enhance mixing, primary production, and secondary production. Many authors suggest that tidal plume fronts increase energy flow to fish-eating predators by attracting planktivorous fishes to feed on plankton aggregated by the fronts. However, few studies of plume fronts directly examine piscivorous predator response to plume fronts. Our work examined densities of piscivorous seabirds relative to the plume region and plume fronts of the Columbia River, USA. Common murres (Uria aalge) and sooty shearwaters (Puffinus griseus) composed 83% of all birds detected on mesoscale surveys of the Washington and Oregon coasts (June 2003-2006), and 91.3% of all birds detected on fine scale surveys of the plume region less than 40 km from the river mouth (May 2003 and 2006). Mesoscale comparisons showed consistently more predators in the central plume area compared to the surrounding marine area (murres: 10.1-21.5 vs. 3.4-8.2 birds km-2; shearwaters: 24.2-75.1 vs. 11.8-25.9 birds km-2). Fine scale comparisons showed that murre density in 2003 and shearwater density in both 2003 and 2006 were significantly elevated in the tidal plume region composed of the most recently discharged river water. Murres tended to be more abundant on the north face of the plume. In May 2003, more murres and shearwaters were found within 3 km of the front on any given transect, although maximum bird density was not necessarily found in the same location as the front itself. Predator density on a given transect was not correlated with frontal strength in either year. The high bird densities we observed associated with the tidal plume demonstrate that the turbid Columbia River plume does not necessarily provide fish with refuge from visual predators. Bird predation in the plume region may therefore impact early marine survival of Pacific salmon (Oncorhynchus spp.), which must migrate through the
Sullivan, John T.; McGee, Thomas J.; Langford, Andrew O.; Alvarez, Raul J.; Senff, Christoph J.; Reddy, Patrick J.; Thompson, Anne M.; Twigg, Laurence W.; Sumnicht, Grant K.; Lee, Pius; Weinheimer, Andrew; Knote, Christoph; Long, Russell W.; Hoff, Raymond M.
2016-09-01
A high-ozone (O3) pollution episode was observed on 22 July 2014 during the concurrent "Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality" (DISCOVER-AQ) and "Front Range Air Pollution and Photochemistry Experiment" (FRAPPE) campaigns in northern Colorado. Surface O3 monitors at three regulatory sites exceeded the Environmental Protection Agency (EPA) 2008 National Ambient Air Quality Standard (NAAQS) daily maximum 8 h average (MDA8) of 75 ppbv. To further characterize the polluted air mass and assess transport throughout the event, measurements are presented from O3 and wind profilers, O3-sondes, aircraft, and surface-monitoring sites. Observations indicate that thermally driven upslope flow was established throughout the Colorado Front Range during the pollution episode. As the thermally driven flow persisted throughout the day, O3 concentrations increased and affected high-elevation Rocky Mountain sites. These observations, coupled with modeling analyses, demonstrate a westerly return flow of polluted air aloft, indicating that the mountain-plains solenoid circulation was established and impacted surface conditions within the Front Range.
Kuster, S; Riolfo, L A; Zalts, A; El Hasi, C; Almarcha, C; Trevelyan, P M J; De Wit, A; D'Onofrio, A
2011-10-14
Buoyancy-driven hydrodynamic instabilities of acid-base fronts are studied both experimentally and theoretically in the case where an aqueous solution of a strong acid is put above a denser aqueous solution of a color indicator in the gravity field. The neutralization reaction between the acid and the color indicator as well as their differential diffusion modifies the initially stable density profile in the system and can trigger convective motions both above and below the initial contact line. The type of patterns observed as well as their wavelength and the speed of the reaction front are shown to depend on the value of the initial concentrations of the acid and of the color indicator and on their ratio. A reaction-diffusion model based on charge balances and ion pair mobility explains how the instability scenarios change when the concentration of the reactants are varied.
Three-dimensional simulations of ablative hydrodynamic instabilities in indirectly driven targets
Marinak, M.M.; Tipton, R.E.; Remington, B.A. [and others
1996-06-01
To model ignition in a National Ignition Facility (NIF) capsule implosion, the authors must understand the behavior of instabilities that can cause breakup of the pellet shell. During a capsule implosion, shocks that transit the shell cause growth of perturbations at the surface or at an interface because of a Richtmyer-Meshkov type of instability. Following shock breakout, or earlier for a shaped pulse, the low-density ablated plasma accelerates the pusher, and the ablation front is Rayleigh-Taylor (RT) unstable. Ablation and finite density gradients have the effect of stabilizing the short wavelength modes. Unstable modes present on the outer surface grow and feed through to the inner surface. Once the shell encounters the rebounding shock from the capsule center, it decelerates and the inner surface becomes RT unstable. If perturbations grow large enough, pusher material mixes into the core, degrading implosion performance. Capsule designs for the NIF depend on ablative stabilization and saturation to prevent perturbations initially present on the capsule surface from growing large enough to quench ignition. Here, the authors examine the first simulations and experiments to study the effect of 3-D perturbation shape on instability growth and saturation in indirectly driven targets. The first section discusses HYDRA, the radiation hydrodynamics code developed for these simulations. The subsequent section examines 3-D shape effects in single-mode perturbations in planar foil simulations and experiments. A discussion of the evolution of multimode perturbations on planar foils is followed by a discussion of 3-D simulations of instability growth in Nova capsule implosions.
Miles, Aaron
2004-11-01
In this talk we discuss the nature of late-time, broad-banded instability development at an interface when a strong blast wave travels from a heavier to lighter fluid, as is the case in a supernova explosion. After a short period of Richtmyer-Meshkov growth, the interface is unstable via the Rayleigh-Taylor mechanism, which rapidly becomes the dominant energy source for growth. This situation is distinct from the classical case in two important ways, both of which can be understood in terms of a bubble merger model we have developed for blast-wave-driven systems. Rather than the constant acceleration feeding the instability to spawn ever larger scales and accelerate the growth, the decaying acceleration in the blast-wave case leads to a decay in the RT growth rate, and a freezing in of a preferred largest scale, which is dependent on the precise details of the system. In the language of bubble-merger models, this can be understood in terms of the time for the generation of the next largest scale being longer than the lifetime of the blast wave. Secondly, the continual expansion behind the blast front precludes the emergence of a self-similar regime, independent of the initial conditions, in the planar case. Self-similarity may be recovered in diverging systems but may be difficult to observe in reality because of rather restrictive conditions that must be met. These observations are borne out by hi-resolution numerical simulations using the higher order Godunov AMR hydrocode Raptor in 2 and 3D, and explain other simulations of instability growth in supernovae explosions; the initial "interfacial" structure is likely very important in determining the late-time growth. The model predictions are also consistent with numerous images of natural and manmade explosions.
Wei Liu
2013-01-01
Full Text Available This paper takes the electric off-road vehicle with separated driven axles as the research object. To solve the longitudinal dynamics driving control problems, vehicle dynamics model, and control strategies were studied and the corresponding simulation was carried out. An 8-DOF vehicle dynamics model with separated driven axles was built. The driving control strategies on the typical roads were put forward. The recognition algorithm of the typical road surfaces based on the wheels’ slip rates was proposed. And the two control systems were designed including the pedal opening degree adjustment control system based on PI algorithm and the interaxle torque distribution control system based on sliding mode control algorithm. The driving control flow of the proposed vehicle combining the pedal adjustment control system with the interaxle torque distribution control system was developed. And the driven control strategies for the typical roads were simulated. Simulation results show that the proposed drive control strategies can adapt to different typical road surfaces, limit the slip rates of the driving wheels within the stable zone, and ensure the vehicle driving safely and stably in accordance with the driver's intention.
Brannon, Sean
2014-01-01
Magnetic reconnection in the corona results in contracting flare loops, releasing energy into plasma heating and shocks. The hydrodynamic shocks so produced drive thermal conduction fronts (TCFs) which transport energy into the chromosphere and drive upflows (evaporation) and downflows (condensation) in the cooler, denser footpoint plasma. Observations have revealed that certain properties of the transition point between evaporation and condensation (the "flow reversal point" or FRP), such as temperature and velocity-temperature derivative at the FRP, vary between different flares. These properties may provide a diagnostic tool to determine parameters of the coronal energy release mechanism and the loop atmosphere. In this study, we develop a 1-D hydrodynamical flare loop model with a simplified three-region atmosphere (chromosphere/transition region/corona), with TCFs initiated by shocks introduced in the corona. We investigate the effect of two different flare loop parameters (post-shock temperature and tra...
Brannon, Sean; Longcope, D.
2013-07-01
Magnetic reconnection in the corona results in contracting flare loops, releasing energy into plasma heating and shocks. These hydrodynamic shocks drive thermal conduction fronts (TCFs), which deposit energy into the chromosphere, driving upflows (evaporation) and downflows (condensation) across a range of temperatures. Observations have revealed that the transition between evaporation and condensation, the "velocity reversal point" (VRP), occurs at a characteristic temperature and with a characteristic slope, which vary between different flares. In this study, we develop a 1-D hydrodynamical flare loop model with a simplified three-region atmosphere (chromosphere / transition region (TR) / corona), with TCFs initiated by piston shocks introduced in the corona. We investigate the effect of three different flare loop parameters (post-shock temperature, TR temperature ratio, and TR thickness) on the temperature and slope of the VRP. We find that both of the evaporation characteristics have power-law relationships to the varied flare parameters, and we report the scaling exponents for our model. Finally, we develop a method to determine the best-fit post-shock temperature and TR temperature ratio based on the observed quantities, and discuss the results for two sets of published data.
Buoyancy driven turbulence and distributed chaos
Bershadskii, A
2016-01-01
It is shown, using results of recent direct numerical simulations, laboratory experiments and atmospheric measurements, that buoyancy driven turbulence exhibits a broad diversity of the types of distributed chaos with its stretched exponential spectrum $\\exp(-k/k_{\\beta})^{\\beta}$. The distributed chaos with $\\beta = 1/3$ (determined by the helicity correlation integral) is the most common feature of the stably stratified turbulence (due to the strong helical waves presence). These waves mostly dominate spectral properties of the vertical component of velocity field, while the horizontal component is dominated by the diffusive processes both for the weak and strong stable stratification ($\\beta =2/3$). For the last case influence of the low boundary can overcome the wave effects and result in $\\beta =1/2$ for the vertical component of the velocity field (the spontaneous breaking of the space translational symmetry - homogeneity). For the unstably stratified turbulence in the Rayleigh-Taylor mixing zone the di...
Long term instability growth of radiatively driven thin planar shells
Mason, R.J.; Hollowell, D.E. [and others
2000-10-01
The authors study Rayleigh-Taylor instability of radiatively driven thin copper foils under pure ablation, as well as with beryllium tampers to provide additional pressure drive. Modeling was done with the RAGE adaptive mesh refinement code of experiments done on the NOVA and OMEGA lasers. The copper foils were typically 11.5 {micro}m thick with 0.45 {micro}m amplitude, 45 {micro}m wavelength cosine surface perturbations. The beryllium layer was 5 {micro}m thick. The drive was a P26-like laser pulse delivering a peak 160-185 eV radiation temperatures. Good agreement between experiment and simulation has been obtained out to 4.5 ns. Mechanisms for late time agreement are discussed.
Miles, A
2004-04-27
In core-collapse supernovae, strong blast waves drive interfaces susceptible to Rayleigh-Taylor (RT), Richtmyer-Meshkov (RM), and Kelvin-Helmholtz (KH) instabilities. In addition, perturbation growth can result from material expansion in large-scale velocity gradients behind the shock front. Laser-driven experiments are designed to produce a strongly shocked interface whose evolution is a scaled version of the unstable hydrogen-helium interface in core-collapse supernovae such as SN 1987A. The ultimate goal of this research is to develop an understanding of the effect of hydrodynamic instabilities and the resulting transition to turbulence on supernovae observables that remain as yet unexplained. In this dissertation, we present a computational study of unstable systems driven by high Mach number shock and blast waves. Using multi-physics radiation hydrodynamics codes and theoretical models, we consider the late nonlinear instability evolution of single mode, few mode, and multimode interfaces. We rely primarily on 2D calculations but present recent 3D results as well. For planar multimode systems, we show that compressibility effects preclude the emergence of a regime of self-similar instability growth independent of the initial conditions (IC's) by allowing for memory of the initial conditions to be retained in the mix-width at all times. The loss of transverse spectral information is demonstrated, however, along with the existence of a quasi-self-similar regime over short time intervals. Aspects of the IC's are shown to have a strong effect on the time to transition to the quasi-self-similar regime. With higher-dimensional blast waves, divergence restores the properties necessary for establishment of the self-similar state, but achieving it requires very high initial characteristic mode number and high Mach number for the incident blast wave. We point to recent stellar calculations that predict IC's we find incompatible with self-similarity, and
Miles, Aaron R. [Univ. of Maryland, College Park, MD (United States)
2004-01-01
In core-collapse supernovae, strong blast waves drive interfaces susceptible to Rayleigh-Taylor (RT), Richtmyer-Meshkov (RM), and Kelvin-Helmholtz (KH) instabilities. In addition, perturbation growth can result from material expansion in large-scale velocity gradients behind the shock front. Laser-driven experiments are designed to produce a strongly shocked interface whose evolution is a scaled version of the unstable hydrogen-helium interface in core-collapse supernovae such as SN 1987A. The ultimate goal of this research is to develop an understanding of the effect of hydrodynamic instabilities and the resulting transition to turbulence on supernovae observables that remain as yet unexplained. In this dissertation, we present a computational study of unstable systems driven by high Mach number shock and blast waves. Using multi-physics radiation hydrodynamics codes and theoretical models, we consider the late nonlinear instability evolution of single mode, few mode, and multimode interfaces. We rely primarily on 2D calculations but present recent 3D results as well. For planar multimode systems, we show that compressibility effects preclude the emergence of a regime of self-similar instability growth independent of the initial conditions (IC's) by allowing for memory of the initial conditions to be retained in the mix-width at all times. The loss of transverse spectral information is demonstrated, however, along with the existence of a quasi-self-similar regime over short time intervals. Aspects of the IC's are shown to have a strong effect on the time to transition to the quasi-self-similar regime. With higher-dimensional blast waves, divergence restores the properties necessary for establishment of the self-similar state, but achieving it requires very high initial characteristic mode number and high Mach number for the incident blast wave. We point to recent stellar calculations that predict IC's we find incompatible with self-similarity, and
Rayleigh Taylor Instability Growth in NIC Capsules with Engineered Defects
Peterson, K. J.; Hammel, B. A.; Suter, L. J.; Clark, D. S.; Farley, D. R.; Landen, O. L.; Scott, H.; Moreno, K.; Vesey, R. A.; Herrmann, M. C.; Nakhleh, C. W.; Golovkin, I.; Regan, S. P.; Epstein, R.
2011-10-01
In order to achieve thermonuclear burn and energy gain in ICF capsules, the growth of hydrodynamic instabilities must be understood and controlled. Experiments are planned to measure time dependent hydrodynamic instability growth of engineered defects on the surface of NIC capsules using x-ray radiography. We will present an analysis of synthetic radiography from 2D and 3D HYDRA simulations with various x-ray drive fluxes and show how these results will be used to assess code predictions of instability growth and mix. We will also discuss how these results correlate with capsule performance and observables from hot spot self emission imaging and Ge spectroscopy. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Rochoux, M. C.; Emery, C.; Ricci, S.; Cuenot, B.; Trouve, A.
2015-08-01
This paper is the second part in a series of two articles, which aims at presenting a data-driven modeling strategy for forecasting wildfire spread scenarios based on the assimilation of the observed fire front location and on the sequential correction of model parameters or model state. This model relies on an estimation of the local rate of fire spread (ROS) as a function of environmental conditions based on Rothermel's semi-empirical formulation, in order to propagate the fire front with an Eulerian front-tracking simulator. In Part I, a data assimilation (DA) system based on an ensemble Kalman filter (EnKF) was implemented to provide a spatially uniform correction of biomass fuel and wind parameters and thereby, produce an improved forecast of the wildfire behavior (addressing uncertainties in the input parameters of the ROS model only). In Part II, the objective of the EnKF algorithm is to sequentially update the two-dimensional coordinates of the markers along the discretized fire front, in order to provide a spatially distributed correction of the fire front location and thereby, a more reliable initial condition for further model time-integration (addressing all sources of uncertainties in the ROS model). The resulting prototype data-driven wildfire spread simulator is first evaluated in a series of verification tests using synthetically generated observations; tests include representative cases with spatially varying biomass properties and temporally varying wind conditions. In order to properly account for uncertainties during the EnKF update step and to accurately represent error correlations along the fireline, it is shown that members of the EnKF ensemble must be generated through variations in estimates of the fire's initial location as well as through variations in the parameters of the ROS model. The performance of the prototype simulator based on state estimation (SE) or parameter estimation (PE) is then evaluated by comparison with data taken from
Foster, M. A.; Dühnforth, M.; Anderson, R. S.
2013-12-01
Large strath terraces adjacent to the Colorado Front Range record the local history of fluvial planation and incision into the erodible rocks of the Denver basin over the last 2 million years. Terrace surfaces have been correlated into ~6 alluvial units using elevation and soil development; each alluvial unit was thought to represent a fairly consistent elevation of the Denver basin during various stages of exhumation, driven by base-level fall of the South Platte River. Here we show instead that (1) strath terraces in the western High Plains cannot be correlated based on elevation alone and (2) exhumation of the Denver basin is likely spatially and temporally variable due to climatically-driven variations in sediment supply from the source basins. We collected samples for cosmogenic radionuclide (CRN) profiles (10Be and 26Al) and a soil chronosequence from three strath terraces adjacent to Lefthand Creek near Boulder, CO. 10Be profile data on the upper- and middle-elevation terraces yield dates of 95 ka and 91 ka; these dates are much younger than the correlative alluvial units to the south of Boulder, which date to 1.5 Ma and 250 ka, respectively. Soils on the upper and middle terraces are similar in soil development and clast weathering, consistent with the narrow time window obtained from CRN dating of the two units. 10Be-derived rates for catchment-wide paleo-denudation are ~8.0 cm/ka from the flat and broad upper-terrace gravels and ~3.5 cm/ka from the steeper and narrower middle-terrace gravels. Young terraces at Lefthand Canyon are more consistent with a model of fluvial incision and aggradation driven by climate-controlled variations in sediment production from source basins in the Front Range. High catchment-wide denudation rates generate a high sediment supply, leading to aggradation and lateral planation. Terrace sediments are likely deposited and eroded multiple times during periods of lateral planation; the most recent occupation is preserved in the
An experimental investigation of blast driven turbulence
Musci, Benjamin; Ranjan, Devesh
2016-11-01
In the Georgia Tech Shock and Advanced Mixing Lab, a facility is being built to study blast driven turbulence. Motivated by the discrepancies observed between actual and modeled supernovae, this facility aims to resolve the important spatial scales in the extensive mixing of the outer layers. These outer layers will be modeled by subjecting two-three gases of varying density to a blast wave generated by Exploding Bridge Wires. The blast wave's interaction with perturbations at the gaseous, membrane-less, interfaces will induce the Richtmeyer-Meshkov or Rayleigh Taylor Instability, depending on the acceleration history and perturbation amplitude. Through the use of simultaneous Particle Image Velocimetry, and Planar Laser Induced Fluorescence, this project aims to determine the effect of interface initial conditions on turbulence. A 2D Diverging Wedge and 3D Diverging Conical Tube are being built to enable repeatable blast-wave production, continuous optical viewing of the flow, reproducible multi-layer interface creation, and the collection of simultaneous density-velocity measurements to directly measure turbulent quantities. The preliminary analysis informing the design of this facility, the construction progress, and updates on newly realized design constraints are presented.
On the spreading and instability of gravity current fronts of arbitrary shape
Zgheib, N.; Bonometti, T.; Balachandar, S.
2012-11-01
Experiments, simulations and theoretical analysis were carried out to study the influence of geometry on the spreading of gravity currents. The horizontal spreading of three different intial planforms of initial release were investigated: an extended ellipse, a cross, and a circle. The experiments used a pulley system for a swift nearly instantaneous release. The case of the axisymmetric cylinder compared favorably with earlier simulations. We ran experiments for multiple aspect ratios for all three configurations. Perhaps the most intriguing of the three cases is the ``ellipse,'' which within a short period of release flipped the major and minor axes. This behavior cannot be captured by current theoretical methods (such as the Box Model). These cases have also been investigated using shallow water and direct numerical simulations. Also, in this study, we investigate the possibility of a Rayleigh-Taylor (RT) instability of the radially moving, but decelerating front. We present a simple theoretical framework based on the inviscid Shallow Water Equations. The theoretical results are supplemented and compared to highly resolved three-dimensional simulations with the Boussinesq approximation. Chateaubriand Fellowship - NSF PIRE grant OISE-0968313.
Casner, A.; Masse, L.; Delorme, B.; Martinez, D.; Huser, G.; Galmiche, D.; Liberatore, S.; Igumenshchev, I.; Olazabal-Loumé, M.; Nicolaï, Ph.; Breil, J.; Michel, D. T.; Froula, D.; Seka, W.; Riazuelo, G.; Fujioka, S.; Sunahara, A.; Grech, M.; Chicanne, C.; Theobald, M.; Borisenko, N.; Orekhov, A.; Tikhonchuk, V. T.; Remington, B.; Goncharov, V. N.; Smalyuk, V. A.
2014-12-01
Understanding and mitigating hydrodynamic instabilities and the fuel mix are the key elements for achieving ignition in Inertial Confinement Fusion. Cryogenic indirect-drive implosions on the National Ignition Facility have evidenced that the ablative Rayleigh-Taylor Instability (RTI) is a driver of the hot spot mix. This motivates the switch to a more flexible higher adiabat implosion design [O. A. Hurricane et al., Phys. Plasmas 21, 056313 (2014)]. The shell instability is also the main candidate for performance degradation in low-adiabat direct drive cryogenic implosions [Goncharov et al., Phys. Plasmas 21, 056315 (2014)]. This paper reviews recent results acquired in planar experiments performed on the OMEGA laser facility and devoted to the modeling and mitigation of hydrodynamic instabilities at the ablation front. In application to the indirect-drive scheme, we describe results obtained with a specific ablator composition such as the laminated ablator or a graded-dopant emulator. In application to the direct drive scheme, we discuss experiments devoted to the study of laser imprinted perturbations with special phase plates. The simulations of the Richtmyer-Meshkov phase reversal during the shock transit phase are challenging, and of crucial interest because this phase sets the seed of the RTI growth. Recent works were dedicated to increasing the accuracy of measurements of the phase inversion. We conclude by presenting a novel imprint mitigation mechanism based on the use of underdense foams. The foams induce laser smoothing by parametric instabilities thus reducing the laser imprint on the CH foil.
Casner, A., E-mail: alexis.casner@cea.fr; Masse, L.; Huser, G.; Galmiche, D.; Liberatore, S.; Riazuelo, G. [CEA, DAM, DIF, F-91297 Arpajon (France); Delorme, B. [CEA, DAM, DIF, F-91297 Arpajon (France); CELIA, University of Bordeaux-CNRS-CEA, F-33400 Talence (France); Martinez, D.; Remington, B.; Smalyuk, V. A. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Igumenshchev, I.; Michel, D. T.; Froula, D.; Seka, W.; Goncharov, V. N. [Laboratory of Laser Energetics, Rochester, New York 14623-1299 (United States); Olazabal-Loumé, M.; Nicolaï, Ph.; Breil, J.; Tikhonchuk, V. T. [CELIA, University of Bordeaux-CNRS-CEA, F-33400 Talence (France); Fujioka, S. [Institute of Laser Engineering, Osaka University, Suita, Osaka 565 (Japan); and others
2014-12-15
Understanding and mitigating hydrodynamic instabilities and the fuel mix are the key elements for achieving ignition in Inertial Confinement Fusion. Cryogenic indirect-drive implosions on the National Ignition Facility have evidenced that the ablative Rayleigh-Taylor Instability (RTI) is a driver of the hot spot mix. This motivates the switch to a more flexible higher adiabat implosion design [O. A. Hurricane et al., Phys. Plasmas 21, 056313 (2014)]. The shell instability is also the main candidate for performance degradation in low-adiabat direct drive cryogenic implosions [Goncharov et al., Phys. Plasmas 21, 056315 (2014)]. This paper reviews recent results acquired in planar experiments performed on the OMEGA laser facility and devoted to the modeling and mitigation of hydrodynamic instabilities at the ablation front. In application to the indirect-drive scheme, we describe results obtained with a specific ablator composition such as the laminated ablator or a graded-dopant emulator. In application to the direct drive scheme, we discuss experiments devoted to the study of laser imprinted perturbations with special phase plates. The simulations of the Richtmyer-Meshkov phase reversal during the shock transit phase are challenging, and of crucial interest because this phase sets the seed of the RTI growth. Recent works were dedicated to increasing the accuracy of measurements of the phase inversion. We conclude by presenting a novel imprint mitigation mechanism based on the use of underdense foams. The foams induce laser smoothing by parametric instabilities thus reducing the laser imprint on the CH foil.
Buoyancy Driven Mixing with Continuous Volumetric Energy Deposition
Wachtor, Adam J.; Jebrail, Farzaneh F.; Dennisen, Nicholas A.; Andrews, Malcolm J.; Gore, Robert A.
2014-11-01
An experiment involving a miscible fluid pair is presented which transitioned from a Rayleigh-Taylor (RT) stable to RT unstable configuration through continuous volumetric energy deposition (VED) by microwave radiation. Initially a light, low microwave absorbing fluid rested above a heavier, more absorbing fluid. The alignment of the density gradient with gravity made the system stable, and the Atwood number (At) for the initial setup was approximately -0.12. Exposing the fluid pair to microwave radiation preferentially heated the bottom fluid, and caused its density to drop due to thermal expansion. As heating of the bottom fluid continued, the At varied from negative to positive, and after the system passed through the neutral stability point, At = 0, buoyancy driven mixing ensued. Continuous VED caused the At to continue increasing and further drive the mixing process. Successful VED mixing required careful design of the fluid pair used in the experiment. Therefore, fluid selection is discussed, along with challenges and limitations of data collection using the experimental microwave facility. Experimental and model predictions of the neutral stability point, and onset of buoyancy driven mixing, are compared, and differences with classical, constant At RT driven turbulence are discussed.
2013-09-30
can be rapidly damped by a parametric subharmonic instability that forms in fronts as a consequence of frontal horizontal density gradients. This...f, and that grows at the expense of inertial shear. This parametric subharmonic instability (PSI) forms at fronts where thermal wind shear, by...The parametric subharmonic instability that John Taylor and I have discovered represents a sink of KE for inertial motions and a source of small
Olazabal-Loume, M.; Hallo, L. [Bordeaux-1 Univ., CELIA UMR 5107, 33 - Talence (France)
2006-06-15
This study deals with the hydrodynamic stability of a planar target in the context of inertial confinement fusion direct drive. Recently, different schemes have been proposed in order to reduce ablative Rayleigh-Taylor growth. They are based on the target adiabatic shaping in the ablation zone. In this work, we consider an adiabatic shaping scheme by relaxation: a prepulse is followed by a relaxation period where the laser is turned off. A numerical study is performed with a perturbation code dedicated to the linear stability analysis. The simulations show stabilizing effects of the relaxation scheme on the linear Rayleigh-Taylor growth rate. Influence of the picket parameters is also discussed. (authors)
Phenomenology of buoyancy-driven turbulence: recent results
Verma, Mahendra K; Pandey, Ambrish
2016-01-01
In this paper, we review the recent developments in the field of buoyancy-driven turbulence. Scaling and numerical arguments show that the stably-stratified turbulence with moderate stratification has kinetic energy spectrum $E_u(k) \\sim k^{-11/5}$ and the kinetic energy flux $\\Pi_u(k) \\sim k^{-4/5}$, which is called Bolgiano-Obukhov scaling. The energy flux for the Rayleigh-B\\'{e}nard convection (RBC) however is approximately constant in the inertial range that results in Kolmorogorv's spectrum ($E_u(k) \\sim k^{-5/3}$) for the kinetic energy. The phenomenology of RBC should apply to other flows where the buoyancy feeds the kinetic energy, e.g. bubbly turbulence and fully-developed Rayleigh Taylor instability. This paper also covers several models that predict the Reynolds and Nusselt numbers of RBC. Recent works show that the viscous dissipation rate of RBC scales as $\\sim \\mathrm{Ra}^{1.3}$, where $\\mathrm{Ra}$ is the Rayleigh number.
Spike Penetration in Blast-Wave-Driven Instabilities
Drake, R. Paul
2010-05-01
Recent experiments by C. Kuranz and collaborators, motivated by structure in supernovae, have studied systems in which planar blast waves encounter interfaces where the density decreases. During the Rayleigh-Taylor (RT) phase of such experiments, they observed greater penetration of the RT spikes than tends to be seen in simulations. Here we seek to employ semi-analytic theory to understand the general nature and regimes of spike penetration for blast-wave-driven instabilities. This problem is not trivial as one must account for the initial vorticity deposition at the interface, for its time-dependent deceleration, for the expansion of the shocked material in time and space, and for the drag on the broadened tips of the spikes. We offer here an improved evaluation of the material expansion in comparison to past work. The goal is to use such models to increase our ability to interpret the behavior of simulations of such systems, in both the laboratory and astrophysics. Supported by the US DOE NNSA under the Predictive Sci. Academic Alliance Program by grant DE-FC52-08NA28616, the Stewardship Sci. Academic Alliances program by grant DE-FG52-04NA00064, and the Nat. Laser User Facility by grant DE-FG03-00SF22021.
Flow field topology of transient mixing driven by buoyancy
Duval, Walter M B.
2004-01-01
Transient mixing driven by buoyancy occurs through the birth of a symmetric Rayleigh-Taylor morphology (RTM) structure for large length scales. Beyond its critical bifurcation the RTM structure exhibits self-similarity and occurs on smaller and smaller length scales. The dynamics of the RTM structure, its nonlinear growth and internal collision, show that its genesis occurs from an explosive bifurcation which leads to the overlap of resonance regions in phase space. This event shows the coexistence of regular and chaotic regions in phase space which is corroborated with the existence of horseshoe maps. A measure of local chaos given by the topological entropy indicates that as the system evolves there is growth of uncertainty. Breakdown of the dissipative RTM structure occurs during the transition from explosive to catastrophic bifurcation; this event gives rise to annihilation of the separatrices which drives overlap of resonance regions. The global bifurcation of explosive and catastrophic events in phase space for the large length scale of the RTM structure serves as a template for which mixing occurs on smaller and smaller length scales. Copyright 2004 American Institute of Physics.
Waves, instabilities and turbulence properties in Depolarisation Fronts
Lapenta, Giovanni; Goldman, Martin; Newman, David L.; Olshevskyi, Vyacheslav; Eastwood, Jonathan; Divin, Andrey; Pucci, Francesco
2016-04-01
The new mission MMS is currently focusing on the magnetopause but we need to be ready for the study of the tail. An aspect of great importance there are the Dipolarization fronts (DF), formed by reconnection outflows interacting with the pre-existing environment. These regions are host of important energy and wave phenomena [1-3]. Our recent work has investigated these regions via fully kinetic 3D simulations [4-5]. As reported recently on Nature Physics [3], based on 3D fully kinetic simulations started with a well defined x-line, we observe that in the DF reconnection transitions towards a more chaotic regime. In the fronts an instability develops caused by the local gradients of the density and by the unfavourable acceleration and field line curvature. The consequence is the break up of the fronts in a fashion similar to the classical fluid Rayleigh-Taylor instability and the onset of waves and secondary instabilities, transitioning towards a turbulent state. We investigate here especially the wave signatures that are observed in fully 3D simulations, looking for signatures of interchange-type lower hybrid waves [8], of whistler waves [7]. The end result present a vast array of waves and it is best analysed relying on concepts mutated by the turbulence theory. The end result of these waves and particle flows [2,6] are energy exchanges. We evaluate the different terms of the energy exchanges (energy deposition, J.E, and energy fluxes) and evaluate their relative improtance. The results presented are contrasted against existing results [1,9] and will provided useful guidance in analysis of future MMS data. [1] Hamrin, Maria, et al. "The evolution of flux pileup regions in the plasma sheet: Cluster observations." Journal of Geophysical Research: Space Physics 118.10 (2013): 6279-6290. [2] Angelopoulos, V., et al. "Electromagnetic energy conversion at reconnection fronts." Science 341.6153 (2013): 1478-1482. [3] Zhou, Meng, et al. "THEMIS observation of multiple
Structure and dynamics of plasma interfaces in laser-driven hohlraums
Li, C. K.; Sio, H.; Frenje, J. A.; Séguin, F. H.; Birkel, A.; Petrasso, R. D.; Wilks, S. C.; Amendt, P. A.; Remington, B. A.; Masson-Laborde, P.-E.; Laffite, S.; Tassin, V.; Betti, R.; Sanster, T. C.; Fitzsimmons, P.; Farrell, M.
2016-10-01
Understanding the structure and dynamics of plasma interfaces in laser-driven hohlraums is important because of their potential effects on capsule implosion dynamics. To that end, a series of experiments was performed to explore critical aspects of the hohlraum environment, with particular emphasis on the role of self-generated spontaneous electric and magnetic fields at plasma interfaces, including the interface between fill-gas and Au-blowoff. The charged fusion products (3-MeV DD protons and 14.7-MeV D3He protons generated in shock-driven, D3He filled backlighter capsule) pass through the subject hohlraum and form images on CR-39 nuclear track detectors, providing critical information. Important physics topics, including ion diffusive mix and Rayleigh-Taylor instabilities, will be studied to illuminate ion kinetic dynamics and hydrodynamic instability at plasma interfaces in laser-driven hohlraums. This work was supported in part by LLE, the U.S. DoE (NNSA, NLUF) and LLNL.
Direct drive heavy-ion-beam inertial fusion at high coupling efficiency
Logan, B.G.; Perkins, L.J.; Barnard, J.J.
2008-05-16
Issues with coupling efficiency, beam illumination symmetry, and Rayleigh-Taylor instability are discussed for spherical heavy-ion-beam-driven targets with and without hohlraums. Efficient coupling of heavy-ion beams to compress direct-drive inertial fusion targets without hohlraums is found to require ion range increasing several-fold during the drive pulse. One-dimensional implosion calculations using the LASNEX inertial confinement fusion target physics code shows the ion range increasing fourfold during the drive pulse to keep ion energy deposition following closely behind the imploding ablation front, resulting in high coupling efficiencies (shell kinetic energy/incident beam energy of 16% to 18%). Ways to increase beam ion range while mitigating Rayleigh-Taylor instabilities are discussed for future work.
Sabrina G. Sobel
2009-01-01
Full Text Available Imperfect mixing is a concern in industrial processes, everyday processes (mixing paint, bread machines, and in understanding salt water-fresh water mixing in ecosystems. The effects of imperfect mixing become evident in the unstirred ferroin-catalyzed Belousov-Zhabotinsky reaction, the prototype for chemical pattern formation. Over time, waves of oxidation (high ferriin concentration, blue propagate into a background of low ferriin concentration (red; their structure reflects in part the history of mixing in the reaction vessel. However, it may be difficult to separate mixing effects from reaction effects. We describe a simpler model system for visualizing density-driven pattern formation in an essentially unmixed chemical system: the reaction of pale yellow Fe3+ with colorless SCN− to form the blood-red Fe(SCN2+ complex ion in aqueous solution. Careful addition of one drop of Fe(NO33 to KSCN yields striped patterns after several minutes. The patterns appear reminiscent of Rayleigh-Taylor instabilities and convection rolls, arguing that pattern formation is caused by density-driven mixing.
Bret, Antoine; Tahir, Naeem
2012-01-01
Cylindrical implosions driven by intense heavy ions beams should be instrumental in a near future to study High Energy Density Matter. By rotating the beam by means of a high frequency wobbler, it should be possible to deposit energy in the outer layers of a cylinder, compressing the material deposited in its core. The beam temporal profile should however generate an inevitable irradiation asymmetry likely to feed the Rayleigh-Taylor instability (RTI) during the implosion phase. In this paper, we compute the Fourier components of the target irradiation in order to make the junction with previous works on RTI performed in this setting. Implementing a 1D and 2D beam models, we find these components can be expressed exactly in terms of the Fourier transform of the temporal beam profile. If $T$ is the beam duration and $\\Omega$ its rotation frequency, "magic products" $\\Omega T$ can be identified which cancel the first harmonic of the deposited density, resulting in an improved irradiation symmetry.
Analytic approach to nonlinear hydrodynamic instabilities driven by time-dependent accelerations
Mikaelian, K O
2009-09-28
We extend our earlier model for Rayleigh-Taylor and Richtmyer-Meshkov instabilities to the more general class of hydrodynamic instabilities driven by a time-dependent acceleration g(t) . Explicit analytic solutions for linear as well as nonlinear amplitudes are obtained for several g(t)'s by solving a Schroedinger-like equation d{sup 2}{eta}/dt{sup 2} - g(t)kA{eta} = 0 where A is the Atwood number and k is the wavenumber of the perturbation amplitude {eta}(t). In our model a simple transformation k {yields} k{sub L} and A {yields} A{sub L} connects the linear to the nonlinear amplitudes: {eta}{sup nonlinear} (k,A) {approx} (1/k{sub L})ln{eta}{sup linear} (k{sub L}, A{sub L}). The model is found to be in very good agreement with direct numerical simulations. Bubble amplitudes for a variety of accelerations are seen to scale with s defined by s = {integral} {radical}g(t)dt, while spike amplitudes prefer scaling with displacement {Delta}x = {integral}[{integral}g(t)dt]dt.
黄秋波; 余维臻
2014-01-01
Based on the banking industry , this paper investigates the driven mechanism of the effect of organization support on the generation of service innovation ideas by front office staff through individual perceptions .Empirical analysis shows that job satis-faction, organizational support and services contact quality have direct positive effect on their generation of service innovation ide -as.In addition, organizational support and job satisfaction also have indirect positive impact on their generation of service innova -tion ideas through the service contact quality .Organization emotional commitment has positive mediating effect while emotional exhaustion has negative mediating effect on the front office staff generation of service innovation ideas by service contact quality . The results show that service-oriented organization should increase the support and attention to the front office staff to improve service contact quality , which will increase service innovation idea .%以银行业为研究对象，实证分析组织环境因素通过个体感知影响服务型组织前台员工服务创新创意产生的驱动机制。研究结果显示，组织支持、工作满意度和服务接触质量对前台服务创新创意产生都存在正向直接作用。组织支持和工作满意度还通过服务接触对创意产生存在正向间接影响。而前台员工对组织的情感承诺通过服务接触的中介作用也对创意产生存在正向影响，员工情感耗竭通过服务接触的中介作用对服务创新创意的产生存在负向影响。因此，服务型组织应增加对前台员工的支持和关注，改善前台员工对组织工作的感受，进而改善服务接触质量以增强其发现服务创新机会和传递服务创新创意的意愿。
Zhou, Yijie [ORNL; Lim, Hyun-Kyung [ORNL; de Almeida, Valmor F [ORNL; Navamita, Ray [State University of New York, Stony Brook; Wang, Shuqiang [State University of New York, Stony Brook; Glimm, James G [ORNL; Li, Xiao-lin [State University of New York, Stony Brook; Jiao, Xiangmin [ORNL
2012-06-01
This progress report describes the development of a front tracking method for the solution of the governing equations of motion for two-phase micromixing of incompressible, viscous, liquid-liquid solvent extraction processes. The ability to compute the detailed local interfacial structure of the mixture allows characterization of the statistical properties of the two-phase mixture in terms of droplets, filaments, and other structures which emerge as a dispersed phase embedded into a continuous phase. Such a statistical picture provides the information needed for building a consistent coarsened model applicable to the entire mixing device. Coarsening is an undertaking for a future mathematical development and is outside the scope of the present work. We present here a method for accurate simulation of the micromixing dynamics of an aqueous and an organic phase exposed to intense centrifugal force and shearing stress. The onset of mixing is the result of the combination of the classical Rayleigh- Taylor and Kelvin-Helmholtz instabilities. A mixing environment that emulates a sector of the annular mixing zone of a centrifugal contactor is used for the mathematical domain. The domain is small enough to allow for resolution of the individual interfacial structures and large enough to allow for an analysis of their statistical distribution of sizes and shapes. A set of accurate algorithms for this application requires an advanced front tracking approach constrained by the incompressibility condition. This research is aimed at designing and implementing these algorithms. We demonstrate verification and convergence results for one-phase and unmixed, two-phase flows. In addition we report on preliminary results for mixed, two-phase flow for realistic operating flow parameters.
The Blast-Wave-Driven Instability as a Vehicle for Understanding Supernova Explosion Structure
Miles, A R
2008-05-27
Blast-wave-driven instabilities play a rich and varied role throughout the evolution of supernovae from explosion to remnant, but interpreting their role is difficult due to the enormous complexity of the stellar systems. We consider the simpler and fundamental hydrodynamic instability problem of a material interface between two constant-density fluids perturbed from spherical and driven by a divergent central Taylor-Sedov blast wave. The existence of unified solutions at high Mach number and small density ratio suggests that general conclusions can be drawn about the likely asymptotic structure of the mixing zone. To this end we apply buoyancy-drag and bubble merger models modified to include the effects of divergence and radial velocity gradients. In general, these effects preclude the true self-similar evolution of classical Raleigh-Taylor, but can be incorporated into a quasi-self-similar growth picture. Loss of memory of initial conditions can occur in the quasi-self-similar model, but requires initial mode numbers higher than those predicted for pre-explosion interfaces in Type II SNe, suggesting that their late-time structure is likely strongly influenced by details of the initial perturbations. Where low-modes are dominant, as in the Type Ia Tycho remnant, they result from initial perturbations rather than generation from smaller scales. Therefore, structure observed now contains direct information about the explosion process. When large-amplitude modes are present in the initial conditions, the contribution to the perturbation growth from the Richtmyer-Meshkov instability is significant or dominant compared to Rayleigh-Taylor. Such Richtmyer-Meshkov growth can yield proximity of the forward shock to the growing spikes and structure that strongly resembles that observed in the Tycho. Laser-driven high-energy-density laboratory experiments offer a promising avenue for testing model and simulation descriptions of blast-wave-driven instabilities and making
Study of Plasma Liner Driven Magnetized Target Fusion Via Advanced Simulations
Samulyak, Roman V. [State Univ. of New York (SUNY), Stony Brook, NY (United States); Brookhaven National Lab. (BNL), Upton, NY (United States); Parks, Paul [General Atomics, San Diego, CA (United States)
2013-08-31
The feasibility of the plasma liner driven Magnetized Target Fusion (MTF) via terascale numerical simulations will be assessed. In the MTF concept, a plasma liner, formed by merging of a number (60 or more) of radial, highly supersonic plasma jets, implodes on the target in the form of two compact plasma toroids, and compresses it to conditions of the fusion ignition. By avoiding major difficulties associated with both the traditional laser driven inertial confinement fusion and solid liner driven MTF, the plasma liner driven MTF potentially provides a low-cost and fast R&D path towards the demonstration of practical fusion energy. High fidelity numerical simulations of full nonlinear models associated with the plasma liner MTF using state-of-art numerical algorithms and terascale computing are necessary in order to resolve uncertainties and provide guidance for future experiments. At Stony Brook University, we have developed unique computational capabilities that ideally suite the MTF problem. The FronTier code, developed in collaboration with BNL and LANL under DOE funding including SciDAC for the simulation of 3D multi-material hydro and MHD flows, has beenbenchmarked and used for fundamental and engineering problems in energy science applications. We have performed 3D simulations of converging supersonic plasma jets, their merger and the formation of the plasma liner, and a study of the corresponding oblique shock problem. We have studied the implosion of the plasma liner on the magnetized plasma target by resolving Rayleigh-Taylor instabilities in 2D and 3D and other relevant physics and estimate thermodynamic conditions of the target at the moment of maximum compression and the hydrodynamic efficiency of the method.
Cherniavski, V M
2013-01-01
The potential flow of an incompressible inviscid heavy fluid over a light one is considered. The integral version of the method of matched asymptotic expansion is applied to the construction of the solution over long intervals of time. The asymptotic solution describes the flow in which a bubble rises with constant speed and the "tongue" is in free fall. The outer expansion is stationary, but the inner one depends on time. It is shown that the solution exists within the same range of Froude number obtained previously by Vanden-Broeck (1984a,b). The Froude number and the solution depend on the initial energy of the disturbance. At the top of the bubble, the derivative of the free-surface curvature has a discontinuity when the Froude number is not equal to 0.23. This makes it possible to identify the choice of the solution obtained in a number of studies with the presence of an artificial numerical surface tension. The first correction term in the neighborhood of the tongue is obtained when large surface tensio...
Simulating Rayleigh-Taylor (RT) instability using PPM hydrodynamics @scale on Roadrunner (u)
Woodward, Paul R [Los Alamos National Laboratory; Dimonte, Guy [Los Alamos National Laboratory; Rockefeller, Gabriel M [Los Alamos National Laboratory; Fryer, Christopher L [Los Alamos National Laboratory; Dimonte, Guy [Los Alamos National Laboratory; Dai, W [Los Alamos National Laboratory; Kares, R. J. [Los Alamos National Laboratory
2011-01-05
The effect of initial conditions on the self-similar growth of the RT instability is investigated using a hydrodynamics code based on the piecewise-parabolic-method (PPM). The PPM code was converted to the hybrid architecture of Roadrunner in order to perform the simulations at extremely high speed and spatial resolution. This paper describes the code conversion to the Cell processor, the scaling studies to 12 CU's on Roadrunner and results on the dependence of the RT growth rate on initial conditions. The relevance of the Roadrunner implementation of this PPM code to other existing and anticipated computer architectures is also discussed.
Long-wave analysis and control of the viscous Rayleigh-Taylor instability with electric fields
Cimpeanu, Radu; Anderson, Thomas; Petropoulos, Peter; Papageorgiou, Demetrios
2016-11-01
We investigate the electrostatic stabilization of a viscous thin film wetting the underside of a solid surface in the presence of a horizontally acting electric field. The competition between gravity, surface tension and the nonlocal effect of the applied electric field is captured analytically in the form of a nonlinear evolution equation. A semi-spectral solution strategy is employed to resolve the dynamics of the resulting partial differential equation. Furthermore, we conduct direct numerical simulations (DNS) of the Navier-Stokes equations and assess the accuracy of the obtained solutions when varying the electric field strength from zero up to the point when complete stabilization at the target finite wavelengths occurs. We employ DNS to examine the limitations of the asymptotically derived behavior in the context of increasing liquid film heights, with agreement found to be excellent even beyond the target lengthscales. Regimes in which the thin film assumption is no longer valid and droplet pinch-off occurs are then analyzed. Finally, the asymptotic and computational approaches are used in conjunction to identify efficient active control mechanisms allowing the manipulation of the fluid interface in light of engineering applications at small scales, such as mixing.
Fingering Instability in a Water-Sand Mixture
Lange, A; Scherer, M A; Engel, A; Rehberg, I
1997-01-01
The temporal evolution of a water-sand interface driven by gravity is experimentally investigated. By means of a Fourier analysis of the evolving interface the growth rates are determined for the different modes appearing in the developing front. To model the observed behavior we apply the idea of the Rayleigh-Taylor instability for two stratified fluids. Carrying out a linear stability analysis we calculate the growth rates from the corresponding dispersion relations for finite and infinite cell sizes. Taking into account the uncertainty in the viscosity measurements for sand dispersed in water, the theoretical results catch the essence of the experiment but also demonstrate the limitations of this approach.
2015-01-01
, Horizon 2020. Beside reports about technology transfer support and building ecosystems and value chains to ensure better time to market and higher impact of knowledge-based technologies, the acceptability of solutions, especially considering security and privacy aspects have been presented and deeply discussed. The pHealth 2015 Conference addresses mobile technologies, knowledge-driven applications and computer-assisted decision support, but also apps designed to support elderly as well as chronic patients in their daily and possibly independent living. Invited contributions consider fundamental scientific and methodological challenges of adaptive, autonomous, and intelligent pHealth approaches, the new role of patients as consumers and active party with growing autonomy and related responsibilities, but also requirements and solutions for mHealth in low- and medium income countries. It aims at sharing experiences and results, and opening up for the future. The pHealth 2015 presentations are complemented by demonstrations of practical artifacts and solutions as well as by a students' poster competition. More insights in the pHealth challenge are provided by a Satellite Conference of NovaMedTech. Embedded Sensor Systems for Health, NovaMedTech, and HL7 Sweden, but - following a long-term tradition - also the Working Groups "Electronic Health Records (EHR)", "Personal Portable Devices (PPD)" and "Security, Safety and Ethics (SSE)" of the European Federation for Medical Informatics (EFMI) have been actively involved in the preparation and realization of the pHealth 2015 Conference. This proceedings volume covers 3 keynotes and 2 specially invited talks, but also 23 oral presentations selected from more than 50 submissions to the pHealth 2015 conference, and 8 poster presentations. All submissions have been carefully and critically reviewed by at least two independent experts from other than the authors' home countries, and additionally by at least one member of the
Interfacial Instabilities Driven by Self-Gravity in the ISM: Onset and Evolution
Hueckstaedt, R. M.; Hunter, J. H., Jr.
2000-12-01
As the sites of all present day star formation within the Milky Way, cold molecular clouds are a vital link in the evolution of tenuous interstellar gas into stars. Any comprehensive theory of star formation must include a study of the hydrodynamic processes that effect molecular cloud morphology. In the ISM, hydrodynamic instabilities and turbulence play large roles in shaping clouds and creating regions capable of gravitational collapse. One of the key forces in the interstellar environment is self-gravity. Regardless of the mechanism initially responsible for creating density enhancements, self-gravity must ultimately drive the final collapse. A recent study has shown that self-gravity also gives rise to an interfacial instability that persists in the static limit when a density discontinuity exists (Hunter, Whitaker & Lovelace 1997). This instability also persists in the absence of a constant gravitational acceleration, unlike the familiar Rayleigh-Taylor instability. Analytic studies in Cartesian geometry predict that for perturbations proportional to exp(-iωt), the instability has an incompressible growth rate ω2= -2πG(ρ 1-ρ 2)2/(ρ1+ρ2). The growth rate is independent of the perturbation wavelength. Studies have also included cases in cylindrical geometry in which a static density interface has proven stable to kink modes but unstable to sausage modes. In the case of sausage modes, (perturbations in the radial direction), there exists a critical wavelength below which the instability does not appear. In this paper, we present two-dimensional numerical models designed to examine this self-gravity driven instability. A hydrodynamic code with self-gravity is used to test the analytic predictions in Cartesian and cylindrical geometries and to follow the instability into the nonlinear regime. We consider how the growth of hydrodynamic instabilities, including self-gravity driven instabilities, can have a role in shaping the ISM. We discuss implications for
Budroni, M. A.
2015-12-01
Cross diffusion, whereby a flux of a given species entrains the diffusive transport of another species, can trigger buoyancy-driven hydrodynamic instabilities at the interface of initially stable stratifications. Starting from a simple three-component case, we introduce a theoretical framework to classify cross-diffusion-induced hydrodynamic phenomena in two-layer stratifications under the action of the gravitational field. A cross-diffusion-convection (CDC) model is derived by coupling the fickian diffusion formalism to Stokes equations. In order to isolate the effect of cross-diffusion in the convective destabilization of a double-layer system, we impose a starting concentration jump of one species in the bottom layer while the other one is homogeneously distributed over the spatial domain. This initial configuration avoids the concurrence of classic Rayleigh-Taylor or differential-diffusion convective instabilities, and it also allows us to activate selectively the cross-diffusion feedback by which the heterogeneously distributed species influences the diffusive transport of the other species. We identify two types of hydrodynamic modes [the negative cross-diffusion-driven convection (NCC) and the positive cross-diffusion-driven convection (PCC)], corresponding to the sign of this operational cross-diffusion term. By studying the space-time density profiles along the gravitational axis we obtain analytical conditions for the onset of convection in terms of two important parameters only: the operational cross-diffusivity and the buoyancy ratio, giving the relative contribution of the two species to the global density. The general classification of the NCC and PCC scenarios in such parameter space is supported by numerical simulations of the fully nonlinear CDC problem. The resulting convective patterns compare favorably with recent experimental results found in microemulsion systems.
Universal power law for front propagation in all fiber resonators.
Coulibaly, S; Taki, M; Tlidi, M
2014-01-13
We consider a bistable system consisting of all fiber cavity driven by an external injected continuous wave. We report on front propagation in a high finesse cavity. We study the asymptotic behavior of the front velocity. We show that the front velocity is affected by the distance from the critical point associated with bistability. We provide a scaling low governing its evolution near the up-switching point of the bistable curve. We show also that the velocity of front propagation obeys a generic power law when the front velocity approaches asymptotically its linear growing value.
Shocks and cold fronts in galaxy clusters
Markevitch, M L; Markevitch, Maxim; Vikhlinin, Alexey
2007-01-01
The currently operating X-ray imaging observatories provide us with an exquisitely detailed view of the Megaparsec-scale plasma atmospheres in nearby galaxy clusters. At z < 0.05, the Chandra's 1" angular resolution corresponds to linear resolution of less than a kiloparsec, which is smaller than some interesting linear scales in the intracluster plasma. This enables us to study the previously unseen hydrodynamic phenomena in clusters: classic bow shocks driven by the infalling subclusters, and the unanticipated "cold fronts," or sharp contact discontinuities between regions of gas with different entropies. The ubiquitous cold fronts are found in mergers as well as around the central density peaks in "relaxed" clusters. They are caused by motion of cool, dense gas clouds in the ambient higher-entropy gas. These clouds are either remnants of the infalling subclusters, or the displaced gas from the cluster's own cool cores. Both shock fronts and cold fronts provide novel tools to study the intracluster plasm...
Botterweck, Goetz
Multi Front-End Engineering (MFE) deals with the design of multiple consistent user interfaces (UI) for one application. One of the main challenges is the conflict between commonality (all front-ends access the same application core) and variability (multiple front-ends on different platforms). This can be overcome by extending techniques from model-driven user interface engineering.We present the MANTRA approach, where the common structure of all interfaces of an application is modelled in an abstract UI model (AUI) annotated with temporal constraints on interaction tasks. Based on these constraints we adapt the AUI, e.g., to tailor presentation units and dialogue structures for a particular platform. We use model transformations to derive concrete, platform-specific UI models (CUI) and implementation code. The presented approach generates working prototypes for three platforms (GUI, web, mobile) integrated with an application core via web service protocols. In addition to static evaluation, such prototypes facilitate early functional evaluations by practical use cases.
The dynamics of neutrino-driven supernova explosions after shock revival in 2D and 3D
Müller, B.
2015-10-01
We study the growth of the explosion energy after shock revival in neutrino-driven explosions in two and three dimensions (2D/3D) using multi-group neutrino hydrodynamics simulations of an 11.2 M⊙ star. The 3D model shows a faster and steadier growth of the explosion energy and already shows signs of subsiding accretion after one second. By contrast, the growth of the explosion energy in 2D is unsteady, and accretion lasts for several seconds as confirmed by additional long-time simulations of stars of similar masses. Appreciable explosion energies can still be reached, albeit at the expense of rather high neutron star masses. In 2D, the binding energy at the gain radius is larger because the strong excitation of downward-propagating g modes removes energy from the freshly accreted material in the downflows. Consequently, the mass outflow rate is considerably lower in 2D than in 3D. This is only partially compensated by additional heating by outward-propagating acoustic waves in 2D. Moreover, the mass outflow rate in 2D is reduced because much of the neutrino energy deposition occurs in downflows or bubbles confined by secondary shocks without driving outflows. Episodic constriction of outflows and vertical mixing of colder shocked material and hot, neutrino-heated ejecta due to Rayleigh-Taylor instability further hamper the growth of the explosion energy in 2D. Further simulations will be necessary to determine whether these effects are generic over a wider range of supernova progenitors.
Volume Ignition via Time-like Detonation in Pellet Fusion
Csernai, L P
2015-01-01
Relativistic fluid dynamics and the theory of relativistic detonation fronts are used to estimate the space-time dynamics of the burning of the D-T fuel in Laser driven pellet fusion experiments. The initial "High foot" heating of the fuel makes the compressed target transparent to radiation, and then a rapid ignition pulse can penetrate and heat up the whole target to supercritical temperatures in a short time, so that most of the interior of the target ignites almost simultaneously and instabilities will have no time to develop. In these relativistic, radiation dominated processes both the interior, time-like burning front and the surrounding space-like part of the front will be stable against Rayleigh-Taylor instabilities. To achieve this rapid, volume ignition the pulse heating up the target to supercritical temperature should provide the required energy in less than ~ 10 ps.
Hard X-Ray Burst Detected From Caltech Plasma Jet Experiment Magnetic Reconnection Event
Marshall, Ryan S.; Bellan, Paul M.
2016-10-01
In the Caltech plasma jet experiment a 100 kA MHD driven jet becomes kink unstable leading to a Rayleigh-Taylor instability that quickly causes a magnetic reconnection event. Movies show that the Rayleigh-Taylor instability is simultaneous with voltage spikes across the electrodes that provide the current that drives the jet. Hard x-rays between 4 keV and 9 keV have now been observed using an x-ray scintillator detector mounted just outside of a kapton window on the vacuum chamber. Preliminary results indicate that the timing of the x-ray burst coincides with a voltage spike on the electrodes occurring in association with the Rayleigh-Taylor event. The x-ray signal accompanies the voltage spike and Rayleigh-Taylor event in approximately 50% of the shots. A possible explanation for why the x-ray signal is sometimes missing is that the magnetic reconnection event may be localized to a specific region of the plasma outside the line of sight of the scintillator. The x-ray signal has also been seen accompanying the voltage spike when no Rayleigh-Taylor is observed. This may be due to the interframe timing on the camera being longer than the very short duration of the Rayleigh-Taylor instability.
Brodsky, S J
2004-01-01
In these lectures, I survey a number of applications of light-front methods to hadron and nuclear physics phenomenology and dynamics, Light-front Fock-state wavefunctions provide a frame-independent representation of hadrons in terms of their fundamental quark and gluon degrees of freedom. Nonperturbative methods for computing LFWFs in QCD are discussed, including string/gauge duality which predicts the power-law fall-off at high momentum transfer of light-front Fock-state hadronic wavefunctions with an arbitrary number of constituents and orbital angular momentum. The AdS/CFT correspondence has important implications for hadron phenomenology in the conformal limit, including an all-orders derivation of counting rules for exclusive processes. One can also compute the hadronic spectrum of near-conformal QCD assuming a truncated AdS/CFT space. The quantum fluctuations represented by the light-front Fock expansion leads to novel QCD phenomena such as color transparency, intrinsic heavy quark distributions, diffr...
Michael Oshins
2013-04-01
Full Text Available The role of hotel front desks has not changed significantly in more than a century. The activities of welcoming guests upon arrival, assisting guests during their stay, and settling accounts upon departure are still the mainstay of the front desk. Although the function of the front desk has remained static, its form has evolved. Front desks now differ widely in terms of aesthetics and, in some cases, even operational patterns. This article offers photographs of numerous hotel front desks in Boston and provides brief commentaries that provide insight about the changing nature of front desk design.
何民卿; 董全力; 盛政明; 张杰
2015-01-01
implies that the magnetic amplification in the space is possibly due to the local field generation rather than the field compression. An amplification ratio of tens of the external magnetic field is achieved due to the pseudo Rayleigh-Taylor instability, but still much smaller than that around the astrophysical shock front, indicating that other eﬃcient mechanisms are responsible for the observed magnetic amplification around shocks in the supernova remnants.%冲击波是天体物理观测中常见的现象，其对粒子的加速被认为是高能宇宙射线的来源。宇宙中冲击波周围往往存在很强的磁场，但人们对于此类强磁场的产生放大过程的理解并不充分。本文利用二维粒子模拟程序研究了激光与磁化或者非磁化等离子体相互作用产生的冲击波现象，给出了冲击波波前处磁场的产生放大特性。研究发现，作用过程中的自生磁场可以储存能量，从而进一步加速电子；当存在外加磁场时，由冲击波加速的电子和离子的能量都比同条件下非磁化等离子体的能量高；而且外加磁场藉由冲击波放大倍数则与其值有极大关系。与天文观测中推断的磁场与背景磁场相比放大千倍这一研究结果的比较可以看出，天体冲击波周围磁场放大主要是由局域内生磁场导致的。
Pelce, Pierre
1989-01-01
In recent years, much progress has been made in the understanding of interface dynamics of various systems: hydrodynamics, crystal growth, chemical reactions, and combustion. Dynamics of Curved Fronts is an important contribution to this field and will be an indispensable reference work for researchers and graduate students in physics, applied mathematics, and chemical engineering. The book consist of a 100 page introduction by the editor and 33 seminal articles from various disciplines.
Radiative thermal conduction fronts
Borkowski, Kazimierz J.; Balbus, Steven A.; Fristrom, Carl C.
1990-01-01
The discovery of the O VI interstellar absorption lines in our Galaxy by the Copernicus observatory was a turning point in our understanding of the Interstellar Medium (ISM). It implied the presence of widespread hot (approx. 10 to the 6th power K) gas in disk galaxies. The detection of highly ionized species in quasi-stellar objects' absorption spectra may be the first indirect observation of this hot phase in external disk galaxies. Previous efforts to understand extensive O VI absorption line data from our Galaxy were not very successful in locating the regions where this absorption originates. The location at interfaces between evaporating ISM clouds and hot gas was favored, but recent studies of steady-state conduction fronts in spherical clouds by Ballet, Arnaud, and Rothenflug (1986) and Bohringer and Hartquist (1987) rejected evaporative fronts as the absorption sites. Researchers report here on time-dependent nonequilibrium calculations of planar conductive fronts whose properties match well with observations, and suggest reasons for the difference between the researchers' results and the above. They included magnetic fields in additional models, not reported here, and the conclusions are not affected by their presence.
Pennington, D; Jovanovic, I; Comaskey, B J
2001-02-01
The next generation of Petawatt class lasers will require the development of new laser technology. Optical parametric chirped pulse amplification (OPCPA) holds a potential to increase the peak power level to >10 PW with existing grating technology through ultrashort pulses. Furthermore, by utilizing a new type of front-end system based on optical parametric amplification, pulses can be produced with substantially higher contrast than with Ti:sapphire regenerative amplifier technology. We performed extensive study of OPCPA using a single crystal-based OPA. We developed a replacement for Ti:sapphire regenerative amplifier for high peak power lasers based on OPCPA, with an output of 30 mJ, at 10 Hz repetition rate and 16.5 nm spectral bandwidth. We developed a 3D numerical model for OPCPA and we performed a theoretical study of influences of pump laser beam quality on optical parametric amplification. Our results indicate that OPCPA represents a valid replacement for Ti:sapphire in the front end of high energy short pulse lasers.
Order Parameter Equations for Front Transitions Planar and Circular Fronts
Hagberg, A; Rubinstein, I; Zaltzman, B; Hagberg, Aric; Meron, Ehud
1997-01-01
Near a parity breaking front bifurcation, small perturbations may reverse the propagation direction of fronts. Often this results in nonsteady asymptotic motion such as breathing and domain breakup. Exploiting the time scale differences of an activator-inhibitor model and the proximity to the front bifurcation, we derive equations of motion for planar and circular fronts. The equations involve a translational degree of freedom and an order parameter describing transitions between left and right propagating fronts. Perturbations, such as a space dependent advective field or uniform curvature (axisymmetric spots), couple these two degrees of freedom. In both cases this leads to a transition from stationary to oscillating fronts as the parity breaking bifurcation is approached. For axisymmetric spots, two additional dynamic behaviors are found: rebound and collapse.
Price, Stephen [Los Alamos National Laboratory
2009-01-01
The causes of recent dynamic thinning of Greenland's outlet glaciers have been debated. Realistic simulations suggest that changes at the marine fronts of these glaciers are to blame, implying that dynamic thinning will cease once the glaciers retreat to higher ground. For the last decade, many outlet glaciers in Greenland that terminate in the ocean have accelerated, thinned, and retreated. To explain these dynamic changes, two hypotheses have been discussed. Atmospheric warming has increased surface melting and may also have increased the amount of meltwater reaching the glacier bed, increasing lubrication at the base and hence the rate of glacier sliding. Alternatively, a change in the delicate balance of forces where the glacier fronts meet the ocean could trigger the changes. Faezeh Nick and colleagues5 present ice-sheet modeling experiments that mimic the observations on Helheim glacier, East Greenland, and suggest that the dynamic behaviour of outlet glaciers follows from perturbations at their marine fronts. Greenland's ice sheet loses mass partly through surface melting and partly through fast flowing outlet glaciers that connect the vast plateau of inland ice with the ocean. Earlier ice sheet models have failed to reproduce the dynamic variability exhibited by ice sheets over time. It has therefore not been possible to distinguish with confidence between basal lubrication from surface meltwater and changes at the glaciers' marine fronts as causes for the observed changes on Greenland's outlet glaciers. But this distinction bears directly on future sea-level rise, the raison d'etre of much of modern-day glaciology: If the recent dynamic mass loss Greenland's outlet glaciers is linked to changing atmospheric temperatures, it may continue for as long as temperatures continue to increase. On the other hand, if the source of the dynamic mass loss is a perturbation at the ice-ocean boundary, these glaciers will lose contact with
Front propagation in vortex-dominated flows
O'Malley, Garrett; Winokur, Justin; Solomon, Tom
2008-11-01
We present experiments that explore how the propagation of a reaction front is affected by a two-dimensional flow dominated by vortices. The reaction is the excitable Belousov-Zhabotinsky chemical reaction. The flow is driven by the interaction between an electrical current passing through the fluid and a spatially-varying magnetic field produced by an array of magnets below the fluid. For some of the experiments, the forcing is strong enough to produce a weakly turbulent flow. Measurements are made both of the enhanced diffusion coefficient D^* describing transport in the flow and of the propagation speed v of a reaction front in the same flow. Scaling of v versus D^* is compared with that for the standard Fisher-Kolmogorov-Petrovsky-Piskunov prediction v ˜√D (with D as the molecular diffusion coefficient) for the reaction-diffusion limit with no fluid advection. We also study the effects of superdiffusive transport and Lévy flights on front propagation in a time-dependent vortex array with wavy jet regions.
Biological Activity at Oceanic Fronts.
1985-12-01
and/or phytoplankton concentrations between the adjacent areas. High particle concentrations are associated with a front east of the Galapagos Islands...yeTlowfin, albacore, and bluefin tunas, mackerel, salmon, and some whales (Uda, 1938, 1952,. 9.=, 1973; Uda and Ishino, 1958). Behavioral responses of...Marine mammals ,Gaskin, 1976) also utilize tidal fronts. Minke whales were observed to feed on herring or capelin collected in fronts and fin whales fed
Photoionization effects in ionization fronts
Arrayas, Manuel [Departamento de Electromagnetismo, Universidad Rey Juan Carlos, Tulipan s/n, 28933 Mostoles, Madrid (Spain); Fontelos, Marco A [Departamento de Matematicas, Instituto de Matematicas y Fisica Fundamental, Consejo Superior de Investigaciones CientIficas, C/Serrano 123, 28006 Madrid (Spain); Trueba, Jose L [Departamento de Electromagnetismo, Universidad Rey Juan Carlos, Tulipan s/n, 28933 Mostoles, Madrid (Spain)
2006-12-21
In this paper we study the effects of photoionization processes on the propagation of both negative and positive ionization fronts in streamer discharge. We show that negative fronts accelerate in the presence of photoionization events. The appearance and propagation of positive ionization fronts travelling with constant velocity is explained as the result of the combined effects of photoionization and electron diffusion. The photoionization range plays an important role in the selection of the velocity of the ionization front as we show in this work.
Active learning of Pareto fronts.
Campigotto, Paolo; Passerini, Andrea; Battiti, Roberto
2014-03-01
This paper introduces the active learning of Pareto fronts (ALP) algorithm, a novel approach to recover the Pareto front of a multiobjective optimization problem. ALP casts the identification of the Pareto front into a supervised machine learning task. This approach enables an analytical model of the Pareto front to be built. The computational effort in generating the supervised information is reduced by an active learning strategy. In particular, the model is learned from a set of informative training objective vectors. The training objective vectors are approximated Pareto-optimal vectors obtained by solving different scalarized problem instances. The experimental results show that ALP achieves an accurate Pareto front approximation with a lower computational effort than state-of-the-art estimation of distribution algorithms and widely known genetic techniques.
Light Front Boson Model Propagation
Jorge Henrique Sales; Alfredo Takashi Suzuki
2011-01-01
stract The scope and aim of this work is to describe the two-body interaction mediated by a particle (either the scalar or the gauge boson) within the light-front formulation. To do this, first of all we point out the importance of propagators and Green functions in Quantum Mechanics. Then we project the covariant quantum propagator onto the light front time to get the propagator for scalar particles in these coordinates. This operator propagates the wave function from x+ = 0 to x+ ＞ O. It corresponds to the definition of the time ordering operation in the light front time x+. We calculate the light-front Green's function for 2 interacting bosons propagating forward in x+. We also show how to write down the light front Green's function from the Feynman propagator and finally make a generalization to N bosons.
"Front" hotshet izvinitsja / Aleksandr Ikonnikov
Ikonnikov, Aleksandr
2003-01-01
Põhiliselt vene rahvusest noori ühendava liikumise "Front" esindajad kavatsevad kohtuda USA suursaadikuga Eestis ja vabandada kevadel suursaatkonna ees vägivallatsemisega lõppenud meeleavalduse pärast
Stability of oblique shock front
CHEN; Shuxing(陈恕行)
2002-01-01
The stability of the weak planar oblique shock front with respect to the perturbation of the wall is discussed. By the analysis of the formation and the global construction of shock and its asymptotic behaviour for stationary supersonic flow along a smooth rigid wall we obtain the stability of the solution containing a weak planar shock front. The stability can be used to single out a physically reasonable solution together with the entropy condition.
Radiative magnetized thermal conduction fronts
Borkowski, Kazimierz J.; Balbus, Steven A.; Fristrom, Carl C.
1990-01-01
The evolution of plane-parallel magnetized thermal conduction fronts in the interstellar medium (ISM) was studied. Separating the coronal ISM phase and interstellar clouds, these fronts have been thought to be the site of the intermediate-temperature regions whose presence was inferred from O VI absorption-line studies. The front evolution was followed numerically, starting from the initial discontinuous temperature distribution between the hot and cold medium, and ending in the final cooling stage of the hot medium. It was found that, for the typical ISM pressure of 4000 K/cu cm and the hot medium temperature of 10 to the 6th K, the transition from evaporation to condensation in a nonmagnetized front occurs when the front thickness is 15 pc. This thickness is a factor of 5 smaller than previously estimated. The O VI column densities in both evaporative and condensation stages agree with observations if the initial hot medium temperature Th exceeds 750,000 K. Condensing conduction fronts give better agreement with observed O VI line profiles because of lower gas temperatures.
Laser Acceleration of Quasi-Monoenergetic Protons via Radiation Pressure Driven Thin Foil
Liu, Chuan S.; Shao, Xi; Eliasson, Bengt; Liu, T. C.; Dudnikova, Galina; Sagdeev, Roald Z.
2011-01-01
We present a theoretical and simulation study of laser acceleration of quasi-monoenergetic protons in a thin foil irradiated by high intensity laser light. The underlying physics of radiation pressure acceleration (RPA) is discussed, including the importance of optimal thickness and circularly polarized light for efficient acceleration of ions to quasi-monoenergetic beams. Preliminary two-dimensional simulation studies show that certain parameter regimes allow for stabilization of the Rayleigh-Taylor instability and possibility of acceleration of monoenergetic ions to an excess of 200 MeV, making them suitable for important applications such as medical cancer therapy and fast ignition.
Convective chemical fronts in a Poiseuille flow.
Vasquez, Desiderio A
2007-11-01
Autocatalytic reaction fronts propagating in a Poiseuille flow present a change of speed and curvature depending on the strength of the flow and on the direction of front propagation. These chemical fronts separate reacted and unreacted fluids of different densities, consequently convection will always be present due to the horizontal density gradient of the curved front. In this paper, we find the change of speed caused by gravity for fronts propagating in vertical tubes under a Poiseuille flow. For small density differences, we find axisymmetric fronts. Our theory predicts a transition to nonaxisymmetric fronts as the distance between the walls is increased. The transition depends on the average speed of the Poiseuille flow.
A spiral wave front beacon for underwater navigation: basic concept and modeling.
Hefner, Brian T; Dzikowicz, Benjamin R
2011-06-01
A spiral wave front source produces an acoustic field that has a phase that is proportional to the azimuthal angle about the source. The concept of a spiral wave front beacon is developed by combining this source with a reference source that has a phase that is constant with the angle. The phase difference between these sources contains information about the receiver's azimuthal angle relative to the beacon and can be used for underwater navigation. To produce the spiral wave front, two sources are considered: a "physical-spiral" source, which produces the appropriate phase by physically deforming the active element of the source into a spiral, and a "phased-spiral" source, which uses an array of active elements, each driven with the appropriate phase, to produce the spiral wave front. Using finite element techniques, the fields produced by these sources are examined in the context of the spiral wave front beacon, and the advantages of each source are discussed.
Perry, Jim
1995-01-01
Discussion of management styles and front-end analysis focuses on a review of Douglas McGregor's theories. Topics include Theories X, Y, and Z; leadership skills; motivational needs of employees; intrinsic and extrinsic rewards; and faulty implementation of instructional systems design processes. (LRW)
Multiple WH-Fronting Constructions.
Rudin, Catherine
The unique position of WH words in Slavic languages is discussed, with specific reference to Bulgarian and Serbo-Croatian. The multiple fronting characteristics of Bulgarian and Serbo-Croatian differ in terms of the following positions and behaviors: extraction from embedded questions; clitic placement and other indications of constituent status;…
Herrmann, Marc
2015-01-01
Background: The vacuum in the light-front representation of quantum field theory is trivial while vacuum in the equivalent canonical representation of the same theory is non-trivial. Purpose: Understand the relation between the vacuum in light-front and canonical representations of quantum field theory and the role of zero-modes in this relation. Method: Vacuua are defined as linear functionals on an algebra of field operators. The role of the algebra in the definition of the vacuum is exploited to understand this relation. Results: The vacuum functional can be extended from the light-front Fock algebra to an algebra of local observables. The extension to the algebra of local observables is responsible for the inequivalence. The extension defines a unitary mapping between the physical representation of the local algebra and a sub-algebra of the light-front Fock algebra. Conclusion: There is a unitary mapping from the physical representation of the algebra of local observables to a sub-algebra of the light-fro...
Perry, Jim
1995-01-01
Discussion of management styles and front-end analysis focuses on a review of Douglas McGregor's theories. Topics include Theories X, Y, and Z; leadership skills; motivational needs of employees; intrinsic and extrinsic rewards; and faulty implementation of instructional systems design processes. (LRW)
Light Front Fermion Model Propagation
Jorge Henrique Sales; Alfredo Takashi Suzuki
2013-01-01
In this work we consider the propagation of two fermion fields interacting with each other by the exchange of intermediate scalar bosons in the light front.We obtain the corrections up to fourth order in the coupling constant using hierarchical equations in order to obtain the bound state equation (Bethe-Salpeter equation).
Salomon F.; Edelbruck P.; Brulin G.; Boiano A.; Tortone G.; Ordine A.; Bini M.; Barlini S.; Valdré S.
2015-01-01
FAZIA is a multi-detector specifically designed to optimize ion identification in heavy-ion experiments. Its electronic is fully digital; it was designed in the laboratories of the collaboration. This paper presents the front-end part of this electronic.
Salomon F.
2015-01-01
Full Text Available FAZIA is a multi-detector specifically designed to optimize ion identification in heavy-ion experiments. Its electronic is fully digital; it was designed in the laboratories of the collaboration. This paper presents the front-end part of this electronic.
Subgrid Modeling of AGN-Driven Turbulence in Galaxy Clusters
Scannapieco, Evan
2008-01-01
Hot, underdense bubbles powered by active galactic nuclei (AGN) are likely to play a key role in halting catastrophic cooling in the centers of cool-core galaxy clusters. We present three-dimensional simulations that capture the evolution of such bubbles, using an adaptive-mesh hydrodynamic code, FLASH3, to which we have added a subgrid model of turbulence and mixing. While pure-hydro simulations indicate that AGN bubbles are disrupted into resolution-dependent pockets of underdense gas, proper modeling of subgrid turbulence indicates that this a poor approximation to a turbulent cascade that continues far beyond the resolution limit. Instead, Rayleigh-Taylor instabilities act to effectively mix the heated region with its surroundings, while at the same time preserving it as a coherent structure, consistent with observations. Thus bubbles are transformed into hot clouds of mixed material as they move outwards in the hydrostatic intracluster medium (ICM), much as large airbursts lead to a distinctive ``mushroo...
Design of laboratory experiments to study photoionization fronts
Drake, R. P.; Hazak, G.; Keiter, P. A.; Davis, J. S.; Patterson, C. R.; Frank, A.; Blackman, E.; Busquet, M.
2016-10-01
This paper analyzes the requirements of a photoionization-front experiment that could be driven in the laboratory, using thermal sources to produce the necessary flux of ionizing photons. It reports several associated conclusions. Such experiments will need to employ the largest available facilities, capable of delivering many kJ to MJ of energy to an x-ray source. They will use this source to irradiate a volume of neutral gas, likely of N, on a scale of a few mm to a few cm, increasing with source energy. For a gas pressure of several to ten atmospheres at room temperature, and a source temperature near 100 eV, one will be able to drive a photoionization front through a system of tens to hundreds of photon mean free paths. The front should make the familiar transition from the so-called R-Type to D-Type as the radiation flux diminishes with distance. The N is likely to reach the He-like state. Preheating from the energetic photons appears unlikely to become large enough to alter the essential dynamics of the front beyond some layer near the surface. For well-chosen experimental conditions, competing energy transport mechanisms are small. Supported by the U.S. DOE by NNSA Grants DE-NA0002956 (SSAA) and DE-NA0002719 (NLUF), by LLE, and by LLNL.
Weather fronts and acute myocardial infarction
Kveton, Vit
1991-03-01
Some methodological aspects are discussed of the investigation of acute infarct myocarditis (AIM) in relation to weather fronts. Results of a new method of analysis are given. Data were analysed from about the hour of the onset of symptoms, and led to the diagnosis of AIM either immediately or within a few hours or days (3019 cases observed over 4.5 years during 1982 1986 in Plzen, Czechoslovakia). Weather classification was based on three factors (the type of the foregoing front, the type of the subsequent front, the time section of the time interval demarcated by the passage of the surfaces of the fronts). AIM occurrence increased in particular types of weather fronts: (i) by 30% during 7 12 h after a warm front, if the time span between fronts exceeded 24 h; (ii) by 10% in time at least 36 h distant from the foregoing cold or occlusion front and from the succeeding warm or occlusion front; (iii) by 20% during 0 2 h before the passage of the front, provided the foregoing front was not warm and the interval between fronts exceeded 5 h. AIM occurrence decreased by 15% 20% for time span between fronts > 24 h at times 6 11, 6 23 and 6 35 h before a coming warm or occlusion front (for interfrontal intervals 25 48, 49 72 and possibly > 72 h), and also at 12 23 and possibly 12 35 h before a cold front (for intervals 49 72 and possibly > 72 h), if the foregoing front was cold or an occlusion front.
Wetting front instability in an initially wet unsaturated fracture
Nicholl, M.J.; Glass, R.J.; Nguyen, H.A.
1992-12-31
Experimental results exploring gravity-driven wetting front instability in a pre-wetted, rough-walled analog fracture are presented. Initial conditions considered include a uniform moisture field wetted to field capacity of the analog fracture and the structured moisture field created by unstable infiltration into an initially dry fracture. As in previous studies performed under dry initial conditions, instability was found to result both at the cessation of stable infiltration and at flux lower than the fracture capacity under gravitational driving force. Individual fingers were faster, narrower, longer, and more numerous than observed under dry initial conditions. Wetting fronts were found to follow existing wetted structure, providing a mechanism for rapid recharge and transport.
Electrostatic Instabilities at High Frequency in a Plasma Shock Front
LV Jian-Hong; HE Yong; HU Xi-Wei
2007-01-01
New electrostatic instabilities in the plasma shock front are reported.These instabilities are driven by the electrostatic field which is caused by charge separation and the parameter gradients in a plasma shock front.The linear analysis to the high frequency branch of electrostatic instabilities has been carried out and the dispersion relations are obtained numerically.There are unstable disturbing waves in both the parallel and perpendicular directions of shock propagation.The real frequencies of both unstable waves are similar to the electron electrostatic wave,and the unstable growth rate in the parallel direction is much greater than the one in the perpendicular direction.The dependence of growth rates on the electric field and parameter gradients is also presented.
Pozdeyev, E; Machicoane, G; Morgan, G; Rao, X; Zhao, Q; Stovall, J; Vorozhtsov, S; Sun, L
2013-01-01
The Facility for Rare Isotope Beams (FRIB) will provide a wide range of primary ion beams for nuclear physics research with rare isotope beams. The FRIB SRF linac will be capable of accelerating medium and heavy ion beams to energies beyond 200 MeV/u with a power of 400 kW on the fragmentation target. This paper presents the status of the FRIB Front End designed to produce uranium and other medium and heavy mass ion beams at world-record intensities. The paper describes the FRIB high performance superconducting ECR ion source, the beam transport designed to transport two-charge state ion beams and prepare them for the injection in to the SRF linac, and the design of a 4-vane 80.5 MHz RFQ. The paper also describes the integration of the front end with other accelerator and experimental systems.
Disk Instabilities and Cooling Fronts
Vishniac, E T
1998-01-01
Accretion disk outbursts, and their subsequent decline, offer a unique opportunity to constrain the physics of angular momentum transport in hot accretion disks. Recent work has centered on the claim by Cannizzo et al. that the exponential decay of luminosity following an outburst in black hole accretion disk systems is only consistent with a particular form for the dimensionless viscosity, $\\alpha=35(c_s/r\\Omega)^{3/2}$. This result can be understood in terms of a simple model of the evolution of cooling fronts in accretion disks. In particular, the cooling front speed during decline is $\\sim cooling front, and the exact value of $n$ depends on the hot state opacity, (although generally $n\\approx 1/2$). Setting this speed proportional to $r$ constrains the functional form of $\\alpha$ in the hot phase of the disk, which sets it apart from previous arguments based on the relative durations of outburst and quiescence. However, it remains uncertain how well we know the exponent $n$. In addition, more work is nee...
Olazabal-Loume, M; Breil, J; Hallo, L; Ribeyre, X [CELIA, UMR 5107 Universite Bordeaux 1-CNRS-CEA, 351 cours de la Liberation, 33405 Talence (France); Sanz, J, E-mail: olazabal@celia.u-bordeaux1.f [ETSI Aeronauticos, Universidad Politecnica de Madrid, Madrid 28040 (Spain)
2011-01-15
The linear and non-linear sensitivity of the 180 kJ baseline HiPER target to high-mode perturbations, i.e. surface roughness, is addressed using two-dimensional simulations and a complementary analysis by linear and non-linear ablative Rayleigh-Taylor models. Simulations provide an assessment of an early non-linear stage leading to a significant deformation of the ablation surface for modes of maximum linear growth factor. A design using a picket prepulse evidences an improvement in the target stability inducing a delay of the non-linear behavior. Perturbation evolution and shape, evidenced by simulations of the non-linear stage, are analyzed with existing self-consistent non-linear theory.
Nonspherical supernova remnants. IV - Sequential explosions in OB associations
Tenorio-Tagle, G.; Bodenheimer, P.; Rozyczka, M.
1987-01-01
Multisupernova remnants, driven by sequential supernova explosions in OB associations, are modelled by means of two-dimensional hydrodynamical calculations. It is shown that due to the Rayleigh-Taylor instability the remnants quickly evolve into highly irregular structures. A critical evaluation of the multisupernova model as an explanation for supershells is given.
Fluctuation charge effects in ionization fronts
Arrayas, Manuel; Trueba, Jose L [Area de Electromagnetismo, Universidad Rey Juan Carlos, Camino del Molino s/n, 28943 Fuenlabrada, Madrid (Spain); Baltanas, J P [Departamento de Fisica Aplicada II, Universidad de Sevilla, Av. Reina Mercedes 2, 41012 Sevilla (Spain)
2008-05-21
In this paper, we study the effects of charge fluctuations on the propagation of both negative and positive ionization fronts in streamer discharges. We show that fronts accelerate when random charge creation events are present. This effect might play a similar role to photoionization in order to make the front move faster.
Instrument Front-Ends at Fermilab During Run II
Meyer, Thomas; Voy, Duane; 10.1088/1748-0221/6/11/T11004
2012-01-01
The optimization of an accelerator relies on the ability to monitor the behavior of the beam in an intelligent and timely fashion. The use of processor-driven front-ends allowed for the deployment of smart systems in the field for improved data collection and analysis during Run II. This paper describes the implementation of the two main systems used: National Instruments LabVIEW running on PCs, and WindRiver's VxWorks real-time operating system running in a VME crate processor.
Instrument Front-Ends at Fermilab During Run II
Meyer, Thomas; Slimmer, David; Voy, Duane; /Fermilab
2011-07-13
The optimization of an accelerator relies on the ability to monitor the behavior of the beam in an intelligent and timely fashion. The use of processor-driven front-ends allowed for the deployment of smart systems in the field for improved data collection and analysis during Run II. This paper describes the implementation of the two main systems used: National Instruments LabVIEW running on PCs, and WindRiver's VxWorks real-time operating system running in a VME crate processor.
Influence of Marangoni flows on the dynamics of isothermal A + B → C reaction fronts
Tiani, R.; Rongy, L.
2016-09-01
The nonlinear dynamics of A + B → C fronts is analyzed both numerically and theoretically in the presence of Marangoni flows, i.e., convective motions driven by surface tension gradients. We consider horizontal aqueous solutions where the three species A, B, and C can affect the surface tension of the solution, thereby driving Marangoni flows. The resulting dynamics is studied by numerically integrating the incompressible Navier-Stokes equations coupled to reaction-diffusion-convection (RDC) equations for the three chemical species. We show that the dynamics of the front cannot be predicted solely on the basis of the one-dimensional reaction-diffusion profiles as is the case for buoyancy-driven convection around such fronts. We relate this observation to the structure of Marangoni flows which lead to more complex and exotic dynamics. We find in particular the surprising possibility of a reversal of the front propagation direction in time for some sets of Marangoni numbers, quantifying the influence of each chemical species concentration on the solution surface tension. We explain this reversal analytically and propose a new classification of the convective effects on A + B → C reaction fronts as a function of the Marangoni numbers. The influence of the layer thickness on the RDC dynamics is also presented. Those results emphasize the importance of flow symmetry properties when studying convective front dynamics in a given geometry.
Hydrodynamic instabilities in an ablation front
Piriz, A R; Portugues, R F [E.T.S.I. Industriales, Universidad de Castilla-La Mancha, 13071 Ciudad Real (Spain)
2004-06-01
The hydrodynamic stability of an ablation front is studied for situations in which the wavelength of the perturbations is larger than the distance to the critical surface where the driving radiation is absorbed. An analytical model is presented, and it shows that under conditions in which the thermal flux is limited within the supercritical region of the ablative corona, the front may behave like a flame or like an ablation front, depending on the perturbation wavelength. For relatively long wavelengths the critical and ablation surfaces practically lump together into a unique surface and the front behaves like a flame, whereas for the shortest wavelengths the ablation front substructure is resolved.
Toshiaki KANEMOTO; Seita SEKI; Kazunori IDENO; Ahmed Mohamed GALAL
2005-01-01
It is desired to increase the rotational speed of the core engine of the turbofan so as to get the best efficiency for the next leap of engine technology. The conventional mechanism in which the front fan is directly connected to the output shaft of a core engine, have a limit of increasing the spool speed, because the fan diameter is very large. The authors have proposed a new driving system in which the front fan is driven through the aerodynamic torque converter. The front fan can work at the best performance at slower speed while the core engine runs more efficiently at higher speed. Continuously, this paper discusses the response of the front fan in the unsteady operation of the core engine, accompanying with the internal flow. The system has the acceptable responsibility in the unsteady operation which is very important for the aircrafts.
Gubin, S. A.; Sumskoi, S. I.; Victorov, S. B.
According to the theory of detonation, in a detonation wave there is a sound plane, named Chapman-Jouguet (CJ) plane. There are certain stationary parameters for this plane. In this work the possibility of the second CJ plane is shown. This second CJ plane is stationary as well. The physical mechanism of non-equilibrium transition providing the existence of the second CJ plane is presented. There is a non-equilibrium state, when the heat is removed from the reaction zone and the heat capacity decreases sharply. As a result of this non-equilibrium state, the sound velocity increases, and the local supersonic zone with second sonic plane (second CJ plane) appears. So the new mode of detonation wave is predicted. Equations describing this mode of detonation are presented. The exact analytical solution for the second CJ plane parameters is obtained. The example of double-front detonation in high explosive (TNT) is presented. In this double-front structure "nanodiamond-nanographite" phase transition takes place in condensed particles of detonation products.
Front Propagation in Stochastic Neural Fields
Bressloff, Paul C.
2012-01-01
We analyze the effects of extrinsic multiplicative noise on front propagation in a scalar neural field with excitatory connections. Using a separation of time scales, we represent the fluctuating front in terms of a diffusive-like displacement (wandering) of the front from its uniformly translating position at long time scales, and fluctuations in the front profile around its instantaneous position at short time scales. One major result of our analysis is a comparison between freely propagating fronts and fronts locked to an externally moving stimulus. We show that the latter are much more robust to noise, since the stochastic wandering of the mean front profile is described by an Ornstein-Uhlenbeck process rather than a Wiener process, so that the variance in front position saturates in the long time limit rather than increasing linearly with time. Finally, we consider a stochastic neural field that supports a pulled front in the deterministic limit, and show that the wandering of such a front is now subdiffusive. © 2012 Society for Industrial and Applied Mathematics.
Supporting radical front end innovation
Aagaard, Annabeth; Gertsen, Frank
2011-01-01
). Pharmaceutical innovation is unique, as it opposed to most other industries’ product development is science-driven and not customer-driven. In addition, the pharmaceutical FEI, as represented by research, lasts up to 5 years and the entire R&D process constitutes a period of 10-12 years, which is highly...... regulated by external authorities, e.g. The American Food and Drug Administration (FDA). The research aim of this paper is: to contribute to the field of FEI by studying how FEI can be actively supported within the industry specific context of the pharmaceutical industry, and through a conceptual discussion...... of FEI, pharmaceutical FEI and radical innovation. Based on this understanding, empirical research through exploratory and inductive case studies is analyzed. The value added and the contribution of this article to the existing FEI literature is in the study of the theoretical fields of research...
Front propagation and rejuvenation in flipping processes
Ben-naim, Eli [Los Alamos National Laboratory; Krapivsky, P I [BOSTON UNIV; Antal, T [HARVARD UNIV; Ben - Avrahm, D [HARVARD UNIV
2008-01-01
We study a directed flipping process that underlies the performance of the random edge simplex algorithm. In this stochastic process, which takes place on a one-dimensional lattice whose sites may be either occupied or vacant, occupied sites become vacant at a constant rate and simultaneously cause all sites to the right to change their state. This random process exhibits rich phenomenology. First, there is a front, defined by the position of the leftmost occupied site, that propagates at a nontrivial velocity. Second, the front involves a depletion zone with an excess of vacant sites. The total excess {Delta}{sub k} increases logarithmically, {Delta}{sub k} {approx_equal}ln k, with the distance k from the front. Third, the front exhibits ageing -- young fronts are vigorous but old fronts are sluggish. We investigate these phenomena using a quasi-static approximation, direct solutions of small systems and numerical simulations.
Wind-induced subduction at the South Atlantic subtropical front
Calil, Paulo H. R.
2017-10-01
The South Atlantic Subtropical Front, associated with the eastward-flowing South Atlantic Current, separates the colder, nutrient-rich waters of the subpolar gyre from the warmer, nutrient-poor waters of the subtropical gyre. Perturbations to the quasi-geostrophic, eastward flow generate meanders and filaments which induce cross-frontal exchange of water properties. Down-front winds transport denser waters from the South over warm waters from the North, inducing convective instability and subduction. Such processes occur over spatial scales of the order of 1 km and thus require high horizontal spatial resolution. In this modeling study, a high-resolution (4 km) regional grid is embedded in a basin-wide configuration (12 km) of the South Atlantic Ocean in order to test the importance of submesoscale processes in water mass subduction along the subtropical front. Stronger and more numerous eddies obtained in the high-resolution run yield more intense zonal jets along the frontal zone. Such stronger jets are more susceptible to instabilities, frontogenesis, and the generation of submesoscale meanders and filaments with O(1) Rossby number. As a consequence, vertical velocities larger than 100 md 1 are obtained in the high-resolution run, one order of magnitude larger than in the low-resolution run. Wind-driven subduction occurs along the frontal region, associated with negative Ertel potential vorticity in the surface layer. Such processes are not observed in the low-resolution run. A passive tracer experiment shows that waters with density characteristics similar to subtropical mode waters are preferentially subducted along the frontal region. The wind-driven buoyancy flux is shown to be much larger than thermal or haline fluxes during the wintertime, which highlights the importance of the frictional component in extracting PV from the surface ocean and inducing subduction, a process that has been overlooked in subtropical mode water formation in the region.
Kilian, Patrick
2015-09-14
The magnetic field of the sun is not a simple static dipole field but comprises much more complicated structures. When magnetic reconnection changes the topology of a structure the large amount of energy that was stored in the magnetic field is released and can eject the remainder of the magnetic structure and the plasma that is frozen to the magnetic field lines from the solar corona at large velocities. This event is called a coronal mass ejection (CME). Given that the upward motion happens at velocities larger than the local Alfven speed, the critical speed in the solar wind, the CME will act as a piston that drives a shock front through the solar wind ahead of itself. Satellites that monitor solar wind conditions detect an enhanced flux of high energy particles associated with the shock front. Radio instruments typically pick up bursts of electromagnetic emission, termed radio bursts, that are also consistent with processes driven by energetic particles. Thus, and due to theoretical considerations, it is safe to assume that particles can be accelerated at the shock front. Particle acceleration at collisionless shock fronts is an interesting topic for another reason. Earth is constantly bombarded by very energetic particles called (due to historical reasons) cosmic rays. The leading theory for the production of at least the fraction of cosmic rays that originate in our galaxy is acceleration at shock fronts, e.g. in super nova remnants. The large distance and consequently limited observation of these shock fronts restrict more detailed investigations. It is therefore useful to study the process of shock acceleration at shocks in the solar system that are much closer and more approachable to develop and test models and simulation methods that can be applied in different regimes. This dissertation aims at simulations of shock fronts with parameters that are close to the ones occurring in CME driven shocks. Since the goal is the investigation of the changing
Progress in front propagation research
Fort, Joaquim; Pujol, Toni
2008-08-01
We review the progress in the field of front propagation in recent years. We survey many physical, biophysical and cross-disciplinary applications, including reduced-variable models of combustion flames, Reid's paradox of rapid forest range expansions, the European colonization of North America during the 19th century, the Neolithic transition in Europe from 13 000 to 5000 years ago, the description of subsistence boundaries, the formation of cultural boundaries, the spread of genetic mutations, theory and experiments on virus infections, models of cancer tumors, etc. Recent theoretical advances are unified in a single framework, encompassing very diverse systems such as those with biased random walks, distributed delays, sequential reaction and dispersion, cohabitation models, age structure and systems with several interacting species. Directions for future progress are outlined.
Muon front end for the neutrino factory
C. T. Rogers
2013-04-01
Full Text Available In the neutrino factory, muons are produced by firing high-energy protons onto a target to produce pions. The pions decay to muons and pass through a capture channel known as the muon front end, before acceleration to 12.6 GeV. The muon front end comprises a variable frequency rf system for longitudinal capture and an ionization cooling channel. In this paper we detail recent improvements in the design of the muon front end.
Muon front end for the neutrino factory
Rogers, C T; Prior, G; Gilardoni, S; Neuffer, D; Snopok, P; Alekou, A; Pasternak, J
2013-01-01
In the neutrino factory, muons are produced by firing high-energy protons onto a target to produce pions. The pions decay to muons and pass through a capture channel known as the muon front end, before acceleration to 12.6 GeV. The muon front end comprises a variable frequency rf system for longitudinal capture and an ionization cooling channel. In this paper we detail recent improvements in the design of the muon front end.
Burning invariant manifolds in reactive front propagation
Mahoney, John; Mitchell, Kevin; Solomon, Tom
2011-01-01
We present theory and experiments on the dynamics of reaction fronts in a two-dimensional flow composed of a chain of alternating vortices. Inspired by the organization of passive transport by invariant manifolds, we introduce burning invariant manifolds (BIMs), which act as one-sided barriers to front propagation. The BIMs emerge from the theory when the advection-reaction- diffusion system is recast as an ODE for reaction front elements. Experimentally, we demonstrate how these BIMs can be measured and compare their behavior with simulation. Finally, a topological BIM formalism yields a maximum front propagation speed.
Front blind spot crashes in Hong Kong.
Cheng, Yuk Ki; Wong, Koon Hung; Tao, Chi Hang; Tam, Cheok Ning; Tam, Yiu Yan; Tsang, Cheuk Nam
2016-09-01
In 2012-2014, our laboratory had investigated a total of 9 suspected front blind spot crashes, in which the medium and heavy goods vehicles pulled away from rest and rolled over the pedestrians, who were crossing immediately in front of the vehicles. The drivers alleged that they did not see any pedestrians through the windscreens or the front blind spot mirrors. Forensic assessment of the goods vehicles revealed the existence of front blind spot zones in 3 out of these 9 accident vehicles, which were attributed to the poor mirror adjustments or even the absence of a front blind spot mirror altogether. In view of this, a small survey was devised involving 20 randomly selected volunteers and their goods vehicles and 5 out of these vehicles had blind spots at the front. Additionally, a short questionnaire was conducted on these 20 professional lorry drivers and it was shown that most of them were not aware of the hazards of blind spots immediately in front of their vehicles, and many did not use the front blind spot mirrors properly. A simple procedure for quick measurements of the coverage of front blind spot mirrors using a coloured plastic mat with dimensional grids was also introduced and described in this paper.
U. Ebert (Ute); W. van Saarloos
1999-01-01
textabstractDepending on the nonlinear equation of motion and on the initial conditions, different regions of a front may dominate the propagation mechanism. The most familiar case is the so-called pushed front, whose speed is determined by the nonlinearities in the front region itself. Pushed dynam
Laplacian Instability of Planar Streamer Ionization Fronts: An Example of Pulled Front Analysis
Derks, G.; Ebert, U.; Meulenbroek, B.
2008-01-01
Streamer ionization fronts are pulled fronts that propagate into a linearly unstable state; the spatial decay of the initial condition of a planar front selects dynamically one specific long-time attractor out of a continuous family. A stability analysis for perturbations in the transverse direction
Laplacian Instability of Planar Streamer Ionization Fronts: An Example of Pulled Front Analysis
Derks, G.; Ebert, U.; Meulenbroek, B.
2008-01-01
Streamer ionization fronts are pulled fronts that propagate into a linearly unstable state; the spatial decay of the initial condition of a planar front selects dynamically one specific long-time attractor out of a continuous family. A stability analysis for perturbations in the transverse direction
The Role of Front-Back Features in Children's 'Front', 'Back', and 'Beside' Placements of Objects.
Harris, Lauren; Strommen, Ellen
1970-01-01
In a study of spatial orientation, 40 boys and 40 girls from kindergarten and first grade placed a series of objects in front, behind, and beside themselves, and in front, behind, and beside other objects. Some objects had distinguishable front and back sides; others lacked such features. Placements were highly consistent within and across…
Light-Front Holography, Light-Front Wavefunctions, and Novel QCD Phenomena
Brodsky, S. J.; de Teramond, G. F.
2012-01-01
amplitudes in a higher dimensional anti-de Sitter (AdS) space to be mapped to frame-independent light-front wavefunctions of hadrons in physical space-time. The model leads to an effective confining light-front QCD Hamiltonian and a single-variable light-front Schrodinger equation which determines...
Multiple front propagation into unstable states
Montagne, R; Hernández-García, E; Miguel, M S
1993-01-01
The dynamics of transient patterns formed by front propagation in extended nonequilibrium systems is considered. Under certain circumstances, the state left behind a front propagating into an unstable homogeneous state can be an unstable periodic pattern. It is found by a numerical solution of a model of the Fr\\'eedericksz transition in nematic liquid crystals that the mechanism of decay of such periodic unstable states is the propagation of a second front which replaces the unstable pattern by a another unstable periodic state with larger wavelength. The speed of this second front and the periodicity of the new state are analytically calculated with a generalization of the marginal stability formalism suited to the study of front propagation into periodic unstable states. PACS: 47.20.Ky, 03.40.Kf, 47.54.+r
Hern, W M
1994-01-01
Warren Hern's reminiscences about his experiences as medical director of the Boulder (Colorado) Abortion Clinic and as an abortion provider in private practice provide support for his statement, "Every doctor in America who does abortions lives under a death threat." Shortly after the clinic was opened, a group of anti-abortion physicians pressured the Boulder County Medical Society to pass a resolution declaring the clinic a "clear and present danger" that should be shut down by local health boards. As the only freestanding abortion clinic in the state in the mid-1970's, the Boulder center was targeted by the Right-to-Life Committee picketers and Dr. Hern was harassed in his home and in public. When Dr. Hern left the clinic a year later to establish a private practice specializing in pregnancy termination, the picketers followed. After release of a textbook he prepared on abortion practice, the publisher was deluged with hate mail and threats of boycott, leading them to withdraw the text from its list. Violent attacks on abortion clinics accelerated after Reagan's election and bullets were fired into Hern's waiting room. Randall Terry, national head of Operation Rescue, prayed for Hern's death at a rally in front of his clinic. By the time Dr. David Gunn was assassinated by an anti-abortionist in March 1993, there had been over 1285 acts of violence against abortion facilities and more than 100 facilities had been completely destroyed. The transgression for which Dr. Gunn was murdered was that he sought to save the lives and futures of countless women and support their right to become full participants in society.
2000-01-01
Jupiter's four largest satellites, including Io, the golden ornament in front of Jupiter in this image from NASA's Cassini spacecraft, have fascinated Earthlings ever since Galileo Galilei discovered them in 1610 in one of his first astronomical uses of the telescope.Images from Cassini that will be released over the next several days capture each of the four Galilean satellites in their orbits around the giant planet.This true-color composite frame, made from narrow angle images taken on Dec. 12, 2000, captures Io and its shadow in transit against the disk of Jupiter. The distance of the spacecraft from Jupiter was 19.5 million kilometers (12.1 million miles). The image scale is 117 kilometers (73 miles) per pixel.The entire body of Io, about the size of Earth's Moon, is periodically flexed as it speeds around Jupiter and feels, as a result of its non-circular orbit, the periodically changing gravitational pull of the planet. The heat arising in Io's interior from this continual flexure makes it the most volcanically active body in the solar system, with more than 100 active volcanoes. The white and reddish colors on its surface are due to the presence of different sulfurous materials. The black areas are silicate rocks.Cassini is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini mission for NASA's Office of Space Science, Washington, D.C.
Dipolarization front and current disruption
Lui, A. T. Y.
2016-10-01
The modification of current density on the dawn-dusk cross section of the magnetotail with the earthward approach of a dipolarization front (DF) is examined through the recently published results of a three-dimensional (3-D) particle-in-cell (PIC) simulation. It is found that the current density intensifies by 37% abruptly within 1.5 ion gyrotime as the DF approaches and shows localized regions with north-south extrusions. After reaching its peak value, it undergoes a drastic current reduction (DCR) by 65% within 2 ion gyrotime. Breakdown of the frozen-in condition occurs in the neutral sheet region in association with DCR, demonstrating the non-MHD behavior of the phenomenon. The evolution of current density from this 3-D PIC simulation bears several similarities to those observed for the current disruption (CD) phenomenon, such as explosive growth and disruption of the current density leading to a breakdown of the frozen-in condition. The evolution is also similar to those from a previous two-dimensional (2-D) PIC simulation specially designed to investigate the nonlinear evolution of the cross-field current instability for CD. One interpretation of these findings is that CD and substorm triggering can be associated with earthward intrusion of a DF into the near-Earth plasma sheet as indicated by previous Cluster and Time History of Events and Macroscale Interactions during Substorms observations. An alternative interpretation is that both DF and CD are consequences of a global evolution from an ion-tearing-like instability of the magnetotail.
Blocking-resistant communication through domain fronting
Fifield David
2015-06-01
Full Text Available We describe “domain fronting,” a versatile censorship circumvention technique that hides the remote endpoint of a communication. Domain fronting works at the application layer, using HTTPS, to communicate with a forbidden host while appearing to communicate with some other host, permitted by the censor. The key idea is the use of different domain names at different layers of communication. One domain appears on the “outside” of an HTTPS request—in the DNS request and TLS Server Name Indication—while another domain appears on the “inside”—in the HTTP Host header, invisible to the censor under HTTPS encryption. A censor, unable to distinguish fronted and nonfronted traffic to a domain, must choose between allowing circumvention traffic and blocking the domain entirely, which results in expensive collateral damage. Domain fronting is easy to deploy and use and does not require special cooperation by network intermediaries. We identify a number of hard-to-block web services, such as content delivery networks, that support domain-fronted connections and are useful for censorship circumvention. Domain fronting, in various forms, is now a circumvention workhorse. We describe several months of deployment experience in the Tor, Lantern, and Psiphon circumvention systems, whose domain-fronting transports now connect thousands of users daily and transfer many terabytes per month.
Coevolutionary success-driven multigames
Szolnoki, Attila
2014-01-01
Wealthy individuals may be less tempted to defect than those with comparatively low payoffs. To take this into consideration, we introduce coevolutionary success-driven multigames in structured populations. While the core game is always the weak prisoner's dilemma, players whose payoffs from the previous round exceed a threshold adopt only a minimally low temptation to defect in the next round. Along with the strategies, the perceived strength of the social dilemma thus coevolves with the success of each individual player. We show that the lower the threshold for using the small temptation to defect, the more the evolution of cooperation is promoted. Importantly, the promotion of cooperation is not simply due to a lower average temptation to defect, but rather due to a dynamically reversed direction of invasion along the interfaces that separate cooperators and defectors on regular networks. Conversely, on irregular networks, in the absence of clear invasion fronts, the promotion of cooperation is due to inte...
Breaking the sound barrier in recombination fronts
Williams, R J R
1995-01-01
We exploit a generic instability in the integration of steady, sonic near-isothermal flows to find the complete transition diagram for recombination fronts (for a model system of equations). The instability requires the integration of the flow equations for speeds between the isothermal and adiabatic sound speeds to be performed with particular care. As a result of this, the previous work of Newman & Axford on the structure of recombination fronts neglected an important class of solution, that of transonic fronts; our method is readily extensible to a more complete treatment of the ionization structure. Future papers will apply these results in models of the structure of ultracompact HII regions.
Pressure transient method for front tracking
Benson, S.M.; Bodvarsson, G.S.
1983-08-01
A pressure transient technique for tracking the advance of cold water fronts during water flooding and goethermal injection operations has been developed. The technique is based on the concept that the steady state pressure buildup in the reservoir region inside the front can be calculated by a fluid skin factor. By analyzing successive pressure falloff tests, the advance of the front in the reservoir can be monitored. The validity of the methods is demonstrated by application to three numerically simulated data sets, a nonisothermal step-rate injection test, a series of pressure falloffs in a multilayered reservoir, and a series of pressure falloff tests in a water flooded oil reservoir.
FACE RECOGNITION FROM FRONT-VIEW FACE
Wu Lifang; Shen Lansun
2003-01-01
This letter presents a face normalization algorithm based on 2-D face model to recognize faces with variant postures from front-view face. A 2-D face mesh model can be extracted from faces with rotation to left or right and the corresponding front-view mesh model can be estimated according to the facial symmetry. Then based on the inner relationship between the two mesh models, the normalized front-view face is formed by gray level mapping. Finally, the face recognition will be finished based on Principal Component Analysis (PCA). Experiments show that better face recognition performance is achieved in this way.
Collisionless ion dynamics in the shock front
Gedalin, Michael
2016-07-01
In the vicinity of the shock front the dynamics of ions is governed by the macroscopic regular electric and magnetic field of the shock. Upon crossing the shock the thermal ions form a non-gyrotropic distribution. The pressure of these non-gyrotropic ions shapes the downstream magnetic field. High-energy ions behave in the shock front as test particles under the influence on the macroscopic fields. The reflection and transmission coefficients of high-energy ions at an oblique shock front is not sensitive to the shock structure and depends only on the global magnetic field change at the shock.
Unstable fronts and stable "critters" formed by microrollers
Driscoll, Michelle; Youssef, Mena; Sacanna, Stefano; Donev, Aleksandar; Chaikin, Paul
2016-01-01
Condensation of objects into stable clusters occurs naturally in equilibrium and driven systems. It is commonly held that potential interactions, depletion forces, or sensing are the only mechanisms which can create long-lived compact structures. Here we show that persistent motile structures can form spontaneously from hydrodynamic interactions alone with no sensing or potential interactions. We study this structure formation in a system of colloidal rollers suspended and translating above a floor, using both experiments and large-scale 3D simulations. In this system, clusters originate from a previously unreported fingering instability, where fingers pinch off from an unstable front to form autonomous "critters", whose size is selected by the height of the particles above the floor. These critters are a stable state of the system, move much faster than individual particles, and quickly respond to a changing drive. With speed and direction set by a rotating magnetic field, these active structures offer inter...
Nonperturbative light-front Hamiltonian methods
Hiller, J R
2016-01-01
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, $\\phi^4$ 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...
Front Matter: Volume 1 (Proceedings of CBU
Petr Hájek
2013-06-01
Full Text Available This PDF file contains the front matter associated with CBU Proceedings Volume 1 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.
Front Matter: Volume 3 (Proceedings of CBU
Petr Hájek
2015-09-01
Full Text Available This PDF file contains the front matter associated with CBU Proceedings Volume 1 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.
Optimizing emergency department front-end operations.
Wiler, Jennifer L; Gentle, Christopher; Halfpenny, James M; Heins, Alan; Mehrotra, Abhi; Mikhail, Michael G; Fite, Diana
2010-02-01
As administrators evaluate potential approaches to improve cost, quality, and throughput efficiencies in the emergency department (ED), "front-end" operations become an important area of focus. Interventions such as immediate bedding, bedside registration, advanced triage (triage-based care) protocols, physician/practitioner at triage, dedicated "fast track" service line, tracking systems and whiteboards, wireless communication devices, kiosk self check-in, and personal health record technology ("smart cards") have been offered as potential solutions to streamline the front-end processing of ED patients, which becomes crucial during periods of full capacity, crowding, and surges. Although each of these operational improvement strategies has been described in the lay literature, various reports exist in the academic literature about their effect on front-end operations. In this report, we present a review of the current body of academic literature, with the goal of identifying select high-impact front-end operational improvement solutions.
Nonperturbative light-front Hamiltonian methods
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.
Hydrodynamic dispersion broadening of a sedimentation front
Martin, J.; Rakotomalala, N.; Salin, D.
1994-10-01
Hydrodynamic dispersion is responsible for the spreading of the sedimentation front even in a noncolloidal monodisperse suspension. Measurements of the broadening of the top front observed during sedimentation have been used in determining the hydrodynamic dispersion coefficient. Hindered settling has an opposed effect and leads to the self-sharpening of the front. Both effects have to be taken into account simultaneously. This Letter provides a simple, but complete determination of the space and time concentration profile and shows that the final front should consist of a steady-shape profile propagating at constant velocity. With such a solution, the data of Davis et al. [AIChE J. 34, 123 (1988); J. Fluid Mech. 196, 107 (1988)] give hydrodynamic dispersion coefficient five times larger than their former analysis, in agreement with Lee et al. [Phys. Fluids A 4, 2601 (1992)].
Detecting Lagrangian fronts with favourable fishery conditions
Prants, S V; Uleysky, M Yu
2012-01-01
Lagrangian fronts in the ocean delineate boundaries between surface waters with different Lagrangian properties. They can be accurately detected in a given velocity field by computing synoptic maps of the drift of synthetic tracers, their Lyapunov exponents, and other Lagrangian indicators. Using Russian ship's catch and location data for a number of commercial fishing seasons in the region of the northwest Pacific with one of the richest fishery in the world, it is shown that the saury fishing grounds with maximal catches are located mainly along those Lagrangian fronts where productive cold waters of the Oyashio Current, warmer waters of the southern branch of the Soya Current, and waters of warm-core Kuroshio rings converge. Computation of those fronts with the altimetric geostrophic velocity fields both in the years with the First and Second Oyashio Intrusions shows that in spite of different oceanographic conditions in both the cases the front locations may serve good indicators of potential fishing grou...
On Front Slope Stability of Berm Breakwaters
Burcharth, Hans F.
2013-01-01
The short communication presents application of the conventional Van der Meer stability formula for low-crested breakwaters for the prediction of front slope erosion of statically stable berm breakwaters with relatively high berms. The method is verified (Burcharth, 2008) by comparison with the r......The short communication presents application of the conventional Van der Meer stability formula for low-crested breakwaters for the prediction of front slope erosion of statically stable berm breakwaters with relatively high berms. The method is verified (Burcharth, 2008) by comparison...... test results including tests presented in Sigurdarson and Van der Meer (2011) are discussed. A proposal is presented for performance of new model tests with the purpose of developing more accurate formulae for the prediction of front slope erosion as a function of front slope, relative berm height...
Front formation in an active scalar equation.
Constantin, P; Nie, Q; Schörghofer, N
1999-09-01
We study the formation of thermal fronts in an active scalar equation that is similar to the Euler equation. For a particular initial condition, an earlier candidate for finite-time blowup, the front forms in a generalized self-similar way with constant hyperbolicity at the center. The behavior belongs to a class of scenarios for which finite-time blowup is impossible. A systematic exploration of many different initial conditions reveals no evidence of singular solutions.
Hern, W M
1993-01-01
honor those who advanced the cause of women's rights. They honored the physician who had to shout over hecklers to make his remarks heard. After a year of operation, the physician encountered differences with the Board of Directors of the clinic. Soon after that, he resigned and opened his own clinic with a bank loan of $7000. Within 4 years, his clinic had expanded, and he purchased its building. The harassment from antiabortion protesters continued, with broken windows, pickets, and, in February 1988, bullets fired through the front windows of the waiting room. This necessitated the installation of bullet-proof glass and a security system which cost $17,000. As of March 1, 1993, there had been 1285 acts of violence towards abortion clinics, which led to the destruction of more than 100. On March 10 of that year, a physician who performed abortions in Florida was gunned down by an anti-abortion protestor. People who provide abortions hope for legal protection and respect for their civil liberties, but they will continue to provide this service even if conditions do not improve.
Brodsky, Stanley J.; de Teramond, Guy F.; /SLAC /Southern Denmark U., CP3-Origins /Costa Rica U.
2011-01-10
AdS/QCD, the correspondence between theories in a dilaton-modified five-dimensional anti-de Sitter space and confining field theories in physical space-time, provides a remarkable semiclassical model for hadron physics. Light-front holography allows hadronic amplitudes in the AdS fifth dimension to be mapped to frame-independent light-front wavefunctions of hadrons in physical space-time. The result is a single-variable light-front Schroedinger equation which determines the eigenspectrum and the light-front wavefunctions of hadrons for general spin and orbital angular momentum. The coordinate z in AdS space is uniquely identified with a Lorentz-invariant coordinate {zeta} which measures the separation of the constituents within a hadron at equal light-front time and determines the off-shell dynamics of the bound state wavefunctions as a function of the invariant mass of the constituents. The hadron eigenstates generally have components with different orbital angular momentum; e.g., the proton eigenstate in AdS/QCD with massless quarks has L = 0 and L = 1 light-front Fock components with equal probability. Higher Fock states with extra quark-anti quark pairs also arise. The soft-wall model also predicts the form of the nonperturbative effective coupling and its {beta}-function. The AdS/QCD model can be systematically improved by using its complete orthonormal solutions to diagonalize the full QCD light-front Hamiltonian or by applying the Lippmann-Schwinger method to systematically include QCD interaction terms. Some novel features of QCD are discussed, including the consequences of confinement for quark and gluon condensates. A method for computing the hadronization of quark and gluon jets at the amplitude level is outlined.
Light-Front Holography and the Light-Front Schrodinger Equation
Brodsky, Stanley J.; de Teramond, Guy
2012-08-15
One of the most important nonperturbative methods for solving QCD is quantization at fixed light-front time {tau} = t+z=c - Dirac's 'Front Form'. The eigenvalues of the light-front QCD Hamiltonian predict the hadron spectrum and the eigensolutions provide the light-front wavefunctions which describe hadron structure. More generally, we show that the valence Fock-state wavefunctions of the light-front QCD Hamiltonian satisfy a single-variable relativistic equation of motion, analogous to the nonrelativistic radial Schrodinger equation, with an effective confining potential U which systematically incorporates the effects of higher quark and gluon Fock states. We outline a method for computing the required potential from first principles in QCD. The holographic mapping of gravity in AdS space to QCD, quantized at fixed light-front time, yields the same light front Schrodinger equation; in fact, the soft-wall AdS/QCD approach provides a model for the light-front potential which is color-confining and reproduces well the light-hadron spectrum. One also derives via light-front holography a precise relation between the bound-state amplitudes in the fifth dimension of AdS space and the boost-invariant light-front wavefunctions describing the internal structure of hadrons in physical space-time. The elastic and transition form factors of the pion and the nucleons are found to be well described in this framework. The light-front AdS/QCD holographic approach thus gives a frame-independent first approximation of the color-confining dynamics, spectroscopy, and excitation spectra of relativistic light-quark bound states in QCD.
Light-Front Quantization of Gauge Theories
Brodskey, Stanley
2002-12-01
Light-front wavefunctions provide a frame-independent representation of hadrons in terms of their physical quark and gluon degrees of freedom. The light-front Hamiltonian formalism provides new nonperturbative methods for obtaining the QCD spectrum and eigensolutions, including resolvant methods, variational techniques, and discretized light-front quantization. A new method for quantizing gauge theories in light-cone gauge using Dirac brackets to implement constraints is presented. In the case of the electroweak theory, this method of light-front quantization leads to a unitary and renormalizable theory of massive gauge particles, automatically incorporating the Lorentz and 't Hooft conditions as well as the Goldstone boson equivalence theorem. Spontaneous symmetry breaking is represented by the appearance of zero modes of the Higgs field leaving the light-front vacuum equal to the perturbative vacuum. I also discuss an ''event amplitude generator'' for automatically computing renormalized amplitudes in perturbation theory. The importance of final-state interactions for the interpretation of diffraction, shadowing, and single-spin asymmetries in inclusive reactions such as deep inelastic lepton-hadron scattering is emphasized.
QCD and Light-Front Holography
Brodsky, Stanley J
2010-01-01
The soft-wall AdS/QCD model, modified by a positive-sign dilaton metric, leads to a remarkable one-parameter description of nonperturbative hadron dynamics. The model predicts a zero-mass pion for zero-mass quarks and a Regge spectrum of linear trajectories with the same slope in the leading orbital angular momentum $L$ of hadrons and the radial quantum number $N$. Light-Front Holography maps the amplitudes which are functions of the fifth dimension variable $z$ of anti-de Sitter space to a corresponding hadron theory quantized on the light front. The resulting Lorentz-invariant relativistic light-front wave equations are functions of an invariant impact variable $\\zeta$ which measures the separation of the quark and gluonic constituents within the hadron at equal light-front time. The result is a semi-classical frame-independent first approximation to the spectra and light-front wavefunctions of meson and baryon light-quark bound states, which in turn predict the behavior of the pion and nucleon form factors...
Stream of Reaction Products behind the Detonation Wave Front
无
2001-01-01
Embedded copper foils in a high explosive charge allow to see the stream of the reaction products behind the detonation front. With three individual firings in front of FXR it can be shown that the reaction products behind the detonation front are immediately going in the direction of the detonation front. But then the rarefaction fans are influencing strongly the further displacements.
Front instability and energy of the free surface
Beltrame, Philippe
2014-05-01
In recent years, there has been a proliferation of research devoted to the formation of preferential flow paths occurring without macroscopic heterogeneity of the porous media. DiCarlo (2013) points out the connection between "overshoot" and the front instability. Extension of the standard Richards equation is required to capture this phenomenon. In most of the improvements, interfacial phenomena as the triple line at the front are considered. For instance, velocity dependent contact angle (Wang et al., 2013) or contact angle hysteresis (Rätz and Schweizer, 2012) allow to simulate successfully the instability. Another approach proposed by Cueto-Felgueroso and Juanes (2009) introduces a macroscopic surface tension related to the existence of the water/air interface. As previously, the simulation of an advancing front displays physical looking fingering displacements. The goal of this contribution is to better understand the role of the different surface energies in the emergence of the front instability. We propose a model involving both the macroscopic surface tension and the soil wettability. This latter allows to define a contact angle and possibly hysteresis using heterogeneous wettability (Beltrame et al., 2011). Therefore, we employ the phase field approach developed by Felgueroso and Juanes, 2009 to which we add a free energy term corresponding to the wettability: a disjoining or conjoining pressure resulting from effective molecular interactions between the substrate and the free surface (DeGennes, 1985). The difference with the classical suction pressure is the hydrophobic behavior for ultra-thin film (small water saturation). Such a water repellency was recently estimated in the soil (Diamantopoulos et al. 2013). Stability analysis of an advancing front in an uniform porous media shows that macroscopic surface tension and wettability may independently produce the instability growth. In contrast, for a front stopping when reaching the layers interface of
Front-end conceptual platform modeling
Guðlaugsson, Tómas Vignir; Ravn, Poul Martin; Mortensen, Niels Henrik
2014-01-01
Platform thinking has been the subject of investigation and deployment in many projects in both academia and industry. Most contributions involve the restructuring of product programs, and only a few support front-end development of a new platform in parallel with technology development....... This contribution deals with the development of product platforms in front-end projects and introduces a modeling tool: the Conceptual Product Platform model. State of the art within platform modeling forms the base of a modeling formalism for a Conceptual Product Platform model. The modeling formalism is explored...... through an example and applied in a case in which the Conceptual Product Platform model has supported the front-end development of a platform for an electro-active polymer technology. The case describes the contents of the model and how its application supported the development work in the project...
Gauge Theories on the Light-Front
Brodsky, S J
2004-01-01
The light-front quantization of gauge theories in light-cone gauge provides a frame-independent wavefunction representation of relativistic bound states, simple forms for current matrix elements, explicit unitary, and a trivial vacuum. The light-front Hamiltonian form of QCD provides an alternative to lattice gauge theory for the computation of nonperturbative quantities such as the hadronic spectrum and the corresponding eigenfunctions. In the case of the electroweak theory, spontaneous symmetry breaking is represented by the appearance of zero modes of the Higgs field. Light-front quantization then leads to an elegant ghost-free theory of massive gauge particles, automatically incorporating the Lorentz and 't Hooft conditions, as well as the Goldstone boson equivalence theorem.
RF front-end world class designs
Love, Janine
2009-01-01
All the design and development inspiration and direction a harware engineer needs in one blockbuster book! Janine Love site editor for RF Design Line,columnist, and author has selected the very best RF design material from the Newnes portfolio and has compiled it into this volume. The result is a book covering the gamut of RF front end design from antenna and filter design fundamentals to optimized layout techniques with a strong pragmatic emphasis. In addition to specific design techniques and practices, this book also discusses various approaches to solving RF front end design problems and h
2016-12-21
The JMP Add-In TopN-PFS provides an automated tool for finding layered Pareto front to identify the top N solutions from an enumerated list of candidates subject to optimizing multiple criteria. The approach constructs the N layers of Pareto fronts, and then provides a suite of graphical tools to explore the alternatives based on different prioritizations of the criteria. The tool is designed to provide a set of alternatives from which the decision-maker can select the best option for their study goals.
Pole solutions for flame front propagation
Kupervasser, Oleg
2015-01-01
This book deals with solving mathematically the unsteady flame propagation equations. New original mathematical methods for solving complex non-linear equations and investigating their properties are presented. Pole solutions for flame front propagation are developed. Premixed flames and filtration combustion have remarkable properties: the complex nonlinear integro-differential equations for these problems have exact analytical solutions described by the motion of poles in a complex plane. Instead of complex equations, a finite set of ordinary differential equations is applied. These solutions help to investigate analytically and numerically properties of the flame front propagation equations.
Pulse front control with adaptive optics
Sun, B.; Salter, P. S.; Booth, M. J.
2016-03-01
The focusing of ultrashort laser pulses is extremely important for processes including microscopy, laser fabrication and fundamental science. Adaptive optic elements, such as liquid crystal spatial light modulators or membrane deformable mirrors, are routinely used for the correction of aberrations in these systems, leading to improved resolution and efficiency. Here, we demonstrate that adaptive elements used with ultrashort pulses should not be considered simply in terms of wavefront modification, but that changes to the incident pulse front can also occur. We experimentally show how adaptive elements may be used to engineer pulse fronts with spatial resolution.
Discretionary Power on the Front-line
Sanden, Guro Refsum; Lønsmann, Dorte
This article investigates the communication practices used by front-line employees to cross language boundaries in the context of English language policies implemented by the management of three multinational corporations (MNCs) headquartered in Scandinavia. Based on an analysis of interview......-line employees diverge from the corporate language policies, and emphasise the role of individual agency in the implementation of language policy. With a focus on the communication practices of front-line employees, the article contributes with a bottom-up, employee-centred perspective on corporate language...... management, emphasising the importance of paying attention to the micro level of everyday interactions in the study of language policy and practice....
UNIX NSW Front End Enhancements. Volume I.
1981-06-01
Implementation UNIX MSG is implemented in the programming language C (D.M. Ritchie, S.C. Johnson, M.E. Lesk, and B.W. Kernighan , "The C Programming Language...8URC-0062 UNCLASSIFIED B BN4b I VOL-1 RADC-TR-81-lbA VOL-1 NL fRADCTR-81-164, Vol I (of two) Final Technical Report June 1981 .. UNIX NSW FRONT END...ABSTRACT (Conti--- on re0-r8. side If necessary and idenfify by block number) The effort to develop a UNIX NSW Front End is part of the National Software
Developer Driven and User Driven Usability Evaluations
Bruun, Anders
2013-01-01
Usability evaluation provide software development teams with insights on the degree to which a software application enables a user to achieve his/her goals, how fast these goals can be achieved, how easy it is to learn and how satisfactory it is in use Although usability evaluations are crucial....... The four primary findings from my studies are: 1) The developer driven approach reveals a high level of thoroughness and downstream utility. 2) The user driven approach has higher performance regarding validity 3) The level of reliability is comparable between the two approaches. 4) The user driven...
Numerical Simulations of Radiatively-Driven Dusty Winds
Krumholz, Mark R
2013-01-01
Radiation pressure on dust grains may be an important mechanism in driving winds in a wide variety of astrophysical systems. However, the efficiency of the coupling between the radiation field and the dusty gas is poorly understood in environments characterized by high optical depths like those in ultra-luminous infrared galaxies (ULIRGs) and massive dense star clusters. We present a series of idealized numerical experiments, performed with the radiation-hydrodynamic code \\textsc{orion}, in which we study the dynamics of such winds and quantify their properties. We find that, after wind acceleration begins, radiation Rayleigh-Taylor instability forces the gas into a configuration that reduces the rate of momentum transfer from the radiation field to the gas by a factor ~ 10 - 100 compared to an estimate based on the optical depth at the base of the atmosphere; instead, the rate of momentum transfer from a driving radiation field of luminosity L to the gas is roughly L/c multiplied by half the optical depth at...
Neutrino-driven convection versus advection in core collapse supernovae
Foglizzo, T; Janka, H T
2005-01-01
A toy model is analyzed in order to evaluate the linear stability of the gain region immediately behind a stalled accretion shock, after core bounce. This model demonstrates that a negative entropy gradient is not sufficient to warrant linear instability. The stability criterion is governed by the ratio "chi" of the advection time through the gain region divided by the local timescale of buoyancy. The gain region is linearly stable if chi>3. For chi>3, perturbations are unstable in a limited range of horizontal wavelengths centered around twice the vertical size H of the gain region. The threshold horizontal wavenumbers k_{min} and k_{max} follow simple scaling laws such that Hk_{min}\\propto 1/chi and Hk_{max}\\propto chi. These scaling laws are understood as the consequence of a vortical-acoustic cycle within the gain region, fed by the Rayleigh-Taylor growth of vorticity perturbations during advection. The stability of short wavelength perturbations is compared to the "ablative stabilization" of accelerated ...
Hydrodynamic instabilities and mix studies on NIF: predictions, observations, and a path forward
Remington, B. A.; Atherton, L. J.; Benedetti, L. R.; Berzak-Hopkins, L.; Bradley, D. K.; Callahan, D. A.; Casey, D. T.; Celliers, P. M.; Cerjan, C. J.; Clark, D. S.; Dewald, E. L.; Dittrich, T. R.; Dixit, S. N.; Döppner, T.; Edgell, D. H.; Edwards, M. J.; Epstein, R.; Frenje, J.; Gatu-Johnson, M.; Glenn, S.; Glenzer, S. H.; Grim, G.; Haan, S. W.; Hammel, B. A.; Hamza, A.; Hicks, D.; Hsing, W. W.; Hurricane, O.; Izumi, N.; Jones, O. S.; Key, M. H.; Khan, S. F.; Kilkenny, J. D.; Kline, J. L.; Kyrala, G. A.; Landen, O. L.; Le Pape, S.; Lindl, J. D.; Ma, T.; MacGowan, B. J.; Mackinnon, A. J.; MacPhee, A. G.; Meezan, N. B.; Moody, J. D.; Moses, E. I.; Nikroo, A.; Pak, A.; Parham, T.; Park, H.-S.; Patel, P. K.; Petrasso, R.; Pino, J.; Ralph, J. E.; Raman, K.; Regan, S. P.; Robey, H. F.; Ross, J. S.; Spears, B. K.; Smalyuk, V. A.; Springer, P. T.; Suter, L. J.; Tipton, R.; Tommasini, R.; Town, R. P.; Weber, S. V.
2016-03-01
The goals of the Mix Campaign are to determine how mix affects performance, locate the “mix cliff”, locate the source of the mix, and develop mitigation methods that allow performance to be increased. We have used several different drive pulse shapes and capsule designs in the Mix Campaign, to understand sensitivity to drive peak power, level of coast, rise time to peak power, adiabat, and dopant level in the capsule. Ablator material mixing into the hot spot has been shown conclusively with x-ray spectroscopy. The observed neutron yield drops steeply when the hot spot mix mass becomes too large. The mix appears to be driven by ablation- front Rayleigh-Taylor instabilities. A high foot, higher adiabat drive has a more stable ablation front and has allowed the mix mass in the hot spot to be reduced significantly. Two recent high foot shots achieved neutron yields > 1015 and measured neutron yield over clean 1D simulation (YOC) > 50%, which was one of the central goals of the Mix Campaign.
Positional Velar Fronting: An Updated Articulatory Account
Byun, Tara McAllister
2012-01-01
This study develops the hypothesis that the child-specific phenomenon of positional velar fronting can be modeled as the product of phonologically encoded articulatory limitations unique to immature speakers. Children have difficulty executing discrete tongue movements, preferring to move the tongue and jaw as a single unit. This predisposes the…
A preliminary ultrasound study of velar fronting
Wodzinski, Sylvie M.; Frisch, Stefan A.
2003-10-01
The purpose of this study is to (1) evaluate the effectiveness of ultrasound imaging to measure velar consonant closure location, and (2) conduct a thorough study of velar fronting by measuring several productions of velar stops in the context of every English vowel. Word onset velar stops were measured in both words (CV or CVC) and nonwords (VCV) within a carrier phrase. Other coarticulatory influences were minimized by using words with no coda or labial coda consonants (e.g., ``Say a gap again,'' ``Say /oIkoI/ again''). Measurements were made at the point of maximal closure. Closure location was measured using the radial angle from the center of the ultrasound probe to the center of the velar closure. Pilot data for one subject has been analyzed to date. Closure location appears consistent across all central and back vowels. For front vowels, the degree of fronting of the velar appears to be correlated with the frontness of the vowel. Measures of closure location for diphthongs followed the back vowel pattern in the word targets. For nonwords, the closure location was influenced by the preceding diphthong offset quality and the following diphthong onset quality. Theoretical implications for the phonetics/phonology interface will be discussed.
On Multiple Questions and Multiple WH Fronting.
Rudin, Catherine
An analysis of languages with multiple fronting of WH words (who, what, whom, etc.) looks in detail at Polish, Serbo-Croatian, Czech, Bulgarian (Slavic languages), and Romanian (a Romance language). In spite of their superficial similarity, the Slavic and East European languages that normally put all WH words at the beginning of clauses fall into…
New Results in Light-Front Phenomenology
Brodsky, S J
2004-01-01
The light-front quantization of gauge theories such as QCD in light-cone gauge provides a frame-independent wavefunction representation of relativistic bound states, simple forms for current matrix elements, explicit unitarity, and a trivial vacuum. The freedom to choose the light-like quantization four-vector provides an explicitly covariant formulation of light-front quantization and can be used to determine the analytic structure of light-front wave functions and to define a kinematical definition of angular momentum. The AdS/CFT correspondence of large $N_C$ supergravity theory in higher-dimensional anti-de Sitter space with supersymmetric QCD in 4-dimensional space-time has interesting implications for hadron phenomenology in the conformal limit, including an all-orders demonstration of counting rules for exclusive processes. String/gauge duality also predicts the QCD power-law behavior of light-front Fock-state hadronic wavefunctions with arbitrary orbital angular momentum at high momentum transfer. The...
Front propagation in a chaotic flow field
Mehrvarzi, C. O.; Paul, M. R.
2014-07-01
We investigate numerically the dynamics of a propagating front in the presence of a spatiotemporally chaotic flow field. The flow field is the three-dimensional time-dependent state of spiral defect chaos generated by Rayleigh-Bénard convection in a spatially extended domain. Using large-scale parallel numerical simulations, we simultaneously solve the Boussinesq equations and a reaction-advection-diffusion equation with a Fischer-Kolmogorov-Petrovskii-Piskunov reaction for the transport of the scalar species in a large-aspect-ratio cylindrical domain for experimentally accessible conditions. We explore the front dynamics and geometry in the low-Damköhler-number regime, where the effect of the flow field is significant. Our results show that the chaotic flow field enhances the front propagation when compared with a purely cellular flow field. We quantify this enhancement by computing the spreading rate of the reaction products for a range of parameters. We use our results to quantify the complexity of the three-dimensional front geometry for a range of chaotic flow conditions.
Morphology of solidification front in eutectic
M. Trepczyńska - Łent
2009-07-01
Full Text Available In this paper the analysis of morphology of solidification front in eutectic made. It was present influence of composition, solidification velocity, concentration micro-field and capillarity effects on the morphology of the solid/liquid interface. It was introduced phase-field model.
FRED, a Front End for Databases.
Crystal, Maurice I.; Jakobson, Gabriel E.
1982-01-01
FRED (a Front End for Databases) was conceived to alleviate data access difficulties posed by the heterogeneous nature of online databases. A hardware/software layer interposed between users and databases, it consists of three subsystems: user-interface, database-interface, and knowledge base. Architectural alternatives for this database machine…
Computer simulation and vehicle front optimisation.
Sluis, J. van der
1993-01-01
The influence of the stiffness and shape of a car-front on injuries of bicyclists caused by side collisions was studied by computer simulation. Simulation was a suitable method in this case because of two reasons: variation of shape and stiffness is more difficult to perform in case of an experiment
Managing Controversies in the Fuzzy Front End
Christiansen, John K.; Gasparin, Marta
2016-01-01
. The analysis investigates the microprocesses around the controversies that emerge during the fuzzy front end of four products. Five different types of controversies are identified: profit, production, design, brand and customers/market. Each controversy represents a threat, but also an opportunity to search...
Time Line Visualization of Research Fronts.
Morris, Steven A.; Yen, G.; Wu, Zheng; Asnake, Benyam
2003-01-01
Research fronts, defined as clusters of documents that tend to cite a fixed, time invariant set of base documents, are plotted as time lines for visualization and exploration. Illustrates the construction, exploration, and interpretation of time lines for identifying and visualizing temporal changes in research activity through journal articles.…
QCD and Light-Front Holography
Brodsky, Stanley J.; /SLAC /Southern Denmark U., CP3-Origins; de Teramond, Guy F.; /Costa Rica U.
2010-10-27
The soft-wall AdS/QCD model, modified by a positive-sign dilaton metric, leads to a remarkable one-parameter description of nonperturbative hadron dynamics. The model predicts a zero-mass pion for zero-mass quarks and a Regge spectrum of linear trajectories with the same slope in the leading orbital angular momentum L of hadrons and the radial quantum number N. Light-Front Holography maps the amplitudes which are functions of the fifth dimension variable z of anti-de Sitter space to a corresponding hadron theory quantized on the light front. The resulting Lorentz-invariant relativistic light-front wave equations are functions of an invariant impact variable {zeta} which measures the separation of the quark and gluonic constituents within the hadron at equal light-front time. The result is to a semi-classical frame-independent first approximation to the spectra and light-front wavefunctions of meson and baryon light-quark bound states, which in turn predict the behavior of the pion and nucleon form factors. The theory implements chiral symmetry in a novel way: the effects of chiral symmetry breaking increase as one goes toward large interquark separation, consistent with spectroscopic data, and the the hadron eigenstates generally have components with different orbital angular momentum; e.g., the proton eigenstate in AdS/QCD with massless quarks has L = 0 and L = 1 light-front Fock components with equal probability. The soft-wall model also predicts the form of the non-perturbative effective coupling {alpha}{sub s}{sup AdS} (Q) and its {beta}-function which agrees with the effective coupling {alpha}{sub g1} extracted from the Bjorken sum rule. The AdS/QCD model can be systematically improved by using its complete orthonormal solutions to diagonalize the full QCD light-front Hamiltonian or by applying the Lippmann-Schwinger method in order to systematically include the QCD interaction terms. A new perspective on quark and gluon condensates is also reviewed.
Stability of Kuramoto-Sivashinsky fronts in moving fluid
Vilela, P. M.; Vasquez, Desiderio A.
2014-12-01
We analyze the effects of an external Couette flow on reactions fronts described by the Kuramoto-Sivashinsky equation. The fronts propagate in a two-dimensional slab confined by two parallel plates moving in opposite directions. The fronts can propagate in the same direction or against the external flow. We obtain steady front solutions by solving numerically the nonlinear time-independent equations. A linear stability analysis determines the stability of the fronts. The fronts and their stability depend on the slab width and on the relative velocity between the plates. These parameters have the potential to modify unstable fronts into stable fronts. We compare our results with fronts developed under a Poiseuille flow.
QCD Phenomenology and Light-Front Wavefunctions
Brodsky, Stanley J.
2001-11-21
A natural calculus for describing the bound-state structure of relativistic composite systems in quantum field theory is the light-front Fock expansion which encodes the properties of a hadrons in terms of a set of frame-independent n-particle wavefunctions. Light-front quantization in the doubly-transverse light-cone gauge has a number of remarkable advantages, including explicit unitarity, a physical Fock expansion, the absence of ghost degrees of freedom, and the decoupling properties needed to prove factorization theorems in high momentum transfer inclusive and exclusive reactions. A number of applications are discussed in these lectures, including semileptonic B decays, two-photon exclusive reactions, diffractive dissociation into jets, and deeply virtual Compton scattering. The relation of the intrinsic sea to the light-front wavefunctions is discussed. Light-front quantization can also be used in the Hamiltonian form to construct an event generator for high energy physics reactions at the amplitude level. The light-cone partition function, summed over exponentially weighted light-cone energies, has simple boost properties which may be useful for studies in heavy ion collisions. I also review recent work which shows that the structure functions measured in deep inelastic lepton scattering are affected by final-state rescattering, thus modifying their connection to light-front probability distributions. In particular, the shadowing of nuclear structure functions is due to destructive interference effects from leading-twist diffraction of the virtual photon, physics not included in the nuclear light-cone wavefunctions.
Effects of Initial Conditions on Compressible Mixing in Supernova-Relevant Laboratory Experiments
Miles, A R; Edwards, M; Greenough, J
2004-04-30
In core-collapse supernovae, strong blast waves drive interfaces susceptible to Rayleigh-Taylor (RT), Richtmyer-Meshkov (RM), and Kelvin-Helmholtz (KH) instabilities. In addition, perturbation growth can result from material expansion in large-scale velocity gradients behind the shock front. Laser-driven experiments are designed to produce a strongly shocked interface whose evolution is a scaled version of the unstable hydrogen-helium interface in core-collapse supernovae such as SN 1987A. The ultimate goal of this research is to develop an understanding of the effect of hydrodynamic instabilities and the resulting transition to turbulence on supernovae observables that remain as yet unexplained. In this paper, we summarize recent results from our computational study of unstable systems driven by high Mach number shock and blast waves. For planar multimode systems, compressibility effects preclude the emergence of a regime of self-similar instability growth independent of the initial conditions (IC's) by allowing for memory of the initial conditions to be retained in the mix-width at all times. With higher-dimensional blast waves, divergence restores the properties necessary for establishment of the self-similar state, but achieving it requires very high initial characteristic mode number and high Mach number for the incident blast wave. Initial conditions predicted by some recent stellar calculations are incompatible with self-similarity.
Generation of seiches by cold fronts over the southern North Sea
de Jong, M. P. C.; Holthuijsen, L. H.; Battjes, J. A.
2003-04-01
Seiches affecting the Port of Rotterdam are generated in the Southern North Sea. Their generation is investigated with observations and numerical simulations. A wavelet analysis of the observations, both at sea and in the harbor, shows that low-frequency energy (0.1-2.0 mHz) does indeed occur at sea prior to each seiche event in Rotterdam. An analysis of 6 years of weather charts indicates that all 51 seiche events in this period (with amplitude exceeding 0.25 m) coincided with the passage of a low-pressure weather system. Some of these low-pressure systems included a sharp cold front (classical or ana), whereas others included a more diffuse cold front (split or kata). Numerical simulations with a hydrodynamic model driven by meteorological observations reproduced the seiches for situations with the sharp cold fronts correctly. The seiches that were simulated for situations with the gradual cold fronts do not agree with the observations, which is ascribed to the inadequate atmospheric forcing of the hydrodynamical model.
Summary Report of Working Group 4: Electron Beam Driven Concepts
Hogan, Mark J
2003-04-07
Although the title ''Electron Beam Driven Concepts'' can in principle cover a broad range of advanced accelerator schemes, in the context of this workshop and the various other working groups, working group 4 discussions centered primarily around the many active investigations of the electron or positron beam driven plasma wakefield accelerator. The past year has seen advances along three main fronts: experiment, simulation and theory. This paper will give a brief summary of the various talks presented to the group, summarize group discussions and conclude with a few comments on future directions.
Structure on Interplanetary Shock Fronts: Type II Radio Burst Source Regions
Pulupa, M
2007-01-01
We present \\emph{in situ} observations of the source regions of interplanetary (IP) type II radio bursts, using data from the Wind spacecraft during the period 1996-2002. We show the results of this survey as well as in-depth analysis of several individual events. Each event analyzed in detail is associated with an interplanetary coronal mass ejection (ICME) and an IP shock driven by the ICME. Immediately prior to the arrival of each shock, electron beams along the interplanetary magnetic field (IMF) and associated Langmuir waves are detected, implying magnetic connection to a quasiperpendicular shock front acceleration site. These observations are analogous to those made in the terrestrial foreshock region, indicating that a similar foreshock region exists on IP shock fronts. The analogy suggests that the electron acceleration process is a fast Fermi process, and this suggestion is borne out by loss cone features in the electron distribution functions. The presence of a foreshock region requires nonplanar st...
Interaction Dynamics of Singular Wave Fronts
Holm, Darryl D
2013-01-01
Some of the most impressive singular wave fronts seen in Nature are the transbasin oceanic internal waves, which may be observed from the Space Shuttle as they propagate and interact with each other, for example, in the South China Sea. The characteristic feature of these strongly nonlinear wavefronts is that they reconnect when two of them collide transversely. We derive the EPDiff equation, and use it to model this phenomenon as elastic collisions between singular wave fronts (solitons) whose momentum is distributed along curves moving in the plane. Numerical methods for EPDiff based on compatible differencing algorithms (CDAs) are used for simulating these collisions among curves. The numerical results show the same nonlinear behavior of wavefront reconnections as that observed for internal waves in the South China Sea. We generalize the singular solutions of EPDiff for other applications, in computational anatomy and in imaging science, where the singular wavefronts are evolving image outlines, whose mome...
Crack front propagation by kink formation
Roesch, Frohmut; Trebin, Hans-Rainer [Universitaet Stuttgart, Institut fuer Theoretische und Angewandte Physik, 70550 Stuttgart (Germany)
2010-07-01
In a brittle material a travelling crack generates an upper and a lower fracture surface, which meet at a one-dimensional crack front. From a macroscopic point of view there is no reason why this curve should deviate from a straight line, contrary to the atomistic point of view, where a crack propagates by successive rupture of cohesive bonds. We investigate fracture of the C15 NbCr{sub 2} Friauf-laves phase on an atomic level by means of molecular dynamics simulations. The numerical experiments highlight that crack fronts in general do not form a straight line and propagate by kink-pair formation at low loads (EPL 87 (2009) 66004). This mechanism should be relevant for crack propagation in any ordered brittle solid.
Effect of Microscopic Noise on Front Propagation
Brunet, Éric; Derrida, Bernard
2001-04-01
We study the effect of the noise due to microscopic fluctuations on the position of a one dimensional front propagating from a stable to an unstable region in the "linearly marginal stability case." By simulating a very simple system for which the effective number N of particles can be as large as N=10150, we measure the N dependence of the diffusion constant DN of the front and the shift of its velocity vN. Our results indicate that DN˜(log N)-3. They also confirm our recent claim that the shift of velocity scales like vmin-vN≃K(log N)-2 and indicate that the numerical value of K is very close to the analytical expression Kapprox obtained in our previous work using a simple cut-off approximation.
Multiclass gene selection using Pareto-fronts.
Rajapakse, Jagath C; Mundra, Piyushkumar A
2013-01-01
Filter methods are often used for selection of genes in multiclass sample classification by using microarray data. Such techniques usually tend to bias toward a few classes that are easily distinguishable from other classes due to imbalances of strong features and sample sizes of different classes. It could therefore lead to selection of redundant genes while missing the relevant genes, leading to poor classification of tissue samples. In this manuscript, we propose to decompose multiclass ranking statistics into class-specific statistics and then use Pareto-front analysis for selection of genes. This alleviates the bias induced by class intrinsic characteristics of dominating classes. The use of Pareto-front analysis is demonstrated on two filter criteria commonly used for gene selection: F-score and KW-score. A significant improvement in classification performance and reduction in redundancy among top-ranked genes were achieved in experiments with both synthetic and real-benchmark data sets.
Front roughening of flames in discrete media
Lam, Fredric; Mi, XiaoCheng; Higgins, Andrew J.
2017-07-01
The morphology of flame fronts propagating in reactive systems composed of randomly positioned, pointlike sources is studied. The solution of the temperature field and the initiation of new sources is implemented using the superposition of the Green's function for the diffusion equation, eliminating the need to use finite-difference approximations. The heat released from triggered sources diffuses outward from each source, activating new sources and enabling a mechanism of flame propagation. Systems of 40 000 sources in a 200 ×200 two-dimensional domain were tracked using computer simulations, and statistical ensembles of 120 realizations of each system were averaged to determine the statistical properties of the flame fronts. The reactive system of sources is parameterized by two nondimensional values: the heat release time (normalized by interparticle diffusion time) and the ignition temperature (normalized by adiabatic flame temperature). These two parameters were systematically varied for different simulations to investigate their influence on front propagation. For sufficiently fast heat release and low ignition temperature, the front roughness [defined as the root mean square deviation of the ignition temperature contour from the average flame position] grew following a power-law dependence that was in excellent agreement with the Kardar-Parisi-Zhang (KPZ) universality class (β =1 /3 ). As the reaction time was increased, lower values of the roughening exponent were observed, and at a sufficiently great value of reaction time, reversion to a steady, constant-width thermal flame was observed that matched the solution from classical combustion theory. Deviation away from KPZ scaling was also observed as the ignition temperature was increased. The features of this system that permit it to exhibit both KPZ and non-KPZ scaling are discussed.
The COral-REef Front (COREF Project
John A. and Katherine G. Jackson
2007-09-01
Full Text Available The First International Workshop on the COral-REef Front (COREF project was held on 14−19 January 2007 in Okinawa-jima, southwestern Japan to discuss objectives, required laboratory analyses and techniques, potential drilling sites, and scientific proposals for the Integrated Ocean Drilling Program (IODP and the International Continental Scientific Drilling Program (ICDP. This article briefly introduces the project and reports the outcome of the First International Workshop on the COREF Project.
Idiosyncrasies of the Front-back Organization
小橋, 勉; 許斐, ナタリー
2015-01-01
"As a new kind of organization, the front-back (F/B) organization has been analyzed in many researches. Referring to them, we identify the idiosyncrasies of the F/B organization theoretically. In doing so, we will make a comparison among multi-divisional organization, F/B organization, and matrix organization. Next, based on the development model of global organization, we point out its idiosyncrasies. "
Prototype ALICE front-end card
Maximilien Brice
2004-01-01
This circuit board is a prototype 48-channel front end digitizer card for the ALICE time projection chamber (TPC), which takes electrical signals from the wire sensors in the TPC and shapes the data before converting the analogue signal to digital data. A total of 4356 cards will be required to process the data from the ALICE TPC, the largest of this type of detector in the world.
Observations of phytoplankton spring bloom onset triggered by a density front in NW Mediterranean
A. Olita
2013-09-01
Full Text Available Phytoplankton bloom in NW Mediterranan sea is a seasonal event that mainly occurrs in a limited area (Gulf of Lyon and Provençal basin where this phenomenon is promoted by a cyclonic circulation, strong wind-driven mixing and subsequent spring restratification. At the southern boundary of this area a density front (North Balearic Front separating denser waters from the lighter Modified Atlantic Waters reservoir at south is suspected to trigger weaker and earlier (late winter blooms by (a enhanced pumping of nutrients into the euphotic layer and (b promoting an early restratification of the water column (by frontal instabilities. A multisensor glider round trip, equipped with CTD and fluorimeter, crossing the frontal area in February–March 2013, allowed to observe the bloom triggering after the decrease of intense wind-driven turbulent convection and mixing. Satellite imagery supports and confirms in-situ observations. It was shown that frontal activity has a relevant role in the promotion and acceleration of the dynamical restratification, with a consequent biological response in terms of primary production. Restratification is necessary preconditioning factor for bloom triggering in frontal area, net of other involved mechanism promoting the bloom as the enhanced biological pump. So, like for high-latitude fronts (Taylor and Ferrari, 2011a, also for this mid-latitude oligotrophic region front seems to promote new production by dynamically enahnced restratification inhibiting mixing. Finally, we argued that Sverdrup's Critical Depth criterion seems to apply in the northern well-mixed area, where the zeroing of heat fluxes (and related turbulent convection does not correspond to a prompt onset of the bloom (which appeared 1 month later.
Ice-ocean interaction and calving front morphology at two west Greenland tidewater outlet glaciers
Chauché, N.; Hubbard, A.; Gascard, J.-C.; Box, J. E.; Bates, R.; Koppes, M.; Sole, A.; Christoffersen, P.; Patton, H.
2014-08-01
Warm, subtropical-originating Atlantic water (AW) has been identified as a primary driver of mass loss across the marine sectors of the Greenland Ice Sheet (GrIS), yet the specific processes by which this water mass interacts with and erodes the calving front of tidewater glaciers is frequently modelled and much speculated upon but remains largely unobserved. We present a suite of fjord salinity, temperature, turbidity versus depth casts along with glacial runoff estimation from Rink and Store glaciers, two major marine outlets draining the western sector of the GrIS during 2009 and 2010. We characterise the main water bodies present and interpret their interaction with their respective calving fronts. We identify two distinct processes of ice-ocean interaction which have distinct spatial and temporal footprints: (1) homogenous free convective melting which occurs across the calving front where AW is in direct contact with the ice mass, and (2) localised upwelling-driven melt by turbulent subglacial runoff mixing with fjord water which occurs at distinct injection points across the calving front. Throughout the study, AW at 2.8 ± 0.2 °C was consistently observed in contact with both glaciers below 450 m depth, yielding homogenous, free convective submarine melting up to ~200 m depth. Above this bottom layer, multiple interactions are identified, primarily controlled by the rate of subglacial fresh-water discharge which results in localised and discrete upwelling plumes. In the record melt year of 2010, the Store Glacier calving face was dominated by these runoff-driven plumes which led to a highly crenulated frontal geometry characterised by large embayments at the subglacial portals separated by headlands which are dominated by calving. Rink Glacier, which is significantly deeper than Store has a larger proportion of its submerged calving face exposed to AW, which results in a uniform, relatively flat overall frontal geometry.
Phenomenological Theory of the Photoevaporation Front Instability
Ryutov, D D; Kane, J O; Mizuta, A; Pound, M W; Remington, B A
2006-04-10
The dynamics of photoevaporated molecular clouds is determined by the ablative pressure acting on the ionization front. An important step in the understanding of the ensuing motion is to develop the linear stability theory for the initially flat front. Despite the simplifications introduced by the linearization, the problem remains quite complex and still draws a lot of attention. The complexity is related to the large number of effects that have to be included in the analysis: acceleration of the front, possible temporal variation of the intensity of the ionizing radiation, the tilt of the radiation flux with respect to the normal to the surface, and partial absorption of the incident radiation in the ablated material. In this paper, we describe a model where all these effects can be taken into account simultaneously, and a relatively simple and universal dispersion relation can be obtained. The proposed phenomenological model may prove to be a helpful tool in assessing the feasibility of the laboratory experiments directed towards scaled modeling of astrophysical phenomena.
Lightweight design of automotive front crossbeam assembly
Yao Zaiqi; Liu Qiang; Ma Fangwu; Zhao Fuquan; Liu Zongwei; Wang Guan; Wan Yinhui; Li Luoxing
2012-01-01
This paper reviews the development course of the front crossbeam assembly for a self-owned brand vehicle model based on lightweight and passive safety performance. Combining with an A00 model variant, the paper details the design of extruded aluminum-alloy front crossbeam assembly from the perspectives of optimal design, performance verifi- cation, lightweight effect and cost control. The following results in the technical and engineering applications have been achieved. The weight of the developed aluminum-alloy crossbeam can be reduced by 51%. The simulated analysis of the collision rigid wall, the 40 % offset hammering as well as the static crush test of energy-absorbing box show that af- ter reasonable materials matching and size optimization of the crossbeam and the energy-absorbing boxes, the level of crash safety can be improved. The price of aluminum-alloy front crossbeam can be lowered by using the extruding die in- stead of the stamping die to reduce the die cost-sharing.
2016-06-05
intimately related to fast reconnection. 8. Bellan et al. (2015) provided an overview of the experimental activities by the Bellan plasma group at...wave. Physics of Plasmas, 20(4). 042117. Bellan, P. M. 2014. Fast , purely growing collisionless reconnection as an eigen- function problem related to...induced by kink-driven Rayleigh-Taylor instability. Physics of Plasmas, 23. 032122. Chaplin, Vernon H., & Bellan, Paul M. 2013. Fast Ignitron Trigger
Multiple front propagation in a potential non-gradient system
Miguel, M S; Amengual, A; Hernández-García, E
1995-01-01
A classification of dynamical systems in terms of their variational properties is reviewed. Within this classification, front propagation is discussed in a non-gradient relaxational potential flow. The model is motivated by transient pattern phenomena in nematics. A front propagating into an unstable homogenous state leaves behind an unstable periodic pattern, which decays via a second front and a second periodic state. An interface between unstable periodic states is shown to be a source of propagating fronts in opposite directions.
Sediment Transport at Density Fronts in Shallow Water
2012-09-30
in the Hudson occurred at multiple locations along the salinity gradient rather than a single interface between salty and fresh water . The fronts in...1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Sediment Transport at Density Fronts in Shallow Water ...suspended sediment concentration at density fronts in shallow water (< 1 m), - characterize flow and suspended sediment at a density front through the
Fronts of Stress Wave in Anisotropic Piezoelectric Media
刘颖; 刘凯欣; 高凌天
2004-01-01
The characteristic of wave fronts in anisotropic piezoelectric media is analysed by adopting the generalized characteristic theory. Analytical expressions for wave velocities and wave fronts are formulated. Apart from the ordinary characteristics, a new phenomenon, energy velocity funnel, is formed on the wave fronts of quasitransverse waves in anisotropic piezoelectric materials. A three-dimensional representation of wave fronts in anisotropic piezoelectric materials is given for a better understanding of the new phenomena.
SR front ends of VEPP-4M storage ring
Fedotov, M G; Kuz'minykh, V S; Mironenko, L A; Mishnev, S I; Panchenko, V E; Protopopov, I Ya; Rachkova, V V; Rukhlyada, L P; Selivanov, A N
2001-01-01
The VEPP-4M storage ring system of SR front ends is described. SR is released by means of 14 front ends. Eleven of them are intended for beamlines of experimental stations. One front end is technical. For the permanent stabilization of an orbit of a beam with respect to a coordinate and angle in the vertical direction, two monitoring front ends are used. They take out SR from emission regions, which are at a large distance from one another.
Unstable fronts and motile structures formed by microrollers
Driscoll, Michelle; Delmotte, Blaise; Youssef, Mena; Sacanna, Stefano; Donev, Aleksandar; Chaikin, Paul
2017-04-01
Condensation of objects into stable clusters occurs naturally in equilibrium and driven systems. It is commonly held that potential interactions, depletion forces, or sensing are the only mechanisms which can create long-lived compact structures. Here we show that persistent motile structures can form spontaneously from hydrodynamic interactions alone, with no sensing or potential interactions. We study this structure formation in a system of colloidal rollers suspended and translating above a floor, using both experiments and large-scale three-dimensional simulations. In this system, clusters originate from a previously unreported fingering instability, where fingers pinch off from an unstable front to form autonomous `critters’, whose size is selected by the height of the particles above the floor. These critters are a stable state of the system, move much faster than individual particles, and quickly respond to a changing drive. With speed and direction set by a rotating magnetic field, these active structures offer interesting possibilities for guided transport, flow generation, and mixing at the microscale.
Topology optimization of front metallization patterns for solar cells
Gupta, D.K.; Langelaar, M.; Barink, M.; Keulen, F. van
2015-01-01
This paper presents the application of topology optimization (TO) for designing the front electrode patterns for solar cells. Improving the front electrode design is one of the approaches to improve the performance of the solar cells. It serves to produce the voltage distribution for the front surfa
Buddelmeijer, Hugo
2011-01-01
The request driven way of deriving data in Astro-WISE is extended to a query driven way of visualization. This allows scientists to focus on the science they want to perform, because all administration of their data is automated. This can be done over an abstraction layer that enhances control and flexibility for the scientist.
A Study of an Intense Density Front in the Eastern Alboran Sea: The Almeria-Oran Front
1988-10-01
SeWr ClnificatI 12 ) A Study or an iTntense Density Front in the Eastern Alboran Sea: The Almeria -Oran Front 12. PERSONAL AUTHOR(S) J. Tintore...is present between Almeria , Spain, and Oran, Algeria, which is part of the easternuost segment of the Eastern Alboran Gyre. Based on these satellite...studies, the first in situ investigation of the - front, called here the Almeria -Oran Front, was conducted () in March 1986 as part of the winter
Growth and gravitational collapse of a mountain front of the Eastern Cordillera of Colombia
Kammer, Andreas; Montana, Jorge; Piraquive, Alejandro
2016-04-01
The Eastern Cordillera of Colombia is bracketed between the moderately east-dipping flank of the Central Cordillera on its western and the gently bent Guayana shield on its eastern side. It evolved as a response to a considerable displacement transfer from the Nazca to the Southamerican plate since the Oligocene break-up of the Farallon plate. One of its distinctive traits refers to its significant shortening by penetrative strain at lower and folding at higher structural levels, approximating a wholesale pure-shear in analogy to a vice model or a crustal welt sandwiched between rigid buttresses. This contrasting behavior may be explained by the spatial coincidence between Neogene mountain belt and a forebulge that shaped the foreland trough during a Cretaceous subduction cycle and was very effective in localizing a weakening of the backarc region comprised between two basin margin faults. In this paper we examine a two-phase evolution of the Eastern mountain front. Up to the late Miocene deformation was restrained by the inherited eastern basin margin fault and as the cordilleran crust extruded, a deformation front with an amplitude similar the present structural relief of up to 10.000 m may have built up. In the Pliocene convergence changed from a roughly strike-perpendicular to an oblique E-W direction and caused N-S trending faults to branch off from the deformation front. This shortening was partly driven by a gravitational collapse of the Miocene deformation front, that became fragmented by normal faults and extruded E on newly formed Pliocene thrust faults. Normal faults display displacements of up to 3000 m and channelized hydrothermal fluids, leading to the formation of widely distributed fault breccias and giving rise to a prolific Emerald mineralization. In terms of wedge dynamics, the Pliocene breaching of the early formed deformation front helped to establish a critical taper.
Observations and numerical modelling of a non-buoyant front in the Tay Estuary, Scotland
Neill, S. P.; Copeland, G. J. M.; Ferrier, G.; Folkard, A. M.
2004-01-01
Acoustic Doppler current profiler (ADCP) and density data have been collected for a section of front which consistently occurs on the flood tide along a break in bathymetry in the Tay Estuary. Lateral velocity shear in a vertical profile through the front was measured to be 0.52 s -1. An estuarine cross-sectional numerical model was developed with buoyancy-driven flow. Results from the numerical model showed that shears of such magnitude cannot be produced by buoyancy alone. Instead, a hypothesis was devised for the generation of the bathymetry-aligned front, and tested using the numerical model. The flooding current flows over sandbanks at the southern bank of the estuary and is then directed over (rather than along) the bathymetry break due to a sudden topographic restriction at the Tayport Narrows. Due to tidal phase effects, this overbank flow has a lower density than the ambient main channel water, hence behaving as a buoyant plume. The plume entrains higher density bottom water and a recirculation cell is set up in the lee of the bathymetry break. A surface convergent front occurs because a corresponding towards-bank flow (confirmed by field data) occurs in the centre of the channel. The numerical model was applied to this configuration using suitable initial and boundary conditions based on field observations. Lateral velocity profiles and the strength of shear show good agreement with the field data. It is suggested that the presence of a density gradient is required to generate the front but is not the main driving force.
Kanarachos, S.A.; Alirezaei, M.; Jansen, S.T.H.; Maurice, J.P.
2014-01-01
In this paper the systematic development of an integrated braking controller for a vehicle driven by an electric motor on the front axle is presented. The objective is to engage the electric motor only during braking, up to the point at which the vehicle reaches its manoeuvrability and stability lim
STRUCTURE OF WAVE FRONT AND ORGANIZATION CENTER IN EXCITABLE MEDIA
刘深泉
2004-01-01
With help of establishing the moving coordinate on the wave front surface and the perturbation analysis in the boundary layer, the structures of wave front and organization center in excitable media were studied. The eikonal equation of wave front surface and general equation of organization center were obtained. These eikonal equations reveal the wave front surfaces have structures of twisted scroll wave and Mobius band, the organization centers have structures of knotted and linked ring. These theoretical results not only explain the wave patterns of BZ ( Belousov-Zhabotinskii ) chemical reaction but also give several possibility structures of wave front surface and organization center in general excitable media.
Novel Perspectives from Light-Front QCD, Super-Conformal Algebra, and Light-Front Holography
Brodsky, Stanley J. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2015-12-01
Light-Front Quantization – Dirac’s “Front Form” – provides a physical, frame-independent formalism for hadron dynamics and structure. Observables such as structure functions, transverse momentum distributions, and distribution amplitudes are defined from the hadronic LFWFs. One obtains new insights into the hadronic mass scale, the hadronic spectrum, and the functional form of the QCD running coupling in the nonperturbative domain using light-front holography. In addition, superconformal algebra leads to remarkable supersymmetric relations between mesons and baryons. I also discuss evidence that the antishadowing of nuclear structure functions is nonuniversal; i.e., flavor dependent, and why shadowing and antishadowing phenomena may be incompatible with the momentum and other sum rules for the nuclear parton distribution functions.
Front-like entire solutions for equations with convection
Crooks, E. C. M.; Tsai, Je-Chiang
We construct families of front-like entire solutions for problems with convection, both for bistable and monostable reaction-diffusion-convection equations, and, via vanishing-viscosity arguments, for bistable and monostable balance laws. The unified approach employed is inspired by ideas of Chen and Guo and based on a robust method using front-dependent sub and supersolutions. Unlike convectionless problems, the equations studied here lack symmetry between increasing and decreasing travelling waves, which affects the choice of sub and supersolutions used. Our entire solutions include both those that behave like two fronts coming together and annihilating as time increases, and, for bistable equations, those that behave like two fronts merging to propagate like a single front. We also characterise the long-time behaviour of each family of entire solutions, which in the case of solutions constructed from a monostable front merging with a bistable front answers a question that was open even for reaction-diffusion equations without convection.
Speed and structure of turbulent fronts in pipe flow
Song, Baofang; Hof, Björn; Avila, Marc
2016-01-01
The dynamics of laminar-turbulent fronts in pipe flow is investigated for Reynolds numbers between Re=1900 and Re=5500 using extensive direct numerical simulations. In this range the flow undergoes a continuous transition from localised puffs to weakly expanding and ultimately to strongly expanding turbulent slugs (Barkley et al. 2015). We here investigate the physical distinction between these two types of slug by analysing time-resolved statistics of their downstream fronts in the frame moving at the bulk turbulent advection speed. While weak fronts travel slower than the bulk turbulent advection speed, implying local relaminarisation, strong fronts travel faster and so feed on the laminar flow ahead. At Re$\\approx$2900 the downstream front speed becomes faster than the advection speed, marking the onset of strong fronts. We argue that large temporal fluctuations of production and dissipation at the laminar-turbulent interface drive the dynamical switches between the two types of front observed up to Re$\\si...
CME front and severe space weather
Balan, N.; Skoug, R.; Tulasi Ram, S.; Rajesh, P. K.; Shiokawa, K.; Otsuka, Y.; Batista, I. S.; Ebihara, Y.; Nakamura, T.
2014-12-01
Thanks to the work of a number of scientists who made it known that severe space weather can cause extensive social and economic disruptions in the modern high-technology society. It is therefore important to understand what determines the severity of space weather and whether it can be predicted. We present results obtained from the analysis of coronal mass ejections (CMEs), solar energetic particle (SEP) events, interplanetary magnetic field (IMF), CME-magnetosphere coupling, and geomagnetic storms associated with the major space weather events since 1998 by combining data from the ACE and GOES satellites with geomagnetic parameters and the Carrington event of 1859, the Quebec event of 1989, and an event in 1958. The results seem to indicate that (1) it is the impulsive energy mainly due to the impulsive velocity and orientation of IMF Bz at the leading edge of the CMEs (or CME front) that determine the severity of space weather. (2) CMEs having high impulsive velocity (sudden nonfluctuating increase by over 275 km s-1 over the background) caused severe space weather (SvSW) in the heliosphere (failure of the solar wind ion mode of Solar Wind Electron Proton Alpha Monitor in ACE) probably by suddenly accelerating the high-energy particles in the SEPs ahead directly or through the shocks. (3) The impact of such CMEs which also show the IMF Bz southward from the leading edge caused SvSW at the Earth including extreme geomagnetic storms of mean DstMP power outages happened during some of these SvSW events. (4) The higher the impulsive velocity, the more severe the space weather, like faster weather fronts and tsunami fronts causing more severe damage through impulsive action. (5) The CMEs having IMF Bz northward at the leading edge do not seem to cause SvSW on Earth, although, later when the IMF Bz turns southward, they can lead to super geomagnetic storms of intensity (Dstmin) less than even -400 nT.
Direct drive ablation front stability: numerical predictions against flame front model
Masse, L. [Phd Student at IRPHE St Jerome, 13 - Marseille (France)]|[CEA/DAM-Ile de France, 91 - Bruyeres Le Chatel (France); Hallo, L.; Tallot, C. [CEA/DAM-Ile de France, 91 - Bruyeres Le Chatel (France)
2000-07-01
We study the linear stability of flows resulting from constant heating of planar targets by a laser. In the coordinate system of the ablation front there is a flow from the cold to hot region, which is situated in a gravity field oriented from hot to cold region. Similar types of flow can be observed in combustion systems, which involve propagation of flame fronts. A spectral model which studies linear perturbation is directly taken from the combustion community. Here we present the results for state as well as perturbed flows. Growth rate determined from the models are compared to each other, and preliminary numerical results from FC12 simulations are shown. (authors)
Light-Front Perturbation Without Spurious Singularities
Przeszowski, Jerzy A.; Dzimida-Chmielewska, Elżbieta; Żochowski, Jan
2016-07-01
A new form of the light front Feynman propagators is proposed. It contains no energy denominators. Instead the dependence on the longitudinal subinterval x^2_L = 2 x+ x- is explicit and a new formalism for doing the perturbative calculations is invented. These novel propagators are implemented for the one-loop effective potential and various 1-loop 2-point functions for a massive scalar field. The consistency with results for the standard covariant Feynman diagrams is obtained and no spurious singularities are encountered at all. Some remarks on the calculations with fermion and gauge fields in QED and QCD are added.
Refraction and reflection of diffusion fronts.
Remhof, A; Wijngaarden, R J; Griessen, R
2003-04-11
Diffusion waves form the basis of several measurement technologies in materials science as well as in biological systems. They are, however, so heavily damped that their observation is a real challenge to the experimentalist. We show that accurate information about the refraction-like and reflection-like behavior of diffusion waves can be obtained by studying diffusion fronts. For this we use hydrogen in a metal as a model system and visualize its 2D migration with an optical indicator. The similarities between classical optics and diffusion, in particular, the applicability of Snell's law to diffusive systems are discussed. Our measurements are in good agreement with numerical simulations.
FLUID EXCHANGE ACROSS THE EQUATORIAL FRONT
无
2001-01-01
In this paper, the cusp-shaped wave pattern (Legeckis wave) along the Equatorial Front (EF) is modeled by a meandering jet, and the motion of fluid parcels in a two-dimensional kinematic model of the meandering jet along EF is studied using Melnikov's method. Results indicated that the velocity field of the cusp-shaped wave pattern can indeed be modeled by a meandering jet; that the EF will act as a barrier to fluid exchange if there is no variability, but that it is just the variability that moves the buoy across the EF.
FLUID EXCHANGE ACROSS THE EQUATORIAL FRONT
姜传丽; 吕建; 吴德星
2001-01-01
In this paper, the cusp-shaped wave pattern (Legeckis wave) along the Equatorial Front (EF) is modeled by a meandering jet, and the motion of fluid parcels in a two-dimensional kine-matic model of the meandering jet along EF is studied using Melnikov's method. Results indicated that the velocity field of the cusp-shaped wave pattern can indeed be modeled by a meandering jet; that the EF will act as a barrier to fluid exchange if there is no variability, but that it is just the variability that moves the buoy across the EF.
Phase fronts and synchronization patterns in forced oscillatory systems
Ehud Meron
2000-01-01
Full Text Available This is a review of recent studies of extended oscillatory systems that are subjected to periodic temporal forcing. The periodic forcing breaks the continuous time translation symmetry and leaves a discrete set of stable uniform phase states. The multiplicity of phase states allows for front structures that shift the oscillation phase by π/n where n=1,2,…, hereafter π/n-fronts. The main concern here is with front instabilities and their implications on pattern formation. Most theoretical studies have focused on the 2:1 resonance where the system oscillates at half the driving frequency. All front solutions in this case are π-fronts. At high forcing strengths only stationary fronts exist. Upon decreasing the forcing strength the stationary fronts lose stability to pairs of counter-propagating fronts. The coexistence of counter-propagating fronts allows for traveling domains and spiral waves. In the 4:1 resonance stationary π-fronts coexist with π/2-fronts. At high forcing strengths the stationary π-fronts are stable and standing two-phase waves, consisting of successive oscillatory domains whose phases differ by π,, prevail. Upon decreasing the forcing strength the stationary π-fronts lose stability and decompose into pairs of propagating π/2-fronts. The instability designates a transition from standing two-phase waves to traveling four-phase waves. Analogous decomposition instabilities have been found numerically in higher 2n:1 resonances. The available theory is used to account for a few experimental observations made on the photosensitive Belousov–Zhabotinsky reaction subjected to periodic illumination. Observations not accounted for by the theory are pointed out.
Scrambled and Unscrambled Turbulence
Ramaprabhu, P; Lawrie, A G W
2013-01-01
The linked fluid dynamics videos depict Rayleigh-Taylor turbulence when driven by a complex acceleration profile involving two stages of acceleration interspersed with a stage of stabilizing deceleration. Rayleigh-Taylor (RT) instability occurs at the interface separating two fluids of different densities, when the lighter fluid is accelerated in to the heavier fluid. The turbulent mixing arising from the development of the miscible RT instability is of key importance in the design of Inertial Confinement Fusion capsules, and to the understanding of astrophysical events, such as Type Ia supernovae. By driving this flow with an accel-decel-accel profile, we have investigated how structures in RT turbulence are affected by a sudden change in the direction of the acceleration first from destabilizing acceleration to deceleration, and followed by a restoration of the unstable acceleration. By studying turbulence under such highly non-equilibrium conditions, we hope to develop an understanding of the response and ...
RANS modeling of RTI and HVDT with BHR3
Trettel, Ben [Los Alamos National Laboratory
2012-08-15
The BHR3 turbulence model was improved to include two different scales as suggested by Livescu et al. [Liv+09, {section}4.4.6]: one for turbulent transport and the other for turbulent dissipation. Additionally, destruction terms modeled analogously to production terms were added to the turbulent mass-weighted velocity equation. New model coefficients were developed for this model. The first change was to use C{sub 2} = 1.77 for the isotropic turbulence decay coefficient rather than the k-e model's 1.92, which is outside of the experimentally measured values [ML90; KF09]. The new model coefficients were developed to accurately model a wide range of experimental and numerical results: constant and variable density Kelvin-Helmholtz instabilities, Rayleigh-Taylor instabilities, and homogeneous variable density turbulence (HVDT) [LR07]. My work focused on the buoyancy-driven flows: Rayleigh-Taylor instabilities and HVDT.
Gibson, A. F.
1980-01-01
Discusses the present status and future prospects of laser-driven fusion. Current research (which is classified under three main headings: laser-matter interaction processes, compression, and laser development) is also presented. (HM)
Biomechanics of front and back squat exercises
Braidot, A. A.; Brusa, M. H.; Lestussi, F. E.; Parera, G. P.
2007-11-01
Squat constitutes one of the most popular exercises to strengthen the muscles of the lower limbs. It is considered one of the most widely spread exercises for muscle sport training and is part of the competition movements comprised within olympic weight-lifting. In physical rehabilitation, squats are used for muscular recovery after different injuries of the lower limbs, especially the knee. In previous anterior cruciate ligament injuries, the mini-squats are generally used, in a knee flexion motion range from 0° to 50° because in this range the shear forces, the tibiofemoral and patellofemoral compression forces decrease related to greater flexion angles. The aim of this work is to make a comparative bidimensional study of the kinematic and dynamic variables of the excecution of the parallel squat exercise with the front and back bar. It is observed in the knee a better development of energy with the front bar, allowing a better muscular exercise with the same load. The mean power absorbed by the hip with the back bar is considerably greater, associated to the speed of the gesture.
AFEII Analog Front End Board Design Specifications
Rubinov, Paul; /Fermilab
2005-04-01
This document describes the design of the 2nd iteration of the Analog Front End Board (AFEII), which has the function of receiving charge signals from the Central Fiber Tracker (CFT) and providing digital hit pattern and charge amplitude information from those charge signals. This second iteration is intended to address limitations of the current AFE (referred to as AFEI in this document). These limitations become increasingly deleterious to the performance of the Central Fiber Tracker as instantaneous luminosity increases. The limitations are inherent in the design of the key front end chips on the AFEI board (the SVXIIe and the SIFT) and the architecture of the board itself. The key limitations of the AFEI are: (1) SVX saturation; (2) Discriminator to analog readout cross talk; (3) Tick to tick pedestal variation; and (4) Channel to channel pedestal variation. The new version of the AFE board, AFEII, addresses these limitations by use of a new chip, the TriP-t and by architectural changes, while retaining the well understood and desirable features of the AFEI board.
Internal waves and temperature fronts on slopes
S. A. Thorpe
Full Text Available Time series measurements from an array of temperature miniloggers in a line at constant depth along the sloping boundary of a lake are used to describe the `internal surf zone' where internal waves interact with the sloping boundary. More small positive temperature time derivatives are recorded than negative, but there are more large negative values than positive, giving the overall distribution of temperature time derivatives a small negative skewness. This is consistent with the internal wave dynamics; fronts form during the up-slope phase of the motion, bringing cold water up the slope, and the return flow may become unstable, leading to small advecting billows and weak warm fronts. The data are analysed to detect `events', periods in which the temperature derivatives exceed a set threshold. The speed and distance travelled by `events' are described. The motion along the slope may be a consequence of (a instabilities advected by the flow (b internal waves propagating along-slope or (c internal waves approaching the slope from oblique directions. The propagation of several of the observed 'events' can only be explained by (c, evidence that the internal surf zone has some, but possibly not all, the characteristics of the conventional 'surface wave' surf zone, with waves steepening as they approach the slope at oblique angles.
Key words. Oceanography: general (benthic boundary layers; limnology, Oceanography: physical (internal and inertial waves
Biomechanics of front and back squat exercises
Braidot, A A [Laboratorio de Biomecanica FI-UNER. Ruta 11 Km 10 Oro Verde Entre Rios (Argentina); Brusa, M H [Laboratorio de Biomecanica FI-UNER. Ruta 11 Km 10 Oro Verde Entre Rios (Argentina); Lestussi, F E [Laboratorio de Biomecanica FI-UNER. Ruta 11 Km 10 Oro Verde Entre Rios (Argentina); Parera, G P [Licenciatura en KinesiologIa y FisiatrIa Universidad Abierta Interamericana. Sede Regional Rosario (Argentina)
2007-11-15
Squat constitutes one of the most popular exercises to strengthen the muscles of the lower limbs. It is considered one of the most widely spread exercises for muscle sport training and is part of the competition movements comprised within olympic weight-lifting. In physical rehabilitation, squats are used for muscular recovery after different injuries of the lower limbs, especially the knee. In previous anterior cruciate ligament injuries, the mini-squats are generally used, in a knee flexion motion range from 0 deg. to 50 deg. because in this range the shear forces, the tibiofemoral and patellofemoral compression forces decrease related to greater flexion angles. The aim of this work is to make a comparative bidimensional study of the kinematic and dynamic variables of the excecution of the parallel squat exercise with the front and back bar. It is observed in the knee a better development of energy with the front bar, allowing a better muscular exercise with the same load. The mean power absorbed by the hip with the back bar is considerably greater, associated to the speed of the gesture.
Travelling fronts in stochastic Stokes’ drifts
Blanchet, Adrien
2008-10-01
By analytical methods we study the large time properties of the solution of a simple one-dimensional model of stochastic Stokes\\' drift. Semi-explicit formulae allow us to characterize the behaviour of the solutions and compute global quantities such as the asymptotic speed of the center of mass or the effective diffusion coefficient. Using an equivalent tilted ratchet model, we observe that the speed of the center of mass converges exponentially to its limiting value. A diffuse, oscillating front attached to the center of mass appears. The description of the front is given using an asymptotic expansion. The asymptotic solution attracts all solutions at an algebraic rate which is determined by the effective diffusion coefficient. The proof relies on an entropy estimate based on homogenized logarithmic Sobolev inequalities. In the travelling frame, the macroscopic profile obeys to an isotropic diffusion. Compared with the original diffusion, diffusion is enhanced or reduced, depending on the regime. At least in the limit cases, the rate of convergence to the effective profile is always decreased. All these considerations allow us to define a notion of efficiency for coherent transport, characterized by a dimensionless number, which is illustrated on two simple examples of travelling potentials with a sinusoidal shape in the first case, and a sawtooth shape in the second case. © 2008 Elsevier B.V. All rights reserved.
Franci Steinman
2002-01-01
Full Text Available Maritime construction in front of Izola restitutes an enriched former state. The island is positioned in a place where there are no legal regimes enforced by the state or local community. Legal regimes that determine the exploitation of water rights and limitations (management, exploitation, use can actually limit all. Therefore their synthesis has to be the starting point for analysing the harmony of present uses and for planning future uses of the sea and coastal area. For example the aquatorium of the shellfish mariculture positioned in the Strunjan Bay without adequate analysis of the prevailing conditions is causing conflicts of uses, unacceptable limiting of general use of the sea and prohibitive limitations in neighbouring areas. The analysis done for the island in front of Izola shows that there are no such consequences. Only uses in the public interest were proposed, since when assessing suitability first public and then common interests where considered, possible specific (e.g. entrepreneurial uses were permitted only if the afore mentioned weren’t obstructed. Thus integral management of the coastal area was enabled, with respect to functional ties between the land and sea.
Universal Millimeter-Wave Radar Front End
Perez, Raul M.
2010-01-01
A quasi-optical front end allows any arbitrary polarization to be transmitted by controlling the timing, amplitude, and phase of the two input ports. The front end consists of two independent channels horizontal and vertical. Each channel has two ports transmit and receive. The transmit signal is linearly polarized so as to pass through a periodic wire grid. It is then propagated through a ferrite Faraday rotator, which rotates the polarization state 45deg. The received signal is propagated through the Faraday rotator in the opposite direction, undergoing a further 45 of polarization rotation due to the non-reciprocal action of the ferrite under magnetic bias. The received signal is now polarized at 90deg relative to the transmit signal. This signal is now reflected from the wire grid and propagated to the receive port. The horizontal and vertical channels are propagated through, or reflected from, another wire grid. This design is an improvement on the state of the art in that any transmit signal polarization can be chosen in whatever sequence desired. Prior systems require switching of the transmit signal from the amplifier, either mechanically or by using high-power millimeter-wave switches. This design can have higher reliability, lower mass, and more flexibility than mechanical switching systems, as well as higher reliability and lower losses than systems using high-power millimeter-wave switches.
Unstable infiltration fronts in porous media on laboratory scale
Schuetz, Cindi; Neuweiler, Insa
2014-05-01
, while the inclusions act as a storage that is filled during the infiltration process. References: Chouke, R.L., van Meurs, P., and van der Poel, C., 1959. The instability of slow immiscible, viscous liquid-liquid displacements in permeable media, Trans. AIME. 216:188-194. Glass, R.J., Steenhuis, T.S., and Parlange J.-Y., 1989a. Mechanism for finger persistence in homogeneous, unsaturated, porous media: Theory and verification, Soil Sci. 148:60-70. Glass R.J., Parlange, J.-Y., and Steenhuis, T.S., 1991. Immiscible displacement in porous media: Stability analysis of three-dimensional, axisymmetric disturbances with application to gravity-driven wetting front instability, Water Resour. Res., 27, 1947-1956. Guarracino, L., 2007. Estimation of saturated hydraulic conductivity Ks from the van Genuchten shape parameter , Water Resour. Res., 43, W11502. Parlange, J.-Y. and Hill, D.E., 1976a. Theoretical analysis of wetting front instability in soils, Soil Sci. 122:236-239. Philip, J. 1975a. Stability analysis of infiltration, Soil Sci. Soc. Am. Proc. 39:1042-1049. Saffman, P.G. and Taylor, G., 1958. The penetration of a fluid into a porous medium or hele-shaw cell containing a more viscous liquid, Proc. R. Soc. London, 245:312-329. Wang Z., Feyen, J., Nielsen, D.R., and van Genuchten, M.T., 1997. Two-phase flow infiltration equations accounting for air entrapment effects, Water Resour. Res., 33:2759-2767. Wang, Z., Feyen, J., and Elrick, D.E., 1998c. Prediction of fingering in porous media, Water Resour. Res. 34(9):2183-2190. Wang Z., Wu, L., and Wu, Q.J., 2000. Water-entry value as an alternative indicator of soil water-repellency and wettability, Journal of Hydrology., 231-232, 76-83. White, I., Colombera, P.M., and Philip, J.R., 1976. Experimental studies of wetting front instability induced by sudden changes of pressure gradient, Soil Sci. Soc. Am. Proc., 40:824-829.
Bukh, Per Nikolaj
2009-01-01
Anmeldelse af Discovery Driven Growh : A breakthrough process to reduce risk and seize opportunity, af Rita G. McGrath & Ian C. MacMillan, Boston: Harvard Business Press. Udgivelsesdato: 14 august......Anmeldelse af Discovery Driven Growh : A breakthrough process to reduce risk and seize opportunity, af Rita G. McGrath & Ian C. MacMillan, Boston: Harvard Business Press. Udgivelsesdato: 14 august...
Front Office and Reception; An Approach to Front Office and Reception Training.
Hotel and Catering Industry Training Board, Wembley (England).
This manual is concerned with the tasks and training needs of front office personnel in hotels. After discussion of selection and qualifications of such personnel, the perfect receptionist is described in terms of personality, appearance, and deportment. Then follows a detailed listing of tasks--basic tasks, such as reception, bookkeeping, cash,…
Idea Screening in Engineering Design Using Employee-Driven Wisdom of the Crowds
Onarheim, Balder; Christensen, Bo Thomas
The paper investigates the question of screening ideas in the ‘fuzzy front end’ of engineering design, examining the validity of employee voting schemes and related biases. After an employee-driven innovation project at {Company Name removed for review}, 99 ideas were to be screened for further d...
Modeling the Controls on the Front Position of a Tidewater Glacier in Svalbard
Jaime Otero
2017-04-01
Full Text Available Calving is an important mass-loss process at ice sheet and marine-terminating glacier margins, but identifying and quantifying its principal driving mechanisms remains challenging. Hansbreen is a grounded tidewater glacier in southern Spitsbergen, Svalbard, with a rich history of field and remote sensing observations. The available data make this glacier suitable for evaluating mechanisms and controls on calving, some of which are considered in this paper. We use a full-Stokes thermomechanical 2D flow model (Elmer/Ice, paired with a crevasse-depth calving criterion, to estimate Hansbreen's front position at a weekly time resolution. The basal sliding coefficient is re-calibrated every 4 weeks by solving an inverse model. We investigate the possible role of backpressure at the front (a function of ice mélange concentration and the depth of water filling crevasses by examining the model's ability to reproduce the observed seasonal cycles of terminus advance and retreat. Our results suggest that the ice-mélange pressure plays an important role in the seasonal advance and retreat of the ice front, and that the crevasse-depth calving criterion, when driven by modeled surface meltwater, closely replicates observed variations in terminus position. These results suggest that tidewater glacier behavior is influenced by both oceanic and atmospheric processes, and that neither of them should be ignored.
Modelling the controls on the front position of a tidewater glacier in Svalbard
Otero, Jaime; Navarro, Francisco J.; Lapazaran, Javier J.; Welty, Ethan; Puczko, Darek; Finkelnburg, Roman
2017-04-01
Calving is an important mass-loss process at ice sheet and marine-terminating glacier margins, but identifying and quantifying its principal driving mechanisms remains challenging. Hansbreen is a grounded tidewater glacier in southern Spitsbergen, Svalbard, with a rich history of field and remote sensing observations. The available data make this glacier suitable for evaluating mechanisms and controls on calving, some of which are considered in this paper. We use a full-Stokes thermomechanical 2D flow model (Elmer/Ice), paired with a crevasse-depth calving criterion, to estimate Hansbreen’s front position at a weekly time resolution. The basal sliding coefficient is re-calibrated every four weeks by solving an inverse model. We investigate the possible role of backpressure at the front (a function of ice mélange concentration) and the depth of water filling crevasses by examining the model’s ability to reproduce the observed seasonal cycles of terminus advance and retreat. Our results suggest that the ice-mélange pressure plays an important role in the seasonal advance and retreat of the ice front, and that the crevasse-depth calving criterion, when driven by modelled surface meltwater, closely replicates observed variations in terminus position. These results suggest that tidewater glacier behavior is influenced by both oceanic and atmospheric processes, and that neither of them should be ignored.
Marangoni flows induced by A + B -> C reaction fronts with arbitrary diffusion coefficients
Tiani, Reda; Rongy, Laurence
2016-11-01
We consider horizontal aqueous solutions in contact with air where three reacting species A, B, and C can affect the surface tension of the solution, thereby driving Marangoni flows. When the two reactants A and B, that are initially separated, are brought into contact, a reaction front producing species C is formed and evolves in time due to diffusion, convection and reaction processes. The resulting dynamics is studied by numerically integrating the incompressible Navier-Stokes equations coupled to reaction-diffusion-convection equations for the three chemical species. For equal initial concentrations of reactants and equal diffusion coefficients, we have explained how chemically-driven Marangoni flows can lead to complex dynamics of the front propagation. Here we extend such results for arbitrary values of the diffusion coefficients and initial concentrations of reactants. We give the general classification of the surface tension profiles as a function of the Marangoni numbers quantifying the effect of each species on the surface tension, the ratio of initial concentrations of reactants and the ratios of diffusion coefficients. Such a classification allows us then to study the resulting structure of the convective rolls as well as the nonlinear dynamics of the reaction front. F.R.S.- FNRS, ARC.
Can we use ice calving on glacier fronts as a proxy for rock slope failures?
Abellan, Antonio; Penna, Ivanna; Daicz, Sergio; Carrea, Dario; Derron, Marc-Henri; Jaboyedoff, Michel; Riquelme, Adrian; Tomas, Roberto
2015-04-01
Ice failures on glacier terminus show very similar fingerprints to rock-slope failure (RSF) processes, nevertheless, the investigation of gravity-driven instabilities that shape rock cliffs and glacier's fronts are currently dissociated research topics. Since both materials (ice and rocks) have very different rheological properties, the development of a progressive failure on mountain cliffs occurs at a much slower rate than that observed on glacier fronts, which leads the latter a good proxy for investigating RSF. We utilized a terrestrial Laser Scanner (Ilris-LR system from Optech) for acquiring successive 3D point clouds of one of the most impressive calving glacier fronts, the Perito Moreno glacier located in the Southern Patagonian Ice Fields (Argentina). We scanned the glacier terminus during five days (from 10th to 14th of March 2014) with very high accuracy (0.7cm standard deviation of the error at 100m) and a high density of information (200 points per square meter). Each data series was acquired at a mean interval of 20 minutes. The maximum attainable range for the utilized wavelength of the Ilris-LR system (1064 nm) was around 500 meters over massive ice (showing no-significant loss of information), being this distance considerably reduced on crystalline or wet ice short after the occurrence of calving events. As for the data treatment, we have adapted our innovative algorithms originally developed for the investigation of both precursory deformation and rockfalls to study calving events. By comparing successive three-dimensional datasets, we have investigated not only the magnitude and frequency of several ice failures at the glacier's terminus (ranging from one to thousands of cubic meters), but also the characteristic geometrical features of each failure. In addition, we were able to quantify a growing strain rate on several areas of the glacier's terminus shortly after their final collapse. For instance, we investigated the spatial extent of the
The Origin and Kinematics of Cold Gas in Galactic Winds: Insight from Numerical Simulations
Fujita, Akimi; Mac Low, Mordecai-Mark; New, Kimberly C B; Weaver, Robert
2008-01-01
We study the origin of Na I absorbing gas in ultraluminous infrared galaxies motivated by the recent observations by Martin of extremely superthermal linewidths in this cool gas. We model the effects of repeated supernova explosions driving supershells in the central regions of molecular disks with M_d=10^{10} M_{\\odot}, using cylindrically symmetric gas dynamical simulations run with ZEUS-3D. The shocked swept-up shells quickly cool and fragment by Rayleigh-Taylor instability as they accelerate out of the dense, stratified disks. The numerical resolution of the cooling and compression at the shock fronts determines the peak shell density, and so the speed of Rayleigh-Taylor fragmentation. We identify cooled shells and shell fragments as Na I absorbing gas and study its kinematics along various sightlines across the grid. We find that simulations with a numerical resolution of \\le 0.2 pc produce multiple Rayleigh-Taylor fragmented shells in a given line of sight that appear to explain the observed kinematics....
Colorado Front Range Surface Ozone Analysis
McClure-Begley, A.; Petropavlovskikh, I. V.; Oltmans, S. J.; Kofler, J.; Petron, G.; Cothrel, H.
2014-12-01
The Colorado Front Range is a unique geographical region for air quality studies, including research of surface level ozone. Not only does surface ozone play a critical role in regulating the oxidation capacity of the atmosphere, but is a primary contributor to local smog and leads to public health complications and altered ecosystem functioning. The high frequency of sunny days, increasing population and pollution, and Mountain/Valley air dynamics of this region provide atmospheric conditions suitable for production and accumulation of ozone at the surface. This region of Colorado is currently in an ozone non-attainment status due to an assortment of contributing factors. Precursor emissions from pollution, wild-fires, and gas and oil production; along with stratosphere-troposphere exchange, can all result in high ozone episodes over the Colorado Front Range. To understand the dynamics of ozone accumulation in this region, Thermo-Scientific ozone monitors have been continuously sampling ozone from 4 different altitudes since the early 2000s. Analysis of ozone data in relation to Nitrogen Oxides (NOx), Methane (CH4), Carbon Monoxide (CO), wind-conditions and back-trajectory air mass origins help to address local ozone precursor emissions and resulting high ozone episodes. Increased ozone episodes are scrutinized with regards to dominant wind direction to determine main precursor emission sources. Analysis of this data reveals a strong influence of precursor emissions from the North-East wind sector, with roughly 50% of ozone exceedances originating from winds prevailing from this direction. Further, correlation with methane is enhanced when prevailing winds are from the North-East; indicative of influence from natural gas processes and feedlot activity. Similar analysis is completed for the North-West wind sector exceedances, with strong correlation to carbon monoxide; likely related to emissions from biomass burning events and forest fires. In depth analysis of
Light-Front Holography, Light-Front Wavefunctions, and Novel QCD Phenomena
Brodsky, Stanley J.; /SLAC /Southern Denmark U., CP3-Origins; de Teramond, Guy F.; /Costa Rica U.
2012-02-16
Light-Front Holography is one of the most remarkable features of the AdS/CFT correspondence. In spite of its present limitations it provides important physical insights into the nonperturbative regime of QCD and its transition to the perturbative domain. This novel framework allows hadronic amplitudes in a higher dimensional anti-de Sitter (AdS) space to be mapped to frame-independent light-front wavefunctions of hadrons in physical space-time. The model leads to an effective confining light-front QCD Hamiltonian and a single-variable light-front Schroedinger equation which determines the eigenspectrum and the light-front wavefunctions of hadrons for general spin and orbital angular momentum. The coordinate z in AdS space is uniquely identified with a Lorentz-invariant coordinate {zeta} which measures the separation of the constituents within a hadron at equal light-front time and determines the off-shell dynamics of the bound-state wavefunctions, and thus the fall-off as a function of the invariant mass of the constituents. The soft-wall holographic model modified by a positive-sign dilaton metric, leads to a remarkable one-parameter description of nonperturbative hadron dynamics - a semi-classical frame-independent first approximation to the spectra and light-front wavefunctions of meson and baryons. The model predicts a Regge spectrum of linear trajectories with the same slope in the leading orbital angular momentum L of hadrons and the radial quantum number n. The hadron eigensolutions projected on the free Fock basis provides the complete set of valence and non-valence light-front Fock state wavefunctions {Psi}{sub n/H} (x{sub i}, k{sub {perpendicular}i}, {lambda}{sub i}) which describe the hadron's momentum and spin distributions needed to compute the direct measures of hadron structure at the quark and gluon level, such as elastic and transition form factors, distribution amplitudes, structure functions, generalized parton distributions and transverse
A Data-Driven Analytic Model for Proton Acceleration by Large-Scale Solar Coronal Shocks
Kozarev, Kamen A
2016-01-01
We have recently studied the development of an eruptive filament-driven, large-scale off-limb coronal bright front (OCBF) in the low solar corona (Kozarev et al. 2015), using remote observations from Solar Dynamics Observatory's Advanced Imaging Assembly EUV telescopes. In that study, we obtained high-temporal resolution estimates of the OCBF parameters regulating the efficiency of charged particle acceleration within the theoretical framework of diffusive shock acceleration (DSA). These parameters include the time-dependent front size, speed, and strength, as well as the upstream coronal magnetic field orientations with respect to the front's surface normal direction. Here we present an analytical particle acceleration model, specifically developed to incorporate the coronal shock/compressive front properties described above, derived from remote observations. We verify the model's performance through a grid of idealized case runs using input parameters typical for large-scale coronal shocks, and demonstrate ...
Light-Front quantization of field theory
Srivastava, P P
1996-01-01
Some basic topics in Light-Front (LF) quantized field theory are reviewed. Poincarè algebra and the LF Spin operator are discussed. The local scalar field theory of the conventional framework is shown to correspond to a non-local Hamiltonian theory on the LF in view of the constraint equations on the phase space, which relate the bosonic condensates to the non-zero modes. This new ingredient is useful to describe the spontaneous symmetry breaking on the LF. The instability of the symmetric phase in two dimensional scalar theory when the coupling constant grows is shown in the LF theory renormalized to one loop order. Chern-Simons gauge theory regarded to describe excitations with fractional statistics, is quantized in the light-cone gauge and a simple LF Hamiltonian obtained which may allow us to construct renormalized theory of anyons.
Wave front distortion based fluid flow imaging
Iffa, Emishaw; Heidrich, Wolfgang
2013-03-01
In this paper, a transparent flow surface reconstruction based on wave front distortion is investigated. A camera lens is used to focus the image formed by the micro-lens array to the camera imaging plane. The irradiance of the captured image is transformed to frequency spectrum and then the x and y spatial components are separated. A rigid spatial translation followed by low pass filtering yields a single frequency component of the image intensity. Index of refraction is estimated from the inverse Fourier transform of the spatial frequency spectrum of the irradiance. The proposed method is evaluated with synthetic data of a randomly generated index of refraction value and used to visualize a fuel injection volumetric data.
ACTIVE FRONT STEERING DURING BRAKING PROCESS
CHEN Deling; CHEN Li; YIN Chengliang; ZHANG Yong
2008-01-01
An active front steering (AFS) intervention control during braking for vehicle stability is presented. Based on the investigation of AFS mechanism, a simplified model of steering system is established and integrated with vehicle model. Then the AFS control on vehicle handling dynamics during braking is designed. Due to the difficulties associated with the sideslip angle measurement of vehicle, a state observer is designed to provide real time estimation. Thereafter, the controller with the feedback of both sideslip and yaw angle is implemented. To evaluate the system control, the proposed AFS controlled vehicle has been tested in the Hardware-in-the-loop-simulation (HILS) system and compared with that of conventional vehicle. Results show that AFS can improve vehicle lateral stability effectively without reducing the braking performance.
On General Plane Fronted Waves. Geodesics
Candela, A M; Sánchez, M; Sanchez, Miguel
2003-01-01
A general class of Lorentzian metrics, $M_0 x R^2$, $ds^2 = + 2 du dv + H(x,u) du^2$, with $(M_0, $ any Riemannian manifold, is introduced in order to generalize classical exact plane fronted waves. Here, we start a systematic study of their main geodesic properties: geodesic completeness, geodesic connectedness and multiplicity, causal character of connecting geodesics. These results are independent of the possibility of a full integration of geodesic equations. Variational and geometrical techniques are applied systematically. In particular, we prove that the asymptotic behavior of $H(x,u)$ with $x$ at infinity determines many properties of geodesics. Essentially, a subquadratic growth of $H$ ensures geodesic completeness and connectedness, while the critical situation appears when $H(x,u)$ behaves in some direction as $|x|^2$, as in the classical model of exact gravitational waves
Shocks and Thermal Conduction Fronts in Retracting Reconnected Flux Tubes
Guidoni, S. E.; Longcope, D. W.
2010-08-01
We present a model for plasma heating produced by time-dependent, spatially localized reconnection within a flare current sheet separating skewed magnetic fields. The reconnection creates flux tubes of new connectivity which subsequently retract at Alfvénic speeds from the reconnection site. Heating occurs in gas-dynamic shocks (GDSs) which develop inside these tubes. Here we present generalized thin flux tube equations for the dynamics of reconnected flux tubes, including pressure-driven parallel dynamics as well as temperature-dependent, anisotropic viscosity and thermal conductivity. The evolution of tubes embedded in a uniform, skewed magnetic field, following reconnection in a patch, is studied through numerical solutions of these equations, for solar coronal conditions. Even though viscosity and thermal conductivity are negligible in the quiet solar corona, the strong GDSs generated by compressing plasma inside reconnected flux tubes generate large velocity and temperature gradients along the tube, rendering the diffusive processes dominant. They determine the thickness of the shock that evolves up to a steady state value, although this condition may not be reached in the short times involved in a flare. For realistic solar coronal parameters, this steady state shock thickness might be as long as the entire flux tube. For strong shocks at low Prandtl numbers, typical of the solar corona, the GDS consists of an isothermal sub-shock where all the compression and cooling occur, preceded by a thermal front where the temperature increases and most of the heating occurs. We estimate the length of each of these sub-regions and the speed of their propagation.
MMIC front-ends for optical communication systems
Petersen, Anders Kongstad
1993-01-01
Two different types of optical front-end MMIC amplifiers for a 2.5-Gb/s coherent heterodyne optical receiver are presented. A bandwidth of 6-12 GHz has been obtained for a tuned front-end and 3-13 GHz for a distributed front-end. An input noise current density of 5-15 pA/√Hz has been obtained for...
Pacific flyway white-fronted goose management plan
US Fish and Wildlife Service, Department of the Interior — Objectives, distribution, population status, human utilization, problems, regulations, and recommendations for management of the white fronted goose.
Wave-front analysis of personal eye protection.
Eppig, Timo; Zoric, Katja; Speck, Alexis; Zelzer, Benedikt; Götzelmann, Jens; Nagengast, Dieter; Langenbucher, Achim
2012-07-30
Shack-Hartmann wave-front sensing has been successfully applied to many fields of optical testing including the human eye itself. We propose wave-front measurement for testing protective eye wear for production control and investigation of aberrations. Refractive power data is derived from the wave-front data and compared to a subjective measurement technique based on a focimeter. Additional image quality classification was performed with a multivariate model using objective parameters to resample a subjectively determined visual quality. Wave-front measurement advances optical testing of protective eye wear and may be used for objective quality control.
White-fronted Goose Telementry, 1998-2000 [ds330
California Department of Resources — Using radio-telemetry, greater white-fronted geese (Anser albifrons frontalis) distribution and movements during winter in Central California were determined during...
Rasmussen, Anders Rønne; Sørensen, Mads Peter; Gaididei, Yuri Borisovich
2008-01-01
A wave equation, that governs nite amplitude acoustic disturbances in a thermoviscous Newtonian fluid, and includes nonlinear terms up to second order, is proposed. In contrast to the model known as the Kuznetsov equation, the proposed nonlinear wave equation preserves the Hamiltonian structure...... of the fundamental fluid dynamical equations in the non-dissipative limit. An exact traveling front solution is obtained from a generalized traveling wave assumption. This solution is, in an overall sense, equivalent to the Taylor shock solution of the Burgers equation. However, in contrast to the Burgers equation...... with respect to the fluid ahead of it, and subsonic speed with respect to the fluid behind it, similarly to the fluid dynamical shock. Linear stability analysis reveals that the front is stable when the acoustic pressure belongs to a critical interval, and is otherwise unstable. These results are veried...
The structure of precipitation fronts for finite relaxation time
Stechmann, Samuel N.; Majda, Andrew J. [New York University, Department of Mathematics and Center for Atmosphere Ocean Science, Courant Institute of Mathematical Sciences, New York, NY (United States)
2006-11-15
When convection is parameterized in an atmospheric circulation model, what types of waves are supported by the parameterization? Several studies have addressed this question by finding the linear waves of simplified tropical climate models with convective parameterizations. In this paper's simplified tropical climate model, convection is parameterized by a nonlinear precipitation term, and the nonlinearity gives rise to precipitation front solutions. Precipitation fronts are solutions where the spatial domain is divided into two regions, and the precipitation (and other model variables) changes abruptly at the boundary of the two regions. In one region the water vapor is below saturation and there is no precipitation, and in the other region the water vapor is above saturation level and precipitation is nonzero. The boundary between the two regions is a free boundary that moves at a constant speed. It is shown that only certain front speeds are allowed. The three types of fronts that exist for this model are drying fronts, slow moistening fronts, and fast moistening fronts. Both types of moistening fronts violate Lax's stability criterion, but they are robustly realizable in numerical experiments that use finite relaxation times. Remarkably, here it is shown that all three types of fronts are robustly realizable analytically for finite relaxation time. All three types of fronts may be physically unreasonable if the front spans an unrealistically large physical distance; this depends on various model parameters, which are investigated below. From the viewpoint of applied mathematics, these model equations exhibit novel phenomena as well as features in common with the established applied mathematical theories of relaxation limits for conservation laws and waves in reacting gas flows. (orig.)
Grosu, Ioan; Featonby, David
2016-01-01
This driven top is quite a novelty and can, with some trials, be made using the principles outlined here. This new top has many applications in developing both understanding and skills and these are detailed in the article. Depending on reader's available time and motivation they may feel an urge to make one themselves, or simply invest a few…
Grosu, Ioan; Featonby, David
2016-01-01
This driven top is quite a novelty and can, with some trials, be made using the principles outlined here. This new top has many applications in developing both understanding and skills and these are detailed in the article. Depending on reader's available time and motivation they may feel an urge to make one themselves, or simply invest a few…
Henry Riche, Nathalie
2017-01-01
This book is an accessible introduction to data-driven storytelling, resulting from discussions between data visualization researchers and data journalists. This book will be the first to define the topic, present compelling examples and existing resources, as well as identify challenges and new opportunities for research.
Chiral Boson Theory on the Light-Front
Srivastava, P P
1999-01-01
The {\\it front form} framework for describing the quantized theory of chiral boson is discussed. It avoids the conflict with the requirement of the principle of microcausality as is found in the conventional equal- time treatment. The discussion of the Floreanini-Jackiw model and its modified version for describing the chiral boson becomes very transparent on the light-front.
An improved front tracking method for the Euler equations
J.A.S. Witteveen (Jeroen); B. Koren (Barry); P.G. Bakker
2007-01-01
textabstractAn improved front tracking method for hyperbolic conservation laws is presented. The improved method accurately resolves discontinuities as well as continuous phenomena. The method is based on an improved front interaction model for a physically more accurate modeling of the Euler
FACILITATING RADICAL FRONT-END INNOVATION THROUGH TARGETED HR PRACTICES
Aagaard, Annabeth
2017-01-01
This study examines how radical front end innovation can be actively facilitated through selected and targeted HR practices and bundles of HR practices. The empirical field is an explorative case study of front end innovation and HR practices in the pharmaceutical industry, with an in-depth case ...
An improved front tracking method for the Euler equations
Witteveen, J.A.S.; Koren, B.; Bakker, P.G.
2007-01-01
An improved front tracking method for hyperbolic conservation laws is presented. The improved method accurately resolves discontinuities as well as continuous phenomena. The method is based on an improved front interaction model for a physically more accurate modeling of the Euler equations, as comp
UWB front-end for SAR-based imaging system
Monni, S.; Grooters, R.; Neto, A.; Nennie, F.A.
2010-01-01
A planarly fed UWB leaky lens antenna is presented integrated with wide band transmit and receive front-end electronics, to be used in a SAR-based imaging system. The unique non-dispersive characteristics of this antenna over a very wide bandwidth, together with the dual band front-end electronics b
Pattern formation in the wake of triggered pushed fronts
Goh, Ryan; Scheel, Arnd
2016-08-01
Pattern-forming fronts are often controlled by an external stimulus which progresses through a stable medium at a fixed speed, rendering it unstable in its wake. By controlling the speed of excitation, such stimuli, or ‘triggers’, can mediate pattern forming fronts which freely invade an unstable equilibrium and control which pattern is selected. In this work, we analytically and numerically study when the trigger perturbs an oscillatory pushed free front. In such a situation, the resulting patterned front, which we call a pushed trigger front, exhibits a variety of phenomenon, including snaking, non-monotonic wave-number selection, and hysteresis. Assuming the existence of a generic oscillatory pushed free front, we use heteroclinic bifurcation techniques to prove the existence of trigger fronts in an abstract setting motivated by the spatial dynamics approach. We then derive a leading order expansion for the selected wave-number in terms of the trigger speed. Furthermore, we show that such a bifurcation curve is governed by the difference of certain strong-stable and weakly-stable spatial eigenvalues associated with the decay of the free pushed front. We also study prototypical examples of these phenomena in the cubic-quintic complex Ginzburg Landau equation and a modified Cahn-Hilliard equation.
Interaction of Oblique Incident Electromagnetic Wave with Relativistic Ionization Front
无
2005-01-01
Interactions of oblique incident probe wave with oncoming ionization fronts have been investigated using moving boundary conditions. Field conversion coefficients of reflection,transmission and magnetic modes produced in the interactions are derived. Phase matching conditions at the front and frequency up-shifting formulas for the three modes are also presented.
The CF6 jet engine performance improvement: New front mount
Fasching, W. A.
1979-01-01
The New Front Mount was evaluated in component tests including stress, deflection/distortion and fatigue tests. The test results demonstrated a performance improvement of 0.1% in cruise sfc, 16% in compressor stall margin and 10% in compressor stator angle margin. The New Front Mount hardware successfully completed 35,000 simulated flight cycles endurance testing.
Self-calibrating quadrature mixing front-end for SDR
De Witt, JJ
2008-01-01
Full Text Available A quadrature mixing front-end is well-suited toward software define radio (SDR) applications, due to its low complexity and the inherent flexibility that it affords the radio front-end. Its performance is, however, severely affected by gain...
Chemotaxis : signalling modules join hands at front and tail
Haastert, Peter J.M. van; Devreotes, Peter N.
2004-01-01
Chemotaxis is the result of a refined interplay among various intracellular molecules that process spatial and temporal information. Here we present a modular scheme of the complex interactions between the front and the back of cells that allows them to navigate. First, at the front of the cell, act
Fronts and Thermohaline Structure of the Brazil Current Confluence System
Severov, Dimitri
and Thermohaline Structure of the Brazil Current Confluence System (BCCS) are stud-ied from climatic data, "Marathon Exp. Leg.8, 1984"data, and two Sea surface temperature (SST) data bases: "Meteor satellite"(1989-1994) and "ds277-Reynolds" (1981-2000).The South Atlantic Central Water (SACW) is divided in two main types: tropical (TW) and subtropical water (ST). Water masses, fronts, inter-frontal and frontal zones are analysed and classified: a) the water masses: Tropical Low-Salinity Water, Tropical Surface Water, Tropical Tropospheric Water, Subtropical Low-Salinity Water, Subtropical Surface Water, Subtropical Tropospheric Water. T,S characteristics of intermediate, deep and bottom water defined by different authors are confirmed and completed; b) the Inter-frontal Zones: Tropical/Brazil Current Zone, Sub-tropical Zone and Subantarctic Zone; c) the Frontal Zones: Subtropical, Subantarctic and Polar, and d) the Fronts: Subtropical Front of the Brazil Current, Principal Subtropical Front, North Subtropical Front, Subtropical Surface Front, South Subtropical Front, Subantarctic Surface Front, Subantarctic Front and Polar Front. Several stable T-S relationships are found below the friction layer and at the Fronts. The maximum gradient of the oceanographic characteris-tics occurs at the Brazil Current Front, which can be any of the subtropical fronts, depending on season. Minimum mean depth of the pycnocline coincides with the fronts of the BCCS, indicating the paths of low-salinity shelf waters into the open ocean. D. N. Severov (a) , V. Pshennikov (b) and A.V. Remeslo (c) a -Sección Oceanologé Facultad de Ciencia, Universidad de la Republica, Igué 4225, 11400 ıa, a Montevideo, Uruguay. Tel. (598-2) 525-8618, Fax (598-2) 525-8617, mail: dima@fcien.edu.uy b -Instituto de Física, Facultad de Ciencias, Universidad de la Republica, Igué 4225, 11400 Mon-a tevideo, Uruguay, mail: seva@fisica.edu.uy c -Atlantic Research Inst. For Fisheries Oceanology (Atlant
Nonvariational mechanism of front propagation: Theory and experiments
Alvarez-Socorro, A. J.; Clerc, M. G.; González-Cortés, G.; Wilson, M.
2017-01-01
Multistable systems exhibit a rich front dynamics between equilibria. In one-dimensional scalar gradient systems, the spread of the fronts is proportional to the energy difference between equilibria. Fronts spreading proportionally to the energetic difference between equilibria is a characteristic of one-dimensional scalar gradient systems. Based on a simple nonvariational bistable model, we show analytically and numerically that the direction and speed of front propagation is led by nonvariational dynamics. We provide experimental evidence of nonvariational front propagation between different molecular orientations in a quasi-one-dimensional liquid-crystal light valve subjected to optical feedback. Free diffraction length allows us to control the variational or nonvariational nature of this system. Numerical simulations of the phenomenological model have quite good agreement with experimental observations.
Design of Laboratory Experiments to Study Photoionization Fronts
Gray, William James; Davis, Josh; Drake, R. Paul
2017-06-01
Here we present the theoretical foundation for a laboratory experiment to study photoionization fronts. Photoionization fronts play important roles in the formation and evolution of structure in the Universe. A properly designed experiment will have to control the recombination rate, electron impact ionization rate, and the initial thermal spectrum. We show that such an experiment can be designed, but requires the use of the largest high-energy-density laser facilities, such as Omega, Z, and NIF. We also show that prior experiments do not actually generate photoionization fronts, rather a heat front is produced by heat conductions. We show some initial simulation results of the current experimental design and characterize the ionization front.
Flame front propagation in a channel with porous walls
Golovastov, S. V.; Bivol, G. Yu
2016-11-01
Propagation of the detonation front in hydrogen-air mixture was investigated in rectangular cross-section channels with sound-absorbing boundaries. The front of luminescence was detected in a channel with acoustically absorbing walls as opposed to a channel with solid walls. Flame dynamics was recorded using a high-speed camera. The flame was observed to have a V-shaped profile in the acoustically absorbing section. The possible reason for the formation of the V-shaped flame front is friction under the surface due to open pores. In these shear flows, the kinetic energy of the flow on the surface can be easily converted into heat. A relatively small disturbance may eventually lead to significant local stretching of the flame front surface. Trajectories of the flame front along the axis and the boundary are presented for solid and porous surfaces.
Pareto-front shape in multiobservable quantum control
Sun, Qiuyang; Wu, Re-Bing; Rabitz, Herschel
2017-03-01
Many scenarios in the sciences and engineering require simultaneous optimization of multiple objective functions, which are usually conflicting or competing. In such problems the Pareto front, where none of the individual objectives can be further improved without degrading some others, shows the tradeoff relations between the competing objectives. This paper analyzes the Pareto-front shape for the problem of quantum multiobservable control, i.e., optimizing the expectation values of multiple observables in the same quantum system. Analytic and numerical results demonstrate that with two commuting observables the Pareto front is a convex polygon consisting of flat segments only, while with noncommuting observables the Pareto front includes convexly curved segments. We also assess the capability of a weighted-sum method to continuously capture the points along the Pareto front. Illustrative examples with realistic physical conditions are presented, including NMR control experiments on a 1H-13C two-spin system with two commuting or noncommuting observables.
Front tracking for characterizing and quantifying reactive mixing
Kelley, Douglas; Nevins, Thomas
2016-11-01
Mixing in industrial chemical reactors involves complicated interactions between advection, reaction, and diffusion that are difficult to simulate or measure in detail. However, in large-Damköhler-number systems which show sharp fronts between reacted and unreacted regions, reactor dynamics might be more simply and usefully characterized in terms of the reaction fronts themselves. In fact, prior work has already shown that the reaction rate and material diffusivity can be calculated directly if front speed and front thickness are known. We have developed methods to optically track reaction fronts, measuring their speed and thickness throughout space and time. We will present such measurements in both simulation and experiment, consider their statistics, and discuss future efforts to characterize and quantify mixing in chemical reactors.
Front speed in reactive compressible stirred media
Bianco, Federico; Vergni, Davide; Vulpiani, Angelo
2013-01-01
We investigated a nonlinear advection-diffusion-reaction equation for a passive scalar field. The purpose is to understand how the compressibility can affect the front dynamics and the bulk burning rate. We study two classes of flows: periodic shear flow and cellular flow both in the case of fast advection regime, analysing the system at varying the extent of compressibility and the reaction rate. We find that the bulk burning rate in a shear flow increases with compressibility intensity. Furthermore, the faster the reaction the more important the difference with respect to the laminar case. The effect has been quantitatively measured and it turns out to be generally little. For the cellular flow, the two extreme cases have been investigated, with the whole perturbation situated either in the centre of the vortex or in the periphery. The dependence in this case does not show a monotonic scaling with different behaviour in the two cases. The enhancing remains modest and always less than 20%
The PHENIX Drift Chamber Front End Electroncs
Pancake, C.; Velkovska, J.; Pantuev, V.; Fong, D.; Hemmick, T.
1998-04-01
The PHENIX Drift Chamber (DC) is designed to operate in the high particle flux environment of the Relativistic Heavy Ion Collider and provide high resolution track measurements. It is segmented into 80 keystones with 160 readout channels each. The Front End Electronics (FEE) developed to meet the demanding operating conditions and the large number of readout channels of the DC will be discussed. It is based on two application specific integrated circuits: the ASD8 and the TMC-PHX1. The ASD8 chip contains 8 channels of bipolar amplifier-shaper-discriminator with 6 ns shaping time and ≈ 20 ns pulse width, which satisfies the two track resolution requirements. The TMC-PHX1 chip is a high-resolution multi-hit Time-to-Digital Converter. The outputs from the ASD8 are digitized in the Time Memory Cell (TMC) every (clock period)/32 or 0.78 ns (at 40 MHz), which gives the intrinsic time resolution of the system. A 256 words deep dual port memory keeps 6.4 μs time history of data at 40 MHz clock. Each DC keystone is supplied with 4 ASD8/TMC boards and one FEM board, which performs the readout of the TMC-PHX1's, buffers and formats the data to be transmitted over the Glink. The slow speed control communication between the FEM and the system is carried out over ARCNET. The full readout chain and the data aquisition system are being tested.
Front tracking for hyperbolic conservation laws
Holden, Helge
2002-01-01
Hyperbolic conservation laws are central in the theory of nonlinear partial differential equations and in science and technology. The reader is given a self-contained presentation using front tracking, which is also a numerical method. The multidimensional scalar case and the case of systems on the line are treated in detail. A chapter on finite differences is included. "It is already one of the few best digests on this topic. The present book is an excellent compromise between theory and practice. Students will appreciate the lively and accurate style." D. Serre, MathSciNet "I have read the book with great pleasure, and I can recommend it to experts as well as students. It can also be used for reliable and very exciting basis for a one-semester graduate course." S. Noelle, Book review, German Math. Soc. "Making it an ideal first book for the theory of nonlinear partial differential equations...an excellent reference for a graduate course on nonlinear conservation laws." M. Laforest, Comp. Phys. Comm.
Alemtuzumab in the up-front setting
Matthew Kaufman
2008-04-01
Full Text Available Matthew Kaufman, Kanti R RaiLong Island Jewish Medical Center, New Hyde Park, NY, USAAbstract: Alemtuzumab is a humanized chimeric monoclonal antibody targeting CD52. Although this agent already has an important role in the treatment of chronic lymphocytic leukemia (CLL, many of its uses are still being defined. Early trials showed alemtuzumab’s value in refractory disease and helped to define its excellent activity in the bone marrow, spleen and 17p deleted patients. The CAM307 trial has demonstrated alemtuzumab’s efficacy as monotherapy in the front-line setting, and ultimately led to its FDA approval as frontline therapy. Especially promising is the trend toward improved response in patients with high risk cytogenic abnormalities (17p del, 11q del, trisomy 12. The various consolidation trials have also provided promising results of achieving eradication of minimal residual disease (MRD. Although the ultimate benefit of achieving MRD negativity remains under investigation, alemtuzumab’s potent activity on the bone marrow will likely make it an important part of combination therapy.Keywords: alemtuzumab, chronic lymphocytic leukemia, consolidation, minimal residual disease, 17p deletion, 11q deletion
Front tracking for hyperbolic conservation laws
Holden, Helge
2015-01-01
This is the second edition of a well-received book providing the fundamentals of the theory hyperbolic conservation laws. Several chapters have been rewritten, new material has been added, in particular, a chapter on space dependent flux functions, and the detailed solution of the Riemann problem for the Euler equations. Hyperbolic conservation laws are central in the theory of nonlinear partial differential equations and in science and technology. The reader is given a self-contained presentation using front tracking, which is also a numerical method. The multidimensional scalar case and the case of systems on the line are treated in detail. A chapter on finite differences is included. From the reviews of the first edition: "It is already one of the few best digests on this topic. The present book is an excellent compromise between theory and practice. Students will appreciate the lively and accurate style." D. Serre, MathSciNet "I have read the book with great pleasure, and I can recommend it to experts ...
Wick Rotation in the Light-Front
de Melo, J P B C J; Frederico, T
2008-01-01
We study the electroweak properties of pseudo-scalar mesons in the light and heavy-light sectors. In particular, we address the electromagnetic form factors and decay constants of the pion, kaon and D mesons. The structure of composite systems are given by the Bethe-Salpeter (BS) amplitude of a meson formed by a confined pair of constituent quark and antiquark, which in our work is written in terms of Pauli-Villars regulators. The analytical structure contains single poles in the complex momentum space. The BS amplitude takes into account poles due to the regulator parameters, while the quark-antiquark cut is avoided, implying in confined quarks with the property that the sum of the constituents masses can be larger than the mass of the meson. The one-loop expressions of the electroweak transition amplitudes are conveniently written in terms of light-front momentum. Technically, we introduce a Wick-rotation of he minus component of the momentum (k-minus) in the one-loop amplitudes allowing to avoid the cuts i...
The sharp-front magnetic diffusion wave of a strong magnetic field diffusing into a solid metal
Xiao, Bo; Gu, Zhuo-Wei; Kan, Ming-Xian; Wang, Gang-Hua; Zhao, Jian-Heng; Computational Physics Team
2016-10-01
When a mega-gauss magnetic field diffuses into a solid metal, the Joule heat would rise rapidly the temperature of the metal, and the rise of temperature leads to an increase of the metal's resistance, which in turn accelerates the magnetic field diffusion. Those positive feedbacks acting iteratively would lead to an interesting sharp-front magnetic diffusion wave. By assuming that the metal's resistance has an abrupt change from a small value ηS to larger value ηL at some critical temperature Tc, the sharp-front magnetic diffusion wave can be solved analytically. The conditions for the emerging of the sharp-front magnetic diffusion wave are B0 >Bc , ηL /ηS >> 1 , and ηL/ηSB0/-Bc Bc >> 1 , where Bc =√{ 2μ0Jc } , B0 is the vacuum magnetic field strength, and Jc is the critical Joule heat density. The wave-front velocity of the diffusion wave is Vc =ηL/μ0B0/-Bc Bc1/xc , where xc is the depth the wave have propagated in the metal. In this presentation we would like to discuss the derivation of the formulas and its impact to magnetically driven experiments. The work is supported by the Foundation of China Academy of Engineering Physics (No. 2015B0201023).
The Hatteras Front: August 2004 velocity and density structure
Savidge, Dana K.; Austin, Jay A.
2007-07-01
The Hatteras Front is a persistent mesoscale cross-shelf oriented front off Cape Hatteras, North Carolina. It is the boundary between relatively cool, fresh Mid-Atlantic Bight shelf waters and warmer, saltier shelf waters of the South Atlantic Bight, which both converge along-shelf upon Cape Hatteras year round. The Frontal Interaction Near Cape Hatteras (FINCH) project was conducted in 2004-2005 to intensively sample the Hatteras Front with shipboard ADCP and undulating towed CTD. This paper documents velocity and density structures associated with the cross-shelf oriented zone of Hatteras Front during the August 2004 field season. Property gradients across the Hatteras Front are large, with temperature (T) and salinity (S) differences of ˜4-6°C, 2-5 psu, respectively over distances of 1-2 km. The T and S are not completely compensating, and a strong density (ρ) gradient also exists, with Δρ of ˜2 kg/m3 across a gentler 10 km wide front. The density gradient results in a steric sea-level height gradient of ˜1-2 cm across the Front, which is in approximate geostrophic balance with a surface intensified jet, directed shoreward along the cross-shelf oriented Front. The velocity is sheared with depth at 3.0 × 10-2 to 5.0 × 10-2 s-1 in the upper 5 m of the jet; a rate consistent with the density gradient according to the thermal wind relationship. Shoreward transport of ˜4.8 × 104 m3/s results from the surface intensified jet. The structure of the velocity field associated with the Hatteras Front resembles that of a slope-controlled buoyant plume, as described by Lentz and Helfrich (2002). Velocity and density structures are similar during both advancing (southwestward) and retreating (northeastward) motion of the Front.
Vanessa Voisin
2008-07-01
Full Text Available Front voennykh prokurorov is a collection of essays written by two writers who are not known as specialists of military history, but obviously have access to archives, as proves the reprint, in the middle of the book, of several pages from the personal files of Afanas’ev, former Main Military Prosecutor of Soviet Armed Forces.The first part of the book is devoted to Nikolai Porfir’evich Afanas’ev’s memoirs, written, according to the editors, after his retirement in 1950. Afanas’ev, though les...
Front End Spectroscopy ASIC for Germanium Detectors
Wulf, Eric
Large-area, tracking, semiconductor detectors with excellent spatial and spectral resolution enable exciting new access to soft (0.2-5 MeV) gamma-ray astrophysics. The improvements from semiconductor tracking detectors come with the burden of high density of strips and/or pixels that require high-density, low-power, spectroscopy quality readout electronics. CMOS ASIC technologies are a natural fit to this requirement and have led to high-quality readout systems for all current semiconducting tracking detectors except for germanium detectors. The Compton Spectrometer and Imager (COSI), formerly NCT, at University of California Berkeley and the Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS) at Goddard Space Flight Center utilize germanium cross-strip detectors and are on the forefront of NASA's Compton telescope research with funded missions of long duration balloon flights. The development of a readout ASIC for germanium detectors would allow COSI to replace their discrete electronics readout and would enable the proposed Gamma-Ray Explorer (GRX) mission utilizing germanium strip-detectors. We propose a 3-year program to develop and test a germanium readout ASIC to TRL 5 and to integrate the ASIC readout onto a COSI detector allowing a TRL 6 demonstration for the following COSI balloon flight. Our group at NRL led a program, sponsored by another government agency, to produce and integrate a cross-strip silicon detector ASIC, designed and fabricated by Dr. De Geronimo at Brookhaven National Laboratory. The ASIC was designed to handle the large (>30 pF) capacitance of three 10 cm^2 detectors daisy-chained together. The front-end preamplifier, selectable inverter, shaping times, and gains make this ASIC compatible with a germanium cross-strip detector as well. We therefore have the opportunity and expertise to leverage the previous investment in the silicon ASIC for a new mission. A germanium strip detector ASIC will also require precise timing of the signals at
Electrically driven optical antennas
Kern, Johannes; Kullock, René; Prangsma, Jord; Emmerling, Monika; Kamp, Martin; Hecht, Bert
2015-09-01
Unlike radiowave antennas, so far optical nanoantennas cannot be fed by electrical generators. Instead, they are driven by light or indirectly via excited discrete states in active materials in their vicinity. Here we demonstrate the direct electrical driving of an in-plane optical antenna by the broadband quantum-shot noise of electrons tunnelling across its feed gap. The spectrum of the emitted photons is determined by the antenna geometry and can be tuned via the applied voltage. Moreover, the direction and polarization of the light emission are controlled by the antenna resonance, which also improves the external quantum efficiency by up to two orders of magnitude. The one-material planar design offers facile integration of electrical and optical circuits and thus represents a new paradigm for interfacing electrons and photons at the nanometre scale, for example for on-chip wireless communication and highly configurable electrically driven subwavelength photon sources.
Georgiev, Bozhidar; Georgieva, Adriana
2013-12-01
In this paper, are presented some possibilities concerning the implementation of a test-driven development as a programming method. Here is offered a different point of view for creation of advanced programming techniques (build tests before programming source with all necessary software tools and modules respectively). Therefore, this nontraditional approach for easier programmer's work through building tests at first is preferable way of software development. This approach allows comparatively simple programming (applied with different object-oriented programming languages as for example JAVA, XML, PYTHON etc.). It is predictable way to develop software tools and to provide help about creating better software that is also easier to maintain. Test-driven programming is able to replace more complicated casual paradigms, used by many programmers.
Long duration X-ray drive hydrodynamics experiments relevant for laboratory astrophysics
Casner, A.; Martinez, D.; Smalyuk, V.; Masse, L.; Kane, J. O.; Villette, B.; Fariaut, J.; Oudot, G.; Liberatore, S.; Mancini, R. C.; Remington, B. A.; Heeter, R. F.
2015-12-01
The advent of high-power lasers facilities such as the National Ignition Facility (NIF), and the Laser Megajoule (LMJ) in the near future, opens a new era in the field of High Energy Density Laboratory Astrophysics. These versatile laser facilities will provide unique platforms to study the rich physics of nonlinear and turbulent mixing flows. The extended laser pulse duration could be harnessed to accelerate targets over much larger distances and longer time periods than previously achieved. We report on the first results acquired on NIF with the ablative Rayleigh-Taylor Instability (RTI) platform. A 20-ns X-ray drive is tailored to accelerate planar modulated samples into the highly-nonlinear bubble merger regime. Based on the analogy between flames front and ablation front, highly nonlinear RTI measurements at ablation front can provide important insights into the initial deflagration stage of thermonuclear supernova of Type Ia. We also report on an innovative concept used to create even longer drive on multi-beam laser facilities. The multi-barrel hohlraum (Gattling Gun) approach consists, here, of three adjacent cavities, driven in succession in time. This novel concept has been validated on the Omega EP laser system. The three cavities were irradiated with three 6-10 ns pulse UV beams and a 30 ns, 90 eV X-ray radiation drive was measured with the time-resolved X-ray spectrometer μDMX. This concept is promising to investigate the pillar structures in the Eagle Nebula or for photoionization studies which require a steady light source of sufficient duration to recreate relevant physics.
Bringing the Fuzzy Front End into Focus
Beck, D.F.; Boyack, K.W.; Bray, O.H.; Siemens, W.D.
1999-03-03
Technology planning is relatively straightforward for well-established research and development (R and D) areas--those areas in which an organization has a history, the competitors are well understood, and the organization clearly knows where it is going with that technology. What we are calling the fuzzy front-end in this paper is that condition in which these factors are not well understood--such as for new corporate thrusts or emerging areas where the applications are embryonic. While strategic business planning exercises are generally good at identifying technology areas that are key to future success, they often lack substance in answering questions like: (1) Where are we now with respect to these key technologies? ... with respect to our competitors? (2) Where do we want or need to be? ... by when? (3) What is the best way to get there? In response to its own needs in answering such questions, Sandia National Laboratories is developing and implementing several planning tools. These tools include knowledge mapping (or visualization), PROSPERITY GAMES and technology roadmapping--all three of which are the subject of this paper. Knowledge mapping utilizes computer-based tools to help answer Question 1 by graphically representing the knowledge landscape that we populate as compared with other corporate and government entities. The knowledge landscape explored in this way can be based on any one of a number of information sets such as citation or patent databases. PROSPERITY GAMES are high-level interactive simulations, similar to seminar war games, which help address Question 2 by allowing us to explore consequences of various optional goals and strategies with all of the relevant stakeholders in a risk-free environment. Technology roadmapping is a strategic planning process that helps answer Question 3 by collaboratively identifying product and process performance targets and obstacles, and the technology alternatives available to reach those targets.
Affinity driven social networks
Ruyú, B.; Kuperman, M. N.
2007-04-01
In this work we present a model for evolving networks, where the driven force is related to the social affinity between individuals of a population. In the model, a set of individuals initially arranged on a regular ordered network and thus linked with their closest neighbors are allowed to rearrange their connections according to a dynamics closely related to that of the stable marriage problem. We show that the behavior of some topological properties of the resulting networks follows a non trivial pattern.
The ITER neutral beam front end components integration
Urbani, M., E-mail: marc.urbani@iter.org [ITER Organization, Route de Vinon sur Verdon, 13115 St Paul Lez Durance (France); Hemsworth, R.; Schunke, B.; Graceffa, J.; Delmas, E.; Svensson, L.; Boilson, D. [ITER Organization, Route de Vinon sur Verdon, 13115 St Paul Lez Durance (France); Krylov, A.; Panasenkov, A. [RRC Kurchatov Institute, 1, Kurchatov Square, Moscow 123182 (Russian Federation); Agarici, G. [Fusion For Energy, C/Josep Pla 2, Torres Diagonal Litoral-B3, E-08019 Barcelona (Spain); Stafford Allen, R.; Jones, C.; Kalsey, M.; Muir, A.; Milnes, J. [Culham Centre for Fusion Energy, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Geli, F. [FGI Consulting, Le Garde d’Estienne, 4565 route du Puy Sainte Reparade, 13540 Puyricard (France); Sherlock, P. [AMEC Limited, Booths Park Chelford Road, Knutsford Cheshire WA16 8QZ (United Kingdom)
2013-10-15
The neutral beam (NB) system for ITER is composed of two heating neutral beam injectors (HNBs) and a diagnostic neutral beam injector (DNB). A third HNB can be installed as a future up-grade. This paper will present the design development of the components between the injectors and the tokamak; the so-called ‘front end components’: the drift duct consists of the NB bellows and the drift duct liner, the vacuum vessel pressure suppression system box (VVPSS box), the absolute valve, and the fast shutter. These components represent the key links between the ITER tokamak and the vessels of the NB injectors. The design of these components is demanding due to the different loads that these components will have to stand. The paper will describe the different design solutions which have to be implemented regarding the primary vacuum confinement, the power handling capability and the remote maintenance operations. The sizes of the components are determined by the large cross section of the neutral beam. The power handling capability is driven by the anticipated re-ionization of the neutral beam and the electromagnetic fields in this region. The drift duct bellows (with an inner diameter of 2.5 m) shall guarantee a leak tight vacuum enclosure during the vertical and radial displacements of the ITER vacuum vessel. The conductance of the VVPSS box must be maximized in the available space. The absolute valve remains a challenging development. The total leak rate through the valve must be ≤1 × 10{sup −8} Pa m{sup 3}/s when the valve is closed. Due to the radiation environment, the seals of the gate valve will be metallic. An R and D program has been launched to develop a suitable metallic seal solution with the required dimensions. The maximum allowed closing time for the fast shutter shall be less than 1 s. For all these components the leak tightness will be guaranteed by a welded lip seal and the mechanical stability by bolted structures.
Muon capture for the front end of a muon collider
Neuffer, D
2011-01-01
We discuss the design of the muon capture front end for a \\mu+-\\mu- Collider. In the front end, a proton bunch on a target creates secondary pions that drift into a capture transport channel, decaying into muons. A sequence of rf cavities forms the resulting muon beams into strings of bunches of differing energies, aligns the bunches to (nearly) equal central energies, and initiates ionization cooling. The muons are then cooled and accelerated to high energy into a storage ring for high-energy high luminosity collisions. Our initial design is based on the somewhat similar front end of the International Design Study (IDS) neutrino factory.
Adaptive RF front-ends for hand-held applications
van Bezooijen, Andre; van Roermund, Arthur
2010-01-01
The RF front-end - antenna combination is a vital part of a mobile phone because its performance is very relevant to the link quality between hand-set and cellular network base-stations. The RF front-end performance suffers from changes in operating environment, like hand-effects, that are often unpredictable. ""Adaptive RF Front-Ends for Hand-Held Applications"" presents an analysis on the impact of fluctuating environmental parameters. In order to overcome undesired behavior two different adaptive control methods are treated that make RF frond-ends more resilient: adaptive impedance control,
Determination of cut front position in laser cutting
Pereira, M.; Thombansen, U.
2016-07-01
Laser cutting has a huge importance to manufacturing industry. Laser cutting machines operate with fixed technological parameters and this does not guarantee the best productivity. The adjustment of the cutting parameters during operation can improve the machine performance. Based on a coaxial measuring device it is possible to identify the cut front position during the cutting process. This paper describes the data analysis approach used to determine the cut front position for different feed rates. The cut front position was determined with good resolution, but improvements are needed to make the whole process more stable.
Electron g-2 in Light-front Quantization
Xingbo Zhao
2014-10-01
Full Text Available Basis Light-front Quantization has been proposed as a nonperturbative framework for solving quantum field theory. We apply this approach to Quantum Electrodynamics and explicitly solve for the light-front wave function of a physical electron. Based on the resulting light-front wave function, we evaluate the electron anomalous magnetic moment. Nonperturbative mass renormalization is performed. Upon extrapolation to the infinite basis limit our numerical results agree with the Schwinger result obtained in perturbation theory to an accuracy of 0.06%.