Origin of Polar Order in Dense Suspensions of Phototactic Micro-Swimmers

PubMed Central

Furlan, Silvano; Comparini, Diego; Ciszak, Marzena; Beccai, Lucia; Mancuso, Stefano; Mazzolai, Barbara

2012-01-01

A main question for the study of collective motion in living organisms is the origin of orientational polar order, i.e., how organisms align and what are the benefits of such collective behaviour. In the case of micro-organisms swimming at a low Reynolds number, steric repulsion and long-range hydrodynamic interactions are not sufficient to explain a homogeneous polar order state in which the direction of motion is aligned. An external symmetry-breaking guiding field such as a mechanism of taxis appears necessary to understand this phonemonon. We have investigated the onset of polar order in the velocity field induced by phototaxis in a suspension of a motile micro-organism, the algae Chlamydomonas reinhardtii, for density values above the limit provided by the hydrodynamic approximation of a force dipole model. We show that polar order originates from a combination of both the external guiding field intensity and the population density. In particular, we show evidence for a linear dependence of a phototactic guiding field on cell density to determine the polar order for dense suspensions and demonstrate the existence of a density threshold for the origin of polar order. This threshold represents the density value below which cells undergoing phototaxis are not able to maintain a homogeneous polar order state and marks the transition to ordered collective motion. Such a transition is driven by a noise dominated phototactic reorientation where the noise is modelled as a normal distribution with a variance that is inversely proportional to the guiding field strength. Finally, we discuss the role of density in dense suspensions of phototactic micro-swimmers. PMID:22723904

Models for the dynamics of dust-like matter in the self-gravity field: The method of hydrodynamic substitutions

NASA Astrophysics Data System (ADS)

Zhuravlev, V. M.

2017-09-01

Models for the dynamics of a dust-like medium in the self-gravity field are investigated. Solutions of the corresponding problems are constructed by the method of hydrodynamic substitutions generalizing the Cole-Hopf substitutions. The method is extended to multidimensional ideal and viscous fluid flows with cylindrical and spherical symmetries for which exact solutions are constructed. Solutions for the dynamics of self-gravitating dust with arbitrary initial distributions of both fluid density and velocity are constructed using special coordinate transformations. In particular, the problem of cosmological expansion is considered in terms of Newton's gravity theory. Models of a one-dimensional viscous dust fluid flow and some problems of gas hydrodynamics are considered. Examples of exact solutions and their brief analysis are provided.

Self-organized shocks in the sedimentation of a granular gas

NASA Astrophysics Data System (ADS)

Almazán, Lidia; Serero, Dan; Salueña, Clara; Pöschel, Thorsten

2015-06-01

A granular gas in gravity heated from below develops a certain stationary density profile. When the heating is switched off, the granular gas collapses. We investigate the process of sedimentation using computational hydrodynamics, based on the Jenkins-Richman theory, and find that the process is significantly more complex than generally acknowledged. In particular, during its evolution, the system passes several stages which reveal distinct spatial regions of inertial (supersonic) and diffusive (subsonic) dynamics. During the supersonic stages, characterized by Mach>1 , the system develops supersonic shocks which are followed by a steep front of the hydrodynamic fields of temperature and density, traveling upward.

Towards physics responsible for large-scale Lyman-α forest bias parameters

DOE PAGES

Agnieszka M. Cieplak; Slosar, Anze

2016-03-08

Using a series of carefully constructed numerical experiments based on hydrodynamic cosmological SPH simulations, we attempt to build an intuition for the relevant physics behind the large scale density (b δ) and velocity gradient (b η) biases of the Lyman-α forest. Starting with the fluctuating Gunn-Peterson approximation applied to the smoothed total density field in real-space, and progressing through redshift-space with no thermal broadening, redshift-space with thermal broadening and hydrodynamically simulated baryon fields, we investigate how approximations found in the literature fare. We find that Seljak's 2012 analytical formulae for these bias parameters work surprisingly well in the limit ofmore » no thermal broadening and linear redshift-space distortions. We also show that his b η formula is exact in the limit of no thermal broadening. Since introduction of thermal broadening significantly affects its value, we speculate that a combination of large-scale measurements of b η and the small scale flux PDF might be a sensitive probe of the thermal state of the IGM. Lastly, we find that large-scale biases derived from the smoothed total matter field are within 10–20% to those based on hydrodynamical quantities, in line with other measurements in the literature.« less

Towards physics responsible for large-scale Lyman-α forest bias parameters

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

Agnieszka M. Cieplak; Slosar, Anze

Using a series of carefully constructed numerical experiments based on hydrodynamic cosmological SPH simulations, we attempt to build an intuition for the relevant physics behind the large scale density (b δ) and velocity gradient (b η) biases of the Lyman-α forest. Starting with the fluctuating Gunn-Peterson approximation applied to the smoothed total density field in real-space, and progressing through redshift-space with no thermal broadening, redshift-space with thermal broadening and hydrodynamically simulated baryon fields, we investigate how approximations found in the literature fare. We find that Seljak's 2012 analytical formulae for these bias parameters work surprisingly well in the limit ofmore » no thermal broadening and linear redshift-space distortions. We also show that his b η formula is exact in the limit of no thermal broadening. Since introduction of thermal broadening significantly affects its value, we speculate that a combination of large-scale measurements of b η and the small scale flux PDF might be a sensitive probe of the thermal state of the IGM. Lastly, we find that large-scale biases derived from the smoothed total matter field are within 10–20% to those based on hydrodynamical quantities, in line with other measurements in the literature.« less

On hydrodynamic phase field models for binary fluid mixtures

NASA Astrophysics Data System (ADS)

Yang, Xiaogang; Gong, Yuezheng; Li, Jun; Zhao, Jia; Wang, Qi

2018-05-01

Two classes of thermodynamically consistent hydrodynamic phase field models have been developed for binary fluid mixtures of incompressible viscous fluids of possibly different densities and viscosities. One is quasi-incompressible, while the other is incompressible. For the same binary fluid mixture of two incompressible viscous fluid components, which one is more appropriate? To answer this question, we conduct a comparative study in this paper. First, we visit their derivation, conservation and energy dissipation properties and show that the quasi-incompressible model conserves both mass and linear momentum, while the incompressible one does not. We then show that the quasi-incompressible model is sensitive to the density deviation of the fluid components, while the incompressible model is not in a linear stability analysis. Second, we conduct a numerical investigation on coarsening or coalescent dynamics of protuberances using the two models. We find that they can predict quite different transient dynamics depending on the initial conditions and the density difference although they predict essentially the same quasi-steady results in some cases. This study thus cast a doubt on the applicability of the incompressible model to describe dynamics of binary mixtures of two incompressible viscous fluids especially when the two fluid components have a large density deviation.

Exact time-dependent nonlinear dispersive wave solutions in compressible magnetized plasmas exhibiting collapse.

PubMed

Chakrabarti, Nikhil; Maity, Chandan; Schamel, Hans

2011-04-08

Compressional waves in a magnetized plasma of arbitrary resistivity are treated with the lagrangian fluid approach. An exact nonlinear solution with a nontrivial space and time dependence is obtained with boundary conditions as in Harris' current sheet. The solution shows competition among hydrodynamic convection, magnetic field diffusion, and dispersion. This results in a collapse of density and the magnetic field in the absence of dispersion. The dispersion effects arrest the collapse of density but not of the magnetic field. A possible application is in the early stage of magnetic star formation.

A new hydrodynamic analysis of double layers

NASA Technical Reports Server (NTRS)

Hora, Heinrich

1987-01-01

A genuine two-fluid model of plasmas with collisions permits the calculation of dynamic (not necessarily static) electric fields and double layers inside of plasmas including oscillations and damping. For the first time a macroscopic model for coupling of electromagnetic and Langmuir waves was achieved with realistic damping. Starting points were laser-produced plasmas showing very high dynamic electric fields in nonlinear force-produced cavitous and inverted double layers in agreement with experiments. Applications for any inhomogeneous plasma as in laboratory or in astrophysical plasmas can then be followed up by a transparent hydrodynamic description. Results are the rotation of plasmas in magnetic fields and a new second harmonic resonance, explanation of the measured inverted double layers, explanation of the observed density-independent, second harmonics emission from laser-produced plasmas, and a laser acceleration scheme by the very high fields of the double layers.

Optical Electronic Bragg Reflection Sensor System with Hydrodynamic Flow Applications

NASA Technical Reports Server (NTRS)

Lyons, D. R.

2003-01-01

This project, as described in the following report, involved design and fabrication of fiber optic sensors for the detection and measurement of dynamic fluid density variations. These devices are created using UV (ultraviolet) ablation and generally modified transverse holographic fiber grating techniques. The resulting phase gratings created on or immediately underneath the flat portion of D-shaped optical waveguides are characterized as evanescent field sensing devices. The primary applications include the sensor portion of a real-time localized or distributed measurement system for hydrodynamic flow, fluid density measurements, and phase change phenomena. Several design modifications were implemented in an attempt to accomplish the tasks specified in our original proposal. In addition, we have established key collaborative relationships with numerous people and institutions.

Hydrodynamic Instabilities in High-Energy-Density Settings

NASA Astrophysics Data System (ADS)

Smalyuk, Vladimir

2016-10-01

Our understanding of hydrodynamic instabilities, such as the Rayleigh-Taylor (RT), Richtmyer-Meshkov (RM), and Kelvin-Helmholtz (KH) instabilities, in high-energy-density (HED) settings over past two decades has progressed enormously. The range of conditions where hydrodynamic instabilities are experimentally observed now includes direct and indirect drive inertial confinement fusion (ICF) where surprises continue to emerge, linear and nonlinear regimes, classical interfaces vs. stabilized ablation fronts, tenuous ideal plasmas vs. high density Fermi degenerate plasmas, bulk fluid interpenetration vs. mixing down to the atomic level, in the presence of magnetic fields and/or intense radiation, and in solid state plastic flow at high pressures and strain rates. Regimes in ICF can involve extreme conditions of matter with temperatures up to kilovolts, densities of a thousand times solid densities, and time scales of nanoseconds. On the other hand, scaled conditions can be generated that map to exploding stars (supernovae) with length and time scales of millions of kilometers and hours to days or even years of instability evolution, planetary formation dynamics involving solid-state plastic flow which severely modifies the RT growth and continues to challenge reliable theoretical descriptions. This review will look broadly at progress in probing and understanding hydrodynamic instabilities in these very diverse HED settings, and then will examine a few cases in more depth to illustrate the detailed science involved. Experimental results on large-scale HED facilities such as the Omega, Nike, Gekko, and Shenguang lasers will be reviewed and the latest developments at the National Ignition Facility (NIF) and Z machine will be covered. Finally, current overarching questions and challenges will be summarized to motivate research directions for future. This work was performed under the auspices of the U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344.

Improved locality of the phase-field lattice-Boltzmann model for immiscible fluids at high density ratios

NASA Astrophysics Data System (ADS)

Fakhari, Abbas; Mitchell, Travis; Leonardi, Christopher; Bolster, Diogo

2017-11-01

Based on phase-field theory, we introduce a robust lattice-Boltzmann equation for modeling immiscible multiphase flows at large density and viscosity contrasts. Our approach is built by modifying the method proposed by Zu and He [Phys. Rev. E 87, 043301 (2013), 10.1103/PhysRevE.87.043301] in such a way as to improve efficiency and numerical stability. In particular, we employ a different interface-tracking equation based on the so-called conservative phase-field model, a simplified equilibrium distribution that decouples pressure and velocity calculations, and a local scheme based on the hydrodynamic distribution functions for calculation of the stress tensor. In addition to two distribution functions for interface tracking and recovery of hydrodynamic properties, the only nonlocal variable in the proposed model is the phase field. Moreover, within our framework there is no need to use biased or mixed difference stencils for numerical stability and accuracy at high density ratios. This not only simplifies the implementation and efficiency of the model, but also leads to a model that is better suited to parallel implementation on distributed-memory machines. Several benchmark cases are considered to assess the efficacy of the proposed model, including the layered Poiseuille flow in a rectangular channel, Rayleigh-Taylor instability, and the rise of a Taylor bubble in a duct. The numerical results are in good agreement with available numerical and experimental data.

Energy density and energy flow of surface waves in a strongly magnetized graphene

NASA Astrophysics Data System (ADS)

Moradi, Afshin

2018-01-01

General expressions for the energy density and energy flow of plasmonic waves in a two-dimensional massless electron gas (as a simple model of graphene) are obtained by means of the linearized magneto-hydrodynamic model and classical electromagnetic theory when a strong external magnetic field perpendicular to the system is present. Also, analytical expressions for the energy velocity, wave polarization, wave impedance, transverse and longitudinal field strength functions, and attenuation length of surface magneto-plasmon-polariton waves are derived, and numerical results are prepared.

Fully dynamical simulation of central nuclear collisions.

PubMed

van der Schee, Wilke; Romatschke, Paul; Pratt, Scott

2013-11-27

We present a fully dynamical simulation of central nuclear collisions around midrapidity at LHC energies. Unlike previous treatments, we simulate all phases of the collision, including the equilibration of the system. For the simulation, we use numerical relativity solutions to anti-de Sitter space/conformal field theory for the preequilibrium stage, viscous hydrodynamics for the plasma equilibrium stage, and kinetic theory for the low-density hadronic stage. Our preequilibrium stage provides initial conditions for hydrodynamics, resulting in sizable radial flow. The resulting light particle spectra reproduce the measurements from the ALICE experiment at all transverse momenta.

Experimental Observation of Thin-shell Instability in a Collisionless Plasma

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

Ahmed, H.; Doria, D.; Sarri, G.

We report on the experimental observation of the instability of a plasma shell, which formed during the expansion of a laser-ablated plasma into a rarefied ambient medium. By means of a proton radiography technique, the evolution of the instability is temporally and spatially resolved on a timescale much shorter than the hydrodynamic one. The density of the thin shell exceeds that of the surrounding plasma, which lets electrons diffuse outward. An ambipolar electric field grows on both sides of the thin shell that is antiparallel to the density gradient. Ripples in the thin shell result in a spatially varying balancemore » between the thermal pressure force mediated by this field and the ram pressure force that is exerted on it by the inflowing plasma. This mismatch amplifies the ripples by the same mechanism that drives the hydrodynamic nonlinear thin-shell instability (NTSI). Our results thus constitute the first experimental verification that the NTSI can develop in colliding flows.« less

Experimental Observation of Thin-shell Instability in a Collisionless Plasma

NASA Astrophysics Data System (ADS)

Ahmed, H.; Doria, D.; Dieckmann, M. E.; Sarri, G.; Romagnani, L.; Bret, A.; Cerchez, M.; Giesecke, A. L.; Ianni, E.; Kar, S.; Notley, M.; Prasad, R.; Quinn, K.; Willi, O.; Borghesi, M.

2017-01-01

We report on the experimental observation of the instability of a plasma shell, which formed during the expansion of a laser-ablated plasma into a rarefied ambient medium. By means of a proton radiography technique, the evolution of the instability is temporally and spatially resolved on a timescale much shorter than the hydrodynamic one. The density of the thin shell exceeds that of the surrounding plasma, which lets electrons diffuse outward. An ambipolar electric field grows on both sides of the thin shell that is antiparallel to the density gradient. Ripples in the thin shell result in a spatially varying balance between the thermal pressure force mediated by this field and the ram pressure force that is exerted on it by the inflowing plasma. This mismatch amplifies the ripples by the same mechanism that drives the hydrodynamic nonlinear thin-shell instability (NTSI). Our results thus constitute the first experimental verification that the NTSI can develop in colliding flows.

Fluctuations and instabilities of a holographic metal

NASA Astrophysics Data System (ADS)

Jokela, Niko; Järvinen, Matti; Lippert, Matthew

2013-02-01

We analyze the quasinormal modes of the D2-D8' model of 2+1-dimensional, strongly-coupled, charged fermions in a background magnetic field and at non-zero density. The model is known to include a quantum Hall phase with integer filling fraction. As expected, we find a hydrodynamical diffusion mode at small momentum and the nonzero-temperature holographic zero sound, which becomes massive above a critical magnetic field. We confirm the previously-known thermodynamic instability. In addition, we discover an instability at low temperature, large mass, and in a charge density and magnetic field range near the quantum Hall phase to an inhomogeneous striped phase.

Phase-field-based lattice Boltzmann model for incompressible binary fluid systems with density and viscosity contrasts.

PubMed

Zu, Y Q; He, S

2013-04-01

A lattice Boltzmann model (LBM) is proposed based on the phase-field theory to simulate incompressible binary fluids with density and viscosity contrasts. Unlike many existing diffuse interface models which are limited to density matched binary fluids, the proposed model is capable of dealing with binary fluids with moderate density ratios. A new strategy for projecting the phase field to the viscosity field is proposed on the basis of the continuity of viscosity flux. The new LBM utilizes two lattice Boltzmann equations (LBEs): one for the interface tracking and the other for solving the hydrodynamic properties. The LBE for interface tracking can recover the Chan-Hilliard equation without any additional terms; while the LBE for hydrodynamic properties can recover the exact form of the divergence-free incompressible Navier-Stokes equations avoiding spurious interfacial forces. A series of 2D and 3D benchmark tests have been conducted for validation, which include a rigid-body rotation, stationary and moving droplets, a spinodal decomposition, a buoyancy-driven bubbly flow, a layered Poiseuille flow, and the Rayleigh-Taylor instability. It is shown that the proposed method can track the interface with high accuracy and stability and can significantly and systematically reduce the parasitic current across the interface. Comparisons with momentum-based models indicate that the newly proposed velocity-based model can better satisfy the incompressible condition in the flow fields, and eliminate or reduce the velocity fluctuations in the higher-pressure-gradient region and, therefore, achieve a better numerical stability. In addition, the test of a layered Poiseuille flow demonstrates that the proposed scheme for mixture viscosity performs significantly better than the traditional mixture viscosity methods.

Radiation hydrodynamics of triggered star formation: the effect of the diffuse radiation field

NASA Astrophysics Data System (ADS)

Haworth, Thomas J.; Harries, Tim J.

2012-02-01

We investigate the effect of including diffuse field radiation when modelling the radiatively driven implosion of a Bonnor-Ebert sphere (BES). Radiation-hydrodynamical calculations are performed by using operator splitting to combine Monte Carlo photoionization with grid-based Eulerian hydrodynamics that includes self-gravity. It is found that the diffuse field has a significant effect on the nature of radiatively driven collapse which is strongly coupled to the strength of the driving shock that is established before impacting the BES. This can result in either slower or more rapid star formation than expected using the on-the-spot approximation depending on the distance of the BES from the source object. As well as directly compressing the BES, stronger shocks increase the thickness and density in the shell of accumulated material, which leads to short, strong, photoevaporative ejections that reinforce the compression whenever it slows. This happens particularly effectively when the diffuse field is included as rocket motion is induced over a larger area of the shell surface. The formation and evolution of 'elephant trunks' via instability is also found to vary significantly when the diffuse field is included. Since the perturbations that seed instabilities are smeared out elephant trunks form less readily and, once formed, are exposed to enhanced thermal compression.

Thermal chiral vortical and magnetic waves: New excitation modes in chiral fluids

DOE PAGES

Kalaydzhyan, Tigran; Murchikova, Elena

2017-03-24

In certain circumstances, chiral (parity-violating) medium can be described hydrodynamically as a chiral fluid with microscopic quantum anomalies. Possible examples of such systems include strongly coupled quark–gluon plasma, liquid helium 3He-A, neutron stars and the Early Universe. Here, we study first-order hy-drodynamics of a chiral fluid on a vortex background and in an external magnetic field. We show that there are two previously undiscovered modes describing heat waves propagating along the vortex and magnetic field. We call them the Thermal Chiral Vortical Wave and Thermal Chiral Magnetic Wave. We also identify known gapless excitations of density (chiral vortical and chiralmore » magnetic waves) and transverse velocity (chiral Alfvén wave). We also demonstrate that the velocity of the chiral vortical wave is zero, when the full hydrodynamic framework is applied, and hence the wave is absent and the excitation reduces to the charge diffusion mode. We also comment on the frame-dependent contributions to the obtained propagation velocities.« less

The shock/shear platform for planar radiation-hydrodynamics experiments on the National Ignition Facility

DOE PAGES

Doss, F. W.; Kline, J. L.; Flippo, K. A.; ...

2015-04-17

An indirectly-driven shock tube experiment fielded on the National Ignition Facility (NIF) was used to create a high-energy-density hydrodynamics platform at unprecedented scale. Scaling up a shear-induced mixing experiment previously fielded at OMEGA, the NIF shear platform drives 130 μm/ns shocks into a CH foam-filled shock tube (~ 60 mg/cc) with interior dimensions of 1.5 mm diameter and 5 mm length. The pulse-shaping capabilities of the NIF are used to extend the drive for >10 ns, and the large interior tube volumes are used to isolate physics-altering edge effects from the region of interest. The scaling of the experiment tomore » the NIF allows for considerable improvement in maximum driving time of hydrodynamics, in fidelity of physics under examination, and in diagnostic clarity. Details of the experimental platform and post-shot simulations used in the analysis of the platform-qualifying data are presented. Hydrodynamic scaling is used to compare shear data from OMEGA with that from NIF, suggesting a possible change in the dimensionality of the instability at late times from one platform to the other.« less

An updated Lagrangian discontinuous Galerkin hydrodynamic method for gas dynamics

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

Wu, Tong; Shashkov, Mikhail Jurievich; Morgan, Nathaniel Ray

Here, we present a new Lagrangian discontinuous Galerkin (DG) hydrodynamic method for gas dynamics. The new method evolves conserved unknowns in the current configuration, which obviates the Jacobi matrix that maps the element in a reference coordinate system or the initial coordinate system to the current configuration. The density, momentum, and total energy (ρ, ρu, E) are approximated with conservative higher-order Taylor expansions over the element and are limited toward a piecewise constant field near discontinuities using a limiter. Two new limiting methods are presented for enforcing the bounds on the primitive variables of density, velocity, and specific internal energymore » (ρ, u, e). The nodal velocity, and the corresponding forces, are calculated by solving an approximate Riemann problem at the element nodes. An explicit second-order method is used to temporally advance the solution. This new Lagrangian DG hydrodynamic method conserves mass, momentum, and total energy. 1D Cartesian coordinates test problem results are presented to demonstrate the accuracy and convergence order of the new DG method with the new limiters.« less

An updated Lagrangian discontinuous Galerkin hydrodynamic method for gas dynamics

DOE PAGES

Wu, Tong; Shashkov, Mikhail Jurievich; Morgan, Nathaniel Ray; ...

2018-04-09

Here, we present a new Lagrangian discontinuous Galerkin (DG) hydrodynamic method for gas dynamics. The new method evolves conserved unknowns in the current configuration, which obviates the Jacobi matrix that maps the element in a reference coordinate system or the initial coordinate system to the current configuration. The density, momentum, and total energy (ρ, ρu, E) are approximated with conservative higher-order Taylor expansions over the element and are limited toward a piecewise constant field near discontinuities using a limiter. Two new limiting methods are presented for enforcing the bounds on the primitive variables of density, velocity, and specific internal energymore » (ρ, u, e). The nodal velocity, and the corresponding forces, are calculated by solving an approximate Riemann problem at the element nodes. An explicit second-order method is used to temporally advance the solution. This new Lagrangian DG hydrodynamic method conserves mass, momentum, and total energy. 1D Cartesian coordinates test problem results are presented to demonstrate the accuracy and convergence order of the new DG method with the new limiters.« less

Dielectric response in Bloch’s hydrodynamic model of an electron-ion plasma

NASA Astrophysics Data System (ADS)

Ishikawa, K.; Felderhof, B. U.

The linear response of an electron-ion plasma to an applied oscillating electric field is studied within the framework of Bloch’s classical hydrodynamic model. The ions are assumed to be fixed in space and distributed according to a known probability distribution. The linearized equations of motion for electron density and flow velocity are studied with the aid of a multiple scattering analysis and cluster expansion. This allows systematic reduction of the many-ion problem to a composition of few-ion problems, and shows how the longitudinal dielectric response function can in principle be calculated.

Hydrodynamics of Turning Flocks.

PubMed

Yang, Xingbo; Marchetti, M Cristina

2015-12-18

We present a hydrodynamic model of flocking that generalizes the familiar Toner-Tu equations to incorporate turning inertia of well-polarized flocks. The continuum equations controlled by only two dimensionless parameters, orientational inertia and alignment strength, are derived by coarse-graining the inertial spin model recently proposed by Cavagna et al. The interplay between orientational inertia and bend elasticity of the flock yields anisotropic spin waves that mediate the propagation of turning information throughout the flock. The coupling between spin-current density to the local vorticity field through a nonlinear friction gives rise to a hydrodynamic mode with angular-dependent propagation speed at long wavelengths. This mode becomes unstable as a result of the growth of bend and splay deformations augmented by the spin wave, signaling the transition to complex spatiotemporal patterns of continuously turning and swirling flocks.

Biological characterization of the skin of shortfin mako shark Isurus oxyrinchus and preliminary study of the hydrodynamic behaviour through computational fluid dynamics.

PubMed

Díez, G; Soto, M; Blanco, J M

2015-07-01

This study characterized the morphology, density and orientation of the dermal denticles along the body of a shortfin mako shark Isurus oxyrinchus and identified the hydrodynamic parameters of its body through a computational fluid-dynamics model. The study showed a great variability in the morphology, size, shape, orientation and density of dermal denticles along the body of I. oxyrinchus. There was a significant higher density in dorsal and ventral areas of the body and their highest angular deviations were found in the lower part of the mouth and in the areas between the pre-caudal pit and the second dorsal and pelvic fins. A detailed three-dimensional geometry from a scanned body of a shark was carried out to evaluate the hydrodynamic properties such as drag coefficient, lift coefficient and superficial (skin) friction coefficient of the skin together with flow velocity field, according to different roughness coefficients simulating the effect of the dermal denticles. This preliminary approach contributed to detailed information of the denticle interactions. As the height of the denticles was increased, flow velocity and the effect of lift decreased whereas drag increased. The highest peaks of skin friction coefficient were observed around the pectoral fins. © 2015 The Fisheries Society of the British Isles.

The Richtmyer-Meshkov Instability on a Circular Interface in Magnetohydrodynamics

NASA Astrophysics Data System (ADS)

Black, Wolfgang; Maxon, W. Curtis; Denissen, Nicholas; McFarland, Jacob

2017-11-01

Hydrodynamic instabilities (HI) are ubiquitous in high energy density (HED) applications such as astrophysics, thermonuclear weapons, and inertial fusion. In these systems, fluid mixing is encouraged by the HI which can reduce the energy yield and eventually drive the system to equilibrium. The Richtmyer-Meshkov (RM) instability is one such HI and is created when a perturbed interface between a density gradient is impulsively accelerated. The physics can be complicated one step further by the inclusion of Magnetohydrodynamics (MHD), where HED systems experience the effects of magnetic and electric fields. These systems provide unique challenges and as such can be used to validate hydrodynamic codes capable of predicting HI. The work presented here will outline efforts to study the RMI in MHD for a circular interface utilizing the hydrocode FLAG, developed at Los Alamos National Laboratory.

Hydrodynamic electronic fluid instability in GaAs MESFETs at terahertz frequencies

NASA Astrophysics Data System (ADS)

Li, Kang; Hao, Yue; Jin, Xiaoqi; Lu, Wu

2018-01-01

III-V compound semiconductor field effect transistors (FETs) are potential candidates as solid state THz emitters and detectors due to plasma wave instability in these devices. Using a 2D hydrodynamic model, here we present the numerical studies of electron fluid instability in a FET structure. The model is implemented in a GaAs MESFET structure with a gate length of 0.2 µm as a testbed by taking into account the non-equilibrium transport and multi-valley non-parabolicity energy bands. The results show that the electronic density instability in the channel can produce stable periodic oscillations at THz frequencies. Along with stable oscillations, negative differential resistance in output characteristics is observed. The THz emission energy density increases monotonically with the drain bias. The emission frequency of electron density oscillations can be tuned by both gate and drain biases. The results suggest that III-V FETs can be a kind of versatile THz devices with good tunability on both radiative power and emission frequency.

Magnetic Fields and Multiple Protostar Formation

NASA Astrophysics Data System (ADS)

Boss, A. P.

2001-12-01

Recent observations of star-forming regions suggest that binary and multiple young stars are the rule rather than the exception, and implicate fragmentation as the likely mechanism for their formation. Most numerical hydrodynamical calculations of fragmentation have neglected the possibly deleterious effects of magnetic fields, in spite of ample evidence for the importance of magnetic support of pre-collapse clouds. We present here the first numerical hydrodynamical survey of the full effects of magnetic fields on the collapse and fragmentation of dense cloud cores. The models are calculated with a three dimensional, finite differences code which solves the equations of hydrodynamics, gravitation, and radiative transfer in the Eddington and diffusion approximations. Magnetic field effects are included through two simple approximations: magnetic pressure is added to the gas pressure, and magnetic tension is approximated by gravity dilution once collapse is well underway. Ambipolar diffusion of the magnetic field leading to cloud collapse is treated approximately as well. Models are calculated for a variety of initial cloud density profiles, shapes, and rotation rates. We find that in spite of the inclusion of magnetic field effects, dense cloud cores are capable of fragmenting into binary and multiple protostar systems. Initially prolate clouds tend to fragment into binary protostars, while initially oblate clouds tend to fragment into multiple protostar systems containing a small number (of order four) of fragments. The latter are likely to be subject to rapid orbital evolution, with close encounters possibly leading to the ejection of fragments. Contrary to expectation, magnetic tension effects appear to enhance fragmentation, allowing lower mass fragments to form than would otherwise be possible, because magnetic tension helps to prevent a central density singularity from forming and producing a dominant single object. Magnetically-supported dense cloud cores thus seem to be capable of collapsing and fragmenting into sufficient numbers of binary and multiple protostar systems to be compatible with observations of the relative rarity of single protostars. This work was partially supported by NSF grants AST-9983530 and MRI-9976645.

Collapse and Fragmentation of Molecular Cloud Cores. VII. Magnetic Fields and Multiple Protostar Formation

NASA Astrophysics Data System (ADS)

Boss, Alan P.

2002-04-01

Recent observations of star-forming regions suggest that binary and multiple young stars are the rule rather than the exception and implicate fragmentation as the likely mechanism for their formation. Most numerical hydrodynamic calculations of fragmentation have neglected the possibly deleterious effects of magnetic fields, despite ample evidence for the importance of magnetic support of precollapse clouds. We present here the first numerical hydrodynamic survey of the collapse and fragmentation of initially magnetically supported clouds that takes into account several magnetic field effects in an approximate manner. The models are calculated with a three-dimensional, finite differences code that solves the equations of hydrodynamics, gravitation, and radiative transfer in the Eddington and diffusion approximations. Magnetic field effects are included through two simple approximations: magnetic pressure is added to the gas pressure, and magnetic tension is approximated by gravity dilution once collapse is well underway. Ambipolar diffusion of the magnetic field leading to cloud collapse is treated approximately as well. Models are calculated for a variety of initial cloud density profiles, shapes, and rotation rates. We find that in spite of the inclusion of magnetic field effects, dense cloud cores are capable of fragmenting into binary and multiple protostar systems. Initially prolate clouds tend to fragment into binary protostars, while initially oblate clouds tend to fragment into multiple protostar systems containing a small number (of the order of 4) of fragments. The latter are likely to be subject to rapid orbital evolution, with close encounters possibly leading to the ejection of fragments. Contrary to expectation, magnetic tension effects appear to enhance fragmentation, allowing lower mass fragments to form than would otherwise be possible, because magnetic tension helps to prevent a central density singularity from forming and producing a dominant single object. Magnetically supported dense cloud cores thus seem to be capable of collapsing and fragmenting into sufficient numbers of binary and multiple protostar systems to be compatible with observations of the relative rarity of single protostars.

Harmonic generation in magnetized quantum plasma

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

Kumar, Punit; Singh, Abhisek Kumar; Singh, Shiv

2016-05-06

A study of second harmonic generation by propagation of a linearly polarized electromagnetic wave through homogeneous high density quantum plasma in the presence of transverse magnetic field. The nonlinear current density and dispersion relations for the fundamental and second harmonic frequencies have been obtained using the recently developed quantum hydrodynamic (QHD) model. The effect of quantum Bohm potential, Fermi pressure and the electron spin have been taken into account. The second harmonic is found to be less dispersed than the first.

Collective motion of squirmers in a quasi-2D geometry

NASA Astrophysics Data System (ADS)

Zöttl, Andreas; Stark, Holger

2013-03-01

Microorganisms like bacteria, algae or spermatozoa typically move in an aqueous environment where they interact via hydrodynamic flow fields. Recent experiments studied the collective motion of dense suspensions of bacteria where swarming and large-scale turbulence emerged. Moreover, spherical artificial microswimmers, so-called squirmers, have been constructed and studied in a quasi-2D geometry. Here we present a numerical study of the collective dynamics of squirmers confined in quasi-2D between two parallel walls. Because of their spherical shape the reorientation of squirmers is solely due to noise and hydrodynamic interactions via induced flow fields. This is in contrast to elongated swimmers like bacteria which locally align due to steric interactions. We study the collective motion of pushers, pullers and potential swimmers at different densities. At small densities the squirmers are oriented parallel to the walls and pairwise collisions determine the reorientation rate. In dense suspensions rotational diffusion is greatly enhanced and pushers, in particular, tend to orient perpendicular to the walls. This effects the dynamics of the emerging clusters. In very dense suspensions we observe active jamming and long-lived crystalline structures.

Simulating nanostorm heating in coronal loops using hydrodynamics and non-thermal particle evolution

NASA Astrophysics Data System (ADS)

Migliore, Christina; Winter, Henry; Murphy, Nicholas

2018-01-01

The solar corona is filled with loop-like structures that appear bright against the background when observed in the extreme ultraviolet (EUV). These loops have several remarkable properties that are not yet well understood. Warm loops (∼ 1 MK) appear to be ∼ 2 ‑ 9 times as dense at their apex as the predictions of hydrostatic atmosphere models. These loops also appear to be of constant cross-section despite the fact that the field strength in a potential magnetic field should decrease in the corona, causing the loops to expand. It is not clear why many active region loops appear to be of constant cross-section. Theories range from an internal twist of the magnetic field to observational effects. In this work we simulate active region loops heated by nanoflare storms using a dipolar magnetic field. We calculate the hydrodynamic properties for each loop using advanced hydrodynamics codes to simulate the corona and chromospheric response and basic dipole models to represent the magnetic fields of the loops. We show that even modest variations of the magnetic field strength along the loop can lead to drastic changes in the density profiles of active region loops, and they can also explain the overpressure at the apex of these loops. Synthetic AIA images of each loop are made to show the observable consequences of varying magnetic field strengths along the loop’s axis of symmetry. We also show how this work can lead to improved modeling of larger solar and stellar flares.

Front dynamics and entanglement in the XXZ chain with a gradient

NASA Astrophysics Data System (ADS)

Eisler, Viktor; Bauernfeind, Daniel

2017-11-01

We consider the XXZ spin chain with a magnetic field gradient and study the profiles of the magnetization as well as the entanglement entropy. For a slowly varying field, it is shown that, by means of a local density approximation, the ground-state magnetization profile can be obtained with standard Bethe ansatz techniques. Furthermore, it is argued that the low-energy description of the theory is given by a Luttinger liquid with slowly varying parameters. This allows us to obtain a very good approximation of the entanglement profile using a recently introduced technique of conformal field theory in curved spacetime. Finally, the front dynamics is also studied after the gradient field has been switched off, following arguments of generalized hydrodynamics for integrable systems. While for the XX chain the hydrodynamic solution can be found analytically, the XXZ case appears to be more complicated and the magnetization profiles are recovered only around the edge of the front via an approximate numerical solution.

Nanoparticle Brownian motion and hydrodynamic interactions in the presence of flow fields

PubMed Central

Uma, B.; Swaminathan, T. N.; Radhakrishnan, R.; Eckmann, D. M.; Ayyaswamy, P. S.

2011-01-01

We consider the Brownian motion of a nanoparticle in an incompressible Newtonian fluid medium (quiescent or fully developed Poiseuille flow) with the fluctuating hydrodynamics approach. The formalism considers situations where both the Brownian motion and the hydrodynamic interactions are important. The flow results have been modified to account for compressibility effects. Different nanoparticle sizes and nearly neutrally buoyant particle densities are also considered. Tracked particles are initially located at various distances from the bounding wall to delineate wall effects. The results for thermal equilibrium are validated by comparing the predictions for the temperatures of the particle with those obtained from the equipartition theorem. The nature of the hydrodynamic interactions is verified by comparing the velocity autocorrelation functions and mean square displacements with analytical and experimental results where available. The equipartition theorem for a Brownian particle in Poiseuille flow is verified for a range of low Reynolds numbers. Numerical predictions of wall interactions with the particle in terms of particle diffusivities are consistent with results, where available. PMID:21918592

Anomalous hydrodynamics and normal fluids in rapidly rotating Bose-Einstein condensates.

PubMed

Bourne, A; Wilkin, N K; Gunn, J M F

2006-06-23

In rapidly rotating condensed Bose systems we show that there is a regime of anomalous hydrodynamics which coincides with the mean field quantum Hall regime. A consequence is the absence of a normal fluid in any conventional sense. However, even the superfluid hydrodynamics is not described by conventional Bernoulli and continuity equations. We show that there are constraints which connect spatial variations of density and phase and that the vortex positions are not the simplest description of the dynamics. We demonstrate, inter alia, a simple relation between vortices and surface waves. We show that the surface waves can emulate a "normal fluid," allowing dissipation by energy and angular momentum absorbtion from vortex motion in the trap. The time scale is sensitive to the initial configuration, which can lead to long-lived vortex patches--perhaps related to those observed at JILA.

Hydrodynamic description of spin Calogero-Sutherland model

NASA Astrophysics Data System (ADS)

Abanov, Alexander; Kulkarni, Manas; Franchini, Fabio

2009-03-01

We study a non-linear collective field theory for an integrable spin-Calogero-Sutherland model. The hydrodynamic description of this SU(2) model in terms of charge density, charge velocity and spin currents is used to study non-perturbative solutions (solitons) and examine their correspondence with known quantum numbers of elementary excitations [1]. A conventional linear bosonization or harmonic approximation is not sufficient to describe, for example, the physics of spin-charge (non)separation. Therefore, we need this new collective bosonic field description that captures the effects of the band curvature. In the strong coupling limit [2] this model reduces to integrable SU(2) Haldane-Shastry model. We study a non-linear coupling of left and right spin currents which form a Kac-Moody algebra. Our quantum hydrodynamic description for the spin case is an extension for the one found in the spinless version in [3].[3pt] [1] Y. Kato,T. Yamamoto, and M. Arikawa, J. Phys. Soc. Jpn. 66, 1954-1961 (1997).[0pt] [2] A. Polychronakos, Phys Rev Lett. 70,2329-2331(1993).[0pt] [3] A.G.Abanov and P.B. Wiegmann, Phys Rev Lett 95, 076402(2005)

SPAMCART: a code for smoothed particle Monte Carlo radiative transfer

NASA Astrophysics Data System (ADS)

Lomax, O.; Whitworth, A. P.

2016-10-01

We present a code for generating synthetic spectral energy distributions and intensity maps from smoothed particle hydrodynamics simulation snapshots. The code is based on the Lucy Monte Carlo radiative transfer method, I.e. it follows discrete luminosity packets as they propagate through a density field, and then uses their trajectories to compute the radiative equilibrium temperature of the ambient dust. The sources can be extended and/or embedded, and discrete and/or diffuse. The density is not mapped on to a grid, and therefore the calculation is performed at exactly the same resolution as the hydrodynamics. We present two example calculations using this method. First, we demonstrate that the code strictly adheres to Kirchhoff's law of radiation. Secondly, we present synthetic intensity maps and spectra of an embedded protostellar multiple system. The algorithm uses data structures that are already constructed for other purposes in modern particle codes. It is therefore relatively simple to implement.

Effective field theory of dissipative fluids

DOE PAGES

Crossley, Michael; Glorioso, Paolo; Liu, Hong

2017-09-20

We develop an effctive fi eld theory for dissipative fluids which governs the dynamics of long-lived gapless modes associated with conserved quantities. The resulting theory gives a path integral formulation of fluctuating hydrodynamics which systematically incorporates nonlinear interactions of noises. The dynamical variables are mappings between a "fluid spacetime" and the physical spacetime and an essential aspect of our formulation is to identify the appropriate symmetries in the fluid spacetime. The theory applies to nonlinear disturbances around a general density matrix. For a thermal density matrix, we require an additional Z2 symmetry, to which we refer as the local KMSmore » condition. This leads to the standard constraints of hydrodynamics, as well as a nonlinear generalization of the Onsager relations. It also leads to an emergent supersymmetry in the classical statistical regime, and a higher derivative deformation of supersymmetry in the full quantum regime.« less

Effective field theory of dissipative fluids

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

Crossley, Michael; Glorioso, Paolo; Liu, Hong

We develop an effctive fi eld theory for dissipative fluids which governs the dynamics of long-lived gapless modes associated with conserved quantities. The resulting theory gives a path integral formulation of fluctuating hydrodynamics which systematically incorporates nonlinear interactions of noises. The dynamical variables are mappings between a "fluid spacetime" and the physical spacetime and an essential aspect of our formulation is to identify the appropriate symmetries in the fluid spacetime. The theory applies to nonlinear disturbances around a general density matrix. For a thermal density matrix, we require an additional Z2 symmetry, to which we refer as the local KMSmore » condition. This leads to the standard constraints of hydrodynamics, as well as a nonlinear generalization of the Onsager relations. It also leads to an emergent supersymmetry in the classical statistical regime, and a higher derivative deformation of supersymmetry in the full quantum regime.« less

Comparison of hydrodynamic and semi-kinetic treatments for plasma flow along closed field lines

NASA Technical Reports Server (NTRS)

Singh, Nagendra; Wilson, G. R.; Horwitz, J. L.

1993-01-01

Hydrodynamic and semi-kinetic treatments of plasma flow along closed geomagnetic field lines are compared. The hydrodynamic treatment is based on a simplified 16-moment set of transport equations as the equations for the heat flows are not solved; the heat flows are treated heuristically. The semi-kinetic treatment is based on a particle code. The comparison deals with the distributions of the plasma density, flow velocity, and parallel and perpendicular temperatures as obtained from the two treatments during the various stages of the flow. In the kinetic treatment, the appropriate boundary condition is the prescription of the velocity distribution functions for the particles entering the flux tubes at the ionospheric boundaries; those particles leaving the system are determined by the processes occurring in the flux tube. The prescribed distributions are half-Maxwellian with temperature T(sub 0) and density n(sub 0). In the hydrodynamic model, the prescribed boundary conditions are on density (n(sub 0)), flow velocity (V(sub 0)) and temperature (T(sub 0). It was found that results from the hydrodynamic treatment critically depend on V(sub 0); for early stages of the flow this treatment yields results in good agreement with those from the kinetic treatment, when V(sub 0) = square root of (kT(sub 0)/2 (pi)m), which is the average velocity of particles moving in a given direction for a Maxwellian distribution. During this early stage, the flows developing form the conjugate ionospheres show some distinct transitions. For the first hour or so, the flows are highly supersonic and penetrate deep into the opposite hemispheres, and both hydrodynamics and kinetic treatments yield almost similar features. It is found that during this period heatflow effects are negligibly small. When a flow penetrates deep into the opposite hemisphere, the kinetic treatment predicts reflection and setting up of counterstreaming. In contrast, the hydrodynamic treatment yields a shock in the flow. The reasons for this difference in the two treatments is discussed, showing that in view of the relatively warm ions, the coupling of ion beams and the consequent shock formation in the offequatorial region are not likely due to the enhancements in the beam temperatures. The counterstreaming in the kinetic treatment and the shock in the hydrodynamic treatment first advance upward to the equator and then downward to the ionospheric boundary from where the flow originated. The transit time for this advancement is found to be about 1 hour for the respective models. After 2 hours or so, both models predict that the flows from the ionospheric boundaries are generally subsonic with respect to the local ion-sound speed. At late stages of the flow, when a substantial fraction of ions entering the flux tube begin to return back in the kinetic treatment, the hydrodynamic treatment with the boundary condition V(sub 0) = square root of (kT(sub 0)/2(pi)m) yields an over-refilling, and the choice of V(sub 0) becomes uncertain.

Modeling an anode layer Hall thruster and its plume

NASA Astrophysics Data System (ADS)

Choi, Yongjun

This thesis consists of two parts: a study of the D55 Hall thruster channel using a hydrodynamic model; and particle simulations of plasma plume flow from the D55 Hall thruster. The first part of this thesis investigates the xenon plasma properties within the D55 thruster channel using a hydrodynamic model. The discharge voltage (V) and current (I) characteristic of the D55 Hall thruster are studied. The hydrodynamic model fails to accurately predict the V-I characteristics. This analysis shows that the model needs to be improved. Also, the hydrodynamic model is used to simulate the plasma flow within the D55 Hall thruster. This analysis is performed to investigate the plasma properties of the channel exit. It is found that the hydrodynamic model is very sensitive to initial conditions, and fails to simulate the complete domain of the D55 Hall thruster. However, the model successfully calculates the channel domain of the D55 Hall thruster. The results show that, at the thruster exit, the plasma density has a maximum value while the ion velocity has a minimum at the channel center. Also, the results show that the flow angle varies almost linearly across the exit plane and increases from the center to the walls. Finally, the hydrodynamic model results are used to estimate the plasma properties at the thruster nozzle exit. The second part of the thesis presents two dimensional axisymmetric simulations of xenon plasma plume flow fields from the D55 anode layer Hall thruster. A hybrid particle-fluid method is used for the simulations. The magnetic field near the Hall thruster exit is included in the calculation. The plasma properties obtained from the hydrodynamic model are used to determine boundary conditions for the simulations. In these simulations, the Boltzmann model and a detailed fluid model are used to compute the electron properties, the direct simulation Monte Carlo method models the collisions of heavy particles, and the Particle-In-Cell method models the transport of ions in an electric field. The accuracy of the simulation is assessed through comparison with various sets of measured data. It is found that a magnetic field significantly affects the profile of the plasma in the Detailed model. For instance, the plasma potential decreases more rapidly with distance from the thruster in the presence of a magnetic field. Results predicted by the Detailed model with the magnetic field are in better agreement with experimental data than those obtained with other models investigated.

On the fragmentation boundary in magnetized self-gravitating discs

NASA Astrophysics Data System (ADS)

Forgan, Duncan; Price, Daniel J.; Bonnell, Ian

2017-04-01

We investigate the role of magnetic fields in the fragmentation of self-gravitating discs using 3D global ideal magnetohydrodynamic simulations performed with the PHANTOM smoothed particle hydrodynamics code. For initially toroidal fields, we find two regimes. In the first, where the cooling time is greater than five times the dynamical time, magnetic fields reduce spiral density wave amplitudes, which in turn suppresses fragmentation. This is the case even if the magnetic pressure is only a 10th of the thermal pressure. The second regime occurs when the cooling time is sufficiently short that magnetic fields cannot halt fragmentation. We find that magnetized discs produce more massive fragments, due to both the additional pressure exerted by the magnetic field and the additional angular momentum transport induced by Maxwell stresses. The fragments are confined to a narrower range of initial semimajor axes than those in unmagnetized discs. The orbital eccentricity and inclination distributions of unmagnetized and magnetized disc fragments are similar. Our results suggest that the fragmentation boundary could be at cooling times a factor of 2 lower than predicted by purely hydrodynamical models.

Ion-temperature-gradient sensitivity of the hydrodynamic instability caused by shear in the magnetic-field-aligned plasma flow

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

Mikhailenko, V. V., E-mail: vladimir@pusan.ac.kr; Mikhailenko, V. S.; Faculty of Transportation Systems, Kharkiv National Automobile and Highway University, 61002 Kharkiv

2014-07-15

The cross-magnetic-field (i.e., perpendicular) profile of ion temperature and the perpendicular profile of the magnetic-field-aligned (parallel) plasma flow are sometimes inhomogeneous for space and laboratory plasma. Instability caused either by a gradient in the ion-temperature profile or by shear in the parallel flow has been discussed extensively in the literature. In this paper, (1) hydrodynamic plasma stability is investigated, (2) real and imaginary frequency are quantified over a range of the shear parameter, the normalized wavenumber, and the ratio of density-gradient and ion-temperature-gradient scale lengths, and (3) the role of inverse Landau damping is illustrated for the case of combinedmore » ion-temperature gradient and parallel-flow shear. We find that increasing the ion-temperature gradient reduces the instability threshold for the hydrodynamic parallel-flow shear instability, also known as the parallel Kelvin-Helmholtz instability or the D'Angelo instability. We also find that a kinetic instability arises from the coupled, reinforcing action of both free-energy sources. For the case of comparable electron and ion temperature, we illustrate analytically the transition of the D'Angelo instability to the kinetic instability as (a) the shear parameter, (b) the normalized wavenumber, and (c) the ratio of density-gradient and ion-temperature-gradient scale lengths are varied and we attribute the changes in stability to changes in the amount of inverse ion Landau damping. We show that near a normalized wavenumber k{sub ⊥}ρ{sub i} of order unity (i) the real and imaginary values of frequency become comparable and (ii) the imaginary frequency, i.e., the growth rate, peaks.« less

The Initial Flow of Classical Gluon Fields in Heavy Ion Collisions

NASA Astrophysics Data System (ADS)

Fries, Rainer J.; Chen, Guangyao

2015-03-01

Using analytic solutions of the Yang-Mills equations we calculate the initial flow of energy of the classical gluon field created in collisions of large nuclei at high energies. We find radial and elliptic flow which follows gradients in the initial energy density, similar to a simple hydrodynamic behavior. In addition we find a rapidity-odd transverse flow field which implies the presence of angular momentum and should lead to directed flow in final particle spectra. We trace those energy flow terms to transverse fields from the non-abelian generalization of Gauss' Law and Ampere's and Faraday's Laws.

Ordering dynamics of self-propelled particles in an inhomogeneous medium

NASA Astrophysics Data System (ADS)

Das, Rakesh; Mishra, Shradha; Puri, Sanjay

2018-02-01

Ordering dynamics of self-propelled particles in an inhomogeneous medium in two dimensions is studied. We write coarse-grained hydrodynamic equations of motion for density and polarisation fields in the presence of an external random disorder field, which is quenched in time. The strength of inhomogeneity is tuned from zero disorder (clean system) to large disorder. In the clean system, the polarisation field grows algebraically as LP ∼ t0.5 . The density field does not show clean power-law growth; however, it follows Lρ ∼ t0.8 approximately. In the inhomogeneous system, we find a disorder-dependent growth. For both the density and the polarisation, growth slows down with increasing strength of disorder. The polarisation shows a disorder-dependent power-law growth LP(t,Δ) ∼ t1/\\bar zP(Δ) for intermediate times. At late times, there is a crossover to logarithmic growth LP(t,Δ) ∼ (\\ln t)1/\\varphi , where φ is a disorder-independent exponent. Two-point correlation functions for the polarisation show dynamical scaling, but the density does not.

Anomalous Hydrodynamics and Normal Fluids in Rapidly Rotating Bose-Einstein Condensates

NASA Astrophysics Data System (ADS)

Bourne, A.; Wilkin, N. K.; Gunn, J. M. F.

2006-06-01

In rapidly rotating condensed Bose systems we show that there is a regime of anomalous hydrodynamics which coincides with the mean field quantum Hall regime. A consequence is the absence of a normal fluid in any conventional sense. However, even the superfluid hydrodynamics is not described by conventional Bernoulli and continuity equations. We show that there are constraints which connect spatial variations of density and phase and that the vortex positions are not the simplest description of the dynamics. We demonstrate, inter alia, a simple relation between vortices and surface waves. We show that the surface waves can emulate a “normal fluid,” allowing dissipation by energy and angular momentum absorbtion from vortex motion in the trap. The time scale is sensitive to the initial configuration, which can lead to long-lived vortex patches—perhaps related to those observed at JILA.

Model experiment of magnetic field amplification in laser-produced plasmas via the Richtmyer-Meshkov instability

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

Kuramitsu, Y., E-mail: yasu@ncu.edu.tw; Moritaka, T.; Ohnishi, N.

2016-03-15

A model experiment of magnetic field amplification (MFA) via the Richtmyer-Meshkov instability (RMI) in supernova remnants (SNRs) was performed using a high-power laser. In order to account for very-fast acceleration of cosmic rays observed in SNRs, it is considered that the magnetic field has to be amplified by orders of magnitude from its background level. A possible mechanism for the MFA in SNRs is stretching and mixing of the magnetic field via the RMI when shock waves pass through dense molecular clouds in interstellar media. In order to model the astrophysical phenomenon in laboratories, there are three necessary factors formore » the RMI to be operative: a shock wave, an external magnetic field, and density inhomogeneity. By irradiating a double-foil target with several laser beams with focal spot displacement under influence of an external magnetic field, shock waves were excited and passed through the density inhomogeneity. Radiative hydrodynamic simulations show that the RMI evolves as the density inhomogeneity is shocked, resulting in higher MFA.« less

The Enskog Equation for Confined Elastic Hard Spheres

NASA Astrophysics Data System (ADS)

Maynar, P.; García de Soria, M. I.; Brey, J. Javier

2018-03-01

A kinetic equation for a system of elastic hard spheres or disks confined by a hard wall of arbitrary shape is derived. It is a generalization of the modified Enskog equation in which the effects of the confinement are taken into account and it is supposed to be valid up to moderate densities. From the equation, balance equations for the hydrodynamic fields are derived, identifying the collisional transfer contributions to the pressure tensor and heat flux. A Lyapunov functional, H[f], is identified. For any solution of the kinetic equation, H decays monotonically in time until the system reaches the inhomogeneous equilibrium distribution, that is a Maxwellian distribution with a density field consistent with equilibrium statistical mechanics.

Study on antidiabetic activity of wheat and barley starch using asymmetrical flow field-flow fractionation coupled with multiangle light scattering.

PubMed

Dou, Haiyang; Zhou, Bing; Jang, Hae-Dong; Lee, Seungho

2014-05-02

The ability of asymmetrical flow field-flow fractionation (AF4) coupled online with multiangle light scattering (MALS) and refractive index detector (RI) (AF4-MALS-RI) for monitoring of change in molecular conformation of wheat and barley starch during germination process was evaluated. AF4 provides separation of starch molecules based on their hydrodynamic sizes, and MALS yields the molar mass and molecular size (radius of gyration, Rg). In vitro and in vivo anti-hyperglycemic effect of germinated wheat and barley was studied. The relationship between antidiabetic activity and molecular conformation was, for the first time, investigated. The ratio of Rg to the hydrodynamic radius (Rh) and the apparent density were proven to be important parameters as they offer an insight into molecular conformation. Results showed that, when geminated, the apparent density and the antidiabetic activity of barley were significantly increased, suggesting germination makes the molecules more compact which could contribute to enhancement of their antidiabetic activity. The information obtained by AF4-MALS-RI is valuable for understanding of germination mechanism, and thus for developing functional foods. Copyright © 2014 Elsevier B.V. All rights reserved.

Two-dimensional simulations of thermonuclear burn in ignition-scale inertial confinement fusion targets under compressed axial magnetic fields

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

Perkins, L. J.; Logan, B. G.; Zimmerman, G. B.

2013-07-15

We report for the first time on full 2-D radiation-hydrodynamic implosion simulations that explore the impact of highly compressed imposed magnetic fields on the ignition and burn of perturbed spherical implosions of ignition-scale cryogenic capsules. Using perturbations that highly convolute the cold fuel boundary of the hotspot and prevent ignition without applied fields, we impose initial axial seed fields of 20–100 T (potentially attainable using present experimental methods) that compress to greater than 4 × 10{sup 4} T (400 MG) under implosion, thereby relaxing hotspot areal densities and pressures required for ignition and propagating burn by ∼50%. The compressed fieldmore » is high enough to suppress transverse electron heat conduction, and to allow alphas to couple energy into the hotspot even when highly deformed by large low-mode amplitudes. This might permit the recovery of ignition, or at least significant alpha particle heating, in submarginal capsules that would otherwise fail because of adverse hydrodynamic instabilities.« less

Effective field theory of dissipative fluids (II): classical limit, dynamical KMS symmetry and entropy current

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

Glorioso, Paolo; Crossley, Michael; Liu, Hong

2017-09-20

Here in this paper we further develop the fluctuating hydrodynamics proposed in a number of ways. We first work out in detail the classical limit of the hydrodynamical action, which exhibits many simplifications. In particular, this enables a transparent formulation of the action in physical spacetime in the presence of arbitrary external fields. It also helps to clarify issues related to field redefinitions and frame choices. We then propose that the action is invariant under a Z2 symmetry to which we refer as the dynamical KMS symmetry. The dynamical KMS symmetry is physically equivalent to the previously proposed local KMSmore » condition in the classical limit, but is more convenient to implement and more general. It is applicable to any states in local equilibrium rather than just thermal density matrix perturbed by external background fields. Finally we elaborate the formulation for a conformal fluid, which contains some new features, and work out the explicit form of the entropy current to second order in derivatives for a neutral conformal fluid.« less

Continuous theory of active matter systems with metric-free interactions.

PubMed

Peshkov, Anton; Ngo, Sandrine; Bertin, Eric; Chaté, Hugues; Ginelli, Francesco

2012-08-31

We derive a hydrodynamic description of metric-free active matter: starting from self-propelled particles aligning with neighbors defined by "topological" rules, not metric zones-a situation advocated recently to be relevant for bird flocks, fish schools, and crowds-we use a kinetic approach to obtain well-controlled nonlinear field equations. We show that the density-independent collision rate per particle characteristic of topological interactions suppresses the linear instability of the homogeneous ordered phase and the nonlinear density segregation generically present near threshold in metric models, in agreement with microscopic simulations.

Modeling of nanoscale liquid mixture transport by density functional hydrodynamics

NASA Astrophysics Data System (ADS)

Dinariev, Oleg Yu.; Evseev, Nikolay V.

2017-06-01

Modeling of multiphase compositional hydrodynamics at nanoscale is performed by means of density functional hydrodynamics (DFH). DFH is the method based on density functional theory and continuum mechanics. This method has been developed by the authors over 20 years and used for modeling in various multiphase hydrodynamic applications. In this paper, DFH was further extended to encompass phenomena inherent in liquids at nanoscale. The new DFH extension is based on the introduction of external potentials for chemical components. These potentials are localized in the vicinity of solid surfaces and take account of the van der Waals forces. A set of numerical examples, including disjoining pressure, film precursors, anomalous rheology, liquid in contact with heterogeneous surface, capillary condensation, and forward and reverse osmosis, is presented to demonstrate modeling capabilities.

Validation of a coupled wave-flow model in a high-energy setting: the mouth of the Columbia River

USGS Publications Warehouse

Elias, Edwin P.L.; Gelfenbaum, Guy R.; van der Westhuysen, André J.

2012-01-01

 A monthlong time series of wave, current, salinity, and suspended-sediment measurements was made at five sites on a transect across the Mouth of Columbia River (MCR). These data were used to calibrate and evaluate the performance of a coupled hydrodynamic and wave model for the MCR based on the Delft3D modeling system. The MCR is a dynamic estuary inlet in which tidal currents, river discharge, and wave-driven currents are all important. Model tuning consisted primarily of spatial adjustments to bottom drag coefficients. In combination with (near-) default parameter settings, the MCR model application is able to simulate the dominant features in the tidal flow, salinity and wavefields observed in field measurements. The wave-orbital averaged method for representing the current velocity profile in the wave model is considered the most realistic for the MCR. The hydrodynamic model is particularly effective in reproducing the observed vertical residual and temporal variations in current structure. Density gradients introduce the observed and modeled reversal of the mean flow at the bed and augment mean and peak flow in the upper half of the water column. This implies that sediment transport during calmer summer conditions is controlled by density stratification and is likely net landward due to the reversal of flow near the bed. The correspondence between observed and modeled hydrodynamics makes this application a tool to investigate hydrodynamics and associated sediment transport.

Validation of a coupled wave-flow model in a high-energy setting: The mouth of the Columbia River

NASA Astrophysics Data System (ADS)

Elias, Edwin P. L.; Gelfenbaum, Guy; Van der Westhuysen, André J.

2012-09-01

A monthlong time series of wave, current, salinity, and suspended-sediment measurements was made at five sites on a transect across the Mouth of Columbia River (MCR). These data were used to calibrate and evaluate the performance of a coupled hydrodynamic and wave model for the MCR based on the Delft3D modeling system. The MCR is a dynamic estuary inlet in which tidal currents, river discharge, and wave-driven currents are all important. Model tuning consisted primarily of spatial adjustments to bottom drag coefficients. In combination with (near-) default parameter settings, the MCR model application is able to simulate the dominant features in the tidal flow, salinity and wavefields observed in field measurements. The wave-orbital averaged method for representing the current velocity profile in the wave model is considered the most realistic for the MCR. The hydrodynamic model is particularly effective in reproducing the observed vertical residual and temporal variations in current structure. Density gradients introduce the observed and modeled reversal of the mean flow at the bed and augment mean and peak flow in the upper half of the water column. This implies that sediment transport during calmer summer conditions is controlled by density stratification and is likely net landward due to the reversal of flow near the bed. The correspondence between observed and modeled hydrodynamics makes this application a tool to investigate hydrodynamics and associated sediment transport.

Low-noise phase of a two-dimensional active nematic system

NASA Astrophysics Data System (ADS)

Shankar, Suraj; Ramaswamy, Sriram; Marchetti, M. Cristina

2018-01-01

We consider a collection of self-driven apolar particles on a substrate that organize into an active nematic phase at sufficiently high density or low noise. Using the dynamical renormalization group, we systematically study the two-dimensional fluctuating ordered phase in a coarse-grained hydrodynamic description involving both the nematic director and the conserved density field. In the presence of noise, we show that the system always displays only quasi-long-ranged orientational order beyond a crossover scale. A careful analysis of the nonlinearities permitted by symmetry reveals that activity is dangerously irrelevant over the linearized description, allowing giant number fluctuations to persist although now with strong finite-size effects and a nonuniversal scaling exponent. Nonlinear effects from the active currents lead to power-law correlations in the density field, thereby preventing macroscopic phase separation in the thermodynamic limit.

Turbulence in transient solar phenomena

NASA Technical Reports Server (NTRS)

Cross, M.

1982-01-01

If theta dependence is kept in the Navier-Stokes equations for the solar wind, than a density enhancement will grow. This growth is followed in the nonlinear equations until a streamer is formed. Viscosity stops the streamer's growth when there is a large difference in speeds inside and outside of the streamer. Using classical fluid mechanics and a latitude dependent hydrodynamical model, it is shown that unmagnetized perturbed flow evolves into high and low density regions. The growth mechanisms for density enrichments are discussed along with a nonlinear solution for their large amplitude development. It was found that a higher Reynolds number is needed to start turbulence in the presence of a magnetic field because energy is required to bend the field lines attached to the fluid. If cosmological gas was turbulent shortly after the big bang, then galaxies could have been formed by turbulent eddies.

On the Foundation of Equipartition in Supernova Remnants

NASA Astrophysics Data System (ADS)

Urošević, Dejan; Pavlović, Marko Z.; Arbutina, Bojan

2018-03-01

A widely accepted paradigm is that equipartition (eqp) between the energy density of cosmic rays (CRs) and the energy density of the magnetic field cannot be sustained in supernova remnants (SNRs). However, our 3D hydrodynamic supercomputer simulations, coupled with a nonlinear diffusive shock acceleration model, provide evidence that eqp may be established at the end of the Sedov phase of evolution in which most SNRs spend the longest portions of their lives. We introduce the term “constant partition” for any constant ratio between the CR energy density and the energy density of the magnetic field in an SNR, while the term “equipartition” should be reserved for the case of approximately the same values of the energy density (also, it is constant partition in the order of magnitude) of ultra-relativistic electrons only (or CRs in total) and the energy density of the magnetic field. Our simulations suggest that this approximate constant partition exists in all but the youngest SNRs. We speculate that since evolved SNRs at the end of the Sedov phase of evolution can reach eqp between CRs and magnetic fields, they may be responsible for initializing this type of eqp in the interstellar medium. Additionally, we show that eqp between the electron component of CRs and the magnetic field may be used for calculating the magnetic field strength directly from observations of synchrotron emission from SNRs. The values of magnetic field strengths in SNRs given here are approximately 2.5 times lower than values calculated by Arbutina et al.

Photoionization of High-altitude Gas in a Supernova-driven Turbulent Interstellar Medium

NASA Astrophysics Data System (ADS)

Wood, Kenneth; Hill, Alex S.; Joung, M. Ryan; Mac Low, Mordecai-Mark; Benjamin, Robert A.; Haffner, L. Matthew; Reynolds, R. J.; Madsen, G. J.

2010-10-01

We investigate models for the photoionization of the widespread diffuse ionized gas (DIG) in galaxies. In particular, we address the long standing question of the penetration of Lyman continuum photons from sources close to the galactic midplane to large heights in the galactic halo. We find that recent hydrodynamical simulations of a supernova-driven interstellar medium (ISM) have low-density paths and voids that allow for ionizing photons from midplane OB stars to reach and ionize gas many kiloparsecs above the midplane. We find that ionizing fluxes throughout our simulation grids are larger than predicted by one-dimensional slab models, thus allowing for photoionization by O stars of low altitude neutral clouds in the Galaxy that are also detected in Hα. In previous studies of such clouds, the photoionization scenario had been rejected and the Hα had been attributed to enhanced cosmic ray ionization or scattered light from midplane H II regions. We do find that the emission measure distributions in our simulations are wider than those derived from Hα observations in the Milky Way. In addition, the horizontally averaged height dependence of the gas density in the hydrodynamical models is lower than inferred in the Galaxy. These discrepancies are likely due to the absence of magnetic fields in the hydrodynamic simulations and we discuss how magnetohydrodynamic effects may reconcile models and observations. Nevertheless, we anticipate that the inclusion of magnetic fields in the dynamical simulations will not alter our primary finding that midplane OB stars are capable of producing high-altitude DIG in a realistic three-dimensional ISM.

Horizontal density-gradient effects on simulation of flow and transport in the Potomac Estuary

USGS Publications Warehouse

Schaffranek, Raymond W.; Baltzer, Robert A.; ,

1990-01-01

A two-dimensional, depth-integrated, hydrodynamic/transport model of the Potomac Estuary between Indian Head and Morgantown, Md., has been extended to include treatment of baroclinic forcing due to horizontal density gradients. The finite-difference model numerically integrates equations of mass and momentum conservation in conjunction with a transport equation for heat, salt, and constituent fluxes. Lateral and longitudinal density gradients are determined from salinity distributions computed from the convection-diffusion equation and an equation of state that expresses density as a function of temperature and salinity; thus, the hydrodynamic and transport computations are directly coupled. Horizontal density variations are shown to contribute significantly to momentum fluxes determined in the hydrodynamic computation. These fluxes lead to enchanced tidal pumping, and consequently greater dispersion, as is evidenced by numerical simulations. Density gradient effects on tidal propagation and transport behavior are discussed and demonstrated.

Hydrodynamic Models for Multicomponent Plasmas with Collisional-Radiative Kinetics

DTIC Science & Technology

2014-12-01

16, 17]. The plasma, typically created by electric discharges , can deposit heat locally in the vicinity the flame, which quickly raises the gas...the corona layer of laser produced plasmas (LPP). Secondly, the self-consistent coupling of the plasma with the field gives rise to particle...excited species and reaction radicals; 7 n ncr solid transport layer (overdense) corona layer (underdense) temperature density shock wave ablation

A broadband proton backlighting platform to probe shock propagation in low-density systems

DOE PAGES

Sio, H.; Hua, R.; Ping, Y.; ...

2017-01-17

A proton backlighting platform has been developed for the study of strong shock propagation in low-density systems in planar geometry. Electric fields at the converging shock front in inertial confinement fusion implosions have been previously observed, demonstrating the presence of—and the need to understand—strong electric fields not modeled in standard radiation-hydrodynamic simulations. In this planar configuration, long-pulse ultraviolet lasers are used to drive a strong shock into a gas-cell target, while a short-pulse proton backlighter side-on radiographs the shock propagation. Finally, the capabilities of the platform are presented here. Future experiments will vary shock strength and gas fill, to probemore » shock conditions at different Z and T e.« less

Early Time Dynamics of Gluon Fields in High Energy Nuclear Collisions

NASA Astrophysics Data System (ADS)

Kapusta, Joseph I.; Chen, Guangyao; Fries, Rainer J.; Li, Yang

2016-12-01

Nuclei colliding at very high energy create a strong, quasi-classical gluon field during the initial phase of their interaction. We present an analytic calculation of the initial space-time evolution of this field in the limit of very high energies using a formal recursive solution of the Yang-Mills equations. We provide analytic expressions for the initial chromo-electric and chromo-magnetic fields and for their energy-momentum tensor. In particular, we discuss event-averaged results for energy density and energy flow as well as for longitudinal and transverse pressure of this system. Our results are generally applicable if τ < 1 /Qs. The transverse energy flow of the gluon field exhibits hydrodynamic-like contributions that follow transverse gradients of the energy density. In addition, a rapidity-odd energy flow also emerges from the non-abelian analog of Gauss' Law and generates non-vanishing angular momentum of the field. We will discuss the space-time picture that emerges from our analysis and its implications for observables in heavy ion collisions.

The Density-Magnetic Field Relation in the Atomic ISM

NASA Astrophysics Data System (ADS)

Gazol, A.; Villagran, M. A.

2018-04-01

We present numerical experiments aimed to study the correlation between the magnetic field strength, B, and the density, n, in the cold atomic interstellar medium (CNM). We analyze 24 magneto-hydrodynamic models with different initial magnetic field intensities (B0 =0.4, 2.1, 4.2, and 8.3 μG) and/or mean densities (2, 3, and 4 cm-3), in the presence of driven and decaying turbulence, with and without self-gravity, in a cubic computational domain with 100 pc by side. Our main findings are: i) For forced simulations, which reproduce the main observed physical conditions of the CNM in the Solar neighborhood, a positive correlation between B and n develops for all the B0 values. ii) The density at which this correlation becomes significant (≲ 30 cm-3) depends on B0 but is not sensitive to the presence of self-gravity. iii) The effect of self-gravity, when noticeable, consists of producing a shallower correlation at high densities, suggesting that, in the studied regime, self-gravity induces motions along the field lines. iv) Self-gravitating decaying models where the CNM is subsonic and sub-Alfvénic with β ≲ 1 develop a high density positive correlation whose slopes are consistent with a constant β(n). v) Decaying models where the low density CNM is subsonic and sub-Alfvénic with β > 1 show a negative correlation at intermediate densities, followed by a high density positive correlation.

Hydrodynamic Interactions in Active and Passive Matter

NASA Astrophysics Data System (ADS)

Krafnick, Ryan C.

Active matter is present at all biological length scales, from molecular apparatuses interior to cells, to swimming microscopic organisms, to birds, fish, and people. Its properties are varied and its applications diverse, but our understanding of the fundamental driving forces of systems with these constituents remains incomplete. This thesis examines active matter suspensions, exploring the role of hydrodynamic interactions on the unique and emergent properties therein. Both qualitative and quantitative impacts are considered, and care is taken in determining the physical origin of the results in question. It is found that fluid dynamical interactions are fundamentally, qualitatively important, and much of the properties of a system can be explained with an effective energy density defined via the fluid fields arising from the embedded self-propelling entities themselves.

Evolution of jets driven by relativistic radiation hydrodynamics as Long and Low Luminosity GRBs

NASA Astrophysics Data System (ADS)

Rivera-Paleo, F. J.; Guzmán, F. S.

2018-06-01

We present numerical simulations of jets modeled with Relativistic Radiation Hydrodynamics (RRH), that evolve across two environments: i) a stratified surrounding medium and ii) a 16TI progenitor model. We consider opacities consistent with various processes of interaction between the fluid and radiation, specifically, free-free, bound-free, bound-bound and electron scattering. We explore various initial conditions, with different radiation energy densities of the beam in hydrodynamical and radiation pressure dominated scenarios, considering only highly-relativistic jets. In order to investigate the impact of the radiation field on the evolution of the jets, we compare our results with purely hydrodynamical jets. Comparing among jets driven by RRH, we find that radiation pressure dominated jets propagate slightly faster than gas pressure dominated ones. Finally, we construct the luminosity Light Curves (LCs) associated with the two cases. The construction of LCs uses the fluxes of the radiation field which is fully coupled to the hydrodynamics equations during the evolution. The main properties of the jets propagating on the stratified surrounding medium are that the LCs show the same order of magnitude as the gamma-ray luminosity of typical Long Gamma-Ray Bursts 1050 - 1054erg/s and the difference between the radiation and gas temperatures is of nearly one order of magnitude. The properties of jets breaking out from the progenitor star model are that the LCs are of the order of magnitude of low-luminosity GRBs 1046 - 1049 erg/s, and in this scenario the difference between the gas and radiation temperature is of four orders of magnitude, which is a case far from thermal equilibrium.

A hydrodynamic approach to cosmology - Texture-seeded cold dark matter and hot dark matter cosmogonies

NASA Technical Reports Server (NTRS)

Cen, R. Y.; Ostriker, J. P.; Spergel, D. N.; Turok, N.

1991-01-01

Hydrodynamical simulations of galaxy formation in a texture-seeded cosmology are presented, with attention given to Omega = 1 galaxies dominated by both hot dark matter (HDM) and cold dark matter (CDM). The simulations include both gravitational and hydrodynamical physics with a detailed treatment of collisional and radiative thermal processes, and use a cooling criterion to estimate galaxy formation. Background radiation fields and Zel'dovich-Sunyaev fluctuations are explicitly computed. The derived galaxy mass function is well fitted by the observed Schechter luminosity function for a baryonic M/L of 3 and total M/L of 60 in galaxies. In both HDM and CDM texture scenarios, the 'galaxies' and 'clusters' are significantly more strongly correlated than the dark matter due to physical bias processes. The slope of the correlation function in both cases is consistent with observations. In contrast to Gaussian models, peaks in the dark matter density distributrion are less correlated than average.

Density profiles around A+B→C reaction-diffusion fronts in partially miscible systems: A general classification.

PubMed

Loodts, V; Trevelyan, P M J; Rongy, L; De Wit, A

2016-10-01

Various spatial density profiles can develop in partially miscible stratifications when a phase A dissolves with a finite solubility into a host phase containing a dissolved reactant B. We investigate theoretically the impact of an A+B→C reaction on such density profiles in the host phase and classify them in a parameter space spanned by the ratios of relative contributions to density and diffusion coefficients of the chemical species. While the density profile is either monotonically increasing or decreasing in the nonreactive case, reactions combined with differential diffusivity can create eight different types of density profiles featuring up to two extrema in density, at the reaction front or below it. We use this framework to predict various possible hydrodynamic instability scenarios inducing buoyancy-driven convection around such reaction fronts when they propagate parallel to the gravity field.

Postfragmentation density function for bacterial aggregates in laminar flow

PubMed Central

Byrne, Erin; Dzul, Steve; Solomon, Michael; Younger, John

2014-01-01

The postfragmentation probability density of daughter flocs is one of the least well-understood aspects of modeling flocculation. We use three-dimensional positional data of Klebsiella pneumoniae bacterial flocs in suspension and the knowledge of hydrodynamic properties of a laminar flow field to construct a probability density function of floc volumes after a fragmentation event. We provide computational results which predict that the primary fragmentation mechanism for large flocs is erosion. The postfragmentation probability density function has a strong dependence on the size of the original floc and indicates that most fragmentation events result in clumps of one to three bacteria eroding from the original floc. We also provide numerical evidence that exhaustive fragmentation yields a limiting density inconsistent with the log-normal density predicted in the literature, most likely due to the heterogeneous nature of K. pneumoniae flocs. To support our conclusions, artificial flocs were generated and display similar postfragmentation density and exhaustive fragmentation. PMID:21599205

Attraction of swimming microorganisms by solid surfaces

NASA Astrophysics Data System (ADS)

Lauga, Eric; Berke, Allison; Turner, Linda; Berg, Howard

2007-11-01

Swimming microorganisms such as spermatozoa or bacteria are usually observed to accumulate near surfaces. Here, we report on an experiment aiming at measuring the distribution of smooth-swimming E. coli when moving in a density-matched fluid and between two glass plates. The distribution for the bacteria concentration is found to peak near the glass plates, in agreement with a simple physical model based on the far-field hydrodynamics of swimming cells.

Accelerating hydrodynamic description of pseudorapidity density and the initial energy density in p +p , Cu + Cu, Au + Au, and Pb + Pb collisions at energies available at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider

NASA Astrophysics Data System (ADS)

Ze-Fang, Jiang; Chun-Bin, Yang; Csanád, Máté; Csörgő, Tamás

2018-06-01

A known class of analytic, exact, accelerating solutions of prefect relativistic hydrodynamics with longitudinal acceleration is utilized to describe results on the pseudorapidity distributions for different collision systems. These results include d N /d η measured in p +p , Cu+Cu, Au+Au, and Pb+Pb collisions at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider, in a broad centrality range. Going beyond the traditional Bjorken model, from the accelerating hydrodynamic description we determine the initial energy density and other thermodynamic quantities in those collisions.

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

Zhu Zhaohuan; Stone, James M.; Rafikov, Roman R., E-mail: zhzhu@astro.princeton.edu, E-mail: jstone@astro.princeton.edu, E-mail: rrr@astro.princeton.edu

Some regions in protoplanetary disks are turbulent, while some regions are quiescent (e.g. the dead zone). In order to study how planets open gaps in both inviscid hydrodynamic disk (e.g. the dead zone) and the disk subject to magnetorotational instability (MRI), we carried out both shearing box two-dimensional inviscid hydrodynamical simulations and three-dimensional unstratified magnetohydrodynamical (MHD) simulations (having net vertical magnetic fields) with a planet at the box center. We found that, due to the nonlinear wave steepening, even a low mass planet can open gaps in both cases, in contradiction to the ''thermal criterion'' for gap opening. In ordermore » to understand if we can represent the MRI turbulent stress with the viscous {alpha} prescription for studying gap opening, we compare gap properties in MRI-turbulent disks to those in viscous HD disks having the same stress, and found that the same mass planet opens a significantly deeper and wider gap in net vertical flux MHD disks than in viscous HD disks. This difference arises due to the efficient magnetic field transport into the gap region in MRI disks, leading to a larger effective {alpha} within the gap. Thus, across the gap, the Maxwell stress profile is smoother than the gap density profile, and a deeper gap is needed for the Maxwell stress gradient to balance the planetary torque density. Comparison with previous results from net toroidal flux/zero flux MHD simulations indicates that the magnetic field geometry plays an important role in the gap opening process. We also found that long-lived density features (termed zonal flows) produced by the MRI can affect planet migration. Overall, our results suggest that gaps can be commonly produced by low mass planets in realistic protoplanetary disks, and caution the use of a constant {alpha}-viscosity to model gaps in protoplanetary disks.« less

Normal modes of weak colloidal gels

NASA Astrophysics Data System (ADS)

Varga, Zsigmond; Swan, James W.

2018-01-01

The normal modes and relaxation rates of weak colloidal gels are investigated in calculations using different models of the hydrodynamic interactions between suspended particles. The relaxation spectrum is computed for freely draining, Rotne-Prager-Yamakawa, and accelerated Stokesian dynamics approximations of the hydrodynamic mobility in a normal mode analysis of a harmonic network representing several colloidal gels. We find that the density of states and spatial structure of the normal modes are fundamentally altered by long-ranged hydrodynamic coupling among the particles. Short-ranged coupling due to hydrodynamic lubrication affects only the relaxation rates of short-wavelength modes. Hydrodynamic models accounting for long-ranged coupling exhibit a microscopic relaxation rate for each normal mode, λ that scales as l-2, where l is the spatial correlation length of the normal mode. For the freely draining approximation, which neglects long-ranged coupling, the microscopic relaxation rate scales as l-γ, where γ varies between three and two with increasing particle volume fraction. A simple phenomenological model of the internal elastic response to normal mode fluctuations is developed, which shows that long-ranged hydrodynamic interactions play a central role in the viscoelasticity of the gel network. Dynamic simulations of hard spheres that gel in response to short-ranged depletion attractions are used to test the applicability of the density of states predictions. For particle concentrations up to 30% by volume, the power law decay of the relaxation modulus in simulations accounting for long-ranged hydrodynamic interactions agrees with predictions generated by the density of states of the corresponding harmonic networks as well as experimental measurements. For higher volume fractions, excluded volume interactions dominate the stress response, and the prediction from the harmonic network density of states fails. Analogous to the Zimm model in polymer physics, our results indicate that long-ranged hydrodynamic interactions play a crucial role in determining the microscopic dynamics and macroscopic properties of weak colloidal gels.

Hydrodynamic Model for Density Gradients Instability in Hall Plasmas Thrusters

NASA Astrophysics Data System (ADS)

Singh, Sukhmander

2017-10-01

There is an increasing interest for a correct understanding of purely growing electromagnetic and electrostatic instabilities driven by a plasma gradient in a Hall thruster devices. In Hall thrusters, which are typically operated with xenon, the thrust is provided by the acceleration of ions in the plasma generated in a discharge chamber. The goal of this paper is to study the instabilities due to gradients of plasma density and conditions for the growth rate and real part of the frequency for Hall thruster plasmas. Inhomogeneous plasmas prone a wide class of eigen modes induced by inhomogeneities of plasma density and called drift waves and instabilities. The growth rate of the instability has a dependences on the magnetic field, plasma density, ion temperature and wave numbers and initial drift velocities of the plasma species.

An MHD 3-D solution to the evolution of a CME observed by the STEREO mission on May 2007

NASA Astrophysics Data System (ADS)

Berdichevsky, D. B.; Stenborg, G. A.

2009-12-01

Nature offers a variety of examples on the dynamics of matter trapped electromagnetic fields. In particular, sudden ejections of large amounts of solar mass embedded in magnetic field structures develop in the heliosphere, their evolution being affected by the background solar wind. Their plasma and magnetic field values can be obtained by in-situ instruments onboard existing space missions. A particular example of such process is the passage of a magnetic field flux tube-like structure (~ 0.1 AU in cross section) exhibiting a flux-rope topology observed on May 2007 with their in-situ instruments by the Venus Express and Messenger missions. STEREO remote observations obtained with the SECCHI instruments allowed the tracking of this quite weak event from its origins in the Sun to approximately the orbit of Mercury. In this work, we i) discuss on the dynamic evolution of the event as described by the magnetic force-free magneto-hydrodynamic solution proposed in [1], and ii) generalize it to add curvature to the MHD solution. The magneto-hydrodynamic analytical solution obtained allows us to make quantitative estimates on the size of the flux tube just after the ejection, magnetic field intensity, and mass density. [1] Berdichevsky, DB, RP Lepping, and CJ Farrugia, Phys Rev E, 67(3), 036405, 2003.

Pair aligning improved motility of Quincke rollers.

PubMed

Lu, Shi Qing; Zhang, Bing Yue; Zhang, Zhi Chao; Shi, Yan; Zhang, Tian Hui

2018-06-06

Density-dependent speed is studied in a two-dimensional active colloid in which the colloidal particles are propelled by an external electric field via a Quincke rotation. Above the critcal electric field, dense dynamic clusters form spotaneously, in which the particles are highly aligned in velocity and move much faster than isolated units. Detailed observations on pair collision reveal that the alignment of velocity is induced by the long-ranged hydrodynamic interactions and the improvement of speed in the clusters arises from pair aligning in which two particles are closely paired and rotate synchronically. In the aligning state, the short-range in-plane dipole-dipole attraction enhances the rotation torque and gives rises to a larger rolling speed. The pair aligning becomes difficult and unstable at high electric field where the normal dipole-dipole repulsion becomes dominant. As a consequence, the dependence of speed on density becomes weak increasingly upon the increase of the electric field. This result offers an interpretation for the discrepancy between our and previous observations on Quincke rollers.

Hydrodynamic instabilities at an oblique interface: Experiments and Simulations

NASA Astrophysics Data System (ADS)

Douglas-Mann, E.; Fiedler Kawaguchi, C.; Trantham, M. A.; Malamud, G.; Wan, W. C.; Klein, S. R.; Kuranz, C. C.

2017-10-01

Hydrodynamic instabilities are important phenomena that occur in high-energy-density systems, such as astrophysical systems and inertial confinement fusion experiments, where pressure, density, and velocity gradients are present. Using a 30 ns laser pulse from the Omega EP laser system, a steady shock wave is driven into a target. A Spherical Crystal Imager provides high-resolution x-ray radiographs to study the evolution of complex hydrodynamic structures. This experiment has a light-to-heavy interface at an oblique angle with a precision-machined perturbation. The incident shock wave deposits shear and vorticity at the interface causing the perturbation to grow via Richtmyer-Meshkov and Kelvin-Helmholtz processes. We present results from analysis of radiographic data and hydrodynamics simulations showing the evolution of the shock and unstable structure. This work is supported by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, Grant Number DE-NA0002956 and the National Science Foundation through the Basic Plasma Science and Engineering program and LILAC.

Thermal and active fluctuations of a compressible bilayer vesicle

NASA Astrophysics Data System (ADS)

Sachin Krishnan, T. V.; Yasuda, Kento; Okamoto, Ryuichi; Komura, Shigeyuki

2018-05-01

We discuss thermal and active fluctuations of a compressible bilayer vesicle by using the results of hydrodynamic theory for vesicles. Coupled Langevin equations for the membrane deformation and the density fields are employed to calculate the power spectral density matrix of membrane fluctuations. Thermal contribution is obtained by means of the fluctuation dissipation theorem, whereas active contribution is calculated from exponentially decaying time correlation functions of active random forces. We obtain the total power spectral density as a sum of thermal and active contributions. An apparent response function is further calculated in order to compare with the recent microrheology experiment on red blood cells. An enhanced response is predicted in the low-frequency regime for non-thermal active fluctuations.

Holographic constraints on Bjorken hydrodynamics at finite coupling

NASA Astrophysics Data System (ADS)

DiNunno, Brandon S.; Grozdanov, Sašo; Pedraza, Juan F.; Young, Steve

2017-10-01

In large- N c conformal field theories with classical holographic duals, inverse coupling constant corrections are obtained by considering higher-derivative terms in the corresponding gravity theory. In this work, we use type IIB supergravity and bottom-up Gauss-Bonnet gravity to study the dynamics of boost-invariant Bjorken hydrodynamics at finite coupling. We analyze the time-dependent decay properties of non-local observables (scalar two-point functions and Wilson loops) probing the different models of Bjorken flow and show that they can be expressed generically in terms of a few field theory parameters. In addition, our computations provide an analytically quantifiable probe of the coupling-dependent validity of hydrodynamics at early times in a simple model of heavy-ion collisions, which is an observable closely analogous to the hydrodynamization time of a quark-gluon plasma. We find that to third order in the hydrodynamic expansion, the convergence of hydrodynamics is improved and that generically, as expected from field theory considerations and recent holographic results, the applicability of hydrodynamics is delayed as the field theory coupling decreases.

Fast and accurate Voronoi density gridding from Lagrangian hydrodynamics data

NASA Astrophysics Data System (ADS)

Petkova, Maya A.; Laibe, Guillaume; Bonnell, Ian A.

2018-01-01

Voronoi grids have been successfully used to represent density structures of gas in astronomical hydrodynamics simulations. While some codes are explicitly built around using a Voronoi grid, others, such as Smoothed Particle Hydrodynamics (SPH), use particle-based representations and can benefit from constructing a Voronoi grid for post-processing their output. So far, calculating the density of each Voronoi cell from SPH data has been done numerically, which is both slow and potentially inaccurate. This paper proposes an alternative analytic method, which is fast and accurate. We derive an expression for the integral of a cubic spline kernel over the volume of a Voronoi cell and link it to the density of the cell. Mass conservation is ensured rigorously by the procedure. The method can be applied more broadly to integrate a spherically symmetric polynomial function over the volume of a random polyhedron.

Analytic Modeling of the Hydrodynamic, Thermal, and Structural Behavior of Foil Thrust Bearings

NASA Technical Reports Server (NTRS)

Bruckner, Robert J.; DellaCorte, Christopher; Prahl, Joseph M.

2005-01-01

A simulation and modeling effort is conducted on gas foil thrust bearings. A foil bearing is a self acting hydrodynamic device capable of separating stationary and rotating components of rotating machinery by a film of air or other gaseous lubricant. Although simple in appearance these bearings have proven to be complicated devices in analysis. They are sensitive to fluid structure interaction, use a compressible gas as a lubricant, may not be in the fully continuum range of fluid mechanics, and operate in the range where viscous heat generation is significant. These factors provide a challenge to the simulation and modeling task. The Reynolds equation with the addition of Knudsen number effects due to thin film thicknesses is used to simulate the hydrodynamics. The energy equation is manipulated to simulate the temperature field of the lubricant film and combined with the ideal gas relationship, provides density field input to the Reynolds equation. Heat transfer between the lubricant and the surroundings is also modeled. The structural deformations of the bearing are modeled with a single partial differential equation. The equation models the top foil as a thin, bending dominated membrane whose deflections are governed by the biharmonic equation. A linear superposition of hydrodynamic load and compliant foundation reaction is included. The stiffness of the compliant foundation is modeled as a distributed stiffness that supports the top foil. The system of governing equations is solved numerically by a computer program written in the Mathematica computing environment. Representative calculations and comparisons with experimental results are included for a generation I gas foil thrust bearing.

Cross-diffusion-driven hydrodynamic instabilities in a double-layer system: General classification and nonlinear simulations

NASA Astrophysics Data System (ADS)

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.

One-dimensional Ar-SF{sub 6} hydromodel at low-pressure in e-beam generated plasmas

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

Petrov, George M., E-mail: george.petrov@nrl.navy.mil; Boris, David R.; Petrova, Tzvetelina B.

2016-03-15

A one-dimensional steady-state hydrodynamic model of electron beam generated plasmas produced in Ar-SF{sub 6} mixtures at low pressure in a constant magnetic field was developed. Simulations were performed for a range of SF{sub 6} partial pressures at constant 30 mTorr total gas pressure to determine the spatial distribution of species densities and fluxes. With the addition of small amount of SF{sub 6} (∼1%), the confining electrostatic field sharply decreases with respect to the pure argon case. This effect is due to the applied magnetic field inhibiting electron diffusion. The hallmark of electronegative discharge plasmas, positive ion—negative ion core and positivemore » ion—electron edge, was not observed. Instead, a plasma with large electronegativity (∼100) is formed throughout the volume, and only a small fraction (≈30%) of the parent SF{sub 6} molecules were dissociated to F{sub 2}, SF{sub 2}, and SF{sub 4}. Importantly, F radical densities were found to be very low, on the order of the ion density. Model predictions for the electron density, ion density, and plasma electronegativity are in good agreement with experimental data over the entire range of SF{sub 6} concentrations investigated.« less

Role of radial nonuniformities in the interaction of an intense laser with atomic clusters

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

Holkundkar, Amol R.; Gupta, N. K.

A model for the interaction of an intense laser with atomic clusters is presented. The model takes into account the spatial nonuniformities of the cluster as it evolves in time. The cluster is treated as a stratified sphere having an arbitrary number of layers. Electric and magnetic fields are obtained by solving the vector Helmholtz equation coupled with one-dimensional Lagrangian hydrodynamics. Results are compared with the uniform density nanoplasma model. Enhancement in the amount of energy absorbed is seen over the uniform density model. In some cases the absorbed energy increases by as much as a factor of 40.

Modeling Laboratory Astrophysics Experiments in the High-Energy-Density Regime Using the CRASH Radiation-Hydrodynamics Model

NASA Astrophysics Data System (ADS)

Grosskopf, M. J.; Drake, R. P.; Trantham, M. R.; Kuranz, C. C.; Keiter, P. A.; Rutter, E. M.; Sweeney, R. M.; Malamud, G.

2012-10-01

The radiation hydrodynamics code developed by the Center for Radiative Shock Hydrodynamics (CRASH) at the University of Michigan has been used to model experimental designs for high-energy-density physics campaigns on OMEGA and other high-energy laser facilities. This code is an Eulerian, block-adaptive AMR hydrodynamics code with implicit multigroup radiation transport and electron heat conduction. CRASH model results have shown good agreement with a experimental results from a variety of applications, including: radiative shock, Kelvin-Helmholtz and Rayleigh-Taylor experiments on the OMEGA laser; as well as laser-driven ablative plumes in experiments by the Astrophysical Collisionless Shocks Experiments with Lasers (ACSEL), collaboration. We report a series of results with the CRASH code in support of design work for upcoming high-energy-density physics experiments, as well as comparison between existing experimental data and simulation results. This work is funded by the Predictive Sciences Academic Alliances Program in NNSA-ASC via grant DEFC52- 08NA28616, by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number DE-FG52-09NA29548, and by the National Laser User Facility Program, grant number DE-NA0000850.

A Platform for X-Ray Thomson Scattering Measurements of Radiation Hydrodynamics Experiments on the NIF

NASA Astrophysics Data System (ADS)

Lefevre, Heath; Ma, Kevin; Belancourt, Patrick; MacDonald, Michael; Doeppner, Tilo; Keiter, Paul; Kuranz, Carolyn

2017-10-01

A recent experiment on the National Ignition Facility (NIF) radiographed the evolution of the Rayleigh-Taylor (RT) instability under high and low drive cases. This experiment showed that under a high drive the growth rate of the RT instability is reduced relative to the low drive case. The high drive launches a radiative shock, increases the temperature of the post-shock region, and ablates the spikes, which reduces the RT growth rate. The plasma parameters must be measured to validate this claim. We present a target design for making X-Ray Thomson Scattering (XRTS) measurements on radiation hydrodynamics experiments on NIF to measure the electron temperature of the shocked region in the above cases. Specifically, we show that a previously fielded NIF radiation hydrodynamics platform can be modified to allow sufficient signal and temperature resolution for XRTS measurements. This work is funded by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, Grant Number DE-NA0002956 and the National Science Foundation through the Basic Plasma Science and Engineering program.

Magnetic particles guided by ellipsoidal AC magnetic fields in a shallow viscous fluid: Controlling trajectories and chain lengths

NASA Astrophysics Data System (ADS)

Jorge, Guillermo A.; Llera, María; Bekeris, Victoria

2017-12-01

We study the propulsion of superparamagnetic particles dispersed in a viscous fluid upon the application of an elliptically polarized rotating magnetic field. Reducing the fluid surface tension the particles sediment due to density mismatch and rotate close to the low recipient confining plate. We study the net translational motion arising from the hydrodynamic coupling with the plate and find that, above a cross over magnetic field, magnetically assembled doublets move faster than single particles. In turn, particles are driven in complex highly controlled trajectories by rotating the plane containing the magnetic field vector. The effect of the field rotation on long self assembled chains is discussed and the alternating breakup and reformation of the particle chains is described.

Postfragmentation density function for bacterial aggregates in laminar flow.

PubMed

Byrne, Erin; Dzul, Steve; Solomon, Michael; Younger, John; Bortz, David M

2011-04-01

The postfragmentation probability density of daughter flocs is one of the least well-understood aspects of modeling flocculation. We use three-dimensional positional data of Klebsiella pneumoniae bacterial flocs in suspension and the knowledge of hydrodynamic properties of a laminar flow field to construct a probability density function of floc volumes after a fragmentation event. We provide computational results which predict that the primary fragmentation mechanism for large flocs is erosion. The postfragmentation probability density function has a strong dependence on the size of the original floc and indicates that most fragmentation events result in clumps of one to three bacteria eroding from the original floc. We also provide numerical evidence that exhaustive fragmentation yields a limiting density inconsistent with the log-normal density predicted in the literature, most likely due to the heterogeneous nature of K. pneumoniae flocs. To support our conclusions, artificial flocs were generated and display similar postfragmentation density and exhaustive fragmentation. ©2011 American Physical Society

Effects of in-plane magnetic field on the transport of 2D electron vortices in non-uniform plasmas

NASA Astrophysics Data System (ADS)

Angus, Justin; Richardson, Andrew; Schumer, Joseph; Pulsed Power Team

2015-11-01

The formation of electron vortices in current-carrying plasmas is observed in 2D particle-in-cell (PIC) simulations of the plasma-opening switch. In the presence of a background density gradient in Cartesian systems, vortices drift in the direction found by crossing the magnetic field with the background density gradient as a result of the Hall effect. However, most of the 2D simulations where electron vortices are seen and studied only allow for in-plane currents and thus only an out-of-plane magnetic field. Here we present results of numerical simulations of 2D, seeded electron vortices in an inhomogeneous background using the generalized 2D electron-magneto-hydrodynamic model that additionally allows for in-plane components of the magnetic field. By seeding vortices with a varying axial component of the velocity field, so that the vortex becomes a corkscrew, it is found that a pitch angle of around 20 degrees is sufficient to completely prevent the vortex from propagating due to the Hall effect for typical plasma parameters. This work is supported by the NRL Base Program.

Spontaneous emergence of rogue waves in partially coherent waves: A quantitative experimental comparison between hydrodynamics and optics

NASA Astrophysics Data System (ADS)

El Koussaifi, R.; Tikan, A.; Toffoli, A.; Randoux, S.; Suret, P.; Onorato, M.

2018-01-01

Rogue waves are extreme and rare fluctuations of the wave field that have been discussed in many physical systems. Their presence substantially influences the statistical properties of a partially coherent wave field, i.e., a wave field characterized by a finite band spectrum with random Fourier phases. Their understanding is fundamental for the design of ships and offshore platforms. In many meteorological conditions waves in the ocean are characterized by the so-called Joint North Sea Wave Project (JONSWAP) spectrum. Here we compare two unique experimental results: the first one has been performed in a 270 m wave tank and the other in optical fibers. In both cases, waves characterized by a JONSWAP spectrum and random Fourier phases have been launched at the input of the experimental device. The quantitative comparison, based on an appropriate scaling of the two experiments, shows a very good agreement between the statistics in hydrodynamics and optics. Spontaneous emergence of heavy tails in the probability density function of the wave amplitude is observed in both systems. The results demonstrate the universal features of rogue waves and provide a fundamental and explicit bridge between two important fields of research. Numerical simulations are also compared with experimental results.

Spontaneous emergence of rogue waves in partially coherent waves: A quantitative experimental comparison between hydrodynamics and optics.

PubMed

El Koussaifi, R; Tikan, A; Toffoli, A; Randoux, S; Suret, P; Onorato, M

2018-01-01

Rogue waves are extreme and rare fluctuations of the wave field that have been discussed in many physical systems. Their presence substantially influences the statistical properties of a partially coherent wave field, i.e., a wave field characterized by a finite band spectrum with random Fourier phases. Their understanding is fundamental for the design of ships and offshore platforms. In many meteorological conditions waves in the ocean are characterized by the so-called Joint North Sea Wave Project (JONSWAP) spectrum. Here we compare two unique experimental results: the first one has been performed in a 270 m wave tank and the other in optical fibers. In both cases, waves characterized by a JONSWAP spectrum and random Fourier phases have been launched at the input of the experimental device. The quantitative comparison, based on an appropriate scaling of the two experiments, shows a very good agreement between the statistics in hydrodynamics and optics. Spontaneous emergence of heavy tails in the probability density function of the wave amplitude is observed in both systems. The results demonstrate the universal features of rogue waves and provide a fundamental and explicit bridge between two important fields of research. Numerical simulations are also compared with experimental results.

Evaporating Atmospheres Around Close-in Exoplanets.

NASA Astrophysics Data System (ADS)

Owen, J.; Jackson, A.; Wu, Y.; Adams, F.

2014-12-01

The majority of currently observed exoplanets appear exceeding close to the central star (<0.1 AU) and as such are subject to intense high energy radiation from UV & X-ray photons. We will discuss that in such environments the atmospheres these planets are heated sufficiently that they can escape the planet's gravitational field in a hydrodynamic trans-sonic wind. We will show that this hydrodynamic mass-loss occurs for the majority of exoplanets at short periods, and for low-mass planets (<50 Mearth) is vigorous enough to significantly alter the planet's evolution. In some cases we will argue that an originally gas rich exoplanet can be completely evaporated leaving behind a bare rock core. In addition, we will present new multi-dimensional simulations of evaporation that include realistic treatment of the radiative transfer. These new simulations show that evaporation from 'hot' Jupiters is likely to be magnetically controlled, where mass-loss can only occur along open filed lines, where the interaction between the stellar and planetary magnetic field strongly controls the geometry of the evaporative flow. We will indicate how these new multi-dimensional radiation-magneto-hydrodynamic calculations can be used to study the time-dependence of the outflow and link the small but growing number of observations of exoplanet evaporation to the theoretical models. Finally, we will indicate that asymmetric evaporative flows can lead to orbital evolution of planets at close separations. Figure Caption: "Flow structure from an evaporating Hot Jupiter with a magnetic field strength of 0.3 Gauss. Top panels show density and magnetic field configuration and bottom panel shows plasma beta and velocity structure; left panels show simulation domain, right panels show a zoom in on the planet."

A relativistic dissipative hydrodynamic description for systems including particle number changing processes

NASA Astrophysics Data System (ADS)

El, Andrej; Muronga, Azwinndini; Xu, Zhe; Greiner, Carsten

2010-12-01

Relativistic dissipative hydrodynamic equations are extended by taking into account particle number changing processes in a gluon system, which expands in one dimension boost-invariantly. Chemical equilibration is treated by a rate equation for the particle number density based on Boltzmann equation and Grad's ansatz for the off-equilibrium particle phase space distribution. We find that not only the particle production, but also the temperature and the momentum spectra of the gluon system, obtained from the hydrodynamic calculations, are sensitive to the rates of particle number changing processes. Comparisons of the hydrodynamic calculations with the transport ones employing the parton cascade BAMPS show the inaccuracy of the rate equation at large shear viscosity to entropy density ratio. To improve the rate equation, Grad's ansatz has to be modified beyond the second moments in momentum.

Experimental measurements of hydrodynamic instabilities on NOVA of relevance to astrophysics

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

Budil, K S; Cherfils, C; Drake, R P

1998-09-11

Large lasers such as Nova allow the possibility of achieving regimes of high energy densities in plasmas of millimeter spatial scales and nanosecond time scales. In those plasmas where thermal conductivity and viscosity do not play a significant role, the hydrodynamic evolution is suitable for benchmarking hydrodynamics modeling in astrophysical codes. Several experiments on Nova examine hydrodynamically unstable interfaces. A typical Nova experiment uses a gold millimeter-scale hohlraum to convert the laser energy to a 200 eV blackbody source lasting about a nanosecond. The x-rays ablate a planar target, generating a series of shocks and accelerating the target. The evolvingmore » area1 density is diagnosed by time-resolved radiography, using a second x-ray source. Data from several experiments are presented and diagnostic techniques are discussed.« less

Hydraulic concentration of magnetic fields in the solar photosphere. III - Fields of one or two kilogauss

NASA Technical Reports Server (NTRS)

Parker, E. N.

1976-01-01

Detailed analysis of weak and strong lines suggests that the magnetic fields in isolated intense flux tubes in supergranule boundaries in the solar photosphere may be as large as 2000 gauss. This paper is a concise systematic review of hydrodynamic effects that might compress a magnetic field to great intensity. The properties of force-free fields are reviewed to show that they do not contribute to concentration of magnetic fields, in spite of the popular notion to the contrary. Of the seven effects considered, it is concluded that only cooling of the gas within the field can produce the high field densities inferred from observation. It is shown that inhibition of convection appears not to possess the necessary qualitative cooling features and that overstability, generating transverse hydromagnetic waves - essentially Alfven waves - is the only way to account for the cooling and field intensification.

Initialization of hydrodynamics in relativistic heavy ion collisions with an energy-momentum transport model

NASA Astrophysics Data System (ADS)

Naboka, V. Yu.; Akkelin, S. V.; Karpenko, Iu. A.; Sinyukov, Yu. M.

2015-01-01

A key ingredient of hydrodynamical modeling of relativistic heavy ion collisions is thermal initial conditions, an input that is the consequence of a prethermal dynamics which is not completely understood yet. In the paper we employ a recently developed energy-momentum transport model of the prethermal stage to study influence of the alternative initial states in nucleus-nucleus collisions on flow and energy density distributions of the matter at the starting time of hydrodynamics. In particular, the dependence of the results on isotropic and anisotropic initial states is analyzed. It is found that at the thermalization time the transverse flow is larger and the maximal energy density is higher for the longitudinally squeezed initial momentum distributions. The results are also sensitive to the relaxation time parameter, equation of state at the thermalization time, and transverse profile of initial energy density distribution: Gaussian approximation, Glauber Monte Carlo profiles, etc. Also, test results ensure that the numerical code based on the energy-momentum transport model is capable of providing both averaged and fluctuating initial conditions for the hydrodynamic simulations of relativistic nuclear collisions.

Solitonic Dispersive Hydrodynamics: Theory and Observation

NASA Astrophysics Data System (ADS)

Maiden, Michelle D.; Anderson, Dalton V.; Franco, Nevil A.; El, Gennady A.; Hoefer, Mark A.

2018-04-01

Ubiquitous nonlinear waves in dispersive media include localized solitons and extended hydrodynamic states such as dispersive shock waves. Despite their physical prominence and the development of thorough theoretical and experimental investigations of each separately, experiments and a unified theory of solitons and dispersive hydrodynamics are lacking. Here, a general soliton-mean field theory is introduced and used to describe the propagation of solitons in macroscopic hydrodynamic flows. Two universal adiabatic invariants of motion are identified that predict trapping or transmission of solitons by hydrodynamic states. The result of solitons incident upon smooth expansion waves or compressive, rapidly oscillating dispersive shock waves is the same, an effect termed hydrodynamic reciprocity. Experiments on viscous fluid conduits quantitatively confirm the soliton-mean field theory with broader implications for nonlinear optics, superfluids, geophysical fluids, and other dispersive hydrodynamic media.

The propagation of ion-acoustic waves carrying orbital angular momentum in the electron-positron-ion plasmas

NASA Astrophysics Data System (ADS)

Mehdian, H.; Nobahar, D.; Hajisharifi, K.

2018-02-01

Ion-acoustic (IA) waves carrying orbital angular momentum (OAM) are investigated in an unmagnetized, uniform, and collisionless electron-positron-ion (e-p-i) plasma system. Employing the hydrodynamic theory, the paraxial equation in term of ion perturbed number density is derived and discussed about its Laguerre-Gaussian (LG) beam solutions. Obtaining an approximate solution for the electrostatic potential, the IA wave characteristics including helical electric field structure, energy density, and OAM density are theoretically studied. Based on the numerical analysis, the effects of positron concentration, radial and angular mode number as well as beam waist on the obtained potential profile are investigated. It is shown that the depth (height) and width of the LG potential profile wells (barriers) are considerably modify by the variation of positron concentration.

Relativistic thermodynamics, a Lagrangian field theory for general flows including rotation

NASA Astrophysics Data System (ADS)

Frønsdal, Christian

Any theory that is based on an action principle has a much greater predictive power than one that does not have such a formulation. The formulation of a dynamical theory of General Relativity, including matter, is here viewed as a problem of coupling Einstein’s theory of pure gravity to an independently chosen and well-defined field theory of matter. It is well known that this is accomplished in a most natural way when both theories are formulated as relativistic, Lagrangian field theories, as is the case with Einstein-Maxwell theory. Special matter models of this type have been available; here a more general thermodynamical model that allows for vortex flows is presented. In a wider context, the problem of subjecting hydrodynamics and thermodynamics to an action principle is one that has been pursued for at least 150 years. A solution to this problem has been known for some time, but only under the strong restriction to potential flows. A variational principle for general flows has become available. It represents a development of the Navier-Stokes-Fourier approach to fluid dynamics. The principal innovation is the recognition that two kinds of flow velocity fields are needed, one the gradient of a scalar field and the other the time derivative of a vector field, the latter closely associated with vorticity. In the relativistic theory that is presented here, the latter is the Hodge dual of an exact 3-form, well known as the notoph field of Ogievetskij and Palubarinov, the B-field of Kalb and Ramond and the vorticity field of Lund and Regge. The total number of degrees of freedom of a unary system, including the density and the two velocity fields is 4, as expected — as in classical hydrodynamics. In this paper, we do not reduce Einstein’s dynamical equation for the metric to phenomenology, which would have denied the relevance of any intrinsic dynamics for the matter sector, nor do we abandon the equation of continuity - the very soul of hydrodynamics.

Scaled-down particle-in-cell simulation of cathode plasma expansion in magnetically insulated coaxial diode

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

Zhu, Danni; Zhang, Jun, E-mail: zhangjun@nudt.edu.cn; Zhong, Huihuang

2016-03-15

The expansion of cathode plasma in magnetically insulated coaxial diode (MICD) is investigated in theory and particle-in-cell (PIC) simulation. The temperature and density of the cathode plasma are about several eV and 10{sup 13}–10{sup 16 }cm{sup −3}, respectively, and its expansion velocity is of the level of few cm/μs. Through hydrodynamic theory analysis, expressions of expansion velocities in axial and radial directions are obtained. The characteristics of cathode plasma expansion have been simulated through scaled-down PIC models. Simulation results indicate that the expansion velocity is dominated by the ratio of plasma density other than the static electric field. The electric fieldmore » counteracts the plasma expansion reverse of it. The axial guiding magnetic field only reduces the radial transport coefficients by a correction factor, but not the axial ones. Both the outward and inward radial expansions of a MICD are suppressed by the much stronger guiding magnetic field and even cease.« less

The kinetic regime of the Vicsek model

NASA Astrophysics Data System (ADS)

Chepizhko, A. A.; Kulinskii, V. L.

2009-12-01

We consider the dynamics of the system of self-propelling particles modeled via the Vicsek algorithm in continuum time limit. It is shown that the alignment process for the velocities can be subdivided into two regimes: "fast" kinetic and "slow" hydrodynamic ones. In fast kinetic regime the alignment of the particle velocity to the local neighborhood takes place with characteristic relaxation time. So, that the bigger regions arise with the velocity alignment. These regions align their velocities thus giving rise to hydrodynamic regime of the dynamics. We propose the mean-field-like approach in which we take into account the correlations between density and velocity. The comparison of the theoretical predictions with the numerical simulations is given. The relation between Vicsek model in the zero velocity limit and the Kuramoto model is stated. The mean-field approach accounting for the dynamic change of the neighborhood is proposed. The nature of the discontinuity of the dependence of the order parameter in case of vectorial noise revealed in Gregorie and Chaite, Phys. Rev. Lett., 92, 025702 (2004) is discussed and the explanation of it is proposed.

Multi-Band Light Curves from Two-Dimensional Simulations of Gamma-Ray Burst Afterglows

NASA Astrophysics Data System (ADS)

MacFadyen, Andrew

2010-01-01

The dynamics of gamma-ray burst outflows is inherently multi-dimensional. 1.) We present high resolution two-dimensional relativistic hydrodynamics simulations of GRBs in the afterglow phase using adaptive mesh refinement (AMR). Using standard synchrotron radiation models, we compute multi-band light curves, from the radio to X-ray, directly from the 2D hydrodynamics simulation data. We will present on-axis light curves for both constant density and wind media. We will also present off-axis light curves relevant for searches for orphan afterglows. We find that jet breaks are smoothed due to both off-axis viewing and wind media effects. 2.) Non-thermal radiation mechanisms in GRB afterglows require substantial magnetic field strengths. In turbulence driven by shear instabilities in relativistic magnetized gas, we demonstrate that magnetic field is naturally amplified to half a percent of the total energy (epsilon B = 0.005). We will show high resolution three dimensional relativistic MHD simulations of this process as well as particle in cell (PIC) simulations of mildly relativistic collisionless shocks.

Warm Dense Matter: Another Application for Pulsed Power Hydrodynamics

DTIC Science & Technology

2009-06-01

Pulsed power hydrodynamic techniques, such as large convergence liner compression of a large volume, modest density, low temperature plasma to...controlled than are similar high explosively powered hydrodynamic experiments. While the precision and controllability of gas- gun experiments is...well established, pulsed power techniques using imploding liner offer access to convergent conditions, difficult to obtain with guns – and essential

Properties of large scale plasma flow during the early stage of the plasmaspheric refilling

NASA Technical Reports Server (NTRS)

Singh, Nagendra; Craven, P.; Torr, D. G.; Richards, P. G.

1990-01-01

The objective is to better characterize the macroscopic properties of the interhemisphere plasma flow by solving a more complete set of hydrodynamic equations than that solved previously. Specifically, the ion continuity, momentum and energy equations were solved for the plasma flow along the closed magnetic field lines. During the initial stage of the supersonic outflow in the equatorial region, the ions cool substantially. Using the hydrodynamic model for the large-scale plasma flow, the dynamics of shocks was examined which form in the geomagnetic flux tubes during the early stages of refilling. These shocks are more like those forming in neutral gases than the electrostatic shocks driven by microinstabilities involving ion-ion interaction. Therefore, the shocks seen in the hydrodynamic model are termed as hydrodynamic shocks. Such shocks are generally unsteady and therefore the usual shock jump conditions given by Rankine-Hugoniot relations are not strictly applicable to them. The density, flow velocity and temperature structures associated with the shocks are examined for both asymmetrical and symmetrical flows. In the asymmetrical flow the outflow from one of two conjugate ionospheres is dominant. On the other hand, in the symmetrical case outflows from the two ionospheric sources are identical. Both cases are treated by a two-stream model. In the late type of flow, the early-time refilling shows a relaxation type of oscillation, which is driven by the large-scale interactions between the two identical streams. After this early stage, the resulting temperature structure shows some interesting features. In the equatorial region the streams are isothermal, but in the off-equatorial regions the streams have quite different temperatures, and also densities and flow velocities. The dense and slow stream is found to be warmer than the low-density fast stream. In the late stage of refilling, the temperature is found to steadily increase from the conjugate ionospheres towards the equator; the equatorial temperature is found to be as high as about 8000 K compared to the ionospheric temperature of 3600 K.

Nonlinear waves and shocks in relativistic two-fluid hydrodynamics

NASA Astrophysics Data System (ADS)

Haim, L.; Gedalin, M.; Spitkovsky, A.; Krasnoselskikh, V.; Balikhin, M.

2012-06-01

Relativistic shocks are present in a number of objects where violent processes are accompanied by relativistic outflows of plasma. The magnetization parameter σ = B2/4πnmc2 of the ambient medium varies in wide range. Shocks with low σ are expected to substantially enhance the magnetic fields in the shock front. In non-relativistic shocks the magnetic compression is limited by nonlinear effects related to the deceleration of flow. Two-fluid analysis of perpendicular relativistic shocks shows that the nonlinearities are suppressed for σ<<1 and the magnetic field reaches nearly equipartition values when the magnetic energy density is of the order of the ion energy density, Beq2 ~ 4πnmic2γ. A large cross-shock potential eφ/mic2γ0 ~ B2/Beq2 develops across the electron-ion shock front. This potential is responsible for electron energization.

The impact of stellar feedback on the density and velocity structure of the interstellar medium

NASA Astrophysics Data System (ADS)

Grisdale, Kearn; Agertz, Oscar; Romeo, Alessandro B.; Renaud, Florent; Read, Justin I.

2017-04-01

We study the impact of stellar feedback in shaping the density and velocity structure of neutral hydrogen (H I) in disc galaxies. For our analysis, we carry out ˜4.6 pc resolution N-body+adaptive mesh refinement hydrodynamic simulations of isolated galaxies, set up to mimic a Milky Way and a Large and Small Magellanic Cloud. We quantify the density and velocity structure of the interstellar medium using power spectra and compare the simulated galaxies to observed H I in local spiral galaxies from THINGS (The H I Nearby Galaxy Survey). Our models with stellar feedback give an excellent match to the observed THINGS H I density power spectra. We find that kinetic energy power spectra in feedback-regulated galaxies, regardless of galaxy mass and size, show scalings in excellent agreement with supersonic turbulence (E(k) ∝ k-2) on scales below the thickness of the H I layer. We show that feedback influences the gas density field, and drives gas turbulence, up to large (kpc) scales. This is in stark contrast to density fields generated by large-scale gravity-only driven turbulence. We conclude that the neutral gas content of galaxies carries signatures of stellar feedback on all scales.

Effect of truncated cone roughness element density on hydrodynamic drag

NASA Astrophysics Data System (ADS)

Womack, Kristofer; Schultz, Michael; Meneveau, Charles

2017-11-01

An experimental study was conducted on rough-wall, turbulent boundary layer flow with roughness elements whose idealized shape model barnacles that cause hydrodynamic drag in many applications. Varying planform densities of truncated cone roughness elements were investigated. Element densities studied ranged from 10% to 79%. Detailed turbulent boundary layer velocity statistics were recorded with a two-component LDV system on a three-axis traverse. Hydrodynamic roughness length (z0) and skin-friction coefficient (Cf) were determined and compared with the estimates from existing roughness element drag prediction models including Macdonald et al. (1998) and other recent models. The roughness elements used in this work model idealized barnacles, so implications of this data set for ship powering are considered. This research was supported by the Office of Naval Research and by the Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program.

Density and spin modes in imbalanced normal Fermi gases from collisionless to hydrodynamic regime

NASA Astrophysics Data System (ADS)

Narushima, Masato; Watabe, Shohei; Nikuni, Tetsuro

2018-03-01

We study the mass- and population-imbalance effect on density (in-phase) and spin (out-of-phase) collective modes in a two-component normal Fermi gas. By calculating the eigenmodes of the linearized Boltzmann equation as well as the density/spin dynamic structure factor, we show that mass- and population-imbalance effects offer a variety of collective mode crossover behaviors from collisionless to hydrodynamic regimes. The mass-imbalance effect shifts the crossover regime to the higher-temperature, and a significant peak of the spin dynamic structure factor emerges only in the collisionless regime. This is in contrast to the case of mass- and population-balanced normal Fermi gases, where the spin dynamic response is always absent. Although the population-imbalance effect does not shift the crossover regime, the spin dynamic structure factor survives both in the collisionless and hydrodynamic regimes.

Hydrodynamic evolution of plasma waveguides for soft-x-ray amplifiers

NASA Astrophysics Data System (ADS)

Oliva, Eduardo; Depresseux, Adrien; Cotelo, Manuel; Lifschitz, Agustín; Tissandier, Fabien; Gautier, Julien; Maynard, Gilles; Velarde, Pedro; Sebban, Stéphane

2018-02-01

High-density, collisionally pumped plasma-based soft-x-ray lasers have recently delivered hundreds of femtosecond pulses, breaking the longstanding barrier of one picosecond. To pump these amplifiers an intense infrared pulse must propagate focused throughout all the length of the amplifier, which spans several Rayleigh lengths. However, strong nonlinear effects hinder the propagation of the laser beam. The use of a plasma waveguide allows us to overcome these drawbacks provided the hydrodynamic processes that dominate the creation and posterior evolution of the waveguide are controlled and optimized. In this paper we present experimental measurements of the radial density profile and transmittance of such waveguide, and we compare them with numerical calculations using hydrodynamic and particle-in-cell codes. Controlling the properties (electron density value and radial gradient) of the waveguide with the help of numerical codes promises the delivery of ultrashort (tens of femtoseconds), coherent soft-x-ray pulses.

Navier-Stokes hydrodynamics of thermal collapse in a freely cooling granular gas.

PubMed

Kolvin, Itamar; Livne, Eli; Meerson, Baruch

2010-08-01

We show that, in dimension higher than one, heat diffusion and viscosity cannot arrest thermal collapse in a freely evolving dilute granular gas, even in the absence of gravity. Thermal collapse involves a finite-time blowup of the gas density. It was predicted earlier in ideal, Euler hydrodynamics of dilute granular gases in the absence of gravity, and in nonideal, Navier-Stokes granular hydrodynamics in the presence of gravity. We determine, analytically and numerically, the dynamic scaling laws that characterize the gas flow close to collapse. We also investigate bifurcations of a freely evolving dilute granular gas in circular and wedge-shaped containers. Our results imply that, in general, thermal collapse can only be arrested when the gas density becomes comparable with the close-packing density of grains. This provides a natural explanation to the formation of densely packed clusters of particles in a variety of initially dilute granular flows.

Testing hydrodynamics schemes in galaxy disc simulations

NASA Astrophysics Data System (ADS)

Few, C. G.; Dobbs, C.; Pettitt, A.; Konstandin, L.

2016-08-01

We examine how three fundamentally different numerical hydrodynamics codes follow the evolution of an isothermal galactic disc with an external spiral potential. We compare an adaptive mesh refinement code (RAMSES), a smoothed particle hydrodynamics code (SPHNG), and a volume-discretized mesh-less code (GIZMO). Using standard refinement criteria, we find that RAMSES produces a disc that is less vertically concentrated and does not reach such high densities as the SPHNG or GIZMO runs. The gas surface density in the spiral arms increases at a lower rate for the RAMSES simulations compared to the other codes. There is also a greater degree of substructure in the SPHNG and GIZMO runs and secondary spiral arms are more pronounced. By resolving the Jeans length with a greater number of grid cells, we achieve more similar results to the Lagrangian codes used in this study. Other alterations to the refinement scheme (adding extra levels of refinement and refining based on local density gradients) are less successful in reducing the disparity between RAMSES and SPHNG/GIZMO. Although more similar, SPHNG displays different density distributions and vertical mass profiles to all modes of GIZMO (including the smoothed particle hydrodynamics version). This suggests differences also arise which are not intrinsic to the particular method but rather due to its implementation. The discrepancies between codes (in particular, the densities reached in the spiral arms) could potentially result in differences in the locations and time-scales for gravitational collapse, and therefore impact star formation activity in more complex galaxy disc simulations.

Separability of electrostatic and hydrodynamic forces in particle electrophoresis

NASA Astrophysics Data System (ADS)

Todd, Brian A.; Cohen, Joel A.

2011-09-01

By use of optical tweezers we explicitly measure the electrostatic and hydrodynamic forces that determine the electrophoretic mobility of a charged colloidal particle. We test the ansatz of O'Brien and White [J. Chem. Soc. Faraday IIJCFTBS0300-923810.1039/f29787401607 74, 1607 (1978)] that the electrostatically and hydrodynamically coupled electrophoresis problem is separable into two simpler problems: (1) a particle held fixed in an applied electric field with no flow field and (2) a particle held fixed in a flow field with no applied electric field. For a system in the Helmholtz-Smoluchowski and Debye-Hückel regimes, we find that the electrostatic and hydrodynamic forces measured independently accurately predict the electrophoretic mobility within our measurement precision of 7%; the O'Brien and White ansatz holds under the conditions of our experiment.

The dynamical role of the central molecular ring within the framework of a seven-component Galaxy model

NASA Astrophysics Data System (ADS)

Simin, A. A.; Fridman, A. M.; Haud, U. A.

1991-09-01

A Galaxy model in which the surface density of the gas component has a sharp (two orders of magnitude) jump in the region of the outer radius of the molecular ring is constructed on the basis of observational data. This model is used to calculate the contributions of each population to the model curve of Galactic rotation. The value of the dimensionless increment of hydrodynamical instability for the gas component, being much less than 1, coincides with a similar magnitude for the same gas in the gravity field of the entire Galaxy. It is concluded that the unstable gas component of the Galaxy lies near the limit of the hydrodynamical instability, which is in accordance with the Le Chatelier principle. The stellar populations of the Galaxy probably do not affect the generation of the spiral structure in the gaseous component.

Hydrodynamics of a cold one-dimensional fluid: the problem of strong shock waves

NASA Astrophysics Data System (ADS)

Hurtado, Pablo I.

2005-03-01

We study a shock wave induced by an infinitely massive piston propagating into a one-dimensional cold gas. The cold gas is modelled as a collection of hard rods which are initially at rest, so the temperature is zero. Most of our results are based on simulations of a gas of rods with binary mass distribution, and we partcularly focus on the case of spatially alternating masses. We find that the properties of the resulting shock wave are in striking contrast with those predicted by hydrodynamic and kinetic approaches, e.g., the flow-field profiles relax algebraically toward their equilibrium values. In addition, most relevant observables characterizing local thermodynamic equilibrium and equipartition decay as a power law of the distance to the shock layer. The exponents of these power laws depend non-monotonously on the mass ratio. Similar interesting dependences on the mass ratio also characterize the shock width, density and temperature overshoots, etc.

Transverse electron-scale instability in relativistic shear flows.

PubMed

Alves, E P; Grismayer, T; Fonseca, R A; Silva, L O

2015-08-01

Electron-scale surface waves are shown to be unstable in the transverse plane of a sheared flow in an initially unmagnetized collisionless plasma, not captured by (magneto)hydrodynamics. It is found that these unstable modes have a higher growth rate than the closely related electron-scale Kelvin-Helmholtz instability in relativistic shears. Multidimensional particle-in-cell simulations verify the analytic results and further reveal the emergence of mushroomlike electron density structures in the nonlinear phase of the instability, similar to those observed in the Rayleigh Taylor instability despite the great disparity in scales and different underlying physics. This transverse electron-scale instability may play an important role in relativistic and supersonic sheared flow scenarios, which are stable at the (magneto)hydrodynamic level. Macroscopic (≫c/ωpe) fields are shown to be generated by this microscopic shear instability, which are relevant for particle acceleration, radiation emission, and to seed magnetohydrodynamic processes at long time scales.

Transport of particles, drops, and small organisms in density stratified fluids

NASA Astrophysics Data System (ADS)

Ardekani, Arezoo M.; Doostmohammadi, Amin; Desai, Nikhil

2017-10-01

Sedimenting particles and motile organisms are ubiquitously found in oceans and lakes, where density stratification naturally occurs due to temperature or salinity gradients. We explore the effects of stratification on the fundamental hydrodynamics of settling particles, rising drops, and small organisms. The results of our direct numerical simulations of the sedimentation of particles show that the presence of vertical density gradients in the water column can substantially affect the settling dynamics of a particle, interaction between a pair of particles, and settling rates and microstructure of suspension of particles. We show that elongation of particles affects both the settling orientation and the settling rate of particles in stratified fluids, which will have direct consequences on the vertical flux of particulate matter and carbon flux in the ocean. We further demonstrate an unexpected effect of buoyancy, potentially affecting a broad range of processes at pycnoclines in oceans and lakes. In particular, stratification has a major effect on the flow field, energy expenditure, and nutrient uptake of small organisms. In addition, the role of stratification in pattern formation of bioconvection plumes of algal cells and in biogenic mixing is investigated. In particular, the numerical approach allows for considering the effects of background turbulence and hydrodynamic perturbations produced by swimming organisms, shedding light on the contribution of organisms in the mixing process in aqueous environments.

Conformal field theory as microscopic dynamics of incompressible Euler and Navier-Stokes equations.

PubMed

Fouxon, Itzhak; Oz, Yaron

2008-12-31

We consider the hydrodynamics of relativistic conformal field theories at finite temperature. We show that the limit of slow motions of the ideal hydrodynamics leads to the nonrelativistic incompressible Euler equation. For viscous hydrodynamics we show that the limit of slow motions leads to the nonrelativistic incompressible Navier-Stokes equation. We explain the physical reasons for the reduction and discuss the implications. We propose that conformal field theories provide a fundamental microscopic viewpoint of the equations and the dynamics governed by them.

Effective dynamical coupling of hydrodynamics and transport for heavy-ion collisions

NASA Astrophysics Data System (ADS)

Oliinychenko, Dmytro; Petersen, Hannah

2017-04-01

Present hydrodynamics-based simulations of heavy-ion collisions neglect the feedback from the frozen-out particles flying back into the hydrodynamical region. This causes an artefact called “negative Cooper-Frye contributions”, which is negligible for high collision energies, but becomes significant for lower RHIC BES energies and for event-by-event simulations. To avoid negative Cooper-Frye contributions, while still preserving hydrodynamical behavior, we propose a pure hadronic transport approach with forced thermalization in the regions of high energy density. It is demonstrated that this approach exhibits enhancement of strangeness and mean transverse momenta compared to conventional transport - an effect typical for hydrodynamical approaches.

Hydrodynamic model of temperature change in open ionic channels.

PubMed Central

Chen, D P; Eisenberg, R S; Jerome, J W; Shu, C W

1995-01-01

Most theories of open ionic channels ignore heat generated by current flow, but that heat is known to be significant when analogous currents flow in semiconductors, so a generalization of the Poisson-Nernst-Planck theory of channels, called the hydrodynamic model, is needed. The hydrodynamic theory is a combination of the Poisson and Euler field equations of electrostatics and fluid dynamics, conservation laws that describe diffusive and convective flow of mass, heat, and charge (i.e., current), and their coupling. That is to say, it is a kinetic theory of solute and solvent flow, allowing heat and current flow as well, taking into account density changes, temperature changes, and electrical potential gradients. We integrate the equations with an essentially nonoscillatory shock-capturing numerical scheme previously shown to be stable and accurate. Our calculations show that 1) a significant amount of electrical energy is exchanged with the permeating ions; 2) the local temperature of the ions rises some tens of degrees, and this temperature rise significantly alters for ionic flux in a channel 25 A long, such as gramicidin-A; and 3) a critical parameter, called the saturation velocity, determines whether ionic motion is overdamped (Poisson-Nernst-Planck theory), is an intermediate regime (called the adiabatic approximation in semiconductor theory), or is altogether unrestricted (requiring the full hydrodynamic model). It seems that significant temperature changes are likely to accompany current flow in the open ionic channel. PMID:8599638

SPHYNX: an accurate density-based SPH method for astrophysical applications

NASA Astrophysics Data System (ADS)

Cabezón, R. M.; García-Senz, D.; Figueira, J.

2017-10-01

Aims: Hydrodynamical instabilities and shocks are ubiquitous in astrophysical scenarios. Therefore, an accurate numerical simulation of these phenomena is mandatory to correctly model and understand many astrophysical events, such as supernovas, stellar collisions, or planetary formation. In this work, we attempt to address many of the problems that a commonly used technique, smoothed particle hydrodynamics (SPH), has when dealing with subsonic hydrodynamical instabilities or shocks. To that aim we built a new SPH code named SPHYNX, that includes many of the recent advances in the SPH technique and some other new ones, which we present here. Methods: SPHYNX is of Newtonian type and grounded in the Euler-Lagrange formulation of the smoothed-particle hydrodynamics technique. Its distinctive features are: the use of an integral approach to estimating the gradients; the use of a flexible family of interpolators called sinc kernels, which suppress pairing instability; and the incorporation of a new type of volume element which provides a better partition of the unity. Unlike other modern formulations, which consider volume elements linked to pressure, our volume element choice relies on density. SPHYNX is, therefore, a density-based SPH code. Results: A novel computational hydrodynamic code oriented to Astrophysical applications is described, discussed, and validated in the following pages. The ensuing code conserves mass, linear and angular momentum, energy, entropy, and preserves kernel normalization even in strong shocks. In our proposal, the estimation of gradients is enhanced using an integral approach. Additionally, we introduce a new family of volume elements which reduce the so-called tensile instability. Both features help to suppress the damp which often prevents the growth of hydrodynamic instabilities in regular SPH codes. Conclusions: On the whole, SPHYNX has passed the verification tests described below. For identical particle setting and initial conditions the results were similar (or better in some particular cases) than those obtained with other SPH schemes such as GADGET-2, PSPH or with the recent density-independent formulation (DISPH) and conservative reproducing kernel (CRKSPH) techniques.

Simulations of controlled spectral emission of Al plasmas generated by temporally tailored laser irradiation

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

Colombier, J. P.; Guillermin, M.; Garrelie, F.

2010-10-08

Hydrodynamics simulations and irradiation experiments were performed to correlate ul-trashort intensity envelopes of the laser fields and thermodynamical states reached by the emerging plasma phase in ablation regimes. We discuss the efficiency of energy coupling as a function of different intensity envelopes and the resulting temperature, density and ionization states since the energy delivery rate is an essential factor that predetermines the material thermodynamic evolution. Subsequently, we examine the plasma composition in calculating the proportion of neutral/ion species typical of LIBS signals and comparing it with neutral/ion ratios given by experimental results. Moreover, the calculations allow to investigate the efficiencymore » of nanoparticles generation from materials subjected to different heating rates. These can be related to hydrodynamic ejection of nanosized liquid layers upon the action of mechanic waves. With support from numerical simulations of the hydrodynamic advance of the excited matter, experiments revealed that mastering intensity envelopes of ultrashort laser pulse leads to further control on the ablation products. Emerging plasma phase in a hot state generates specific spectral emission patterns that can serve as indicators for its controlled formation and kinetic evolution.« less

LPWA using supersonic gas jet with tailored density profile

NASA Astrophysics Data System (ADS)

Kononenko, O.; Bohlen, S.; Dale, J.; D'Arcy, R.; Dinter, M.; Erbe, J. H.; Indorf, G.; di Lucchio, L.; Goldberg, L.; Gruse, J. N.; Karstensen, S.; Libov, V.; Ludwig, K.; Martinez de La Ossa, A.; Marutzky, F.; Niroula, A.; Osterhoff, J.; Quast, M.; Schaper, L.; Schwinkendorf, J.-P.; Streeter, M.; Tauscher, G.; Weichert, S.; Palmer, C.; Horbatiuk, Taras

2016-10-01

Laser driven plasma wakefield accelerators have been explored as a potential compact, reproducible source of relativistic electron bunches, utilising an electric field of many GV/m. Control over injection of electrons into the wakefield is of crucial importance in producing stable, mono-energetic electron bunches. Density tailoring of the target, to control the acceleration process, can also be used to improve the quality of the bunch. By using gas jets to provide tailored targets it is possible to provide good access for plasma diagnostics while also producing sharp density gradients for density down-ramp injection. OpenFOAM hydrodynamic simulations were used to investigate the possibility of producing tailored density targets in a supersonic gas jet. Particle-in-cell simulations of the resulting density profiles modelled the effect of the tailored density on the properties of the accelerated electron bunch. Here, we present the simulation results together with preliminary experimental measurements of electron and x-ray properties from LPWA experiments using gas jet targets and a 25 TW, 25 fs Ti:Sa laser system at DESY.

Wiggler magnetic field assisted third harmonic generation in expanding clusters

NASA Astrophysics Data System (ADS)

Vij, Shivani

2018-04-01

A simple theoretical model is constructed to study the wiggler magnetic field assisted third harmonic generation of intense short pulse laser in a cluster in its expanding phase. The ponderomotive force of laser causes density perturbations in cluster electron density which couples with wiggler magnetic field to produce a nonlinear current that generates transverse third harmonic. An intense short pulse laser propagating through a gas embedded with atomic clusters, converts it into hot plasma balls via tunnel ionization. Initially, the electron plasma frequency inside the clusters ω pe > \\sqrt{3}{ω }1 (with ω 1 being the frequency of the laser). As the cluster expands under Coulomb force and hydrodynamic pressure, ω pe decreases to \\sqrt{3}{ω }1. At this time, there is resonant enhancement in the efficiency of the third harmonic generation. The efficiency of third harmonic generation is enhanced due to cluster plasmon resonance and by phase matching due to wiggler magnetic field. The effect of cluster size on the expansion rate is studied to observe that the clusters of different radii would expand differently. The impact of laser intensity and wiggler magnetic field on the efficiency of third harmonic generation is also explored.

Microwave produced plasma in a Toroidal Device

NASA Astrophysics Data System (ADS)

Singh, A. K.; Edwards, W. F.; Held, E. D.

2010-11-01

A currentless toroidal plasma device exhibits a large range of interesting basic plasma physics phenomena. Such a device is not in equilibrium in a strict magneto hydrodynamic sense. There are many sources of free energy in the form of gradients in plasma density, temperature, the background magnetic field and the curvature of the magnetic field. These free energy sources excite waves and instabilities which have been the focus of studies in several devices in last two decades. A full understanding of these simple plasmas is far from complete. At Utah State University we have recently designed and installed a microwave plasma generation system on a small tokamak borrowed from the University of Saskatchewan, Saskatoon, Canada. Microwaves are generated at 2.45 GHz in a pulsed dc mode using a magnetron from a commercial kitchen microwave oven. The device is equipped with horizontal and vertical magnetic fields and a transformer to impose a toroidal electric field for current drive. Plasmas can be obtained over a wide range of pressure with and without magnetic fields. We present some preliminary measurements of plasma density and potential profiles. Measurements of plasma temperature at different operating conditions are also presented.

Metric anisotropies and emergent anisotropic hydrodynamics

NASA Astrophysics Data System (ADS)

Dash, Ashutosh; Jaiswal, Amaresh

2018-05-01

Expansion of a locally equilibrated fluid is considered in an anisotropic space-time given by the Bianchi type-I metric. Starting from the isotropic equilibrium phase-space distribution function in the local rest frame, we obtain expressions for components of the energy-momentum tensor and conserved current, such as number density, energy density, and pressure components. In the case of an axissymmetric Bianchi type-I metric, we show that they are identical to those obtained within the setup of anisotropic hydrodynamics. We further consider the case in which the Bianchi type-I metric is a vacuum solution of the Einstein equation: the Kasner metric. For the axissymmetric Kasner metric, we discuss the implications of our results in the context of anisotropic hydrodynamics.

A Computational Study of a Circular Interface Richtmyer-Meshkov Instability in MHD

NASA Astrophysics Data System (ADS)

Maxon, William; Black, Wolfgang; Denissen, Nicholas; McFarland, Jacob; Los Alamos National Laboratory Collaboration; University of Missouri Shock Tube Laboratory Team

2017-11-01

The Richtmyer-Meshkov instability (RMI) is a hydrodynamic instability that appears in several high energy density applications such as inertial confinement fusion (ICF). In ICF, as the thermonuclear fuel is being compressed it begins to mix due to fluid instabilities including the RMI. This mixing greatly decreases the energy output. The RMI occurs when two fluids of different densities are impulsively accelerated and the pressure and density gradients are misaligned. In magnetohydrodynamics (MHD), the RMI may be suppressed by introducing a magnetic field in an electrically conducting fluid, such as a plasma. This suppression has been studied as a possible mechanism for improving confinement in ICF targets. In this study,ideal MHD simulations are performed with a circular interface impulsively accelerated by a shock wave in the presence of a magnetic field. These simulations are executed with the research code FLAG, a multiphysics, arbitrary Lagrangian/Eulerian, hydrocode developed and utilized at Los Alamos National Laboratory. The simulation results will be assessed both quantitatively and qualitatively to examine the stabilization mechanism. These simulations will guide ongoing MHD experiments at the University of Missouri Shock Tube Facility.

Quasinormal modes of charged magnetic black branes & chiral magnetic transport

NASA Astrophysics Data System (ADS)

Ammon, Martin; Kaminski, Matthias; Koirala, Roshan; Leiber, Julian; Wu, Jackson

2017-04-01

We compute quasinormal modes (QNMs) of the metric and gauge field perturbations about black branes electrically and magnetically charged in the Einstein-Maxwell-Chern-Simons theory. By the gauge/gravity correspondence, this theory is dual to a particular class of field theories with a chiral anomaly, in a thermal charged plasma state subjected to a constant external magnetic field, B. The QNMs are dual to the poles of the two-point functions of the energy-momentum and axial current operators, and they encode information about the dissipation and transport of charges in the plasma. Complementary to the gravity calculation, we work out the hydrodynamic description of the dual field theory in the presence of a chiral anomaly, and a constant external B. We find good agreement with the weak field hydrodynamics, which can extend beyond the weak B regime into intermediate regimes. Furthermore, we provide results that can be tested against thermodynamics and hydrodynamics in the strong B regime. We find QNMs exhibiting Landau level behavior, which become long-lived at large B if the anomaly coefficient exceeds a critical magnitude. Chiral transport is analyzed beyond the hydrodynamic approximation for the five (formerly) hydrodynamic modes, including a chiral magnetic wave.

Axial magnetic field and toroidally streaming fast ions in the dense plasma focus are natural consequences of conservation laws in the curved axisymmetric geometry of the current sheath. II. Towards a first principles theory

NASA Astrophysics Data System (ADS)

Auluck, S. K. H.

2017-11-01

This paper continues earlier discussion [S. K. H. Auluck, Phys. Plasmas 21, 102515 (2014)] concerning the formulation of conservation laws of mass, momentum, and energy in a local curvilinear coordinate system in the dense plasma focus. This formulation makes use of the revised Gratton-Vargas snowplow model [S. K. H. Auluck, Phys. Plasmas 20, 112501 (2013)], which provides an analytically defined imaginary surface in three dimensions which resembles the experimentally determined shape of the plasma. Unit vectors along the local tangent to this surface, along the azimuth, and along the local normal define a right-handed orthogonal local curvilinear coordinate system. The simplifying assumption that physical quantities have significant variation only along the normal enables writing laws of conservation of mass, momentum, and energy in the form of effectively one-dimensional hyperbolic conservation law equations using expressions for various differential operators derived for this coordinate system. This formulation demonstrates the highly non-trivial result that the axial magnetic field and toroidally streaming fast ions, experimentally observed by multiple prestigious laboratories, are natural consequences of conservation of mass, momentum, and energy in the curved geometry of the dense plasma focus current sheath. The present paper continues the discussion in the context of a 3-region shock structure similar to the one experimentally observed: an unperturbed region followed by a hydrodynamic shock containing some current followed by a magnetic piston. Rankine-Hugoniot conditions are derived, and expressions are obtained for the specific volumes and pressures using the mass-flux between the hydrodynamic shock and the magnetic piston and current fraction in the hydrodynamic shock as unknown parameters. For the special case of a magnetic piston that remains continuously in contact with the fluid being pushed, the theory gives closed form algebraic results for the fraction of current flowing in the hydrodynamic shock, specific volume, pressure, and fluid velocity of the hydrodynamic shock region, the tangential, normal, and azimuthal components of velocity in the magnetized plasma, the density of the magnetized plasma, the normal and tangential components of the magnetic field, and the tangential, normal, and azimuthal components of the electric field. This explains the occurrence of azimuthally streaming high energy deuterons experimentally observed by Frascati and Stuttgart. The expression derived for the azimuthal component of vector potential can serve as the basis for a proposed experimental test of the theory.

Hydrodynamic model for conductivity in graphene.

PubMed

Mendoza, M; Herrmann, H J; Succi, S

2013-01-01

Based on the recently developed picture of an electronic ideal relativistic fluid at the Dirac point, we present an analytical model for the conductivity in graphene that is able to describe the linear dependence on the carrier density and the existence of a minimum conductivity. The model treats impurities as submerged rigid obstacles, forming a disordered medium through which graphene electrons flow, in close analogy with classical fluid dynamics. To describe the minimum conductivity, we take into account the additional carrier density induced by the impurities in the sample. The model, which predicts the conductivity as a function of the impurity fraction of the sample, is supported by extensive simulations for different values of ε, the dimensionless strength of the electric field, and provides excellent agreement with experimental data.

Dynamic density functional theory with hydrodynamic interactions and fluctuations

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

Donev, Aleksandar, E-mail: donev@courant.nyu.edu; Vanden-Eijnden, Eric, E-mail: eve2@courant.nyu.edu

2014-06-21

We derive a closed equation for the empirical concentration of colloidal particles in the presence of both hydrodynamic and direct interactions. The ensemble average of our functional Langevin equation reproduces known deterministic Dynamic Density Functional Theory (DDFT) [M. Rex and H. Löwen, “Dynamical density functional theory with hydrodynamic interactions and colloids in unstable traps,” Phys. Rev. Lett. 101(14), 148302 (2008)], and, at the same time, it also describes the microscopic fluctuations around the mean behavior. We suggest separating the ideal (non-interacting) contribution from additional corrections due to pairwise interactions. We find that, for an incompressible fluid and in the absencemore » of direct interactions, the mean concentration follows Fick's law just as for uncorrelated walkers. At the same time, the nature of the stochastic terms in fluctuating DDFT is shown to be distinctly different for hydrodynamically-correlated and uncorrelated walkers. This leads to striking differences in the behavior of the fluctuations around Fick's law, even in the absence of pairwise interactions. We connect our own prior work [A. Donev, T. G. Fai, and E. Vanden-Eijnden, “A reversible mesoscopic model of diffusion in liquids: from giant fluctuations to Fick's law,” J. Stat. Mech.: Theory Exp. (2014) P04004] on fluctuating hydrodynamics of diffusion in liquids to the DDFT literature, and demonstrate that the fluid cannot easily be eliminated from consideration if one wants to describe the collective diffusion in colloidal suspensions.« less

Hydrodynamics simulations of 2{omega} laser propagation in underdense gasbag plasmas

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

Meezan, N.B.; Divol, L.; Marinak, M.M.

2004-12-01

Recent 2{omega} laser propagation and stimulated Raman backscatter (SRS) experiments performed on the Helen laser have been analyzed using the radiation-hydrodynamics code HYDRA [M. M. Marinak, G. D. Kerbel, N. A. Gentile, O. Jones, D. Munro, S. Pollaine, T. R. Dittrich, and S. W. Haan, Phys. Plasmas 8, 2275 (2001)]. These experiments utilized two diagnostics sensitive to the hydrodynamics of gasbag targets: a fast x-ray framing camera (FXI) and a SRS streak spectrometer. With a newly implemented nonlocal thermal transport model, HYDRA is able to reproduce many features seen in the FXI images and the SRS streak spectra. Experimental andmore » simulated side-on FXI images suggest that propagation can be explained by classical laser absorption and the resulting hydrodynamics. Synthetic SRS spectra generated from the HYDRA results reproduce the details of the experimental SRS streak spectra. Most features in the synthetic spectra can be explained solely by axial density and temperature gradients. The total SRS backscatter increases with initial gasbag fill density up to {approx_equal}0.08 times the critical density, then decreases. Data from a near-backscatter imaging camera show that severe beam spray is not responsible for the trend in total backscatter. Filamentation does not appear to be a significant factor in gasbag hydrodynamics. The simulation and analysis techniques established here can be used in ongoing experimental campaigns on the Omega laser facility and the National Ignition Facility.« less

Dynamics of Mesoscale Magnetic Field in Diffusive Shock Acceleration

NASA Astrophysics Data System (ADS)

Diamond, P. H.; Malkov, M. A.

2007-01-01

We present a theory for the generation of mesoscale (krg<<1, where rg is the cosmic-ray gyroradius) magnetic fields during diffusive shock acceleration. The decay or modulational instability of resonantly excited Alfvén waves scattering off ambient density perturbations in the shock environment naturally generates larger scale fields. For a broad spectrum of perturbations, the physical mechanism of energy transfer is random refraction, represented by the diffusion of Alfvén wave packets in k-space. The scattering field can be produced directly by the decay instability or by the Drury instability, a hydrodynamic instability driven by the cosmic-ray pressure gradient. This process is of interest to acceleration since it generates waves of longer wavelength, and so enables the confinement and acceleration of higher energy particles. This process also limits the intensity of resonantly generated turbulent magnetic fields on rg scales.

Numerical simulations of Z-Pinch experiments to create supersonic differentially-rotating plasma flows

NASA Astrophysics Data System (ADS)

Bocchi, M.; Ummels, B.; Chittenden, J. P.; Lebedev, S. V.

2012-02-01

In the context of high energy density laboratory astrophysics, we aim to produce and study a rotating plasma relevant to accretion discs physics. We devised an experimental setup based on a modified cylindrical wire array and we studied it numerically with the three-dimensional, resistive magneto-hydrodynamic code GORGON. The simulations show that a rotating plasma cylinder is formed, with typical rotation velocity ~35 km/s and Mach number ~5. In addition, the plasma ring is differentially rotating and strongly radiatively cooled. The introduction of external magnetic fields is discussed.

Hydrodynamic Instability in an Extended Landau/Levich Model of Liquid-Propellant Combustion

NASA Technical Reports Server (NTRS)

Margolis, Stephen B.; Sackesteder, Kurt (Technical Monitor)

1998-01-01

The classical Landau/Levich models of liquid propellant combustion, which serve as seminal examples of hydrodynamic instability in reactive systems, have been combined and extended to account for a dynamic dependence, absent in the original formulations, of the local burning rate on the local pressure and/or temperature fields. The resulting model admits an extremely rich variety of both hydrodynamic and reactive/diffusive instabilities that can be analyzed in various limiting parameter regimes. In the present work, a formal asymptotic analysis, based on the realistic smallness of the gas-to-liquid density ratio, is developed to investigate the combined effects of gravity, surface tension and viscosity on the hydrodynamic instability of the propagating liquid/gas interface. In particular, a composite asymptotic expression, spanning three distinguished wavenumber regimes, is derived for both cellular and pulsating hydrodynamic neutral stability boundaries A(sub p)(k), where A(sub p) is the pressure sensitivity of the burning rate and k is the disturbance wavenumber. For the case of cellular (Landau) instability, the results demonstrate explicitly the stabilizing effect of gravity on long-wave disturbances, the stabilizing effect of viscosity and surface tension on short-wave perturbations, and the instability associated with intermediate wavenumbers for critical negative values of A(sub p). In the limiting case of weak gravity, it is shown that cellular hydrodynamic instability in this context is a long-wave instability phenomenon, whereas at normal gravity, this instability is first manifested through O(l) wavenumber disturbances. It is also demonstrated that, in the large wavenumber regime, surface tension and both liquid and gas viscosity all produce comparable stabilizing effects in the large-wavenumber regime, thereby providing significant modifications to previous analyses of Landau instability in which one or more of these effects were neglected. In contrast, the pulsating hydrodynamic stability boundary is found to be insensitive to gravitational and surface-tension effects, but is more sensitive to the effects of liquid viscosity, which is a significant stabilizing effect for O(l) and higher wavenumbers. Liquid-propellant combustion is predicted to be stable (i.e., steady and planar) only for a range of negative pressure sensitivities that lie between the two types of hydrodynamic stability boundaries.

Observations of two-dimensional magnetic field evolution in a plasma opening switch

NASA Astrophysics Data System (ADS)

Shpitalnik, R.; Weingarten, A.; Gomberoff, K.; Krasik, Ya.; Maron, Y.

1998-03-01

The time dependent magnetic field distribution was studied in a coaxial 100-ns positive-polarity Plasma Opening Switch (POS) by observing the Zeeman effect in ionic line emission. Measurements local in three dimensions are obtained by doping the plasma using laser evaporation techniques. Fast magnetic field penetration with a relatively sharp magnetic field front (⩽1 cm) is observed at the early stages of the pulse (t≲25). Later in the pulse, the magnetic field is observed at the load-side edge of the plasma, leaving "islands" of low magnetic field at the plasma center that last for about 10 ns. The two-dimensional (2-D) structure of the magnetic field in the r,z plane is compared to the results of an analytical model based on electron-magneto-hydrodynamics, that utilizes the measured 2-D plasma density distribution and assumes fast magnetic field penetration along both POS electrodes. The model results provide quantitative explanation for the magnetic field evolution observed.

Analytic H I-to-H2 Photodissociation Transition Profiles

NASA Astrophysics Data System (ADS)

Bialy, Shmuel; Sternberg, Amiel

2016-05-01

We present a simple analytic procedure for generating atomic (H I) to molecular ({{{H}}}2) density profiles for optically thick hydrogen gas clouds illuminated by far-ultraviolet radiation fields. Our procedure is based on the analytic theory for the structure of one-dimensional H I/{{{H}}}2 photon-dominated regions, presented by Sternberg et al. Depth-dependent atomic and molecular density fractions may be computed for arbitrary gas density, far-ultraviolet field intensity, and the metallicity-dependent H2 formation rate coefficient, and dust absorption cross section in the Lyman-Werner photodissociation band. We use our procedure to generate a set of {{H}} {{I}}{-}{to}{-}{{{H}}}2 transition profiles for a wide range of conditions, from the weak- to strong-field limits, and from super-solar down to low metallicities. We show that if presented as functions of dust optical depth, the {{H}} {{I}} and {{{H}}}2 density profiles depend primarily on the Sternberg “α G parameter” (dimensionless) that determines the dust optical depth associated with the total photodissociated {{H}} {{I}} column. We derive a universal analytic formula for the {{H}} {{I}}{-}{to}{-}{{{H}}}2 transition points as a function of just α G. Our formula will be useful for interpreting emission-line observations of H I/{{{H}}}2 interfaces, for estimating star formation thresholds, and for sub-grid components in hydrodynamics simulations.

Fine-scale hydrodynamics influence the spatio-temporal distribution of harbour porpoises at a coastal hotspot

NASA Astrophysics Data System (ADS)

Jones, A. R.; Hosegood, P.; Wynn, R. B.; De Boer, M. N.; Butler-Cowdry, S.; Embling, C. B.

2014-11-01

The coastal Runnelstone Reef, off southwest Cornwall (UK), is characterised by complex topography and strong tidal flows and is a known high-density site for harbour porpoise (Phocoena phocoena); a European protected species. Using a multidisciplinary dataset including: porpoise sightings from a multi-year land-based survey, Acoustic Doppler Current Profiling (ADCP), vertical profiling of water properties and high-resolution bathymetry; we investigate how interactions between tidal flow and topography drive the fine-scale porpoise spatio-temporal distribution at the site. Porpoise sightings were distributed non-uniformly within the survey area with highest sighting density recorded in areas with steep slopes and moderate depths. Greater numbers of sightings were recorded during strong westward (ebbing) tidal flows compared to strong eastward (flooding) flows and slack water periods. ADCP and Conductivity Temperature Depth (CTD) data identified fine-scale hydrodynamic features, associated with cross-reef tidal flows in the sections of the survey area with the highest recorded densities of porpoises. We observed layered, vertically sheared flows that were susceptible to the generation of turbulence by shear instability. Additionally, the intense, oscillatory near surface currents led to hydraulically controlled flow that transitioned from subcritical to supercritical conditions; indicating that highly turbulent and energetic hydraulic jumps were generated along the eastern and western slopes of the reef. The depression and release of isopycnals in the lee of the reef during cross-reef flows revealed that the flow released lee waves during upslope currents at specific phases of the tidal cycle when the highest sighting rates were recorded. The results of this unique, fine-scale field study provide new insights into specific hydrodynamic features, produced through tidal forcing, that may be important for creating predictable foraging opportunities for porpoises at a local scale. Information on the functional mechanisms linking porpoise distribution to static and dynamic physical habitat variables is extremely valuable to the monitoring and management of the species within the context of European conservation policies and marine renewable energy infrastructure development.

Hydrodynamics Defines the Stable Swimming Direction of Spherical Squirmers in a Nematic Liquid Crystal.

PubMed

Lintuvuori, J S; Würger, A; Stratford, K

2017-08-11

We present a study of the hydrodynamics of an active particle-a model squirmer-in an environment with a broken rotational symmetry: a nematic liquid crystal. By combining simulations with analytic calculations, we show that the hydrodynamic coupling between the squirmer flow field and liquid crystalline director can lead to reorientation of the swimmers. The preferred orientation depends on the exact details of the squirmer flow field. In a steady state, pushers are shown to swim parallel with the nematic director while pullers swim perpendicular to the nematic director. This behavior arises solely from hydrodynamic coupling between the squirmer flow field and anisotropic viscosities of the host fluid. Our results suggest that an anisotropic swimming medium can be used to characterize and guide spherical microswimmers in the bulk.

Solvable Hydrodynamics of Quantum Integrable Systems

NASA Astrophysics Data System (ADS)

Bulchandani, Vir B.; Vasseur, Romain; Karrasch, Christoph; Moore, Joel E.

2017-12-01

The conventional theory of hydrodynamics describes the evolution in time of chaotic many-particle systems from local to global equilibrium. In a quantum integrable system, local equilibrium is characterized by a local generalized Gibbs ensemble or equivalently a local distribution of pseudomomenta. We study time evolution from local equilibria in such models by solving a certain kinetic equation, the "Bethe-Boltzmann" equation satisfied by the local pseudomomentum density. Explicit comparison with density matrix renormalization group time evolution of a thermal expansion in the XXZ model shows that hydrodynamical predictions from smooth initial conditions can be remarkably accurate, even for small system sizes. Solutions are also obtained in the Lieb-Liniger model for free expansion into vacuum and collisions between clouds of particles, which model experiments on ultracold one-dimensional Bose gases.

Model development of supersonic trough wind with shocks

NASA Technical Reports Server (NTRS)

Grebowsky, J. M.

1972-01-01

The time dependent one dimensional hydrodynamic equations describe the evolution of the thermal plasma flow along closed magnetic field lines outside of the plasmasphere. The convection of the supersonic polar wind onto a closed fieldline results in the assumed formation of collisionless plasma shocks. These shocks move earthward as the field line with its frozen-in plasma remains fixed or contracts with time to smaller L coordinates. The high equatorial plasma temperature (of the order of electron volts) produced by the shock process decreases with time if the flow is isothermal but it will increase if the contraction is under adiabatic conditions. Assuming adiabaticity a peak in the temperature forms at the equator in conjunction with a depression in the ion density. After an initial contraction, if the flux tube drifts to higher L coordinates the direction of the shock motion can be reversed so that the supersonic region will expand along the field line towards the state characterizing the supersonic polar wind. A rapid expansion will lower the equatorial density while the temperature decreases with time under adiabatic but not isothermal conditions.

Baryonic impact on the dark matter orbital properties of Milky Way-sized haloes

NASA Astrophysics Data System (ADS)

Zhu, Qirong; Hernquist, Lars; Marinacci, Federico; Springel, Volker; Li, Yuexing

2017-04-01

We study the orbital properties of dark matter haloes by combining a spectral method and cosmological simulations of Milky Way-sized Galaxies. We compare the dynamics and orbits of individual dark matter particles from both hydrodynamic and N-body simulations, and find that the fraction of box, tube and resonant orbits of the dark matter halo decreases significantly due to the effects of baryons. In particular, the central region of the dark matter halo in the hydrodynamic simulation is dominated by regular, short-axis tube orbits, in contrast to the chaotic, box and thin orbits dominant in the N-body run. This leads to a more spherical dark matter halo in the hydrodynamic run compared to a prolate one as commonly seen in the N-body simulations. Furthermore, by using a kernel-based density estimator, we compare the coarse-grained phase-space densities of dark matter haloes in both simulations and find that it is lower by ˜0.5 dex in the hydrodynamic run due to changes in the angular momentum distribution, which indicates that the baryonic process that affects the dark matter is irreversible. Our results imply that baryons play an important role in determining the shape, kinematics and phase-space density of dark matter haloes in galaxies.

Bacterial growth, flow, and mixing shape human gut microbiota density and composition.

PubMed

Arnoldini, Markus; Cremer, Jonas; Hwa, Terence

2018-03-13

The human gut microbiota is highly dynamic, and host physiology and diet exert major influences on its composition. In our recent study, we integrated new quantitative measurements on bacterial growth physiology with a reanalysis of published data on human physiology to build a comprehensive modeling framework. This can generate predictions of how changes in different host factors influence microbiota composition. For instance, hydrodynamic forces in the colon, along with colonic water absorption that manifests as transit time, exert a major impact on microbiota density and composition. This can be mechanistically explained by their effect on colonic pH which directly affects microbiota competition for food. In this addendum, we describe the underlying analysis in more detail. In particular, we discuss the mixing dynamics of luminal content by wall contractions and its implications for bacterial growth and density, as well as the broader implications of our insights for the field of gut microbiota research.

Recent research on the hydrodynamics of the Sacramento - San Joaquin River Delta and north San Francisco Bay

USGS Publications Warehouse

Burau, J.R.; Monismith, S.G.; Stacey, M.T.; Oltmann, R.N.; Lacy, J.R.; Schoellhamer, D.H.

1999-01-01

This article presents an overview of recent findings from hydrodynamic research on circulation and mixing in the Sacramento-San Joaquin Delta (Delta) (Figure 1) and North San Francisco Bay (North Bay) (Figure 2). For the purposes of this article, North Bay includes San Pablo Bay, Carquinez Strait, and Suisun Bay. The findings presented are those gained from field studies carried out by the U.S. Geological Survey (USGS), as part of the Interagency Ecological Program (IEP), and Stanford University beginning about 1993. The premise behind these studies was that a basic understanding of circulation and mixing patterns in the Bay and Delta is an essential part of understanding how biota and water quality are affected by natural hydrologic variability, water appropriation, and development activities. Data collected for the field studies described in this article have significantly improved our understanding of Bay and Delta hydrodynamics. Measured flows ,in the Delta have provided valuable information on how water moves through the Delta's network of channels and how export pumping affects flows. Studies of the shallows and shallow-channel exchange processes conducted in Honker Bay have shown that the water residence time in Honker Bay is much shorter than previously reported (on the order of hours to several tidal cycles instead ofweeks). Suisun Bay studies have provided data on hydrodynamic transport and accumulation mechanisms that operate primarily in the channels. The Suisun Bay studies have caused us to revise our understanding of residual circulation in the channels of North Bay and of "entrapment" mechanisms in the low salinity zone. Finally, detailed tidal and residual (tidally averaged) time-scale studies of the mechanisms that control gravitational circulation in the estuary show that density-driven transport in the channels is governed by turbulence time-scale (seconds) interactions between the mean flow and stratification. The hydrodynamic research summarized in this article spans a range of estuarine environments (deep water channels to shallow water habitats and brackish water to freshwater) at time scales that range from seconds to years.

Large density expansion of a hydrodynamic theory for self-propelled particles

NASA Astrophysics Data System (ADS)

Ihle, T.

2015-07-01

Recently, an Enskog-type kinetic theory for Vicsek-type models for self-propelled particles has been proposed [T. Ihle, Phys. Rev. E 83, 030901 (2011)]. This theory is based on an exact equation for a Markov chain in phase space and is not limited to small density. Previously, the hydrodynamic equations were derived from this theory and its transport coefficients were given in terms of infinite series. Here, I show that the transport coefficients take a simple form in the large density limit. This allows me to analytically evaluate the well-known density instability of the polarly ordered phase near the flocking threshold at moderate and large densities. The growth rate of a longitudinal perturbation is calculated and several scaling regimes, including three different power laws, are identified. It is shown that at large densities, the restabilization of the ordered phase at smaller noise is analytically accessible within the range of validity of the hydrodynamic theory. Analytical predictions for the width of the unstable band, the maximum growth rate, and for the wave number below which the instability occurs are given. In particular, the system size below which spatial perturbations of the homogeneous ordered state are stable is predicted to scale with where √ M is the average number of collision partners. The typical time scale until the instability becomes visible is calculated and is proportional to M.

Field-flow fractionation and hydrodynamic chromatography on a microfluidic chip.

PubMed

Shendruk, Tyler N; Tahvildari, Radin; Catafard, Nicolas M; Andrzejewski, Lukasz; Gigault, Christian; Todd, Andrew; Gagne-Dumais, Laurent; Slater, Gary W; Godin, Michel

2013-06-18

We present gravitational field-flow fractionation and hydrodynamic chromatography of colloids eluting through 18 μm microchannels. Using video microscopy and mesoscopic simulations, we investigate the average retention ratio of colloids with both a large specific weight and neutral buoyancy. We consider the entire range of colloid sizes, including particles that barely fit in the microchannel and nanoscopic particles. Ideal theory predicts four operational modes, from hydrodynamic chromatography to Faxén-mode field-flow fractionation. We experimentally demonstrate, for the first time, the existence of the Faxén-mode field-flow fractionation and the transition from hydrodynamic chromatography to normal-mode field-flow fractionation. Furthermore, video microscopy and simulations show that the retention ratios are largely reduced above the steric-inversion point, causing the variation of the retention ratio in the steric- and Faxén-mode regimes to be suppressed due to increased drag. We demonstrate that theory can accurately predict retention ratios if hydrodynamic interactions with the microchannel walls (wall drag) are added to the ideal theory. Rather than limiting the applicability, these effects allow the microfluidic channel size to be tuned to ensure high selectivity. Our findings indicate that particle velocimetry methods must account for the wall-induced lag when determining flow rates in highly confining systems.

Hydrodynamic Instability in an Extended Landau/Levich Model of Liquid-Propellant Combustion at Normal and Reduced Gravity

NASA Technical Reports Server (NTRS)

Margolis, Stephen B.

1998-01-01

The classical Landau/Levich models of liquid-propellant combustion, despite their relative simplicity, serve as seminal examples that correctly describe the onset of hydrodynamic instability in reactive systems. Recently, these two separate models have been combined and extended to account for a dynamic dependence, absent in the original formulations, of the local burning rate on the local pressure and temperature fields. The resulting model admits an extremely rich variety of both hydrodynamic and reactive/diffusive instabilities that can be analyzed either numerically or analytically in various limiting parameter regimes. In the present work, a formal asymptotic analysis, based on the realistic smallness of the gas-to-liquid density ratio, is developed to investigate the combined effects of gravity and other parameters on the hydrodynamic instability of the propagating liquid/gas interface. In particular, an analytical expression is derived for the neutral stability boundary A(sub p)(k), where A(sub p) is the pressure sensitivity of the burning rate and k is the wavenumber of the disturbance. The results demonstrate explicitly the stabilizing effect of gravity on long-wave disturbances, the stabilizing effect of viscosity (both liquid and gas) and surface tension on short-wave perturbations, and the instability associated with intermediate wavenumbers for critical negative values of A(sub p). In the limiting case of weak gravity, it is shown that hydrodynamic instability in liquid-propellant combustion is a long-wave instability phenomenon, whereas at normal gravity, this instability is first manifested through O(1) wavenumber disturbances. It is also demonstrated that, in general, surface tension and the viscosity of both the liquid and gas phases each produce comparable stabilizing effects in the large-wavenumber regime, thereby providing important modifications to previous analyses in which one or more of these effects were neglected.

Hydrodynamic Instability in an Extended Landau/Levich Model of Liquid-Propellant Combustion at Normal and Reduced Gravity

NASA Technical Reports Server (NTRS)

Margolis, S. B.

1997-01-01

The classical Landau/Levich models of liquid-propellant combustion, despite their relative simplicity, serve as seminal examples that correctly describe the onset of hydrodynamic instability in reactive systems. Recently, these two separate models have been combined and extended to account for a dynamic dependence, absent in the original formulations, of the local burning rate on the local pressure and temperature fields. The resulting model admits an extremely rich variety of both hydrodynamic and reactive/diffusive instabilities that can be analyzed either numerically or analytically in various limiting parameter regimes. In the present work, a formal asymptotic analysis, based on the realistic smallness of the gas-to-liquid density ratio, is developed to investigate the combined effects of gravity and other parameters on the hydrodynamic instability of the propagating liquid/gas interface. In particular, an analytical expression is derived for the neutral stability boundary A(p)(k), where A(p) is the pressure sensitivity of the burning rate and k is the wavenumber of the disturbance. The results demonstrate explicitly the stabilizing effect of gravity on long-wave disturbances, the stabilizing effect of viscosity (both liquid and gas) and surface tension on short-wave perturbations, and the instability associated with intermediate wavenumbers for negative values of A(p). In the limiting case of weak gravity, it is shown that hydrodynamic instability in liquid-propellant combustion is a long-wave instability phenomenon, whereas at normal gravity, this instability is first manifested through O(1) wavenumber disturbances. it is also demonstrated that, in general, surface tension and the viscosity of both the liquid and gas phases each produce comparable stabilizing effects in the long-wavenumber regime, thereby providing important modifications to previous analyses in which one or more of these effects were neglected.

Tuning bacterial hydrodynamics with magnetic fields

NASA Astrophysics Data System (ADS)

Pierce, C. J.; Mumper, E.; Brown, E. E.; Brangham, J. T.; Lower, B. H.; Lower, S. K.; Yang, F. Y.; Sooryakumar, R.

2017-06-01

Magnetotactic bacteria are a group of motile prokaryotes that synthesize chains of lipid-bound, magnetic nanoparticles called magnetosomes. This study exploits their innate magnetism to investigate previously unexplored facets of bacterial hydrodynamics at surfaces. Through use of weak, uniform, external magnetic fields and local, micromagnetic surface patterns, the relative strength of hydrodynamic, magnetic, and flagellar force components is tuned through magnetic control of the bacteria's orientation. The resulting swimming behaviors provide a means to experimentally determine hydrodynamic parameters and offer a high degree of control over large numbers of living microscopic entities. The implications of this controlled motion for studies of bacterial motility near surfaces and for micro- and nanotechnology are discussed.

Modeling the Lyα Forest in Collisionless Simulations

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

Sorini, Daniele; Oñorbe, José; Lukić, Zarija

2016-08-11

Cosmological hydrodynamic simulations can accurately predict the properties of the intergalactic medium (IGM), but only under the condition of retaining the high spatial resolution necessary to resolve density fluctuations in the IGM. This resolution constraint prohibits simulating large volumes, such as those probed by BOSS and future surveys, like DESI and 4MOST. To overcome this limitation, we present in this paper "Iteratively Matched Statistics" (IMS), a novel method to accurately model the Lyα forest with collisionless N-body simulations, where the relevant density fluctuations are unresolved. We use a small-box, high-resolution hydrodynamic simulation to obtain the probability distribution function (PDF) andmore » the power spectrum of the real-space Lyα forest flux. These two statistics are iteratively mapped onto a pseudo-flux field of an N-body simulation, which we construct from the matter density. We demonstrate that our method can reproduce the PDF, line of sight and 3D power spectra of the Lyα forest with good accuracy (7%, 4%, and 7% respectively). We quantify the performance of the commonly used Gaussian smoothing technique and show that it has significantly lower accuracy (20%–80%), especially for N-body simulations with achievable mean inter-particle separations in large-volume simulations. Finally, in addition, we show that IMS produces reasonable and smooth spectra, making it a powerful tool for modeling the IGM in large cosmological volumes and for producing realistic "mock" skies for Lyα forest surveys.« less

MODELING THE Ly α FOREST IN COLLISIONLESS SIMULATIONS

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

Sorini, Daniele; Oñorbe, José; Hennawi, Joseph F.

2016-08-20

Cosmological hydrodynamic simulations can accurately predict the properties of the intergalactic medium (IGM), but only under the condition of retaining the high spatial resolution necessary to resolve density fluctuations in the IGM. This resolution constraint prohibits simulating large volumes, such as those probed by BOSS and future surveys, like DESI and 4MOST. To overcome this limitation, we present “Iteratively Matched Statistics” (IMS), a novel method to accurately model the Ly α forest with collisionless N -body simulations, where the relevant density fluctuations are unresolved. We use a small-box, high-resolution hydrodynamic simulation to obtain the probability distribution function (PDF) and themore » power spectrum of the real-space Ly α forest flux. These two statistics are iteratively mapped onto a pseudo-flux field of an N -body simulation, which we construct from the matter density. We demonstrate that our method can reproduce the PDF, line of sight and 3D power spectra of the Ly α forest with good accuracy (7%, 4%, and 7% respectively). We quantify the performance of the commonly used Gaussian smoothing technique and show that it has significantly lower accuracy (20%–80%), especially for N -body simulations with achievable mean inter-particle separations in large-volume simulations. In addition, we show that IMS produces reasonable and smooth spectra, making it a powerful tool for modeling the IGM in large cosmological volumes and for producing realistic “mock” skies for Ly α forest surveys.« less

Reactive-transport modelling of gypsum dissolution in a coastal karst aquifer in Puglia, southern Italy

NASA Astrophysics Data System (ADS)

Campana, Claudia; Fidelibus, Maria Dolores

2015-11-01

The gypsum coastal aquifer of Lesina Marina (Puglia, southern Italy) has been affected by sinkhole formation in recent decades. Previous studies based on geomorphologic and hydrogeological data ascribed the onset of collapse phenomena to the erosion of material that fills palaeo-cavities (suffosion sinkholes). The change in the hydrodynamic conditions of groundwater induced by the excavation of a canal within the evaporite formation nearly 100 years ago was identified as the major factor in triggering the erosion, while the contribution of gypsum dissolution was considered negligible. A combined reactive-transport/density-dependent flow model was applied to the gypsum aquifer to evaluate whether gypsum dissolution rate is a dominant or insignificant factor in recent sinkhole formation under current hydrodynamic conditions. The conceptual model was first defined with a set of assumptions based on field and laboratory data along a two-dimensional transect of the aquifer, and then a density-dependent, tide-influenced flow model was set up and solved using the numerical code SEAWAT. Finally, the resulting transient flow field was used by the reactive multicomponent transport model PHT3D to estimate the gypsum dissolution rate. The validation tests show that the model accurately represents the real system, and the multi-disciplinary approach provides consistent information about the causes and evolution time of dissolution processes. The modelled porosity development rate is too low to represent a significant contribution to the recent sinkhole formation in the Lesina Marina area, although it justifies cavity formation and cavity position over geological time.

Close-packed floating clusters: granular hydrodynamics beyond the freezing point?

PubMed

Meerson, Baruch; Pöschel, Thorsten; Bromberg, Yaron

2003-07-11

Monodisperse granular flows often develop regions with hexagonal close packing of particles. We investigate this effect in a system of inelastic hard spheres driven from below by a "thermal" plate. Molecular dynamics simulations show, in a wide range of parameters, a close-packed cluster supported by a low-density region. Surprisingly, the steady-state density profile, including the close-packed cluster part, is well described by a variant of Navier-Stokes granular hydrodynamics (NSGH). We suggest a simple explanation for the success of NSGH beyond the freezing point.

Macromolecular geometries determined with field-flow fractionation and their impact on the overlap concentration.

PubMed

Rojas, Cinthia Carola; Wahlund, Karl-Gustav; Bergenståhl, Björn; Nilsson, Lars

2008-06-01

In this paper we aim to understand the size/conformation relationship in waxy barley starch, a polydisperse and ultrahigh molar mass biomacromolecule. Characterizations are performed with asymmetrical flow field-flow fractionation (AsFlFFF). Furthermore, we study the effect of homogenization on the molar mass, rms radius (r rms) and hydrodynamic radius (r h). For the untreated sample, the macromolecules are elongated objects with low apparent density. As a result of homogenization, molar mass, and r rms decrease, while r h remains unaffected. The process also induces an increase, and scaling with size, of apparent density as well as changes in conformation, represented qualitatively by r rms/ r h. Finally, results from AsFlFFF are compared with viscosimetry and discussed in terms of concentration and close-packing in relation to macromolecular shape and conformation. Hence, the results show that AsFlFFF and our novel methodology enable the determination of several physical properties with high relevance for the solution behavior of polydisperse macromolecules.

Dynamical models for the formation of elephant trunks in HII regions

NASA Astrophysics Data System (ADS)

Mackey, Jonathan; Lim, Andrew J.

2010-04-01

The formation of pillars of dense gas at the boundaries of HII regions is investigated with hydrodynamical numerical simulations including ionizing radiation from a point source. We show that shadowing of ionizing radiation by an inhomogeneous density field is capable of forming so-called elephant trunks (pillars of dense gas as in e.g. M16) without the assistance of self-gravity or of ionization front and cooling instabilities. A large simulation of a density field containing randomly generated clumps of gas is shown to naturally generate elephant trunks with certain clump configurations. These configurations are simulated in isolation and analysed in detail to show the formation mechanism and determine possible observational signatures. Pillars formed by the shadowing mechanism are shown to have rather different velocity profiles depending on the initial gas configuration, but asymmetries mean that the profiles also vary significantly with perspective, limiting their ability to discriminate between formation scenarios. Neutral and molecular gas cooling are shown to have a strong effect on these results.

Characterisation of cationic potato starch by asymmetrical flow field-flow fractionation. Influence of ionic strength and degree of substitution.

PubMed

Santacruz, Stalin

2014-06-15

The properties of a paper sheet depend on the absorption together with the physico-chemical properties of additives used in the paper processing. The effect of ionic strength and degree of substitution of cationic potato starch on the elution pattern of asymmetrical flow field-flow fractionation was analysed. The effect of starch derivatisation, in either dry or wet phase, was also investigated. Average molar mass showed no difference between the starches obtained from the two derivatisation processes. Apparent densities showed that dry cationic starch had higher density than wet cationic starch for a hydrodynamic radius between 50 and 100 nm. Elution times of native and three cationic starches increased when the ionic strength increased from 50 to 100mM. No differences in the molar mass among cationic starches with different degree of substitution suggested no degradation due to a derivatisation process. Large sample loads can be used at 100mM without overloading. Copyright © 2014 Elsevier Ltd. All rights reserved.

Modelling of Resonantly Forced Density Waves in Dense Planetary Rings

NASA Astrophysics Data System (ADS)

Lehmann, M.; Schmidt, J.; Salo, H.

2014-04-01

Density wave theory, originally proposed to explain the spiral structure of galactic disks, has been applied to explain parts of the complex sub-structure in Saturn's rings, such as the wavetrains excited at the inner Lindblad resonances (ILR) of various satellites. The linear theory for the excitation and damping of density waves in Saturn's rings is fairly well developed (e.g. Goldreich & Tremaine [1979]; Shu [1984]). However, it fails to describe certain aspects of the observed waves. The non-applicability of the linear theory is already indicated by the "cusplike" shape of many of the observed wave profiles. This is a typical nonlinear feature which is also present in overstability wavetrains (Schmidt & Salo [2003]; Latter & Ogilvie [2010]). In particular, it turns out that the detailed damping mechanism, as well as the role of different nonlinear effects on the propagation of density waves remain intransparent. First attemps are being made to investigate the excitation and propagation of nonlinear density waves within a hydrodynamical formalism, which is also the natural formalism for describing linear density waves. A simple weakly nonlinear model, derived from a multiple-scale expansion of the hydrodynamic equations, is presented. This model describes the damping of "free" spiral density waves in a vertically integrated fluid disk with density dependent transport coefficients, where the effects of the hydrodynamic nonlinearities are included. The model predicts that density waves are linearly unstable in a ring region where the conditions for viscous overstability are met, which translates to a steep dependence of the shear viscosity with respect to the disk's surface density. The possibility that this dependence could lead to a growth of density waves with increasing distance from the resonance, was already mentioned in Goldreich & Tremaine [1978]. Sufficiently far away from the ILR, the surface density perturbation caused by the wave, is predicted to saturate to a constant value due to the effects of nonlinear viscous damping. A qualitatively similar behaviour has also been predicted for the damping of nonlinear density waves, as described within a streamline formalism (Borderies, Goldreich & Tremaine [1985]). The damping lengths which follow from the weakly nonlinear model depend more or less strongly on a set of different input parameters, such as the viscosity and the surface density of the unperturbed ring state. Further, they depend on the wave's amplitude at resonance. For a real wave, which has been excited by an external satellite, this amplitude can be deduced from the magnitude of the satellite's forcing potential. Appart from that, hydrodynamical simulations are being developed to study the nonlinear damping of resonantly forced density waves.

Magnetohydrodynamic Simulations of the Wiggle Instability in Spiral Galaxies

NASA Astrophysics Data System (ADS)

Tanaka, Minoru; Wada, Keiichi; Machida, Mami; Matsumoto, Ryoji; Miyaji, Shigeki

2005-09-01

We studied the stability of galactic spiral shocks through two dimensional global magnetohydrodynamic simulations. Recently, Wada & Koda (2003) showed, using global hydrodynamic simulations, that galactic gas flows behind a spiral shock becomes unstable against a perturbation parallel to the shock front and form spur-like density structures. They attributed the origin of this wiggle instability to the Kelvin-Helmholtz (K-H) instability triggered by the acceleration of the gas behind the shock. We carried out global simulations including galactic magnetic fields. The initial magnetic field is assumed to be either uniform or purely toroidal. We found that although the magnetic field reduces the growth rate of the K-H instability, wiggle instability develops even in galaxies with μG magnetic fields. We also present the results of local simulations to demonstrate the dependence of the growth rate of the instability with the wavelength. The interval of spurs is determined by the most unstable wavelength of the wiggle instability.

Modeling Electric Field Influences on Plasmaspheric Refilling

NASA Technical Reports Server (NTRS)

Liemohn, M. W.; Kozyra, J. U.; Khazanov, G. V.; Craven, Paul D.

1998-01-01

We have a new model of ion transport that we have applied to the problem of plasmaspheric flux tube refilling after a geomagnetic disturbance. This model solves the Fokker-Planck kinetic equation by applying discrete difference numerical schemes to the various operators. Features of the model include a time-varying ionospheric source, self-consistent Coulomb collisions, field-aligned electric field, hot plasma interactions, and ion cyclotron wave heating. We see refilling rates similar to those of earlier observations and models, except when the electric field is included. In this case, the refilling rates can be quite different that previously predicted. Depending on the populations included and the values of relevant parameters, trap zone densities can increase or decrease. In particular, the inclusion of hot populations near the equatorial region (specifically warm pancake distributions and ring current ions) can dramatically alter the refilling rate. Results are compared with observations as well as previous hydrodynamic and kinetic particle model simulations.

The effective temperature for the thermal fluctuations in hot Brownian motion

NASA Astrophysics Data System (ADS)

Srivastava, Mayank; Chakraborty, Dipanjan

2018-05-01

We revisit the effective parameter description of hot Brownian motion—a scenario where a colloidal particle is kept at an elevated temperature than the ambient fluid. Due to the time scale separation between heat diffusion and particle motion, a stationary halo of hot fluid is carried along with the particle resulting in a spatially varying comoving temperature and viscosity profile. The resultant Brownian motion in the overdamped limit can be well described by a Langevin equation with effective parameters such as effective temperature THBM and friction coefficient ζHBM that quantifies the thermal fluctuations and the diffusivity of the particle. These parameters can exactly be calculated using the framework of fluctuating hydrodynamics and require the knowledge of the complete flow field and the temperature field around the particle. Additionally, it was also observed that configurational and kinetic degrees of freedom admit to different effective temperatures, THB M x and THB M v, respectively, with the former predicted accurately from fluctuating hydrodynamics. A more rigorous calculation by Falasco et al. [Phys. Rev. E 90, 032131-10 (2014)] extends the overdamped description to a generalized Langevin equation where the effective temperature becomes frequency dependent and consequently, for any temperature measurement from a Brownian trajectory requires the knowledge of this frequency dependence. We use this framework to expand on the earlier work and look at the first order correction to the limiting values in the hydrodynamic limit and the kinetic limit. We use the linearized Stokes equation and a constant viscosity approximation to calculate the dissipation function in the fluid. The effective temperature is calculated from the weighted average of the temperature field with the dissipation function. Further, we provide a closed form analytical result for effective temperature in the small as well as high frequency limit. Since hot Brownian motion can be used to probe the local environment in complex systems, we have also calculated the effective diffusivity of the particle in the small frequency limit. To look into the kinetic temperature, the velocity autocorrelation function is computed from the generalized Langevin equation and the Wiener-Khinchine theorem and numerically integrated to evaluate THB M v as a function of the ratio of particle density and fluid density ρP/ρ0. The two limiting cases of ρP/ρ0 → 0 and ρP/ρ0 → ∞ is also discussed.

Asymmetric (1+1)-dimensional hydrodynamics in high-energy collisions

NASA Astrophysics Data System (ADS)

Bialas, A.; Peschanski, R.

2011-05-01

The possibility that particle production in high-energy collisions is a result of two asymmetric hydrodynamic flows is investigated using the Khalatnikov form of the (1+1)-dimensional approximation of hydrodynamic equations. The general solution is discussed and applied to the physically appealing “generalized in-out cascade” where the space-time and energy-momentum rapidities are equal at initial temperature but boost invariance is not imposed. It is demonstrated that the two-bump structure of the entropy density, characteristic of the asymmetric input, changes easily into a single broad maximum compatible with data on particle production in symmetric processes. A possible microscopic QCD interpretation of asymmetric hydrodynamics is proposed.

Note on zero temperature holographic superfluids

NASA Astrophysics Data System (ADS)

Guo, Minyong; Lan, Shanquan; Niu, Chao; Tian, Yu; Zhang, Hongbao

2016-06-01

In this note, we have addressed various issues on zero temperature holographic superfluids. First, inspired by our numerical evidence for the equality between the superfluid density and particle density, we provide an elegant analytic proof for this equality by a boost trick. Second, using not only the frequency domain analysis but also the time domain analysis from numerical relativity, we identify the hydrodynamic normal modes and calculate out the sound speed, which is shown to increase with the chemical potential and saturate to the value predicted by the conformal field theory in the large chemical potential limit. Third, the generic non-thermalization is demonstrated by the fully nonlinear time evolution from a non-equilibrium state for our zero temperature holographic superfluid. Furthermore, a conserved Noether charge is proposed in support of this behavior.

Density Relaxation of Liquid-Vapor Critical Fluids Examined in Earth's Gravity

NASA Technical Reports Server (NTRS)

Wilkinson, R. Allen

2000-01-01

This work shows quantitatively the pronounced differences between the density equilibration of very compressible dense fluids in Earth's gravity and those in microgravity. The work was performed onsite at the NASA Glenn Research Center at Lewis Field and is complete. Full details are given in references 1 and 2. Liquid-vapor critical fluids (e.g., water) at their critical temperature and pressure, are very compressible. They collapse under their own weight in Earth's gravity, allowing only a thin meniscus-like layer with the critical pressure to survive. This critical layer, however, greatly slows down the equilibration process of the entire sample. A complicating feature is the buoyancy-driven slow flows of layers of heavier and lighter fluid. This work highlights the incomplete understanding of the hydrodynamics involved in these fluids.

Hydrodynamic Model for Conductivity in Graphene

PubMed Central

Mendoza, M.; Herrmann, H. J.; Succi, S.

2013-01-01

Based on the recently developed picture of an electronic ideal relativistic fluid at the Dirac point, we present an analytical model for the conductivity in graphene that is able to describe the linear dependence on the carrier density and the existence of a minimum conductivity. The model treats impurities as submerged rigid obstacles, forming a disordered medium through which graphene electrons flow, in close analogy with classical fluid dynamics. To describe the minimum conductivity, we take into account the additional carrier density induced by the impurities in the sample. The model, which predicts the conductivity as a function of the impurity fraction of the sample, is supported by extensive simulations for different values of ε, the dimensionless strength of the electric field, and provides excellent agreement with experimental data. PMID:23316277

Numerical study of hydrodynamic and salinity transport processes in the Pink Beach wetlands of the Liao River estuary, China

NASA Astrophysics Data System (ADS)

Qiao, Huiting; Zhang, Mingliang; Jiang, Hengzhi; Xu, Tianping; Zhang, Hongxing

2018-06-01

Interaction studies of vegetation within flow environments are essential for the determination of bank protection, morphological characteristics and ecological conditions for wetlands. This paper uses the MIKE 21 hydrodynamic and salinity model to simulate the hydrodynamic characteristics and salinity transport processes in the Pink Beach wetlands of the Liao River estuary. The effect of wetland plants on tidal flow in wetland areas is represented by a varying Manning coefficient in the bottom friction term. Acquisition of the vegetation distribution is based on Landsat TM satellites by remote sensing techniques. Detailed comparisons between field observation and simulated results of water depth, salinity and tidal currents are presented in the vegetated domain of the Pink Beach wetlands. Satisfactory results were obtained from simulations of both flow characteristics and salinity concentration, with or without vegetation. A numerical experiment was conducted based on variations in vegetation density, and compared with the tidal currents in non-vegetated areas; the computed current speed decreased remarkably with an increase in vegetation density. The impact of vegetation on water depth and salinity was simulated, and the findings revealed that wetland vegetation has an insignificant effect on the water depth and salinity in this wetland domain. Several stations (from upstream to downstream) in the Pink Beach wetlands were selected to estimate the longitudinal variation of salinity under different river runoff conditions; the results showed that salinity concentration decreases with an increase in river runoff. This study can consequently help increase the understanding of favourable salinity conditions for particular vegetation growth in the Pink Beach wetlands of the Liao River estuary. The results also provide crucial guidance for related interaction studies of vegetation, flow and salinity in other wetland systems.

CIFOG: Cosmological Ionization Fields frOm Galaxies

NASA Astrophysics Data System (ADS)

Hutter, Anne

2018-03-01

CIFOG is a versatile MPI-parallelised semi-numerical tool to perform simulations of the Epoch of Reionization. From a set of evolving cosmological gas density and ionizing emissivity fields, it computes the time and spatially dependent ionization of neutral hydrogen (HI), neutral (HeI) and singly ionized helium (HeII) in the intergalactic medium (IGM). The code accounts for HII, HeII, HeIII recombinations, and provides different descriptions for the photoionization rate that are used to calculate the residual HI fraction in ionized regions. This tool has been designed to be coupled to semi-analytic galaxy formation models or hydrodynamical simulations. The modular fashion of the code allows the user to easily introduce new descriptions for recombinations and the photoionization rate.

Propulsion and hydrodynamic particle transport of magnetically twisted colloidal ribbons

NASA Astrophysics Data System (ADS)

Massana-Cid, Helena; Martinez-Pedrero, Fernando; Navarro-Argemí, Eloy; Pagonabarraga, Ignacio; Tierno, Pietro

2017-10-01

We describe a method to trap, transport and release microscopic particles in a viscous fluid using the hydrodynamic flow field generated by a magnetically propelled colloidal ribbon. The ribbon is composed of ferromagnetic microellipsoids that arrange with their long axis parallel to each other, a configuration that is energetically favorable due to their permanent magnetic moments. We use an external precessing magnetic field to torque the anisotropic particles forming the ribbon, and to induce propulsion of the entire structure due to the hydrodynamic coupling with the close substrate. The propulsion speed of the ribbon can be controlled by varying the driving frequency, or the amplitude of the precessing field. The latter parameter is also used to reduce the average inter particle distance and to induce the twisting of the ribbon due to the increase in the attraction between the rotating ellipsoids. Furthermore, non magnetic particles are attracted or repelled with the hydrodynamic flow field generated by the propelling ribbon. The proposed method may be used in channel free microfluidic applications, where the precise trapping and transport of functionalized particles via non invasive magnetic fields is required.

Dispersive hydrodynamics: Preface

NASA Astrophysics Data System (ADS)

Biondini, G.; El, G. A.; Hoefer, M. A.; Miller, P. D.

2016-10-01

This Special Issue on Dispersive Hydrodynamics is dedicated to the memory and work of G.B. Whitham who was one of the pioneers in this field of physical applied mathematics. Some of the papers appearing here are related to work reported on at the workshop "Dispersive Hydrodynamics: The Mathematics of Dispersive Shock Waves and Applications" held in May 2015 at the Banff International Research Station. This Preface provides a broad overview of the field and summaries of the various contributions to the Special Issue, placing them in a unified context.

The role of magnetic fields in the structure and interaction of supershells

NASA Astrophysics Data System (ADS)

Ntormousi, Evangelia; Dawson, Joanne R.; Hennebelle, Patrick; Fierlinger, Katharina

2017-03-01

Context. Large-scale shocks formed by clustered feedback of young OB stars are considered an important source of mechanical energy for the interstellar medium (ISM) and a trigger of molecular cloud formation. Their interaction sites are locations where kinetic energy and magnetic fields are redistributed between ISM phases. Aims: In this work we address two questions, both involving the role of galactic magnetic fields in the dynamics of supershells and their interactions. On the one hand, we study the effect of the magnetic field on the expansion and fragmentation of supershells and, on the other hand, we look for the signatures of supershell collisions on dense structures and on the kinetic and magnetic energy distribution of the ISM. Methods: We performed a series of high-resolution, three-dimensional simulations of colliding supershells. The shocks are created by time-dependent feedback and evolve in a diffuse turbulent environment that is either unmagnetized or has different initial magnetic field configurations. Results: In the hydrodynamical situation, the expansion law of the superbubbles is consistent with the radius-time relation R ∝ t3/5 that is theoretically predicted for wind-blown bubbles. The supershells fragment over their entire surface into small dense clumps that carry more than half of the total kinetic energy in the volume. However, this is not the case when a magnetic field is introduced, either in the direction of the collision or perpendicular to the collision. In both situations, the shell surfaces are more stable to dynamical instabilities. When the magnetic field opposes the collision, the expansion law of the supershells also becomes significantly flatter than in the hydrodynamical case. Although a two-phase medium arises in all cases, in the magnetohydrodynamical (MHD) simulations the cold phase is limited to lower densities and the cold clumps are located further away from the shocks with respect to the hydrodynamical simulations. Conclusions: For the parameters we explored, self-gravity has no effect on either the superbubble expansion or the shock fragmentation. In contrast, a magnetic field, whether mostly parallel or mostly perpendicular to the collision axis, causes a deceleration of the shocks, deforms them significantly, and largely suppresses the formation of the dense gas on their surface. The result is a multi-phase medium in which the cold clumps are not spatially correlated with the supershells.

Relaxation of microparticles exposed to hydrodynamic forces in microfluidic conduits.

PubMed

Janča, Josef; Halabalová, Věra; Polášek, Vladimír; Vašina, Martin; Menshikova, Anastasia Yu

2011-02-01

The behavior of microparticles exposed to gravitational and lift forces and to the velocity gradient in flow velocity profile formed in microfluidic conduits is studied from the viewpoint of the transient period (the relaxation) between the moment at which a particle starts to be transported by the hydrodynamic flow and the time at which it reaches an equilibrium position, characterized by a balance of all active forces. The theoretical model allowing the calculation of the relaxation time is proposed. The numerical calculus based on the proposed model is compared with the experimental data obtained under different experimental conditions, namely, for different lengths of microfluidic channels, different average linear velocities of the carrier liquid, and different sizes and densities of the particles used in the study. The results are important for the optimization of microfluidic separation units such as microthermal field-flow fractionation channels in which the separation or manipulation of the microparticles of various origin, synthetic, natural, biological, etc., is performed under similar experimental conditions but by applying an additional thermodynamic force.

Some factors influencing radiation of sound from flow interaction with edges of finite surfaces

NASA Technical Reports Server (NTRS)

Hayden, R. E.; Fox, H. L.; Chanaud, R. C.

1976-01-01

Edges of surfaces which are exposed to unsteady flow cause both strictly acoustic effects and hydrodynamic effects, in the form of generation of new hydrodynamic sources in the immediate vicinity of the edge. An analytical model is presented which develops the explicit sound-generation role of the velocity and Mach number of the eddy convection past the edge, and the importance of relative scale lengths of the turbulence, as well as the relative intensity of pressure fluctuations. The Mach number (velocity) effects show that the important paramater is the convection Mach number of the eddies. The effects of turbulence scale lengths, isotropy, and spatial density (separation) are shown to be important in determining the level and spectrum of edge sound radiated for the edge dipole mechanism. Experimental data is presented which provides support for the dipole edge noise model in terms of Mach number (velocity) scaling, parametric dependence on flow field parameter, directivity, and edge diffraction effects.

First experimental evidence of hydrodynamic tunneling of ultra-relativistic protons in extended solid copper target at the CERN HiRadMat facility

NASA Astrophysics Data System (ADS)

Schmidt, R.; Blanco Sancho, J.; Burkart, F.; Grenier, D.; Wollmann, D.; Tahir, N. A.; Shutov, A.; Piriz, A. R.

2014-08-01

A novel experiment has been performed at the CERN HiRadMat test facility to study the impact of the 440 GeV proton beam generated by the Super Proton Synchrotron on extended solid copper cylindrical targets. Substantial hydrodynamic tunneling of the protons in the target material has been observed that leads to significant lengthening of the projectile range, which confirms our previous theoretical predictions [N. A. Tahir et al., Phys. Rev. Spec. Top.-Accel. Beams 15, 051003 (2012)]. Simulation results show very good agreement with the experimental measurements. These results have very important implications on the machine protection design for powerful machines like the Large Hadron Collider (LHC), the future High Luminosity LHC, and the proposed huge 80 km circumference Future Circular Collider, which is currently being discussed at CERN. Another very interesting outcome of this work is that one may also study the field of High Energy Density Physics at this test facility.

Time-dependent MHD modeling of the global structure of the heliosphere

NASA Technical Reports Server (NTRS)

Liewer, P. C.; Brackbill, J. U.; Karmesin, S. Roy

1995-01-01

We present results from time-dependent modeling of the global structure of the heliosphere with neutral and magnetic field effects included. The magnetic field is assumed parallel to the interstellar flow in this two-dimensional axisymmetric model; the neutrals are treated as a fluid. The effects of interstellar neutrals and the interplanetary magnetic field on the location of the termination shock are studied using the most recent estimate of the interstellar medium parameters, results will be compared to those of Baranov and Zaitsev. The effect of the solar wind - VLISM interaction on the density and velocity of interstellar neutrals within the heliosphere will also be presented and related to observations. The response of the termination shock to the solar cycle variation in the solar wind will be compared to the response found previously using an axisymmetric hydrodynamic model without neutrals.

Hydrodynamic study of plasma amplifiers for soft-x-ray lasers: a transition in hydrodynamic behavior for plasma columns with widths ranging from 20 μm to 2 mm.

PubMed

Oliva, Eduardo; Zeitoun, Philippe; Velarde, Pedro; Fajardo, Marta; Cassou, Kevin; Ros, David; Sebban, Stephan; Portillo, David; le Pape, Sebastien

2010-11-01

Plasma-based seeded soft-x-ray lasers have the potential to generate high energy and highly coherent short pulse beams. Due to their high density, plasmas created by the interaction of an intense laser with a solid target should store the highest amount of energy density among all plasma amplifiers. Our previous numerical work with a two-dimensional (2D) adaptive mesh refinement hydrodynamic code demonstrated that careful tailoring of plasma shapes leads to a dramatic enhancement of both soft-x-ray laser output energy and pumping efficiency. Benchmarking of our 2D hydrodynamic code in previous experiments demonstrated a high level of confidence, allowing us to perform a full study with the aim of the way for 10-100 μJ seeded soft-x-ray lasers. In this paper, we describe in detail the mechanisms that drive the hydrodynamics of plasma columns. We observed transitions between narrow plasmas, where very strong bidimensional flow prevents them from storing energy, to large plasmas that store a high amount of energy. Millimeter-sized plasmas are outstanding amplifiers, but they have the limitation of transverse lasing. In this paper, we provide a preliminary solution to this problem.

Systematic parameter study of hadron spectra and elliptic flow from viscous hydrodynamic simulations of Au+Au collisions at sNN=200 GeV

NASA Astrophysics Data System (ADS)

Shen, Chun; Heinz, Ulrich; Huovinen, Pasi; Song, Huichao

2010-11-01

Using the (2+1)-dimensional viscous hydrodynamic code vish2+1 [H. Song and U. Heinz, Phys. Lett. BPYLBAJ0370-269310.1016/j.physletb.2007.11.019 658, 279 (2008); H. Song and U. Heinz, Phys. Rev. CPRVCAN0556-281310.1103/PhysRevC.77.064901 77, 064901 (2008); H. Song, Ph. D. thesis, The Ohio State University, 2009], we present systematic studies of the dependence of pion and proton transverse-momentum spectra and their elliptic flow in 200A GeV Au+Au collisions on the parameters of the hydrodynamic model (thermalization time, initial entropy density distribution, decoupling temperature, equation of state, and specific shear viscosity η/s). We identify a tension between the slope of the proton spectra, which (within hydrodynamic simulations that assume a constant shear viscosity to entropy density ratio) prefer larger η/s values, and the slope of the pT dependence of charged hadron elliptic flow, which prefers smaller values of η/s. Changing other model parameters does not appear to permit dissolution of this tension.

Systematic parameter study of hadron spectra and elliptic flow from viscous hydrodynamic simulations of Au+Au collisions at {radical}(s{sub NN})=200 GeV

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

Shen Chun; Heinz, Ulrich; Huovinen, Pasi

2010-11-15

Using the (2+1)-dimensional viscous hydrodynamic code vish2+1[H. Song and U. Heinz, Phys. Lett. B 658, 279 (2008); H. Song and U. Heinz, Phys. Rev. C 77, 064901 (2008); H. Song, Ph. D. thesis, The Ohio State University, 2009], we present systematic studies of the dependence of pion and proton transverse-momentum spectra and their elliptic flow in 200A GeV Au+Au collisions on the parameters of the hydrodynamic model (thermalization time, initial entropy density distribution, decoupling temperature, equation of state, and specific shear viscosity {eta}/s). We identify a tension between the slope of the proton spectra, which (within hydrodynamic simulations that assumemore » a constant shear viscosity to entropy density ratio) prefer larger {eta}/s values, and the slope of the p{sub T} dependence of charged hadron elliptic flow, which prefers smaller values of {eta}/s. Changing other model parameters does not appear to permit dissolution of this tension.« less

Numerical 3D Hydrodynamics Study of Gravitational Instabilities in a Circumbinary Disk

NASA Astrophysics Data System (ADS)

Desai, Karna Mahadev; Steiman-Cameron, Thomas Y.; Michael, Scott; Cai, Kai; Durisen, Richard H.

2016-01-01

We present a 3D hydrodynamical study of gravitational instabilities (GIs) in a circumbinary protoplanetary disk around a Solar mass star and a brown dwarf companion (0.02 M⊙). GIs can play an important, and at times dominant, role in driving the structural evolution of protoplanetary disks. The reported simulations were performed employing CHYMERA, a radiative 3D hydrodynamics code developed by the Indiana University Hydrodynamics Group. The simulations include disk self-gravity and radiative cooling governed by realistic dust opacities. We examine the role of GIs in modulating the thermodynamic state of the disks, and determine the strengths of GI-induced density waves, non-axisymmetric density structures, radial mass transport, and gravitational torques. The principal goal of this study is to determine how the presence of the companion affects the nature and strength of GIs. Results are compared with a parallel simulation of a protoplanetary disk without the presence of the brown dwarf binary companion. We detect no fragmentation in either disk. A persistent vortex forms in the inner region of both disks. The vortex seems to be stabilized by the presence of the binary companion.

Advances in colloidal manipulation and transport via hydrodynamic interactions.

PubMed

Martínez-Pedrero, F; Tierno, P

2018-06-01

In this review article, we highlight many recent advances in the field of micromanipulation of colloidal particles using hydrodynamic interactions (HIs), namely solvent mediated long-range interactions. At the micrsocale, the hydrodynamic laws are time reversible and the flow becomes laminar, features that allow precise manipulation and control of colloidal matter. We focus on different strategies where externally operated microstructures generate local flow fields that induce the advection and motion of the surrounding components. In addition, we review cases where the induced flow gives rise to hydrodynamic bound states that may synchronize during the process, a phenomenon essential in different systems such as those that exhibit self-assembly and swarming. Copyright © 2018 Elsevier Inc. All rights reserved.

Friction on the Bond and the Vibrational Relaxation in Simple Liquids.

NASA Astrophysics Data System (ADS)

Mishra, Bimalendu Kumar

In chapter 1, the energy relaxation of a stiff Morse oscillator dissolved in a simple LJ fluid is calculated using a reversible integrator (r-RESPA) in molecular dynamics generated from the Trotter factorization of the classical propagator. We compare the "real" relaxation from full MD simulations with that predicted by the Generalized Langevin Equation (GLE) with memory friction determined from the full Molecular Dynamics for a series of fluid densities. It is found that the GLE gives very good agreement with MD for the vibrational energy relaxation for this nonlinear oscillator far from equilibrium only for high density fluids, but reduced densities rho < 0.5 the energy relaxation from the MD simulation becomes considered slower than that from the GLE. An analysis of the statistical properties of the random force shows that as the density is lowered the non-Gaussian behavior of the random force becomes more prominent. This behavior is consistent with a simple model in which the oscillator undergoes generalized Langevin dynamics between strong binary collisions with solvent atoms. In chapter 2, molecular hydrodynamics is used to calculate the memory friction on the intramolecular vibrational coordinate of a homonuclear diatomic molecule dissolved in a simple liquid. The predicted memory friction is then compared to recent computer experiments. Agreement with the experimental memory functions is obtained when the linearized hydrodynamics is modified to include gaussian viscoelasticity and compressibility. The hydrodynamic friction on the bond appears to agree qualitatively very well, although quantitative agreement is not found at high frequencies. Various limits of the hydrodynamic friction are discussed.

Analysis of Mid-Latitude Plasma Density Irregularities in the Presence of Finite Larmor Radius Effects

NASA Astrophysics Data System (ADS)

Sotnikov, V. I.; Kim, T. C.; Mishin, E. V.; Kil, H.; Kwak, Y. S.; Paraschiv, I.

2017-12-01

Ionospheric irregularities cause scintillations of electromagnetic signals that can severely affect navigation and transionospheric communication, in particular during space storms. At mid-latitudes the source of F-region Field Aligned Irregularities (FAI) is yet to be determined. They can be created in enhanced subauroral flow channels (SAI/SUBS), where strong gradients of electric field, density and plasma temperature are present. Another important source of FAI is connected with Medium-scale travelling ionospheric disturbances (MSTIDs). Related shear flows and plasma density troughs point to interchange and Kelvin-Helmholtz type instabilities as a possible source of plasma irregularities. A model of nonlinear development of these instabilities based on the two-fluid hydrodynamic description with inclusion of finite Larmor radius effects will be presented. This approach allows to resolve density irregularities on the meter scale. A numerical code in C language to solve the derived nonlinear equations for analysis of interchange and flow velocity shear instabilities in the ionosphere was developed. This code will be used to analyze competition between interchange and Kelvin-Helmholtz instabilities in the mid-latitude region. The high-resolution simulations with continuous density and velocity profiles will be driven by the ambient conditions corresponding to the in situ data obtained during the 2016 Daejeon (Korea) and MU (Japan) radar campaign and data collected simultaneously by the Swarm satellites passed over Korea and Japan. PA approved #: 88ABW-2017-3641

Detectability of primordial gravitational waves produced in bouncing models

NASA Astrophysics Data System (ADS)

Pinto-Neto, Nelson; Scardua, Arthur

2017-06-01

It is widely known that bouncing models with a dust hydrodynamical fluid satisfying cs2=pd/ρd≈0 , where cs , pd , ρd are the sound velocity, pressure, and energy density of the dust fluid, respectively, have almost scale invariant spectrum of scalar perturbations and negligible primordial gravitational waves. We investigate whether adding another fluid with 1 /3

Numerical Hydrodynamics in General Relativity.

PubMed

Font, José A

2003-01-01

The current status of numerical solutions for the equations of ideal general relativistic hydrodynamics is reviewed. With respect to an earlier version of the article, the present update provides additional information on numerical schemes, and extends the discussion of astrophysical simulations in general relativistic hydrodynamics. Different formulations of the equations are presented, with special mention of conservative and hyperbolic formulations well-adapted to advanced numerical methods. A large sample of available numerical schemes is discussed, paying particular attention to solution procedures based on schemes exploiting the characteristic structure of the equations through linearized Riemann solvers. A comprehensive summary of astrophysical simulations in strong gravitational fields is presented. These include gravitational collapse, accretion onto black holes, and hydrodynamical evolutions of neutron stars. The material contained in these sections highlights the numerical challenges of various representative simulations. It also follows, to some extent, the chronological development of the field, concerning advances on the formulation of the gravitational field and hydrodynamic equations and the numerical methodology designed to solve them. Supplementary material is available for this article at 10.12942/lrr-2003-4.

Tuning Bacterial Hydrodynamics with Magnetic Fields: A Path to Bacterial Robotics

NASA Astrophysics Data System (ADS)

Pierce, Christopher; Mumper, Eric; Brangham, Jack; Wijesinghe, Hiran; Lower, Stephen; Lower, Brian; Yang, Fengyuan; Sooryakumar, Ratnasingham

Magnetotactic Bacteria (MTB) are a group of motile prokaryotes that synthesize chains of lipid-bound, magnetic nano-particles. In this study, the innate magnetism of these flagellated swimmers is exploited to explore their hydrodynamics near confining surfaces, using the magnetic field as a tuning parameter. With weak (Gauss), uniform, external, magnetic ?elds and the field gradients arising from micro-magnetic surface patterns, the relative strength of hydrodynamic, magnetic and ?agellar force components is tuned through magnetic control of the bacteria's orientation and position. In addition to direct measurement of several hydrodynamic quantities related to the motility of individual cells, their tunable dynamics reveal a number of novel, highly controllable swimming behaviors with potential value in micro-robotics applications. Specifically, the experiments permit the MTB cells to be directed along parallel or divergent trajectories, suppress their flagellar forces through magnetic means, and induce transitions between planar, circulating trajectories and drifting, vertically oriented ``top-like'' motion. The implications of the work for fundamental hydrodynamics research as well as bacterially driven robotics applications will be discussed.

Modeling of the merging of two colliding field reversed configuration plasmoids

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

Wang, Guanqiong; Wang, Xiaoguang; Li, Lulu

2016-06-15

The field reversed configuration (FRC) is one of the candidate plasma targets for the magneto-inertial fusion, and a high temperature FRC can be formed by using the collision-merging technology. Although the merging process and mechanism of FRC are quite complicated, it is thinkable to build a simple model to investigate the macroscopic equilibrium parameters including the density, the temperature and the separatrix volume, which may play an important role in the collision-merging process of FRC. It is quite interesting that the estimates of the related results based on our simple model are in agreement with the simulation results of amore » two-dimensional magneto-hydrodynamic code (MFP-2D), which has being developed by our group since the last couple of years, while these results can qualitatively fit the results of C-2 experiments by Tri-alpha energy company. On the other hand, the simple model can be used to investigate how to increase the density of the merged FRC. It is found that the amplification of the density depends on the poloidal flux-increase factor and the temperature increases with the translation speed of two plasmoids.« less

Decorrelation dynamics and spectra in drift-Alfven turbulence

NASA Astrophysics Data System (ADS)

Fernandez Garcia, Eduardo

Motivated by the inability of one-fluid magnetohydrodynamics (MHD) to explain key turbulence characteristics in systems ranging from the solar wind and interstellar medium to fusion devices like the reversed field pinch, this thesis studies magnetic turbulence using a drift-Alfven model that extends MHD by including electron density dynamics. Electron effects play a significant role in the dynamics by changing the structure of turbulent decorrelation in the Alfvenic regime (where fast Alfvenic propagation provides the fastest decorrelation of the system): besides the familiar counter-propagating Alfvenic branches of MHD, an additional branch tied to the diamagnetic and eddy-turn- over rates enters in the turbulent response. This kinematic branch gives hydrodynamic features to turbulence that is otherwise strongly magnetic. Magnetic features are observed in the RMS frequency, energy partitions, cross-field energy transfer and in the turbulent response, whereas hydrodynamic features appear in the average frequency, self-field transfer, turbulent response and finally the wavenumber spectrum. These features are studied via renormalized closure theory and numerical simulation. The closure calculation naturally incorporates the eigenmode structure of the turbulent response in specifying spectral energy balance equations for the magnetic, kinetic and internal (density) energies. Alfvenic terms proportional to cross correlations and involved in cross field transfer compete with eddy-turn-over, self transfer, auto-correlation terms. In the steady state, the kinematic terms dominate the energy balances and yield a 5/3 Kolmogorov spectrum (as observed in the interstellar medium) for the three field energies in the strong turbulence, long wavelength limit. Alfvenic terms establish equipartition of kinetic and magnetic energies. In the limit where wavelengths are short compared to the gyroradius, the Alfvenic terms equipartition the internal and magnetic energies resulting in a steep (-2) spectrum fall-off for those energies while the largely uncoupled kinetic modes still obey a 5/3 law. From the numerical simulations, the response function of drift-Alfven turbulence is measured. Here, a statistical ensemble is constructed from small perturbations of the turbulent amplitudes at fixed wavenumber. The decorrelation structure born out of the eigenmode calculation is verified in the numerical measurement.

A High Density Storm Surge Monitoring Network: Evaluating the Ability of Wetland Vegetation to Reduce Storm Surge

NASA Astrophysics Data System (ADS)

Lawler, S.; Denton, M.; Ferreira, C.

2013-12-01

Recent tropical storm activity in the Chesapeake Bay and a potential increase in the predicted frequency and magnitude of weather systems have drawn increased attention to the need for improved tools for monitoring, modeling and predicting the magnitude of storm surge, coastal flooding and the respective damage to infrastructure and wetland ecosystems. Among other forms of flood protection, it is believed that coastal wetlands and vegetation can act as a natural barrier that slows hurricane flooding, helping to reduce the impact of storm surge. However, quantifying the relationship between the physical process of storm surge and its attenuation by wetland vegetation is an active area of research and the deployment of in-situ measuring devices is crucial to data collection efforts in this field. The United States Geological Survey (USGS) mobile storm-surge network has already successfully provided a framework for evaluating hurricane induced storm surge water levels on a regional scale through the use of in-situ devices installed in areas affected by storm surge during extreme events. Based on the success of the USGS efforts, in this study we adapted the monitoring network to cover relatively small areas of wetlands and coastal vegetation with an increased density of sensors. Groups of 6 to 10 water level sensors were installed in sites strategically selected in three locations on the Virginia coast of the lower Chesapeake Bay area to monitor different types of vegetation and the resulting hydrodynamic patterns (open coast and inland waters). Each group of sensors recorded time series data of water levels for both astronomical tide circulation and meteorological induced surge. Field campaigns were carried out to survey characteristics of vegetation contributing to flow resistance (i.e. height, diameter and stem density) and mapped using high precision GPS. A geodatabase containing data from field campaigns will support the development and calibration of computational models to simulate storm surge flow over wetlands specifically designed to represent Virginia's aquatic vegetation and to improve our fundamental knowledge of tide and storm surge hydrodynamics in estuarine wetlands. This poster will present the results of the field measurements for events during the 2013 Hurricane Season, tidal flows within the study areas, and surge attenuation rates according to vegetation characteristics.

Hydrodynamic cavitation for sonochemical effects.

PubMed

Moholkar, V S; Kumar, P S; Pandit, A B

1999-03-01

A comparative study of hydrodynamic and acoustic cavitation has been made on the basis of numerical solutions of the Rayleigh-Plesset equation. The bubble/cavity behaviour has been studied under both acoustic and hydrodynamic cavitation conditions. The effect of varying pressure fields on the collapse of the cavity (sinusoidal for acoustic and linear for hydrodynamic) and also on the latter's dynamic behaviour has been studied. The variations of parameters such as initial cavity size, intensity of the acoustic field and irradiation frequency in the case of acoustic cavitation, and initial cavity size, final recovery pressure and time for pressure recovery in the case of hydrodynamic cavitation, have been found to have significant effects on cavity/bubble dynamics. The simulations reveal that the bubble/cavity collapsing behaviour in the case of hydrodynamic cavitation is accompanied by a large number of pressure pulses of relatively smaller magnitude, compared with just one or two pulses under acoustic cavitation. It has been shown that hydrodynamic cavitation offers greater control over operating parameters and the resultant cavitation intensity. Finally, a brief summary of the experimental results on the oxidation of aqueous KI solution with a hydrodynamic cavitation set-up is given which supports the conclusion of this numerical study. The methodology presented allows one to manipulate and optimise of specific process, either physical or chemical.

Hydrodynamic evolution and jet energy loss in Cu + Cu collisions

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

Schenke, Bjoern; Department of Physics, McGill University, 3600 University Street, Montreal, Quebec, H3A 2T8; Jeon, Sangyong

2011-04-15

We present results from a hybrid description of Cu + Cu collisions using (3 + 1)-dimensional hydrodynamics (music) for the bulk evolution and a Monte Carlo simulation (martini) for the evolution of high-momentum partons in the hydrodynamical background. We explore the limits of this description by going to small system sizes and determine the dependence on different fractions of wounded nucleon and binary collisions scaling of the initial energy density. We find that Cu + Cu collisions are well described by the hybrid description at least up to 20% central collisions.

Dynamo efficiency controlled by hydrodynamic bistability.

PubMed

Miralles, Sophie; Herault, Johann; Herault, Johann; Fauve, Stephan; Gissinger, Christophe; Pétrélis, François; Daviaud, François; Dubrulle, Bérengère; Boisson, Jean; Bourgoin, Mickaël; Verhille, Gautier; Odier, Philippe; Pinton, Jean-François; Plihon, Nicolas

2014-06-01

Hydrodynamic and magnetic behaviors in a modified experimental setup of the von Kármán sodium flow-where one disk has been replaced by a propeller-are investigated. When the rotation frequencies of the disk and the propeller are different, we show that the fully turbulent hydrodynamic flow undergoes a global bifurcation between two configurations. The bistability of these flow configurations is associated with the dynamics of the central shear layer. The bistable flows are shown to have different dynamo efficiencies; thus for a given rotation rate of the soft-iron disk, two distinct magnetic behaviors are observed depending on the flow configuration. The hydrodynamic transition controls the magnetic field behavior, and bifurcations between high and low magnetic field branches are investigated.

Role of co-occurring competition and facilitation in plant spacing hydrodynamics in water-limited environments

PubMed Central

2017-01-01

Plant performance (i.e., fecundity, growth, survival) depends on an individual’s access to space and resources. At the community level, plant performance is reflected in observable vegetation patterning (i.e., spacing distance, density) often controlled by limiting resources. Resource availability is, in turn, strongly dependent on plant patterning mediated by competitive and facilitative plant–plant interactions. Co-occurring competition and facilitation has never been specifically investigated from a hydrodynamic perspective. To address this knowledge gap, and to overcome limitations of field studies, three intermediate-scale laboratory experiments were conducted using a climate-controlled wind tunnel–porous media test facility to simulate the soil–plant–atmosphere continuum. The spacing between two synthetic plants, a design consideration introduced by the authors in a recent publication, was varied between experiments; edaphic and mean atmospheric conditions were held constant. The strength of the above- and belowground plant–plant interactions changed with spacing distance, allowing the creation of a hydrodynamic conceptual model based on established ecological theories. Greatest soil water loss was observed for the experiment with the smallest spacing where competition dominated. Facilitation dominated at the intermediate spacing; little to no interactions were observed for the largest plant spacing. Results suggest that there exists an optimal spacing distance range that lowers plant environmental stress, thus improving plant performance through reduced atmospheric demand and conservation of available soil water. These findings may provide a foundation for improving our understanding of many climatological, ecohydrological, and hydrological problems pertaining to the hydrodynamics of water-limited environments where plant–plant interactions and community self-organization are important. PMID:28807999

Role of co-occurring competition and facilitation in plant spacing hydrodynamics in water-limited environments.

PubMed

Trautz, Andrew C; Illangasekare, Tissa H; Rodriguez-Iturbe, Ignacio

2017-08-29

Plant performance (i.e., fecundity, growth, survival) depends on an individual's access to space and resources. At the community level, plant performance is reflected in observable vegetation patterning (i.e., spacing distance, density) often controlled by limiting resources. Resource availability is, in turn, strongly dependent on plant patterning mediated by competitive and facilitative plant-plant interactions. Co-occurring competition and facilitation has never been specifically investigated from a hydrodynamic perspective. To address this knowledge gap, and to overcome limitations of field studies, three intermediate-scale laboratory experiments were conducted using a climate-controlled wind tunnel-porous media test facility to simulate the soil-plant-atmosphere continuum. The spacing between two synthetic plants, a design consideration introduced by the authors in a recent publication, was varied between experiments; edaphic and mean atmospheric conditions were held constant. The strength of the above- and belowground plant-plant interactions changed with spacing distance, allowing the creation of a hydrodynamic conceptual model based on established ecological theories. Greatest soil water loss was observed for the experiment with the smallest spacing where competition dominated. Facilitation dominated at the intermediate spacing; little to no interactions were observed for the largest plant spacing. Results suggest that there exists an optimal spacing distance range that lowers plant environmental stress, thus improving plant performance through reduced atmospheric demand and conservation of available soil water. These findings may provide a foundation for improving our understanding of many climatological, ecohydrological, and hydrological problems pertaining to the hydrodynamics of water-limited environments where plant-plant interactions and community self-organization are important.

One-dimensional multispecies hydrodynamic models of the wakeside ionosphere of Titan

NASA Technical Reports Server (NTRS)

Keller, C. N.; Cravens, T. E.

1994-01-01

The passage of Voyager 1 through the wakeside region of Titan's ionosphere provided an interesting probe of this plasma environment. A one-dimensional multispecies hydrodynamic model was developed to study the wakeside ionosphere for radial distances ranging from 1.3 to 4.5 R(sub T) and included the ion species H2CN(+), C(sub n) H(sub m)(+), C2H5(+), CH5(+), H(+), H2(+), and H3(+). Plasma transport only along magnetic field lines was included. The only source of ion production was from electron impact ionization of Titan's atmosphere by radially streaming Saturnian magnetospheric electrons (i.e., the nightside wakeside ionosphere). We found that ion production rates due to hot (200 eV) magnetospheric electrons impacting Titan's neutral atmosphere along radial field lines were comparable to the dayside ion production rates due to solar EUV flux. The magnetic flux tube area was varied along with electron temperature, and the results were compared to the ion densities and velocities measured during the Voyager 1 encounter. We found outward ion flows of about (2 to 7 x 10(exp 6)/sq cm/s, resulting in a total ion loss from Titan into Saturn's magnetosphere of about (6 to 20) x 10(exp 24)/s.

Far-from-equilibrium magnetic granular layers: dynamic patterns, magnetic order and self-assembled swimmers

NASA Astrophysics Data System (ADS)

Snezhko, Alexey

2010-03-01

Ensembles of interacting particles subject to an external periodic forcing often develop nontrivial collective behavior and self-assembled dynamic patterns. We study emergent phenomena in magnetic granular ensembles suspended at a liquid-air and liquid-liquid interfaces and subjected to a transversal alternating magnetic field. Experiments reveal a new type of nontrivially ordered dynamic self-assembled structures (in particular, ``magnetic snakes'', ``asters'', ``clams'') emerging in such systems in a certain range of excitation parameters. These non-equilibrium dynamic structures emerge as a result of the competition between magnetic and hydrodynamic forces and have complex magnetic ordering. Transition between different self-assembled phases with parameters of external driving magnetic field is observed. I will show that above some frequency threshold magnetic snakes spontaneously break the symmetry of the self-induced surface flows (symmetry breaking instability) and turn into swimmers. Self-induced surface flows symmetry can be also broken in a controlled fashion by introduction of a large bead to a magnetic snake (bead-snake hybrid), that transforms it into a robust self-locomoting entity. Some features of the self-localized structures can be understood in the framework of an amplitude equation for parametric waves coupled to the conservation law equation describing the evolution of the magnetic particle density and the Navier-Stokes equation for hydrodynamic flows.

Collective orientational dynamics of pinned chemically-propelled nanorotors

NASA Astrophysics Data System (ADS)

Robertson, Bryan; Stark, Holger; Kapral, Raymond

2018-04-01

Collections of chemically propelled nanomotors free to move in solution can form dynamic clusters with diverse properties as a result of interactions through hydrodynamic flow and concentration fields, as well as direct intermolecular interactions between motors. Here, we study the collective rotational behavior of pinned sphere-dimer motors where direct motor-motor interactions play no role. Since the centers of mass of the motors are pinned, they cannot execute directed translational motion, but they can pump fluid and rotate; thus, the rotors remain coupled through hydrodynamic and chemical fields. Using a microscopic simulation method that accounts for coupling through both these fields, we show that different rotor configurations with a high degree of correlation exist and their forms depend on the nature of the fluid-rotor interactions. The correlations are greatly reduced or completely destroyed when the chemical interactions are removed, indicating that hydrodynamic coupling, while present, plays a lesser role in determining the collective rotor dynamics. These conclusions are supported by Langevin dynamics simulations that neglect hydrodynamics and include an approximate form of coupling through chemical fields.

Coupled Electro-Hydrodynamic Effects of Electro-Osmosis from Pore Scale to Darcy Scale

NASA Astrophysics Data System (ADS)

Schotting, R.; Joekar-Niasar, V.; Leijnse, A.

2011-12-01

Electro-osmosis is "movement of a fluid under the effect of an electric field in a porous medium". This phenomenon has many applications in civil engineering (slope stabilization, dewatering), environmental engineering (soil remediation, sludge dewatering), chemical engineering (micro- or nano- mixers), medical engineering (drug delivery), etc. The key factor in electro-osmosis is the competition between the electrochemical and hydrodynamic forces as well as the coupling between the solid surface and the electrolyte properties. The objective of this research is to understand the influence of pore-scale heterogeneities of surface properties on the Darcy-scale behavior. We develop novel analytical solutions for the flow and transport of electrolyte including electro-hydrodynamic forces in a single micro-channel. We propose the complete analytical solution for monovalent electrolyte at full range overlapping double layers, and nonlinear electric field, including the Donan effect in transport of ions. These pore-scale formulations are numerically upscaled to obtain the Darcy-scale behavior. Our results show the contribution of electro-osmotic, chemical-osmotic and hydrodynamic components of the flow equation on pressure field evolution and multi-directional flow field at Darcy scale.

Characterization of submicrometer aqueous iron(III) colloids formed in the presence of phosphate by sedimentation field flow fractionation with multiangle laser light scattering detection.

PubMed

Magnuson, M L; Lytle, D A; Frietch, C M; Kelty, C A

2001-10-15

Iron colloids play a major role in the water chemistry of natural watersheds and of engineered drinking water distribution systems. Phosphate is frequently added to distribution systems to control corrosion problems, so iron-phosphate colloids may form through reaction of iron in water pipes. In this study, sedimentation field flow fractionation (SdFFF) is coupled on-line with multiangle laser light scattering (MALLS) detection to characterize these iron colloids formed following the oxygenation of iron(II) in the presence of phosphate. The SdFFF-MALLS data were used to calculate the hydrodynamic diameter, density, and particle size distribution of these submicrometer colloids. The system was first verified with standard polystyrene beads, and the results compared well with certified values. Iron(III) colloids were formed in the presence of phosphate at a variety of pH conditions. The colloids' hydrodynamic diameters, which ranged from 218 +/- 3 (pH 7) to 208 +/- 4 nm (pH 10), did not change significantly within the 95% confidence limit. Colloid density did increase significantly from 1.12 +/- 0.01 (pH 7) to 1.36 +/- 0.02 g/mL (pH 10). Iron(III) colloids formed at pH 10 in the presence of phosphate were compared to iron(III) colloids formed without phosphate and also to iron(III) colloids formed with silicate. The iron(III) colloids formed without phosphate or silicate were 0.46 g/mL more dense than any other colloids and were >6 times more narrowly distributed than the other colloids. The data suggest competitive incorporation of respective anions into the colloid during formation.

Collective Modes in a Trapped Gas from Second-Order Hydrodynamics

NASA Astrophysics Data System (ADS)

Lewis, William; Romatschke, Paul

Navier-Stokes equations are often used to analyze collective oscillations and expansion dynamics of strongly interacting quantum gases. However, their use, for example, in precision determination of transport properties such as the ratio shear viscosity to entropy density (η / s) in strongly interacting Fermi gases problematic. Second-order hydrodynamics addresses this by promoting the viscous stress tensor to a hydrodynamic variable relaxing to the Navier-Stokes form on a timescale τπ. We derive frequencies, damping rates, and spatial structure of collective oscillations up to the decapole mode of a harmonically trapped gas in this framework. We find damping of higher-order modes (i.e. beyond quadrupolar) exhibits greater sensitivity to shear viscosity. Thus measurement of the hexapolar mode, for example, may lead to a stronger experimental constraint on η / s . Additionally, we find ``non-hydrodynamic'' modes not contained in a Navier-Stokes description. We calculate excitation amplitudes of non-hydrodynamic modes demonstrating they should be observable. Non-hydrodynamic modes may have implications for the hydrodynamization timescale, the existence of quasi-particles, and universal transport behavior in strongly interacting quantum fluids.

Separated spin-up and spin-down quantum hydrodynamics of degenerated electrons: Spin-electron acoustic wave appearance.

PubMed

Andreev, Pavel A

2015-03-01

The quantum hydrodynamic (QHD) model of charged spin-1/2 particles contains physical quantities defined for all particles of a species including particles with spin-up and with spin-down. Different populations of states with different spin directions are included in the spin density (the magnetization). In this paper I derive a QHD model, which separately describes spin-up electrons and spin-down electrons. Hence electrons with different projections of spins on the preferable direction are considered as two different species of particles. It is shown that the numbers of particles with different spin directions do not conserve. Hence the continuity equations contain sources of particles. These sources are caused by the interactions of the spins with the magnetic field. Terms of similar nature arise in the Euler equation. The z projection of the spin density is no longer an independent variable. It is proportional to the difference between the concentrations of the electrons with spin-up and the electrons with spin-down. The propagation of waves in the magnetized plasmas of degenerate electrons is considered. Two regimes for the ion dynamics, the motionless ions and the motion of the degenerate ions as the single species with no account of the spin dynamics, are considered. It is shown that this form of the QHD equations gives all solutions obtained from the traditional form of QHD equations with no distinction of spin-up and spin-down states. But it also reveals a soundlike solution called the spin-electron acoustic wave. Coincidence of most solutions is expected since this derivation was started with the same basic equation: the Pauli equation. Solutions arise due to the different Fermi pressures for the spin-up electrons and the spin-down electrons in the magnetic field. The results are applied to degenerate electron gas of paramagnetic and ferromagnetic metals in the external magnetic field. The dispersion of the spin-electron acoustic waves in the partially spin-polarized degenerate neutron matter are also considered.

Observation of sand waves in the Taiwan Banks using HJ-1A/1B sun glitter imagery

NASA Astrophysics Data System (ADS)

Zhang, Hua-guo; Lou, Xiu-lin; Shi, Ai-qin; He, Xie-kai; Guan, Wei-bing; Li, Dong-ling

2014-01-01

This study focuses on the large sand waves in the Taiwan Banks. Our goals are to observe the sand waves as completely as possible, to obtain their direction, wavelength, density, and ridge length, to analyze their spatial distributions, and to understand the effects of the current field and water depth on the sand waves. This study demonstrates the possibility of using HJ-1A/1B sun glitter imagery with a large swath width and rapid coverage in studying sand waves. Six cloud-free HJ-1A/1B optical images with sun glitter signals received during 2009 to 2011 were processed. The sand waves were mapped based on their features in the images; their direction, wavelength, density, and ridge length were measured and analyzed. We identified 4604 sand waves distributed in an area of 16,400 km2. The distributions of sand waves and their characteristics were analyzed, and the differences of sand waves between the northwestern subregion and the southeastern subregion are reported. Further analysis and discussion of the relationships between spatial distribution of the sand waves and both the tidal current field from a numerical simulation and water depth led to some interesting conclusions. The current field determines the orientation of the sand wave, while the hydrodynamic conditions and water depth influence the shape, size, and density of sand waves to a certain degree.

Dynamics of zonal shear collapse with hydrodynamic electrons

NASA Astrophysics Data System (ADS)

Hajjar, R. J.; Diamond, P. H.; Malkov, M. A.

2018-06-01

This paper presents a theory for the collapse of the edge zonal shear layer, as observed at the density limit at low β. This paper investigates the scaling of the transport and mean profiles with the adiabaticity parameter α, with special emphasizes on fluxes relevant to zonal flow (ZF) generation. We show that the adiabaticity parameter characterizes the strength of production of zonal flows and so determines the state of turbulence. A 1D reduced model that self-consistently describes the spatiotemporal evolution of the mean density n ¯ , the azimuthal flow v¯ y , and the turbulent potential enstrophy ɛ=⟨(n˜ -∇2ϕ˜ ) 2/2 ⟩ —related to fluctuation intensity—is presented. Quasi-linear analysis determines how the particle flux Γn and vorticity flux Π=-χy∇2vy+Πre s scale with α, in both hydrodynamic and adiabatic regimes. As the plasma response passes from adiabatic (α > 1) to hydrodynamic (α < 1), the particle flux Γn is enhanced and the turbulent viscosity χy increases. However, the residual flux Πres—which drives the flow—drops with α. As a result, the mean vorticity gradient ∇2v¯ y=Πre s/χy —representative of the strength of the shear—also drops. The shear layer then collapses and turbulence is enhanced. The collapse is due to a decrease in ZF production, not an increase in damping. A physical picture for the onset of collapse is presented. The findings of this paper are used to motivate an explanation of the phenomenology of low β density limit evolution. A change from adiabatic ( α=kz2vth 2/(|ω|νei)>1 ) to hydrodynamic (α < 1) electron dynamics is associated with the density limit.

Equalizing resolution in smoothed-particle hydrodynamics calculations using self-adaptive sinc kernels

NASA Astrophysics Data System (ADS)

García-Senz, Domingo; Cabezón, Rubén M.; Escartín, José A.; Ebinger, Kevin

2014-10-01

Context. The smoothed-particle hydrodynamics (SPH) technique is a numerical method for solving gas-dynamical problems. It has been applied to simulate the evolution of a wide variety of astrophysical systems. The method has a second-order accuracy, with a resolution that is usually much higher in the compressed regions than in the diluted zones of the fluid. Aims: We propose and check a method to balance and equalize the resolution of SPH between high- and low-density regions. This method relies on the versatility of a family of interpolators called sinc kernels, which allows increasing the interpolation quality by varying only a single parameter (the exponent of the sinc function). Methods: The proposed method was checked and validated through a number of numerical tests, from standard one-dimensional Riemann problems in shock tubes, to multidimensional simulations of explosions, hydrodynamic instabilities, and the collapse of a Sun-like polytrope. Results: The analysis of the hydrodynamical simulations suggests that the scheme devised to equalize the accuracy improves the treatment of the post-shock regions and, in general, of the rarefacted zones of fluids while causing no harm to the growth of hydrodynamic instabilities. The method is robust and easy to implement with a low computational overload. It conserves mass, energy, and momentum and reduces to the standard SPH scheme in regions of the fluid that have smooth density gradients.

On the stability of self-gravitating magnetized dusty plasmas

NASA Astrophysics Data System (ADS)

Salimullah, M.; Shukla, P. K.

1999-03-01

The effects of a homogeneous magnetic field and the plasma nonuniformity on the dispersion relations of various electrostatic waves in self-gravitating magnetized dusty plasmas have been investigated. For this purpose, the kinetic dielectric response functions for the electrons and ions distributions have been used and the dielectric response function for the magnetized dust grains has been derived from the hydrodynamic equations that include the self-gravitational potential. Thus, extremely massive charged dust grains are subjected to both the electromagnetic and gravitational forces. Analytical studies of the dispersion relations in various frequency and wave number regimes reveal that both the magnetic fields and plasma inhomogeneities contribute to the stability of a self-gravitating dusty plasma system. The results of this investigation should be useful in understanding the stability of dusty proto-stars and dusty dark molecular clouds, which are held in strong magnetic fields and equilibrium density gradients.

Kinetic Equation for a Soliton Gas and Its Hydrodynamic Reductions

NASA Astrophysics Data System (ADS)

El, G. A.; Kamchatnov, A. M.; Pavlov, M. V.; Zykov, S. A.

2011-04-01

We introduce and study a new class of kinetic equations, which arise in the description of nonequilibrium macroscopic dynamics of soliton gases with elastic collisions between solitons. These equations represent nonlinear integro-differential systems and have a novel structure, which we investigate by studying in detail the class of N-component `cold-gas' hydrodynamic reductions. We prove that these reductions represent integrable linearly degenerate hydrodynamic type systems for arbitrary N which is a strong evidence in favour of integrability of the full kinetic equation. We derive compact explicit representations for the Riemann invariants and characteristic velocities of the hydrodynamic reductions in terms of the `cold-gas' component densities and construct a number of exact solutions having special properties (quasiperiodic, self-similar). Hydrodynamic symmetries are then derived and investigated. The obtained results shed light on the structure of a continuum limit for a large class of integrable systems of hydrodynamic type and are also relevant to the description of turbulent motion in conservative compressible flows.

Non-equilibrium magnetic colloidal dispersions at liquid-air interfaces: dynamic patterns, magnetic order and self-assembled swimmers.

PubMed

Snezhko, Alexey

2011-04-20

Colloidal dispersions of interacting particles subjected to an external periodic forcing often develop nontrivial self-assembled patterns and complex collective behavior. A fundamental issue is how collective ordering in such non-equilibrium systems arises from the dynamics of discrete interacting components. In addition, from a practical viewpoint, by working in regimes far from equilibrium new self-organized structures which are generally not available through equilibrium thermodynamics can be created. In this review spontaneous self-assembly phenomena in magnetic colloidal dispersions suspended at liquid-air interfaces and driven out of equilibrium by an alternating magnetic field are presented. Experiments reveal a new type of nontrivially ordered self-assembled structures emerging in such systems in a certain range of excitation parameters. These dynamic structures emerge as a result of the competition between magnetic and hydrodynamic forces and have complex unconventional magnetic ordering. Nontrivial self-induced hydrodynamic fields accompany each out-of-equilibrium pattern. Spontaneous symmetry breaking of the self-induced surface flows leading to a formation of self-propelled microstructures has been discovered. Some features of the self-localized structures can be understood in the framework of the amplitude equation (Ginzburg-Landau type equation) for parametric waves coupled to the conservation law equation describing the evolution of the magnetic particle density and the Navier-Stokes equation for hydrodynamic flows. To understand the fundamental microscopic mechanisms governing self-assembly processes in magnetic colloidal dispersions at liquid-air interfaces a first-principle model for a non-equilibrium self-assembly is presented. The latter model allows us to capture in detail the entire process of out-of-equilibrium self-assembly in the system and reproduces most of the observed phenomenology.

Equilibration in one-dimensional quantum hydrodynamic systems

NASA Astrophysics Data System (ADS)

Sotiriadis, Spyros

2017-10-01

We study quench dynamics and equilibration in one-dimensional quantum hydrodynamics, which provides effective descriptions of the density and velocity fields in gapless quantum gases. We show that the information content of the large time steady state is inherently connected to the presence of ballistically moving localised excitations. When such excitations are present, the system retains memory of initial correlations up to infinite times, thus evading decoherence. We demonstrate this connection in the context of the Luttinger model, the simplest quantum hydrodynamic model, and in the quantum KdV equation. In the standard Luttinger model, memory of all initial correlations is preserved throughout the time evolution up to infinitely large times, as a result of the purely ballistic dynamics. However nonlinear dispersion or interactions, when separately present, lead to spreading and delocalisation that suppress the above effect by eliminating the memory of non-Gaussian correlations. We show that, for any initial state that satisfies sufficient clustering of correlations, the steady state is Gaussian in terms of the bosonised or fermionised fields in the dispersive or interacting case respectively. On the other hand, when dispersion and interaction are simultaneously present, a semiclassical approximation suggests that localisation is restored as the two effects compensate each other and solitary waves are formed. Solitary waves, or simply solitons, are experimentally observed in quantum gases and theoretically predicted based on semiclassical approaches, but the question of their stability at the quantum level remains to a large extent an open problem. We give a general overview on the subject and discuss the relevance of our findings to general out of equilibrium problems. Dedicated to John Cardy on the occasion of his 70th birthday.

Dynamic simulation of concentrated macromolecular solutions with screened long-range hydrodynamic interactions: Algorithm and limitations

PubMed Central

Ando, Tadashi; Chow, Edmond; Skolnick, Jeffrey

2013-01-01

Hydrodynamic interactions exert a critical effect on the dynamics of macromolecules. As the concentration of macromolecules increases, by analogy to the behavior of semidilute polymer solutions or the flow in porous media, one might expect hydrodynamic screening to occur. Hydrodynamic screening would have implications both for the understanding of macromolecular dynamics as well as practical implications for the simulation of concentrated macromolecular solutions, e.g., in cells. Stokesian dynamics (SD) is one of the most accurate methods for simulating the motions of N particles suspended in a viscous fluid at low Reynolds number, in that it considers both far-field and near-field hydrodynamic interactions. This algorithm traditionally involves an O(N3) operation to compute Brownian forces at each time step, although asymptotically faster but more complex SD methods are now available. Motivated by the idea of hydrodynamic screening, the far-field part of the hydrodynamic matrix in SD may be approximated by a diagonal matrix, which is equivalent to assuming that long range hydrodynamic interactions are completely screened. This approximation allows sparse matrix methods to be used, which can reduce the apparent computational scaling to O(N). Previously there were several simulation studies using this approximation for monodisperse suspensions. Here, we employ newly designed preconditioned iterative methods for both the computation of Brownian forces and the solution of linear systems, and consider the validity of this approximation in polydisperse suspensions. We evaluate the accuracy of the diagonal approximation method using an intracellular-like suspension. The diffusivities of particles obtained with this approximation are close to those with the original method. However, this approximation underestimates intermolecular correlated motions, which is a trade-off between accuracy and computing efficiency. The new method makes it possible to perform large-scale and long-time simulation with an approximate accounting of hydrodynamic interactions. PMID:24089734

Energetic consequences of an inducible morphological defence in crucian carp.

PubMed

Pettersson, Lars B; Brönmark, Christer

1999-10-01

Crucian carp (Carassius carassius) increases in body depth in response to chemical cues from piscivores and the deeper body constitutes a morphological defence against gape-limited piscivores. In the field, deep-bodied individuals suffer a density-dependent cost when competing with shallow-bodied conspecifics. Here, we use hydrodynamic theory and swimming respirometry to investigate the proposed mechanism underlying this effect, high drag caused by the deep-bodied morphology. Our study confirms that drag is higher for deep-bodied crucian carp, both in terms of estimated theoretical drag and power curve steepness. However, deep-bodied fish swimming at the velocity associated with minimum cost of transport, U mc , did not experience higher costs of transport than shallow-bodied fish. Deep-bodied crucian carp had significantly lower standard metabolic rates, i.e. metabolic rates at rest, and also lower U mc , and the resulting costs of transport were similar for the two morphs. Nevertheless, when deep-bodied individuals deviate from U mc , e.g. when increasing foraging effort under competition, their steeper power curves will cause substantial energy costs relative to shallow-bodied conspecifics. Furthermore, there is evidence that reductions in standard metabolic rate incur costs in terms of lower stress tolerance, reduced growth rate, and life history changes. Thus, this work provides links between hydrodynamics, a cost-reducing mechanism, and a density-dependent fitness cost associated with an inducible defence.

Multiscale Molecular Dynamics Model for Heterogeneous Charged Systems

NASA Astrophysics Data System (ADS)

Stanton, L. G.; Glosli, J. N.; Murillo, M. S.

2018-04-01

Modeling matter across large length scales and timescales using molecular dynamics simulations poses significant challenges. These challenges are typically addressed through the use of precomputed pair potentials that depend on thermodynamic properties like temperature and density; however, many scenarios of interest involve spatiotemporal variations in these properties, and such variations can violate assumptions made in constructing these potentials, thus precluding their use. In particular, when a system is strongly heterogeneous, most of the usual simplifying assumptions (e.g., spherical potentials) do not apply. Here, we present a multiscale approach to orbital-free density functional theory molecular dynamics (OFDFT-MD) simulations that bridges atomic, interionic, and continuum length scales to allow for variations in hydrodynamic quantities in a consistent way. Our multiscale approach enables simulations on the order of micron length scales and 10's of picosecond timescales, which exceeds current OFDFT-MD simulations by many orders of magnitude. This new capability is then used to study the heterogeneous, nonequilibrium dynamics of a heated interface characteristic of an inertial-confinement-fusion capsule containing a plastic ablator near a fuel layer composed of deuterium-tritium ice. At these scales, fundamental assumptions of continuum models are explored; features such as the separation of the momentum fields among the species and strong hydrogen jetting from the plastic into the fuel region are observed, which had previously not been seen in hydrodynamic simulations.

Self-contained filtered density function

DOE PAGES

Nouri, Arash G.; Nik, Mehdi B.; Givi, Pope; ...

2017-09-18

The filtered density function (FDF) closure is extended to a “self-contained” format to include the subgrid-scale (SGS) statistics of all of the hydro-thermo-chemical variables in turbulent flows. These are the thermodynamic pressure, the specific internal energy, the velocity vector, and the composition field. In this format, the model is comprehensive and facilitates large-eddy simulation (LES) of flows at both low and high compressibility levels. A transport equation is developed for the joint pressure-energy-velocity-composition filtered mass density function (PEVC-FMDF). In this equation, the effect of convection appears in closed form. The coupling of the hydrodynamics and thermochemistry is modeled via amore » set of stochastic differential equation for each of the transport variables. This yields a self-contained SGS closure. We demonstrated how LES is conducted of a turbulent shear flow with transport of a passive scalar. Finally, the consistency of the PEVC-FMDF formulation is established, and its overall predictive capability is appraised via comparison with direct numerical simulation (DNS) data.« less

Spatio-temporal variations in bloom of the red-tide dinoflagellate Karenia mikimotoi in Imari Bay, Japan, in 2014: Factors controlling horizontal and vertical distribution.

PubMed

Aoki, Kazuhiro; Kameda, Takahiko; Yamatogi, Toshifumi; Ishida, Naoya; Hirae, Sou; Kawaguchi, Mayumi; Syutou, Toshio

2017-11-15

A massive bloom of the dinoflagellate Karenia mikimotoi appeared in 2014 in Imari Bay, Japan. Bloom dynamics and hydrographical conditions were examined by field survey. The bloom initially developed in the eastern area of Imari Bay, subsequently after rainfall during the neap tides, cell density exceeded over 10,000cellsml. Vertical distribution of K. mikimotoi was primarily controlled by the light intensity and secondarily by the water quality during the daytime. Almost all cell-density maxima occurred in depths with weak daytime light intensities of <300μmolm -2 s -1 . In some cases of weak light intensity, cell-density maxima occurred in depths with favorable hydrodynamic conditions for the growth. Spatially classified areas were identified by cluster analysis using the growth rate calculated from seawater temperature and salinity. This study quantitatively evaluated the environmental factors of the eastern area, where the bloom initially occurred, during the development of the bloom. Copyright © 2017 Elsevier Ltd. All rights reserved.

Self-contained filtered density function

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

Nouri, Arash G.; Nik, Mehdi B.; Givi, Pope

The filtered density function (FDF) closure is extended to a “self-contained” format to include the subgrid-scale (SGS) statistics of all of the hydro-thermo-chemical variables in turbulent flows. These are the thermodynamic pressure, the specific internal energy, the velocity vector, and the composition field. In this format, the model is comprehensive and facilitates large-eddy simulation (LES) of flows at both low and high compressibility levels. A transport equation is developed for the joint pressure-energy-velocity-composition filtered mass density function (PEVC-FMDF). In this equation, the effect of convection appears in closed form. The coupling of the hydrodynamics and thermochemistry is modeled via amore » set of stochastic differential equation for each of the transport variables. This yields a self-contained SGS closure. We demonstrated how LES is conducted of a turbulent shear flow with transport of a passive scalar. Finally, the consistency of the PEVC-FMDF formulation is established, and its overall predictive capability is appraised via comparison with direct numerical simulation (DNS) data.« less

Self-contained filtered density function

NASA Astrophysics Data System (ADS)

Nouri, A. G.; Nik, M. B.; Givi, P.; Livescu, D.; Pope, S. B.

2017-09-01

The filtered density function (FDF) closure is extended to a "self-contained" format to include the subgrid-scale (SGS) statistics of all of the hydro-thermo-chemical variables in turbulent flows. These are the thermodynamic pressure, the specific internal energy, the velocity vector, and the composition field. In this format, the model is comprehensive and facilitates large-eddy simulation (LES) of flows at both low and high compressibility levels. A transport equation is developed for the joint pressure-energy-velocity-composition filtered mass density function (PEVC-FMDF). In this equation, the effect of convection appears in closed form. The coupling of the hydrodynamics and thermochemistry is modeled via a set of stochastic differential equation for each of the transport variables. This yields a self-contained SGS closure. For demonstration, LES is conducted of a turbulent shear flow with transport of a passive scalar. The consistency of the PEVC-FMDF formulation is established, and its overall predictive capability is appraised via comparison with direct numerical simulation (DNS) data.

Multiparticle collision simulations of two-dimensional one-component plasmas: Anomalous transport and dimensional crossovers

NASA Astrophysics Data System (ADS)

Di Cintio, Pierfrancesco; Livi, Roberto; Lepri, Stefano; Ciraolo, Guido

2017-04-01

By means of hybrid multiparticle collsion-particle-in-cell (MPC-PIC) simulations we study the dynamical scaling of energy and density correlations at equilibrium in moderately coupled two-dimensional (2D) and quasi-one-dimensional (1D) plasmas. We find that the predictions of nonlinear fluctuating hydrodynamics for the structure factors of density and energy fluctuations in 1D systems with three global conservation laws hold true also for 2D systems that are more extended along one of the two spatial dimensions. Moreover, from the analysis of the equilibrium energy correlators and density structure factors of both 1D and 2D neutral plasmas, we find that neglecting the contribution of the fluctuations of the vanishing self-consistent electrostatic fields overestimates the interval of frequencies over which the anomalous transport is observed. Such violations of the expected scaling in the currents correlation are found in different regimes, hindering the observation of the asymptotic scaling predicted by the theory.

Dynamical density functional theory for microswimmers

NASA Astrophysics Data System (ADS)

Menzel, Andreas M.; Saha, Arnab; Hoell, Christian; Löwen, Hartmut

2016-01-01

Dynamical density functional theory (DDFT) has been successfully derived and applied to describe on one hand passive colloidal suspensions, including hydrodynamic interactions between individual particles. On the other hand, active "dry" crowds of self-propelled particles have been characterized using DDFT. Here, we go one essential step further and combine these two approaches. We establish a DDFT for active microswimmer suspensions. For this purpose, simple minimal model microswimmers are introduced. These microswimmers self-propel by setting the surrounding fluid into motion. They hydrodynamically interact with each other through their actively self-induced fluid flows and via the common "passive" hydrodynamic interactions. An effective soft steric repulsion is also taken into account. We derive the DDFT starting from common statistical approaches. Our DDFT is then tested and applied by characterizing a suspension of microswimmers, the motion of which is restricted to a plane within a three-dimensional bulk fluid. Moreover, the swimmers are confined by a radially symmetric trapping potential. In certain parameter ranges, we find rotational symmetry breaking in combination with the formation of a "hydrodynamic pumping state," which has previously been observed in the literature as a result of particle-based simulations. An additional instability of this pumping state is revealed.

Introduction to the Focus Issue: Chemo-Hydrodynamic Patterns and Instabilities

NASA Astrophysics Data System (ADS)

De Wit, A.; Eckert, K.; Kalliadasis, S.

2012-09-01

Pattern forming instabilities are often encountered in a wide variety of natural phenomena and technological applications, from self-organization in biological and chemical systems to oceanic or atmospheric circulation and heat and mass transport processes in engineering systems. Spatio-temporal structures are ubiquitous in hydrodynamics where numerous different convective instabilities generate pattern formation and complex spatiotemporal dynamics, which have been much studied both theoretically and experimentally. In parallel, reaction-diffusion processes provide another large family of pattern forming instabilities and spatio-temporal structures which have been analyzed for several decades. At the intersection of these two fields, "chemo-hydrodynamic patterns and instabilities" resulting from the coupling of hydrodynamic and reaction-diffusion processes have been less studied. The exploration of the new instability and symmetry-breaking scenarios emerging from the interplay between chemical reactions, diffusion and convective motions is a burgeoning field in which numerous exciting problems have emerged during the last few years. These problems range from fingering instabilities of chemical fronts and reactive fluid-fluid interfaces to the dynamics of reaction-diffusion systems in the presence of chaotic mixing. The questions to be addressed are at the interface of hydrodynamics, chemistry, engineering or environmental sciences to name a few and, as a consequence, they have started to draw the attention of several communities including both the nonlinear chemical dynamics and hydrodynamics communities. The collection of papers gathered in this Focus Issue sheds new light on a wide range of phenomena in the general area of chemo-hydrodynamic patterns and instabilities. It also serves as an overview of the current research and state-of-the-art in the field.

Sound Transmission through Cylindrical Shell Structures Excited by Boundary Layer Pressure Fluctuations

NASA Technical Reports Server (NTRS)

Tang, Yvette Y.; Silcox, Richard J.; Robinson, Jay H.

1996-01-01

This paper examines sound transmission into two concentric cylindrical sandwich shells subject to turbulent flow on the exterior surface of the outer shell. The interior of the shells is filled with fluid medium and there is an airgap between the shells in the annular space. The description of the pressure field is based on the cross-spectral density formulation of Corcos, Maestrello, and Efimtsov models of the turbulent boundary layer. The classical thin shell theory and the first-order shear deformation theory are applied for the inner and outer shells, respectively. Modal expansion and the Galerkin approach are used to obtain closed-form solutions for the shell displacements and the radiation and transmission pressures in the cavities including both the annular space and the interior. The average spectral density of the structural responses and the transmitted interior pressures are expressed explicitly in terms of the summation of the cross-spectral density of generalized force induced by the boundary layer turbulence. The effects of acoustic and hydrodynamic coincidences on the spectral density are observed. Numerical examples are presented to illustrate the method for both subsonic and supersonic flows.

A new method to quantify the effects of baryons on the matter power spectrum

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

Schneider, Aurel; Teyssier, Romain, E-mail: aurel@physik.uzh.ch, E-mail: teyssier@physik.uzh.ch

2015-12-01

Future large-scale galaxy surveys have the potential to become leading probes for cosmology provided the influence of baryons on the total mass distribution is understood well enough. As hydrodynamical simulations strongly depend on details in the feedback implementations, no unique and robust predictions for baryonic effects currently exist. In this paper we propose a baryonic correction model that modifies the density field of dark-matter-only N-body simulations to mimic the effects of baryons from any underlying adopted feedback recipe. The model assumes haloes to consist of 4 components: 1- hot gas in hydrostatical equilibrium, 2- ejected gas from feedback processes, 3-more » central galaxy stars, and 4- adiabatically relaxed dark matter, which all modify the initial dark-matter-only density profiles. These altered profiles allow to define a displacement field for particles in N-body simulations and to modify the total density field accordingly. The main advantage of the baryonic correction model is to connect the total matter density field to the observable distribution of gas and stars in haloes, making it possible to parametrise baryonic effects on the matter power spectrum. We show that the most crucial quantities are the mass fraction of ejected gas and its corresponding ejection radius. The former controls how strongly baryons suppress the power spectrum, while the latter provides a measure of the scale where baryonic effects become important. A comparison with X-ray and Sunyaev-Zel'dovich cluster observations suggests that baryons suppress wave modes above k∼0.5 h/Mpc with a maximum suppression of 10-25 percent around k∼ 2 h/Mpc. More detailed observations of the gas in the outskirts of groups and clusters are required to decrease the large uncertainties of these numbers.« less

High resolution field monitoring in coastal wetlands of the U.S. Mid-Atlantic to support quantification of storm surge attenuation at the regional scale

NASA Astrophysics Data System (ADS)

Paquier, A. E.; Haddad, J.; Lawler, S.; Garzon Hervas, J. L.; Ferreira, C.

2015-12-01

Hurricane Sandy (2012) demonstrated the vulnerability of the US East Coast to extreme events, and motivated the exploration of resilient coastal defenses that incorporate both hard engineering and natural strategies such as the restoration, creation and enhancement of coastal wetlands and marshes. Past laboratory and numerical studies have indicated the potential of wetlands to attenuate storm surge, and have demonstrated the complexity of the surge hydrodynamic interactions with wetlands. Many factors control the propagation of surge in these natural systems including storm characteristics, storm-induced hydrodynamics, landscape complexity, vegetation biomechanical properties and the interactions of these different factors. While previous field studies have largely focused on the impact of vegetation characteristics on attenuation processes, few have been undertaken with holistic consideration of these factors and their interactions. To bridge this gap of in-situ field data and to support the calibration of storm surge and wave numerical models such that wetlands can be correctly parametrized on a regional scale, we are carrying out high resolution surveys of hydrodynamics (pressure, current intensity and direction), morphology (topo-bathymetry, micro-topography) and vegetation (e.g. stem density, height, vegetation frontal area) in 4 marshes along the Chesapeake Bay. These areas are representative of the ecosystems and morphodynamic functions present in this region, from the tidal Potomac marshes to the barrier-island back-bays of the Delmarva Peninsula. The field monitoring program supports the investigation of the influence of different types of vegetation on water level, swell and wind wave attenuation and morphological evolution during storm surges. This dataset is also used to calibrate and validate numerical simulations of hurricane storm surge propagation at regional and local scales and to support extreme weather coastal resilience planning in the region. Figure 1 shows an area prone to storm surge impact within one of the 4 study sites: the Dameron Marsh Natural Area Preserve, located on the shoreline of the Northern Peninsula of Virginia, along the Chesapeake Bay.

Use of limonene in countercurrent chromatography: a green alkane substitute.

PubMed

Faure, Karine; Bouju, Elodie; Suchet, Pauline; Berthod, Alain

2013-05-07

Counter-current chromatography (CCC) is a preparative separation technique working with the two liquid phases of a biphasic liquid system. One phase is used as the mobile phase when the other, the stationary phase, is held in place by centrifugal fields. Limonene is a biorenewable cycloterpene solvent coming from orange peel waste. It was evaluated as a possible substitute for heptane in CCC separations. The limonene/methanol/water and heptane/methanol/water phase diagrams are very similar at room temperature. The double bonds of the limonene molecule allows for possible π-π interactions with solutes rendering limonene slightly more polar than heptane giving small differences in solute partition coefficients in the two systems. The 24% higher limonene density is a difference with heptane that has major consequences in CCC. The polar and apolar phases of the limonene/methanol/water 10/9/1 v/v have -0.025 g/cm(3) density difference (lower limonene phase) compared to +0.132 g/cm(3) with heptane (upper heptane phase). This precludes the use of this limonene system with hydrodynamic CCC columns that need significant density difference to retain a liquid stationary phase. It is an advantage with hydrostatic CCC columns because density difference is related to the working pressure drop: limonene allows one to work with high centrifugal fields and moderate pressure drop. Limonene has the capability to be a "green" alternative to petroleum-based solvents in CCC applications.

Seagrass blade motion under waves and its impact on wave decay

NASA Astrophysics Data System (ADS)

Luhar, M.; Infantes, E.; Nepf, H.

2017-05-01

The hydrodynamic drag generated by seagrass meadows can dissipate wave-energy, causing wave decay. It is well known that this drag depends on the relative motion between the water and the seagrass blades, yet the impact of blade motion on drag and wave-energy dissipation remains to be fully characterized. In this experimental study, we examined the impact of blade motion on wave decay by concurrently recording blade posture during a wave cycle and measuring wave decay over a model seagrass meadow. We also identified a scaling law that predicts wave decay over the model meadow for a range of seagrass blade density, wave period, wave height, and water depth scaled from typical field conditions. Blade flexibility led to significantly lower drag and wave decay relative to theoretical predictions for rigid, upright blades. To quantify the impact of blade motion on wave decay, we employed an effective blade length, le, defined as the rigid blade length that leads to equivalent wave-energy dissipation. We estimated le directly from images of blade motion. Consistent with previous studies, these estimates showed that the effective blade length depends on the dimensionless Cauchy number, which describes the relative magnitude of the wave hydrodynamic drag and the restoring force due to blade rigidity. As the hydrodynamic forcing increases, the blades exhibit greater motion. Greater blade motion leads to smaller relative velocities, reducing drag, and wave-energy dissipation (i.e., smaller le).

Mitigation of X-ray shadow seeding of hydrodynamic instabilities on inertial confinement fusion capsules using a reduced diameter fuel fill-tube

NASA Astrophysics Data System (ADS)

MacPhee, A. G.; Smalyuk, V. A.; Landen, O. L.; Weber, C. R.; Robey, H. F.; Alfonso, E. L.; Biener, J.; Bunn, T.; Crippen, J. W.; Farrell, M.; Felker, S.; Field, J. E.; Hsing, W. W.; Kong, C.; Milovich, J.; Moore, A.; Nikroo, A.; Rice, N.; Stadermann, M.; Wild, C.

2018-05-01

We report a reduced X-ray shadow imprint of hydrodynamic instabilities on the high-density carbon ablator surface of inertial confinement fusion (ICF) capsules using a reduced diameter fuel fill tube on the National Ignition Facility (NIF). The perturbation seed mass from hydrodynamic instabilities was reduced by approximately an order of magnitude by reducing both the diameter and wall thickness of the fill tube by ˜2×, consistent with analytical estimates. This work demonstrates a successful mitigation strategy for engineered features for ICF implosions on the NIF.

Modeling Electron Transport within the Framework of Hydrodynamic Description of Hall Thrusters (Preprint)

DTIC Science & Technology

2008-06-16

Framework of Hydrodynamic Description of Hall Thrusters (Preprint) 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) M . keidar (The George...within the framework of hydrodynamic description of Hall thrusters (PREPRINT) M . Keidar 1 and L. Brieda 2 1) Department of Mechanical and...the electron current density: y yw y m ew y w z w ew dV V y kT mV kT e kT e kT m B E nj y )sin() 2 exp()exp()exp( 2 2 2 2 2/1 0 (2) In this case, a

Observational discrimination between modes of shock propagation in interstellar clouds: Predictions of CH+ and SH+ column densities in diffuse clouds

NASA Technical Reports Server (NTRS)

Flower, D. R.; Desforets, G. P.; Roueff, E.; Hartquist, T. W.

1986-01-01

Considerable effort in recent years has been devoted to the study of shocks in the diffuse interstellar medium. This work has been motivated partly by the observations of rotationally excited states of H2, and partly by the realization that species such as CH(+), OH and H2O might be formed preferentially in hot, post-shock gas. The problem of CH(+) and the difficulties encountered when trying to explain the high column densities, observed along lines of sight to certain hot stars, have been reviewed earlier. The importance of a transverse magnetic field on the structure of an interstellar shock was also demonstrated earlier. Transverse magnetic fields above a critical strength give rise to an acceleration zone or precursor, in which the parameters on the flow vary continuously. Chemical reactions, which change the degree of ionization of the gas, also modify the structure of the shock considerably. Recent work has shown that large column densities of CH(+) can be produced in magnetohydrodynamic shock models. Shock speeds U sub s approx. = 10 km/s and initial magnetic field strengths of a few micro G are sufficient to produce ion-neutral drift velocities which can drive the endothermic C(+)(H2,H)CH(+) reaction. It was also shown that single-fluid hydrodynamic models do not generate sufficiently large column densities of CH(+) unless unacceptably high shock velocities (u sub s approx. 20 km/s) are assumed in the models. Thus, the observed column densities of CH(+) provide a constraint on the mode of shock propagation in diffuse clouds. More precisely, they determine a lower limit to the ion-neutral drift velocity.

Study on aggregation behavior of low density lipoprotein in hen egg yolk plasma by asymmetrical flow field-flow fractionation coupled with multiple detectors.

PubMed

Dou, Haiyang; Magnusson, Emma; Choi, Jaeyeong; Duan, Fei; Nilsson, Lars; Lee, Seungho

2016-02-01

In this study, asymmetrical flow field-flow fractionation (AF4) coupled online with UV, multiangle light scattering (MALS), and fluorescence (FS) detectors (AF4-UV-MALS-FS) was employed for separation and characterization of egg yolk plasma. AF4 provided separation of three major components of the egg yolk plasma i.e. soluble proteins, low density lipoproteins (LDL) and their aggregates, based on their respective hydrodynamic sizes. Identification of LDL was confirmed by staining the sample with a fluorescent dye, Nile Red. The effect of carrier liquids on aggregation of LDL was investigated. Collected fractions of soluble proteins were characterized using sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE). Moreover, the effect of heat and enzymatic treatment on egg yolk plasma was investigated. The results suggest that enzymatic treatment with phospholipase A2 (PLA2) significantly enhances the heat stability of LDL. The results show that AF4-UV-MALS-FS is a powerful tool for the fractionation and characterization of egg yolk plasma components. Copyright © 2015 Elsevier Ltd. All rights reserved.

Multi-layer accretion disks around black holes and formation of a hot ion-torus

NASA Astrophysics Data System (ADS)

Hujeirat, A.; Camenzind, M.

2000-08-01

We present the first 2D steady-state numerical radiative hydrodynamical calculations showing the formation of a low-density hot torus in the very inner region of accretion disks around a black hole. The inner part of the disk is found to be thermally unstable when Bremsstrahlung is the dominant cooling mechanism. Within the parameter regime used and in the absence of magnetic fields, the torus-plasma is highly time-dependent with supersonic oscillating motion with respect to the electron temperature. When the soft photons from the disk comptonize the electrons efficiently, the ion-pressure supported torus shrinks in volume, but decelerates further the inward motion into the hole. We speculate that magnetic fields would stabilize the tori by lowering its energy package through initiating jets and/or outflows. In the outer region, we find that the scale height of the angular velocity HΩ largely exceeds the scale height of the density Hρ. This yields a multi-layer flow-structure in the vertical direction which slows the inwards motion into the BH significantly, enhancing further the formation of the hot torus.

Hydrodynamic limit of Wigner-Poisson kinetic theory: Revisited

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

Akbari-Moghanjoughi, M.; International Centre for Advanced Studies in Physical Sciences and Institute for Theoretical Physics, Ruhr University Bochum, D-44780 Bochum

2015-02-15

In this paper, we revisit the hydrodynamic limit of the Langmuir wave dispersion relation based on the Wigner-Poisson model in connection with that obtained directly from the original Lindhard dielectric function based on the random-phase-approximation. It is observed that the (fourth-order) expansion of the exact Lindhard dielectric constant correctly reduces to the hydrodynamic dispersion relation with an additional term of fourth-order, beside that caused by the quantum diffraction effect. It is also revealed that the generalized Lindhard dielectric theory accounts for the recently discovered Shukla-Eliasson attractive potential (SEAP). However, the expansion of the exact Lindhard static dielectric function leads tomore » a k{sup 4} term of different magnitude than that obtained from the linearized quantum hydrodynamics model. It is shown that a correction factor of 1/9 should be included in the term arising from the quantum Bohm potential of the momentum balance equation in fluid model in order for a correct plasma dielectric response treatment. Finally, it is observed that the long-range oscillatory screening potential (Friedel oscillations) of type cos(2k{sub F}r)/r{sup 3}, which is a consequence of the divergence of the dielectric function at point k = 2k{sub F} in a quantum plasma, arises due to the finiteness of the Fermi-wavenumber and is smeared out in the limit of very high electron number-densities, typical of white dwarfs and neutron stars. In the very low electron number-density regime, typical of semiconductors and metals, where the Friedel oscillation wavelength becomes much larger compared to the interparticle distances, the SEAP appears with a much deeper potential valley. It is remarked that the fourth-order approximate Lindhard dielectric constant approaches that of the linearized quantum hydrodynamic in the limit if very high electron number-density. By evaluation of the imaginary part of the Lindhard dielectric function, it is shown that the Landau-damping region in ω-k plane increases dramatically by increase of the electron number-density.« less

Absence of Disorder-Driven Metal-Insulator Transitions in Simple Holographic Models

NASA Astrophysics Data System (ADS)

Grozdanov, Sašo; Lucas, Andrew; Sachdev, Subir; Schalm, Koenraad

2015-11-01

We study electrical transport in a strongly coupled strange metal in two spatial dimensions at finite temperature and charge density, holographically dual to the Einstein-Maxwell theory in an asymptotically four-dimensional anti-de Sitter space spacetime, with arbitrary spatial inhomogeneity, up to mild assumptions including emergent isotropy. In condensed matter, these are candidate models for exotic strange metals without long-lived quasiparticles. We prove that the electrical conductivity is bounded from below by a universal minimal conductance: the quantum critical conductivity of a clean, charge-neutral plasma. Beyond nonperturbatively justifying mean-field approximations to disorder, our work demonstrates the practicality of new hydrodynamic insight into holographic transport.

Stable spin domains in a nondegenerate ultracold gas

NASA Astrophysics Data System (ADS)

Graham, S. D.; Niroomand, D.; Ragan, R. J.; McGuirk, J. M.

2018-05-01

We study the stability of two-domain spin structures in an ultracold gas of magnetically trapped 87Rb atoms above quantum degeneracy. Adding a small effective magnetic field gradient stabilizes the domains via coherent collective spin rotation effects, despite negligibly perturbing the potential energy relative to the thermal energy. We demonstrate that domain stabilization is accomplished through decoupling the dynamics of longitudinal magnetization, which remains in time-independent domains, from transverse magnetization, which undergoes a purely transverse spin wave trapped within the domain wall. We explore the effect of temperature and density on the steady-state domains, and compare our results to a hydrodynamic solution to a quantum Boltzmann equation.

Hydrodynamic mode associated with the pinch flow in RFP simulations

NASA Astrophysics Data System (ADS)

Delzanno, Gian Luca; Chacon, Luis; Finn, John

2007-11-01

We present a systematic study of single helicity (SH) states and quasi-single helicity (QSH) states in RFPs. We begin with cylindrical paramagnetic pinch equilibria with uniform resistivity, characterized by a single dimensionless parameter proportional to the toroidal electric field, or the RFP toroidal current parameter θ. For sufficiently high θ, there are several unstable m=1 ideal MHD instabilities, typically one of which is nonresonant, with 1/n just above q(r=0). We evolve these modes nonlinearly to saturation for low Hartmann number H. We show the existence of a new class of unstable modes [1], besides the electromagnetic kink modes typically responsible for the reversal of the axial magnetic field at the edge in RFPs. This new instability is hydrodynamic in nature and is due to the inward equilibrium pinch flow and suitable boundary conditions. In these circumstances, the total angular momentum of the system must grow in response to the flux of particles coming from the boundary. The hydrodynamic mode dominates the nonlinear phase of the velocity field but has little effect on the dynamics of the magnetic field. [1] G.L. Delzanno, L. Chac'on, J.M. Finn, Hydrodynamic mode associated with the pinch flow in Reversed Field Pinch simulations, submitted (2007).

Mathematical modeling of the thermal and hydrodynamic structure of the cooling reservoir

NASA Astrophysics Data System (ADS)

Saminskiy, G.; Debolskaya, E.

2012-04-01

Hydrothermal conditions of the cooling reservoir is determined by the heat and mass transfer from the water surface to the atmosphere and the processes of heat transfer directly in the water mass of the reservoir. As the capacity of power plants, the corresponding increase in the volume of heated water and the use of deep lakes and reservoirs as coolers there is a need to develop new, more accurate, and the application of existing methods for the numerical simulation. In calculating the hydrothermal regime it must take into account the effect of wind, density (buoyancy) forces, and other data of the cooling reservoir. In addition to solving practical problems it is important to know not only the magnitude of the average temperature, but also its area and depth distribution. A successful solution can be achieved through mathematical modeling of general systems of equations of transport processes and the correct formulation of the problem, based on appropriate initial data. The purpose of the work is application of software package GETM for simulating the hydrothermal regime of cooling reservoir with an estimate of three-dimensional structure of transfer processes, the effects of wind, the friction of the water surface. Three-dimensional models are rarely applied, especially for far-field problems. If such models are required, experts in the field must develop and apply them. Primary physical processes included are surface heat transfer, short-wave and long-wave radiation and penetration, convective mixing, wind and flow induced mixing, entrainment of ambient water by pumped-storage inflows, inflow density stratification as impacted by temperature and dissolved and suspended solids. The model forcing data consists of the system bathymetry developed into the model grid; the boundary condition flow and temperature; the tributary and flow and temperature; and the system meteorology. Ivankovskoe reservoir belongs to the reservoirs of valley type (Tver region, Russia). It is used as a cooling reservoir for Konakovskaya power plant. It dumps the heated water in the Moshkovichevsky bay. Thermal and hydrodynamic structure of the Moshkovichevsky Bay is particular interest as the object of direct influence of heated water discharge. To study the effect of thermal discharge into the Ivankovskoe reservoir the model of the Moshkovichevsky Bay was built, which is subject to the largest thermal pollution. Step of the calculation grid is 25 meters. For further verification of the model field investigations were conducted in August-September 2011. The modeling results satisfactorily describe the thermal and hydrodynamic structure of the Moshkovichevsky Bay.

Anomalous sea surface structures as an object of statistical topography

NASA Astrophysics Data System (ADS)

Klyatskin, V. I.; Koshel, K. V.

2015-06-01

By exploiting ideas of statistical topography, we analyze the stochastic boundary problem of emergence of anomalous high structures on the sea surface. The kinematic boundary condition on the sea surface is assumed to be a closed stochastic quasilinear equation. Applying the stochastic Liouville equation, and presuming the stochastic nature of a given hydrodynamic velocity field within the diffusion approximation, we derive an equation for a spatially single-point, simultaneous joint probability density of the surface elevation field and its gradient. An important feature of the model is that it accounts for stochastic bottom irregularities as one, but not a single, perturbation. Hence, we address the assumption of the infinitely deep ocean to obtain statistic features of the surface elevation field and the squared elevation gradient field. According to the calculations, we show that clustering in the absolute surface elevation gradient field happens with the unit probability. It results in the emergence of rare events such as anomalous high structures and deep gaps on the sea surface almost in every realization of a stochastic velocity field.

Normal stress effects on Knudsen flow

NASA Astrophysics Data System (ADS)

Eu, Byung Chan

2018-01-01

Normal stress effects are investigated on tube flow of a single-component non-Newtonian fluid under a constant pressure gradient in a constant temperature field. The generalized hydrodynamic equations are employed, which are consistent with the laws of thermodynamics. In the cylindrical tube flow configuration, the solutions of generalized hydrodynamic equations are exactly solvable and the flow velocity is obtained in a simple one-dimensional integral quadrature. Unlike the case of flow in the absence of normal stresses, the flow develops an anomaly in that the flow in the boundary layer becomes stagnant and the thickness of such a stagnant velocity boundary layer depends on the pressure gradient, the aspect ratio of the radius to the length of the tube, and the pressure (or density and temperature) at the entrance of the tube. The volume flow rate formula through the tube is derived for the flow. It generalizes the Knudsen flow rate formula to the case of a non-Newtonian stress tensor in the presence of normal stress differences. It also reduces to the Navier-Stokes theory formula in the low shear rate limit near equilibrium.

Lubrication and thermal characteristics of mechanical seal with porous surface based on cavitation

NASA Astrophysics Data System (ADS)

Huilong, Chen; Muzi, Zuo; Tong, Liu; Yu, Wang; Cheng, Xu; Qiangbo, Wu

2014-04-01

The theory model of mechanical seals with laser-textured porous surface (LST-MS) was established. The liquid film of LST-MS was simulated by the Fluent software, using full cavitation model and non-cavitation model separately. Dynamic mesh technique and relationship between viscosity and temperature were applied to simulate the internal flow field and heat characteristics of LST-MS, based on the more accurate cavitation model. Influence of porous depth ratio porous diameter ɛ and porous density SP on lubrication performance and the variation of lubrication and thermal properties with shaft speed and sealing pressure were analyzed. The results indicate that the strongest hydrodynamic pressure effect and the biggest thickness of liquid film are obtained when ɛ and SP are respectively about 0.025 and 0.5 which were thought to be the optimum value. The frictional heat leads to the increase of liquid film temperature and the decrease of medium viscosity with the shaft speed increasing. The hydrodynamic pressure effect increases as shaft speed increasing, however it decreases as the impact of frictional heat.

First experimental evidence of hydrodynamic tunneling of ultra–relativistic protons in extended solid copper target at the CERN HiRadMat facility

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

Schmidt, R.; Grenier, D.; Wollmann, D.

2014-08-15

A novel experiment has been performed at the CERN HiRadMat test facility to study the impact of the 440 GeV proton beam generated by the Super Proton Synchrotron on extended solid copper cylindrical targets. Substantial hydrodynamic tunneling of the protons in the target material has been observed that leads to significant lengthening of the projectile range, which confirms our previous theoretical predictions [N. A. Tahir et al., Phys. Rev. Spec. Top.-Accel. Beams 15, 051003 (2012)]. Simulation results show very good agreement with the experimental measurements. These results have very important implications on the machine protection design for powerful machines like themore » Large Hadron Collider (LHC), the future High Luminosity LHC, and the proposed huge 80 km circumference Future Circular Collider, which is currently being discussed at CERN. Another very interesting outcome of this work is that one may also study the field of High Energy Density Physics at this test facility.« less

Experimental observations of the hydrodynamic behavior of solvent systems in high-speed counter-current chromatography. I. Hydrodynamic distribution of two solvent phases in a helical column subjected to two types of synchronous planetary motion.

PubMed

Ito, Y

1984-10-05

Hydrodynamic distribution of two-phase solvent systems in a rotating helical column subjected to centrifugal fields produced by two different types of synchronous planetary motion has been studied by the use of the combined horizontal flow-through coil planet centrifuge. With continuous elution of the mobile phase, the simpler type of motion resulted in low retention of the stationary phase in the column whereas a more complex motion, which produces a quasi-radial centrifugal field varying in both intensity and direction, yielded high stationary phase retention for commonly used solvent systems having a wide range of hydrophobicity. These solvent systems display highly complex modes of hydrodynamic interaction in the coil according to their particular physical properties.

Large-Scale Description of Interacting One-Dimensional Bose Gases: Generalized Hydrodynamics Supersedes Conventional Hydrodynamics

NASA Astrophysics Data System (ADS)

Doyon, Benjamin; Dubail, Jérôme; Konik, Robert; Yoshimura, Takato

2017-11-01

The theory of generalized hydrodynamics (GHD) was recently developed as a new tool for the study of inhomogeneous time evolution in many-body interacting systems with infinitely many conserved charges. In this Letter, we show that it supersedes the widely used conventional hydrodynamics (CHD) of one-dimensional Bose gases. We illustrate this by studying "nonlinear sound waves" emanating from initial density accumulations in the Lieb-Liniger model. We show that, at zero temperature and in the absence of shocks, GHD reduces to CHD, thus for the first time justifying its use from purely hydrodynamic principles. We show that sharp profiles, which appear in finite times in CHD, immediately dissolve into a higher hierarchy of reductions of GHD, with no sustained shock. CHD thereon fails to capture the correct hydrodynamics. We establish the correct hydrodynamic equations, which are finite-dimensional reductions of GHD characterized by multiple, disjoint Fermi seas. We further verify that at nonzero temperature, CHD fails at all nonzero times. Finally, we numerically confirm the emergence of hydrodynamics at zero temperature by comparing its predictions with a full quantum simulation performed using the NRG-TSA-abacus algorithm. The analysis is performed in the full interaction range, and is not restricted to either weak- or strong-repulsion regimes.

Calculation of the gain of a self-launched high-density free-electron laser by using a newly confirmed law stated as the impossibility of free-electron net stimulated radiation and modal analysis based on plasma hydrodynamics

NASA Astrophysics Data System (ADS)

Kim, S. H.

2017-05-01

We reason based on the concept of stationary plasma fluctuation that in the free-electron laser (FEL), the Coulomb force from the surrounding electrons and the Ampérian force arising from the beam current do not disrupt the density-deviation mode driven by the laser field in cooperation with the magnetic wiggler. We adopt the synchronization principle that in the state of a stationary plasma density-wave and laser wave, all electrons arriving at the same position can emit laser photons all together only at t = NT + t o , where N is an integer and T is the laser period. We find that in the FEL, the incident laser radiation acts as a dummy field in net stimulated radiation. Using these findings and noticing a previously-recognized concept that the radiation power from an electron is given by Δ E/T, where Δ E is the amplitude of the net work done by the electron during T [1], we derive the laser gain of a self-launched FEL. The thusly derived gain is in excellent agreement with the measured gain.

An analytic expression for the sheath criterion in magnetized plasmas with multi-charged ion species

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

Hatami, M. M., E-mail: m-hatami@kntu.ac.ir

2015-04-15

The generalized Bohm criterion in magnetized multi-component plasmas consisting of multi-charged positive and negative ion species and electrons is analytically investigated by using the hydrodynamic model. It is assumed that the electrons and negative ion density distributions are the Boltzmann distribution with different temperatures and the positive ions enter into the sheath region obliquely. Our results show that the positive and negative ion temperatures, the orientation of the applied magnetic field and the charge number of positive and negative ions strongly affect the Bohm criterion in these multi-component plasmas. To determine the validity of our derived generalized Bohm criterion, itmore » reduced to some familiar physical condition and it is shown that monotonically reduction of the positive ion density distribution leading to the sheath formation occurs only when entrance velocity of ion into the sheath satisfies the obtained Bohm criterion. Also, as a practical application of the obtained Bohm criterion, effects of the ionic temperature and concentration as well as magnetic field on the behavior of the charged particle density distributions and so the sheath thickness of a magnetized plasma consisting of electrons and singly charged positive and negative ion species are studied numerically.« less

Elliptic flow from Coulomb interaction and low density elastic scattering

NASA Astrophysics Data System (ADS)

Sun, Yuliang; Li, Qingfeng; Wang, Fuqiang

2018-04-01

In high energy heavy ion collisions and interacting cold atom systems, large elliptic flow anisotropies have been observed. For the large opacity (ρ σ L ˜103 ) of the latter hydrodynamics is a natural consequence, but for the small opacity (ρ σ L ˜1 ) of the former the hydrodynamic description is questionable. To shed light onto the situation, we simulate the expansion of a low density argon ion (or atom) system, initially trapped in an elliptical region, under the Coulomb interaction (or elastic scattering). Significant elliptic anisotropy is found in both cases, and the anisotropy depends on the initial spatial eccentricity and the density of the system. The results may provide insights into the physics of anisotropic flow in high energy heavy ion collisions and its role in the study of quantum chromodynamics.

Theory of hydrodynamic transport in fluctuating electronic charge density wave states

NASA Astrophysics Data System (ADS)

Delacrétaz, Luca V.; Goutéraux, Blaise; Hartnoll, Sean A.; Karlsson, Anna

2017-11-01

We describe the collective hydrodynamic motion of an incommensurate charge density wave state in a clean electronic system. Our description simultaneously incorporates the effects of both pinning due to weak disorder and also phase relaxation due to proliferating dislocations. We show that the interplay between these two phenomena has important consequences for charge and momentum transport. For instance, it can lead to metal-insulator transitions. We furthermore identify signatures of fluctuating density waves in frequency and spatially resolved conductivities. Phase disordering is well known to lead to a large viscosity. We derive a precise formula for the phase relaxation rate in terms of the viscosity in the dislocation cores. We thereby determine the viscosity of the superconducting state of BSCCO from the observed melting dynamics of Abrikosov lattices and show that the result is consistent with dissipation into Bogoliubov quasiparticles.

Hydrodynamic limit of the Yukawa one-component plasma

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

Salin, Gwenaeel

This paper presents a detailed mathematical analysis of the dynamical correlation of density fluctuations of the Yukawa one component plasma in the framework of linearized hydrodynamics. In particular, expressions for the hydrodynamic modes which hold both for the plasma and the neutral fluid are derived. This work constitutes an extension of the computation of the dynamical structure factor in the hydrodynamic limit done by Vieillefosse and Hansen [Phys. Rev. A 12, 1106 (1975)]. As a typical result of Yukawa plasma, a coupling appears between thermal and mechanical effects in the damping of the sound modes, which does not exist inmore » the classical one component plasma. Theoretical and numerical results obtained by means of equilibrium molecular-dynamic simulations in the microcanonical ensemble are compared and discussed.« less

Numerical simulation of the hydrodynamical combustion to strange quark matter

NASA Astrophysics Data System (ADS)

Niebergal, Brian; Ouyed, Rachid; Jaikumar, Prashanth

2010-12-01

We present results from a numerical solution to the burning of neutron matter inside a cold neutron star into stable u,d,s quark matter. Our method solves hydrodynamical flow equations in one dimension with neutrino emission from weak equilibrating reactions, and strange quark diffusion across the burning front. We also include entropy change from heat released in forming the stable quark phase. Our numerical results suggest burning front laminar speeds of 0.002-0.04 times the speed of light, much faster than previous estimates derived using only a reactive-diffusive description. Analytic solutions to hydrodynamical jump conditions with a temperature-dependent equation of state agree very well with our numerical findings for fluid velocities. The most important effect of neutrino cooling is that the conversion front stalls at lower density (below ≈2 times saturation density). In a two-dimensional setting, such rapid speeds and neutrino cooling may allow for a flame wrinkle instability to develop, possibly leading to detonation.

Activity-induced clustering in model dumbbell swimmers: the role of hydrodynamic interactions.

PubMed

Furukawa, Akira; Marenduzzo, Davide; Cates, Michael E

2014-08-01

Using a fluid-particle dynamics approach, we numerically study the effects of hydrodynamic interactions on the collective dynamics of active suspensions within a simple model for bacterial motility: each microorganism is modeled as a stroke-averaged dumbbell swimmer with prescribed dipolar force pairs. Using both simulations and qualitative arguments, we show that, when the separation between swimmers is comparable to their size, the swimmers' motions are strongly affected by activity-induced hydrodynamic forces. To further understand these effects, we investigate semidilute suspensions of swimmers in the presence of thermal fluctuations. A direct comparison between simulations with and without hydrodynamic interactions shows these to enhance the dynamic clustering at a relatively small volume fraction; with our chosen model the key ingredient for this clustering behavior is hydrodynamic trapping of one swimmer by another, induced by the active forces. Furthermore, the density dependence of the motility (of both the translational and rotational motions) exhibits distinctly different behaviors with and without hydrodynamic interactions; we argue that this is linked to the clustering tendency. Our study illustrates the fact that hydrodynamic interactions not only affect kinetic pathways in active suspensions, but also cause major changes in their steady state properties.

Activity-induced clustering in model dumbbell swimmers: The role of hydrodynamic interactions

NASA Astrophysics Data System (ADS)

Furukawa, Akira; Marenduzzo, Davide; Cates, Michael E.

2014-08-01

Using a fluid-particle dynamics approach, we numerically study the effects of hydrodynamic interactions on the collective dynamics of active suspensions within a simple model for bacterial motility: each microorganism is modeled as a stroke-averaged dumbbell swimmer with prescribed dipolar force pairs. Using both simulations and qualitative arguments, we show that, when the separation between swimmers is comparable to their size, the swimmers' motions are strongly affected by activity-induced hydrodynamic forces. To further understand these effects, we investigate semidilute suspensions of swimmers in the presence of thermal fluctuations. A direct comparison between simulations with and without hydrodynamic interactions shows these to enhance the dynamic clustering at a relatively small volume fraction; with our chosen model the key ingredient for this clustering behavior is hydrodynamic trapping of one swimmer by another, induced by the active forces. Furthermore, the density dependence of the motility (of both the translational and rotational motions) exhibits distinctly different behaviors with and without hydrodynamic interactions; we argue that this is linked to the clustering tendency. Our study illustrates the fact that hydrodynamic interactions not only affect kinetic pathways in active suspensions, but also cause major changes in their steady state properties.

Hydrodynamics in a Degenerate, Strongly Attractive Fermi Gas

NASA Technical Reports Server (NTRS)

Thomas, John E.; Kinast, Joseph; Hemmer, Staci; Turlapov, Andrey; O'Hara, Ken; Gehm, Mike; Granade, Stephen

2004-01-01

In summary, we use all-optical methods with evaporative cooling near a Feshbach resonance to produce a strongly interacting degenerate Fermi gas. We observe hydrodynamic behavior in the expansion dynamics. At low temperatures, collisions may not explain the expansion dynamics. We observe hydrodynamics in the trapped gas. Our observations include collisionally-damped excitation spectra at high temperature which were not discussed above. In addition, we observe weakly damped breathing modes at low temperature. The observed temperature dependence of the damping time and hydrodynamic frequency are not consistent with collisional dynamics nor with collisionless mean field interactions. These observations constitute the first evidence for superfluid hydrodynamics in a Fermi gas.

Hydrodynamical model of anisotropic, polarized turbulent superfluids. I: constraints for the fluxes

NASA Astrophysics Data System (ADS)

Mongiovì, Maria Stella; Restuccia, Liliana

2018-02-01

This work is the first of a series of papers devoted to the study of the influence of the anisotropy and polarization of the tangle of quantized vortex lines in superfluid turbulence. A thermodynamical model of inhomogeneous superfluid turbulence previously formulated is here extended, to take into consideration also these effects. The model chooses as thermodynamic state vector the density, the velocity, the energy density, the heat flux, and a complete vorticity tensor field, including its symmetric traceless part and its antisymmetric part. The relations which constrain the constitutive quantities are deduced from the second principle of thermodynamics using the Liu procedure. The results show that the presence of anisotropy and polarization in the vortex tangle affects in a substantial way the dynamics of the heat flux, and allow us to give a physical interpretation of the vorticity tensor here introduced, and to better describe the internal structure of a turbulent superfluid.

Logarithmic Superdiffusion in Two Dimensional Driven Lattice Gases

NASA Astrophysics Data System (ADS)

Krug, J.; Neiss, R. A.; Schadschneider, A.; Schmidt, J.

2018-03-01

The spreading of density fluctuations in two-dimensional driven diffusive systems is marginally anomalous. Mode coupling theory predicts that the diffusivity in the direction of the drive diverges with time as (ln t)^{2/3} with a prefactor depending on the macroscopic current-density relation and the diffusion tensor of the fluctuating hydrodynamic field equation. Here we present the first numerical verification of this behavior for a particular version of the two-dimensional asymmetric exclusion process. Particles jump strictly asymmetrically along one of the lattice directions and symmetrically along the other, and an anisotropy parameter p governs the ratio between the two rates. Using a novel massively parallel coupling algorithm that strongly reduces the fluctuations in the numerical estimate of the two-point correlation function, we are able to accurately determine the exponent of the logarithmic correction. In addition, the variation of the prefactor with p provides a stringent test of mode coupling theory.

Electrostatic twisted modes in multi-component dusty plasmas

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

Ayub, M. K.; National Centre for Physics, Shahdra Valley Road, Quaid-i-Azam University Campus, Islamabad 44000; Pohang University of Sciences and Technology, Pohang, Gyeongbuk 790-784

Various electrostatic twisted modes are re-investigated with finite orbital angular momentum in an unmagnetized collisionless multi-component dusty plasma, consisting of positive/negative charged dust particles, ions, and electrons. For this purpose, hydrodynamical equations are employed to obtain paraxial equations in terms of density perturbations, while assuming the Gaussian and Laguerre-Gaussian (LG) beam solutions. Specifically, approximated solutions for potential problem are studied by using the paraxial approximation and expressed the electric field components in terms of LG functions. The energy fluxes associated with these modes are computed and corresponding expressions for orbital angular momenta are derived. Numerical analyses reveal that radial/angular modemore » numbers as well as dust number density and dust charging states strongly modify the LG potential profiles attributed to different electrostatic modes. Our results are important for understanding particle transport and energy transfer due to wave excitations in multi-component dusty plasmas.« less

Impacts of blending on dilution of negatively buoyant brine discharge in a shallow tidal sea.

PubMed

Kämpf, Jochen

2009-07-01

A fine-resolution three-dimensional hydrodynamic model is applied to study the dilution of desalination brine discharged into a tidal sea. Based on given inflow rate and salinity excess of discharge brine, this study explores variations in mid-field dilutions when other low-salinity wastewater is added to the discharge. Findings reveal that this blending leads to a decrease in dilution in the mixing zone and therefore to higher levels of pollutants in this zone, while, on the other hand, the mixing zone occupies a smaller area. The reason is that the discharge of brine creates a density-driven flow that operates to partially remove effluent from the discharge location. This removal is less efficient for the decrease in density excess of the discharge. Hence, in an ambient sea of moderate mixing, blending can be expected to increase the risk of marine pollution in the mixing zone.

Self-regulation in self-propelled nematic fluids.

PubMed

Baskaran, A; Marchetti, M C

2012-09-01

We consider the hydrodynamic theory of an active fluid of self-propelled particles with nematic aligning interactions. This class of materials has polar symmetry at the microscopic level, but forms macrostates of nematic symmetry. We highlight three key features of the dynamics. First, as in polar active fluids, the control parameter for the order-disorder transition, namely the density, is dynamically convected by the order parameter via active currents. The resulting dynamical self-regulation of the order parameter is a generic property of active fluids and destabilizes the uniform nematic state near the mean-field transition. Secondly, curvature-driven currents render the system unstable deep in the nematic state, as found previously. Finally, and unique to self-propelled nematics, nematic order induces local polar order that in turn leads to the growth of density fluctuations. We propose this as a possible mechanism for the smectic order of polar clusters seen in numerical simulations.

Diagnosing laser-preheated magnetized plasmas relevant to magnetized liner inertial fusion

DOE PAGES

Harvey-Thompson, Adam James; Sefkow, Adam B.; Nagayama, Taisuke N.; ...

2015-12-22

In this paper, we present a platform on the OMEGA EP Laser Facility that creates and diagnoses the conditions present during the preheat stage of the MAGnetized Liner Inertial Fusion (MagLIF) concept. Experiments were conducted using 9 kJ of 3ω (355 nm) light to heat an underdense deuterium gas (electron density: 2.5 × 10 20 cm -3 = 0.025 of critical density) magnetized with a 10 T axial field. Results show that the deuterium plasma reached a peak electron temperature of 670 ± 140 eV, diagnosed using streaked spectroscopy of an argon dopant. The results demonstrate that plasmas relevant tomore » the preheat stage of MagLIF can be produced at multiple laser facilities, thereby enabling more rapid progress in understanding magnetized preheat. Results are compared with magneto-radiation-hydrodynamics simulations, and plans for future experiments are described.« less

Coexistence of negative and positive polarity electrostatic solitary waves in ultradense relativistic negative-ion-beam permeated plasmas

NASA Astrophysics Data System (ADS)

Elkamash, I. S.; Kourakis, I.

2018-05-01

The criteria for occurrence and the dynamical features of electrostatic solitary waves in a homogeneous, unmagnetized ultradense plasma penetrated by a negative ion beam are investigated, relying on a quantum hydrodynamic model. The ionic components are modeled as inertial fluids, while the relativistic electrons obey Fermi-Dirac statistics. A new set of exact analytical conditions for localized solitary pulses to exist is obtained, in terms of plasma density. The algebraic analysis reveals that these depend sensitively on the negative ion beam characteristics, that is, the beam velocity and density. Particular attention is paid to the simultaneous occurrence of positive and negative potential pulses, identified by their respective distinct ambipolar electric field structure forms. It is shown that the coexistence of positive and negative potential pulses occurs in a certain interval of parameter values, where the ion beam inertia becomes significant.

Computational Study of the Richtmyer-Meshkov Instability with a Complex Initial Condition

NASA Astrophysics Data System (ADS)

McFarland, Jacob; Reilly, David; Greenough, Jeffrey; Ranjan, Devesh

2014-11-01

Results are presented for a computational study of the Richtmyer-Meshkov instability with a complex initial condition. This study covers experiments which will be conducted at the newly-built inclined shock tube facility at the Georgia Institute of Technology. The complex initial condition employed consists of an underlying inclined interface perturbation with a broadband spectrum of modes superimposed. A three-dimensional staggered mesh arbitrary Lagrange Eulerian (ALE) hydrodynamics code developed at Lawerence Livermore National Laboratory called ARES was used to obtain both qualitative and quantitative results. Qualitative results are discussed using time series of density plots from which mixing width may be extracted. Quantitative results are also discussed using vorticity fields, circulation components, and energy spectra. The inclined interface case is compared to the complex interface case in order to study the effect of initial conditions on shocked, variable-density flows.

Constraining cosmology with the velocity function of low-mass galaxies

NASA Astrophysics Data System (ADS)

Schneider, Aurel; Trujillo-Gomez, Sebastian

2018-04-01

The number density of field galaxies per rotation velocity, referred to as the velocity function, is an intriguing statistical measure probing the smallest scales of structure formation. In this paper we point out that the velocity function is sensitive to small shifts in key cosmological parameters such as the amplitude of primordial perturbations (σ8) or the total matter density (Ωm). Using current data and applying conservative assumptions about baryonic effects, we show that the observed velocity function of the Local Volume favours cosmologies in tension with the measurements from Planck but in agreement with the latest findings from weak lensing surveys. While the current systematics regarding the relation between observed and true rotation velocities are potentially important, upcoming data from H I surveys as well as new insights from hydrodynamical simulations will dramatically improve the situation in the near future.

The `Henry Problem' of `density-driven' groundwater flow versus Tothian `groundwater flow systems' with variable density: A review of the influential Biscayne aquifer data.

NASA Astrophysics Data System (ADS)

Weyer, K. U.

2017-12-01

Coastal groundwater flow investigations at the Biscayne Bay, south of Miami, Florida, gave rise to the concept of density-driven flow of seawater into coastal aquifers creating a saltwater wedge. Within that wedge, convection-driven return flow of seawater and a dispersion zone were assumed by Cooper et al. (1964) to be the cause of the Biscayne aquifer `sea water wedge'. This conclusion was based on the chloride distribution within the aquifer and on an analytical model concept assuming convection flow within a confined aquifer without taking non-chemical field data into consideration. This concept was later labelled the `Henry Problem', which any numerical variable density flow program must be able to simulate to be considered acceptable. Both, `density-driven flow' and Tothian `groundwater flow systems' (with or without variable density conditions) are driven by gravitation. The difference between the two are the boundary conditions. 'Density-driven flow' occurs under hydrostatic boundary conditions while Tothian `groundwater flow systems' occur under hydrodynamic boundary conditions. Revisiting the Cooper et al. (1964) publication with its record of piezometric field data (heads) showed that the so-called sea water wedge has been caused by discharging deep saline groundwater driven by gravitational flow and not by denser sea water. Density driven flow of seawater into the aquifer was not found reflected in the head measurements for low and high tide conditions which had been taken contemporaneously with the chloride measurements. These head measurements had not been included in the flow interpretation. The very same head measurements indicated a clear dividing line between shallow local fresh groundwater flow and saline deep groundwater flow without the existence of a dispersion zone or a convection cell. The Biscayne situation emphasizes the need for any chemical interpretation of flow pattern to be supported by head data as energy indicators of flow fields. At the Biscayne site density-driven flow of seawater did and does not exist. Instead this site and the Florida coast line in general are the end points of local fresh and regional saline groundwater flow systems driven by gravity forces and not by density differences.

Ensemble Monte Carlo particle investigation of hot electron induced source-drain burnout characteristics of GaAs field-effect transistors

NASA Astrophysics Data System (ADS)

Moglestue, C.; Buot, F. A.; Anderson, W. T.

1995-08-01

The lattice heating rate has been calculated for GaAs field-effect transistors of different source-drain channel design by means of the ensemble Monte Carlo particle model. Transport of carriers in the substrate and the presence of free surface charges are also included in our simulation. The actual heat generation was obtained by accounting for the energy exchanged with the lattice of the semiconductor during phonon scattering. It was found that the maximum heating rate takes place below the surface near the drain end of the gate. The results correlate well with a previous hydrodynamic energy transport estimate of the electronic energy density, but shifted slightly more towards the drain. These results further emphasize the adverse effects of hot electrons on the Ohmic contacts.

Electrohydrodynamics and other hydrodynamic phenomena in continuous flow electrophoresis

NASA Technical Reports Server (NTRS)

Saville, D. A.

1982-01-01

The process known as continuous flow electrophoresis employs an electric field to separate the constituents of particulate samples suspended in a liquid. Complications arise because the electric field generates temperature gradients due to Joule heating and derives an electrohydrodynamic crossflow. Several aspects of the flow are discussed including entrance effects, hydrodynamic stability and a flow restructuring due to the combined effects of buoyancy and the crossflow.

New Exact Solutions of Relativistic Hydrodynamics for Longitudinally Expanding Fireballs

NASA Astrophysics Data System (ADS)

Csörgő, Tamás; Kasza, Gábor; Csanád, Máté; Jiang, Zefang

2018-06-01

We present new, exact, finite solutions of relativistic hydrodynamics for longitudinally expanding fireballs for arbitrary constant value of the speed of sound. These new solutions generalize earlier, longitudinally finite, exact solutions, from an unrealistic to a reasonable equation of state, characterized by a temperature independent (average) value of the speed of sound. Observables like the rapidity density and the pseudorapidity density are evaluated analytically, resulting in simple and easy to fit formulae that can be matched to the high energy proton-proton and heavy ion collision data at RHIC and LHC. In the longitudinally boost-invariant limit, these new solutions approach the Hwa-Bjorken solution and the corresponding rapidity distributions approach a rapidity plateaux.

On the numerical calculation of hydrodynamic shock waves in atmospheres by an FCT method

NASA Astrophysics Data System (ADS)

Schmitz, F.; Fleck, B.

1993-11-01

The numerical calculation of vertically propagating hydrodynamic shock waves in a plane atmosphere by the ETBFCT-version of the Flux Corrected Transport (FCT) method by Boris and Book is discussed. The results are compared with results obtained by a characteristic method with shock fitting. We show that the use of the internal energy density as a dependent variable instead of the total energy density can give very inaccurate results. Consequent discretization rules for the gravitational source terms are derived. The improvement of the results by an additional iteration step is discussed. It appears that the FCT method is an excellent method for the accurate calculation of shock waves in an atmosphere.

Mixing-model Sensitivity to Initial Conditions in Hydrodynamic Predictions

NASA Astrophysics Data System (ADS)

Bigelow, Josiah; Silva, Humberto; Truman, C. Randall; Vorobieff, Peter

2017-11-01

Amagat and Dalton mixing-models were studied to compare their thermodynamic prediction of shock states. Numerical simulations with the Sandia National Laboratories shock hydrodynamic code CTH modeled University of New Mexico (UNM) shock tube laboratory experiments shocking a 1:1 molar mixture of helium (He) and sulfur hexafluoride (SF6) . Five input parameters were varied for sensitivity analysis: driver section pressure, driver section density, test section pressure, test section density, and mixture ratio (mole fraction). We show via incremental Latin hypercube sampling (LHS) analysis that significant differences exist between Amagat and Dalton mixing-model predictions. The differences observed in predicted shock speeds, temperatures, and pressures grow more pronounced with higher shock speeds. Supported by NNSA Grant DE-0002913.

Modeling tidal hydrodynamics of San Diego Bay, California

USGS Publications Warehouse

Wang, P.-F.; Cheng, R.T.; Richter, K.; Gross, E.S.; Sutton, D.; Gartner, J.W.

1998-01-01

In 1983, current data were collected by the National Oceanic and Atmospheric Administration using mechanical current meters. During 1992 through 1996, acoustic Doppler current profilers as well as mechanical current meters and tide gauges were used. These measurements not only document tides and tidal currents in San Diego Bay, but also provide independent data sets for model calibration and verification. A high resolution (100-m grid), depth-averaged, numerical hydrodynamic model has been implemented for San Diego Bay to describe essential tidal hydrodynamic processes in the bay. The model is calibrated using the 1983 data set and verified using the more recent 1992-1996 data. Discrepancies between model predictions and field data in beth model calibration and verification are on the order of the magnitude of uncertainties in the field data. The calibrated and verified numerical model has been used to quantify residence time and dilution and flushing of contaminant effluent into San Diego Bay. Furthermore, the numerical model has become an important research tool in ongoing hydrodynamic and water quality studies and in guiding future field data collection programs.

2D hydrodynamic simulations of a variable length gas target for density down-ramp injection of electrons into a laser wakefield accelerator

NASA Astrophysics Data System (ADS)

Kononenko, O.; Lopes, N. C.; Cole, J. M.; Kamperidis, C.; Mangles, S. P. D.; Najmudin, Z.; Osterhoff, J.; Poder, K.; Rusby, D.; Symes, D. R.; Warwick, J.; Wood, J. C.; Palmer, C. A. J.

2016-09-01

In this work, two-dimensional (2D) hydrodynamic simulations of a variable length gas cell were performed using the open source fluid code OpenFOAM. The gas cell was designed to study controlled injection of electrons into a laser-driven wakefield at the Astra Gemini laser facility. The target consists of two compartments: an accelerator and an injector section connected via an aperture. A sharp transition between the peak and plateau density regions in the injector and accelerator compartments, respectively, was observed in simulations with various inlet pressures. The fluid simulations indicate that the length of the down-ramp connecting the sections depends on the aperture diameter, as does the density drop outside the entrance and the exit cones. Further studies showed, that increasing the inlet pressure leads to turbulence and strong fluctuations in density along the axial profile during target filling, and consequently, is expected to negatively impact the accelerator stability.

Molecular dynamics approach to dissipative relativistic hydrodynamics: Propagation of fluctuations

NASA Astrophysics Data System (ADS)

Shahsavar, Leila; Ghodrat, Malihe; Montakhab, Afshin

2016-12-01

Relativistic generalization of hydrodynamic theory has attracted much attention from a theoretical point of view. However, it has many important practical applications in high energy as well as astrophysical contexts. Despite various attempts to formulate relativistic hydrodynamics, no definitive consensus has been achieved. In this work, we propose to test the predictions of four types of first-order hydrodynamic theories for nonperfect fluids in the light of numerically exact molecular dynamics simulations of a fully relativistic particle system in the low density regime. In this regard, we study the propagation of density, velocity, and heat fluctuations in a wide range of temperatures using extensive simulations and compare them to the corresponding analytic expressions we obtain for each of the proposed theories. As expected, in the low temperature classical regime all theories give the same results, consistent with the numerics. In the high temperature extremely relativistic regime, not all considered theories are distinguishable from one another. However, in the intermediate regime, a meaningful distinction exists in the predictions of various theories considered here. We find that the predictions of the recent formulation due to Tsumura, Kunihiro, and Ohnishi are more consistent with our numerical results than the traditional theories: the Meixner, modified Eckart, and modified Marle-Stewart theories.

Model of Collective Fish Behavior with Hydrodynamic Interactions

NASA Astrophysics Data System (ADS)

Filella, Audrey; Nadal, François; Sire, Clément; Kanso, Eva; Eloy, Christophe

2018-05-01

Fish schooling is often modeled with self-propelled particles subject to phenomenological behavioral rules. Although fish are known to sense and exploit flow features, these models usually neglect hydrodynamics. Here, we propose a novel model that couples behavioral rules with far-field hydrodynamic interactions. We show that (1) a new "collective turning" phase emerges, (2) on average, individuals swim faster thanks to the fluid, and (3) the flow enhances behavioral noise. The results of this model suggest that hydrodynamic effects should be considered to fully understand the collective dynamics of fish.

Development of a novel electric field-assisted modified hydrodynamic cavitation system for disintegration of waste activated sludge.

PubMed

Jung, Kyung-Won; Hwang, Min-Jin; Yun, Yeo-Myeong; Cha, Min-Jung; Ahn, Kyu-Hong

2014-09-01

In this current study, we present a modified hydrodynamic cavitation device that combines an electric field to substitute for the chemical addition. A modified HC system is basically an orifice plate and crisscross pipe assembly, in which the crisscross pipe imparts some turbulence, which creates collision events. This study shows that for maximizing disintegration, combining HC system, which called electric field-assisted modified orifice plate hydrodynamic cavitation (EFM-HC) in this study, with an electric field is important. Various HC systems were compared in terms of disintegration of WAS, and, among them, the EFM-HC system exhibited the best performance with the highest disintegration efficiency of 47.0±2.0% as well as the destruction of WAS morphological characteristics. The experimental results clearly show that a conventional HC system was successfully modified. In addition, electric field has a great potential for efficient disintegration of WAS for as a additional option in a combination treatment. This study suggests continued research in this field may lead to an appropriate design for commercial use. Copyright © 2014 Elsevier B.V. All rights reserved.

Relativistic fluid dynamics with spin

NASA Astrophysics Data System (ADS)

Florkowski, Wojciech; Friman, Bengt; Jaiswal, Amaresh; Speranza, Enrico

2018-04-01

Using the conservation laws for charge, energy, momentum, and angular momentum, we derive hydrodynamic equations for the charge density, local temperature, and fluid velocity, as well as for the polarization tensor, starting from local equilibrium distribution functions for particles and antiparticles with spin 1/2. The resulting set of differential equations extends the standard picture of perfect-fluid hydrodynamics with a conserved entropy current in a minimal way. This framework can be used in space-time analyses of the evolution of spin and polarization in various physical systems including high-energy nuclear collisions. We demonstrate that a stationary vortex, which exhibits vorticity-spin alignment, corresponds to a special solution of the spin-hydrodynamical equations.

Hydrodynamic theory of diffusion in two-temperature multicomponent plasmas

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

Ramshaw, J.D.; Chang, C.H.

Detailed numerical simulations of multicomponent plasmas require tractable expressions for species diffusion fluxes, which must be consistent with the given plasma current density J{sub q} to preserve local charge neutrality. The common situation in which J{sub q} = 0 is referred to as ambipolar diffusion. The use of formal kinetic theory in this context leads to results of formidable complexity. We derive simple tractable approximations for the diffusion fluxes in two-temperature multicomponent plasmas by means of a generalization of the hydrodynamical approach used by Maxwell, Stefan, Furry, and Williams. The resulting diffusion fluxes obey generalized Stefan-Maxwell equations that contain drivingmore » forces corresponding to ordinary, forced, pressure, and thermal diffusion. The ordinary diffusion fluxes are driven by gradients in pressure fractions rather than mole fractions. Simplifications due to the small electron mass are systematically exploited and lead to a general expression for the ambipolar electric field in the limit of infinite electrical conductivity. We present a self-consistent effective binary diffusion approximation for the diffusion fluxes. This approximation is well suited to numerical implementation and is currently in use in our LAVA computer code for simulating multicomponent thermal plasmas. Applications to date include a successful simulation of demixing effects in an argon-helium plasma jet, for which selected computational results are presented. Generalizations of the diffusion theory to finite electrical conductivity and nonzero magnetic field are currently in progress.« less

Hydrodynamic interactions in dense active suspensions: From polar order to dynamical clusters

NASA Astrophysics Data System (ADS)

Yoshinaga, Natsuhiko; Liverpool, Tanniemola B.

2017-08-01

We study the role of hydrodynamic interactions in the collective behavior of collections of microscopic active particles suspended in a fluid. We introduce a calculational framework that allows us to separate the different contributions to their collective dynamics from hydrodynamic interactions on different length scales. Hence we are able to systematically show that lubrication forces when the particles are very close to each other play as important a role as long-range hydrodynamic interactions in determining their many-body behavior. We find that motility-induced phase separation is suppressed by near-field interactions, leading to open gel-like clusters rather than dense clusters. Interestingly, we find a globally polar ordered phase appears for neutral swimmers with no force dipole that is enhanced by near-field lubrication forces in which the collision process rather than long-range interaction dominates the alignment mechanism.

Plasmons and Polaritons in Low Dimensional Systems

NASA Astrophysics Data System (ADS)

Sun, Zhiyuan

Nearly everything relies on the electromagnetic (EM) force to be in its current form. Therefore, light-matter interaction is both a fundamental and a practical subject in physics. Focusing on the electromagnetic field, the matter degrees of freedom can be encoded into its response to the EM field in the form of charge density and urrent. Reshaped by the EM response, the photons in condensed matter systems appear as various collective modes. In this doctoral dissertation, I present our investigation of the linear and nonlinear EM response theory especially in the hydrodynamic regime of electron systems. Electrons in pristine solids behave as a hydrodynamic fluid in a certain range of temperatures and frequencies. We show that the response of such a fluid to electromagnetic field is different from what is predicted by the usual kinetic theory. Certain aspects of this response are universal, for example, a direct relation between the linear and second-order nonlinear optical conductivities. Discovery of this relation enriches our understanding of the light-matter interaction in diverse electron systems and new materials such as graphene. Subsequently, I study the properties of the charged collective modes, the plasmons and demons in 2D Dirac fluids, e.g., the electron-hole system in graphene. Under non-equilibrium situation, the amplitudes of these collective modes could possibly grow due to an effect of adiabatic amplification. I also present our study of the hyperbolic polaritons, the EM modes in hyperbolic materials. When confined in cavities, they develop isolated eigen modes which could be efficiently predicted by applying semi-classical quantization rules to fictitious particles. We demonstrate this Hamiltonian Optics analytically for cavities of spheroidal shapes, and predict novel geometric patterns of the electric field distribution due to classical periodic orbits.

Magnetic Nozzle and Plasma Detachment Experiment

NASA Technical Reports Server (NTRS)

Chavers, Gregory; Dobson, Chris; Jones, Jonathan; Martin, Adam; Bengtson, Roger D.; Briezman, Boris; Arefiev, Alexey; Cassibry, Jason; Shuttpelz, Branwen; Deline, Christopher

2006-01-01

High power plasma propulsion can move large payloads for orbit transfer (such as the ISS), lunar missions, and beyond with large savings in fuel consumption owing to the high specific impulse. At high power, lifetime of the thruster becomes an issue. Electrodeless devices with magnetically guided plasma offer the advantage of long life since magnetic fields confine the plasma radially and keep it from impacting the material surfaces. For decades, concerns have been raised about the plasma remaining attached to the magnetic field and returning to the vehicle along the closed magnetic field lines. Recent analysis suggests that this may not be an issue of the magnetic field is properly shaped in the nozzle region and the plasma has sufficient energy density to stretch the magnetic field downstream. An experiment was performed to test the theory regarding the Magneto-hydrodynamic (MHD) detachment scenario. Data from this experiment will be presented. The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) being developed by the Ad Astra Rocket Company uses a magnetic nozzle as described above. The VASIMR is also a leading candidate for exploiting an electric propulsion test platform being considered for the ISS.

Modeling Laser-Driven Laboratory Astrophysics Experiments Using the CRASH Code

NASA Astrophysics Data System (ADS)

Grosskopf, Michael; Keiter, P.; Kuranz, C. C.; Malamud, G.; Trantham, M.; Drake, R.

2013-06-01

Laser-driven, laboratory astrophysics experiments can provide important insight into the physical processes relevant to astrophysical systems. The radiation hydrodynamics code developed by the Center for Radiative Shock Hydrodynamics (CRASH) at the University of Michigan has been used to model experimental designs for high-energy-density laboratory astrophysics campaigns on OMEGA and other high-energy laser facilities. This code is an Eulerian, block-adaptive AMR hydrodynamics code with implicit multigroup radiation transport and electron heat conduction. The CRASH model has been used on many applications including: radiative shocks, Kelvin-Helmholtz and Rayleigh-Taylor experiments on the OMEGA laser; as well as laser-driven ablative plumes in experiments by the Astrophysical Collisionless Shocks Experiments with Lasers (ACSEL) collaboration. We report a series of results with the CRASH code in support of design work for upcoming high-energy-density physics experiments, as well as comparison between existing experimental data and simulation results. This work is funded by the Predictive Sciences Academic Alliances Program in NNSA-ASC via grant DEFC52- 08NA28616, by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number DE-FG52-09NA29548, and by the National Laser User Facility Program, grant number DE-NA0000850.

Dancing drops over vibrating substrates

NASA Astrophysics Data System (ADS)

Borcia, Rodica; Borcia, Ion Dan; Helbig, Markus; Meier, Martin; Egbers, Christoph; Bestehorn, Michael

2017-04-01

We study the motion of a liquid drop on a solid plate simultaneously submitted to horizontal and vertical harmonic vibrations. The investigation is done via a phase field model earlier developed for describing static and dynamic contact angles. The density field is nearly constant in every bulk region (ρ = 1 in the liquid phase, ρ ≈ 0 in the vapor phase) and varies continuously from one phase to the other with a rapid but smooth variation across the interfaces. Complicated explicit boundary conditions along the interface are avoided and captured implicitly by gradient terms of ρ in the hydrodynamic basic equations. The contact angle θ is controlled through the density at the solid substrate ρ S , a free parameter varying between 0 and 1 [R. Borcia, I.D. Borcia, M. Bestehorn, Phys. Rev. E 78, 066307 (2008)]. We emphasize the swaying and the spreading modes, earlier theoretically identified by Benilov and Billingham via a shallow-water model for drops climbing uphill along an inclined plane oscillating vertically [E.S. Benilov, J. Billingham, J. Fluid Mech. 674, 93 (2011)]. The numerical phase field simulations will be completed by experiments. Some ways to prevent the release of the dancing drops along a hydrophobic surface into the gas atmosphere are also discussed in this paper.

General dynamical density functional theory for classical fluids.

PubMed

Goddard, Benjamin D; Nold, Andreas; Savva, Nikos; Pavliotis, Grigorios A; Kalliadasis, Serafim

2012-09-21

We study the dynamics of a colloidal fluid including inertia and hydrodynamic interactions, two effects which strongly influence the nonequilibrium properties of the system. We derive a general dynamical density functional theory which shows very good agreement with full Langevin dynamics. In suitable limits, we recover existing dynamical density functional theories and a Navier-Stokes-like equation with additional nonlocal terms.

Bethe-Boltzmann hydrodynamics and spin transport in the XXZ chain

NASA Astrophysics Data System (ADS)

Bulchandani, Vir B.; Vasseur, Romain; Karrasch, Christoph; Moore, Joel E.

2018-01-01

Quantum integrable systems, such as the interacting Bose gas in one dimension and the XXZ quantum spin chain, have an extensive number of local conserved quantities that endow them with exotic thermalization and transport properties. We discuss recently introduced hydrodynamic approaches for such integrable systems from the viewpoint of kinetic theory and extend the previous works by proposing a numerical scheme to solve the hydrodynamic equations for finite times and arbitrary locally equilibrated initial conditions. We then discuss how such methods can be applied to describe nonequilibrium steady states involving ballistic heat and spin currents. In particular, we show that the spin Drude weight in the XXZ chain, previously accessible only by rigorous techniques of limited scope or controversial thermodynamic Bethe ansatz arguments, may be evaluated from hydrodynamics in very good agreement with density-matrix renormalization group calculations.

Utilizing dimensional analysis with observed data to determine the significance of hydrodynamic solutions in coastal hydrology

USGS Publications Warehouse

Swain, Eric D.; Decker, Jeremy D.; Hughes, Joseph D.

2014-01-01

In this paper, the authors present an analysis of the magnitude of the temporal and spatial acceleration (inertial) terms in the surface-water flow equations and determine the conditions under which these inertial terms have sufficient magnitude to be required in the computations. Data from two South Florida field sites are examined and the relative magnitudes of temporal acceleration, spatial acceleration, and the gravity and friction terms are compared. Parameters are derived by using dimensionless numbers and applied to quantify the significance of the hydrodynamic effects. The time series of the ratio of the inertial and gravity terms from field sites are presented and compared with both a simplified indicator parameter and a more complex parameter called the Hydrodynamic Significance Number (HSN). Two test-case models were developed by using the SWIFT2D hydrodynamic simulator to examine flow behavior with and without the inertial terms and compute the HSN. The first model represented one of the previously-mentioned field sites during gate operations of a structure-managed coastal canal. The second model was a synthetic test case illustrating the drainage of water down a sloped surface from an initial stage while under constant flow. The analyses indicate that the times of substantial hydrodynamic effects are sporadic but significant. The simplified indicator parameter correlates much better with the hydrodynamic effect magnitude for a constant width channel such as Miami Canal than at the non-uniform North River. Higher HSN values indicate flow situations where the inertial terms are large and need to be taken into account.

Study of Super- and Subsonic Ionization Fronts in Low-Density, Soft X-Ray-Irradiated Foam Targets

NASA Astrophysics Data System (ADS)

Willi, O.; Barringer, L.; Vickers, C.; Hoarty, D.

2000-04-01

The transition from super- to subsonic propagation of an ionization front has been studied in X-ray irradiated, low-density foam targets using soft X-ray imaging and point projection absorption spectroscopy. The foams were doped with chlorine and irradiated with an intense pulse of soft X-ray radiation with a temperature up to 120 eV produced by laser heating a burnthrough converter foil. The cylindrical foam targets were radiographed side-on allowing the change in the chlorine ionization and hence the front to be observed. From the absolute target transmission the density profile was obtained. Comparison of experimental absorption spectra with simulated ones allowed the temperature of the heated material to be inferred for the first time without reliance on detailed hydrodynamic simulations to interpret the data. The experimental observations were compared to radiation hydrodynamic simulations.

AXIALLY ORIENTED SECTIONS OF NUMMULITIDS: A TOOL TO INTERPRET LARGER BENTHIC FORAMINIFERAL DEPOSITS

PubMed Central

Hohenegger, Johann; Briguglio, Antonino

2015-01-01

The “critical shear velocity” and “settling velocity” of foraminiferal shells are important parameters for determining hydrodynamic conditions during deposition of Nummulites banks. These can be estimated by determining the size, shape, and density of nummulitid shells examined in axial sections cut perpendicular to the bedding plane. Shell size and shape can be determined directly from the shell diameter and thickness, but density must be calculated indirectly from the thin section. Calculations using the half-tori method approximate shell densities by equalizing the chamber volume of each half whorl, based on the half whorl’s lumen area and its center of gravity. Results from this method yield the same lumen volumes produced empirically by micro-computed tomography. The derived hydrodynamic parameters help estimate the minimum flow velocities needed to entrain nummulitid tests and provide a potential tool to account for the nature of their accumulations. PMID:26166914

AXIALLY ORIENTED SECTIONS OF NUMMULITIDS: A TOOL TO INTERPRET LARGER BENTHIC FORAMINIFERAL DEPOSITS.

PubMed

Hohenegger, Johann; Briguglio, Antonino

2012-04-01

The "critical shear velocity" and "settling velocity" of foraminiferal shells are important parameters for determining hydrodynamic conditions during deposition of Nummulites banks. These can be estimated by determining the size, shape, and density of nummulitid shells examined in axial sections cut perpendicular to the bedding plane. Shell size and shape can be determined directly from the shell diameter and thickness, but density must be calculated indirectly from the thin section. Calculations using the half-tori method approximate shell densities by equalizing the chamber volume of each half whorl, based on the half whorl's lumen area and its center of gravity. Results from this method yield the same lumen volumes produced empirically by micro-computed tomography. The derived hydrodynamic parameters help estimate the minimum flow velocities needed to entrain nummulitid tests and provide a potential tool to account for the nature of their accumulations.

Comparison of plastic, high density carbon, and beryllium as indirect drive NIF ablators

NASA Astrophysics Data System (ADS)

Kritcher, A. L.; Clark, D.; Haan, S.; Yi, S. A.; Zylstra, A. B.; Callahan, D. A.; Hinkel, D. E.; Berzak Hopkins, L. F.; Hurricane, O. A.; Landen, O. L.; MacLaren, S. A.; Meezan, N. B.; Patel, P. K.; Ralph, J.; Thomas, C. A.; Town, R.; Edwards, M. J.

2018-05-01

Detailed radiation hydrodynamic simulations calibrated to experimental data have been used to compare the relative strengths and weaknesses of three candidate indirect drive ablator materials now tested at the NIF: plastic, high density carbon or diamond, and beryllium. We apply a common simulation methodology to several currently fielded ablator platforms to benchmark the model and extrapolate designs to the full NIF envelope to compare on a more equal footing. This paper focuses on modeling of the hohlraum energetics which accurately reproduced measured changes in symmetry when changes to the hohlraum environment were made within a given platform. Calculations suggest that all three ablator materials can achieve a symmetric implosion at a capsule outer radius of ˜1100 μm, a laser energy of 1.8 MJ, and a DT ice mass of 185 μg. However, there is more uncertainty in the symmetry predictions for the plastic and beryllium designs. Scaled diamond designs had the most calculated margin for achieving symmetry and the highest fuel absorbed energy at the same scale compared to plastic or beryllium. A comparison of the relative hydrodynamic stability was made using ultra-high resolution capsule simulations and the two dimensional radiation fluxes described in this work [Clark et al., Phys. Plasmas 25, 032703 (2018)]. These simulations, which include low and high mode perturbations, suggest that diamond is currently the most promising for achieving higher yields in the near future followed by plastic, and more data are required to understand beryllium.

Hydrodynamic Models of Line-Driven Accretion Disk Winds III: Local Ionization Equilibrium

NASA Technical Reports Server (NTRS)

Pereyra, Nicolas Antonio; Kallman, Timothy R.; White, Nicholas E. (Technical Monitor)

2002-01-01

We present time-dependent numerical hydrodynamic models of line-driven accretion disk winds in cataclysmic variable systems and calculate wind mass-loss rates and terminal velocities. The models are 2.5-dimensional, include an energy balance condition with radiative heating and cooling processes, and includes local ionization equilibrium introducing time dependence and spatial dependence on the line radiation force parameters. The radiation field is assumed to originate in an optically thick accretion disk. Wind ion populations are calculated under the assumption that local ionization equilibrium is determined by photoionization and radiative recombination, similar to a photoionized nebula. We find a steady wind flowing from the accretion disk. Radiative heating tends to maintain the temperature in the higher density wind regions near the disk surface, rather than cooling adiabatically. For a disk luminosity L (sub disk) = solar luminosity, white dwarf mass M(sub wd) = 0.6 solar mass, and white dwarf radii R(sub wd) = 0.01 solar radius, we obtain a wind mass-loss rate of M(sub wind) = 4 x 10(exp -12) solar mass yr(exp -1) and a terminal velocity of approximately 3000 km per second. These results confirm the general velocity and density structures found in our earlier constant ionization equilibrium adiabatic CV wind models. Further we establish here 2.5D numerical models that can be extended to QSO/AGN winds where the local ionization equilibrium will play a crucial role in the overall dynamics.

High-resolution modeling assessment of tidal stream resource in Western Passage of Maine, USA

NASA Astrophysics Data System (ADS)

Yang, Zhaoqing; Wang, Taiping; Feng, Xi; Xue, Huijie; Kilcher, Levi

2017-04-01

Although significant efforts have been taken to assess the maximum potential of tidal stream energy at system-wide scale, accurate assessment of tidal stream energy resource at project design scale requires detailed hydrodynamic simulations using high-resolution three-dimensional (3-D) numerical models. Extended model validation against high quality measured data is essential to minimize the uncertainties of the resource assessment. Western Passage in the State of Maine in U.S. has been identified as one of the top ranking sites for tidal stream energy development in U.S. coastal waters, based on a number of criteria including tidal power density, market value and transmission distance. This study presents an on-going modeling effort for simulating the tidal hydrodynamics in Western Passage using the 3-D unstructured-grid Finite Volume Community Ocean Model (FVCOM). The model domain covers a large region including the entire the Bay of Fundy with grid resolution varies from 20 m in the Western Passage to approximately 1000 m along the open boundary near the mouth of Bay of Fundy. Preliminary model validation was conducted using existing NOAA measurements within the model domain. Spatial distributions of tidal power density were calculated and extractable tidal energy was estimated using a tidal turbine module embedded in FVCOM under different tidal farm scenarios. Additional field measurements to characterize resource and support model validation were discussed. This study provides an example of high resolution resource assessment based on the guidance recommended by the International Electrotechnical Commission Technical Specification.

Derivation of a hydrodynamic theory for mesoscale dynamics in microswimmer suspensions

NASA Astrophysics Data System (ADS)

Reinken, Henning; Klapp, Sabine H. L.; Bär, Markus; Heidenreich, Sebastian

2018-02-01

In this paper, we systematically derive a fourth-order continuum theory capable of reproducing mesoscale turbulence in a three-dimensional suspension of microswimmers. We start from overdamped Langevin equations for a generic microscopic model (pushers or pullers), which include hydrodynamic interactions on both small length scales (polar alignment of neighboring swimmers) and large length scales, where the solvent flow interacts with the order parameter field. The flow field is determined via the Stokes equation supplemented by an ansatz for the stress tensor. In addition to hydrodynamic interactions, we allow for nematic pair interactions stemming from excluded-volume effects. The results here substantially extend and generalize earlier findings [S. Heidenreich et al., Phys. Rev. E 94, 020601 (2016), 10.1103/PhysRevE.94.020601], in which we derived a two-dimensional hydrodynamic theory. From the corresponding mean-field Fokker-Planck equation combined with a self-consistent closure scheme, we derive nonlinear field equations for the polar and the nematic order parameter, involving gradient terms of up to fourth order. We find that the effective microswimmer dynamics depends on the coupling between solvent flow and orientational order. For very weak coupling corresponding to a high viscosity of the suspension, the dynamics of mesoscale turbulence can be described by a simplified model containing only an effective microswimmer velocity.

Nonlinear theory of nonstationary low Mach number channel flows of freely cooling nearly elastic granular gases.

PubMed

Meerson, Baruch; Fouxon, Itzhak; Vilenkin, Arkady

2008-02-01

We employ hydrodynamic equations to investigate nonstationary channel flows of freely cooling dilute gases of hard and smooth spheres with nearly elastic particle collisions. This work focuses on the regime where the sound travel time through the channel is much shorter than the characteristic cooling time of the gas. As a result, the gas pressure rapidly becomes almost homogeneous, while the typical Mach number of the flow drops well below unity. Eliminating the acoustic modes and employing Lagrangian coordinates, we reduce the hydrodynamic equations to a single nonlinear and nonlocal equation of a reaction-diffusion type. This equation describes a broad class of channel flows and, in particular, can follow the development of the clustering instability from a weakly perturbed homogeneous cooling state to strongly nonlinear states. If the heat diffusion is neglected, the reduced equation becomes exactly soluble, and the solution develops a finite-time density blowup. The blowup has the same local features at singularity as those exhibited by the recently found family of exact solutions of the full set of ideal hydrodynamic equations [I. Fouxon, Phys. Rev. E 75, 050301(R) (2007); I. Fouxon,Phys. Fluids 19, 093303 (2007)]. The heat diffusion, however, always becomes important near the attempted singularity. It arrests the density blowup and brings about previously unknown inhomogeneous cooling states (ICSs) of the gas, where the pressure continues to decay with time, while the density profile becomes time-independent. The ICSs represent exact solutions of the full set of granular hydrodynamic equations. Both the density profile of an ICS and the characteristic relaxation time toward it are determined by a single dimensionless parameter L that describes the relative role of the inelastic energy loss and heat diffusion. At L>1 the intermediate cooling dynamics proceeds as a competition between "holes": low-density regions of the gas. This competition resembles Ostwald ripening (only one hole survives at the end), and we report a particular regime where the "hole ripening" statistics exhibits a simple dynamic scaling behavior.

Comparing cosmological hydrodynamic simulations with observations of high- redshift galaxy formation

NASA Astrophysics Data System (ADS)

Finlator, Kristian Markwart

We use cosmological hydrodynamic simulations to study the impact of outflows and radiative feedback on high-redshift galaxies. For outflows, we consider simulations that assume (i) no winds, (ii) a "constant-wind" model in which the mass-loading factor and outflow speed are constant, and (iii) "momentum-driven" winds in which both parameters vary smoothly with mass. In order to treat radiative feedback, we develop a moment-based radiative transfer technique that operates in both post-processing and coupled radiative hydrodynamic modes. We first ask how outflows impact the broadband spectral energy distributions (SEDs) of six observed reionization-epoch galaxies. Simulations reproduce five regardless of the outflow prescription, while the sixth suggests an unusually bursty star formation history. We conclude that (i) simulations broadly account for available constraints on reionization-epoch galaxies, (ii) individual SEDs do not constrain outflows, and (iii) SED comparisons efficiently isolate objects that challenge simulations. We next study how outflows impact the galaxy mass metallicity relation (MZR). Momentum-driven outflows uniquely reproduce observations at z = 2. In this scenario, galaxies obey two equilibria: (i) The rate at which a galaxy processes gas into stars and outflows tracks its inflow rate; and (ii) The gas enrichment rate owing to star formation balances the dilution rate owing to inflows. Combining these conditions indicates that the MZR is dominated by the (instantaneous) variation of outflows with mass, with more-massive galaxies driving less gas into outflows per unit stellar mass formed. Turning to radiative feedback, we use post-processing simulations to study the topology of reionization. Reionization begins in overdensities and then "leaks" directly into voids, with filaments reionizing last owing to their high density and low emissivity. This result conflicts with previous findings that voids ionize last. We argue that it owes to the uniqely-biased emissivity field produced by our star formation prescriptions, which have previously been shown to reproduce numerous post-reionization constraints. Finally, preliminary results from coupled radiative hydrodynamic simulations indicate that reionization suppresses the star formation rate density by at most 10-20% by z = 5. This is much less than previous estimates, which we attribute to our unique reionization topology although confirmation will have to await more detailed modeling.

Diagnostics of red-shifted H-alpha line emission from a C-class flare with full non-LTE radiative and hydrodynamic approach

NASA Astrophysics Data System (ADS)

Druett, M. K.; Zharkova, V. V.; Scullion, E.; Zharkov, S.; Matthews, S. A.

2016-12-01

We analyse H-alpha line profiles with strong redshifts during the C1.8 flare on 1st July 2012 obtained from the Swedish Solar Telescope (SST) closely resembling the previous observations (Wuelser and Marti, 1989). The flare has a magnetic field configuration with two levels of loop structures. The kernels with red shifts are observed in one of the H-alpha ribbons in the south-west location formed after the main impulse recorded in the north-east. The locations of H-alpha kernels with red shifts reveal close temporal and spatial correlation with weaker HXR signatures and coincide with the locations of coronal jets observed with AIA/SDO. For interpretation we apply a revised 1D hydrodynamic and non-LTE (NLTE) radiative model for 5 level plus continuum model hydrogen atom (Druett & Zharkova, 2016) considering radiative, thermal and non-thermal excitation and ionisation by beam electrons with the updated beam densities (Zharkova & Dobranskis, 2016) and analytical excitation/ionisation rates (Zharkova& Kobylinskijj, 1993). We find the simultaneous solutions of steady state and radiative transfer equations in all optically-thick lines and continua. The electron and ion temperatures, ambient density and macrovelocity of the ambient plasma are derived from a 1D hydrodynamic model with initial condition of the pre-flaring photosphere for the two fluid ambient plasma heated by beam electrons (Zharkova & Zharkov, 2007). We simulate distributions over precipitation depth of ionisation and departure coefficients for all the hydrogen atom transitions including the deviation of ionisation from Saha equation affected by non-thermal electron beams. We show that in the very first seconds after the beam onset Balmer line profiles are sensitive to the effect of beam electrons. The combination of the additional ionisation caused by beam electrons leading to a very strong Stark effect in Balmer lines with the hydrodynamic heating and formation of a low temperature shock in the chromosphere is shown to closely account for the visible asymmetric H-alpha line profiles with strong red shifts observed now and in the past. The interplay between the ambient plasma heating and non-thermal collisional excitation and ionisation rates by beam electrons is shown to define the Balmer line red shifts and continuum enhancements.

Observation of ionization fronts in low density foam targets

NASA Astrophysics Data System (ADS)

Hoarty, D.; Willi, O.; Barringer, L.; Vickers, C.; Watt, R.; Nazarov, W.

1999-05-01

Ionization fronts have been observed in low density chlorinated foam targets and low density foams confined in gold tubes using time resolved K-shell absorption spectroscopy. The front was driven by an intense pulse of soft x-rays produced by high power laser irradiation. The density and temperature profiles inferred from the radiographs provided detailed measurement of the conditions. The experimental data were compared to radiation hydrodynamics simulations and reasonable agreement was obtained.

Nanometer-scale characterization of laser-driven plasmas, compression, shocks and phase transitions, by coherent small angle x-ray scattering

NASA Astrophysics Data System (ADS)

Kluge, Thomas

2015-11-01

Combining ultra-intense short-pulse and high-energy long-pulse lasers, with brilliant coherent hard X-ray FELs, such as the Helmholtz International Beamline for Extreme Fields (HIBEF) under construction at the HED Instrument of European XFEL, or MEC at LCLS, holds the promise to revolutionize our understanding of many High Energy Density Physics phenomena. Examples include the relativistic electron generation, transport, and bulk plasma response, and ionization dynamics and heating in relativistic laser-matter interactions, or the dynamics of laser-driven shocks, quasi-isentropic compression, and the kinetics of phase transitions at high pressure. A particularly promising new technique is the use of coherent X-ray diffraction to characterize electron density correlations, and by resonant scattering to characterize the distribution of specific charge-state ions, either on the ultrafast time scale of the laser interaction, or associated with hydrodynamic motion. As well one can image slight density changes arising from phase transitions inside of shock-compressed high pressure matter. The feasibility of coherent diffraction techniques in laser-driven matter will be discussed. including recent results from demonstration experiments at MEC. Among other things, very sharp density changes from laser-driven compression are observed, having an effective step width of 10 nm or smaller. This compares to a resolution of several hundred nm achievedpreviously with phase contrast imaging. and on behalf of HIBEF User Consortium, for the Helmholtz International Beamline for Extreme Fields at the European XFEL.

Effects of convection electric field on upwelling and escape of ionospheric O(+)

NASA Technical Reports Server (NTRS)

Cladis, J. B.; Chiu, Yam T.; Peterson, William K.

1992-01-01

A Monte Carlo code is used to explore the full effects of the convection electric field on distributions of upflowing O(+) ions from the cusp/cleft ionosphere. Trajectories of individual ions/neutrals are computed as they undergo multiple charge-exchange collisions. In the ion state, the trajectories are computed in realistic models of the magnetic field and the convection, corotation, and ambipolar electric fields. The effects of ion-ion collisions are included, and the trajectories are computed with and without simultaneous stochastic heating perpendicular to the magnetic field by a realistic model of broadband, low frequency waves. In the neutral state, ballistic trajectories in the gravitational field are computed. The initial conditions of the ions, in addition to ambipolar electric field and the number densities and temperatures of O(+), H(+), and electrons as a function of height in the cusp/cleft region were obtained from the results of Gombosi and Killeen (1987), who used a hydrodynamic code to simulate the time-dependent frictional-heating effects in a magnetic tube during its motion though the convection throat. The distribution of the ion fluxes as a function of height are constructed from the case histories.

The effect of extreme ionization rates during the initial collapse of a molecular cloud core

NASA Astrophysics Data System (ADS)

Wurster, James; Bate, Matthew R.; Price, Daniel J.

2018-05-01

What cosmic ray ionization rate is required such that a non-ideal magnetohydrodynamics (MHD) simulation of a collapsing molecular cloud will follow the same evolutionary path as an ideal MHD simulation or as a purely hydrodynamics simulation? To investigate this question, we perform three-dimensional smoothed particle non-ideal MHD simulations of the gravitational collapse of rotating, one solar mass, magnetized molecular cloud cores, which include Ohmic resistivity, ambipolar diffusion, and the Hall effect. We assume a uniform grain size of ag = 0.1 μm, and our free parameter is the cosmic ray ionization rate, ζcr. We evolve our models, where possible, until they have produced a first hydrostatic core. Models with ζcr ≳ 10-13 s-1 are indistinguishable from ideal MHD models, and the evolution of the model with ζcr = 10-14 s-1 matches the evolution of the ideal MHD model within 1 per cent when considering maximum density, magnetic energy, and maximum magnetic field strength as a function of time; these results are independent of ag. Models with very low ionization rates (ζcr ≲ 10-24 s-1) are required to approach hydrodynamical collapse, and even lower ionization rates may be required for larger ag. Thus, it is possible to reproduce ideal MHD and purely hydrodynamical collapses using non-ideal MHD given an appropriate cosmic ray ionization rate. However, realistic cosmic ray ionization rates approach neither limit; thus, non-ideal MHD cannot be neglected in star formation simulations.

Radiation Hydrodynamical Turbulence in Protoplanetary Disks: Numerical Models and Observational Constraints

NASA Astrophysics Data System (ADS)

Flock, Mario; Nelson, Richard P.; Turner, Neal J.; Bertrang, Gesa H.-M.; Carrasco-González, Carlos; Henning, Thomas; Lyra, Wladimir; Teague, Richard

2017-12-01

Planets are born in protostellar disks, which are now observed with enough resolution to address questions about internal gas flows. Magnetic forces are possibly drivers of the flows, but ionization state estimates suggest that much of the gas mass decouples from magnetic fields. Thus, hydrodynamical instabilities could play a major role. We investigate disk dynamics under conditions typical for a T Tauri system, using global 3D radiation-hydrodynamics simulations with embedded particles and a resolution of 70 cells per scale height. Stellar irradiation heating is included with realistic dust opacities. The disk starts in joint radiative balance and hydrostatic equilibrium. The vertical shear instability (VSI) develops into turbulence that persists up to at least 1600 inner orbits (143 outer orbits). Turbulent speeds are a few percent of the local sound speed at the midplane, increasing to 20%, or 100 m s-1, in the corona. These are consistent with recent upper limits on turbulent speeds from optically thin and thick molecular line observations of TW Hya and HD 163296. The predominantly vertical motions induced by the VSI efficiently lift particles upward. Grains 0.1 and 1 mm in size achieve scale heights greater than expected in isotropic turbulence. We conclude that while kinematic constraints from molecular line emission do not directly discriminate between magnetic and nonmagnetic disk models, the small dust scale heights measured in HL Tau and HD 163296 favor turbulent magnetic models, which reach lower ratios of the vertical kinetic energy density to the accretion stress.

Laser Pencil Beam Based Techniques for Visualization and Analysis of Interfaces Between Media

NASA Technical Reports Server (NTRS)

Adamovsky, Grigory; Giles, Sammie, Jr.

1998-01-01

Traditional optical methods that include interferometry, Schlieren, and shadowgraphy have been used successfully for visualization and evaluation of various media. Aerodynamics and hydrodynamics are major fields where these methods have been applied. However, these methods have such major drawbacks as a relatively low power density and suppression of the secondary order phenomena. A novel method introduced at NASA Lewis Research Center minimizes disadvantages of the 'classical' methods. The method involves a narrow pencil-like beam that penetrates a medium of interest. The paper describes the laser pencil beam flow visualization methods in detail. Various system configurations are presented. The paper also discusses interfaces between media in general terms and provides examples of interfaces.

Maxwell-Chern-Simons hydrodynamics for the chiral magnetic effect

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

Oezoender, Sener

2010-06-15

The rate of vacuum-changing topological solutions of the gluon field, sphalerons, is estimated to be large at the typical temperatures of heavy-ion collisions, particularly at the Relativistic Heavy Ion Collider. Such windings in the gluon field are expected to produce parity-odd bubbles, which cause separation of positively and negatively charged quarks along the axis of the external magnetic field. This chiral magnetic effect can be mimicked by Chern-Simons modified electromagnetism. Here we present a model of relativistic hydrodynamics including the effects of axial anomalies via the Chern-Simons term.

Nano-electro-mechanical pump: Giant pumping of water in carbon nanotubes

PubMed Central

Farimani, Amir Barati; Heiranian, Mohammad; Aluru, Narayana R.

2016-01-01

A fully controllable nano-electro-mechanical device that can pump fluids at nanoscale is proposed. Using molecular dynamics simulations, we show that an applied electric field to an ion@C60 inside a water-filled carbon nanotube can pump water with excellent efficiency. The key physical mechanism governing the fluid pumping is the conversion of electrical energy into hydrodynamic flow with efficiencies as high as 64%. Our results show that water can be compressed up to 7% higher than its bulk value by applying electric fields. High flux of water (up to 13,000 molecules/ns) is obtained by the electro-mechanical, piston-cylinder-like moving mechanism of the ion@C60 in the CNT. This large flux results from the piston-like mechanism, compressibility of water (increase in density of water due to molecular ordering), orienting dipole along the electric field and efficient electrical to mechanical energy conversion. Our findings can pave the way towards efficient energy conversion, pumping of fluids at nanoscale, and drug delivery. PMID:27193507

Nano-electro-mechanical pump: Giant pumping of water in carbon nanotubes

NASA Astrophysics Data System (ADS)

Farimani, Amir Barati; Heiranian, Mohammad; Aluru, Narayana R.

2016-05-01

A fully controllable nano-electro-mechanical device that can pump fluids at nanoscale is proposed. Using molecular dynamics simulations, we show that an applied electric field to an ion@C60 inside a water-filled carbon nanotube can pump water with excellent efficiency. The key physical mechanism governing the fluid pumping is the conversion of electrical energy into hydrodynamic flow with efficiencies as high as 64%. Our results show that water can be compressed up to 7% higher than its bulk value by applying electric fields. High flux of water (up to 13,000 molecules/ns) is obtained by the electro-mechanical, piston-cylinder-like moving mechanism of the ion@C60 in the CNT. This large flux results from the piston-like mechanism, compressibility of water (increase in density of water due to molecular ordering), orienting dipole along the electric field and efficient electrical to mechanical energy conversion. Our findings can pave the way towards efficient energy conversion, pumping of fluids at nanoscale, and drug delivery.

Nano-electro-mechanical pump: Giant pumping of water in carbon nanotubes.

PubMed

Farimani, Amir Barati; Heiranian, Mohammad; Aluru, Narayana R

2016-05-19

A fully controllable nano-electro-mechanical device that can pump fluids at nanoscale is proposed. Using molecular dynamics simulations, we show that an applied electric field to an ion@C60 inside a water-filled carbon nanotube can pump water with excellent efficiency. The key physical mechanism governing the fluid pumping is the conversion of electrical energy into hydrodynamic flow with efficiencies as high as 64%. Our results show that water can be compressed up to 7% higher than its bulk value by applying electric fields. High flux of water (up to 13,000 molecules/ns) is obtained by the electro-mechanical, piston-cylinder-like moving mechanism of the ion@C60 in the CNT. This large flux results from the piston-like mechanism, compressibility of water (increase in density of water due to molecular ordering), orienting dipole along the electric field and efficient electrical to mechanical energy conversion. Our findings can pave the way towards efficient energy conversion, pumping of fluids at nanoscale, and drug delivery.

Cosmic ray sources, acceleration and propagation

NASA Technical Reports Server (NTRS)

Ptuskin, V. S.

1986-01-01

A review is given of selected papers on the theory of cosmic ray (CR) propagation and acceleration. The high isotropy and a comparatively large age of galactic CR are explained by the effective interaction of relativistic particles with random and regular electromagnetic fields in interstellar medium. The kinetic theory of CR propagation in the Galaxy is formulated similarly to the elaborate theory of CR propagation in heliosphere. The substantial difference between these theories is explained by the necessity to take into account in some cases the collective effects due to a rather high density of relativisitc particles. In particular, the kinetic CR stream instability and the hydrodynamic Parker instability is studied. The interaction of relativistic particles with an ensemble of given weak random magnetic fields is calculated by perturbation theory. The theory of CR transfer is considered to be basically completed for this case. The main problem consists in poor information about the structure of the regular and the random galactic magnetic fields. An account is given of CR transfer in a turbulent medium.

Fluid dynamics analysis of a gas attenuator for X-ray FELs under high-repetition-rate operation

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

Yang, Bo; Wu, Juhao; Raubenheimer, Tor O.

Newtonian fluid dynamics simulations were performed using the Navier–Stokes–Fourier formulations to elucidate the short time-scale (µs and longer) evolution of the density and temperature distributions in an argon-gas-filled attenuator for an X-ray free-electron laser under high-repetition-rate operation. Both hydrodynamic motions of the gas molecules and thermal conductions were included in a finite-volume calculation. It was found that the hydrodynamic wave motions play the primary role in creating a density depression (also known as a filament) by advectively transporting gas particles away from the X-ray laser–gas interaction region, where large pressure and temperature gradients have been built upon the initial energymore » depositionviaX-ray photoelectric absorption and subsequent thermalization. Concurrent outward heat conduction tends to reduce the pressure in the filament core region, generating a counter gas flow to backfill the filament, but on an initially slower time scale. If the inter-pulse separation is sufficiently short so the filament cannot recover, the depth of the filament progressively increases as the trailing pulses remove additional gas particles. Since the rate of hydrodynamic removal decreases while the rate of heat conduction back flow increases as time elapses, the two competing mechanisms ultimately reach a dynamic balance, establishing a repeating pattern for each pulse cycle. Finally, by performing simulations at higher repetition rates but lower per pulse energies while maintaining a constant time-averaged power, the amplitude of the hydrodynamic motion per pulse becomes smaller, and the evolution of the temperature and density distributions approach asymptotically towards, as expected, those calculated for a continuous-wave input of the equivalent power.« less

Fluid dynamics analysis of a gas attenuator for X-ray FELs under high-repetition-rate operation

DOE PAGES

Yang, Bo; Wu, Juhao; Raubenheimer, Tor O.; ...

2017-05-01

Newtonian fluid dynamics simulations were performed using the Navier–Stokes–Fourier formulations to elucidate the short time-scale (µs and longer) evolution of the density and temperature distributions in an argon-gas-filled attenuator for an X-ray free-electron laser under high-repetition-rate operation. Both hydrodynamic motions of the gas molecules and thermal conductions were included in a finite-volume calculation. It was found that the hydrodynamic wave motions play the primary role in creating a density depression (also known as a filament) by advectively transporting gas particles away from the X-ray laser–gas interaction region, where large pressure and temperature gradients have been built upon the initial energymore » depositionviaX-ray photoelectric absorption and subsequent thermalization. Concurrent outward heat conduction tends to reduce the pressure in the filament core region, generating a counter gas flow to backfill the filament, but on an initially slower time scale. If the inter-pulse separation is sufficiently short so the filament cannot recover, the depth of the filament progressively increases as the trailing pulses remove additional gas particles. Since the rate of hydrodynamic removal decreases while the rate of heat conduction back flow increases as time elapses, the two competing mechanisms ultimately reach a dynamic balance, establishing a repeating pattern for each pulse cycle. Finally, by performing simulations at higher repetition rates but lower per pulse energies while maintaining a constant time-averaged power, the amplitude of the hydrodynamic motion per pulse becomes smaller, and the evolution of the temperature and density distributions approach asymptotically towards, as expected, those calculated for a continuous-wave input of the equivalent power.« less

Numerical Hydrodynamics and Magnetohydrodynamics in General Relativity.

PubMed

Font, José A

2008-01-01

This article presents a comprehensive overview of numerical hydrodynamics and magneto-hydrodynamics (MHD) in general relativity. Some significant additions have been incorporated with respect to the previous two versions of this review (2000, 2003), most notably the coverage of general-relativistic MHD, a field in which remarkable activity and progress has occurred in the last few years. Correspondingly, the discussion of astrophysical simulations in general-relativistic hydrodynamics is enlarged to account for recent relevant advances, while those dealing with general-relativistic MHD are amply covered in this review for the first time. The basic outline of this article is nevertheless similar to its earlier versions, save for the addition of MHD-related issues throughout. Hence, different formulations of both the hydrodynamics and MHD equations are presented, with special mention of conservative and hyperbolic formulations well adapted to advanced numerical methods. A large sample of numerical approaches for solving such hyperbolic systems of equations is discussed, paying particular attention to solution procedures based on schemes exploiting the characteristic structure of the equations through linearized Riemann solvers. As previously stated, a comprehensive summary of astrophysical simulations in strong gravitational fields is also presented. These are detailed in three basic sections, namely gravitational collapse, black-hole accretion, and neutron-star evolutions; despite the boundaries, these sections may (and in fact do) overlap throughout the discussion. The material contained in these sections highlights the numerical challenges of various representative simulations. It also follows, to some extent, the chronological development of the field, concerning advances in the formulation of the gravitational field, hydrodynamics and MHD equations and the numerical methodology designed to solve them. To keep the length of this article reasonable, an effort has been made to focus on multidimensional studies, directing the interested reader to earlier versions of the review for discussions on one-dimensional works. Supplementary material is available for this article at 10.12942/lrr-2008-7.

Coupling hydrodynamics with comoving frame radiative transfer. I. A unified approach for OB and WR stars

NASA Astrophysics Data System (ADS)

Sander, A. A. C.; Hamann, W.-R.; Todt, H.; Hainich, R.; Shenar, T.

2017-07-01

Context. For more than two decades, stellar atmosphere codes have been used to derive the stellar and wind parameters of massive stars. Although they have become a powerful tool and sufficiently reproduce the observed spectral appearance, they can hardly be used for more than measuring parameters. One major obstacle is their inconsistency between the calculated radiation field and the wind stratification due to the usage of prescribed mass-loss rates and wind-velocity fields. Aims: We present the concepts for a new generation of hydrodynamically consistent non-local thermodynamical equilibrium (non-LTE) stellar atmosphere models that allow for detailed studies of radiation-driven stellar winds. As a first demonstration, this new kind of model is applied to a massive O star. Methods: Based on earlier works, the PoWR code has been extended with the option to consistently solve the hydrodynamic equation together with the statistical equations and the radiative transfer in order to obtain a hydrodynamically consistent atmosphere stratification. In these models, the whole velocity field is iteratively updated together with an adjustment of the mass-loss rate. Results: The concepts for obtaining hydrodynamically consistent models using a comoving-frame radiative transfer are outlined. To provide a useful benchmark, we present a demonstration model, which was motivated to describe the well-studied O4 supergiant ζPup. The obtained stellar and wind parameters are within the current range of literature values. Conclusions: For the first time, the PoWR code has been used to obtain a hydrodynamically consistent model for a massive O star. This has been achieved by a profound revision of earlier concepts used for Wolf-Rayet stars. The velocity field is shaped by various elements contributing to the radiative acceleration, especially in the outer wind. The results further indicate that for more dense winds deviations from a standard β-law occur.

Influence of the Aral Sea negative water balance on its seasonal circulation and ventilation patterns: use of a 3d hydrodynamic model.

NASA Astrophysics Data System (ADS)

Sirjacobs, D.; Grégoire, M.; Delhez, E.; Nihoul, J.

2003-04-01

Within the context of the EU INCO-COPERNICUS program "Desertification in the Aral Sea Region: A study of the Natural and Anthropogenic Impacts" (Contract IAC2-CT-2000-10023), a large-scale 3D hydrodynamic model was adapted to address specifically the macroscale processes affecting the Aral Sea water circulation and ventilation. The particular goal of this research is to simulate the effect of lasting negative water balance on the 3D seasonal circulation, temperature, salinity and water-mixing fields of the Aral Sea. The original Aral Sea seasonal hydrodynamism is simulated with the average seasonal forcings corresponding to the period from 1956 to 1960. This first investigation concerns a period of relative stability of the water balance, before the beginning of the drying process. The consequences of the drying process on the hydrodynamic of the Sea will be studied by comparing this first results with the simulation representing the average situation for the years 1981 to 1985, a very low river flow period. For both simulation periods, the forcing considered are the seasonal fluctuations of wind fields, precipitation, evaporation, river discharge and salinity, cloud cover, air temperature and humidity. The meteorological forcings were adapted to the common optimum one-month temporal resolution of the available data sets. Monthly mean kinetic energy flux and surface tensions were calculated from daily ECMWF wind data. Monthly in situ precipitation, surface air temperature and humidity fields were interpolated from data obtained from the Russian Hydrological and Meteorological Institute. Monthly water discharge and average salinity of the river water were considered for both Amu Darya and Syr Darya river over each simulation periods. The water mass conservation routines allowed the simulation of a changing coastline by taking into account local drying and flooding events of particular grid points. Preliminary barotropic runs were realised (for the 1951-1960 situation, before drying up began) in order to get a first experience of the behaviour of the hydrodynamic model. These first runs provide results about the evolution of the following state variables: elevation of the sea surface, 3D fields of vertical and horizontal flows, 2D fields of average horizontal flows and finally the 3D fields of turbulent kinetic energy. The mean seasonal salinity and temperature fields (in-situ data gathered by the Russian Hydrological and Meteorological Institute) are available for the two simulated periods and will allow a first validation of the hydrodynamic model. Various satellites products were identified, collected and processed in the frame of this research project and will be used for the validation of the model outputs. Seasonal level changes measurements derived from water table change will serve for water balance validation and sea surface temperature for hydrodynamics validation.

Fluctuation, dissipation, and a non-equilibrium ``equation of state'' via nonlinear microrheology of hydrodynamically interacting colloids

NASA Astrophysics Data System (ADS)

Chu, Henry; Zia, Roseanna

2014-11-01

In our recently developed non-equilibrium Stokes-Einstein relation for microrheology, we showed that, in the absence of hydrodynamic interactions, the stress in a suspension is given by a balance between fluctuation and dissipation. Here we generalize our theory to develop a simple analytical relation connecting diffusive fluctuation, viscous dissipation and suspension stress in systems of hydrodynamically interacting colloids. In active microrheology, a Brownian probe is driven through a complex medium. The strength of probe forcing compared to the entropic restoring force defines a Peclet number, Pe. In the absence of hydrodynamics, normal stress differences scale as Pe4 and Pe for weak and strong probe forcing, respectively. But as hydrodynamics become important, interparticle forces give way to lubrication interactions and the normal stresses scale as Pe2 and Peδln(Pe), where 0.773 <= δ <= 1 as hydrodynamics vary from strong to weak. The new phenomenological theory is shown to agree with standard micromechanical definitions of the stress. A connection is made between the stress and an effective temperature of the medium, prompting the interpretation of the particle stress as the energy density, and the expression for osmotic pressure as a ``non-equilibrium equation of state.''

The way from microscopic many-particle theory to macroscopic hydrodynamics.

PubMed

Haussmann, Rudolf

2016-03-23

Starting from the microscopic description of a normal fluid in terms of any kind of local interacting many-particle theory we present a well defined step by step procedure to derive the hydrodynamic equations for the macroscopic phenomena. We specify the densities of the conserved quantities as the relevant hydrodynamic variables and apply the methods of non-equilibrium statistical mechanics with projection operator techniques. As a result we obtain time-evolution equations for the hydrodynamic variables with three kinds of terms on the right-hand sides: reversible, dissipative and fluctuating terms. In their original form these equations are completely exact and contain nonlocal terms in space and time which describe nonlocal memory effects. Applying a few approximations the nonlocal properties and the memory effects are removed. As a result we find the well known hydrodynamic equations of a normal fluid with Gaussian fluctuating forces. In the following we investigate if and how the time-inversion invariance is broken and how the second law of thermodynamics comes about. Furthermore, we show that the hydrodynamic equations with fluctuating forces are equivalent to stochastic Langevin equations and the related Fokker-Planck equation. Finally, we investigate the fluctuation theorem and find a modification by an additional term.

Optimization Design of Bipolar Plate Flow Field in PEM Stack

NASA Astrophysics Data System (ADS)

Wen, Ming; He, Kanghao; Li, Peilong; Yang, Lei; Deng, Li; Jiang, Fei; Yao, Yong

2017-12-01

A new design of bipolar plate flow field in proton exchange membrane (PEM) stack was presented to develop a high-performance transfer efficiency of the two-phase flow. Two different flow fields were studied by using numerical simulations and the performance of the flow fields was presented. the hydrodynamic properties include pressure gap between inlet and outlet, the Reynold’s number of the two types were compared based on the Navier-Stokes equations. Computer aided optimization software was implemented in the design of experiments of the preferable flow field. The design of experiments (DOE) for the favorable concept was carried out to study the hydrodynamic properties when changing the design parameters of the bipolar plate.

Validation of Vehicle Panel/Equipment Response from Diffuse Acoustic Field Excitation Using Spatially Correlated Transfer Function Approach

NASA Technical Reports Server (NTRS)

Smith, Andrew; LaVerde, Bruce; Fulcher, Clay; Hunt, Ron

2012-01-01

An approach for predicting the vibration, strain, and force responses of a flight-like vehicle panel assembly to acoustic pressures is presented. Important validation for the approach is provided by comparison to ground test measurements in a reverberant chamber. The test article and the corresponding analytical model were assembled in several configurations to demonstrate the suitability of the approach for response predictions when the vehicle panel is integrated with equipment. Critical choices in the analysis necessary for convergence of the predicted and measured responses are illustrated through sensitivity studies. The methodology includes representation of spatial correlation of the pressure field over the panel surface. Therefore, it is possible to demonstrate the effects of hydrodynamic coincidence in the response. The sensitivity to pressure patch density clearly illustrates the onset of coincidence effects on the panel response predictions.

Validation of non-local electron heat conduction model for radiation MHD simulation in magnetized laser plasma

NASA Astrophysics Data System (ADS)

Nagatomo, Hideo; Matsuo, Kazuki; Nicolai, Pilippe; Asahina, Takashi; Fujioka, Shinsuke

2017-10-01

In laser plasma physics, application of an external magnetic field is an attractive method for various research of high energy density physics including fast ignition. Meanwhile, in the high intense laser plasma the behavior of hot electron cannot be ignored. In the radiation hydrodynamic simulation, a classical electron conduction model, Spitzer-Harm model has been used in general. However the model has its limit, and modification of the model is necessary if it is used beyond the application limit. Modified SNB model, which considering the influence of magnetic field is applied to 2-D radiation magnetohydrodynamic code PINOCO. Some experiments related the non-local model are carried out at GXII, Osaka University. In this presentation, these experimental results are shown briefly. And comparison between simulation results considering the non-local electron heat conduction mode are discussed. This study was supported JSPS KAKENHI Grant No. 17K05728.

Shear waves in inhomogeneous, compressible fluids in a gravity field.

PubMed

Godin, Oleg A

2014-03-01

While elastic solids support compressional and shear waves, waves in ideal compressible fluids are usually thought of as compressional waves. Here, a class of acoustic-gravity waves is studied in which the dilatation is identically zero, and the pressure and density remain constant in each fluid particle. These shear waves are described by an exact analytic solution of linearized hydrodynamics equations in inhomogeneous, quiescent, inviscid, compressible fluids with piecewise continuous parameters in a uniform gravity field. It is demonstrated that the shear acoustic-gravity waves also can be supported by moving fluids as well as quiescent, viscous fluids with and without thermal conductivity. Excitation of a shear-wave normal mode by a point source and the normal mode distortion in realistic environmental models are considered. The shear acoustic-gravity waves are likely to play a significant role in coupling wave processes in the ocean and atmosphere.

Towards the concept of hydrodynamic cavitation control

NASA Astrophysics Data System (ADS)

Chatterjee, Dhiman; Arakeri, Vijay H.

1997-02-01

A careful study of the existing literature available in the field of cavitation reveals the potential of ultrasonics as a tool for controlling and, if possible, eliminating certain types of hydrodynamic cavitation through the manipulation of nuclei size present in a flow. A glass venturi is taken to be an ideal device to study the cavitation phenomenon at its throat and its potential control. A piezoelectric transducer, driven at the crystal resonant frequency, is used to generate an acoustic pressure field and is termed an ‘ultrasonic nuclei manipulator (UNM)’. Electrolysis bubbles serve as artificial nuclei to produce travelling bubble cavitation at the venturi throat in the absence of a UNM but this cavitation is completely eliminated when a UNM is operative. This is made possible because the nuclei, which pass through the acoustic field first, cavitate, collapse violently and perhaps fragment and go into dissolution before reaching the venturi throat. Thus, the potential nuclei for travelling bubble cavitation at the venturi throat seem to be systematically destroyed through acoustic cavitation near the UNM. From the solution to the bubble dynamics equation, it has been shown that the potential energy of a bubble at its maximum radius due to an acoustic field is negligible compared to that for the hydrodynamic field. Hence, even though the control of hydrodynamic macro cavitation achieved in this way is at the expense of acoustic micro cavitation, it can still be considered to be a significant gain. These are some of the first results in this direction.

Mitigating reentry radio blackout by using a traveling magnetic field

NASA Astrophysics Data System (ADS)

Zhou, Hui; Li, Xiaoping; Xie, Kai; Liu, Yanming; Yu, Yuanyuan

2017-10-01

A hypersonic flight or a reentry vehicle is surrounded by a plasma layer that prevents electromagnetic wave transmission, which results in radio blackout. The magnetic-window method is considered a promising means to mitigate reentry communication blackout. However, the real application of this method is limited because of the need for strong magnetic fields. To reduce the required magnetic field strength, a novel method that applies a traveling magnetic field (TMF) is proposed in this study. A mathematical model based on magneto-hydrodynamic theory is adopted to analyze the effect of TMF on plasma. The mitigating effects of the TMF on the blackout of typical frequency bands, including L-, S-, and C-bands, are demonstrated. Results indicate that a significant reduction of plasma density occurs in the magnetic-window region by applying a TMF, and the reduction ratio is positively correlated with the velocity of the TMF. The required traveling velocities for eliminating the blackout of the Global Positioning System (GPS) and the typical telemetry system are also discussed. Compared with the constant magnetic-window method, the TMF method needs lower magnetic field strength and is easier to realize in the engineering field.

Self-Consistent Superthermal Electron Effects on Plasmaspheric Refilling

NASA Technical Reports Server (NTRS)

Liemohn, M. W.; Khazanov, G. V.; Moore, T. E.; Guiter, S. M.

1997-01-01

The effects of self-consistently including superthermal electrons in the definition of the ambipolar electric field are investigated for the case of plasmaspheric refilling after a geomagnetic storm. By using the total electron population in the hydrodynamic equations, a method for incorporating superthermal electron parameters in the electric field and electron temperature calculation is developed. Also, the ambipolar electric field is included in the kinetic equation for the superthermal electrons through a change of variables using the total energy and the first adiabatic invariant. Calculations based on these changes are performed by coupling time-dependent models of the thermal plasma and superthermal electrons. Results from this treatment of the electric field and the self-consistent development of the solution are discussed in detail. Specifically, there is a decreased thermal electron density in the plasmasphere during the first few minutes of refilling, a slightly accelerated proton shock front, and a decreased superthermal electron flux due to the deceleration by the electric field. The timescales of plasmaspheric refilling are discussed and determined to be somewhat shorter than previously calculated for the thermal plasma and superthermal electron population due to the effects of the field-aligned potential.

Bulk dynamics of Brownian hard disks: Dynamical density functional theory versus experiments on two-dimensional colloidal hard spheres

NASA Astrophysics Data System (ADS)

Stopper, Daniel; Thorneywork, Alice L.; Dullens, Roel P. A.; Roth, Roland

2018-03-01

Using dynamical density functional theory (DDFT), we theoretically study Brownian self-diffusion and structural relaxation of hard disks and compare to experimental results on quasi two-dimensional colloidal hard spheres. To this end, we calculate the self-van Hove correlation function and distinct van Hove correlation function by extending a recently proposed DDFT-approach for three-dimensional systems to two dimensions. We find that the theoretical results for both self-part and distinct part of the van Hove function are in very good quantitative agreement with the experiments up to relatively high fluid packing fractions of roughly 0.60. However, at even higher densities, deviations between the experiment and the theoretical approach become clearly visible. Upon increasing packing fraction, in experiments, the short-time self-diffusive behavior is strongly affected by hydrodynamic effects and leads to a significant decrease in the respective mean-squared displacement. By contrast, and in accordance with previous simulation studies, the present DDFT, which neglects hydrodynamic effects, shows no dependence on the particle density for this quantity.

Three-dimensional three-phase model for simulation of hydrodynamics, oxygen mass transfer, carbon oxidation, nitrification and denitrification in an oxidation ditch.

PubMed

Lei, Li; Ni, Jinren

2014-04-15

A three-dimensional three-phase fluid model, supplemented by laboratory data, was developed to simulate the hydrodynamics, oxygen mass transfer, carbon oxidation, nitrification and denitrification processes in an oxidation ditch. The model provided detailed phase information on the liquid flow field, gas hold-up distribution and sludge sedimentation. The three-phase model described water-gas, water-sludge and gas-sludge interactions. Activated sludge was taken to be in a pseudo-solid phase, comprising an initially separated solid phase that was transported and later underwent biological reactions with the surrounding liquidmedia. Floc parameters were modified to improve the sludge viscosity, sludge density, oxygen mass transfer rate, and carbon substrate uptake due to adsorption onto the activated sludge. The validation test results were in very satisfactory agreement with laboratory data on the behavior of activated sludge in an oxidation ditch. By coupling species transport and biological process models, reasonable predictions are made of: (1) the biochemical kinetics of dissolved oxygen, chemical oxygen demand (COD) and nitrogen variation, and (2) the physical kinematics of sludge sedimentation. Copyright © 2014 Elsevier Ltd. All rights reserved.

Hydrodynamics with conserved current via AdS/CFT correspondence in the Maxwell-Gauss-Bonnet gravity

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

Hu Yapeng; Sun Peng; Zhang Jianhui

2011-06-15

Using the AdS/CFT correspondence, we study the hydrodynamics with conserved current from the dual Maxwell-Gauss-Bonnet gravity. After constructing the perturbative solution to the first order based on the boosted black brane solution in the bulk Maxwell-Gauss-Bonnet gravity, we extract the stress tensor and conserved current of the dual conformal fluid on its boundary, and also find the effect of the Gauss-Bonnet term on the dual conformal fluid. Our results show that the Gauss-Bonnet term can affect the parameters such as the shear viscosity {eta}, entropy density s, thermal conductivity {kappa} and electrical conductivity {sigma}. However, it does not affect themore » so-called Wiedemann-Franz law which relates {kappa} to {sigma}, while it affects the ratio {eta}/s. In addition, another interesting result is that {eta}/s can also be affected by the bulk Maxwell field in our case, which is consistent with some previous results predicted through the Kubo formula. Moreover, the anomalous magnetic and vortical effects by adding the Chern-Simons term are also considered in our case in the Maxwell-Gauss-Bonnet gravity.« less

A computational modeling approach of the jet-like acoustic streaming and heat generation induced by low frequency high power ultrasonic horn reactors.

PubMed

Trujillo, Francisco Javier; Knoerzer, Kai

2011-11-01

High power ultrasound reactors have gained a lot of interest in the food industry given the effects that can arise from ultrasonic-induced cavitation in liquid foods. However, most of the new food processing developments have been based on empirical approaches. Thus, there is a need for mathematical models which help to understand, optimize, and scale up ultrasonic reactors. In this work, a computational fluid dynamics (CFD) model was developed to predict the acoustic streaming and induced heat generated by an ultrasonic horn reactor. In the model it is assumed that the horn tip is a fluid inlet, where a turbulent jet flow is injected into the vessel. The hydrodynamic momentum rate of the incoming jet is assumed to be equal to the total acoustic momentum rate emitted by the acoustic power source. CFD velocity predictions show excellent agreement with the experimental data for power densities higher than W(0)/V ≥ 25kWm(-3). This model successfully describes hydrodynamic fields (streaming) generated by low-frequency-high-power ultrasound. Crown Copyright © 2011. Published by Elsevier B.V. All rights reserved.

Hydrodynamic & Transport Properties of Dirac Materials in the Quantum Limit

NASA Astrophysics Data System (ADS)

Gochan, Matthew; Bedell, Kevin

Dirac materials are a versatile class of materials in which an abundance of unique physical phenomena can be observed. Such materials are found in all dimensions, with the shared property that their low-energy fermionic excitations behave as massless Dirac fermions and are therefore governed by the Dirac equation. The most popular Dirac material, its two dimensional version in graphene, is the focus of this work. We seek a deeper understanding of the interactions in the quantum limit within graphene. Specifically, we derive hydrodynamic and transport properties, such as the conductivity, viscosity, and spin diffusion, in the low temperature regime where electron-electron scattering is dominant. To conclude, we look at the so-called universal lower bound conjectured by the anti-de Sitter/conformal field theory (AdS/CFT) correspondence for the ratio of shear viscosity to entropy density ratio. The lower bound, given by η / s >= ℏ / (4 πkB) , is supposedly obeyed by all quantum fluids. This leads us to ask whether or not graphene can be considered a quantum fluid and perhaps a ''nearly perfect fluid''(NPF) if this is the case, is it possible to find a violation of this bound at low temperatures.

Modeling of Optoelectronic Devices

NASA Technical Reports Server (NTRS)

Li, Jian-Zhong; Woo, Alex C. (Technical Monitor)

2000-01-01

Ultrafast modulation of semiconductor quantum well (QW) laser is of technological importance for information technology. Improvement by order(s) of magnitude in data transfer rate is possible as terahertz (THz) radiation is available for heating the laser at picosecond time scale. Optical gain modulation in the QW is achieved via temperature modulation of electron-hole plasma (EHP). Applications include free-space THz communication, optical switching, and pulse generation. The EHP in the semiconductor QW is described with a two-band model. Semiconductor Bloch equations with many-body effects are used to derive a hydrodynamical model for the active QW region. Because of ultrafast carrier-carrier scatterings in the order of 50 fs, EHP follows quasiequilibrium Fermi-Dirac distributions and THz field interacts incoherently with it. Carrier-longitudinal optical (LO) phonon scatterings and coherent laser-EHP interaction are treated microscopically in our physical model. A set of hydrodynamical equations for plasma density, temperature, and laser envelop amplitude are derived and Runge-Kutta method is adopted for numerical simulation. A typical 8 nm GaAs/Al(0.3)Ga(0.7) As single QW at 300 K is used. Additional information is contained in the original extended abstract.

Taming axial dispersion in hydrodynamic chromatography columns through wall patterning

NASA Astrophysics Data System (ADS)

Adrover, Alessandra; Cerbelli, Stefano; Giona, Massimiliano

2018-04-01

A well-known limitation of hydrodynamic chromatography arises from the synergistic interaction between transverse diffusion and streamwise convection, which enhances axial dispersion through the Taylor-Aris mechanism. We show that a periodic sequence of slip/no-slip conditions at the channel walls (e.g., representing wall indentations hosting stable air pockets) can significantly reduce axial dispersion, thus enhancing separation performance. The theoretical/numerical analysis is based on a generalization of Brenner's macrotransport approach to solute transport, here modified to account for the finite-size of the suspended particles. The most effective dispersion-taming outcome is observed when the alternating sequence of slip/no-slip conditions yields non-vanishing cross-sectional flow components. The combination of these components with the hindering interaction between the channel boundaries and the finite-sized particles gives rise to a non-trivial solution of Brenner's problem on the unit periodic cell, where the cross-sectional particle number density departs from the spatially homogeneous condition. In turn, this effect impacts upon the solution of the so-called b-field defining the large-scale dispersion tensor, with an overall decremental effect on the axial dispersion coefficient and on the Height Equivalent of a Theoretical Plate.

Low-momentum dynamic structure factor of a strongly interacting Fermi gas at finite temperature: A two-fluid hydrodynamic description

NASA Astrophysics Data System (ADS)

Hu, Hui; Zou, Peng; Liu, Xia-Ji

2018-02-01

We provide a description of the dynamic structure factor of a homogeneous unitary Fermi gas at low momentum and low frequency, based on the dissipative two-fluid hydrodynamic theory. The viscous relaxation time is estimated and is used to determine the regime where the hydrodynamic theory is applicable and to understand the nature of sound waves in the density response near the superfluid phase transition. By collecting the best knowledge on the shear viscosity and thermal conductivity known so far, we calculate the various diffusion coefficients and obtain the damping width of the (first and second) sounds. We find that the damping width of the first sound is greatly enhanced across the superfluid transition and very close to the transition the second sound might be resolved in the density response for the transferred momentum up to half of Fermi momentum. Our work is motivated by the recent measurement of the local dynamic structure factor at low momentum at Swinburne University of Technology and the ongoing experiment on sound attenuation of a homogeneous unitary Fermi gas at Massachusetts Institute of Technology. We discuss how the measurement of the velocity and damping width of the sound modes in low-momentum dynamic structure factor may lead to an improved determination of the universal superfluid density, shear viscosity, and thermal conductivity of a unitary Fermi gas.

Stokes-Einstein relation for pure simple fluids.

PubMed

Cappelezzo, M; Capellari, C A; Pezzin, S H; Coelho, L A F

2007-06-14

The authors employed the equilibrium molecular dynamics technique to calculate the self-diffusion coefficient and the shear viscosity for simple fluids that obey the Lennard-Jones 6-12 potential in order to investigate the validity of the Stokes-Einstein (SE) relation for pure simple fluids. They performed calculations in a broad range of density and temperature in order to test the SE relation. The main goal of this work is to exactly calculate the constant, here denominated by alpha, present in the SE relation. Also, a modified SE relation where a fluid density is raised to a power in the usual expression is compared to the classical expression. According to the authors' simulations slip boundary conditions (alpha=4) can be satisfied in some state points. An intermediate value of alpha=5 was found in some regions of the phase diagram confirming the mode coupling theory. In addition depending on the phase diagram point and the definition of hydrodynamics radius, stick boundary condition (alpha=6) can be reproduced. The authors investigated the role of the hydrodynamic radius in the SE relation using three different definitions. The authors also present calculations for alpha in a hard-sphere system showing that the slip boundary conditions hold at very high density. They discuss possible explanations for their results and the role of the hydrodynamic radius for different definitions in the SE relation.

Competing effects of collisional ionization and radiative cooling in inertially confined plasmas

NASA Astrophysics Data System (ADS)

Woolsey, N. C.; Hammel, B. A.; Keane, C. J.; Back, C. A.; Moreno, J. C.; Nash, J. K.; Calisti, A.; Mossé, C.; Stamm, R.; Talin, B.; Asfaw, A.; Klein, L. S.; Lee, R. W.

1998-04-01

We describe an experimental investigation, a detailed analysis of the Ar XVII 1s2 1S-1s3p 1P (Heβ) line shape formed in a high-energy-density implosion, and report on one-dimensional radiation-hydrodynamics simulation of the implosion. In this experiment trace quantities of argon are doped into a lower-Z gas-filled core of a plastic microsphere. The dopant level is controlled to ensure that the Heβ transition is optically thin and easily observable. Then the observed line shape is used to derive electron temperatures (Te) and electron densities (ne). The high-energy density plasma, with Te approaching 1 keV and ne=1024 cm-3, is created by placing the microsphere in a gold cylindrical enclosure, the interior of which is directly irradiated by a high-energy laser; the x rays produced by this laser-gold interaction indirectly implode the microsphere. Central to the interpretation of the hydrodynamics of the implosions is the characterization and understanding of the formation of these plasmas. To develop an understanding of the plasma and its temporal evolution, time-resolved Te and ne measurements are extracted using techniques that are independent of the plasma hydrodynamics. Comparing spectroscopic diagnostics with measurements derived from other diagnostic methods, we find the spectroscopic measurements to be reliable and further we find that the experiment-to-experiment comparison shows that these implosions are reproducible.

Effect of Central Mass Concentration on the Formation of Nuclear Spirals in Barred Galaxies

NASA Astrophysics Data System (ADS)

Thakur, Parijat; Ann, H. B.; Jiang, Ing-Guey

2009-03-01

We have performed smoothed particle hydrodynamics simulations to study the response of the central kiloparsec region of a gaseous disk to the imposition of nonaxisymmetric bar potentials. The model galaxies are composed of three axisymmetric components (halo, disk, and bulge) and a nonaxisymmetric bar. These components are assumed to be invariant in time in the frame corotating with the bar. The potential of spherical γ-models of Dehnen is adopted for the bulge component whose density varies as r -γ near the center and r -4 at larger radii and, hence, possesses a central density core for γ = 0 and cusps for γ>0. Since the central mass concentration of the model galaxies increases with the cusp parameter γ, we have examined here the effect of the central mass concentration by varying the cusp parameter γ on the mechanism responsible for the formation of the symmetric two-armed nuclear spirals in barred galaxies. Our simulations show that the symmetric two-armed nuclear spirals are formed by hydrodynamic spiral shocks driven by the gravitational torque of the bar for the models with γ = 0 and 0.5. On the other hand, the symmetric two-armed nuclear spirals in the models with γ = 1 and 1.5 are explained by gas density waves. Thus, we conclude that the mechanism responsible for the formation of symmetric two-armed nuclear spirals in barred galaxies changes from hydrodynamic shocks to gas density waves as the central mass concentration increases from γ = 0 to 1.5.

Smoothed particle hydrodynamics simulations of evaporation and explosive boiling of liquid drops in microgravity.

PubMed

Sigalotti, Leonardo Di G; Troconis, Jorge; Sira, Eloy; Peña-Polo, Franklin; Klapp, Jaime

2015-07-01

The rapid evaporation and explosive boiling of a van der Waals (vdW) liquid drop in microgravity is simulated numerically in two-space dimensions using the method of smoothed particle hydrodynamics. The numerical approach is fully adaptive and incorporates the effects of surface tension, latent heat, mass transfer across the interface, and liquid-vapor interface dynamics. Thermocapillary forces are modeled by coupling the hydrodynamics to a diffuse-interface description of the liquid-vapor interface. The models start from a nonequilibrium square-shaped liquid of varying density and temperature. For a fixed density, the drop temperature is increased gradually to predict the point separating normal boiling at subcritical heating from explosive boiling at the superheat limit for this vdW fluid. At subcritical heating, spontaneous evaporation produces stable drops floating in a vapor atmosphere, while at near-critical heating, a bubble is nucleated inside the drop, which then collapses upon itself, leaving a smaller equilibrated drop embedded in its own vapor. At the superheat limit, unstable bubble growth leads to either fragmentation or violent disruption of the liquid layer into small secondary drops, depending on the liquid density. At higher superheats, explosive boiling occurs for all densities. The experimentally observed wrinkling of the bubble surface driven by rapid evaporation followed by a Rayleigh-Taylor instability of the thin liquid layer and the linear growth of the bubble radius with time are reproduced by the simulations. The predicted superheat limit (T(s)≈0.96) is close to the theoretically derived value of T(s)=1 at zero ambient pressure for this vdW fluid.

Theoretical study of the criteria and consequences of hydrodynamic electron flow in graphene.

NASA Astrophysics Data System (ADS)

Adam, Shaffique; Ho, Derek; Yudhistira, Indra; Chakraborty, Nilotpal

Experiments on graphene electrons have succeeded in entering the hydrodynamic regime, as demonstrated by successful observations of Wiedemann-Franz law violations, and evidence for electron vortices. The hydrodynamic regime is expected to occur when electron-electron interactions dominate over all other electron collision mechanisms. We calculate the electron-electron, electron-impurity and electron-phonon scattering rates as a function of temperature, charge doping and disorder (charge puddle) strength. We find that there exists a window in parameter space where electron-electron scattering dominates and hydrodynamic effects become observable. However, we also find that disorder induced carrier density inhomogeneity continues to play an important role in the vicinity of charge neutrality, even in the strongly interacting hydrodynamic regime. For example, although the ratio of thermal conductivity and electrical conductivity show a violation of the Wiedemann-Franz law in the aforementioned experiment, the electrical conductivity as a function of temperature still follows a disorder-driven universal scaling theory first predicted in This work was supported by the National Research Foundation of Singapore (NRF-NRFF2012-01).

Simulating the effect of high column density absorbers on the one-dimensional Lyman α forest flux power spectrum

NASA Astrophysics Data System (ADS)

Rogers, Keir K.; Bird, Simeon; Peiris, Hiranya V.; Pontzen, Andrew; Font-Ribera, Andreu; Leistedt, Boris

2018-03-01

We measure the effect of high column density absorbing systems of neutral hydrogen (H I) on the one-dimensional (1D) Lyman α forest flux power spectrum using cosmological hydrodynamical simulations from the Illustris project. High column density absorbers (which we define to be those with H I column densities N(H I) > 1.6 × 10^{17} atoms cm^{-2}) cause broadened absorption lines with characteristic damping wings. These damping wings bias the 1D Lyman α forest flux power spectrum by causing absorption in quasar spectra away from the location of the absorber itself. We investigate the effect of high column density absorbers on the Lyman α forest using hydrodynamical simulations for the first time. We provide templates as a function of column density and redshift, allowing the flexibility to accurately model residual contamination, i.e. if an analysis selectively clips out the largest damping wings. This flexibility will improve cosmological parameter estimation, for example, allowing more accurate measurement of the shape of the power spectrum, with implications for cosmological models containing massive neutrinos or a running of the spectral index. We provide fitting functions to reproduce these results so that they can be incorporated straightforwardly into a data analysis pipeline.

New theories of relativistic hydrodynamics in the LHC era

NASA Astrophysics Data System (ADS)

Florkowski, Wojciech; Heller, Michal P.; Spaliński, Michał

2018-04-01

The success of relativistic hydrodynamics as an essential part of the phenomenological description of heavy-ion collisions at RHIC and the LHC has motivated a significant body of theoretical work concerning its fundamental aspects. Our review presents these developments from the perspective of the underlying microscopic physics, using the language of quantum field theory, relativistic kinetic theory, and holography. We discuss the gradient expansion, the phenomenon of hydrodynamization, as well as several models of hydrodynamic evolution equations, highlighting the interplay between collective long-lived and transient modes in relativistic matter. Our aim to provide a unified presentation of this vast subject—which is naturally expressed in diverse mathematical languages—has also led us to include several new results on the large-order behaviour of the hydrodynamic gradient expansion.

Three-dimensional modeling of the neutron spectrum to infer plasma conditions in cryogenic inertial confinement fusion implosions

NASA Astrophysics Data System (ADS)

Weilacher, F.; Radha, P. B.; Forrest, C.

2018-04-01

Neutron-based diagnostics are typically used to infer compressed core conditions such as areal density and ion temperature in deuterium-tritium (D-T) inertial confinement fusion (ICF) implosions. Asymmetries in the observed neutron-related quantities are important to understanding failure modes in these implosions. Neutrons from fusion reactions and their subsequent interactions including elastic scattering and neutron-induced deuteron breakup reactions are tracked to create spectra. It is shown that background subtraction is important for inferring areal density from backscattered neutrons and is less important for the forward-scattered neutrons. A three-dimensional hydrodynamic simulation of a cryogenic implosion on the OMEGA Laser System [Boehly et al., Opt. Commun. 133, 495 (1997)] using the hydrodynamic code HYDRA [Marinak et al., Phys. Plasmas 8, 2275 (2001)] is post-processed using the tracking code IRIS3D. It is shown that different parts of the neutron spectrum from the view can be mapped into different regions of the implosion, enabling an inference of an areal-density map. It is also shown that the average areal-density and an areal-density map of the compressed target can be reconstructed with a finite number of detectors placed around the target chamber. Ion temperatures are inferred from the width of the D-D and D-T fusion neutron spectra. Backgrounds can significantly alter the inferred ion temperatures from the D-D reaction, whereas they insignificantly influence the inferred D-T ion temperatures for the areal densities typical of OMEGA implosions. Asymmetries resulting in fluid flow in the core are shown to influence the absolute inferred ion temperatures from both reactions, although relative inferred values continue to reflect the underlying asymmetry pattern. The work presented here is part of the wide range of the first set of studies performed with IRIS3D. This code will continue to be used for post-processing detailed hydrodynamic simulations and interpreting observed neutron spectra in ICF implosions.

Holography, black holes and condensed matter physics

NASA Astrophysics Data System (ADS)

Gentle, Simon Adam

In this thesis we employ holographic techniques to explore strongly-coupled quantum field theories at non-zero temperature and density. First we consider a state dual to a charged black hole with planar horizon and compute retarded Green's functions for conserved currents in the shear channel. We demonstrate the intricate motion of their poles and stress the importance of the residues at the poles beyond the hydrodynamic regime. We then explore the collective excitations of holographic quantum liquids arising on D3/D5 and D3/D7 brane intersections as a function of temperature and magnetic field in the probe limit. We observe a crossover from hydrodynamic charge diffusion to a sound mode similar to the zero sound mode in the collisionless regime of a Landau Fermi liquid. The location of this crossover is approximately independent of the magnetic field. The sound mode has a gap proportional to the magnetic field, leading to strong suppression of spectral weight for intermediate frequencies and sufficiently large magnetic fields. In the second part we explore the solution space of AdS gravity in the hope of learning general lessons about such theories. First we study charged scalar solitons in global AdS4. These solutions have a rich phase space and exhibit critical behaviour as a function of the scalar charge and scalar boundary conditions. We demonstrate how the planar limit of global solitons coincides generically with the zero-temperature limit of black branes with charged scalar hair. We exhibit these features in both phenomenological models and consistent truncations of eleven-dimensional supergravity. We then discover new branches of hairy black brane in SO(6) gauged supergravity. Despite the imbalance provided by three chemical potentials conjugate to the three R-charges, there is always at least one branch with charged scalar hair, emerging at a temperature where the normal phase is locally thermodynamically stable.

Radio Evolution of Supernova Remnants Including Nonlinear Particle Acceleration: Insights from Hydrodynamic Simulations

NASA Astrophysics Data System (ADS)

Pavlović, Marko Z.; Urošević, Dejan; Arbutina, Bojan; Orlando, Salvatore; Maxted, Nigel; Filipović, Miroslav D.

2018-01-01

We present a model for the radio evolution of supernova remnants (SNRs) obtained by using three-dimensional hydrodynamic simulations coupled with nonlinear kinetic theory of cosmic-ray (CR) acceleration in SNRs. We model the radio evolution of SNRs on a global level by performing simulations for a wide range of the relevant physical parameters, such as the ambient density, supernova (SN) explosion energy, acceleration efficiency, and magnetic field amplification (MFA) efficiency. We attribute the observed spread of radio surface brightnesses for corresponding SNR diameters to the spread of these parameters. In addition to our simulations of Type Ia SNRs, we also considered SNR radio evolution in denser, nonuniform circumstellar environments modified by the progenitor star wind. These simulations start with the mass of the ejecta substantially higher than in the case of a Type Ia SN and presumably lower shock speed. The magnetic field is understandably seen as very important for the radio evolution of SNRs. In terms of MFA, we include both resonant and nonresonant modes in our large-scale simulations by implementing models obtained from first-principles, particle-in-cell simulations and nonlinear magnetohydrodynamical simulations. We test the quality and reliability of our models on a sample consisting of Galactic and extragalactic SNRs. Our simulations give Σ ‑ D slopes between ‑4 and ‑6 for the full Sedov regime. Recent empirical slopes obtained for the Galactic samples are around ‑5, while those for the extragalactic samples are around ‑4.

Hydrodynamic correlation functions of hard-sphere fluids at short times

NASA Astrophysics Data System (ADS)

Leegwater, Jan A.; van Beijeren, Henk

1989-11-01

The short-time behavior of the coherent intermediate scattering function for a fluid of hard-sphere particles is calculated exactly through order t 4, and the other hydrodynamic correlation functions are calculated exactly through order t 2. It is shown that for all of the correlation functions considered the Enskog theory gives a fair approximation. Also, the initial time behavior of various Green-Kubo integrands is studied. For the shear-viscosity integrand it is found that at density nσ3=0.837 the prediction of the Enskog theory is 32% too low. The initial value of the bulk viscosity integrand is nonzero, in contrast to the Enskog result. The initial value of the thermal conductivity integrand at high densities is predicted well by Enskog theory.

Controlling dynamics of imploded core plasma for fast ignition

NASA Astrophysics Data System (ADS)

Nagatomo, H.; Johzaki, T.; Sunahara, A.; Shiraga, H.; Sakagami, H.; Cai, H.; Mima, K.

2010-08-01

In the Fast ignition, formation of highly compressed core plasma is one of critical issue. In this work, the effect hydrodynamic instability in cone-guided shell implosion is studied. Two-dimensional radiation hydrodynamic simulations are carried out where realistic seeds of Rayleigh-Taylor instability are imposed. Preliminary results suggest that the instability reduces implosion performance, such as implosion velocity, areal density, and maximum density. In perturbed target implosion, the break-up time of the tip of the cone is earlier than that of ideal unperturbed target implosion case. This is crucial matter for the Fast ignition because the pass for the heating laser is filled with plasma before the shot of heating laser. A sophisticated implosion design of stable and low in-flight aspect ratio is necessary for cone-guided shell implosion.

Variational principles for relativistic smoothed particle hydrodynamics

NASA Astrophysics Data System (ADS)

Monaghan, J. J.; Price, D. J.

2001-12-01

In this paper we show how the equations of motion for the smoothed particle hydrodynamics (SPH) method may be derived from a variational principle for both non-relativistic and relativistic motion when there is no dissipation. Because the SPH density is a function of the coordinates the derivation of the equations of motion through variational principles is simpler than in the continuum case where the density is defined through the continuity equation. In particular, the derivation of the general relativistic equations is more direct and simpler than that of Fock. The symmetry properties of the Lagrangian lead immediately to the familiar additive conservation laws of linear and angular momentum and energy. In addition, we show that there is an approximately conserved quantity which, in the continuum limit, is the circulation.

Computation of the Hydrodynamic Forces and Moments on a Body of Revolution with and without Appendages

DTIC Science & Technology

1991-08-01

SUPPLEMENTARY NOTATION 1 COSA. CODES 18 SUBJECT TERMS (,ontnuo 0 ner of necessary Atdi, block n" mbr ) FIELD GROUP SUB.GROUP Submarine ’hyoroaynamic ’~ aDS...hydrodynamic forces and moments developed on the hull and appendages of a submerged vehicle is required for determining its stability, control, and...an approximate method has been developed to compute the hydrodynamic forces and moments for a submerged vehicle. As discussed in Reference 1, the

Hydrodynamic Torques and Rotations of Superparamagnetic Bead Dimers

NASA Astrophysics Data System (ADS)

Pease, Christopher; Etheridge, J.; Wijesinghe, H. S.; Pierce, C. J.; Prikockis, M. V.; Sooryakumar, R.

Chains of micro-magnetic particles are often rotated with external magnetic fields for many lab-on-a-chip technologies such as transporting beads or mixing fluids. These applications benefit from faster responses of the actuated particles. In a rotating magnetic field, the magnetization of superparamagnetic beads, created from embedded magnetic nano-particles within a polymer matrix, is largely characterized by induced dipoles mip along the direction of the field. In addition there is often a weak dipole mop that orients out-of-phase with the external rotating field. On a two-bead dimer, the simplest chain of beads, mop contributes a torque Γm in addition to the torque from mip. For dimers with beads unbound to each other, mop rotates individual beads which generate an additional hydrodynamic torque on the dimer. Whereas, mop directly torques bound dimers. Our results show that Γm significantly alters the average frequency-dependent dimer rotation rate for both bound and unbound monomers and, when mop exceeds a critical value, increases the maximum dimer rotation frequency. Models that include magnetic and hydrodynamics torques provide good agreement with the experimental findings over a range of field frequencies.

A modified thermal conductivity for low density plasma magnetic flux tubes

NASA Technical Reports Server (NTRS)

Comfort, R. H.; Craven, P. D.; Richards, P. G.

1995-01-01

In response to inconsistencies which have arisen in results from a hydrodynamic model in simulation of high ion temperature (1-2 eV) observed in low density, outer plasmasphere flux tubes, we postulate a reduced thermal conductivity coefficient in which only particles in the loss cone of the quasi-collisionless plasma contribute to the thermal conduction. Other particles are assumed to magnetically mirror before they reach the topside ionosphere and therefore not to remove thermal energy from the plasmasphere. This concept is used to formulate a mathematically simple, but physically limiting model for a modified thermal conductivity coefficient. When this modified coefficient is employed in the hydrodynamic model in a case study, the inconsistencies between simulation results and observations are largely resolved. The high simulated ion temperatures are achieved with significantly lower ion temperatures in the topside ionosphere. We suggest that this mechanism may be operative under the limited low density, refilling conditions in which high ion temperatures are observed.

Magneto-hydrodynamical model for plasma

NASA Astrophysics Data System (ADS)

Liu, Ruikuan; Yang, Jiayan

2017-10-01

Based on the Newton's second law and the Maxwell equations for the electromagnetic field, we establish a new 3-D incompressible magneto-hydrodynamics model for the motion of plasma under the standard Coulomb gauge. By using the Galerkin method, we prove the existence of a global weak solution for this new 3-D model.

Inertial confinement fusion and fast ignitor studies

NASA Astrophysics Data System (ADS)

Willi, O.; Barringer, L.; Bell, A.; Borghesi, M.; Davies, J.; Gaillard, R.; Iwase, A.; MacKinnon, A.; Malka, G.; Meyer, C.; Nuruzzaman, S.; Taylor, R.; Vickers, C.; Hoarty, D.; Gobby, P.; Johnson, R.; Watt, R. G.; Blanchot, N.; Canaud, B.; Croso, H.; Meyer, B.; Miquel, J. L.; Reverdin, C.; Pukhov, A.; Meyer-ter-Vehn, J.

2000-03-01

Laser imprinting has been studied and, in particular, saturation of areal density perturbations induced by near single mode laser imprinting was observed. Several issues important for the foam buffered direct drive scheme have been investigated. These studies included measurements of the absolute levels of stimulated Brillouin and Raman scattering observed from laser irradiated low density foam targets, either bare or overcoated with a thin layer of gold. A novel scheme is proposed to increase the pressure in indirectly driven targets. By heating a foam supersonically that is attached to a solid target the pressure generated is not only the ablation pressure but also the combined pressure due to ablation at the foam-foil interface and the heated foam material. Planar brominated plastic foil targets overcoated with a low density foam were irradiated by a soft X ray pulse. The pressure was obtained by comparing the rear side trajectory of the driven target observed by soft X ray radiography with one dimensional radiation hydrodynamic simulations. Observations were also carried out of the transition from supersonic to subsonic propagation of an ionization front in low density chlorinated foam targets irradiated by an intense soft X ray pulse. The diagnostic for these measurements was K shell point projection absorption spectroscopy. In the fast ignitor area the channelling and guiding of picosecond laser pulses through underdense plasmas, preformed density channels and microtubes were investigated. It was observed that a large fraction of the incident laser energy can be propagated. Megagauss magnetic fields were measured, with a polarimetric technique, during and after propagation of intense picosecond pulses in preionized plasmas. Two types of toroidal fields, of opposite orientation, were detected. In addition, the production and propagation of an electron beam through solid glass targets irradiated at intensities above 1019W/cm2 were observed using optical probing techniques.

Influence of lead ions on the macromorphology of electrodeposited zinc

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

Tsuda, Tetsuaki; Tobias, Charles W.

1981-09-01

The morphology of zinc as it is electrodeposited from acid solutions demonstrates a remarkable imprint of electrolyte flow conditions. The development of macromorphology of zinc deposits has been investigated under galvanostatic conditions on a rotating plantinum disk electrode by use of photomacrography, scanning electron microscopy, electron probe microanalysis and Auger microprobe analysis. Logarithmic spiral markings, which reflect the hydrodynamic flow on a rotating disk, appear in a certain region of current density well below the limiting current density. Morphological observations revealed the major influence of trace lead ions on the amplifications of surface roughness through coalescence and preferred growth ofmore » initial protrusions. Results obtained from ultra-pure electrolyte suggest preferred crystal growth towards well-mixed orientation in the concentration field caused by slight differences in crystallization overpotential. A qualitative model involving a coupling mechanism between the evolving surface roughness and instability phenomena in the boundary layer is advanced to explain the formation of spiral patterns.« less

Automata network models of galaxy evolution

NASA Technical Reports Server (NTRS)

Chappell, David; Scalo, John

1993-01-01

Two ideas appear frequently in theories of star formation and galaxy evolution: (1) star formation is nonlocally excitatory, stimulating star formation in neighboring regions by propagation of a dense fragmenting shell or the compression of preexisting clouds; and (2) star formation is nonlocally inhibitory, making H2 regions and explosions which can create low-density and/or high temperature regions and increase the macroscopic velocity dispersion of the cloudy gas. Since it is not possible, given the present state of hydrodynamic modeling, to estimate whether one of these effects greatly dominates the other, it is of interest to investigate the predicted spatial pattern of star formation and its temporal behavior in simple models which incorporate both effects in a controlled manner. The present work presents preliminary results of such a study which is based on lattice galaxy models with various types of nonlocal inhibitory and excitatory couplings of the local SFR to the gas density, temperature, and velocity field meant to model a number of theoretical suggestions.

PEVC-FMDF for Large Eddy Simulation of Compressible Turbulent Flows

NASA Astrophysics Data System (ADS)

Nouri Gheimassi, Arash; Nik, Mehdi; Givi, Peyman; Livescu, Daniel; Pope, Stephen

2017-11-01

The filtered density function (FDF) closure is extended to a ``self-contained'' format to include the subgrid scale (SGS) statistics of all of the hydro-thermo-chemical variables in turbulent flows. These are the thermodynamic pressure, the specific internal energy, the velocity vector, and the composition field. In this format, the model is comprehensive and facilitates large eddy simulation (LES) of flows at both low and high compressibility levels. A transport equation is developed for the joint ``pressure-energy-velocity-composition filtered mass density function (PEVC-FMDF).'' In this equation, the effect of convection appears in closed form. The coupling of the hydrodynamics and thermochemistry is modeled via a set of stochastic differential equation (SDE) for each of the transport variables. This yields a self-contained SGS closure. For demonstration, LES is conducted of a turbulent shear flow with transport of a passive scalar. The consistency of the PEVC-FMDF formulation is established, and its overall predictive capability is appraised via comparison with direct numerical simulation (DNS) data.

X-ray clusters in a cold dark matter + lambda universe: A direct, large-scale, high-resolution, hydrodynamic simulation

NASA Technical Reports Server (NTRS)

Cen, Renyue; Ostriker, Jeremiah P.

1994-01-01

A new, three-dimensional, shock-capturing, hydrodynamic code is utilized to determine the distribution of hot gas in a cold dark matter (CDM) + lambda model universe. Periodic boundary conditions are assumed: a box with size 85/h Mpc, having cell size 0.31/h Mpc, is followed in a simulation with 270(exp 3) = 10(exp 7.3) cells. We adopt omega = 0.45, lambda = 0.55, h identically equal to H/100 km/s/Mpc = 0.6, and then, from the cosmic background explorer (COBE) and light element nucleosynthesis, sigma(sub 8) = 0.77, omega(sub b) = 0.043. We identify the X-ray emitting clusters in the simulation box, compute the luminosity function at several wavelength bands, the temperature function and estimated sizes, as well as the evolution of these quantities with redshift. This open model succeeds in matching local observations of clusters in contrast to the standard omega = 1, CDM model, which fails. It predicts an order of magnitude decline in the number density of bright (h nu = 2-10 keV) clusters from z = 0 to z = 2 in contrast to a slight increase in the number density for standard omega = 1, CDM model. This COBE-normalized CDM + lambda model produces approximately the same number of X-ray clusters having L(sub x) greater than 10(exp 43) erg/s as observed. The background radiation field at 1 keV due to clusters is approximately the observed background which, after correction for numerical effects, again indicates that the model is consistent with observations.

Radio emission in Mercury magnetosphere

NASA Astrophysics Data System (ADS)

Varela, J.; Reville, V.; Brun, A. S.; Pantellini, F.; Zarka, P.

2016-10-01

Context. Active stars possess magnetized wind that has a direct impact on planets that can lead to radio emission. Mercury is a good test case to study the effect of the solar wind and interplanetary magnetic field (IMF) on radio emission driven in the planet magnetosphere. Such studies could be used as proxies to characterize the magnetic field topology and intensity of exoplanets. Aims: The aim of this study is to quantify the radio emission in the Hermean magnetosphere. Methods: We use the magnetohydrodynamic code PLUTO in spherical coordinates with an axisymmetric multipolar expansion for the Hermean magnetic field, to analyze the effect of the IMF orientation and intensity, as well as the hydrodynamic parameters of the solar wind (velocity, density and temperature), on the net power dissipated on the Hermean day and night side. We apply the formalism derived by Zarka et al. (2001, Astrophys. Space Sci., 277, 293), Zarka (2007, Planet. Space Sci., 55, 598) to infer the radio emission level from the net dissipated power. We perform a set of simulations with different hydrodynamic parameters of the solar wind, IMF orientations and intensities, that allow us to calculate the dissipated power distribution and infer the existence of radio emission hot spots on the planet day side, and to calculate the integrated radio emission of the Hermean magnetosphere. Results: The obtained radio emission distribution of dissipated power is determined by the IMF orientation (associated with the reconnection regions in the magnetosphere), although the radio emission strength is dependent on the IMF intensity and solar wind hydro parameters. The calculated total radio emission level is in agreement with the one estimated in Zarka et al. (2001, Astrophys. Space Sci., 277, 293) , between 5 × 105 and 2 × 106 W.

Fluid and particle transport of a hairy structure

NASA Astrophysics Data System (ADS)

Lee, Hongki; Lahooti, Mohsen; Kim, Daegyoum; Jung, Seyeong

2017-11-01

Hairy appendages of animals are used to capture particles, sense surrounding flow, and generate propulsive force. Due to the small size of the hairy structures, their hydrodynamics have been studied mostly in very low Reynolds number. In this work, in a broad range of Reynolds number, O(1) - O(100), flow structure and inertial particle dynamics around an array of two-dimensional cylinders are investigated numerically by using an immersed boundary method. Given flow fields, Maxey-Riley equation is adopted to examine particle dynamics. Here, we discuss the effects of Reynolds number, density ratio of inertial particles and fluid, and distance between cylinders on particle behaviors around a moving structure. In addition, drift volume of inertial particles is correlated with the model parameters.

Self-Assembled Magnetic Surface Swimmers: Theoretical Model

NASA Astrophysics Data System (ADS)

Aranson, Igor; Belkin, Maxim; Snezhko, Alexey

2009-03-01

The mechanisms of self-propulsion of living microorganisms are a fascinating phenomenon attracting enormous attention in the physics community. A new type of self-assembled micro-swimmers, magnetic snakes, is an excellent tool to model locomotion in a simple table-top experiment. The snakes self-assemble from a dispersion of magnetic microparticles suspended on the liquid-air interface and subjected to an alternating magnetic field. Formation and dynamics of these swimmers are captured in the framework of theoretical model coupling paradigm equation for the amplitude of surface waves, conservation law for the density of particles, and the Navier-Stokes equation for hydrodynamic flows. The results of continuum modeling are supported by hybrid molecular dynamics simulations of magnetic particles floating on the surface of fluid.

Hole-cyclotron instability in semiconductor quantum plasmas

NASA Astrophysics Data System (ADS)

Areeb, F.; Rasheed, A.; Jamil, M.; Siddique, M.; Sumera, P.

2018-01-01

The excitation of electrostatic hole-cyclotron waves generated by an externally injected electron beam in semiconductor plasmas is examined using a quantum hydrodynamic model. The quantum effects such as tunneling potential, Fermi degenerate pressure, and exchange-correlation potential are taken care of. The growth rate of the wave is analyzed on varying the parameters normalized by hole-plasma frequency, like the angle θ between propagation vector and B0∥z ̂ , speed of the externally injected electron beam v0∥k , thermal temperature of the electron beam τ, external magnetic field B0∥z ̂ that modifies the hole-cyclotron frequency, and finally, the semiconductor electron number density. The instability of the hole-cyclotron wave seeks its applications in semiconductor devices.

Hydrodynamic interaction of a self-propelling particle with a wall : Comparison between an active Janus particle and a squirmer model.

PubMed

Shen, Zaiyi; Würger, Alois; Lintuvuori, Juho S

2018-03-27

Using lattice Boltzmann simulations we study the hydrodynamics of an active spherical particle near a no-slip wall. We develop a computational model for an active Janus particle, by considering different and independent mobilities on the two hemispheres and compare the behaviour to a standard squirmer model. We show that the topology of the far-field hydrodynamic nature of the active Janus particle is similar to the standard squirmer model, but in the near-field the hydrodynamics differ. In order to study how the near-field effects affect the interaction between the particle and a flat wall, we compare the behaviour of a Janus swimmer and a squirmer near a no-slip surface via extensive numerical simulations. Our results show generally a good agreement between these two models, but they reveal some key differences especially with low magnitudes of the squirming parameter [Formula: see text]. Notably the affinity of the particles to be trapped at a surface is increased for the active Janus particles when compared to standard squirmers. Finally, we find that when the particle is trapped on the surface, the velocity parallel to the surface exceeds the bulk swimming speed and scales linearly with [Formula: see text].

Fragmentation of protostars dust shells at the Hayashi stage

NASA Astrophysics Data System (ADS)

Abdulmyanov, T. R.

2017-09-01

The aim of this study is to determine the density variations of a protostars dust shells at the Hayashi stage. The simplified model of the density wave perturbations are obtained on the base hydrodynamic equations. According to this model, the fragmentation of dust shells may occur at the stage of slow compression of protostar. Using the solution of the wave equation, the 3-D profiles of the density of the dust shell are defined.

The potential of imposed magnetic fields for enhancing ignition probability and fusion energy yield in indirect-drive inertial confinement fusion

NASA Astrophysics Data System (ADS)

Perkins, L. J.; Ho, D. D.-M.; Logan, B. G.; Zimmerman, G. B.; Rhodes, M. A.; Strozzi, D. J.; Blackfield, D. T.; Hawkins, S. A.

2017-06-01

We examine the potential that imposed magnetic fields of tens of Tesla that increase to greater than 10 kT (100 MGauss) under implosion compression may relax the conditions required for ignition and propagating burn in indirect-drive inertial confinement fusion (ICF) targets. This may allow the attainment of ignition, or at least significant fusion energy yields, in presently performing ICF targets on the National Ignition Facility (NIF) that today are sub-marginal for thermonuclear burn through adverse hydrodynamic conditions at stagnation [Doeppner et al., Phys. Rev. Lett. 115, 055001 (2015)]. Results of detailed two-dimensional radiation-hydrodynamic-burn simulations applied to NIF capsule implosions with low-mode shape perturbations and residual kinetic energy loss indicate that such compressed fields may increase the probability for ignition through range reduction of fusion alpha particles, suppression of electron heat conduction, and potential stabilization of higher-mode Rayleigh-Taylor instabilities. Optimum initial applied fields are found to be around 50 T. Given that the full plasma structure at capsule stagnation may be governed by three-dimensional resistive magneto-hydrodynamics, the formation of closed magnetic field lines might further augment ignition prospects. Experiments are now required to further assess the potential of applied magnetic fields to ICF ignition and burn on NIF.

On the linearity of tracer bias around voids

NASA Astrophysics Data System (ADS)

Pollina, Giorgia; Hamaus, Nico; Dolag, Klaus; Weller, Jochen; Baldi, Marco; Moscardini, Lauro

2017-07-01

The large-scale structure of the Universe can be observed only via luminous tracers of the dark matter. However, the clustering statistics of tracers are biased and depend on various properties, such as their host-halo mass and assembly history. On very large scales, this tracer bias results in a constant offset in the clustering amplitude, known as linear bias. Towards smaller non-linear scales, this is no longer the case and tracer bias becomes a complicated function of scale and time. We focus on tracer bias centred on cosmic voids, I.e. depressions of the density field that spatially dominate the Universe. We consider three types of tracers: galaxies, galaxy clusters and active galactic nuclei, extracted from the hydrodynamical simulation Magneticum Pathfinder. In contrast to common clustering statistics that focus on auto-correlations of tracers, we find that void-tracer cross-correlations are successfully described by a linear bias relation. The tracer-density profile of voids can thus be related to their matter-density profile by a single number. We show that it coincides with the linear tracer bias extracted from the large-scale auto-correlation function and expectations from theory, if sufficiently large voids are considered. For smaller voids we observe a shift towards higher values. This has important consequences on cosmological parameter inference, as the problem of unknown tracer bias is alleviated up to a constant number. The smallest scales in existing data sets become accessible to simpler models, providing numerous modes of the density field that have been disregarded so far, but may help to further reduce statistical errors in constraining cosmology.

Challenges for mass production of nematodes in submerged culture.

PubMed

de la Torre, Mayra

2003-08-01

Nematodes of Steinernema and Heterorhabditis genera are used as agents in insect biocontrol programs. They are associated with specific bacteria which are also involved in the mechanism of pathogenicity and which are consumed by nematodes as living food. S. feltiae has various developmental stages in its life cycle, including four juvenile stages, adults and the free living form. During mating, males coil themselves around the female, which is around 1 cm long. Successful commercialization of nematode-bacteria biocontrol products depends on the ability to produce sufficient quantities of these products at competitive prices for a full pest control program. This could be feasible if high cell density submerged cultures are designed and implemented; however, major problems related to nematodes mass production in a bioreactor remain unsolved due to the lack of knowledge about the physiological aspects of the nematode, bacteria and nematode-bacteria association, interaction between the three phases present in the bioreactor (liquid, gas, nematodes-bacteria), possibility of mating under hydrodynamic stress conditions, etc. We have found that the two most important engineering aspects to take into account the mass propagation of nematodes are oxygen transfer rate and hydrodynamics to allow mating and to avoid mechanical damage of juveniles in stage 2. This article focuses on several aspects related to the fermentation system such as kinetics of growth, shear stress, hydrodynamics fields in the bioreactor and oxygen demand. Also, results published by other groups, together with those of our own, will be discussed in relation to the main challenges found during the fermentation process.

Frequency-dependent hydrodynamic interaction between two solid spheres

NASA Astrophysics Data System (ADS)

Jung, Gerhard; Schmid, Friederike

2017-12-01

Hydrodynamic interactions play an important role in many areas of soft matter science. In simulations with implicit solvent, various techniques such as Brownian or Stokesian dynamics explicitly include hydrodynamic interactions a posteriori by using hydrodynamic diffusion tensors derived from the Stokes equation. However, this equation assumes the interaction to be instantaneous which is an idealized approximation and only valid on long time scales. In the present paper, we go one step further and analyze the time-dependence of hydrodynamic interactions between finite-sized particles in a compressible fluid on the basis of the linearized Navier-Stokes equation. The theoretical results show that at high frequencies, the compressibility of the fluid has a significant impact on the frequency-dependent pair interactions. The predictions of hydrodynamic theory are compared to molecular dynamics simulations of two nanocolloids in a Lennard-Jones fluid. For this system, we reconstruct memory functions by extending the inverse Volterra technique. The simulation data agree very well with the theory, therefore, the theory can be used to implement dynamically consistent hydrodynamic interactions in the increasingly popular field of non-Markovian modeling.

Observation of Burial and Migration of Instrumented Surrogate Munitions Deployed in the Swash Zone

NASA Astrophysics Data System (ADS)

Cristaudo, D.; Puleo, J. A.; Bruder, B. L.

2017-12-01

Munitions (also known as unexploded ordnance; UXO) in the nearshore environment due to past military activities, may be found on the beach, constituting a risk for beach users. Munitions may be transported from offshore to shallower water and/or migrate along the coast. In addition, munitions may bury in place or be exhumed due to hydrodynamic forcing. Observations on munitions mobility have generally been collected offshore, while observations in the swash zone are scarce. The swash zone is the region of the beach alternately covered by wave runup where hydrodynamic processes may be intense. Studies of munitions mobility require the use of realistic surrogates to quantify mobility/burial and hydrodynamic forcing conditions. Four surrogates (BLU-61 Cluster Bomb, 81 mm Mortar, M151-70 Hydra Rocket and M107 155 mm High Explosive Howitzer) were developed and tested during large-scale laboratory and field studies. Surrogates house sensors that measure different components of motion. Errors between real munitions and surrogate parameters (mass, center of gravity and axial moment of inertia) are all within an absolute error of 20%. Internal munitions sensors consist of inertial motion units (for acceleration and angular velocity in and around the three directions and orientation), pressure transducers (for water depth above surrogate), shock recorders (for high frequency acceleration to detect wave impact on the surrogate), and an in-house designed array of optical sensors (for burial/exposure and rolling). An in situ array of sensors to measure hydrodynamics, bed morphology and sediment concentrations, was deployed in the swash zone, aligned with the surrogate deployment. Data collected during the studies will be shown highlighting surrogate sensor capabilities. Sensors response will be compared with GPS measurements and imagery from cameras overlooking the study sites of surrogate position as a function of time. Examples of burial/exposure and migration of surrogates will be discussed. Relationships between burial/migration and incoming forcing conditions, bed slope and munitions characteristics (such as specific density, length/diameter) will all be shown.

Aspects of hot Galilean field theory

NASA Astrophysics Data System (ADS)

Jensen, Kristan

2015-04-01

We reconsider general aspects of Galilean-invariant thermal field theory. Using the proposal of our companion paper, we recast non-relativistic hydrodynamics in a manifestly covariant way and couple it to a background spacetime. We examine the concomitant consequences for the thermal partition functions of Galilean theories on a time-independent, but weakly curved background. We work out both the hydrodynamics and partition functions in detail for the example of parity-violating normal fluids in two dimensions to first order in the gradient expansion, finding results that differ from those previously reported in the literature. As for relativistic field theories, the equality-type constraints imposed by the existence of an entropy current appear to be in one-to-one correspondence with those arising from the existence of a hydrostatic partition function. Along the way, we obtain a number of useful results about non-relativistic hydrodynamics, including a manifestly boost-invariant presentation thereof, simplified Ward identities, the systematics of redefinitions of the fluid variables, and the positivity of entropy production.

Dynamics of Vortex and Magnetic Lines in Ideal Hydrodynamics and MHD

NASA Astrophysics Data System (ADS)

Kuznetsov, E. A.; Ruban, V. P.

Vortex line and magnetic line representations are introduced for description of flows in ideal hydrodynamics and MHD, respectively. For incompressible fluids it is shown that the equations of motion for vorticity φ and magnetic field with the help of this transformation follow from the variational principle. By means of this representation it is possible to integrate the system of hydrodynamic type with the Hamiltonian H=|φ|dr. It is also demonstrated that these representations allow to remove from the noncanonical Poisson brackets, defined on the space of divergence-free vector fields, degeneracy connected with the vorticity frozenness for the Euler equation and with magnetic field frozenness for ideal MHD. For MHD a new Weber type transformation is found. It is shown how this transformation can be obtained from the two-fluid model when electrons and ions can be considered as two independent fluids. The Weber type transformation for ideal MHD gives the whole Lagrangian vector invariant. When this invariant is absent this transformation coincides with the Clebsch representation analog introduced in [1].

Cooperation of sperm in two dimensions: synchronization, attraction, and aggregation through hydrodynamic interactions.

PubMed

Yang, Yingzi; Elgeti, Jens; Gompper, Gerhard

2008-12-01

Sperm swimming at low Reynolds number have strong hydrodynamic interactions when their concentration is high in vivo or near substrates in vitro. The beating tails not only propel the sperm through a fluid, but also create flow fields through which sperm interact with each other. We study the hydrodynamic interaction and cooperation of sperm embedded in a two-dimensional fluid by using a particle-based mesoscopic simulation method, multiparticle collision dynamics. We analyze the sperm behavior by investigating the relationship between the beating-phase difference and the relative sperm position, as well as the energy consumption. Two effects of hydrodynamic interaction are found, synchronization and attraction. With these hydrodynamic effects, a multisperm system shows swarm behavior with a power-law dependence of the average cluster size on the width of the distribution of beating frequencies.

Application of Hydrodynamic Cavitation for Food and Bioprocessing

NASA Astrophysics Data System (ADS)

Gogate, Parag R.

Hydrodynamic cavitation can be simply generated by the alterations in the flow field in high speed/high pressure devices and also by passage of the liquid through a constriction such as orifice plate, venturi, or throttling valve. Hydrodynamic cavitation results in the formation of local hot spots, release of highly reactive free radicals, and enhanced mass transfer rates due to turbulence generated as a result of liquid circulation currents. These conditions can be suitably applied for intensification of different bioprocessing applications in an energy-efficient manner as compared to conventionally used ultrasound-based reactors. The current chapter aims at highlighting different aspects related to hydrodynamic cavitation, including the theoretical aspects for optimization of operating parameters, reactor designs, and overview of applications relevant to food and bioprocessing. Some case studies highlighting the comparison of hydrodynamic cavitation and acoustic cavitation reactors will also be discussed.

Plasmon excitation in metal slab by fast point charge: The role of additional boundary conditions in quantum hydrodynamic model

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

Zhang, Ying-Ying; Department of Applied Mathematics, University of Waterloo, Waterloo, Ontario N2L 3G1; An, Sheng-Bai

2014-10-15

We study the wake effect in the induced potential and the stopping power due to plasmon excitation in a metal slab by a point charge moving inside the slab. Nonlocal effects in the response of the electron gas in the metal are described by a quantum hydrodynamic model, where the equation of electronic motion contains both a quantum pressure term and a gradient correction from the Bohm quantum potential, resulting in a fourth-order differential equation for the perturbed electron density. Thus, besides using the condition that the normal component of the electron velocity should vanish at the impenetrable boundary ofmore » the metal, a consistent inclusion of the gradient correction is shown to introduce two possibilities for an additional boundary condition for the perturbed electron density. We show that using two different sets of boundary conditions only gives rise to differences in the wake potential at large distances behind the charged particle. On the other hand, the gradient correction in the quantum hydrodynamic model is seen to cause a reduction in the depth of the potential well closest to the particle, and a reduction of its stopping power. Even for a particle moving in the center of the slab, we observe nonlocal effects in the induced potential and the stopping power due to reduction of the slab thickness, which arise from the gradient correction in the quantum hydrodynamic model.« less

NDCX-II target experiments and simulations

DOE PAGES

Barnard, J. J.; More, R. M.; Terry, M.; ...

2013-06-13

The ion accelerator NDCX-II is undergoing commissioning at Lawrence Berkeley National Laboratory (LBNL). Its principal mission is to explore ion-driven High Energy Density Physics (HEDP) relevant to Inertial Fusion Energy (IFE) especially in the Warm Dense Matter (WDM) regime. We have carried out hydrodynamic simulations of beam-heated targets for parameters expected for the initial configuration of NDCX-II. For metal foils of order one micron thick (thin targets), the beam is predicted to heat the target in a timescale comparable to the hydrodynamic expansion time for experiments that infer material properties from measurements of the resulting rarefaction wave. We have alsomore » carried out hydrodynamic simulations of beam heating of metallic foam targets several tens of microns thick (thick targets) in which the ion range is shorter than the areal density of the material. In this case shock waves will form and we derive simple scaling laws for the efficiency of conversion of ion energy into kinetic energy of fluid flow. Geometries with a tamping layer may also be used to study the merging of a tamper shock with the end-of-range shock. As a result, this process can occur in tamped, direct drive IFE targets.« less

The hydrodynamic design and critical techniques for 1m×1m water tunnel

NASA Astrophysics Data System (ADS)

Jiang, Yubiao; Gao, Chao; Geng, Zihai; Chen, Cheng

2018-04-01

China aerodynamics research and development Center has built 1m×1m water tunnel featured by good flow field quality and comprehensive experimental abilities for the researches on flow visualization and measurement. In detail, it has several advantages, such as low turbulence intensity, spatially homogeneous velocity field, stable flow velocity and convenience for use. The experimental section has low turbulence intensity and good quality of flow field over a wide range of flow velocity from 0.1m/s to 1m/s, implying that the hydrodynamic design method and critical techniques for the tunnel are worthy of popularization.

Hydrodynamic Modeling and Its Application in AUC.

PubMed

Rocco, Mattia; Byron, Olwyn

2015-01-01

The hydrodynamic parameters measured in an AUC experiment, s(20,w) and D(t)(20,w)(0), can be used to gain information on the solution structure of (bio)macromolecules and their assemblies. This entails comparing the measured parameters with those that can be computed from usually "dry" structures by "hydrodynamic modeling." In this chapter, we will first briefly put hydrodynamic modeling in perspective and present the basic physics behind it as implemented in the most commonly used methods. The important "hydration" issue is also touched upon, and the distinction between rigid bodies versus those for which flexibility must be considered in the modeling process is then made. The available hydrodynamic modeling/computation programs, HYDROPRO, BEST, SoMo, AtoB, and Zeno, the latter four all implemented within the US-SOMO suite, are described and their performance evaluated. Finally, some literature examples are presented to illustrate the potential applications of hydrodynamics in the expanding field of multiresolution modeling. © 2015 Elsevier Inc. All rights reserved.

Numerical Study of Motion of Falling Conical Graupel

NASA Astrophysics Data System (ADS)

Chueh, Chih-Che; Wang, Pao K.; Hashino, Tempei

2018-01-01

In the present study, the attitudes of freely-falling conical graupel with a realistic range of densities are investigated numerically by solving the transient Navier-Stokes equations and the body dynamics equations representing the 6-degrees-of-freedom motion. This framework allows us to determine the position and orientation of the graupel in response to the hydrodynamic force of the flow fields. The results show more significant horizontal movements than those cases with a fixed bulk density of ice assumed in our previous study. This is because the real graupel particles possess the density less than the bulk density of ice, which, in turn, leads to a relatively small mass and a relatively small set of moments of inertia. We demonstrate that, with the six degrees of freedom considered together, when Reynolds number is small, a typical damped oscillation occurs, whereas when Reynolds number is high, amplifying oscillation may occur which leads to more complicated and unpredictable flying attitudes such as tumbling. The drag coefficients obtained in the present study agree with the previous studies and can be approximated by that of spheres of the same Reynolds numbers. We also show that conical graupel can perform significant horizontal translations which can be on the order of 1 km in 1 h.

Hydrodynamical models of cometary H II regions

NASA Astrophysics Data System (ADS)

Steggles, H. G.; Hoare, M. G.; Pittard, J. M.

2017-04-01

We have modelled the evolution of cometary H II regions produced by zero-age main-sequence stars of O and B spectral types, which are driving strong winds and are born off-centre from spherically symmetric cores with power-law (α = 2) density slopes. A model parameter grid was produced that spans stellar mass, age and core density. Exploring this parameter space, we investigated limb-brightening, a feature commonly seen in cometary H II regions. We found that stars with mass M⋆ ≥ 12 M⊙ produce this feature. Our models have a cavity bounded by a contact discontinuity separating hot shocked wind and ionized ambient gas that is similar in size to the surrounding H II region. Because of early pressure confinement, we did not see shocks outside of the contact discontinuity for stars with M⋆ ≤ 40 M⊙, but the cavities were found to continue to grow. The cavity size in each model plateaus as the H II region stagnates. The spectral energy distributions of our models are similar to those from identical stars evolving in uniform density fields. The turn-over frequency is slightly lower in our power-law models as a result of a higher proportion of low-density gas covered by the H II regions.

Comparison of hydrodynamic simulations with two-shockwave drive target experiments

NASA Astrophysics Data System (ADS)

Karkhanis, Varad; Ramaprabhu, Praveen; Buttler, William

2015-11-01

We consider hydrodynamic continuum simulations to mimic ejecta generation in two-shockwave target experiments, where metallic surface is loaded by two successive shock waves. Time of second shock in simulations is determined to match experimental amplitudes at the arrival of the second shock. The negative Atwood number (A --> - 1) of ejecta simulations leads to two successive phase inversions of the interface corresponding to the passage of the shocks from heavy to light media in each instance. Metallic phase of ejecta (solid/liquid) depends on shock loading pressure in the experiment, and we find that hydrodynamic simulations quantify the liquid phase ejecta physics with a fair degree of accuracy, where RM instability is not suppressed by the strength effect. In particular, we find that our results of free surface velocity, maximum ejecta velocity, and maximum ejecta areal density are in excellent agreement with their experimental counterparts, as well as ejecta models. We also comment on the parametric space for hydrodynamic simulations in which they can be used to compare with the target experiments.

Hydrodynamic starvation in first-feeding larval fishes

PubMed Central

China, Victor; Holzman, Roi

2014-01-01

Larval fishes suffer prodigious mortality rates, eliminating 99% of the brood within a few days after first feeding. Hjort (1914) famously attributed this “critical period” of low survival to the larvae’s inability to obtain sufficient food [Hjort (1914) Rapp P-v Réun Cons Int Explor Mer 20:1–228]. However, the cause of this poor feeding success remains to be identified. Here, we show that hydrodynamic constraints on the ubiquitous suction mechanism in first-feeding larvae limit their ability to capture prey, thereby reducing their feeding rates. Dynamic-scaling experiments revealed that larval size is the primary determinant of feeding rate, independent of other ontogenetic effects. We conclude that first-feeding larvae experience “hydrodynamic starvation,” in which low Reynolds numbers mechanistically limit their feeding performance even under high prey densities. Our results provide a hydrodynamic perspective on feeding of larval fishes that focuses on the physical properties of the larvae and prey, rather than on prey concentration and the rate of encounters. PMID:24843180

Generalized hydrodynamics and non-equilibrium steady states in integrable many-body quantum systems

NASA Astrophysics Data System (ADS)

Vasseur, Romain; Bulchandani, Vir; Karrasch, Christoph; Moore, Joel

The long-time dynamics of thermalizing many-body quantum systems can typically be described in terms of a conventional hydrodynamics picture that results from the decay of all but a few slow modes associated with standard conservation laws (such as particle number, energy, or momentum). However, hydrodynamics is expected to fail for integrable systems that are characterized by an infinite number of conservation laws, leading to unconventional transport properties and to complex non-equilibrium states beyond the traditional dogma of statistical mechanics. In this talk, I will describe recent attempts to understand such stationary states far from equilibrium using a generalized hydrodynamics picture. I will discuss the consistency of ``Bethe-Boltzmann'' kinetic equations with linear response Drude weights and with density-matrix renormalization group calculations. This work was supported by the Department of Energy through the Quantum Materials program (R. V.), NSF DMR-1206515, AFOSR MURI and a Simons Investigatorship (J. E. M.), DFG through the Emmy Noether program KA 3360/2-1 (C. K.).

The role of hydrodynamic stress on the phenotypic characteristics of single and binary biofilms of Pseudomonas fluorescens.

PubMed

Simões, M; Pereira, M O; Vieira, M J

2007-01-01

This study investigates the phenotype of turbulent (Re = 5,200) and laminar (Re = 2,000) flow-generated Pseudomonas fluorescens biofilms. Three P. fluorescens strains, the type strain ATCC 13525 and two strains isolated from an industrial processing plant, D3-348 and D3-350, were used throughout this study. The isolated strains were used to form single and binary biofilms. The biofilm physiology (metabolic activity, cellular density, mass, extracellular polymeric substances, structural characteristics and outer membrane proteins [OMP] expression) was compared. The results indicate that, for every situation, turbulent flow-generated biofilms were more active (p < 0.05), had more mass per cm(2) (p < 0.05), a higher cellular density (p < 0.05), distinct morphology, similar matrix proteins (p > 0.1) and identical (isolated strains -single and binary biofilms) and higher (type strain) matrix polysaccharides contents (p < 0.05) than laminar flow-generated biofilms. Flow-generated biofilms formed by the type strain revealed a considerably higher cellular density and amount of matrix polysaccharides than single and binary biofilms formed by the isolated strains (p < 0.05). Similar OMP expression was detected for the several single strains and for the binary situation, not dependent on the hydrodynamic conditions. Binary biofilms revealed an equal coexistence of the isolated strains with apparent neutral interactions. In summary, the biofilms formed by the type strain represent, apparently, the worst situation in a context of control. The results obtained clearly illustrate the importance of considering strain variation and hydrodynamics in biofilm development, and complement previous studies which have focused on physical aspects of structural and density differences.

Atomic detail brownian dynamics simulations of concentrated protein solutions with a mean field treatment of hydrodynamic interactions.

PubMed

Mereghetti, Paolo; Wade, Rebecca C

2012-07-26

High macromolecular concentrations are a distinguishing feature of living organisms. Understanding how the high concentration of solutes affects the dynamic properties of biological macromolecules is fundamental for the comprehension of biological processes in living systems. In this paper, we describe the implementation of mean field models of translational and rotational hydrodynamic interactions into an atomically detailed many-protein brownian dynamics simulation method. Concentrated solutions (30-40% volume fraction) of myoglobin, hemoglobin A, and sickle cell hemoglobin S were simulated, and static structure factors, oligomer formation, and translational and rotational self-diffusion coefficients were computed. Good agreement of computed properties with available experimental data was obtained. The results show the importance of both solvent mediated interactions and weak protein-protein interactions for accurately describing the dynamics and the association properties of concentrated protein solutions. Specifically, they show a qualitative difference in the translational and rotational dynamics of the systems studied. Although the translational diffusion coefficient is controlled by macromolecular shape and hydrodynamic interactions, the rotational diffusion coefficient is affected by macromolecular shape, direct intermolecular interactions, and both translational and rotational hydrodynamic interactions.

Nuclear magnetic resonance characterization of the stationary dynamics of partially saturated media during steady-state infiltration flow

NASA Astrophysics Data System (ADS)

Rassi, Erik M.; Codd, Sarah L.; Seymour, Joseph D.

2011-01-01

Flow in porous media and the resultant hydrodynamics are important in fields including but not limited to the hydrology, chemical, medical and petroleum industries. The observation and understanding of the hydrodynamics in porous media are critical to the design and optimal utilization of porous media, such as those seen in trickle-bed reactors, medical filters, subsurface flows and carbon sequestration. Magnetic resonance (MR) provides for a non-invasive technique that can probe the hydrodynamics on pore and bulk scale lengths; many previous works have characterized fully saturated porous media, while rapid MR imaging (MRI) methods in particular have previously been applied to partially saturated flows. We present time- and ensemble-averaged MR measurements to observe the effects on a bead pack partially saturated with air under flowing water conditions. The 10 mm internal diameter bead pack was filled with 100 μm borosilicate glass beads. Air was injected into the bead pack as water flowed simultaneously through the sample at 25 ml h-1. The initial partially saturated state was characterized with MRI density maps, free induction decay (FID) experiments, propagators and velocity maps before the water flow rate was increased incrementally from 25 to 500 ml h-1. After the maximum flow rate of 500 ml h-1, the MRI density maps, FID experiments, propagators and velocity maps were repeated and compared to the data taken before the maximum flow rate. This work shows that a partially saturated single-phase flow has global flow dynamics that return to characteristic flow statistics once a steady-state high flow rate has been reached. This high flow rate pushed out a significant amount of the air in the bead pack and caused the return of a preferential flow pattern. Velocity maps indicated that local flow statistics were not the same for the before and after blow out conditions. It has been suggested and shown previously that a flow pattern can return to similar statistics if the preceding flow history is similar.

Hydrodynamics, wall-slip, and normal-stress differences in rarefied granular Poiseuille flow

NASA Astrophysics Data System (ADS)

Gupta, Ronak; Alam, Meheboob

2017-02-01

Hydrodynamic fields, macroscopic boundary conditions, and non-Newtonian rheology of the acceleration-driven Poiseuille flow of a dilute granular gas are probed using "direct simulation Monte Carlo" method for a range of Knudsen numbers (Kn, the ratio between the mean free path and the macroscopic length), spanning the rarefied regime of slip and transitional flows. It is shown that the "dissipation-induced clustering" (for 1 -en>0 , where en is the restitution coefficient), leading to inhomogeneous density profiles along the transverse direction, competes with "rarefaction-induced declustering" (for Kn>0 ) phenomenon, leaving seemingly "anomalous" footprints on several hydrodynamic and rheological quantities; one example is the well-known rarefaction-induced temperature bimodality, which could also result from inelastic dissipation that dominates in the continuum limit (Kn→0 ) as found recently [Alam et al., J. Fluid Mech. 782, 99 (2015), 10.1017/jfm.2015.523]. The simulation data on the slip velocity and the temperature slip are contrasted with well-established boundary conditions for molecular gases. A modified Maxwell-Navier-type boundary condition is found to hold in granular Poiseuille flow, with the velocity slip length following a power-law relation with Knudsen number Knδ, with δ ≈0.95 , for Kn≤0.1 . Transverse profiles of both first [N1(y ) ] and second [N2(y ) ] normal stress differences seem to correlate well with respective density profiles at small Kn; their centerline values [N1(0 ) and N2(0 ) ] can be of "odd" sign with respect to their counterparts in molecular gases. The phase diagrams are constructed in the (Kn,1 -en ) plane that demarcates the regions of influence of inelasticity and rarefaction, which compete with each other resulting in the sign change of both N1(0 ) and N2(0 ) . The results on normal stress differences are rationalized via a comparison with a Burnett-order theory [Sela and Goldhirsch, J. Fluid Mech. 361, 41 (1998), 10.1017/S0022112098008660], which is able to predict their correct behavior at small values of the Knudsen number. Lastly, the Knudsen paradox and its dependence on inelasticity are analyzed and contrasted with related recent works.

A NEW DENSITY VARIANCE-MACH NUMBER RELATION FOR SUBSONIC AND SUPERSONIC ISOTHERMAL TURBULENCE

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

Konstandin, L.; Girichidis, P.; Federrath, C.

The probability density function of the gas density in subsonic and supersonic, isothermal, driven turbulence is analyzed using a systematic set of hydrodynamical grid simulations with resolutions of up to 1024{sup 3} cells. We perform a series of numerical experiments with root-mean-square (rms) Mach number M ranging from the nearly incompressible, subsonic (M=0.1) to the highly compressible, supersonic (M=15) regime. We study the influence of two extreme cases for the driving mechanism by applying a purely solenoidal (divergence-free) and a purely compressive (curl-free) forcing field to drive the turbulence. We find that our measurements fit the linear relation between themore » rms Mach number and the standard deviation (std. dev.) of the density distribution in a wide range of Mach numbers, where the proportionality constant depends on the type of forcing. In addition, we propose a new linear relation between the std. dev. of the density distribution {sigma}{sub {rho}} and that of the velocity in compressible modes, i.e., the compressible component of the rms Mach number, M{sub comp}. In this relation the influence of the forcing is significantly reduced, suggesting a linear relation between {sigma}{sub {rho}} and M{sub comp}, independent of the forcing, and ranging from the subsonic to the supersonic regime.« less

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

Chisolm, Eric D.

I explain how to evaluate a multiphase EOS at a given density and energy, which is the standard case in hydrodynamic simulations, when the EOS is provided in the form of individual EOS for each phase and tabulated phase boundaries.

Isochoric heating and strong blast wave formation driven by fast electrons in solid-density targets

NASA Astrophysics Data System (ADS)

Santos, J. J.; Vauzour, B.; Touati, M.; Gremillet, L.; Feugeas, J.-L.; Ceccotti, T.; Bouillaud, R.; Deneuville, F.; Floquet, V.; Fourment, C.; Hadj-Bachir, M.; Hulin, S.; Morace, A.; Nicolaï, Ph; d'Oliveira, P.; Reau, F.; Samaké, A.; Tcherbakoff, O.; Tikhonchuk, V. T.; Veltcheva, M.; Batani, D.

2017-10-01

We experimentally investigate the fast (< 1 {ps}) isochoric heating of multi-layer metallic foils and subsequent high-pressure hydrodynamics induced by energetic electrons driven by high-intensity, high-contrast laser pulses. The early-time temperature profile inside the target is measured from the streaked optical pyrometry of the target rear side. This is further characterized from benchmarked simulations of the laser-target interaction and the fast electron transport. Despite a modest laser energy (< 1 {{J}}), the early-time high pressures and associated gradients launch inwards a strong compression wave developing over ≳ 10 ps into a ≈ 140 {Mbar} blast wave, according to hydrodynamic simulations, consistent with our measurements. These experimental and numerical findings pave the way to a short-pulse-laser-based platform dedicated to high-energy-density physics studies.

ALARIC: An algorithm for constructing arbitrarily complex initial density distributions with low particle noise for SPH/SPMHD applications

NASA Astrophysics Data System (ADS)

Vela Vela, Luis; Sanchez, Raul; Geiger, Joachim

2018-03-01

A method is presented to obtain initial conditions for Smoothed Particle Hydrodynamic (SPH) scenarios where arbitrarily complex density distributions and low particle noise are needed. Our method, named ALARIC, tampers with the evolution of the internal variables to obtain a fast and efficient profile evolution towards the desired goal. The result has very low levels of particle noise and constitutes a perfect candidate to study the equilibrium and stability properties of SPH/SPMHD systems. The method uses the iso-thermal SPH equations to calculate hydrodynamical forces under the presence of an external fictitious potential and evolves them in time with a 2nd-order symplectic integrator. The proposed method generates tailored initial conditions that perform better in many cases than those based on purely crystalline lattices, since it prevents the appearance of anisotropies.

CHOLLA: A New Massively Parallel Hydrodynamics Code for Astrophysical Simulation

NASA Astrophysics Data System (ADS)

Schneider, Evan E.; Robertson, Brant E.

2015-04-01

We present Computational Hydrodynamics On ParaLLel Architectures (Cholla ), a new three-dimensional hydrodynamics code that harnesses the power of graphics processing units (GPUs) to accelerate astrophysical simulations. Cholla models the Euler equations on a static mesh using state-of-the-art techniques, including the unsplit Corner Transport Upwind algorithm, a variety of exact and approximate Riemann solvers, and multiple spatial reconstruction techniques including the piecewise parabolic method (PPM). Using GPUs, Cholla evolves the fluid properties of thousands of cells simultaneously and can update over 10 million cells per GPU-second while using an exact Riemann solver and PPM reconstruction. Owing to the massively parallel architecture of GPUs and the design of the Cholla code, astrophysical simulations with physically interesting grid resolutions (≳2563) can easily be computed on a single device. We use the Message Passing Interface library to extend calculations onto multiple devices and demonstrate nearly ideal scaling beyond 64 GPUs. A suite of test problems highlights the physical accuracy of our modeling and provides a useful comparison to other codes. We then use Cholla to simulate the interaction of a shock wave with a gas cloud in the interstellar medium, showing that the evolution of the cloud is highly dependent on its density structure. We reconcile the computed mixing time of a turbulent cloud with a realistic density distribution destroyed by a strong shock with the existing analytic theory for spherical cloud destruction by describing the system in terms of its median gas density.

Dissipative hydrodynamics for multi-component systems

NASA Astrophysics Data System (ADS)

El, Andrej; Bouras, Ioannis; Wesp, Christian; Xu, Zhe; Greiner, Carsten

2012-11-01

Second-order dissipative hydrodynamic equations for each component of a multi-component system are derived using the entropy principle. Comparison of the solutions with kinetic transport results demonstrates validity of the obtained equations. We demonstrate how the shear viscosity of the total system can be calculated in terms of the involved cross-sections and partial densities. The presence of the inter-species interactions leads to a characteristic time dependence of the shear viscosity of the mixture, which also means that the shear viscosity of a mixture cannot be calculated using the Green-Kubo formalism the way it has been done recently. This finding is of interest for understanding of the shear viscosity of a quark-gluon plasma extracted from comparisons of hydrodynamic simulations with experimental results from RHIC and LHC.

Dissipative quantum hydrodynamics model of x-ray Thomson scattering in dense plasmas

NASA Astrophysics Data System (ADS)

Diaw, Abdourahmane; Murillo, Michael

2017-10-01

X-ray Thomson scattering (XRTS) provides detailed diagnostic information about dense plasma experiments. The inferences made rely on an accurate model for the form factor, which is typically expressed in terms of a well-known response function. Here, we develop an alternate approach based on quantum hydrodynamics using a viscous form of dynamical density functional theory. This approach is shown to include the equation of state self-consistently, including sum rules, as well as irreversibility arising from collisions. This framework is used to generate a model for the scattering spectrum, and it offers an avenue for measuring hydrodynamic properties, such as transport coefficients, using XRTS. This work was supported by the Air Force Office of Scientific Research (Grant No. FA9550-12-1-0344).

Unconventional transport in ultraclean graphene constriction devices

NASA Astrophysics Data System (ADS)

Pita Vidal, Marta; Ma, Qiong; Watanabe, Kenji; Taniguchi, Takashi; Jarillo-Herrero, Pablo

Under mesoscopic conditions, strong electron-electron interactions and weak electron-phonon coupling in graphene lead to hydrodynamic behavior of electrons, resulting in unusual and unexpected transport phenomena. Specifically, this hydrodynamical collective cooperation of electrons is predicted to enhance the flow of electrical current, leading to a striking higher-than-ballistic conductance through a narrow geometrical constriction. To access the hydrodynamic regime, we fabricated high-quality, low-disorder graphene nano-constriction devices encapsulated by hexagonal boron nitride, where electron-electron scattering dominates impurity scattering. We will report on our systematic four-probe conductance measurements on devices with different constriction widths as a function of number density and temperature. The observation of quantum transport phenomena that are inconsistent with the non-interacting ballistic free-fermion model would suggest a macroscopic transport signature of electron viscosity.

A conservative MHD scheme on unstructured Lagrangian grids for Z-pinch hydrodynamic simulations

NASA Astrophysics Data System (ADS)

Wu, Fuyuan; Ramis, Rafael; Li, Zhenghong

2018-03-01

A new algorithm to model resistive magnetohydrodynamics (MHD) in Z-pinches has been developed. Two-dimensional axisymmetric geometry with azimuthal magnetic field Bθ is considered. Discretization is carried out using unstructured meshes made up of arbitrarily connected polygons. The algorithm is fully conservative for mass, momentum, and energy. Matter energy and magnetic energy are managed separately. The diffusion of magnetic field is solved using a derivative of the Symmetric-Semi-Implicit scheme, Livne et al. (1985) [23], where unconditional stability is obtained without needing to solve large sparse systems of equations. This MHD package has been integrated into the radiation-hydrodynamics code MULTI-2D, Ramis et al. (2009) [20], that includes hydrodynamics, laser energy deposition, heat conduction, and radiation transport. This setup allows to simulate Z-pinch configurations relevant for Inertial Confinement Fusion.

Lagrangian formulation and symmetrical description of liquid dynamics.

PubMed

Trachenko, K

2017-12-01

Theoretical description of liquids has been primarily based on the hydrodynamic approach and its generalization to the solid-like regime. We show that the same liquid properties can be derived starting from solid-like equations and generalizing them to account for the hydrodynamic flow. Both approaches predict propagating shear waves with the notable gap in k-space. This gives an important symmetry of liquids regarding their description. We subsequently construct a two-field Lagrangian of liquid dynamics where the dissipative hydrodynamic and solid-like terms are treated on equal footing. The Lagrangian predicts two gapped waves propagating in opposite space-time directions. The dissipative and mass terms compete by promoting gaps in k-space and energy, respectively. When bare mass is close to the field hopping frequency, both gaps close and the dissipative term annihilates the bare mass.

Lagrangian formulation and symmetrical description of liquid dynamics

NASA Astrophysics Data System (ADS)

Trachenko, K.

2017-12-01

Theoretical description of liquids has been primarily based on the hydrodynamic approach and its generalization to the solid-like regime. We show that the same liquid properties can be derived starting from solid-like equations and generalizing them to account for the hydrodynamic flow. Both approaches predict propagating shear waves with the notable gap in k -space. This gives an important symmetry of liquids regarding their description. We subsequently construct a two-field Lagrangian of liquid dynamics where the dissipative hydrodynamic and solid-like terms are treated on equal footing. The Lagrangian predicts two gapped waves propagating in opposite space-time directions. The dissipative and mass terms compete by promoting gaps in k -space and energy, respectively. When bare mass is close to the field hopping frequency, both gaps close and the dissipative term annihilates the bare mass.

Observation of Transonic Ionization Fronts in Low-Density Foam Targets

NASA Astrophysics Data System (ADS)

Hoarty, D.; Barringer, L.; Vickers, C.; Willi, O.; Nazarov, W.

1999-04-01

Transonic ionization fronts have been observed in low-density chlorinated foam targets using time-resolved K-shell absorption spectroscopy. The front was driven by an intense pulse of soft x rays produced by high-power laser irradiation of a thin foil. The density and temperature profiles inferred from the radiographs provided detailed measurement of the conditions at a number of times. The experimental data were compared to radiation hydrodynamics simulations and reasonable agreement was obtained.

Fluctuating Hydrodynamics Confronts the Rapidity Dependence of Transverse Momentum Fluctuations

NASA Astrophysics Data System (ADS)

Pokharel, Rajendra; Gavin, Sean; Moschelli, George

2012-10-01

Interest in the development of the theory of fluctuating hydrodynamics is growing [1]. Early efforts suggested that viscous diffusion broadens the rapidity dependence of transverse momentum correlations [2]. That work stimulated an experimental analysis by STAR [3]. We attack this new data along two fronts. First, we compute STAR's fluctuation observable using the NeXSPheRIO code, which combines fluctuating initial conditions from a string fragmentation model with deterministic viscosity-free hydrodynamic evolution. We find that NeXSPheRIO produces a longitudinal narrowing, in contrast to the data. Second, we study the hydrodynamic evolution using second order causal viscous hydrodynamics including Langevin noise. We obtain a deterministic evolution equation for the transverse momentum density correlation function. We use the latest theoretical equations of state and transport coefficients to compute STAR's observable. The results are in excellent accord with the measured broadening. In addition, we predict features of the distribution that can distinguish 2nd and 1st order diffusion. [4pt] [1] J. Kapusta, B. Mueller, M. Stephanov, arXiv:1112.6405 [nucl-th].[0pt] [2] S. Gavin and M. Abdel-Aziz, Phys. Rev. Lett. 97, 162302 (2006)[0pt] [3] H. Agakishiev et al., STAR, STAR, Phys. Lett. B704

Thermo-electric transport in gauge/gravity models with momentum dissipation

NASA Astrophysics Data System (ADS)

Amoretti, Andrea; Braggio, Alessandro; Maggiore, Nicola; Magnoli, Nicodemo; Musso, Daniele

2014-09-01

We present a systematic definition and analysis of the thermo-electric linear response in gauge/gravity systems focusing especially on models with massive gravity in the bulk and therefore momentum dissipation in the dual field theory. A precise treatment of finite counter-terms proves to be essential to yield a consistent physical picture whose hydrodynamic and beyond-hydrodynamics behaviors noticeably match with field theoretical expectations. The model furnishes a possible gauge/gravity description of the crossover from the quantum-critical to the disorder-dominated Fermi-liquid behaviors, as expected in graphene.

Kinetic Theory of Electronic Transport in Random Magnetic Fields

NASA Astrophysics Data System (ADS)

Lucas, Andrew

2018-03-01

We present the theory of quasiparticle transport in perturbatively small inhomogeneous magnetic fields across the ballistic-to-hydrodynamic crossover. In the hydrodynamic limit, the resistivity ρ generically grows proportionally to the rate of momentum-conserving electron-electron collisions at large enough temperatures T . In particular, the resulting flow of electrons provides a simple scenario where viscous effects suppress conductance below the ballistic value. This new mechanism for ρ ∝T2 resistivity in a Fermi liquid may describe low T transport in single-band SrTiO3 .

Kinetic Theory of Electronic Transport in Random Magnetic Fields.

PubMed

Lucas, Andrew

2018-03-16

We present the theory of quasiparticle transport in perturbatively small inhomogeneous magnetic fields across the ballistic-to-hydrodynamic crossover. In the hydrodynamic limit, the resistivity ρ generically grows proportionally to the rate of momentum-conserving electron-electron collisions at large enough temperatures T. In particular, the resulting flow of electrons provides a simple scenario where viscous effects suppress conductance below the ballistic value. This new mechanism for ρ∝T^{2} resistivity in a Fermi liquid may describe low T transport in single-band SrTiO_{3}.

The fluid mechanics of continuous flow electrophoresis in perspective

NASA Technical Reports Server (NTRS)

Saville, D. A.

1980-01-01

Buoyancy alters the flow in continuous flow electrophoresis chambers through the mechanism of hydrodynamic instability and, when the instability is supressed by careful cooling of the chamber boundaries, by restructuring the axial flow. The expanded roles of buoyancy follow upon adapting the size of the chamber and the electric field so as to fractionate certain sorts of cell populations. Scale-up problems, hydrodynamic stability and the altered flow fields are discussed to show how phenomena overlooked in the design and operations of narrow-gap devices take on an overwhelming importance in wide-gap chambers

Hydrodynamic stability and Ti-tracer distribution in low-adiabat OMEGA direct-drive implosions

NASA Astrophysics Data System (ADS)

Joshi, Tirtha R.

We discuss the hydrodynamic stability of low-adiabat OMEGA direct-drive implosions based on results obtained from simultaneous emission and absorption spectroscopy of a titanium tracer added to the target. The targets were deuterium filled, warm plastic shells of varying thicknesses and filling gas pressures with a submicron Ti-doped tracer layer initially located on the inner surface of the shell. The spectral features from the titanium tracer are observed during the deceleration and stagnation phases of the implosion, and recorded with a time integrated spectrometer (XRS1), streaked crystal spectrometer (SSCA) and three gated, multi-monochromatic X-ray imager (MMI) instruments fielded along quasi-orthogonal lines-of-sight. The time-integrated, streaked and gated data show simultaneous emission and absorption spectral features associated with titanium K-shell line transitions but only the MMI data provides spatially resolved information. The arrays of gated spectrally resolved images recorded with MMI were processed to obtain spatially resolved spectra characteristic of annular contour regions on the image. A multi-zone spectroscopic analysis of the annular spatially resolved spectra permits the extraction of plasma conditions in the core as well as the spatial distribution of tracer atoms. In turn, the titanium atom distribution provides direct evidence of tracer penetration into the core and thus of the hydrodynamic stability of the shell. The observations, timing and analysis indicate that during fuel burning the titanium atoms have migrated deep into the core and thus shell material mixing is likely to impact the rate of nuclear fusion reactions, i.e. burning rate, and the neutron yield of the implosion. We have found that the Ti atom number density decreases towards the center in early deceleration phase, but later in time the trend is just opposite, i.e., it increases towards the center of the implosion core. This is in part a consequence of the convergent effect of spherical geometry. The spatial profiles of Ti areal densities in the implosion core are extracted from space-resolved spectra and also evaluated using 1D spherical scaling. The trends are similar to the Ti number density spatial profiles. The areal densities extracted from data and 1D spherical scaling are very comparable in the outer spherical zones of the implosion core but significantly deviate in the innermost zone. We have observed that approximately 85% of the Ti atoms migrate into the hot core, while 15% of the atoms are still on the shell-fuel interface and contributing to the absorption. In addition, a method to extract the hot spot size based on the formation of the absorption feature in a sequence of annular spectra will be discussed. Results and trends are discussed as a function of target shell thickness and filling pressure, and laser pulse shape.

FESTR: Finite-Element Spectral Transfer of Radiation spectroscopic modeling and analysis code

DOE PAGES

Hakel, Peter

2016-10-01

Here we report on the development of a new spectral postprocessor of hydrodynamic simulations of hot, dense plasmas. Based on given time histories of one-, two-, and three-dimensional spatial distributions of materials, and their local temperature and density conditions, spectroscopically-resolved signals are computed. The effects of radiation emission and absorption by the plasma on the emergent spectra are simultaneously taken into account. This program can also be used independently of hydrodynamic calculations to analyze available experimental data with the goal of inferring plasma conditions.

Multiscale molecular dynamics/hydrodynamics implementation of two dimensional "Mercedes Benz" water model

NASA Astrophysics Data System (ADS)

Scukins, A.; Nerukh, D.; Pavlov, E.; Karabasov, S.; Markesteijn, A.

2015-09-01

A multiscale Molecular Dynamics/Hydrodynamics implementation of the 2D Mercedes Benz (MB or BN2D) [1] water model is developed and investigated. The concept and the governing equations of multiscale coupling together with the results of the two-way coupling implementation are reported. The sensitivity of the multiscale model for obtaining macroscopic and microscopic parameters of the system, such as macroscopic density and velocity fluctuations, radial distribution and velocity autocorrelation functions of MB particles, is evaluated. Critical issues for extending the current model to large systems are discussed.

FESTR: Finite-Element Spectral Transfer of Radiation spectroscopic modeling and analysis code

NASA Astrophysics Data System (ADS)

Hakel, Peter

2016-10-01

We report on the development of a new spectral postprocessor of hydrodynamic simulations of hot, dense plasmas. Based on given time histories of one-, two-, and three-dimensional spatial distributions of materials, and their local temperature and density conditions, spectroscopically-resolved signals are computed. The effects of radiation emission and absorption by the plasma on the emergent spectra are simultaneously taken into account. This program can also be used independently of hydrodynamic calculations to analyze available experimental data with the goal of inferring plasma conditions.

Study of Lambda polarization at RHIC BES and LHC energies

NASA Astrophysics Data System (ADS)

Karpenko, Iurii; Becattini, Francesco

2018-02-01

In hydrodynamic approach to relativistic heavy ion collisions, hadrons with nonzero spin, produced out of the hydrodynamic medium, can acquire polarization via spin-vorticity thermodynamic coupling mechanism. The hydrodynamical quantity steering the polarization is the thermal vorticity, that is minus the antisymmetric part of the gradient of four-temperature field. Based on this mechanism there have been several calculations in hydrodynamic and non-hydrodynamic models for non-central heavy ion collisions in the RHIC Beam Energy Scan energy range, showing that the amount of polarization of produced Λ hyperons ranges from few percents to few permille, and decreases with collision energy. We report on an extension of our existing calculation of global Λ polarization in UrQMD+vHLLE model to full RHIC and LHC energies, and discuss the component of polarization along the beam direction, which is the dominant one at high energies.

Riemann Solvers in Relativistic Hydrodynamics: Basics and Astrophysical Applications

NASA Astrophysics Data System (ADS)

Ibanez, Jose M.

2001-12-01

My contribution to these proceedings summarizes a general overview on t High Resolution Shock Capturing methods (HRSC) in the field of relativistic hydrodynamics with special emphasis on Riemann solvers. HRSC techniques achieve highly accurate numerical approximations (formally second order or better) in smooth regions of the flow, and capture the motion of unresolved steep gradients without creating spurious oscillations. In the first part I will show how these techniques have been extended to relativistic hydrodynamics, making it possible to explore some challenging astrophysical scenarios. I will review recent literature concerning the main properties of different special relativistic Riemann solvers, and discuss several 1D and 2D test problems which are commonly used to evaluate the performance of numerical methods in relativistic hydrodynamics. In the second part I will illustrate the use of HRSC methods in several astrophysical applications where special and general relativistic hydrodynamical processes play a crucial role.

Nonstationary magnetosonic wave dynamics in plasmas exhibiting collapse.

PubMed

Chakrabarti, Nikhil; Maity, Chandan; Schamel, Hans

2013-08-01

In a Lagrangian fluid approach, an explicit method has been presented previously to obtain an exact nonstationary magnetosonic-type wave solution in compressible magnetized plasmas of arbitrary resistivity showing competition among hydrodynamic convection, magnetic field diffusion, and dispersion [Chakrabarti et al., Phys. Rev. Lett. 106, 145003 (2011)]. The purpose of the present work is twofold: it serves (i) to describe the physical and mathematical background of the involved magnetosonic wave dynamics in more detail, as proposed by our original Letter, and (ii) to present an alternative approach, which utilizes the Lagrangian mass variable as a new spatial coordinate [Schamel, Phys. Rep. 392, 279 (2004)]. The obtained exact nonlinear wave solutions confirm the correctness of our previous results, indicating a collapse of the magnetic field irrespective of the presence of dispersion and resistivity. The mean plasma density, on the other hand, is less singular, showing collapse only when dispersive effects are negligible. These results may contribute to our understanding of the generation of strongly localized magnetic fields (and currents) in plasmas, and they are expected to be of special importance in the astrophysical context of magnetic star formation.

Evolutionary sheath structure in magnetized collisionless plasma with electron inertia

NASA Astrophysics Data System (ADS)

Gohain, M.; Karmakar, P. K.

2017-09-01

A classical hydrodynamic model is methodologically formulated to see the equilibrium properties of a planar plasma sheath in two-component magnetized bounded plasma. It incorporates the weak but finite electron inertia instead of asymptotically inertialess electrons. The effects of the externally applied oblique (relative to the bulk plasma flow) magnetic field are judiciously accented. It is, for the sake of simplicity, assumed that the relevant physical parameters (plasma density, electrostatic potential, and flow velocity) vary only in a direction normal to the confining wall boundary. It is noticed for the first time that the derived Bohm condition for sheath formation is modified conjointly by the electron inertia, magnetic field, and field orientation. It is manifested that the electron inertia in the presence of plasma gyrokinetic effects slightly enhances the ion Mach threshold value (typically, M i0 ≥ 1.139) toward the sheath entrance. This flow supercriticality is in contrast with the heuristic formalism ( M i0 ≥ 1) for the zero-inertia electrons. A numerical illustrative scheme on the parametric sheath features on diverse nontrivial apposite arguments is constructed alongside ameliorative scope.

Optimizing BAO measurements with non-linear transformations of the Lyman-α forest

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

Wang, Xinkang; Font-Ribera, Andreu; Seljak, Uroš, E-mail: xinkang.wang@berkeley.edu, E-mail: afont@lbl.gov, E-mail: useljak@berkeley.edu

2015-04-01

We explore the effect of applying a non-linear transformation to the Lyman-α forest transmitted flux F=e{sup −τ} and the ability of analytic models to predict the resulting clustering amplitude. Both the large-scale bias of the transformed field (signal) and the amplitude of small scale fluctuations (noise) can be arbitrarily modified, but we were unable to find a transformation that increases significantly the signal-to-noise ratio on large scales using Taylor expansion up to the third order. In particular, however, we achieve a 33% improvement in signal to noise for Gaussianized field in transverse direction. On the other hand, we explore anmore » analytic model for the large-scale biasing of the Lyα forest, and present an extension of this model to describe the biasing of the transformed fields. Using hydrodynamic simulations we show that the model works best to describe the biasing with respect to velocity gradients, but is less successful in predicting the biasing with respect to large-scale density fluctuations, especially for very nonlinear transformations.« less

Response theory of the ergodic many-body delocalized phase: Keldysh Finkel'stein sigma models and the 10-fold way

NASA Astrophysics Data System (ADS)

Liao, Yunxiang; Levchenko, Alex; Foster, Matthew S.

2017-11-01

We derive the finite temperature Keldysh response theory for interacting fermions in the presence of quenched short-ranged disorder, as applicable to any of the 10 Altland-Zirnbauer classes in an Anderson delocalized phase with at least a U(1) continuous symmetry. In this formulation of the interacting Finkel'stein nonlinear sigma model, the statistics of one-body wave functions are encoded by the constrained matrix field, while physical correlations follow from the hydrodynamic density or spin response field, which decouples the interactions. Integrating out the matrix field first, we obtain weak (anti) localization and Altshuler-Aronov quantum conductance corrections from the hydrodynamic response function. This procedure automatically incorporates the correct infrared cutoff physics, and in particular gives the Altshuler-Aronov-Khmelnitsky (AAK) equations for dephasing of weak (anti)localization due to electron-electron collisions. We explicate the method by deriving known quantumcorrections in two dimensions for the symplectic metal class AII, as well as the spin-SU(2) invariant superconductor classes C and CI. We show that quantum conductance corrections due to the special modes at zero energy in nonstandard classes are automatically cut off by temperature, as previously expected, while the Wigner-Dyson class Cooperon modes that persist to all energies are cut by dephasing. We also show that for short-ranged interactions, the standard self-consistent solution for the dephasing rate is equivalent to a particular summation of diagrams via the self-consistent Born approximation. This should be compared to the corresponding AAK solution for long-ranged Coulomb interactions, which exploits the Markovian noise correlations induced by thermal fluctuations of the electromagnetic field. We discuss prospects for exploring the many-body localization transition as a dephasing catastrophe in short-range interacting models, as encountered by approaching from the ergodic side.

Characterization and modeling of turbidity density plume induced into stratified reservoir by flood runoffs.

PubMed

Chung, S W; Lee, H S

2009-01-01

In monsoon climate area, turbidity flows typically induced by flood runoffs cause numerous environmental impacts such as impairment of fish habitat and river attraction, and degradation of water supply efficiency. This study was aimed to characterize the physical dynamics of turbidity plume induced into a stratified reservoir using field monitoring and numerical simulations, and to assess the effect of different withdrawal scenarios on the control of downstream water quality. Three different turbidity models (RUN1, RUN2, RUN3) were developed based on a two-dimensional laterally averaged hydrodynamic and transport model, and validated against field data. RUN1 assumed constant settling velocity of suspended sediment, while RUN2 estimated the settling velocity as a function of particle size, density, and water temperature to consider vertical stratification. RUN3 included a lumped first-order turbidity attenuation rate taking into account the effects of particles aggregation and degradable organic particles. RUN3 showed best performance in replicating the observed variations of in-reservoir and release turbidity. Numerical experiments implemented to assess the effectiveness of different withdrawal depths showed that the alterations of withdrawal depth can modify the pathway and flow regimes of the turbidity plume, but its effect on the control of release water quality could be trivial.

Simulation of Cosmic Ray Acceleration, Propagation and Interaction in SNR Environment

NASA Astrophysics Data System (ADS)

Lee, S. H.; Kamae, T.; Ellison, D. C.

2007-07-01

Recent studies of young supernova remnants (SNRs) with Chandra, XMM, Suzaku and HESS have revealed complex morphologies and spectral features of the emission sites. The critical question of the relative importance of the two competing gamma-ray emission mechanisms in SNRs; inverse-Compton scattering by high-energy electrons and pion production by energetic protons, may be resolved by GLAST-LAT. To keep pace with the improved observations, we are developing a 3D model of particle acceleration, diffusion, and interaction in a SNR where broad-band emission from radio to multi-TeV energies, produced by shock accelerated electrons and ions, can be simulated for a given topology of shock fronts, magnetic field, and ISM densities. The 3D model takes as input, the particle spectra predicted by a hydrodynamic simulation of SNR evolution where nonlinear diffusive shock acceleration is coupled to the remnant dynamics (e.g., Ellison, Decourchelle & Ballet; Ellison & Cassam-Chenai Ellison, Berezhko & Baring). We will present preliminary models of the Galactic Ridge SNR RX J1713-3946 for selected choices of SNR parameters, magnetic field topology, and ISM density distributions. When constrained by broad-band observations, our models should predict the extent of coupling between spectral shape and morphology and provide direct information on the acceleration efficiency of cosmic-ray electrons and ions in SNRs.

Molecular hydrodynamics: Vortex formation and sound wave propagation

DOE PAGES

Han, Kyeong Hwan; Kim, Changho; Talkner, Peter; ...

2018-01-14

In the present study, quantitative feasibility tests of the hydrodynamic description of a two-dimensional fluid at the molecular level are performed, both with respect to length and time scales. Using high-resolution fluid velocity data obtained from extensive molecular dynamics simulations, we computed the transverse and longitudinal components of the velocity field by the Helmholtz decomposition and compared them with those obtained from the linearized Navier-Stokes (LNS) equations with time-dependent transport coefficients. By investigating the vortex dynamics and the sound wave propagation in terms of these field components, we confirm the validity of the LNS description for times comparable to ormore » larger than several mean collision times. The LNS description still reproduces the transverse velocity field accurately at smaller times, but it fails to predict characteristic patterns of molecular origin visible in the longitudinal velocity field. Based on these observations, we validate the main assumptions of the mode-coupling approach. The assumption that the velocity autocorrelation function can be expressed in terms of the fluid velocity field and the tagged particle distribution is found to be remarkably accurate even for times comparable to or smaller than the mean collision time. This suggests that the hydrodynamic-mode description remains valid down to the molecular scale.« less

Molecular hydrodynamics: Vortex formation and sound wave propagation

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

Han, Kyeong Hwan; Kim, Changho; Talkner, Peter

In the present study, quantitative feasibility tests of the hydrodynamic description of a two-dimensional fluid at the molecular level are performed, both with respect to length and time scales. Using high-resolution fluid velocity data obtained from extensive molecular dynamics simulations, we computed the transverse and longitudinal components of the velocity field by the Helmholtz decomposition and compared them with those obtained from the linearized Navier-Stokes (LNS) equations with time-dependent transport coefficients. By investigating the vortex dynamics and the sound wave propagation in terms of these field components, we confirm the validity of the LNS description for times comparable to ormore » larger than several mean collision times. The LNS description still reproduces the transverse velocity field accurately at smaller times, but it fails to predict characteristic patterns of molecular origin visible in the longitudinal velocity field. Based on these observations, we validate the main assumptions of the mode-coupling approach. The assumption that the velocity autocorrelation function can be expressed in terms of the fluid velocity field and the tagged particle distribution is found to be remarkably accurate even for times comparable to or smaller than the mean collision time. This suggests that the hydrodynamic-mode description remains valid down to the molecular scale.« less

Modeling and measurement of electrostatic spray behavior in a rectangular throat of Pease-Anthony venturi scrubber.

PubMed

Yang, H T; Viswanathan, S; Balachandran, W; Ray, M B

2003-06-01

This paper presents the simulation and experimental results of the distribution of droplets produced by electrostatic nozzles inside a venturi scrubber. The simulation model takes into account initial liquid momentum, hydrodynamic, gravitational and electric forces, and eddy diffusion. The velocity and concentration profile of charged droplets injected from an electrostatic nozzle in the scrubber under the combined influence of hydrodynamic and electric fields were simulated. The effects of operating parameters, such as gas velocity, diameter of the scrubbing droplets, charge-to-mass ratio, and liquid-to-gas ratio on the distribution of the water droplets within the scrubber, were also investigated. The flux distribution of scrubbing liquid in the presence of electric field is improved considerably over a conventional venturi scrubber, and the effect increases with the increase in charge-to-mass ratio. Improved flux distribution using charged droplets increases the calculated overall collection efficiency of the submicron particles. However, the effect of an electric field on the droplet distribution pattern for small drop sizes in strong hydrodynamic field conditions is negligible. Simulated results are in good agreement with the experimental data obtained in the laboratory.

Mass loss from inhomogeneous hot star winds. I. Resonance line formation in 2D models

NASA Astrophysics Data System (ADS)

Sundqvist, J. O.; Puls, J.; Feldmeier, A.

2010-01-01

Context. The mass-loss rate is a key parameter of hot, massive stars. Small-scale inhomogeneities (clumping) in the winds of these stars are conventionally included in spectral analyses by assuming optically thin clumps, a void inter-clump medium, and a smooth velocity field. To reconcile investigations of different diagnostics (in particular, unsaturated UV resonance lines vs. Hα/radio emission) within such models, a highly clumped wind with very low mass-loss rates needs to be invoked, where the resonance lines seem to indicate rates an order of magnitude (or even more) lower than previously accepted values. If found to be realistic, this would challenge the radiative line-driven wind theory and have dramatic consequences for the evolution of massive stars. Aims: We investigate basic properties of the formation of resonance lines in small-scale inhomogeneous hot star winds with non-monotonic velocity fields. Methods: We study inhomogeneous wind structures by means of 2D stochastic and pseudo-2D radiation-hydrodynamic wind models, constructed by assembling 1D snapshots in radially independent slices. A Monte-Carlo radiative transfer code, which treats the resonance line formation in an axially symmetric spherical wind (without resorting to the Sobolev approximation), is presented and used to produce synthetic line spectra. Results: The optically thin clumping limit is only valid for very weak lines. The detailed density structure, the inter-clump medium, and the non-monotonic velocity field are all important for the line formation. We confirm previous findings that radiation-hydrodynamic wind models reproduce observed characteristics of strong lines (e.g., the black troughs) without applying the highly supersonic “microturbulence” needed in smooth models. For intermediate strong lines, the velocity spans of the clumps are of central importance. Current radiation-hydrodynamic models predict spans that are too large to reproduce observed profiles unless a very low mass-loss rate is invoked. By simulating lower spans in 2D stochastic models, the profile strengths become drastically reduced, and are consistent with higher mass-loss rates. To simultaneously meet the constraints from strong lines, the inter-clump medium must be non-void. A first comparison to the observed Phosphorus V doublet in the O6 supergiant λ Cep confirms that line profiles calculated from a stochastic 2D model reproduce observations with a mass-loss rate approximately ten times higher than that derived from the same lines but assuming optically thin clumping. Tentatively this may resolve discrepancies between theoretical predictions, evolutionary constraints, and recent derived mass-loss rates, and suggests a re-investigation of the clump structure predicted by current radiation-hydrodynamic models.

Hydrodynamic Instability and Thermal Coupling in a Dynamic Model of Liquid-Propellant Combustion

NASA Technical Reports Server (NTRS)

Margolis, S. B.

1999-01-01

For liquid-propellant combustion, the Landau/Levich hydrodynamic models have been combined and extended to account for a dynamic dependence of the burning rate on the local pressure and temperature fields. Analysis of these extended models is greatly facilitated by exploiting the realistic smallness of the gas-to-liquid density ratio rho. Neglecting thermal coupling effects, an asymptotic expression was then derived for the cellular stability boundary A(sub p)(k) where A(sub p) is the pressure sensitivity of the burning rate and k is the disturbance wavenumber. The results explicitly indicate the stabilizing effects of gravity on long-wave disturbances, and those of viscosity and surface tension on short-wave perturbations, and the instability associated with intermediate wavenumbers for critical negative values of A(sub p). In the limit of weak gravity, hydrodynamic instability in liquid-propellant combustion becomes a long-wave, instability phenomenon, whereas at normal gravity, this instability is first manifested through O(1) wavenumbers. In addition, surface tension and viscosity (both liquid and gas) each produce comparable effects in the large-wavenumber regime, thereby providing important modifications to the previous analyses in which one or more of these effects was neglected. For A(sub p)= O, the Landau/Levich results are recovered in appropriate limiting cases, although this typically corresponds to a hydrodynamically unstable parameter regime for p << 1. In addition to the classical cellular form of hydrodynamic stability, there exists a pulsating form corresponding to the loss of stability of steady, planar burning to time-dependent perturbations. This occurs for negative values of the parameter A(sub p), and is thus absent from the original Landau/Levich models. In the extended model, however, there exists a stable band of negative pressure sensitivities bounded above by the Landau type of instability, and below by this pulsating form of hydrodynamic instability. Indeed, nonsteady modes of combustion have been observed at low pressures in hydroxylammonium nitrate (HAN)-based liquid propellants, which often exhibit negative pressure sensitivities. While nonsteady combustion may correspond to secondary and higher-order bifurcations above the cellular boundary, it may also be a manifestation of this pulsating type of hydrodynamic instability. In the present work, a nonzero temperature sensitivity is incorporated into our previous asymptotic analyses. This entails a coupling of the energy equation to the previous purely hydrodynamic problem, and leads to a significant modification of the pulsating boundary such that, for sufficiently large values of the temperature-sensitivity parameter, liquid-propellant combustion can become intrinsically unstable to this alternative form of hydrodynamic instability. For simplicity, further attention is confined here to the inviscid version of the problem since, despite the fact that viscous and surface-tension effects are comparable, the qualitative nature of the cellular boundary remains preserved in the zero-viscosity limit, as does the existence of the pulsating boundary. The mathematical model adopts the classical assumption that there is no distributed reaction in either the liquid or gas phases, but now the reaction sheet, representing either a pyrolysis reaction or an exothermic decomposition at the liquid/gas interface, is assumed to depend on local conditions there.

Circulation and physical processes within the San Gabriel River Estuary during summer 2005

USGS Publications Warehouse

Rosenberger, Kurt J.; Xu, Jingping; Stein, Eric D.; Noble, Marlene A.; Gartner, Anne L.

2007-01-01

The Southern California Coastal Water Research Project (SCCWRP) is developing a hydrodynamic model of the SGR estuary, which is part of the comprehensive water-quality model of the SGR estuary and watershed investigated by SCCWRP and other local agencies. The hydrodynamic model will help understanding of 1) the exchange processes between the estuary and coastal ocean; 2) the circulation patterns in the estuary; 3) upstream natural runoff and the cooling discharge from PGS. Like all models, the SGR hydrodynamic model is only useful after it is fully calibrated and validated. In May 2005, SCCWRP requested the assistance of the U.S. geological Survey (USGS) Coastal and Marine Geology team (CMG) in collecting data on the hydrodynamic conditions in the estuary during the summer dry season. The summer was chosen for field data collection as this was assumed to be the season with the greatest potential for chronic degraded water quality due to low river flow and high thermal stratification within the estuary (due to both higher average air temperature and PGS output). Water quality can be degraded in winter as well, when higher river discharge events bring large volumes of water from the Los Angeles basin into the estuary. The objectives of this project were to 1) collect hydrodynamic data along the SGR estuary; 2) study exchange processes within the estuary through analysis of the hydrodynamic data; and 3) provide field data for model calibration and validation. As the data only exist for the summer season, the results herein only apply to summer conditions.

Coalescing neutron stars - a step towards physical models. I. Hydrodynamic evolution and gravitational-wave emission.

NASA Astrophysics Data System (ADS)

Ruffert, M.; Janka, H.-T.; Schaefer, G.

1996-07-01

We investigate the dynamics and evolution of coalescing neutron stars. The three-dimensional Newtonian equations of hydrodynamics are integrated by the "Piecewise Parabolic Method" on an equidistant Cartesian grid with a resolution of 64^3^ or 128^3^. Although the code is purely Newtonian, we do include the emission of gravitational waves and their backreaction on the hydrodynamic flow. The properties of neutron star matter are described by the physical equation of state of Lattimer & Swesty (1991). In addition to the fundamental hydrodynamic quantities, density, momentum, and energy, we follow the time evolution of the electron density in the stellar gas. Energy loss by all types of neutrinos and changes of the electron fraction due to the emission of electron neutrinos and antineutrinos are taken into account by an elaborate "neutrino leakage scheme". We simulate the coalescence of two identical, cool neutron stars with a baryonic mass of =~1.6Msun_ and a radius of =~15km and with an initial center-to-center distance of 42km. The initial distributions of density and electron concentration are given from a model of a cold neutron star in hydrostatic equilibrium, the temperature in our initial models is increased such that the thermal energy is about 3% of the degeneracy energy for given density and electron fraction (central temperature about 8MeV). We investigate three cases which differ by the initial velocity distribution in the neutron stars, representing different cases of the neutron star spins relative to the direction of the orbital angular momentum vector. The orbit decays due to gravitational-wave emission, and after half a revolution the stars are so close that dynamical instability sets in. Within about 1ms they merge into a rapidly spinning (P_spin_=~1ms), high-density body (ρ=~10^14^g/cm^3^) with a surrounding thick disk of material with densities ρ=~10^10^-10^12^g/cm^3^ and orbital velocities of 0.3-0.5c. In this work we evaluate the models in detail with respect to the gravitational wave emission using the quadrupole approximation. In a forthcoming paper we will concentrate on the neutrino emission and implications for gamma-ray bursters. The peak emission of gravitational waves is short but powerful. A maximum luminosity in excess of 10^55^erg/s is reached for about 1ms. The amplitudes of the gravitational waves are close to 3x10^-23^ at a distance of 1Gpc, and the typical frequencies are between 1KHz and 2KHz, near the dynamical frequency of the orbital motion of the merging and coalescing neutron stars. In contrast to the diverging gravitational wave amplitude of two coalescing point-masses, our models show decreasing amplitudes of the waves because of the finite extension of the neutron stars and the nearly spherical shape of the merged object toward the end of the simulations. The structure and temporal development of the gravitational wave signal and energy spectrum show systematic trends with the amount of angular momentum in the system and depend on the details of the hydrodynamic mass motions.

Radiation from Accelerated Particles in Shocks and Reconnections

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Zhang, B.; Niemiec, J.; Medvedev, M.; Hardee, P.; Mizuno, Y.; Nordlund, A.; Frederiksen, J. T.; Sol, H.; Pohl, M.;

Exploring Astrophysical Magnetohydrodynamics in the Laboratory

NASA Astrophysics Data System (ADS)

Manuel, Mario

2014-10-01

Plasma evolution in many astrophysical systems is dominated by magnetohydrodynamics. Specifically of interest to this talk are collimated outflows from accretion systems. Away from the central object, the Euler equations can represent the plasma dynamics well and may be scaled to a laboratory system. We have performed experiments to investigate the effects of a background magnetic field on an otherwise hydrodynamically collimated plasma. Laser-irradiated, cone targets produce hydrodynamically collimated plasma jets and a pulse-powered solenoid provides a constant background magnetic field. The application of this field is shown to completely disrupt the original flow and a new magnetically-collimated, hollow envelope is produced. Results from these experiments and potential implications for their astrophysical analogs will be discussed.

Non-linear, non-monotonic effect of nano-scale roughness on particle deposition in absence of an energy barrier: Experiments and modeling

PubMed Central

Jin, Chao; Glawdel, Tomasz; Ren, Carolyn L.; Emelko, Monica B.

2015-01-01

Deposition of colloidal- and nano-scale particles on surfaces is critical to numerous natural and engineered environmental, health, and industrial applications ranging from drinking water treatment to semi-conductor manufacturing. Nano-scale surface roughness-induced hydrodynamic impacts on particle deposition were evaluated in the absence of an energy barrier to deposition in a parallel plate system. A non-linear, non-monotonic relationship between deposition surface roughness and particle deposition flux was observed and a critical roughness size associated with minimum deposition flux or “sag effect” was identified. This effect was more significant for nanoparticles (<1 μm) than for colloids and was numerically simulated using a Convective-Diffusion model and experimentally validated. Inclusion of flow field and hydrodynamic retardation effects explained particle deposition profiles better than when only the Derjaguin-Landau-Verwey-Overbeek (DLVO) force was considered. This work provides 1) a first comprehensive framework for describing the hydrodynamic impacts of nano-scale surface roughness on particle deposition by unifying hydrodynamic forces (using the most current approaches for describing flow field profiles and hydrodynamic retardation effects) with appropriately modified expressions for DLVO interaction energies, and gravity forces in one model and 2) a foundation for further describing the impacts of more complicated scales of deposition surface roughness on particle deposition. PMID:26658159

Non-linear, non-monotonic effect of nano-scale roughness on particle deposition in absence of an energy barrier: Experiments and modeling

NASA Astrophysics Data System (ADS)

Jin, Chao; Glawdel, Tomasz; Ren, Carolyn L.; Emelko, Monica B.

2015-12-01

Deposition of colloidal- and nano-scale particles on surfaces is critical to numerous natural and engineered environmental, health, and industrial applications ranging from drinking water treatment to semi-conductor manufacturing. Nano-scale surface roughness-induced hydrodynamic impacts on particle deposition were evaluated in the absence of an energy barrier to deposition in a parallel plate system. A non-linear, non-monotonic relationship between deposition surface roughness and particle deposition flux was observed and a critical roughness size associated with minimum deposition flux or “sag effect” was identified. This effect was more significant for nanoparticles (<1 μm) than for colloids and was numerically simulated using a Convective-Diffusion model and experimentally validated. Inclusion of flow field and hydrodynamic retardation effects explained particle deposition profiles better than when only the Derjaguin-Landau-Verwey-Overbeek (DLVO) force was considered. This work provides 1) a first comprehensive framework for describing the hydrodynamic impacts of nano-scale surface roughness on particle deposition by unifying hydrodynamic forces (using the most current approaches for describing flow field profiles and hydrodynamic retardation effects) with appropriately modified expressions for DLVO interaction energies, and gravity forces in one model and 2) a foundation for further describing the impacts of more complicated scales of deposition surface roughness on particle deposition.

Vertical structure of currents in Algeciras Bay (Strait of Gibraltar): implications on oil spill modeling under different typical scenarios

NASA Astrophysics Data System (ADS)

Megías Trujillo, Bárbara; Caballero de Frutos, Isabel; López Comi, Laura; Tejedor Alvarez, Begoña.; Izquierdo González, Alfredo; Gonzales Mejías, Carlos Jose; Alvarez Esteban, Óscar; Mañanes Salinas, Rafael; Comerma, Eric

2010-05-01

Algeciras Bay constitutes a physical environment of special characteristics, due to its bathymetric configuration and geographical location, at the eastern boundary of the Strait of Gibraltar. Hence, the Bay is subject to the complex hydrodynamics of the Strait of Gibraltar, characterized by a mesotidal, semidiurnal regime and the high density-stratification of the water column due to the presence of the upper Atlantic and the lower Mediterranean (more salty and cold) water layers. In addition, this environment is affected by powerful Easterly and Westerly winds episodes. The intense maritime traffic of oil tankers sailing across the Strait and inside the Bay, together with the presence of an oil refinery at its northern coast, imply high risks of oil spilling inside these waters, and unfortunately it has constituted a matter of usual occurrence through the last decades. The above paragraph clearly manifests the necessity of a detailed knowledge on the Bay's hydrodynamics, and the related system of currents, for a correct management and contingency planning in case of oil spilling in this environment. In order to evaluate the range of affectation of oil spills in the Bay's waters and coasts, the OILMAP oil spill model was used, the currents fields being provided by the three-dimensional, nonlinear, finite-differences, sigma-coordinates, UCA 3D hydrodynamic model. Numerical simulations were carried out for a grid domain extended from the western Strait boundary to the Alboran Sea, having a horizontal spatial resolution of 500 m and 50 sigma-levels in the vertical dimension. The system was forced by the tidal constituents M2 (main semidiurnal) and Z0 (constant or zero-frequency), considering three different typical wind conditions: Easterlies, Westerlies and calm (no wind). The most remarkable results from the numerical 3D simulations of Algeciras Bay's hydrodynamics were: a) the occurrence of opposite tidal currents between the upper Atlantic and lower Mediterranean water layers (i.e., there is a phase-lag of about 180° among them); b) the presence of high-frequency perturbations due to the penetration of internal waves; and c) high variability in the vertical profiles of both tidal and residual (mean) currents. All these phenomena contribute to obtain differences between the water-surface currents and their depth-averaged values (as they are provided by most of 2D hydrodynamic models). Resultant currents from the 3D numerical simulations were implemented into the OILMAP model to evaluate the response of a control oil spill inside Algeciras Bay, considering different scenarios. Results were analyzed focusing in the differences between the more realistic surface currents fields given by the UCA 3D model and the depth averaged fields provided by faster 2D schemes, as well as the influence of implementations of wind effects having different complexities. The relative adequacy between the more accurate (but more expensive in computational time) and the faster (but more unrealistic) modeling strategies, especially in cases of emergency and very short decision times, was discussed.

Gas-solid fluidized bed reactors: Scale-up, flow regimes identification and hydrodynamics

NASA Astrophysics Data System (ADS)

Zaid, Faraj Muftah

This research studied the scale-up, flow regimes identification and hydrodynamics of fluidized beds using 6-inch and 18- inch diameter columns and different particles. One of the objectives was to advance the scale-up of gas-solid fluidized bed reactors by developing a new mechanistic methodology for hydrodynamic similarity based on matching the radial or diameter profile of gas phase holdup, since gas dynamics dictate the hydrodynamics of these reactors. This has been successfully achieved. However, the literature reported scale-up methodology based on matching selected dimensionless groups was examined and it was found that it was not easy to match the dimensionless groups and hence, there was some deviation in the hydrodynamics of the studied two different fluidized beds. A new technique based on gamma ray densitometry (GRD) was successfully developed and utilized to on-line monitor the implementation of scale-up, to identify the flow regime, and to measure the radial or diameter profiles of gas and solids holdups. CFD has been demonstrated as a valuable tool to enable the implementation of the newly developed scale-up methodology based on finding the conditions that provide similar or closer radial profile or cross sectional distribution of the gas holdup. As gas velocity increases, solids holdup in the center region of the column decreases in the fully developed region of both 6 inch and 18 inch diameter columns. Solids holdup increased with the increase in the particles size and density. Upflowing particles velocity increased with the gas velocity and became steeper at high superficial gas velocity at all axial heights where the center line velocity became higher than that in the wall region. Smaller particles size and lower density gave larger upflowing particles velocity. Minimum fluidization velocity and transition velocity from bubbly to churn turbulent flow regimes were found to be lower in 18 inch diameter column compared to those obtained in 6 inch diameter column. Also the absolute fluctuation of upflowing particles velocity multiplied by solids holdups vś 3ś as one of the terms for solids mass flux estimation was found to be larger in 18-inch diameter column than that in 6-inch diameter column using same particles size and density.

General framework for fluctuating dynamic density functional theory

NASA Astrophysics Data System (ADS)

Durán-Olivencia, Miguel A.; Yatsyshin, Peter; Goddard, Benjamin D.; Kalliadasis, Serafim

2017-12-01

We introduce a versatile bottom-up derivation of a formal theoretical framework to describe (passive) soft-matter systems out of equilibrium subject to fluctuations. We provide a unique connection between the constituent-particle dynamics of real systems and the time evolution equation of their measurable (coarse-grained) quantities, such as local density and velocity. The starting point is the full Hamiltonian description of a system of colloidal particles immersed in a fluid of identical bath particles. Then, we average out the bath via Zwanzig’s projection-operator techniques and obtain the stochastic Langevin equations governing the colloidal-particle dynamics. Introducing the appropriate definition of the local number and momentum density fields yields a generalisation of the Dean-Kawasaki (DK) model, which resembles the stochastic Navier-Stokes description of a fluid. Nevertheless, the DK equation still contains all the microscopic information and, for that reason, does not represent the dynamical law of observable quantities. We address this controversial feature of the DK description by carrying out a nonequilibrium ensemble average. Adopting a natural decomposition into local-equilibrium and nonequilibrium contribution, where the former is related to a generalised version of the canonical distribution, we finally obtain the fluctuating-hydrodynamic equation governing the time-evolution of the mesoscopic density and momentum fields. Along the way, we outline the connection between the ad hoc energy functional introduced in previous DK derivations and the free-energy functional from classical density-functional theory. The resultant equation has the structure of a dynamical density-functional theory (DDFT) with an additional fluctuating force coming from the random interactions with the bath. We show that our fluctuating DDFT formalism corresponds to a particular version of the fluctuating Navier-Stokes equations, originally derived by Landau and Lifshitz. Our framework thus provides the formal apparatus for ab initio derivations of fluctuating DDFT equations capable of describing the dynamics of soft-matter systems in and out of equilibrium.

Analytical study of acoustically perturbed Brillouin active magnetized semiconductor plasma

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

Shukla, Arun, E-mail: arunshuklaujn@gmail.com; Jat, K. L.

2015-07-31

An analytical study of acoustically perturbed Brillouin active magnetized semiconductor plasma has been reported. In the present analytical investigation, the lattice displacement, acousto-optical polarization, susceptibility, acousto-optical gain constant arising due to the induced nonlinear current density and acousto-optical process are deduced in an acoustically perturbed Brillouin active magnetized semiconductor plasma using the hydrodynamical model of plasma and coupled mode scheme. The influence of wave number and magnetic field has been explored. The analysis has been applied to centrosymmetric crystal. Numerical estimates are made for n-type InSb crystal duly irradiated by a frequency doubled 10.6 µm CO{sub 2} laser. It is foundmore » that lattice displacement, susceptibility and acousto-optical gain increase linearly with incident wave number and applied dc magnetic field, while decrease with scattering angle. The gain also increases with electric amplitude of incident laser beam. Results are found to be well in agreement with available literature.« less

Phase-field crystal modeling of heteroepitaxy and exotic modes of crystal nucleation

NASA Astrophysics Data System (ADS)

Podmaniczky, Frigyes; Tóth, Gyula I.; Tegze, György; Pusztai, Tamás; Gránásy, László

2017-01-01

We review recent advances made in modeling heteroepitaxy, two-step nucleation, and nucleation at the growth front within the framework of a simple dynamical density functional theory, the Phase-Field Crystal (PFC) model. The crystalline substrate is represented by spatially confined periodic potentials. We investigate the misfit dependence of the critical thickness in the StranskiKrastanov growth mode in isothermal studies. Apparently, the simulation results for stress release via the misfit dislocations fit better to the PeopleBean model than to the one by Matthews and Blakeslee. Next, we investigate structural aspects of two-step crystal nucleation at high undercoolings, where an amorphous precursor forms in the first stage. Finally, we present results for the formation of new grains at the solid-liquid interface at high supersaturations/supercoolings, a phenomenon termed Growth Front Nucleation (GFN). Results obtained with diffusive dynamics (applicable to colloids) and with a hydrodynamic extension of the PFC theory (HPFC, developed for simple liquids) will be compared. The HPFC simulations indicate two possible mechanisms for GFN.

Dynamical mean-field theory and weakly non-linear analysis for the phase separation of active Brownian particles

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

Speck, Thomas; Menzel, Andreas M.; Bialké, Julian

2015-06-14

Recently, we have derived an effective Cahn-Hilliard equation for the phase separation dynamics of active Brownian particles by performing a weakly non-linear analysis of the effective hydrodynamic equations for density and polarization [Speck et al., Phys. Rev. Lett. 112, 218304 (2014)]. Here, we develop and explore this strategy in more detail and show explicitly how to get to such a large-scale, mean-field description starting from the microscopic dynamics. The effective free energy emerging from this approach has the form of a conventional Ginzburg-Landau function. On the coarsest scale, our results thus agree with the mapping of active phase separation ontomore » that of passive fluids with attractive interactions through a global effective free energy (motility-induced phase transition). Particular attention is paid to the square-gradient term necessary for the phase separation kinetics. We finally discuss results from numerical simulations corroborating the analytical results.« less

Momentum and charge transport in non-relativistic holographic fluids from Hořava gravity

NASA Astrophysics Data System (ADS)

Davison, Richard A.; Grozdanov, Sašo; Janiszewski, Stefan; Kaminski, Matthias

2016-11-01

We study the linearized transport of transverse momentum and charge in a conjectured field theory dual to a black brane solution of Hořava gravity with Lifshitz exponent z = 1. As expected from general hydrodynamic reasoning, we find that both of these quantities are diffusive over distance and time scales larger than the inverse temperature. We compute the diffusion constants and conductivities of transverse momentum and charge, as well the ratio of shear viscosity to entropy density, and find that they differ from their relativistic counterparts. To derive these results, we propose how the holographic dictionary should be modified to deal with the multiple horizons and differing propagation speeds of bulk excitations in Hořava gravity. When possible, as a check on our methods and results, we use the covariant Einstein-Aether formulation of Hořava gravity, along with field redefinitions, to re-derive our results from a relativistic bulk theory.

Enhanced proton acceleration from an ultrathin target irradiated by laser pulses with plateau ASE.

PubMed

Wang, Dahui; Shou, Yinren; Wang, Pengjie; Liu, Jianbo; Li, Chengcai; Gong, Zheng; Hu, Ronghao; Ma, Wenjun; Yan, Xueqing

2018-02-07

We report a simulation study on proton acceleration driven by ultraintense laser pulses with normal contrast (10 7 -10 9 ) containing nanosecond plateau amplified spontaneous emission (ASE). It's found in hydrodynamic simulations that if the thickness of the targets lies in the range of hundreds nanometer matching the intensity and duration of ASE, the ablation pressure would push the whole target in the forward direction with speed exceeding the expansion velocity of plasma, resulting in a plasma density profile with a long extension at the target front and a sharp gradient at the target rear. When the main pulse irradiates the plasma, self-focusing happens at the target front, producing highly energetic electrons through direct laser acceleration(DLA) building the sheath field. The sharp plasma gradient at target rear ensures a strong sheath field. 2D particle-in-cell(PIC) simulations reveal that the proton energy can be enhanced by a factor of 2 compared to the case of using micrometer-thick targets.

Gas loss in simulated galaxies as they fall into clusters

PubMed Central

Cen, Renyue; Pop, Ana Roxana; Bahcall, Neta A.

2014-01-01

We use high-resolution cosmological hydrodynamic galaxy formation simulations to gain insights into how galaxies lose their cold gas at low redshift as they migrate from the field to the high-density regions of clusters of galaxies. We find that beyond three cluster virial radii, the fraction of gas-rich galaxies is constant, representing the field. Within three cluster-centric radii, the fraction of gas-rich galaxies declines steadily with decreasing radius, reaching <10% near the cluster center. Our results suggest galaxies start to feel the effect of the cluster environment on their gas content well beyond the cluster virial radius. We show that almost all gas-rich galaxies at the cluster virial radius are falling in for the first time at nearly radial orbits. Furthermore, we find that almost no galaxy moving outward at the cluster virial radius is gas-rich (with a gas-to-baryon ratio greater than 1%). These results suggest that galaxies that fall into clusters lose their cold gas within a single radial round-trip. PMID:24843167

Gas loss in simulated galaxies as they fall into clusters.

PubMed

Cen, Renyue; Pop, Ana Roxana; Bahcall, Neta A

2014-06-03

We use high-resolution cosmological hydrodynamic galaxy formation simulations to gain insights into how galaxies lose their cold gas at low redshift as they migrate from the field to the high-density regions of clusters of galaxies. We find that beyond three cluster virial radii, the fraction of gas-rich galaxies is constant, representing the field. Within three cluster-centric radii, the fraction of gas-rich galaxies declines steadily with decreasing radius, reaching <10% near the cluster center. Our results suggest galaxies start to feel the effect of the cluster environment on their gas content well beyond the cluster virial radius. We show that almost all gas-rich galaxies at the cluster virial radius are falling in for the first time at nearly radial orbits. Furthermore, we find that almost no galaxy moving outward at the cluster virial radius is gas-rich (with a gas-to-baryon ratio greater than 1%). These results suggest that galaxies that fall into clusters lose their cold gas within a single radial round-trip.

Investigation of the hydrodynamic response of cells in drop on demand piezoelectric inkjet nozzles.

PubMed

Cheng, Eric; Yu, Haoran; Ahmadi, Ali; Cheung, Karen C

2016-01-29

Cell motion within a liquid suspension inside a piezoelectrically actuated, cylindrical inkjet printhead was studied using high speed imaging and a low depth of field setup. For each ejected droplet, a cell within the inkjet nozzle was observed to exhibit one of three possible behaviors which are termed: cell travel, cell ejection and cell reflection. Cell reflection is an undesirable phenomenon which may adversely affect an inkjet's capability in dispensing cells and a possible reason why it was previously reported that the rate of cells dispensed did not follow the expected Poisson distribution. Through the study of the cells motions, it was hypothesized that the rheological properties of the media in the cell suspension play an important role in influencing the cell behaviors exhibited. This was experimentally studied with the tracking of cells within the inkjet nozzle in a 10% w/v Ficoll PM400 cell suspension. The effect of cell reflection was eliminated using the higher density and viscosity Ficoll PM400 suspension. The presented work is the first in-depth study of the cell behaviors occurring within a piezoelectric inkjet nozzle during the printing process. The understanding of the hydrodynamics during a droplet ejection and its effect on the suspended cells are imperative towards achieving reliable cell dispensing for biofabrication applications.

THE STRUCTURE OF SPIRAL SHOCKS EXCITED BY PLANETARY-MASS COMPANIONS

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

Zhu, Zhaohuan; Stone, James M.; Rafikov, Roman R.

2015-11-10

Direct imaging observations have revealed spiral structures in protoplanetary disks. Previous studies have suggested that planet-induced spiral arms cannot explain some of these spiral patterns, due to the large pitch angle and high contrast of the spiral arms in observations. We have carried out three-dimensional (3D) hydrodynamical simulations to study spiral wakes/shocks excited by young planets. We find that, in contrast with linear theory, the pitch angle of spiral arms does depend on the planet mass, which can be explained by the nonlinear density wave theory. A secondary (or even a tertiary) spiral arm, especially for inner arms, is alsomore » excited by a massive planet. With a more massive planet in the disk, the excited spiral arms have larger pitch angle and the separation between the primary and secondary arms in the azimuthal direction is also larger. We also find that although the arms in the outer disk do not exhibit much vertical motion, the inner arms have significant vertical motion, which boosts the density perturbation at the disk atmosphere. Combining hydrodynamical models with Monte-Carlo radiative transfer calculations, we find that the inner spiral arms are considerably more prominent in synthetic near-IR images using full 3D hydrodynamical models than images based on two-dimensional models assuming vertical hydrostatic equilibrium, indicating the need to model observations with full 3D hydrodynamics. Overall, companion-induced spiral arms not only pinpoint the companion’s position but also provide three independent ways (pitch angle, separation between two arms, and contrast of arms) to constrain the companion’s mass.« less

Precision cosmology with baryons: non-radiative hydrodynamics of galaxy groups

NASA Astrophysics Data System (ADS)

Rabold, Manuel; Teyssier, Romain

2017-05-01

The effect of baryons on the matter power spectrum is likely to have an observable effect for future galaxy surveys, like Euclid or Large Synoptic Survey Telescope (LSST). As a first step towards a fully predictive theory, we investigate the effect of non-radiative hydrodynamics on the structure of galaxy groups sized haloes, which contribute the most to the weak-lensing power spectrum. We perform high-resolution (more than one million particles per halo and one kilo-parsec resolution) non-radiative hydrodynamical zoom-in simulations of a sample of 16 haloes, comparing the profiles to popular analytical models. We find that the total mass profile is well fitted by a Navarro, Frenk & White model, with parameters slightly modified from the dark matter only simulation. We also find that the Komatsu & Seljak hydrostatic solution provides a good fit to the gas profiles, with however significant deviations, arising from strong turbulent mixing in the core and from non-thermal, turbulent pressure support in the outskirts. The turbulent energy follows a shallow, rising linear profile with radius, and correlates with the halo formation time. Using only three main structural halo parameters as variables (total mass, concentration parameter and central gas density), we can predict, with an accuracy better than 20 per cent, the individual gas density and temperature profiles. For the average total mass profile, which is relevant for power spectrum calculations, we even reach an accuracy of 1 per cent. The robustness of these predictions has been tested against resolution effects, different types of initial conditions and hydrodynamical schemes.

Fast electric control of the droplet size in a microfluidic T-junction droplet generator

NASA Astrophysics Data System (ADS)

Shojaeian, Mostafa; Hardt, Steffen

2018-05-01

The effect of DC electric fields on the generation of droplets of water and xanthan gum solutions in sunflower oil at a microfluidic T-junction is experimentally studied. The electric field leads to a significant reduction of the droplet diameter, by about a factor of 2 in the case of water droplets. The droplet size can be tuned by varying the electric field strength, an effect that can be employed to produce a stream of droplets with a tailor-made size sequence. Compared to the case of purely hydrodynamic droplet production without electric fields, the electric control has about the same effect on the droplet size if the electric stress at the liquid/liquid interface is the same as the hydrodynamic stress.

Use of Genetic Algorithms to solve Inverse Problems in Relativistic Hydrodynamics

NASA Astrophysics Data System (ADS)

Guzmán, F. S.; González, J. A.

2018-04-01

We present the use of Genetic Algorithms (GAs) as a strategy to solve inverse problems associated with models of relativistic hydrodynamics. The signal we consider to emulate an observation is the density of a relativistic gas, measured at a point where a shock is traveling. This shock is generated numerically out of a Riemann problem with mildly relativistic conditions. The inverse problem we propose is the prediction of the initial conditions of density, velocity and pressure of the Riemann problem that gave origin to that signal. For this we use the density, velocity and pressure of the gas at both sides of the discontinuity, as the six genes of an organism, initially with random values within a tolerance. We then prepare an initial population of N of these organisms and evolve them using methods based on GAs. In the end, the organism with the best fitness of each generation is compared to the signal and the process ends when the set of initial conditions of the organisms of a later generation fit the Signal within a tolerance.

Calibration of the Oscillating Screen Viscometer

NASA Technical Reports Server (NTRS)

Berg, Robert F.; Moldover, Michael R.

1993-01-01

We have devised a calibration procedure for the oscillating screen viscometer which can provide the accuracy needed for the flight measurement of viscosity near the liquid-vapor critical point of xenon. The procedure, which makes use of the viscometer's wide bandwidth and hydrodynamic similarity, allows the viscometer to be self-calibrating. To demonstrate the validity of this procedure we measured the oscillator's transfer function under a wide variety of conditions. We obtained data using CO2 at temperatures spanning a temperature range of 35 K and densities varying by a factor of 165, thereby encountering viscosity variations as great as 50%. In contrast the flight experiment will be performed over a temperature range of 29 K and at only a single density, and the viscosity is expected to change by less than 40%. The measurements show that, after excluding data above 10 Hz (where frequency-dependent corrections are poorly modeled) and making a plausible adjustment to the viscosity value used at high density, the viscometer's behavior is fully consistent with the use of hydrodynamic similarity for calibration. Achieving this agreement required understanding a 1% anelastic effect present in the oscillator's torsion fiber.

Three-dimensional modeling of the neutron spectrum to infer plasma conditions in cryogenic inertial confinement fusion implosions

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

Weilacher, F.; Radha, P. B.; Forrest, C.

Neutron-based diagnostics are typically used to infer compressed core conditions such as areal density and ion temperature in deuterium–tritium (D–T) inertial confinement fusion (ICF) implosions. Asymmetries in the observed neutron-related quantities are important to understanding failure modes in these implosions. Neutrons from fusion reactions and their subsequent interactions including elastic scattering and neutron-induced deuteron breakup reactions are tracked to create spectra. Here, it is shown that background subtraction is important for inferring areal density from backscattered neutrons and is less important for the forward-scattered neutrons. A three-dimensional hydrodynamic simulation of a cryogenic implosion on the OMEGA Laser System [T. R.more » Boehly et al., Opt. Commun. 133, 495 (1997)] using the hydrodynamic code HYDRA [M. M. Marinak et al., Phys. Plasmas 8, 2275 (2001)] is post-processed using the tracking code IRIS3D. It is shown that different parts of the neutron spectrum from the view can be mapped into different regions of the implosion, enabling an inference of an areal-density map. It is also shown that the average areal-density and an areal-density map of the compressed target can be reconstructed with a finite number of detectors placed around the target chamber. Ion temperatures are inferred from the width of the D–D and D–T fusion neutron spectra. Backgrounds can significantly alter the inferred ion temperatures from the D–D reaction, whereas they insignificantly influence the inferred D–T ion temperatures for the areal densities typical of OMEGA implosions. Asymmetries resulting in fluid flow in the core are shown to influence the absolute inferred ion temperatures from both reactions, although relative inferred values continue to reflect the underlying asymmetry pattern. The work presented here is part of the wide range of the first set of studies performed with IRIS3D. Finally, this code will continue to be used for post-processing detailed hydrodynamic simulations and interpreting observed neutron spectra in ICF implosions.« less

Three-dimensional modeling of the neutron spectrum to infer plasma conditions in cryogenic inertial confinement fusion implosions

DOE PAGES

Weilacher, F.; Radha, P. B.; Forrest, C.

2018-04-26

Neutron-based diagnostics are typically used to infer compressed core conditions such as areal density and ion temperature in deuterium–tritium (D–T) inertial confinement fusion (ICF) implosions. Asymmetries in the observed neutron-related quantities are important to understanding failure modes in these implosions. Neutrons from fusion reactions and their subsequent interactions including elastic scattering and neutron-induced deuteron breakup reactions are tracked to create spectra. Here, it is shown that background subtraction is important for inferring areal density from backscattered neutrons and is less important for the forward-scattered neutrons. A three-dimensional hydrodynamic simulation of a cryogenic implosion on the OMEGA Laser System [T. R.more » Boehly et al., Opt. Commun. 133, 495 (1997)] using the hydrodynamic code HYDRA [M. M. Marinak et al., Phys. Plasmas 8, 2275 (2001)] is post-processed using the tracking code IRIS3D. It is shown that different parts of the neutron spectrum from the view can be mapped into different regions of the implosion, enabling an inference of an areal-density map. It is also shown that the average areal-density and an areal-density map of the compressed target can be reconstructed with a finite number of detectors placed around the target chamber. Ion temperatures are inferred from the width of the D–D and D–T fusion neutron spectra. Backgrounds can significantly alter the inferred ion temperatures from the D–D reaction, whereas they insignificantly influence the inferred D–T ion temperatures for the areal densities typical of OMEGA implosions. Asymmetries resulting in fluid flow in the core are shown to influence the absolute inferred ion temperatures from both reactions, although relative inferred values continue to reflect the underlying asymmetry pattern. The work presented here is part of the wide range of the first set of studies performed with IRIS3D. Finally, this code will continue to be used for post-processing detailed hydrodynamic simulations and interpreting observed neutron spectra in ICF implosions.« less

Lyapunov exponents of stochastic systems—from micro to macro

NASA Astrophysics Data System (ADS)

Laffargue, Tanguy; Tailleur, Julien; van Wijland, Frédéric

2016-03-01

Lyapunov exponents of dynamical systems are defined from the rates of divergence of nearby trajectories. For stochastic systems, one typically assumes that these trajectories are generated under the ‘same noise realization’. The purpose of this work is to critically examine what this expression means. For Brownian particles, we consider two natural interpretations of the noise: intrinsic to the particles or stemming from the fluctuations of the environment. We show how they lead to different distributions of the largest Lyapunov exponent as well as different fluctuating hydrodynamics for the collective density field. We discuss, both at microscopic and macroscopic levels, the limits in which these noise prescriptions become equivalent. We close this paper by providing an estimate of the largest Lyapunov exponent and of its fluctuations for interacting particles evolving with Dean-Kawasaki dynamics.

Non local-thermodynamical-equilibrium effects in the simulation of laser-produced plasmas

NASA Astrophysics Data System (ADS)

Klapisch, M.; Bar-Shalom, A.; Oreg, J.; Colombant, D.

1998-05-01

Local thermodynamic equilibrium (LTE) breaks down in directly or indirectly driven laser plasmas because of sharp gradients, energy deposition, etc. For modeling non-LTE effects in hydrodynamical simulations, Busquet's model [Phys. Fluids B 5, 4191 (1993)] is very convenient and efficient. It uses off-line generated LTE opacities and equation of states via an effective, radiation-dependent ionization temperature Tz. An overview of the model is given. The results are compared with an elaborate collisional radiative model based on superconfigurations. The agreements for average charge Z* and opacities are surprisingly good, even more so when the plasma is immersed in a radiation field. Some remaining discrepancy at low density is attributed to dielectronic recombination. Improvement appears possible, especially for emissivities, because the concept of ionization temperature seems to be validated.

Definition and solution of a stochastic inverse problem for the Manning's n parameter field in hydrodynamic models.

PubMed

Butler, T; Graham, L; Estep, D; Dawson, C; Westerink, J J

2015-04-01

The uncertainty in spatially heterogeneous Manning's n fields is quantified using a novel formulation and numerical solution of stochastic inverse problems for physics-based models. The uncertainty is quantified in terms of a probability measure and the physics-based model considered here is the state-of-the-art ADCIRC model although the presented methodology applies to other hydrodynamic models. An accessible overview of the formulation and solution of the stochastic inverse problem in a mathematically rigorous framework based on measure theory is presented. Technical details that arise in practice by applying the framework to determine the Manning's n parameter field in a shallow water equation model used for coastal hydrodynamics are presented and an efficient computational algorithm and open source software package are developed. A new notion of "condition" for the stochastic inverse problem is defined and analyzed as it relates to the computation of probabilities. This notion of condition is investigated to determine effective output quantities of interest of maximum water elevations to use for the inverse problem for the Manning's n parameter and the effect on model predictions is analyzed.

Definition and solution of a stochastic inverse problem for the Manning's n parameter field in hydrodynamic models

NASA Astrophysics Data System (ADS)

Butler, T.; Graham, L.; Estep, D.; Dawson, C.; Westerink, J. J.

2015-04-01

The uncertainty in spatially heterogeneous Manning's n fields is quantified using a novel formulation and numerical solution of stochastic inverse problems for physics-based models. The uncertainty is quantified in terms of a probability measure and the physics-based model considered here is the state-of-the-art ADCIRC model although the presented methodology applies to other hydrodynamic models. An accessible overview of the formulation and solution of the stochastic inverse problem in a mathematically rigorous framework based on measure theory is presented. Technical details that arise in practice by applying the framework to determine the Manning's n parameter field in a shallow water equation model used for coastal hydrodynamics are presented and an efficient computational algorithm and open source software package are developed. A new notion of "condition" for the stochastic inverse problem is defined and analyzed as it relates to the computation of probabilities. This notion of condition is investigated to determine effective output quantities of interest of maximum water elevations to use for the inverse problem for the Manning's n parameter and the effect on model predictions is analyzed.

Hydrodynamic characteristics of the two-phase flow field at gas-evolving electrodes: numerical and experimental studies

NASA Astrophysics Data System (ADS)

Liu, Cheng-Lin; Sun, Ze; Lu, Gui-Min; Yu, Jian-Guo

2018-05-01

Gas-evolving vertical electrode system is a typical electrochemical industrial reactor. Gas bubbles are released from the surfaces of the anode and affect the electrolyte flow pattern and even the cell performance. In the current work, the hydrodynamics induced by the air bubbles in a cold model was experimentally and numerically investigated. Particle image velocimetry and volumetric three-component velocimetry techniques were applied to experimentally visualize the hydrodynamics characteristics and flow fields in a two-dimensional (2D) plane and a three-dimensional (3D) space, respectively. Measurements were performed at different gas rates. Furthermore, the corresponding mathematical model was developed under identical conditions for the qualitative and quantitative analyses. The experimental measurements were compared with the numerical results based on the mathematical model. The study of the time-averaged flow field, three velocity components, instantaneous velocity and turbulent intensity indicate that the numerical model qualitatively reproduces liquid motion. The 3D model predictions capture the flow behaviour more accurately than the 2D model in this study.

Hydrodynamic characteristics of the two-phase flow field at gas-evolving electrodes: numerical and experimental studies.

PubMed

Liu, Cheng-Lin; Sun, Ze; Lu, Gui-Min; Yu, Jian-Guo

2018-05-01

Gas-evolving vertical electrode system is a typical electrochemical industrial reactor. Gas bubbles are released from the surfaces of the anode and affect the electrolyte flow pattern and even the cell performance. In the current work, the hydrodynamics induced by the air bubbles in a cold model was experimentally and numerically investigated. Particle image velocimetry and volumetric three-component velocimetry techniques were applied to experimentally visualize the hydrodynamics characteristics and flow fields in a two-dimensional (2D) plane and a three-dimensional (3D) space, respectively. Measurements were performed at different gas rates. Furthermore, the corresponding mathematical model was developed under identical conditions for the qualitative and quantitative analyses. The experimental measurements were compared with the numerical results based on the mathematical model. The study of the time-averaged flow field, three velocity components, instantaneous velocity and turbulent intensity indicate that the numerical model qualitatively reproduces liquid motion. The 3D model predictions capture the flow behaviour more accurately than the 2D model in this study.

Hydrodynamic characteristics of the two-phase flow field at gas-evolving electrodes: numerical and experimental studies

PubMed Central

Lu, Gui-Min; Yu, Jian-Guo

2018-01-01

Gas-evolving vertical electrode system is a typical electrochemical industrial reactor. Gas bubbles are released from the surfaces of the anode and affect the electrolyte flow pattern and even the cell performance. In the current work, the hydrodynamics induced by the air bubbles in a cold model was experimentally and numerically investigated. Particle image velocimetry and volumetric three-component velocimetry techniques were applied to experimentally visualize the hydrodynamics characteristics and flow fields in a two-dimensional (2D) plane and a three-dimensional (3D) space, respectively. Measurements were performed at different gas rates. Furthermore, the corresponding mathematical model was developed under identical conditions for the qualitative and quantitative analyses. The experimental measurements were compared with the numerical results based on the mathematical model. The study of the time-averaged flow field, three velocity components, instantaneous velocity and turbulent intensity indicate that the numerical model qualitatively reproduces liquid motion. The 3D model predictions capture the flow behaviour more accurately than the 2D model in this study. PMID:29892347

Ab Initio Simulations of a Supernova-driven Galactic Dynamo in an Isolated Disk Galaxy

DOE PAGES

Butsky, Iryna; Zrake, Jonathan; Kim, Ji-hoon; ...

2017-07-10

Here, we study the magnetic field evolution of an isolated spiral galaxy, using isolated Milky Way–mass galaxy formation simulations and a novel prescription for magnetohydrodynamic (MHD) supernova feedback. Our main result is that a galactic dynamo can be seeded and driven by supernova explosions, resulting in magnetic fields whose strength and morphology are consistent with observations. In our model, supernovae supply thermal energy and a low-level magnetic field along with their ejecta. The thermal expansion drives turbulence, which serves a dual role by efficiently mixing the magnetic field into the interstellar medium and amplifying it by means of a turbulentmore » dynamo. The computational prescription for MHD supernova feedback has been implemented within the publicly available ENZO code and is fully described in this paper. This improves upon ENZO's existing modules for hydrodynamic feedback from stars and active galaxies. We find that the field attains microgauss levels over gigayear timescales throughout the disk. The field also develops a large-scale structure, which appears to be correlated with the disk's spiral arm density structure. We find that seeding of the galactic dynamo by supernova ejecta predicts a persistent correlation between gas metallicity and magnetic field strength. We also generate all-sky maps of the Faraday rotation measure from the simulation-predicted magnetic field, and we present a direct comparison with observations.« less

Ab Initio Simulations of a Supernova-driven Galactic Dynamo in an Isolated Disk Galaxy

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

Butsky, Iryna; Zrake, Jonathan; Kim, Ji-hoon

We study the magnetic field evolution of an isolated spiral galaxy, using isolated Milky Way–mass galaxy formation simulations and a novel prescription for magnetohydrodynamic (MHD) supernova feedback. Our main result is that a galactic dynamo can be seeded and driven by supernova explosions, resulting in magnetic fields whose strength and morphology are consistent with observations. In our model, supernovae supply thermal energy and a low-level magnetic field along with their ejecta. The thermal expansion drives turbulence, which serves a dual role by efficiently mixing the magnetic field into the interstellar medium and amplifying it by means of a turbulent dynamo.more » The computational prescription for MHD supernova feedback has been implemented within the publicly available ENZO code and is fully described in this paper. This improves upon ENZO 's existing modules for hydrodynamic feedback from stars and active galaxies. We find that the field attains microgauss levels over gigayear timescales throughout the disk. The field also develops a large-scale structure, which appears to be correlated with the disk’s spiral arm density structure. We find that seeding of the galactic dynamo by supernova ejecta predicts a persistent correlation between gas metallicity and magnetic field strength. We also generate all-sky maps of the Faraday rotation measure from the simulation-predicted magnetic field, and we present a direct comparison with observations.« less

Ab Initio Simulations of a Supernova-driven Galactic Dynamo in an Isolated Disk Galaxy

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

Butsky, Iryna; Zrake, Jonathan; Kim, Ji-hoon

Here, we study the magnetic field evolution of an isolated spiral galaxy, using isolated Milky Way–mass galaxy formation simulations and a novel prescription for magnetohydrodynamic (MHD) supernova feedback. Our main result is that a galactic dynamo can be seeded and driven by supernova explosions, resulting in magnetic fields whose strength and morphology are consistent with observations. In our model, supernovae supply thermal energy and a low-level magnetic field along with their ejecta. The thermal expansion drives turbulence, which serves a dual role by efficiently mixing the magnetic field into the interstellar medium and amplifying it by means of a turbulentmore » dynamo. The computational prescription for MHD supernova feedback has been implemented within the publicly available ENZO code and is fully described in this paper. This improves upon ENZO's existing modules for hydrodynamic feedback from stars and active galaxies. We find that the field attains microgauss levels over gigayear timescales throughout the disk. The field also develops a large-scale structure, which appears to be correlated with the disk's spiral arm density structure. We find that seeding of the galactic dynamo by supernova ejecta predicts a persistent correlation between gas metallicity and magnetic field strength. We also generate all-sky maps of the Faraday rotation measure from the simulation-predicted magnetic field, and we present a direct comparison with observations.« less

Different elution modes and field programming in gravitational field-flow fractionation. III. Field programming by flow-rate gradient generated by a programmable pump.

PubMed

Plocková, J; Chmelík, J

2001-05-25

Gravitational field-flow fractionation (GFFF) utilizes the Earth's gravitational field as an external force that causes the settlement of particles towards the channel accumulation wall. Hydrodynamic lift forces oppose this action by elevating particles away from the channel accumulation wall. These two counteracting forces enable modulation of the resulting force field acting on particles in GFFF. In this work, force-field programming based on modulating the magnitude of hydrodynamic lift forces was implemented via changes of flow-rate, which was accomplished by a programmable pump. Several flow-rate gradients (step gradients, linear gradients, parabolic, and combined gradients) were tested and evaluated as tools for optimization of the separation of a silica gel particle mixture. The influence of increasing amount of sample injected on the peak resolution under flow-rate gradient conditions was also investigated. This is the first time that flow-rate gradients have been implemented for programming of the resulting force field acting on particles in GFFF.

Force-moment line element method for flexible slender bodies in Stokes flow.

PubMed

Jiang, H; Yang, B

2013-09-01

The hydrodynamics of flexible slender bodies in Stokes flow is studied by taking into account the fluid-structure interaction through both forces and coupled moments. The fluid subjected to line sources of forces and moments is described by using integral equations. Meanwhile, the flexible slender body is modeled using finite beam elements. The two sides are linked through interfacial continuity conditions. Upon discretization, it results in a higher-order line element method for efficient and accurate solution of slender-body hydrodynamics. Four examples are presented to demonstrate the validity and efficiency of the present method: (a) hydrodynamics of a flexible slender rod subjected to a torque at one end, (b) hydrodynamics of a flexible slender rod subjected to a bending moment at one end, (c) hydrodynamics of a flexible slender rod subjected to a cyclic force, and (d) hydrodynamics of a flexible slender rod with a magnetized head within a rotating magnetic field. Examples (a) and (b) may serve as benchmark solutions and examples (c) and (d) show how planar and spiral waves can be excited in a slender body.

Hydrodynamic control of microphytoplankton bloom in a coastal sea

NASA Astrophysics Data System (ADS)

Murty, K. Narasimha; Sarma, Nittala S.; Pandi, Sudarsana Rao; Chiranjeevulu, Gundala; Kiran, Rayaprolu; Muralikrishna, R.

2017-08-01

The influence of hydrodynamics on phytoplankton bloom occurrence/formation has not been adequately reported. Here, we document diurnal observations in the tropical Bay of Bengal's mid-western shelf region which reveal microphytoplankton cell density maxima in association with neap tide many times more than what could be accounted for by solar insolation and nutrient levels. When in summer, phytoplankton cells were abundant and the cell density of Guinardia delicatula reached critical value by tide caused zonation, aggregation happened to an intense bloom. Mucilaginous exudates from the alga due to heat and silicate stress likely promoted and stable water column and weak winds left undisturbed, the transient bloom. The phytoplankton aggregates have implication as food resource in the benthic region implying higher fishery potential, in carbon dioxide sequestration (carbon burial) and in efforts towards improving remote sensing algorithms for chlorophyll in the coastal region.

Study of the hydrodynamics of the formation of flows caused by the interaction of a shock wave with two-dimensional density perturbations on the Iskra-5 laser facility

NASA Astrophysics Data System (ADS)

Babanov, A. V.; Barinov, M. A.; Barinov, S. P.; Garanin, R. V.; Zhidkov, N. V.; Kalmykov, N. A.; Kovalenko, V. P.; Kokorin, S. N.; Pinegin, A. V.; Solomatina, E. Yu.; Solomatin, I. I.; Suslov, N. A.

2017-03-01

The hydrodynamics of the flow formation due to the interaction of a shock wave with two-dimensional density perturbations is experimentally investigated on the Iskra-5 laser facility. Shadow images of a jet arising as a result of the impact of a shock wave (formed by a soft X-ray pulse from a target-illuminator) on a flat aluminium target with a blind cylindrical cavity are recorded in experiments with point-like X-ray backlighting having a photon energy of ~4.5 keV. The sizes and mass of the jet ejected from the aluminium cavity by this shock wave are estimated. The experimental data are compared with the results of numerical simulation of the jet formation and dynamics according to the two-dimensional MID-ND2D code.

Measurements of shock-front structure in multi-species plasmas on OMEGA

NASA Astrophysics Data System (ADS)

Rinderknecht, Hans G.; Park, H.-S.; Ross, J. S.; Wilks, S. C.; Amendt, P. A.; Heeter, R. F.; Katz, J.; Hoffman, N. M.; Vold, E.; Taitano, W.; Simakov, A.; Chacon, L.

2016-10-01

The structure of a shock front in a plasma with multiple ion species is measured for the first time in experiments on the OMEGA laser. Thomson scattering of a 263.25 nm probe beam is used to diagnose electron density, electron and ion temperature, ion species concentration, and flow velocity in strong shocks (M 5) propagating through low-density (ρ 0.1 mg/cc) plasmas composed of H(98%)+Ne(2%) and H(98%)+C(2%). Separation of the ion species within the shock front is inferred. Although shocks play an important role in ICF and astrophysical plasmas, the intrinsically kinetic nature of the shock front indicates the need for experiments to benchmark hydrodynamic models. Comparison with PIC, Vlasov-Fokker-Planck, and multi-component hydrodynamic simulations will be presented. This work performed under auspices of U.S. DOE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Hydrodynamics of the Polyakov line in SU(N c) Yang-Mills

DOE PAGES

Liu, Yizhuang; Warchoł, Piotr; Zahed, Ismail

2015-12-08

We discuss a hydrodynamical description of the eigenvalues of the Polyakov line at large but finite N c for Yang-Mills theory in even and odd space-time dimensions. The hydro-static solutions for the eigenvalue densities are shown to interpolate between a uniform distribution in the confined phase and a localized distribution in the de-confined phase. The resulting critical temperatures are in overall agreement with those measured on the lattice over a broad range of N c, and are consistent with the string model results at N c = ∞. The stochastic relaxation of the eigenvalues of the Polyakov line out ofmore » equilibrium is captured by a hydrodynamical instanton. An estimate of the probability of formation of a Z(N c)bubble using a piece-wise sound wave is suggested.« less

Review of factors affecting recovery of freshwater stored in saline aquifers

USGS Publications Warehouse

Merritt, Michael L.

1989-01-01

A simulation analysis reported previously, and summarized herein, identified the effects of various geohydrologic and operational factors on recoverability of the injected water. Buoyancy stratification, downgradient advection, and hydrodynamic dispersion are the principal natural processes that reduce the amount of injected water that can be recovered. Buoyancy stratification is shown to depend on injection-zone permeability and the density contrast between injected and saline native water. Downgradient advection occurs as a result of natural or induced hydraulic gradients in the aquifer. Hydrodynamic dispersion reduces recovery efficiency by mixing some of the injected water with native saline aquifer water. In computer simulations, the relation of recovery efficiency to volume injected and its improvement during successive injection-recovery cycles was shown to depend on changes in the degree of hydrodynamic dispersion that occurs. Additional aspects of the subject are discussed.

Numerical Simulation of Hydrodynamics of a Heavy Liquid Drop Covered by Vapor Film in a Water Pool

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

Ma, W.M.; Yang, Z.L.; Giri, A.

2002-07-01

A numerical study on the hydrodynamics of a droplet covered by vapor film in water pool is carried out. Two level set functions are used as to implicitly capture the interfaces among three immiscible fluids (melt-drop, vapor and coolant). This approach leaves only one set of conservation equations for the three phases. A high-order Navier-Stokes solver, called Cubic-Interpolated Pseudo-Particle (CIP) algorithm, is employed in combination with level set approach, which allows large density ratios (up to 1000), surface tension and jump in viscosity. By this calculation, the hydrodynamic behavior of a melt droplet falling into a volatile coolant is simulated,more » which is of great significance to reveal the mechanism of steam explosion during a hypothetical severe reactor accident. (authors)« less

Longitudinal hydrodynamics from event-by-event Landau initial conditions

DOE PAGES

Sen, Abhisek; Gerhard, Jochen; Torrieri, Giorgio; ...

2015-02-02

Here we investigate three-dimensional ideal hydrodynamic evolution, with Landau initial conditions, incorporating event-by-event variation with many events and transverse density inhomogeneities. We show that the transition to boost-invariant flow occurs too late for realistic setups, with corrections of θ (20%-30%) expected at freeze-out for most scenarios. Moreover, the deviation from boost invariance is correlated with both transverse flow and elliptic flow, with the more highly transversely flowing regions also showing the most violation of boost invariance. Therefore, if longitudinal flow is not fully developed at the early stages of heavy ion collisions, hydrodynamics where boost invariance holds at midrapidity ismore » inadequate to extract transport coefficients of the quark-gluon plasma. We conclude by arguing that developing experimental probes of boost invariance is necessary, and suggest some promising directions in this regard.« less

Chromatin hydrodynamics.

PubMed

Bruinsma, Robijn; Grosberg, Alexander Y; Rabin, Yitzhak; Zidovska, Alexandra

2014-05-06

Following recent observations of large scale correlated motion of chromatin inside the nuclei of live differentiated cells, we present a hydrodynamic theory-the two-fluid model-in which the content of a nucleus is described as a chromatin solution with the nucleoplasm playing the role of the solvent and the chromatin fiber that of a solute. This system is subject to both passive thermal fluctuations and active scalar and vector events that are associated with free energy consumption, such as ATP hydrolysis. Scalar events drive the longitudinal viscoelastic modes (where the chromatin fiber moves relative to the solvent) while vector events generate the transverse modes (where the chromatin fiber moves together with the solvent). Using linear response methods, we derive explicit expressions for the response functions that connect the chromatin density and velocity correlation functions to the corresponding correlation functions of the active sources and the complex viscoelastic moduli of the chromatin solution. We then derive general expressions for the flow spectral density of the chromatin velocity field. We use the theory to analyze experimental results recently obtained by one of the present authors and her co-workers. We find that the time dependence of the experimental data for both native and ATP-depleted chromatin can be well-fitted using a simple model-the Maxwell fluid-for the complex modulus, although there is some discrepancy in terms of the wavevector dependence. Thermal fluctuations of ATP-depleted cells are predominantly longitudinal. ATP-active cells exhibit intense transverse long wavelength velocity fluctuations driven by force dipoles. Fluctuations with wavenumbers larger than a few inverse microns are dominated by concentration fluctuations with the same spectrum as thermal fluctuations but with increased intensity. Copyright © 2014 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Molecular transport properties through carbon nanotube membrane

NASA Astrophysics Data System (ADS)

Majumder, Mainak

Molecular transport through hollow cores of crystalline carbon nanotubes (CNTs) are of considerable interest from the fundamental and application point of view. This dissertation focuses on understanding molecular transport through a membrane platform consisting of open ended CNTs with ˜ 7 nm core diameter and ˜ 1010 CNTs/cm2 encapsulated in an inert polymer matrix. While ionic diffusion through the membrane is close to bulk diffusion expectations, gases and liquids were respectively observed to be transported ˜ 10 times faster than Knudsen diffusion and ˜ 10000--100000 times faster than hydrodynamic flow predictions. This phenomenon has been attributed to the non-interactive and frictionless graphitic interface. Functionalization of the CNT tips was observed to change selectivity and flux through the CNT membranes with analogy to 'gate-keeper' functionality in biological membranes. An electro-chemical diazonium grafting chemistry was utilized for enhancing the functional density on the CNT membranes. A strategy to confine the reactions at the CNT tips by a fast flowing liquid column was also designed. Characterization using electrochemical impedance spectroscopy and dye assay indicated ˜ 5--6 times increase in functional density. Electrochemical impedance spectroscopy experiments on CNT membrane/electrode functionalized with charged macro-molecules showed voltage-controlled conformational change. Similar chemistry has been applied for realizing 'voltage-gated' transport channels with potential application in trans-dermal drug delivery. Electrically-facilitated transport (a geometry in which an electric field gradient acts across the membrane) through the CNT and functionalized CNT membranes was observed to be electrosmotically controlled. Finally, a simulation framework based on continuum electrostatics and finite elements has been developed to further the understanding of transport through the CNT membranes. KEYWORDS: carbon nanotube membrane, nano-scale hydrodynamics, diazonium grafting, voltage-gated membrane, finite element analysis

Chromatin Hydrodynamics

PubMed Central

Bruinsma, Robijn; Grosberg, Alexander Y.; Rabin, Yitzhak; Zidovska, Alexandra

2014-01-01

Following recent observations of large scale correlated motion of chromatin inside the nuclei of live differentiated cells, we present a hydrodynamic theory—the two-fluid model—in which the content of a nucleus is described as a chromatin solution with the nucleoplasm playing the role of the solvent and the chromatin fiber that of a solute. This system is subject to both passive thermal fluctuations and active scalar and vector events that are associated with free energy consumption, such as ATP hydrolysis. Scalar events drive the longitudinal viscoelastic modes (where the chromatin fiber moves relative to the solvent) while vector events generate the transverse modes (where the chromatin fiber moves together with the solvent). Using linear response methods, we derive explicit expressions for the response functions that connect the chromatin density and velocity correlation functions to the corresponding correlation functions of the active sources and the complex viscoelastic moduli of the chromatin solution. We then derive general expressions for the flow spectral density of the chromatin velocity field. We use the theory to analyze experimental results recently obtained by one of the present authors and her co-workers. We find that the time dependence of the experimental data for both native and ATP-depleted chromatin can be well-fitted using a simple model—the Maxwell fluid—for the complex modulus, although there is some discrepancy in terms of the wavevector dependence. Thermal fluctuations of ATP-depleted cells are predominantly longitudinal. ATP-active cells exhibit intense transverse long wavelength velocity fluctuations driven by force dipoles. Fluctuations with wavenumbers larger than a few inverse microns are dominated by concentration fluctuations with the same spectrum as thermal fluctuations but with increased intensity. PMID:24806919

Self-Diffusion and Heteroassociation in an Acetone-Chloroform Mixture at 298 K

NASA Astrophysics Data System (ADS)

Golubev, V. A.; Gurina, D. L.; Kumeev, R. S.

2018-01-01

The self-diffusion coefficients of acetone and chloroform in a binary acetone-chloroform mixture at 298 K are determined via pulsed field gradient NMR spectroscopy. It is estimated that the hydrodynamic radii of the mixture's components, calculated using the Stokes-Einstein equation, grow as the concentrations of the components fall. It is shown that such behavior of hydrodynamic radii is due to acetone-chloroform heteroassociation. The hydrodynamic radii of monomers and heteroassociates in a 1: 1 ratio are determined along with the constant of heteroassociation, using the proposed model of an associated solution.

Studies of Magnetic Reconnection in Colliding Laser-Produced Plasmas

NASA Astrophysics Data System (ADS)

Rosenberg, Michael

2013-10-01

Novel images of magnetic fields and measurements of electron and ion temperatures have been obtained in the magnetic reconnection region of high- β, laser-produced plasmas. Experiments using laser-irradiated foils produce expanding, hemispherical plasma plumes carrying MG Biermann-battery magnetic fields, which can be driven to interact and reconnect. Thomson-scattering measurements of electron and ion temperatures in the interaction region of two colliding, magnetized plasmas show no thermal enhancement due to reconnection, as expected for β ~ 8 plasmas. Two different proton radiography techniques used to image the magnetic field structures show deformation, pileup, and annihilation of magnetic flux. High-resolution images reveal unambiguously reconnection-induced jets emerging from the interaction region and show instabilities in the expanding plasma plumes and supersonic, hydrodynamic jets due to the plasma collision. Quantitative magnetic flux data show that reconnection in experiments with asymmetry in the scale size, density, temperature, and plasma flow across the reconnection region occurs less efficiently than in similar, symmetric experiments. This result is attributed to disruption of the Hall mechanism mediating collisionless reconnection. The collision of plasmas carrying parallel magnetic fields has also been probed, illustrating the deformation of magnetic field structures in high-energy-density plasmas in the absence of reconnection. These experiments are particularly relevant to high- β reconnection environments, such as the magnetopause. This work was performed in collaboration with C. Li, F. Séguin, A. Zylstra, H. Rinderknecht, H. Sio, J. Frenje, and R. Petrasso (MIT), I. Igumenshchev, V. Glebov, C. Stoeckl, and D. Froula (LLE), J. Ross and R. Town (LLNL), W. Fox (UNH), and A. Nikroo (GA), and was supported in part by the NLUF, FSC/UR, U.S. DOE, LLNL, and LLE.

Pair mobility functions for rigid spheres in concentrated colloidal dispersions: Stresslet and straining motion couplings

NASA Astrophysics Data System (ADS)

Su, Yu; Swan, James W.; Zia, Roseanna N.

2017-03-01

Accurate modeling of particle interactions arising from hydrodynamic, entropic, and other microscopic forces is essential to understanding and predicting particle motion and suspension behavior in complex and biological fluids. The long-range nature of hydrodynamic interactions can be particularly challenging to capture. In dilute dispersions, pair-level interactions are sufficient and can be modeled in detail by analytical relations derived by Jeffrey and Onishi [J. Fluid Mech. 139, 261-290 (1984)] and Jeffrey [Phys. Fluids A 4, 16-29 (1992)]. In more concentrated dispersions, analytical modeling of many-body hydrodynamic interactions quickly becomes intractable, leading to the development of simplified models. These include mean-field approaches that smear out particle-scale structure and essentially assume that long-range hydrodynamic interactions are screened by crowding, as particle mobility decays at high concentrations. Toward the development of an accurate and simplified model for the hydrodynamic interactions in concentrated suspensions, we recently computed a set of effective pair of hydrodynamic functions coupling particle motion to a hydrodynamic force and torque at volume fractions up to 50% utilizing accelerated Stokesian dynamics and a fast stochastic sampling technique [Zia et al., J. Chem. Phys. 143, 224901 (2015)]. We showed that the hydrodynamic mobility in suspensions of colloidal spheres is not screened, and the power law decay of the hydrodynamic functions persists at all concentrations studied. In the present work, we extend these mobility functions to include the couplings of particle motion and straining flow to the hydrodynamic stresslet. The couplings computed in these two articles constitute a set of orthogonal coupling functions that can be utilized to compute equilibrium properties in suspensions at arbitrary concentration and are readily applied to solve many-body hydrodynamic interactions analytically.

How Expanded Ionospheres of Hot Jupiters Can Prevent Escape of Radio Emission Generated by the Cyclotron Maser Instability

NASA Astrophysics Data System (ADS)

Weber, Christof; Lammer, Helmut; Shaikhislamov, Ildar F.; Erkaev, Nikolai; Chadney, Joshua M.; Khodachenko, Maxim L.; Grießmeier, Jean-Mathias; Rucker, Helmut O.; Vocks, Christian; Macher, Wolfgang; Odert, Petra; Kislyakova, Kristina G.

2017-04-01

We present a study of the plasma conditions in the atmospheres of the Hot Jupiters HD 209458b and HD 189733b and for an HD 209458b-like planet at orbit locations between 0.2-1 AU around a Sun-like star. We discuss how these conditions influence the radio emission we expect from their planetary magnetospheres. We find that the environmental conditions for the cyclotron maser instability (CMI), the process which is responsible for the generation of radio waves at magnetic planets in the solar system, most likely will not operate at Hot Jupiters. The reason for that is that hydrodynamically expanding atmospheres possess extended ionospheres whose plasma densities within the magnetosphere are so large that the plasma frequency is much higher than the cyclotron frequency, which contradicts the necessary condition for the production of radio emission and prevents the escape of radio waves from close-in extrasolar planets at distances <0.05 AU from a Sun-like host star. The upper atmosphere structure of Hot Jupiters around stars similar to the Sun changes between 0.2 and 0.5 AU from the hydrodynamic to a hydrostatic regime and this results in conditions similar to solar system planets with a region of depleted plasma between the exobase and the magnetopause where the plasma frequency can be lower than the cyclotron frequency. In such an environment a beam of highly energetic electrons accelerated along the field lines towards the planet can produce radio emission. However, even if the CMI could operate the extended ionospheres of Hot Jupiters are too dense to let the radio emission escape from the planets. We also investigate the possible radio emission of the Hot Jupiter Tau Bootis b by placing it at different orbital distances from the host star, i.e. 0.1 and 0.2 AU. In particular we check if the atmosphere of Tau Bootis b at 0.046 AU is in the hydrostatic or in the hydrodynamic regime. If it is in the hydrodynamic regime it's ionosphere is extended and will constitute an obstacle for possibly generated radio waves or the generation via the Cyclotron Maser Instability (CMI) might even be prevented completely. Furthermore we investigate at which orbital location the atmosphere undergoes the transformation from hydrodynamic to hydrostatic, i.e. the transformation to more favourable conditions for the CMI.

Experimental study and discrete element method simulation of Geldart Group A particles in a small-scale fluidized bed

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

Li, Tingwen; Rabha, Swapna; Verma, Vikrant

Geldart Group A particles are of great importance in various chemical processes because of advantages such as ease of fluidization, large surface area, and many other unique properties. It is very challenging to model the fluidization behavior of such particles as widely reported in the literature. In this study, a pseudo-2D experimental column with a width of 5 cm, a height of 45 cm, and a depth of 0.32 cm was developed for detailed measurements of fluidized bed hydrodynamics of fine particles to facilitate the validation of computational fluid dynamic (CFD) modeling. The hydrodynamics of sieved FCC particles (Sauter meanmore » diameter of 148 µm and density of 1300 kg/m3) and NETL-32D sorbents (Sauter mean diameter of 100 µm and density of 480 kg/m3) were investigated mainly through the visualization by a high-speed camera. Numerical simulations were then conducted by using NETL’s open source code MFIX-DEM. Both qualitative and quantitative information including bed expansion, bubble characteristics, and solid movement were compared between the numerical simulations and the experimental measurement. Furthermore, the cohesive van der Waals force was incorporated in the MFIX-DEM simulations and its influences on the flow hydrodynamics were studied.« less

Experimental study and discrete element method simulation of Geldart Group A particles in a small-scale fluidized bed

DOE PAGES

Li, Tingwen; Rabha, Swapna; Verma, Vikrant; ...

2017-09-19

Geldart Group A particles are of great importance in various chemical processes because of advantages such as ease of fluidization, large surface area, and many other unique properties. It is very challenging to model the fluidization behavior of such particles as widely reported in the literature. In this study, a pseudo-2D experimental column with a width of 5 cm, a height of 45 cm, and a depth of 0.32 cm was developed for detailed measurements of fluidized bed hydrodynamics of fine particles to facilitate the validation of computational fluid dynamic (CFD) modeling. The hydrodynamics of sieved FCC particles (Sauter meanmore » diameter of 148 µm and density of 1300 kg/m3) and NETL-32D sorbents (Sauter mean diameter of 100 µm and density of 480 kg/m3) were investigated mainly through the visualization by a high-speed camera. Numerical simulations were then conducted by using NETL’s open source code MFIX-DEM. Both qualitative and quantitative information including bed expansion, bubble characteristics, and solid movement were compared between the numerical simulations and the experimental measurement. Furthermore, the cohesive van der Waals force was incorporated in the MFIX-DEM simulations and its influences on the flow hydrodynamics were studied.« less

Exploration of the Transition from the Hydrodynamic-like to the Strongly Kinetic Regime in Shock-Driven Implosions

DOE PAGES

Rosenberg, M. J.; Rinderknecht, H. G.; Hoffman, N. M.; ...

2014-05-05

Clear evidence of the transition from hydrodynamiclike to strongly kinetic shock-driven implosions is, for the first time, revealed and quantitatively assessed. Implosions with a range of initial equimolar D 3He gas densities show that as the density is decreased, hydrodynamic simulations strongly diverge from and increasingly over-predict the observed nuclear yields, from a factor of ~2 at 3.1 mg/cm 3 to a factor of 100 at 0.14 mg/cm 3. (The corresponding Knudsen number, the ratio of ion mean-free path to minimum shell radius, varied from 0.3 to 9; similarly, the ratio of fusion burn duration to ion diffusion time, anothermore » figure of merit of kinetic effects, varied from 0.3 to 14.) This result is shown to be unrelated to the effects of hydrodynamic mix. As a first step to garner insight into this transition, a reduced ion kinetic (RIK) model that includes gradient-diffusion and loss-term approximations to several transport processes was implemented within the framework of a one-dimensional radiation-transport code. After empirical calibration, the RIK simulations reproduce the observed yield trends, largely as a result of ion diffusion and the depletion of the reacting tail ions.« less

Hydrodynamic evaluation of a full-scale facultative pond by computational fluid dynamics (CFD) and field measurements.

PubMed

Passos, Ricardo Gomes; von Sperling, Marcos; Ribeiro, Thiago Bressani

2014-01-01

Knowledge of the hydraulic behaviour is very important in the characterization of a stabilization pond, since pond hydrodynamics plays a fundamental role in treatment efficiency. An advanced hydrodynamics characterization may be achieved by carrying out measurements with tracers, dyes and drogues or using mathematical simulation employing computational fluid dynamics (CFD). The current study involved experimental determinations and mathematical simulations of a full-scale facultative pond in Brazil. A 3D CFD model showed major flow lines, degree of dispersion, dead zones and short circuit regions in the pond. Drogue tracking, wind measurements and dye dispersion were also used in order to obtain information about the actual flow in the pond and as a means of assessing the performance of the CFD model. The drogue, designed and built as part of this research, and which included a geographical positioning system (GPS), presented very satisfactory results. The CFD modelling has proven to be very useful in the evaluation of the hydrodynamic conditions of the facultative pond. A virtual tracer test allowed an estimation of the real mean hydraulic retention time and mixing conditions in the pond. The computational model in CFD corresponded well to what was verified in the field.

The Green's function in a channel with a sound-absorbing cover in the case of a uniform flow

NASA Astrophysics Data System (ADS)

Sobolev, A. F.

2012-07-01

We study the modal structure of an acoustic field of a point source as function of channel wall admittance in the case of a two-dimensional channel. The characteristic equation for determining the eigen-values corresponding to the boundary problem is studied in the form of this equation's dependence on the admittance, which varies in the entire complex plane. All modes, without exception, existing in the channel and forming the source field are classified based on the obtained topography of the characteristic equation. The expressions that describe the amplitudes and spatial distribution of the hydrodynamic modes, attenuation rate (for stable modes), or increment (for unstable modes) were obtained as functions of the wall admittance and flow velocity. It is shown that in addition to the hydrodynamic unstable modes existing downstream from the source, hydrodynamic unstable modes exist upstream from the source at any admittance. They appear only when the admittance has an elastic character. It is shown that hydrodynamic modes are induced only in the case when the source is located close to the wall or on the wall. The amplitude of these modes decreases exponentially with distance from the wall.

Colloidal Microworms Propelling via a Cooperative Hydrodynamic Conveyor Belt.

PubMed

Martinez-Pedrero, Fernando; Ortiz-Ambriz, Antonio; Pagonabarraga, Ignacio; Tierno, Pietro

2015-09-25

We study propulsion arising from microscopic colloidal rotors dynamically assembled and driven in a viscous fluid upon application of an elliptically polarized rotating magnetic field. Close to a confining plate, the motion of this self-assembled microscopic worm results from the cooperative flow generated by the spinning particles which act as a hydrodynamic "conveyor belt." Chains of rotors propel faster than individual ones, until reaching a saturation speed at distances where induced-flow additivity vanishes. By combining experiments and theoretical arguments, we elucidate the mechanism of motion and fully characterize the propulsion speed in terms of the field parameters.

Applications of Density Functional Theory in Soft Condensed Matter

NASA Astrophysics Data System (ADS)

Löwen, Hartmut

Applications of classical density functional theory (DFT) to soft matter systems like colloids, liquid crystals and polymer solutions are discussed with a focus on the freezing transition and on nonequilibrium Brownian dynamics. First, after a brief reminder of equilibrium density functional theory, DFT is applied to the freezing transition of liquids into crystalline lattices. In particular, spherical particles with radially symmetric pair potentials will be treated (like hard spheres, the classical one-component plasma or Gaussian-core particles). Second, the DFT will be generalized towards Brownian dynamics in order to tackle nonequilibrium problems. After a general introduction to Brownian dynamics using the complementary Smoluchowski and Langevin pictures appropriate for the dynamics of colloidal suspensions, the dynamical density functional theory (DDFT) will be derived from the Smoluchowski equation. This will be done first for spherical particles (e.g. hard spheres or Gaussian-cores) without hydrodynamic interactions. Then we show how to incorporate hydrodynamic interactions between the colloidal particles into the DDFT framework and compare to Brownian dynamics computer simulations. Third orientational degrees of freedom (rod-like particles) will be considered as well. In the latter case, the stability of intermediate liquid crystalline phases (isotropic, nematic, smectic-A, plastic crystals etc) can be predicted. Finally, the corresponding dynamical extension of density functional theory towards orientational degrees of freedom is proposed and the collective behaviour of "active" (self-propelled) Brownian particles is briefly discussed.

Effects of initial-state dynamics on collective flow within a coupled transport and viscous hydrodynamic approach

NASA Astrophysics Data System (ADS)

Chattopadhyay, Chandrodoy; Bhalerao, Rajeev S.; Ollitrault, Jean-Yves; Pal, Subrata

2018-03-01

We evaluate the effects of preequilibrium dynamics on observables in ultrarelativistic heavy-ion collisions. We simulate the initial nonequilibrium phase within a multiphase transport (AMPT) model, while the subsequent near-equilibrium evolution is modeled using (2+1)-dimensional relativistic viscous hydrodynamics. We match the two stages of evolution carefully by calculating the full energy-momentum tensor from AMPT and using it as input for the hydrodynamic evolution. We find that when the preequilibrium evolution is taken into account, final-state observables are insensitive to the switching time from AMPT to hydrodynamics. Unlike some earlier treatments of preequilibrium dynamics, we do not find the initial shear viscous tensor to be large. With a shear viscosity to entropy density ratio of 0.12, our model describes quantitatively a large set of experimental data on Pb+Pb collisions at the Large Hadron Collider over a wide range of centrality: differential anisotropic flow vn(pT) (n =2 -6 ) , event-plane correlations, correlation between v2 and v3, and cumulant ratio v2{4 } /v2{2 } .

Evaporation effects in a shock-driven multiphase instability with a spherical interface

NASA Astrophysics Data System (ADS)

Paudel, Manoj; Dahal, Jeevan; McFarland, Jacob

2017-11-01

This talk presents results from 3D numerical simulations of a shock driven instability of a gas-particle system with a spherical interface. Two cases, one with an evaporating particle cloud and another with a gas only approximation of this particle cloud, were run in the hydrodynamics code FLASH, developed at University of Chicago. It is shown that the gas only approximation, a classical Richtmyer Meshkov instability, cannot replicate effects from particles like, lag, clustering, and evaporation. Instead, both gas hydrodynamics and particle properties influence one another and are coupled. Results are presented to highlight the coupling of interface evolution and particle evaporation. Qualitative and quantitative differences in the RMI and SDMI are presented by studying the change in gas properties like density and vorticity within the interface. Similarly, the effect of gas hydrodynamics on particles distribution and evaporation is studied. Particle evaporation rates are compared with 1D models and show poor agreement. The variation in evaporation rates for similar sized particles and the role of gas hydrodynamics in these variation is explored.

Hydrodynamic Properties of Planing Surfaces and Flying Boats

NASA Technical Reports Server (NTRS)

Sokolov, N. A.

1950-01-01

The study of the hydrodynamic properties of planing bottom of flying boats and seaplane floats is at the present time based exclusively on the curves of towing tests conducted in tanks. In order to provide a rational basis for the test procedure in tanks and practical design data, a theoretical study must be made of the flow at the step and relations derived that show not only qualitatively but quantitatively the inter-relations of the various factors involved. The general solution of the problem of the development of hydrodynamic forces during the motion of the seaplane float or flying boat is very difficult for it is necessary to give a three-dimensional solution, which does not always permit reducing the analysis to the form of workable computation formulas. On the other had, the problem is complicated by the fact that the object of the analysis is concerned with two fluid mediums, namely, air and water, which have a surface of density discontinuity between them. The theoretical and experimental investigations on the hydrodynamics of a ship cannot be completely carried over to the design of floats and flying-boat hulls, because of the difference in the shape of the contour lines of the bodies, and, because of the entirely different flow conditions from the hydrodynamic viewpoint.

Requirement for serum in medium supplemented with insulin-transferrin-selenium for hydrodynamic cultivation of engineered cartilage.

PubMed

Yang, Yueh-Hsun; Barabino, Gilda A

2011-08-01

Achievement of viable engineered tissues through in vitro cultivation in bioreactor systems requires a thorough understanding of the complex interplay between hydrodynamic forces and biochemical cues such as serum. To this end, chondrocyte-seeded constructs were cultured under continuous fluid-induced shear forces with reduced serum content (0%-2%, v/v), which was partially or completely replaced by a potential substitute, insulin-transferrin-selenium, to minimize deleterious effects associated with the use of culture media containing high levels of serum (10%-20%). Low-serum cultures yielded constructs with similar biochemical properties to those cultivated with high-serum supplements, whereas the serum-free constructs exhibited poor cell proliferation, insufficient extracellular matrix production, and rapid degradation of and/or shear-induced damage to polyglycolic acid scaffolds. A fibrous outer capsule typically observed in hydrodynamic cultures and characterized by increased cell density and decreased (virtually none) glycosaminoglycan deposition was eliminated when serum concentration was equal to or <0.2% in the presence of hydrodynamic stimuli. Our findings suggest that serum is a requirement in insulin-transferrin-selenium-supplemented cultures in order for constructs to exhibit improved properties in response to hydrodynamic forces, and that mechanical and biochemical stimuli may synergistically modulate tissue properties and morphology through shear-responsive signals.

IInvestigations of space-time variability of the sea level in the Barents Sea and the White Sea by satellite altimetry data and results of hydrodynamic modelling

NASA Astrophysics Data System (ADS)

Lebedev, S. A.; Zilberstein, O. I.; Popov, S. K.; Tikhonova, O. V.

2003-04-01

The problem of retrieving of the sea level anomalies in the Barents and White Seas from satellite can be considered as two different problems. The first one is to calculate the anomalies of sea level along the trek taking into account all amendments including tidal heights. The second one is to obtain of fields of the sea level anomalies on the grid over one cycle of the exact repeat altimetry mission. Experience results show that there is preferable to use the regional tidal model for calculating tidal heights. To construct of the anomalies fields of the sea level during the exact repeat mission (cycle 35 days for ERS-1 and ERS-2), when a density of the coverage of the area of water of the Barents and White Seas by satellite measurements achieves maximum. It is necessary to solve the problem of the error minimum. This error is based by the temporal difference of the measurements over one cycle and by the specific of the hydrodynamic regime of the both seas (tidal, storm surge variations, tidal currents). To solve this problem it is assumed to use the results of the hydrodynamic modeling. The error minimum is preformed by the regression of the model results and satellite measurements. As a version it is considered the possibility of the utilizing of the neuronet obtained by the model results to construct maps of the sea level anomalies. The comparison of the model results and the calculation of the satellite altimetry variability of the sea level of Barents and White Seas shows a good coincidence between them. The satellite altimetry data of ERS-1/2 and TOPEX/POSEIDON of Ocean Altimeter Pathfinder Project (NASA/GSFC) has been used in this study. Results of the regional tidal model computations and three dimensional baroclinic model created in the Hydrometeocenter have been used as well. This study also exploited the atmosphere date of the Project REANALYSIS. The research was undertaken with partial support from the Russian Basic Research Foundation (Project No. 01-07-90106).

Out-of-Bounds Hydrodynamics in Anisotropic Dirac Fluids

NASA Astrophysics Data System (ADS)

Link, Julia M.; Narozhny, Boris N.; Kiselev, Egor I.; Schmalian, Jörg

2018-05-01

We study hydrodynamic transport in two-dimensional, interacting electronic systems with merging Dirac points at charge neutrality. The dispersion along one crystallographic direction is Dirac-like, while it is Newtonian-like in the orthogonal direction. As a result, the electrical conductivity is metallic in one and insulating in the other direction. The shear viscosity tensor contains six independent components, which can be probed by measuring an anisotropic thermal flow. One of the viscosity components vanishes at zero temperature leading to a generalization of the previously conjectured lower bound for the shear viscosity to entropy density ratio.

Extended hydrodynamic theory of the peak and minimum pool boiling heat fluxes

NASA Technical Reports Server (NTRS)

Linehard, J. H.; Dhir, V. K.

1973-01-01

The hydrodynamic theory of the extreme pool boiling heat fluxes is expanded to embrace a variety of problems that have not previously been analyzed. These problems include the prediction of the peak heat flux on a variety of finite heaters, the influence of viscosity on the Taylor and Helmoltz instability mechanisms with application to film boiling and to the peak heat flux in viscous liquids, the formalization of the analogy between high-current-density electrolysis and boiling, and the description of boiling in the low-gravity limit. The predictions are verified with a large number of new data.

Impacts of variable channel hydraulics on the stratigraphic record: an example provided from the Tullig Sandstone, Western Irish Namurian Basin

NASA Astrophysics Data System (ADS)

Wu, C.; Nittrouer, J. A.; Burmeister, K. C.

2017-12-01

River hydrodynamic conditions are modified where a system approaches its terminal basin, characterized by the onset of non-uniform "backwater" flow. A decrease in boundary shear stress in the backwater region reduces transport capacity and results in sediment deposition on the channel bed. Although such morphodynamic conditions are common in modern fluvial-deltaic channels, the extent to which these processes are prevalent in the stratigraphic record remains unclear. For example, a few studies documenting changes in fluvial sandstone channel dimensions and grain size distributions near a river terminus attributed this variability to backwater hydrodynamics. However, quantitative tests using morphodynamic models bolstered by a variety of field observations, which could then be linked to sediment depositional patterns and stratigraphy, have yet to be produced. Here we calibrate a one-dimensional river flow model with measurements of paleo-slope and channel depth, and use the output to constrain a sediment transport model, with data from the Tullig Sandstone in the Western Irish Namurian Basin. Based on the model results, our analyses indicate that: (1) backwater hydrodynamics influence the spatial variation of sandstone dimensions and grain size across the delta, and (2) backwater hydrodynamics drive channel bed aggradation and progradation of the river mouth for conditions of constant sea level. Field data indicate that the reach-average story thickness increases, and then decreases, progressing downstream over the backwater reach. Based on the inferred transport and depositional processes, the measured deltaic stratigraphy patterns shown here are assumed to be associated with backwater hydrodynamics, and are therefore largely autogenic in origin. These analyses indicate that non-uniform hydrodynamics can generate stratigraphic patterns that could be conflated as arising due to allogenic effects, based on traditional geometric or diffusion-based depositional models. Moreover, the signals of river hydrodynamics preserved in the stratigraphic record can be a useful tool for differentiating between short-term autogenic and long-term allogenic processes.

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

Strozzi, David J.; Perkins, L. J.; Marinak, M. M.

The effects of an imposed, axial magnetic fieldmore » $$B_{z0}$$ on hydrodynamics and energetic electrons in inertial confinement fusion indirect-drive hohlraums are studied. We present simulations from the radiation-hydrodynamics code HYDRA of a low-adiabat ignition design for the National Ignition Facility, with and without $$B_{z0}=70~\\text{T}$$. The field’s main hydrodynamic effect is to significantly reduce electron thermal conduction perpendicular to the field. This results in hotter and less dense plasma on the equator between the capsule and hohlraum wall. The inner laser beams experience less inverse bremsstrahlung absorption before reaching the wall. The X-ray drive is thus stronger from the equator with the imposed field. We study superthermal, or ‘hot’, electron dynamics with the particle-in-cell code ZUMA, using plasma conditions from HYDRA. During the early-time laser picket, hot electrons based on two-plasmon decay in the laser entrance hole (Regan et al., Phys. Plasmas, vol. 17(2), 2010, 020703) are guided to the capsule by a 70 T field. Twelve times more energy deposits in the deuterium–tritium fuel. For plasma conditions early in peak laser power, we present mono-energetic test-case studies with ZUMA as well as sources based on inner-beam stimulated Raman scattering. Furthermore, the effect of the field on deuterium–tritium deposition depends strongly on the source location, namely whether hot electrons are generated on field lines that connect to the capsule.« less

Spatio-temporal dynamics of an active, polar, viscoelastic ring.

PubMed

Marcq, Philippe

2014-04-01

Constitutive equations for a one-dimensional, active, polar, viscoelastic liquid are derived by treating the strain field as a slow hydrodynamic variable. Taking into account the couplings between strain and polarity allowed by symmetry, the hydrodynamics of an active, polar, viscoelastic body include an evolution equation for the polarity field that generalizes the damped Kuramoto-Sivashinsky equation. Beyond thresholds of the active coupling coefficients between the polarity and the stress or the strain rate, bifurcations of the homogeneous state lead first to stationary waves, then to propagating waves of the strain, stress and polarity fields. I argue that these results are relevant to living matter, and may explain rotating actomyosin rings in cells and mechanical waves in epithelial cell monolayers.

Plasma Relaxation and Topological Aspects in Electron Magnetohydrodynamics

NASA Astrophysics Data System (ADS)

Shivamoggi, Bhimsen

2016-10-01

Parker's formulation of isotopological plasma relaxation process toward minimum magnetics energy states in magnetohydrodynamics (MHD) is extended to electron MHD (EMHD). The lower bound on magnetic energy in EMHD is determined by both the magnetic field and the electron vorticity field topologies, and is shown to be reduced further in EMHD by an amount proportional to the sum of total electron-flow kinetic energy and total electron-flow enstrophy. The EMHD Beltrami condition becomes equivalent to the potential vorticity conservation equation in two-dimensional (2D) hydrodynamics, and the torsion coefficient and turns out to be proportional to potential vorticity. The winding pattern of the magnetic field lines appears to evolve therefore in the same way as potential vorticity lines in 2D hydrodynamics.

Plasma relaxation and topological aspects in electron magnetohydrodynamics

NASA Astrophysics Data System (ADS)

Shivamoggi, B. K.

2016-07-01

Parker's formulation of isotopological plasma relaxation process toward minimum magnetics energy states in magnetohydrodynamics (MHD) is extended to electron MHD (EMHD). The lower bound on magnetic energy in EMHD is determined by both the magnetic field and the electron vorticity field topologies, and is shown to be reduced further in EMHD by an amount proportional to the sum of total electron-flow kinetic energy and total electron-flow enstrophy. The EMHD Beltrami condition becomes equivalent to the potential vorticity conservation equation in two-dimensional (2D) hydrodynamics, and the torsion coefficient α turns out to be proportional to potential vorticity. The winding pattern of the magnetic field lines appears to evolve, therefore, in the same way as potential vorticity lines in 2D hydrodynamics.

Numerical investigation of frequency spectrum in the Hasegawa-Wakatani model

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

Kim, Juhyung; Terry, P. W.

2013-10-15

The wavenumber-frequency spectrum of the two-dimensional Hasegawa-Wakatani model is investigated in the hydrodynamic, intermediate, and adiabatic regimes. A nonlinear frequency and a line width related to energy transfer properties provide a measure of the average frequency and spectral broadening, respectively. In the adiabatic regime, narrow spectra, typical of wave turbulence, are observed with a nonlinear frequency shift in the electron drift direction. In the hydrodynamic regime, broad spectra with almost zero nonlinear frequencies are observed. Nonlinear frequency shifts are shown to be related to nonlinear energy transfer by vorticity advection through the high frequency region of the spectrum. In themore » intermediate regime, the nonlinear frequency shift for density fluctuations is observed to be weaker than that of electrostatic potential fluctuations. The weaker frequency shift of the density fluctuations is due to nonlinear density advection, which favors energy transfer in the low frequency range. Both the nonlinear frequency and the spectral width increase with poloidal wavenumber k{sub y}. In addition, in the adiabatic regime where the nonlinear interactions manifest themselves in the nonlinear frequency shift, the cross-phase between the density and potential fluctuations is observed to match a linear relation, but only if the linear response of the linearly stable eigenmode branch is included. Implications of these numerical observations are discussed.« less

Nonlocal effects in nonisothermal hydrodynamics from the perspective of beyond-equilibrium thermodynamics.

PubMed

Hütter, Markus; Brader, Joseph M

2009-06-07

We examine the origins of nonlocality in a nonisothermal hydrodynamic formulation of a one-component fluid of particles that exhibit long-range correlations, e.g., due to a spherically symmetric, long-range interaction potential. In order to furnish the continuum modeling with physical understanding of the microscopic interactions and dynamics, we make use of systematic coarse graining from the microscopic to the continuum level. We thus arrive at a thermodynamically admissible and closed set of evolution equations for the densities of momentum, mass, and internal energy. From the consideration of an illustrative special case, the following main conclusions emerge. There are two different source terms in the momentum balance. The first is a body force, which in special circumstances can be related to the functional derivative of a nonlocal Helmholtz free energy density with respect to the mass density. The second source term is proportional to the temperature gradient, multiplied by the nonlocal entropy density. These two source terms combine into a pressure gradient only in the absence of long-range effects. In the irreversible contributions to the time evolution, the nonlocal contributions arise since the self-correlations of the stress tensor and heat flux, respectively, are nonlocal as a result of the microscopic nonlocal correlations. Finally, we point out specific points that warrant further discussions.

Impact of solvent granularity and layering on tracer hydrodynamics in confinement.

PubMed

Bollinger, Jonathan A; Carmer, James; Jain, Avni; Truskett, Thomas M

2016-11-28

Classic hydrodynamic arguments establish that when a spherical tracer particle is suspended between parallel walls, tracer-wall coupling mediated by the solvent will cause the tracer to exhibit position-dependent diffusivity. We investigate how the diffusivity profiles of confined tracers are impacted by the diameter size-ratio of the tracer to solvent: starting from the classic limit of infinite size-ratio (i.e., continuum solvent), we consider size-ratios of four or less to examine how hydrodynamic predictions are disrupted for systems where the tracer and solvent are of similar scale. We use computer simulations and techniques based on the Fokker-Planck formalism to calculate the diffusivity profiles of hard-sphere tracer particles in hard-sphere solvents, focusing on the dynamics perpendicular to the walls. Given wall separations of several tracer diameters, we first consider confinement between hard walls, where anisotropic structuring at the solvent lengthscale generates inhomogeneity in the tracer free-energy landscape and undermines hydrodynamic predictions locally. We then introduce confining planes that we term transparent walls, which restrict tracer and solvent center-accessibilities while completely eliminating static anisotropy, and reveal position-dependent signatures in tracer diffusivity solely attributable to confinement. With or without suppressing static heterogeneity, we find that tracer diffusivity increasingly deviates on a local basis from hydrodynamic predictions at smaller size-ratios. However, hydrodynamic theory still approximately captures spatially-averaged dynamics across the pores even for very small tracer-solvent size-ratios over a wide range of solvent densities and wall separations.

Shape and evolution of wind-blown bubbles of massive stars: on the effect of the interstellar magnetic field

NASA Astrophysics Data System (ADS)

van Marle, A. J.; Meliani, Z.; Marcowith, A.

2015-12-01

Context. The winds of massive stars create large (>10 pc) bubbles around their progenitors. As these bubbles expand they encounter the interstellar coherent magnetic field which, depending on its strength, can influence the shape of the bubble. Aims: We wish to investigate if, and how much, the interstellar magnetic field can contribute to the shape of an expanding circumstellar bubble around a massive star. Methods: We use the MPI-AMRVAC code to make magneto-hydrodynamical simulations of bubbles, using a single star model, combined with several different field strengths: B = 5, 10, and 20 μG for the interstellar magnetic field. This covers the typical field strengths of the interstellar magnetic fields found in the galactic disk and bulge. Furthermore, we present two simulations that include both a 5 μG interstellar magnetic field and a warm (10 000 K) interstellar medium (ISM) and two different ISM densities to demonstrate how the magnetic field can combine with other external factors to influence the morphology of the circumstellar bubbles. Results: Our results show that low magnetic fields, as found in the galactic disk, inhibit the growth of the circumstellar bubbles in the direction perpendicular to the field. As a result, the bubbles become ovoid, rather than spherical. Strong interstellar fields, such as observed for the galactic bulge, can completely stop the expansion of the bubble in the direction perpendicular to the field, leading to the formation of a tube-like bubble. When combined with an ISM that is both warm and high density the bubble is greatly reduced in size, causing a dramatic change in the evolution of temporary features inside the bubble such as Wolf-Rayet ring nebulae. Conclusions: The magnetic field of the interstellar medium can affect the shape of circumstellar bubbles. This effect may have consequences for the shape and evolution of circumstellar nebulae and supernova remnants, which are formed within the main wind-blown bubble. Appendices and movies associated to Figs. A.1-A.12 are available in electronic form at http://www.aanda.org

Imposed magnetic field and hot electron propagation in inertial fusion hohlraums

DOE PAGES

Strozzi, David J.; Perkins, L. J.; Marinak, M. M.; ...

2015-12-02

The effects of an imposed, axial magnetic fieldmore » $$B_{z0}$$ on hydrodynamics and energetic electrons in inertial confinement fusion indirect-drive hohlraums are studied. We present simulations from the radiation-hydrodynamics code HYDRA of a low-adiabat ignition design for the National Ignition Facility, with and without $$B_{z0}=70~\\text{T}$$. The field’s main hydrodynamic effect is to significantly reduce electron thermal conduction perpendicular to the field. This results in hotter and less dense plasma on the equator between the capsule and hohlraum wall. The inner laser beams experience less inverse bremsstrahlung absorption before reaching the wall. The X-ray drive is thus stronger from the equator with the imposed field. We study superthermal, or ‘hot’, electron dynamics with the particle-in-cell code ZUMA, using plasma conditions from HYDRA. During the early-time laser picket, hot electrons based on two-plasmon decay in the laser entrance hole (Regan et al., Phys. Plasmas, vol. 17(2), 2010, 020703) are guided to the capsule by a 70 T field. Twelve times more energy deposits in the deuterium–tritium fuel. For plasma conditions early in peak laser power, we present mono-energetic test-case studies with ZUMA as well as sources based on inner-beam stimulated Raman scattering. Furthermore, the effect of the field on deuterium–tritium deposition depends strongly on the source location, namely whether hot electrons are generated on field lines that connect to the capsule.« less

Interpreting tracer breakthrough tailing from different forced-gradient tracer experiment configurations in fractured bedrock

USGS Publications Warehouse

Becker, M.W.; Shapiro, A.M.

2003-01-01

Conceptual and mathematical models are presented that explain tracer breakthrough tailing in the absence of significant matrix diffusion. Model predictions are compared to field results from radially convergent, weak-dipole, and push-pull tracer experiments conducted in a saturated crystalline bedrock. The models are based upon the assumption that flow is highly channelized, that the mass of tracer in a channel is proportional to the cube of the mean channel aperture, and the mean transport time in the channel is related to the square of the mean channel aperture. These models predict the consistent -2 straight line power law slope observed in breakthrough from radially convergent and weak-dipole tracer experiments and the variable straight line power law slope observed in push-pull tracer experiments with varying injection volumes. The power law breakthrough slope is predicted in the absence of matrix diffusion. A comparison of tracer experiments in which the flow field was reversed to those in which it was not indicates that the apparent dispersion in the breakthrough curve is partially reversible. We hypothesize that the observed breakthrough tailing is due to a combination of local hydrodynamic dispersion, which always increases in the direction of fluid velocity, and heterogeneous advection, which is partially reversed when the flow field is reversed. In spite of our attempt to account for heterogeneous advection using a multipath approach, a much smaller estimate of hydrodynamic dispersivity was obtained from push-pull experiments than from radially convergent or weak dipole experiments. These results suggest that although we can explain breakthrough tailing as an advective phenomenon, we cannot ignore the relationship between hydrodynamic dispersion and flow field geometry at this site. The design of the tracer experiment can severely impact the estimation of hydrodynamic dispersion and matrix diffusion in highly heterogeneous geologic media.

Covariant relativistic hydrodynamics of multispecies plasma and generalized Ohm's law

NASA Astrophysics Data System (ADS)

Gedalin, Michael

1996-04-01

Fully covariant hydrodynamical equations for a multispecies relativistic plasma in an external electromagnetic field are derived. The derived multifluid description takes into account binary Coulomb collisions, annihilation, and interaction with the photon background in terms of the invariant collision cross sections. A generalized Ohm's law is derived in a manifestly covariant form. Particular attention is devoted to the relativistic electron-positron plasma.

Advancing Traffic Flow Theory Using Empirical Microscopic Data

DOT National Transportation Integrated Search

2015-01-01

As reviewed in Section 1.1, much of traffic flow theory depends a fundamental relationship (FR) between flow, density, and space mean speed; either explicitly, e.g., hydrodynamic models such as LWR (Lighthill and Whitham, 1955, and Richards, 1956) or...

Onset of hydrodynamic mix in high-velocity, highly compressed inertial confinement fusion implosions.

PubMed

Ma, T; Patel, P K; Izumi, N; Springer, P T; Key, M H; Atherton, L J; Benedetti, L R; Bradley, D K; Callahan, D A; Celliers, P M; Cerjan, C J; Clark, D S; Dewald, E L; Dixit, S N; Döppner, T; Edgell, D H; Epstein, R; Glenn, S; Grim, G; Haan, S W; Hammel, B A; Hicks, D; Hsing, W W; Jones, O S; Khan, S F; Kilkenny, J D; Kline, J L; Kyrala, G A; Landen, O L; Le Pape, S; MacGowan, B J; Mackinnon, A J; MacPhee, A G; Meezan, N B; Moody, J D; Pak, A; Parham, T; Park, H-S; Ralph, J E; Regan, S P; Remington, B A; Robey, H F; Ross, J S; Spears, B K; Smalyuk, V; Suter, L J; Tommasini, R; Town, R P; Weber, S V; Lindl, J D; Edwards, M J; Glenzer, S H; Moses, E I

2013-08-23

Deuterium-tritium inertial confinement fusion implosion experiments on the National Ignition Facility have demonstrated yields ranging from 0.8 to 7×10(14), and record fuel areal densities of 0.7 to 1.3 g/cm2. These implosions use hohlraums irradiated with shaped laser pulses of 1.5-1.9 MJ energy. The laser peak power and duration at peak power were varied, as were the capsule ablator dopant concentrations and shell thicknesses. We quantify the level of hydrodynamic instability mix of the ablator into the hot spot from the measured elevated absolute x-ray emission of the hot spot. We observe that DT neutron yield and ion temperature decrease abruptly as the hot spot mix mass increases above several hundred ng. The comparison with radiation-hydrodynamic modeling indicates that low mode asymmetries and increased ablator surface perturbations may be responsible for the current performance.

Three dimensional, numerical analysis of an elasto hydrodynamic lubrication using fluid structure interaction (FSI) approach

NASA Astrophysics Data System (ADS)

Hanoca, P.; Ramakrishna, H. V.

2018-03-01

This work is related to develop a methodology to model and simulate the TEHD using the sequential application of CFD and CSD. The FSI analyses are carried out using ANSYS Workbench. In this analysis steady state, 3D Navier-Stoke equations along with energy equation are solved. Liquid properties are introduced where the viscosity and density are the function of pressure and temperature. The cavitation phenomenon is adopted in the analysis. Numerical analysis has been carried at different speeds and surfaces temperatures. During the analysis, it was found that as speed increases, hydrodynamic pressures will also increases. The pressure profile obtained from the Roelands equation is more sensitive to the temperature as compared to the Barus equation. The stress distributions specify the significant positions in the bearing structure. The developed method is capable of giving latest approaching into the physics of elasto hydrodynamic lubrication.