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Sample records for ray current-driven instability

  1. Current-Driven Filament Instabilities in Relativistic Plasmas. Final report

    SciTech Connect

    Ren, Chuang

    2013-02-13

    This grant has supported a study of some fundamental problems in current- and flow-driven instabilities in plasmas and their applications in inertial confinement fusion (ICF) and astrophysics. It addressed current-driven instabilities and their roles in fast ignition, and flow-driven instabilities and their applications in astrophysics.

  2. Current-driven Instabilities of Poynting-flux-dominated Jets

    NASA Astrophysics Data System (ADS)

    Nakamura, M.; Meier, D. L.

    2003-12-01

    Non-relativistic 3-D magnetohydrodynamic simulations of Poynting-flux-dominated (PFD) jets are presented. Our study focuses on the propagation of strongly magnetized hypersonic but sub-Alfvénic flow (C s2 << V jet2 < V A2) and the development of a current-driven instability (CDI). This instability may be responsible for the "wiggled" structures seen in VLBI-scale AGN jets. In the present paper we investigate the nonlinear behavior of PFD jets in a variety of external ambient magnetized gas distributions, including those with density, pressure, and temperature gradients. Our numerical results show that PFD jets can develop kink distortions in the trans-Alfvénic flow case, even when the flow itself is still strongly magnetically dominated. In the nonlinear development of the instability, a non-axisymmetric mode grows on time scales of order the Alfvén crossing time (in the jet frame) and proceeds to disrupt the kinematic and magnetic structure of the jet. Because of a large scale poloidal magnetic field in the ambient medium, the growth of surface modes (i.e., MHD Kelvin-Helmholtz instabilities) is suppressed. The CDI kink mode (m = 1) grows faster than the other higher order modes (m > 1), driven in large part by the radial component of the Lorentz force. Detailed studies of the CDI of PFD outflows using high-resolution computations, and application of these physical processes to sub-pc to pc scales structures of AGN jets, will be discussed. M.N. is supported by a NRC Resident Research Associateship, sponsored by the National Aeronautics and Space Administration.

  3. Filamentation instability of current-driven dust ion-acoustic waves in a collisional dusty plasma

    SciTech Connect

    Niknam, A. R.; Haghtalab, T.; Khorashadizadeh, S. M.

    2011-11-15

    A theoretical investigation has been made of the dust ion-acoustic filamentation instability in an unmagnetized current-driven dusty plasma by using the Lorentz transformation formulas. The effect of collision between the charged particles with neutrals and their thermal motion on this instability is considered. Developing the filamentation instability of the current-driven dust ion-acoustic wave allows us to determine the period and the establishment time of the filamentation structure and threshold for instability development.

  4. Filamentation instability of nonextensive current-driven plasma in the ion acoustic frequency range

    SciTech Connect

    Khorashadizadeh, S. M. Rastbood, E.; Niknam, A. R.

    2014-12-15

    The filamentation and ion acoustic instabilities of nonextensive current-driven plasma in the ion acoustic frequency range have been studied using the Lorentz transformation formulas. Based on the kinetic theory, the possibility of filamentation instability and its growth rate as well as the ion acoustic instability have been investigated. The results of the research show that the possibility and growth rate of these instabilities are significantly dependent on the electron nonextensive parameter and drift velocity. Besides, the increase of electrons nonextensive parameter and drift velocity lead to the increase of the growth rates of both instabilities. In addition, the wavelength region in which the filamentation instability occurs is more stretched in the presence of higher values of drift velocity and nonextensive parameter. Finally, the results of filamentation and ion acoustic instabilities have been compared and the conditions for filamentation instability to be dominant mode of instability have been presented.

  5. THREE-DIMENSIONAL RELATIVISTIC MAGNETOHYDRODYNAMIC SIMULATIONS OF CURRENT-DRIVEN INSTABILITY. III. ROTATING RELATIVISTIC JETS

    SciTech Connect

    Mizuno, Yosuke; Lyubarsky, Yuri; Nishikawa, Ken-Ichi; Hardee, Philip E.

    2012-09-20

    We have investigated the influence of jet rotation and differential motion on the linear and nonlinear development of the current-driven (CD) kink instability of force-free helical magnetic equilibria via three-dimensional relativistic magnetohydrodynamic simulations. In this study, we follow the temporal development within a periodic computational box. Displacement of the initial helical magnetic field leads to the growth of the CD kink instability. We find that, in accordance with the linear stability theory, the development of the instability depends on the lateral distribution of the poloidal magnetic field. If the poloidal field significantly decreases outward from the axis, then the initial small perturbations grow strongly, and if multiple wavelengths are excited, then nonlinear interaction eventually disrupts the initial cylindrical configuration. When the profile of the poloidal field is shallow, the instability develops slowly and eventually saturates. We briefly discuss implications of our findings for Poynting-dominated jets.

  6. Nonlinear development of strong current-driven instabilities and selective acceleration of ^3He ions

    NASA Astrophysics Data System (ADS)

    Toida, Mieko; Okumura, Hayato

    2003-10-01

    In some solar flares, the abundance of high-energy ^3He ions is extremely increased. As a mechanism for these ^3He rich events, current-driven instabilities are believed to be important. Nonlinear development of the strong current-driven instabilities and associated energy transfer to ^3He ions are studied theoretically and numerically [1]. First, by means of a two-dimensional, electrostatic, particle simulation code, it is demonstrated that ^3He ions are selectively accelerated by fundamental H cyclotron waves with frequencies ω ≃ 2Ω_3He (Ω_3He is the cyclotron frequency of ^3He). Then, from the analysis of the dispersion relation of these waves, it is found that the ω ≃ 2 Ω_ 3He waves have the greatest growth rate, if Te > 10 T_H. Energies of the ^3He ions are also discussed. Theoretical expression for the maximum ^3He energy is presented, which is in good agreement with the simulation results. Based on this theory, it is shown that when the initial electron drift energy is of the order of 10 keV, many ^3He ions can be accelerated to energies of the order of MeV/n. [1] M. Toida and H. Okumura, J. Phys. Soc. Jpn. 72,1098 (2003)

  7. Current-Driven Instabilities and Energy Dissipation Rates As a Predictive Tool for Solar Probe Plus

    NASA Astrophysics Data System (ADS)

    Wilson, L. B., III; Breneman, A. W.; Malaspina, D.; Le Contel, O.; Cully, C. M.

    2014-12-01

    We present recent observational evidence of current-driven instabilities in the terrestrial bow shock. We use an observed positive correlation between |δE| and |jo| to extrapolate the results to currently inaccessible regions of space (e.g., the solar corona). Magnitudes of energy dissipation per unit volume in the solar corona due to current-driven instabilities can be estimated using electric and magnetic fields values extrapolated to coronal values. The energy dissipation values estimated this way represent an upper bound on the true energy dissipation in these regions. For instance, previous studies have estimated current densities in the solar corona to range from 104 to 107 μA m-2, which correspond to extrapolated δE magnitudes in excess of 12,000 mV/m and thus, energy dissipation rates in excess of 108 μW m-3. These rates are six orders of magnitude higher than is necessary to explain the temperature of the corona. Similar extrapolations can be made for astrophysical phenomena such as the surface of a neutron star. The results are of particular importance for future missions like Solar Probe Plus and Solar Orbiter.

  8. Nonlocal effects on the convective properties of the electrostatic current-driven ion-cyclotron instability

    NASA Technical Reports Server (NTRS)

    Ganguli, G.; Bakshi, P.; Palmadesso, P.

    1984-01-01

    The convective behavior of the current-driven ion-cyclotron instability (CDICI) in the presence of nonlocal magnetic-shear and current-channel-width effects is investigated theoretically using the analytical approach of Bakshi et al. (1983). The results are presented in graphs and discussed. Three different CDICI regimes defined by the ratio of the channel width to the shear length are obtained: a purely nonlocal regime with reduced temporal growth rate and group velocity in the z direction going to zero (ratios greater than about 0.1); a regime corresponding to the results of local theory (ratios less than 0.01); and a regime characterized by decreasing temporal growth rate and by z and y group velocities which become negative when the channel width becomes less than the mean ion Larmor radius (ratios 0.001 or less).

  9. Relaxation of Pulsar Wind Nebula via Current-Driven Kink Instability

    NASA Astrophysics Data System (ADS)

    Mizuno, Yosuke; Lyubarsky, Yuri; Nishikawa, Ken-Ichi; Hardee, Philip E.

    We have investigated the relaxation of a hydrostatic hot plasma column containing toroidal magnetic field by the Current-Driven (CD) kink instability as a model of pulsar wind nebulae. In our simulations the CD kink instability was excited by a small initial velocity perturbation and developed turbulent structure inside the hot plasma column. We demonstrated that, as envisioned by Begelman, the hoop stress declines and the initial gas pressure excess near the axis decreases. The magnetization parameter "σ", the ratio of the magnetic energy to the thermal energy for a hot plasma, declined from an initial value of 0.3 to about 0.01 when the CD kink instability saturated. Our simulations demonstrated that axisymmetric models strongly overestimate the elongation of the pulsar wind nebulae. Therefore, the previous requirement for an extremely low pulsar wind magnetization can be abandoned. The observed structure of the pulsar wind nebulae do not contradict the natural assumption that the magnetic energy flux still remains a good fraction of the total energy flux after dissipation of alternating fields.

  10. Spatial growth of the current-driven instability in relativistic jets

    SciTech Connect

    Mizuno, Yosuke; Hardee, Philip E.; Nishikawa, Ken-Ichi

    2014-04-01

    We investigated the influence of velocity shear and a radial density profile on the spatial development of the current-driven (CD) kink instability along helically magnetized relativistic jets via three-dimensional relativistic magnetohydrodynamic simulations. In this study, we use a nonperiodic computational box, the jet flow is initially established across the computational grid, and a precessional perturbation at the inlet triggers growth of the kink instability. If the velocity shear radius is located inside the characteristic radius of the helical magnetic field, a static nonpropagating CD kink is excited as the perturbation propagates down the jet. Temporal growth disrupts the initial flow across the computational grid not too far from the inlet. On the other hand, if the velocity shear radius is outside the characteristic radius of the helical magnetic field, the kink is advected with the flow and grows spatially down the jet. In this case, flow is maintained to much larger distances from the inlet. The effect of different radial density profiles is more subtle. When the density increases with radius, the kink appears to saturate by the end of the simulation without apparent disruption of the helical twist. This behavior suggests that relativistic jets consisting of a tenuous spine surrounded by a denser medium with a velocity shear radius outside the radius of the maximum toroidal magnetic field have a relatively stable configuration.

  11. Spatial Growth of Current-driven Instability in Relativistic Rotating Jets and the Search for Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Singh, Chandra B.; Mizuno, Yosuke; de Gouveia Dal Pino, Elisabete M.

    2016-06-01

    Using the three-dimensional relativistic magnetohydrodynamic code RAISHIN, we investigated the influence of the radial density profile on the spatial development of the current-driven kink instability along magnetized rotating, relativistic jets. For the purposes of our study, we used a nonperiodic computational box, the jet flow is initially established across the computational grid, and a precessional perturbation at the inlet triggers the growth of the kink instability. We studied light and heavy jets with respect to the environment depending on the density profile. Different angular velocity amplitudes have been also tested. The results show the propagation of a helically kinked structure along the jet and a relatively stable configuration for the lighter jets. The jets appear to be collimated by the magnetic field, and the flow is accelerated owing to conversion of electromagnetic into kinetic energy. We also identify regions of high current density in filamentary current sheets, indicative of magnetic reconnection, which are associated with the kink-unstable regions and correlated with the decrease of the sigma parameter of the flow. We discuss the implications of our findings for Poynting-flux-dominated jets in connection with magnetic reconnection processes. We find that fast magnetic reconnection may be driven by the kink-instability turbulence and govern the transformation of magnetic into kinetic energy, thus providing an efficient way to power and accelerate particles in active galactic nucleus and gamma-ray-burst relativistic jets.

  12. Effect of dust charge fluctuations on current-driven electrostatic ion-cyclotron instability in a collisional magnetized plasma

    SciTech Connect

    Sharma, Suresh C.; Sharma, Kavita; Gahlot, Ajay

    2013-05-15

    Current-driven electrostatic ion-cyclotron (EIC) instability is studied in a collisional magnetized dusty plasma. The growth rate and unstable mode frequencies were evaluated based on existing physical parameters relevant to ion cyclotron waves in dusty plasmas. It is found that the unstable mode frequency and growth rate of current-driven EIC instability increase with δ (ion-to-electron density ratio). Moreover, the increase in electron neutral collisional frequency (ν{sub e}) has no effect on the unstable mode frequency while the normalized growth rate has linear dependence on ν{sub e}.

  13. Dielectric permittivity tensor and low frequency instabilities of a magnetoactive current-driven plasma with nonextensive distribution

    SciTech Connect

    Niknam, A. R.; Rastbood, E.; Khorashadizadeh, S. M.

    2015-12-15

    The dielectric permittivity tensor of a magnetoactive current-driven plasma is obtained by employing the kinetic theory based on the Vlasov equation and Lorentz transformation formulas with an emphasize on the q-nonextensive statistics. By deriving the q-generalized dispersion relation of the low frequency modes in this plasma system, the possibility and properties of filamentation and ion acoustic instabilities are then studied. It is shown that the occurrence and the growth rate of these instabilities depend strongly on the nonextensive parameters, external magnetic field strength, and drift velocity. It is observed that the growth rate of ion acoustic instability is affected by the magnetic field strength much more than that of the filamentation instability in the low frequency range. The external magnetic field facilitates the development of the ion-acoustic instability. It is also shown that the filamentation is the dominant instability only for the high value of drift velocity.

  14. Dielectric permittivity tensor and low frequency instabilities of a magnetoactive current-driven plasma with nonextensive distribution

    NASA Astrophysics Data System (ADS)

    Niknam, A. R.; Rastbood, E.; Khorashadizadeh, S. M.

    2015-12-01

    The dielectric permittivity tensor of a magnetoactive current-driven plasma is obtained by employing the kinetic theory based on the Vlasov equation and Lorentz transformation formulas with an emphasize on the q-nonextensive statistics. By deriving the q-generalized dispersion relation of the low frequency modes in this plasma system, the possibility and properties of filamentation and ion acoustic instabilities are then studied. It is shown that the occurrence and the growth rate of these instabilities depend strongly on the nonextensive parameters, external magnetic field strength, and drift velocity. It is observed that the growth rate of ion acoustic instability is affected by the magnetic field strength much more than that of the filamentation instability in the low frequency range. The external magnetic field facilitates the development of the ion-acoustic instability. It is also shown that the filamentation is the dominant instability only for the high value of drift velocity.

  15. Nonlinear dynamics of filamentation instability and current filament merging in a high density current-driven plasma

    NASA Astrophysics Data System (ADS)

    Khorashadizadeh, S. M.; Taghadosi, M. R.; Niknam, A. R.

    2015-12-01

    The magnetic field generation due to the filamentation instability (FI) of a high density current-driven plasma is studied through a new nonlinear diffusion equation. This equation is obtained on the basis of quantum hydrodynamic model and numerically solved by applying the Crank-Nicolson method. The spatiotemporal evolution of the magnetic field and the electron density distribution exhibits the current filament merging as a nonlinear phase of the FI which is responsible for the strong magnetic fields in the current-driven plasmas. It is found that the general behaviour of the FI is the same as that of the classical case but the instability growth rate, its magnitude, and the saturation time are affected by the quantum effects. It is eventually concluded that the quantum effects can play a stabilizing role in such situation.

  16. Verification of gyrokinetic particle simulation of current-driven instability in fusion plasmas. I. Internal kink mode

    SciTech Connect

    McClenaghan, J.; Lin, Z.; Holod, I.; Deng, W.; Wang, Z.

    2014-12-15

    The gyrokinetic toroidal code (GTC) capability has been extended for simulating internal kink instability with kinetic effects in toroidal geometry. The global simulation domain covers the magnetic axis, which is necessary for simulating current-driven instabilities. GTC simulation in the fluid limit of the kink modes in cylindrical geometry is verified by benchmarking with a magnetohydrodynamic eigenvalue code. Gyrokinetic simulations of the kink modes in the toroidal geometry find that ion kinetic effects significantly reduce the growth rate even when the banana orbit width is much smaller than the radial width of the perturbed current layer at the mode rational surface.

  17. Kinetic theory of the filamentation instability in a collisional current-driven plasma with nonextensive distribution

    SciTech Connect

    Khorashadizadeh, S. M. Rastbood, E.; Niknam, A. R.

    2015-07-15

    The evolution of filamentation instability in a weakly ionized current-carrying plasma with nonextensive distribution was studied in the diffusion frequency region, taking into account the effects of electron-neutral collisions. Using the kinetic theory, Lorentz transformation formulas, and Bhatnagar-Gross-Krook collision model, the generalized dielectric permittivity functions of this plasma system were achieved. By obtaining the dispersion relation of low-frequency waves, the possibility of filamentation instability and its growth rate were investigated. It was shown that collisions can increase the maximum growth rate of instability. The analysis of temporal evolution of filamentation instability revealed that the growth rate of instability increased by increasing the q-parameter and electron drift velocity. Finally, the results of Maxwellian and q-nonextensive velocity distributions were compared and discussed.

  18. Particle in cell simulations of Buneman instability of a current-driven plasma with q-nonextensive electron velocity distribution

    SciTech Connect

    Niknam, A. R. Roozbahani, H.; Komaizi, D.; Hashemzadeh, M.

    2014-09-15

    The nonlinear evolution of low frequency Buneman instability in an unmagnetized current-driven plasma with q-nonextensive electron velocity distribution is investigated using particle in cell simulation. Simulation results show that the generation of electron phase space holes and the counter-streaming current induced in the plasma strongly depend on the q-parameter. It is found that by increasing the nonextensive parameter, the distribution of electron density becomes highly peaked. This density steepening or grating-like pattern occurs at the saturation time. In addition, a generalized dispersion relation is obtained using the kinetic theory. Analysis of the dispersion relation and the temporal evolution of the electric field energy density reveal that the growth rate of instability increases by increasing the q-parameter. Finally, the results of Maxwellian and q-nonextensive velocity distributions have been compared and discussed.

  19. Current-driven plasmonic boom instability in three-dimensional gated periodic ballistic nanostructures

    NASA Astrophysics Data System (ADS)

    Aizin, G. R.; Mikalopas, J.; Shur, M.

    2016-05-01

    An alternative approach of using a distributed transmission line analogy for solving transport equations for ballistic nanostructures is applied for solving the three-dimensional problem of electron transport in gated ballistic nanostructures with periodically changing width. The structures with varying width allow for modulation of the electron drift velocity while keeping the plasma velocity constant. We predict that in such structures biased by a constant current, a periodic modulation of the electron drift velocity due to the varying width results in the instability of the plasma waves if the electron drift velocity to plasma wave velocity ratio changes from below to above unity. The physics of such instability is similar to that of the sonic boom, but, in the periodically modulated structures, this analog of the sonic boom is repeated many times leading to a larger increment of the instability. The constant plasma velocity in the sections of different width leads to resonant excitation of the unstable plasma modes with varying bias current. This effect (that we refer to as the superplasmonic boom condition) results in a strong enhancement of the instability. The predicted instability involves the oscillating dipole charge carried by the plasma waves. The plasmons can be efficiently coupled to the terahertz electromagnetic radiation due to the periodic geometry of the gated structure. Our estimates show that the analyzed instability should enable powerful tunable terahertz electronic sources.

  20. Finite-width currents, magnetic shear, and the current-driven ion-cyclotron instability

    NASA Technical Reports Server (NTRS)

    Bakshi, P.; Ganguli, G.; Palmadesso, P.

    1983-01-01

    Our earlier results that non-local effects due to even a small magnetic shear produce a significant reduction of the growth rate of the ion cyclotron instability driven by a uniform current are now generalized to finite width currents. Externally prescribed as well as self-consistent shears are considered. If the current width Lc exceeds the shear length Ls, the previous results are recovered. Shear becomes less effective with reduction of Lc, and for typical parameters, the growth rate attains its (shearless) local value for Lc/Ls approximately less than 10 to the minus 2. Non-local effects of the finite current width itself come into play if Lc is further reduced to a few ion Larmor radii and can quench the instability. Previously announced in STAR as N83-28996

  1. Microphysics of Cosmic Ray Driven Plasma Instabilities

    NASA Astrophysics Data System (ADS)

    Bykov, A. M.; Brandenburg, A.; Malkov, M. A.; Osipov, S. M.

    2013-10-01

    Energetic nonthermal particles (cosmic rays, CRs) are accelerated in supernova remnants, relativistic jets and other astrophysical objects. The CR energy density is typically comparable with that of the thermal components and magnetic fields. In this review we discuss mechanisms of magnetic field amplification due to instabilities induced by CRs. We derive CR kinetic and magnetohydrodynamic equations that govern cosmic plasma systems comprising the thermal background plasma, comic rays and fluctuating magnetic fields to study CR-driven instabilities. Both resonant and non-resonant instabilities are reviewed, including the Bell short-wavelength instability, and the firehose instability. Special attention is paid to the longwavelength instabilities driven by the CR current and pressure gradient. The helicity production by the CR current-driven instabilities is discussed in connection with the dynamo mechanisms of cosmic magnetic field amplification.

  2. Microphysics of Cosmic Ray Driven Plasma Instabilities

    NASA Astrophysics Data System (ADS)

    Bykov, A. M.; Brandenburg, A.; Malkov, M. A.; Osipov, S. M.

    Energetic nonthermal particles (cosmic rays, CRs) are accelerated in supernova remnants, relativistic jets and other astrophysical objects. The CR energy density is typically comparable with that of the thermal components and magnetic fields. In this review we discuss mechanisms of magnetic field amplification due to instabilities induced by CRs. We derive CR kinetic and magnetohydrodynamic equations that govern cosmic plasma systems comprising the thermal background plasma, comic rays and fluctuating magnetic fields to study CR-driven instabilities. Both resonant and non-resonant instabilities are reviewed, including the Bell short-wavelength instability, and the firehose instability. Special attention is paid to the longwavelength instabilities driven by the CR current and pressure gradient. The helicity production by the CR current-driven instabilities is discussed in connection with the dynamo mechanisms of cosmic magnetic field amplification.

  3. A current-driven resistive instability and its nonlinear effects in simulations of coaxial helicity injection in a tokamak

    NASA Astrophysics Data System (ADS)

    Hooper, E. B.; Sovinec, C. R.

    2016-10-01

    An instability observed in whole-device, resistive magnetohydrodynamic simulations of the driven phase of coaxial helicity injection in the National Spherical Torus eXperiment is identified as a current-driven resistive mode in an unusual geometry that transiently generates a current sheet. The mode consists of plasma flow velocity and magnetic field eddies in a tube aligned with the magnetic field at the surface of the injected magnetic flux. At low plasma temperatures (˜10-20 eV), the mode is benign, but at high temperatures (˜100 eV) its amplitude undergoes relaxation oscillations, broadening the layer of injected current and flow at the surface of the injected toroidal flux and background plasma. The poloidal-field structure is affected and the magnetic surface closure is generally prevented while the mode undergoes relaxation oscillations during injection. This study describes the mode and uses linearized numerical computations and an analytic slab model to identify the unstable mode.

  4. THREE-DIMENSIONAL RELATIVISTIC MAGNETOHYDRODYNAMIC SIMULATIONS OF CURRENT-DRIVEN INSTABILITY WITH A SUB-ALFVENIC JET: TEMPORAL PROPERTIES

    SciTech Connect

    Mizuno, Yosuke; Nishikawa, Ken-Ichi; Hardee, Philip E.

    2011-06-10

    We have investigated the influence of a velocity shear surface on the linear and nonlinear development of the current-driven (CD) kink instability of force-free helical magnetic equilibria in three dimensions. In this study, we follow the temporal development within a periodic computational box and concentrate on flows that are sub-Alfvenic on the cylindrical jet's axis. Displacement of the initial force-free helical magnetic field leads to the growth of CD kink instability. We find that helically distorted density structure propagates along the jet with speed and flow structure dependent on the radius of the velocity shear surface relative to the characteristic radius of the helically twisted force-free magnetic field. At small velocity shear surface radius, the plasma flows through the kink with minimal kink propagation speed. The kink propagation speed increases as the velocity shear radius increases and the kink becomes more embedded in the plasma flow. A decreasing magnetic pitch profile and faster flow enhance the influence of velocity shear. Simulations show continuous transverse growth in the nonlinear phase of the instability. The growth rate of the CD kink instability and the nonlinear behavior also depend on the velocity shear surface radius and flow speed, and the magnetic pitch radial profile. Larger velocity shear radius leads to slower linear growth, makes a later transition to the nonlinear stage, and with larger maximum amplitude than that occuring for a static plasma column. However, when the velocity shear radius is much greater than the characteristic radius of the helical magnetic field, linear and nonlinear development can be similar to the development of a static plasma column.

  5. COSMIC-RAY CURRENT-DRIVEN TURBULENCE AND MEAN-FIELD DYNAMO EFFECT

    SciTech Connect

    Rogachevskii, Igor; Kleeorin, Nathan; Brandenburg, Axel; Eichler, David

    2012-07-01

    We show that an {alpha} effect is driven by the cosmic-ray (CR) Bell instability exciting left-right asymmetric turbulence. Alfven waves of a preferred polarization have maximally helical motion, because the transverse motion of each mode is parallel to its curl. We show how large-scale Alfven modes, when rendered unstable by CR streaming, can create new net flux over any finite region, in the direction of the original large-scale field. We perform direct numerical simulations (DNSs) of a magnetohydrodynamic fluid with a forced CR current and use the test-field method to determine the {alpha} effect and the turbulent magnetic diffusivity. As follows from DNS, the dynamics of the instability has the following stages: (1) in the early stage, the small-scale Bell instability that results in the production of small-scale turbulence is excited; (2) in the intermediate stage, there is formation of larger-scale magnetic structures; (3) finally, quasi-stationary large-scale turbulence is formed at a growth rate that is comparable to that expected from the dynamo instability, but its amplitude over much longer timescales remains unclear. The results of DNS are in good agreement with the theoretical estimates. It is suggested that this dynamo is what gives weakly magnetized relativistic shocks such as those from gamma-ray bursts (GRBs) a macroscopic correlation length. It may also be important for large-scale magnetic field amplification associated with CR production and diffusive shock acceleration in supernova remnants (SNRs) and blast waves from GRBs. Magnetic field amplification by Bell turbulence in SNRs is found to be significant, but it is limited owing to the finite time available to the super-Alfvenicly expanding remnant. The effectiveness of the mechanisms is shown to be dependent on the shock velocity. Limits on magnetic field growth in longer-lived systems, such as the Galaxy and unconfined intergalactic CRs, are also discussed.

  6. Numerical study of the two-species Vlasov-Ampère system: Energy-conserving schemes and the current-driven ion-acoustic instability

    NASA Astrophysics Data System (ADS)

    Cheng, Yingda; Christlieb, Andrew J.; Zhong, Xinghui

    2015-05-01

    In this paper, we propose energy-conserving Eulerian solvers for the two-species Vlasov-Ampère (VA) system and apply the methods to simulate current-driven ion-acoustic instability. The two-species VA systems are of practical importance in applications, and they conserve many physical quantities including the particle number of each species and the total energy that is comprised of kinetic energy for both species and the electric energy. The main goal of this paper is to generalize our previous work for the single-species VA system [9] and Vlasov-Maxwell (VM) system [8] to the two-species case. The methodologies proposed involve careful design of temporal discretization and the use of the discontinuous Galerkin (DG) spatial discretizations. We show that the energy-conserving time discretizations for single-species equations [9,8] can also work for the two-species case if extended properly. Compared to other high order schemes, we emphasize that our schemes can preserve the total particle number and total energy on the fully discrete level regardless of mesh size, making them very attractive for long time simulations. We benchmark our algorithms on a test example to check the one-species limit, and the current-driven ion-acoustic instability. To simulate the current-driven ion-acoustic instability, a slight modification for the implicit method is necessary to fully decouple the split equations. This is achieved by a Gauss-Seidel type iteration technique. Numerical results verified the conservation and performance of our methods. Finally, we remark that the schemes in this paper can be readily extended to applications when the models take more general form, such as the multi-species VM equations.

  7. Current-driven Langmuir oscillations and formation of wave packets via modulational instability: Relevance to STEREO observations

    NASA Astrophysics Data System (ADS)

    Sauer, K.; Sydora, R. D.

    2016-07-01

    Recently, it has been shown that Langmuir oscillations (LOs) at the plasma frequency can be driven by an electron current without any electrostatic instability. This current may appear due to a (small) drift of the whole electron population against the ions or by beam electrons after their relaxation to a plateau-like distribution. The consequences of LOs for nonlinear wave phenomena in this scenario are studied by means of kinetic plasma simulations. It is shown that the electric field of LOs can act as a pump wave and generate Langmuir envelope solitons via the modulational instability. In this way, both counterstreaming Langmuir and ion-acoustic waves arise with the same wave number. For solar wind conditions the Doppler shift leads to the generation of satellite peaks with frequencies symmetric around the plasma frequency. Simultaneously, a peak appears in the ion-acoustic branch. These results agree well with recent STEREO observations in the solar wind.

  8. Current-driven ion-acoustic and potential-relaxation instabilities excited in plasma plume during electron beam welding

    SciTech Connect

    Trushnikov, D. N.; Mladenov, G. M. Koleva, E. G.; Belenkiy, V. Ya. Varushkin, S. V.

    2014-04-15

    Many papers have sought correlations between the parameters of secondary particles generated above the beam/work piece interaction zone, dynamics of processes in the keyhole, and technological processes. Low- and high-frequency oscillations of the current, collected by plasma have been observed above the welding zone during electron beam welding. Low-frequency oscillations of secondary signals are related to capillary instabilities of the keyhole, however; the physical mechanisms responsible for the high-frequency oscillations (>10 kHz) of the collected current are not fully understood. This paper shows that peak frequencies in the spectra of the collected high-frequency signal are dependent on the reciprocal distance between the welding zone and collector electrode. From the relationship between current harmonics frequency and distance of the collector/welding zone, it can be estimated that the draft velocity of electrons or phase velocity of excited waves is about 1600 m/s. The dispersion relation with the properties of ion-acoustic waves is related to electron temperature 10 000 K, ion temperature 2 400 K and plasma density 10{sup 16} m{sup −3}, which is analogues to the parameters of potential-relaxation instabilities, observed in similar conditions. The estimated critical density of the transported current for creating the anomalous resistance state of plasma is of the order of 3 A·m{sup −2}, i.e. 8 mA for a 3–10 cm{sup 2} collector electrode. Thus, it is assumed that the observed high-frequency oscillations of the current collected by the positive collector electrode are caused by relaxation processes in the plasma plume above the welding zone, and not a direct demonstration of oscillations in the keyhole.

  9. Thermal Electron Contributions to Current-Driven Instabilities: SCIFER Observations in the 1400-km Cleft Ion Fountain and Their Implications to Thermal Ion Energization

    NASA Technical Reports Server (NTRS)

    Adrian, Mark L.; Pollock, C. J.; Moore, T. E.; Kintner, P. M.; Arnoldy, R. L.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    SCIFER TECHS observations of the variations in the thermal electron distribution in the 1400-km altitude cleft are associated with periods of intense ion heating and field-aligned currents. Energization of the thermal ion plasma in the mid-altitude cleft occurs within density cavities accompanied by enhanced thermal electron temperatures, large field-aligned thermal electron plasma flows and broadband low-frequency electric fields. Variations in the thermal electron contribution to field-aligned current densities indicate small scale (approximately 100's m) filamentary structure embedded within the ion energization periods. TECHS observations of the field-aligned drift velocities and temperatures of the thermal electron distribution are presented to evaluate the critical velocity thresholds necessary for the generation of electrostatic ion cyclotron and ion acoustic instabilities. This analysis suggests that, during periods of thermal ion energization, sufficient drift exists in the thermal electron distribution to excite the electrostatic ion cyclotron instability. In addition, brief periods exist within the same interval where the drift of the thermal electron distribution is sufficient to marginally excite the ion acoustic instability. In addition, the presence an enhancement in Langmuir emission at the plasma frequency at the center of the ion energization region, accompanied by the emission's second-harmonic, and collocated with observations of high-frequency electric field solitary structures suggest the presence of electron beam driven decay of Langmuir waves to ion acoustic modes as an additional free energy source for ion energization.

  10. A cosmic ray driven instability

    NASA Technical Reports Server (NTRS)

    Dorfi, E. A.; Drury, L. O.

    1985-01-01

    The interaction between energetic charged particles and thermal plasma which forms the basis of diffusive shock acceleration leads also to interesting dynamical phenomena. For a compressional mode propagating in a system with homogeneous energetic particle pressure it is well known that friction with the energetic particles leads to damping. The linear theory of this effect has been analyzed in detail by Ptuskin. Not so obvious is that a non-uniform energetic particle pressure can addition amplify compressional disturbances. If the pressure gradient is sufficiently steep this growth can dominate the frictional damping and lead to an instability. It is important to not that this effect results from the collective nature of the interaction between the energetic particles and the gas and is not connected with the Parker instability, nor with the resonant amplification of Alfven waves.

  11. Current driven instability in finite beta plasmas

    NASA Astrophysics Data System (ADS)

    Pusztai, Istvan; Catto, Peter J.; Parra, Felix I.; Barnes, Michael

    2013-10-01

    The induced electric field in a tokamak drives a parallel electron current flow. In an inhomogeneous, finite beta plasma, when this electron flow is non-negligible compared to the ion thermal speed, the Alfvén mode wave solutions of the electromagnetic gyrokinetic equation can become an almost purely growing kink mode. Using the new ``low-flow'' version of the gyrokinetic code GS2 developed for momentum transport studies [Barnes et al. 2013 to appear in Phys. Rev. Lett., arXiv: 1304.3633], we are able to model the effect of the induced parallel electric field on the electron distribution to study the impact of a current on stability. We identify high mode number kink modes in GS2 simulations and make comparisons to analytical theory in a sheared magnetic geometry. We find a reassuring agreement with analytical results both in terms of parametric dependences of mode frequencies and growth rates, and regarding the radial mode structure.

  12. MOMENTUM TRANSPORT FROM CURRENT-DRIVEN RECONNECTION IN ASTROPHYSICAL DISKS

    SciTech Connect

    Ebrahimi, F.; Prager, S. C.

    2011-12-20

    Current-driven reconnection is investigated as a possible mechanism for angular momentum transport in astrophysical disks. A theoretical and computational study of angular momentum transport from current-driven magnetohydrodynamic instabilities is performed. It is found that both a single resistive tearing instability and an ideal instability can transport momentum in the presence of azimuthal Keplerian flow. The structure of the Maxwell stress is examined for a single mode through analytic quasilinear theory and computation. Full nonlinear multiple-mode computation shows that a global Maxwell stress causes significant momentum transport.

  13. Plasma Instabilities in Gamma-Ray Bursts

    SciTech Connect

    Tautz, Robert C.

    2008-12-24

    Magnetic fields are important in a variety of astrophysical scenarios, ranging from possible creation mechanisms of cosmological magnetic fields through relativistic jets such as that from Active Galactic Nuclei and gamma-ray bursts to local phenomena in the solar system. Here, the outstanding importance of plasma instabilities to astrophysics is illustrated by applying the so-called neutral point method to gamma-ray bursts (GRBs), which are assumed to have a homogeneous background magnetic field. It is shown how magnetic turbulence, which is a prerequisite for the creation of dissipation and, subsequently, radiation, is created by the highly relativistic particles in the GRB jet. Using the fact that different particle compositions lead to different instability conditions, conclusions can be drawn about the particle composition of the jet, showing that it is more likely of baryonic nature.

  14. X-RAY STRIPES IN TYCHO'S SUPERNOVA REMNANT: SYNCHROTRON FOOTPRINTS OF A NONLINEAR COSMIC-RAY-DRIVEN INSTABILITY

    SciTech Connect

    Bykov, Andrei M.; Osipov, Sergei M.; Uvarov, Yury A.; Ellison, Donald C.; Pavlov, George G. E-mail: osm@astro.ioffe.ru E-mail: don_ellison@ncsu.edu

    2011-07-10

    High-resolution Chandra observations of Tycho's supernova remnant (SNR) have revealed several sets of quasi-steady, high-emissivity, nearly parallel X-ray stripes in some localized regions of the SNR. These stripes are most likely the result of cosmic-ray (CR) generated magnetic turbulence at the SNR blast wave. However, for the amazingly regular pattern of these stripes to appear, simultaneous action of a number of shock-plasma phenomena is required, which is not predicted by most models of magnetic field amplification. A consistent explanation of these stripes yields information on the complex nonlinear plasma processes connecting efficient CR acceleration and magnetic field fluctuations in strong collisionless shocks. The nonlinear diffusive shock acceleration (NL-DSA) model described here, which includes magnetic field amplification from a CR-current-driven instability, does predict stripes consistent with the synchrotron observations of Tycho's SNR. We argue that the local ambient mean magnetic field geometry determines the orientation of the stripes and therefore it can be reconstructed with the high-resolution X-ray imaging. The estimated maximum energy of the CR protons responsible for the stripes is {approx}10{sup 15} eV. Furthermore, the model predicts that a specific X-ray polarization pattern, with a polarized fraction {approx}50%, accompanies the stripes, which can be tested with future X-ray polarimeter missions.

  15. Acoustic instability driven by cosmic-ray streaming

    NASA Astrophysics Data System (ADS)

    Begelman, Mitchell C.; Zweibel, Ellen G.

    1994-08-01

    We study the linear stability of compressional waves in a medium through which cosmic rays stream at the Alfven speed due to strong coupling with Alfven waves. Acoustic waves can be driven unstable by the cosmic-ray drift, provided that the streaming speed is sufficiently large compared to the thermal sound speed. Two effects can cause instability: (1) the heating of the thermal gas due to the damping of Alfven waves driven unstable by cosmic-ray streaming; and (2) phase shifts in the cosmic-ray pressure perturbation caused by the combination of cosmic-ray streaming and diffusion. The instability does not depend on the magnitude of the background cosmic-ray pressure gradient, and occurs whether or not cosmic-ray diffusion is important relative to streaming. When the cosmic-ray pressure is small compared to the gas pressure, or cosmic-ray diffusion is strong, the instability manifests itself as a weak overstability of slow magnetosonic waves. Larger cosmic-ray pressure gives rise to new hybrid modes, which can be strongly unstable in the limits of both weak and strong cosmic-ray diffusion and in the presence of thermal conduction. Parts of our analysis parallel earlier work by McKenzie & Webb (which were brought to our attention after this paper was accepted for publication), but our treatment of diffusive effects, thermal conduction, and nonlinearities represent significant extensions. Although the linear growth rate of instability is independent of the background cosmic-ray pressure gradient, the onset of nonlinear eff ects does depend on absolute value of DEL (vector differential operator) Pc. At the onset of nonlinearity the fractional amplitude of cosmic-ray pressure perturbations is delta PC/PC approximately (kL) -1 much less than 1, where k is the wavenumber and L is the pressure scale height of the unperturbed cosmic rays. We speculate that the instability may lead to a mode of cosmic-ray transport in which plateaus of uniform cosmic-ray pressure are

  16. COSMIC-RAY-INDUCED FILAMENTATION INSTABILITY IN COLLISIONLESS SHOCKS

    SciTech Connect

    Caprioli, D.; Spitkovsky, A.

    2013-03-01

    We used unprecedentedly large two-dimensional and three-dimensional hybrid (kinetic ions-fluid electrons) simulations of non-relativistic collisionless strong shocks in order to investigate the effects of self-consistently accelerated ions on the overall shock dynamics. The current driven by suprathermal particles streaming ahead of the shock excites modes transverse to the background magnetic field. The Lorentz force induced by these self-amplified fields tends to excavate tubular, underdense, magnetic-field-depleted cavities that are advected with the fluid and perturb the shock surface, triggering downstream turbulent motions. These motions further amplify the magnetic field, up to factors of 50-100 in knot-like structures. Once downstream, the cavities tend to be filled by hot plasma plumes that compress and stretch the magnetic fields in elongated filaments; this effect is particularly evident if the shock propagates parallel to the background field. Highly magnetized knots and filaments may provide explanations for the rapid X-ray variability observed in RX J1713.7-3946 and for the regular pattern of X-ray bright stripes detected in Tycho's supernova remnant.

  17. Current-Driven Nanowire Formation on Crystalline Conducting Substrate Surfaces

    NASA Astrophysics Data System (ADS)

    Dasgupta, Dwaipayan; Kumar, Ashish; Maroudas, Dimitrios

    Using a simulation study, we demonstrate a new, driven-assembly-based approach to single-layer nanowire formation on fcc crystalline substrate surfaces. In this approach, we manipulate individual epitaxial islands using an external electric field to drive the formation of single nanowires or arrays of them. We have developed and validated a fully nonlinear model of current-driven island evolution mediated by diffusional mass transport along the island edge and accounting for edge diffusional anisotropy and island coalescence and breakup. Using a linear stability theory, we analyze the morphological stability of islands with equilibrium shapes and predict the occurrence of morphological instability for islands larger than a critical size under the action of an electric field along the slowest edge diffusion direction on { 110 } , { 100 } , and { 111 } substrate surfaces. Consistent with the theoretical prediction, dynamical simulations show that large-size islands undergo a fingering instability which, following finger growth and, depending on the substrate orientation, necking instability, leads to formation of single or multiple nanowires. We find that the nanowires have constant widths, on the order of tens of nanometers, and explain analytically the nanowire dimensions.

  18. A Plasma Instability Theory of Gamma-Ray Burst Emission

    NASA Technical Reports Server (NTRS)

    Brainerd, Jerome J.

    1999-01-01

    A plasma instability theory is presented for the prompt radiation from gamma-ray bursts. In the theory, a highly relativistic shell interacts with the interstellar medium through the filamentation and the two-stream instabilities to convert bulk kinetic energy into electron thermal energy and magnetic field energy. The processes are not efficient enough to satisfy the Rankine-Hugoniot conditions, so a shock cannot form through this mechanism. Instead, the interstellar medium passes through the shell, with the electrons radiating during this passage. Gamma-rays are produced by synchrotron self-Compton emission. Prompt optical emission is also produced through this mechanism, while prompt radio emission is produced through synchrotron emission. The model timescales are consistent with the shortest burst timescales. To emit gamma-rays, the shell's bulk Lorentz factor must be $\\simg 10(exp 3)$. For the radiative processes to be efficient, the interstellar medium density must satisfy a lower limit that is a function of the bulk Lorentz factor. Because the limits operate as selection effects, bursts that violate them constitute new classes. In particular, a class of optical and ultraviolet bursts with no gamma-ray emission should exist. The lower limit on the density of the interstellar medium is consistent with the requirements of the Compton attenuation theory, providing an explanation for why all burst spectra appear to be attenuated. Several tests of the theory are discussed, as are the next theoretical investigations that should be conducted.

  19. COSMIC RAY TRANSPORT THROUGH GYRORESONANCE INSTABILITY IN COMPRESSIBLE TURBULENCE

    SciTech Connect

    Yan Huirong; Lazarian, A. E-mail: alazarian@wisc.edu

    2011-04-10

    We study the nonlinear growth of kinetic gyroresonance instability of cosmic rays (CRs) induced by large-scale compressible turbulence. This feedback of CRs on turbulence was shown to induce an important scattering mechanism in addition to direct interaction with the compressible turbulence. The linear growth is bound to saturate due to the wave-particle interactions. By balancing the increase of CR anisotropy via the large-scale compression and its decrease via the wave-particle scattering, we find the steady-state solutions. The nonlinear suppression due to the wave-particle scattering limits the energy range of CRs that can excite the instabilities and be scattered by the induced slab waves. The direct interaction with large-scale compressible modes still appears to be the dominant mechanism for isotropization of high-energy CRs (>100 GeV).

  20. Experimental Study of Current-Driven Turbulence During Magnetic Reconnection

    SciTech Connect

    Porkolab, Miklos; Egedal-Pedersen, Jan; Fox, William

    2010-08-31

    CMPD Final Report Experimental Study of Current-Driven Turbulence During Magnetic Reconnection Miklos Porkolab, PI, Jan Egedal, co-PI, William Fox, graduate student. This is the final report for Grant DE-FC02-04ER54786, MIT Participation in the Center for Multiscale Plasma Dynamics, which was active from 8/1/2004 to 7/31/2010. This Grant supported the thesis work of one MIT graduate student, William Fox, The thesis research consisted of an experimental study of the fluctuations arising during magnetic reconnection in plasmas on the Versatile Toroidal Facility (VTF) at MIT Plasma Science and Fusion Center (PSFC). The thesis was submitted and accepted by the MIT physics Department,. Fox, Experimental Study of Current-Driven Turbulence During Magnetic Reconnection, Ph.D. Thesis, MIT (2009). In the VTF experiment reconnection and current-sheet formation is driven by quickly changing currents in a specially arranged set of internal conductors. Previous work on this device [Egedal, et al, PRL 98, 015003, (2007)] identified a spontaneous reconnection regime. In this work fluctuations were studied using impedance-matched, high-bandwidth Langmuir probes. Strong, broadband fluctuations, with frequencies extending from near the lower-hybrid frequency [fLH = (fcefci)1/2] to the electron cyclotron frequency fce were found to arise during the reconnection events. Based on frequency and wavelength measurements, lower-hybrid waves and Trivelpiece-Gould waves were identified. The lower-hybrid waves are easiest to drive with strong perpendicular drifts or gradients which arise due to the reconnection events; an appealing possibility is strong temperature gradients. The Trivelpiece-Gould modes can result from kinetic, bump-on-tail instability of a runaway electron population energized by the reconnection events. We also observed that the turbulence is often spiky, consisting of discrete positive-potential spikes, which were identified as electron phase-space holes, a class of

  1. Magnetic field amplification in nonlinear diffusive shock acceleration including resonant and non-resonant cosmic-ray driven instabilities

    SciTech Connect

    Bykov, Andrei M.; Osipov, Sergei M.; Ellison, Donald C.; Vladimirov, Andrey E. E-mail: osm2004@mail.ru E-mail: avenovo@gmail.com

    2014-07-10

    We present a nonlinear Monte Carlo model of efficient diffusive shock acceleration where the magnetic turbulence responsible for particle diffusion is calculated self-consistently from the resonant cosmic-ray (CR) streaming instability, together with non-resonant short- and long-wavelength CR-current-driven instabilities. We include the backpressure from CRs interacting with the strongly amplified magnetic turbulence which decelerates and heats the super-Alfvénic flow in the extended shock precursor. Uniquely, in our plane-parallel, steady-state, multi-scale model, the full range of particles, from thermal (∼eV) injected at the viscous subshock to the escape of the highest energy CRs (∼PeV) from the shock precursor, are calculated consistently with the shock structure, precursor heating, magnetic field amplification, and scattering center drift relative to the background plasma. In addition, we show how the cascade of turbulence to shorter wavelengths influences the total shock compression, the downstream proton temperature, the magnetic fluctuation spectra, and accelerated particle spectra. A parameter survey is included where we vary shock parameters, the mode of magnetic turbulence generation, and turbulence cascading. From our survey results, we obtain scaling relations for the maximum particle momentum and amplified magnetic field as functions of shock speed, ambient density, and shock size.

  2. Spin-current-driven thermoelectric coating.

    PubMed

    Kirihara, Akihiro; Uchida, Ken-ichi; Kajiwara, Yosuke; Ishida, Masahiko; Nakamura, Yasunobu; Manako, Takashi; Saitoh, Eiji; Yorozu, Shinichi

    2012-06-17

    Energy harvesting technologies, which generate electricity from environmental energy, have been attracting great interest because of their potential to power ubiquitously deployed sensor networks and mobile electronics. Of these technologies, thermoelectric (TE) conversion is a particularly promising candidate, because it can directly generate electricity from the thermal energy that is available in various places. Here we show a novel TE concept based on the spin Seebeck effect, called 'spin-thermoelectric (STE) coating', which is characterized by a simple film structure, convenient scaling capability, and easy fabrication. The STE coating, with a 60-nm-thick bismuth-substituted yttrium iron garnet (Bi:YIG) film, is applied by means of a highly efficient process on a non-magnetic substrate. Notably, spin-current-driven TE conversion is successfully demonstrated under a temperature gradient perpendicular to such an ultrathin STE-coating layer (amounting to only 0.01% of the total sample thickness). We also show that the STE coating is applicable even on glass surfaces with amorphous structures. Such a versatile implementation of the TE function may pave the way for novel applications making full use of omnipresent heat.

  3. Dust-acoustic filamentation of a current-driven dusty plasma

    SciTech Connect

    Khorashadizadeh, S. M.; Haghtalab, T.; Niknam, A. R.

    2011-06-15

    The thermal motion effect of charged particles in the filamentation of a current-driven dusty plasma in the dust-acoustic frequency region is investigated by using the Lorentz transformed conductivity of the dusty plasma components and the total dielectric permittivity tensor of the dusty plasma in the laboratory frame. Obtaining the dispersion relation for dust-acoustic waves and considering the filamentation instability, the establishment time of the filamentation structure and the instability development threshold are derived. Moreover, it is shown that the current layer divides into separate current filaments.

  4. Influence of the backreaction of streaming cosmic rays on magnetic field generation and thermal instability

    SciTech Connect

    Nekrasov, Anatoly K.; Shadmehri, Mohsen E-mail: nekrasov.anatoly@gmail.com

    2014-06-10

    Using a multifluid approach, we investigate streaming and thermal instabilities of the electron-ion plasma with homogeneous cold cosmic rays propagating perpendicular to the background magnetic field. Perturbations are also considered to be across the magnetic field. The backreaction of cosmic rays resulting in strong streaming instabilities is taken into account. It is shown that, for sufficiently short wavelength perturbations, the growth rates can exceed the growth rate of cosmic-ray streaming instability along the magnetic field, found by Nekrasov and Shadmehri, which is in turn considerably larger than the growth rate of the Bell instability. The thermal instability is shown not to be subject to the action of cosmic rays in the model under consideration. The dispersion relation for the thermal instability has been derived, which includes sound velocities of plasma and cosmic rays and Alfvén and cosmic-ray streaming velocities. The relation between these parameters determines the kind of thermal instability ranging from the Parker to the Field instabilities. The results obtained can be useful for a more detailed investigation of electron-ion astrophysical objects, such as supernova remnant shocks, galaxy clusters, and others, including the dynamics of streaming cosmic rays.

  5. Particle and fluid simulations of resistive current-driven electrostatic ion cyclotron waves

    NASA Technical Reports Server (NTRS)

    Seyler, Charles E.; Providakes, Jason

    1987-01-01

    The results from 1-D numerical simulations of electrostatic ion cyclotron waves (EIC) are presented for a model in which the electrons are a resistive (collisional) fluid. Simulations of both the kinetic and fluid descriptions are performed and compared in order to assess the fundamental limitations of fluid theory for EIC waves. The effect of ion-neutral collisions is also included using a simple Monte Carlo technique. It is found that a small ion-neutral collision frequency destroys the frequency harmonic coupling of kinetic EIC waves and tends to validate the fluid description. The saturation amplitude of the current-driven EIC instability is in agreement with recent laboratory experiments. The coherent nature (extremely narrow spectral width) and phase velocity agree with ground based (coherent backscatter radars) and in situ observations of current-driven EIC waves in the high latitude ionosphere.

  6. Current-driven morphological evolution of single-layer epitaxial islands on crystalline substrates

    NASA Astrophysics Data System (ADS)

    Dasgupta, Dwaipayan; Sfyris, Georgios I.; Maroudas, Dimitrios

    2013-12-01

    We develop and validate a nonlinear model for the current-driven dynamics of single-layer epitaxial islands on crystalline substrates. Simulations based on the model show that the dependence of the stable steady island migration speed vm on the inverse of the island size is not linear for larger-than-critical island sizes. In this nonlinear regime, we report morphological transitions, Hopf bifurcations, and instabilities for various surface crystallographic orientations and island misfit strains. Proper rescaling of vm gives a universal linear relationship for its dependence on island size.

  7. The effect of beam-driven return current instability on solar hard X-ray bursts

    NASA Technical Reports Server (NTRS)

    Cromwell, D.; Mcquillan, P.; Brown, J. C.

    1986-01-01

    The problem of electrostatic wave generation by a return current driven by a small area electron beam during solar hard X-ray bursts is discussed. The marginal stability method is used to solve numerically the electron and ion heating equations for a prescribed beam current evolution. When ion-acoustic waves are considered, the method appears satisfactory and, following an initial phase of Coulomb resistivity in which T sub e/T sub i rise, predicts a rapid heating of substantial plasma volumes by anomalous ohmic dissipation. This hot plasma emits so much thermal bremsstrahlung that, contrary to previous expectations, the unstable beam-plasma system actually emits more hard X-rays than does the beam in the purely collisional thick target regime relevant to larger injection areas. Inclusion of ion-cyclotron waves results in ion-acoustic wave onset at lower T sub e/T sub i and a marginal stability treatment yields unphysical results.

  8. Suppression of X-rays from radiative shocks by their thin-shell instability

    NASA Astrophysics Data System (ADS)

    Kee, Nathaniel Dylan; Owocki, Stanley; ud-Doula, Asif

    2014-03-01

    We examine X-rays from radiatively cooled shocks, focusing on how their thin-shell instability reduces X-ray emission. For 2D simulations of collision between equal expanding winds, we carry out a parameter study of such instability as a function of the ratio of radiative versus adiabatic-expansion cooling lengths. In the adiabatic regime, the extended cooling layer suppresses instability, leading to planar shock compression with X-ray luminosity that follows closely the expected (L_X ˜ dot{M}^2) quadratic scaling with mass-loss rate dot{M}. In the strongly radiative limit, the X-ray emission now follows an expected linear scaling with mass-loss (L_X ˜ dot{M}), but the instability deforms the shock compression into extended shear layers with oblique shocks along fingers of cooled, dense material. The spatial dispersion of shock thermalization limits strong X-ray emission to the tips and troughs of the fingers, and so reduces the X-ray emission (here by about a factor 1/50) below what is expected from analytic radiative-shock models without unstable structure. Between these two limits, X-ray emission can switch between a high-state associated with extended shock compression, and a low-state characterized by extensive shear. Further study is needed to clarify the origin of this `shear mixing reduction factor' in X-ray emission, and its dependence on parameters like the shock Mach number.

  9. STREAMING COLD COSMIC-RAY BACK-REACTION AND THERMAL INSTABILITIES ALONG THE BACKGROUND MAGNETIC FIELD

    SciTech Connect

    Nekrasov, Anatoly K.; Shadmehri, Mohsen E-mail: nekrasov.anatoly@gmail.com

    2012-09-01

    Using a multi-fluid approach, we investigate the streaming and thermal instabilities of electron-ion-cosmic-ray astrophysical objects in which homogeneous cold cosmic rays have a drift velocity perpendicular to the background magnetic field. One-dimensional perturbations along the magnetic field are considered. The induced return current of the background plasma and back-reaction of cosmic rays are taken into account. It is shown that the cosmic-ray back-reaction results in a streaming instability with considerably higher growth rates than that due to the return current of the background plasma. This increase is by a factor of the square root of the ratio of the background plasma mass density to the cosmic-ray mass density. The maximal growth rate and the corresponding wavenumber are then found. Thermal instability is shown to be not subject to the action of cosmic rays in the model under consideration. The dispersion relation for thermal instability includes ion inertia. In the limit of a fast thermal energy exchange between electrons and ions, the isobaric and isochoric growth rates are obtained. The results can be useful for the investigation of electron-ion astrophysical objects such as galaxy clusters, including the dynamics of streaming cosmic rays.

  10. Thermal instability accretion disk model for the X-ray transient A0620-00

    NASA Technical Reports Server (NTRS)

    Huang, Min; Wheeler, J. Craig

    1989-01-01

    The limit-cycle thermal instability model for accretion disks is used to study the soft X-ray transient A0620-00. Thermal instability in geometrically thin, Keplerian alpha-model disks is reviewed. The observational constraints on A0620-00 are presented and the parameters chosen for the model are discussed. It is found that, with the adopted parameters, the model requires a central object mass of about 7 solar masses to fit the burst recurrence time. This is consistent with a black hole as the central object. The results suggest that a mass transfer instability may be responsible for outbursts.

  11. Linear growth of the Kelvin-Helmholtz instability with an adiabatic cosmic-ray gas

    SciTech Connect

    Suzuki, Akihiro; Takahashi, Hiroyuki R.; Kudoh, Takahiro

    2014-06-01

    We investigate effects of cosmic rays on the linear growth of the Kelvin-Helmholtz instability. Cosmic rays are treated as an adiabatic gas and allowed to diffuse along magnetic field lines. We calculated the dispersion relation of the instability for various sets of two free parameters, the ratio of the cosmic-ray pressure to the thermal gas pressure, and the diffusion coefficient. Including cosmic-ray effects, a shear layer is more destabilized and the growth rates can be enhanced in comparison with the ideal magnetohydrodynamical case. Whether the growth rate is effectively enhanced or not depends on the diffusion coefficient of cosmic rays. We obtain the criterion for effective enhancement by comparing the growing timescale of the instability with the diffusion timescale of cosmic rays. These results can be applied to various astrophysical phenomena where a velocity shear is present, such as outflows from star-forming galaxies, active galactic nucleus jet, channel flows resulting from the nonlinear development of the magnetorotational instability, and galactic disks.

  12. Current Driven Magnetic Damping in Dipolar-Coupled Spin System

    NASA Astrophysics Data System (ADS)

    Lee, Sung Chul; Pi, Ung Hwan; Kim, Keewon; Kim, Kwang Seok; Shin, Jaikwang; -in Chung, U.

    2012-07-01

    Magnetic damping of the spin, the decay rate from the initial spin state to the final state, can be controlled by the spin transfer torque. Such an active control of damping has given birth to novel phenomena like the current-driven magnetization reversal and the steady spin precession. The spintronic devices based on such phenomena generally consist of two separate spin layers, i.e., free and pinned layers. Here we report that the dipolar coupling between the two layers, which has been considered to give only marginal effects on the current driven spin dynamics, actually has a serious impact on it. The damping of the coupled spin system was greatly enhanced at a specific field, which could not be understood if the spin dynamics in each layer was considered separately. Our results give a way to control the magnetic damping of the dipolar coupled spin system through the external magnetic field.

  13. Current-driven complex dynamics of single-layer epitaxial islands on substrates

    NASA Astrophysics Data System (ADS)

    Dasgupta, Dwaipayan; Maroudas, Dimitrios

    2015-03-01

    We study theoretically the current-driven dynamics of isolated single-layer epitaxial islands on crystalline substrates, which provides important guidance toward surface nanopatterning approaches based on the current-driven assembly of such islands. We develop and validate a fully nonlinear model for the islands' driven morphological evolution on elastic substrates of face-centered cubic crystals in the regime where diffusional mass transport is limited to the island edge. For islands on <110>-, <100>-, and <111>-oriented substrate surfaces, we report a transition in the asymptotic states reached by such driven island dynamics from steady to oscillatory, mediated by Hopf bifurcation. We characterize the bifurcation and explore the dependence of the stable time-periodic state beyond the Hopf point on the misorientation angle between the applied electric field and fast edge diffusion directions, the strength of the edge diffusional anisotropy, and the island size. For islands larger than a critical size, depending on the orientation of the substrate surface, we observe fingering and necking instabilities in the island morphology. We carry out a comprehensive numerical simulation study and explore the complexity of the driven island dynamics with the variation of the problem parameters.

  14. Magnetohydrodynamic plasma instability driven by Alfven waves excited by cosmic rays

    NASA Astrophysics Data System (ADS)

    McKenzie, J. F.; Webb, G. M.

    1984-04-01

    Hydrodynamical equations describing the mutual interaction of cosmic rays, thermal plasma, magnetic field, and Alfven waves scattering the cosmic rays used in cosmic ray shock acceleration theory are analyzed for long-wavelength linear compressible instabilities. It is shown that the backward propagating slow magnetoacoustic mode is driven convectively unstable by the wave pressure of self-excited Alfven waves. The marginal stability curve is derived and the stabilizing effects of a preexisting wave field and propagation oblique to the magnetic field are discussed along with the dependence of the growth rates of the instability on the various parameters. A similar analysis is performed for a plasma which does not behave adiabatically, being dissipatively heated by the self-excited Alfven field. This system is found to be unstale to compressions associated with both backward and forward propagating slow magnetoacoustic waves.

  15. Evidence of Branching Phenomena in Current-Driven Ionization Waves.

    PubMed

    Loebner, Keith T K; Underwood, Thomas C; Cappelli, Mark A

    2015-10-23

    This Letter reports the first fully consistent experimental observations of current-driven ionization waves conforming to the magnetohydrodynamic Rankine-Hugoniot model for hydromagnetic shocks. Detailed measurements of the thermodynamic and electrodynamic plasma state variables across the ionization region confirm the existence of two types of waves, corresponding to the upper and lower solution branches of the Hugoniot curve. These waves are generated by pulsed currents in a coaxial gas-fed plasma accelerator. The coupling between the state variables of this complex, transient, three-dimensional system shows a remarkable quantitative agreement of less than 8% deviation from the quasisteady, one-dimensional theoretical model. PMID:26551118

  16. Evidence of Branching Phenomena in Current-Driven Ionization Waves

    NASA Astrophysics Data System (ADS)

    Loebner, Keith T. K.; Underwood, Thomas C.; Cappelli, Mark A.

    2015-10-01

    This Letter reports the first fully consistent experimental observations of current-driven ionization waves conforming to the magnetohydrodynamic Rankine-Hugoniot model for hydromagnetic shocks. Detailed measurements of the thermodynamic and electrodynamic plasma state variables across the ionization region confirm the existence of two types of waves, corresponding to the upper and lower solution branches of the Hugoniot curve. These waves are generated by pulsed currents in a coaxial gas-fed plasma accelerator. The coupling between the state variables of this complex, transient, three-dimensional system shows a remarkable quantitative agreement of less than 8% deviation from the quasisteady, one-dimensional theoretical model.

  17. Current-driven spin dynamics of artificially constructed quantum magnets.

    PubMed

    Khajetoorians, Alexander Ako; Baxevanis, Benjamin; Hübner, Christoph; Schlenk, Tobias; Krause, Stefan; Wehling, Tim Oliver; Lounis, Samir; Lichtenstein, Alexander; Pfannkuche, Daniela; Wiebe, Jens; Wiesendanger, Roland

    2013-01-01

    The future of nanoscale spin-based technologies hinges on a fundamental understanding and dynamic control of atomic-scale magnets. The role of the substrate conduction electrons on the dynamics of supported atomic magnets is still a question of interest lacking experimental insight. We characterized the temperature-dependent dynamical response of artificially constructed magnets, composed of a few exchange-coupled atomic spins adsorbed on a metallic substrate, to spin-polarized currents driven and read out by a magnetic scanning tunneling microscope tip. The dynamics, reflected by two-state spin noise, is quantified by a model that considers the interplay between quantum tunneling and sequential spin transitions driven by electron spin-flip processes and accounts for an observed spin-transfer torque effect.

  18. COULD COSMIC RAYS AFFECT INSTABILITIES IN THE TRANSITION LAYER OF NONRELATIVISTIC COLLISIONLESS SHOCKS?

    SciTech Connect

    Stroman, Thomas; Pohl, Martin; Niemiec, Jacek; Bret, Antoine

    2012-02-10

    There is an observational correlation between astrophysical shocks and nonthermal particle distributions extending to high energies. As a first step toward investigating the possible feedback of these particles on the shock at the microscopic level, we perform particle-in-cell (PIC) simulations of a simplified environment consisting of uniform, interpenetrating plasmas, both with and without an additional population of cosmic rays. We vary the relative density of the counterstreaming plasmas, the strength of a homogeneous parallel magnetic field, and the energy density in cosmic rays. We compare the early development of the unstable spectrum for selected configurations without cosmic rays to the growth rates predicted from linear theory, for assurance that the system is well represented by the PIC technique. Within the parameter space explored, we do not detect an unambiguous signature of any cosmic-ray-induced effects on the microscopic instabilities that govern the formation of a shock. We demonstrate that an overly coarse distribution of energetic particles can artificially alter the statistical noise that produces the perturbative seeds of instabilities, and that such effects can be mitigated by increasing the density of computational particles.

  19. New quantum oscillations in current driven small junctions

    NASA Technical Reports Server (NTRS)

    Ben-Jacob, E.; Gefen, Y.

    1985-01-01

    The response of current-biased Josephson and normal tunnel junctions (JJs and NTJs) such as those fabricated by Voss and Webb (1981) is predicted from a quantum-mechanical description based on the observation that the response of a current-driven open system is equivalent to that of a closed system subject to an external time-dependent voltage bias. Phenomena expected include voltage oscillations with no dc voltage applied, inverse Shapiro steps of dc voltage in the presence of microwave radiation, voltage oscillation in a JJ and an NTJ coupled by a capacitance to a current-biased junction, JJ voltage oscillation frequency = I/e rather than I/2e, and different NTJ resistance than in the voltage-driven case. The effects require approximate experimental parameter values Ic = 15 nA, C = 1 fF, and T much less than 0.4 K for JJs and Ic = a few nA, C = 1 fF, and R = 3 kiloohms for 100-microV inverse Shapiro steps at 10 GHz in NTJs.

  20. Nonconservative current-driven dynamics: beyond the nanoscale

    PubMed Central

    Todorov, Tchavdar N; Dundas, Daniel

    2015-01-01

    Summary Long metallic nanowires combine crucial factors for nonconservative current-driven atomic motion. These systems have degenerate vibrational frequencies, clustered about a Kohn anomaly in the dispersion relation, that can couple under current to form nonequilibrium modes of motion growing exponentially in time. Such motion is made possible by nonconservative current-induced forces on atoms, and we refer to it generically as the waterwheel effect. Here the connection between the waterwheel effect and the stimulated directional emission of phonons propagating along the electron flow is discussed in an intuitive manner. Nonadiabatic molecular dynamics show that waterwheel modes self-regulate by reducing the current and by populating modes in nearby frequency, leading to a dynamical steady state in which nonconservative forces are counter-balanced by the electronic friction. The waterwheel effect can be described by an appropriate effective nonequilibrium dynamical response matrix. We show that the current-induced parts of this matrix in metallic systems are long-ranged, especially at low bias. This nonlocality is essential for the characterisation of nonconservative atomic dynamics under current beyond the nanoscale. PMID:26665086

  1. Novel current driven domain wall dynamics in synthetic antiferromagnets

    NASA Astrophysics Data System (ADS)

    Yang, See-Hun

    It was reported that the domain walls in nanowires can be moved efficiently by electrical currents by a new type of torque, chiral spin torque (CST), the combination of spin Hall effect and Dzyaloshinskii-Moriya interaction. Recently we domonstrated that ns-long current pulses can move domain walls at extraordinarily high speeds (up to ~750 m s -1) in synthetic antiferromagnetic (SAF) nanowires that have almost zero net magnetization, which is much more efficient compared with similar nanowires in which the sub-layers are coupled ferromagnetically (SF). This high speed is found to be due to a new type of powerful torque, exchange coupling torque (ECT) that is directly proportional to the strength of the antiferromagnetic exchange coupling between the two sub-layers, showing that the ECT is effective only in SAF not in SF. Moreover, it is found that the dependence of the wall velocity on the magnetic field applied along the nanowire is non-monotonic. Most recently we predict an Walker-breakdown-like domain wall precession in SAF nanowires in the presence of in-plane field based on the model we develop, and this extraordinary precession has been observed. In this talk I will discuss this in details by showing a unique characteristics of SAF sublayers' DW boost-and-drag mechanism along with CST and ECT. Novel current driven domain wall dynamics in synthetic antiferromagnets.

  2. Experiments to Observe the Weibel Instability: The Origin of Gamma Ray Burst Afterglow

    NASA Astrophysics Data System (ADS)

    Huntington, Channing; Matsuoka, T.; Maksimchuk, A.; Yanovsky, V.; Krushelnick, K.; Katsouleas, T.; Medvedev, M. V.; Silva, L. O.; Mori, W. B.; Bingham, R.; Drake, R. P.

    2008-05-01

    Recent theories suggest that the radiation signature of gamma ray bursts may be the result of the interaction of ultrarelativistic electrons, ejected from supernova shocks, with small-scale magnetic fields.a These tiny "tangled" magnetic fields are thought to be created by the two-stream filamentation instability, or Weibel Instability, of the beaming electrons. As the charged particles propagate, local density perturbations form lines of current, which create magnetic fields within the beam. These fields act to pinch the areas of higher electron density, forming filaments of characteristic diameter c/ωp, where c is the speed of light and ωp is the electron plasma frequency. Using the Hercules laser facility at the University of Michigan, we are conducting an experiment to create an electron beam by the laser wakefield technique, produce such filaments by passing the electron beam through another plasma, and image the resulting structure. Analysis of the beam structure will be compared with theory and simulation and will provide direction for future investigation of gamma ray burst signatures. a. Medvedev MV., Loeb A. Generation of Magnetic Fields in the Relativistic Shock of Gamma-Ray-Burst Sources. Astrophys.J. 526 (1999) 697-706 This research was sponsored by the National Science Foundation through Grant PHY-0114336 and by NNSA Stewardship Sciences Academic Alliances through DOE Research Grant DE-FG52-04NA00064.

  3. Screw Instability of Magnetic Field and Gamma-Ray Bursts in Type Ib/c Supernovae

    NASA Astrophysics Data System (ADS)

    Wang, Ding-Xiong; Lei, Wei-Hua; Ye, Yong-Chun

    2006-06-01

    A toy model of gamma-ray burst supernovae (GRB SNe) is discussed by considering the effects of the screw instability of the magnetic field in the black hole (BH) magnetosphere. The screw instability in the Blandford-Znajek (BZ) process (henceforth the SIBZ) can coexist with the screw instability in the magnetic coupling (MC) process (henceforth the SIMC). It turns out that both the SIBZ and SIMC occur inevitably, provided that the following parameters are greater than some critical values: (1) the BH spin, (2) the power-law index describing the magnetic field at the disk, and (3) the vertical height of the astrophysical load above the equatorial plane of the rotating BH. The features of several GRBs are well fitted. In our model the durations of the long GRBs depend on the evolution time of the half-opening angle. A small fraction of energy is extracted from the BH via the BZ process to power a GRB, while a large fraction of energy is extracted from the BH via the MC process to power an associated supernova. In addition, the variability timescales of tens of milliseconds in the light curves of the GRBs are fitted by two successive flares due to the SIBZ.

  4. Current-driven non-linear magnetodynamics in exchange-biased spin valves

    SciTech Connect

    Seinige, Heidi; Wang, Cheng; Tsoi, Maxim

    2015-05-07

    This work investigates the excitation of parametric resonance in exchange-biased spin valves (EBSVs). Using a mechanical point contact, high density dc and microwave currents were injected into the EBSV sample. Observing the reflected microwave power and the small rectification voltage that develops across the contact allows detecting the current-driven magnetodynamics not only in the bulk sample but originating exclusively from the small contact region. In addition to ferromagnetic resonance (FMR), parametric resonance at twice the natural FMR frequency was observed. In contrast to FMR, this non-linear resonance was excited only in the vicinity of the point contact where current densities are high. Power-dependent measurements displayed a typical threshold-like behavior of parametric resonance and a broadening of the instability region with increasing power. Parametric resonance showed a linear shift as a function of applied dc bias which is consistent with the field-like spin-transfer torque induced by current on magnetic moments in EBSV.

  5. Disk instability and the time-dependent X-ray emission from the intermediate polar GK Persei

    NASA Technical Reports Server (NTRS)

    Yi, Insu; Kim, Soon-Wook; Vishniac, Ethan T.; Wheeler, J. C.

    1992-01-01

    The correlation between the disk instability model for the 1981-1989 optical outbursts of the intermediate polar GK Per and the accompanying X-ray emission is examined, and the self-consistency of the combined optical-X-ray model is investigated. Special attention is given to the nature of the transition in the X-ray emission due to the time-dependent accretion rates in the simple column accretion model. The large variation in the efficiency of hard X-ray production is explained.

  6. Simulations of Edge Current Driven Kink Modes with BOUT + + code

    NASA Astrophysics Data System (ADS)

    Li, G. Q.; Xu, X. Q.; Snyder, P. B.; Turnbull, A. D.; Xia, T. Y.; Ma, C. H.; Xi, P. W.

    2013-10-01

    Edge kink modes (or peeling modes) play a key role in the ELMs. The edge kink modes are driven by peak edge current, which comes from the bootstrap current. We calculated sequences of equilibria with different edge current using CORSICA by keeping total current and pressure profile fixed. Based on these equilibria, with the 3-field BOUT + + code, we calculated the MHD instabilities driven by edge current. For linear low-n ideal MHD modes, BOUT + + results agree with GATO results. With the edge current increasing, the dominant modes are changed from high-n ballooning modes to low-n kink modes. The edge current provides also stabilizing effects on high-n ballooning modes. Furthermore, for edge current scan without keeping total current fixed, the increasing edge current can stabilize the high-n ballooning modes and cannot drive kink modes. The diamagnetic effect can stabilize the high-n ballooning modes, but has no effect on the low-n kink modes. Also, the nonlinear behavior of kink modes is analyzed. Work supported by China MOST grant 2013GB111000 and by China NSF grant 10975161. Also performed for USDOE by LLNL under DE-AC52-07NA27344.

  7. TWO-DIMENSIONAL PARTICLE-IN-CELL SIMULATIONS OF THE NONRESONANT, COSMIC-RAY-DRIVEN INSTABILITY IN SUPERNOVA REMNANT SHOCKS

    SciTech Connect

    Ohira, Yutaka; Takahara, Fumio; Reville, Brian; Kirk, John G.

    2009-06-10

    In supernova remnants, the nonlinear amplification of magnetic fields upstream of collisionless shocks is essential for the acceleration of cosmic rays to the energy of the 'knee' at 10{sup 15.5} eV. A nonresonant instability driven by the cosmic ray current is thought to be responsible for this effect. We perform two-dimensional, particle-in-cell simulations of this instability. We observe an initial growth of circularly polarized nonpropagating magnetic waves as predicted in linear theory. It is demonstrated that in some cases the magnetic energy density in the growing waves can grow to at least 10 times its initial value. We find no evidence of competing modes, nor of significant modification by thermal effects. At late times, we observe saturation of the instability in the simulation, but the mechanism responsible is an artifact of the periodic boundary conditions and has no counterpart in the supernova-shock scenario.

  8. Ataxia telangiectasia derived iPS cells show preserved x-ray sensitivity and decreased chromosomal instability

    PubMed Central

    Fukawatase, Yoshihiro; Toyoda, Masashi; Okamura, Kohji; Nakamura, Ken-ichi; Nakabayashi, Kazuhiko; Takada, Shuji; Yamazaki-Inoue, Mayu; Masuda, Akira; Nasu, Michiyo; Hata, Kenichiro; Hanaoka, Kazunori; Higuchi, Akon; Takubo, Kaiyo; Umezawa, Akihiro

    2014-01-01

    Ataxia telangiectasia is a neurodegenerative inherited disease with chromosomal instability and hypersensitivity to ionizing radiation. iPS cells lacking ATM (AT-iPS cells) exhibited hypersensitivity to X-ray irradiation, one of the characteristics of the disease. While parental ataxia telangiectasia cells exhibited significant chromosomal abnormalities, AT-iPS cells did not show any chromosomal instability in vitro for at least 80 passages (560 days). Whole exome analysis also showed a comparable nucleotide substitution rate in AT-iPS cells. Taken together, these data show that ATM is involved in protection from irradiation-induced cell death. PMID:24970375

  9. On the current-driven model in the classical electrodynamics of continuous media.

    PubMed

    Markel, Vadim A

    2010-12-01

    The current-driven model in which a continuous medium is excited by a pre-determined current which overlaps with the medium in all points in space but is not subject to constitutive relations is critically analyzed.

  10. ANALYSIS OF MAGNETOROTATIONAL INSTABILITY WITH THE EFFECT OF COSMIC-RAY DIFFUSION

    SciTech Connect

    Kuwabara, Takuhito; Ko, Chung-Ming E-mail: cmko@astro.ncu.edu.tw

    2015-01-10

    We present the results obtained from the linear stability analysis and 2.5 dimensional magnetohydrodynamic (MHD) simulations of magnetorotational instability (MRI), including the effects of cosmic rays (CRs). We took into account the CR diffusion along the magnetic field but neglected the cross-field-line diffusion. Two models are considered in this paper: the shearing box model and differentially rotating cylinder model. We studied how MRI is affected by the initial CR pressure (i.e., energy) distribution. In the shearing box model, the initial state is uniform distribution. Linear analysis shows that the growth rate of MRI does not depend on the value of the CR diffusion coefficient. In the differentially rotating cylinder model, the initial state is a constant angular momentum polytropic disk threaded by a weak uniform vertical magnetic field. Linear analysis shows that the growth rate of MRI becomes larger if the CR diffusion coefficient is larger. Both results are confirmed by MHD simulations. The MHD simulation results show that the outward movement of matter by the growth of MRI is not impeded by the CR pressure gradient, and the centrifugal force that acts on the concentrated matter becomes larger. Consequently, the growth rate of MRI is increased. On the other hand, if the initial CR pressure is uniform, then the growth rate of the MRI barely depends on the value of the CR diffusion coefficient.

  11. Z-pinch diagnostics, plasma and liner instabilities and new x-ray techniques

    SciTech Connect

    Oona, H.; Anderson, B.; Benage, J.

    1996-09-01

    Pulse power experiments of the last several decades have contributed greatly to the understanding of high temperature and high density plasmas and, more recently, to the study of hydrodynamic effects in thick imploding cylinders. Common to all these experiments is the application of a large current pulse to a cylindrically symmetric load, with the resulting Lorenz force compressing the load to produce hydrodynamic motion and/or high temperature, high density plasma. In Los Alamos, Pulsed power experiments are carried out at two facilities. Experiments at low current (from several million to ten million Amperes) are conducted on the Pegasus II capacitor bank. Experiments with higher currents (10`s to 100`s MA range) are performed in Ancho Canyon with the explosively driven Procyon and MAGO magnetic flux compression generator systems. In this paper, the authors present a survey of diagnostic capabilities and results from several sets of experiments. First, they discuss the initiation and growth of instabilities in plasmas generated from the implosion of hollow z-pinches in the pegasus and Procyon experiments. Next they discuss spectroscopic data from the plasmas produced by the MAGO system. They also show time resolved imaging data from thick ({approximately} .4 mm) liner implosions. Finally, the authors discuss improvements to x-ray and visible light imaging and spectrographic diagnostic techniques. The emphasis of this paper is not so much a detailed discussion of the experiments, but a presentation of imaging and spectroscopic results and the implications of these observations to the experiments.

  12. Tomographic analysis of the nonthermal x-ray bursts during disruption instability in the T-10 tokamak

    SciTech Connect

    Savrukhin, P. V.; Ermolaeva, A. I.; Shestakov, E. A.; Khramenkov, A. V.

    2014-10-01

    Non-thermal x-ray radiation (E{sub γ} up to 150 keV) is measured in the T-10 tokamaks during disruption instability using two sets of CdTe detectors (10 vertical and 7 horizontal view detectors). Special narrow cupper tubes collimators with lead screening and CdTe detectors integrated with amplifiers inside metallic containers provides enhanced spatial resolution of the system (r ~ 3 cm) and assures protection from the parasitic hard x-ray (E{sub γ} up to 1.5 MeV) and electromagnetic loads during disruption. Spatial localization of the nonthermal x-ray emissivity is reconstructed using tomographic Cormack technique with SVD matrix inversion. Analysis indicated appearance of an intensive non-thermal x-ray bursts during initial stage of the disruptions at high density. The bursts are characterized by repetitive spikes (2–3 kHz) of the x-ray emissivity from the plasma core area. Analysis indicated that the spikes can be connected with acceleration of the non-thermal electrons in enhanced longitudinal electric fields induced during energy quench at the disruption instability.

  13. Disc instability models for X-ray transients: evidence for evaporation and low α-viscosity?

    NASA Astrophysics Data System (ADS)

    Menou, Kristen; Hameury, Jean-Marie; Lasota, Jean-Pierre; Narayan, Ramesh

    2000-05-01

    We construct time-dependent models of accretion discs around black holes and neutron stars. We investigate the effect that evaporation of the inner disc regions during quiescence has upon the predictions of the disc instability model (DIM) for these systems. We do not include irradiation of the disc in the models. Removing the inner, most unstable, parts of the accretion disc increases the predicted recurrence times. However, DIMs with values of the viscosity parameter αhot~0.1 and αcold~0.02 (values typically used in applications of the DIM to standard dwarf nova outbursts) fail to reproduce the long recurrence times of soft X-ray transients (unless we resort to fine-tuning the parameters), independent of the evaporation strength. We show that models in which evaporation is included and a smaller value of αcold (~0.005) used do reproduce the long recurrence times and the accretion rates at the level of the Eddington rate observed in outburst. The large difference between the values of αhot and αcold, if confirmed once disc irradiation is included, suggests that several viscosity mechanisms operate in these accretion discs. For some parameter sets our models predict re-flares during the decline from outburst. The re-flares are a physical property of the model and result from the formation of a heating front in the wake of an initial cooling front, and subsequent multiple front reflections. The re-flares disappear in low-α models where front reflection cannot occur.

  14. Observation of room-temperature magnetic skyrmions and their current-driven dynamics in ultrathin metallic ferromagnets

    NASA Astrophysics Data System (ADS)

    Woo, Seonghoon; Litzius, Kai; Krüger, Benjamin; Im, Mi-Young; Caretta, Lucas; Richter, Kornel; Mann, Maxwell; Krone, Andrea; Reeve, Robert M.; Weigand, Markus; Agrawal, Parnika; Lemesh, Ivan; Mawass, Mohamad-Assaad; Fischer, Peter; Kläui, Mathias; Beach, Geoffrey S. D.

    2016-05-01

    Magnetic skyrmions are topologically protected spin textures that exhibit fascinating physical behaviours and large potential in highly energy-efficient spintronic device applications. The main obstacles so far are that skyrmions have been observed in only a few exotic materials and at low temperatures, and fast current-driven motion of individual skyrmions has not yet been achieved. Here, we report the observation of stable magnetic skyrmions at room temperature in ultrathin transition metal ferromagnets with magnetic transmission soft X-ray microscopy. We demonstrate the ability to generate stable skyrmion lattices and drive trains of individual skyrmions by short current pulses along a magnetic racetrack at speeds exceeding 100 m s-1 as required for applications. Our findings provide experimental evidence of recent predictions and open the door to room-temperature skyrmion spintronics in robust thin-film heterostructures.

  15. Detection of current-driven magnetic domains in [Co/Pd] nanowire by tunneling magnetoresistive sensor

    NASA Astrophysics Data System (ADS)

    Okuda, Mitsunobu; Miyamoto, Yasuyoshi; Miyashita, Eiichi; Saito, Nobuo; Hayashi, Naoto; Nakagawa, Shigeki

    2015-05-01

    Current-driven magnetic domain walls in magnetic nanowires have attracted a great deal of interest in terms of both physical studies and engineering applications. The anomalous Hall effect measurement is widely used for detecting the magnetization direction of current-driven magnetic domains in a magnetic nanowire. However, the problem with this measurement is that the detection point for current-driven domain wall motion is fixed at only the installed sensing wire across the specimen nanowire. A potential solution is the magnetic domain scope method, whereby the distribution of the magnetic flux leaking from the specimen can be analyzed directly by contact-scanning a tunneling magnetoresistive field sensor on a sample. In this study, we fabricated specimen nanowires consisting of [Co (0.3)/Pd (1.2)]21/Ta(3) films (units in nm) with perpendicular magnetic anisotropy on Si substrates. A tunneling magnetoresistive sensor was placed on the nanowire surface and a predetermined current pulse was applied. Real-time detection of the current-driven magnetic domain motion was successful in that the resistance of the tunneling magnetoresistive sensor was changed with the magnetization direction beneath the sensor. This demonstrates that magnetic domain detection using a tunneling magnetoresistive sensor is effective for the direct analysis of micro magnetic domain motion.

  16. Efficient stopping of current-driven domain wall using a local Rashba field

    NASA Astrophysics Data System (ADS)

    Tatara, Gen; Saarikoski, Henri; Mitsumata, Chiharu

    2016-10-01

    We show theoretically that a locally embedded Rashba interaction acts as a strong pinning center for current-driven domain walls and demonstrate efficient capturing and depinning of the wall using a weak Rashba interaction of the order of 0.01 eV Å. Our discovery is expected to be useful for highly reliable control of domain walls in racetrack memories.

  17. Rayleigh-Taylor instabilities in Type Ia supernova remnants undergoing cosmic ray particle acceleration - low adiabatic index solutions

    NASA Astrophysics Data System (ADS)

    Wang, Chih-Yueh

    2011-07-01

    This study investigates the evolution of Rayleigh-Taylor (R-T) instabilities in Type Ia supernova remnants that are associated with a low adiabatic index γ, where γ < 5/3, which reflects the expected change in the supernova shock structure as a result of cosmic ray particle acceleration. Extreme cases, such as the case with the maximum compression ratio that corresponds to γ= 1.1, are examined. As γ decreases, the shock compression ratio rises, and an increasingly narrow intershock region with a more pronounced initial mixture of R-T unstable gas is produced. Consequently, the remnant outline may be perturbed by small-amplitude, small-wavelength bumps. However, as the instability decays over time, the extent of convective mixing in terms of the ratio of the radius of the R-T fingers to the blast wave does not strongly depend on the value of γ for γ≥ 1.2. As a result of the age of the remnant, the unstable gas cannot extend sufficiently far to form metal-enriched filaments of ejecta material close to the periphery of Tycho's supernova remnant. The consistency of the dynamic properties of Tycho's remnant with the adiabatic model γ= 5/3 reveals that the injection of cosmic rays is too weak to alter the shock structure. Even with very efficient acceleration of cosmic rays at the shock, significantly enhanced mixing is not expected in Type Ia supernova remnants.

  18. Implications of plasma beam instabilities for the statistics of the Fermi hard gamma-ray blazars and the origin of the extragalactic gamma-ray background

    SciTech Connect

    Broderick, Avery E.; Pfrommer, Christoph; Puchwein, Ewald; Chang, Philip

    2014-08-01

    Fermi has been instrumental in constraining the luminosity function and redshift evolution of gamma-ray bright BL Lac objects, a subpopulation of blazars with almost featureless optical spectra. This includes limits on the spectrum and anisotropy of the extragalactic gamma-ray background (EGRB), redshift distribution of nearby Fermi active galactic nuclei (AGNs), and the construction of a logN-log S relation. Based on these, it has been argued that the evolution of the gamma-ray bright BL Lac population must be much less dramatic than that of other AGNs. However, critical to such claims is the assumption that inverse Compton cascades reprocess emission above a TeV into the Fermi energy range, substantially enhancing the strength of the observed limits. Here we demonstrate that in the absence of such a process, due, e.g., to the presence of virulent plasma beam instabilities that preempt the cascade, a population of TeV-bright BL Lac objects that evolve similarly to quasars is consistent with the population of hard gamma-ray BL Lac objects observed by Fermi. Specifically, we show that a simple model for the properties and luminosity function is simultaneously able to reproduce their logN-log S relation, local redshift distribution, and contribution to the EGRB and its anisotropy without any free parameters. Insofar as the naturalness of a picture in which the hard gamma-ray BL Lac population exhibits the strong redshift evolution observed in other tracers of the cosmological history of accretion onto halos is desirable, this lends support for the absence of the inverse Compton cascades and the existence of the beam plasma instabilities.

  19. Induction of Genomic Instability In Vivo by Low Doses of 137Cs gamma rays

    SciTech Connect

    Rithidech, Kanokporn; Simon, Sanford, R.; Whorton, Elbert, B.

    2006-01-06

    The overall goal of this project is to determine if low doses (below or equal to the level traditionally requiring human radiation protection, i.e. less than or equal to 10 cGy) of low LET radiation can induce genomic instability. The magnitude of genomic instability was measured as delayed chromosome instability in bone marrow cells of exposed mice with different levels of endogenous DNA-dependent protein kinase catalytic subunit (DNA-PKcs) activity, i.e. high (C57BL/6J mice), intermediate (BALB/cJ mice), and extremely low (Scid mice). In addition, at early time points (1 and 4 hrs) following irradiation, levels of activation of nuclear factor-kappa B (NF-{kappa}B), a transcription factor known to be involved in regulating the expression of genes responsible for cell protection following stimuli, were measured in these cells. Bone marrow cells were collected at different times following irradiation, i.e. 1 hr, 4 hrs, 1 month, and 6 months. A total of five mice per dose per strain were sacrificed at each time point for sample collection. As a result, a total of 80 mice from each strain were used. The frequency and the type of metaphase chromosome aberrations in bone marrow cells collected from exposed mice at different times following irradiation were used as markers for radiation-induced genomic instability. A three-color fluorescence in situ hybridization (FISH) protocol for mouse chromosomes 1, 2, and 3 was used for the analysis of delayed stable chromosomal aberrations in metaphase cells. All other visible chromatid-type aberrations and gross structural abnormalities involving non-painted chromosomes were also evaluated on the same metaphase cells used for scoring the stable chromosomal aberrations of painted chromosomes. Levels of nuclear factor-kappa B (NF-{kappa}B) activation were also determined in cells at 1 and 4 hrs following irradiation (indicative of early responses).

  20. Investigations into the seeding of instabilities due to x-ray preheat in beryllium-based inertial confinement fusion targets

    SciTech Connect

    Loomis, E. N.; Greenfield, S. R.; Johnson, R. P.; Cobble, J. A.; Luo, S. N.; Montgomery, D. S.; Marinak, M. M.

    2010-05-15

    The geometry of inertial confinement fusion (ICF) capsules makes them susceptible to various types of hydrodynamic instabilities at different stages during an ICF implosion. From the beginnings of ICF research, it has been known that grain-level anisotropy and defects could be a significant source of instability seeding in solid beryllium capsules. We report on experiments conducted at the Trident laser facility [S. H. Batha et al., Rev. Sci. Instrum. 79, 10F305 (2008)] to measure dynamic surface roughening from hard x-ray preheat due to anisotropic thermal expansion. M-band emission from laser-produced gold plasma was used to heat beryllium targets with different amounts of copper doping to temperatures comparable to ICF ignition preheat levels. Dynamic roughening measurements were made on the surface away from the plasma at discrete times up to 8 ns after the beginning of the drive pulse using a surface displacement interferometer with nanometer scale sensitivity. Undoped large-grained targets were measured to roughen between 15 and 50 nm rms. Fine-grained, copper-doped targets were observed to roughen near the sensitivity limit of the interferometer. The results of this work have shed light on the effects of high-Z doping and microstructural refinement on the dynamics of differential thermal expansion and have shown that current ICF capsule designs using beryllium are very effective in reducing preheat related roughening ahead of the first shock.

  1. Chromosome instability and X-ray hypersensitivity in a microcephalic and growth-retarded child

    SciTech Connect

    Barbi, G.; Scheres, J.M.; Schindler, D.; Taalman, R.D.; Rodens, K.; Mehnert, K.; Mueller, M.S.; Seyschab, H. )

    1991-07-01

    The authors report on a microcephalic, growth-retarded newborn girl without major anomalies who has chromosome instability in lymphocytes and fibroblasts. Frequent involvement of bands 7p13, 7q34, 14q11, and 14q32 suggested the diagnosis of ataxia telangiectasia (AT) or a related disorder. Supportive evidence was radioresistant DNA synthesis in fibroblasts and radiation hypersensitivity of short-term lymphocyte cultures. Follow-up for nearly 4 years showed largely normal development, and no signs of telangiectasia, ataxia, or immunodeficiency. Serum AFP levels turned from elevated at age 5 months to normal at age 2 years. They propose that their patient belongs to the expanding category of AT-related genetic disorders, probably to the Nijmegen breakage syndrome.

  2. Investigations into the Seeding of Instabilities due to X-ray Preheat in Beryllium-Based Inertial Confinement Fusion Targets

    NASA Astrophysics Data System (ADS)

    Loomis, Eric

    2009-11-01

    The geometry of inertial confinement fusion (ICF) capsules makes them susceptible to various types of hydrodynamic instabilities at different stages during an ICF implosion. From the beginnings of ICF research, it has been known that grain-level anisotropy and defects could be a primary source of instability seeding in solid capsules. This has steered ICF designs to include amorphous materials such as plastic; however, the benefits of low-Z metallic materials, i.e. beryllium, has kept these materials the focus of much research. Recently, experiments were conducted at the Trident laser facility to measure dynamic surface roughening from hard x-ray preheat. M-band emission from laser produced gold plasma was used to heat beryllium targets with different amounts of copper doping to temperatures comparable to National Ignition Facility (NIF) preheat levels. Temporal and spectral x-ray diagnostics were used to estimate the target heating, which was also predicted by multi-dimensional radiation hydrodynamics calculations. Wave profiles of varying complexity due to differences in copper doping were observed with free surface line imaging velocity interferometry. Dynamic roughening measurements were made on the surface away from the plasma at discrete times up to 8 ns after the beginning of the drive pulse using a surface displacement interferometer with nanometer scale sensitivity. Undoped, large-grained targets were measured to roughen between 15 and 50 nm rms depending on variations in x-ray absorption through the target thickness. Fine-grained, copper-doped targets were observed to roughen near the sensitivity limit of the interferometer and approached the Rev2 NIC design point of 0.9 nm. The results of this combined experimental and modeling effort have shed light on the effects of high-Z doping and microstructural refinement on the dynamics of differential thermal expansion and have shown that current NIF capsule designs using beryllium are very effective in reducing

  3. A kinetic approach to cosmic ray induced streaming instability at supernova shocks

    SciTech Connect

    Amato, Elena; Blasi, Pasquale; /Arcetri Observ. /Fermilab /Gran Sasso

    2008-06-01

    We show here that a purely kinetic approach to the excitation of waves by cosmic rays in the vicinity of a shock front leads to predict the appearance of a non-alfvenic fastly growing mode which has the same dispersion relation as that previously found by Bell (2004) by treating the plasma in the MHD approximation. The kinetic approach allows us to investigate the dependence of the dispersion relation of these waves on the microphysics of the current which compensates the cosmic ray flow. We also show that a resonant and a non-resonant mode may appear at the same time and one of the two may become dominant on the other depending on the conditions in the acceleration region. We discuss the role of the unstable modes for magnetic field amplification and particle acceleration in supernova remnants at different stages of the remnant evolution.

  4. Resonant field amplification with feedback-stabilized regime in current driven resistive wall mode

    SciTech Connect

    Liu Yueqiang; In, Y.; Okabayashi, M.

    2010-07-15

    The stability and resonant field response of current driven resistive wall modes are numerically studied for DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] low pressure plasmas. The resonant field response of the feedback-stabilized resistive wall mode is investigated both analytically and numerically, and compared with the response from intrinsically stable or marginally stable modes. The modeling qualitatively reproduces the experimental results. Furthermore, based on some recent results and on the indirect numerical evidence in this work, it is suggested that the mode stability behavior observed in DIII-D experiments is due to the kink-peeling mode stabilization by the separatrix geometry. The phase inversion radius of the computed plasma displacement does not generally coincide with the radial locations of rational surfaces, also supporting experimental observations.

  5. Numerical Simulation of Non-Inductive Current Driven Scenario in EAST Using Neutral Beam Injection

    NASA Astrophysics Data System (ADS)

    Li, Hao; Wu, Bin; Wang, Jinfang; Wang, Ji; Hu, Chundong

    2015-01-01

    For achieving the scientific mission of long pulse and high performance operation, experimental advanced superconducting tokamak (EAST) applies fully superconducting magnet technology and is equiped with high power auxiliary heating system. Besides RF (Radio Frequency) wave heating, neutral beam injection (NBI) is an effective heating and current drive method in fusion research. NBCD (Neutral Beam Current Drive) as a viable non-inductive current drive source plays an important role in quasi-steady state operating scenario for tokamak. The non-inductive current driven scenario in EAST only by NBI is predicted using the TSC/NUBEAM code. At the condition of low plasma current and moderate plasma density, neutral beam injection heats the plasma effectively and NBCD plus bootstrap current accounts for a large proportion among the total plasma current for the flattop time.

  6. Importance of Richtmyer-Meshkov Instability on Measurements of Cosmic-Ray Acceleration Efficiency at Supernova Remnants

    NASA Astrophysics Data System (ADS)

    Shimoda, Jiro; Inoue, Tsuyoshi; Ohira, Yutaka; Yamazaki, Ryo; Bamba, Aya; Vink, Jacco

    2016-06-01

    Using three-dimensional (3D) magnetohydrodynamics (MHD) simulations, we show that the effi- ciency of cosmic-ray (CR) acceleration in supernova remnants (SNRs) is over-predicted if it could be estimated based on proper motion measurements of Hα filaments in combination with shock-jump conditions. The CR acceleration efficiency at the SNR has been widely discussed, which seems to be ubiquitously so high that back reaction of CRs onto background shock structure is significant, with assuming that SNRs shock is plane parallel. The role of the Richtmyer-Meshkov Instability (RMI) has recently been studied using MHD simulations that have shown that the forward shock of SNRs is rippled due to the interaction with interstellar medium, which has Kolmogorov-like density power spectrum. The kinetic energy of the shock wave is transferred into that of downstream turbulence as well as thermal energy that is related to the shock velocity component normal to the shock surface. Our synthetic observation shows that the CR acceleration efficiency is overestimated by 10-40% despite of no CR acceleration. Furthermore, our simple analytical argument gives upper and lower bounds of apparent CR production efficiency, which is roughly consistent with our numerical results.

  7. Oscillatory dependence of current-driven magnetic domain wall motion on current pulse length

    NASA Astrophysics Data System (ADS)

    Thomas, Luc; Hayashi, Masamitsu; Jiang, Xin; Moriya, Rai; Rettner, Charles; Parkin, Stuart S. P.

    2006-09-01

    Magnetic domain walls, in which the magnetization direction varies continuously from one direction to another, have long been objects of considerable interest. New concepts for devices based on such domain walls are made possible by the direct manipulation of the walls using spin-polarized electrical current through the phenomenon of spin momentum transfer. Most experiments to date have considered the current-driven motion of domain walls under quasi-static conditions, whereas for technological applications, the walls must be moved on much shorter timescales. Here we show that the motion of domain walls under nanosecond-long current pulses is surprisingly sensitive to the pulse length. In particular, we find that the probability of dislodging a domain wall, confined to a pinning site in a permalloy nanowire, oscillates with the length of the current pulse, with a period of just a few nanoseconds. Using an analytical model and micromagnetic simulations, we show that this behaviour is connected to a current-induced oscillatory motion of the domain wall. The period is determined by the wall's mass and the slope of the confining potential. When the current is turned off during phases of the domain wall motion when it has enough momentum, the domain wall is driven out of the confining potential in the opposite direction to the flow of spin angular momentum. This dynamic amplification effect could be exploited in magnetic nanodevices based on domain wall motion.

  8. Current-driven vortex domain wall motion in wire-tube nanostructures

    SciTech Connect

    Espejo, A. P.; Vidal-Silva, N.; López-López, J. A.; Goerlitz, D.; Nielsch, K.; Escrig, J.

    2015-03-30

    We have investigated the current-driven domain wall motion in nanostructures comprised of a pair of nanotube and nanowire segments. Under certain values of external magnetic fields, it is possible to pin a vortex domain wall in the transition zone between the wire and tube segments. We explored the behavior of this domain wall under the action of an electron flow applied in the opposite direction to the magnetic field. Thus, for a fixed magnetic field, it is possible to release a domain wall pinned simply by increasing the intensity of the current density, or conversely, for a fixed current density, it is possible to release the domain wall simply decreasing the magnetic external field. When the domain wall remains pinned due to the competition between the current density and the magnetic external field, it exhibits a oscillation frequency close to 8 GHz. The amplitude of the oscillations increases with the current density and decreases over time. On the other hand, when the domain wall is released and propagated through the tube segment, this shows the standard separation between a steady and a precessional regime. The ability to pin and release a domain wall by varying the geometric parameters, the current density, or the magnetic field transforms these wire-tube nanostructures in an interesting alternative as an on/off switch nano-transistor.

  9. Hydrodynamic instability growth of three-dimensional, “native-roughness” modulations in x-ray driven, spherical implosions at the National Ignition Facility

    SciTech Connect

    Smalyuk, V. A.; Weber, S. V.; Casey, D. T.; Clark, D. S.; Field, J. E.; Haan, S. W.; Hammel, B. A.; Hamza, A. V.; Landen, O. L.; Robey, H. F.; Weber, C. R.; Hoover, D. E.; Nikroo, A.

    2015-07-15

    Hydrodynamic instability growth experiments with three-dimensional (3-D) surface-roughness modulations were performed on plastic (CH) shell spherical implosions at the National Ignition Facility (NIF) [E. M. Campbell, R. Cauble, and B. A. Remington, AIP Conf. Proc. 429, 3 (1998)]. The initial capsule outer-surface roughness was similar to the standard specifications (“native roughness”) used in a majority of implosions on NIF. The experiments included instability growth measurements of the perturbations seeded by the thin membranes (or tents) used to hold the capsules inside the hohlraums. In addition, initial modulations included two divots used as spatial fiducials to determine the convergence in the experiments and to check the accuracy of 3D simulations in calculating growth of known initial perturbations. The instability growth measurements were performed using x-ray, through-foil radiography of one side of the imploding shell, based on time-resolved pinhole imaging. Averaging over 30 similar images significantly increases the signal-to-noise ratio, making possible a comparison with 3-D simulations. At a convergence ratio of ∼3, the measured tent and divot modulations were close to those predicted by 3-D simulations (within ∼15%–20%), while measured 3-D, broadband modulations were ∼3–4 times larger than those simulated based on the growth of the known imposed initial surface modulations. In addition, some of the measured 3-D features in x-ray radiographs did not resemble those characterized on the outer capsule surface before the experiments. One of the hypotheses to explain the results is based on the increased instability amplitudes due to modulations of the oxygen content in the bulk of the capsule. As the target assembly and handling procedures involve exposure to UV light, this can increase the uptake of the oxygen into the capsule, with irregularities in the oxygen seeding hydrodynamic instabilities. These new experimental results have

  10. Effects of line-tied boundary conditions on internal current-driven kink mode

    NASA Astrophysics Data System (ADS)

    Mirnov, V. V.; Forest, C. B.; Hegna, C. C.

    2006-04-01

    MHD kink instabilities caused by current passing though high temperature plasma in magnetic field is a topic of importance to astrophysical and lab plasmas. Recent theoretical study of external kink mode stability in line-tied geometry[1] has shown the existence of complex axial wave numbers kz in spatial spectrum of the system. Similar to the external kink mode complex kz were found in numerical calculations performed at LANL for line-tied internal kink instability. We are developing an analytical model for internal mode in line-tied cylindrical geometry to follow transition from the case of periodic cylinder where all axial wave numbers are real to line-tied boundary conditions (BC). The model allows us to determine whether line-tying BC change axial modes globally or their effect is ``shielded'' in long systems in the vicinity of the end-plates. This is important for mode structure and, specifically, for perturbed current profile (``current sheet'') which is localized on the resonance surface in periodic case and is broadened due to superposition of ``quasi-resonances'' in line-tied geometry. [1] V.V.Mirnov et al., Bull. of the APS, v.50, No 8, p.238, DPP Meeting, Oct. 24-28, 2005

  11. Current-driven nanowire formation on surfaces of crystalline conducting substrates

    NASA Astrophysics Data System (ADS)

    Kumar, Ashish; Dasgupta, Dwaipayan; Dimitrakopoulos, Christos; Maroudas, Dimitrios

    2016-05-01

    The formation and precise manipulation of nanoscale features by controlling macroscopic forces is essential to advancing nanotechnology. Toward this end, we report here a theoretical study on formation of nanowires with precisely controlled widths, starting from single-layer conducting islands on crystalline conducting substrates under the controlled action of macroscopic forcing provided by an externally applied electric field that drives island edge electromigration. Numerical simulations based on an experimentally validated model and supported by linear stability theory show that large-size islands undergo a current-induced fingering instability, leading to nanowire formation after finger growth. Depending on the substrate surface crystallographic orientation, necking instabilities after fingering lead to the formation of multiple parallel nanowires per island. In all cases, the axis of the formed nanowires is aligned with the direction of the externally applied electric field. The nanowires have constant widths, on the order of 10 nm, which can be tuned by controlling the externally applied electric field strength. Our findings have important implications for developing future lithography-free nanofabrication and nanoelectronic patterning techniques.

  12. Investigation of domain wall motion in RE-TM magnetic wire towards a current driven memory and logic

    NASA Astrophysics Data System (ADS)

    Awano, Hiroyuki

    2015-06-01

    Current driven magnetic domain wall (DW) motions of ferri-magnetic TbFeCo wires have been investigated. In the case of a Si substrate, the critical current density (Jc) of DW motion was successfully reduced to 3×106 A/cm2. Moreover, by using a polycarbonate (PC) substrate with a molding groove of 600 nm width, the Jc was decreased to 6×105 A/cm2. In order to fabricate a logic in memory, a current driven spin logics (AND, OR, NOT) have been proposed and successfully demonstrated under the condition of low Jc. These results indicate that TbFeCo nanowire is an excellent candidate for next generation power saving memory and logic.

  13. Local control of electric current driven shell etching of multiwalled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Subramanian, A.; Choi, T.-Y.; Dong, L. X.; Tharian, J.; Sennhauser, U.; Poulikakos, D.; Nelson, B. J.

    2007-10-01

    The stability problem of low-speed plane Couette-Poiseuille flow of air under heat transfer effects is solved numerically using the linear stability theory. Stability equations obtained from two-dimensional equations of motion and their boundary conditions result in an eigenvalue problem that is solved using an efficient shoot-search technique. Variable fluid properties are accounted for both in the basic flow and the perturbation (stability) equations. A parametric study is performed in order to assess the roles of moving wall velocity and heat transfer. It is found that the moving wall velocity and the location of the critical layers play decisive roles in the instability mechanism. The flow becomes unconditionally stable whenever the moving wall velocity exceeds half of the maximum velocity in the channel. With wall heating and Mach number effects included, the flow is stabilized.

  14. Suppression of self-pulsing regime of direct current driven microplasma discharges

    NASA Astrophysics Data System (ADS)

    Mahamud, Rajib; Farouk, Tanvir

    2016-05-01

    An instability suppressor circuit for self-pulsing direct current (DC) driven microplasma discharge is proposed and experimentally tested over a range of pd values for helium feed gas. The external circuit configuration suppresses self-pulsing of the discharge, extending the normal glow regime to lower currents. The negative differential resistance (NDR) region was observed to shift further left in the voltage-current parametric space (i.e., lower current), and the slope of the NDR region was decreased substantially. In addition, the suppressor element decreased the pulsing frequency as well as the static positive resistance of the discharge in the shifted NDR region. Modeling of the discharge configuration indicated that the inductor element of the suppressor circuit increases the time lag of the plasma response, which increases the stable region of operation. A stability map in terms of the external circuit parameters is introduced.

  15. Linear calculations of edge current driven kink modes with BOUT++ code

    SciTech Connect

    Li, G. Q. Xia, T. Y.; Xu, X. Q.; Snyder, P. B.; Turnbull, A. D.; Ma, C. H.; Xi, P. W.

    2014-10-15

    This work extends previous BOUT++ work to systematically study the impact of edge current density on edge localized modes, and to benchmark with the GATO and ELITE codes. Using the CORSICA code, a set of equilibria was generated with different edge current densities by keeping total current and pressure profile fixed. Based on these equilibria, the effects of the edge current density on the MHD instabilities were studied with the 3-field BOUT++ code. For the linear calculations, with increasing edge current density, the dominant modes are changed from intermediate-n and high-n ballooning modes to low-n kink modes, and the linear growth rate becomes smaller. The edge current provides stabilizing effects on ballooning modes due to the increase of local shear at the outer mid-plane with the edge current. For edge kink modes, however, the edge current does not always provide a destabilizing effect; with increasing edge current, the linear growth rate first increases, and then decreases. In benchmark calculations for BOUT++ against the linear results with the GATO and ELITE codes, the vacuum model has important effects on the edge kink mode calculations. By setting a realistic density profile and Spitzer resistivity profile in the vacuum region, the resistivity was found to have a destabilizing effect on both the kink mode and on the ballooning mode. With diamagnetic effects included, the intermediate-n and high-n ballooning modes can be totally stabilized for finite edge current density.

  16. Linear calculations of edge current driven kink modes with BOUT++ code

    NASA Astrophysics Data System (ADS)

    Li, G. Q.; Xu, X. Q.; Snyder, P. B.; Turnbull, A. D.; Xia, T. Y.; Ma, C. H.; Xi, P. W.

    2014-10-01

    This work extends previous BOUT++ work to systematically study the impact of edge current density on edge localized modes, and to benchmark with the GATO and ELITE codes. Using the CORSICA code, a set of equilibria was generated with different edge current densities by keeping total current and pressure profile fixed. Based on these equilibria, the effects of the edge current density on the MHD instabilities were studied with the 3-field BOUT++ code. For the linear calculations, with increasing edge current density, the dominant modes are changed from intermediate-n and high-n ballooning modes to low-n kink modes, and the linear growth rate becomes smaller. The edge current provides stabilizing effects on ballooning modes due to the increase of local shear at the outer mid-plane with the edge current. For edge kink modes, however, the edge current does not always provide a destabilizing effect; with increasing edge current, the linear growth rate first increases, and then decreases. In benchmark calculations for BOUT++ against the linear results with the GATO and ELITE codes, the vacuum model has important effects on the edge kink mode calculations. By setting a realistic density profile and Spitzer resistivity profile in the vacuum region, the resistivity was found to have a destabilizing effect on both the kink mode and on the ballooning mode. With diamagnetic effects included, the intermediate-n and high-n ballooning modes can be totally stabilized for finite edge current density.

  17. Current-driven asymmetric magnetization switching in perpendicularly magnetized CoFeB/MgO heterostructures

    NASA Astrophysics Data System (ADS)

    Torrejon, Jacob; Garcia-Sanchez, Felipe; Taniguchi, Tomohiro; Sinha, Jaivardhan; Mitani, Seiji; Kim, Joo-Von; Hayashi, Masamitsu

    2015-06-01

    The flow of in-plane current through ultrathin magnetic heterostructures can cause magnetization switching or domain-wall nucleation owing to bulk and interfacial effects. Within the magnetic layer, the current can create magnetic instabilities via spin transfer torques (STT). At interface(s), spin current generated from the spin Hall effect in a neighboring layer can exert torques, referred to as the spin Hall torques, on the magnetic moments. Here, we study current-induced magnetization switching in perpendicularly magnetized CoFeB/MgO heterostructures with a heavy metal (HM) underlayer. Depending on the thickness of the HM underlayer, we find distinct differences in the in-plane field dependence of the threshold switching current. The STT is likely responsible for the magnetization reversal for the thinner underlayer films whereas the spin Hall torques cause the switching for thicker underlayer films. For the latter, we find differences in the switching current for positive and negative currents and initial magnetization directions. We find that the growth process during the film deposition introduces an anisotropy that breaks the symmetry of the system and causes the asymmetric switching. The presence of such symmetry-breaking anisotropy enables deterministic magnetization switching at zero external fields.

  18. Magnetic dipole discharges. III. Instabilities

    SciTech Connect

    Stenzel, R. L.; Urrutia, J. M.; Ionita, C.; Schrittwieser, R.

    2013-08-15

    Instabilities in a cross-field discharge around a permanent magnet have been investigated. The permanent magnet serves as a cold cathode and the chamber wall as an anode. The magnet is biased strongly negative and emits secondary electrons due to impact of energetic ions. The electrons outside the sheath are confined by the strong dipolar magnetic field and by the ion-rich sheath surrounding the magnet. The electron energy peaks in the equatorial plane where most ionization occurs and the ions are trapped in a negative potential well. The discharge mechanism is the same as that of cylindrical and planar magnetrons, but here extended to a 3-D cathode geometry using a single dipole magnet. While the basic properties of the discharge are presented in a companion paper, the present focus is on various observed instabilities. The first is an ion sheath instability which oscillates the plasma potential outside the sheath below the ion plasma frequency. It arises in ion-rich sheaths with low electron supply, which is the case for low secondary emission yields. Sheath oscillations modulate the discharge current creating oscillating magnetic fields. The second instability is current-driven ion sound turbulence due to counter-streaming electrons and ions. The fluctuations have a broad spectrum and short correlation lengths in all directions. The third type of fluctuations is spiky potential and current oscillations in high density discharges. These appear to be due to unstable emission properties of the magnetron cathode.

  19. Low-Dose Studies with Focused X-rays in Cell and Tissue Models: Mechanisms of Bystander and Genomic Instability Responses

    SciTech Connect

    Michael, Barry D.; Held, Kathryn D.

    2001-06-01

    This project is part of the DOE research program on the biological effects of low dose and dose rate ionizing radiation. This DOE program is designed to support and conduct science that can impact the subsequent development of health risk policy for low dose radiation exposures in the US. The overall, long-term goal of this project is to increase understanding of the responses of cells to the low doses of ionizing radiation typically encountered in environmental level exposures. To achieve this objective, we couple use of a unique focused soft X-ray facility for low dose irradiation of individual cells or irradiation of specific subcellular regions of cells with studies of the effects of reactive oxygen species (ROS) produced in cells. The project includes seven specific goals: (1) Determine the response of individual cells to low doses of ionizing radiation from a focused soft X-ray beam with a 250 nm diameter beam spot. (2) Determine the response of cells to ROS generated by chemical agents in a fashion that mimics the endogenous cellular generation of ROS. (3) Study the interaction between cellular oxidative processes and ionizing radiation. (4) Determine the importance of the subcellular distribution of ROS from focused soft X-rays on cellular response. (5) Determine whether damage deposited in individual cells by focused soft X-rays or by chemically-generated ROS can elicit a response in other, surrounding, untreated cells, a ''bystander'' effect. (6) Quantify the low dose response and the targets involved in the genomic instability phenotype in cells exposed to low LET radiation and the relationship with the bystander response.

  20. Low-Dose Studies with Focused X-rays in Cell and Tissue Models: Mechanisms of Bystander and Genomic Instability Responses

    SciTech Connect

    Michael, Barry D.; Held, Kathryn D.

    2002-06-01

    This project is part of the DOE research program on the biological effects of low dose and dose rate ionizing radiation. This DOE program is designed to support and conduct science that can impact the subsequent development of health risk policy for low dose radiation exposures in the US. The overall, long-term goal of this project is to increase understanding of the responses of cells to the low doses of ionizing radiation typically encountered in environmental level exposures. To achieve this objective, we couple use of a unique focused soft X-ray facility for low dose irradiation of individual cells or irradiation of specific subcellular regions of cells with studies of the effects of reactive oxygen species (ROS) produced in cells. The project includes seven specific goals: (1) Determine the response of individual cells to low doses of ionizing radiation from a focused soft X-ray beam with a 250 nm diameter beam spot. (2) Determine the response of cells to ROS generated by chemical agents in a fashion that mimics the endogenous cellular generation of ROS. (3) Study the interaction between cellular oxidative processes and ionizing radiation. (4) Determine the importance of the subcellular distribution of ROS from focused soft X-rays on cellular response. (5) Determine whether damage deposited in individual cells by focused soft X-rays or by chemically-generated ROS can elicit a response in other, surrounding, untreated cells, a ''bystander'' effect. (6) Quantify the low dose response and the targets involved in the genomic instability phenotype in cells exposed to low LET radiation and the relationship with the bystander response. (7) Develop tissue explant systems for the measurement of low dose effects in multicellular systems.

  1. Radio-protective effect of cinnamic acid, a phenolic phytochemical, on genomic instability induced by X-rays in human blood lymphocytes in vitro.

    PubMed

    Cinkilic, Nilufer; Tüzün, Ece; Çetintaş, Sibel Kahraman; Vatan, Özgür; Yılmaz, Dilek; Çavaş, Tolga; Tunç, Sema; Özkan, Lütfi; Bilaloğlu, Rahmi

    2014-08-01

    The present study was designed to determine the protective activity of cinnamic acid against induction by X-rays of genomic instability in normal human blood lymphocytes. This radio-protective activity was assessed by use of the cytokinesis-block micronucleus test and the alkaline comet assay, with human blood lymphocytes isolated from two healthy donors. A Siemens Mevatron MD2 (Siemens AG, USA, 1994) linear accelerator was used for the irradiation with 1 or 2 Gy. Treatment of the lymphocytes with cinnamic acid prior to irradiation reduced the number of micronuclei when compared with that in control samples. Treatment with cinnamic acid without irradiation did not increase the number of micronuclei and did not show a cytostatic effect in the lymphocytes. The results of the alkaline comet assay revealed that cinnamic acid reduces the DNA damage induced by X-rays, showing a significant radio-protective effect. Cinnamic acid decreased the frequency of irradiation-induced micronuclei by 16-55% and reduced DNA breakage by 17-50%, as determined by the alkaline comet assay. Cinnamic acid may thus act as a radio-protective compound, and future studies may focus on elucidating the mechanism by which cinnamic acid offers radioprotection.

  2. Effects of Stress and Void-Void Interactions on Current-Driven Void Surface Evolution in Metallic Thin Films

    NASA Astrophysics Data System (ADS)

    Cho, Jaeseol; Gungor, M. Rauf; Maroudas, Dimitrios

    2006-03-01

    We report results of electromigration- and stress-induced migration and morphological evolution of voids in metallic thin films based on self-consistent numerical simulations. The analysis reveals the complex nature of void-void interactions and their implications for the evolution of metallic thin-film electrical resistance, providing interpretation for experimental measurements in interconnect lines. Interestingly, for two voids migrating in the same direction under certain conditions, we find that a smaller void does not always approach and coalesce with a larger one, while a larger void may approach and coalesce with a smaller one. In addition, we find that under certain electromechanical conditions, biaxially applied mechanical stress can cause substantial retardation of void motion, as measured by the constant speed of electromigration-induced translation of morphologically stable voids. This effect suggests the possibility for complete inhibition of current-driven void motion under stress.

  3. Hip instability.

    PubMed

    Smith, Matthew V; Sekiya, Jon K

    2010-06-01

    Hip instability is becoming a more commonly recognized source of pain and disability in patients. Traumatic causes of hip instability are often clear. Appropriate treatment includes immediate reduction, early surgery for acetabular rim fractures greater than 25% or incarcerated fragments in the joint, and close follow-up to monitor for avascular necrosis. Late surgical intervention may be necessary for residual symptomatic hip instability. Atraumatic causes of hip instability include repetitive external rotation with axial loading, generalized ligamentous laxity, and collagen disorders like Ehlers-Danlos. Symptoms caused by atraumatic hip instability often have an insidious onset. Patients may have a wide array of hip symptoms while demonstrating only subtle findings suggestive of capsular laxity. Traction views of the affected hip can be helpful in diagnosing hip instability. Open and arthroscopic techniques can be used to treat capsular laxity. We describe an arthroscopic anterior hip capsular plication using a suture technique. PMID:20473129

  4. Collective instabilities

    SciTech Connect

    K.Y. Ng

    2003-08-25

    The lecture covers mainly Sections 2.VIII and 3.VII of the book ''Accelerator Physics'' by S.Y. Lee, plus mode-coupling instabilities and chromaticity-driven head-tail instability. Besides giving more detailed derivation of many equations, simple interpretations of many collective instabilities are included with the intention that the phenomena can be understood more easily without going into too much mathematics. The notations of Lee's book as well as the e{sup jwt} convention are followed.

  5. Effect of a RF Wave on Ion Cyclotron Instability in Size Distributed Impurities Containing Plasmas

    SciTech Connect

    Sharma, A. K.; Tripathi, V. K.; Annou, R.

    2008-09-07

    The effect of a large amplitude lower hybrid wave on current driven ion cyclotron waves in a dusty plasma where dust grains are size distributed is examined. The influence of the lower hybrid wave on the stabilization of the instability is studied. The efficacy of rf is dust density dependent.

  6. Was the soft X-ray flare in NGC 3599 due to an AGN disc instability or a delayed tidal disruption event?

    NASA Astrophysics Data System (ADS)

    Saxton, R. D.; Motta, S. E.; Komossa, S.; Read, A. M.

    2015-12-01

    We present unpublished data from a tidal disruption candidate in NGC 3599 which show that the galaxy was already X-ray bright 18 months before the measurement which led to its classification. This removes the possibility that the flare was caused by a classical, fast-rising, short-peaked, tidal disruption event. Recent relativistic simulations indicate that the majority of disruptions will actually take months or years to rise to a peak, which will then be maintained for longer than previously thought. NGC 3599 could be one of the first identified examples of such an event. The optical spectra of NGC 3599 indicate that it is a low-luminosity Seyfert/low-ionization nuclear emission-line region (LINER) with Lbol ˜ 1040 erg s-1. The flare may alternatively be explained by a thermal instability in the accretion disc, which propagates through the inner region at the sound speed, causing an increase of the disc scaleheight and local accretion rate. This can explain the ≤9 yr rise time of the flare. If this mechanism is correct then the flare may repeat on a time-scale of several decades as the inner disc is emptied and refilled.

  7. Optimizing the internal electric field distribution of alternating current driven organic light-emitting devices for a reduced operating voltage

    NASA Astrophysics Data System (ADS)

    Fröbel, Markus; Hofmann, Simone; Leo, Karl; Gather, Malte C.

    2014-02-01

    The influence of the thickness of the insulating layer and the intrinsic organic layer on the driving voltage of p-i-n based alternating current driven organic light-emitting devices (AC-OLEDs) is investigated. A three-capacitor model is employed to predict the basic behavior of the devices, and good agreement with the experimental values is found. The proposed charge regeneration mechanism based on Zener tunneling is studied in terms of field strength across the intrinsic organic layers. A remarkable consistency between the measured field strength at the onset point of light emission (3-3.1 MV/cm) and the theoretically predicted breakdown field strength of around 3 MV/cm is obtained. The latter value represents the field required for Zener tunneling in wide band gap organic materials according to Fowler-Nordheim theory. AC-OLEDs with optimized thickness of the insulating and intrinsic layers show a reduction in the driving voltage required to reach a luminance of 1000 cd/m2 of up to 23% (8.9 V) and a corresponding 20% increase in luminous efficacy.

  8. Diffusive Magnetohydrodynamic Instabilities beyond the Chandrasekhar Theorem

    NASA Astrophysics Data System (ADS)

    Rüdiger, Günther; Schultz, Manfred; Stefani, Frank; Mond, Michael

    2015-10-01

    We consider the stability of axially unbounded cylindrical flows that contain a toroidal magnetic background field with the same radial profile as their azimuthal velocity. For ideal fluids, Chandrasekhar had shown the stability of this configuration if the Alfvén velocity of the field equals the velocity of the background flow, i.e., if the magnetic Mach number {Mm}=1. We demonstrate that magnetized Taylor-Couette flows with such profiles become unstable against non-axisymmetric perturbations if at least one of the diffusivities is finite. We also find that for small magnetic Prandtl numbers {Pm} the lines of marginal instability scale with the Reynolds number and the Hartmann number. In the limit {Pm}\\to 0 the lines of marginal instability completely lie below the line for {Mm}=1 and for {Pm}\\to ∞ they completely lie above this line. For any finite value of {Pm}, however, the lines of marginal instability cross the line {Mm}=1, which separates slow from fast rotation. The minimum values of the field strength and the rotation rate that are needed for the instability (slightly) grow if the rotation law becomes flat. In this case, the electric current of the background field becomes so strong that the current-driven Tayler instability (which also exists without rotation) appears in the bifurcation map at low Hartmann numbers.

  9. Relativistic MHD simulations of core-collapse GRB jets: 3D instabilities and magnetic dissipation

    NASA Astrophysics Data System (ADS)

    Bromberg, Omer; Tchekhovskoy, Alexander

    2016-02-01

    Relativistic jets are associated with extreme astrophysical phenomena, like the core collapse of massive stars in gamma-ray bursts (GRBs) and the accretion on to supermassive black holes in active galactic nuclei. It is generally accepted that these jets are powered electromagnetically, by the magnetized rotation of a central compact object (black hole or neutron star). However, how the jets produce the observed emission and survive the propagation for many orders of magnitude in distance without being disrupted by current-driven instabilities is the subject of active debate. We carry out time-dependent 3D relativistic magnetohydrodynamic (MHD) simulations of relativistic, Poynting-flux-dominated jets. The jets are launched self-consistently by the rotation of a strongly magnetized central object. This determines the natural degree of azimuthal magnetic field winding, a crucial factor that controls jet stability. We find that the jets are susceptible to two types of instability: (i) a global, external kink mode that grows on long time-scales. It bodily twists the jet, reducing its propagation velocity. We show analytically that in flat density profiles, like the ones associated with galactic cores, the external mode grows and may stall the jet. In the steep profiles of stellar envelopes the external kink weakens as the jet propagates outward. (ii) a local, internal kink mode that grows over short time-scales and causes small-angle magnetic reconnection and conversion of about half of the jet electromagnetic energy flux into heat. We suggest that internal kink instability is the main dissipation mechanism responsible for powering GRB prompt emission.

  10. ELM phenomenon as an interaction between bootstrap-current driven peeling modes and pressure-driven ballooning modes

    NASA Astrophysics Data System (ADS)

    Saarelma, S.; Günter, S.; Kurki-Suonio, T.; Zehrfeld, H.-P.

    2000-05-01

    An ELMy ASDEX Upgrade plasma equilibrium is reconstructed taking into account the bootstrap current. The peeling mode stability of the equilibrium is numerically analysed using the GATO [1] code, and it is found that the bootstrap current can drive the plasma peeling mode unstable. A high-n ballooning mode stability analysis of the equilibria revealed that, while destabilizing the peeling modes, the bootstrap current has a stabilizing effect on the ballooning modes. A combination of these two instabilities is a possible explanation for the type I ELM phenomenon. A triangularity scan showed that increasing triangularity stabilizes the peeling modes and can produce ELM-free periods observed in the experiments.

  11. [Carpal instability].

    PubMed

    Redeker, J; Vogt, P M

    2011-01-01

    Carpal instability can be understood as a disturbed anatomical alignment between bones articulating in the carpus. This disturbed balance occurs either only dynamically (with movement) under the effect of physiological force or even statically at rest. The most common cause of carpal instability is wrist trauma with rupture of the stabilizing ligaments and adaptive misalignment following fractures of the radius or carpus. Carpal collapse plays a special role in this mechanism due to non-healed fracture of the scaphoid bone. In addition degenerative inflammatory alterations, such as chondrocalcinosis or gout, more rarely aseptic bone necrosis of the lunate or scaphoid bones or misalignment due to deposition (Madelung deformity) can lead to wrist instability. Under increased pressure the misaligned joint surfaces lead to bone arrosion with secondary arthritis of the wrist. In order to arrest or slow down this irreversible process, diagnosis must occur as early as possible. Many surgical methods have been thought out to regain stability ranging from direct reconstruction of the damaged ligaments, through ligament replacement to partial stiffening of the wrist joint.

  12. Current driven vortex-antivortex pair breaking and vortex explosion in the Bi2Te3/FeTe interfacial superconductor

    NASA Astrophysics Data System (ADS)

    Dean, C. L.; Kunchur, M. N.; He, Q. L.; Liu, H.; Wang, J.; Lortz, R.; Sou, I. K.

    2016-08-01

    We investigated the dissipative regime of the Bi2Te3/FeTe topological insulator-chalcogenide interface superconductor at temperatures well below the Berezinski-Kosterlitz-Thouless transition. We observe a transition in the current-resistance and temperature-resistance curves that quantitatively agrees with the Likharev vortex-explosion phenomenon. In the limit of low temperatures and high current densities, we were able to demonstrate the regime of complete vortex-antivortex dissociation arising from current driven vortex-antivortex pair breaking.

  13. Laboratory blast wave driven instabilities

    NASA Astrophysics Data System (ADS)

    Kuranz, Carolyn

    2008-11-01

    This presentation discusses experiments involving the evolution of hydrodynamic instabilities in the laboratory under high-energy-density (HED) conditions. These instabilities are driven by blast waves, which occur following a sudden, finite release of energy, and consist of a shock front followed by a rarefaction wave. When a blast wave crosses an interface with a decrease in density, hydrodynamic instabilities will develop. Instabilities evolving under HED conditions are relevant to astrophysics. These experiments include target materials scaled in density to the He/H layer in SN1987A. About 5 kJ of laser energy from the Omega Laser facility irradiates a 150 μm plastic layer that is followed by a low-density foam layer. A blast wave structure similar to those in supernovae is created in the plastic layer. The blast wave crosses an interface having a 2D or 3D sinusoidal structure that serves as a seed perturbation for hydrodynamic instabilities. This produces unstable growth dominated by the Rayleigh-Taylor (RT) instability in the nonlinear regime. We have detected the interface structure under these conditions using x-ray backlighting. Recent advances in our diagnostic techniques have greatly improved the resolution of our x-ray radiographic images. Under certain conditions, the improved images show some mass extending beyond the RT spike and penetrating further than previously observed or predicted by current simulations. The observed effect is potentially of great importance as a source of mass transport to places not anticipated by current theory and simulation. I will discuss the amount of mass in these spike extensions, the associated uncertainties, and hypotheses regarding their origin We also plan to show comparisons of experiments using single mode and multimode as well as 2D and 3D initial conditions. This work is sponsored by DOE/NNSA Research Grants DE-FG52-07NA28058 (Stewardship Sciences Academic Alliances) and DE-FG52-04NA00064 (National Laser User

  14. Experiments on current-driven three-dimensional ion sound turbulence. I - Return-current limited electron beam injection. II - Wave dynamics

    NASA Technical Reports Server (NTRS)

    Stenzel, R. L.

    1978-01-01

    Pulsed electron beam injection into a weakly collisional magnetized background plasma is investigated experimentally; properties of the electron beam and background plasma, as well as the low-frequency instabilities and wave dynamics, are discussed. The current of the injected beam closes via a field-aligned return current of background electrons. Through study of the frequency and wavenumber distribution, together with the electron distribution function, the low-frequency instabilities associated with the pulsed injection are identified as ion acoustic waves driven unstable by the return current. The frequency cut-off of the instabilities predicted from renormalized plasma turbulence theory, has been verified experimentally.

  15. Dependence of synergy current driven by lower hybrid wave and electron cyclotron wave on the frequency and parallel refractive index of electron cyclotron wave for Tokamaks

    SciTech Connect

    Huang, J.; Chen, S. Y. Tang, C. J.

    2014-01-15

    The physical mechanism of the synergy current driven by lower hybrid wave (LHW) and electron cyclotron wave (ECW) in tokamaks is investigated using theoretical analysis and simulation methods in the present paper. Research shows that the synergy relationship between the two waves in velocity space strongly depends on the frequency ω and parallel refractive index N{sub //} of ECW. For a given spectrum of LHW, the parameter range of ECW, in which the synergy current exists, can be predicted by theoretical analysis, and these results are consistent with the simulation results. It is shown that the synergy effect is mainly caused by the electrons accelerated by both ECW and LHW, and the acceleration of these electrons requires that there is overlap of the resonance regions of the two waves in velocity space.

  16. Radiative heat transport instability in a laser produced inhomogeneous plasma

    SciTech Connect

    Bychenkov, V. Yu.; Rozmus, W.

    2015-08-15

    A laser produced high-Z plasma in which an energy balance is achieved due to radiation emission and radiative heat transfer supports ion acoustic instability. A linear dispersion relation is derived, and instability is compared to the radiation cooling instability [R. G. Evans, Plasma Phys. Controlled Fusion 27, 751 (1985)]. Under conditions of indirect drive fusion experiments, the driving term for the instability is the radiative heat flux and, in particular, the density dependence of the radiative heat conductivity. A specific example of thermal Bremsstrahlung radiation source has been considered. This instability may lead to plasma jet formation and anisotropic x-ray generation, thus affecting inertial confinement fusion related experiments.

  17. Current-driven atomic waterwheels.

    PubMed

    Dundas, Daniel; McEniry, Eunan J; Todorov, Tchavdar N

    2009-02-01

    A current induces forces on atoms inside the conductor that carries it. It is now possible to compute these forces from scratch, and to perform dynamical simulations of the atomic motion under current. One reason for this interest is that current can be a destructive force--it can cause atoms to migrate, resulting in damage and in the eventual failure of the conductor. But one can also ask, can current be made to do useful work on atoms? In particular, can an atomic-scale motor be driven by electrical current, as it can be by other mechanisms? For this to be possible, the current-induced forces on a suitable rotor must be non-conservative, so that net work can be done per revolution. Here we show that current-induced forces in atomic wires are not conservative and that they can be used, in principle, to drive an atomic-scale waterwheel. PMID:19197311

  18. Three-dimensional magnetic reconnection under coupling of tearing and lower-hybrid-drift instabilities

    NASA Astrophysics Data System (ADS)

    Hoshino, Masahiro

    2016-07-01

    Understanding of the particle acceleration and plasma heating in a current sheet is an important problem in space and astrophysical plasmas. So far the inertia resistivity associated with tearing instability and the current driven instability such as the lower hybrid drift instability (LHDI) have been discussed as possible candidates for the origin of microscopic process of magnetic energy dissipation. It is known that the inertia resistivity effectively works at the neutral sheet, while the LHDI is mainly excited in the plasma sheet boundary. Then it is commonly understood that the role of the LHDI to the magnetic field dissipation is less important than that of the inertia resistivity. However, the heated electrons together with the activity of lower hybrid drift waves are often observed in the plasma sheet boundary by modern satellite observations, and their impact on the magnetic field dissipation at the neutral sheet might not be necessarily neglected. In addition, the nonlinear coupling between them is not theoretically understood yet. In this talk, we study the coupling of the collisionless reconnection and the LHDI by using a three-dimensional PIC simulation, and discuss that the current driven instabilities dynamically play an important role on magnetic reconnection.

  19. Turbine instabilities: Case histories

    NASA Technical Reports Server (NTRS)

    Laws, C. W.

    1985-01-01

    Several possible causes of turbine rotor instability are discussed and the related design features of a wide range of turbomachinery types and sizes are considered. The instrumentation options available for detecting rotor instability and assessing its severity are also discussed.

  20. Current driven transition from Abrikosov-Josephson to Josephson-like vortex in mesoscopic lateral S/S’/S superconducting weak links

    PubMed Central

    Carapella, G.; Sabatino, P.; Barone, C.; Pagano, S.; Gombos, M.

    2016-01-01

    Vortices are topological defects accounting for many important effects in superconductivity, superfluidity, and magnetism. Here we address the stability of a small number of such excitations driven by strong external forces. We focus on Abrikosov-Josephson vortex that appears in lateral superconducting S/S’/S weak links with suppressed superconductivity in S’. In such a system the vortex is nucleated and confined in the narrow S’ region by means of a small magnetic field and moves under the effect of a force proportional to an applied electrical current with a velocity proportional to the measured voltage. Our numerical simulations show that when a slow moving Abrikosov-Josephson vortex is driven by a strong constant current it becomes unstable with respect to a faster moving excitation: the Josephon-like vortex. Such a current-driven transition explains the structured dissipative branches that we observe in the voltage-current curve of the weak link. When vortex matter is strongly confined phenomena as magnetoresistance oscillations and reentrance of superconductivity can possibly occur. We experimentally observe these phenomena in our weak links. PMID:27752137

  1. Effects of the radial dependence of the fast electron diffusion coefficient on the current driven by lower-hybrid waves in tokamak

    SciTech Connect

    Zhang Xianmei; Wang Yanhui; Yu Limin; Shen Xin; Wang Jianbin

    2012-07-15

    The lower hybrid current drive (LHCD) is one of the promising methods not only for driving the non-inductive current required for steady-state tokamak operation, but also for controlling the plasma current profile to improve confinement in tokamak experiments. A direct consequence of experimental imperfection is difficult to obtain reliable estimate of the radial diffusion coefficient (D{sub st}) of the lower hybrid driven current. In this paper, the radial profile of D{sub st} is estimated to investigate its effect on the current driven by lower hybrid wave (LHW) in Experimental Advanced Superconducting Tokamak. Compared with the case of the constant radial diffusion coefficient, the efficiency of LHW driven current with the radial dependent diffusion coefficient D{sub st} ({rho}) becomes either higher or lower with respect to the plasma parameters, such as the density and the magnetic fluctuation. It is also found that the profiles of the LHW driven current are different. Therefore, it is necessary to consider the radial dependence of D{sub st} in order to get an accurate and reliable result in the numerical simulation of LHCD.

  2. Effects of the radial dependence of the fast electron diffusion coefficient on the current driven by lower-hybrid waves in tokamak

    NASA Astrophysics Data System (ADS)

    Zhang, Xianmei; Wang, Yanhui; Yu, Limin; Shen, Xin; Wang, Jianbin

    2012-07-01

    The lower hybrid current drive (LHCD) is one of the promising methods not only for driving the non-inductive current required for steady-state tokamak operation, but also for controlling the plasma current profile to improve confinement in tokamak experiments. A direct consequence of experimental imperfection is difficult to obtain reliable estimate of the radial diffusion coefficient (Dst) of the lower hybrid driven current. In this paper, the radial profile of Dst is estimated to investigate its effect on the current driven by lower hybrid wave (LHW) in Experimental Advanced Superconducting Tokamak. Compared with the case of the constant radial diffusion coefficient, the efficiency of LHW driven current with the radial dependent diffusion coefficient Dst (ρ) becomes either higher or lower with respect to the plasma parameters, such as the density and the magnetic fluctuation. It is also found that the profiles of the LHW driven current are different. Therefore, it is necessary to consider the radial dependence of Dst in order to get an accurate and reliable result in the numerical simulation of LHCD.

  3. Instability of rectangular jets

    NASA Technical Reports Server (NTRS)

    Tam, Christopher K. W.; Thies, Andrew T.

    1992-01-01

    The instability of rectangular jets is investigated using a vortex sheet model. It is shown that such jets support four linearly independent families of instability waves. Within each family there are infinitely many modes. A way to classify these modes according to the characteristics of their mode shapes or eigenfunctions is proposed. A parametric study of the instability wave characteristics has been carried out. A sample of the numerical results is reported here. It is found that the first and third modes of each instability wave family are corner modes. The pressure fluctuations associated with these instability waves are localized near the corners of the jet. The second mode, however, is a center mode with maximum fluctuations concentrated in the central portion of the jet flow. The center mode has the largest spatial growth rate. It is anticipated that as the instability waves propagate downstream the center mode would emerge as the dominant instability of the jet.

  4. Radiative heat transport instability in ICF plasmas

    NASA Astrophysics Data System (ADS)

    Rozmus, W.; Bychenkov, V. Yu.

    2015-11-01

    A laser produced high-Z plasma in which an energy balance is achieved due to radiation losses and radiative heat transfer supports ion acoustic wave instability. A linear dispersion relation is derived and instability is compared to the radiation cooling instability. This instability develops in the wide range of angles and wavenumbers with the typical growth rate on the order of cs/LT (cs is the sound speed, LT is the temperature scale length). In addition to radiation dominated systems, a similar thermal transport driven ion acoustic instability was found before in plasmas where the thermal transport coefficient depends on electron density. However, under conditions of indirect drive ICF experiments the driving term for the instability is the radiative heat flux and in particular, the density dependence of the radiative heat conductivity. A specific example of thermal Bremsstrahlung radiation source has been considered corresponding to a thermal conductivity coefficient that is inversely proportional to the square of local particle density. In the nonlinear regime this instability may lead to plasma jet formation and anisotropic x-ray generation.

  5. Flow instabilities in turbomachines

    NASA Astrophysics Data System (ADS)

    Greitzer, E. M.

    Instabilities occurring in systems involving the movement of a fluid through pipes, ducts, etc., by means of turbomachinery are discussed. While static instabilities may be inferred from system transient performance that is viewed as a sequence of quasi-steady states, such parameters as system interfaces and capacitances must be included in the prediction of dynamic instability, since they play an essential role in determining the transient response of the system to disturbances. A pumping system can be statically stable and still exhibit dynamic instability. Attention is given to rotating stall compressor instability, inlet distortion effects on axial compressor instability, the stability effects of downstream components, and the stability of centrifugal compressors and pumps.

  6. Joint Instability and Osteoarthritis

    PubMed Central

    Blalock, Darryl; Miller, Andrew; Tilley, Michael; Wang, Jinxi

    2015-01-01

    Joint instability creates a clinical and economic burden in the health care system. Injuries and disorders that directly damage the joint structure or lead to joint instability are highly associated with osteoarthritis (OA). Thus, understanding the physiology of joint stability and the mechanisms of joint instability-induced OA is of clinical significance. The first section of this review discusses the structure and function of major joint tissues, including periarticular muscles, which play a significant role in joint stability. Because the knee, ankle, and shoulder joints demonstrate a high incidence of ligament injury and joint instability, the second section summarizes the mechanisms of ligament injury-associated joint instability of these joints. The final section highlights the recent advances in the understanding of the mechanical and biological mechanisms of joint instability-induced OA. These advances may lead to new opportunities for clinical intervention in the prevention and early treatment of OA. PMID:25741184

  7. Instability in Rotating Machinery

    NASA Technical Reports Server (NTRS)

    1985-01-01

    The proceedings contain 45 papers on a wide range of subjects including flow generated instabilities in fluid flow machines, cracked shaft detection, case histories of instability phenomena in compressors, turbines, and pumps, vibration control in turbomachinery (including antiswirl techniques), and the simulation and estimation of destabilizing forces in rotating machines. The symposium was held to serve as an update on the understanding and control of rotating machinery instability problems.

  8. Nonlocal magnetorotational instability

    SciTech Connect

    Mikhailovskii, A. B.; Erokhin, N. N.; Lominadze, J. G.; Galvao, R. M. O.; Churikov, A. P.; Kharshiladze, O. A.; Amador, C. H. S.

    2008-05-15

    An analytical theory of the nonlocal magnetorotational instability (MRI) is developed for the simplest astrophysical plasma model. It is assumed that the rotation frequency profile has a steplike character, so that there are two regions in which it has constant different values, separated by a narrow transition layer. The surface wave approach is employed to investigate the MRI in this configuration. It is shown that the main regularities of the nonlocal MRI are similar to those of the local instability and that driving the nonaxisymmetric MRI is less effective than the axisymmetric one, also for the case of the nonlocal instability. The existence of nonlocal instabilities in nonmagnetized plasma is predicted.

  9. Absolute instability from linear conversion of counter-propagating positive and negative energy waves

    SciTech Connect

    Kaufman, A.N.; Brizard, A.J.; Morehead, J.J.; Tracy, E.R.

    1997-12-31

    The resonant interaction of a negative-energy wave with a positive-energy wave gives rise to a linear instability. Whereas a single crossing of rays in a nonuniform medium leads to a convectively saturated instability, we show that a double crossing can yield an absolute instability.

  10. THE PARKER INSTABILITY IN DISK GALAXIES

    SciTech Connect

    Rodrigues, L. F. S.; Sarson, G. R.; Shukurov, A.; Bushby, P. J.; Fletcher, A. E-mail: graeme.sarson@newcastle.ac.uk E-mail: paul.bushby@newcastle.ac.uk

    2016-01-01

    We examine the evolution of the Parker instability in galactic disks using 3D numerical simulations. We consider a local Cartesian box section of a galactic disk, where gas, magnetic fields, and cosmic rays are all initially in a magnetohydrostatic equilibrium. This is done for different choices of initial cosmic-ray density and magnetic field. The growth rates and characteristic scales obtained from the models, as well as their dependences on the density of cosmic rays and magnetic fields, are in broad agreement with previous (linearized, ideal) analytical work. However, this nonideal instability develops a multimodal 3D structure, which cannot be quantitatively predicted from the earlier linearized studies. This 3D signature of the instability will be of importance in interpreting observations. As a preliminary step toward such interpretations, we calculate synthetic polarized intensity and Faraday rotation measure (RM) maps, and the associated structure functions of the latter, from our simulations; these suggest that the correlation scales inferred from RM maps are a possible probe for the cosmic-ray content of a given galaxy. Our calculations highlight the importance of cosmic rays in these measures, making them an essential ingredient of realistic models of the interstellar medium.

  11. The Parker Instability in Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Rodrigues, L. F. S.; Sarson, G. R.; Shukurov, A.; Bushby, P. J.; Fletcher, A.

    2016-01-01

    We examine the evolution of the Parker instability in galactic disks using 3D numerical simulations. We consider a local Cartesian box section of a galactic disk, where gas, magnetic fields, and cosmic rays are all initially in a magnetohydrostatic equilibrium. This is done for different choices of initial cosmic-ray density and magnetic field. The growth rates and characteristic scales obtained from the models, as well as their dependences on the density of cosmic rays and magnetic fields, are in broad agreement with previous (linearized, ideal) analytical work. However, this nonideal instability develops a multimodal 3D structure, which cannot be quantitatively predicted from the earlier linearized studies. This 3D signature of the instability will be of importance in interpreting observations. As a preliminary step toward such interpretations, we calculate synthetic polarized intensity and Faraday rotation measure (RM) maps, and the associated structure functions of the latter, from our simulations; these suggest that the correlation scales inferred from RM maps are a possible probe for the cosmic-ray content of a given galaxy. Our calculations highlight the importance of cosmic rays in these measures, making them an essential ingredient of realistic models of the interstellar medium.

  12. Targets for, and consequences of, radiation-induced chromosomal instability

    NASA Astrophysics Data System (ADS)

    Kaplan, Mark Isaac

    Chromosomal instability has been demonstrated in a human- hamster hybrid cell line, GM10115, after exposure to x- rays. Chromosomal instability in these cells is characterized by the appearance of novel chromosomal rearrangements multiple generations after exposure to ionizing radiation. To identify the cellular target(s) for radiation-induced chromosomal instability, cells were treated with 125I-labeled compounds. Labeling cells with 125I-iododeoxyuridine, which caused radiation damage to the DNA and associated nuclear structures, did induce chromosomal instability. While cell killing and first-division chromosomal rearrangements increased with increasing numbers of 125I decays, the frequency of chromosomal instability was independent of dose. Incorporation of an 125I-labeled protein, 125I-succinyl- concanavalin A, into either the plasma membrane or the cytoplasm, failed to elicit chromosomal instability. These results show that radiation damage to the nucleus, and not to extranuclear regions, contributes to the induction of chromosomal instability. To determine the role of DNA strand breaks as a molecular lesion responsible for initiating chromosomal instability, cells were treated with a variety of DNA strand breaking agents. Agents capable of producing complex DNA double strand breaks, including X-rays, Neocarzinostatin and bleomycin, were able to induce chromosomal instability. In contrast, double strand breaks produced by restriction endonucleases as well as DNA strand breaks produced by hydrogen peroxide failed to induce chromosomal instability. This demonstrates that the type of DNA breakage is important in the eventual manifestation of chromosomal instability. In order to understand the relationship between chromosomal instability and other end points of genomic instability, chromosomally stable and unstable clones were analyzed for sister chromatid exchange, delayed reproductive cell death, delayed mutation, mismatch repair and delayed gene amplification

  13. Buckling instability in arteries.

    PubMed

    Vandiver, Rebecca M

    2015-04-21

    Arteries can become tortuous in response to abnormal growth stimuli, genetic defects and aging. It is suggested that a buckling instability is a mechanism that might lead to artery tortuosity. Here, the buckling instability in arteries is studied by examining asymmetric modes of bifurcation of two-layer cylindrical structures that are residually stressed. These structures are loaded by an axial force, internal pressure and have nonlinear, anisotropic, hyperelastic responses to stresses. Strain-softening and reduced opening angle are shown to lower the critical internal pressure leading to buckling. In addition, the ratio of the media thickness to the adventitia thickness is shown to have a dramatic impact on arterial instability.

  14. Imaging in carpal instability.

    PubMed

    Ramamurthy, N K; Chojnowski, A J; Toms, A P

    2016-01-01

    Carpal instability is a complex and heterogeneous clinical condition. Management requires accurate identification of structural injury with an understanding of the resultant movement (kinematic) and load transfer (kinetic) failure. Static imaging techniques, such as plain film radiography, stress views, ultrasound, magnetic resonance, MR arthrography and computerized tomography arthrography, may accurately depict major wrist ligamentous injury. Dynamic ultrasound and videofluoroscopy may demonstrate dynamic instability and kinematic dysfunction. There is a growing evidence base for the diagnostic accuracy of these techniques in detecting intrinsic ligament tears, but there are limitations. Evidence of their efficacy and relevance in detection of non-dissociative carpal instability and extrinsic ligament tears is weak. Further research into the accuracy of existing imaging modalities is still required. Novel techniques, including four-dimensional computerized tomography and magnetic resonance, can evaluate both cross-sectional and functional carpal anatomy. This is a narrative review of level-III studies evaluating the role of imaging in carpal instability. PMID:26586689

  15. Bacterial Genome Instability

    PubMed Central

    Darmon, Elise

    2014-01-01

    SUMMARY Bacterial genomes are remarkably stable from one generation to the next but are plastic on an evolutionary time scale, substantially shaped by horizontal gene transfer, genome rearrangement, and the activities of mobile DNA elements. This implies the existence of a delicate balance between the maintenance of genome stability and the tolerance of genome instability. In this review, we describe the specialized genetic elements and the endogenous processes that contribute to genome instability. We then discuss the consequences of genome instability at the physiological level, where cells have harnessed instability to mediate phase and antigenic variation, and at the evolutionary level, where horizontal gene transfer has played an important role. Indeed, this ability to share DNA sequences has played a major part in the evolution of life on Earth. The evolutionary plasticity of bacterial genomes, coupled with the vast numbers of bacteria on the planet, substantially limits our ability to control disease. PMID:24600039

  16. Parametric instabilities in picosecond time scales

    SciTech Connect

    Baldis, H.A.; Rozmus, W.; Labaune, C.; Mounaix, Ph.; Pesme, D.; Baton, S.; Tikhonchuk, V.T.

    1993-03-01

    The coupling of intense laser light with plasmas is a rich field of plasma physics, with many applications. Among these are inertial confinement fusion (ICF), x-ray lasers, particle acceleration, and x-ray sources. Parametric instabilities have been studied for many years because of their importance to ICF; with laser pulses with duration of approximately a nanosecond, and laser intensities in the range 10{sup 14}--10{sup 15}W/cm{sup 2} these instabilities are of crucial concern because of a number of detrimental effects. Although the laser pulse duration of interest for these studies are relatively long, it has been evident in the past years that to reach an understanding of these instabilities requires their characterization and analysis in picosecond time scales. At the laser intensities of interest, the growth rate for stimulated Brillouin scattering (SBS) is of the order of picoseconds, and of an order of magnitude shorter for stimulated Raman scattering (SRS). In this paper the authors discuss SBS and SRS in the context of their evolution in picosecond time scales. They describe the fundamental concepts associated with their growth and saturation, and recent work on the nonlinear treatment required for the modeling of these instabilities at high laser intensities.

  17. Nonlinear instabilities driven by coherent phase-space structures

    NASA Astrophysics Data System (ADS)

    Lesur, Maxime

    2012-10-01

    Coherent phase-space (PS) structures are an important feature of plasma turbulence. They can drive nonlinear instabilities [1], intermittency in drift-wave turbulence [2], and transport [3]. We aim at a comprehensive understanding of turbulence, not just as an ensemble of waves, as quasilinear theory implies, but as a mixture of coupled waves and localized structures. This work, which focuses on isolated PS structures, is a fundamental advance in this direction. We analyze the effects of self-binding negative fluctuations (PS holes) on stability, intermittency and anomalous resistivity, both analytically and numerically. We present a new theory which describes the growth of a hole or clump [4]. We find that PS holes grow nonlinearly, independently of linear stability. Numerical simulations clarify the physics of nonlinear instabilities in both subcritical and supercritical conditions. When many resonances are unstable, several holes can coalesce into one main macro-scale structure, which survives much longer than a quasilinear diffusion time, suggesting that it may be crucial to resolve phase-space turbulence in analytical and numerical studies of transport. These findings are applied to two fundamental paradigms of plasma physics: bump-on-tail instabilities in 1D electronic plasma and current-driven ion-acoustic instabilities electron-ion plasma. Our results expose important limits of routinely-used linear and quasilinear theories.[4pt] [1] T.H. Dupree, Phys. Fluids 15, 334 (1972); R.H. Berman et al., Phys. Rev. Lett. 48, 1249 (1982).[0pt] [2] P.W. Terry, P.H. Diamond, and T.S. Hahm, Phys. Fluids B 2, 2048 (1990).[0pt] [3] H. Biglari et al., Phys. Fluids 31, 2644 (1988); Y. Kosuga et al., Phys. Plasmas 18, 122305 (2011).[0pt] [4] M. Lesur, P.H. Diamond, submitted to Phys. Rev. Lett.

  18. Laser driven hydrodynamic instability experiments. Revision 1

    SciTech Connect

    Remington, B.A.; Weber, S.V.; Haan, S.W.; Kilkenny, J.D.; Glendinning, S.G.; Wallace, R.J.; Goldstein, W.H.; Wilson, B.G.; Nash, J.K.

    1993-02-17

    An extensive series of experiments has been conducted on the Nova laser to measure hydrodynamic instabilities in planar foils accelerated by x-ray ablation. Single mode experiments allow a measurement of the fundamental growth rates from the linear well into the nonlinear regime. Two-mode foils allow a first direct observation of mode coupling. Surface-finish experiments allow a measurement of the evolution of a broad spectrum of random initial modes.

  19. Filamentation instability of a self-pinched hollow electron beam

    SciTech Connect

    Uhm, H.S.; Hughes, T.P.

    1986-09-01

    Filamentation stability properties of a self-pinched hollow electron beam propagating through a collisional plasma channel are investigated within the framework of linearized Vlasov--Maxwell equations, assuming that the beam is thin and that the equilibrium and perturbed space-charge fields are neutralized by background plasma. It is further assumed that the perturbations are well tuned with k-italic..beta../sub b-italic/c-italic+l-italic..omega../sub b-italic/ and satisfy l-italica-italic<current driven instability and the resistively driven instability. It is also found that high-l-italic-mode perturbations are easily stabilized by a spread in the canonical angular momentum. Making use of a linearized particle-in-cell code, numerical simulations are performed. The agreement between the analytical results and those of simulations is excellent.

  20. Measurements of the momentum and current transport from tearing instability in the Madison Symmetric Torus reversed-field pincha)

    NASA Astrophysics Data System (ADS)

    Kuritsyn, A.; Fiksel, G.; Almagri, A. F.; Brower, D. L.; Ding, W. X.; Miller, M. C.; Mirnov, V. V.; Prager, S. C.; Sarff, J. S.

    2009-05-01

    In this paper measurements of momentum and current transport caused by current driven tearing instability are reported. The measurements are done in the Madison Symmetric Torus reversed-field pinch [R. N. Dexter, D. W. Kerst, T. W. Lovell, S. C. Prager, and J. C. Sprott, Fusion Technol. 19, 131 (1991)] in a regime with repetitive bursts of tearing instability causing magnetic field reconnection. It is established that the plasma parallel momentum profile flattens during these reconnection events: The flow decreases in the core and increases at the edge. The momentum relaxation phenomenon is similar in nature to the well established relaxation of the parallel electrical current and could be a general feature of self-organized systems. The measured fluctuation-induced Maxwell and Reynolds stresses, which govern the dynamics of plasma flow, are large and almost balance each other such that their difference is approximately equal to the rate of change of plasma momentum. The Hall dynamo, which is directly related to the Maxwell stress, drives the parallel current profile relaxation at resonant surfaces at the reconnection events. These results qualitatively agree with analytical calculations and numerical simulations. It is plausible that current-driven instabilities can be responsible for momentum transport in other laboratory and astrophysical plasmas.

  1. Gauging magnetorotational instability

    NASA Astrophysics Data System (ADS)

    Herron, Isom; Goodman, Jeremy

    2010-08-01

    Previously (Z. Angew. Math. Phys. 57:615-622, 2006), we examined the axisymmetric stability of viscous resistive magnetized Couette flow with emphasis on flows that would be hydrodynamically stable according to Rayleigh’s criterion: opposing gradients of angular velocity and specific angular momentum. A uniform axial magnetic field permeates the fluid. In this regime, magnetorotational instability (MRI) may occur. It was proved that MRI is suppressed, in fact no instability at all occurs, with insulating boundary conditions, when a term multipling the magnetic Prandtl number is neglected. Likewise, in the current work, including this term, when the magnetic resistivity is sufficiently large, MRI is suppressed. This shows conclusively that small magnetic dissipation is a feature of this instability for all magnetic Prandtl numbers. A criterion is provided for the onset of MRI.

  2. The Walking Droplet Instability

    NASA Astrophysics Data System (ADS)

    Bostwick, Joshua; Steen, Paul

    2013-11-01

    A droplet of liquid that partially wets a solid substrate assumes a spherical-cap equilibrium shape. We show that the spherical-cap with a mobile contact-line is unstable to a non-axisymmetric disturbance and we characterize the instability mechanism, as it depends upon the wetting properties of the substrate. We then solve the hydrodynamic problem for inviscid motions showing that the flow associated with the instability correlates with horizontal motion of the droplet's center-of-mass. We calculate the resulting ``walking speed.'' A novel feature is that the energy conversion mechanism is not unique, so long as the contact-line is mobilized. Hence, the walking droplet instability is potentially significant to a number of industrial applications, such as self-cleansing surfaces or energy harvesting devices.

  3. Instability of the heliopause driven by charge exchange interactions

    SciTech Connect

    Avinash, K.; Zank, G. P.; Dasgupta, B.; Bhadoria, Shikha

    2014-08-20

    The stability of the heliopause that separates the tenuous hot magnetized heliosheath plasma from the dense cool local interstellar magnetized plasma is examined using a fully general model that includes all the essential physical processes. Charge exchange coupling between plasma protons and primary interstellar neutral atoms provides an effective gravity that drives Rayleigh-Taylor (RT)-like instabilities. The velocity difference or shear between the heliosheath and interstellar flows, when coupled to energetic neutral atoms (ENAs), drives a Kelvin-Helmholtz (KH)-like instability on the heliopause. The shoulder region of the heliopause is unstable to a new instability that has characteristics of a mixed RT-KH-like mode. The instabilities are not stabilized by typical values of the magnetic fields in the inner and outer heliosheath (OHS). ENAs play an essential role in driving the KH-like instability, which is fully stabilized in their absence by magnetic fields. The nonlinear phase of these instabilities is briefly discussed. We also discuss the possibility that RT-like or mixed KH-RT-like instabilities drag outer heliosheath/very local interstellar medium (OHS/VLISM) magnetic field lines into the inner heliosheath (IHS) with the VLISM flow, and the possibility that IHS and VLISM magnetic field lines experience reconnection. Such reconnection may (1) greatly enhance the mixing of plasmas across the heliopause and (2) provide open magnetic field lines that allow easy ingress of galactic cosmic rays into the heliosphere and corresponding easy loss of anomalous cosmic rays from the heliosphere.

  4. Dislocation motion and instability

    NASA Astrophysics Data System (ADS)

    Zhu, Yichao; Chapman, Stephen Jonathan; Acharya, Amit

    2013-08-01

    The Peach-Koehler expression for the stress generated by a single (non-planar) curvilinear dislocation is evaluated to calculate the dislocation self stress. This is combined with a law of motion to give the self-induced motion of a general dislocation curve. A stability analysis of a rectilinear, uniformly translating dislocation is then performed. The dislocation is found to be susceptible to a helical instability, with the maximum growth rate occurring when the dislocation is almost, but not exactly, pure screw. The non-linear evolution of the instability is determined numerically, and implications for slip band formation and non-Schmid behavior in yielding are discussed.

  5. Global Linear Instability

    NASA Astrophysics Data System (ADS)

    Theofilis, Vassilios

    2011-01-01

    This article reviews linear instability analysis of flows over or through complex two-dimensional (2D) and 3D geometries. In the three decades since it first appeared in the literature, global instability analysis, based on the solution of the multidimensional eigenvalue and/or initial value problem, is continuously broadening both in scope and in depth. To date it has dealt successfully with a wide range of applications arising in aerospace engineering, physiological flows, food processing, and nuclear-reactor safety. In recent years, nonmodal analysis has complemented the more traditional modal approach and increased knowledge of flow instability physics. Recent highlights delivered by the application of either modal or nonmodal global analysis are briefly discussed. A conscious effort is made to demystify both the tools currently utilized and the jargon employed to describe them, demonstrating the simplicity of the analysis. Hopefully this will provide new impulses for the creation of next-generation algorithms capable of coping with the main open research areas in which step-change progress can be expected by the application of the theory: instability analysis of fully inhomogeneous, 3D flows and control thereof.

  6. Capillary instability of jets

    NASA Astrophysics Data System (ADS)

    Chauhan, Anuj

    This thesis studies the capillary instability of a compound jet. A compound jet comprises an inner core of a primary fluid surrounded by an annulus of an immiscible secondary fluid. The compound jet is unstable due to capillarity. A compound jet finds applications in a variety of fields, such as, ink jet printing, particle sorting, extrusion, molding, particle production etc. In some of these applications such as molding, the disturbances that could cause the jet breakup start as periodic spatial disturbances of Fourier wave number k and grow in time. This is the temporal instability. In some other applications, such as, ink-jet printing, the disturbances initiate at the edge of the nozzle from which the jet issues out. These disturbances grow in space. This is the spatial instability. At small velocities, even if the initial disturbances are periodic in time, they grow exponentially in time. This is the absolute instability. We perform the temporal, spatial and the absolute stability analysis of an inviscid compound jet in a unified framework using the theory of transforms. Further, we solve the temporal instability problem for a viscous jet to understand the effect of viscosity on breakup dynamics. In the temporal analysis, we show that each interface of the compound jet contributes one mode to the instability. The modes contributed by the inner and outer interfaces grow for waves longer than the inner and the outer circumference of the undisturbed jet, respectively. The inner interface mode has a higher growth rate and hence dominates the breakup. The two interfaces grow exactly in phase in this mode and hence it is refereed to as the stretching mode. The other mode is the squeezing mode because the two interfaces grow exactly out of phase. The same two modes are also present in the spatial analysis. At high Weber numbers the predictions of the spatial theory reduce to those of the temporal theory because the waves simply convect with the jet velocity and there

  7. Genomic Instability and Cancer

    PubMed Central

    Yao, Yixin; Dai, Wei

    2014-01-01

    Genomic instability is a characteristic of most cancer cells. It is an increased tendency of genome alteration during cell division. Cancer frequently results from damage to multiple genes controlling cell division and tumor suppressors. It is known that genomic integrity is closely monitored by several surveillance mechanisms, DNA damage checkpoint, DNA repair machinery and mitotic checkpoint. A defect in the regulation of any of these mechanisms often results in genomic instability, which predisposes the cell to malignant transformation. Posttranslational modifications of the histone tails are closely associated with regulation of the cell cycle as well as chromatin structure. Nevertheless, DNA methylation status is also related to genomic integrity. We attempt to summarize recent developments in this field and discuss the debate of driving force of tumor initiation and progression. PMID:25541596

  8. A trickle instability

    NASA Astrophysics Data System (ADS)

    Bossa, Benjamin

    2005-11-01

    We address the problem of the free fall of a long, horizontal and narrow liquid layer squeezed in a vertical open Hele-Shaw cell. The layer destabilizes as it falls down, evolving into a series of liquid blobs linked together by thin bridges, which ultimately break, leaving the initially connex fluid layer as a set a disjointed drops. The mechanism of this instability is the onset of a vertical pressure gradient due to the curvature difference of the moving contact line between the advancing interface and the rear interface. This instability, whose growth rate scales with a non-trivial power of the capillary number, amplifies indifferently a broad band of wavenumbers because of the flat shape of its dispersion relation in the thin layer limit. We will finally comment on the nature of the final fragmentation process and drop size distributions.

  9. Sessile Rayleigh drop instability

    NASA Astrophysics Data System (ADS)

    Steen, Paul; Bostwick, Josh

    2012-11-01

    Rayleigh (1879) determined the mode shapes and frequencies of the inviscid motion of a free drop held by surface tension. We study the inviscid motions of a sessile Rayleigh drop - a drop which rests on a planar solid and whose contact-line is free to move. Linear stability analysis gives the modes and frequencies of the droplet motions. In this talk, we focus on the ``walking instability,'' an unstable mode wherein the drop moves across a planar substrate in an inviscid rocking-like motion. The mode shape is non-axisymmetric. Although the experimental literature has hinted at such a mode, this is the first prediction from linear stability analysis, as far as we are aware. The ``walking instability'' of the drop converts energy stored in the liquid shape into the energy of liquid motion - which represents a heretofore unknown pathway of energy conversion of potentially wide significance for a broad range of applications.

  10. Open field lines instabilities

    SciTech Connect

    Pozzoli, R. |

    1995-09-01

    The results of some recent theoretical papers dealing with flute-like instabilities in the scrape-off layer of a tokamak with limiter configuration, where the magnetic field intersects conducting walls, are briefly recalled. Attention is then paid to the instability driven by the electron temperature gradient across the field in conjunction with the formation of the Debye sheath at the boundary, and to the effects due to the inclination of the end walls with respect to the magnetic field. When a divertor configuration is considered, important modifications are found owing to the strong deformations of the flux tubes passing near the {ital x}-point, which contrast the onset of flute-like perturbations, and to the stochasticity of field lines that can be excited by magnetic field perturbations. {copyright} {ital 1995 American Institute of Physics.}

  11. Instabilities in sensory processes

    NASA Astrophysics Data System (ADS)

    Balakrishnan, J.

    2014-07-01

    In any organism there are different kinds of sensory receptors for detecting the various, distinct stimuli through which its external environment may impinge upon it. These receptors convey these stimuli in different ways to an organism's information processing region enabling it to distinctly perceive the varied sensations and to respond to them. The behavior of cells and their response to stimuli may be captured through simple mathematical models employing regulatory feedback mechanisms. We argue that the sensory processes such as olfaction function optimally by operating in the close proximity of dynamical instabilities. In the case of coupled neurons, we point out that random disturbances and fluctuations can move their operating point close to certain dynamical instabilities triggering synchronous activity.

  12. Modulation instability: The beginning

    NASA Astrophysics Data System (ADS)

    Zakharov, V. E.; Ostrovsky, L. A.

    2009-03-01

    We discuss the early history of an important field of “sturm and drang” in modern theory of nonlinear waves. It is demonstrated how scientific demand resulted in independent and almost simultaneous publications by many different authors on modulation instability, a phenomenon resulting in a variety of nonlinear processes such as envelope solitons, envelope shocks, freak waves, etc. Examples from water wave hydrodynamics, electrodynamics, nonlinear optics, and convection theory are given.

  13. Chromosomal instability induced by heavy ion irradiation

    NASA Technical Reports Server (NTRS)

    Limoli, C. L.; Ponnaiya, B.; Corcoran, J. J.; Giedzinski, E.; Morgan, W. F.

    2000-01-01

    PURPOSE: To establish the dose-response relationship for the induction of chromosomal instability in GM10115 cells exposed to high-energy iron ions (1 GeV/nucleon, mean LET 146 keV/microm) and gold ions (11 GeV/nucleon, mean LET 1450 keV/microm). Past work has established that sparsely ionizing X-rays can induce a long-lived destabilization of chromosomes in a dose-dependent manner at an incidence of approximately 3% per gray. The present investigation assesses the capacity of High-Z and High-energy (HZE) particles to elicit this same endpoint. MATERIALS AND METHODS: Clonal populations derived from single progenitor cells surviving heavy-ion irradiation were analyzed cytogenetically to identify those clones showing a persistent destablization of chromosomes. RESULTS: Dose-response data, with a particular emphasis at low dose (< 1.0 Gy), indicate a frequency of approximately 4% per gray for the induction of chromosomal instability in clones derived from single progenitor cells surviving exposure to iron ions. The induction of chromosomal instability by gold ions was, however, less responsive to applied dose, as the observed incidence of this phenotype varied from 0 to 10% over 1-8 Gy. Both iron and gold ions gave dose-dependent increases in the yield of chromosomal aberrations (both chromosome- and chromatid-type) measured at the first mitosis following irradiation, as well as shoulderless survival curves having D0=0.87 and 1.1 Gy respectively. CONCLUSIONS: Based on the present dose-response data, the relative biological effectiveness of iron ions is 1.3 for the induction of chromosomal instability, and this indicates that heavy ions are only slightly more efficient than X-rays at eliciting this delayed phenotype.

  14. Robust dynamic mitigation of instabilities

    NASA Astrophysics Data System (ADS)

    Kawata, S.; Karino, T.

    2015-04-01

    A dynamic mitigation mechanism for instability growth was proposed and discussed in the paper [S. Kawata, Phys. Plasmas 19, 024503 (2012)]. In the present paper, the robustness of the dynamic instability mitigation mechanism is discussed further. The results presented here show that the mechanism of the dynamic instability mitigation is rather robust against changes in the phase, the amplitude, and the wavelength of the wobbling perturbation applied. Generally, instability would emerge from the perturbation of the physical quantity. Normally, the perturbation phase is unknown so that the instability growth rate is discussed. However, if the perturbation phase is known, the instability growth can be controlled by a superposition of perturbations imposed actively: If the perturbation is induced by, for example, a driving beam axis oscillation or wobbling, the perturbation phase could be controlled, and the instability growth is mitigated by the superposition of the growing perturbations.

  15. Robust dynamic mitigation of instabilities

    SciTech Connect

    Kawata, S.; Karino, T.

    2015-04-15

    A dynamic mitigation mechanism for instability growth was proposed and discussed in the paper [S. Kawata, Phys. Plasmas 19, 024503 (2012)]. In the present paper, the robustness of the dynamic instability mitigation mechanism is discussed further. The results presented here show that the mechanism of the dynamic instability mitigation is rather robust against changes in the phase, the amplitude, and the wavelength of the wobbling perturbation applied. Generally, instability would emerge from the perturbation of the physical quantity. Normally, the perturbation phase is unknown so that the instability growth rate is discussed. However, if the perturbation phase is known, the instability growth can be controlled by a superposition of perturbations imposed actively: If the perturbation is induced by, for example, a driving beam axis oscillation or wobbling, the perturbation phase could be controlled, and the instability growth is mitigated by the superposition of the growing perturbations.

  16. Instabilities of twisted strings

    NASA Astrophysics Data System (ADS)

    Forgács, Péter; Lukács, Árpád

    2009-12-01

    A linear stability analysis of twisted flux-tubes (strings) in an SU(2) semilocal theory — an Abelian-Higgs model with two charged scalar fields with a global SU(2) symmetry — is carried out. Here the twist refers to a relative phase between the two complex scalars (with linear dependence on, say, the z coordinate), and importantly it leads to a global current flowing along the the string. Such twisted strings bifurcate with the Abrikosov-Nielsen-Olesen (ANO) solution embedded in the semilocal theory. Our numerical investigations of the small fluctuation spectrum confirm previous results that twisted strings exhibit instabilities whose amplitudes grow exponentially in time. More precisely twisted strings with a single magnetic flux quantum admit a continuous family of unstable eigenmodes with harmonic z dependence, indexed by a wavenumber kin[-km, km]. Carrying out a perturbative semi-analytic analysis of the bifurcation, it is found that the purely numerical results are very well reproduced. This way one obtains not only a good qualitative description of the twisted solutions themselves as well as of their instabilities, but also a quantitative description of the numerical results. Our semi-analytic results indicate that in close analogy to the known instability of the embedded ANO vortex a twisted string is also likely to expand in size caused by the spreading out of its magnetic flux.

  17. Combustion instability analysis

    NASA Technical Reports Server (NTRS)

    Chung, T. J.

    1990-01-01

    A theory and computer program for combustion instability analysis are presented. The basic theoretical foundation resides in the concept of entropy-controlled energy growth or decay. Third order perturbation expansion is performed on the entropy-controlled acoustic energy equation to obtain the first order integrodifferential equation for the energy growth factor in terms of the linear, second, and third order energy growth parameters. These parameters are calculated from Navier-Stokes solutions with time averages performed on as many Navier-Stokes time steps as required to cover at least one peak wave period. Applications are made for a 1-D Navier-Stokes solution for the Space Shuttle Main Engine (SSME) thrust chamber with cross section area variations taken into account. It is shown that instability occurs when the mean pressure is set at 2000 psi with 30 percent disturbances. Instability also arises when the mean pressure is set at 2935 psi with 20 percent disturbances. The system with mean pressures and disturbances more adverse that these cases were shown to be unstable.

  18. Instabilities and constitutive modelling.

    PubMed

    Wilson, Helen J

    2006-12-15

    The plastics industry today sees huge wastage through product defects caused by unstable flows during the manufacturing process. In addition, many production lines are throughput-limited by a flow speed threshold above which the process becomes unstable. Therefore, it is critically important to understand the mechanisms behind these instabilities. In order to investigate the flow of a molten plastic, the first step is a model of the liquid itself, a relation between its current stress and its flow history called a constitutive relation. These are derived in many ways and tested on several benchmark flows, but rarely is the stability of the model used as a criterion for selection. The relationship between the constitutive model and the stability properties of even simple flows is not yet well understood. We show that in one case a small change to the model, which does not affect the steady flow behaviour, entirely removes a known instability. In another, a change that makes a qualitative difference to the steady flow makes only tiny changes to the stability.The long-term vision of this research is to exactly quantify what are the important properties of a constitutive relation as far as stability is concerned. If we could understand that, not only could very simple stability experiments be used to choose the best constitutive models for a particular material, but our ability to predict and avoid wasteful industrial instabilities would also be vastly improved.

  19. Carpal instability nondissociative.

    PubMed

    Wolfe, Scott W; Garcia-Elias, Marc; Kitay, Alison

    2012-09-01

    Carpal instability nondissociative (CIND) represents a spectrum of conditions characterized by kinematic dysfunction of the proximal carpal row, often associated with a clinical "clunk." CIND is manifested at the midcarpal and/or radiocarpal joints, and it is distinguished from carpal instability dissociative (CID) by the lack of disruption between bones within the same carpal row. There are four major subcategories of CIND: palmar, dorsal, combined, and adaptive. In palmar CIND, instability occurs across the entire proximal carpal row. When nonsurgical management fails, surgical options include arthroscopic thermal capsulorrhaphy, soft-tissue reconstruction, or limited radiocarpal or intercarpal fusions. In dorsal CIND, the capitate subluxates dorsally from its reduced resting position. Dorsal CIND usually responds to nonsurgical management; refractory cases respond to palmar ligament reefing and/or dorsal intercarpal capsulodesis. Combined CIND demonstrates signs of both palmar and dorsal CIND and can be treated with soft-tissue or bony procedures. In adaptive CIND, the volar carpal ligaments are slackened and are less capable of inducing the physiologic shift of the proximal carpal row from flexion into extension as the wrist ulnarly deviates. Treatment of choice is a corrective osteotomy to restore the normal volar tilt of the distal radius.

  20. Weibel instability in colliding electron-positron-ion plasmas

    NASA Astrophysics Data System (ADS)

    Silva, Luis

    2008-04-01

    The new regimes accessed in ultra intense laser plasma interactions and recent developments in relativistic astrophysics are giving rise to an increased interest in the Weibel instability. In fact, whenever colliding streams of plasmas (arbitrary mixtures of electrons-positrons-ions) are present, a fraction of the kinetic energy of the plasma flows can be converted to a sub-equipartition magnetic field. In this talk, and using a combination of particle-in-cell simulations and relativistic kinetic theory, I will first describe the recent theoretical advances in our understanding of the Weibel instability and the connection with the electromagnetic beam plasma instability. Emphasis will be given to the coupling with longitudinal modes, leading to the formation of tilted filaments, and to the effects of the collisions and the merging of the Weibel instability with the resistive filamentation instability. In light of these results, the relevance of Weibel instability to ultra intense laser matter interactions (e.g. fast ignition) and to astrophysical scenarios (e.g. in gamma ray bursters and for cluster magnetic fields) will be discussed. Finally, the role of the Weibel instability in the formation of relativistic shocks and in particle acceleration in these structures will also be addressed.

  1. Magnetorotational instability in cool cores of galaxy clusters

    NASA Astrophysics Data System (ADS)

    Nipoti, Carlo; Posti, L.; Ettori, S.; Bianconi, M.

    2015-10-01

    > Clusters of galaxies are embedded in halos of optically thin, gravitationally stratified, weakly magnetized plasma at the system's virial temperature. Owing to radiative cooling and anisotropic heat conduction, such intracluster medium (ICM) is subject to local instabilities, which are combinations of the thermal, magnetothermal and heat-flux-driven buoyancy instabilities. If the ICM rotates significantly, its stability properties are substantially modified and, in particular, also the magnetorotational instability (MRI) can play an important role. We study simple models of rotating cool-core clusters and we demonstrate that the MRI can be the dominant instability over significant portions of the clusters, with possible implications for the dynamics and evolution of the cool cores. Our results give further motivation for measuring the rotation of the ICM with future X-ray missions such as ASTRO-H and ATHENA.

  2. Ion-cyclotron instability in current-carrying Lorentzian (kappa) and Maxwellian plasmas with anisotropic temperatures: A comparative study

    SciTech Connect

    Basu, B.; Grossbard, N. J.

    2011-09-15

    Current-driven electrostatic ion-cyclotron instability has so far been studied for Maxwellian plasma with isotropic and anisotropic temperatures. Since satellite-measured particle velocity distributions in space are often better modeled by the generalized Lorentzian (kappa) distributions and since temperature anisotropy is quite common in space plasmas, theoretical analysis of the current-driven, electrostatic ion-cyclotron instability is carried out in this paper for electron-proton plasma with anisotropic temperatures, where the particle parallel velocity distributions are modeled by kappa distributions and the perpendicular velocity distributions are modeled by Maxwellian distributions. Stability properties of the excited ion cyclotron modes and, in particular, their dependence on electron to ion temperature ratio and ion temperature anisotropy are presented in more detail. For comparison, the corresponding results for bi-Maxwellian plasma are also presented. Although the stability properties of the ion cyclotron modes in the two types of plasmas are qualitatively similar, significant quantitative differences can arise depending on the values of {kappa}{sub e} and {kappa}{sub i}. The comparative study is based on the numerical solutions of the respective linear dispersion relations. Quasilinear estimates of the resonant ion heating rates due to ion-cyclotron turbulence in the two types of plasma are also presented for comparison.

  3. Radiation Induced Genomic Instability

    SciTech Connect

    Morgan, William F.

    2011-03-01

    Radiation induced genomic instability can be observed in the progeny of irradiated cells multiple generations after irradiation of parental cells. The phenotype is well established both in vivo (Morgan 2003) and in vitro (Morgan 2003), and may be critical in radiation carcinogenesis (Little 2000, Huang et al. 2003). Instability can be induced by both the deposition of energy in irradiated cells as well as by signals transmitted by irradiated (targeted) cells to non-irradiated (non-targeted) cells (Kadhim et al. 1992, Lorimore et al. 1998). Thus both targeted and non-targeted cells can pass on the legacy of radiation to their progeny. However the radiation induced events and cellular processes that respond to both targeted and non-targeted radiation effects that lead to the unstable phenotype remain elusive. The cell system we have used to study radiation induced genomic instability utilizes human hamster GM10115 cells. These cells have a single copy of human chromosome 4 in a background of hamster chromosomes. Instability is evaluated in the clonal progeny of irradiated cells and a clone is considered unstable if it contains three or more metaphase sub-populations involving unique rearrangements of the human chromosome (Marder and Morgan 1993). Many of these unstable clones have been maintained in culture for many years and have been extensively characterized. As initially described by Clutton et al., (Clutton et al. 1996) many of our unstable clones exhibit persistently elevated levels of reactive oxygen species (Limoli et al. 2003), which appear to be due dysfunctional mitochondria (Kim et al. 2006, Kim et al. 2006). Interestingly, but perhaps not surprisingly, our unstable clones do not demonstrate a “mutator phenotype” (Limoli et al. 1997), but they do continue to rearrange their genomes for many years. The limiting factor with this system is the target – the human chromosome. While some clones demonstrate amplification of this chromosome and thus lend

  4. Radiative-convective instability

    NASA Astrophysics Data System (ADS)

    Emanuel, Kerry; Wing, Allison A.; Vincent, Emmanuel M.

    2014-03-01

    equilibrium (RCE) is a simple paradigm for the statistical equilibrium the earth's climate would exhibit in the absence of lateral energy transport. It has generally been assumed that for a given solar forcing and long-lived greenhouse gas concentration, such a state would be unique, but recent work suggests that more than one stable equilibrium may be possible. Here we show that above a critical specified sea surface temperature, the ordinary RCE state becomes linearly unstable to large-scale overturning circulations. The instability migrates the RCE state toward one of the two stable equilibria first found by Raymond and Zeng (2000). It occurs when the clear-sky infrared opacity of the lower troposphere becomes so large, owing to high water vapor concentration, that variations of the radiative cooling of the lower troposphere are governed principally by variations in upper tropospheric water vapor. We show that the instability represents a subcritical bifurcation of the ordinary RCE state, leading to either a dry state with large-scale descent, or to a moist state with mean ascent; these states may be accessed by finite amplitude perturbations to ordinary RCE in the subcritical state, or spontaneously in the supercritical state. As first suggested by Raymond (2000) and Sobel et al. (2007), the latter corresponds to the phenomenon of self-aggregation of moist convection, taking the form of cloud clusters or tropical cyclones. We argue that the nonrobustness of self-aggregation in cloud system resolving models may be an artifact of running such models close to the critical temperature for instability.

  5. The cosmic Doppler instability

    NASA Technical Reports Server (NTRS)

    Hogan, Craig J.

    1993-01-01

    The equations governing the behavior of perturbations of a mixture of nearly homogeneous and isotropic matter and radiation are derived, using a diffusion approximation where spatial perturbations in the radiation spectrum are allowed to vary with frequency. A simple model of line opacity leads to dispersion relations which display a new bulk instability. The model is used to derive an approximate dispersion relation for radiation interacting via resonance scattering opacity in atomic hydrogen at low density and low temperature. Possible applications to cosmology are briefly discussed.

  6. Gas turbine combustion instability

    SciTech Connect

    Richards, G.A.; Lee, G.T.

    1996-09-01

    Combustion oscillations are a common problem in development of LPM (lean premix) combustors. Unlike earlier, diffusion style combustors, LPM combustors are especially susceptible to oscillations because acoustic losses are smaller and operation near lean blowoff produces a greater combustion response to disturbances in reactant supply, mixing, etc. In ongoing tests at METC, five instability mechanisms have been identified in subscale and commercial scale nozzle tests. Changes to fuel nozzle geometry showed that it is possible to stabilize combustion by altering the timing of the feedback between acoustic waves and the variation in heat release.

  7. Chemically Driven Hydrodynamic Instabilities

    NASA Astrophysics Data System (ADS)

    Almarcha, C.; Trevelyan, P. M. J.; Grosfils, P.; de Wit, A.

    2010-01-01

    In the gravity field, density changes triggered by a kinetic scheme as simple as A+B→C can induce or affect buoyancy-driven instabilities at a horizontal interface between two solutions containing initially the scalars A and B. On the basis of a general reaction-diffusion-convection model, we analyze to what extent the reaction can destabilize otherwise buoyantly stable density stratifications. We furthermore show that, even if the underlying nonreactive system is buoyantly unstable, the reaction breaks the symmetry of the developing patterns. This is demonstrated both numerically and experimentally on the specific example of a simple acid-base neutralization reaction.

  8. Booming Dune Instability

    NASA Astrophysics Data System (ADS)

    Andreotti, B.; Bonneau, L.

    2009-12-01

    Sand avalanches flowing down the leeward face of some desert dunes spontaneously produce a loud sound with a characteristic vibrato around a well-defined frequency, a phenomenon called the “song of dunes.” Here, we show through theory that a homogenous granular surface flow is linearly unstable towards growing elastic waves when a localized shear band forms at the interface between the avalanche and the static part of the dune. We unravel the nature of the acoustic amplifying mechanism at the origin of this booming instability. The dispersion relation and the shape of the most unstable modes are computed and compared to field measurements.

  9. Booming dune instability.

    PubMed

    Andreotti, B; Bonneau, L

    2009-12-01

    Sand avalanches flowing down the leeward face of some desert dunes spontaneously produce a loud sound with a characteristic vibrato around a well-defined frequency, a phenomenon called the "song of dunes." Here, we show through theory that a homogenous granular surface flow is linearly unstable towards growing elastic waves when a localized shear band forms at the interface between the avalanche and the static part of the dune. We unravel the nature of the acoustic amplifying mechanism at the origin of this booming instability. The dispersion relation and the shape of the most unstable modes are computed and compared to field measurements. PMID:20366176

  10. Shilnikov instabilities in laser systems

    SciTech Connect

    Swetits, J.J.; Buoncristiani, A.M.

    1988-11-15

    Experiments on a CO/sub 2/ laser with feedback (F. T. Arecchi, R. Meucci, and W. Gadomski, Phys. Rev. Lett. 58, 2205 (1987)) displayed an extraordinary set of instabilities, identified as Shilnikov chaos. We have investigated the stability structure of a theoretical model developed to describe this laser system and carried out an extensive numerical search for the Shilnikov instability. No computational evidence to support the claim of a Shilnikov instability for model parameters corresponding to the experimental region can be found.

  11. Study of cavitating inducer instabilities

    NASA Technical Reports Server (NTRS)

    Young, W. E.; Murphy, R.; Reddecliff, J. M.

    1972-01-01

    An analytic and experimental investigation into the causes and mechanisms of cavitating inducer instabilities was conducted. Hydrofoil cascade tests were performed, during which cavity sizes were measured. The measured data were used, along with inducer data and potential flow predictions, to refine an analysis for the prediction of inducer blade suction surface cavitation cavity volume. Cavity volume predictions were incorporated into a linearized system model, and instability predictions for an inducer water test loop were generated. Inducer tests were conducted and instability predictions correlated favorably with measured instability data.

  12. Turbulence and instabilities

    NASA Astrophysics Data System (ADS)

    Belotserkovskii, Oleg

    2001-06-01

    The main principles for constructing of mathematical models for fully developed free shear turbulence and hydrodynamic instabilities are considered in the report. Such a “rational” modeling is applied for a variety of unsteady multidimensional problems. For the wide class of phenomena, by the large Reynolds numbers within the low-frequency and inertial intervals of turbulent motion, the effect of molecular viscosity and of the small elements of flow in the largest part of perturbation domain are not practically essential neither for the general characteristics of macroscopic structures of the flow developed, nor the flow pattern as a whole. This makes it possible not to take into consideration the effects of molecular viscosity when studying the dynamics of large vortices, and to implement the study of those on the basis of models of the ideal gas (using the methods of “rational” averaging, but without application of semi-empirical models of turbulence). Among the problems, which have been studied by such a way, there are those of the jet-type flow in the wake behind the body, the motions of ship frames with stern shearing, the formation of anterior stalling zones by the flow about blunted bodies with jets or needles directed to meet the flow, etc. As applications the problems of instability development and of spreading of smoke cloud from large-scale source of the fire are considered.

  13. [Aspirin suppresses microsatellite instability].

    PubMed

    Wallinger, S; Dietmaier, W; Beyser, K; Bocker, T; Hofstädter, F; Fishel, R; Rüschoff, J

    1999-01-01

    Nonsteroidal anti-inflammatory drugs (NSAIDs) exhibit cancer preventive effects and have been shown to induce regression of adenomas in FAP patients. In order to elucidate the probable underlying mechanism, the effect of NSAIDs on mismatch repair related microsatellite instability was investigated. Six colorectal cancer cell lines all but one deficient for human mismatch repair (MMR) genes were examined for microsatellite instability (MSI) prior and after treatment with Aspirin or Sulindac. For rapid in vitro analysis of MSI a microcloning assay was developed by combining Laser microdissection and random (PEP-) PCR prior to specific MSI-PCR. Effects of NSAIDs on cell cycle and apoptosis were systematically investigated by using flow cytometry and cell-sorting. MSI frequency in cells deficient of MMR genes (hMSH2, hMLH1, hMSH6) was markedly reduced after long-term (> 10 weeks) NSAID treatment. This effect was reversible, time- and concentration dependent. However, in the hPMS2 deficient endometrial cancer cell line (HEC-1-A) the MSI phenotype kept unchanged. According to cell sorting, non-apoptotic cells were stable and apoptotic cells were unstable. These results suggest that aspirin/sulindac induces a genetic selection for microsatellite stability in a subset of MMR-deficient cells and may thus provide an effective prophylactic therapy for HNPCC related colorectal carcinomas.

  14. Experimental Evidence for a Transient Tayler Instability in a Cylindrical Liquid-Metal Column

    NASA Astrophysics Data System (ADS)

    Seilmayer, Martin; Stefani, Frank; Gundrum, Thomas; Weier, Tom; Gerbeth, Gunter; Gellert, Marcus; Rüdiger, Günther

    2012-06-01

    In the current-driven, kink-type Tayler instability (TI) a sufficiently strong azimuthal magnetic field becomes unstable against nonaxisymmetric perturbations. The TI has been discussed as a possible ingredient of the solar dynamo mechanism and a source of the helical structures in cosmic jets. It is also considered as a size-limiting factor for liquid metal batteries. We report on a liquid metal TI experiment using a cylindrical column of the eutectic alloy GaInSn to which electrical currents of up to 8 kA are applied. We present results of external magnetic field measurements that indicate the transient occurrence of the TI in good agreement with numerical predictions. The interference of TI with the competing large-scale convection, resulting from Joule heating, is also discussed.

  15. Sausage Instabilities on top of Kinking Lengthening Current-Carrying Magnetic Flux Tubes

    NASA Astrophysics Data System (ADS)

    von der Linden, Jens; You, Setthivoine

    2015-11-01

    Observations indicate that the dynamics of magnetic flux tubes in our cosmos and terrestrial experiments involve fast topological change beyond MHD reconnection. Recent experiments suggest that hierarchies of instabilities coupling disparate plasma scales could be responsible for this fast topological change by accessing two-fluid and kinetic scales. This study will explore the possibility of sausage instabilities developing on top of a kink instability in lengthening current-carrying magnetic flux tubes. Current driven flux tubes evolve over a wide range of aspect ratios k and current to magnetic flux ratios λ . An analytical stability criterion and numerical investigations, based on applying Newcomb's variational approach to idealized magnetic flux tubes with core and skin currents, indicate a dependence of the stability boundaries on current profiles and overlapping kink and sausage unstable regions in the k - λ trajectory of the flux tubes. A triple electrode planar plasma gun (Mochi.LabJet) is designed to generate flux tubes with discrete core and skin currents. Measurements from a fast-framing camera and a high resolution magnetic probe are being assembled into stability maps of the k - λ space of flux tubes. This work was sponsored in part by the US DOE Grant DE-SC0010340.

  16. Relativistic electromagnetic ion cyclotron instabilities.

    PubMed

    Chen, K R; Huang, R D; Wang, J C; Chen, Y Y

    2005-03-01

    The relativistic instabilities of electromagnetic ion cyclotron waves driven by MeV ions are analytically and numerically studied. As caused by wave magnetic field and in sharp contrast to the electrostatic case, interesting characteristics such as Alfve nic behavior and instability transition are discovered and illuminated in detail. The instabilities are reactive and are raised from the coupling of slow ions' first-order resonance and fast ions' second-order resonance, that is an essential extra mechanism due to relativistic effect. Because of the wave magnetic field, the nonresonant plasma dielectric is usually negative and large, that affects the instability conditions and scaling laws. A negative harmonic cyclotron frequency mismatch between the fast and slow ions is required for driving a cubic (and a coupled quadratic) instability; the cubic (square) root scaling of the peak growth rate makes the relativistic effect more important than classical mechanism, especially for low fast ion density and Lorentz factor being close to unity. For the cubic instability, there is a threshold (ceiling) on the slow ion temperature and density (the external magnetic field and the fast ion energy); the Alfve n velocity is required to be low. This Alfve nic behavior is interesting in physics and important for its applications. The case of fast protons in thermal deuterons is numerically studied and compared with the analytical results. When the slow ion temperature or density (the external magnetic field or the fast ion energy) is increased (reduced) to about twice (half) the threshold (ceiling), the same growth rate peak transits from the cubic instability to the coupled quadratic instability and a different cubic instability branch appears. The instability transition is an interesting new phenomenon for instability. PMID:15903591

  17. A current-driven nanometer water pump.

    PubMed

    Su, Jiaye; Yang, Keda

    2016-03-01

    The design of a water pump, which has huge potential for applications in nanotechnology and daily life, is the dream of many scientists. In this paper, we successfully design a nanometer water pump by using molecular dynamics simulations. Ions of either sodium or chlorine in a narrow channel will generate electric current under electric fields, which then drives the water through a wider channel, similar to recent experimental setups. Considerable water flux is achieved within small field strengths that are accessible by experimentation. Of particular interest, is that for sodium the water flux increases almost linearly with field strengths; while for chlorine there exists a critical field strength, the water flux exhibits a plateau before the critical value and increases linearly after it. This result follows the behavior of ion velocity, which is related to friction behavior. We also estimate the power and energy consumption for such a pump, and compare it to the macroscopic mechanical pumps. A further comparison suggests that different ions will have different pumping abilities. This study not only provides new, significant results with possible connection to existing research, but has tremendous potential application in the design of nanofluidic devices. PMID:26822782

  18. A current-driven nanometer water pump

    NASA Astrophysics Data System (ADS)

    Su, Jiaye; Yang, Keda

    2016-03-01

    The design of a water pump, which has huge potential for applications in nanotechnology and daily life, is the dream of many scientists. In this paper, we successfully design a nanometer water pump by using molecular dynamics simulations. Ions of either sodium or chlorine in a narrow channel will generate electric current under electric fields, which then drives the water through a wider channel, similar to recent experimental setups. Considerable water flux is achieved within small field strengths that are accessible by experimentation. Of particular interest, is that for sodium the water flux increases almost linearly with field strengths; while for chlorine there exists a critical field strength, the water flux exhibits a plateau before the critical value and increases linearly after it. This result follows the behavior of ion velocity, which is related to friction behavior. We also estimate the power and energy consumption for such a pump, and compare it to the macroscopic mechanical pumps. A further comparison suggests that different ions will have different pumping abilities. This study not only provides new, significant results with possible connection to existing research, but has tremendous potential application in the design of nanofluidic devices.

  19. Chromosomal Instability in the progeny of human irradiated cells

    NASA Astrophysics Data System (ADS)

    Testard, I.; Boissière, A.; Martins, L. M.; Sabatier, L.

    Manned space missions recently increased in number and duration, thus it became important to estimate the biological risks encountered by astronauts. They are exposed to cosmic and galactic rays, a complex mixture of different radiations. In addition to the measurements realized by physical dosimeters, it becomes essential to estimate real biologically effective doses and compare them to physical doses. Biological dosimetry of radiation exposures has been widely performed using cytogenetic analysis of chromosomes. This approach has been used for many years in order to estimate absorbed doses in accidental or chronic overexposures of humans. Recent studies show that some alterations can appear many cell generations after the initial radiation exposure as a delayed genomic instability. This delayed instability is characterized by the accumulation of cell alterations leading to cell transformation, delayed cell death and mutations. Chromosome instability was shown in vitro in different model systems (Sabatier et al., 1992; Marder and Morgan, 1993; Kadhim et al., 1994 and Holmberg et al., 1993, 1995). All types of radiation used induce chromosome instability; however, heavy ions cause the most damage. The period of chromosome instability followed by the formation of clones with unbalanced karyotypes seems to be shared by cancer cells. The shortening of telomere sequences leading to the formation of telomere fusions is an important factor in the appearance of this chromosome instability.

  20. Weibel Instability Driven by Spatially Anisotropic Density Structures

    NASA Astrophysics Data System (ADS)

    Tomita, Sara; Ohira, Yutaka

    2016-07-01

    Observations of afterglows of gamma-ray bursts (GRBs) suggest that post-shock magnetic fields are strongly amplified to about 100 times the shock-compressed value. The Weibel instability appears to play an important role in generating the magnetic field. However, recent simulations of collisionless shocks in homogeneous plasmas show that the magnetic field generated by the Weibel instability rapidly decays. There must be some density fluctuations in interstellar and circumstellar media. The density fluctuations are anisotropically compressed in the downstream region of relativistic shocks. In this paper, we study the Weibel instability in electron-positron plasmas with spatially anisotropic density distributions by means of two-dimensional particle-in-cell simulations. We find that large magnetic fields are maintained for a longer time by the Weibel instability driven by spatially anisotropic density structure. Particles anisotropically escape from the high density region, so that a temperature anisotropy is generated and the Weibel instability becomes unstable. Our simulation results suggest that the Weibel instability driven by an anisotropic density structure can generate sufficiently large magnetic fields and they can cover sufficiently large regions to explain the afterglow emission of GRBs.

  1. Research on aviation fuel instability

    NASA Technical Reports Server (NTRS)

    Baker, C. E.; Bittker, D. A.; Cohen, S. M.; Seng, G. T.

    1983-01-01

    The underlying causes of fuel thermal degradation are discussed. Topics covered include: nature of fuel instability and its temperature dependence, methods of measuring the instability, chemical mechanisms involved in deposit formation, and instrumental methods for characterizing fuel deposits. Finally, some preliminary thoughts on design approaches for minimizing the effects of lowered thermal stability are briefly discussed.

  2. Liquid propellant rocket combustion instability

    NASA Technical Reports Server (NTRS)

    Harrje, D. T.

    1972-01-01

    The solution of problems of combustion instability for more effective communication between the various workers in this field is considered. The extent of combustion instability problems in liquid propellant rocket engines and recommendations for their solution are discussed. The most significant developments, both theoretical and experimental, are presented, with emphasis on fundamental principles and relationships between alternative approaches.

  3. Cohabitation and Children's Family Instability

    ERIC Educational Resources Information Center

    Kelly Raley, R.; Wildsmith, Elizabeth

    2004-01-01

    This study estimates how much children's family instability is missed when we do not count transitions into and out of cohabitation, and examines early life course trajectories of children to see whether children who experience maternal cohabitation face more family instability than children who do not. Using data from the 1995 National Survey of…

  4. Neurocardiovascular Instability and Cognition

    PubMed Central

    O’Callaghan, Susan; Kenny, Rose Anne

    2016-01-01

    Neurocardiovascular instability (NCVI) refers to abnormal neural control of the cardiovascular system affecting blood pressure and heart rate behavior. Autonomic dysfunction and impaired cerebral autoregulation in aging contribute to this phenomenon characterized by hypotension and bradyarrhythmia. Ultimately, this increases the risk of falls and syncope in older people. NCVI is common in patients with neurodegenerative disorders including dementia. This review discusses the various syndromes that characterize NCVI icluding hypotension, carotid sinus hypersensitivity, postprandial hypotension and vasovagal syncope and how they may contribute to the aetiology of cognitive decline. Conversely, they may also be a consequence of a common neurodegenerative process. Regardless, recognition of their association is paramount in optimizing management of these patients. PMID:27505017

  5. The booming dune instability

    NASA Astrophysics Data System (ADS)

    Andreotti, B.; Bonneau, L.

    2009-12-01

    Sand avalanches flowing down the leeward face of some desert dunes spontaneously produce a loud sound with a characteristic vibrato around a well defined frequency, a phenomenon called the "song of dunes". Here, we show theoretically that an homogenous granular surface flow is linearly unstable towards growing elastic waves when a localized shear band form at the interface between the avalanche and the static part of the dune. We unravel the nature of the acoustic amplifying mechanism at the origin of this booming instability. The dispersion relation and the shape of the most unstable modes are computed and compared to field records performed in the Atlantic Sahara. We finally show that several characteristics predicted by the model and observed in the field allow to dismiss former hypothesis based on resonances or the synchronisation of sand grain collisions.

  6. Instability of canopy flows

    NASA Astrophysics Data System (ADS)

    Zampogna, Giuseppe A.; Pluvinage, Franck; Kourta, Azeddine; Bottaro, Alessandro

    2016-07-01

    Honami and monami waves are caused by large-scale coherent vortex structures which form in shear layers generated by canopies. In order to reach new insights on the onset of such waves, the instability of these shear layers is studied. Two different approaches are used. In the first approach, the presence of the canopy is modeled via a drag coefficient, taken to vary along the canopy as by experimental indications. The second approach considers the canopy as a porous medium and different governing equations for the fluid flow are deduced. In this second case, the anisotropy of the canopy, composed by rigid cylindrical elements, is accounted for via an apparent permeability tensor. The results obtained with the latter approach approximate better experimental correlations for the synchronous oscillations of the canopy.

  7. Instability saturation by the oscillating two-stream instability in a weakly relativistic plasma

    SciTech Connect

    Pal, Barnali; Poria, Swarup; Sahu, Biswajit

    2015-04-15

    The two-stream instability has wide range of astrophysical applications starting from gamma-ray bursts and pulsar glitches to cosmology. We consider one dimensional weakly relativistic Zakharov equations and describe nonlinear saturation of the oscillating two-stream instability using a three dimensional dynamical system resulting form a truncation of the nonlinear Schrodinger equation to three modes. The equilibrium points of the model are determined and their stability natures are discussed. Using the tools of nonlinear dynamics such as the bifurcation diagram, Poincaré maps, and Lyapunav exponents, existence of periodic, quasi-periodic, and chaotic solutions are established in the dynamical system. Interestingly, we observe the multistable behavior in this plasma model. The system has multiple attractors depending on the initial conditions. We also notice that the relativistic parameter plays the role of control parameter in the model. The theoretical results presented in this paper may be helpful for better understanding of space and astrophysical plasmas.

  8. Internal rotor friction instability

    NASA Technical Reports Server (NTRS)

    Walton, J.; Artiles, A.; Lund, J.; Dill, J.; Zorzi, E.

    1990-01-01

    The analytical developments and experimental investigations performed in assessing the effect of internal friction on rotor systems dynamic performance are documented. Analytical component models for axial splines, Curvic splines, and interference fit joints commonly found in modern high speed turbomachinery were developed. Rotor systems operating above a bending critical speed were shown to exhibit unstable subsynchronous vibrations at the first natural frequency. The effect of speed, bearing stiffness, joint stiffness, external damping, torque, and coefficient of friction, was evaluated. Testing included material coefficient of friction evaluations, component joint quantity and form of damping determinations, and rotordynamic stability assessments. Under conditions similar to those in the SSME turbopumps, material interfaces experienced a coefficient of friction of approx. 0.2 for lubricated and 0.8 for unlubricated conditions. The damping observed in the component joints displayed nearly linear behavior with increasing amplitude. Thus, the measured damping, as a function of amplitude, is not represented by either linear or Coulomb friction damper models. Rotordynamic testing of an axial spline joint under 5000 in.-lb of static torque, demonstrated the presence of an extremely severe instability when the rotor was operated above its first flexible natural frequency. The presence of this instability was predicted by nonlinear rotordynamic time-transient analysis using the nonlinear component model developed under this program. Corresponding rotordynamic testing of a shaft with an interference fit joint demonstrated the presence of subsynchronous vibrations at the first natural frequency. While subsynchronous vibrations were observed, they were bounded and significantly lower in amplitude than the synchronous vibrations.

  9. Combustion Instabilities Modeled

    NASA Technical Reports Server (NTRS)

    Paxson, Daniel E.

    1999-01-01

    NASA Lewis Research Center's Advanced Controls and Dynamics Technology Branch is investigating active control strategies to mitigate or eliminate the combustion instabilities prevalent in lean-burning, low-emission combustors. These instabilities result from coupling between the heat-release mechanisms of the burning process and the acoustic flow field of the combustor. Control design and implementation require a simulation capability that is both fast and accurate. It must capture the essential physics of the system, yet be as simple as possible. A quasi-one-dimensional, computational fluid dynamics (CFD) based simulation has been developed which may meet these requirements. The Euler equations of mass, momentum, and energy have been used, along with a single reactive species transport equation to simulate coupled thermoacoustic oscillations. A very simple numerical integration scheme was chosen to reduce computing time. Robust boundary condition procedures were incorporated to simulate various flow conditions (e.g., valves, open ends, and choked inflow) as well as to accommodate flow reversals that may arise during large flow-field oscillations. The accompanying figure shows a sample simulation result. A combustor with an open inlet, a choked outlet, and a large constriction approximately two thirds of the way down the length is shown. The middle plot shows normalized, time-averaged distributions of the relevant flow quantities, and the bottom plot illustrates the acoustic mode shape of the resulting thermoacoustic oscillation. For this simulation, the limit cycle peak-to-peak pressure fluctuations were 13 percent of the mean. The simulation used 100 numerical cells. The total normalized simulation time was 50 units (approximately 15 oscillations), which took 26 sec on a Sun Ultra2.

  10. Gravitational Instabilities in Circumstellar Disks

    NASA Astrophysics Data System (ADS)

    Kratter, Kaitlin; Lodato, Giuseppe

    2016-09-01

    Star and planet formation are the complex outcomes of gravitational collapse and angular momentum transport mediated by protostellar and protoplanetary disks. In this review, we focus on the role of gravitational instability in this process. We begin with a brief overview of the observational evidence for massive disks that might be subject to gravitational instability and then highlight the diverse ways in which the instability manifests itself in protostellar and protoplanetary disks: the generation of spiral arms, small-scale turbulence-like density fluctuations, and fragmentation of the disk itself. We present the analytic theory that describes the linear growth phase of the instability supplemented with a survey of numerical simulations that aim to capture the nonlinear evolution. We emphasize the role of thermodynamics and large-scale infall in controlling the outcome of the instability. Despite apparent controversies in the literature, we show a remarkable level of agreement between analytic predictions and numerical results. In the next part of our review, we focus on the astrophysical consequences of the instability. We show that the disks most likely to be gravitationally unstable are young and relatively massive compared with their host star, Md/M*≥0.1. They will develop quasi-stable spiral arms that process infall from the background cloud. Although instability is less likely at later times, once infall becomes less important, the manifestations of the instability are more varied. In this regime, the disk thermodynamics, often regulated by stellar irradiation, dictates the development and evolution of the instability. In some cases the instability may lead to fragmentation into bound companions. These companions are more likely to be brown dwarfs or stars than planetary mass objects. Finally, we highlight open questions related to the development of a turbulent cascade in thin disks and the role of mode-mode coupling in setting the maximum angular

  11. The nucleus is the target for radiation-induced chromosomal instability

    NASA Technical Reports Server (NTRS)

    Kaplan, M. I.; Morgan, W. F.

    1998-01-01

    We have previously described chromosomal instability in cells of a human-hamster hybrid cell line after exposure to X rays. Chromosomal instability in these cells is characterized by the appearance of novel chromosomal rearrangements multiple generations after exposure to ionizing radiation. To identify the cellular target(s) for radiation-induced chromosomal instability, cells were treated with 125I-labeled compounds and frozen. Radioactive decays from 125I cause damage to the cell primarily at the site of their decay, and freezing the cells allows damage to accumulate in the absence of other cellular processes. We found that the decay of 125I-iododeoxyuridine, which is incorporated into the DNA, caused chromosomal instability. While cell killing and first-division chromosomal rearrangements increased with increasing numbers of 125I decays, the frequency of chromosomal instability was independent of dose. Chromosomal instability could also be induced from incorporation of 125I-iododeoxyuridine without freezing the cells for accumulation of decays. This indicates that DNA double-strand breaks in frozen cells resulting from 125I decays failed to lead to instability. Incorporation of an 125I-labeled protein (125I-succinyl-concanavalin A), which was internalized into the cell and/or bound to the plasma membrane, neither caused chromosomal instability nor potentiated chromosomal instability induced by 125I-iododeoxyuridine. These results show that the target for radiation-induced chromosomal instability in these cells is the nucleus.

  12. Temperature anisotropy and beam type whistler instabilities

    NASA Technical Reports Server (NTRS)

    Hashimoto, K.; Matsumoto, H.

    1976-01-01

    Whistler instabilities have been investigated for two different types; i.e., a temperature-anisotropy type instability and a beam-type instability. A comparison between the two types of whistler instabilities is made within the framework of linear theory. A transition from one type to the other is also discussed, which is an extension of the work on electrostatic beam and Landau instabilities performed by O'Neil and Malmberg (1968) for electromagnetic whistler instabilities. It is clarified that the essential source of the whistler instability is not beam kinetic energy but a temperature anisotropy, even for the beam-type whistler instability.

  13. Yet another instability in glasma

    NASA Astrophysics Data System (ADS)

    Tsutsui, Shoichiro; Iida, Hideaki; Kunihiro, Teiji; Ohnishi, Akira

    2014-09-01

    In relativistic heavy ion collisions (HIC), hydrodynamic models can describe many experimental data and suggest that the quark-gluon plasma formed at RHIC and LHC is almost perfect fluid. We need very short thermalization time and far-from-equilibrium dynamics may be important in thermalization processes of HIC. In the earliest stages of HIC, classical gluon dynamics is dominant and many types of instabilities emerge there. These instabilities may strongly affect the later stages of dynamics; realization of chaoticity and field-particle conversions. We investigate instabilities of classical gluon fields under the homogeneous, but time dependent background color magnetic fields. The background field become periodic function of time and we can analyze the stability of fluctuations based on the Floquet theory which consists the basis of the Bloch theory. As a result, we get the complete structure of instability bands for physical degrees of freedom appearing from parametric resonance. We also find that the parametric instabilities considered here have different natures from the several known instabilities; Weibel and Nielsen-Olesen instabilities. We also discuss some implications of parametric resonance to the particle productions in HIC.

  14. Microbunching Instability in Velocity Bunching

    SciTech Connect

    Xiang, D; Wu, J.; /SLAC

    2009-05-26

    Microbunching instability is one of the most challenging threats to FEL performances. The most effective ways to cure the microbunching instability include suppression of the density modulation sources and suppression of the amplification process. In this paper we study the microbunching instability in velocity bunching. Our simulations show that the initial current and energy modulations are suppressed in velocity bunching process, which may be attributed to the strong plasma oscillation and Landau damping from the relatively low beam energy and large relative slice energy spread. A heating effect that may be present in a long solenoid is also preliminarily analyzed.

  15. Longitudinal instability of the forearm.

    PubMed

    Phadnis, J; Watts, A C

    2016-10-01

    The Essex Lopresti lesion is a rare triad of injury to the radial head, interosseous membrane of the forearm and distal radio-ulnar joint, which results in longitudinal instability of the radius. If unrecognized this leads to chronic pain and disability which is difficult to salvage. Early recognition and appropriate treatment is therefore desirable to prevent long-term problems. The aim of this article is to review the pathoanatomy of longitudinal radius instability and use the existing literature and authors' experience to provide recommendations for recognition and treatment of acute and chronic forearm instability, including description of the author's technique for interosseous membrane reconstruction. PMID:27628434

  16. Hydrodynamic instability modeling for ICF

    SciTech Connect

    Haan, S.W.

    1993-03-31

    The intent of this paper is to review how instability growth is modeled in ICF targets, and to identify the principal issues. Most of the material has been published previously, but is not familiar to a wide audience. Hydrodynamic instabilities are a key issue in ICF. Along with laser-plasma instabilities, they determine the regime in which ignition is possible. At higher laser energies, the same issues determine the achievable gain. Quantitative predictions are therefore of the utmost importance to planning the ICF program, as well as to understanding current Nova results. The key fact that underlies all this work is the stabilization of short wavelengths.

  17. New instability of Saturn's ring

    SciTech Connect

    Goertz, C.K.; Morfill, G.

    1988-05-01

    Perturbations in the Saturn ring's mass density are noted to be prone to instabilities through the sporadic elevation of submicron-size dust particles above the rings, which furnishes an effective angular momentum exchange between the rings and Saturn. The dust thus elevated from the ring settles back onto it at a different radial distance. The range of wavelength instability is determinable in light of the dust charge, the average radial displacement of the dust, and the fluctuation of these quantities. It is suggested that at least some of the B-ring's ringlets may arise from the instability.

  18. Suppression of microbunching instability via a transverse gradient undulator

    NASA Astrophysics Data System (ADS)

    Feng, Chao; Huang, Dazhang; Deng, Haixiao; Gu, Qiang; Zhao, Zhentang

    2015-07-01

    The microbunching instability in the linear accelerator (linac) of a free-electron laser facility has always been a problem that degrades the electron beam quality. In this paper, a quite simple and inexpensive technique is proposed to smooth the electron beam current profile to suppress the instability. By directly adding a short undulator with a transverse gradient field right after the injector to couple the transverse spread into the longitudinal direction, additional density mixing in the electron beam is introduced to smooth the current profile, which results in the reduction of the gain of the microbunching instability. The magnitude of the density mixing can be easily controlled by varying the strength of the undulator magnetic field. Theoretical analysis and numerical simulations demonstrate the capability of the proposed technique in the accelerator of an x-ray free-electron laser.

  19. Collisionless shock experiments with lasers and observation of Weibel instabilities

    SciTech Connect

    Park, H. -S.; Huntington, C. M.; Fiuza, F.; Drake, R. P.; Froula, D. H.; Gregori, G.; Koenig, M.; Kugland, N. L.; Kuranz, C. C.; Lamb, D. Q.; Levy, M. C.; Li, C. K.; Meinecke, J.; Morita, T.; Petrasso, R. D.; Pollock, B. B.; Remington, B. A.; Rinderknecht, H. G.; Rosenberg, M.; Ross, J. S.; Ryutov, D. D.; Sakawa, Y.; Spitkovsky, A.; Takabe, H.; Turnbull, D. P.; Tzeferacos, P.; Weber, S. V.; Zylstra, A. B.

    2015-05-13

    Astrophysical collisionless shocks are common in the universe, occurring in supernova remnants, gamma ray bursts, and protostellar jets. They appear in colliding plasma flows when the mean free path for ion-ion collisions is much larger than the system size. It is believed that such shocks could be mediated via the electromagnetic Weibel instability in astrophysical environments without preexisting magnetic fields. Here, we present laboratory experiments using high-power lasers and investigate the dynamics of high-Mach-number collisionless shock formation in two interpenetrating plasma streams. Our recent proton-probe experiments on Omega show the characteristic filamentary structures of the Weibel instability that are electromagnetic in nature with an inferred magnetization level as high as ~1% These results imply that electromagnetic instabilities are significant in the interaction of astrophysical conditions.

  20. Collisionless shock experiments with lasers and observation of Weibel instabilities

    DOE PAGESBeta

    Park, H. -S.; Huntington, C. M.; Fiuza, F.; Drake, R. P.; Froula, D. H.; Gregori, G.; Koenig, M.; Kugland, N. L.; Kuranz, C. C.; Lamb, D. Q.; et al

    2015-05-13

    Astrophysical collisionless shocks are common in the universe, occurring in supernova remnants, gamma ray bursts, and protostellar jets. They appear in colliding plasma flows when the mean free path for ion-ion collisions is much larger than the system size. It is believed that such shocks could be mediated via the electromagnetic Weibel instability in astrophysical environments without preexisting magnetic fields. Here, we present laboratory experiments using high-power lasers and investigate the dynamics of high-Mach-number collisionless shock formation in two interpenetrating plasma streams. Our recent proton-probe experiments on Omega show the characteristic filamentary structures of the Weibel instability that are electromagneticmore » in nature with an inferred magnetization level as high as ~1% These results imply that electromagnetic instabilities are significant in the interaction of astrophysical conditions.« less

  1. Instabilities in counterstreaming plasmas

    NASA Astrophysics Data System (ADS)

    Park, Hye-Sook

    2013-10-01

    We are performing high power laser experiments showing large, stable, reproducible electromagnetic field structures that arise in counter-streaming interpenetrating supersonic plasma flows in the laboratory. Self organization, whereby energy progressively transfers from smaller to larger scales in an inverse cascade, is widely observed in fluid flows, such as in the nonlinear evolution of multimode Rayleigh-Taylor and Kelvin-Helmholtz instabilities. There are many scenarios in astrophysics where self organization involving magnetic or electric fields in collisionless settings is observed. These surprising structures, predominantly oriented transverse to the primary flow direction, extend for much larger distances than the intrinsic plasma spatial scales, and persist for much longer than the plasma kinetic timescales. Their origin may be magnetic field advection from the recompression of the Biermann battery fields in the midplane. Understanding interactions of high velocity plasma flows is interests to the ICF and astrophysics. This paper will present experimental results and interpretation of these counterstreaming plasma experiments. This work was performed under the auspices of the Lawrence Livermore National Security, LLC, (LLNS) under Contract No. DE-AC52-07NA27344.

  2. Resistive instabilities in tokamaks

    SciTech Connect

    Rutherford, P.H.

    1985-10-01

    Low-m tearing modes constitute the dominant instability problem in present-day tokamaks. In this lecture, the stability criteria for representative current profiles with q(0)-values slightly less than unit are reviewed; ''sawtooth'' reconnection to q(0)-values just at, or slightly exceeding, unity is generally destabilizing to the m = 2, n = 1 and m = 3, n = 2 modes, and severely limits the range of stable profile shapes. Feedback stabilization of m greater than or equal to 2 modes by rf heating or current drive, applied locally at the magnetic islands, appears feasible; feedback by island current drive is much more efficient, in terms of the radio-frequency power required, then feedback by island heating. Feedback stabilization of the m = 1 mode - although yielding particularly beneficial effects for resistive-tearing and high-beta stability by allowing q(0)-values substantially below unity - is more problematical, unless the m = 1 ideal-MHD mode can be made positively stable by strong triangular shaping of the central flux surfaces. Feedback techniques require a detectable, rotating MHD-like signal; the slowing of mode rotation - or the excitation of non-rotating modes - by an imperfectly conducting wall is also discussed.

  3. Instabilities in the aether

    SciTech Connect

    Carroll, Sean M.; Dulaney, Timothy R.; Gresham, Moira I.; Tam, Heywood

    2009-03-15

    We investigate the stability of theories in which Lorentz invariance is spontaneously broken by fixed-norm vector 'aether' fields. Models with generic kinetic terms are plagued either by ghosts or by tachyons, and are therefore physically unacceptable. There are precisely three kinetic terms that are not manifestly unstable: a sigma model ({partial_derivative}{sub {mu}}A{sub {nu}}){sup 2}, the Maxwell Lagrangian F{sub {mu}}{sub {nu}}F{sup {mu}}{sup {nu}}, and a scalar Lagrangian ({partial_derivative}{sub {mu}}A{sup {mu}}){sup 2}. The timelike sigma-model case is well defined and stable when the vector norm is fixed by a constraint; however, when it is determined by minimizing a potential there is necessarily a tachyonic ghost, and therefore an instability. In the Maxwell and scalar cases, the Hamiltonian is unbounded below, but at the level of perturbation theory there are fewer degrees of freedom and the models are stable. However, in these two theories there are obstacles to smooth evolution for certain choices of initial data.

  4. The TP53 dependence of radiation-induced chromosome instability in human lymphoblastoid cells

    NASA Technical Reports Server (NTRS)

    Schwartz, Jeffrey L.; Jordan, Robert; Evans, Helen H.; Lenarczyk, Marek; Liber, Howard

    2003-01-01

    The dose and TP53 dependence for the induction of chromosome instability were examined in cells of three human lymphoblastoid cell lines derived from WIL2 cells: TK6, a TP53-normal cell line, NH32, a TP53-knockout created from TK6, and WTK1, a WIL2-derived cell line that spontaneously developed a TP53 mutation. Cells of each cell line were exposed to (137)Cs gamma rays, and then surviving clones were isolated and expanded in culture for approximately 35 generations before the frequency and characteristics of the instability were analyzed. The presence of dicentric chromosomes, formed by end-to-end fusions, served as a marker of chromosomal instability. Unexposed TK6 cells had low levels of chromosomal instability (0.002 +/- 0.001 dicentrics/cell). Exposure of TK6 cells to doses as low as 5 cGy gamma rays increased chromosome instability levels nearly 10-fold to 0.019 +/- 0.008 dicentrics/cell. There was no further increase in instability levels beyond 5 cGy. In contrast to TK6 cells, unexposed cultures of WTK1 and NH32 cells had much higher levels of chromosome instability of 0.034 +/- 0.007 and 0.041 +/- 0.009, respectively, but showed little if any effect of radiation on levels of chromosome instability. The results suggest that radiation exposure alters the normal TP53-dependent cell cycle checkpoint controls that recognize alterations in telomere structure and activate apoptosis.

  5. Coupling of Kelvin-Helmholtz instability and buoyancy instability in a thermally laminar plasma

    SciTech Connect

    Ren Haijun; Wu Zhengwei; Cao Jintao; Dong Chao; Chu, Paul K.

    2011-02-15

    Thermal convective instability is investigated in a thermally stratified plasma in the presence of shear flow, which is known to give rise to the Kelvin-Helmholtz (KH) instability. We examine how the KH instability and magnetothermal instability (MTI) affect each other. Based on the sharp boundary model, the KH instability coupled with the MTI is studied. We present the growth rate and instability criteria. The shear flow is shown to significantly alter the critical condition for the occurrence of thermal convective instability.

  6. Cosmic instability from radiation pressure

    NASA Technical Reports Server (NTRS)

    Hogan, Craig J.

    1990-01-01

    The Cosmic Background Explorer has recently confirmed the blackbody character of the microwave background to high accuracy (Mather et al., 1990), and will have the capability to detect other cosmic backgrounds throughout the infrared. A detection of cosmic background radiation dating from the pregalactic era would have important consequences for theories of cosmic structure. During the creation of such a background the pressure of the radiation itself causes an instability which leads inevitably to the growth of large-scale structure in the matter distribution. In contrast to conventional gravitational-instability models, the statistical properties of this structure are determined primarily by the self-organizing dynamics of the instability rather than details of cosmological initial conditions. The behavior of the instability is described here.

  7. Instabilities of High Temperature Superconductors

    PubMed Central

    Matthias, B. T.; Corenzwit, E.; Cooper, A. S.; Longinotti, L. D.

    1971-01-01

    We have observed the transition temperature of both the cubic and tetragonal phases of several high-temperature β-W superconductors. The instability of the cubic lattice appears to be characteristic of high-temperature superconductors. PMID:16591897

  8. Instability-driven quantum dots

    NASA Astrophysics Data System (ADS)

    Aqua, Jean-Noël; Frisch, Thomas

    2015-10-01

    When a film is strained in two dimensions, it can relax by developing a corrugation in the third dimension. We review here the resulting morphological instability that occurs by surface diffusion, called the Asaro-Tiller-Grinfel'd instability (ATG), especially on the paradigmatic silicon/germanium system. The instability is dictated by the balance between the elastic relaxation induced by the morphological evolution, and its surface energy cost. We focus here on its development at the nanoscales in epitaxial systems when a crystal film is coherently deposited on a substrate with a different lattice parameter, thence inducing epitaxial stresses. It eventually leads to the self-organization of quantum dots whose localization is dictated by the instability long-time dynamics. In these systems, new effects, such as film/substrate wetting or crystalline anisotropy, come into play and lead to a variety of behaviors. xml:lang="fr"

  9. Fluid Instabilities inside Astrophysical Explosions

    NASA Astrophysics Data System (ADS)

    Chen, Ke-Jung; Woosley, Stan; Heger, Alexander; Almgren, Ann; Zheng, Weiqun

    2014-11-01

    We present our results from the simulations of fluid instabilities inside supernovae with a new radiation-hydrodynamic code, CASTRO. Massive stars are ten times more massive than Sun. Observational and theoretical studies suggest that these massive stars tend to end their lives with energetic explosions, so-called supernovae. Many fluid instabilities occur during the supernova explosions. The fluid instabilities can be driven by hydrodynamics, nuclear burning, or radiation. In this talk, we discuss about the possible physics of fluid instabilities found in our simulations and how the resulting mixing affects the observational signatures of supernovae. This work was supported by the DOE HEP Program under contract DE-SC0010676; the National Science Foundation (AST 0909129) and the NASA Theory Program (NNX14AH34G).

  10. Waves and instabilities in plasmas

    SciTech Connect

    Chen, L.

    1987-01-01

    The contents of this book are: Plasma as a Dielectric Medium; Nyquist Technique; Absolute and Convective Instabilities; Landau Damping and Phase Mixing; Particle Trapping and Breakdown of Linear Theory; Solution of Viasov Equation via Guilding-Center Transformation; Kinetic Theory of Magnetohydrodynamic Waves; Geometric Optics; Wave-Kinetic Equation; Cutoff and Resonance; Resonant Absorption; Mode Conversion; Gyrokinetic Equation; Drift Waves; Quasi-Linear Theory; Ponderomotive Force; Parametric Instabilities; Problem Sets for Homework, Midterm and Final Examinations.

  11. Material Instabilities in Particulate Systems

    NASA Technical Reports Server (NTRS)

    Goddard, J. D.

    1999-01-01

    Following is a brief summary of a theoretical investigation of material (or constitutive) instability associated with shear induced particle migration in dense particulate suspensions or granular media. It is shown that one can obtain a fairly general linear-stability analysis, including the effects of shear-induced anisotropy in the base flow as well as Reynolds dilatancy. A criterion is presented here for simple shearing instability in the absence of inertia and dilatancy.

  12. Aerodynamic instability: A case history

    NASA Technical Reports Server (NTRS)

    Eisenmann, R. C.

    1985-01-01

    The identification, diagnosis, and final correction of complex machinery malfunctions typically require the correlation of many parameters such as mechanical construction, process influence, maintenance history, and vibration response characteristics. The progression is reviewed of field testing, diagnosis, and final correction of a specific machinery instability problem. The case history presented addresses a unique low frequency instability problem on a high pressure barrel compressor. The malfunction was eventually diagnosed as a fluidic mechanism that manifested as an aerodynamic disturbance to the rotor assembly.

  13. Astrophysical Weibel instability in counterstreaming laser-produced plasmas

    NASA Astrophysics Data System (ADS)

    Fox, William; Fiksel, Gennady; Bhattacharjee, Amitava; Change, Po-Yu; Germaschewski, Kai; Hu, Suxing; Nilson, Philip

    2014-06-01

    Astrophysical shock waves play diverse roles, including energizing cosmic rays in the blast waves of astrophysical explosions, and generating primordial magnetic fields during the formation of galaxies and clusters. These shocks are typically collisionless and require collective electromagnetic fields to couple the upstream and downstream plasmas. The Weibel instability has been proposed to provide the requisite interaction mechanism for shock formation in weakly-magnetized shocks by generating turbulent electric and magnetic fields in the shock front. This work presents the first laboratory identification of this Weibel instability between counterstreaming supersonic plasma flows and confirms its basic features, a significant step towards understanding these shocks. In the experiments, conducted on the OMEGA EP laser facility at the University of Rochester, a pair of plasmas plumes are generated by irradiating of a pair of opposing parallel plastic (CH) targets. The ion-ion interaction between the two plumes is collisionless, so as the plumes interpenetrate, supersonic, counterstreaming ion flow conditions are obtained. Electromagnetic fields formed in the interaction of the two plumes were probed with an ultrafast laser-driven proton beam, and we observed the growth of a highly striated, transverse instability with extended filaments parallel to the flows. The instability is identified as an ion-driven Weibel instability through agreement with analytic theory and particle-in-cell simulations, paving the way for further detailed laboratory study of this instability and its consequences for particle energization and shock formation.[1] W. Fox, G. Fiksel, A. Bhattacharjee, P. Y. Chang, K. Germaschewski, S. X. Hu, and P. M. Nilson, “Filamentation instability of counterstreaming laser-driven plasmas,” Phys. Rev. Lett. 111, 225002 (2013).

  14. Pattern Formation in Convective Instabilities

    NASA Astrophysics Data System (ADS)

    Friedrich, R.; Bestehorn, M.; Haken, H.

    The present article reviews recent progress in the study of pattern formation in convective instabilities. After a brief discussion of the relevant basic hydrodynamic equations as well as a short outline of the mathematical treatment of pattern formation in complex systems the self-organization of spatial and spatio-temporal structures due to convective instabilities is considered. The formation of various forms of convective patterns arising in the Bénard experiment, i.e. in a horizontal fluid layer heated from below, is discussed. Then the review considers pattern formation in the Bénard instability in spherical geometries. In that case it can be demonstrated how the interaction among several convective cells may lead to time dependent as well as chaotic evolution of the spatial structures. Finally, the convective instability in a binary fluid mixture is discussed. In contrast to the instability in a single component fluid the instability may be oscillatory. In that case convection sets in in the form of travelling wave patterns which in addition to a complicated and chaotic temporal behaviour exhibit more or less spatial irregularity already close to threshold.

  15. Instability of enclosed horizons

    NASA Astrophysics Data System (ADS)

    Kay, Bernard S.

    2015-03-01

    We point out that there are solutions to the scalar wave equation on dimensional Minkowski space with finite energy tails which, if they reflect off a uniformly accelerated mirror due to (say) Dirichlet boundary conditions on it, develop an infinite stress-energy tensor on the mirror's Rindler horizon. We also show that, in the presence of an image mirror in the opposite Rindler wedge, suitable compactly supported arbitrarily small initial data on a suitable initial surface will develop an arbitrarily large stress-energy scalar near where the two horizons cross. Also, while there is a regular Hartle-Hawking-Israel-like state for the quantum theory between these two mirrors, there are coherent states built on it for which there are similar singularities in the expectation value of the renormalized stress-energy tensor. We conjecture that in other situations with analogous enclosed horizons such as a (maximally extended) Schwarzschild black hole in equilibrium in a (stationary spherical) box or the (maximally extended) Schwarzschild-AdS spacetime, there will be similar stress-energy singularities and almost-singularities—leading to instability of the horizons when gravity is switched on and matter and gravity perturbations are allowed for. All this suggests it is incorrect to picture a black hole in equilibrium in a box or a Schwarzschild-AdS black hole as extending beyond the past and future horizons of a single Schwarzschild (/Schwarzschild-AdS) wedge. It would thus provide new evidence for 't Hooft's brick wall model while seeming to invalidate the picture in Maldacena's ` Eternal black holes in AdS'. It would thereby also support the validity of the author's matter-gravity entanglement hypothesis and of the paper ` Brick walls and AdS/CFT' by the author and Ortíz.

  16. Fast ion effects on magnetic instabilities in the PDX tokamak

    SciTech Connect

    Buchenauer, D.A.J.

    1985-01-01

    A study of the modification and excitation of nondisruptive magnetic instabilities due to near perpendicular neutral beam injection on the PDX tokamak was made to determine the importance of these instabilities at low q. The instabilities consisted of resistive MHD modes, beam driven ideal MHD modes, and beam driven ion cyclotron modes. Evidence of enhanced transport (beyond the anomalous transport associated with auxiliary heating) is presented for several of these instabilities as well as comparison of the experimental results with theory. The main results can be summarized as follows: (1) The loss of electron thermal energy due to sawteeth oscillations, although small, increases with increasing auxiliary power and decreasing q, but it was suppressed with high power perpendicular injection due to a loss of the beam ions. (2) m = 2 resistive modes have a disastrous effect on the achieved density, but at present power levels, they can be controlled. (3) Evidence from Mirnov coils, soft x-ray emission, neutron emission, and fast charge-exchange flux indicates that a degradation of the global energy confinement above ..beta../sub T/q approx. = 0.045 is due to a rapid loss of beam ions from the bulk plasma (fishbone instability).

  17. [Surgical treatment of craniocervical instability. Review paper].

    PubMed

    Alpizar-Aguirre, Armando; Lara Cano, Jorge Giovanni; Rosales, Luis; Míramontes, Victor; Reyes-Sánchez, Alejandro Antonio

    2007-01-01

    The concept of spinal instability is still controversial. Anatomical, biomechanical, clinical and radiographic variants are involved and make the definition complicated. There are solid diagnostic bases in cases of fractures and degenerative disorders; however, pure spinal instability is still under study. The latter may be defined as increased mobility that goes beyond the physiological limits of one vertebra over another in at least one of the three spinal planes of motion. In the case of the craniocervical region, its understanding becomes even more challenging, since its anatomy and physiology are more complex and it is more mobile. Surgical treatment is possible with either an anterior or a posterior approach. Best results are obtained with occipitocervical or atlantoaxial stabilization through a posterior approach, since the anterior one has its limitations. For example, a transoral approach with a bone graft provides compression strength but does not enable immediate appropriate fixation and involves the risk of infection. The choice of the surgical approach must consider the patient's medical status, the specific spine levels involved, the extent of neurological compromise, the X-ray abnormalities and the individual pathology. The goals of surgery are achieved through an appropriate anatomical alignment, assuring the protection of the neural elements and achieving proper spine stabilization with as much preservation of the mobile vertebral segments as possible. PMID:17970561

  18. [Surgical treatment of craniocervical instability. Review paper].

    PubMed

    Alpizar-Aguirre, Armando; Lara Cano, Jorge Giovanni; Rosales, Luis; Míramontes, Victor; Reyes-Sánchez, Alejandro Antonio

    2007-01-01

    The concept of spinal instability is still controversial. Anatomical, biomechanical, clinical and radiographic variants are involved and make the definition complicated. There are solid diagnostic bases in cases of fractures and degenerative disorders; however, pure spinal instability is still under study. The latter may be defined as increased mobility that goes beyond the physiological limits of one vertebra over another in at least one of the three spinal planes of motion. In the case of the craniocervical region, its understanding becomes even more challenging, since its anatomy and physiology are more complex and it is more mobile. Surgical treatment is possible with either an anterior or a posterior approach. Best results are obtained with occipitocervical or atlantoaxial stabilization through a posterior approach, since the anterior one has its limitations. For example, a transoral approach with a bone graft provides compression strength but does not enable immediate appropriate fixation and involves the risk of infection. The choice of the surgical approach must consider the patient's medical status, the specific spine levels involved, the extent of neurological compromise, the X-ray abnormalities and the individual pathology. The goals of surgery are achieved through an appropriate anatomical alignment, assuring the protection of the neural elements and achieving proper spine stabilization with as much preservation of the mobile vertebral segments as possible.

  19. Instabilities and Structure Evolution in Radiative Shocks

    NASA Astrophysics Data System (ADS)

    Doss, F. W.; Drake, R. P.; Visco, A. J.; Kuranz, C. C.; Grosskopf, M. J.; Reighard, A. B.; Knauer, J.

    2007-11-01

    Radiative shocks, systems in which radiation transport across the shock front contributes substantially to the properties and dynamics of the shock, occur frequently in astrophysical systems, motivating our high-energy-density experiments. Recent laser-driven experiments have produced collapsed shocks by launching 10-20 μm drive disks of Be into shock tubes of Xe gas at atmospheric pressure. This method produces strongly radiative shocks at well over 100 km/sec. Experiments using x-ray pinhole radiography of collapsed radiative shocks have revealed evidence of structure evolution, perhaps through instability mechanisms. Recent experiments provided simultaneous normal and oblique data. Theoretical work related to structure growth will also be reported. This research was sponsored by the NNSA through DOE Research Grants DE-FG52-07NA28058, DE-FG52-04NA0064, and the NNSA Stewardship Science Graduate Fellowship.

  20. Ab initio determination of the instability growth rate of warm dense beryllium-deuterium interface

    SciTech Connect

    Wang, Cong; Zhang, Ping; Li, Zi; Li, DaFang

    2015-10-15

    Accurate knowledge about the interfacial unstable growth is of great importance in inertial confinement fusion. During implosions, the deuterium-tritium capsule is driven by laser beams or X-rays to access the strongly coupled and partially degenerated warm dense matter regime. At this stage, the effects of dissipative processes, such as diffusion and viscosity, have significant impact on the instability growth rates. Here, we present ab initio molecular dynamics simulations to determine the equations of state and the transport coefficients. Several models are used to estimate the reduction in the growth rate dispersion curves of Rayleigh-Taylor and Richtmyer-Meshkov instabilities with considering the presence of these dissipative effects. We show that these instability growth rates are effectively reduced when considering diffusion. The findings provide significant insights into the microscopic mechanism of the instability growth at the ablator-fuel interface and will refine the models used in the laser-driven hydrodynamic instability experiments.

  1. Three-dimensional non-linear instability of spontaneous fast magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Shimizu, T.; Kondoh, K.; Ugai, M.

    2009-05-01

    Three-dimensional instability of spontaneous fast magnetic reconnection is studied using MHD (magnetohydro- dynamic) simulation. Previous two-dimensional MHD studies have demonstrated that, if a current-driven anomalous resistivity is assumed, two-dimensional fast magnetic reconnection occurs and two-dimensional largescale magnetic loops, i.e., plasmoids, are ejected from the reconnection region. In most two-dimensional MHD studies, the structure of the current sheet is initially one-dimensinal. On the other hand, in recent space plasma observations, fully three-dimensional magnetic loops frequently appear even in the almost one-dimensional current sheet. This suggests that the classical two-dimensional fast magnetic reconnection may be unstable to any three-dimensional perturbation, resulting in three-dimensional fast magnetic reconnection. In this paper, we show that a three-dimensional resistive perturbation destabilizes two-dimensional fast magnetic reconnection and results in three-dimensional fast magnetic reconnection. The resulting three-dimensional fast reconnection repeatedly ejects three-dimensional magnetic loops downstream. The obtained numerical results are similar to the pulsating downflows observed in solar flares. According to the Fourier analysis of the ejected magnetic loops, the time evolution of this three-dimensional instability is fully non-linear.

  2. Beta-limiting Instabilities and Global Mode Stabilization in NSTX

    NASA Astrophysics Data System (ADS)

    Sabbagh, Steven

    2001-10-01

    Low aspect ratio and high edge q theoretically alter the plasma stability and mode structure compared to standard tokamak configurations. Below the no-wall limit, stability calculations with PEST, GATO, and DCON show the perturbed radial field is maximized near the center column and DCON and VALEN calculations show that mode stability is not greatly improved by a nearby conducting wall due to the short poloidal wavelength in this region. In contrast, as beta reaches and exceeds the no-wall limit, the mode becomes strongly ballooning with long poloidal wavelength at large major radius and is highly wall stabilized. In this way, wall stabilization is more effective at higher beta in low aspect ratio geometry. Research on the stability of spherical torus plasmas at and above the no-wall beta limit is being addressed on NSTX, which has produced low aspect ratio plasmas, R/a = 1.27 at plasma current up to 1.4 MA with high energy confinement (TauE/TauE-ITER89P = 2). Toroidal and normalized beta have reached 22%, and 4.3, respectively in q = 7 plasmas. The beta limit is observed to increase with increasing plasma internal inductance, li, and the stability factor betaN/li has reached 5.8, limited by sudden beta collapses at low li that was achieved by use of high-harmonic fast wave heating (HHFW). DCON stability analysis of equilibria reconstructed with EFIT using external magnetics show that the plasmas are below or at the no-wall beta limit for the n = 1 mode, which has characteristics of a current-driven kink. With more peaked current profiles (li greater than 0.7), core MHD instabilities are observed which saturate or slowly degrade beta. Sawteeth with large inversion radii can also cause substantial beta collapses, although current profile modification using HHFW, altered plasma growth, and increased toroidal field have each been successful in mitigating this effect.

  3. The Energetics of Centrifugal Instability

    NASA Astrophysics Data System (ADS)

    Dewar, W. K.; Jiao, Y.

    2014-12-01

    A recent study has argued that the California Undercurrent, and poleward eastern boundary currents in general, generate mixing events through centrifugal instability (CI). Conditions favorable for CI are created by the strong horizontal shears developed in turbulent bottom layers of currents flowing in the direction of topographic waves. At points of abrupt topographic change, like promontories and capes, the coastal current separates from the boundary and injects gravitationally stable but dynamically unstable flow into the interior. The resulting finite amplitude development of the instability involves overturnings and diabatic mixing. The purpose of this study is to examine the energetics of CI in order to characterize it as has been done for other instabilities and develop a framework in which to estimate its regional and global impacts. We argue that CI is roughly twice as efficient at mixing as is Kelvin-Helmholtz instability, and that roughly 10% of the initial energy in a CUC-like current is lost to either local mixing or the generation of unbalanced flows. The latter probably leads to non-local mixing. Thus centrifugal instability is an effective process by which energy is lost from the balanced flow and spent in mixing neighboring water masses. We argue the importance of the mixing is regional in nature, but of less importance to the global budgets given its regional specificity.

  4. Interfacial Instability during Granular Erosion

    NASA Astrophysics Data System (ADS)

    Lefebvre, Gautier; Merceron, Aymeric; Jop, Pierre

    2016-02-01

    The complex interplay between the topography and the erosion and deposition phenomena is a key feature to model granular flows such as landslides. Here, we investigated the instability that develops during the erosion of a wet granular pile by a dry dense granular flow. The morphology and the propagation of the generated steps are analyzed in relation to the specific erosion mechanism. The selected flowing angle of the confined flow on a dry heap appears to play an important role both in the final state of the experiment, and for the shape of the structures. We show that the development of the instability is governed by the inertia of the flow through the Froude number. We model this instability and predict growth rates that are in agreement with the experiment results.

  5. Hydrodynamick instabilities on ICF capsules

    SciTech Connect

    Haan, S.W.

    1991-06-07

    This article summarizes our current understanding of hydrodynamic instabilities as relevant to ICF. First we discuss classical, single mode Rayleigh-Taylor instability, and nonlinear effects in the evolution of a single mode. Then we discuss multimode systems, considering: (1) the onset of nonlinearity; (2) a second order mode coupling theory for weakly nonlinear effects, and (3) the fully nonlinear regime. Two stabilization mechanisms relevant to ICF are described next: gradient scale length and convective stabilization. Then we describe a model which is meant to estimate the weakly nonlinear evolution of multi-mode systems as relevant to ICF, given the short-wavelength stabilization. Finally, we discuss the relevant code simulation capability, and experiments. At this time we are quite optimistic about our ability to estimate instability growth on ICF capsules, but further experiments and simulations are needed to verify the modeling. 52 refs.

  6. Instability of EDS maglev systems

    SciTech Connect

    Cai, Y.; Chen, S.S.

    1993-09-01

    Instabilities of an EDS maglev suspension system with 3 D.O.F. and 5 D.O.F. vehicles traveling on a double L-shaped set of guideway conductors have been investigated with various experimentally measured magnetical force data incorporated into the theoretical models. Divergence and flutter are obtained from both analytical and numerical solutions for coupled vibration of the 3 D.O.F. maglev vehicle model. Instabilities of five direction motions (heave, slip, rill, pitch and yaw) are observed for the 4 D.O.F. vehicle model. It demonstrates that system parameters, such as, system damping, vehicle geometry and coupling effects among five different motions play very important roles in the occurrence of dynamic instabilities of maglev vehicles.

  7. Performance through Deformation and Instability

    NASA Astrophysics Data System (ADS)

    Bertoldi, Katia

    2015-03-01

    Materials capable of undergoing large deformations like elastomers and gels are ubiquitous in daily life and nature. An exciting field of engineering is emerging that uses these compliant materials to design active devices, such as actuators, adaptive optical systems and self-regulating fluidics. Compliant structures may significantly change their architecture in response to diverse stimuli. When excessive deformation is applied, they may eventually become unstable. Traditionally, mechanical instabilities have been viewed as an inconvenience, with research focusing on how to avoid them. Here, I will demonstrate that these instabilities can be exploited to design materials with novel, switchable functionalities. The abrupt changes introduced into the architecture of soft materials by instabilities will be used to change their shape in a sudden, but controlled manner. Possible and exciting applications include materials with unusual properties such negative Poisson's ratio, phononic crystals with tunable low-frequency acoustic band gaps and reversible encapsulation systems.

  8. Faraday instability in deformable domains

    NASA Astrophysics Data System (ADS)

    Pucci, Giuseppe; Ben Amar, Martine; Couder, Yves

    2014-11-01

    We investigate the Faraday instability in floating liquid lenses, as an example of hydrodynamic instability that develops in a domain with flexible boundaries. We show that a mutual adaptation of the instability pattern and the domain shape occurs, as a result of the competition between the wave radiation pressure and the capillary response of the lens border. Two archetypes of behaviour are observed. In the first, stable shapes are obtained experimentally and predicted theoretically as the exact solutions of a Riccati equation, and they result from the equilibrium between wave radiation pressure and capillarity. In the second, the radiation pressure exceeds the capillary response of the lens border and leads to non-equilibrium behaviours, with breaking into smaller domains that have a complex dynamics including spontaneous propagation. The authors are grateful to Université Franco-Italienne (UFI) for financial support.

  9. Interfacial instabilities and Kapitsa pendula

    NASA Astrophysics Data System (ADS)

    Krieger, Madison

    2015-11-01

    Determining the critera for onset and amplitude growth of instabilities is one of the central problems of fluid mechanics. We develop a parallel between the Kapitsa effect, in which a pendulum subject to high-frequency low-amplitude vibrations becomes stable in the inverted position, and interfaces separating fluids of different density. It has long been known that such interfaces can be stabilized by vibrations, even when the denser fluid is on top. We demonstrate that the stability diagram for these fluid interfaces is identical to the stability diagram for an appopriate Kapitsa pendulum. We expand the robust, ``dictionary''-type relationship between Kapitsa pendula and interfacial instabilities by considering the classical Rayleigh-Taylor, Kelvin-Helmholtz and Plateau instabilities, as well as less-canonical examples ranging in scale from the micron to the width of a galaxy.

  10. Stellar explosions, instabilities, and turbulence

    SciTech Connect

    Drake, R. P.; Kuranz, C. C.; Miles, A. R.; Muthsam, H. J.; Plewa, T.

    2009-04-15

    It has become very clear that the evolution of structure during supernovae is centrally dependent on the pre-existing structure in the star. Modeling of the pre-existing structure has advanced significantly, leading to improved understanding and to a physically based assessment of the structure that will be present when a star explodes. It remains an open question whether low-mode asymmetries in the explosion process can produce the observed effects or whether the explosion mechanism somehow produces jets of material. In any event, the workhorse processes that produce structure in an exploding star are blast-wave driven instabilities. Laboratory experiments have explored these blast-wave-driven instabilities and specifically their dependence on initial conditions. Theoretical work has shown that the relative importance of Richtmyer-Meshkov and Rayleigh-Taylor instabilities varies with the initial conditions and does so in ways that can make sense of a range of astrophysical observations.

  11. Gravitational instabilities in protostellar disks

    NASA Technical Reports Server (NTRS)

    Tohline, J. E.

    1994-01-01

    The nonaxisymmetric stability of self-gravitating, geometrically thick accretion disks has been studied for protostellar systems having a wide range of disk-to-central object mass ratios. Global eigenmodes with four distinctly different characters were identified using numerical, nonlinear hydrodynamic techniques. The mode that appears most likely to arise in normal star formation settings, however, resembles the 'eccentric instability' that was identified earlier in thin, nearly Keplerian disks: It presents an open, one-armed spiral pattern that sweeps continuously in a trailing direction through more than 2-pi radians, smoothly connecting the inner and outer edges of the disk, and requires cooperative motion of the point mass for effective amplification. This particular instability promotes the development of a single, self-gravitating clump of material in orbit about the point mass, so its routine appearance in our simulations supports the conjecture that the eccentric instability provides a primary route to the formation of short-period binaries in protostellar systems.

  12. Interfacial Instability during Granular Erosion.

    PubMed

    Lefebvre, Gautier; Merceron, Aymeric; Jop, Pierre

    2016-02-12

    The complex interplay between the topography and the erosion and deposition phenomena is a key feature to model granular flows such as landslides. Here, we investigated the instability that develops during the erosion of a wet granular pile by a dry dense granular flow. The morphology and the propagation of the generated steps are analyzed in relation to the specific erosion mechanism. The selected flowing angle of the confined flow on a dry heap appears to play an important role both in the final state of the experiment, and for the shape of the structures. We show that the development of the instability is governed by the inertia of the flow through the Froude number. We model this instability and predict growth rates that are in agreement with the experiment results. PMID:26919014

  13. Chondral Injury in Patellofemoral Instability

    PubMed Central

    Lustig, Sébastien; Servien, Elvire; Neyret, Philippe

    2014-01-01

    Objective: Patellofemoral instability is common and affects a predominantly young age group. Chondral injury occurs in up to 95%, and includes osteochondral fractures and loose bodies acutely and secondary degenerative changes in recurrent cases. Biomechanical abnormalities, such as trochlear dysplasia, patella alta, and increased tibial tuberosity-trochlear groove distance, predispose to both recurrent dislocations and patellofemoral arthrosis. Design: In this article, we review the mechanisms of chondral injury in patellofemoral instability, diagnostic modalities, the distribution of lesions seen in acute and episodic dislocation, and treatments for articular cartilage lesions of the patellofemoral joint. Results: Little specific evidence exists for cartilage treatments in patellofemoral instability. In general, the results of reparative and restorative procedures in the patellofemoral joint are inferior to those observed in other compartments of the knee. Conclusion: Given the increased severity of chondral lesions and progression to osteoarthritis seen with recurrent dislocations, careful consideration should be given to early stabilisation in patients with predisposing factors. PMID:26069693

  14. Beam instabilities in hadron synchrotrons

    DOE PAGESBeta

    Metral, E.; T. Argyropoulos; Bartosik, H.; Biancacci, N.; Buffat, X.; Esteban Muller, J. F.; Herr, W.; Iadarola, G.; Lasheen, A.; Li, K.; et al

    2016-04-01

    Beam instabilities cover a wide range of effects in particle accelerators and they have been the subjects of intense research for several decades. As the machines performance was pushed new mechanisms were revealed and nowadays the challenge consists in studying the interplays between all these intricate phenomena, as it is very often not possible to treat the different effects separately. Furthermore, the aim of this paper is to review the main mechanisms, discussing in particular the recent developments of beam instability theories and simulations.

  15. Hopf bifurcation and plasma instabilities

    SciTech Connect

    Crawford, J.D.

    1983-11-01

    Center manifold theory and the theory of normal forms are applied to examples of Hopf bifurcation in two models of plasma dynamics. A finite dimensional model of a 3-wave system with quadratic nonlinearities provides a simple example of both supercritical and subcritical Hopf bifurcation. In the second model, the electrostatic instabilities of a collisional plasma correspond to Hopf bifurcations. In this problem, the Vlasov-Poisson equations with a Krook collision term describe the electron dynamics in a weakly ionized gas. The one mode in instability is analyzed in detail; near criticality it always saturates in a small amplitude nonlinear oscillation.

  16. Undulation Instability of Epithelial Tissues

    NASA Astrophysics Data System (ADS)

    Basan, Markus; Joanny, Jean-François; Prost, Jacques; Risler, Thomas

    2011-04-01

    Treating the epithelium as an incompressible fluid adjacent to a viscoelastic stroma, we find a novel hydrodynamic instability that leads to the formation of protrusions of the epithelium into the stroma. This instability is a candidate for epithelial fingering observed in vivo. It occurs for sufficiently large viscosity, cell-division rate and thickness of the dividing region in the epithelium. Our work provides physical insight into a potential mechanism by which interfaces between epithelia and stromas undulate and potentially by which tissue dysplasia leads to cancerous invasion.

  17. Lending sociodynamics and economic instability

    NASA Astrophysics Data System (ADS)

    Hawkins, Raymond J.

    2011-11-01

    We show how the dynamics of economic instability and financial crises articulated by Keynes in the General Theory and developed by Minsky as the Financial Instability Hypothesis can be formalized using Weidlich’s sociodynamics of opinion formation. The model addresses both the lending sentiment of a lender in isolation as well as the impact on that lending sentiment of the behavior of other lenders. The risk associated with lending is incorporated through a stochastic treatment of loan dynamics that treats prepayment and default as competing risks. With this model we are able to generate endogenously the rapid changes in lending opinion that attend slow changes in lending profitability and find these dynamics to be consistent with the rise and collapse of the non-Agency mortgage-backed securities market in 2007/2008. As the parameters of this model correspond to well-known phenomena in cognitive and social psychology, we can both explain why economic instability has proved robust to advances in risk measurement and suggest how policy for reducing economic instability might be formulated in an experimentally sound manner.

  18. Finite element shell instability analysis

    NASA Technical Reports Server (NTRS)

    1975-01-01

    Formulation procedures and the associated computer program for finite element thin shell instability analysis are discussed. Data cover: (1) formulation of basic element relationships, (2) construction of solution algorithms on both the conceptual and algorithmic levels, and (3) conduction of numerical analyses to verify the accuracy and efficiency of the theory and related programs therein are described.

  19. The Chemistry of Beer Instability

    ERIC Educational Resources Information Center

    Stewart, Graham G.

    2004-01-01

    Brewing of beer, one of the oldest biotechnology industries was one of the earliest processes to be undertaken on commercial basis. Biological instability involves contamination of bacteria, yeast, or mycelia fungi and there is always a risk in brewing that beer can become contaminated by micro-organisms.

  20. Urge incontinence and detrusor instability.

    PubMed

    Jabs, C F; Stanton, S L

    2001-01-01

    Detrusor instability is a syndrome of urinary frequency, urgency and urge incontinence which can be demonstrated using urodynamic studies to document uninhibited bladder contractions. Idiopathic cases account for 90% and 10% are related to neurologic disorders. Several different treatment modalities are available, including bladder training/drill, electrical stimulation, medical and surgical therapies.

  1. Edge instabilities of topological superconductors

    NASA Astrophysics Data System (ADS)

    Hofmann, Johannes S.; Assaad, Fakher F.; Schnyder, Andreas P.

    2016-05-01

    Nodal topological superconductors display zero-energy Majorana flat bands at generic edges. The flatness of these edge bands, which is protected by time-reversal and translation symmetry, gives rise to an extensive ground-state degeneracy. Therefore, even arbitrarily weak interactions lead to an instability of the flat-band edge states towards time-reversal and translation-symmetry-broken phases, which lift the ground-state degeneracy. We examine the instabilities of the flat-band edge states of dx y-wave superconductors by performing a mean-field analysis in the Majorana basis of the edge states. The leading instabilities are Majorana mass terms, which correspond to coherent superpositions of particle-particle and particle-hole channels in the fermionic language. We find that attractive interactions induce three different mass terms. One is a coherent superposition of imaginary s -wave pairing and current order, and another combines a charge-density-wave and finite-momentum singlet pairing. Repulsive interactions, on the other hand, lead to ferromagnetism together with spin-triplet pairing at the edge. Our quantum Monte Carlo simulations confirm these findings and demonstrate that these instabilities occur even in the presence of strong quantum fluctuations. We discuss the implications of our results for experiments on cuprate high-temperature superconductors.

  2. Weathering instability and landscape evolution

    NASA Astrophysics Data System (ADS)

    Phillips, Jonathan D.

    2005-04-01

    The argument in this paper is that the fundamental control on landscape evolution in erosional landscapes is weathering. The possibility of and evidence for instability in weathering at four scales is examined. The four scales are concerned with weathering processes, allocation of weathered products, the interrelations of weathering and denudation, and the topographic and isostatic responses to weathering-limited denudation (the regolith, hillslope, landscape unit, and landscape scales, respectively). The stability conditions for each model, and the circumstances under which the models themselves are relevant, are used to identify scale-related domains of stability and instability. At the regolith scale, the interactions among weathering rates, resistance, and moisture are unstable, but there are circumstances—over long timescales and where weathering is well advanced—under which the instability is irrelevant. At the hillslope scale, the system is stable when denudation is transport rather than weathering limited and where no renewal of exposure via regolith stripping occurs. At the level of landscape units, the stability model is based entirely on the mutual reinforcements of weathering and erosion. While this should generally lead to instability, the model would be stable where other, external controls of both weathering and erosion rates are stronger than the weathering-erosion feedbacks. At the broadest landscape scale, the inclusion of isostatic responses destabilizes erosion-topography-uplift relationships. Thus, if the spatial or temporal scale is such that isostatic responses are not relevant, the system may be stable. Essentially, instability is prevalent at local spatial scales at all but the longest timescales. Stability at intermediate spatial scales is contingent on whether weathering-erosion feedbacks are strong or weak, with stability being more likely at shorter and less likely at longer timescales. At the broadest spatial scales, instability is

  3. Collisionless shock experiments with lasers and observation of Weibel instabilities

    SciTech Connect

    Park, H.-S. Huntington, C. M.; Fiuza, F.; Levy, M. C.; Pollock, B. B.; Remington, B. A.; Ross, J. S.; Ryutov, D. D.; Turnbull, D. P.; Weber, S. V.; Drake, R. P.; Kuranz, C. C.; Froula, D. H.; Rosenberg, M.; Gregori, G.; Meinecke, J.; Koenig, M.; Kugland, N. L.; Lamb, D. Q.; Tzeferacos, P.; and others

    2015-05-15

    Astrophysical collisionless shocks are common in the universe, occurring in supernova remnants, gamma ray bursts, and protostellar jets. They appear in colliding plasma flows when the mean free path for ion-ion collisions is much larger than the system size. It is believed that such shocks could be mediated via the electromagnetic Weibel instability in astrophysical environments without pre-existing magnetic fields. Here, we present laboratory experiments using high-power lasers and investigate the dynamics of high-Mach-number collisionless shock formation in two interpenetrating plasma streams. Our recent proton-probe experiments on Omega show the characteristic filamentary structures of the Weibel instability that are electromagnetic in nature with an inferred magnetization level as high as ∼1% [C. M. Huntington et al., “Observation of magnetic field generation via the weibel instability in interpenetrating plasma flows,” Nat. Phys. 11, 173–176 (2015)]. These results imply that electromagnetic instabilities are significant in the interaction of astrophysical conditions.

  4. Towards Fully Diagnosed Ablative Rayleigh-Taylor Instability

    NASA Astrophysics Data System (ADS)

    Azechi, Hiroshi

    2002-11-01

    The Rayleigh-Taylor (RT) instability with material ablation through the unstable interface is the key physics that determines the success or failure of inertial fusion energy. The ablative RT instability has also general resemblance to hydrodynamic instabilities occurring in Type Ia supernovae and in interstellar clouds, such as the Eagle Nebula. In the laser fusion community, it is generally accepted that the Bodner-Takabe formula [1] with significant improvement by Betti [2] may predict correct dispersion relation of the growth rates of the ablative RT instability. However, there still exist theoretical uncertainties due to the different treatment of electron transport from the laser absorption region to the ablation region. The difference in the electron transport is most pronounced at short wavelength perturbation that is below spatial resolution of most x-ray imagers. The direct effect of the transport is the ablation density profile, which measurement is also a formidable task with conventional diagnostic techniques. We will present our RT growth as well as the ablation density measurements based on recently developed novel techniques of high spatial resolution: moir interferometry, penumbral imaging, and Fresnel-phase-zone-plate imaging. [1] S. Bodner, Phys. Rev. Lett. 33, 761 (1974); H. Takabe et al., Phys. Fluids 28, 3676 (1985). [2] R. Betti et al., Phys. Plasmas 5, 1446 (1998).

  5. Singlet and triplet instability theorems

    SciTech Connect

    Yamada, Tomonori; Hirata, So

    2015-09-21

    A useful definition of orbital degeneracy—form-degeneracy—is introduced, which is distinct from the usual energy-degeneracy: Two canonical spatial orbitals are form-degenerate when the energy expectation value in the restricted Hartree–Fock (RHF) wave function is unaltered upon a two-electron excitation from one of these orbitals to the other. Form-degenerate orbitals tend to have isomorphic electron densities and occur in the highest-occupied and lowest-unoccupied molecular orbitals (HOMOs and LUMOs) of strongly correlated systems. Here, we present a mathematical proof of the existence of a triplet instability in a real or complex RHF wave function of a finite system in the space of real or complex unrestricted Hartree–Fock wave functions when HOMO and LUMO are energy- or form-degenerate. We also show that a singlet instability always exists in a real RHF wave function of a finite system in the space of complex RHF wave functions, when HOMO and LUMO are form-degenerate, but have nonidentical electron densities, or are energy-degenerate. These theorems provide Hartree–Fock-theory-based explanations of Hund’s rule, a singlet instability in Jahn–Teller systems, biradicaloid electronic structures, and a triplet instability during some covalent bond breaking. They also suggest (but not guarantee) the spontaneous formation of a spin density wave (SDW) in a metallic solid. The stability theory underlying these theorems extended to a continuous orbital-energy spectrum proves the existence of an oscillating (nonspiral) SDW instability in one- and three-dimensional homogeneous electron gases, but only at low densities or for strong interactions.

  6. Singlet and triplet instability theorems

    NASA Astrophysics Data System (ADS)

    Yamada, Tomonori; Hirata, So

    2015-09-01

    A useful definition of orbital degeneracy—form-degeneracy—is introduced, which is distinct from the usual energy-degeneracy: Two canonical spatial orbitals are form-degenerate when the energy expectation value in the restricted Hartree-Fock (RHF) wave function is unaltered upon a two-electron excitation from one of these orbitals to the other. Form-degenerate orbitals tend to have isomorphic electron densities and occur in the highest-occupied and lowest-unoccupied molecular orbitals (HOMOs and LUMOs) of strongly correlated systems. Here, we present a mathematical proof of the existence of a triplet instability in a real or complex RHF wave function of a finite system in the space of real or complex unrestricted Hartree-Fock wave functions when HOMO and LUMO are energy- or form-degenerate. We also show that a singlet instability always exists in a real RHF wave function of a finite system in the space of complex RHF wave functions, when HOMO and LUMO are form-degenerate, but have nonidentical electron densities, or are energy-degenerate. These theorems provide Hartree-Fock-theory-based explanations of Hund's rule, a singlet instability in Jahn-Teller systems, biradicaloid electronic structures, and a triplet instability during some covalent bond breaking. They also suggest (but not guarantee) the spontaneous formation of a spin density wave (SDW) in a metallic solid. The stability theory underlying these theorems extended to a continuous orbital-energy spectrum proves the existence of an oscillating (nonspiral) SDW instability in one- and three-dimensional homogeneous electron gases, but only at low densities or for strong interactions.

  7. Singlet and triplet instability theorems.

    PubMed

    Yamada, Tomonori; Hirata, So

    2015-09-21

    A useful definition of orbital degeneracy—form-degeneracy—is introduced, which is distinct from the usual energy-degeneracy: Two canonical spatial orbitals are form-degenerate when the energy expectation value in the restricted Hartree-Fock (RHF) wave function is unaltered upon a two-electron excitation from one of these orbitals to the other. Form-degenerate orbitals tend to have isomorphic electron densities and occur in the highest-occupied and lowest-unoccupied molecular orbitals (HOMOs and LUMOs) of strongly correlated systems. Here, we present a mathematical proof of the existence of a triplet instability in a real or complex RHF wave function of a finite system in the space of real or complex unrestricted Hartree-Fock wave functions when HOMO and LUMO are energy- or form-degenerate. We also show that a singlet instability always exists in a real RHF wave function of a finite system in the space of complex RHF wave functions, when HOMO and LUMO are form-degenerate, but have nonidentical electron densities, or are energy-degenerate. These theorems provide Hartree-Fock-theory-based explanations of Hund's rule, a singlet instability in Jahn-Teller systems, biradicaloid electronic structures, and a triplet instability during some covalent bond breaking. They also suggest (but not guarantee) the spontaneous formation of a spin density wave (SDW) in a metallic solid. The stability theory underlying these theorems extended to a continuous orbital-energy spectrum proves the existence of an oscillating (nonspiral) SDW instability in one- and three-dimensional homogeneous electron gases, but only at low densities or for strong interactions. PMID:26395692

  8. Measurements of fast transition instability in RHIC

    SciTech Connect

    Ptitsyn, V.; Blaskiewicz, M.; Fischer, W.; Lee, R.; Zhang, S.Y.

    2010-05-23

    A fast transition instability presents a limiting factor for ion beam intensity in RHIC. Several pieces of evidence show that electron clouds play an important role in establishing the threshold of this instability. In RHIC Runs8 the measurements of the instability, using a button BPM, were done in order to observe details of the instability development on the scale over hundreds and thousands turns. The paper presents and discusses the results of those measurements in time and frequency domains.

  9. Mood instability: significance, definition and measurement.

    PubMed

    Broome, M R; Saunders, K E A; Harrison, P J; Marwaha, S

    2015-10-01

    Mood instability is common, and an important feature of several psychiatric disorders. We discuss the definition and measurement of mood instability, and review its prevalence, characteristics, neurobiological correlates and clinical implications. We suggest that mood instability has underappreciated transdiagnostic potential as an investigational and therapeutic target. PMID:26429679

  10. Control of laser plasma instabilities in hohlraums

    SciTech Connect

    Kruer, W.L.

    1996-12-01

    Laser plasma instabilities are an important constraint on the operating regime for inertial fusion. Many techniques have been developed to control the various laser-driven instabilities. Experiments with long scale length plasmas are testing these instability levels, the nonlinear regimes, and the control mechanisms.

  11. Particular Threshold Behavior of Dusty Plasma Instabilities

    SciTech Connect

    Mikikian, M.; Cavarroc, M.; Coueedel, L.; Tessier, Y.; Boufendi, L.

    2008-09-07

    We show that some experimentally observed instabilities, concerning the void region of a dust cloud, are similar to oscillations obtained in chemical systems or neuronal dynamics. The time evolution of these instabilities follows a well-defined process particularly visible in the instability shape and frequency.

  12. Transverse instability at the recycler ring

    SciTech Connect

    Ng, K.Y.; /Fermilab

    2004-10-01

    Sporadic transverse instabilities have been observed at the Fermilab Recycler Ring leading to increase in transverse emittances and beam loss. The driving source of these instabilities has been attributed to the resistive-wall impedance with space-charge playing an important role in suppressing Landau damping. Growth rates of the instabilities are computed. Remaining problems are discussed.

  13. X-RAY TRANSIENTS: HYPER- OR HYPO-LUMINOUS?

    SciTech Connect

    Lasota, Jean-Pierre; Dubus, Guillaume; King, Andrew R. E-mail: lasota@iap.fr

    2015-03-01

    The disk instability picture gives a plausible explanation for the behavior of soft X-ray transient systems if self-irradiation of the disk is included. We show that there is a simple relation between the peak luminosity (at the start of an outburst) and the decay timescale. We use this relation to place constraints on systems assumed to undergo disk instabilities. The observable X-ray populations of elliptical galaxies must largely consist of long-lived transients, as deduced on different grounds by Piro and Bildsten (2002). The strongly varying X-ray source HLX-1 in the galaxy ESO 243-49 can be modeled as disk instability of a highly super-Eddington stellar-mass binary similar to SS 433. A fit to the disk instability picture is not possible with an intermediate-mass black hole model for HLX-1. Other recently identified super-Eddington ULXs might be subject to disk instability.

  14. Generalized laser filamentation instability coupled to cooling instability

    SciTech Connect

    Liang, E.P.; Wong, J.; Garrison, J.

    1984-04-24

    We consider the propagation of laser light in an initially slightly nonuniform plasma. The classical dispersion relation for the laser filamentation growth rate (see e.g., B. Langdon, in the 1980 Lawrence Livermore National Laboratory Laser Program Annual Report, pp. 3-56, UCRL-50021-80, 1981) can be generalized to include other acoustical effects. For example, we find that the inclusion of potential imbalances in the heating and cooling rates of the ambient medium due to density and temperature perturbations can cause the laser filamentation mode to bifurcate into a cooling instability mode at long acoustic wavelengths. We also attempt to study semi-analytically the nonlinear evolution of this and related instabilities. These results have wide applications to a variety of chemical gas lasers and phenomena related to laser-target interactions (e.g., jet-like behavior).

  15. Amplitude Equation for Instabilities Driven at Deformable Surfaces - Rosensweig Instability

    NASA Astrophysics Data System (ADS)

    Pleiner, Harald; Bohlius, Stefan; Brand, Helmut R.

    2008-11-01

    The derivation of amplitude equations from basic hydro-, magneto-, or electrodynamic equations requires the knowledge of the set of adjoint linear eigenvectors. This poses a particular problem for the case of a free and deformable surface, where the adjoint boundary conditions are generally non-trivial. In addition, when the driving force acts on the system via the deformable surface, not only Fredholm's alternative in the bulk, but also the proper boundary conditions are required to get amplitude equations. This is explained and demonstrated for the normal field (or Rosensweig) instability in ferrofluids as well as in ferrogels. An important aspect of the problem is its intrinsic dynamic nature, although at the end the instability is stationary. The resulting amplitude equation contains cubic and quadratic nonlinearities as well as first and (in the gel case) second order time derivatives. Spatial variations of the amplitudes cannot be obtained by using simply Newell's method in the bulk.

  16. Interface instability modes in freezing colloidal suspensions: revealed from onset of planar instability

    PubMed Central

    Wang, Lilin; You, Jiaxue; Wang, Zhijun; Wang, Jincheng; Lin, Xin

    2016-01-01

    Freezing colloidal suspensions widely exists in nature and industry. Interface instability has attracted much attention for the understandings of the pattern formation in freezing colloidal suspensions. However, the interface instability modes, the origin of the ice banding or ice lamellae, are still unclear. In-situ experimental observation of the onset of interface instability remains absent up to now. Here, by directly imaging the initial transient stage of planar interface instability in directional freezing colloidal suspensions, we proposed three interface instability modes, Mullins-Sekerka instability, global split instability and local split instability. The intrinsic mechanism of the instability modes comes from the competition of the solute boundary layer and the particle boundary layer, which only can be revealed from the initial transient stage of planar instability in directional freezing. PMID:26996630

  17. Front instability in stratified media

    NASA Astrophysics Data System (ADS)

    Beltrame, Philippe

    2013-04-01

    Preferential flow in unsaturated soil may due to local heterogeneities like worm burrows but also to front instability leading to unstable finger flow (fingered pattern) in sandy textured soils. This last spontaneous preferential flow cannot be described by the standard Richards equation. Cueto-Felgueroso and Juanes proposed recently a phase field model in order to take into account a macroscopic surface tension effect at the front [1]. Their model simulates successfully the interface instability of an advancing front. We aim at simulating and understanding front instability passing a textural soil discontinuity for which the finger flow is particularly visible. We consider sand layers with different characteristics such as granulometry. Moreover, the wettability is taken into account by adding a hydrophobic term in the free energy of the phase field model. The hydrophobicity part is not only relevant for repellent soil but also to model the ultra-thin films [2]. Therefore, in our framework, this may have an influence at the front because the water saturation is nearly zero. Such a wettability influence on infiltration in porous media has recently been measured in [3]. The governing equation is analogous to the lubrication equation for which we pointed out the specific numerical difficulties [4]. A numerical code to perform time integration and bifurcation analysis was developed in [4] allowing to determine the onset of instability and its resulting dynamics in the parameter space [5]. We compute the parameter range for which the front stops when reaching the layers interface. As in [4], there is two main mechanisms that allow water to cross over the discontinuity. A first mechanism, called «depinning», leads to an intermittent flow and the second one, to a front instability and then to a finger flow. There is a parameter domain where both instabilities are present leading to a complex spatio-temporal dynamics. Finally, it is noteworthy that the wettability

  18. A Numerical Study of Feathering Instability

    NASA Astrophysics Data System (ADS)

    Lee, Wing-Kit; Wang, Hsiang-Hsu

    2016-06-01

    The stability of a spiral shock of self-gravitating, magnetized interstellar medium is studied by performing two-dimensional numerical simulations of a local patch of tight-winding spiral arm. As previously suggested by the linear studies, two types of instabilities are identified, namely, wiggle instability and feathering instability. The former instability occurs in the hydrodynamics limit and results in short wavelength perturbations. On the other hand, the feathering instability requires both self-gravitating and magnetic fields and results in wider structures.

  19. New Instabilities in Line Driven Winds

    NASA Technical Reports Server (NTRS)

    Martens, P. C. H.

    1985-01-01

    The physical mechanisms which potentially lead to instabilities in line driven winds, the drift instability and the line shape instability, are discussed. A general three dimensional treatment of the stability problem of line driven winds which leads to the general dispersion equation is proposed. From this dispersion equation automatically a third physical mechanism driving instability in stellar winds is deduced; the thermal drift instability which is related to changes in absorption of radiation caused by temperature perturbations. This mechanism results in growing inwardly propagating sound waves.

  20. Effect of pressure anisotropy on magnetorotational instability

    SciTech Connect

    Mikhailovskii, A. B.; Lominadze, J. G. Churikov, A. P.; Erokhin, N. N.; Erokhin, N. S.; Tsypin, V. S

    2008-02-15

    It is shown that two new instabilities of hybrid type can occur in a rotating magnetized plasma with anisotropic pressure, i.e., the rotational firehose instability and the rotational mirror instability. In the case of {beta}{sub parallel} > {beta}{sub perpendicular}, where {beta}{sub parallel} and {beta}{sub -perpendicular} are the ratios of the parallel and perpendicular plasma pressure to the magnetic field pressure, the pressure anisotropy tends to suppress both new instabilities; in the case {beta}{sub perpendicular} > {beta}{sub parallel}, it leads to their strengthening. In the latter case, the perturbations considered can be unstable even if the Velikhov instability criterion is not satisfied.

  1. Lumbar instability: an evolving and challenging concept

    PubMed Central

    Beazell, James R; Mullins, Melise; Grindstaff, Terry L

    2010-01-01

    Identification and management of chronic lumbar spine instability is a clinical challenge for manual physical therapists. Chronic lumbar instability is presented as a term that can encompass two types of lumbar instability: mechanical (radiographic) and functional (clinical) instability (FLI). The components of mechanical and FLI are presented relative to the development of a physical therapy diagnosis and management. The purpose of this paper is to review the historical framework of chronic lumbar spine instability from a physical therapy perspective and to summarize current research relative to clinical diagnosis in physical therapy. PMID:21655418

  2. MHD Instabilities at the Heliopause

    SciTech Connect

    Dasgupta, B.; Florinski, V.; Heerikhuisen, J.; Zank, G. P.

    2006-09-26

    The heliopause (HP) is the outer edge of the heliosphere which separates the tenuous and hot heliosheath plasma on one side and the relatively dense and cool magnetized interstellar plasma on the other side. As a surface of tangential discontinuity, the HP is subjected to both Rayleigh-Taylor (RT) and Kelvin-Helmholtz (KH) instabilities. The coupling between plasma ions and neutral atoms through the process of charge exchange provides an ''effective gravity'' at the HP, while a shear flow exists across it. We derive analytically the linearized dispersion relation for waves propagating along the surface of this discontinuity, which represents a combined RT/KH analysis. We investigate both the purely hydrodynamic, as well as magnetohydrodynamic, cases, and find that interstellar and heliospheric magnetic fields can help stabilize the HP for RT and KH-type instabilities.

  3. Granular Rayleigh-Taylor instability

    SciTech Connect

    Vinningland, Jan Ludvig; Johnsen, Oistein; Flekkoey, Eirik G.; Maaloey, Knut Joergen; Toussaint, Renaud

    2009-06-18

    A granular instability driven by gravity is studied experimentally and numerically. The instability arises as grains fall in a closed Hele-Shaw cell where a layer of dense granular material is positioned above a layer of air. The initially flat front defined by the grains subsequently develops into a pattern of falling granular fingers separated by rising bubbles of air. A transient coarsening of the front is observed right from the start by a finger merging process. The coarsening is later stabilized by new fingers growing from the center of the rising bubbles. The structures are quantified by means of Fourier analysis and quantitative agreement between experiment and computation is shown. This analysis also reveals scale invariance of the flow structures under overall change of spatial scale.

  4. Instability of supersymmetric microstate geometries

    NASA Astrophysics Data System (ADS)

    Eperon, Felicity C.; Reall, Harvey S.; Santos, Jorge E.

    2016-10-01

    We investigate the classical stability of supersymmetric, asymptotically flat, microstate geometries with five non-compact dimensions. Such geometries admit an "evanescent ergosurface": a timelike hypersurface of infinite redshift. On such a surface, there are null geodesics with zero energy relative to infinity. These geodesics are stably trapped in the potential well near the ergosurface. We present a heuristic argument indicating that this feature is likely to lead to a nonlinear instability of these solutions. We argue that the precursor of such an instability can be seen in the behaviour of linear perturbations: nonlinear stability would require that all linear perturbations decay sufficiently rapidly but the stable trapping implies that some linear perturbation decay very slowly. We study this in detail for the most symmetric microstate geometries. By constructing quasinormal modes of these geometries we show that generic linear perturbations decay slower than any inverse power of time.

  5. Feedback control of resistive instabilities

    SciTech Connect

    White, R.B.; Rutherford, P.H.; Furth, H.P.; Park, W.; Chen, L.

    1985-12-01

    Resistive instabilities are responsible for much of the global behavior and the determination of the possible domains of operation of tokamaks. Their successful control could have definite advantages, even making available new regimes of operation. Elimination of sawtoothing might allow operation with higher currents and more peaked current profiles, with q on axis well below unity. In this work different feedback schemes are explored. Simple analytical derivations of the effects of local heating and current drive feedback are presented. Although control of modes with m greater than or equal to 2 is fairly straightforward, the control of the m = 1 mode is more difficult because of its proximity to ideal instability. The most promising scheme utilizes high energy trapped particles. 20 refs., 3 figs.

  6. Combustion instability modeling and analysis

    SciTech Connect

    Santoro, R.J.; Yang, V.; Santavicca, D.A.; Sheppard, E.J.

    1995-12-31

    It is well known that the two key elements for achieving low emissions and high performance in a gas turbine combustor are to simultaneously establish (1) a lean combustion zone for maintaining low NO{sub x} emissions and (2) rapid mixing for good ignition and flame stability. However, these requirements, when coupled with the short combustor lengths used to limit the residence time for NO formation typical of advanced gas turbine combustors, can lead to problems regarding unburned hydrocarbons (UHC) and carbon monoxide (CO) emissions, as well as the occurrence of combustion instabilities. The concurrent development of suitable analytical and numerical models that are validated with experimental studies is important for achieving this objective. A major benefit of the present research will be to provide for the first time an experimentally verified model of emissions and performance of gas turbine combustors. The present study represents a coordinated effort between industry, government and academia to investigate gas turbine combustion dynamics. Specific study areas include development of advanced diagnostics, definition of controlling phenomena, advancement of analytical and numerical modeling capabilities, and assessment of the current status of our ability to apply these tools to practical gas turbine combustors. The present work involves four tasks which address, respectively, (1) the development of a fiber-optic probe for fuel-air ratio measurements, (2) the study of combustion instability using laser-based diagnostics in a high pressure, high temperature flow reactor, (3) the development of analytical and numerical modeling capabilities for describing combustion instability which will be validated against experimental data, and (4) the preparation of a literature survey and establishment of a data base on practical experience with combustion instability.

  7. Secular instability of Saturn's rings.

    NASA Astrophysics Data System (ADS)

    Griv, E.; Chiueh, T.

    1996-07-01

    Kinetic theory with the Boltzmann and Poisson's equations is used to determine the stability and oscillations of the two-dimensional collisional system of identical particles of Saturn's rings. The effects of physical collisions between particles are taken into account by using in the Bolztmann kinetic equation a phenomenological Bhatnagar-Gross-Krook collisional integral (Bhatnagar et al. 1954). This model collisional integral was modified following Shu & Stewart (1985) to allow collisions to be inelastic. The dynamics of a system with rare collisions is considered, that is, {OMEGA}^2^>>ν_c_^2^, with {OMEGA} being the orbital angular frequency and ν_c_ the collision frequency. It is shown that in a Jeans-stable system the simultaneous action of self-gravity and collisions leads to a secular dissipative type instability. It is also shown that generally the growth rate of this aperiodic instability is small, Im ω_*_~ν_c_. However, in the marginally Jeans-stable gravitationally parts of the disk, the growth rate is a maximum, and may become a large, Im ω_*_=~(ν_cOMEGA^2^)^1/3^>>ν_c_. In such parts of the Saturn's system the instability will develop on the time scale only of several revolutions even at moderately low values of the local optical depth, τ=~ν_c_/{OMEGA}~0.1. The radial wavelength of the most unstable oscillations is of the order λ=~2πρ, where ρ=~c/{OMEGA} is the epicyclic radius and c is the mean dispersion of random velocities of particles. The secular instability may be suggested as the cause of much of the irregular, narrow ~2πρ~100m structure in low optical depth regions of Saturn's rings. Cassini spacecraft high-resolution images may resolve such hyperfine structure in the C ring, the inner B ring and the A ring.

  8. Migrational Instabilities in Particle Suspensions

    NASA Technical Reports Server (NTRS)

    Goddard, Joe D.

    1996-01-01

    This work deals with an instability arising from the shear-induced migration of particles in dense suspensions coupled with a dependence of viscosity on particle concentration. The analysis summarized here treats the inertialess (Re = O) linear stability of homogeneous simple shear flows for a Stokesian suspension model of the type proposed by Leighton and Acrivos (1987). Depending on the importance of shear-induced migration relative to concentration-driven diffusion, this model admits short-wave instability arising from wave-vector stretching by the base flow and evolving into particle-depleted shear bands. Moreover, this instability in the time-dependent problem corresponds to loss of ellipticity in the associated static problem (Re = O, Pe = O). While the isotropic version of the Leighton-Acrivos model is found to be stable with their experimentally determined parameters for simple shear, it is known that the stable model does not give a good quantitative description of particle clustering in the core of pipe flow (Nott and Brady 1994). This leads to the conjecture that an appropriate variant on the above model could explain such clustering as a two-phase bifurcation in the base flow.

  9. Hopf bifurcation and plasma instabilities

    SciTech Connect

    Crawford, J.D.

    1983-01-01

    In this research, center manifold theory and the theory of normal forms are applied to examples of Hopf bifurcation in two models of plasma dynamics. A finite dimensional model of a 3-wave system with quadratic nonlinearities provides a simple example of both supercritical and subcritical Hopf bifurcation. In the second model, the electrostatic instabilities of a collisional plasma correspond to Hopf bifurcations. In this problem, the Vlasov-Poisson equations with a Krook collision term describe the electron dynamics in a weakly ionized gas. The one mode in instability is analyzed in detail; near criticality it always saturates in a small amplitude nonlinear oscillation. The theory of the center manifold accomplishes two things. First, it establishes that the dynamics of a finite mode instability is always of a finite dimensional character, even when the equations of motion are partial differential equations. Secondly, it provides practical methods for deriving the relevant reduced set of equations that describe the transition. Thus the center manifold methods provide a geometric and rigorous basis for the reduction in dimension which characterizes classical amplitude expansions.

  10. Non-linear mirror instability

    NASA Astrophysics Data System (ADS)

    Rincon, F.; Schekochihin, A. A.; Cowley, S. C.

    2015-02-01

    Slow dynamical changes in magnetic-field strength and invariance of the particles' magnetic moments generate ubiquitous pressure anisotropies in weakly collisional, magnetized astrophysical plasmas. This renders them unstable to fast, small-scale mirror and firehose instabilities, which are capable of exerting feedback on the macroscale dynamics of the system. By way of a new asymptotic theory of the early non-linear evolution of the mirror instability in a plasma subject to slow shearing or compression, we show that the instability does not saturate quasi-linearly at a steady, low-amplitude level. Instead, the trapping of particles in small-scale mirrors leads to non-linear secular growth of magnetic perturbations, δB/B ∝ t2/3. Our theory explains recent collisionless simulation results, provides a prediction of the mirror evolution in weakly collisional plasmas and establishes a foundation for a theory of non-linear mirror dynamics with trapping, valid up to δB/B = O(1).

  11. Evidence of locally enhanced target heating due to instabilities of counter-streaming fast electron beams

    SciTech Connect

    Koester, Petra; Cecchetti, Carlo A.; Booth, Nicola; Woolsey, Nigel; Chen, Hui; Evans, Roger G.; Gregori, Gianluca; Li, Bin; Mithen, James; Murphy, Christopher D.; Labate, Luca; Gizzi, Leonida A.; Levato, Tadzio; Makita, Mikako; Riley, David; Notley, Margaret; Pattathil, Rajeev

    2015-02-15

    The high-current fast electron beams generated in high-intensity laser-solid interactions require the onset of a balancing return current in order to propagate in the target material. Such a system of counter-streaming electron currents is unstable to a variety of instabilities such as the current-filamentation instability and the two-stream instability. An experimental study aimed at investigating the role of instabilities in a system of symmetrical counter-propagating fast electron beams is presented here for the first time. The fast electron beams are generated by double-sided laser-irradiation of a layered target foil at laser intensities above 10{sup 19 }W/cm{sup 2}. High-resolution X-ray spectroscopy of the emission from the central Ti layer shows that locally enhanced energy deposition is indeed achieved in the case of counter-propagating fast electron beams.

  12. Lightman-Eardley instabilities and accretion disk thickening. [for compact astronomical objects

    NASA Technical Reports Server (NTRS)

    Stoeger, W. R.

    1979-01-01

    After reviewing the role of Compton scattering in accretion disks around black holes, it is discussed whether Lightman-Eardley (LE) secular instabilities can trigger and maintain Pringle-Rees (PR) thermal instabilities. The radiative-transfer-equation and equation-of-state criteria for LE stability in alpha-viscosity-law disk models and dynamic viscosity criteria for more general situations is derived. On the basis of these considerations the LE instability is insufficient for inducing PR instabilities and hot thick inner regions important in accretion-disk models of compact hard X-ray sources. The density thinning due to radial velocity gradients in the accretion flow is suggested as a more likely and satisfactory mechanism.

  13. Perturbations of the Black Hole-Torus System: Instabilities and QPOs

    NASA Astrophysics Data System (ADS)

    Donmez, Orhan

    2016-07-01

    The existence of the black hole (BH)-torus system has been given a considerable attention to explain the variability of X-ray and Gamma-ray (γ-ray) data. The perturbation of the black hole-torus system creates instabilities and some of these instabilities are responsible for a quasi-periodic oscillation. In this talk, we present the results from numerical simulation of the dynamical instability of a pressure-supported relativistic torus, rotating around the black hole with a constant specific angular momentum on a fixed space-time background, in case of perturbation. The types of instabilities and their amplitudes strongly depend on what kind of perturbation is applied. The types of perturbations can be a blob of hot gas, Bondi-Hoyle accretion from a finite distance, radial and angular velocity perturbations of the stable accreted torus, and non-spherical accretion as a consequence of isotropic fall of the spherical-shell which has finite thickness. We study the effects of perturbations onto the torus-black hole system by solving the hydrodynamical equations and we have found that the torus around the black hole would have an instability, which is called the Papaloizou-Pringle, and a quasi-periodic oscillation only if we choose a suitable perturbations and initial data. It is noted that, while the perturbations, which are called blob of hot gas, radial velocity perturbations and Bondi-Hoyle accretion, create the Papaloizou-Pringle instability, the Papaloizou-Pringle instability is softly developed and removed in a short time scale for spherical shell accretion. Our studies also indicate that QPOs are common phenomena on the disc around the black holes. If the accretion disc or torus has a quasi-periodic behavior, it emits continuous radiation during the oscillation.

  14. Modes of storage ring coherent instabilities

    SciTech Connect

    Wang, J.M.

    1986-12-01

    Longitudinal impedance in a beam and various modes of longitudinal coherent instabilities are discussed. The coasting beam coherent instability, microwave instability, and single-bunch longitudinal coherent instabilities are considered. The Vlasov equation is formulated, and a method of solving it is developed. The synchrotron modes are treated, which take the possible bunch shape distortion fully into consideration. A method of treating the synchrotron mode coupling in the case of a small bunch is discussed which takes advantage of the fact that only a few of the synchrotron modes can contribute in such a case. The effect of many bunches on the coherent motion of the beam and the longitudinal symmetric coupled bunch modes are discussed. The transverse impedance is then introduced, and the transverse coasting beam instability is discussed. Various bunched beam instabilities are discussed, including both single bunch instabilities and coupled bunch instabilities. The Vlasov equation for transverse as well as longitudinal motion of particles is introduced as well as a method of solving it within a linear approximation. Head-tail modes and short bunch instabilities and strong coupling instabilities in the long bunch case are covered. (LEW)

  15. Microscale instabilities in stream interaction regions

    NASA Technical Reports Server (NTRS)

    Eviatar, A.; Goldstein, M. L.

    1979-01-01

    The microstructure of solar wind stream interaction regions is considered theoretically with emphasis on the role of several electrostatic kinetic instabilities which may be important within the stream interface and the compression region. Inside of 1 AU, the interface is likely to be stable against the electrostatic streaming instabilities considered. Between 1 and 2 AU, the interface will excite the magnetized ion-ion instability. The compression region is also found to be unstable beyond 1 AU where the modified two-stream instability, beam-cyclotron instability, and ion-acoustic instability are important in determining the structure of the compressive pulses as they evolve into forward and reverse shocks. It is concluded that the modified two-stream instability and beam-cyclotron instability predominately play a role in heating the electrons to the threshold for the ion-acoustic instability. Various electrostatic plasma waves, ranging in frequency from the lower-hybrid to harmonics of the electron cyclotron frequency, would be produced by these instabilities. Their signature should also be seen by high time resolution measurements of the temperature of the various plasma species.

  16. Study of the microbunching instability in single-pass systemsusing a direct 2D Vlasov solver

    SciTech Connect

    Venturini, Marco

    2007-06-30

    We apply a recently developed Vlasov solver to the study ofthemicrobunching instability generated by shot noise in the beamdeliverysystems of x-ray Free Electron Lasers (FELs). We discusstwo latticespresently under consideration for the FEL FERMI project at Elettra andshow that at least one of the two lattices appears capable of deliveringa beam with the desired quality in the longitudinal phasespace.

  17. Convergent instability in the ionosphere

    SciTech Connect

    Ponyatov, A.A.

    1994-04-01

    A linear theory of the convergent instability (CI) of ionospheric plasma associated with the nonuniform nature of its regular motion is examined. The conditions under which CI appears in the E- and F-layers for vertical ion motion caused by various physical factors are analyzed. The possibility of small-scale strongly geomagnetic-field-aligned nonuniformities of electron concentration (l{sub min} {approximately} 10-30 m) is demonstrated. The altitude dependence of collision frequency is shown to play a large role in CI.

  18. Convective Instabilities in Liquid Foams

    NASA Technical Reports Server (NTRS)

    Veretennikov, Igor; Glazier, James A.

    2004-01-01

    The main goal of this work is to better understand foam behavior both on the Earth and in microgravity conditions and to determine the relation between a foam's structure and wetness and its rheological properties. Our experiments focused on the effects of the bubble size distribution (BSD) on the foam behavior under gradual or stepwise in the liquid flow rate and on the onset of the convective instability. We were able to show experimentally, that the BSD affects foam rheology very strongly so any theory must take foam texture into account.

  19. Dynamic Instability of Barlike Modes

    NASA Astrophysics Data System (ADS)

    Durisen, Richard H.; Pickett, Brian K.; Bate, Matthew R.; Imamura, James N.; Brandl, Andreas; Sterzik, Michael F.

    Numerical simulations during the 1980's established that prompt binary formation (or ``fission'') through dynamic growth of barlike modes is aborted by gravitational torques. Because these instabilities may occur during star formation and because their outcome over long times is still uncertain, we have combined various linear analyses with simulations by hydrodynamics codes to refine our understanding. We show that it is in fact the torques which cause nonlinear saturation of the mode amplitude. Excellent agreement for the early nonlinear phase is obtained using radically different hydrodynamics codes. However, the ultimate outcome is sensitive to assumptions about dissipative heating and is also somewhat code-dependent.

  20. Ergoregion instability: The hydrodynamic vortex

    NASA Astrophysics Data System (ADS)

    Oliveira, Leandro A.; Cardoso, Vitor; Crispino, Luís C. B.

    2014-06-01

    Four-dimensional, asymptotically flat spacetimes with an ergoregion but no horizon have been shown to be linearly unstable against a superradiant-triggered mechanism. This result has wide implications in the search for astrophysically viable alternatives to black holes, but also in the understanding of black holes and Hawking evaporation. Here we investigate this instability in detail for a particular setup that can be realized in the laboratory: the hydrodynamic vortex, an effective geometry for sound waves, with ergoregion and without an event horizon.

  1. Sheet Beam Klystron Instability Analysis

    SciTech Connect

    Bane, K.L.F.; Jensen, A.; Li, Z.; Stupakov, G.; Adolphsen, C.; /SLAC

    2009-05-08

    Using the principle of energy balance we develop a 2D theory for calculating growth rates of instability in a two-cavity model of a sheet beam klystron. An important ingredient is a TE-like mode in the gap that also gives a longitudinal kick to the beam. When compared with a self-consistent particle-in-cell calculation, with sheet beam klystron-type parameters, agreement is quite good up to half the design current, 65 A; at full current, however, other, current-dependent effects come in and the results deviate significantly.

  2. Arthroscopic Repair of Ankle Instability.

    PubMed

    Sorensen, Matthew D; Baca, John; Arbuckle, Keith

    2016-10-01

    Arthroscopic lateral ankle stabilization procedures have been described for many years. New technological advances and a deeper understanding of the pathobiomechanics involved in chronic lateral ankle instability have allowed an expansion of arthroscopic approaches to this common pathology. As experience is gained and outcomes within the patient profile are understood, the authors feel that the arthroscopic approach to lateral ankle stabilization may prove superior to traditional methods secondary to the risk and traditional complications that are mitigated within minimally invasive arthroscopic approaches. Additionally, the arthroscopic approach may allow a quicker return to ballistic sport and decrease time for rehabilitation. PMID:27599440

  3. Mode-locking via dissipative Faraday instability

    PubMed Central

    Tarasov, Nikita; Perego, Auro M.; Churkin, Dmitry V.; Staliunas, Kestutis; Turitsyn, Sergei K.

    2016-01-01

    Emergence of coherent structures and patterns at the nonlinear stage of modulation instability of a uniform state is an inherent feature of many biological, physical and engineering systems. There are several well-studied classical modulation instabilities, such as Benjamin–Feir, Turing and Faraday instability, which play a critical role in the self-organization of energy and matter in non-equilibrium physical, chemical and biological systems. Here we experimentally demonstrate the dissipative Faraday instability induced by spatially periodic zig-zag modulation of a dissipative parameter of the system—spectrally dependent losses—achieving generation of temporal patterns and high-harmonic mode-locking in a fibre laser. We demonstrate features of this instability that distinguish it from both the Benjamin–Feir and the purely dispersive Faraday instability. Our results open the possibilities for new designs of mode-locked lasers and can be extended to other fields of physics and engineering. PMID:27503708

  4. Mode-locking via dissipative Faraday instability

    NASA Astrophysics Data System (ADS)

    Tarasov, Nikita; Perego, Auro M.; Churkin, Dmitry V.; Staliunas, Kestutis; Turitsyn, Sergei K.

    2016-08-01

    Emergence of coherent structures and patterns at the nonlinear stage of modulation instability of a uniform state is an inherent feature of many biological, physical and engineering systems. There are several well-studied classical modulation instabilities, such as Benjamin-Feir, Turing and Faraday instability, which play a critical role in the self-organization of energy and matter in non-equilibrium physical, chemical and biological systems. Here we experimentally demonstrate the dissipative Faraday instability induced by spatially periodic zig-zag modulation of a dissipative parameter of the system--spectrally dependent losses--achieving generation of temporal patterns and high-harmonic mode-locking in a fibre laser. We demonstrate features of this instability that distinguish it from both the Benjamin-Feir and the purely dispersive Faraday instability. Our results open the possibilities for new designs of mode-locked lasers and can be extended to other fields of physics and engineering.

  5. Absolute instability of the Gaussian wake profile

    NASA Technical Reports Server (NTRS)

    Hultgren, Lennart S.; Aggarwal, Arun K.

    1987-01-01

    Linear parallel-flow stability theory has been used to investigate the effect of viscosity on the local absolute instability of a family of wake profiles with a Gaussian velocity distribution. The type of local instability, i.e., convective or absolute, is determined by the location of a branch-point singularity with zero group velocity of the complex dispersion relation for the instability waves. The effects of viscosity were found to be weak for values of the wake Reynolds number, based on the center-line velocity defect and the wake half-width, larger than about 400. Absolute instability occurs only for sufficiently large values of the center-line wake defect. The critical value of this parameter increases with decreasing wake Reynolds number, thereby indicating a shrinking region of absolute instability with decreasing wake Reynolds number. If backflow is not allowed, absolute instability does not occur for wake Reynolds numbers smaller than about 38.

  6. Mode-locking via dissipative Faraday instability.

    PubMed

    Tarasov, Nikita; Perego, Auro M; Churkin, Dmitry V; Staliunas, Kestutis; Turitsyn, Sergei K

    2016-01-01

    Emergence of coherent structures and patterns at the nonlinear stage of modulation instability of a uniform state is an inherent feature of many biological, physical and engineering systems. There are several well-studied classical modulation instabilities, such as Benjamin-Feir, Turing and Faraday instability, which play a critical role in the self-organization of energy and matter in non-equilibrium physical, chemical and biological systems. Here we experimentally demonstrate the dissipative Faraday instability induced by spatially periodic zig-zag modulation of a dissipative parameter of the system-spectrally dependent losses-achieving generation of temporal patterns and high-harmonic mode-locking in a fibre laser. We demonstrate features of this instability that distinguish it from both the Benjamin-Feir and the purely dispersive Faraday instability. Our results open the possibilities for new designs of mode-locked lasers and can be extended to other fields of physics and engineering. PMID:27503708

  7. Transverse Instabilities in the Fermilab Recycler

    SciTech Connect

    Prost, L.R.; Burov, A.; Shemyakin, A.; Bhat, C.M.; Crisp, J.; Eddy, N.; /Fermilab

    2011-07-01

    Transverse instabilities of the antiproton beam have been observed in the Recycler ring soon after its commissioning. After installation of transverse dampers, the threshold for the instability limit increased significantly but the instability is still found to limit the brightness of the antiprotons extracted from the Recycler for Tevatron shots. In this paper, we describe observations of the instabilities during the extraction process as well as during dedicated studies. The measured instability threshold phase density agrees with the prediction of the rigid beam model within a factor of 2. Also, we conclude that the instability threshold can be significantly lowered for a bunch contained in a narrow and shallow potential well due to effective exclusion of the longitudinal tails from Landau damping.

  8. COSMIC-RAY STREAMING FROM SUPERNOVA REMNANTS AND GAMMA-RAY EMISSION FROM NEARBY MOLECULAR CLOUDS

    SciTech Connect

    Yan Huirong; Lazarian, A.; Schlickeiser, R.

    2012-02-01

    High-energy gamma-ray emission has been detected recently from supernova remnants (SNRs) and their surroundings. The existence of molecular clouds near some of the SNRs suggests that the gamma rays originate predominantly from p-p interactions with cosmic rays (CRs) accelerated at a closeby SNR shock wave. Here we investigate the acceleration of CRs and the gamma-ray production in the cloud self-consistently by taking into account the interactions of the streaming instability and the background turbulence both at the shock front and in the ensuing propagation to the clouds. We focus on the later evolution of SNRs, when the conventional treatment of the streaming instability is valid but the magnetic field is enhanced due to Bell's current instability and/or the dynamo generation of magnetic field in the precursor region. We calculate the time dependence of the maximum energy of the accelerated particles. This result is then used to determine the diffusive flux of the runaway particles escaping the shock region, from which we obtain the gamma spectrum consistent with observations. Finally, we check the self-consistency of our results by comparing the required level of diffusion with the level of the streaming instability attainable in the presence of turbulence damping. The energy range of CRs subject to the streaming instability is able to produce the observed energy spectrum of gamma rays.

  9. Observation of Parametric Instability in Advanced LIGO.

    PubMed

    Evans, Matthew; Gras, Slawek; Fritschel, Peter; Miller, John; Barsotti, Lisa; Martynov, Denis; Brooks, Aidan; Coyne, Dennis; Abbott, Rich; Adhikari, Rana X; Arai, Koji; Bork, Rolf; Kells, Bill; Rollins, Jameson; Smith-Lefebvre, Nicolas; Vajente, Gabriele; Yamamoto, Hiroaki; Adams, Carl; Aston, Stuart; Betzweiser, Joseph; Frolov, Valera; Mullavey, Adam; Pele, Arnaud; Romie, Janeen; Thomas, Michael; Thorne, Keith; Dwyer, Sheila; Izumi, Kiwamu; Kawabe, Keita; Sigg, Daniel; Derosa, Ryan; Effler, Anamaria; Kokeyama, Keiko; Ballmer, Stefan; Massinger, Thomas J; Staley, Alexa; Heinze, Matthew; Mueller, Chris; Grote, Hartmut; Ward, Robert; King, Eleanor; Blair, David; Ju, Li; Zhao, Chunnong

    2015-04-24

    Parametric instabilities have long been studied as a potentially limiting effect in high-power interferometric gravitational wave detectors. Until now, however, these instabilities have never been observed in a kilometer-scale interferometer. In this Letter, we describe the first observation of parametric instability in a gravitational wave detector, and the means by which it has been removed as a barrier to progress. PMID:25955042

  10. Observations of the PSR transverse instability

    SciTech Connect

    Colton, E. ); Fitzgerald, D.; Hardek, T.; Macek, R.J.; Plum, M.A.; Thiessen, H.A.; Wang, T.S. ); Neuffer, D. )

    1991-01-01

    A fast instability with beam loss is observed in the Los Alamos Proton Storage Ring (PSR) when the injected beam current exceeds thresholds, with both bunched and unbunched beams. Large coherent transverse oscillations occur before and during beam loss. Recent observations of the instability indicate that it is an e-p''-type instability, driven by coupled oscillations due to electrons trapped within the proton beam. 5 refs., 3 figs.

  11. Filamentation instability in a quantum magnetized plasma

    SciTech Connect

    Bret, A.

    2008-02-15

    The filamentation instability occurring when a nonrelativistic electron beam passes through a quantum magnetized plasma is investigated by means of a cold quantum magnetohydrodynamic model. It is proved that the instability can be completely suppressed by quantum effects if and only if a finite magnetic field is present. A dimensionless parameter is identified that measures the strength of quantum effects. Strong quantum effects allow for a much smaller magnetic field to suppress the instability than in the classical regime.

  12. Radiation-induced genomic instability in Caenorhabditis elegans.

    PubMed

    Huumonen, Katriina; Immonen, Hanna-Kaisa; Baverstock, Keith; Hiltunen, Mikko; Korkalainen, Merja; Lahtinen, Tapani; Parviainen, Juha; Viluksela, Matti; Wong, Garry; Naarala, Jonne; Juutilainen, Jukka

    2012-10-01

    Radiation-induced genomic instability has been well documented, particularly in vitro. However, the understanding of its mechanisms and their consequences in vivo is still limited. In this study, Caenorhabditis elegans (C. elegans; strain CB665) nematodes were exposed to X-rays at doses of 0.1, 1, 3 or 10Gy. The endpoints were measured several generations after exposure and included mutations in the movement-related gene unc-58, alterations in gene expression analysed with oligoarrays containing the entire C. elegans genome, and micro-satellite mutations measured by capillary electrophoresis. The progeny of the irradiated nematodes showed an increased mutation frequency in the unc-58 gene, with a maximum response observed at 1Gy. Significant differences were also found in gene expression between the irradiated (1Gy) and non-irradiated nematode lines. Differences in gene expression did not show clear clustering into certain gene categories, suggesting that the instability might be a chaotic process rather than a result of changes in the function of few specific genes such as, e.g., those responsible for DNA repair. Increased heterogeneity in gene expression, which has previously been described in irradiated cultured human lymphocytes, was also observed in the present study in C. elegans, the coefficient of variation of gene expression being higher in the progeny of irradiated nematodes than in control nematodes. To the best of our knowledge, this is the first publication reporting radiation-induced genomic instability in C. elegans.

  13. Radiation-induced chromosomal instability in human mammary epithelial cells

    NASA Astrophysics Data System (ADS)

    Durante, M.; Grossi, G. F.; Yang, T. C.

    Karyotypes of human cells surviving X- and alpha-irradiation have been studied. Human mammary epithelial cells of the immortal, non-tumorigenic cell line H184B5 F5-1 M/10 were irradiated and surviving clones isolated and expanded in culture. Cytogenetic analysis was performed using dedicated software with an image analyzer. We have found that both high- and low-LET radiation induced chromosomal instability in long-term cultures, but with different characteristics. Complex chromosomal rearrangements were observed after X-rays, while chromosome loss predominated after alpha-particles. Deletions were observed in both cases. In clones derived from cells exposed to alpha-particles, some cells showed extensive chromosome breaking and double minutes. Genomic instability was correlated to delayed reproductive death and neoplastic transformation. These results indicate that chromosomal instability is a radiation-quality-dependent effect which could determine late genetic effects, and should therefore be carefully considered in the evaluation of risk for space missions.

  14. Baryon loading and the Weibel instability in GRBs

    NASA Astrophysics Data System (ADS)

    Fiore, M.; Fonseca, R. A.; Silva, L. O.; Ren, C.; Tzoufras, M. A.; Mori, W. B.

    2004-11-01

    One of the unsolved problems in the astrophysics of extreme events is the magnetic field generation in gamma-ray bursts. Synchrotron radiation measurements indicate the presence of near-equipartition magnetic fields, but the origin of these fields is still under strong debate [1]. The Weibel instability seems to be a good candidate to explain magnetic fields in GRBs [2]. Using relativistic kinetic theory we show that, even if thermal effects may slow down the instability, the thermal spread does not shutdown the Weibel instability due to the ion presence. Baryons lead to a non-negligible growth rate beyond the threshold predicted for purely electromagnetic waves in electron-positron counter-streaming shells. Two-dimensional and three-dimensional fully relativistic particle-in-cell simulations, carried out with the OSIRIS framework [3], confirm our theoretical results for these scenarios. [1] E. Waxman, Nature 423, 388 (2003); W. E. Coburn, S. E. Boggs, Nature 423, 415 (2003) [2] M. Medvedev and A. Loeb, ApJ 526, 697 (1999); L. O. Silva et al., ApJLett 596, 121 (2003) [3] R. A. Fonseca et al., LNCS 2331, 342 (2002)

  15. Radiation-induced chromosomal instability in human mammary epithelial cells

    NASA Technical Reports Server (NTRS)

    Durante, M.; Grossi, G. F.; Yang, T. C.

    1996-01-01

    Karyotypes of human cells surviving X- and alpha-irradiation have been studied. Human mammary epithelial cells of the immortal, non-tumorigenic cell line H184B5 F5-1 M/10 were irradiated and surviving clones isolated and expanded in culture. Cytogenetic analysis was performed using dedicated software with an image analyzer. We have found that both high- and low-LET radiation induced chromosomal instability in long-term cultures, but with different characteristics. Complex chromosomal rearrangements were observed after X-rays, while chromosome loss predominated after alpha-particles. Deletions were observed in both cases. In clones derived from cells exposed to alpha-particles, some cells showed extensive chromosome breaking and double minutes. Genomic instability was correlated to delayed reproductive death and neoplastic transformation. These results indicate that chromosomal instability is a radiation-quality-dependent effect which could determine late genetic effects, and should therefore be carefully considered in the evaluation of risk for space missions.

  16. Two-Fluid Interface Instability Being Studied

    NASA Technical Reports Server (NTRS)

    Niederhaus, Charles E.

    2003-01-01

    The interface between two fluids of different density can experience instability when gravity acts normal to the surface. The relatively well known Rayleigh-Taylor (RT) instability results when the gravity is constant with a heavy fluid over a light fluid. An impulsive acceleration applied to the fluids results in the Richtmyer-Meshkov (RM) instability. The RM instability occurs regardless of the relative orientation of the heavy and light fluids. In many systems, the passing of a shock wave through the interface provides the impulsive acceleration. Both the RT and RM instabilities result in mixing at the interface. These instabilities arise in a diverse array of circumstances, including supernovas, oceans, supersonic combustion, and inertial confinement fusion (ICF). The area with the greatest current interest in RT and RM instabilities is ICF, which is an attempt to produce fusion energy for nuclear reactors from BB-sized pellets of deuterium and tritium. In the ICF experiments conducted so far, RM and RT instabilities have prevented the generation of net-positive energy. The $4 billion National Ignition Facility at Lawrence Livermore National Laboratory is being constructed to study these instabilities and to attempt to achieve net-positive yield in an ICF experiment.

  17. Phase space evolution in linear instabilities

    SciTech Connect

    Pantellini, F.G.E.; Burgess, D.; Schwartz, S.J. )

    1994-12-01

    A simple and powerful way to investigate the linear evolution of particle distribution functions in kinetic instabilities in a homogeneous collisionless plasma is presented. The method can be applied to any kind of instability, provided the characteristics (growth rate, frequency, wave vector, and polarization) of the mode are known and can also be used to estimate the amplitude of the waves at the end of the linear phase of growth. Two didactic examples are used to illustrate the versatility of the technique: the Alfven Ion Cyclotron (AIC) instability, which is electromagnetic, and the Electron Ion Cyclotron (EIC) instability, which is electrostatic.

  18. Two-Beam Instability in Electron Cooling

    SciTech Connect

    Burov, Alexey V.; /Fermilab

    2006-04-01

    The drift motion of cooling electrons makes them able to respond to transverse perturbations of a cooled ion beam. This response may lead to dipole or quadrupole transverse instabilities at specific longitudinal wave numbers. While the dipole instabilities can be suppressed by a combination of the Landau damping, machine impedance, and the active damper, the quadrupole and higher order modes can lead to either emittance growth, or a lifetime degradation, or both. The growth rates of these instabilities are strongly determined by the machine x-y coupling. Thus, tuning out of the coupling resonance and/or reduction of the machine coupling can be an efficient remedy for these instabilities.

  19. [Cervical spine instability in the surgical patient].

    PubMed

    Barbeito, A; Guerri-Guttenberg, R A

    2014-03-01

    Many congenital and acquired diseases, including trauma, may result in cervical spine instability. Given that airway management is closely related to the movement of the cervical spine, it is important that the anesthesiologist has detailed knowledge of the anatomy, the mechanisms of cervical spine instability, and of the effects that the different airway maneuvers have on the cervical spine. We first review the normal anatomy and biomechanics of the cervical spine in the context of airway management and the concept of cervical spine instability. In the second part, we review the protocols for the management of cervical spine instability in trauma victims and some of the airway management options for these patients.

  20. Higgs instability in gapless superfluidity/superconductivity

    SciTech Connect

    Giannakis, Ioannis; Hou Defu; Huang Mei; Ren Haicang

    2007-01-01

    In this letter we explore the Higgs instability in the gapless superfluid/superconducting phase. This is in addition to the (chromo)magnetic instability that is related to the fluctuations of the Nambu-Goldstone bosonic fields. While the latter may induce a single-plane-wave Larkin-Ovchinnikov-Fulde-Ferrel state, the Higgs instability favors spatial inhomogeneity. In the case of the 2-flavor color superconductivity state the Higgs instability can only be partially removed by the electric Coulomb energy. But this does not exclude the possibility that it can be completely removed in other exotic states such as the gapless color-flavor locked state.

  1. Internet worms and global routing instabilities

    NASA Astrophysics Data System (ADS)

    Cowie, James; Ogielski, Andy T.; Premore, B. J.; Yuan, Yougu

    2002-07-01

    We analyze the global BGP routing instabilities observed during the Code Red II and Nimda worm attacks in July and September 2001, respectively. Compelling analysis is shown on the correlation between the observed instabilities and the worm attacks. We analyze router failure modes that can be triggered by the abnormal traffic during the worm attack and how they can lead to global routing instability. Independent research has partially confirmed that such failure modes can and likely do occur in practice. Highly detailed large-scale simulations help close the loop, indicating that such failure modes do in fact trigger the kind of widespread BGP instabilities that were observed empirically.

  2. Active control of combustion instability

    SciTech Connect

    Lang, W.; Poinsot, T.; Candel, S.

    1987-12-01

    The principle of 'antisound' is used to construct a method for the suppression of combustion instabilities. This active instability control (AIC) method uses external acoustic excitation by a loudspeaker to suppress the oscillations of a flame. The excitation signal is provided by a microphone located upstream of the flame. This signal is filtered, processed, amplified, and sent to the loudspeaker. The AIC method is validated on a laboratory combustor. It allows the suppression of all unstable modes of the burner for any operating ratio. The influence of the microphone and loudspeaker locations on the performance of the AIC system is described. For a given configuration, domains of stability, i.e., domains where the AIC system parameters provide suppression of the oscillation, are investigated. Measurements of the electric input of the loudspeaker show that the energy consumption of the AIC system is almost negligible and suggest that this method could be used for industrial combustor stabilization. Finally, a simple model describing the effects of the AIC system is developed and its results compared to the experiment.

  3. The Chemistry of Beer Instability

    NASA Astrophysics Data System (ADS)

    Stewart, Graham G.

    2004-07-01

    Compared to most other alcoholic beverages, beer is unique because it is unstable when in the final package. This instability can be divided into biological and nonbiological instability. Nonbiological stability of beer involves a wide range of chemical processes and can be considered in a number of categories: physical, flavor, light, foam, and gushing. It is the balance between flavanoid polyphenols (tannoids) and sensitive proteins that specifically combine with polyphenols to form haze that largely dictates physical stability. The flavor stability of beer primarily depends on the oxygen concentration of packaged beer but is influenced by all stages of the brewing process. Foam stability in a glass of beer reflects the quality of the beverage. The backbone of foam is hydrophobic polypeptides. Novel brewing processes such as high-gravity brewing result in a disproportionate loss of these polypeptides and have a negative effect on the foam stability of the resulting beer. Beer is light sensitive, especially in the 350 500 nm range. Beer exposed to this wavelength range in clear or green glass containers quickly develop nauseous skunky-like off-flavors resulting from the formation of 3-methyl-2-butene-1-thiol. Methods of enhancing all of these types of beer stability are discussed.

  4. Electric Field Induced Interfacial Instabilities

    NASA Technical Reports Server (NTRS)

    Kusner, Robert E.; Min, Kyung Yang; Wu, Xiao-Lun; Onuki, Akira

    1996-01-01

    The study of the interface in a charge-free, nonpolar, critical and near-critical binary fluid in the presence of an externally applied electric field is presented. At sufficiently large fields, the interface between the two phases of the binary fluid should become unstable and exhibit an undulation with a predefined wavelength on the order of the capillary length. As the critical point is approached, this wavelength is reduced, potentially approaching length-scales such as the correlation length or critical nucleation radius. At this point the critical properties of the system may be affected. In zero gravity, the interface is unstable at all long wavelengths in the presence of a field applied across it. It is conjectured that this will cause the binary fluid to break up into domains small enough to be outside the instability condition. The resulting pattern formation, and the effects on the critical properties as the domains approach the correlation length are of acute interest. With direct observation, laser light scattering, and interferometry, the phenomena can be probed to gain further understanding of interfacial instabilities and the pattern formation which results, and dimensional crossover in critical systems as the critical fluctuations in a particular direction are suppressed by external forces.

  5. Genome instability, cancer and aging

    PubMed Central

    Maslov, Alexander Y.; Vijg, Jan

    2015-01-01

    DNA damage-driven genome instability underlies the diversity of life forms generated by the evolutionary process but is detrimental to the somatic cells of individual organisms. The cellular response to DNA damage can be roughly divided in two parts. First, when damage is severe, programmed cell death may occur or, alternatively, temporary or permanent cell cycle arrest. This protects against cancer but can have negative effects on the long term, e.g., by depleting stem cell reservoirs. Second, damage can be repaired through one or more of the many sophisticated genome maintenance pathways. However, erroneous DNA repair and incomplete restoration of chromatin after damage is resolved, produce mutations and epimutations, respectively, both of which have been shown to accumulate with age. An increased burden of mutations and/or epimutations in aged tissues increases cancer risk and adversely affects gene transcriptional regulation, leading to progressive decline in organ function. Cellular degeneration and uncontrolled cell proliferation are both major hallmarks of aging. Despite the fact that one seems to exclude the other, they both may be driven by a common mechanism. Here, we review age related changes in the mammalian genome and their possible functional consequences, with special emphasis on genome instability in stem/progenitor cells. PMID:19344750

  6. Combustion instability modeling and analysis

    SciTech Connect

    Santoro, R.J.; Yang, V.; Santavicca, D.A.

    1995-10-01

    It is well known that the two key elements for achieving low emissions and high performance in a gas turbine combustor are to simultaneously establish (1) a lean combustion zone for maintaining low NO{sub x} emissions and (2) rapid mixing for good ignition and flame stability. However, these requirements, when coupled with the short combustor lengths used to limit the residence time for NO formation typical of advanced gas turbine combustors, can lead to problems regarding unburned hydrocarbons (UHC) and carbon monoxide (CO) emissions, as well as the occurrence of combustion instabilities. Clearly, the key to successful gas turbine development is based on understanding the effects of geometry and operating conditions on combustion instability, emissions (including UHC, CO and NO{sub x}) and performance. The concurrent development of suitable analytical and numerical models that are validated with experimental studies is important for achieving this objective. A major benefit of the present research will be to provide for the first time an experimentally verified model of emissions and performance of gas turbine combustors.

  7. Feedback control of multibunch instabilities

    SciTech Connect

    Galayda, J. )

    1992-03-10

    This lecture is intended to be an introduction to the use of feedback control to counteract multibunch instabilities. Furthermore, the intent is to make the most direct connection possible between feedback system design and the linear equations of motion of a single particle in an accelerator. Descriptions of the electronic design and considerations of gain versus stability have been treated in the literature (1,2,3) and will be glossed over in this lecture. The exposition is aimed at an audience with reasonable background in linear charged particle optics and minimal familiarity with circuit theory and electronics design. We begin with a brief description of the sources of instability and a description of the function of a feedback system in terms of the equation of motion of a beam bunch. We will try to list the fundamentals of the design process of a feedback system in such a way as to give the reader a framework within which to evaluate the subsequent material. Section 2 develops simple definitions of feedback system performance parameters: damping time constant, gain, and power requirements. Sections 3 and 4 give a perspective on feedback signal processing, using several betatron damping systems to exemplify time domain signal processing. Section 5 views the signal processing problem in frequency domain, using the CERN PS Booster longitudinal damper as an example.

  8. Adhesional instabilities and gecko locomotion

    NASA Astrophysics Data System (ADS)

    Williams, John A.

    2015-01-01

    Geckos possess a remarkable ability to run rapidly on both walls and ceilings and in recent years the mechanisms that underlie this facility have come under close scrutiny. It is now generally agreed that one of the principal mechanisms of adhesion relies on the action of van der Waal forces acting between the final extremely fine structure of the gecko toe and the underlying substrate. High speed video analysis shows that adhesive contact is both made and broken in intervals of less than 20 ms and this suggests that the mechanism of detachment is one of adhesive instability rather than steady-state peeling. By considering the gecko seta/spatula as a Euler-Bernoulli cantilever it is possible to model this instability in non-dimensional terms and thus to test the analysis at a much larger scale with more conventional engineering materials. When applied to the scale and material combination appropriate to a gecko spatula, the predicted critical load, of around 10 nN, is close to values that have been observed using and AFM cantilever and a single detached spatula.

  9. Electrokinetic instability of isotachophoresis shocks

    NASA Astrophysics Data System (ADS)

    Garcia, Giancarlo; Santiago, Juan; Mani, Ali

    2013-11-01

    Isotachophoresis (ITP) is an electrokinetic focusing technique used in a variety of life science and analytical chemistry applications. In ITP, an electrokinetic shock wave forms at the interface between leading and trailing electrolytes with relatively high and low conductivities. The ITP interface is self-sharpening, as restoring electromigration fluxes counteract molecular diffusion. However, the large electric field gradient at the shock interface also gives rise to free charge and strong electrostatic body forces. At large applied currents, electrostatic forces cause recirculating flows which destabilize the ITP interface. We performed stability analysis and direct simulation of ITP shocks through numerical solutions to the coupled Nernst-Planck and Navier-Stokes equations using a quasi-electroneutral approximation. In both experiments and numerical simulations, we observe two modes of instability: 1) a distorted ITP interface which is steady in time, and 2) an oscillating perturbation which persists. In addition, at the highest simulated electric fields, we observe transition towards more chaotic oscillatory modes. We use our stability analysis and numerical simulations to characterize instability of ITP shocks using two dimensionless parameters.

  10. Radiation-induced genomic instability

    NASA Technical Reports Server (NTRS)

    Kronenberg, A.

    1994-01-01

    Quantitative assessment of the heritable somatic effects of ionizing radiation exposures has relied upon the assumption that radiation-induced lesions were 'fixed' in the DNA prior to the first postirradiation mitosis. Lesion conversion was thought to occur during the initial round of DNA replication or as a consequence of error-prone enzymatic processing of lesions. The standard experimental protocols for the assessment of a variety of radiation-induced endpoints (cell death, specific locus mutations, neoplastic transformation and chromosome aberrations) evaluate these various endpoints at a single snapshot in time. In contrast with the aforementioned approaches, some studies have specifically assessed radiation effects as a function of time following exposure. Evidence has accumulated in support of the hypothesis that radiation exposure induces a persistent destabilization of the genome. This instability has been observed as a delayed expression of lethal mutations, as an enhanced rate of accumulation of non-lethal heritable alterations, and as a progressive intraclonal chromosomal heterogeneity. The genetic controls and biochemical mechanisms underlying radiation-induced genomic instability have not yet been delineated. The aim is to integrate the accumulated evidence that suggests that radiation exposure has a persistent effect on the stability of the mammalian genome.

  11. Rogue Waves and Modulational Instability

    NASA Astrophysics Data System (ADS)

    Zakharov, V. E.; Dyachenko, A.

    2015-12-01

    The most plausible cause of rogue wave formation in a deep ocean is development of modulational instability of quasimonochromatic wave trains. An adequate model for study of this phenomenon is the Euler equation for potential flow of incompressible fluid with free surface in 2-D geometry. Numerical integration of these equations confirms completely the conjecture of rogue wave formation from modulational instability but the procedure is time consuming for determination of rogue wave appearance probability for a given shape of wave energy spectrum. This program can be realized in framework of simpler model using replacement of the exact interaction Hamiltonian by more compact Hamiltonian. There is a family of such models. The popular one is the Nonlinear Schrodinger equation (NLSE). This model is completely integrable and suitable for numerical simulation but we consider that it is oversimplified. It misses such important phenomenon as wave breaking. Recently, we elaborated much more reliable model that describes wave breaking but is as suitable as NLSE from the point of numerical modeling. This model allows to perform massive numerical experiments and study statistics of rogue wave formation in details.

  12. Fast Ion Effects on Magnetic Instabilities in the Pdx Tokamak

    NASA Astrophysics Data System (ADS)

    Buchenauer, Dean Alan James

    A study of the modification and excitation of nondisruptive magnetic instabilities due to near perpendicular neutral beam injection on the PDX tokamak has been made to determine the importance of these instabilities at low q. The instabilities consisted of resistive MHD modes, beam driven ideal MHD modes, and beam driven ion cyclotron modes. Evidence of enhanced transport (beyond the anamolous transport associated with auxiliary heating) is presented for several of these instabilities as well as comparison of the experimental results with theory. The main results can be summarized as follows: (1) The loss of electron thermal energy due to sawteeth oscillations, although small, increases with increasing auxiliary power and decreasing q, but it was suppressed with high power perpendicular injection due to a loss of the beam ions. (2) m = 2 resistive modes have a disastrous effect on the achieved density, but at present power levels, they can be controlled. (3) Evidence from Mirnov coils, soft x-ray emission, neutron emission, and fast charge-exchange flux indicates that a degradation of the global energy confinement above (beta)(,T)q (DBLTURN) 0.045 is due to a rapid loss of beam ions from the bulk plasma ("fishbone instability"). Scalings of the data indicate that this loss occurs due to a destabilizing resonance between an internal kink mode and the precessing beam ions. The flux of escaping ions was studied using a charged particle detector calibrated for the fast deuterons injected by the beam and an array of high frequency electromagnetic coils. Bursts in the beam ion flux and the rf emission were found to be correlated with drops in the neutron emission and bursts of 20 kHz magnetic oscillations (fishbones). (4) A quiescent level of rf emission was observed to be correlated with increases in the density of trapped beam ions at the outer edge of the plasma. The harmonic structure of this instability was the same as that during fishbones (harmonics of (OMEGA

  13. Astrophysical Weibel instability in counter-streaming laser-produced plasmas

    NASA Astrophysics Data System (ADS)

    Fox, W.

    2014-10-01

    Astrophysical shock waves play diverse roles, including energizing cosmic rays in the blast waves of astrophysical explosions, and generating primordial magnetic fields during the formation of galaxies and clusters. These shocks are typically collisionless and require collective electromagnetic fields to couple the upstream and downstream plasmas. The Weibel instability has been proposed to provide the requisite interaction mechanism for shock formation in weakly-magnetized shocks by generating turbulent electric and magnetic fields in the shock front. This work presents the first laboratory identification of this Weibel instability between counterstreaming supersonic plasma flows and confirms its basic features, a significant step towards understanding these shocks. In the experiments, conducted on the OMEGA EP laser facility at the University of Rochester, a pair of plasmas plumes are generated by irradiating of a pair of opposing parallel plastic (CH) targets. The ion-ion interaction between the two plumes is collisionless, so as the plumes interpenetrate, supersonic, counterstreaming ion flow conditions are obtained. Electromagnetic fields formed in the interaction of the two plumes were probed with an ultrafast laser-driven proton beam, and we observed the growth of a highly striated, transverse instability with extended filaments parallel to the flows. The instability is identified as an ion-driven Weibel instability through agreement with analytic theory and fully kinetic particle-in-cell simulations of colliding ablation flows, which include a collision operator. The experimental proton-radiography results are compared with synthetic ray-tracing through 3-D simulations.

  14. Bystander effects in radiation-induced genomic instability

    NASA Technical Reports Server (NTRS)

    Morgan, William F.; Hartmann, Andreas; Limoli, Charles L.; Nagar, Shruti; Ponnaiya, Brian

    2002-01-01

    Exposure of GM10115 hamster-human hybrid cells to X-rays can result in the induction of chromosomal instability in the progeny of surviving cells. This instability manifests as the dynamic production of novel sub-populations of cells with unique cytogenetic rearrangements involving the "marker" human chromosome. We have used the comet assay to investigate whether there was an elevated level of endogenous DNA breaks in chromosomally unstable clones that could provide a source for the chromosomal rearrangements and thus account for the persistent instability observed. Our results indicate no significant difference in comet tail measurement between non-irradiated and radiation-induced chromosomally unstable clones. Using two-color fluorescence in situ hybridization we also investigated whether recombinational events involving the interstitial telomere repeat-like sequences in GM10115 cells were involved at frequencies higher than random processes would otherwise predict. Nine of 11 clones demonstrated a significantly higher than expected involvement of these interstitial telomere repeat-like sequences at the recombination junction between the human and hamster chromosomes. Since elevated levels of endogenous breaks were not detected in unstable clones we propose that epigenetic or bystander effects (BSEs) lead to the activation of recombinational pathways that perpetuate the unstable phenotype. Specifically, we expand upon the hypothesis that radiation induces conditions and/or factors that stimulate the production of reactive oxygen species (ROS). These reactive intermediates then contribute to a chronic pro-oxidant environment that cycles over multiple generations, promoting chromosomal recombination and other phenotypes associated with genomic instability.

  15. Simultaneous Excitation and Analysis of Three Instabilities in Magnetized Plasma

    SciTech Connect

    Dimitriu, D. G.; Ionita, C.; Schrittwieser, R. W.

    2008-03-19

    Experimental results are presented on the simultaneous excitation of three low-frequency instabilities in the magnetized plasma column of a Q-machine, namely the potential relaxation instability, the electrostatic ion-cyclotron instability and the Kelvin-Helmholtz instability. The influence of the magnetic field intensity on the appearance of these instabilities was investigated.

  16. Interfacial instabilities in vibrated fluids

    NASA Astrophysics Data System (ADS)

    Porter, Jeff; Laverón-Simavilla, Ana; Tinao Perez-Miravete, Ignacio; Fernandez Fraile, Jose Javier

    2016-07-01

    Vibrations induce a range of different interfacial phenomena in fluid systems depending on the frequency and orientation of the forcing. With gravity, (large) interfaces are approximately flat and there is a qualitative difference between vertical and horizontal forcing. Sufficient vertical forcing produces subharmonic standing waves (Faraday waves) that extend over the whole interface. Horizontal forcing can excite both localized and extended interfacial phenomena. The vibrating solid boundaries act as wavemakers to excite traveling waves (or sloshing modes at low frequencies) but they also drive evanescent bulk modes whose oscillatory pressure gradient can parametrically excite subharmonic surface waves like cross-waves. Depending on the magnitude of the damping and the aspect ratio of the container, these locally generated surfaces waves may interact in the interior resulting in temporal modulation and other complex dynamics. In the case where the interface separates two fluids of different density in, for example, a rectangular container, the mass transfer due to vertical motion near the endwalls requires a counterflow in the interior region that can lead to a Kelvin-Helmholtz type instability and a ``frozen wave" pattern. In microgravity, the dominance of surface forces favors non-flat equilibrium configurations and the distinction between vertical and horizontal applied forcing can be lost. Hysteresis and multiplicity of solutions are more common, especially in non-wetting systems where disconnected (partial) volumes of fluid can be established. Furthermore, the vibrational field contributes a dynamic pressure term that competes with surface tension to select the (time averaged) shape of the surface. These new (quasi-static) surface configurations, known as vibroequilibria, can differ substantially from the hydrostatic state. There is a tendency for the interface to orient perpendicular to the vibrational axis and, in some cases, a bulge or cavity is induced

  17. Electric Field Induced Interfacial Instabilities

    NASA Technical Reports Server (NTRS)

    Kusner, Robert E.; Min, Kyung Yang; Wu, Xiao-lun; Onuki, Akira

    1999-01-01

    The study of the interface in a charge-free, critical and near-critical binary fluid in the presence of an externally applied electric field is presented. At sufficiently large fields, the interface between the two phases of the binary fluid should become unstable and exhibit an undulation with a predefined wavelength on the order of the capillary length. As the critical point is approached, this wavelength is reduced, potentially approaching length-scales such as the correlation length or critical nucleation radius. At this point the critical properties of the system may be affected. In this paper, the flat interface of a marginally polar binary fluid mixture is stressed by a perpendicular alternating electric field and the resulting instability is characterized by the critical electric field E(sub c) and the pattern observed. The character of the surface dynamics at the onset of instability is found to be strongly dependent on the frequency f of the field applied. The plot of E(sub c) vs. f for a fixed temperature shows a sigmoidal shape, whose low and high frequency limits are well described by a power-law relationship, E(sub c) = epsilon(exp zeta) with zeta = 0.35 and zeta = 0.08, respectively. The low-limit exponent compares well with the value zeta = 4 for a system of conducting and non-conducting fluids. On the other hand, the high-limit exponent coincides with what was first predicted by Onuki. The instability manifests itself as the conducting phase penetrates the non-conducting phase. As the frequency increases, the shape of the pattern changes from an array of bifurcating strings to an array of column-like (or rod-like) protrusions, each of which spans the space between the plane interface and one of the electrodes. For an extremely high frequency, the disturbance quickly grows into a parabolic cone pointing toward the upper plate. As a result, the interface itself changes its shape from that of a plane to that of a high sloping pyramid.

  18. Testing the gravitational instability hypothesis?

    NASA Technical Reports Server (NTRS)

    Babul, Arif; Weinberg, David H.; Dekel, Avishai; Ostriker, Jeremiah P.

    1994-01-01

    We challenge a widely accepted assumption of observational cosmology: that successful reconstruction of observed galaxy density fields from measured galaxy velocity fields (or vice versa), using the methods of gravitational instability theory, implies that the observed large-scale structures and large-scale flows were produced by the action of gravity. This assumption is false, in that there exist nongravitational theories that pass the reconstruction tests and gravitational theories with certain forms of biased galaxy formation that fail them. Gravitational instability theory predicts specific correlations between large-scale velocity and mass density fields, but the same correlations arise in any model where (a) structures in the galaxy distribution grow from homogeneous initial conditions in a way that satisfies the continuity equation, and (b) the present-day velocity field is irrotational and proportional to the time-averaged velocity field. We demonstrate these assertions using analytical arguments and N-body simulations. If large-scale structure is formed by gravitational instability, then the ratio of the galaxy density contrast to the divergence of the velocity field yields an estimate of the density parameter Omega (or, more generally, an estimate of beta identically equal to Omega(exp 0.6)/b, where b is an assumed constant of proportionality between galaxy and mass density fluctuations. In nongravitational scenarios, the values of Omega or beta estimated in this way may fail to represent the true cosmological values. However, even if nongravitational forces initiate and shape the growth of structure, gravitationally induced accelerations can dominate the velocity field at late times, long after the action of any nongravitational impulses. The estimated beta approaches the true value in such cases, and in our numerical simulations the estimated beta values are reasonably accurate for both gravitational and nongravitational models. Reconstruction tests

  19. THE EFFECT OF NONLINEAR LANDAU DAMPING ON ULTRARELATIVISTIC BEAM PLASMA INSTABILITIES

    SciTech Connect

    Chang, Philip; Lamberts, Astrid; Broderick, Avery E.; Shalaby, Mohamad; Pfrommer, Christoph; Puchwein, Ewald

    2014-12-20

    Very high energy gamma-rays from extragalactic sources produce pairs from the extragalactic background light, yielding an electron-positron pair beam. This pair beam is unstable to various plasma instabilities, especially the ''oblique'' instability, which can be the dominant cooling mechanism for the beam. However, recently, it has been claimed that nonlinear Landau damping renders it physically irrelevant by reducing the effective damping rate to a low level. Here we show with numerical calculations that the effective damping rate is 8 × 10{sup –4} the growth rate of the linear instability, which is sufficient for the ''oblique'' instability to be the dominant cooling mechanism of these pair beams. In particular, we show that previous estimates of this rate ignored the exponential cutoff in the scattering amplitude at large wave numbers and assumed that the damping of scattered waves entirely depends on collisions, ignoring collisionless processes. We find that the total wave energy eventually grows to approximate equipartition with the beam by increasingly depositing energy into long-wavelength modes. As we have not included the effect of nonlinear wave-wave interactions on these long-wavelength modes, this scenario represents the ''worst case'' scenario for the oblique instability. As it continues to drain energy from the beam at a faster rate than other processes, we conclude that the ''oblique'' instability is sufficiently strong to make it the physically dominant cooling mechanism for high-energy pair beams in the intergalactic medium.

  20. Chromatic instabilities in cesium-doped tungsten bronze nanoparticles

    SciTech Connect

    Adachi, Kenji Ota, Yosuke; Tanaka, Hiroyuki; Okada, Mika; Oshimura, Nobumitsu; Tofuku, Atsushi

    2013-11-21

    Nanoparticles of alkali-doped tungsten bronzes are an excellent near-infrared shielding material, but exhibit slight chromatic instabilities typically upon applications of strong ultra-violet light or heating in humid environment, which acts detrimentally to long-life commercial applications. Origin of the chromatic instabilities in cesium-doped tungsten bronze has been investigated, and it has been found that the coloration and bleaching processes comprised electronic exchanges which accelerate or depress the polaron excitation and the localized surface plasmon resonance. Coloration on UV illumination is evidenced by electron diffraction as due to the formation of H{sub x}WO{sub 3}, which is considered to take place in the surface Cs-deficient WO{sub 3} region via the double charge injection mechanism. On the other hand, bleaching on heating in air and in humid environment is shown to accompany the extraction of Cs and electrons from Cs{sub 0.33}WO{sub 3} by X-ray photoelectron spectroscopy and X-ray diffraction analysis and is concluded to be an oxidation of Cs{sub 0.33}WO{sub 3} on the particle surface.

  1. Waves and instabilities in a magnetized plasma

    NASA Technical Reports Server (NTRS)

    Dawson, J. M.

    1982-01-01

    Work on computer simulation of waves and instabilities in magnetized plasmas is reviewed. Included are verification of linear theory. Particular emphasis is given to investigation of nonlinear processes involved in the saturation of instabilities and of wave damping; these include a nonlinear cyclotron resonance and particle trapping in intense waves.

  2. Perception of Job Instability in Europe

    ERIC Educational Resources Information Center

    Bockerman, Petri

    2004-01-01

    The perception of job instability is an important measure of subjective wellbeing of individuals, because most people derive their income from selling their labour services. The study explores the determination of perception of job instability in Europe. The study is based on a large-scale survey from the year 1998. There are evidently large…

  3. Transverse instability digital damper for the Recycler

    SciTech Connect

    Balbekov, V.; /Fermilab

    2006-02-01

    Transverse beam instability of a coasting beam with a digital damper is examined. Threshold of instability is calculated in specific cases with Landau damping taken into account. The results are applied to the Fermilab Recycler Ring. Some improvement of existing RR damper is proposed.

  4. Cultural Diversity, Economic Development and Societal Instability

    PubMed Central

    Nettle, Daniel; Grace, James B.; Choisy, Marc; Cornell, Howard V.; Guégan, Jean-François; Hochberg, Michael E.

    2007-01-01

    Background Social scientists have suggested that cultural diversity in a nation leads to societal instability. However, societal instability may be affected not only by within-nation or α diversity, but also diversity between a nation and its neighbours or β diversity. It is also necessary to distinguish different domains of diversity, namely linguistic, ethnic and religious, and to distinguish between the direct effects of diversity on societal instability, and effects that are mediated by economic conditions. Methodology/Principal Findings We assembled a large cross-national dataset with information on α and β cultural diversity, economic conditions, and indices of societal instability. Structural equation modeling was used to evaluate the direct and indirect effects of cultural diversity on economics and societal stability. Results show that different types and domains of diversity have interacting effects. As previously documented, linguistic α diversity has a negative effect on economic performance, and we show that it is largely through this economic mechanism that it affects societal instability. For β diversity, the higher the linguistic diversity among nations in a region, the less stable the nation. But, religious β diversity has the opposite effect, reducing instability, particularly in the presence of high linguistic diversity. Conclusions Within-nation linguistic diversity is associated with reduced economic performance, which, in turn, increases societal instability. Nations which differ linguistically from their neighbors are also less stable. However, religious diversity between neighboring nations has the opposite effect, decreasing societal instability. PMID:17895970

  5. Curvature instability in passive diffractive resonators.

    PubMed

    Tlidi, M; Vladimirov, A G; Mandel, Paul

    2002-12-01

    We study the stability of localized structures in a passive optical bistable system. We show that there is a critical value of the input field intensity above which localized structures are unstable with respect to a curvature instability. Beyond this instability boundary, a transition from the localized branch of solutions to stable hexagons is found. PMID:12485009

  6. Partnership Instability, School Readiness, and Gender Disparities

    ERIC Educational Resources Information Center

    Cooper, Carey E.; Osborne, Cynthia A.; Beck, Audrey N.; McLanahan, Sara S.

    2011-01-01

    Trends in family formation during the past several decades have increased children's exposure to mothers' partnership instability, defined as an entrance into or exit from a coresidential union or a dating partnership. Instability, in turn, is associated with negative outcomes for children and adolescents. This study uses data from the Fragile…

  7. Magnetic resonance imaging in glenohumeral instability

    PubMed Central

    Jana, Manisha; Gamanagatti, Shivanand

    2011-01-01

    The glenohumeral joint is the most commonly dislocated joint of the body and anterior instability is the most common type of shoulder instability. Magnetic resonance (MR) imaging, and more recently, MR arthrography, have become the essential investigation modalities of glenohumeral instability, especially for pre-procedure evaluation before arthroscopic surgery. Injuries associated with glenohumeral instability are variable, and can involve the bones, the labor-ligamentous components, or the rotator cuff. Anterior instability is associated with injuries of the anterior labrum and the anterior band of the inferior glenohumeral ligament, in the form of Bankart lesion and its variants; whereas posterior instability is associated with reverse Bankart and reverse Hill-Sachs lesion. Multidirectional instability often has no labral pathology on imaging but shows specific osseous changes such as increased chondrolabral retroversion. This article reviews the relevant anatomy in brief, the MR imaging technique and the arthrographic technique, and describes the MR findings in each type of instability as well as common imaging pitfalls. PMID:22007285

  8. Ion-cyclotron instability in magnetic mirrors

    SciTech Connect

    Pearlstein, L.D.

    1987-02-02

    This report reviews the role of ion-cyclotron frequency instability in magnetic mirrors. The modes discussed here are loss-cone or anisotropy driven. The discussion includes quasilinear theory, explosive instabilities of 3-wave interaction and non-linear Landau damping, and saturation due to non-linear orbits. (JDH)

  9. Observations on instabilities of cavitating inducers

    NASA Technical Reports Server (NTRS)

    Braisted, D.; Brennen, C.

    1978-01-01

    Experimental observations of instability of cavitating inducers were made for two different inducers operating at different flow coefficients. In general, instability occurred just before head breakdown. Auto-oscillation and rotating cavitation were observed. Analysis of small-amplitude behavior of the inducer and hydraulic system is carried out, and analytical predictions of stability limits were compared with experiment.

  10. Cultural diversity, economic development and societal instability

    USGS Publications Warehouse

    Nettle, D.; Grace, J.B.; Choisy, M.; Cornell, H.V.; Guegan, J.-F.; Hochberg, M.E.

    2007-01-01

    Background. Social scientists have suggested that cultural diversity in a nation leads to societal instability. However, societal instability may be affected not only by within-nation on ?? diversity, but also diversity between a nation and its neighbours or ?? diversity. It is also necessary to distinguish different domains of diversity, namely linguistic, ethnic and religious, and to distinguish between the direct effects of diversity on societal instability, and effects that are mediated by economic conditions. Methodology/Principal Findings. We assembled a large cross-national dataset with information on ?? and ?? cultural diversity, economic conditions, and indices of societal instability. Structural equation modeling was used to evaluate the direct and indirect effects of cultural diversity on economics and societal stability. Results show that different type and domains of diversity have interacting effects. As previously documented, linguistic ?? diversity has a negative effect on economic performance, and we show that it is largely through this economic mechanism that it affects societal instability. For ?? diversity, the higher the linguistic diversity among nations in a region, the less stable the nation. But, religious ?? diversity has the opposite effect, reducing instability, particularly in the presence of high linguistic diversity. Conclusions. Within-nation linguistic diversity is associated with reduced economic performance, which, in turn, increases societal instability. Nations which differ linguistically from their neighbors are also less stable. However, religious diversity between, neighboring nations has the opposite effect, decreasing societal instability.

  11. Multiscale instabilities in soft heterogeneous dielectric elastomers

    PubMed Central

    Rudykh, S.; Bhattacharya, K.; deBotton, G.

    2014-01-01

    The development of instabilities in soft heterogeneous dielectric elastomers is investigated. Motivated by experiments and possible applications, we use in our analysis the physically relevant referential electric field instead of electric displacement. In terms of this variable, a closed form solution is derived for the class of layered neo-Hookean dielectrics. A criterion for the onset of electromechanical multiscale instabilities for the layered composites with anisotropic phases is formulated. A general condition for the onset of the macroscopic instability in soft multiphase dielectrics is introduced. In the example of the layered dielectrics, the essential influence of the microstructure on the onset of instabilities is revealed. We found that: (i) macroscopic instabilities dominate at moderate volume fractions of the stiffer phase, (ii) interface instabilities appear at small volume fractions of the stiffer phase and (iii) instabilities of a finite scale, comparable to the microstructure size, occur at large volume fractions of the stiffer phase. The latest new type of instabilities does not appear in the purely mechanical case and dominates in the region of large volume fractions of the stiff phase. PMID:24511258

  12. Superresonant instability of a compressible hydrodynamic vortex

    NASA Astrophysics Data System (ADS)

    Oliveira, Leandro A.; Cardoso, Vitor; Crispino, Luís C. B.

    2016-06-01

    We show that a purely circulating and compressible system, in an adiabatic regime of acoustic propagation, presents superresonant instabilities. To show the existence these instabilities, we compute the quasinormal mode frequencies of this system numerically using two different frequency domain methods.

  13. Instabilities in coaxial rotating jets

    NASA Astrophysics Data System (ADS)

    Ivanic, Tanja; Foucault, Eric; Pecheux, Jean; Gilard, Virginie

    2000-12-01

    The aim of this study is the characterization of the cylindrical mixing layer resulting from the interaction of two coaxial swirling jets. The experimental part of this study was performed in a cylindrical water tunnel, permitting an independent rotation of two coaxial jets. The rotations are generated by means of 2×36 blades localized in two swirling chambers. As expected, the evolution of the main instability modes presents certain differences compared to the plane-mixing-layer case. Experimental results obtained by tomography showed the existence of vortex rings and streamwise vortex pairs in the near field region. This method also permitted the observation of the evolution and interaction of different modes. PIV velocity measurements realized in the meridian plans and the plans perpendicular to the jet axis show that rotation distorts the typical top-hat axial velocity profile. The transition of the axial velocity profile from jet-like into wake-like is also observed.

  14. RADIATIVE RAYLEIGH-TAYLOR INSTABILITIES

    SciTech Connect

    Jacquet, Emmanuel; Krumholz, Mark R. E-mail: krumholz@ucolick.org

    2011-04-01

    We perform analytic linear stability analyses of an interface separating two stratified media threaded by a radiation flux, a configuration relevant in several astrophysical contexts. We develop a general framework for analyzing such systems and obtain exact stability conditions in several limiting cases. In the optically thin, isothermal regime, where the discontinuity is chemical in nature (e.g., at the boundary of a radiation pressure-driven H II region), radiation acts as part of an effective gravitational field, and instability arises if the effective gravity per unit volume toward the interface overcomes that away from it. In the optically thick 'adiabatic' regime where the total (gas plus radiation) specific entropy of a Lagrangian fluid element is conserved, for example at the edge of radiation pressure-driven bubble around a young massive star, we show that radiation acts like a modified equation of state and derive a generalized version of the classical Rayleigh-Taylor stability condition.

  15. Morphological instabilities of polymer crystals.

    PubMed

    Grozev, N; Botiz, I; Reiter, G

    2008-09-01

    We present experimental observations at comparatively low supercooling of morphology transitions from dendritic to faceted structures in polymer crystals growing in thin films of a poly-2-vinylpyridine-block-polyethyleneoxid copolymer. Our results are compared with theoretical concepts describing morphological instabilities of single crystals. Although these concepts originally were not developed for polymers, they allow to describe and interpret our experimental results quite well. In particular, the measured temperature dependence of the width W and frequency of dendritic side branches and the radius of curvature p of the growth tips of the crystals follow these concepts. We present preliminary evidence for the influence of polymer attachment kinetics and reorganisation processes behind the growth front. Polymer thin films provide valuable model systems for studying general concepts of crystallisation and allow to distinguish at which point the connectivity of the crystallising units within chain-like molecules starts to play a measurable role.

  16. Robinson instability and beam loading

    SciTech Connect

    Craft, B.C. III

    1985-01-01

    The Robinson instability problem is developed in three stages. The first step is to derive the synchrotron oscillation equations in the absence of beam loading (unloaded case). Next, the equations are evaluated in the presence of beam loading at the fundamental rf frequency (statically loaded case). Finally, the system is redeveloped taking into account beam loading at the synchrotron sidebands (dynamically loaded case). Following the theoretical development, the results are applied to calculate the synchrotron frequency in the presence of beam-loading, automatic-gain-control, and automatic-tune-control. The results of this calculation are compared with data from the NSLS vuv-ring, a 750 MeV electron storage ring. 1 ref., 3 figs.

  17. Gravitational Instability in Suspension Flows

    NASA Technical Reports Server (NTRS)

    Carpen, Ileana C.; Brady, John F.

    2002-01-01

    The gravity-driven flow of non-neutrally buoyant suspensions is shown to be unstable to spanwise perturbations when the shearing motion generates a density profile that increases with height. The instability is simply due to having heavier material over light. The wavelength of the perturbation is found to be on the order of the thickness of the suspension layer. The parameters important to the problem are the angle of inclination of the layer relative to gravity, the relative density difference between the particles and fluid, the ratio of the particle size to the suspension layer, and the bulk volume fraction of particles. An example showing the growth rate as a function of wave number is shown.

  18. Visco-resistive plasmoid instability

    NASA Astrophysics Data System (ADS)

    Comisso, Luca; Grasso, Daniela

    2016-03-01

    The plasmoid instability in visco-resistive current sheets is analyzed in both the linear and nonlinear regimes. The linear growth rate and the wavenumber are found to scale as S1 /4(1+Pm ) -5 /8 and S3 /8(1+Pm ) -3 /16 with respect to the Lundquist number S and the magnetic Prandtl number Pm. Furthermore, the linear layer width is shown to scale as S-1 /8(1+Pm ) 1 /16 . The growth of the plasmoids slows down from an exponential growth to an algebraic growth when they enter into the nonlinear regime. In particular, the time-scale of the nonlinear growth of the plasmoids is found to be τNL˜S-3 /16(1+Pm) 19 /32τA,L . The nonlinear growth of the plasmoids is radically different from the linear one, and it is shown to be essential to understand the global current sheet disruption. It is also discussed how the plasmoid instability enables fast magnetic reconnection in visco-resistive plasmas. In particular, it is shown that the recursive plasmoid formation can trigger a collisionless reconnection regime if S ≳Lc s(ɛclk) -1(1+Pm) 1 /2 , where Lcs is the half-length of the global current sheet and lk is the relevant kinetic length scale. On the other hand, if the current sheet remains in the collisional regime, the global (time-averaged) reconnection rate is shown to be ≈ɛcvA ,uBu(1+Pm) -1 /2 , where ɛc is the critical inverse aspect ratio of the current sheet, while vA,u and Bu are the Alfvén speed and the magnetic field upstream of the global reconnection layer.

  19. Evolution of genetic instability in heterogeneous tumors.

    PubMed

    Asatryan, Ani D; Komarova, Natalia L

    2016-05-01

    Genetic instability is an important characteristic of cancer. While most cancers develop genetic instability at some stage of their progression, sometimes a temporary rise of instability is followed by the return to a relatively stable genome. Neither the reasons for these dynamics, nor, more generally, the role of instability in tumor progression, are well understood. In this paper we develop a class of mathematical models to study the evolutionary competition dynamics among different sub-populations in a heterogeneous tumor. We observe that despite the complexity of this multi-component and multi-process system, there is only a small number of scenarios expected in the context of the evolution of instability. If the penalty incurred by unstable cells (the decrease in the growth due to deleterious mutations) is high compared with the gain (the production rate of advantageous mutations), then instability does not evolve. In the opposite case, instability evolves and comes to dominate the system. In the intermediate parameter regime, instability is generated but later gives way to stable clones. Moreover, the model also informs us of the patterns of instability for cancer lineages corresponding to different stages of progression. It is predicted that mutations causing instability are merely "passengers" in tumors that have undergone only a small number of malignant mutations. Further down the path of carcinogenesis, however, unstable cells are more likely to give rise to the winning clonal wave that takes over the tumor and carries the evolution forward, thus conferring a causal role of the instability in such cases. Further, each individual clonal wave (i.e. cells harboring a fixed number of malignant driver mutations) experiences its own evolutionary history. It can fall under one of three types of temporal behavior: stable throughout, unstable to stable, or unstable throughout. Which scenario is realized depends on the subtle (but predictable) interplay among

  20. Evolution of genetic instability in heterogeneous tumors.

    PubMed

    Asatryan, Ani D; Komarova, Natalia L

    2016-05-01

    Genetic instability is an important characteristic of cancer. While most cancers develop genetic instability at some stage of their progression, sometimes a temporary rise of instability is followed by the return to a relatively stable genome. Neither the reasons for these dynamics, nor, more generally, the role of instability in tumor progression, are well understood. In this paper we develop a class of mathematical models to study the evolutionary competition dynamics among different sub-populations in a heterogeneous tumor. We observe that despite the complexity of this multi-component and multi-process system, there is only a small number of scenarios expected in the context of the evolution of instability. If the penalty incurred by unstable cells (the decrease in the growth due to deleterious mutations) is high compared with the gain (the production rate of advantageous mutations), then instability does not evolve. In the opposite case, instability evolves and comes to dominate the system. In the intermediate parameter regime, instability is generated but later gives way to stable clones. Moreover, the model also informs us of the patterns of instability for cancer lineages corresponding to different stages of progression. It is predicted that mutations causing instability are merely "passengers" in tumors that have undergone only a small number of malignant mutations. Further down the path of carcinogenesis, however, unstable cells are more likely to give rise to the winning clonal wave that takes over the tumor and carries the evolution forward, thus conferring a causal role of the instability in such cases. Further, each individual clonal wave (i.e. cells harboring a fixed number of malignant driver mutations) experiences its own evolutionary history. It can fall under one of three types of temporal behavior: stable throughout, unstable to stable, or unstable throughout. Which scenario is realized depends on the subtle (but predictable) interplay among

  1. Is delayed genomic instability specifically induced by high-LET particles?

    NASA Astrophysics Data System (ADS)

    Testard, Isabelle; Sabatier, Laure

    1998-12-01

    Ionizing radiation can induce a large variety of damages in the DNA. The processing or repair of this damage occurs in the first minutes up to several hours after irradiation. Afterwhile the remaining lesions are fixed in an irreparable state. However, in recent years, data have accumulated to suggest that genomic instability can manifest in the progeny of irradiated cells leading to accumulation of damage through cell generations. Different biological endpoints were described: delayed cell death, delayed mutations, de novo chromosomal instability. The question regarding the ability of sparsely ionizing X-or γ-rays to induce such phenomenon is still unclear for normal cells. In most of the reports, high linear energy transfer (LET) particles are able to induce genomic instability but not low-LET particles. The mechanisms underlying this phenomenon are still unknown. In human fibroblasts irradiated by heavy ions in a large range of LETs, we showed that the chromosomal instability is characterized by telomeric associations (TAS) involving specific chromosomes. The same instability is observed during the senescence process and during the first passages after viral transfection. The specific chromosomal instability that we observed after irradiation would not be a direct consequence of irradiation but would be a natural phenomenon occurring after many cell divisions. The effect of the irradiation would lie on the bypass of the senescence process that would permit cells with end to end fusions to survive and be transmitted through cell generations, accumulating chromosome rearrangements and chromosome imbalances. Research on molecular mechanisms of chromosomal instability is focused on the role of telomeres in end to end fusions. Such observations could contribute to understand why chromosomal instability is not a dose dependant phenomenon. Why high-LET particles would be so potent in inducing delayed instability? The answer might lie in the study of primary effects of

  2. Tensile Instability in a Thick Elastic Body

    NASA Astrophysics Data System (ADS)

    Overvelde, Johannes T. B.; Dykstra, David M. J.; de Rooij, Rijk; Weaver, James; Bertoldi, Katia

    2016-08-01

    A range of instabilities can occur in soft bodies that undergo large deformation. While most of them arise under compressive forces, it has previously been shown analytically that a tensile instability can occur in an elastic block subjected to equitriaxial tension. Guided by this result, we conducted centimeter-scale experiments on thick elastomeric samples under generalized plane strain conditions and observed for the first time this elastic tensile instability. We found that equibiaxial stretching leads to the formation of a wavy pattern, as regions of the sample alternatively flatten and extend in the out-of-plane direction. Our work uncovers a new type of instability that can be triggered in elastic bodies, enlarging the design space for smart structures that harness instabilities to enhance their functionality.

  3. Magnetothermal instability with generalized Ohm's law

    SciTech Connect

    Bora, M.P.; Talwar, S.P. )

    1993-03-01

    The problem of thermal instability, having bearing on the formation of astrophysical condensations, is investigated for a hydromagnetic fluid obeying generalized Ohm's law, both for self-gravitating and nongravitating configurations. Effects of finite Larmor frequency, resistivity, and finite plasma frequency on the stability of the system are studied and the condition of instabilities are derived for a temperature-dependent and density-dependent heat-loss function. It is found that the condition of instability for propagation parallel to the ambient magnetic field is independent of finite resistivity, Hall current, and electron inertia effects and also of the magnetic field strength. For transverse propagation, however, the instability criterion involves the field strength, resistivity, and electron inertia terms. The Hall current is found to modify the growth rates for generally inclined propagation only. Both monotonically unstable and overstable modes of instability arise in the system depending on the dependence of the heat-loss function on the local density and temperature.

  4. Tidal instability in exoplanetary systems evolution

    NASA Astrophysics Data System (ADS)

    Cébron, D.; Moutou, C.; Le Bars, M.; Le Gal, P.; Farès, R.

    2011-02-01

    A new element is proposed to play a role in the evolution of extrasolar planetary systems: the tidal (or elliptical) instability. It comes from a parametric resonance and takes place in any rotating fluid whose streamlines are (even slightly) elliptically deformed. Based on theoretical, experimental and numerical works, we estimate the growth rate of the instability for hot-jupiter systems, when the rotation period of the star is known. We present the physical process, its application to stars, and preliminary results obtained on a few dozen systems, summarized in the form of a stability diagram. Most of the systems are trapped in the so-called "forbidden zone", where the instability cannot grow. In some systems, the tidal instability is able to grow, at short timescales compared to the system evolution. Implications are discussed in the framework of misaligned transiting systems, as the rotational axis of the star would be unstable in systems where this elliptical instability grows.

  5. Parametric instabilities in the LCGT arm cavity

    NASA Astrophysics Data System (ADS)

    Yamamoto, K.; Uchiyama, T.; Miyoki, S.; Ohashi, M.; Kuroda, K.; Numata, K.

    2008-07-01

    We evaluated the parametric instabilities of LCGT (Japanese interferometric gravitational wave detector project) arm cavity. The number of unstable modes of LCGT is 10-times smaller than that of Advanced LIGO (USA). Since the strength of the instabilities of LCGT depends on the mirror curvature more weakly than that of Advanced LIGO, the requirement of the mirror curvature accuracy is easier to be achieved. The difference in the parametric instabilities between LCGT and Advanced LIGO is because of the thermal noise reduction methods (LCGT, cooling sapphire mirrors; Advanced LIGO, fused silica mirrors with larger laser beams), which are the main strategies of the projects. Elastic Q reduction by the barrel surface (0.2 mm thickness Ta2O5) coating is effective to suppress instabilities in the LCGT arm cavity. Therefore, the cryogenic interferometer is a smart solution for the parametric instabilities in addition to thermal noise and thermal lensing.

  6. Multidirectional Instability Accompanying an Inferior Labral Cyst

    PubMed Central

    Ji, Jong-Hun; Kim, Sung-Jae

    2010-01-01

    Paralabral cyst of the shoulder joint can be observed in 2% to 4% of the general population, particularly in men during the third and fourth decade. On average, these cysts measure 10 mm to 20 mm in diameter and are located preferentially on the postero-superior aspect of the glenoid. The MRI has increased the frequency of the diagnosis of paralabral cysts of the shoulder joint. Paralabral cysts of the shoulder joint usually develop in the proximity of the labrum. The relationship between shoulder instability and labral tears is well known, however, the association of shoulder instability with a paralabral cyst is rare. Shoulder instability may cause labral injury or labral injury may cause shoulder instability, and then injured tear develops paralabral cyst. In our patient, the inferior paralabral cyst may be associated with inferior labral tears and instability MRI. PMID:20514270

  7. Taming contact line instability for pattern formation

    PubMed Central

    Deblais, A.; Harich, R.; Colin, A.; Kellay, H.

    2016-01-01

    Coating surfaces with different fluids is prone to instability producing inhomogeneous films and patterns. The contact line between the coating fluid and the surface to be coated is host to different instabilities, limiting the use of a variety of coating techniques. Here we take advantage of the instability of a receding contact line towards cusp and droplet formation to produce linear patterns of variable spacings. We stabilize the instability of the cusps towards droplet formation by using polymer solutions that inhibit this secondary instability and give rise to long slender cylindrical filaments. We vary the speed of deposition to change the spacing between these filaments. The combination of the two gives rise to linear patterns into which different colloidal particles can be embedded, long DNA molecules can be stretched and particles filtered by size. The technique is therefore suitable to prepare anisotropic structures with variable properties. PMID:27506626

  8. Taylor instability in rhyolite lava flows

    NASA Technical Reports Server (NTRS)

    Baum, B. A.; Krantz, W. B.; Fink, J. H.; Dickinson, R. E.

    1989-01-01

    A refined Taylor instability model is developed to describe the surface morphology of rhyolite lava flows. The effect of the downslope flow of the lava on the structures resulting from the Taylor instability mechanism is considered. Squire's (1933) transformation is developed for this flow in order to extend the results to three-dimensional modes. This permits assessing why ridges thought to arise from the Taylor instability mechanism are preferentially oriented transverse to the direction of lava flow. Measured diapir and ridge spacings for the Little and Big Glass Mountain rhyolite flows in northern California are used in conjunction with the model in order to explore the implications of the Taylor instability for flow emplacement. The model suggests additional lava flow features that can be measured in order to test whether the Taylor instability mechanism has influenced the flows surface morphology.

  9. Tensile Instability in a Thick Elastic Body.

    PubMed

    Overvelde, Johannes T B; Dykstra, David M J; de Rooij, Rijk; Weaver, James; Bertoldi, Katia

    2016-08-26

    A range of instabilities can occur in soft bodies that undergo large deformation. While most of them arise under compressive forces, it has previously been shown analytically that a tensile instability can occur in an elastic block subjected to equitriaxial tension. Guided by this result, we conducted centimeter-scale experiments on thick elastomeric samples under generalized plane strain conditions and observed for the first time this elastic tensile instability. We found that equibiaxial stretching leads to the formation of a wavy pattern, as regions of the sample alternatively flatten and extend in the out-of-plane direction. Our work uncovers a new type of instability that can be triggered in elastic bodies, enlarging the design space for smart structures that harness instabilities to enhance their functionality. PMID:27610857

  10. Effect of pressure anisotropy on magnetorotational instability

    SciTech Connect

    Mikhailovskii, A. B.; Lominadze, J. G.; Churikov, A. P.; Erokhin, N. N.; Erokhin, N. S.; Tsypin, V. S.

    2008-02-15

    It is shown that two new instabilities of hybrid type can occur in a rotating magnetized plasma with anisotropic pressure, i.e., the rotational firehose instability and the rotational mirror instability. In the case of {beta}{sub Parallel-To} > {beta}{sub Up-Tack }, where {beta}{sub Parallel-To} and {beta}{sub Up-Tack} are the ratios of the parallel and perpendicular plasma pressure to the magnetic field pressure, the pressure anisotropy tends to suppress both new instabilities; in the case {beta}{sub Up-Tack} > {beta}{sub Parallel-To }, it leads to their strengthening. In the latter case, the perturbations considered can be unstable even if the Velikhov instability criterion is not satisfied.

  11. Taming contact line instability for pattern formation

    NASA Astrophysics Data System (ADS)

    Deblais, A.; Harich, R.; Colin, A.; Kellay, H.

    2016-08-01

    Coating surfaces with different fluids is prone to instability producing inhomogeneous films and patterns. The contact line between the coating fluid and the surface to be coated is host to different instabilities, limiting the use of a variety of coating techniques. Here we take advantage of the instability of a receding contact line towards cusp and droplet formation to produce linear patterns of variable spacings. We stabilize the instability of the cusps towards droplet formation by using polymer solutions that inhibit this secondary instability and give rise to long slender cylindrical filaments. We vary the speed of deposition to change the spacing between these filaments. The combination of the two gives rise to linear patterns into which different colloidal particles can be embedded, long DNA molecules can be stretched and particles filtered by size. The technique is therefore suitable to prepare anisotropic structures with variable properties.

  12. Resonant instability near the two-ion crossover frequency in the Io plasma torus

    NASA Astrophysics Data System (ADS)

    Thorne, R. M.; Moses, J. J.

    1985-07-01

    Thorne and Scarf (1984) have presented evidence for the existence of intense low-frequency fluctuating electric fields in the Io plasma torus. Two distinct mechanisms have been proposed for this phenomenon, namely, ion cyclotron instability which occurs at intermediate latitude, and whistler instability near the equator. The present investigation is concerned with a quantitative appraisal of each of these mechanisms, taking into account an evaluation of the net convective growth rate of waves along ray paths which traverse the Io torus. Aspects of wave propagation near the crossover frequency are considered along with questions regarding the resonant interaction with energetic particles.

  13. Nonlinear Dynamics of Single Bunch Instability

    SciTech Connect

    Stupakov, G.V.; Breizman, B.N.; Pekker, M.S.; /Texas U.

    2011-09-09

    A nonlinear equation is derived that governs the evolution of the amplitude of unstable oscillations with account of quantum diffusion effects due to the synchrotron radiation. Numerical solutions to this equation predict a variety of possible scenarios of nonlinear evolution of the instability some of which are in good qualitative agreement with experimental observations. Microwave single bunch instability in circular accelerators has been observed in many machines. The instability usually arises when the number of particles in the bunch exceeds some critical value, Nc, which varies depending on the parameters of the accelerating regime. Recent observations on the SLC damping rings at SLAC with a new low-impedance vacuum chamber revealed new interesting features of the instability. In some cases, after initial exponential growth, the instability eventually saturated at a level that remained constant through the accumulation cycle. In other regimes, relaxation-type oscillations were measured in nonlinear phase of the instability. In many cases, the instability was characterized by a frequency close to the second harmonic of the synchrotron oscillations. Several attempts have been made to address the nonlinear stage of the instability based on either computer simulations or some specific assumptions regarding the structure of the unstable mode. An attempt of a more general consideration of the problem is carried out in this paper. We adopt an approach recently developed in plasma physics for analysis of nonlinear behavior of weakly unstable modes in dynamic systems. Assuming that the growth rate of the instability is much smaller than its frequency, we find a time dependent solution to Vlasov equation and derive an equation for the complex amplitude of the oscillations valid in the nonlinear regime. Numerical solutions to this equation predict a variety of possible scenarios of nonlinear evolution of the instability some of which are in good qualitative agreement

  14. Parametric instabilities in large nonuniform laser plasmas

    SciTech Connect

    Baldis, H.A.; Montgomery, D.S.; Moody, J.D.; Estabrook, K.G.; Berger, R.L.; Kruer, W.L.; Labaune, C.; Batha, S.H.

    1992-09-01

    The study of parametric instabilities in laser plasmas is of vital importance for inertial confinement fusion (ICF). The long scale-length plasma encountered in the corona of an ICF target provides ideal conditions for the growth of instabilities such as stimulated Brillouin scattering (SBS), stimulated Raman scattering (SRS), and filamentation. These instabilities can have detrimental effects in ICF and their characterization and understanding is of importance. Scattering instabilities are driven through a feedback loop by which the beating between the electromagnetic EM fields of the laser and the scattered light matches the frequency of a local longitudinal mode of the plasma. Any process which interferes with the coherence of this mechanism can substantially alter the behavior of the instability. Of particular interest is the study of laser beam smoothing techniques on parametric instabilities. These techniques are used to improve irradiation uniformity which can suppress hydrodynamic instabilities. Laser beam smoothing techniques have the potential to control the scattering level from parametric instabilities since they provide not only a smoother laser intensity distribution, but also reduced coherence. Beam smoothing techniques that affect the growth of parametric instabilities include spatial smoothing and temporal smoothing by laser bandwidth. Spatial smoothing modifies the phase fronts and temporal distribution of intensities in the focal volume. The transverse intensity spectrum is shifted towards higher spatial wavenumber and can significantly limit the growth of filamentation. Temporal smoothing reduces the coherence time and consequently limits the growth time. Laser bandwidth is required for most smoothing techniques, and can have an independent effect on the instabilities as well.

  15. Rotordynamic Instability Problems in High-Performance Turbomachinery

    NASA Technical Reports Server (NTRS)

    1982-01-01

    Rotor dynamic instability problems in high performance turbomachinery are reviewed. Mechanical instability mechanisms are discussed. Seal forces and working fluid forces in turbomachinery are discussed. Control of rotor instability is also investigated.

  16. Predictors for Surgery in Shoulder Instability

    PubMed Central

    Lebus, George F.; Raynor, Martin B.; Nwosu, Samuel K.; Wagstrom, Emily; Jani, Sunil S.; Carey, James L.; Hettrich, Carolyn M.; Cox, Charles L.; Kuhn, John E.

    2015-01-01

    Background: Shoulder instability is a common cause of pain and dysfunction in young, active patients. While studies have analyzed risk factors for recurrent instability and failure after instability surgery, few have examined which variables are associated with initial surgery in this patient population. Purpose: To identify variables that may be associated with surgical intervention in patients with shoulder instability in the context of the FEDS (frequency, etiology, direction, severity) classification, a system that may be useful in the surgical treatment of shoulder instability patients. Study Design: Cohort study (prognosis); Level of evidence, 2. Methods: A database of patients treated for shoulder instability from 3 separate institutions from 2005 to 2010 was generated using International Classification of Diseases–9th Revision data. Data were collected via retrospective review. Injury data were categorized according to the FEDS system. Data were analyzed for significance, with the primary outcome of surgical intervention. Summary statistics were used to assess which variables were associated with eventual surgery. To test the unadjusted bivariate associations between shoulder surgery and each data point, Pearson chi-square tests were used for categorical variables and Wilcoxon tests were used for continuous variables. Results: Over the study time period, 377 patients were treated for shoulder instability. Patients who had surgery were more likely younger, had recurrent instability, and had their initial injury while playing a sport. Most patients had anterior instability; however, there was a greater proportion of posterior instability patients in the operative group. Severity of dislocation, measured by whether the patient required help to relocate the shoulder, was not significantly associated with eventual surgery. While imaging was not available for all patients, surgical patients were more likely to have magnetic resonance imaging findings of

  17. Flapping instability of a liquid jet

    NASA Astrophysics Data System (ADS)

    Matas, Jean-Philippe; Cartellier, Alain

    2013-01-01

    We study the flapping instability observed when a liquid jet is incompletely atomized by a fast parallel gas stream: the remaining liquid jet is destabilized over a scale large compared with its radius, and breaks into liquid fragments. We characterize the symmetry of this instability and its frequency. The intact liquid length is measured as a function of gas and liquid velocity, and turns out to be longer than the one predicted by Raynal (1997) for a planar mixing layer. The frequency of the instability is measured with a spectral method, and is in agreement with the frequency observed for the planar shear instability, though slightly smaller. The planar, and not helical, symmetry of the instability makes it akin to a flapping instability, observed when a planar liquid sheet is atomized by two planar gas streams. We next measure drop sizes when the flapping instability is present, with a method based on image processing. Measured size distributions are in agreement with distributions observed in a mixing layer geometry for low gas velocities (long tail distribution). The mean drop diameter depends weakly on liquid velocity, and decreases as d10˜Ug0.9. On the contrary, Sauter diameter depends strongly on liquid velocity.

  18. Baroclinic instability in stellar radiation zones

    SciTech Connect

    Kitchatinov, L. L.

    2014-03-20

    Surfaces of constant pressure and constant density do not coincide in differentially rotating stars. Stellar radiation zones with baroclinic stratification can be unstable. Instabilities in radiation zones are of crucial importance for angular momentum transport, mixing of chemical species, and, possibly, for magnetic field generation. This paper performs linear analysis of baroclinic instability in differentially rotating stars. Linear stability equations are formulated for differential rotation of arbitrary shape and then solved numerically for rotation nonuniform in radius. As the differential rotation increases, r- and g-modes of initially stable global oscillations transform smoothly into growing modes of baroclinic instability. The instability can therefore be interpreted as stability loss to r- and g-modes excitation. Regions of stellar parameters where r- or g-modes are preferentially excited are defined. Baroclinic instability onsets at a very small differential rotation of below 1%. The characteristic time of instability growth is about 1000 rotation periods. Growing disturbances possess kinetic helicity. Magnetic field generation by the turbulence resulting from baroclinic instability in differentially rotating radiation zones is therefore possible.

  19. Secondary instabilities in compressible boundary layers

    NASA Technical Reports Server (NTRS)

    Ng, Lian; Erlebacher, Gordon

    1990-01-01

    Secondary instabilities are examined in compressible boundary layers at Mach numbers M(sub infinity) = 0, 0.8, 1.6, and 4.5. It is found that there is a broad-band of highly unstable 3-d secondary disturbances whose growth rates increase with increasing primary wave amplitude. At M(sub infinity) is less than or equal to 1.6, fundamental resonance dominates at relatively high (2-d) primary disturbance amplitude, while subharmonic resonance is characterized by a low (2-d) primary amplitude. At M(sub infinity) = 4.5, the subharmonic instability which arises from the second mode disturbance is the strongest type of secondary instability. The influence of the inclination, theta, of the primary wave with respect to the mean flow direction on secondary instability is investigated at M(sub infinity) = 1.6 for small to moderate values of theta. It is found that the strongest fundamental instability occurs when the primary wave is inclined at 10 deg to the mean flow direction, although a 2-d primary mode yields the most amplified subharmonic. The subharmonic instability at a high value of theta (namely, theta = 45 deg) is also discussed. Finally, a subset of the secondary instability results are compared against direct numerical simulations.

  20. Elliptical instability in the planetary fluid cores

    NASA Astrophysics Data System (ADS)

    Moradi, Ali

    Elliptical instability may be excited in any rotating flow with elliptically deformed streamlines. Investigating this instability in containers with spheroidal or ellipsoidal boundaries is of geophysical and astrophysical interest as many stars and planets are either rotating ellipsoidal fluid bodies or have substantial fluid cores which are either ellipsoidal, in the absence of a solid inner core, or ellipsoidal shells such as the Earth's fluid core; elliptical instability may be excited in these bodies as a result of the gravitational pull of a secondary body such as a moon or a large asteroid orbiting these bodies. In this thesis, the nonlinear evolution of elliptical instability in an inviscid incompressible rotating triaxial ellipsoid is numerically studied using the least-square finite element method. After validating the method by reproducing some known results, it is applied to other configurations in order to investigate some open questions on this subject, namely, the effects of the oblateness of the ellipsoid and the frequency ratio of the orbital speed of the secondary body on the evolution of the elliptical instability. We have found that if the parameters of the system, i.e. the flattening ratio and the frequency ratio of the background rotation, are in the range of the spin-over instability, a repetitive three-dimensional rigorous motion is maintained indefinitely; otherwise, instability may be excited initially, once the streamlines become elliptical, for certain ranges of the system parameters; however, as time elapses the motion becomes two dimensional with small displacement amplitudes in x- and y- directions.

  1. Smectic layer instabilities in liquid crystals.

    PubMed

    Dierking, Ingo; Mitov, Michel; Osipov, Mikhail A

    2015-02-01

    Scientists aspire to understand the underlying physics behind the formation of instabilities in soft matter and how to manipulate them for diverse investigations, while engineers aim to design materials that inhibit or impede the nucleation and growth of these instabilities in critical applications. The present paper reviews the field-induced rotational instabilities which may occur in chiral smectic liquid-crystalline layers when subjected to an asymmetric electric field. Such instabilities destroy the so-named bookshelf geometry (in which the smectic layers are normal to the cell surfaces) and have a detrimental effect on all applications of ferroelectric liquid crystals as optical materials. The transformation of the bookshelf geometry into horizontal chevron structures (in which each layer is in a V-shaped structure), and the reorientation dynamics of these chevrons, are discussed in details with respect to the electric field conditions, the material properties and the boundary conditions. Particular attention is given to the polymer-stabilisation of smectic phases as a way to forbid the occurrence of instabilities and the decline of related electro-optical performances. It is also shown which benefit may be gained from layer instabilities to enhance the alignment of the liquid-crystalline geometry in practical devices, such as optical recording by ferroelectric liquid crystals. Finally, the theoretical background of layer instabilities is given and discussed in relation to the experimental data.

  2. Weakly nonlinear instability of planar viscoelastic sheets

    NASA Astrophysics Data System (ADS)

    Wang, Chen; Yang, Li-jun; Xie, Luo; Chen, Pi-min

    2015-01-01

    A second-order weakly nonlinear analysis has been made of the temporal instability for the linear sinuous mode of two-dimensional planar viscoelastic liquid sheets moving in an inviscid gas. The convected Jeffreys models including the corotational Jeffreys model, Oldroyd A model, and the Oldroyd B model are considered as the rheology model of the viscoelastic fluid of the sheet. The solution for the second-order gas-to-liquid interface displacement has been derived, and the temporal evolution leading to the breakup has been shown. The second-order interface displacement of the linear sinuous mode is varicose, which causes the sheet to fragment into ligaments. First-order constitutive relations of the three rheology models become identical after linearization, so the linear instability results are also the same. For the second-order weakly nonlinear instability, the second-order constitutive relation varies among the corotational Jeffreys model, Oldroyd A model, and the Oldroyd B model, but although they have different disturbance pressures, their disturbance velocities and interface displacements are the same, and therefore, the sheets of the corotational Jeffreys fluid, Oldroyd A fluid, and the Oldroyd B fluid have the same instability behavior characterized by the wave profile and breakup time. The reason for the identical instability behavior is that the effect of different codeformations of the corotational frame, covariant frame, and the contravariant frame is counteracted by the corresponding change in the second-order disturbance pressure, leaving no influence on the second-order velocity. At wavenumbers with maximum instabilities, an increase in the elasticity, or a reduction of the deformation retardation time, leads to a larger linear temporal growth rate, greater second-order disturbance amplitude, and shorter breakup time, thereby enhancing instability. The mechanism of linear instability has been examined using an energy approach, which shows that the

  3. Fingering instability in combustion: an extended view.

    PubMed

    Zik, O; Moses, E

    1999-07-01

    We detail the experimental situation concerning the fingering instability that occurs when a solid fuel is forced to burn against a horizontal oxidizing wind. The instability appears when the Rayleigh number for convection is below criticality. The focus is on the developed fingering state. We present direct measurements of the depletion of oxygen by the front as well as new results that connect heat losses to the characteristic scale of the instability. In addition, we detail the experimental system, elaborate (qualitatively and quantitatively) on the results that were previously presented, and discuss new observations. We also show that the same phenomenological model applies to electrochemical deposition.

  4. Black Hole Instabilities and Local Penrose Inequalities

    NASA Astrophysics Data System (ADS)

    Figueras, Pau; Murata, Keiju; Reall, Harvey S.

    2015-01-01

    Various higher-dimensional black holes have been shown to be unstable by studying linearized gravitational perturbations. A simpler method for demonstrating instability is to find initial data that describes a small perturbation of the black hole and violates a Penrose inequality. We use the method to confirm the existence of the "ultraspinning" instability of Myers-Perry black holes. We also study black rings and show that "fat" black rings are unstable. We find no evidence of any rotationally symmetric instability of "thin" black rings.

  5. Anatomy, pathophysiology, and biomechanics of shoulder instability.

    PubMed

    Doukas, W C; Speer, K P

    2001-07-01

    Instability in the athlete presents a unique challenge to the orthopaedic surgeon. A spectrum of both static and dynamic pathophysiology, as well as gross and microscopic histopathology, contribute to this complex clinical continuum. Biomechanical studies of the shoulder and ligament cutting studies in recent years have generated a more precise understanding of the individual contributions of the various ligaments and capsular regions to shoulder instability. An understanding of the underlying pathology and accurate assessment of degree and direction of the instability by clinical examination and history are essential to developing appropriate treatment algorithms.

  6. Inviscid instability of streamwise corner flow

    NASA Technical Reports Server (NTRS)

    Balachandar, S.; Malik, M. R.

    1993-01-01

    Linear stability of the incompressible flow along a stream wise corner is studied by solving the two-dimensional eigenvalue problem governed by partial differential equations. It is found that this fully three-dimensional flow is subject to inviscid instability due to the inflectional nature of the stream wise velocity profile. The higher growth rates for the inviscid instability mode, which is symmetric about the corner bisector, as compared to the viscous Tollmien-Schlichting instability operative away from the corner is consistent with the experimental findings that the corner flow transitions to turbulence earlier than the two-dimensional Blasius flow away from the corner.

  7. Rayleigh-Taylor instability in binary condensates

    SciTech Connect

    Gautam, S.; Angom, D.

    2010-05-15

    We propose a well-controlled experimental scheme to initiate and examine the Rayleigh-Taylor instability in two-species Bose-Einstein condensates. We identify the {sup 85}Rb-{sup 87}Rb mixture as an excellent candidate to observe experimentally. The instability is initiated by tuning the {sup 85}Rb-{sup 85}Rb interaction through a magnetic Feshbach resonance. We show that the observable signature of the instability is the damping of the radial oscillations. We also propose a semianalytic scheme to determine the stationary state of binary condensates with the Thomas-Fermi approximation for axisymmetric traps.

  8. A drift model of interchange instability

    SciTech Connect

    Benilov, E. S.; Power, O. A.

    2007-08-15

    A set of asymptotic equations is derived, describing the dynamics of the flute mode in a magnetized plasma with cold ions, under a 'local' approximation (i.e., near a particular point). The asymptotic set is then used to calculate the growth rate of interchange instability in the slab model. It is shown that, unlike the magnetohydrodynamic ordering, the drift one allows instability to occur for either sign of the pressure gradient (i.e., for both 'bad' and 'good' curvature of the magnetic field). It is also demonstrated that finite beta gives rise to an extra instability that does not exist in the small-beta limit.

  9. A new formulation of longitudinal coherent instabilities

    SciTech Connect

    Zhang, S.Y.; Weng, W.T.

    1993-01-01

    The quadrature response of longitudinal impedance is shown to be the effective impedance for the beam instability. The results of the application of this formulation are compared with that obtained using the Robinson-Pedersen approach and the Sacherer integral equation. The formulation is further generalized to the rigid bunch motion using signal analysis method, where a form factor shows up naturally. Finally, the formulation is applied to solve the coupled bunch instabilities. Examples of the AGS Booster and the AGS coupled bunch instabilities are used to illustrate the applications of the formulation.

  10. A new formulation of longitudinal coherent instabilities

    SciTech Connect

    Zhang, S.Y.; Weng, W.T.

    1993-06-01

    The quadrature response of longitudinal impedance is shown to be the effective impedance for the beam instability. The results of the application of this formulation are compared with that obtained using the Robinson-Pedersen approach and the Sacherer integral equation. The formulation is further generalized to the rigid bunch motion using signal analysis method, where a form factor shows up naturally. Finally, the formulation is applied to solve the coupled bunch instabilities. Examples of the AGS Booster and the AGS coupled bunch instabilities are used to illustrate the applications of the formulation.

  11. Meniscus Instability in a Thin Elastic Film

    NASA Astrophysics Data System (ADS)

    Ghatak, Animangsu; Chaudhury, Manoj K.; Shenoy, Vijay; Sharma, Ashutosh

    2000-11-01

    A new kind of meniscus instability leading to the formation of stationary fingers with a well-defined spacing has been observed in experiments with elastomeric films confined between a plane rigid glass and a thin curved glass plate. The wavelength of the instability increases linearly with the thickness of the confined film, but it is remarkably insensitive to the compliance and the energetics of the system. However, lateral amplitude (length) of the fingers depends on the compliance of the system and on the radius of curvature of the glass plate. A simple linear stability analysis is used to explain the underlying physics and the key observed features of the instability.

  12. Sawtooth Stabilization and Onset of Alfvenic Instabilities

    NASA Astrophysics Data System (ADS)

    Nishimura, Y.; Cheng, C. Z.

    2011-10-01

    Tokamak sawtooth instabilities can be stabilized by high energy particles as a consequence of conservation of the third adiabatic invariant.On the other hand, termination of the stabilized period is reported due to the onset of Alfvenic instabilities (and thus the absence of the stabilizing mechanism). In this work, employing a kinetic-fluid model, the interaction of m=1 resistive kink mode and high energy particles is investigated. The onset of Alfvenic instabilities is examined as a function of the inversion radius location. D.J. Campbell et al., Phys. Rev. Lett. 60, 2148 (1988); F. Porcelli, Plasma Phys. Controlled Fusion 33, 1601 (1991).

  13. RICHTMYER-MESHKOV-TYPE INSTABILITY OF A CURRENT SHEET IN A RELATIVISTICALLY MAGNETIZED PLASMA

    SciTech Connect

    Inoue, Tsuyoshi

    2012-11-20

    The linear stability of a current sheet that is subject to an impulsive acceleration due to shock passage with the effect of a guide magnetic field is studied. We find that a current sheet embedded in relativistically magnetized plasma always shows a Richtmyer-Meshkov-type instability, while the stability depends on the density structure in the Newtonian limit. The growth of the instability is expected to generate turbulence around the current sheet, which can induce the so-called turbulent reconnection, the rate of which is essentially free from plasma resistivity. Thus, the instability can be applied as a triggering mechanism for rapid magnetic energy release in a variety of high-energy astrophysical phenomena such as pulsar wind nebulae, gamma-ray bursts, and active galactic nuclei, where the shock wave is thought to play a crucial role.

  14. Suppression of microbunching instability using bending magnets in free-electron-laser linacs.

    PubMed

    Qiang, Ji; Mitchell, Chad E; Venturini, Marco

    2013-08-01

    The microbunching instability driven by collective effects of the beam inside an accelerator can significantly degrade the final electron beam quality for free electron laser (FEL) radiation. In this Letter, we propose an inexpensive scheme to suppress such an instability in accelerators for next generation FEL light sources. Instead of using an expensive device such as a laser heater or RF deflecting cavities, this scheme uses longitudinal mixing associated with the transverse spread of the beam through bending magnets inside the accelerator transport system to suppress the instability. The final uncorrelated energy spread increases roughly by the current compression factor, which is important in seeded FEL schemes in order to achieve high harmonic short-wavelength x-ray radiation.

  15. Chromosomal instability determines taxane response

    PubMed Central

    Swanton, Charles; Nicke, Barbara; Schuett, Marion; Eklund, Aron C.; Ng, Charlotte; Li, Qiyuan; Hardcastle, Thomas; Lee, Alvin; Roy, Rajat; East, Philip; Kschischo, Maik; Endesfelder, David; Wylie, Paul; Kim, Se Nyun; Chen, Jie-Guang; Howell, Michael; Ried, Thomas; Habermann, Jens K.; Auer, Gert; Brenton, James D.; Szallasi, Zoltan; Downward, Julian

    2009-01-01

    Microtubule-stabilizing (MTS) agents, such as taxanes, are important chemotherapeutics with a poorly understood mechanism of action. We identified a set of genes repressed in multiple cell lines in response to MTS agents and observed that these genes are overexpressed in tumors exhibiting chromosomal instability (CIN). Silencing 22/50 of these genes, many of which are involved in DNA repair, caused cancer cell death, suggesting that these genes are involved in the survival of aneuploid cells. Overexpression of these “CIN-survival” genes is associated with poor outcome in estrogen receptor–positive breast cancer and occurs frequently in basal-like and Her2-positive cases. In diploid cells, but not in chromosomally unstable cells, paclitaxel causes repression of CIN-survival genes, followed by cell death. In the OV01 ovarian cancer clinical trial, a high level of CIN was associated with taxane resistance but carboplatin sensitivity, indicating that CIN may determine MTS response in vivo. Thus, pretherapeutic assessment of CIN may optimize treatment stratification and clinical trial design using these agents. PMID:19458043

  16. Chromosomal instability determines taxane response.

    PubMed

    Swanton, Charles; Nicke, Barbara; Schuett, Marion; Eklund, Aron C; Ng, Charlotte; Li, Qiyuan; Hardcastle, Thomas; Lee, Alvin; Roy, Rajat; East, Philip; Kschischo, Maik; Endesfelder, David; Wylie, Paul; Kim, Se Nyun; Chen, Jie-Guang; Howell, Michael; Ried, Thomas; Habermann, Jens K; Auer, Gert; Brenton, James D; Szallasi, Zoltan; Downward, Julian

    2009-05-26

    Microtubule-stabilizing (MTS) agents, such as taxanes, are important chemotherapeutics with a poorly understood mechanism of action. We identified a set of genes repressed in multiple cell lines in response to MTS agents and observed that these genes are overexpressed in tumors exhibiting chromosomal instability (CIN). Silencing 22/50 of these genes, many of which are involved in DNA repair, caused cancer cell death, suggesting that these genes are involved in the survival of aneuploid cells. Overexpression of these "CIN-survival" genes is associated with poor outcome in estrogen receptor-positive breast cancer and occurs frequently in basal-like and Her2-positive cases. In diploid cells, but not in chromosomally unstable cells, paclitaxel causes repression of CIN-survival genes, followed by cell death. In the OV01 ovarian cancer clinical trial, a high level of CIN was associated with taxane resistance but carboplatin sensitivity, indicating that CIN may determine MTS response in vivo. Thus, pretherapeutic assessment of CIN may optimize treatment stratification and clinical trial design using these agents. PMID:19458043

  17. Taylor Instability of Incompressible Liquids

    DOE R&D Accomplishments Database

    Fermi, E.; von Neumann, J.

    1955-11-01

    A discussion is presented in simplified form of the problem of the growth of an initial ripple on the surface of an incompressible liquid in the presence of an acceleration, g, directed from the outside into the liquid. The model is that of a heavy liquid occupying at t = 0 the half space above the plane z = 0, and a rectangular wave profile is assumed. The theory is found to represent correctly one feature of experimental results, namely the fact that the half wave of the heavy liquid into the vacuum becomes rapidly narrower while the half wave pushing into the heavy liquid becomes more and more blunt. The theory fails to account for the experimental results according to which the front of the wave pushing into the heavy liquid moves with constant velocity. The case of instability at the boundary of 2 fluids of different densities is also explored. Similar results are obtained except that the acceleration of the heavy liquid into the light liquid is reduced.

  18. Gravitational Instability in Planetesimal Disks

    NASA Astrophysics Data System (ADS)

    Bolin, Bryce T.; Lithwick, Yoram; Pan, Margaret; Rein, Hanno; Wu, Yanqin

    2014-11-01

    Gravitational instability (GI) has been proposed as a method of forming giant gas planets enhanced by disk thermodynamics in a protoplanetary disk (Boss, 1997, Science 276; Durisen et al., 2007, Protostars and Planets V) and as a method of forming planetesimals through the focusing of boulders by the interaction between solids and gases in a turbulent circumstellar disk (Johansen et al., 2007, Nature 448; Youdin & Goodman, 2005, Astrophys. J. 620). GI is mediated through a gaseous circumstellar disk in each each of these scenarios. We explore the possibility of GI occurring in a planetesimal disk devoid of gas. In this regime, mutual collisions between planetesimals are required to dissipate their orbital shear and velocity dispersion enough for collapse to occur as described by the Toomre stability criterion (Toomre, 1964, Astrophys. J. 139; Toomre, 1981, Structure and Evolution of Normal Galaxies). How frequent must collisions be between planetesimals in a gravitationally stable planetesimal disk for GI to occur? Are there collisional rates where GI is postponed indefinitely in an equilibrium state between gravitational stirring and collisional cooling? We present 3D shearing sheet simulations using the REBOUND N-body code with the symplectic epicyclic integrator (Rein & Liu, 2011, A&A 537; Rein & Tremaine, 2011, MNRAS 415) in which the candidate collision rates are within a few orders of magnitude of the disk dynamical lifetime. Our simulations suggest that collisions rate directly controls disk cooling. The shape of the disk cooling curve is independent of the collision rate when scaled to the collision time.

  19. Boyle's law and gravitational instability

    NASA Astrophysics Data System (ADS)

    Lombardi, M.; Bertin, G.

    2001-09-01

    We have re-examined the classical problem of the macroscopic equation of state for a hydrostatic isothermal self-gravitating gas cloud bounded by an external medium at constant pressure. We have obtained analytical conditions for its equilibrium and stability without imposing any specific shape and symmetry to the cloud density distribution. The equilibrium condition can be stated in the form of an upper limit to the cloud mass; this is found to be inversely proportional to the power 3/2 of a form factor mu characterizing the shape of the cloud. In this respect, the spherical solution, associated with the maximum value of the form factor, mu = 1, turns out to correspond to the shape that is most difficult to realize. Surprisingly, the condition that defines the onset of the Bonnor instability (or gravothermal catastrophe) can be cast in the form of an upper limit to the density contrast within the cloud that is independent of the cloud shape. We have then carried out a similar analysis in the two-dimensional case of infinite cylinders, without assuming axisymmetry. The results obtained in this paper generalize well-known results available for spherical or axisymmetric cylindrical isothermal clouds that have had wide astrophysical applications, especially in the study of the interstellar medium.

  20. Thermal instability of cell nuclei

    NASA Astrophysics Data System (ADS)

    Warmt, Enrico; Kießling, Tobias R.; Stange, Roland; Fritsch, Anatol W.; Zink, Mareike; Käs, Josef A.

    2014-07-01

    DNA is known to be a mechanically and thermally stable structure. In its double stranded form it is densely packed within the cell nucleus and is thermo-resistant up to 70\\:^\\circ {\\rm{C}}. In contrast, we found a sudden loss of cell nuclei integrity at relatively moderate temperatures ranging from 45 to 55\\:^\\circ {\\rm{C}}. In our study, suspended cells held in an optical double beam trap were heated under controlled conditions while monitoring the nuclear shape. At specific critical temperatures, an irreversible sudden shape transition of the nuclei was observed. These temperature induced transitions differ in abundance and intensity for various normal and cancerous epithelial breast cells, which clearly characterizes different cell types. Our results show that temperatures slightly higher than physiological conditions are able to induce instabilities of nuclear structures, eventually leading to cell death. This is a surprising finding since recent thermorheological cell studies have shown that cells have a lower viscosity and are thus more deformable upon temperature increase. Since the nucleus is tightly coupled to the outer cell shape via the cytoskeleton, the force propagation of nuclear reshaping to the cell membrane was investigated in combination with the application of cytoskeletal drugs.

  1. Polygonal instability of Marangoni flows

    NASA Astrophysics Data System (ADS)

    Roché, Matthieu; Labousse, Matthieu; El Hadj Maiga, Baba; Nya, Loïc; Le Roux, Sébastien; Cantat, Isabelle; Saint-Jalmes, Arnaud

    2015-11-01

    The transport of pepper grains floating at the surface of a bowl of water after the release of a drop of dishwashing liquid is a classical experiment to demonstrate the Marangoni effect, i.e. the flow of a liquid layer induced by interfacial tension gradients at its surface. In this case, the interfacial tension gradient results from a surfactant interfacial concentration gradient. Recently, we showed that continuous injection of an aqueous solution of hydrosoluble surfactants at the surface of a cm-thick pure water layer induced finite-size Marangoni flows surrounded by a region characterized by the presence of several pairs of interfacial vortices arranged along the the vertices of polygons. During this talk, I will show that we can understand the flow structure induced by these Marangoni flows, in particular their tendency to have polygonal shapes. I will describe how flow features such as the number of interfacial vortices or bulk recirculation flows depend on flow geometry. Finally, I will compare these results to a model that explains similar polygonal instabilities in other flows such as the hydraulic jump.

  2. THE MAGNETOVISCOUS-THERMAL INSTABILITY

    SciTech Connect

    Islam, Tanim

    2012-02-10

    Accretion flows onto underluminous black holes, such as Sagittarius A* at the center of our galaxy, are dilute (mildly collisional to highly collisionless), optically thin, and radiatively inefficient. Therefore, the accretion properties of such dilute flows are expected to be modified by their large viscosities and thermal conductivities. Second, turbulence within these systems needs to transport angular momentum as well as thermal energy generated through gravitational infall outward in order to allow accretion to occur. This is in contrast to classical accretion flows, in which the energy generated through accretion down a gravitational well is locally radiated. In this paper, using an incompressible fluid treatment of an ionized gas, we expand on previous research by considering the stability properties of a magnetized rotating plasma wherein the thermal conductivity and viscosity are not negligible and may be dynamically important. We find a class of MHD instabilities that can transport angular momentum and thermal energy outward. They are plausible candidates to describe accretion in radiatively inefficient accretion flows. We finish by discussing the implications for analytic models and numerical MHD simulations of mildly dilute or collisionless astrophysical plasmas, and immediate directions for further research.

  3. Instability of viscoelastic compound jets

    NASA Astrophysics Data System (ADS)

    Ye, Han-Yu; Yang, Li-Jun; Fu, Qing-Fei

    2016-04-01

    This paper investigates the axisymmetric instability of a viscoelastic compound jet, for which the constitutive relation is described by the Oldroyd B model. It is found that a viscoelastic compound jet is more unstable than a Newtonian compound jet, regardless of whether the viscoelastic compound jet is inner-Newtonian-outer-viscoelastic, inner-viscoelastic-outer-Newtonian, or fully viscoelastic. It is also found that an increase in the stress relaxation time of the inner or outer fluid renders the jet more unstable, while an increase in the time constant ratio makes the jet less unstable. An analysis of the energy budget of the destabilization process is performed, in which a formulation using the relative rate of change of energy is adopted. The formulation is observed to provide a quantitative analysis of the contribution of each physical factor (e.g., release of surface energy and viscous dissipation) to the temporal growth rate. The energy analysis reveals the mechanisms of various trends in the temporal growth rate, including not only how the growth rate changes with the parameters, but also how the growth rate changes with the wavenumber. The phenomenon of the dispersion relation presenting two local maxima, which occurred in previous research, is explained by the present energy analysis.

  4. Plasma effects on extragalactic ultra-high-energy cosmic ray hadron beams in cosmic voids

    SciTech Connect

    Krakau, S.; Schlickeiser, R. E-mail: rsch@tp4.rub.de

    2014-07-01

    The linear instability of an ultrarelativistic hadron beam (Γ {sub b} ≈ 10{sup 6}) in the unmagnetized intergalactic medium (IGM) is investigated with respect to the excitation of collective electrostatic and aperiodic electromagnetic fluctuations. This analysis is important for the propagation of extragalactic ultrarelativistic cosmic rays (E > 10{sup 15} eV) from their distant sources to Earth. We calculate minimum instability growth times that are orders of magnitude shorter than the cosmic ray propagation time in the IGM. Due to nonlinear effects, especially the modulation instability, the cosmic ray beam stabilizes and can propagate with nearly no energy loss through the IGM.

  5. Overview of Rayleigh-Taylor instability

    SciTech Connect

    Sharp, D.H.

    1983-01-01

    The aim of this talk is to survey Rayleigh-Taylor instability, describing the phenomenology that occurs at a Taylor unstable interface, and reviewing attempts to understand these phenomena quantitatively.

  6. Magnetorotational decay instability in Keplerian disks.

    PubMed

    Shtemler, Yuri; Liverts, Edward; Mond, Michael

    2013-12-01

    The saturation of the magnetorotational instability (MRI) in thin Keplerian disks through three-wave resonant interactions is introduced and discussed. That mechanism is a natural generalization of the fundamental decay instability discovered five decades ago for infinite, homogeneous, and immovable plasmas. The decay instability relies on the energy transfer from the MRI to stable slow Alfvén-Coriolis as well as magnetosonic waves. A second-order forced Duffing amplitude equation for the initially unstable MRI as well as two first-order equations for the other two waves are derived. The solutions of those equations exhibit bounded bursty nonlinear oscillations for the MRI as well as unbounded growth for the linearly stable slow Alfvén-Coriolis and magnetosonic perturbations, thus giving rise to the magnetorotational decay instability. PMID:24476249

  7. Hydrodynamic instability of solar thermosyphon water heaters

    SciTech Connect

    Du, S.C.; Huang, B.J.; Yen, R.H. . Dept. of Mechanical Engineering)

    1994-02-01

    The flow instability of a solar thermosyphon water heater is studied analytically. A system dynamics model is derived by means of a one-dimensional approach and a linear perturbation method. The characteristic equation is obtained and the Nyquist criterion is used to examine the flow stability. The parameter M is a dimensionless parameter of system stability. The stability maps are plotted in terms of 14 parameters. The occurrence of hydrodynamic instability is determined by comparing the stability curves and the designed values of M. Flow instability is shown not to occur in most of solar water heaters commercially available, because the loop friction is relatively high in the design and because solar irradiation in field operation is still not high enough to cause flow instability.

  8. Nonlinear dynamics: When instability makes sense

    NASA Astrophysics Data System (ADS)

    Ashwin, Peter; Timme, Marc

    2005-07-01

    Mathematical models that use instabilities to describe changes of weather patterns or spacecraft trajectories are well established. Could such principles apply to the sense of smell, and to other aspects of neural computation?

  9. Stepper motor instabilities in an aerospace application

    NASA Technical Reports Server (NTRS)

    Kackley, Russell; Mccully, Sean

    1992-01-01

    Stepper motors are frequently used in positioning mechanisms because they have several advantages over ordinary DC motors. However, there is frequently no feedback loop and the motor may exhibit instabilities under some conditions. A stepper motor in an aerospace positioning mechanism was investigated. During testing, the motor exhibited unstable behavior, such as backrunning and forward running. The instability was dependent on voltage pulse characteristics, temperature, positioning angle, step rate, and interaction between the two motors in the system. Both testing and analysis results verified the instability. A special purpose FORTRAN code was written to simulate the system. This code was combined with another simpler code to show the performance of the system in the phase plane so that instability boundaries could be displayed along with the motor performance. The analysis was performed to verify that proposed modifications would produce stable performance before implementation in the hardware. Subsequent testing verified the analytic stability predictions.

  10. INSTABILITY ISSUES AT THE SNS STORAGE RING

    SciTech Connect

    ZHANG,S.Y.

    1999-06-28

    The impedance and beam instability issues of the SNS storage ring is reviewed, and the effort toward solutions at the BNL is reported. Some unsettled issues are raised, indicating the direction of planned works.

  11. Experimental Replication of an Aeroengine Combustion Instability

    NASA Technical Reports Server (NTRS)

    Cohen, J. M.; Hibshman, J. R.; Proscia, W.; Rosfjord, T. J.; Wake, B. E.; McVey, J. B.; Lovett, J.; Ondas, M.; DeLaat, J.; Breisacher, K.

    2000-01-01

    Combustion instabilities in gas turbine engines are most frequently encountered during the late phases of engine development, at which point they are difficult and expensive to fix. The ability to replicate an engine-traceable combustion instability in a laboratory-scale experiment offers the opportunity to economically diagnose the problem (to determine the root cause), and to investigate solutions to the problem, such as active control. The development and validation of active combustion instability control requires that the causal dynamic processes be reproduced in experimental test facilities which can be used as a test bed for control system evaluation. This paper discusses the process through which a laboratory-scale experiment was designed to replicate an instability observed in a developmental engine. The scaling process used physically-based analyses to preserve the relevant geometric, acoustic and thermo-fluid features. The process increases the probability that results achieved in the single-nozzle experiment will be scalable to the engine.

  12. Parametric instabilities in weakly magnetized plasma

    SciTech Connect

    Weatherall, J.C.; Goldman, M.V.; Nicholson, D.R.

    1981-05-15

    Parametric instabilities in a weakly magnetized plasma are discussed. The results are applied to waves excited by electron streams which travel outward from the Sun along solar-wind magnetic field lines, as in a type III solar radio burst.

  13. Instabilities of geared couplings: Theory and practice

    NASA Technical Reports Server (NTRS)

    Kirk, R. G.; Mondy, R. E.; Murphy, R. C.

    1982-01-01

    The use of couplings for high speed turbocompressors or pumps is essential to transmit power from the driver. Typical couplings are either of the lubricated gear or dry diaphragm type design. Gear couplings have been the standard design for many years and recent advances in power and speed requirements have pushed the standard design criteria to the limit. Recent test stand and field data on continuous lube gear type couplings have forced a closer examination of design tolerances and concepts to avoid operational instabilities. Two types of mechanical instabilities are reviewed in this paper: (1) entrapped fluid, and (2) gear mesh instability resulting in spacer throw-out onset. Test stand results of these types of instabilities and other directly related problems are presented together with criteria for proper coupling design to avoid these conditions. An additional test case discussed shows the importance of proper material selection and processing and what can happen to an otherwise good design.

  14. Electrostatic ion cyclotron velocity shear instability

    NASA Technical Reports Server (NTRS)

    Lemons, D. S.; Winske, D.; Gary, S. P.

    1992-01-01

    A local electrostatic dispersion equation is derived for a shear flow perpendicular to an ambient magnetic field, which includes all kinetic effects and involves only one important parameter. The dispersion equation is cast in the form of Gordeyev integrals and is solved numerically. Numerical solutions indicate that an ion cyclotron instability is excited. The instability occurs roughly at multiples of the ion cyclotron frequency (modified by the shear), with the growth rate or the individual harmonics overlapping in the wavenumber. At large values of the shear parameter, the instability is confined to long wavelengths, but at smaller shear, a second distinct branch at shorter wavelengths also appears. The properties of the instability obtained are compared with those obtained in the nonlocal limit by Ganguli et al. (1985, 1988).

  15. The universal instability in general geometry

    SciTech Connect

    Helander, P.; Plunk, G. G.

    2015-09-15

    The “universal” instability has recently been revived by Landreman et al. [Phys. Rev. Lett. 114, 095003 (2015)], who showed that it indeed exists in plasma geometries with straight (but sheared) magnetic field lines. Here, it is demonstrated analytically that this instability can be presented in more general sheared and toroidal geometries. In a torus, the universal instability is shown to be closely related to the trapped-electron mode, although the trapped-electron drive is usually dominant. However, this drive can be weakened or eliminated, as in the case in stellarators with the maximum-J property, leaving the parallel Landau resonance to drive a residual mode, which is identified as the universal instability.

  16. The nature of symmetric instability and its similarity to convective and inertial instability

    NASA Technical Reports Server (NTRS)

    Xu, Q.; Clark, J. H. E.

    1985-01-01

    It is shown that there exists a local similarity among SI (Symmetric Instability), BI (Buoyancy or Convective Instability), and II (Inertial Instability) even for fully nonlinear viscous motion. The most unstable slope angles for SI and Moist SI motions are analyzed based on parcel energetics. These considerations also suggest qualitatively that CSI (Conditional SI) circulations will be slantwise and lie between the moist most unstable slope and dry least stable slope of the basic state.

  17. Reduced modeling of the magnetorotational instability

    NASA Astrophysics Data System (ADS)

    Jamroz, Ben F.

    2009-06-01

    Accretion describes the process by which matter in an astrophysical disk falls onto a central massive object. Accretion disks are present in many astrophysical situations including binary star systems, young stellar objects, and near black holes at the center of galaxies. Measurements from observations of these disks have shown that viscous processes are unable to transport the necessary levels of angular momentum needed for accretion. Therefore, accretion requires an efficient mechanism of angular momentum transport. Mixing by turbulent processes greatly enhances the level of angular momentum transport in a turbulent fluid. Thus, the generation of turbulence in these disks may provide the mechanism needed for accretion. A classical result of hydrodynamic theory is that typical accretion disks are hydrodynamically stable to shear instabilities, since the specific angular momentum increases outwards. Other processes of generating hydrodynamic turbulence (barotropic instability, baroclinic instability, sound wave, shock waves, finite amplitude instabilities) may be present in these disks, however, none of these mechanisms has been shown to produce the level of angular momentum transport needed for accretion. Hydrodynamical turbulence does not produce enough angular momentum transport to produce the level of accretion observed in astrophysical accretion disks. The leading candidate for the source of turbulence leading to the transport of angular momentum is the magnetorotational instability, a linear axisymmetric instability of electrically conducting fluid in the presence of an imposed magnetic field and shear (or differential rotation). This instability is an efficient mechanism of angular momentum transport generating the level of transport needed for accretion. The level of effective angular momentum transport is determined by the saturated state of sustained turbulence generated by the instability. The mechanism of nonlinear saturation of this instability is not

  18. A new inclination instability in planetary systems

    NASA Astrophysics Data System (ADS)

    Madigan, Ann-Marie

    2015-08-01

    I describe a new instability in Keplerian disks of massive particles on eccentric orbits. Gravitational torques between the orbits align their angles of pericenter and drive exponential growth in orbital inclination. This instability implies specific ratios for Kepler elements of the orbits, similar to what is seen in the inner Oort Cloud of our solar system. I also discuss implications for extra-solar planetary systems and for nuclear star clusters in the centers of galaxies.

  19. High-pressure mechanical instability in rocks

    USGS Publications Warehouse

    Byerlee, J.D.; Brace, W.F.

    1969-01-01

    At a confining pressure of a few kilobars, deformation of many sedimentary rocks, altered mafic rocks, porous volcanic rocks, and sand is ductile, in that instabilities leading to audible elastic shocks are absent. At pressures of 7 to 10 kilobars, however, unstable faulting and stick-slip in certain of these rocks was observed. This high pressure-low temperature instability might be responsible for earthquakes in deeply buried sedimentary or volcanic sequences.

  20. Flow instabilities in transonic small disturbance theory

    NASA Technical Reports Server (NTRS)

    Williams, M. H.; Bland, S. R.; Edwards, J. W.

    1985-01-01

    The dynamics of unsteady transonic small disturbance flows about two-dimensional airfoils is examined, with emphasis on the behavior in the region where the steady state flow is nonunique. It is shown that nonuniqueness results from an extremely long time scale instability which occurs in a finite Mach number and angle of attack range. The similarity scaling rules for the instability are presented and the possibility of similar behavior in the Euler equations is discussed.

  1. Computational methods for probability of instability calculations

    NASA Technical Reports Server (NTRS)

    Wu, Y.-T.; Burnside, O. H.

    1990-01-01

    This paper summarizes the development of the methods and a computer program to compute the probability of instability of a dynamic system than can be represented by a system of second-order ordinary linear differential equations. Two instability criteria based upon the roots of the characteristics equation or Routh-Hurwitz test functions are investigated. Computational methods based on system reliability analysis methods and importance sampling concepts are proposed to perform efficient probabilistic analysis. Numerical examples are provided to demonstrate the methods.

  2. Observation of noisy precursors of dynamical instabilities

    SciTech Connect

    Jeffries, C.; Wiesenfeld, K.

    1985-02-01

    We have measured the power spectra of a periodically driven p-n junction in the vicinity of a dynamical instability. The addition of external noise introduces new lines in the spectra, which become more prominent as a bifurcation point is approached. The scaling of the peak, width, area, and line shape of these lines is measured near the onset of two different codimension-one instabilities: the period doubling and Hopf bifurcations. The results are in excellent agreement with recent theoretical predictions.

  3. Anterior instability in the throwing shoulder.

    PubMed

    Savoie, Felix H; O'Brien, Michael J

    2014-06-01

    The disabled throwing shoulder is a multifactorial problem. Laxity of the glenohumeral joint is necessary to achieve a satisfactory velocity. Normal wear and tear with throwing may convert this normal amount of excessive translation into instability. Instability in the throwing athlete manifests itself in 2 forms: traumatic anterior instability that happens to occur in a throwing athlete and excessive anterior subluxation because of overuse that occurs in conjunction with the disabled throwing shoulder. In most cases, it is difficult to determine by physical examination or imaging how much laxity is too much; therefore, the managing physician should always err on the side of caution. A trial of rest and rehabilitation should always be attempted before any consideration of surgery. The multifactorial issues in the disabled throwing athlete should be corrected during this phase of treatment, including assessment and treatment of hip abnormalities, restoration of satisfactory core strength, correction of scapular dyskinesis, and an evaluation and correction of any biomechanical abnormalities in the throwing mechanism. Surgical management of anterior instability in the throwing shoulder depends on the mechanism of injury. The traumatic anterior instability patient is managed by acute surgical repair without a shift, utilizing mattress sutures to prevent suture chondromalacia on the humeral head or glenoid. The anterior laxity management centers on the posterior superior labrum, although occasionally the anterior labrum or capsule may be involved as well. Overall, symptomatic anterior instability is less common in the throwing shoulder. Jobe and colleagues are credited with the first successful technique for the correction of anterior instability in the throwing athlete, the anterior capsulolabral reconstruction by a subscapularis split. The success of this technique paved the way for the adoption of the current arthroscopic techniques that are utilized to correct

  4. Energetic particle instabilities in fusion plasmas

    NASA Astrophysics Data System (ADS)

    Sharapov, S. E.; Alper, B.; Berk, H. L.; Borba, D. N.; Breizman, B. N.; Challis, C. D.; Classen, I. G. J.; Edlund, E. M.; Eriksson, J.; Fasoli, A.; Fredrickson, E. D.; Fu, G. Y.; Garcia-Munoz, M.; Gassner, T.; Ghantous, K.; Goloborodko, V.; Gorelenkov, N. N.; Gryaznevich, M. P.; Hacquin, S.; Heidbrink, W. W.; Hellesen, C.; Kiptily, V. G.; Kramer, G. J.; Lauber, P.; Lilley, M. K.; Lisak, M.; Nabais, F.; Nazikian, R.; Nyqvist, R.; Osakabe, M.; Perez von Thun, C.; Pinches, S. D.; Podesta, M.; Porkolab, M.; Shinohara, K.; Schoepf, K.; Todo, Y.; Toi, K.; Van Zeeland, M. A.; Voitsekhovich, I.; White, R. B.; Yavorskij, V.; TG, ITPA EP; Contributors, JET-EFDA

    2013-10-01

    Remarkable progress has been made in diagnosing energetic particle instabilities on present-day machines and in establishing a theoretical framework for describing them. This overview describes the much improved diagnostics of Alfvén instabilities and modelling tools developed world-wide, and discusses progress in interpreting the observed phenomena. A multi-machine comparison is presented giving information on the performance of both diagnostics and modelling tools for different plasma conditions outlining expectations for ITER based on our present knowledge.

  5. High-pressure mechanical instability in rocks.

    PubMed

    Byerlee, J D; Brace, W F

    1969-05-01

    At a confining pressure of a few kilobars, deformation of many sedimentary rocks, altered mafic rocks, porous volcanic rocks, and sand is ductile, in that instabilities leading to audible elastic shocks are absent. At pressures of 7 to 10 kilobars, however, unstable faulting and stick-slip in certain of these rocks was observed. This high pressure-low temperature instability might be responsible for earthquakes in deeply buried sedimentary or volcanic sequences.

  6. Relativistically modulational instability by strong Langmuir waves

    SciTech Connect

    Liu, X. L.; Liu, S. Q.; Li, X. Q.

    2012-09-15

    Based on the set of nonlinear coupling equations, which has considered the relativistic effects of electrons, modulational instability by strong Langmuir waves has been investigated in this paper. Both the characteristic scale and maximum growth rate of the Langmuir field will enhance with the increase in the electron relativistic effect. The numerical results indicate that longitudinal perturbations induce greater instability than transverse perturbations do, which will lead to collapse and formation of the pancake-like structure.

  7. Magnetorotational instabilities and pulsar kick velocities

    NASA Astrophysics Data System (ADS)

    Heras, Ricardo

    2016-02-01

    At the end of their birth process, neutron stars can be subject to a magnetorotational instability in which a conversion of kinetic energy of differential rotation into radiation and kinetic energies is expected to occur at the Alfvén timescale of a few ms. This birth energy conversion predicts the observed large velocity of neutron stars if during the evolving of this instability the periods are of a few ms and the magnetic fields reach values of 1016 G.

  8. Instabilities In The Flow Between Rotating Disks

    NASA Astrophysics Data System (ADS)

    Moisy, F.; Gauthier, G.; Gondret, P.; Rabaud, M.

    Instabilities in the flow between two close rotating disks enclosed by a cylinder are investigated experimentally. This flow undergoes a large gallery of instability patterns, presented in the plane of parameters (Reb, Ret) of the Reynolds numbers based on the velocity of each disk and the distance between them. The corotation case and the counter-rotation case with low counter-rotation ratio are very similar to the rotor-stator case: instabilities of the Bödewadt type boundary layer leads to axisymmetric vortices and positive spirals. The counter-rotation case with higher counter-rotation ratio is more complex: above a given rotation ratio, the radial recirculation flow gets organized in a two-cell structure with the apparition of a stagnation circle on the slower disk. A new kind of instability pattern is observed, called negative spirals, that may coexist with the positive spirals (Gauthier et al, subm. J. Fluid Mech. 2001). This new spiral pattern seems to arise from an azimuthal shear layer instability, rather than a boundary layer instability as for the two other patterns. Negative spirals are characterized for different aspect ratios (azimuthal mode, phase velocity), allowing comparisons with recent numerical simulations (Lopez et al, to appear in J. Fluid Mech. 2002).

  9. On the chiral imbalance and Weibel instabilities

    NASA Astrophysics Data System (ADS)

    Kumar, Avdhesh; Bhatt, Jitesh R.; Kaw, P. K.

    2016-06-01

    We study the chiral-imbalance and the Weibel instabilities in presence of the quantum anomaly using the Berry-curvature modified kinetic equation. We argue that in many realistic situations, e.g. relativistic heavy-ion collisions, both the instabilities can occur simultaneously. The Weibel instability depends on the momentum anisotropy parameter ξ and the angle (θn) between the propagation vector and the anisotropy direction. It has maximum growth rate at θn = 0 while θn = π / 2 corresponds to a damping. On the other hand the pure chiral-imbalance instability occurs in an isotropic plasma and depends on difference between the chiral chemical potentials of right and left-handed particles. It is shown that when θn = 0, only for a very small values of the anisotropic parameter ξ ∼ξc, growth rates of the both instabilities are comparable. For the cases ξc < ξ ≪ 1 or ξ ≳ 1 at θn = 0, the Weibel modes dominate over the chiral-imbalance instability if μ5 / T ≤ 1. However, when μ5 / T ≥ 1, it is possible to have dominance of the chiral-imbalance modes at certain values of θn for an arbitrary ξ.

  10. Charge instabilities in strongly correlated bilayer systems

    NASA Astrophysics Data System (ADS)

    Seibold, G.

    2003-09-01

    We investigate the charge-instabilities of the Hubbard-Holstein model with two coupled layers. In this system the scattering processes naturally separate into contributions which are either symmetric or antisymmetric combinations with respect to exchange of the layers. It turns out that the short-range strong correlations suppress finite wave-vector nesting instabilities for both symmetries but favor the occurrence of phase separation in the symmetric channel. Inclusion of a sizeable long-range Coulomb (LRC) interaction frustrates the q=0 instabilities and supports the formation of incommensurate charge-density waves (CDW). Upon reducing doping from half-filling and for small electron-phonon coupling g the CDW instability first occurs in the antisymmetric channel but both instability lines merge with increasing g. While LRC forces always suppress the phase separation instability in the symmetric channel, the CDW period in the antisymmetric sector tends to infinity (q_cto 0) for sufficiently small Coulomb interaction. This feature allows for the possibility of singular scattering over the whole Fermi surface. We discuss possible implications of our results for the bilayer high- T c cuprates.

  11. Paradox of inductionless magnetorotational instability

    NASA Astrophysics Data System (ADS)

    Priede, J.; Grants, I.; Gerbeth, G.

    2007-04-01

    We consider the magnetorotational instability (MRI) of a hydrodynamically stable Taylor-Couette flow with a helical external magnetic field in the inductionless approximation defined by a zero magnetic Prandtl number (Pm = 0). This leads to a considerable simplification of the problem eventually containing only hydrodynamic variables. First, we point out that the energy of any perturbation growing in the presence of magnetic field has to grow faster without the field. This is a paradox because the base flow is stable without the magnetic while it is unstable in the presence of a helical magnetic field without being modified by the latter as it has been found recently by Hollerbach and Rüdiger [Phys. Rev. Lett. 95, 124501 (2005)]. We revisit this problem by using a Chebyshev collocation method to calculate the eigenvalue spectrum of the linearized problem. In this way, we confirm that MRI with helical magnetic field indeed works in the inductionless limit where the destabilization effect appears as an effective shift of the Rayleigh line. Second, we integrate the linearized equations in time to study the transient behavior of small amplitude perturbations, thus showing that the energy arguments are correct as well. However, there is no real contradiction between both facts. The linear stability theory predicts the asymptotic development of an arbitrary small-amplitude perturbation, while the energy stability theory yields the instant growth rate of any particular perturbation, but it does not account for the evolution of this perturbation. Thus, although switching off the magnetic field instantly increases the energy growth rate, in the same time the critical perturbation ceases to be an eigenmode without the magnetic field. Consequently, this perturbation is transformed with time and so looses its ability to extract energy from the base flow necessary for the growth.

  12. Transverse to longitudinal phase space coupling in an electron beam for suppression of microbunching instability

    NASA Astrophysics Data System (ADS)

    Huang, Dazhang; Feng, Chao; Deng, Haixiao; Gu, Qiang; Zhao, Zhentang

    2016-10-01

    The microbunching instability developed during the beam compression process in the linear accelerator (LINAC) of a free-electron laser (FEL) facility has always been a problem that degrades the lasing performance, and even no FEL is able to be produced if the beam quality is destroyed too much by the instability. A common way to suppress the microbunching instability is to introduce extra uncorrelated energy spread by the laser heater that heats the beam through the interaction between the electron and laser beam, as what has been successfully implemented in the Linac Coherent Light Source and Fermi@Elettra. In this paper, a simple and effective scheme is proposed to suppress the microbunching instability by adding two transverse gradient undulators (TGU) before and after the magnetic bunch compressor. The additional uncorrelated energy spread and the density mixing from the transverse spread brought up by the first TGU results in significant suppression of the instability. Meanwhile, the extra slice energy spread and the transverse emittance can also be effectively recovered by the second TGU. The magnitude of the suppression can be easily controlled by varying the strength of the magnetic fields of the TGUs. Theoretical analysis and numerical simulations demonstrate the capability of the proposed technique in the LINAC of an x-ray free-electron laser facility.

  13. An Evaluation of the Richtmyer-Meshkov Instability in Supernova Remnant Formation

    SciTech Connect

    Kane, J. |; Drake, R.P. |; Remington, B.A. |

    1999-01-01

    We present an initial evaluation of the role of the Richtmyer-Meshkov (RM) instability in supernova remnant (SNR) formation. Although the Rayleigh-Taylor (RT) instability is most often considered in the canonical picture of SNR formation, the theoretical penetration depths for RM instability suggest that it could play a significant role in the early stages of SNR formation. We have used the code PROMETHEUS to perform a sequence of two-dimensional hydrodynamic simulations in order to test this possibility. Here we discuss a case in which we impose a large perturbation in the expanding ejecta behind the reverse shock. The interaction of the reverse shock with the perturbation produces significant early RM growth, with spikes penetrating from the contact surface to near the forward shock. Then the RM instability weakens, RT growth eventually dominates, and the perturbation of the forward shock diminishes. We conclude that RM instability growth due to the type of perturbation we have studied might contribute to, but alone cannot account for, the observed radio and X-ray structures that extend to the forward shock in such SNRs as supernova 1006. {copyright} {ital {copyright} 1999.} {ital The American Astronomical Society}

  14. Stability of Rotating Magnetized Jets in the Solar Atmosphere. I. Kelvin–Helmholtz Instability

    NASA Astrophysics Data System (ADS)

    Zaqarashvili, Teimuraz V.; Zhelyazkov, Ivan; Ofman, Leon

    2015-11-01

    Observations show various jets in the solar atmosphere with significant rotational motions, which may undergo instabilities leading to heat ambient plasma. We study the Kelvin–Helmholtz instability (KHI) of twisted and rotating jets caused by the velocity jumps near the jet surface. We derive a dispersion equation with appropriate boundary conditions for total pressure (including centrifugal force of tube rotation), which governs the dynamics of incompressible jets. Then, we obtain analytical instability criteria of KHI in various cases, which were verified by numerical solutions to the dispersion equation. We find that twisted and rotating jets are unstable to KHI when the kinetic energy of rotation is more than the magnetic energy of the twist. Our analysis shows that the azimuthal magnetic field of 1–5 G can stabilize observed rotations in spicule/macrospicules and X-ray/extreme-ultraviolet (EUV) jets. On the other hand, nontwisted jets are always unstable to KHI. In this case, the instability growth time is several seconds for spicule/macrospicules and a few minutes (or less) for EUV/X-ray jets. We also find that standing kink and torsional Alfvén waves are always unstable near the antinodes, owing to the jump of azimuthal velocity at the surface, while the propagating waves are generally stable. Kelvin–Helmholtz (KH) vortices may lead to enhanced turbulence development and heating of surrounding plasma therefore, rotating jets may provide energy for chromospheric and coronal heating.

  15. STABILITY OF ROTATING MAGNETIZED JETS IN THE SOLAR ATMOSPHERE. I. KELVIN–HELMHOLTZ INSTABILITY

    SciTech Connect

    Zaqarashvili, Teimuraz V.; Zhelyazkov, Ivan; Ofman, Leon

    2015-11-10

    Observations show various jets in the solar atmosphere with significant rotational motions, which may undergo instabilities leading to heat ambient plasma. We study the Kelvin–Helmholtz instability (KHI) of twisted and rotating jets caused by the velocity jumps near the jet surface. We derive a dispersion equation with appropriate boundary conditions for total pressure (including centrifugal force of tube rotation), which governs the dynamics of incompressible jets. Then, we obtain analytical instability criteria of KHI in various cases, which were verified by numerical solutions to the dispersion equation. We find that twisted and rotating jets are unstable to KHI when the kinetic energy of rotation is more than the magnetic energy of the twist. Our analysis shows that the azimuthal magnetic field of 1–5 G can stabilize observed rotations in spicule/macrospicules and X-ray/extreme-ultraviolet (EUV) jets. On the other hand, nontwisted jets are always unstable to KHI. In this case, the instability growth time is several seconds for spicule/macrospicules and a few minutes (or less) for EUV/X-ray jets. We also find that standing kink and torsional Alfvén waves are always unstable near the antinodes, owing to the jump of azimuthal velocity at the surface, while the propagating waves are generally stable. Kelvin–Helmholtz (KH) vortices may lead to enhanced turbulence development and heating of surrounding plasma; therefore, rotating jets may provide energy for chromospheric and coronal heating.

  16. Critical target and dose and dose-rate responses for the induction of chromosomal instability by ionizing radiation

    NASA Technical Reports Server (NTRS)

    Limoli, C. L.; Corcoran, J. J.; Milligan, J. R.; Ward, J. F.; Morgan, W. F.

    1999-01-01

    To investigate the critical target, dose response and dose-rate response for the induction of chromosomal instability by ionizing radiation, bromodeoxyuridine (BrdU)-substituted and unsubstituted GM10115 cells were exposed to a range of doses (0.1-10 Gy) and different dose rates (0.092-17.45 Gy min(-1)). The status of chromosomal stability was determined by fluorescence in situ hybridization approximately 20 generations after irradiation in clonal populations derived from single progenitor cells surviving acute exposure. Overall, nearly 700 individual clones representing over 140,000 metaphases were analyzed. In cells unsubstituted with BrdU, a dose response was found, where the probability of observing delayed chromosomal instability in any given clone was 3% per gray of X rays. For cells substituted with 25-66% BrdU, however, a dose response was observed only at low doses (<1.0 Gy); at higher doses (>1.0 Gy), the incidence of chromosomal instability leveled off. There was an increase in the frequency and complexity of chromosomal instability per unit dose compared to cells unsubstituted with BrdU. The frequency of chromosomal instability appeared to saturate around approximately 30%, an effect which occurred at much lower doses in the presence of BrdU. Changing the gamma-ray dose rate by a factor of 190 (0.092 to 17.45 Gy min(-1)) produced no significant differences in the frequency of chromosomal instability. The enhancement of chromosomal instability promoted by the presence of the BrdU argues that DNA comprises at least one of the critical targets important for the induction of this end point of genomic instability.

  17. Outbursts in ultracompact X-ray binaries

    NASA Astrophysics Data System (ADS)

    Hameury, J.-M.; Lasota, J.-P.

    2016-10-01

    Context. Very faint X-ray binaries appear to be transient in many cases with peak luminosities much fainter than that of usual soft X-ray transients, but their nature still remains elusive. Aims: We investigate the possibility that this transient behaviour is due to the same thermal/viscous instability which is responsible for outbursts of bright soft X-ray transients, occurring in ultracompact binaries for adequately low mass-transfer rates. More generally, we investigate the observational consequences of this instability when it occurs in ultracompact binaries. Methods: We use our code for modelling the thermal-viscous instability of the accretion disc, assumed here to be hydrogen poor. We also take into account the effects of disc X-ray irradiation, and consider the impact of the mass-transfer rate on the outburst brightness. Results: We find that one can reproduce the observed properties of both the very faint and the brighter short transients (peak luminosity, duration, recurrence times), provided that the viscosity parameter in quiescence is slightly smaller (typically a factor of between two and four) than in bright soft X-ray transients and normal dwarf nova outbursts, the viscosity in outburst being unchanged. This possibly reflects the impact of chemical composition on non-ideal magnetohydrodynamic effects affecting magnetically driven turbulence in poorly ionized discs.

  18. Instability of some divalent rare earth ions and photochromic effect

    NASA Astrophysics Data System (ADS)

    Egranov, A. V.; Sizova, T. Yu.; Shendrik, R. Yu.; Smirnova, N. A.

    2016-03-01

    It was shown that the divalent rare earth ions (La, Ce, Gd, Tb, Lu, and Y) in cubic sites in alkaline earth fluorides are unstable with respect to electron autodetachment since its d1(eg) ground state is located in the conduction band which is consistent with the general tendency of these ions in various compounds. The localization of doubly degenerate d1(eg) level in the conduction band creates a configuration instability around the divalent rare earth ion that leading to the formation of anion vacancy in the nearest neighborhood, as was reported in the previous paper [A. Egranov, T. Sizova, Configurational instability at the excited impurity ions in alkaline earth fluorites, J. Phys. Chem. Solids 74 (2013) 530-534]. Thus, the formation of the stable divalent ions as La, Ce, Gd, Tb, Lu, and Y (PC+ centers) in CaF2 and SrF2 crystals during x-ray irradiation occurs via the formation of charged anion vacancies near divalent ions (Re2+va), which lower the ground state of the divalent ion relative to the conductivity band. Photochromic effect occurs under thermally or optically stimulated electron transition from the divalent rare earth ion to the neighboring anion vacancy and reverse under ultraviolet light irradiation. It is shown that the optical absorption of the PC+ centers due to d → d and d → f transitions of the divalent rare-earth ion.

  19. Plasma instabilities in electronegative inductive discharges

    NASA Astrophysics Data System (ADS)

    Marakhtanov, Alexei Mikhail

    Plasma instabilities have been observed in low-pressure inductive discharges, in the transition between low density capacitive mode and high density inductive mode of the discharge when attaching gases such as SF6 and Ar/SF 6 mixtures are used. Oscillations of charged particles, plasma potential and light emitted from the plasma with the frequencies from a few hertz to tens of kilohertz are seen for gas pressures between 1 and 100 mTorr and the discharge power in the range of 75--1200 W. The region of instability increases as the plasma becomes more electronegative and the frequency of plasma oscillations increases as the power, pressure, and gas flow rate increase. The instability frequencies may also depend on the settings of a matching network. A volume-averaged (global) model of the instability has been developed, for a discharge containing time varying densities of electrons, positive ions, and negative ions, and time invariant excited states and neutral densities. The particle and energy balance equations are integrated to produce the dynamical behavior. As pressure or power is varied to cross a threshold, the instability goes through a series of oscillatory states to large scale relaxation oscillations between higher and lower density states. The model qualitatively agrees with experimental observations, and also shows a significant influence of the matching network. A stability analysis of an electronegative discharge has been performed, using a Hurwitz criterion, for a system of linearized particle and power balance differential equations. Capacitive coupling plays a crucial role in the instability process. A variable electrostatic (Faraday) shield has been used to control the capacitive coupling from the excitation coil to the plasma. The plasma instability disappears when the shielded area exceeds 65% of the total area of the coil. The global model of instability gives a slightly higher value of 85% for instability suppression with the same discharge

  20. Black hole accretion disks - Coronal stabilization of the Lightman-Eardley instability

    NASA Technical Reports Server (NTRS)

    Ionson, J. A.; Kuperus, M.

    1984-01-01

    Physical processes by which the presence of a corona around a black hole can raise the threshold of onset of the Lightman-Eardley (L-E, 1976) instability are explored analytically. The L-E model predicts that an optically thick disk becomes unstable when the disk radiation pressure exceeds the disk gas pressure. The model has important implications for the validity of either the coronal disk or two-temperature disk models for accretion zones around black holes. It is shown that a corona can dissipate accreting gravitational energy through radiative cooling. Specific ratios of hard/soft X-rays are quantified for stable and unstable conditions. X-ray spectra from Cyg X-1 are cited as residing below the instability threshold value and thus are supportive of the coronal disk model.

  1. Parametric instabilities during electron cyclotron heating of tandem mirrors

    NASA Technical Reports Server (NTRS)

    Nicholson, D. R.

    1984-01-01

    Electron cyclotron resonance heating is one of the most commonly used methods of heating electrons in the plugs and in the thermal barriers of tandem mirrors. The intense coherent electromagnetic waves used for such heating are susceptible to parametric decay into other modes. Significant growth rates are found for the decay of either ordinary or extraordinary waves into two magnetized electron plasma waves. This and related effects may result in electron heating mechanisms rather different than those assumed in linear ray-tracing calculations. These results may help explain the unusual effects observed during heating of the Phaedrus tandem mirror device. In the general case, these instabilities may be strongly inhibited by density gradients.

  2. Crystalline instability of Bi-2212 superconducting whiskers near room temperature

    NASA Astrophysics Data System (ADS)

    Cagliero, Stefano; Agostino, Angelo; Khan, Mohammad Mizanur Rahman; Truccato, Marco; Orsini, Francesco; Marinone, Massimo; Poletti, Giulio; Lascialfari, Alessandro

    2009-05-01

    We report new evidences for the thermodynamic instability of whisker crystals in the Bi-Sr-Ca-Cu-O (BSCCO) system. Annealing treatments at 90°C have been performed on two sets of samples, which were monitored by means of X-Rays Diffraction (XRD) and Atomic Force Microscopy (AFM) measurements, respectively. Two main crystalline domains of Bi2Sr2CuCa2O8+ x (Bi-2212) were identified in the samples by the XRD data, which underwent an evident crystalline segregation after about 60 hours. Very fast dynamics of the surface modifications was also described by the AFM monitoring. Two typologies of surface structures formed after about 3 annealing hours: continuous arrays of dome shaped bodies were observed along the edges of the whiskers, while in the central regions a dense texture of flat bodies was found. These modifications are described in terms of the formation of simple oxide clusters involving a degradation of the internal layers.

  3. Flow instabilities of Alaskan glaciers

    NASA Astrophysics Data System (ADS)

    Turrin, James Bradley

    Over 300 of the largest glaciers in southern Alaska have been identified as either surge-type or pulse-type, making glaciers with flow instabilities the norm among large glaciers in that region. Consequently, the bulk of mass loss due to climate change will come from these unstable glaciers in the future, yet their response to future climate warming is unknown because their dynamics are still poorly understood. To help broaden our understanding of unstable glacier flow, the decadal-scale ice dynamics of 1 surging and 9 pulsing glaciers are investigated. Bering Glacier had a kinematic wave moving down its ablation zone at 4.4 +/- 2.0 km/yr from 2002 to 2009, which then accelerated to 13.9 +/- 2.0 km/yr as it traversed the piedmont lobe. The wave first appeared in 2001 near the confluence with Bagley Ice Valley and it took 10 years to travel ~64 km. A surge was triggered in 2008 after the wave activated an ice reservoir in the midablation zone, and it climaxed in 2011 while the terminus advanced several km into Vitus Lake. Ruth Glacier pulsed five times between 1973 and 2012, with peak velocities in 1981, 1989, 1997, 2003, and 2010; approximately every 7 years. A typical pulse increased ice velocity 300%, from roughly 40 m/yr to 160 m/yr in the midablation zone, and involved acceleration and deceleration of the ice en masse; no kinematic wave was evident. The pulses are theorized to be due to deformation of a subglacial till causing enhanced basal motion. Eight additional pulsing glaciers are identified based on the spatiotemporal pattern of their velocity fields. These glaciers pulsed where they were either constricted laterally or joined by a tributary, and their surface slopes are 1-2°. These traits are consistent with an overdeepening. This observation leads to a theory of ice motion in overdeepenings that explains the cyclical behavior of pulsing glaciers. It is based on the concept of glaciohydraulic supercooling, and includes sediment transport and erosion

  4. The microphysics and macrophysics of cosmic rays

    SciTech Connect

    Zweibel, Ellen G.

    2013-05-15

    This review paper commemorates a century of cosmic ray research, with emphasis on the plasma physics aspects. Cosmic rays comprise only ∼10{sup −9} of interstellar particles by number, but collectively their energy density is about equal to that of the thermal particles. They are confined by the Galactic magnetic field and well scattered by small scale magnetic fluctuations, which couple them to the local rest frame of the thermal fluid. Scattering isotropizes the cosmic rays and allows them to exchange momentum and energy with the background medium. I will review a theory for how the fluctuations which scatter the cosmic rays can be generated by the cosmic rays themselves through a microinstability excited by their streaming. A quasilinear treatment of the cosmic ray–wave interaction then leads to a fluid model of cosmic rays with both advection and diffusion by the background medium and momentum and energy deposition by the cosmic rays. This fluid model admits cosmic ray modified shocks, large scale cosmic ray driven instabilities, cosmic ray heating of the thermal gas, and cosmic ray driven galactic winds. If the fluctuations were extrinsic turbulence driven by some other mechanism, the cosmic ray background coupling would be entirely different. Which picture holds depends largely on the nature of turbulence in the background medium.

  5. Three-dimensional Weibel instability in astrophysical scenarios

    NASA Astrophysics Data System (ADS)

    Fonseca, Ricardo A.; Silva, Luís O.; Tonge, John W.; Mori, Warren B.; Dawson, John M.

    2003-05-01

    Near equipartition magnetic fields are predicted by gamma ray bursters models and astronomical observations, in general associated with shocks or regions with colliding streams of particles. These scenarios require the conversion of kinetic energy in the outgoing plasma shells into B-fields. How the magnetic fields are generated and how particles are accelerated is still an open question, that can only be definitely addressed via fully kinetic three-dimensional (3D) numerical simulations. These shocks are collisionless because dissipation is dominated by wave-particle interactions, i.e., it is accomplished by particle scattering in turbulent electromagnetic fields generated at the shock front, or equivalently the mean free path is much longer than the shock front thickness (a few collisionless skin depths or a few Larmor radii, in magnetized plasmas). Plasma instabilities driven by streaming particles, such as the Weibel instability, are responsible for the excitation of these turbulent electromagnetic fields. Three-dimensional fully kinetic electromagnetic relativistic particle-in-cell simulations for the collision of two interpenetrating plasma shells were performed using the code OSIRIS [Fonseca et al., Lect. Notes Comput. Sci. 2331, 342 (2002)], showing (i) the generation of long-lived near-equipartition quasistatic (electro)magnetic fields, (ii) nonthermal particle acceleration, and (iii) short-scale to long-scale B-field evolution. These results may be important to understand magnetic field generation and particle acceleration in relativistic collisionless shock fronts, in gamma ray bursters, pulsar winds, and radio supernovae, and open the way to the full 3D kinetic modeling of relativistic shocks.

  6. Active Suppression of Instabilities in Engine Combustors

    NASA Technical Reports Server (NTRS)

    Kopasakis, George

    2004-01-01

    A method of feedback control has been proposed as a means of suppressing thermo-acoustic instabilities in a liquid- fueled combustor of a type used in an aircraft engine. The basic principle of the method is one of (1) sensing combustor pressure oscillations associated with instabilities and (2) modulating the rate of flow of fuel to the combustor with a control phase that is chosen adaptively so that the pressure oscillations caused by the modulation oppose the sensed pressure oscillations. The need for this method arises because of the planned introduction of advanced, lean-burning aircraft gas turbine engines, which promise to operate with higher efficiencies and to emit smaller quantities of nitrogen oxides, relative to those of present aircraft engines. Unfortunately, the advanced engines are more susceptible to thermoacoustic instabilities. These instabilities are hard to control because they include large dead-time phase shifts, wide-band noise characterized by amplitudes that are large relative to those of the instabilities, exponential growth of the instabilities, random net phase walks, and amplitude fluctuations. In this method (see figure), the output of a combustion-pressure sensor would be wide-band-pass filtered and then further processed to generate a control signal that would be applied to a fast-actuation valve to modulate the flow of fuel. Initially, the controller would rapidly take large phase steps in order to home in, within a fraction of a second, to a favorable phase region within which the instability would be reduced. Then the controller would restrict itself to operate within this phase region and would further restrict itself to operate within a region of stability, as long as the power in the instability signal was decreasing. In the phase-shifting scheme of this method, the phase of the control vector would be made to continuously bounce back and forth from one boundary of an effective stability region to the other. Computationally

  7. Surge instability on a cavitating propeller

    NASA Astrophysics Data System (ADS)

    Duttweiler, Mark Edward

    2001-11-01

    The present study details results from experiments investigating a surge instability on a cavitating propeller. Initially, the stable behavior of the propeller is explored, and the nature and extent of the cavitation is documented at various experimental conditions, including propeller yaw. The cavitation surge instability is first explored through visual observation of the cavitation on the propeller blades and in the tip vortices. Particular note is made of similarities between the behavior of the re-entrant jets and that noted by other investigators. It is also observed that the nature of the instability is closely related to the partial cavity instability observed on single, two-dimensional hydrofoils. The flow conditions that lead to instability are determined and it is shown that onset corresponds to a specific configuration of attached cavity lengths on an individual propeller blade. Pressure measurements are obtained from transducers within the experimental facility, and the acoustic signature of the instability is identified. The magnitude of the fluctuating pressures is very large, presumably capable of producing severe hull vibration. A simple model is developed based on cavity volume estimates obtained from high speed video footage, and the predictions of the model are compared with the experimentally obtained pressures. To assess the significance of the surrounding facility in initiating and sustaining the instability, a model is developed for the experimental facility dynamics. The predictions of this model are then compared with an experimentally determined facility response to a volumetric excitation imposed by an oscillating piston. To quantify the response of the cavitation to fluctuations in test section conditions, quasistatic estimates are obtained for the cavitation compliance and mass flow gain factor of the propeller. These parameters have previously been employed in developing system transfer functions for cavitating pumps. Finally, a model

  8. Bilateral, atraumatic, proximal tibiofibular joint instability.

    PubMed

    Morrison, Troy D; Shaer, James A; Little, Jill E

    2011-01-01

    Dislocation of the tibiofibular joint is rare and usually results from a traumatic event. Only 1 case of atraumatic proximal tibiofibular joint instability in a 14-year-old girl has been reported in the literature, however this condition might occur more frequently than once thought. A wide range of treatment options exist for tibiofibular dislocations. Currently, the first choice is a conservative approach, and when this fails, surgical means such as resection of the fibula head, arthrodesis, and reconstruction are considered. However, no consensus exists on the most effective treatment. This article reports a unique case of bilateral, atraumatic, proximal tibia and fibular joint instability involving a 30-year-old man with a 20-year history of pain and laxity in the right knee. The patient had no trauma to his knees; he reported 2 immediate family members with similar complaints, which suggests that this case is likely congenital. After conservative approaches proved to be ineffective, the patient underwent capsular reconstruction using free autologous gracilis tendon. At 6-month postoperative follow-up, the patient was pain free with no locking and instability. He then underwent surgery on the left knee. At 1-year follow-up after the second surgery, the patient had no symptoms or restrictions in mobility. We provide an alternative surgical approach to arthrodesis and resection for the treatment of chronic proximal tibiofibular instability. In the treatment of chronic tibiofibular instability, we believe that reconstruction of the tibiofibular joint is a safe and effective choice.

  9. Perturbation solutions of combustion instability problems

    NASA Technical Reports Server (NTRS)

    Googerdy, A.; Peddieson, J., Jr.; Ventrice, M.

    1979-01-01

    A method involving approximate modal analysis using the Galerkin method followed by an approximate solution of the resulting modal-amplitude equations by the two-variable perturbation method (method of multiple scales) is applied to two problems of pressure-sensitive nonlinear combustion instability in liquid-fuel rocket motors. One problem exhibits self-coupled instability while the other exhibits mode-coupled instability. In both cases it is possible to carry out the entire linear stability analysis and significant portions of the nonlinear stability analysis in closed form. In the problem of self-coupled instability the nonlinear stability boundary and approximate forms of the limit-cycle amplitudes and growth and decay rates are determined in closed form while the exact limit-cycle amplitudes and growth and decay rates are found numerically. In the problem of mode-coupled instability the limit-cycle amplitudes are found in closed form while the growth and decay rates are found numerically. The behavior of the solutions found by the perturbation method are in agreement with solutions obtained using complex numerical methods.

  10. Multiphase Instabilities in Explosive Dispersal of Particles

    NASA Astrophysics Data System (ADS)

    Rollin, Bertrand; Ouellet, Frederick; Annamalai, Subramanian; Balachandar, S. ``Bala''

    2015-11-01

    Explosive dispersal of particles is a complex multiphase phenomenon that can be observed in volcanic eruptions or in engineering applications such as multiphase explosives. As the layer of particles moves outward at high speed, it undergoes complex interactions with the blast-wave structure following the reaction of the energetic material. Particularly in this work, we are interested in the multiphase flow instabilities related to Richmyer-Meshkov (RM) and Rayleigh-Taylor (RM) instabilities (in the gas phase and particulate phase), which take place as the particle layer disperses. These types of instabilities are known to depend on initial conditions for a relatively long time of their evolution. Using a Eulerian-Lagrangian approach, we study the growth of these instabilities and their dependence on initial conditions related to the particulate phase - namely, (i) particle size, (ii) initial distribution, and (iii) mass ratio (particles to explosive). Additional complexities associated with compaction of the layer of particles are avoided here by limiting the simulations to modest initial volume fraction of particles. A detailed analysis of the initial conditions and its effects on multiphase RM/RT-like instabilities in the context of an explosive dispersal of particles is presented. This work was supported by the U.S. Department of Energy, National Nuclear Security Administration, Advanced Simulation and Computing Program, as a Cooperative Agreement under the Predictive Science Academic Alliance Program, Contract No. DE-NA0002378.

  11. Subtalar instability. Etiology, diagnosis, and management.

    PubMed

    Keefe, Daniel T; Haddad, Steven L

    2002-09-01

    Subtalar instability is an evolving disorder that seems to cause a portion of chronic hindfoot instability. It can be seen as an isolated problem, or more commonly, in combination with ankle instability. There seems to be many injury mechanisms, most of which seem to involve supination of the hindfoot, and all seem to attenuate the lateral ligaments of the ankle and subtalar joints. As the condition progresses, and additional sprains occur as a result of the alteration in subtalar joint mechanics, the remaining ligaments become attenuated. There are many methods described to diagnose subtalar instability, but no conclusive test has been devised. Thus, the diagnosis must be inferred from an accurate history, physical examination, conferring radiographic studies, and failure of nonoperative management (often, for ankle instability). As with other hindfoot injuries, many patients improve with conservative measures. These measures are early (ice and immobilization) and late (bracing and proprioceptive training). When patients do not improve or cannot tolerate bracing, recent studies have shown there is a role for ligamentous reconstruction. Most procedures attempt to recreate the lateral ligament structures, including the calcaneofibular, the cervical, and the interosseous talocalcaneal ligaments, which seem to have the best stabilizing effect on the hindfoot. With the advent of newer procedures and more aggressive surgical management, there may be a role for early anatomic repair and rehabilitation. PMID:12512411

  12. The thermal instability of the warm absorber in NGC 3783

    NASA Astrophysics Data System (ADS)

    Goosmann, R. W.; Holczer, T.; Mouchet, M.; Dumont, A.-M.; Behar, E.; Godet, O.; Gonçalves, A. C.; Kaspi, S.

    2016-05-01

    Context. The X-ray absorption spectra of active galactic nuclei frequently show evidence of winds with velocities in the order of 103 km s-1 extending up to 104 km s-1 in the case of ultra-fast outflows. At moderate velocities, these winds are often spectroscopically explained by assuming a number of absorbing clouds along the line of sight. In some cases it was shown that the absorbing clouds are in pressure equilibrium with each other. Aims: We assume a photo-ionized medium with a uniform total (gas+radiation) pressure. The irradiation causes the wind to be radiation pressure compressed (RPC). We attempt to reproduce the observed spectral continuum shape, ionic column densities, and X-ray absorption measure distribution (AMD) of the extensively observed warm absorber in the Seyfert galaxy NGC 3783. Methods: We compare the observational characteristics derived from the 900 ks Chandra observation to radiative transfer computations in pressure equilibrium using the radiative transfer code titan. We explore different values of the ionization parameter ξ of the incident flux and adjust the hydrogen-equivalent column density, NH0, of the warm absorber to match the observed soft X-ray continuum. From the resulting models we derive the column densities for a broad range of ionic species of iron and neon and a theoretical AMD that we compare to the observations. Results: We find an extension of the degeneracy between ξ and NH0 for the constant pressure models previously discussed for NGC 3783. Including the ionic column densities of iron and neon in the comparison between observations and data we conclude that a range of ionization parameters between 4000 and 8000 erg cm s-1 is preferred. For the first time, we present theoretical AMDs for a constant pressure wind in NGC 3783 that correctly reproduces the observed level and is in approximate agreement with the observational appearance of an instability region. Conclusions: Using a variety of observational indicators, we

  13. Blast Wave Driven Instabilities In Laboratory Astrophysics Experiments

    NASA Astrophysics Data System (ADS)

    Kuranz, Carolyn; Drake, R.; Grosskopf, M.; Robey, H.; Hansen, J.; Miles, A.; Knauer, J.; Arnett, D.; Plewa, T.; Hearn, N.; Meakin, C.

    2008-05-01

    This presentation discusses experiments well scaled to the blast wave driven instabilities at the He/H interface during the explosion phase of SN1987A. This core-collapse supernova was detected about 50 kpc from Earth making it the first supernova observed so closely to earth in modern times. The progenitor star was a blue supergiant with a mass of 18-20 solar masses. A blast wave occurred following the supernova explosion because there was a sudden, finite release of energy. Blast waves consist of a shock front followed by a rarefaction wave. When a blast wave crosses an interface with a decrease in density, hydrodynamic instabilities will develop. These experiments include target materials scaled in density to the He/H layer in SN1987A. About 5 kJ of laser energy from the Omega Laser facility irradiates a 150 µm plastic layer that is followed by a low-density foam layer. A blast wave structure similar to those in supernovae is created in the plastic layer. The blast wave crosses a three-dimensional interface with a wavelength of 71 µm in two orthogonal directions. This produces unstable growth dominated by the Rayleigh-Taylor (RT) instability. We have detected the interface structure under these conditions, using dual orthogonal radiography, and will show some of the resulting data. Recent advancements in our x-ray backlighting techniques have greatly improved the resolution of our x-ray radiographic images. Under certain conditions, the improved images show some mass extending beyond the RT spike and penetrating further than previously observed. Current simulations do not show this phenomenon. This presentation will discuss the amount of mass in these spike extensions. Recent results from an experiment using more realistic initial conditions based on stellar evolution models will also be shown. This research was sponsored by the Stewardship Science Academic Alliance through DOE Research Grants DE-FG52-07NA28058, DE-FG52-04NA00064.

  14. Effects of electron temperature anisotropy on proton mirror instability evolution

    NASA Astrophysics Data System (ADS)

    Ahmadi, Narges; Germaschewski, Kai; Raeder, Joachim

    2016-06-01

    Proton mirror modes are large amplitude nonpropagating structures frequently observed in the magnetosheath. It has been suggested that electron temperature anisotropy can enhance the proton mirror instability growth rate while leaving the proton cyclotron instability largely unaffected, therefore causing the proton mirror instability to dominate the proton cyclotron instability in Earth's magnetosheath. Here we use particle-in-cell simulations to investigate the electron temperature anisotropy effects on proton mirror instability evolution. Contrary to the hypothesis, electron temperature anisotropy leads to excitement of the electron whistler instability. Our results show that the electron whistler instability grows much faster than the proton mirror instability and quickly consumes the electron-free energy so that there is no electron temperature anisotropy left to significantly impact the evolution of the proton mirror instability.

  15. Electrothermal instability growth in magnetically driven pulsed power liners

    SciTech Connect

    Peterson, Kyle J.; Sinars, Daniel B.; Yu, Edmund P.; Herrmann, Mark C.; Cuneo, Michael E.; Slutz, Stephen A.; Smith, Ian C.; Atherton, Briggs W.; Knudson, Marcus D.; Nakhleh, Charles

    2012-09-15

    This paper explores the role of electro-thermal instabilities on the dynamics of magnetically accelerated implosion systems. Electro-thermal instabilities result from non-uniform heating due to temperature dependence in the conductivity of a material. Comparatively little is known about these types of instabilities compared to the well known Magneto-Rayleigh-Taylor (MRT) instability. We present simulations that show electrothermal instabilities form immediately after the surface material of a conductor melts and can act as a significant seed to subsequent MRT instability growth. We also present the results of several experiments performed on Sandia National Laboratories Z accelerator to investigate signatures of electrothermal instability growth on well characterized initially solid aluminum and copper rods driven with a 20 MA, 100 ns risetime current pulse. These experiments show excellent agreement with electrothermal instability simulations and exhibit larger instability growth than can be explained by MRT theory alone.

  16. Filamentation instability of a relativistic hollow electron beam. Final report

    SciTech Connect

    Uhm, H.S.; Siambis, J.G.

    1981-09-01

    The filamentation instability properties of a relativistic hollow electron beam confined in axial flow by a uniform magnetic field in a pipe are investigated via the Vlasov-Maxwell equations. The instability is found to have two side-bands, one with a spectrum of positive wavenumbers k and the other with a spectrum of negative wavenumbers. The spectral point k=0, associated with the diokotron instability, is excluded from the filamentation instability's two unstable sidebands. Only in the limit of zero axial beam flow, the diokotron instability becomes asymptotically part of the filamentation instability spectrum. In this limit the filamentation instability's two sidebands merge asymptotically and symmetrically toward the diokotron instability spectral point, k=0, in agreement with the basic driving physical mechanisms and geometry configurations for these two distinct and different instabilities.

  17. Filamentation instability of a relativistic hollow electron beam

    SciTech Connect

    Siambis, J.G.; Uhm, H.S.

    1982-03-01

    The filamentation instability properties of a relativistic hollow electron beam confined in axial flow by a uniform magnetic field, in the absence of background plasma, in a pipe are investigated via the Vlasov--Maxwell equations. The instability is found to be have two sidebands, one with a spectrum of positive wavenumbers k and the other with a spectrum of negative wavenumbers. The spectral point k = 0, associated with the diokotron instability, is excluded from the two unstable sidebands of the filamentation instability. Only in the limit of zero axial beam flow (..gamma -->..1), does the diokotron instability become asymptotically part of the filamentation instability spectrum. In this limit, the two sidebands of the filamentation instability merge asymptotically and symmetrically toward the diokotron instability spectral point, k = 0, in agreement with the basic driving physical mechanisms and geometry configurations for these two distinct and different instabilities.

  18. Turing instabilities on Cartesian product networks

    PubMed Central

    Asllani, Malbor; Busiello, Daniel M.; Carletti, Timoteo; Fanelli, Duccio; Planchon, Gwendoline

    2015-01-01

    The problem of Turing instabilities for a reaction-diffusion system defined on a complex Cartesian product network is considered. To this end we operate in the linear regime and expand the time dependent perturbation on a basis formed by the tensor product of the eigenvectors of the discrete Laplacian operators, associated to each of the individual networks that build the Cartesian product. The dispersion relation which controls the onset of the instability depends on a set of discrete wavelengths, the eigenvalues of the aforementioned Laplacians. Patterns can develop on the Cartesian network, if they are supported on at least one of its constitutive sub-graphs. Multiplex networks are also obtained under specific prescriptions. In this case, the criteria for the instability reduce to compact explicit formulae. Numerical simulations carried out for the Mimura-Murray reaction kinetics confirm the adequacy of the proposed theory. PMID:26245138

  19. Turing instabilities on Cartesian product networks.

    PubMed

    Asllani, Malbor; Busiello, Daniel M; Carletti, Timoteo; Fanelli, Duccio; Planchon, Gwendoline

    2015-01-01

    The problem of Turing instabilities for a reaction-diffusion system defined on a complex Cartesian product network is considered. To this end we operate in the linear regime and expand the time dependent perturbation on a basis formed by the tensor product of the eigenvectors of the discrete Laplacian operators, associated to each of the individual networks that build the Cartesian product. The dispersion relation which controls the onset of the instability depends on a set of discrete wavelengths, the eigenvalues of the aforementioned Laplacians. Patterns can develop on the Cartesian network, if they are supported on at least one of its constitutive sub-graphs. Multiplex networks are also obtained under specific prescriptions. In this case, the criteria for the instability reduce to compact explicit formulae. Numerical simulations carried out for the Mimura-Murray reaction kinetics confirm the adequacy of the proposed theory. PMID:26245138

  20. Bernstein instability driven by thermal ring distribution

    SciTech Connect

    Yoon, Peter H.; Hadi, Fazal; Qamar, Anisa

    2014-07-15

    The classic Bernstein waves may be intimately related to banded emissions detected in laboratory plasmas, terrestrial, and other planetary magnetospheres. However, the customary discussion of the Bernstein wave is based upon isotropic thermal velocity distribution function. In order to understand how such waves can be excited, one needs an emission mechanism, i.e., an instability. In non-relativistic collision-less plasmas, the only known Bernstein wave instability is that associated with a cold perpendicular velocity ring distribution function. However, cold ring distribution is highly idealized. The present Brief Communication generalizes the cold ring distribution model to include thermal spread, so that the Bernstein-ring instability is described by a more realistic electron distribution function, with which the stabilization by thermal spread associated with the ring distribution is demonstrated. The present findings imply that the excitation of Bernstein waves requires a sufficiently high perpendicular velocity gradient associated with the electron distribution function.

  1. Oscillatory interfacial instability between miscible fluids

    NASA Astrophysics Data System (ADS)

    Shevtsova, Valentina; Gaponenko, Yuri; Mialdun, Aliaksandr; Torregrosa, Marita; Yasnou, Viktar

    Interfacial instabilities occurring between two fluids are of fundamental interest in fluid dynamics, biological systems and engineering applications such as liquid storage, solvent extraction, oil recovery and mixing. Horizontal vibrations applied to stratified layers of immiscible liquids may generate spatially periodic waving of the interface, stationary in the reference frame of the vibrated cell, referred to as a "frozen wave". We present experimental evidence that frozen wave instability exists between two ordinary miscible liquids of similar densities and viscosities. At the experiments and at the numerical model, two superimposed layers of ordinary liquids, water-alcohol of different concentrations, are placed in a closed cavity in a gravitationally stable configuration. The density and viscosity of these fluids are somewhat similar. Similar to the immiscible fluids this instability has a threshold. When the value of forcing is increased the amplitudes of perturbations grow continuously displaying a saw-tooth structure. The decrease of gravity drastically changes the structure of frozen waves.

  2. Instabilities of structured metal films on nanoscale

    NASA Astrophysics Data System (ADS)

    Dong, Nanyi; Wu, Yueying; Fowlkes, Jason; Rack, Philip; Kondic, Lou

    2014-11-01

    We consider instabilities of metal films on nanoscale, with particular focus on the interplay between the initial geometry and instability development. In experiments, metal films are deposited lithographically, allowing for precise control of the initial shape, and then exposed to laser pulses that liquefy them. The considered geometries involve various shapes (cylinders or prisms) superimposed on top of a flat film. We consider this problem within the framework of the long wave (lubrication) theory. Our simulations show that the main features of the instability development could be captured, as long as destabilizing liquid-solid interaction is considered in the model. We conclude by discussing the influence of the distance between the imposed perturbations, their shape, as well as experimental noise on the evolution. Supported by NSF Grant No. CBET-1235710.

  3. Instability limits for spontaneous double layer formation

    SciTech Connect

    Carr, J. Jr.; Galante, M. E.; McCarren, D.; Scime, E. E.; Sears, S.; VanDervort, R. W.; Magee, R. M.; Reynolds, E.

    2013-11-15

    We present time-resolved measurements that demonstrate that large amplitude electrostatic instabilities appear in pulsed, expanding helicon plasmas at the same time as particularly strong double layers appear in the expansion region. A significant cross-correlation between the electrostatic fluctuations and fluctuations in the number of ions accelerated by the double layer electric field is observed. No correlation is observed between the electrostatic fluctuations and ions that have not passed through the double layer. These measurements confirm that the simultaneous appearance of the electrostatic fluctuations and the double layer is not simple coincidence. In fact, the accelerated ion population is responsible for the growth of the instability. The double layer strength, and therefore, the velocity of the accelerated ions, is limited by the appearance of the electrostatic instability.

  4. Plasma wave instabilities in nonequilibrium graphene

    NASA Astrophysics Data System (ADS)

    Aryal, Chinta M.; Hu, Ben Yu-Kuang; Jauho, Antti-Pekka

    2016-09-01

    We study two-stream instabilities in a nonequilibrium system in which a stream of electrons is injected into doped graphene. As with equivalent nonequilibrium parabolic band systems, we find that the graphene systems can support unstable charge-density waves whose amplitudes grow with time. We determine the range of wave vectors q that are unstable, and their growth rates. We find no instability for waves with wave vectors parallel or perpendicular to the direction of the injected carriers. We find that, within the small-wave-vector approximation, the angle between q and the direction of the injected electrons that maximizes the growth rate increases with increasing |q | . We compare the range and strength of the instability in graphene to that of two- and three-dimensional parabolic band systems.

  5. Instabilities of cooled antiproton beam in recycler

    SciTech Connect

    Burov, A.; Lebedev, V.; /Fermilab

    2007-06-01

    The more beam is cooled, the less stable it is. In the 3.3 km Recycler Ring, stacked 8 GeV antiprotons are cooled both with stochastic (transversely) and electron (3D) cooling. Since the machine is staying near the coupling resonance, coupled optical functions should be used for stability analysis. To stabilize beam against the resistive wall instability, a digital damper is used. Digital dampers can be described as linear operators with explicit time dependence, and that makes a principle difference with analogous dampers. Theoretical description of the digital dampers is presented. Electron cooling makes possible a two-beam instability of the cooled beam with the electron beam. Special features of this instability are described, and the remedy is discussed.

  6. Nonlinear amplification of instabilities with longitudinal expansion

    NASA Astrophysics Data System (ADS)

    Berges, Jürgen; Boguslavski, Kirill; Schlichting, Sören

    2012-04-01

    We study the dynamics of nonequilibrium instabilities in anisotropically expanding systems. The most prominent example of such a system is the “glasma” in the context of relativistic heavy-ion collision experiments, where the expansion is a consequence of approximately boost-invariant initial conditions. Here we consider the problem of parametric resonance in scalar N-component quantum field theories with boost-invariant initial conditions, which is similar in spirit. We find that many aspects of the dynamics can be treated analytically by introducing a generalized conformal time. Primary instabilities, which are described by the linearized evolution equations, are seen to lead to a secondary regime of amplifications with strongly enhanced growth rates due to nonlinear corrections. For the secondary instabilities we present a power-counting scheme for weak coupling, and discuss their role for the question of isotropization and the establishment of an equation of state.

  7. Instability of a water-spout flow

    NASA Astrophysics Data System (ADS)

    Carrión, Luis; Herrada, Miguel A.; Shtern, Vladimir N.

    2016-03-01

    The paper studies the linear stability of a steady axisymmetric air-water motion in a vertical sealed cylinder, driven by the rotating top disk, motivated by possible applications in aerial bioreactors. As the flow strength Re increases, a vortex breakdown bubble (VBB) emerges near the bottom center and expands toward the interface. Regions of clockwise meridional circulation of air and water become separated by a thin anticlockwise circulation layer (TCL) adjacent to the interface in water. This study reveals that instability develops for larger Re than those at which VBB and TCL emerge. The instability focuses in the air region being typically of shear-layer type. The instability is centrifugal if the air volume fraction is small.

  8. Current convective instability in detached divertor plasma

    NASA Astrophysics Data System (ADS)

    Krasheninnikov, S. I.; Smolyakov, A. I.

    2016-09-01

    The asymmetry of inner and outer divertors, which cause the inner divertor to detach first, while the outer one is still attached, results in the large temperature difference between the vicinities of inner and outer targets and the onset of large electric potential drop through detached plasma of the inner divertor. A large potential drop along with the inhomogeneity of the resistivity of detached plasma across the divertor leg drives the current convective instability in the inner divertor and subsequent fluctuations of radiation loss similar to that observed in experiments. The estimates of the frequency of plasma parameter fluctuations due to the current convective instability are in a reasonable agreement with experimental data. Once the outer divertor also detaches, the temperature difference between the vicinities of inner and outer targets disappears, and the driving force for the current convective instability, and resulting oscillations of radiation loss, vanishes. This feature is indeed observed in experiments.

  9. MicroRNAs, Genomic Instability and Cancer

    PubMed Central

    Vincent, Kimberly; Pichler, Martin; Lee, Gyeong-Won; Ling, Hui

    2014-01-01

    MicroRNAs (miRNAs) are small non-coding RNA transcripts approximately 20 nucleotides in length that regulate expression of protein-coding genes via complementary binding mechanisms. The last decade has seen an exponential increase of publications on miRNAs, ranging from every aspect of basic cancer biology to diagnostic and therapeutic explorations. In this review, we summarize findings of miRNA involvement in genomic instability, an interesting but largely neglected topic to date. We discuss the potential mechanisms by which miRNAs induce genomic instability, considered to be one of the most important driving forces of cancer initiation and progression, though its precise mechanisms remain elusive. We classify genomic instability mechanisms into defects in cell cycle regulation, DNA damage response, and mitotic separation, and review the findings demonstrating the participation of specific miRNAs in such mechanisms. PMID:25141103

  10. Dynamics and Instabilities of Vortex Pairs

    NASA Astrophysics Data System (ADS)

    Leweke, Thomas; Le Dizès, Stéphane; Williamson, Charles H. K.

    2016-01-01

    This article reviews the characteristics and behavior of counter-rotating and corotating vortex pairs, which are seemingly simple flow configurations yet immensely rich in phenomena. Since the reviews in this journal by Widnall (1975) and Spalart (1998) , who studied the fundamental structure and dynamics of vortices and airplane trailing vortices, respectively, there have been many analytical, computational, and experimental studies of vortex pair flows. We discuss two-dimensional dynamics, including the merging of same-sign vortices and the interaction with the mutually induced strain, as well as three-dimensional displacement and core instabilities resulting from this interaction. Flows subject to combined instabilities are also considered, in particular the impingement of opposite-sign vortices on a ground plane. We emphasize the physical mechanisms responsible for the flow phenomena and clearly present the key results that are useful to the reader for predicting the dynamics and instabilities of parallel vortices.

  11. Radiative instabilities in sheared magnetic field

    NASA Technical Reports Server (NTRS)

    Drake, J. F.; Sparks, L.; Van Hoven, G.

    1988-01-01

    The structure and growth rate of the radiative instability in a sheared magnetic field B have been calculated analytically using the Braginskii fluid equations. In a shear layer, temperature and density perturbations are linked by the propagation of sound waves parallel to the local magnetic field. As a consequence, density clumping or condensation plays an important role in driving the instability. Parallel thermal conduction localizes the mode to a narrow layer where K(parallel) is small and stabilizes short wavelengths k larger-than(c) where k(c) depends on the local radiation and conduction rates. Thermal coupling to ions also limits the width of the unstable spectrum. It is shown that a broad spectrum of modes is typically unstable in tokamak edge plasmas and it is argued that this instability is sufficiently robust to drive the large-amplitude density fluctuations often measured there.

  12. Studies of eRHIC coherent instabilities

    SciTech Connect

    Wang G.; Blaskiewicz, M.

    2012-05-20

    In the presence of an effective coherent electron cooling, the rms ion bunch length in eRHIC will be kept at 8.3 cm for 250 GeV protons, which is much shorter than the current RHIC 45 cm rms bunch length. Together with the increased bunch intensity and total bunch number, coherent instabilities could be a potential limitation for achieving desired machine performance. In this study, we use the tracking code TRANFT to find thresholds and growth rates for single bunch and coupled bunch instabilities with linear chromaticity and amplitude dependent tune shift taken into account. Based on the simulation results, requirements of machine parameters such as rf voltage, linear chromaticity, and tune dependence of betatron amplitude are specified to suppress these instabilities.

  13. Knee instability scores for ACL reconstruction.

    PubMed

    Rahnemai-Azar, Ata A; Naendrup, Jan-Hendrik; Soni, Ashish; Olsen, Adam; Zlotnicki, Jason; Musahl, Volker

    2016-06-01

    Despite abundant biological, biomechanical, and clinical research, return to sport after anterior cruciate ligament (ACL) injury remains a significant challenge. Residual rotatory knee laxity has been identified as one of the factors responsible for poor functional outcome. To improve and standardize the assessment of knee instability, a variety of instability scoring systems is available. Recently, devices to objectively quantify static and dynamic clinical exams have been developed to complement traditional subjective grading systems. These devices enable an improved evaluation of knee instability and possible associated injuries. This additional information may promote the development of new treatment algorithms and allow for individualized treatment. In this review, the different subjective laxity scores as well as complementary objective measuring systems are discussed, along with an introduction of injury to an individualized treatment algorithm. PMID:26980119

  14. Rossby Wave Instability in Astrophysical Disks

    NASA Astrophysics Data System (ADS)

    Lovelace, Richard; Li, Hui

    2014-10-01

    A brief review is given of the Rossby wave instability in astrophysical disks. In non-self-gravitating discs, around for example a newly forming stars, the instability can be triggered by an axisymmetric bump at some radius r0 in the disk surface mass-density. It gives rise to exponentially growing non-axisymmetric perturbation (proportional to Exp[im ϕ], m = 1,2,...) in the vicinity of r0 consisting of anticyclonic vortices. These vortices are regions of high pressure and consequently act to trap dust particles which in turn can facilitate planetesimal growth in protoplanetary disks. The Rossby vortices in the disks around stars and black holes may cause the observed quasi-periodic modulations of the disk's thermal emission. Stirling Colgate's long standing interest in all types of vortices - particularly tornados - had an important part in stimulating the research on the Rossby wave instability.

  15. Filtering of non-linear instabilities

    NASA Technical Reports Server (NTRS)

    Khosla, P. K.; Rubin, S. G.

    1978-01-01

    For Courant numbers larger than one and cell Reynolds numbers larger than two, oscillations and in some cases instabilities are typically found with implicit numerical solutions of the fluid dynamics equations. This behavior has sometimes been associated with the loss of diagonal dominance of the coefficient matrix. It is shown that these problems can be related to the choice of the spatial differences, with the resulting instability related to aliasing or nonlinear interaction. Appropriate filtering can reduce the intensity of these oscillations and possibly eliminate the instability. These filtering procedures are equivalent to a weighted average of conservation and nonconservation differencing. The entire spectrum of filtered equations retains a three point character as well as second order spatial accuracy. Burgers equation was considered as a model.

  16. Turing instabilities on Cartesian product networks

    NASA Astrophysics Data System (ADS)

    Asllani, Malbor; Busiello, Daniel M.; Carletti, Timoteo; Fanelli, Duccio; Planchon, Gwendoline

    2015-08-01

    The problem of Turing instabilities for a reaction-diffusion system defined on a complex Cartesian product network is considered. To this end we operate in the linear regime and expand the time dependent perturbation on a basis formed by the tensor product of the eigenvectors of the discrete Laplacian operators, associated to each of the individual networks that build the Cartesian product. The dispersion relation which controls the onset of the instability depends on a set of discrete wavelengths, the eigenvalues of the aforementioned Laplacians. Patterns can develop on the Cartesian network, if they are supported on at least one of its constitutive sub-graphs. Multiplex networks are also obtained under specific prescriptions. In this case, the criteria for the instability reduce to compact explicit formulae. Numerical simulations carried out for the Mimura-Murray reaction kinetics confirm the adequacy of the proposed theory.

  17. Current-driven electromagnetic soliton collision in a ferromagnetic nanowire.

    PubMed

    Saravanan, M

    2015-07-01

    The propagation of an electromagnetic wave in a uniaxial ferromagnetic nanowire under the spin transfer torque effect is widely investigated in the soliton frame. The magnetization dynamics of the ferromagnetic nanowire is governed by the Landau-Lifshitz-Gilbert (LLG) equation coupled to the Maxwell equation for the electromagnetic wave propagation. A nonuniform multiscale analysis is invoked for the coupled LLG-Maxwell equations and obtains the extended derivative nonlinear Schrödinger (DNLS) equation for the magnetization and external magnetic field. The effect of electric current is explored by constructing multisoliton solutions to the extended DNLS equation and the possibility of the soliton collision is exploited using the Hirota bilinearization procedure. PMID:26274263

  18. Submerged electricity generation plane with marine current-driven motors

    DOEpatents

    Dehlsen, James G.P.; Dehlsen, James B.; Fleming, Alexander

    2014-07-01

    An underwater apparatus for generating electric power from ocean currents and deep water tides. A submersible platform including two or more power pods, each having a rotor with fixed-pitch blades, with drivetrains housed in pressure vessels that are connected by a transverse structure providing buoyancy, which can be a wing depressor, hydrofoil, truss, or faired tube. The platform is connected to anchors on the seafloor by forward mooring lines and a vertical mooring line that restricts the depth of the device in the water column. The platform operates using passive, rather than active, depth control. The wing depressor, along with rotor drag loads, ensures the platform seeks the desired operational current velocity. The rotors are directly coupled to a hydraulic pump that drives at least one constant-speed hydraulic-motor generator set and enables hydraulic braking. A fluidic bearing decouples non-torque rotor loads to the main shaft driving the hydraulic pumps.

  19. Current-driven periodic domain wall creation in ferromagnetic nanowires

    NASA Astrophysics Data System (ADS)

    Sitte, Matthias; Everschor-Sitte, Karin; Valet, Thierry; Rodrigues, Davi R.; Sinova, Jairo; Abanov, Ar.

    2016-08-01

    We predict the electrical generation and injection of domain walls into a ferromagnetic nanowire without the need of an assisting magnetic field. Our analytical and numerical results show that above a critical current jc domain walls are injected into the nanowire with a period T ˜(j-jc) -1 /2 . Importantly, domain walls can be produced periodically even in a simple exchange ferromagnet with uniaxial anisotropy, without requiring any standard "twisting" interaction such as Dzyaloshinskii-Moriya or dipole-dipole interactions. We show analytically that this process and the period exponents are universal and do not depend on the peculiarities of the microscopic Hamiltonian. Finally we give a specific proposal for an experimental realization.

  20. Current-driven vortex oscillations in metallic nanocontacts

    NASA Astrophysics Data System (ADS)

    Hrkac, Gino

    2009-03-01

    In this paper, we performed full micromagnetics simulations of metallic nano-contacts from the TUNAMOS consortium, by solving the Landau Lifshitz Gilbert Slonctewski equation simultaneously with quasi-static Maxwell equations. We take into account the spatially inhomogeneous current distribution flowing through the magnetic free layer and consequently use the Oersted field generated by this current for the magnetization dynamics. The system we simulated was a trilayer CoFe 3.5 nm/Cu 3nm/NiFe 4nm stack. The saturation magnetization of the free layer is taken to be the same as the experimental value Ms =1.1 T, and a GMR ratio of 1% is used. We account for the inhomogeneous current distribution flowing through the free layer by computing the local current density from the local angle between the free and fixed layer magnetizations. The Oersted field is computed with the Biot-Savart law from this current distribution [2], and an asymmetric Slonczewski term for the spin transfer is used [3]. We observe that the additional spin torque drives the vortex out of the contact area and towards a stable orbit around the contact. These simulations reveal that the oscillations observed are related to the large-amplitude translational motion of a magnetic vortex. In contrast to the nanopillar geometry in which the vortex core precesses within the confining part of the Oersted field [1], the dynamics here correspond to an orbital motion outside the contact region. This behavior can be likened to planetary orbital motion under the influence of a gravitational field; the spin-transfer torque leads to a centripetal motion of the vortex core, which is counterbalanced by the attractive potential provided by the Oersted field. Good quantitative agreement between the simulation and experimental frequencies is achieved [4]. [4pt] [1] V. S. Pribiag et al., Nat. Phys. 3, 498 (2007) [0pt] [2] O. Ertl et al., J. Appl. Phys. 99, 08S303 (2006). [0pt] [3] J. Xiao, A. Zangwill, and M. D. Stiles, Phys. Rev. B 70, 172405 (2004). [0pt] [4] Q. Mistral, M. van Kampen, G. Hrkac, et al. PRL 100, 257201 (2008)

  1. Flux flow in current driven mesoscopic superconductors: size effects

    NASA Astrophysics Data System (ADS)

    Sánchez-Lotero, Pedro; Domínguez, Daniel; Albino Aguiar, J.

    2016-06-01

    Flux-flow phenomena in a superconducting mesoscopic stripe submitted to an applied current and external magnetic field is studied. The time-dependent Ginzburg-Landau equations are solved numerically to obtain the electric and magnetic response of the system. It is shown that the I- V curves, for the wider strips, present a universal behaviour. The dependence of the flux-flow resistivity on the magnetic field and width allow us to propose a criterion characterizing, both, the macroscopic and mesoscopic regimes. The power spectrum of the average voltage permits identifying the effect of surface currents in vortices movement. Based on the maximum value of the power spectrum first harmonic we propose a geometric condition for matching between the sample dimensions and the vortex lattice parameter.

  2. Is the Leeuwin Current driven by Pacific heating and winds?

    NASA Astrophysics Data System (ADS)

    Stuart Godfrey, J.; Weaver, Andrew J.

    Warm west Pacific water can flow through the Indonesian channels to create a basin-scale buoyancy-driven circulation in the Indian Ocean, even in the absence of winds. The driving force for this circulation is the generation of meridional steric height gradients (and associated zonal geostrophic flows) by the cooling of Pacific inflow water towards the latitude-dependent Haney equilibrium temperature. Mass continuity requires that eastern and western boundary currents develop to feed or remove this zonal flow; in particular, a Leeuwin Current-like flow develops at the eastern boundary. To illustrate these ideas, we have run a numerical model of a rectangular “Indian Ocean”, connected via a near-equatorial channel to the “Pacific” - which is treated simply as a reservoir of water with fixed vertical profiles of temperature and salinity. No wind stress curl is applied, so no Sverdrup circulation is produced; an equatorward patch of winds at midlatitudes is introduced in some experiments to allow the possibility of wind-driven upwelling near the eastern boundary. The total mass flux from the Pacific to the Indian Ocean is identically zero in our model, but up to 18.6 × 10 6m 3s -1 flow in each direction between the basins. When our “Pacific” temperature and salinity profiles are as observed in the Indonesian region, cooling to the Haney equilibrium temperature produces a strong eastward flow at midlatitudes, fed by a western boundary current which is in turn fed by inflow from the Pacific. At the eastern boundary a Leeuwin Current develops, with deep mixed layers near Cape Leeuwin; the mixed water feeds a Leeuwin Undercurrent which eventually flows back to the “Pacific” through the western boundary current. A “typical” water flow path in this experiment is thus: out of the Pacific in the top 100m, in a westward zonal jet; poleward along the western boundary current, with upwelling close inshore and heat loss to the atmosphere; broad, slow eastward flow across the basin; some poleward flow (the Leeuwin Current), more heat loss and sinking near the eastern boundary; some equatorward flow (the Leeuwin Undercurrent), to join a broad westward subsurface flow across the basin; and finally, equatorwards subsurface flow along the western boundary, to join an eastward subsurface jet back into the Pacific. The depth-integrated mass transport of the Current-Undercurrent system near Western Australia is near zero, as observed in the Leeuwin Current system. This pattern is hardly affected by the imposition of equatorward winds like those found off Western Australia; i.e. the offshore Ekman drift is overwhelmed by the onshore near-surface geostrophic flow. The timescale for establishment of this flow regime is of order 1000 days, due to the generation of low vertical mode internal Rossby waves at the eastern boundary. This timescale is even larger when the eastern boundary current is better resolved since an alongshore advective timescale also becomes important. When the “Pacific” temperature profiles are replaced by the much colder ones observed in the eastern equatorial Pacific, with no other change, none of these phenomena occur; instead, a typical eastern boundary flow regime is obtained. The equatorward winds generate upwelling and shallow surface mixed layers near the eastern boundary, with equatorward surface flow. A shallow layer is heated at low latitudes, but this effect does not penetrate deep enough to generate significant zonal flows in midlatitudes; the heated water mostly returns to the “Pacific” via the western boundary current and a zonal jet. By contrast with the first experiment, this flow regime takes only about 200 days to become established. Quantitatively the large difference between the specific volume anomaly profiles of the eastern and western equatorial Pacific can be explained (in a double-integrated sense) by the action of zonal winds, which cause a large gradient of pressure (and hence of specific volume anomaly and temperature) along the equatorial Pacific. Thus these winds may be the cause of the large difference between the Leeuwin Current flow regime and other eastern boundary flows - and of the large heat losses to the atmosphere in much of the Indian Ocean.

  3. Interaction of bootstrap-current-driven magnetic islands

    SciTech Connect

    Hegna, C.C.; Callen, J.D.

    1991-10-01

    The formation and interaction of fluctuating neoclassical pressure gradient driven magnetic islands is examined. The interaction of magnetic islands produces a stochastic region around the separatrices of the islands. This interaction causes the island pressure profile to be broadened, reducing the island bootstrap current and drive for the magnetic island. A model is presented that describes the magnetic topology as a bath of interacting magnetic islands with low to medium poloidal mode number (m {congruent} 3{minus}30). The islands grow by the bootstrap current effect and damp due to the flattening of the pressure profile near the island separatrix caused by the interaction of the magnetic islands. The effect of this sporadic growth and decay of the islands ( magnetic bubbling'') is not normally addressed in theories of plasma transport due to magnetic fluctuations. The nature of the transport differs from statistical approaches to magnetic turbulence since the radial step size of the plasma transport is now given by the characteristic island width. This model suggests that tokamak experiments have relatively short-lived, coherent, long wavelength magnetic oscillations present in the steep pressure-gradient regions of the plasma. 42 refs.

  4. Experimental Observation of Nonlinear Mode Coupling In the Ablative Rayleigh-Taylor Instability on the NIF

    NASA Astrophysics Data System (ADS)

    Martinez, David

    2015-11-01

    We investigate on the National Ignition Facility (NIF) the ablative Rayleigh-Taylor (RT) instability in the transition from linear to highly nonlinear regimes. This work is part of the Discovery Science Program on NIF and of particular importance to indirect-drive inertial confinement fusion (ICF) where careful attention to the form of the rise to final peak drive is calculated to prevent the RT instability from shredding the ablator in-flight and leading to ablator mixing into the cold fuel. The growth of the ablative RT instability was investigated using a planar plastic foil with pre-imposed two-dimensional broadband modulations and diagnosed using x-ray radiography. The foil was accelerated for 12ns by the x-ray drive created in a gas-filled Au radiation cavity with a radiative temperature plateau at 175 eV. The dependence on initial conditions was investigated by systematically changing the modulation amplitude, ablator material and the modulation pattern. For each of these cases bubble mergers were observed and the nonlinear evolution of the RT instability showed insensitivity to the initial conditions. This experiment provides critical data needed to validate current theories on the ablative RT instability for indirect drive that relies on the ablative stabilization of short-scale modulations for ICF ignition. This paper will compare the experimental data to the current nonlinear theories. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC.

  5. Control and simulation of thermoacoustic instabilities

    NASA Astrophysics Data System (ADS)

    Poinsot, Thierry

    2014-11-01

    Combustion instabilities (CI), due to thermoacoustic coupling between acoustic waves and chemical reaction, constitute a major danger for all combustion systems. They can drive the system to unstable states where the whole combustor can oscillate, vibrate, quench or in extreme cases explode or burn. Such phenomena are commonly observed in the final phases of development programs, leading to major difficulties and significant additional costs. One of the most famous examples of combustion instabilities is the F1 engine of the Apollo program which required more than 1000 engine tests to obtain a stable regime satisfying all other constraints (performance, ignition, etc). CIs constitute one of the most challenging problems in fluid mechanics: they combine turbulence, acoustics, chemistry, unsteady two-phase flow in complex geometries. Since combustion instabilities have been identified (more than hundred years ago), the combustion community has followed two paths: (1) improve our understanding of the phenomena controlling stability to build engines which would be ``stable by design'' and (2) give up on a detailed understanding of mechanisms and add control systems either in open or closed loop devices to inhibit unstable modes. Of course, understanding phenomena driving combustion instabilities to suppress them would be the most satisfying approach but there is no fully reliable theory or numerical method today which can predict whether a combustor will be stable or not before it is fired. This talk will present an overview of combustion instabilities phenomenology before focusing on: (1) active control methods for combustion instabilities and (2) recent methods to predict unstable modes in combustors. These methods are based on recent Large Eddy Simulation codes for compressible reacting flows on HPC systems but we will also describe recent fully analytical methods which provide new insights into unstable modes in annular combustion chambers. Support: European

  6. Drift-induced Benjamin-Feir instabilities

    NASA Astrophysics Data System (ADS)

    Di Patti, F.; Fanelli, D.; Carletti, T.

    2016-06-01

    A modified version of the Ginzburg-Landau equation is introduced which accounts for asymmetric couplings between neighbors sites on a one-dimensional lattice, with periodic boundary conditions. The drift term which reflects the imposed microscopic asymmetry seeds a generalized class of instabilities, reminiscent of the Benjamin-Feir type. The uniformly synchronized solution is spontaneously destabilized outside the region of parameters classically associated to the Benjamin-Feir instability, upon injection of a nonhomogeneous perturbation. The ensuing patterns can be of the traveling wave type or display a patchy, colorful mosaic for the modulus of the complex oscillators amplitude.

  7. An instability in neutron stars at birth

    NASA Technical Reports Server (NTRS)

    Burrows, Adam; Fryxell, Bruce A.

    1992-01-01

    Calculations with a two-dimensional hydrodynamic simulation show that a generic Raleigh-Taylor-like instability occurs in the mantles of nascent neutron stars, that it is possibly violent, and that the standard spherically symmetric models of neutron star birth and supernova explosion may be inadequate. Whether this 'convective' instability is pivotal to the supernova mechanism, pulsar nagnetic fields, or a host of other important issues that attend stellar collapse remains to be seen, but its existence promises to modify all questions concerning this most energetic of astronomical phenomena.

  8. Theory of electrohydrodynamic instabilities in electrolytic cells

    NASA Technical Reports Server (NTRS)

    Bruinsma, R.; Alexander, S.

    1990-01-01

    The paper develops the theory of the hydrodynamic stability of an electrolytic cell as a function of the imposed electric current. A new electrohydrodynamic instability is encountered when the current is forced to exceed the Nernst limit. The convection is driven by the volume force exerted by the electric field on space charges in the electrolyte. This intrinsic instability is found to be easily masked by extrinsic convection sources such as gravity or stirring. A linear stability analysis is performed and a dimensionless number Le is derived whose value determines the convection pattern.

  9. Magnetorotational instability in dissipative dusty plasmas

    SciTech Connect

    Ren Haijun; Wu Zhengwei; Cao Jintao; Chu, Paul K.

    2009-12-15

    The magnetorotational instability (MRI) in differential rotating dusty plasmas with dissipative effects is investigated by using local linear analysis. We assume that the dust grains are heavy enough to be immobile so that the dust effects are contained in our model only by introducing an electric field term in the one-fluid equation of plasma motion. The general local dispersion relation is derived and two limiting cases are discussed with respect to the dust-induced effect. The instability criterions in the different limiting cases are presented and the growth rate of local MRI in the last case is demonstrated.

  10. STREAM INSTABILITIES IN RELATIVISTICALLY HOT PLASMA

    SciTech Connect

    Shaisultanov, Rashid; Lyubarsky, Yuri; Eichler, David

    2012-01-10

    The growth rates for Weibel and Buneman instabilities of relativistic ion beams in a relativistically hot electron background are derived analytically for general propagation angles. The Weibel instability perpendicular to the streaming direction is found to be the fastest growing mode and probably the first to appear. Oblique, quasiperpendicular modes grow almost as fast as the growth rate varies only moderately with angle, and they may distort or corrugate the filaments after the perpendicular mode saturates. The growth rate of the purely longitudinal (Buneman) mode is significantly smaller, contrary to the non-relativistic case. The results are consistent with simulations, which display aligned magnetic filaments and their subsequent disruption.

  11. Influence of Helium in Gravitational Instabilities

    NASA Astrophysics Data System (ADS)

    Corona-Galindo, M. G.; Cardona, O.; Klapp, J.

    1990-11-01

    RESUMEN. Hemos analizado los modos hid rod inamicos de un modelo de fluido de dos componentes (hidr6geno y helio), y hemos obtenido la condici6n de inestabilidad para masas mayores que 1.39 veces la bien conocida masa dejeans. ABSTRACT, We have analysed the hydrodynamical modes of a two component fluid model (hydrogen and helium), and we have obtained the instability condition for masses greater than 1.39 times the well-known Jeans mass. K words: COSMOLOGY - GRAVITATION - INSTABILITIES

  12. Plasma Instabilities in Heavy Ion Collisions

    SciTech Connect

    Attems, M.; Rebhan, A.; Strickland, M.

    2011-05-23

    Non-Abelian plasma instabilities play a crucial role in the nonequilibrium dynamics of a weakly coupled quark-gluon plasma. The Chromo-Weibel instabilities have been proposed as a possible mechanism for the fast apparent thermalization of the quark-gluon plasma and have been extensively studied in stationary anisotropic plasmas using the so-called hard-loop approximation. The generalization to the hard-expanding-loop (HEL) formalism allows the (numerical) calculation of the time evolution of gluonic mean fields in the more realistic dynamical case of anisotropic expansion.

  13. Metal pad instabilities in liquid metal batteries.

    PubMed

    Zikanov, Oleg

    2015-12-01

    A mechanical analogy is used to analyze the interaction between the magnetic field, electric current, and deformation of interfaces in liquid metal batteries. In the framework of a low-mode, nondissipative, linear stability model, it is found that, during charging or discharging, a sufficiently large battery is prone to instabilities of two types. One is similar to the metal pad instability known to exist in the aluminum reduction cells. Another type is new. It is related to the destabilizing effect of the Lorentz force formed by the azimuthal magnetic field induced by the base current, and the current perturbations caused by the local variations of the thickness of the electrolyte layer.

  14. Metal pad instabilities in liquid metal batteries

    NASA Astrophysics Data System (ADS)

    Zikanov, Oleg

    2015-12-01

    A mechanical analogy is used to analyze the interaction between the magnetic field, electric current, and deformation of interfaces in liquid metal batteries. In the framework of a low-mode, nondissipative, linear stability model, it is found that, during charging or discharging, a sufficiently large battery is prone to instabilities of two types. One is similar to the metal pad instability known to exist in the aluminum reduction cells. Another type is new. It is related to the destabilizing effect of the Lorentz force formed by the azimuthal magnetic field induced by the base current, and the current perturbations caused by the local variations of the thickness of the electrolyte layer.

  15. Electro-hydrodynamic instability patterning of polymers

    NASA Astrophysics Data System (ADS)

    Cargill, S.; Desmulliez, M. P. Y.; Yu, W.

    2011-06-01

    Electro-HydroDynamic Instability Patterning, EHDIP, is a novel micro-manufacturing process that makes use of the instability of viscous polymeric thin films when exposed to electrostatic fields. By using non uniform electrostatic fields, it is possible to shape the polymer into defined meso- and micro-scale structures which are subsequently cured to defined 2D and 3D microstructures. The relatively rapid process time, the one-step manufacturing approach, as well as the ability to produce hitherto unrealised topographies - such as continuous profile structures, makes EHDIP an attractive manufacturing process.

  16. Low energy ghosts and the Jeans' instability

    NASA Astrophysics Data System (ADS)

    Gümrükçüoǧlu, A. Emir; Mukohyama, Shinji; Sotiriou, Thomas P.

    2016-09-01

    We show that a massless canonical scalar field minimally coupled to general relativity can become a tachyonic ghost at low energies around a background in which the scalar's gradient is spacelike. By performing a canonical transformation we demonstrate that this low energy ghost can be recast, at the level of the action, in a form of a fluid that undergoes a Jeans-like instability affecting only modes with large wavelength. This illustrates that low energy tachyonic ghosts do not lead to a catastrophic quantum vacuum instability, unlike the usual high-energy ghost degrees of freedom.

  17. Heuristic explanation of journal bearing instability

    NASA Technical Reports Server (NTRS)

    Crandall, S. H.

    1982-01-01

    A fluid-filled journal bearing is viewed as a powerful pump circulating fluid around the annular space between the journal and the bearing. A small whirling motion of the journal generates a wave of thickness variation progressing around the channel. The hypothesis that the fluid flow drives the whirl whenever the mean of the pumped fluid velocity is greater than the peripheral speed of the thickness variation wave is discussed and compared with other simple explanations of journal bearing instability. It is shown that for non-cavitation long bearings the hypothesis predicts instability onset correctly for unloaded bearings but gradually overpredicts the onset speed as the load is increased.

  18. White-light parametric instabilities in plasmas.

    PubMed

    Santos, J E; Silva, L O; Bingham, R

    2007-06-01

    Parametric instabilities driven by partially coherent radiation in plasmas are described by a generalized statistical Wigner-Moyal set of equations, formally equivalent to the full wave equation, coupled to the plasma fluid equations. A generalized dispersion relation for stimulated Raman scattering driven by a partially coherent pump field is derived, revealing a growth rate dependence, with the coherence width sigma of the radiation field, scaling with 1/sigma for backscattering (three-wave process), and with 1/sigma1/2 for direct forward scattering (four-wave process). Our results demonstrate the possibility to control the growth rates of these instabilities by properly using broadband pump radiation fields.

  19. Prediction of instabilities at the atomic scale

    NASA Astrophysics Data System (ADS)

    Delph, T. J.; Zimmerman, J. A.

    2010-06-01

    Atomic-scale instabilities, in which atomic bonds are broken and reform as the body shifts into a lower-energy configuration, are responsible for a wide range of material behaviours of interest. Building upon previous work, we outline here the construction of a criterion for the prediction of such instabilities. The criterion is implemented within the context of the well-known embedded atom method family of interatomic potentials. We present two examples of the application of this criterion: oriented cavitation in an FCC crystal due to uniform triaxial stretching and dislocation nucleation due to nanoindentation of the (0 0 1) face of an FCC crystal.

  20. Interplay of instabilities in mounded surface growth

    SciTech Connect

    Chakrabarti, Buddhapriya; Dasgupta, Chandan

    2005-02-01

    We numerically study a one-dimensional conserved growth equation with competing linear (Ehrlich-Schwoebel) and nonlinear instabilities. As a control parameter is varied, this model exhibits a nonequilibrium phase transition between two mounded states, one of which exhibits slope selection and the other does not. The coarsening behavior of the mounds in these two phases is studied in detail. In the absence of noise, the steady-state configuration depends crucially on which of the two instabilities dominates the early time behavior.

  1. Developmental instability analysis of BKD-infected spring Chinook salmon (Onchorhynchus tshawytscha) prior to seawater exposure

    USGS Publications Warehouse

    Campbell, W.B.; Emlen, J.M.

    1997-01-01

    Stress in organisms results in energy dissipation, making developmental pathways less stable. Effects of chronic stress, manifested as small random departures from phenotypic symmetry, reflect developmental instability, are considered to be epigenetic and an effect produced by compromised fitness. Instability is detectable and effectively interpreted among sites or populations if samples are collected randomly, the stressor is present throughout character development, characters are identified accurately and excessive mortality does not erase the existence of developmental instability. Bacterial kidney disease (BKD) is a chronic systemic disease in salmonids that, after vertical transmission from parent to egg, persists and spreads throughout ontogeny, potentially affecting developmental processes. Because levels of progeny infection reflect parental infection levels, groups of offspring from parents with high and low levels of BKD infection can be compared to assess the effects of disease-mediated developmental stress. Analyses of fluctuating asymmetry in five bilateral characters were inconclusive, but significant reductions in the proportion of unusable scales, in the number of circulus errors, and in the directional asymmetry of branchiostegal rays were observed in fish from the high-BKD group. This group also contained individuals of significantly larger size. These results are opposite to those expected from traditional developmental instability theory in suggesting that surviving high-BKD fish have greater developmental stability. This reversal appears to be produced by selective mortality having a greater effect than sublethal stress in altering developmental instability patterns. These results are discussed with respect to size selectivity, heterosis and the assumptions supporting developmental instability as a tool for detecting chronic sublethal stress.

  2. Viscoelastic Taylor-Couette instability as analog of the magnetorotational instability

    NASA Astrophysics Data System (ADS)

    Bai, Yang; Crumeyrolle, Olivier; Mutabazi, Innocent

    2015-09-01

    A linear stability analysis and an experimental study of a viscoelastic Taylor-Couette flow corotating in the Keplerian ratio allow us to elucidate the analogy between the viscoelastic instability and the magnetorotational instability (MRI). A generalized Rayleigh criterion allows us to determine the potentially unstable zone to pure-elasticity-driven perturbations. Experiments with a viscoelastic polymer solution yield four modes: one pure-elasticity mode and three elastorotational instability (ERI) modes that represent the MRI-analog modes. The destabilization by the polymer viscosity is evidenced for the ERI modes.

  3. X-rays from hot subdwarfs

    NASA Astrophysics Data System (ADS)

    Mereghetti, Sandro; La Palombara, Nicola

    2016-09-01

    Thanks to the high sensitivity of the instruments on board the XMM-Newton and Chandra satellites, it has become possible to explore the properties of the X-ray emission from hot subdwarfs. The small but growing sample of hot subdwarfs detected in X-rays includes binary systems, in which the X-rays result from wind accretion onto a compact companion (white dwarf or neutron star), as well as isolated sdO stars in which X-rays are probably due to shock instabilities in the wind. X-ray observations of these low mass stars provide information which can be useful also for our understanding of the winds of more luminous and massive early-type stars and can lead to the discovery of particularly interesting binary systems.

  4. Particle acceleration, X-rays, and gamma-rays from winds

    NASA Technical Reports Server (NTRS)

    White, Richard L.; Chen, Wan

    1994-01-01

    The instability of the line-driven winds of hot stars leads to the formation of strong shocks. These shocks not only emit thermal X-rays, but also accelerate a small fraction of the thermal electrons and ions to relativistic energies. Synchrotron radiation from these energetic particles can account for the non-thermal radio emission observed from some hot stars, and can also explain the hard X-rays detected in the Einstein X-ray spectra. Our calculations indicate that the gamma-ray emission from non-thermal particles should be detectable by Gamma Ray Observatory (GRO). The detection (or non-detection) of these emissions over a wide energy range, from the radio to gamma-rays, should provide a great deal of information on the structure of the unstable winds and the physics of particle acceleration by shocks.

  5. Instability windows and evolution of rapidly rotating neutron stars.

    PubMed

    Gusakov, Mikhail E; Chugunov, Andrey I; Kantor, Elena M

    2014-04-18

    We consider an instability of rapidly rotating neutron stars in low-mass x-ray binaries (LMXBs) with respect to excitation of r modes (which are analogous to Earth's Rossby waves controlled by the Coriolis force). We argue that finite temperature effects in the superfluid core of a neutron star lead to a resonance coupling and enhanced damping (and hence stability) of oscillation modes at certain stellar temperatures. Using a simple phenomenological model we demonstrate that neutron stars with high spin frequency may spend a substantial amount of time at these "resonance" temperatures. This finding allows us to explain puzzling observations of hot rapidly rotating neutron stars in LMXBs and to predict a new class of hot, nonaccreting, rapidly rotating neutron stars, some of which may have already been observed and tentatively identified as quiescent LMXB candidates. We also impose a new theoretical limit on the neutron star spin frequency, which can explain the cutoff spin frequency ∼730  Hz, following from the statistical analysis of accreting millisecond x-ray pulsars. In addition to explaining the observations, our model provides a new tool to constrain superdense matter properties by comparing measured and theoretically predicted resonance temperatures. PMID:24785021

  6. Instability windows and evolution of rapidly rotating neutron stars.

    PubMed

    Gusakov, Mikhail E; Chugunov, Andrey I; Kantor, Elena M

    2014-04-18

    We consider an instability of rapidly rotating neutron stars in low-mass x-ray binaries (LMXBs) with respect to excitation of r modes (which are analogous to Earth's Rossby waves controlled by the Coriolis force). We argue that finite temperature effects in the superfluid core of a neutron star lead to a resonance coupling and enhanced damping (and hence stability) of oscillation modes at certain stellar temperatures. Using a simple phenomenological model we demonstrate that neutron stars with high spin frequency may spend a substantial amount of time at these "resonance" temperatures. This finding allows us to explain puzzling observations of hot rapidly rotating neutron stars in LMXBs and to predict a new class of hot, nonaccreting, rapidly rotating neutron stars, some of which may have already been observed and tentatively identified as quiescent LMXB candidates. We also impose a new theoretical limit on the neutron star spin frequency, which can explain the cutoff spin frequency ∼730  Hz, following from the statistical analysis of accreting millisecond x-ray pulsars. In addition to explaining the observations, our model provides a new tool to constrain superdense matter properties by comparing measured and theoretically predicted resonance temperatures.

  7. Nonmodal growth and the magnetorotational dynamo instability

    NASA Astrophysics Data System (ADS)

    Squire, Jonathan; Bhattacharjee, Amitava

    2014-10-01

    Unravelling the important dynamo processes in magnetized rotating shear flows remains fundamental in understanding turbulent transport in astrophysical disks. We consider the dynamo of the magnetorotational instability (MRI) in its simplest possible form, studying the unstratified shearing box without a mean magnetic field. Despite the lack of spectral instability, sustained turbulence and dynamo is possible in this system, with the non-normality of the linear operator playing an important role. An analysis of the MRI from this non-normal perspective has proved enlightening, illustrating that the fastest growing non-axisymmetric disturbances are very different from the eigenmodes, invariably resembling waves shearing with the background flow (shear waves). With the goal of understanding the core dynamo process, we evolve an statistical ensemble of shear waves in a quasi-linear version of the shearing box system. Among the most interesting ideas resulting from this approach is the existence of a mean field dynamo instability of homogenous background turbulence. The instability saturates at levels consistent with fully nonlinear turbulence simulations and depends strongly on magnetic Prandtl number. This work was supported by Max Planck/Princeton Center for Plasma Physics and U.S. DOE (DE-AC02-09CH11466).

  8. Streaming instability of aggregating slime mold amoebae

    NASA Astrophysics Data System (ADS)

    Levine, Herbert; Reynolds, William

    1991-05-01

    We propose a new model of aggregation in the cellular slime mold D. Discoideum. Our approach couples the excitable signaling system to amoeba chemotaxis; the resultant system of equations is tractable to analytical and numerical approaches. Using our model, we derive the existence of a streaming instability for the concentric target aggregation pattern.

  9. The collisionless magnetoviscous-thermal instability

    SciTech Connect

    Islam, Tanim

    2014-05-20

    It is likely that nearly all central galactic massive and supermassive black holes are nonradiative: their accretion luminosities are orders of magnitude below what can be explained by efficient black hole accretion within their ambient environments. These objects, of which Sagittarius A* is the best-known example, are also dilute (mildly collisional to highly collisionless) and optically thin. In order for accretion to occur, magnetohydrodynamic (MHD) instabilities must develop that not only transport angular momentum, but also gravitational energy generated through matter infall, outward. A class of new magnetohydrodynamical fluid instabilities—the magnetoviscous-thermal instability (MVTI)—was found to transport angular momentum and energy along magnetic field lines through large (fluid) viscosities and thermal conductivities. This paper describes the analog to the MVTI, the collisionless MVTI (CMVTI), that similarly transports energy and angular momentum outward, expected to be important in describing the flow properties of hot, dilute, and radiatively inefficient accretion flows around black holes. We construct a local equilibrium for MHD stability analysis in this differentially rotating disk. We then find and characterize specific instabilities expected to be important in describing their flow properties, and show their qualitative similarities to instabilities derived using the fluid formalism. We conclude with further work needed in modeling this class of accretion flow.

  10. Flow Instability Past A Rounded Cylinder

    NASA Astrophysics Data System (ADS)

    Park, Doohyun; Yang, Kyung-Soo

    2014-11-01

    Numerical simulation of flow past a rounded cylinder has been performed to study the effects of rounding corners of an angulated cylinder on the primary (2D) and the secondary (3D) instabilities associated with the corresponding flow configuration. We consider the rounded cylinders ranging from a square cylinder of height D to a circular cylinder of diameter D by rounding the four corners of a square cylinder with a quarter circle of fixed radius (r) . An immersed boundary method was adopted for implementation of the cylinder cross-sections in a Cartesian grid system. The key parameters are Reynolds number (Re) and corner radius of curvature (r) . Firstly, the characteristics of the primary instability such as critical Reynolds number (Rec) , force coefficients, and Strouhal number for vortex shedding are reported against r. It was found that Rec is maximum at r / D = 0.25, meaning that this flow is more stable than the two extreme cases of the square and circular cylinders. Furthermore, there are the optimal values of r / D for force coefficients, which vary with Re. Secondly, we studied the onset of 3D instabilities by using Floquet stability analysis. It turned out that the criticalities of 3D instability modes are significantly affected by r. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2012R1A2A2A01013019).

  11. Ultraspinning instability of rotating black holes

    SciTech Connect

    Dias, Oscar J. C.; Figueras, Pau; Monteiro, Ricardo; Santos, Jorge E.

    2010-11-15

    Rapidly rotating Myers-Perry black holes in d{>=}6 dimensions were conjectured to be unstable by Emparan and Myers. In a previous publication, we found numerically the onset of the axisymmetric ultraspinning instability in the singly spinning Myers-Perry black hole in d=7, 8, 9. This threshold also signals a bifurcation to new branches of axisymmetric solutions with pinched horizons that are conjectured to connect to the black ring, black Saturn and other families in the phase diagram of stationary solutions. We firmly establish that this instability is also present in d=6 and in d=10, 11. The boundary conditions of the perturbations are discussed in detail for the first time, and we prove that they preserve the angular velocity and temperature of the original Myers-Perry black hole. This property is fundamental to establishing a thermodynamic necessary condition for the existence of this instability in general rotating backgrounds. We also prove a previous claim that the ultraspinning modes cannot be pure gauge modes. Finally we find new ultraspinning Gregory-Laflamme instabilities of rotating black strings and branes that appear exactly at the critical rotation predicted by the aforementioned thermodynamic criterium. The latter is a refinement of the Gubser-Mitra conjecture.

  12. Resonant instability of supersonic shear layers

    NASA Technical Reports Server (NTRS)

    Tam, C. K. W.; Lele, S. K.

    1990-01-01

    A computer simulation of possible resonant instability of a supersonic shear layer is carried out. The resonance of two acoustic duct modes of the flow induced by periodic Mach waves generated by a wavy wall is sought. Results of the simulations are reported. Simulations are unable to document a resonant instability and the mixing characteristics remain unchanged. Possible weakness of the present simulations are discussed. A second set of simulations involving a mixing layer separating a supersonic and a subsonic stream were performed. A wavy wall placed adjacent to the supersonic stream to produce a set of periodic Mach waves terminating at the shear layer is modelled. The entire flow field is similar to that of an imperfectly expanded supersonic jet discharging into a subsonic coflowing stream for which enhanced mixing due to the onset of screech (feedback instability) is known to occur. The purpose of these simulations is to see if enhanced mixing and feedback instability would, indeed, take place. Some evidence of feedback oscillations is found in the simulated flow.

  13. Treatment of glenohumeral instability in rugby players.

    PubMed

    Funk, Lennard

    2016-02-01

    Rugby is a high-impact collision sport, with impact forces. Shoulder injuries are common and result in the longest time off sport for any joint injury in rugby. The most common injuries are to the glenohumeral joint with varying degrees of instability. The degree of instability can guide management. The three main types of instability presentations are: (1) frank dislocation, (2) subluxations and (3) subclinical instability with pain and clicking. Understanding the exact mechanism of injury can guide diagnosis with classical patterns of structural injuries. The standard clinical examination in a large, muscular athlete may be normal, so specific tests and techniques are needed to unearth signs of pathology. Taking these factors into consideration, along with the imaging, allows a treatment strategy. However, patient and sport factors need to be also considered, particularly the time of the season and stage of sporting career. Surgery to repair the structural damage should include all lesions found. In chronic, recurrent dislocations with major structural lesions, reconstruction procedures such as the Latarjet procedure yields better outcomes. Rehabilitation should be safe, goal-driven and athlete-specific. Return to sport is dependent on a number of factors, driven by the healing process, sport requirements and extrinsic pressures. Level of evidence V. PMID:26786164

  14. General approach to spatiotemporal modulational instability processes

    SciTech Connect

    Bejot, P.; Kibler, B.; Hertz, E.; Lavorel, B.; Faucher, O.

    2011-01-15

    In this article, we derive the general exact solution of the modulation instability gain. The solution described here is valid for 1-D, 2-D, and 3-D cases considering any temporal response function of the medium and with possible higher order Kerr nonlinearities. In particular, we show that the gain induced by modulation instability is initial condition dependent, while the usual calculations do not lead to such a dependence. Applications for current and high-interest nonlinear propagation problems, such as 1-D optical fiber propagation with delayed Raman response and 2-D filamentation in gases, are investigated in detail. More specifically, we demonstrate that the 2-D model of filamentation based on the balance between higher order Kerr terms leads to a modulation instability window. The impact of both self-steepening and space-time defocusing effects is also highlighted. Finally, we discuss the influence of the finite-time response of the different order electronic Kerr effects on the growth of the expected modulation instability bands.

  15. Laboratory experiments on arc deflection and instability

    SciTech Connect

    Zweben, S.; Karasik, M.

    2000-03-21

    This article describes experiments on arc deflection instability carried out during the past few years at the Princeton University Plasma Physics Laboratory (PPPL). The approach has been that of plasma physicists interested in arcs, but they believe these results may be useful to engineers who are responsible for controlling arc behavior in large electric steel furnaces.

  16. Role of genetic background in induced instability

    NASA Technical Reports Server (NTRS)

    Kadhim, Munira A.; Nelson, G. A. (Principal Investigator)

    2003-01-01

    Genomic instability is effectively induced by ionizing radiation. Recently, evidence has accumulated supporting a relationship between genetic background and the radiation-induced genomic instability phenotype. This is possibly due to alterations in proteins responsible for maintenance of genomic integrity or altered oxidative metabolism. Studies in human cell lines, human primary cells, and mouse models have been performed predominantly using high linear energy transfer (LET) radiation, or high doses of low LET radiation. The interplay between genetics, radiation response, and genomic instability has not been fully determined at low doses of low LET radiation. However, recent studies using low doses of low LET radiation suggest that the relationship between genetic background and radiation-induced genomic instability may be more complicated than these same relationships at high LET or high doses of low LET radiation. The complexity of this relationship at low doses of low LET radiation suggests that more of the population may be at risk than previously recognized and may have implications for radiation risk assessment.

  17. Localized surface instabilities of stressed solids

    SciTech Connect

    Colin, J.; Grilhe, J.; Junqua, N.

    1998-12-31

    Localized instabilities formation on the free surface of solids has been studied when sources of non-homogeneous stress such as dislocations or precipitates are present in the bulk. This formalism of localized perturbations has been used to describe the butterfly transformation of cubic precipitates in superalloys and the contraction of rectangular specimens under stress.

  18. Remote feedback stabilization of tokamak instabilities

    SciTech Connect

    Sen, A.K. )

    1994-05-01

    A novel remote suppressor consisting of an injected ion beam has been used for the stabilization of plasma instabilities. A collisionless curvature-driven trapped-particle instability, an [bold E][times][bold B] flute mode and an ion temperature gradient (ITG) instability have been successfully suppressed down to noise levels using this scheme. Furthermore, the first experimental demonstration of a multimode feedback stabilization with a single sensor--suppressor pair has been achieved. Two modes (an [bold E][times][bold B] flute and an ITG mode) were simultaneously stabilized with a simple state-feedback-type method where more state'' information was generated from a single-sensor Langmuir probe by appropriate signal processing. The above experiments may be considered as paradigms for controlling several important tokamak instabilities. First, feedback suppression of edge fluctuations in a tokamak with a suitable form of insulated segmented poloidal limiter sections used as Langmuir-probe-like suppressors is proposed. Other feedback control schemes are proposed for the suppression of electrostatic core fluctuations via appropriately phased ion density input from a modulated neutral beam. Most importantly, a scheme to control major disruptions in tokamaks via feedback suppression of kink (and possibly) tearing modes is discussed. This may be accomplished by using a modulated neutral beam suppressor in a feedback loop, which will supply a momentum input of appropriate phase and amplitude. Simple theoretical models predict modest levels of beam energy, current, and power.

  19. On transit time instability in liquid jets

    NASA Technical Reports Server (NTRS)

    Grabitz, G.; Meier, G.

    1982-01-01

    A basic transit time instability in flows with disturbances of speed is found. It was shown that the mass distribution is established by and large by the described transit time effects. These transit time effects may also be involved for gas jets.

  20. Instabilities and structure formation in laser processing

    SciTech Connect

    Baeuerle, D.; Arenholz, E.; Arnold, N.; Heitz, J.; Kargl, P.B.

    1996-12-31

    This paper gives an overview on different types of instabilities and structure formation in various fields of laser processing. Among the examples discussed in detail are non-coherent structures observed in laser-induced chemical vapor deposition (LCVD), in laser-induced surface modifications, and in laser ablation of polymers.