Two aspects of the stability of a compressible mixing layer: Absolute/Convective instability and the

The effect of viscosity on the capillary instability of a liquid jet is examined. The critical Weber

... is sufficiently above a damping-determined threshold but below a threshold for temporal or absolute instability exists for the backscatter instabilities. ...

Absolute/Convective Instabilities. The concept of absolute and convective insta- ... absolute instability occurs when the zero lies on the real o axis. ...

The theory of absolute and convective instabilities in a plasma is discussed, and it is questionable, as it describes the linear development of instabilities by their behavior in the time asymptotic limit. In order to make sensible predictions on the line...

The theory of absolute and convective instabilities is discussed and we argue that the basis of the theory is questionable, since it describes the linear development of instabilities by their behaviour in the time asymptotic limit. In order to make sensib...

The nonlinear saturation of the absolute stimulated Raman scattering (SRS) instability is considered in a finite homogeneous plasma. The amplitude of the incident wave exceeds the absolute instability threshold by the fractional amount delta (

The threshold for an absolute parametric instability of the decay type along with the growth rates for two types of interacting oscillations are obtained theoretically for an inhomogeneous plasma layer. (AIP)

For one-dimensional three-wave parametric instabilities with oppositely directed group velocities for the decay waves in unbounded plasmas, it is known that for uniform coupling amplitude and constant wave-vector mismatch (dsummationk/sub i//dx = const) there cannot be an absolute instability. It is shown that this is an exceptional ...

... Title : Theory and Experiments on Chemical Instabilities. ... relative rates have been calculated and the challenge of predicting absolute rates remains ...

... effect. At low flow speeds a convective instability is found and at higher flow speeds there is an absolute instability. (Author). ...

... obtain numerical estimates of the growth rates for various parameters, and second to identify the instabilities as being either absolute or convective. ...

... One of them, in which the wave grows indefinitely with time, is called absolute instability, and the other, in which the wave grows spatially as it ...

... rate. The compressibility of the ambient gas, as well as the surface tension, tends to promote absolute instability. The precise ...

... It is shown that for the absolute instability, the demonstration of Polovin has to be completed to avoid an ambiguity. For ...

... PLASMAS(PHYSICS), *ELECTROMAGNETIC WAVE REFLECTIONS, ELECTROMAGNETIC RADIATION, HEATING, ELECTRON DENSITY ...

The full Raman scattering equations have been solved in a linear density profile in an attempt to overcome the local nature of most previous analyses. The global solution obtained elucidates the transition between absolute and convective Raman instabilities. Feedback linking backward and forward Raman scattering can result in an ...

The purpose of the work reported herein is to examine absolute modes of the TPD instability in two dimensions in an infinite homogeneous plasma. Briggs has shown that the condition for absolute instability in this case is the existence of a solution of th...

A two-layer quasigeostrophic model is used to investigate whether dissipation can induce absolute instability in otherwise convectively unstable or stable background states. It is shown that dissipation of either temperature or lower-layer potential vorticity can cause absolute instabilities over a wide range of ...

We examine the interaction of an electron beam penetrating a strongly correlated plasma. Conditions are established for this unstable interaction to lead to an absolute instability. We propose the absolute instability as a means for probing the strongly correlated plasmas.

The electron-cyclotron drift instability is observed to develop an absolute instability in the laboratory frame of stationary electrons. The authors investigate the threshold, temporal and spatial growth, and the saturation mechanism. (Author)

The Karman vortex street in the wake of a circular cylinder is shown to be due to an absolute instability of the flow in the near wake. A new means of instability analysis is used, involving mappings from the complex k plane to the complex ..omega.. plane.

Absolute and convective instabilities of spirals are investigated using the continuous and the so-called absolute spectrum. It is shown that the nature of transport, induced by an absolute instability, is determined by spectral data of the asymptotic wave trains. The results are applied to core ...

The existence of a new instability mechanism of a current-carrying plasma which, for a sufficiently long system, may occur after saturation of the two-stream instability is shown. The instability is due to combined asymmetry and nonuniformity of the elect...

Cylindrical liquid jets are inherently unstable and eventually break into drops due to the Rayleigh-Plateau instability, characterized by the growth of disturbances that are either convective or absolute in nature. Convective instabilities grow in amplitude as they are swept along by the flow, while absolute ...

absolute instability disappeared at all locations establishing buoyancy as the primary instability mechanism in self-excited low-density jets.

Absolute SMBS instability has been observed in a plasma and, in contrast to convective instability, contributes to anomalous heating of the plasma. (AIP)

The problem of convective and absolute instability in the interactions of charged particle beams with plasma and with each other was analyzed. (R.V.J.)

... Abstract : Absolute instability of (Gortler vortices on the severely curved concave pressure side of a gas-turbine blade is the main thrust of the third ...

... As water density ratio in one atmospheric pressure in room tern- ... mode of the jet instability. ... 'A Bers, Handbook of Plasma Physics (North-Holland ...

Dynamical mechanisms underlying the equilibration of absolute instability are examined in a nonlinear, quasigeostrophic, two-layer model. The key to understanding the nonlinear equilibration is in recognizing that linear absolute instabilities can be stabilized by a reduction of the vertical shear and by ...

Two aspects of the stability of a compressible mixing layer: Absolute/Convective instability and the convective Mach number were considered. It was shown that, for Mach numbers less than one, the compressible mixing layer is convectively unstable unless t...

The critical current, oscillation frequency, and characteristic wave number for the excitation of absolute instability in gyropeniotron amplifiers are calculated from the linear dispersion relation by following the Briggs--Bers criterion. Numerical results are presented for some cases of interest.

Contrary to previous theoretical predictions, it is shown that the dissipative drift-wave instabilities are absolute in tokamak plasmas. The existence of unstable eigenmodes is shown to be associated with a new eigenmode branch induced by the finite toroidal couplings.

The absolute and convective instability of a viscous liquid emanating into a viscous gas in a vertical pipe is analyzed in a parameter space spanned by the Reynolds number, the Froude number, the Weber number, the viscosity ratio, the density ratio, and t...

The absolute and convective instability of a jet of an inviscid compressible fluid emanating into another inviscid compressible fluid is investigated. It is shown that the compressibility of the ambient fluid, as well as the surface tension, tends to prom...

Contrary to previous theoretical predictions, it is shown that the dissipative drift-wave instabilities are absolute in tokamak plasmas. The existence of unstable eigenmodes is shown to be associated with a new eigenmode branch induced by the finite toroi...

We investigate the effect of coupling between diffraction and walk-off on secondary instabilities in nondegenerate optical parametric oscillators. We show that traveling waves that propagate in the walk-off direction, which are generated at the onset of absolute instability, experience Eckhaus and zigzag phase ...

The classification of absolute and convective instability is important for the ... one unstable normal mode and the growth rate is uniformly bounded � the ...

High accuracy absolute fields utilize advanced processing techniques. ... scale instabilities. AC Electric Field. ELF Waveforms ...

... The stability of the system is analysed using a causal approach which is able to distinguish between absolute and convective instabilities. ...

... mechanics and aerospace sciences: (1) Flow Control, (2) Chaos and universality in wakes behind circular cylinders, (3) Absolute instability and ...

... The micro-instability is absolute and develops fastest for a critical perturbation wavelength, of the order of several times the thickness of the plasma ...

... The ratio of absolute and convective instability thresholds is large whenever the damping lengths of the linear uncoupled modes have very ...

... These premixed flamelets are quite weak in that ... of a regular subsonic neutral mode was ... absolute instability becomes progressively weaker in that ...

... to four types of interaction which leads to evanescent waves, simple propagating waves, growing waves, and also to an absolute instability. ...

... (2) Understanding the effects of controlled three- dimensional disturbance on the region of absolute instability. Comparison ...

Monsoon depressions over the Bay of Bengal develop almost entirely in July and August. After studies

... to the influence of a powerful pumping wave is unstable relative to the build up of plasma high-frequency electronic waves (plasmons); this is ...

... It is shown that the gas density has the effect of raising ... LIQUID JETS, *STABILITY, RATIOS, CAPILLARY TUBES, GASES, VISCOSITY, REYNOLDS ...

A theoretical model for the instability of two-dimensional turbulent boundary layer over compliant surfaces is described. The principal Reynolds stress is modelled by a well-established mixing-length eddy-viscosity formulation of van Driest. The perturbations of the mean velocity and Reynolds stress fields are coupled via the turbulence model. The investigation of ...

The stability of a viscous film flowing down a vertical fiber under the action of gravity is analyzed both experimentally and theoretically. At large or small film thicknesses, the instability is convective, whereas an absolute instability mode is observed in an intermediate range of film thicknesses for fibers of small enough radius. ...

The capillary instability of an infinitely long jet with respect to temporally growing disturbances was analyzed by Rayleigh. Keller et al. examined the capillary instability of a semi-infinite jet with respect to spatially growing disturbances. They foun...

Using multiple time scale analysis, the nonlinear saturation of the absolute stimulated Raman scattering instability is examined in a finite homogeneous collisional plasma. The amplitude of the incident wave is assumed to exceed the absolute instability threshold by the fractional amount ..delta..(<<1). A ...

The nonlinear saturation of the absolute stimulated Raman scattering (SRS) instability is considered in a finite homogeneous plasma. The amplitude of the incident wave exceeds the absolute instability threshold by the fractional amount (<<1). A single backscattered wave and a single plasma wave grow until ...

A theory is derived for the absolute parametric instabilities which are excited in a nonuniform magnetized plasma by electromagnetic radiation at a frequency comparable to the electron plasma frequency. The thresholds and growth rates are determined for the aperiodic instability, for the decay into a lower-hybrid wave and an ...

It has been confirmed that the normal mode of a surface wave on a corrugated metal plate can be excited by a sheet electron beam. Two types of instabilities are analyzed numerically. One is the Cherenkov instability between the surface normal mode and the slow-space-charge mode of the electron beam. This instability is possibly ...

Whistler mode wave emissions in the magnetosheath, known as lion roars, are thought to be generated by an electron cyclotron instability. Reported satellite data are used to model a magnetosheath medium where lion roars emissions occurred, and the character, absolute or convective, of the associated electron cyclotron instability is ...

The conditions for absolute and convective instabilities of kink waves in the plasma of a positive column of a gas discharge are determined. There is an important difference between these conditions, because of the anisotropic ambipolar drift of kink perturbations in the electron-drift direction in the longitudinal electric field. This drift arises when ...

Pinch-point instability analysis is used to study the effects of finite temperature on the time-asymptotic pulse shapes of electrostatic and electromagnetic two-stream instabilities. Their absolute or convective instability nature is established over the entire regime from instability threshold ...

Filamentation and Brillouin-enhanced four-wave-mixing instabilities caused by the cooperative interaction between two counterpropagating electromagnetic waves are shown to possess larger convective growth rates and smaller absolute instability thresholds than the conventional single-pump instabilities. These ...

If the initial wave is unstable in the upper half plane Im ..omega..>0 and there are no branch points of the quasiwave number, or if waves traveling in the same direction coalesce at a branch point, the instability is convective. On the other hand, if a branch point k(..omega..) does exist in the upper half-plane Im ..omega..>0, and not all the waves that merge at this ...

The possibility of deep parametric decay instability suppression by launching a complementary (small power) pump wave possessing a slightly shifted frequency is demonstrated experimentally. This suppression is achieved at an additional pump wave frequency shift equal to the frequency separation of ion acoustic eigenmodes excited in plasma as a result of ...

Stability analysis of an arbitrary-finesse ring cavity containing a Kerr medium of arbitrary response time reveals an absolute minimum threshold for the driving intensity necessary for realization of self-pulsing instabilities. This threshold is minimized not only with respect to cavity mistuning but also with respect to the medium's response time. The ...

For the phase conjugated wave at four-wave mixing at SBS the transient analytical solution is obtained. A rate of the reflected wave amplitude increasing and a range of values of coupled waves parameters in which time instability is most essential are determined. Conditions of attenuation of absolute instability influence on considered ...

The spatiotemporal instability of a natural convection flow in vertical heated slot is studied theoretically. The two unstable modes, secondary cell and traveling wave, are illustrated to be absolute and convective instabilities, respectively. Using a model to simulate the temperature gradient in the center of the slot, we propose an ...

The absolute instability is a subject of considerable physics interest as well as a major source of self-oscillations in the gyrotron traveling-wave amplifier (gyro-TWT). We present a theoretical study of the absolute instabilities in a TE01 mode, fundamental cyclotron harmonic gyro-TWT with distributed wall ...

Finite-bandwidth effects are investigated by using the random phase approximation. The conditions of validity are checked by solving exactly a particular model. It is found that a finite coherence length for the pump wave can favor the existence of absolute instability. (AIP)

The parametric decay of an electromagnetic wave into two electron plasma waves is considered. The electromagnetic wave is obliquely incident on the density gradient. The resulting analysis shows that the threshold for absolute instability decreases as the...

A laminar flow is absolutely unstable when small perturbations grow without limit at the point of their origin. Convective instability, but absolute stability, occurs when over time perturbations move from their point of origin without perturbing the prim...

The convective stimulated-Brillouin-scattering instability, which is usually considered in the case of an inhomogeneous low-density plasma, occurs only if the dissipation of sound is rapid. If this dissipation is only slight, an absolute stimulated-Brillouin-scattering instability occurs.

A spatially localized instability t..-->..l+s, whose properties are in agreement with the predictions of the linear and nonlinear theories, was detected in the inhomogeneous plasma in the region of the field peak in front of the reflection point of the pump wave.

The decay of an electromagnetic wave into two plasma waves in an inhomogeneous unmagnetized plasma is studied. The resulting instability is of an absolute nature in both collisional and collisionless plasmas. The instability threshold is found as a function of the damping rate of the plasma waves and the characteristic length of the ...

Considered are criteria of strengthening and instability of waves in non-uniform and, particularly, in periodic media. The Green function method is used. It is shown, that absolute instability takes place, if there is a special point of the Green function...

The operation of the gyrotron travelling wave amplifier is based on the convection cyclotron maser instability. It is found that this convective instability may become absolute (nonconvective) at a sufficiently high current level, resulting in oscillation...

The gyrotron traveling-wave amplifier employing the distributed-loss scheme is capable of very high gain and effective in suppressing the global absolute instabilities. This study systematically characterizes the local absolute instabilities and their transitional behavior. The local absolute ...

By using the mathematical formalism of absolute and convective instabilities we study the nature of unstable three-dimensional disturbances of viscoelastic flow convection in a porous medium with horizontal through-flow and vertical temperature gradient. Temporal stability analysis reveals that among three-dimensional (3D) modes the pure down-stream ...

... absolute measurements of RF power, and turbulence measurements over a dynamic range of 80 dB. Very few other university-based plasma ...

An integral equation is derived to describe the absolute instability in an inhomogeneous plasma.(AIP)

The Rosenbluth-Post convective instability in mirrors is discussed. A brief theoretical discussion of the saturation of absolute modes is given. The containment properties of mirrors in the presence of ion cyclotron waves are discussed.

libertarian right (the individual has an absolute right to do as he/she pleases, and the 'market' will ensure instability is kept in bounds), such debates ...

... D heated jets, experiments showed that local absolute instability ... EXCITATION, TURBULENCE, LINEARITY, HEATING, RESONANCE, WAKE, TWO ...

... Various conditions sufficient to guarantee the linear instability of the process are ... acting on a phase boundary to the local absolute temperature and ...

The coefficient of energy conversion from plasma waves to harmonics is calculated for a laser-produced inhomogeneous plasma below the threshold for the absolute instability.

Since a Maxwellian plasma is free of absolute instabilities, steady state solutions of (29) can exist for W real, and most generally k ...

Near forward scattering of electromagnetic radiation from ion acoustic waves in the presence of a density gradient is studied. Two absolutely unstable modes are found, neither of which is suppressed by the density gradient.

... proportional to ei(o - ' ) and, the cyclotron maser instability can be either convective or absolute. Convective, or spatial, growth is ...

The nonlinear stage of the absolute parametric instability in an inhomogeneous bounded plasma is examined theoretically.(AIP)

>Absolute or convective evolutions of instabilities can produce very different signatures of observed radiation from unstable plasmas. This is particularly useful in space plasmas when correlating experimentally observed emissions with theoretical models describing the source regions. A letter has questioned the basis and usefulness of the theory of ...

Although large-scale internal gravity waves of finite amplitude are known to be unstable, they are frequently observed in the lee of topography. We propose an explanation for this paradox by showing that the instability of these waves is convective and not absolute. Hence, in the frame of the mountain, a localized initial perturbation gives rise to a wave ...

Previous absolute instability results for significant growth from a parametric instability involving oppositely directed modes coupled by a uniform pump with phase inflection coupling (..delta..k = k''x/sup 2//2) are extended to higher modes and to thresholds. The results are applied to stimulated Raman scattering ...

The decay interaction of electromagnetic waves with ion-acoustic waves and Langmuir satellites (red and blue) in an unmagnetized inhomogeneous plasma is studied. In many cases the blue satellite leads to an absolute instability, providing a ''feedback'' to the region of resonant convective amplification. The ...

We investigate the consequences of delay in the iodate-arsenous acid reaction under the influence of an electric field at a constant current density. Using the charge balance condition, we show how the electric field may induce an intrinsic delay in the system, which gives rise to instability. The different instability regions in the appropriate parameter ...

The spatiotemporal instability of the buoyancy-driven flow adjacent to a vertically heated wall, which is immersed in thermally stratified medium, is studied theoretically and numerically. The temperature gradients ratio between the wall and the ambient fluid is shown to lead to rich scenario of absolute-convective instability ...

A general approximate criterion is developed (via WKB analysis) for the absolute instability of two parametrically pumped decay waves with one-dimensional inhomogeneity. The absolute instability threshold pump power proves to be higher than that required for amplitude amplification R by a factor ...

The helical magnetorotational instability of the magnetized Taylor-Couette flow is studied numerically in a finite cylinder. A distant upstream insulating boundary is shown to stabilize the convective instability entirely while reducing the growth rate of the absolute instability. The reduction is less severe with ...

The helical magnetorotational instability of the magnetized Taylor-Couette flow is studied numerically in a finite cylinder. A distant upstream insulating boundary is shown to stabilize the convective instability entirely while reducing the growth rate of the absolute instability. The reduction is less severe with ...

The electrostatic instability in a magnetoplasma, omega > omega /sub ce/ , excited by a weak electron beam is found to be either convectively unstable (amplifying) or absolutely unstable (oscillating) depending upon effective plasma electron temperature and beam density. Measurements of the transition between the two types agree with ...

The present paper reports on experimental observations of saturation of absolute beam-plasma instability that can be shown to result from beam trapping. The details of the trapping differ from the convectively unstable case in that the wave is large near the electron gun, and the beam is suddenly trapped in this large-amplitude wave. The experimental ...

Experimental evidence of convective and absolute instabilities in a nonlinear optical system is given. In optics, the presence of spatial nonuniformities brings in additional complexity. Hence, signatures characterizing these two regimes are derived based on analytical and numerical investigations. The corresponding noise-sustained and dynamical patterns ...

The boundary-value problem describing stimulated Raman scattering induced by a plane coherent electromagnetic wave normally incident upon plasma with a monotonic density profile is solved on a global basis. Propagation of amplified electrostatic waves between the resonant backward- and forward-scattering points and reflection of forward-scattered electromagnetic waves into the resonant ...

The roots of an improved analytic eigenvalue equation for the absolute universal or collisionless drift instability in a sheared magnetic field are found numerically and compared with the eigenvalues obtained from a numerical solution of the exact differential equation. The startling result is that both techniques predict stability, no matter how weak the ...

In this Letter, we discuss the effect of slow real modes in reaction-diffusion systems close to a supercritical Hopf bifurcation. The spatiotemporal effects of the slow mode cannot be captured by traditional descriptions in terms of a single complex Ginzburg-Landau equation (CGLE). We show that the slow mode coupling to the CGLE introduces a novel set of finite wavelength ...

A linear fluid code solving the equations for the two-plasmon decay (TPD) instability has been developed and used to study the TPD instability. Both absolute and convective modes are observed in the simulations using this code, which show that the absolute modes are located close to the quarter-critical-density ...

It has been shown recently that the instability of a two-dimensional wake increases when it is confined in the transverse direction by two flat plates. Confinement causes the transition from convective to absolute instability to occur at lower values of shear. This paper examines this effect comprehensively and concludes that it is due ...

The purpose of the work reported herein is to examine absolute modes of the TPD instability in two dimensions in an infinite homogeneous plasma. Briggs has shown that the condition for absolute instability in this case is the existence of a solution of the coupled mode dispersion relation. Analytic solutions for ...

We consider reaction-diffusion instabilities in a flow reactor whose cross-section slowly expands with increasing longitudinal coordinate (cone shaped reactor). Due to deceleration of the flow in this reactor, the instability is convective near the inlet to the reactor and absolute at the downstream end. In sustained regimes the two ...

A plasma subjected to the action of an intense pumping verve is unstable with respect to buildup of plasma high-frequency electron waves (plasmons) due to decay of the pumping wave into two plasmons. The effect of spatial inhomogeneity of the plasma on such parametric instability is studied. It is shown that allowance for spatial inhomogeneity of the plasma leads to ...

Parametric instability l ..-->.. l'+s resulting in anomalous reflection of oblique Langmuir waves in a two-dimensionally nonuniform plasma is studied experimentally and theoretically. The experimental results confirm the theoretical prediction that for low input powers, the instability consists in the spatial amplification of ion-sound noise. ...

An externally applied large amplitude circularly polarized ion cyclotron wave of long wavelength propagating along the static magnetic field can drive instabilities of ion cyclotron waves and ion acoustic waves. The dispersion relation is first derived using a kinetic equation approach. Later, it is shown that the same relation can be derived on the basis of a ...

We analyze numerically the magnetorotational instability of a Taylor-Couette flow in a helical magnetic field [helical magnetorotational instability (HMRI)] using the inductionless approximation defined by a zero magnetic Prandtl number (Pr_{m}=0) . The Chebyshev collocation method is used to calculate the eigenvalue spectrum for small-amplitude ...

We examine the influence of a thermal gradient on a classical reaction-diffusion system. The different instability regions in the appropriate parameter space are examined. We show how the imposed temperature gradient destabilizes a chemical front via the Soret effect, giving rise to both absolute and convective instability. ...

The steep temperature gradients characteristic of laser-produced plasmas generate strong thermal fluxes which can be unstable. Previous theoretical investigations of these instabilities have found temporal growth rates for modes which are uniform in the direction of heat flow. Here the analysis is extended to modes with spatial dependence in this direction. Spatial growth ...

Simple derivation of the condition for the transition point from absolute instability of plane dark solitons to their convective instability is suggested. It is shown that unstable wave packet expands with velocity equal to the minimal group velocity of the disturbance waves propagating along a dark soliton. The growth rate of the ...

The instability resulting from the interaction of a weak, monoenergetic electron beam with a magnetoplasma ($omega$>$omega$/subC//subE/) has been studied experimentally. A calculation, using the dispersion relation appropriate to the experiment, shows that the interaction may take the form of convective or absolute ...

Convective and absolute nature of instabilities in nondegenerate optical parametric oscillators with large transverse section, for negative detunings and in the presence of walkoff, is examined. The asymptotic response of the signal and idler fields to a transverse localized two-dimensional perturbation is evaluated. The presence of walkoff breaks the ...

Electrostatic lower hybrid ''pump'' waves are often launched into tokamak plasmas by structures (e.g., waveguides) whose dimensions are considerably smaller than characteristic plasma sizes. Such waves propagate in well-defined resonance cones and give rise to parametric instabilities driven by electron E x B velocities. The finite size of ...

The parametric instability of an inhomogeneous pump field with respect to the excitation of high-frequency and low-frequency perturbations is analyzed. Near an intensity maximum of the inhomogeneous field, an absolute modulation instability can occur. The instability threshold, the growth rates, and the size of the ...

A linear analysis is presented for pulse shapes produced by a spatial and temporal delta-function disturbance of cyclotron-resonance-maser modes for the case where the initial equilibrium state is free of radiation. A pinch-point analysis based on the theory of Briggs and Bers is employed. Numerical and analytical techniques are developed for the straightforward calculation of pinch-point ...

Absolute instability analysis of the coupled modes for stimulated Brillouin scattering for plasmas drifting at velocities rather greater than Mach 0.5 shows that oblique forward scatter is favored rather than backscatter, which is generally stable. For typical laser-target interaction parameters, a threshold (Ilambda/sup 2/) near 2 x 10/sup 15/ W cm/sup ...

Computer simulations of the free-electron laser have been carried out using a two-and-one-half dimensional fully electromagnetic relativistic particle code. It has been found that waves propagating obliquely with respect to the electron beam are always unstable with appreciable growth rates and, therefore, mode competition is an important consideration in the design of free-electron lasers. ...

Shear slows of magnetised plasmas are routinely observed in the solar atmosphere, in planetary magnetospheres, and in interplanetary space. They are also ubiquitous elements of models of remote astrophysical objects like the interacting stellar winds in binary stellar systems. Studying stability of such flows is paramount for understanding physical processes in space. The simplest shear flow is a ...

We study free surface instabilities of spreading thin films exposed to destabilizing body force (gravity) on partially wetting substrates. For completely wetting films on inverted substrates, we have uncovered rich structure of convective and absolute instabilities which evolve due to contact line presence. ootnotetextT.-S. Lin, L. ...

Using WKB analysis it is shown that for three-wave backscattering type parametric instabilities in inhomogeneous plasmas no spatial (convective) growth is possible for undamped modes. if one coupled mode is more heavily damped than the other, then spatial growth is possible in both forward and back-scattering. The spatial amplification factor is that obtained by ...

Shear flow instabilities are an important aspect of hydrodynamic studies. The present review article discusses the role of an ambient magnetic field which both modifies the Kelvin-Helmholtz instability and may introduce new types of magnetohydrodynamic waves and instabilities. A brief overview of magnetospheric pulsations is presented ...

Shear flow instabilities are an important aspect of hydrodynamic studies. The present review article discusses the role of an ambient magnetic field which both modifies the Kelvin-Helmholtz instability and may introduce new types of magnetohydrodynamic waves and instabilities. A brief overview of magnetospheric pulsations is presented ...

Electrostatic lower hybrid ''pump'' waves often launched into tokamak plasmas by structures (e.g., waveguides) whose dimensions are considerably smaller than characteristic plasma sizes. Such waves propagate in well-defined resonance cones and give rise to parametric instabilities driven by electron E x B velocities. The finite size of the ...

We study the consequences of negative differential electron mobility in FETs using the field model and the gradual channel approximation. We find that the FET may show convective or absolute instability. The fluctuations growths is governed by diffusion l...

Instability regions for typical set of runs. Saturation pressure, 17 pounds per square inch absolute +3 percent; vapor flow rate, 56 pounds per hour ...

The scaling for the ignition of beam plasma discharge observed in many laboratory experiments is consistent with the requirement for triggering an absolute instability near the plasma frequency (omega sub e). The transition in the scaling with pressure can be attributed to transition from Bohm to classical diffusion losses.

A theory is developed of absolute parametric aperiodic instability in a spatially inhomogeneous plasma, when the electromagnetic waves generated in the plasma are trapped by the plasma near the peaks of the pumping-wave field.

The connection between local and global stability properties of free shear flows was investigated. For 2-D inviscid jets, absolute instability was found for ratios of jet to ambient density below 0.9. Low wake heating (density) eliminates all local absolu...

It is argued that some absolute instability model will adequately explain the SRS data of laser-produced plasma under conditions in which large SRS yields have been observed. (AIP)

The decay of an electromagnetic wave into two plasma waves in an inhomogeneous, nonmagnetized plasma is analyzed. It is demonstrated that the instability which arises in this case has an absolute nature both in a plasma with collisions and in a collisionl...

The Weber number is defined as We =- p1 U20d/S where S is the surface tension, p , is the liquid density, U0 is the centre-line velocity of the liquid sheet, ...

The authors derive the equations describing the decay of an intense, coherent EM wave into a scattered EM wave and a plasma wave in an inhomogeneous plasma. The plasma wave becomes nonpropagating in the vicinity of the cut-off of the scattered EM wave. Th...

A plasma which is subjected to the influence of a powerful pumping wave is unstable relative to the build up of plasma high-frequency electronic waves (plasmons); this is caused by the decay of the pumping wave into two plasmons. The article that follows ...

This is a brief report on the properties of round jets of different densities issuing into the ambient air. Different densities were obtained by premixing helium and air in various proportions. We show that these jets have two types of behaviour depending...

The objective is to establish a definitive role of the capillary, viscous, and inertial forces at a liquid-gas interface in the absence of gravity by using the fluid dynamics problem of the stability of a liquid jet as a vehicle. The objective is achieved...

The linearized coupled-mode equations in two dimensions are solved numerically within the paraxial approximation to find the absolute-mode threshold of parametric instabilities driven by an incoherent laser beam. The results show that, for plasma lengths only a few times threshold, a surprisingly small temporal bandwidth {Delta}{omega} that is ...

Previous work on the absolute instability of Brillouin scatter in drifting plasmas is extended to the case of convective amplification. It is found that, similar to temporal growth rates for the absolute instability, forward oblique scatter has the highest spatial gain, with backscatter near a minimum. To agree ...

The linear instability of a viscous liquid flowing in a vertical sheet sandwiched between two viscous gases bounded externally by two vertical walls is investigated. The critical Weber number below which the flow is absolutely unstable and above which the flow is convectively unstable is found to be approximately equal to one and is weakly dependent on the ...

The authors study the morphological instability of the planar solid/liquid interface of a unidirectionally-solidified dilute binary mixture. They use a model developed by Boettinger et al., Aziz, and Jackson et al., which allows for nonequilibrium effects on the interface through velocity-dependent segregation and attachment kinetics. Two types of ...

Proposals for the fast-ignition approach to laser fusion usually depend on the propagation of relativistic electron beams through a plasma from densities near critical where the beam is created by a short-pulse laser, to the compressed core density where the beam deposits its energy. Such beams can be disrupted by the growth of small-scale instabilities such as filamentation ...

The parametric decay of an electromagnetic wave into two electron plasma waves is considered. The electromagnetic wave is obliquely incident on the density gradient. The resulting analysis shows that the threshold for absolute instability decreases as the angle of incidence of the electromagnetic wave relative to the density gradient approaches 90/sup 0/. ...

The parametric decay of an electromagnetic wave into two electron plasma waves in an inhomogeneous plasma is considered. The electromagnetic wave is obliquely incident on the density gradient. The resulting analysis shows that the threshold for absolute instability decreases as the angle of incidence of the electromagnetic wave relative to the density ...

The high-frequency 'convective' loss-cone mode in a mirror-confined plasma is shown to be absolutely unstable as a result of wave reflection from the mirror throats, provided that the plasma length is greater than an axial wavelength. Critical lengths for stability are only a few ion gyroradii for fusion parameters, much smaller than previous estimates. This result places ...

The effect of ambient pressure on the intrinsic instability of rapid vaporization in single droplets boiling exposively at the limit of superhead has been studied experimentally and theoretically. The instability that distortsthe evaporating interface and substantially enhances the mass flux at atmospheric pressure is suppressed at high pressure. The ...

Both long-wave and short-wave ion acoustic fluctuations give rise to an absolute two-plasmon decay instability. The growth rates and thresholds for the instability are studied as functions of the fluctuation wavelength. The threshold reaches a maximum for ion acoustic waves which are excited by stimulated Brillouin scattering.

The effect of spatial background turbulence on parametric interactions in an infinite, inhomogeneous plasma with a linear density profile is considered. It is shown that the well-known convective saturation arising from the density gradient can disappear in the presence of turbulence. Absolute instability then occurs. The criteria for the ...

The Schwarzschild criterion governing the onset of convective instability has been modified to include magnetic field. This may be of importance for solar variability. The revised condition suggests that the underside of field layers are stabilizing and the upper side destabilizing. Absolute instability can be reached to achieve ...

Absolute instability of Gortler vortices on the severely curved concave pressure side of a gas-turbine blade is the main thrust of the third- year work under this grant. For the most part, the Gortler vortices have been investigated in an incompressible b...

We present the linear evolution in space-time of electromagnetic instabilities generated by relativistic beam-type electron distribution functions that characterize highly anisotropic electron plasmas. The plasma is assumed to be infinite, homogeneous and in a static, uniform magnetic field (antiB/sub 0/). For waves propagating along antiB/sub 0/ there are two ...

Parametric instabilities in the presence of sinusoidal plasma density modulation are considered analytically and by numerical integration of the coupled mode equations. The density modulation tends to reduce temporal and spatial growth rates. If there is a linear density gradient in addition to the density modulation, the usual convective saturation exists for small ...

We theoretically and experimentally evidence that fiber systems are convective systems since their nonlocal inherent properties, such as the dispersion and Raman effects, break the reflection symmetry. Theoretical analysis and numerical simulations carried out for a fiber ring cavity demonstrate that the third-order dispersion term leads to the appearance of convective and ...

Absolute instability of Gortler vortices on the severely curved concave pressure side of a gas-turbine blade is the main thrust of the third- year work under this grant. For the most part, the Gortler vortices have been investigated in an incompressible b...

of the instability, dripping and jetting [3,4]. They are familiar to anyone who has watched water drip or flow from in is the density of water, L is a characteristic length scale equal to the diameter of the jet, and uin is the mean,4], the shape of the jets is dramatically different from those generated by the coflow. A water jet falling from

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; ...

Experimental observations show that the beam-plasma instability generates a modified beam distribution function which can destabilize new modes. These sideband modes nonlinearly saturate, modify the beam further, and a cascade proceeds. For strong beams the cascade and attendent phase mixing lead to a quasilinear-like spectrum of waves and a nearly plateau-like beam. ...

Properties of solutions to superfluid hydrodynamic equations as applied to the degenerate Bose gas are considered. The equations are split into two independent pairs of equations. One pair is written for the normal component implies the instability of solutions, which manifests itself in the majorant catastrophe with respect to the total density. The case when the ...

It is shown that an absolute instability arising from the spatial variation of the pump wave can occur in an inhomogeneous plasma. An analysis is carried out for the example of the parametric conversion of a pump wave into a plasma wave and an ion-acoustic wave. In this instability, the perturbations whose amplitudes grow over time are ...

The coherent instability temperatures for continuous ordering have been determined for various binary alloys from absolute intensities of X-ray diffuse scattering. The measured T/sub instability/ are 358.2, 211.4 and 627.6/sup 0/C for alloys of Cu/sub 3/Au, Cu/sub 81/ /sub 5/ and CoPt/sub 3/ respectively. A comparison is made of these ...

We examine a prototypical ionic reaction-diffusion system involving the well-known iodate-arsenous acid reaction in an electric field at a constant current density. By taking into consideration of the spatial inhomogeneities in electric field intensity and charge density due to ionic migration and diffusion using charge balance condition, we look for the different instability ...

Electrostatic instabilities occurring in mirror-confined ion velocity-distributions have been thoroughly investigated. The electromagnetic instability of greatest concern is the Alfven-ion-cyclotron (AIC) mode. In this work we investigate both convective and absolute growth, both in homogeneous plasma and in finite machines, for a ...

Quantum liquids-known to be realized in 3He, 4He and electronsin metals-generally exhibit instabilities unforeseen under classical Newtonian dynamics, such as the superfluid and superconducting transitions. Recently, a new quantum liquid, now known as the quantum spin liquid, has been discovered in frustrated antiferromagnetic spin-1/2 systems. In this state, quantum ...

Resonant forcing of an oscillatory medium has been found to cause irregular spatiotemporal patterns in experiments with a chemical reaction as well as in simulations of model equations. Focusing on the 2:1 case, we show that one type of such chaotic patterns results from the destabilization of rotating spiral waves. For sufficiently large forcing amplitudes, subsequent fronts in wave trains ...

Due to their high plasma frequencies, drifting semiconductor plasmas interacting with slow electromagnetic waves hold promise for terahertz amplifiers and oscillators. In these devices, the gain and the type of instabilities are influenced by electron collisions. To study the effect of collisions, we developed a two-wave model describing the interaction between drifting ...

Electron plasma waves generated by both the absolute-stimulated-Raman scattering and the two-plasmon-decay instabilities in a CO{sub 2}-laser--produced plasma are studied by picosecond-resolution Thomson scattering. The spatial and wave-vector distribution covering the regions of both stimulated Raman scattering and two-plasmon decay are observed. The ...

Airplane trailing vortices have a destabilizing effect on ensuing aircrafts. Security spacings, related to the trailing vortices "lifetime" are actually enforced between take-offs and landings. This spacing limits the maximum take-off and landing frequency in saturated airports [19]. A number of studies have been devoted to the understanding of vortex wake dynamics, usually modeled by a pair of ...

The triple-deck equations for the flow over a hump, a corner and a wedged trailing edge are solved numerically using a novel method based on spectral collocation. It is found that for the flow over a corner, separation begins at a scaled angle g of 2.09, and for the wedged trailing edge for a wedge angle of 2.56. Here g is defined in terms of the small physical angle } by ...

The three dimensional boundary layer over a rotating disk is accordingly subject to an absolute mode of instability, whose role in transition process is still not well understood. Depending upon the methods of investigation and the associated assumptions, the scenario for the last stage of transition appears either convectively or ...

The dynamics of unstable systems crucially depends on the nature of the instability, either convective or absolute. The signalling problem, which is the study of the spatial response to a localized time-harmonic forcing, is generally believed to be relevant only for stable or convectively unstable systems and to be ill-posed for ...

A cold electron beam penetrating a cold plasma is electrostatically unstable. The instability produces a growing electric field that saturates when the beam electrons are suddenly trapped by a single wave. During trapping a significant amount of energy is transferred from the beam to the field and ultimately to the plasma. At Los Alamos experiments are being performed that ...

The space and time behavior of parametric backscattering instabilities is computed analytically in the so-called modified decay regime. The plasma is assumed to be homogeneous and of finite length. The propagation of the pump wave and its finite pulse duration both are taken into account, its depletion is ignored. The parametric growth is solved in terms of fluctuating initial ...

An intense relativistic electron beam with an elongated cross section, propagating in the ion-focused regime through a broad, uniform, unmagnetized plasma, is shown to suffer a transverse flute instability. This instability arises from the electrostatic coupling between the beam and the plasma electrons at the ion-channel edge. The ...

For a better understanding of the high-frequency waves observed during active experiments of electron-beam injection into the ionospheric plasma, we do a complete investigation of the electrostatic-beam--plasma instabilities that do occur in such a situation. The electron beam is cold, it is aligned with the vacuum magnetic field, and has a finite radius; the background plasma ...

The threshold and initial evolution for the decay of a lower-hybrid wave to two lower-hybrid waves are determined. Included are the effects of convective losses in a three-dimensional lower-hybrid resonance cone geometry and the effects of inhomogeneity appropriate to lower-hybrid heating in a tokamak. It is found that the decay to two lower-hybrid waves differs from other such parametric ...

The dissipative instability which occurs in an inhomogeneous plasma as the result of the excitation of longitudinal longwave oscillations by a radiation field is analyzed. Since the noise buildup is due to the excitation of normal modes, the entire plasma volume becomes turbulent, in contrast with the case in which local oscillations are excited. The threshold pump fields ...

Absolute instabilities of counterpropagating pump beams in a dispersive Kerr medium, placed inside a Fabry{endash}Perot cavity, are analytically studied by use of the analysis and the results of part I [J. Opt. Soc. B {bold 14}, {bold 607} (1998)]. Our approach allows characterization of such a complicated nonlinear system in terms of a doubly resonant ...

Two-dimensional homogeneous theory of free-electron lasers with a wiggler magnetic field of constant wavelength is formulated. It has been found from the theory that waves propagating obliquely with respect to the electron beam are always unstable with appreciable growth rates; therefore, mode competition among the on-axis and off-axis modes is an important consideration in the design of the ...

Time-dependent four-wave mixing and phase conjugation in plasmas are treated, taking into account resonant longitudinal plasma modes and effects of spatial nonuniformity. A space-time formulation of four-wave processes in the ponderomotive force regime yields linearized equations, which are solved analytically as a combined initial/boundary-value problem in slab and inhomogeneous geometries. The ...

The problem of spurious oscillations induced by absolute instabilities is the most challenging one that hinders the development of the millimeter-wave gyrotron traveling-wave amplifiers (gyro-TWTs). A spurious oscillation exists as a high order axial mode (HOAM) in the interaction circuit. This paper is devoted to demonstrating the complicated steady ...

Measurements of absolute positions of electron energy loss spectroscopy (EELS) core-loss edges in a transmission electron microscopy (TEM) are hampered by noticeable errors caused by instabilities of the primary energy of the incident electrons. These instabilities originate from a continuous drift and random ripple of the high tension ...

Direct Numerical Simulation of incompressible Navier-Stokes equations has been used to investigate the impulse response of a rotating boundary layer. The aim is to extend recent theoretical works of Pier [J. Fluid Mech. 487, 315 (2003)] and Davies & Carpenter [J. Fluid Mech. 486, 287 (2003)] about the role played by the absolute instability in the ...

The influence of confinement onto the inviscid and incompressible linear stability of the family of wakes introduced by Monkewitz [Phys. Fluids 31, 999 (1988)] is examined. The nondimensional parameters of the model, the velocity ratio ?, defined as ratio of the velocity gap to the mean velocity, the profile shape parameter, which controls the shear layer thickness ?w, and the confinement ...

A spatio-temporal inviscid instability of a mixed forced-free convection boundary layer is investigated. The base flow considered is the self-similar flow with free-stream velocity ue ~ xn. Such a boundary-layer flow presents the unusual behaviour of generating a region of velocity overshoot, in which the streamwise velocity within the boundary layer exceeds the free-stream ...

A new fireball configuration has been developed which produces vircator-like instabilities. Electrons are injected through a transparent anode into a spherical plasma volume. Strong high-frequency oscillations with period corresponding to the electron transit time through the sphere are observed. The frequency is below the electron plasma frequency, hence does not involve ...

Stimulated Brillouin scattering, filamentation, and induced Thomson scattering are studied for a coherent electromagnetic plane wave propagating in a uniform plasma. A generalized Green's function is found that describes the impulse response for stimulated scattering by electron and ion modes. Explicit asymptotic Green's functions are calculated for those parametric ...

It is well known that absolute instabilities can be located by prescribed mappings from the complex-frequency plane to the wavenumber plane through the dispersion relation D(..omega..,k) = 0. However, in many systems of physical interest the dispersion relation is polynomial in ..omega.. while transcendental in k, and the implementation of this mapping ...

This paper is concerned with the active isolation of a system containing a distributed parameter isolator using absolute velocity feedback control. The main differences between this type of system and one with a massless isolator, is that there are isolator resonances. It is shown that the vibration at these resonance frequencies cannot be suppressed using a simple velocity ...

Objective: To evaluate whether rock climbing type exercise would be of value in rehabilitating ankle injuries to improve ankle stability and coordination. Results: The rock climbers showed significantly better results in the stabilometry and greater absolute and relative maximum strength of flexion in the ankle. The soccer players showed greater absolute ...

The high-frequency ''convective'' loss-cone mode in a mirror-confined plasma is shown to be absolutely unstable as a result of wave reflection from the mirror throats, provided that the plasma length is greater than an axial wavelength. Critical lengths for stability are only a few ion gyroradii for fusion parameters, much smaller than ...

A global stability investigation of two-dimensional vertical liquid sheet flows is experimentally carried out. The motivation is that previous investigations addressed the study of the local absolute/convective character of such flows, thus they are not able to predict the actual critical flow Weber number corresponding to sheet rupture. The objective of the paper is twofold: ...

The objective of the study is to determine the absolute/convective nature of the secondary instability experienced by finite-amplitude streaks in the flat-plate boundary layer. A family of parallel streaky base flows is defined by extracting velocity profiles from direct numerical simulations of nonlinearly saturated optimal streaks. The computed impulse ...

For a bunch with charge q moving in a storage ring under the influence of a constant dipole wake potential of amplitude W/sub 1/ and constant transverse beta-function with amplitude ..beta../sub t/, the two-macroparticle model for the transverse single-bunch instability predicts a threshold current. When this work is completed, an absolute prediction of ...

Stimulated Raman scattering in plasmas is a three-wave instability with important practical consequences for laser fusion. Most studies of this process to date have focused on its threshold. Even the linear-theory threshold poses interesting problems; and observed thresholds have been difficult to interpret. However, with increasing evidence that this ...

Stimulated Raman scattering in plasmas is a three-wave instability with important practical consequences for laser fusion. Most studies of this process to date have focused on its threshold. Even the linear-theory threshold poses interesting problems; and observed thresholds have been difficult to interpret. However, with increasing evidence that this ...

The stability of dark solitons generated by supersonic flow of a Bose-Einstein condensate past an obstacle is investigated. It is shown that in the reference frame attached to the obstacle a transition occurs at some critical value of the flow velocity from absolute instability of dark solitons to their convective instability. This ...

We present the first absolute, two-dimensionally resolved measurements of areal mass density of laser-driven ablatively accelerated foils, which show the Rayleigh-Taylor instability developing from initial mass perturbations. Our data are near simulation results which predict that the Rayleigh-Taylor growth rate is less than classical. The measurements ...

The effect of dissipative loss in the grating surface on a Smith Purcell free-electron laser is investigated with the help of a two-dimensional particle-in-cell simulation. The simulation model supposes an open grating driven by a continuous electron beam. With present parameters, simulation results show that such a device can oscillate on absolute ...