Spatiotemporal chaos in the dynamics of buoyantly and diffusively unstable chemical fronts

NASA Astrophysics Data System (ADS)

Baroni, M. P. M. A.; Guéron, E.; De Wit, A.

2012-03-01

Nonlinear dynamics resulting from the interplay between diffusive and buoyancy-driven Rayleigh-Taylor (RT) instabilities of autocatalytic traveling fronts are analyzed numerically for various values of the relevant parameters. These are the Rayleigh numbers of the reactant A and autocatalytic product B solutions as well as the ratio D =DB/DA between the diffusion coefficients of the two key chemical species. The interplay between the coarsening dynamics characteristic of the RT instability and the constant short wavelength modulation of the diffusive instability can lead in some regimes to complex dynamics dominated by irregular succession of birth and death of fingers. By using spectral entropy measurements, we characterize the transition between order and spatial disorder in this system. The analysis of the power spectrum and autocorrelation function, moreover, identifies similarities between the various spatial patterns. The contribution of the diffusive instability to the complex dynamics is discussed.

The MutSβ complex is a modulator of p53-driven tumorigenesis through its functions in both DNA double strand break repair and mismatch repair

PubMed Central

van Oers, Johanna M. M.; Edwards, Yasmin; Chahwan, Richard; Zhang, Weijia; Smith, Cameron; Pechuan, Joaquín; Schaetzlein, Sonja; Jin, Bo; Wang, Yuxun; Bergman, Aviv; Scharff, Matthew D.; Edelmann, Winfried

2014-01-01

Loss of the DNA mismatch repair protein MSH3 leads to the development of a variety of tumors in mice without significantly affecting survival rates, suggesting a modulating role for the MutSβ (MSH2-MSH3) complex in late onset tumorigenesis. To better study the role of MSH3 in tumor progression, we crossed Msh3−/− mice onto a tumor predisposing p53-deficient background. Survival of Msh3/p53 mice was not reduced compared to single p53 mutant mice; however, the tumor spectrum changed significantly from lymphoma to sarcoma, indicating MSH3 as a potent modulator of p53-driven tumorigenesis. Interestingly, Msh3−/− mouse embryonic fibroblasts displayed increased chromatid breaks and persistence of γH2AX foci following ionizing radiation, indicating a defect in DNA double strand break repair. Msh3/p53 tumors showed increased loss of heterozygosity, elevated genome-wide copy number variation, and a moderate microsatellite instability phenotype compared to Msh2/p53 tumors, revealing that MSH2-MSH3 suppresses tumorigenesis by maintaining chromosomal stability. Our results show that the MSH2-MSH3 complex is important for the suppression of late onset tumors due to its role in DNA double strand break repair as well as in DNA mismatch repair. Furthermore, they demonstrate that MSH2-MSH3 suppresses chromosomal instability and modulates the tumor spectrum in p53-deficient tumorigenesis, and possibly plays a role in other chromosomally unstable tumors as well. PMID:24013230

The MutSβ complex is a modulator of p53-driven tumorigenesis through its functions in both DNA double-strand break repair and mismatch repair.

PubMed

van Oers, J M M; Edwards, Y; Chahwan, R; Zhang, W; Smith, C; Pechuan, X; Schaetzlein, S; Jin, B; Wang, Y; Bergman, A; Scharff, M D; Edelmann, W

2014-07-24

Loss of the DNA mismatch repair (MMR) protein MSH3 leads to the development of a variety of tumors in mice without significantly affecting survival rates, suggesting a modulating role for the MutSβ (MSH2-MSH3) complex in late-onset tumorigenesis. To better study the role of MSH3 in tumor progression, we crossed Msh3(-/-) mice onto a tumor predisposing p53-deficient background. Survival of Msh3/p53 mice was not reduced compared with p53 single mutant mice; however, the tumor spectrum changed significantly from lymphoma to sarcoma, indicating MSH3 as a potent modulator of p53-driven tumorigenesis. Interestingly, Msh3(-/-) mouse embryonic fibroblasts displayed increased chromatid breaks and persistence of γH2AX foci following ionizing radiation, indicating a defect in DNA double-strand break repair (DSBR). Msh3/p53 tumors showed increased loss of heterozygosity, elevated genome-wide copy-number variation and a moderate microsatellite instability phenotype compared with Msh2/p53 tumors, revealing that MSH2-MSH3 suppresses tumorigenesis by maintaining chromosomal stability. Our results show that the MSH2-MSH3 complex is important for the suppression of late-onset tumors due to its roles in DNA DSBR as well as in DNA MMR. Further, they demonstrate that MSH2-MSH3 suppresses chromosomal instability and modulates the tumor spectrum in p53-deficient tumorigenesis and possibly has a role in other chromosomally unstable tumors as well.

The effects of control field detuning on the modulation instability in a three-level quantum well system

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

Borgohain, Nitu, E-mail: nituborgohain.ism@gmail.com; Konar, S.

The paper presents a theoretical study of the modulation instability of a continuous or quasi-continuous optical probe in a three level quantum well system under electromagnetically induced transparency. The modulation instability is affected by the control field detuning, as well as even-order dispersion and by the strength of Kerr (third-order) and quintic (fifth-order) nonlinearities. The fourth-order dispersion reduces the bandwidth over which modulation instability occurs, whereas the quintic nonlinearity saturates the growth of the modulation instability. Detuning the control field from resonance can significantly reduce the growth of the modulation instability at both low and high power levels. At lowmore » powers, the system becomes stable against modulation instability for small detuning of the control field and at high powers modulation instability disappears for larger detuning.« less

A frequency standard via spectrum analysis and direct digital synthesis

NASA Astrophysics Data System (ADS)

Li, Dawei; Shi, Daiting; Hu, Ermeng; Wang, Yigen; Tian, Lu; Zhao, Jianye; Wang, Zhong

2014-11-01

We demonstrated a frequency standard based on a detuned coherent population beating phenomenon. In this phenomenon, the beat frequency of the radio frequency for laser modulation and the hyperfine splitting can be obtained by digital signal processing technology. After analyzing the spectrum of the beat frequency, the fluctuation information is obtained and applied to compensate for the frequency shift to generate the standard frequency by the digital synthesis method. Frequency instability of 2.6 × 1012 at 1000 s is observed in our preliminary experiment. By eliminating the phase-locking loop, the method will enable us to achieve a full-digital frequency standard with remarkable stability.

Global characteristics of zonal flows due to the effect of finite bandwidth in drift wave turbulence

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

Uzawa, K.; Li Jiquan; Kishimoto, Y.

2009-04-15

The spectral effect of the zonal flow (ZF) on its generation is investigated based on the Charney-Hasegawa-Mima turbulence model. It is found that the effect of finite ZF bandwidth qualitatively changes the characteristics of ZF instability. A spatially localized (namely, global) nonlinear ZF state with an enhanced, unique growth rate for all spectral components is created under a given turbulent fluctuation. It is identified that such state originates from the successive cross couplings among Fourier components of the ZF and turbulence spectra through the sideband modulation. Furthermore, it is observed that the growth rate of the global ZF is determinedmore » not only by the spectral distribution and amplitudes of turbulent pumps as usual, but also statistically by the turbulence structure, namely, their probabilistic initial phase factors. A ten-wave coupling model of the ZF modulation instability involving the essential effect of the ZF spectrum is developed to clarify the basic features of the global nonlinear ZF state.« less

Solitons in two attractive semiconductor nanowires

NASA Astrophysics Data System (ADS)

Vroumsia, David; Mibaile, Justin; Gambo, Betchewe; Doka, Yamigno Serge; Kofane, Timoleon Crepin

2018-02-01

In this paper, by using two semiconductor nanowires attracted to each other by means of Lorentz force, we construct through similarity transformations, explicit solutions to the coupled nonlinear Schrodinger equations (CNSE) with potentials as a function of time and spatial coordinates. We find explicit solutions of electrons and holes such as periodic, bright and dark solitons. We also study the instability of the modulation (MI) of (CNSE) and note that the velocity of the electrons influences the gain MI spectrum.

Zonal flows and turbulence in fluids and plasmas

NASA Astrophysics Data System (ADS)

Parker, Jeffrey Bok-Cheung

In geophysical and plasma contexts, zonal flows are well known to arise out of turbulence. We elucidate the transition from statistically homogeneous turbulence without zonal flows to statistically inhomogeneous turbulence with steady zonal flows. Starting from the Hasegawa--Mima equation, we employ both the quasilinear approximation and a statistical average, which retains a great deal of the qualitative behavior of the full system. Within the resulting framework known as CE2, we extend recent understanding of the symmetry-breaking 'zonostrophic instability'. Zonostrophic instability can be understood in a very general way as the instability of some turbulent background spectrum to a zonally symmetric coherent mode. As a special case, the background spectrum can consist of only a single mode. We find that in this case the dispersion relation of zonostrophic instability from the CE2 formalism reduces exactly to that of the 4-mode truncation of generalized modulational instability. We then show that zonal flows constitute pattern formation amid a turbulent bath. Zonostrophic instability is an example of a Type I s instability of pattern-forming systems. The broken symmetry is statistical homogeneity. Near the bifurcation point, the slow dynamics of CE2 are governed by a well-known amplitude equation, the real Ginzburg-Landau equation. The important features of this amplitude equation, and therefore of the CE2 system, are multiple. First, the zonal flow wavelength is not unique. In an idealized, infinite system, there is a continuous band of zonal flow wavelengths that allow a nonlinear equilibrium. Second, of these wavelengths, only those within a smaller subband are stable. Unstable wavelengths must evolve to reach a stable wavelength; this process manifests as merging jets. These behaviors are shown numerically to hold in the CE2 system, and we calculate a stability diagram. The stability diagram is in agreement with direct numerical simulations of the quasilinear system. The use of statistically-averaged equations and the pattern formation methodology provide a path forward for further systematic investigations of zonal flows and their interactions with turbulence.

Modulation instability, Akhmediev breathers, and rogue waves in nonlinear fiber optics

NASA Astrophysics Data System (ADS)

Dudley, John M.; Genty, Go"ry; Dias, Frederic; Kibler, Bertrand; Akhmediev, Nail

2010-02-01

The development of the supercontinuum spectrum in the quasi-CW regime is studied analytically, numerically and experimentally. An interpretation in terms of localized periodic structures known as "Akhmediev Breathers" is proposed. Theory, numerical simulation and experiment are in excellent agreement. We also briefly consider the role of breather collisions in the presence of higher order dispersion and show that they lead to the formation of very large amplitude localized structures that may be analogous to the infamous oceanic rogue waves.

The modulational instability for the TDNLS equations for weakly nonlinear dispersive MHD waves

NASA Technical Reports Server (NTRS)

Webb, G. M.; Brio, M.; Zank, G. P.

1995-01-01

In this paper we study the modulational instability for the TDNLS equations derived by Hada (1993) and Brio, Hunter, and Johnson to describe the propagation of weakly nonlinear dispersive MHD waves in beta approximately 1 plasmas. We employ Whitham's averaged Lagrangian method to study the modulational instability. This complements studies of the modulational instability by Hada (1993) and Hollweg (1994), who did not use the averaged Lagrangian approach.

Simulation, Theory, and Observations of the Spectrum of the Rayleigh-Taylor Instability due to Laser Imprint of Planar Targets

NASA Astrophysics Data System (ADS)

Keskinen, M. J.; Karasik, Max; Bates, J. W.; Schmitt, A. J.

2006-10-01

A limitation on the efficiency of high gain direct drive inertial confinement fusion is the extent of pellet disruption caused by the Rayleigh-Taylor (RT) instability. The RT instability can be seeded by pellet surface irregularities and/or laser imprint nonuniformities. It is important to characterize the evolution of the RT instability, e.g., the k-spectrum of areal mass. In this paper we study the time-dependent evolution of the spectrum of the Rayleigh-Taylor instability due to laser imprint in planar targets. This is achieved using the NRL FAST hydrodynamic simulation code together with analytical models. It is found that the optically smoothed laser imprint-driven RT spectrum develops into an inverse power law in k-space after several linear growth times. FAST simulation code results are compared with recent NRL Nike KrF laser experimental data. An analytical model, which is a function of Froude and Atwood numbers, is derived for the RT spectrum and favorably compared with both FAST simulation and Nike observations.

Real-time measurements of spontaneous breathers and rogue wave events in optical fibre modulation instability

PubMed Central

Närhi, Mikko; Wetzel, Benjamin; Billet, Cyril; Toenger, Shanti; Sylvestre, Thibaut; Merolla, Jean-Marc; Morandotti, Roberto; Dias, Frederic; Genty, Goëry; Dudley, John M.

2016-01-01

Modulation instability is a fundamental process of nonlinear science, leading to the unstable breakup of a constant amplitude solution of a physical system. There has been particular interest in studying modulation instability in the cubic nonlinear Schrödinger equation, a generic model for a host of nonlinear systems including superfluids, fibre optics, plasmas and Bose–Einstein condensates. Modulation instability is also a significant area of study in the context of understanding the emergence of high amplitude events that satisfy rogue wave statistical criteria. Here, exploiting advances in ultrafast optical metrology, we perform real-time measurements in an optical fibre system of the unstable breakup of a continuous wave field, simultaneously characterizing emergent modulation instability breather pulses and their associated statistics. Our results allow quantitative comparison between experiment, modelling and theory, and are expected to open new perspectives on studies of instability dynamics in physics. PMID:27991513

Ion heating, burnout of the high-frequency field, and ion sound generation under the development of a modulation instability of an intense Langmuir wave in a plasma

NASA Astrophysics Data System (ADS)

Kirichok, A. V.; Kuklin, V. M.; Pryimak, A. V.; Zagorodny, A. G.

2015-09-01

The development of one-dimensional parametric instabilities of intense long plasma waves is considered in terms of the so-called hybrid models, with electrons being treated as a fluid and ions being regarded as particles. The analysis is performed for both cases when the average plasma field energy is lower (Zakharov's hybrid model—ZHM) or greater (Silin's hybrid model—SHM) than the plasma thermal energy. The efficiency of energy transfer to ions and to ion perturbations under the development of the instability is considered for various values of electron-to-ion mass ratios. The energy of low-frequency oscillations (ion-sound waves) is found to be much lower than the final ion kinetic energy. We also discuss the influence of the changes in the damping rate of the high-frequency (HF) field on the instability development. The decrease of the absorption of the HF field inhibits the HF field burnout within plasma density cavities and gives rise to the broadening of the HF spectrum. At the same time, the ion velocity distribution tends to the normal distribution in both ZHM and SHM.

Ion heating, burnout of the high-frequency field, and ion sound generation under the development of a modulation instability of an intense Langmuir wave in a plasma

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

Kirichok, A. V., E-mail: sandyrcs@gmail.com; Kuklin, V. M.; Pryimak, A. V.

The development of one-dimensional parametric instabilities of intense long plasma waves is considered in terms of the so-called hybrid models, with electrons being treated as a fluid and ions being regarded as particles. The analysis is performed for both cases when the average plasma field energy is lower (Zakharov's hybrid model—ZHM) or greater (Silin's hybrid model—SHM) than the plasma thermal energy. The efficiency of energy transfer to ions and to ion perturbations under the development of the instability is considered for various values of electron-to-ion mass ratios. The energy of low-frequency oscillations (ion-sound waves) is found to be much lowermore » than the final ion kinetic energy. We also discuss the influence of the changes in the damping rate of the high-frequency (HF) field on the instability development. The decrease of the absorption of the HF field inhibits the HF field burnout within plasma density cavities and gives rise to the broadening of the HF spectrum. At the same time, the ion velocity distribution tends to the normal distribution in both ZHM and SHM.« less

Zonal Flows and Turbulence in Fluids and Plasmas

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

Parker, Jeffrey

2014-09-01

In geophysical and plasma contexts, zonal flows are well known to arise out of turbulence. We elucidate the transition from statistically homogeneous turbulence without zonal flows to statistically inhomogeneous turbulence with steady zonal flows. Starting from the Hasegawa--Mima equation, we employ both the quasilinear approximation and a statistical average, which retains a great deal of the qualitative behavior of the full system. Within the resulting framework known as CE2, we extend recent understanding of the symmetry-breaking `zonostrophic instability'. Zonostrophic instability can be understood in a very general way as the instability of some turbulent background spectrum to a zonally symmetricmore » coherent mode. As a special case, the background spectrum can consist of only a single mode. We find that in this case the dispersion relation of zonostrophic instability from the CE2 formalism reduces exactly to that of the 4-mode truncation of generalized modulational instability. We then show that zonal flows constitute pattern formation amid a turbulent bath. Zonostrophic instability is an example of a Type Is instability of pattern-forming systems. The broken symmetry is statistical homogeneity. Near the bifurcation point, the slow dynamics of CE2 are governed by a well-known amplitude equation, the real Ginzburg-Landau equation. The important features of this amplitude equation, and therefore of the CE2 system, are multiple. First, the zonal flow wavelength is not unique. In an idealized, infinite system, there is a continuous band of zonal flow wavelengths that allow a nonlinear equilibrium. Second, of these wavelengths, only those within a smaller subband are stable. Unstable wavelengths must evolve to reach a stable wavelength; this process manifests as merging jets. These behaviors are shown numerically to hold in the CE2 system, and we calculate a stability diagram. The stability diagram is in agreement with direct numerical simulations of the quasilinear system. The use of statistically-averaged equations and the pattern formation methodology provide a path forward for further systematic investigations of zonal flows and their interactions with turbulence.« less

Higher-order modulation instability in nonlinear fiber optics.

PubMed

Erkintalo, Miro; Hammani, Kamal; Kibler, Bertrand; Finot, Christophe; Akhmediev, Nail; Dudley, John M; Genty, Goëry

2011-12-16

We report theoretical, numerical, and experimental studies of higher-order modulation instability in the focusing nonlinear Schrödinger equation. This higher-order instability arises from the nonlinear superposition of elementary instabilities, associated with initial single breather evolution followed by a regime of complex, yet deterministic, pulse splitting. We analytically describe the process using the Darboux transformation and compare with experiments in optical fiber. We show how a suitably low frequency modulation on a continuous wave field induces higher-order modulation instability splitting with the pulse characteristics at different phases of evolution related by a simple scaling relationship. We anticipate that similar processes are likely to be observed in many other systems including plasmas, Bose-Einstein condensates, and deep water waves. © 2011 American Physical Society

Two-dimensional modulated ion-acoustic excitations in electronegative plasmas

NASA Astrophysics Data System (ADS)

Panguetna, Chérif S.; Tabi, Conrad B.; Kofané, Timoléon C.

2017-09-01

Two-dimensional modulated ion-acoustic waves are investigated in an electronegative plasma. Through the reductive perturbation expansion, the governing hydrodynamic equations are reduced to a Davey-Stewartson system with two-space variables. The latter is used to study the modulational instability of ion-acoustic waves along with the effect of plasma parameters, namely, the negative ion concentration ratio (α) and the electron-to-negative ion temperature ratio (σn). A parametric analysis of modulational instability is carried out, where regions of plasma parameters responsible for the emergence of modulated ion-acoustic waves are discussed, with emphasis on the behavior of the instability growth rate. Numerically, using perturbed plane waves as initial conditions, parameters from the instability regions give rise to series of dromion solitons under the activation of modulational instability. The sensitivity of the numerical solutions to plasma parameters is discussed. Some exact solutions in the form one- and two-dromion solutions are derived and their response to the effect of varying α and σn is discussed as well.

On the instability of wave-fields with JONSWAP spectra to inhomogeneous disturbances, and the consequent long-time evolution

NASA Astrophysics Data System (ADS)

Ribal, A.; Stiassnie, M.; Babanin, A.; Young, I.

2012-04-01

The instability of two-dimensional wave-fields and its subsequent evolution in time are studied by means of the Alber equation for narrow-banded random surface-waves in deep water subject to inhomogeneous disturbances. A linear partial differential equation (PDE) is obtained after applying an inhomogeneous disturbance to the Alber's equation and based on the solution of this PDE, the instability of the ocean wave surface is studied for a JONSWAP spectrum, which is a realistic ocean spectrum with variable directional spreading and steepness. The steepness of the JONSWAP spectrum depends on γ and α which are the peak-enhancement factor and energy scale of the spectrum respectively and it is found that instability depends on the directional spreading, α and γ. Specifically, if the instability stops due to the directional spreading, increase of the steepness by increasing α or γ can reactivate it. This result is in qualitative agreement with the recent large-scale experiment and new theoretical results. In the instability area of α-γ plane, a long-time evolution has been simulated by integrating Alber's equation numerically and recurrent evolution is obtained which is the stochastic counterpart of the Fermi-Pasta-Ulam recurrence obtained for the cubic Schrödinger equation.

Dynamic Stabilization of the Ablative Rayleigh-Taylor Instability for Heavy Ion Fusion

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

Qin, Hong; Davidson, Ronald C.; Logan, B. Grant

2012-10-04

Dynamic stabilization of the ablative Rayleigh-Taylor instability of a heavy ion fusion target induced by a beam wobbling system is studied. Using a sharp-boundary model and Courant-Synder theory, it is shown, with an appropriately chosen modulation waveform, that the instability can be sta- bilized in certain parameter regimes. It is found that the stabilization e ect has a strong dependence on the modulation frequency and the waveform. Modulation with frequency comparable to the instability growth rate is the most e ective in terms of stabilizing the instability. A modulation with two frequency components can result in a reduction of themore » growth rate larger than the sum of that due to the two components when applied separately.« less

Modulational instability and discrete breathers in a nonlinear helicoidal lattice model

NASA Astrophysics Data System (ADS)

Ding, Jinmin; Wu, Tianle; Chang, Xia; Tang, Bing

2018-06-01

We investigate the problem on the discrete modulation instability of plane waves and discrete breather modes in a nonlinear helicoidal lattice model, which is described by a discrete nonlinear Schrödinger equation with the first-, second-, and third-neighbor coupling. By means of the linear stability analysis, we present an analytical expression of the instability growth rate and identify the regions of modulational instability of plane waves. It is shown that the introduction of the third-neighbor coupling will affect the shape of the areas of modulational instability significantly. Based on the results obtained by the modulational instability analysis, we predict the existence conditions for the stationary breather modes. Otherwise, by making use of the semidiscrete multiple-scale method, we obtain analytical solutions of discrete breather modes and analyze their properties for different types of nonlinearities. Our results show that the discrete breathers obtained are stable for a long time only when the system exhibits the repulsive nonlinearity. In addition, it is found that the existence of the stable bright discrete breather closely relates to the presence of the third-neighbor coupling.

Power play in the supercontinuum spectra of saturable nonlinear media

NASA Astrophysics Data System (ADS)

Nithyanandan, K.; Vasantha Jayakantha Raja, R.; Porsezian, K.

2014-04-01

We investigate the role of pump power in the generation of supercontinua spectra induced by modulational instability (MI) in saturable nonlinear media (SNL). First, we analyze the dynamics of MI in the SNL using linear stability analysis. We then deal with the generation of a broadband spectrum by virtue of the instability process, and identify the unique behavior of MI in the SNL system. Unlike the case of Kerr-type nonlinearity, the so-called critical modulational frequency (CMF) does not monotonically increase, but behaves in a unique way, such that the increase in power increases the CMF up to the saturation power, and a further increase in power decreases the CMF. This behavior is identified to be unusual in the context of MI and thus makes the study of MI and supercontinuum generation (SCG) of interest. In order to confirm the above stated behavior in relation to SCG, we numerically analyzed the SCG using a split-step Fourier method, and the results confirm that at input power equal to saturation power, phase matching occurs at a short distance relative to other power levels and leads to a maximum enhancement of SCG in certain SNL materials.

Modeling of a Compact Terahertz Source based on the Two-Stream Instability

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

Svimonishvili, Tengiz

2016-05-17

THz radiation straddles the microwave and infrared bands of the electromagnetic spectrum, thus combining the penetrating power of lower-frequency waves and imaging capabilities of higher-energy infrared radiation. THz radiation is employed in various elds such as cancer research, biology, agriculture, homeland security, and environmental monitoring. Conventional vacuum electronic sources of THz radiation (e.g., fast- and slow-wave devices) either require very small structures or are bulky and expensive to operate. Optical sources necessitate cryogenic cooling and are presently capable of producing milliwatt levels of power at THz frequencies. We propose a millimeter and sub-millimeter wave source based on a well-known phenomenonmore » called the two-stream instability. The two-beam source relies on lowenergy and low-current electron beams for operation. Also, it is compact, simple in design, and does not contain expensive parts that require complex machining and precise alignment. In this dissertation, we perform 2-D particle-in-cell (PIC) simulations of the interaction region of the two-beam source. The interaction region consists of a beam pipe of radius ra and two electron beams of radius rb co-propagating and interacting inside the pipe. The simulations involve the interaction of unmodulated (no initial energy modulation) and modulated (energy-modulated, seeded at a given frequency) electron beams. In addition, both cold (monoenergetic) and warm (Gaussian) beams are treated.« less

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

Mode-locking via dissipative Faraday instability.

PubMed

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

2016-08-09

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.

Femtosecond pulse self-shortening in Kerr media: role of modulational instability in the spectrum formation

NASA Astrophysics Data System (ADS)

Grudtsyn, Ya. V.; Koribut, A. V.; Mikheev, L. D.; Trofimov, V. A.

2018-04-01

The mechanism of femtosecond pulse self-shortening in thin optical materials with Kerr nonlinearity is investigated. The experimentally observed spectral-angular distribution of the radiation intensity on the exit surface of a 1-mm-thick fused silica sample is compared with the results of numerical simulation based on solving the nonlinear Schrödinger equation for an electromagnetic wave with a transverse perturbation on the axis. Qualitative agreement between the calculated and experimental results confirms the hypothesis about the transient regime of multiple filamentation as a mechanism of femtosecond pulse self-shortening.

High-frequency combustion instability control through acoustic modulation at the inlet boundary for liquid rocket engine applications

NASA Astrophysics Data System (ADS)

Bennewitz, John William

This research investigation encompasses experimental tests demonstrating the control of a high-frequency combustion instability by acoustically modulating the propellant flow. A model rocket combustor burned gaseous oxygen and methane using a single-element, pentad-style injector. Flow conditions were established that spontaneously excited a 2430 Hz first longitudinal combustion oscillation at an amplitude up to p'/pc ≈ 6%. An acoustic speaker was placed at the base of the oxidizer supply to modulate the flow and alter the oscillatory behavior of the combustor. Two speaker modulation approaches were investigated: (1) Bands of white noise and (2) Pure sinusoidal tones. The first approach adjusted 500 Hz bands of white noise ranging from 0-500 Hz to 2000-2500 Hz, while the second implemented single-frequency signals with arbitrary phase swept from 500-2500 Hz. The results showed that above a modulation signal amplitude threshold, both approaches suppressed 95+% of the spontaneous combustion oscillation. By increasing the applied signal amplitude, a wider frequency range of instability suppression became present for these two acoustic modulation approaches. Complimentary to these experiments, a linear modal analysis was undertaken to investigate the effects of acoustic modulation at the inlet boundary on the longitudinal instability modes of a dump combustor. The modal analysis employed acoustically consistent matching conditions with a specific impedance boundary condition at the inlet to represent the acoustic modulation. From the modal analysis, a naturally unstable first longitudinal mode was predicted in the absence of acoustic modulation, consistent with the spontaneously excited 2430 Hz instability observed experimentally. Subsequently, a detailed investigation involving variation of the modulation signal from 0-2500 Hz and mean combustor temperature from 1248-1685 K demonstrated the unstable to stable transition of a 2300-2500 Hz first longitudinal mode. The model-predicted mode stability transition was consistent with experimental observations, supporting the premise that inlet acoustic modulation is a means to control high-frequency combustion instabilities. From the modal analysis, it may be deduced that the inlet impedance provides a damping mechanism for instability suppression. Combined, this work demonstrates the strategic application of acoustic modulation within an injector as a potential method to control high-frequency combustion instabilities for liquid rocket engine applications.

Modulation Instability and Phase-Shifted Fermi-Pasta-Ulam Recurrence

PubMed Central

Kimmoun, O.; Hsu, H. C.; Branger, H.; Li, M. S.; Chen, Y. Y.; Kharif, C.; Onorato, M.; Kelleher, E. J. R.; Kibler, B.; Akhmediev, N.; Chabchoub, A.

2016-01-01

Instabilities are common phenomena frequently observed in nature, sometimes leading to unexpected catastrophes and disasters in seemingly normal conditions. One prominent form of instability in a distributed system is its response to a harmonic modulation. Such instability has special names in various branches of physics and is generally known as modulation instability (MI). The MI leads to a growth-decay cycle of unstable waves and is therefore related to Fermi-Pasta-Ulam (FPU) recurrence since breather solutions of the nonlinear Schrödinger equation (NLSE) are known to accurately describe growth and decay of modulationally unstable waves in conservative systems. Here, we report theoretical, numerical and experimental evidence of the effect of dissipation on FPU cycles in a super wave tank, namely their shift in a determined order. In showing that ideal NLSE breather solutions can describe such dissipative nonlinear dynamics, our results may impact the interpretation of a wide range of new physics scenarios. PMID:27436005

A coupled "AB" system: Rogue waves and modulation instabilities.

PubMed

Wu, C F; Grimshaw, R H J; Chow, K W; Chan, H N

2015-10-01

Rogue waves are unexpectedly large and localized displacements from an equilibrium position or an otherwise calm background. For the nonlinear Schrödinger (NLS) model widely used in fluid mechanics and optics, these waves can occur only when dispersion and nonlinearity are of the same sign, a regime of modulation instability. For coupled NLS equations, rogue waves will arise even if dispersion and nonlinearity are of opposite signs in each component as new regimes of modulation instability will appear in the coupled system. The same phenomenon will be demonstrated here for a coupled "AB" system, a wave-current interaction model describing baroclinic instability processes in geophysical flows. Indeed, the onset of modulation instability correlates precisely with the existence criterion for rogue waves for this system. Transitions from "elevation" rogue waves to "depression" rogue waves are elucidated analytically. The dispersion relation as a polynomial of the fourth order may possess double pairs of complex roots, leading to multiple configurations of rogue waves for a given set of input parameters. For special parameter regimes, the dispersion relation reduces to a cubic polynomial, allowing the existence criterion for rogue waves to be computed explicitly. Numerical tests correlating modulation instability and evolution of rogue waves were conducted.

Mirror Instability in the Turbulent Solar Wind

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

Hellinger, Petr; Landi, Simone; Verdini, Andrea

2017-04-01

The relationship between a decaying strong turbulence and the mirror instability in a slowly expanding plasma is investigated using two-dimensional hybrid expanding box simulations. We impose an initial ambient magnetic field perpendicular to the simulation box, and we start with a spectrum of large-scale, linearly polarized, random-phase Alfvénic fluctuations that have energy equipartition between kinetic and magnetic fluctuations and a vanishing correlation between the two fields. A turbulent cascade rapidly develops, magnetic field fluctuations exhibit a Kolmogorov-like power-law spectrum at large scales and a steeper spectrum at sub-ion scales. The imposed expansion (taking a strictly transverse ambient magnetic field) leadsmore » to the generation of an important perpendicular proton temperature anisotropy that eventually drives the mirror instability. This instability generates large-amplitude, nonpropagating, compressible, pressure-balanced magnetic structures in a form of magnetic enhancements/humps that reduce the perpendicular temperature anisotropy.« less

Parametric instabilities of the circularly polarized Alfven waves including dispersion. [for solar wind

NASA Technical Reports Server (NTRS)

Wong, H. K.; Goldstein, M. L.

1986-01-01

A class of parametric instabilities of large-amplitude, circularly polarized Alfven waves is considered in which finite frequency (dispersive) effects are included. The dispersion equation governing the instabilities is a sixth-order polynomial which is solved numerically. As a function of K identically equal to k/k-sub-0 (where k-sub-0 and k are the wave number of the 'pump' wave and unstable sound wave, respectively), there are three regionals of instability: a modulation instability at K less than 1, a decay instability at K greater than 1, and a relatively weak and narrow instability at K close to squared divided by v-sub-A squared (where c-sub-s and v-sub-A are the sound and Alfven speeds respectively), the modulational instability occurs when beta is less than 1 (more than 1) for left-hand (right-hand) pump waves, in agreement with the previous results of Sakai and Sonnerup (1983). The growth rate of the decay instability of left-hand waves is greater than the modulational instability at all values of beta. Applications to large-amplitude wave observed in the solar wind, in computer simulations, and in the vicinity of planetary and interplanetary collisionless shocks are discussed.

Modulational instability of beat waves in a transversely magnetized plasma: Ion effects

NASA Astrophysics Data System (ADS)

Ferdous, T.; Amin, M. R.; Salimullah, M.

1996-05-01

The effect of ion dynamics on the modulational instability of the electrostatic beat wave at the difference frequency of two incident laser beams in a hot, collisionless, and transversely magnetized plasma has been studied theoretically. The full Vlasov equation in terms of gyrokinetic variables is employed to obtain the nonlinear response of ions and electrons. It is found that the growth rate of modulational instability is about two orders higher when ion motions are included.

Low power generation of equalized broadband CW supercontinua using a novel technique incorporating modulation instability of line broadened pump

NASA Astrophysics Data System (ADS)

Prakash, Roopa; Choudhury, Vishal; Arun, S.; Supradeepa, V. R.

2018-02-01

Continuous-wave(CW) supercontinuum sources find applications in various domains such as imaging, spectroscopy, test and measurement. They are generated by pumping an optical fiber with a CW laser in the anomalous-dispersion region close to its zero-dispersion wavelength. Modulation instability(MI) sidebands are created, and further broadened and equalized by additional nonlinear processes generating the supercontinuum. This necessitates high optical powers and at lower powers, only MI sidebands can be seen without the formation of the supercontinuum. Obtaining a supercontinuum at low, easily manageable optical powers is attractive for many applications, but current techniques cannot achieve this. In this work, we propose a new mechanism for low power supercontinuum generation utilizing the modified MI gain spectrum for a line-broadened, decorrelated pump. A novel two-stage generation mechanism is demonstrated, where the first stage constituting standard telecom fiber slightly broadens the input pump linewidth. However, this process in the presence of dispersion, acts to de-correlate the different spectral components of the pump signal. When this is sent through highly nonlinear fiber near its zero-dispersion wavelength, the shape of the MI gain spectrum is modified, and this process naturally results in the generation of a broadband, equalized supercontinuum source at much lower powers than possible using conventional single stage spectral broadening. Here, we demonstrate a 0.5W supercontinuum source pumped using a 4W Erbium-Ytterbium co-doped fiber laser with a bandwidth spanning from 1300nm to 2000nm. We also demonstrate an interesting behaviour of this technique of relative insensitivity to the pump wavelength vis-a-vis zero-dispersion wavelength of the fiber.

Formation of matter-wave soliton trains by modulational instability

NASA Astrophysics Data System (ADS)

Nguyen, Jason H. V.; Luo, De; Hulet, Randall G.

2017-04-01

Nonlinear systems can exhibit a rich set of dynamics that are inherently sensitive to their initial conditions. One such example is modulational instability, which is believed to be one of the most prevalent instabilities in nature. By exploiting a shallow zero-crossing of a Feshbach resonance, we characterize modulational instability and its role in the formation of matter-wave soliton trains from a Bose-Einstein condensate. We examine the universal scaling laws exhibited by the system and, through real-time imaging, address a long-standing question of whether the solitons in trains are created with effectively repulsive nearest-neighbor interactions or rather evolve into such a structure.

Progress of plasma wakefield self-modulation experiments at FACET

NASA Astrophysics Data System (ADS)

Adli, E.; Berglyd Olsen, V. K.; Lindstrøm, C. A.; Muggli, P.; Reimann, O.; Vieira, J. M.; Amorim, L. D.; Clarke, C. I.; Gessner, S. J.; Green, S. Z.; Hogan, M. J.; Litos, M. D.; O`Shea, B. D.; Yakimenko, V.; Clayton, C.; Marsh, K. A.; Mori, W. B.; Joshi, C.; Vafaei-Najafabadi, N.; Williams, O.

2016-09-01

Simulations and theory predict that long electron and positron beams may under favorable conditions self-modulate in plasmas. We report on the progress of experiments studying the self-modulation instability in plasma wakefield experiments at FACET. The experimental results obtained so far, while not being fully conclusive, appear to be consistent with the presence of the self-modulation instability.

Modulational Instability and Quantum Discrete Breather States of Cold Bosonic Atoms in a Zig-Zag Optical Lattice

NASA Astrophysics Data System (ADS)

Chang, Xia; Xie, Jiayu; Wu, Tianle; Tang, Bing

2018-07-01

A theoretical study on modulational instability and quantum discrete breather states in a system of cold bosonic atoms in zig-zag optical lattices is presented in this work. The time-dependent Hartree approximation is employed to deal with the multiple body problem. By means of a linear stability analysis, we analytically study the modulational instability, and estimate existence conditions of the bright stationary localized solutions for different values of the second-neighbor hopping constant. On the other hand, we get analytical bright stationary localized solutions, and analyze the influence of the second-neighbor hopping on their existence conditions. The predictions of the modulational instability analysis are shown to be reliable. Using these stationary localized single-boson wave functions, the quantum breather states corresponding to the system with different types of nonlinearities are constructed.

Amplitude modulation of quantum-ion-acoustic wavepackets in electron-positron-ion plasmas: Modulational instability, envelope modes, extreme wavesa)

NASA Astrophysics Data System (ADS)

Rahman, Ata-ur-; Kerr, Michael Mc; El-Taibany, Wael F.; Kourakis, Ioannis; Qamar, A.

2015-02-01

A semirelativistic fluid model is employed to describe the nonlinear amplitude modulation of low-frequency (ionic scale) electrostatic waves in an unmagnetized electron-positron-ion plasma. Electrons and positrons are assumed to be degenerated and inertialess, whereas ions are warm and classical. A multiscale perturbation method is used to derive a nonlinear Schrödinger equation for the envelope amplitude, based on which the occurrence of modulational instability is investigated in detail. Various types of localized ion acoustic excitations are shown to exist, in the form of either bright type envelope solitons (envelope pulses) or dark-type envelope solitons (voids, holes). The plasma configurational parameters (namely, the relativistic degeneracy parameter, the positron concentration, and the ionic temperature) are shown to affect the conditions for modulational instability significantly, in fact modifying the associated threshold as well as the instability growth rate. In particular, the relativistic degeneracy parameter leads to an enhancement of the modulational instability mechanism. Furthermore, the effect of different relevant plasma parameters on the characteristics (amplitude, width) of these envelope solitary structures is also presented in detail. Finally, the occurrence of extreme amplitude excitation (rogue waves) is also discussed briefly. Our results aim at elucidating the formation and dynamics of nonlinear electrostatic excitations in superdense astrophysical regimes.

Modulational instability of an electron plasma wave in a dusty plasma

NASA Astrophysics Data System (ADS)

Amin, M. R.; Ferdous, T.; Salimullah, M.

1997-03-01

The modulational instability of an electron plasma wave in a homogeneous, unmagnetized, hot, and collisionless dusty plasma has been investigated analytically. The Vlasov equation has been solved perturbatively to find the nonlinear response of the plasma particles with random static distribution of massive and charged dust grains having certain correlation. It is noticed that the growth rate of the modulational instability of the electron plasma wave through a new ultra-low-frequency dust mode is more efficient than that through the usual ion-acoustic mode in the dusty plasma.

Hydrodynamic instability experiments with three-dimensional modulations at the National Ignition Facility

DOE PAGES

Smalyuk, V. A.; Weber, S. V.; Casey, D. T.; ...

2015-06-18

The first hydrodynamic instability growth measurements with three-dimensional (3D) surface-roughness modulations were performed on CH shell spherical implosions at the National Ignition Facility (NIF) [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 43, 2841 (2004)]. The initial capsule outer-surface amplitudes were increased approximately four times, compared with the standard specifications, to increase the signal-to-noise ratio, helping to qualify a technique for measuring small 3D modulations. The instability growth measurements were performed using x-ray through-foil radiography based on time-resolved pinhole imaging. Averaging over 15 similar images significantly increased the signal-to-noise ratio, making possible a comparison with 3Dmore » simulations. At a convergence ratio of ~2.4, the measured modulation levels were ~3 times larger than those simulated based on the growth of the known imposed initial surface modulations. Several hypotheses are discussed, including increased instability growth due to modulations of the oxygen content in the bulk of the capsule. In conclusion, future experiments will be focused on measurements with standard 3D ‘native-roughness’ capsules as well as with deliberately imposed oxygen modulations.« less

Evading the Lyth bound in hybrid natural inflation

NASA Astrophysics Data System (ADS)

Hebecker, A.; Kraus, S. C.; Westphal, A.

2013-12-01

Generically, the gravitational-wave or tensor-mode contribution to the primordial curvature spectrum of inflation is tiny if the field range of the inflaton is much smaller than the Planck scale. We show that this pessimistic conclusion is naturally avoided in a rather broad class of small-field models. More specifically, we consider models where an axionlike shift symmetry keeps the inflaton potential flat (up to nonperturbative cosine-shaped modulations), but inflation nevertheless ends in a waterfall regime, as is typical for hybrid inflation. In such hybrid natural inflation scenarios (examples are provided by Wilson line inflation and fluxbrane inflation), the slow-roll parameter ɛ can be sizable during an early period (relevant for the cosmic microwave background spectrum). Subsequently, ɛ quickly becomes very small before the tachyonic instability eventually terminates the slow-roll regime. In this scenario, one naturally generates a considerable tensor-mode contribution in the curvature spectrum, collecting nevertheless the required amount of e-foldings during the final period of inflation. While nonobservation of tensors by Planck is certainly not a problem, a discovery in the medium- to long-term future is realistic.

Dynamics of ultra-broadband terahertz quantum cascade lasers for comb operation.

PubMed

Li, Hua; Laffaille, Pierre; Gacemi, Djamal; Apfel, Marc; Sirtori, Carlo; Leonardon, Jeremie; Santarelli, Giorgio; Rösch, Markus; Scalari, Giacomo; Beck, Mattias; Faist, Jerome; Hänsel, Wolfgang; Holzwarth, Ronald; Barbieri, Stefano

2015-12-28

We present an experimental investigation of the multimode dynamics and the coherence of terahertz quantum cascade lasers emitting over a spectral bandwidth of ~1THz. The devices are studied in free-running and under direct RF modulation. Depending on the pump current we observe different regimes of operation, where RF spectra displaying single and multiple narrow beat-note signals alternate with spectra showing a single beat-note characterized by an intense phase-noise, extending over a bandwidth up to a few GHz. We investigate the relation between this phase-noise and the dynamics of the THz modes through the electro-optic sampling of the laser emission. We find that when the phase-noise is large, the laser operates in an unstable regime where the lasing modes are incoherent. Under RF modulation of the laser current such instability can be suppressed and the modes coherence recovered, while, simultaneously, generating a strong broadening of the THz emission spectrum.

Characterization of Aeromechanics Response and Instability in Fans, Compressors, and Turbine Blades

NASA Technical Reports Server (NTRS)

Tan, Choon S.

2003-01-01

This study investigated the effect of interaction between tip clearance flow, steady and unsteady upstream wakes in rotor and stator blade rows in terms of blade forced response. In a stator blade row, the interaction of steady wakes in the upstream rotor frame with the stator imply a blade forced response whose spectrum contains the Blade passing frequency (BPF) and its harmonics, with a decaying amplitude as the frequency increases. When the incoming wakes are unsteady, however, the spectrum of blade excitation exhibits unexpectedly amplified high frequencies due to the modulation of BPF with the fluctuation frequency. In a rotor blade row, a tip flow instability has been demonstrated with a frequency (TVF) equal to 0.45 times the Blade Passing frequency corresponding to a reduced frequency (F(sub c) (sup +)) of 0.7. Under uniform inlet flow conditions, the frequency and spatial content of the tip flow region have been characterized. The disturbance TVF was the dominant disturbance in the flow field and was found to imply variations of the pressure coefficient of more than 30% on the blade tip (between 35% to 90% chord) and in the rotor-generated wake (from 75% to 100% hub-to-tip position). In an attempt to better understand the origin of the instability, the structure of the tip flow has also been analyzed. The interface between the tip flow region and the core flow has been found to have periodical wave-like flow patterns which proceed downstream at a speed of approximately 0.42 times the core flow speed at a frequency corresponding to TVF. A list of conclusions derived from these interactions is presented.

Modulation Instability of Copropagating Optical Beams in Fractional Coupled Nonlinear Schrödinger Equations

NASA Astrophysics Data System (ADS)

Zhang, Jinggui

2018-06-01

In this paper, we investigate the dynamical behaviors of the modulation instability (MI) of copropagating optical beams in fractional coupled nonlinear Schrödinger equations (NLSE) with the aim of revealing some novel properties different from those in the conventional coupled NLSE. By applying the standard linear stability method, we first derive an expression for the gain resulting from the instability induced by cross-phase modulation (CPM) in the presence of the Lévy indexes related to fractional effects. It is found that the modulation instability of copropagating optical beams still occurs even in the fractional NLSE with self-defocusing nonlinearity. Then, the analysis of our results further reveals that such Lévy indexes increase the fastest growth frequency and the bandwidth of conventional instability not only for the self-focusing case but also for the self-defocusing case, but do not influence the corresponding maximum gain. Numerical simulations are performed to confirm theoretical predictions. These findings suggest that the novel fractional physical settings may open up new possibilities for the manipulation of MI and nonlinear waves.

The effect of a dominant initial single mode on the Kelvin–Helmholtz instability evolution: New insights on previous experimental results

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

Shimony, Assaf; Shvarts, Dov; Malamud, Guy

2016-04-12

This paper brings new insights on an experiment, measuring the Kelvin–Helmholtz (KH) instability evolution, performed on the OMEGA-60 laser facility. Experimental radiographs show that the initial seed perturbations in the experiment are of multimode spectrum with a dominant single-mode of 16 μm wavelength. In single-mode-dominated KH instability flows, the mixing zone (MZ) width saturates to a constant value comparable to the wavelength. However, the experimental MZ width at late times has exceeded 100 μm, an order of magnitude larger. In this work, we use numerical simulations and a statistical model in order to investigate the vortex dynamics of the KHmore » instability for the experimental initial spectrum. Here, we conclude that the KH instability evolution in the experiment is dominated by multimode, vortex-merger dynamics, overcoming the dominant initial mode.« less

Mode suppression of a two-dimensional potential relaxation instability in a weakly magnetized discharge plasma

NASA Astrophysics Data System (ADS)

Gyergyek, T.; Čerček, M.; Jelić, N.; Stanojević, M.

1993-05-01

A potential relaxation instability (PRI) is modulated by an external signal using an additional grid to modulate the radial plasma potential profile in a magnetized plasma column in a linear magnetized discharge plasma device. It is observed that the electrode current oscillations follow the van der Pol equation with an external forcing term, and the linear growth rate of the instability is measured.

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

Wang, Yunliang; International Centre for Advanced Studies in Physical Sciences and Institute for Theoretical Physics, Faculty of Physics and Astronomy, Ruhr University Bochum, D-44780 Bochum; Lü, Xiaoxia

A theoretical and numerical study of the modulational instability of large amplitude quantum magnetosonic waves (QMWs) in a relativistically degenerate plasma is presented. A modified nonlinear Schrödinger equation is derived by using the reductive perturbation method. The modulational instability regions of the QMWs and the corresponding growth rates are significantly affected by the relativistic degeneracy parameter, the Pauli spin magnetization effects, and the equilibrium magnetic field. The dynamics and nonlinear saturation of the modulational instability of QMWs are investigated numerically. It is found that the increase of the relativistic degeneracy parameter can increase the growth rate of the instability, andmore » the system is saturated nonlinearly by the formation of envelope solitary waves. The current investigation may have relevance to astrophysical magnetized compact objects, such as white dwarfs and pulsar magnetospheres.« less

Non-destructive phase and intensity distributed measurements of the nonlinear stage of modulation instability in optical fibers

NASA Astrophysics Data System (ADS)

Mussot, Arnaud; Naveau, Corentin; Szriftgiser, Pascal; Copie, François; Kudlinski, Alexandre; Conforti, Matteo; Trillo, Stefano

2018-02-01

We report a novel experimental setup to perform distributed characterization in intensity and phase of the nonlinear stage of modulation instability by means of a non-invasive experimental setup : a heterodyne time domain reflectometer.

Limiting Charged Particle Flux Spectrum at the Heliopause and Beyond

NASA Astrophysics Data System (ADS)

Cooper, J. F.

2009-04-01

Ongoing Voyager 1 and 2 measurements show proton and heavier ion flux spectra unfolding upwards at MeV energies and in time with presumably decreasing distance to the heliopause interface of the heliosheath and local interstellar medium (LISM) plasma environments. Despite large spatial separation between the two spacecraft, the respective flux measurements are converging to a common spectrum consistent with a source beyond both spacecraft. This trend may conceivably reverse in response to increasing solar modulation of the new sunspot cycle but otherwise it must approach some limiting form of the plasma and energetic particle spectra near and beyond the heliopause. If an outer heliosheath region is bounded outwards by a postulated heliospheric bow shock, there could be an intermediate spectrum of shock-accelerated particles, but otherwise the limiting spectrum is that of the LISM. As reported earlier, a simple power-law extrapolation from known LISM plasma distributions at eV energies to the relatively unmodulated fluxes of galactic protons at GeV energies yields the "universal" stochastic cascade spectrum of Fisk and Gloeckler. Although the heliopause interface of the inner heliosheath and LISM plasma flow environments is usually visualized as laminar with little flow across the interface, boundary instabilities and charge exchange processes at a more chaotic and realistic boundary could enable interpenetrating flows. The limiting heliosheath spectrum now being approached by measurements from both spacecraft is suggested to be the LISM spectrum. Lack of significant and sustained spectral changes in response to increasing solar modulation within the supersonic heliosphere, and continuity of the unfolded spectral form for future measurements across the heliopause, would support direct LISM and/or outer heliosheath origins for the suprathermal ions of the inner heliosheath. This could further require modification of source and transport models for the so-called "anomalous component" ions at higher MeV energies. Unlimited extension of the presently observed suprathermal ion spectrum into the neutral gas environment beyond the heliopause, e.g. within the hydrogen wall region, would also impact energy and directional distributions of energetic neutral atoms now being measured from Earth orbit by the Interstellar Boundary Explorer (IBEX) mission.

Generation of dark solitons and their instability dynamics in two-dimensional condensates

NASA Astrophysics Data System (ADS)

Verma, Gunjan; Rapol, Umakant D.; Nath, Rejish

2017-04-01

We analyze numerically the formation and the subsequent dynamics of two-dimensional matter wave dark solitons in a Thomas-Fermi rubidium condensate using various techniques. An initially imprinted sharp phase gradient leads to the dynamical formation of a stationary soliton as well as very shallow gray solitons, whereas a smooth gradient only creates gray solitons. The depth and hence, the velocity of the soliton is provided by the spatial width of the phase gradient, and it also strongly influences the snake-instability dynamics of the two-dimensional solitons. The vortex dipoles stemming from the unstable soliton exhibit rich dynamics. Notably, the annihilation of a vortex dipole via a transient dark lump or a vortexonium state, the exchange of vortices between either a pair of vortex dipoles or a vortex dipole and a single vortex, and so on. For sufficiently large width of the initial phase gradient, the solitons may decay directly into vortexoniums instead of vortex pairs, and also the decay rate is augmented. Later, we discuss alternative techniques to generate dark solitons, which involve a Gaussian potential barrier and time-dependent interactions, both linear and periodic. The properties of the solitons can be controlled by tuning the amplitude or the width of the potential barrier. In the linear case, the number of solitons and their depths are determined by the quench time of the interactions. For the periodic modulation, a transient soliton lattice emerges with its periodicity depending on the modulation frequency, through a wave number selection governed by the local Bogoliubov spectrum. Interestingly, for sufficiently low barrier potential, both Faraday pattern and soliton lattice coexist. The snake instability dynamics of the soliton lattice is characteristically modified if the Faraday pattern is present.

Control of power, torque, and instability drive using in-shot variable neutral beam energy in tokamaks

DOE PAGES

Pace, D. C.; Collins, C. S.; Crowley, B.; ...

2016-09-28

A first-ever demonstration of controlling power and torque injection through time evolution of neutral beam energy has been achieved in recent experiments at the DIII-D tokamak. Pre-programmed waveforms for the neutral beam energy produce power and torque inputs that can be separately and continuously controlled. Previously, these inputs were tailored using on/off modulation of neutral beams resulting in large perturbations (e.g. power swings of over 1 MW). The new method includes, importantly for experiments, the ability to maintain a fixed injected power while varying the torque. In another case, different beam energy waveforms (in the same plasma conditions) produce significantmore » changes in the observed spectrum of beam ion-driven instabilities. Measurements of beam ion loss show that one energy waveform results in the complete avoidance of coherent losses due to Alfvénic instabilities. This new method of neutral beam operation is intended for further application in a variety of DIII-D experiments including those concerned with high-performance steady state scenarios, fast particle effects, and transport in the low torque regime. As a result, developing this capability would provide similar benefits and improved plasma control for other magnetic confinement fusion facilities.« less

Control of power, torque, and instability drive using in-shot variable neutral beam energy in tokamaks

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

Pace, D. C.; Collins, C. S.; Crowley, B.

A first-ever demonstration of controlling power and torque injection through time evolution of neutral beam energy has been achieved in recent experiments at the DIII-D tokamak. Pre-programmed waveforms for the neutral beam energy produce power and torque inputs that can be separately and continuously controlled. Previously, these inputs were tailored using on/off modulation of neutral beams resulting in large perturbations (e.g. power swings of over 1 MW). The new method includes, importantly for experiments, the ability to maintain a fixed injected power while varying the torque. In another case, different beam energy waveforms (in the same plasma conditions) produce significantmore » changes in the observed spectrum of beam ion-driven instabilities. Measurements of beam ion loss show that one energy waveform results in the complete avoidance of coherent losses due to Alfvénic instabilities. This new method of neutral beam operation is intended for further application in a variety of DIII-D experiments including those concerned with high-performance steady state scenarios, fast particle effects, and transport in the low torque regime. As a result, developing this capability would provide similar benefits and improved plasma control for other magnetic confinement fusion facilities.« less

Control of power, torque, and instability drive using in-shot variable neutral beam energy in tokamaks

NASA Astrophysics Data System (ADS)

Pace, D. C.; Collins, C. S.; Crowley, B.; Grierson, B. A.; Heidbrink, W. W.; Pawley, C.; Rauch, J.; Scoville, J. T.; Van Zeeland, M. A.; Zhu, Y. B.; The DIII-D Team

2017-01-01

A first-ever demonstration of controlling power and torque injection through time evolution of neutral beam energy has been achieved in recent experiments at the DIII-D tokamak (Luxon 2002 Nucl. Fusion 42 614). Pre-programmed waveforms for the neutral beam energy produce power and torque inputs that can be separately and continuously controlled. Previously, these inputs were tailored using on/off modulation of neutral beams resulting in large perturbations (e.g. power swings of over 1 MW). The new method includes, importantly for experiments, the ability to maintain a fixed injected power while varying the torque. In another case, different beam energy waveforms (in the same plasma conditions) produce significant changes in the observed spectrum of beam ion-driven instabilities. Measurements of beam ion loss show that one energy waveform results in the complete avoidance of coherent losses due to Alfvénic instabilities. This new method of neutral beam operation is intended for further application in a variety of DIII-D experiments including those concerned with high-performance steady state scenarios, fast particle effects, and transport in the low torque regime. Developing this capability would provide similar benefits and improved plasma control for other magnetic confinement fusion facilities.

Upgrade of the Mirnov probe arrays on the J-TEXT tokamak.

PubMed

Guo, Daojing; Hu, Qiming; Li, Da; Shen, Chengshuo; Wang, Nengchao; Huang, Zhuo; Huang, Mingxiang; Ding, Yonghua; Xu, Guo; Yu, Qingquan; Tang, Yuejin; Zhuang, Ge

2017-12-01

The magnetic diagnostic of Mirnov probe arrays has been upgraded on the J-TEXT tokamak to measure the magnetohydrodynamic instabilities with higher spatial resolution and better amplitude-frequency characteristics. The upgraded Mirnov probe array contains one poloidal array with 48 probe modules and two toroidal arrays with 25 probe modules. Each probe module contains two probes which measure both the poloidal and the radial magnetic fields (B p and B r ). To ensure that the Mirnov probe possess better amplitude-frequency characteristics, a novel kind of Mirnov probe made of low temperature co-fired ceramics is utilized. The parameters and frequency response of the probe are measured and can meet the experiment requirement. The new Mirnov arrays have been normally applied for a round of experiments, including the observation of tearing modes and their coupling as well as high frequency magnetic perturbation due to the Alfvén eigenmode. In order to extract useful information from raw signals, visualization processing methods based on singular value decomposition and cross-power spectrum are applied to decompose the coupled modes and to determine the mode number.

Upgrade of the Mirnov probe arrays on the J-TEXT tokamak

NASA Astrophysics Data System (ADS)

Guo, Daojing; Hu, Qiming; Li, Da; Shen, Chengshuo; Wang, Nengchao; Huang, Zhuo; Huang, Mingxiang; Ding, Yonghua; Xu, Guo; Yu, Qingquan; Tang, Yuejin; Zhuang, Ge

2017-12-01

The magnetic diagnostic of Mirnov probe arrays has been upgraded on the J-TEXT tokamak to measure the magnetohydrodynamic instabilities with higher spatial resolution and better amplitude-frequency characteristics. The upgraded Mirnov probe array contains one poloidal array with 48 probe modules and two toroidal arrays with 25 probe modules. Each probe module contains two probes which measure both the poloidal and the radial magnetic fields (Bp and Br). To ensure that the Mirnov probe possess better amplitude-frequency characteristics, a novel kind of Mirnov probe made of low temperature co-fired ceramics is utilized. The parameters and frequency response of the probe are measured and can meet the experiment requirement. The new Mirnov arrays have been normally applied for a round of experiments, including the observation of tearing modes and their coupling as well as high frequency magnetic perturbation due to the Alfvén eigenmode. In order to extract useful information from raw signals, visualization processing methods based on singular value decomposition and cross-power spectrum are applied to decompose the coupled modes and to determine the mode number.

Mix and hydrodynamic instabilities on NIF

NASA Astrophysics Data System (ADS)

Smalyuk, V. A.; Robey, H. F.; Casey, D. T.; Clark, D. S.; Döppner, T.; Haan, S. W.; Hammel, B. A.; MacPhee, A. G.; Martinez, D.; Milovich, J. L.; Peterson, J. L.; Pickworth, L.; Pino, J. E.; Raman, K.; Tipton, R.; Weber, C. R.; Baker, K. L.; Bachmann, B.; Berzak Hopkins, L. F.; Bond, E.; Caggiano, J. A.; Callahan, D. A.; Celliers, P. M.; Cerjan, C.; Dixit, S. N.; Edwards, M. J.; Felker, S.; Field, J. E.; Fittinghoff, D. N.; Gharibyan, N.; Grim, G. P.; Hamza, A. V.; Hatarik, R.; Hohenberger, M.; Hsing, W. W.; Hurricane, O. A.; Jancaitis, K. S.; Jones, O. S.; Khan, S.; Kroll, J. J.; Lafortune, K. N.; Landen, O. L.; Ma, T.; MacGowan, B. J.; Masse, L.; Moore, A. S.; Nagel, S. R.; Nikroo, A.; Pak, A.; Patel, P. K.; Remington, B. A.; Sayre, D. B.; Spears, B. K.; Stadermann, M.; Tommasini, R.; Widmayer, C. C.; Yeamans, C. B.; Crippen, J.; Farrell, M.; Giraldez, E.; Rice, N.; Wilde, C. H.; Volegov, P. L.; Gatu Johnson, M.

2017-06-01

Several new platforms have been developed to experimentally measure hydrodynamic instabilities in all phases of indirect-drive, inertial confinement fusion implosions on National Ignition Facility. At the ablation front, instability growth of pre-imposed modulations was measured with a face-on, x-ray radiography platform in the linear regime using the Hydrodynamic Growth Radiography (HGR) platform. Modulation growth of "native roughness" modulations and engineering features (fill tubes and capsule support membranes) were measured in conditions relevant to layered DT implosions. A new experimental platform was developed to measure instability growth at the ablator-ice interface. In the deceleration phase of implosions, several experimental platforms were developed to measure both low-mode asymmetries and high-mode perturbations near peak compression with x-ray and nuclear techniques. In one innovative technique, the self-emission from the hot spot was enhanced with argon dopant to "self-backlight" the shell in-flight. To stabilize instability growth, new "adiabat-shaping" techniques were developed using the HGR platform and applied in layered DT implosions.

Mix and hydrodynamic instabilities on NIF

DOE PAGES

Smalyuk, V. A.; Robey, H. F.; Casey, D. T.; ...

2017-06-01

Several new platforms have been developed to experimentally measure hydrodynamic instabilities in all phases of indirect-drive, inertial confinement fusion implosions on National Ignition Facility. At the ablation front, instability growth of pre-imposed modulations was measured with a face-on, x-ray radiography platform in the linear regime using the Hydrodynamic Growth Radiography (HGR) platform. Modulation growth of "native roughness" modulations and engineering features (fill tubes and capsule support membranes) were measured in conditions relevant to layered DT implosions. A new experimental platform was developed to measure instability growth at the ablator-ice interface. Here in the deceleration phase of implosions, several experimental platformsmore » were developed to measure both low-mode asymmetries and high-mode perturbations near peak compression with x-ray and nuclear techniques. In one innovative technique, the self-emission from the hot spot was enhanced with argon dopant to "self-backlight" the shell in-flight. To stabilize instability growth, new "adiabat-shaping" techniques were developed using the HGR platform and applied in layered DT implosions.« less

Reduction and coding of synthetic aperture radar data with Fourier transforms

NASA Technical Reports Server (NTRS)

Tilley, David G.

1995-01-01

Recently, aboard the Space Radar Laboratory (SRL), the two roles of Fourier Transforms for ocean image synthesis and surface wave analysis have been implemented with a dedicated radar processor to significantly reduce Synthetic Aperture Radar (SAR) ocean data before transmission to the ground. The object was to archive the SAR image spectrum, rather than the SAR image itself, to reduce data volume and capture the essential descriptors of the surface wave field. SAR signal data are usually sampled and coded in the time domain for transmission to the ground where Fourier Transforms are applied both to individual radar pulses and to long sequences of radar pulses to form two-dimensional images. High resolution images of the ocean often contain no striking features and subtle image modulations by wind generated surface waves are only apparent when large ocean regions are studied, with Fourier transforms, to reveal periodic patterns created by wind stress over the surface wave field. Major ocean currents and atmospheric instability in coastal environments are apparent as large scale modulations of SAR imagery. This paper explores the possibility of computing complex Fourier spectrum codes representing SAR images, transmitting the coded spectra to Earth for data archives and creating scenes of surface wave signatures and air-sea interactions via inverse Fourier transformations with ground station processors.

Competing Turing and Faraday Instabilities in Longitudinally Modulated Passive Resonators.

PubMed

Copie, François; Conforti, Matteo; Kudlinski, Alexandre; Mussot, Arnaud; Trillo, Stefano

2016-04-08

We experimentally investigate the interplay of Turing (modulational) and Faraday (parametric) instabilities in a bistable passive nonlinear resonator. The Faraday branch is induced via parametric resonance owing to a periodic modulation of the resonator dispersion. We show that the bistable switching dynamics is dramatically affected by the competition between the two instability mechanisms, which dictates two completely novel scenarios. At low detunings from resonance, switching occurs between the stable stationary lower branch and the Faraday-unstable upper branch, whereas at high detunings we observe the crossover between the Turing and Faraday periodic structures. The results are well explained in terms of the universal Lugiato-Lefever model.

Two-dimensional Nonlinear Simulations of Temperature-anisotropy Instabilities with a Proton-alpha Drift

NASA Astrophysics Data System (ADS)

Markovskii, S. A.; Chandran, Benjamin D. G.; Vasquez, Bernard J.

2018-04-01

We present two-dimensional hybrid simulations of proton-cyclotron and mirror instabilities in a proton-alpha plasma with particle-in-cell ions and a neutralizing electron fluid. The instabilities are driven by the protons with temperature perpendicular to the background magnetic field larger than the parallel temperature. The alpha particles with initially isotropic temperature have a nonzero drift speed with respect to the protons. The minor ions are known to influence the relative effect of the proton-cyclotron and mirror instabilities. In this paper, we show that the mirror mode can dominate the power spectrum at the nonlinear stage even if its linear growth rate is significantly lower than that of the proton-cyclotron mode. The proton-cyclotron instability combined with the alpha-proton drift is a possible cause of the nonzero magnetic helicity observed in the solar wind for fluctuations propagating nearly parallel to the magnetic field. Our simulations generally confirm this concept but reveal a complex helicity spectrum that is not anticipated from the linear theory of the instability.

Real world ocean rogue waves explained without the modulational instability.

PubMed

Fedele, Francesco; Brennan, Joseph; Ponce de León, Sonia; Dudley, John; Dias, Frédéric

2016-06-21

Since the 1990s, the modulational instability has commonly been used to explain the occurrence of rogue waves that appear from nowhere in the open ocean. However, the importance of this instability in the context of ocean waves is not well established. This mechanism has been successfully studied in laboratory experiments and in mathematical studies, but there is no consensus on what actually takes place in the ocean. In this work, we question the oceanic relevance of this paradigm. In particular, we analyze several sets of field data in various European locations with various tools, and find that the main generation mechanism for rogue waves is the constructive interference of elementary waves enhanced by second-order bound nonlinearities and not the modulational instability. This implies that rogue waves are likely to be rare occurrences of weakly nonlinear random seas.

Real world ocean rogue waves explained without the modulational instability

PubMed Central

Fedele, Francesco; Brennan, Joseph; Ponce de León, Sonia; Dudley, John; Dias, Frédéric

2016-01-01

Since the 1990s, the modulational instability has commonly been used to explain the occurrence of rogue waves that appear from nowhere in the open ocean. However, the importance of this instability in the context of ocean waves is not well established. This mechanism has been successfully studied in laboratory experiments and in mathematical studies, but there is no consensus on what actually takes place in the ocean. In this work, we question the oceanic relevance of this paradigm. In particular, we analyze several sets of field data in various European locations with various tools, and find that the main generation mechanism for rogue waves is the constructive interference of elementary waves enhanced by second-order bound nonlinearities and not the modulational instability. This implies that rogue waves are likely to be rare occurrences of weakly nonlinear random seas. PMID:27323897

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.

Active Control of High Frequency Combustion Instability in Aircraft Gas-Turbine Engines

NASA Technical Reports Server (NTRS)

Corrigan, Bob (Technical Monitor); DeLaat, John C.; Chang, Clarence T.

2003-01-01

Active control of high-frequency (greater than 500 Hz) combustion instability has been demonstrated in the NASA single-nozzle combustor rig at United Technologies Research Center. The combustor rig emulates an actual engine instability and has many of the complexities of a real engine combustor (i.e. actual fuel nozzle and swirler, dilution cooling, etc.) In order to demonstrate control, a high-frequency fuel valve capable of modulating the fuel flow at up to 1kHz was developed. Characterization of the fuel delivery system was accomplished in a custom dynamic flow rig developed for that purpose. Two instability control methods, one model-based and one based on adaptive phase-shifting, were developed and evaluated against reduced order models and a Sectored-1-dimensional model of the combustor rig. Open-loop fuel modulation testing in the rig demonstrated sufficient fuel modulation authority to proceed with closed-loop testing. During closed-loop testing, both control methods were able to identify the instability from the background noise and were shown to reduce the pressure oscillations at the instability frequency by 30%. This is the first known successful demonstration of high-frequency combustion instability suppression in a realistic aero-engine environment. Future plans are to carry these technologies forward to demonstration on an advanced low-emission combustor.

Pharmacotherapeutic implications of the association between genomic instability at chromosome 15q13.3 and autism spectrum disorders.

PubMed

Deutsch, Stephen I; Urbano, Maria R; Burket, Jessica A; Herndon, Amy L; Winebarger, Erin E

2011-01-01

Recurrent microdeletions of chromosome 15q13.3 are causally associated with autism spectrum disorders (ASDs), suggesting that haploinsufficiency of CHRNA7, the gene that codes for the α7 nicotinic acetylcholine receptor (α7 nAChR) subunit, is an etiological mechanism. Independent of these genetic data, given the location of α7 nAChRs on γ-aminobutyric acid-inhibitory neurons and their role in maintaining central inhibitory tone, a compelling pharmacological rationale exists for therapeutically targeting the α7 nAChR in persons with ASDs. Given the availability of positive allosteric modulators of nicotinic acetylcholine receptors and selective agonists for the α7 nAChR (eg, choline derived from dietary administration of cytidine 5'diphosphocholine and anabasine derivatives), it is possible to conduct "proof of concept" clinical trials, exploring the effects of α7 nAChR agonist interventional strategies on domains of psychopathology, such as attention, cognition, and memory, in persons with ASDs.

On the Rayleigh-Taylor Instability in Presence of a Background Shear

NASA Astrophysics Data System (ADS)

Shvydkoy, Roman

2018-01-01

In this note we revisit the classical subject of the Rayleigh-Taylor instability in presence of an incompressible background shear flow. We derive a formula for the essential spectral radius of the evolution group generated by the linearization near the steady state and reveal that the velocity variations neutralize shortwave instabilities. The formula is a direct generalization of the result of Hwang and Guo (Arch Ration Mech Anal 167(3):235-253, (2003). Furthermore, we construct a class of steady states which posses unstable discrete spectrum with neutral essential spectrum. The technique involves the WKB analysis of the evolution equation and contains novel compactness criterion for pseudo-differential operators on unbounded domains.

Energy dynamics in a simulation of LAPD turbulence

NASA Astrophysics Data System (ADS)

Friedman, Brett

2012-10-01

It is often assumed that linear instabilities maintain turbulence in plasmas and some fluids, but this is not always the case. It is well known that many fluids display subcritical turbulence at a Reynolds number well below the threashold of linear instability. Certain plasma models such as drift waves in a sheared slab also exhibit subcritical turbulence [1]. In other instances such as drift-ballooning turbulence in tokamak edge plasmas, linear instabilities exist in a system, but they become subdominant to more robust nonlinear mechanisms that sustain a turbulent state [2, 3]. In our simulation of LAPD turbulence, which was previously analyzed in [4], we diagnose the results using an energy dynamics analysis [5]. This allows us to track energy input into turbulent fluctuations and energy dissipation out of them. We also track conservative energy transfer between different energy types (e.g. from potential to kinetic energy) and between different Fourier waves of the system. The result is that a nonlinear instability drives and maintains the turbulence in the steady state saturated phase of the simulation. While a linear restistive drift wave instability resides in the system, the nonlinear drift wave instability dominates when the fluctuation amplitude becomes large enough. The nonlinear instability is identified by its energy growth rate spectrum, which varies significantly from the linear growth rate spectrum. The main differences are the presence of positive growth rates when k|| = 0 and negative growth rates for nonzero k||, which is opposite that of the linear growth rate spectrum.[4pt] [1] B. D. Scott, Phys. Rev. Lett., 65, 3289 (1990).[0pt] [2] A. Zeiler et al, Phys. Plasmas, 3, 2951 (1996).[0pt] [3] B. D. Scott, Phys. Plasmas, 12, 062314 (2005).[0pt] [4] P. Popovich et al, Phys. Plasmas, 17, 122312 (2010).[0pt] [5] [physics.plasm-ph].

Quasiperiodicity and Frequency Locking in Electronic Conduction in Germanium.

NASA Astrophysics Data System (ADS)

Gwinn, Elisabeth Gray

1987-09-01

This thesis presents an experimental study of a driven spatio-temporal instability in high-field transport in cooled, p-type Ge. The instability is produced at liquid He temperatures by d.c. voltage bias above the threshold for breakdown by impurity impact ionization, and is associated experimentally with voltage-controlled negative differential conductivity. The instability is coupled to an external oscillator by applying a sinusoidal voltage bias across the Ge sample. The driven instability exhibits frequency locking, quasiperiodicity, and chaos as the frequency and amplitude of the sinusoidal bias are varied. An iterative map of the circle provides a simple model for such a coupled, dissipative nonlinear oscillator system. The transition from quasiperiodicity to chaos in this model system occurs in a universal way; for example, the circle map has a universal, self-similar power spectrum at the onset of chaos with the golden mean winding number. When normalized appropriately, the power spectrum at the onset of chaos in the driven instability in Ge displays the same structure, with good agreement between the amplitudes of the experimental and theoretical spectral peaks. The relevance of universal theory to experiment can also be tested with a spectrum of scaling indices f( alpha), which is used to compare the probability distribution for the circle map at the onset of chaos with the golden mean winding number to the distribution of probability on a Poincare section of the experimental attractor. The procedure used to find f(alpha ) for the driven transport instability overcomes the sensitivity of f(alpha) to noise and to deviation from the critical amplitude. The f( alpha) curve for the driven instability in Ge is found to be in good agreement with the universal circle map result.

Kinetic effects on Alfven wave nonlinearity. II - The modified nonlinear wave equation

NASA Technical Reports Server (NTRS)

Spangler, Steven R.

1990-01-01

A previously developed Vlasov theory is used here to study the role of resonant particle and other kinetic effects on Alfven wave nonlinearity. A hybrid fluid-Vlasov equation approach is used to obtain a modified version of the derivative nonlinear Schroedinger equation. The differences between a scalar model for the plasma pressure and a tensor model are discussed. The susceptibilty of the modified nonlinear wave equation to modulational instability is studied. The modulational instability normally associated with the derivative nonlinear Schroedinger equation will, under most circumstances, be restricted to left circularly polarized waves. The nonlocal term in the modified nonlinear wave equation engenders a new modulational instability that is independent of beta and the sense of circular polarization. This new instability may explain the occurrence of wave packet steepening for all values of the plasma beta in the vicinity of the earth's bow shock.

Acceleration of High Energy Cosmic Rays in the Nonlinear Shock Precursor

NASA Astrophysics Data System (ADS)

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

2006-10-01

The problem of understanding acceleration of very energetic cosmic rays to energies above the 'knee' in the spectrum at 10^15-10^16eV remains one of the great challenges in modern physics. Recently, we have proposed a new approach to understanding high energy acceleration, based on exploiting scattering of cosmic rays by inhomogenities in the compressive nonlinear shock precursor, rather than by scattering across the main shock, as is conventionally assumed. We extend that theory by proposing a mechanism for the generation of mesoscale magnetic fields (krg<1, where rg is the cosmic ray gyroradius). The mechanism is the decay or modulational instability of resonantly generated Alfven waves scattering off ambient density perturbations in the precursors. Such perturbations can be produced by Drury instability. This mechanism leads to the generation of longer wavelength Alfven waves, thus enabling the confinement of higher energy particles. A simplified version of the theory, cast in the form of a Fokker-Planck equation for the Alfven population, will also be presented. This process also limits field generation on rg scales.

PLASMA TURBULENCE AND KINETIC INSTABILITIES AT ION SCALES IN THE EXPANDING SOLAR WIND

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

Hellinger, Petr; Trávnícek, Pavel M.; Matteini, Lorenzo

The relationship between a decaying strong turbulence and kinetic instabilities in a slowly expanding plasma is investigated using two-dimensional (2D) hybrid expanding box simulations. We impose an initial ambient magnetic field perpendicular to the simulation box, and we start with a spectrum of large-scale, linearly polarized, random-phase Alfvénic fluctuations that have energy equipartition between kinetic and magnetic fluctuations and vanishing correlation between the two fields. A turbulent cascade rapidly develops; magnetic field fluctuations exhibit a power-law spectrum at large scales and a steeper spectrum at ion scales. The turbulent cascade leads to an overall anisotropic proton heating, protons are heatedmore » in the perpendicular direction, and, initially, also in the parallel direction. The imposed expansion leads to generation of a large parallel proton temperature anisotropy which is at later stages partly reduced by turbulence. The turbulent heating is not sufficient to overcome the expansion-driven perpendicular cooling and the system eventually drives the oblique firehose instability in a form of localized nonlinear wave packets which efficiently reduce the parallel temperature anisotropy. This work demonstrates that kinetic instabilities may coexist with strong plasma turbulence even in a constrained 2D regime.« less

Nonlinear modulation near the Lighthill instability threshold in 2+1 Whitham theory

NASA Astrophysics Data System (ADS)

Bridges, Thomas J.; Ratliff, Daniel J.

2018-04-01

The dispersionless Whitham modulation equations in 2+1 (two space dimensions and time) are reviewed and the instabilities identified. The modulation theory is then reformulated, near the Lighthill instability threshold, with a slow phase, moving frame and different scalings. The resulting nonlinear phase modulation equation near the Lighthill surfaces is a geometric form of the 2+1 two-way Boussinesq equation. This equation is universal in the same sense as Whitham theory. Moreover, it is dispersive, and it has a wide range of interesting multi-periodic, quasi-periodic and multi-pulse localized solutions. For illustration the theory is applied to a complex nonlinear 2+1 Klein-Gordon equation which has two Lighthill surfaces in the manifold of periodic travelling waves. This article is part of the theme issue `Stability of nonlinear waves and patterns and related topics'.

Modulation instability initiated high power all-fiber supercontinuum lasers and their applications

NASA Astrophysics Data System (ADS)

Alexander, Vinay V.; Kulkarni, Ojas P.; Kumar, Malay; Xia, Chenan; Islam, Mohammed N.; Terry, Fred L.; Welsh, Michael J.; Ke, Kevin; Freeman, Michael J.; Neelakandan, Manickam; Chan, Allan

2012-09-01

High average power, all-fiber integrated, broadband supercontinuum (SC) sources are demonstrated. Architecture for SC generation using amplified picosecond/nanosecond laser diode (LD) pulses followed by modulation instability (MI) induced pulse breakup is presented and used to demonstrate SC sources from the mid-IR to the visible wavelengths. In addition to the simplicity in implementation, this architecture allows scaling up of the SC average power by increasing the pulse repetition rate and the corresponding pump power, while keeping the peak power, and, hence, the spectral extent approximately constant. Using this process, we demonstrate >10 W in a mid-IR SC extending from ˜0.8 to 4 μm, >5 W in a near IR SC extending from ˜0.8 to 2.8 μm, and >0.7 W in a visible SC extending from ˜0.45 to 1.2 μm. SC modulation capability is also demonstrated in a mid-IR SC laser with ˜3.9 W in an SC extending from ˜0.8 to 4.3 μm. The entire system and SC output in this case is modulated by a 500 Hz square wave at 50% duty cycle without any external chopping or modulation. We also explore the use of thulium doped fiber amplifier (TDFA) stages for mid-IR SC generation. In addition to the higher pump to signal conversion efficiency demonstrated in TDFAs compared to erbium/ytterbium doped fiber amplifier (EYFA), the shifting of the SC pump from ˜1.5 to ˜2 μm is pursued with an attempt to generate a longer extending SC into the mid-IR. We demonstrate ˜2.5 times higher optical conversion efficiency from pump to SC generation in wavelengths beyond 3.8 μm in the TDFA versus the EYFA based SC systems. The TDFA SC spectrum extends from ˜1.9 to 4.5 μm with ˜2.6 W at 50% modulation with a 250 Hz square wave. A variety of applications in defense, health care and metrology are also demonstrated using the SC laser systems presented in this paper.

Dispatching power system for preventive and corrective voltage collapse problem in a deregulated power system

NASA Astrophysics Data System (ADS)

Alemadi, Nasser Ahmed

Deregulation has brought opportunities for increasing efficiency of production and delivery and reduced costs to customers. Deregulation has also bought great challenges to provide the reliability and security customers have come to expect and demand from the electrical delivery system. One of the challenges in the deregulated power system is voltage instability. Voltage instability has become the principal constraint on power system operation for many utilities. Voltage instability is a unique problem because it can produce an uncontrollable, cascading instability that results in blackout for a large region or an entire country. In this work we define a system of advanced analytical methods and tools for secure and efficient operation of the power system in the deregulated environment. The work consists of two modules; (a) contingency selection module and (b) a Security Constrained Optimization module. The contingency selection module to be used for voltage instability is the Voltage Stability Security Assessment and Diagnosis (VSSAD). VSSAD shows that each voltage control area and its reactive reserve basin describe a subsystem or agent that has a unique voltage instability problem. VSSAD identifies each such agent. VS SAD is to assess proximity to voltage instability for each agent and rank voltage instability agents for each contingency simulated. Contingency selection and ranking for each agent is also performed. Diagnosis of where, why, when, and what can be done to cure voltage instability for each equipment outage and transaction change combination that has no load flow solution is also performed. A security constrained optimization module developed solves a minimum control solvability problem. A minimum control solvability problem obtains the reactive reserves through action of voltage control devices that VSSAD determines are needed in each agent to obtain solution of the load flow. VSSAD makes a physically impossible recommendation of adding reactive generation capability to specific generators to allow a load flow solution to be obtained. The minimum control solvability problem can also obtain solution of the load flow without curtailing transactions that shed load and generation as recommended by VSSAD. A minimum control solvability problem will be implemented as a corrective control, that will achieve the above objectives by using minimum control changes. The control includes; (1) voltage setpoint on generator bus voltage terminals; (2) under load tap changer tap positions and switchable shunt capacitors; and (3) active generation at generator buses. The minimum control solvability problem uses the VSSAD recommendation to obtain the feasible stable starting point but completely eliminates the impossible or onerous recommendation made by VSSAD. This thesis reviews the capabilities of Voltage Stability Security Assessment and Diagnosis and how it can be used to implement a contingency selection module for the Open Access System Dispatch (OASYDIS). The OASYDIS will also use the corrective control computed by Security Constrained Dispatch. The corrective control would be computed off line and stored for each contingency that produces voltage instability. The control is triggered and implemented to correct the voltage instability in the agent experiencing voltage instability only after the equipment outage or operating changes predicted to produce voltage instability have occurred. The advantages and the requirements to implement the corrective control are also discussed.

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.

Observation of the Self-Modulation Instability via Time-Resolved Measurements

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

Gross, M.; Engel, J.; Good, J.

Self-modulation of an electron beam in a plasma has been observed. The propagation of a long (several plasma wavelengths) electron bunch in an overdense plasma resulted in the production of multiple bunches via the self-modulation instability. Using a combination of a radio-frequency deflector and a dipole spectrometer, the time and energy structure of the self-modulated beam was measured. The longitudinal phase space measurement showed the modulation of a long electron bunch into three bunches with an approximatelymore » $$200\\text{ }\\text{ }\\mathrm{keV}/c$$ amplitude momentum modulation. Demonstrating this effect is a breakthrough for proton-driven plasma accelerator schemes aiming to utilize the same physical effect.« less

Observation of the Self-Modulation Instability via Time-Resolved Measurements

DOE PAGES

Gross, M.; Engel, J.; Good, J.; ...

2018-04-06

Self-modulation of an electron beam in a plasma has been observed. The propagation of a long (several plasma wavelengths) electron bunch in an overdense plasma resulted in the production of multiple bunches via the self-modulation instability. Using a combination of a radio-frequency deflector and a dipole spectrometer, the time and energy structure of the self-modulated beam was measured. The longitudinal phase space measurement showed the modulation of a long electron bunch into three bunches with an approximatelymore » $$200\\text{ }\\text{ }\\mathrm{keV}/c$$ amplitude momentum modulation. Demonstrating this effect is a breakthrough for proton-driven plasma accelerator schemes aiming to utilize the same physical effect.« less

Sensitivity of echo enabled harmonic generation to sinusoidal electron beam energy structure

DOE PAGES

Hemsing, E.; Garcia, B.; Huang, Z.; ...

2017-06-19

Here, we analytically examine the bunching factor spectrum of a relativistic electron beam with sinusoidal energy structure that then undergoes an echo-enabled harmonic generation (EEHG) transformation to produce high harmonics. The performance is found to be described primarily by a simple scaling parameter. The dependence of the bunching amplitude on fluctuations of critical parameters is derived analytically, and compared with simulations. Where applicable, EEHG is also compared with high gain harmonic generation (HGHG) and we find that EEHG is generally less sensitive to several types of energy structure. In the presence of intermediate frequency modulations like those produced by themore » microbunching instability, EEHG has a substantially narrower intrinsic bunching pedestal.« less

The effect of gravity modulation on thermosolutal convection in an infinite layer of fluid

NASA Astrophysics Data System (ADS)

Saunders, B. V.; Murray, B. T.; McFadden, G. B.; Coriell, S. R.; Wheeler, A. A.

1992-06-01

The effect of time-periodic vertical gravity modulation on the onset of thermosolutal convection in an infinite horizontal layer with stress-free boundaries is investigated using Floquet theory for the linear stability analysis. Situations for which the fluid layer is stably stratified in either the fingering or diffusive regimes of double-diffusive convection are considered. Results are presented both with and without steady background acceleration. Modulation may stabilize an unstable base solution or destabilize a stable base solution. In addition to synchronous and subharmonic response to the modulation frequency, instability in the double diffusive system can occur via a complex conjugate mode. In the diffusive regime, where oscillatory onset occurs in the unmodulated system, regions of resonant instability occur and exhibit strong coupling with the unmodulated oscillatory frequency. The response to modulation of the fundamental instability of the unmodulated system is described both analytically and numerically; in the double-diffusive system this mode persists under subcritical conditions as a high-frequency lobe.

The effect of gravity modulation on thermosolutal convection in an infinite layer of fluid

NASA Technical Reports Server (NTRS)

Saunders, B. V.; Murray, B. T.; Mcfadden, G. B.; Coriell, S. R.; Wheeler, A. A.

1992-01-01

The effect of time-periodic vertical gravity modulation on the onset of thermosolutal convection in an infinite horizontal layer with stress-free boundaries is investigated using Floquet theory for the linear stability analysis. Situations for which the fluid layer is stably stratified in either the fingering or diffusive regimes of double-diffusive convection are considered. Results are presented both with and without steady background acceleration. Modulation may stabilize an unstable base solution or destabilize a stable base solution. In addition to synchronous and subharmonic response to the modulation frequency, instability in the double diffusive system can occur via a complex conjugate mode. In the diffusive regime, where oscillatory onset occurs in the unmodulated system, regions of resonant instability occur and exhibit strong coupling with the unmodulated oscillatory frequency. The response to modulation of the fundamental instability of the unmodulated system is described both analytically and numerically; in the double-diffusive system this mode persists under subcritical conditions as a high-frequency lobe.

Indirect self-modulation instability measurement concept for the AWAKE proton beam

NASA Astrophysics Data System (ADS)

Turner, M.; Petrenko, A.; Biskup, B.; Burger, S.; Gschwendtner, E.; Lotov, K. V.; Mazzoni, S.; Vincke, H.

2016-09-01

AWAKE, the Advanced Proton-Driven Plasma Wakefield Acceleration Experiment, is a proof-of-principle R&D experiment at CERN using a 400 GeV / c proton beam from the CERN SPS (longitudinal beam size σz = 12 cm) which will be sent into a 10 m long plasma section with a nominal density of ≈ 7 ×1014 atoms /cm3 (plasma wavelength λp = 1.2 mm). In this paper we show that by measuring the time integrated transverse profile of the proton bunch at two locations downstream of the AWAKE plasma, information about the occurrence of the self-modulation instability (SMI) can be inferred. In particular we show that measuring defocused protons with an angle of 1 mrad corresponds to having electric fields in the order of GV/m and fully developed self-modulation of the proton bunch. Additionally, by measuring the defocused beam edge of the self-modulated bunch, information about the growth rate of the instability can be extracted. If hosing instability occurs, it could be detected by measuring a non-uniform defocused beam shape with changing radius. Using a 1 mm thick Chromox scintillation screen for imaging of the self-modulated proton bunch, an edge resolution of 0.6 mm and hence an SMI saturation point resolution of 1.2 m can be achieved.

Toward a definition of affective instability.

PubMed

Renaud, Suzane M; Zacchia, Camillo

2012-01-01

Affective instability is a psychophysiological symptom observed in some psychopathologies. It is a complex construct that encompasses (1) primary emotions, or affects, and secondary emotions, with each category having its own characteristics, amplitude, and duration, (2) rapid shifting from neutral or valenced affect to intense affect, and (3) dysfunctional modulation of emotions. Affective instability is often confused with mood lability, as in bipolar disorders, as well as with other terms. To clarify the concept, we searched databases for the term affective instability and read related articles on the topic. In this article we situate the term within the current affective nomenclature and human emotional experience, explore its psychophysiological features, and place it within the context of psychopathology. We explain why the term can potentially be confused with mood pathology and then define affective instability as an inherited temperamental trait modulated by developmental experience.

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

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

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

2011-08-15

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

Modulating action of low frequency oscillations on high frequency instabilities in Hall thrusters

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

Liqiu, Wei, E-mail: weiliqiu@gmail.com, E-mail: weiliqiu@hit.edu.cn; Liang, Han; Ziyi, Yang

2015-02-07

It is found that the low frequency oscillations have modulating action on high frequency instabilities in Hall thrusters. The physical mechanism of this modulation is discussed and verified by numerical simulations. Theoretical analyses indicate that the wide-range fluctuations of plasma density and electric field associated with the low frequency oscillations affect the electron drift velocity and anomalous electron transport across the magnetic field. The amplitude and frequency of high frequency oscillations are modulated by low frequency oscillations, which show the periodic variation in the time scale of low frequency oscillations.

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.

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

Smalyuk, V. A.; Robey, H. F.; Casey, D. T.

Several new platforms have been developed to experimentally measure hydrodynamic instabilities in all phases of indirect-drive, inertial confinement fusion implosions on National Ignition Facility. At the ablation front, instability growth of pre-imposed modulations was measured with a face-on, x-ray radiography platform in the linear regime using the Hydrodynamic Growth Radiography (HGR) platform. Modulation growth of "native roughness" modulations and engineering features (fill tubes and capsule support membranes) were measured in conditions relevant to layered DT implosions. A new experimental platform was developed to measure instability growth at the ablator-ice interface. Here in the deceleration phase of implosions, several experimental platformsmore » were developed to measure both low-mode asymmetries and high-mode perturbations near peak compression with x-ray and nuclear techniques. In one innovative technique, the self-emission from the hot spot was enhanced with argon dopant to "self-backlight" the shell in-flight. To stabilize instability growth, new "adiabat-shaping" techniques were developed using the HGR platform and applied in layered DT implosions.« less

Feedback control of plasma instabilities with charged particle beams and study of plasma turbulence

NASA Technical Reports Server (NTRS)

Tham, Philip Kin-Wah

1994-01-01

A new non-perturbing technique for feedback control of plasma instabilities has been developed in the Columbia Linear Machine (CLM). The feedback control scheme involves the injection of a feedback modulated ion beam as a remote suppressor. The ion beam was obtained from a compact ion beam source which was developed for this purpose. A Langmuir probe was used as the feedback sensor. The feedback controller consisted of a phase-shifter and amplifiers. This technique was demonstrated by stabilizing various plasma instabilities to the background noise level, like the trapped particle instability, the ExB instability and the ion-temperature-gradient (ITG) driven instability. An important feature of this scheme is that the injected ion beam is non-perturbing to the plasma equilibrium parameters. The robustness of this feedback stabilization scheme was also investigated. The principal result is that the scheme is fairly robust, tolerating about 100% variation about the nominal parameter values. Next, this scheme is extended to the unsolved general problem of controlling multimode plasma instabilities simultaneously with a single sensor-suppressor pair. A single sensor-suppressor pair of feedback probes is desirable to reduce the perturbation caused by the probes. Two plasma instabilities the ExB and the ITG modes, were simultaneously stabilized. A simple 'state' feedback type method was used where more state information was generated from the single sensor Langmuir probe by appropriate signal processing, in this case, by differentiation. This proof-of-principle experiment demonstrated for the first time that by designing a more sophisticated electronic feedback controller, many plasma instabilities may be simultaneously controlled. Simple theoretical models showed generally good agreement with the feedback experimental results. On a parallel research front, a better understanding of the saturated state of a plasma instability was sought partly with the help of feedback. A plasma instability is usually observed in its saturated state and appears as a single feature in the frequency spectrum with a single azimuthal and parallel wavenumbers. The physics of the non-zero spectral width was investigated in detail because the finite spectral width can cause "turbulent" transport. One aspect of the "turbulence" was investigated by obtaining the scaling of the linear growth rate of the instabilities with the fluctuation levels. The linear growth rates were measured with the established gated feedback technique. The research showed that the ExB instability evolves into a quasi-coherent state when the fluctuation level is high. The coherent aspects were studied with a bispectral analysis. Moreover, the single spectral feature was discovered to be actually composed of a few radial harmonics. The radial harmonics play a role in the nonlinear saturation of the instability via three-wave coupling.

Dynamic stabilization of Rayleigh-Taylor instability in an ablation front

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

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

2011-01-15

Dynamic stabilization of Rayleigh-Taylor instability in an ablation front is studied by considering a modulation in the acceleration that consists of sequences of Dirac deltas. This allows obtaining explicit analytical expressions for the instability growth rate as well as for the boundaries of the stability region. As a general rule, it is found that it is possible to stabilize all wave numbers above a certain minimum value k{sub m}, but the requirements in the modulation amplitude and frequency become more exigent with smaller k{sub m}. The essential role of compressibility is phenomenologically addressed in order to find the constraint itmore » imposes on the stability region. The results for some different wave forms of the acceleration modulation are also presented.« less

Absolute instabilities of travelling wave solutions in a Keller-Segel model

NASA Astrophysics Data System (ADS)

Davis, P. N.; van Heijster, P.; Marangell, R.

2017-11-01

We investigate the spectral stability of travelling wave solutions in a Keller-Segel model of bacterial chemotaxis with a logarithmic chemosensitivity function and a constant, sublinear, and linear consumption rate. Linearising around the travelling wave solutions, we locate the essential and absolute spectrum of the associated linear operators and find that all travelling wave solutions have parts of the essential spectrum in the right half plane. However, we show that in the case of constant or sublinear consumption there exists a range of parameters such that the absolute spectrum is contained in the open left half plane and the essential spectrum can thus be weighted into the open left half plane. For the constant and sublinear consumption rate models we also determine critical parameter values for which the absolute spectrum crosses into the right half plane, indicating the onset of an absolute instability of the travelling wave solution. We observe that this crossing always occurs off of the real axis.

Ultra wide band supercontinuum generation in air-silica holey fibers by SHG-induced modulation instabilities.

PubMed

Tombelaine, Vincent; Lesvigne, Christelle; Leproux, Philippe; Grossard, Ludovic; Couderc, Vincent; Auguste, Jean-Louis; Blondy, Jean-Marc; Huss, Guillaume; Pioger, Paul-Henri

2005-09-19

Second harmonic generation in an air-silica microstructured optical fiber pumped by subnanosecond pulses is used in order to initiate modulation instability processes in normal and anomalous dispersion regimes. This allows us to generate an ultra wide and flat supercontinuum (350-1750 nm), covering the entire transparency window of silica and exhibiting a singlemode transverse profile in visible range.

Infrasound induced instability by modulation of condensation process in the atmosphere.

PubMed

Naugolnykh, Konstantin; Rybak, Samuil

2008-12-01

A sound wave in supersaturated water vapor can modulate both the process of heat release caused by condensation, and subsequently, as a result, the resonance interaction of sound with the modulated heat release provides sound amplification. High-intensity atmospheric perturbations such as cyclones and thunderstorms generate infrasound, which is detectable at large distances from the source. The wave-condensation instability can lead to variation in the level of infrasound radiation by a developing cyclone, and this can be as a precursor of these intense atmospheric events.

Variability of accretion disks surrounding black holes: The role of inertial-acoustic mode instabilities

NASA Technical Reports Server (NTRS)

Chen, Xingming; Taam, Ronald E.

1995-01-01

The global nonlinear time-dependent evolution of the inertial-acoustic mode instability in accretion disks surrounding black holes has been investigated. The viscous stress is assumed to be proportional to the gas pressure only, i.e., tau = alphap(sub g). It is found that an oscillatory nonsteady behavior exists in the inner regions of disks (r is less than 10r(sub g) where r(sub g) is the Schwarzschild radius) for sufficiently large alpha(greater than or approximately equal to 0.2) and for mass accretion rates less than about 0.3 times the Eddington value. The variations of the integrated bolometric luminosity from the disk, Delta L/L, are less than 3%. A power spectrum analysis of these variations reveals a power spectrum which can be fitted to a power-law function of the frequency Pis proportional to f(exp -gamma), with index gamma = 1.4-2.3 and a low-frequency feature at about 4 Hz in one case. In addition, a narrow peak centered at a frequency corresponding to the maximum epicyclic frequency of the disk at approximately 100-130 Hz and its first harmonic is also seen. The low-frequency modulations are remarkably similar to those observed in black hole candidate systems. The possible existence of a scattering corona in the inner region of the disk and/or other processes contributing to the power at high frequencies in the inner region of the accretion disk may make the detection of the high-frequency component difficult.

Multicarrier orthogonal spread-spectrum (MOSS) data communications

DOEpatents

Smith, Stephen F [London, TN; Dress, William B [Camas, WA

2008-01-01

Systems and methods are described for multicarrier orthogonal spread-spectrum (MOSS) data communication. A method includes individually spread-spectrum modulating at least two of a set of orthogonal frequency division multiplexed carriers, wherein the resulting individually spread-spectrum modulated at least two of a set of orthogonal frequency division multiplexed carriers are substantially mutually orthogonal with respect to both frequency division multiplexing and spread-spectrum modulation.

Mixing the Solar Wind Proton and Electron Scales: Effects of Electron Temperature Anisotropy on the Oblique Proton Firehose Instability

NASA Technical Reports Server (NTRS)

Maneva, Y.; Lazar, M.; Vinas, A.; Poedts, S.

2016-01-01

The double adiabatic expansion of the nearly collisionless solar wind plasma creates conditions for the firehose instability to develop and efficiently prevent the further increase of the plasma temperature in the direction parallel to the interplanetary magnetic field. The conditions imposed by the firehose instability have been extensively studied using idealized approaches that ignore the mutual effects of electrons and protons. Recently, more realistic approaches have been proposed that take into account the interplay between electrons and protons,? unveiling new regimes of the parallel oscillatory modes. However, for oblique wave propagation the instability develops distinct branches that grow much faster and may therefore be more efficient than the parallel firehose instability in constraining the temperature anisotropy of the plasma particles. This paper reports for the first time on the effects of electron plasma properties on the oblique proton firehose (PFH) instability and provides a comprehensive vision of the entire unstable wave-vector spectrum, unifying the proton and the smaller electron scales. The plasma ß and temperature anisotropy regimes considered here are specific for the solar wind and magnetospheric conditions, and enable the electrons and protons to interact via the excited electromagnetic fluctuations. For the selected parameters, simultaneous electron and PFH instabilities can be observed with a dispersion spectrum of the electron firehose (EFH) extending toward the proton scales. Growth rates of the PFH instability are markedly boosted by the anisotropic electrons, especially in the oblique direction where the EFH growth rates are orders of magnitude higher.

MIXING THE SOLAR WIND PROTON AND ELECTRON SCALES: EFFECTS OF ELECTRON TEMPERATURE ANISOTROPY ON THE OBLIQUE PROTON FIREHOSE INSTABILITY

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

Maneva, Y.; Lazar, M.; Poedts, S.

2016-11-20

The double adiabatic expansion of the nearly collisionless solar wind plasma creates conditions for the firehose instability to develop and efficiently prevent the further increase of the plasma temperature in the direction parallel to the interplanetary magnetic field. The conditions imposed by the firehose instability have been extensively studied using idealized approaches that ignore the mutual effects of electrons and protons. Recently, more realistic approaches have been proposed that take into account the interplay between electrons and protons, unveiling new regimes of the parallel oscillatory modes. However, for oblique wave propagation the instability develops distinct branches that grow much fastermore » and may therefore be more efficient than the parallel firehose instability in constraining the temperature anisotropy of the plasma particles. This paper reports for the first time on the effects of electron plasma properties on the oblique proton firehose (PFH) instability and provides a comprehensive vision of the entire unstable wave-vector spectrum, unifying the proton and the smaller electron scales. The plasma β and temperature anisotropy regimes considered here are specific for the solar wind and magnetospheric conditions, and enable the electrons and protons to interact via the excited electromagnetic fluctuations. For the selected parameters, simultaneous electron and PFH instabilities can be observed with a dispersion spectrum of the electron firehose (EFH) extending toward the proton scales. Growth rates of the PFH instability are markedly boosted by the anisotropic electrons, especially in the oblique direction where the EFH growth rates are orders of magnitude higher.« less

Moiré superlattice-level stick-slip instability originated from geometrically corrugated graphene on a strongly interacting substrate

NASA Astrophysics Data System (ADS)

Shi, Ruoyu; Gao, Lei; Lu, Hongliang; Li, Qunyang; Ma, Tian-Bao; Guo, Hui; Du, Shixuan; Feng, Xi-Qiao; Zhang, Shuai; Liu, Yanmin; Cheng, Peng; Hu, Yuan-Zhong; Gao, Hong-Jun; Luo, Jianbin

2017-06-01

Two dimensional (2D) materials often exhibit novel properties due to various coupling effects with their supporting substrates. Here, using friction force microscopy (FFM), we report an unusual moiré superlattice-level stick-slip instability on monolayer graphene epitaxially grown on Ru(0 0 0 1) substrate. Instead of smooth friction modulation, a significant long-range stick-slip sawtooth modulation emerges with a period coinciding with the moiré superlattice structure, which is robust against high external loads and leads to an additional channel of energy dissipation. In contrast, the long-range stick-slip instability reduces to smooth friction modulation on graphene/Ir(1 1 1) substrate. The moiré superlattice-level slip instability could be attributed to the large sliding energy barrier, which arises from the morphological corrugation of graphene on Ru(0 0 0 1) surface as indicated by density functional theory (DFT) calculations. The locally steep humps acting as obstacles opposing the tip sliding, originates from the strong interfacial electronic interaction between graphene and Ru(0 0 0 1). This study opens an avenue for modulating friction by tuning the interfacial atomic interaction between 2D materials and their substrates.

Stereo Particle Image Velocimetry Measurements of Transition Downstream of a Backward-Facing Step in a Swept-Wing Boundary Layer

NASA Technical Reports Server (NTRS)

Eppink, Jenna L.; Yao, Chung-Sheng

2017-01-01

Stereo particle image velocimetry measurements were performed downstream of a backward-facing step in a stationary-cross flow dominated flow. The PIV measurements exhibit excellent quantitative and qualitative agreement with the previously acquired hotwire data. Instantaneous PIV snapshots reveal new information about the nature and cause of the \\spikes" that occurred prior to breakdown in both the hotwire and PIV data. The PIV snapshots show that the events occur simultaneously across multiple stationary cross flow wavelengths, indicating that this is not simply a local event, but is likely caused by the 2D Tollmien-Schlichting instability that is introduced by the step. While the TS instability is a 2D instability, it is also modulated in the spanwise direction due to interactions with the stationary cross flow, as are the other unsteady disturbances present. Because of this modulation, the "spike" events cause an instantaneous increase of the spanwise modulation of the streamwise and spanwise velocity initially caused by the stationary cross flow. Breakdown appears to be caused by this instantaneous modulation, possibly due to a high-frequency secondary instability similar to a traveling-cross flow breakdown scenario. These results further illuminate the respective roles of the stationary cross flow and unsteady disturbances in transition downstream of a backward-facing step.

Stochastic resonance based on modulation instability in spatiotemporal chaos.

PubMed

Han, Jing; Liu, Hongjun; Huang, Nan; Wang, Zhaolu

2017-04-03

A novel dynamic of stochastic resonance in spatiotemporal chaos is presented, which is based on modulation instability of perturbed partially coherent wave. The noise immunity of chaos can be reinforced through this effect and used to restore the coherent signal information buried in chaotic perturbation. A theoretical model with fluctuations term is derived from the complex Ginzburg-Landau equation via Wigner transform. It shows that through weakening the nonlinear threshold and triggering energy redistribution, the coherent component dominates the instability damped by incoherent component. The spatiotemporal output showing the properties of stochastic resonance may provide a potential application of signal encryption and restoration.

Water-waves frequency upshift of the spectral mean due to wind forcing

NASA Astrophysics Data System (ADS)

Eeltink, Debbie; Chabchoub, Amin; Brunetti, Maura; Kasparian, Jerome; Kimmoun, Olivier; Branger, Hubert

2017-04-01

The effect of wind forcing on monochromatic modulated water waves was investigated both numerically and experimentally in the context of the Modified Non-Linear Schrödinger (MNLS) equation framework. While wind is usually associated with a frequency downshift of the dominant spectral peak, we show that it may induce an upshift of the spectral mean due to an asymmetric amplification of the spectrum. Here the weighted average spectral mean is equal to the ratio of the momentum of the envelope to its norm and it detects any asymmetries in the spectrum (Segur et al. 2005). Wind can however indirectly induce frequency downshifts, by promoting dissipative effects like wave breaking. We highlight that the definition of the up- and downshift in terms of peak frequency or average frequency is critical for a relevant discussion. In our model, the wind input consists of a leading order forcing term that amplifies all frequencies equally and induces a broadening of the spectrum, and a higher order asymmetric term (Brunetti et al. 2014; Brunetti & Kasparian 2014) that amplifies higher frequencies more than lower ones and induces a permanent upshift of the spectral mean. The effect of MNLS + wind is exactly opposite to MNLS + viscosity, where the lower order viscosity terms damp the whole spectrum, while the higher order viscosity terms damp higher frequencies more than lower ones and thus causes a permanent downshift, as evidenced by Carter & Govan (2016). We corroborated the model with wave tank experiments conducted in the IRPHE/Pytheas large wind-wave facility located in Marseille, France. Wave data analysis show the temporary downshift in the spectral peak sense caused by the wind, and the temporary upshift in the spectral mean sense characteristic of the MNLS. As the tank-length was limited, we used long-range simulations to obtain upshift in the spectral mean sense caused by the wind. The limit of the model is reached when breaking events occur. We acknowledge financial support from the Swiss National Science Foundation (project 200021-155970), the Labex MEC (French ANR-10-LABX-0092) and the A*MIDEX project (ANR-11-IDEX-0001-02). • Brunetti, M. and Kasparian, J. 2014 "Modulational instability in wind-forced waves". Physics Letters A, 378: 48, 3626-3630. • Brunetti, M., Marchiando, N., Berti, N. and Kasparian, J. 2014 "Nonlinear fast growth of water waves under wind forcing". Physics Letters A 378: 1415, 1025-1030. • Carter, J. D. and Govan, A. 2016 "Frequency downshift in a viscous fluid." Eur. Journ. Mech. - B/Fluids 59: 177-185. • Segur, H., Henderson, D., Carter, J., Hammack, J., Li, C.-M., Pheiff, D. and Socha, K. 2005 "Stabilizing the Benjamin-Feir instability". Journ. Fluid Mechanics, 539: 229-271.

Convective and morphological instabilities during crystal growth: Effect of gravity modulation

NASA Technical Reports Server (NTRS)

Coreill, S. R.; Murray, B. T.; Mcfadden, G. B.; Wheeler, A. A.; Saunders, B. V.

1992-01-01

During directional solidification of a binary alloy at constant velocity in the vertical direction, morphological and convective instabilities may occur due to the temperature and solute gradients associated with the solidification process. The effect of time-periodic modulation (vibration) is studied by considering a vertical gravitational acceleration which is sinusoidal in time. The conditions for the onset of solutal convection are calculated numerically, employing two distinct computational procedures based on Floquet theory. In general, a stable state can be destabilized by modulation and an unstable state can be stabilized. In the limit of high frequency modulation, the method of averaging and multiple-scale asymptotic analysis can be used to simplify the calculations.

Do the freak waves exist in soliton gas?

NASA Astrophysics Data System (ADS)

Shurgalina, Ekaterina; Pelinovsky, Efim

2016-04-01

The possibility of short-lived anomalous large waves (rogue waves) in soliton gas in the frameworks of integrable models like the Korteweg - de Vries - type equations is studied. It is shown that the dynamics of heteropolar soliton gas differs sufficiently from the dynamics of unipolar soliton fields. In particular, in the wave fields consisting of solitons with different polarities the freak wave appearance is possible. It is shown numerically in [Shurgalina and Pelinovsky, 2015]. Freak waves in the framework of the modified Korteweg-de Vries equation have been studied previously in the case of narrowband initial conditions [Grimshaw et al, 2005, 2010; Talipova, 2011]. In this case, the mechanism of freak wave generation was modulation instability of modulated quasi-sinusoidal wave packets. At the same time the modulation instability of modulated cnoidal waves was studied in the mathematical work [Driscoll & O'Neil, 1976]. Since a sequence of solitary waves can be a special case of cnoidal wave, the modulation instability can be a possible mechanism of freak wave appearance in a soliton gas. Thus, we expect that rogue wave phenomenon in soliton gas appears in nonlinear integrable models admitting an existence of modulation instability of periodic waves (like cnoidal waves). References: 1. Shurgalina E.G., Pelinovsky E.N. Dynamics of irregular wave ensembles in the coastal zone, Nizhny Novgorod State Technical University n.a. R.E. Alekseev. - Nizhny Novgorod, 2015, 179 pp. 2. Grimshaw R., Pelinovsky E., Talipova T., Sergeeva A. Rogue internal waves in the ocean: long wave model. European Physical Journal Special Topics, 2010, 185, 195 - 208. 3. Grimshaw R., Pelinovsky E., Talipova T., Ruderman M. Erdelyi R. Short-lived large-amplitude pulses in the nonlinear long-wave model described by the modified Korteweg-de Vries equation. Studied Applied Mathematics, 2005, 114 (2), 189. 4. Talipova T.G. Mechanisms of internal freak waves, Fundamental and Applied Hydrophysics, 2011, 4(4), 58-70. 5. Driscoll F., O'Neil T.M. Modulational instability of cnoidal wave solutions of the modified Korteweg-de Vries equation. Journal of Mathematical Physics, 1976, 17 (7), 1196-1200.

Drive-induced delocalization in the Aubry-André model

NASA Astrophysics Data System (ADS)

Ray, S.; Ghosh, A.; Sinha, S.

2018-01-01

Motivated by the recent experiment by Bordia et al. [Nat. Phys. 13, 460 (2017), 10.1038/nphys4020], we study the single particle delocalization phenomena of the Aubry-André (AA) model subjected to periodic drives. In two distinct cases we construct an equivalent classical description to illustrate that the drive-induced delocalization phenomena stems from an instability and the onset of chaos in the underlying dynamics. In the first case we analyze the delocalization and the thermalization in a time modulated AA potential with respect to driving frequency and demonstrate that there exists a threshold value of the amplitude of the drive. In the next example, we show that the periodic modulation of the phase of the hopping amplitude induced by a gauge field leads to an unusual effect on delocalization with a nonmonotonic dependence on the driving frequency. Within a window of such a driving frequency a delocalized Floquet band with a mobility edge appears, exhibiting multifractality in the spectrum as well as in the Floquet eigenfunctions. Finally, we explore the effect of interaction and discuss how the results of the present analysis can be tested experimentally.

Electronegative nonlinear oscillating modes in plasmas

NASA Astrophysics Data System (ADS)

Panguetna, Chérif Souleman; Tabi, Conrad Bertrand; Kofané, Timoléon Crépin

2018-02-01

The emergence of nonlinear modulated waves is addressed in an unmagnetized electronegative plasma made of Boltzmann electrons, Boltzmann negative ions and cold mobile positive ions. The reductive perturbation method is used to reduce the dynamics of the whole system to a cubic nonlinear Schrödinger equation, whose the nonlinear and dispersion coefficients, P and Q, are function of the negative ion parameters, namely the negative ion concentration ratio (α) and the electron-to-negative ion temperature ratio (σn). It is observed that these parameters importantly affect the formation of modulated ion-acoustic waves, either as exact solutions or via the activation of modulational instability. Especially, the theory of modulational instability is used to show the correlation between the parametric analysis and the formation of modulated solitons, obtained here as bright envelopes and kink-wave solitons.

Evidence for a bubble-competition regime in indirectly driven ablative Rayleigh-Taylor instability experiments on the NIF.

PubMed

Martinez, D A; Smalyuk, V A; Kane, J O; Casner, A; Liberatore, S; Masse, L P

2015-05-29

We investigate on the National Ignition Facility the ablative Rayleigh-Taylor instability in the transition from weakly nonlinear to highly nonlinear regimes. A planar plastic package with preimposed two-dimensional broadband modulations is accelerated for up to 12 ns by the x-ray drive of a gas-filled Au radiation cavity with a radiative temperature plateau at 175 eV. This extended tailored drive allows a distance traveled in excess of 1 mm for a 130  μm thick foil. Measurements of the modulation optical density performed by x-ray radiography show that a bubble-merger regime for the Rayleigh-Taylor instability at an ablation front is achieved for the first time in indirect drive. The mutimode modulation amplitudes are in the nonlinear regime, grow beyond the Haan multimode saturation level, evolve toward the longer wavelengths, and show insensitivity to the initial conditions.

Method and apparatus for detecting combustion instability in continuous combustion systems

DOEpatents

Benson, Kelly J.; Thornton, Jimmy D.; Richards, George A.; Straub, Douglas L.

2006-08-29

An apparatus and method to sense the onset of combustion stability is presented. An electrode is positioned in a turbine combustion chamber such that the electrode is exposed to gases in the combustion chamber. A control module applies a voltage potential to the electrode and detects a combustion ionization signal and determines if there is an oscillation in the combustion ionization signal indicative of the occurrence of combustion stability or the onset of combustion instability. A second electrode held in a coplanar but spaced apart manner by an insulating member from the electrode provides a combustion ionization signal to the control module when the first electrode fails. The control module broadcasts a notice if the parameters indicate the combustion process is at the onset of combustion instability or broadcasts an alarm signal if the parameters indicate the combustion process is unstable.

Evidence for a Bubble-Competition Regime in Indirectly Driven Ablative Rayleigh-Taylor Instability Experiments on the NIF

NASA Astrophysics Data System (ADS)

Martinez, D. A.; Smalyuk, V. A.; Kane, J. O.; Casner, A.; Liberatore, S.; Masse, L. P.

2015-05-01

We investigate on the National Ignition Facility the ablative Rayleigh-Taylor instability in the transition from weakly nonlinear to highly nonlinear regimes. A planar plastic package with preimposed two-dimensional broadband modulations is accelerated for up to 12 ns by the x-ray drive of a gas-filled Au radiation cavity with a radiative temperature plateau at 175 eV. This extended tailored drive allows a distance traveled in excess of 1 mm for a 130 μ m thick foil. Measurements of the modulation optical density performed by x-ray radiography show that a bubble-merger regime for the Rayleigh-Taylor instability at an ablation front is achieved for the first time in indirect drive. The mutimode modulation amplitudes are in the nonlinear regime, grow beyond the Haan multimode saturation level, evolve toward the longer wavelengths, and show insensitivity to the initial conditions.

Instability waves and transition in adverse-pressure-gradient boundary layers

NASA Astrophysics Data System (ADS)

Bose, Rikhi; Zaki, Tamer A.; Durbin, Paul A.

2018-05-01

Transition to turbulence in incompressible adverse-pressure-gradient (APG) boundary layers is investigated by direct numerical simulations. Purely two-dimensional instability waves develop on the inflectional base velocity profile. When the boundary layer is perturbed by isotropic turbulence from the free stream, streamwise elongated streaks form and may interact with the instability waves. Subsequent mechanisms that trigger transition depend on the intensity of the free-stream disturbances. All evidence from the present simulations suggest that the growth rate of instability waves is sufficiently high to couple with the streaks. Under very low levels of free-stream turbulence (˜0.1 % ), transition onset is highly sensitive to the inlet disturbance spectrum and is accelerated if the spectrum contains frequency-wave-number combinations that are commensurate with the instability waves. Transition onset and completion in this regime is characterized by formation and breakdown of Λ vortices, but they are more sporadic than in natural transition. Beneath free-stream turbulence with higher intensity (1-2 % ), bypass transition mechanisms are dominant, but instability waves are still the most dominant disturbances in wall-normal and spanwise perturbation spectra. Most of the breakdowns were by disturbances with critical layers close to the wall, corresponding to inner modes. On the other hand, the propensity of an outer mode to occur increases with the free-stream turbulence level. Higher intensity free-stream disturbances induce strong streaks that favorably distort the boundary layer and suppress the growth of instability waves. But the upward displacement of high amplitude streaks brings them to the outer edge of the boundary layer and exposes them to ambient turbulence. Consequently, high-amplitude streaks exhibit an outer-mode secondary instability.

Modulational instabilities in acetanilide taking into account both the N H and the C=O vibrational self-trappings

NASA Astrophysics Data System (ADS)

Simo, Elie

2007-02-01

A model of crystalline acetanilide, ACN accounting for the C=O and N-H vibrational self-trappings is presented. We develop a fully discrete version of ACN. We show that ACN can be described by a set of two coupled discrete nonlinear Schrödinger (DNLS) equations. Modulational instabilities (MI) are studied both theoretically and numerically. Dispersion laws for the wavenumbers and frequencies of the linear modulation waves are determined. We also derived the criterion for the existence of MI. Numerical simulations are carried out for a variety of selected wave amplitudes in the unstable zone. It is shown that instabilities grow as the wavenumbers and amplitudes of the modulated waves increase. MI grow faster in the N-H mode than in the C=O mode. Temporal evolution of the density probabilities of the vibrational excitons are obtained by the numerical integration of the coupled DNLS equations governing the ACN molecule. These investigations confirm the generation of localized modes by the phenomenon of MI and the predominance of the N-H vibrational mode in the MI process of the ACN.

Ultrafast and Doppler-free femtosecondoptical ranging based on dispersivefrequency-modulated interferometry.

PubMed

Xia, Haiyun; Zhang, Chunxi

2010-03-01

An ultrafast and Doppler-free optical ranging system based on dispersive frequency-modulated interferometry is demonstrated. The principle is similar to the conventional frequency-modulated continuous-wave interferometry where the range information is derived from the beat frequency between the object signal and the reference signal. However, a passive and static frequency scanning is performed based on the chromatic dispersion of a transform-limited femtosecond pulse in the time domain. We point out that the unbalanced dispersion introduced in the Mach-Zehnder interferometer can be optimized to eliminate the frequency chirp in the temporal interferograms pertaining to the third order dispersion of the all-fiber system, if the dynamic range being considered is small. Some negative factors, such as the polarization instability of the femtosecond pulse, the power fluctuation of the optical signal and the nonuniform gain spectrum of the erbium-doped fiber amplifier lead to an obvious envelope deformation of the temporal interferograms from the Gaussian shape. Thus a new data processing method is proposed to guarantee the range resolution. In the experiment, the vibration of a speaker is measured. A range resolution of 1.59 microm is achieved with an exposure time of 394 fs at a sampling rate of 48.6 MHz.

[Signal analysis and spectrum distortion correction for tunable diode laser absorption spectroscopy system].

PubMed

Bao, Wei-Yi; Zhu, Yong; Chen, Jun; Chen, Jun-Qing; Liang, Bo

2011-04-01

In the present paper, the signal of a tunable diode laser absorption spectroscopy (TDLAS) trace gas sensing system, which has a wavelength modulation with a wide range of modulation amplitudes, is studied based on Fourier analysis method. Theory explanation of spectrum distortion induced by laser intensity amplitude modulation is given. In order to rectify the spectrum distortion, a method of synchronous amplitude modulation suppression by a variable optical attenuator is proposed. To validate the method, an experimental setup is designed. Absorption spectrum measurement experiments on CO2 gas were carried out. The results show that the residual laser intensity modulation amplitude of the experimental system is reduced to -0.1% of its original value and the spectrum distortion improvement is 92% with the synchronous amplitude modulation suppression. The modulation amplitude of laser intensity can be effectively reduced and the spectrum distortion can be well corrected by using the given correction method and system. By using a variable optical attenuator in the TDLAS (tunable diode laser absorption spectroscopy) system, the dynamic range requirements of photoelectric detector, digital to analog converter, filters and other aspects of the TDLAS system are reduced. This spectrum distortion correction method can be used for online trace gas analyzing in process industry.

Modulated electron cyclotron drift instability in a high-power pulsed magnetron discharge.

PubMed

Tsikata, Sedina; Minea, Tiberiu

2015-05-08

The electron cyclotron drift instability, implicated in electron heating and anomalous transport, is detected in the plasma of a planar magnetron. Electron density fluctuations associated with the mode are identified via an adapted coherent Thomson scattering diagnostic, under direct current and high-power pulsed magnetron operation. Time-resolved analysis of the mode amplitude reveals that the instability, found at MHz frequencies and millimeter scales, also exhibits a kHz-scale modulation consistent with the observation of larger-scale plasma density nonuniformities, such as the rotating spoke. Sharply collimated axial fluctuations observed at the magnetron axis are consistent with the presence of escaping electrons in a region where the magnetic and electric fields are antiparallel. These results distinguish aspects of magnetron physics from other plasma sources of similar geometry, such as the Hall thruster, and broaden the scope of instabilities which may be considered to dictate magnetron plasma features.

Spectrum of magnetic resonance imaging findings in clinical glenohumeral instability

PubMed Central

Jana, Manisha; Srivastava, Deep Narayan; Sharma, Raju; Gamanagatti, Shivanand; Nag, Hiralal; Mittal, Ravi; Upadhyay, Ashish Dutt

2011-01-01

The glenohumeral joint is the most commonly dislocated joint in the body, and anterior instability is the most common type of shoulder instability. Depending on the etiology and the age of the patient, there may be associated injuries, for example, to the anterior-inferior labro-ligamentous structures (in young individuals with traumatic instability) or to the bony components (commoner in the elderly), which are best visualized using MRI and MR arthrography. Anterior instability is associated with a Bankart lesion and its variants and abnormalities of the anterior band of the inferior glenohumeral ligament (IGHL), whereas posterior instability is associated with reverse Bankart and reverse Hill-Sachs lesions. Cases of multidirectional instability often have no labral pathology on imaging but show specific osseous changes including increased chondrolabral retroversion. This article reviews the relevant anatomy in brief and describes the MRI findings in each type, with the imaging features of the common abnormalities. PMID:21799591

Perspectives of drug-based neuroprotection targeting mitochondria.

PubMed

Procaccio, V; Bris, C; Chao de la Barca, J M; Oca, F; Chevrollier, A; Amati-Bonneau, P; Bonneau, D; Reynier, P

2014-05-01

Mitochondrial dysfunction has been reported in most neurodegenerative diseases. These anomalies include bioenergetic defect, respiratory chain-induced oxidative stress, defects of mitochondrial dynamics, increase sensitivity to apoptosis, and accumulation of damaged mitochondria with instable mitochondrial DNA. Significant progress has been made in our understanding of the pathophysiology of inherited mitochondrial disorders but most have no effective therapies. The development of new metabolic treatments will be useful not only for rare mitochondrial disorders but also for the wide spectrum of common age-related neurodegenerative diseases shown to be associated with mitochondrial dysfunction. A better understanding of the mitochondrial regulating pathways raised several promising perspectives of neuroprotection. This review focuses on the pharmacological approaches to modulate mitochondrial biogenesis, the removal of damaged mitochondria through mitophagy, scavenging free radicals and also dietary measures such as ketogenic diet. Copyright © 2014 Elsevier Masson SAS. All rights reserved.

Pattern formation in a liquid-crystal light valve with feedback, including polarization, saturation, and internal threshold effects

NASA Astrophysics Data System (ADS)

Neubecker, R.; Oppo, G.-L.; Thuering, B.; Tschudi, T.

1995-07-01

The use of liquid-crystal light valves (LCLV's) as nonlinear elements in diffractive optical systems with feedback leads to the formation of a variety of optical patterns. The spectrum of possible spatial instabilities is shown to be even richer when the LCLV's capability for polarization modulation is utilized and internal threshold and saturation effects are considered. We derive a model for the feedback system based on a realistic description of the LCLV's internal function and coupling to a polarizer. Thresholds of pattern formation are compared to the common Kerr-type approximation and show transitions involving rolls, squares, hexagons, and tiled patterns. Numerical and experimental results confirm our theoretical predictions and unveil how patterns and their typical length scales can be easily controlled by changes of the parameters.

Instability growth seeded by oxygen in CH shells on the National Ignition Facility

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

Haan, S. W., E-mail: haan1@llnl.gov; Johnson, M. A.; Stadermann, M.

Fusion targets imploded on the National Ignition Facility are subject to hydrodynamic instabilities. These have generally been assumed to be seeded primarily by surface roughness, as existing work had suggested that internal inhomogeneity was small enough not to contribute significantly. New simulations presented here examine this in more detail, and consider modulations in internal oxygen content in CH plastic ablators. The oxygen is configured in a way motivated by measurement of oxygen in the shells. We find that plausible oxygen nonuniformity, motivated by target characterization experiments, seeds instability growth that is 3–5× bigger than expected from surface roughness. Pertinent existingmore » capsule characterization is discussed, which suggests the presence of internal modulations that could be oxygen at levels large enough to be the dominant seed for hydrodynamic instability growth. Oxygen-seeded growth is smaller for implosions driven by high-foot pulse shapes, consistent with the performance improvement seen with these pulse shapes. Growth is somewhat smaller for planned future pulse shapes that were optimized to minimize growth of surface ripples. A possible modified specification for oxygen modulations is discussed, which is about 1/5 of the current requirement.« less

Independent and collective roles of surface structures at different length scales on pool boiling heat transfer

PubMed Central

Li, Calvin H.; Rioux, Russell P.

2016-01-01

Spherical Cu nanocavity surfaces are synthesized to examine the individual role of contact angles in connecting lateral Rayleigh-Taylor wavelength to vertical Kevin-Helmholtz wavelength on hydrodynamic instability for the onset of pool boiling Critical Heat Flux (CHF). Solid and porous Cu pillar surfaces are sintered to investigate the individual role of pillar structure pitch at millimeter scale, named as module wavelength, on hydrodynamic instability at CHF. Last, spherical Cu nanocavities are coated on the porous Cu pillars to create a multiscale Cu structure, which is studied to examine the collective role and relative significance of contact angles and module wavelength on hydrodynamic instability at CHF, and the results indicate that module wavelength plays the dominant role on hydrodynamic instability at CHF when the height of surface structures is equal or above ¼ Kelvin-Helmholtz wavelength. Pool boiling Heat Transfer Coefficient (HTC) enhancements on spherical Cu nanocavity surfaces, solid and porous Cu pillar surfaces, and the integrated multiscale structure have been investigated, too. The experimental results reveal that the nanostructures and porous pillar structures can be combined together to achieve even higher enhancement of HTC than that of individual structures. PMID:27841322

Power-law modulation of the scalar power spectrum from a heavy field with a monomial potential

NASA Astrophysics Data System (ADS)

Huang, Qing-Guo; Pi, Shi

2018-04-01

The effects of heavy fields modulate the scalar power spectrum during inflation. We analytically calculate the modulations of the scalar power spectrum from a heavy field with a separable monomial potential, i.e. V(phi)~ phin. In general the modulation is characterized by a power-law oscillation which is reduced to the logarithmic oscillation in the case of n=2.

Electromagnetic ion/ion cyclotron instability - Theory and simulations

NASA Technical Reports Server (NTRS)

Winske, D.; Omidi, N.

1992-01-01

Linear theory and 1D and 2D hybrid simulations are employed to study electromagnetic ion/ion cyclotron (EMIIC) instability driven by the relative streaming of two field-aligned ion beams. The characteristics of the instability are studied as a function of beam density, propagation angle, electron-ion temperature ratios, and ion beta. When the propagation angle is near 90 deg the EMIIC instability has the characteristics of an electrostatic instability, while at smaller angles electromagnetic effects play a significant role as does strong beam coupling. The 2D simulations point to a narrowing of the wave spectrum and accompanying coherent effects during the linear growth stage of development. The EMIIC instability is an important effect where ion beta is low such as in the plasma-sheet boundary layer and upstream of slow shocks in the magnetotail.

Apparatus configured for identification of a material and method of identifying a material

DOEpatents

Slater, John M.; Crawford, Thomas M.; Frickey, Dean A.

2001-01-01

The present invention relates to an apparatus configured for identification of a material and method of identifying a material. One embodiment of the present invention provides an apparatus configured for identification of a material including a first region configured to receive a first sample and output a first spectrum responsive to exposure of the first sample to radiation; a signal generator configured to provide a reference signal having a reference frequency and a modulation signal having a modulation frequency; a modulator configured to selectively modulate the first spectrum using the modulation signal according to the reference frequency; a second region configured to receive a second sample and output a second spectrum responsive to exposure of the second sample to the first spectrum; and a detector configured to detect the second spectrum.

Periodic, complexiton solutions and stability for a (2+1)-dimensional variable-coefficient Gross-Pitaevskii equation in the Bose-Einstein condensation

NASA Astrophysics Data System (ADS)

Yin, Hui-Min; Tian, Bo; Zhao, Xin-Chao

2018-06-01

This paper presents an investigation of a (2 + 1)-dimensional variable-coefficient Gross-Pitaevskii equation in the Bose-Einstein condensation. Periodic and complexiton solutions are obtained. Solitons solutions are also gotten through the periodic solutions. Numerical solutions via the split step method are stable. Effects of the weak and strong modulation instability on the solitons are shown: the weak modulation instability permits an observable soliton, and the strong one overwhelms its development.

Anderson localisation and optical-event horizons in rogue-soliton generation.

PubMed

Saleh, Mohammed F; Conti, Claudio; Biancalana, Fabio

2017-03-06

We unveil the relation between the linear Anderson localisation process and nonlinear modulation instability. Anderson localised modes are formed in certain temporal intervals due to the random background noise. Such localised modes seed the formation of solitary waves that will appear during the modulation instability process at those preferred intervals. Afterwards, optical-event horizon effects between dispersive waves and solitons produce an artificial collective acceleration that favours the collision of solitons, which could eventually lead to a rogue-soliton generation.

Nonlinear propagation of electromagnetic waves in negative-refraction-index composite materials.

PubMed

Kourakis, I; Shukla, P K

2005-07-01

We investigate the nonlinear propagation of electromagnetic waves in left-handed materials. For this purpose, we consider a set of coupled nonlinear Schrödinger (CNLS) equations, which govern the dynamics of coupled electric and magnetic field envelopes. The CNLS equations are used to obtain a nonlinear dispersion, which depicts the modulational stability profile of the coupled plane-wave solutions in left-handed materials. An exact (in)stability criterion for modulational interactions is derived, and analytical expressions for the instability growth rate are obtained.

Drifting cavity solitons and dissipative rogue waves induced by time-delayed feedback in Kerr optical frequency comb and in all fiber cavities

NASA Astrophysics Data System (ADS)

Tlidi, Mustapha; Panajotov, Krassimir; Ferré, Michel; Clerc, Marcel G.

2017-11-01

Time-delayed feedback plays an important role in the dynamics of spatially extended systems. In this contribution, we consider the generic Lugiato-Lefever model with delay feedback that describes Kerr optical frequency comb in all fiber cavities. We show that the delay feedback strongly impacts the spatiotemporal dynamical behavior resulting from modulational instability by (i) reducing the threshold associated with modulational instability and by (ii) decreasing the critical frequency at the onset of this instability. We show that for moderate input intensities it is possible to generate drifting cavity solitons with an asymmetric radiation emitted from the soliton tails. Finally, we characterize the formation of rogue waves induced by the delay feedback.

Fermi-Pasta-Ulam recurrence and modulation instability

NASA Astrophysics Data System (ADS)

Kuznetsov, E. A.

2017-01-01

We give a qualitative conceptual explanation of the Fermi-Pasta-Ulam (FPU) like recurrence in the onedimensional focusing nonlinear Schrodinger equation (NLSE). The recurrence can be considered as a result of the nonlinear development of the modulation instability. All known exact localized solitary wave solutions describing propagation on the background of the modulationally unstable condensate show the recurrence to the condensate state after its interaction with solitons. The condensate state locally recovers its original form with the same amplitude but a different phase after soliton leave its initial region. Based on the integrability of the NLSE, we demonstrate that the FPU recurrence takes place not only for condensate, but also for a more general solution in the form of the cnoidal wave. This solution is periodic in space and can be represented as a solitonic lattice. That lattice reduces to isolated soliton solution in the limit of large distance between solitons. The lattice transforms into the condensate in the opposite limit of dense soliton packing. The cnoidal wave is also modulationally unstable due to soliton overlapping. The recurrence happens at the nonlinear stage of the modulation instability. Due to generic nature of the underlying mathematical model, the proposed concept can be applied across disciplines and nonlinear systems, ranging from optical communications to hydrodynamics.

Effect of gravity modulation on thermosolutal convection in an infinite layer of fluid

NASA Astrophysics Data System (ADS)

Saunders, B. V.; Murray, B. T.; McFadden, G. B.; Coriell, S. R.; Wheeler, A. A.

1991-10-01

The effect of time-periodic vertical gravity modulation on the onset of thermosolutal convection in an infinite horizontal layer with stress free boundaries is studied using Floquet theory for the linear stability analysis. Situations are considered for which the fluid layer is stably stratified in either the fingering or diffusive regimes of double diffusive convection. Results are presented both with and without steady background acceleration. Modulation may stabilize an unstable base solution or destabilize a stable base solution. In addition to synchronous and subharmonic response to the modulation frequency, instability in the double diffusive system can occur via a complex conjugate mode. In the diffusive regime, where oscillatory onset occurs in the unmodulated system, regions of resonant instability occur and exhibit strong coupling with the unmodulated oscillatory frequency.

Clinical features of bipolar spectrum with binge eating behaviour.

PubMed

McElroy, Susan L; Crow, Scott; Blom, Thomas J; Cuellar-Barboza, Alfredo B; Prieto, Miguel L; Veldic, Marin; Winham, Stacey J; Bobo, William V; Geske, Jennifer; Seymour, Lisa R; Mori, Nicole; Bond, David J; Biernacka, Joanna M; Frye, Mark A

2016-09-01

To determine whether bipolar spectrum disorder with binge eating behavior (BE) is an important clinical sub-phenotype. Prevalence rates and correlates of different levels of BE were assessed in 1114 bipolar spectrum patients participating in a genetic biobank. BE and eating disorders (EDs) were assessed with the Eating Disorder Diagnostic Scale (EDDS). Psychiatric illness burden was evaluated with measures of suicidality, psychosis, mood instability, anxiety disorder comorbidity, and substance abuse comorbidity. Medical illness burden was evaluated with body mass index (BMI) and the Cumulative Index Rating Scale (CIRS). Thirty percent of patients had any BE and 27% had BE plus an ED diagnosis. Compared with bipolar spectrum patients without BE, bipolar spectrum patients with BE were younger and more likely to be female; had significantly higher levels of eating psychopathology, suicidality, mood instability, and anxiety disorder comorbidity; had a significantly higher mean BMI and a significantly higher rate of obesity; and had a significantly higher medical illness burden. Bipolar spectrum patients with BE but no ED diagnosis were more similar to bipolar spectrum patients without BE than to those with an ED. Nonetheless, the positive predictive value and specificity of BE predicting an ED was 0.90 and 0.96, respectively. As only two patients had co-occurring anorexia nervosa, these results may not generalize to bipolar spectrum patients with restricting EDs. Bipolar spectrum disorder with broadly-defined BE may not be as clinically relevant a sub-phenotype as bipolar spectrum disorder with an ED but may be an adequate proxy for the latter when phenotyping large samples of individuals. Copyright © 2016. Published by Elsevier B.V.

Evidence for a Bubble-Competition Regime in Indirectly Driven Ablative Rayleigh-Taylor Instability Experiments on the NIF

DOE PAGES

Martinez, D. A.; Smalyuk, V. A.; Kane, J. O.; ...

2015-05-29

In this paper, we investigate on the National Ignition Facility the ablative Rayleigh-Taylor instability in the transition from weakly nonlinear to highly nonlinear regimes. A planar plastic package with preimposed two-dimensional broadband modulations is accelerated for up to 12 ns by the x-ray drive of a gas-filled Au radiation cavity with a radiative temperature plateau at 175 eV. This extended tailored drive allows a distance traveled in excess of 1 mm for a 130 μm thick foil. Measurements of the modulation optical density performed by x-ray radiography show that a bubble-merger regime for the Rayleigh-Taylor instability at an ablation frontmore » is achieved for the first time in indirect drive. Finally, the mutimode modulation amplitudes are in the nonlinear regime, grow beyond the Haan multimode saturation level, evolve toward the longer wavelengths, and show insensitivity to the initial conditions.« less

Screech tones from free and ducted supersonic jets

NASA Technical Reports Server (NTRS)

Tam, C. K. W.; Ahuja, K. K.; Jones, R. R., III

1993-01-01

The dependence of the instability wave spectrum on azimuthal mode number, the jet to ambient gas temperature ratio, and the jet Mach number is studied. It is shown that the switch of the dominant screech mode (axisymmetric to helical/flapping) as Mach number increases is due to the switch in dominance of the corresponding mode of instability waves. Super-resonance can occur when the feedback loop is powered by the most amplified instability wave. It is suggested that the large amplitude pressure fluctuations and tone in the test cells are generated by super-resonance.

Active control of reheat buzz

NASA Astrophysics Data System (ADS)

Dowling, A. P.; Hooper, N.; Langhorne, P. J.; Bloxsidge, G. J.

1987-01-01

Reheat buzz is a low-frequency combustion instability involving the propagation of longitudinal pressure waves inside a duct in which a flame is anchored. Active control has been successfully applied to this instability. The controller alters the upstream acoustic boundary condition and thereby changes the energy balance in duct. Control is found to reduce the peak in the pressure spectrum due to the combustion instability by 20 dB. The acoustic energy in the whole 0-800-Hz bandwidth is reduced to about 10 percent of its uncontrolled value. A comparison with numerical calculations is presented.

Instabilities and turbulence in highly ionized plasmas in a magnetic field

NASA Technical Reports Server (NTRS)

Jennings, W. C.

1972-01-01

Physical mechanisms were considered which are responsible for plasma turbulence and the establishment of necessary conditions for energy exchange and transfer in the frequency spectrum. In addition, work was performed to better understand the drift instability in the highly inhomogeneous Rensselaer arc, and methods to suppress this instability using feedback stabilization techniques. Correlation techniques were refined to study plasma turbulence, the diffusion wave technique for monitoring cross-field diffusion was extended to include regimes of high turbulence levels, and a technique for coupling stabilizing RF power to the Rensselaer arc was developed.

Active control: an investigation method for combustion instabilities

NASA Astrophysics Data System (ADS)

Poinsot, T.; Yip, B.; Veynante, D.; Trouvé, A.; Samaniego, J. M.; Candel, S.

1992-07-01

Closed-loop active control methods and their application to combustion instabilities are discussed. In these methods the instability development is impeded with a feedback control loop: the signal provided by a sensor monitoring the flame or pressure oscillations is processed and sent back to actuators mounted on the combustor or on the feeding system. Different active control systems tested on a non-premixed multiple-flame turbulent combustor are described. These systems can suppress all unstable plane modes of oscillation (i.e. low frequency modes). The active instability control (AIC) also constitutes an original and powerful technique for studies of mechanisms leading to instability or resulting from the instability. Two basic applications of this kind are described. In the first case the flame is initially controlled with AIC, the feedback loop is then switched off and the growth of the instability is analysed through high speed Schlieren cinematography and simultaneous sound pressure and reaction rate measurements. Three phases are identified during th growth of the oscillations: (1) a linear phase where acoustic waves induce a flapping motion of the flame sheets without interaction between sheets, (2) a modulation phase, where flame sheets interact randomly and (3) a nonlinear phase where the flame sheets are broken and a limit cycle is reached. In the second case we investigate different types of flame extinctions associated with combustion instability. It is shown that pressure oscillations may lead to partial or total extinctions. Extinctions occur in various forms but usually follow a rapid growth of pressure oscillations. The flame is extinguished during the modulation phase observed in the initiation experiments. In these studies devoted to transient instability phenomena, the control system constitutes a unique investigation tool because it is difficult to obtain the same information by other means. Implications for modelling and prediction of combustion instabilities are discussed.

Dielectric elastomer peristaltic pump module with finite deformation

NASA Astrophysics Data System (ADS)

Mao, Guoyong; Huang, Xiaoqiang; Liu, Junjie; Li, Tiefeng; Qu, Shaoxing; Yang, Wei

2015-07-01

Inspired by various peristaltic structures existing in nature, several bionic peristaltic actuators have been developed. In this study, we propose a novel dielectric elastomer peristaltic pump consisting of short tubular modules, with the saline solution as the electrodes. We investigate the performance of this soft pump module under hydraulic pressure and voltage via experiments and an analytical model based on nonlinear field theory. It is observed that the individual pump module undergoes finite deformation and may experience electromechanical instability during operations. The driving pressure and displaced volume of the peristaltic pump module can be modulated by applied voltage. The efficiency of the pump module is enhanced by alternating current voltage, which can suppress the electromechanical pull-in instability. An analytical model is developed within the framework of the nonlinear field theory, and its predictive capacity is checked by experimental observations. The effects of the prestretch, aspect ratio, and voltage on the performance of the pump modules are characterized by the analytical model. This work can guide the designs of soft active peristaltic pumps in the field of artificial organs and industrial conveying systems.

Neural basis of postural instability identified by VTC and EEG

PubMed Central

Cao, Cheng; Jaiswal, Niharika; Newell, Karl M.

2010-01-01

In this study, we investigated the neural basis of virtual time to contact (VTC) and the hypothesis that VTC provides predictive information for future postural instability. A novel approach to differentiate stable pre-falling and transition-to-instability stages within a single postural trial while a subject was performing a challenging single leg stance with eyes closed was developed. Specifically, we utilized wavelet transform and stage segmentation algorithms using VTC time series data set as an input. The VTC time series was time-locked with multichannel (n = 64) EEG signals to examine its underlying neural substrates. To identify the focal sources of neural substrates of VTC, a two-step approach was designed combining the independent component analysis (ICA) and low-resolution tomography (LORETA) of multichannel EEG. There were two major findings: (1) a significant increase of VTC minimal values (along with enhanced variability of VTC) was observed during the transition-to-instability stage with progression to ultimate loss of balance and falling; and (2) this VTC dynamics was associated with pronounced modulation of EEG predominantly within theta, alpha and gamma frequency bands. The sources of this EEG modulation were identified at the cingulate cortex (ACC) and the junction of precuneus and parietal lobe, as well as at the occipital cortex. The findings support the hypothesis that the systematic increase of minimal values of VTC concomitant with modulation of EEG signals at the frontal-central and parietal–occipital areas serve collectively to predict the future instability in posture. PMID:19655130

Time Resolved Stereo Particle Image Velocimetry Measurements of the Instabilities Downstream of a Backward-Facing Step in a Swept-Wing Boundary Layer

NASA Technical Reports Server (NTRS)

Eppink, Jenna L.; Yao, Chung-Sheng

2017-01-01

Time-resolved particle image velocimetry (TRPIV) measurements are performed down-stream of a swept backward-facing step, with a height of 49% of the boundary-layer thickness. The results agree well qualitatively with previously reported hotwire measurements, though the amplitudes of the fluctuating components measured using TRPIV are higher. Nonetheless, the low-amplitude instabilities in the flow are fairly well resolved using TR- PIV. Proper orthogonal decomposition is used to study the development of the traveling cross flow and Tollmien-Schlichting (TS) instabilities downstream of the step and to study how they interact to form the large velocity spikes that ultimately lead to transition. A secondary mode within the traveling cross flow frequency band develops with a wavelength close to that of the stationary cross flow instability, so that at a certain point in the phase, it causes an increase in the spanwise modulation initially caused by the stationary cross flow mode. This increased modulation leads to an increase in the amplitude of the TS mode, which, itself, is highly modulated through interactions with the stationary cross flow. When the traveling cross flow and TS modes align in time and space, the large velocity spikes occur. Thus, these three instabilities, which are individually of low amplitude when the spikes start to occur (U'rms/Ue <0.03), interact and combine to cause a large flow disturbance that eventually leads to transition.

The effect of gravity modulation on thermosolutal convection

NASA Technical Reports Server (NTRS)

Saunders, Bonita V.; Murray, Bruce T.; Mcfadden, G. B.; Coriell, S. R.; Wheeler, A. A.

1992-01-01

In a gravitational field, the opposing effects of components of different diffusivities, for example, temperature and solute, in the density profile in a fluid may produce convective instabilities that exhibit a broad range of dynamical behavior. The effect of time periodic vertical gravity modulation on the onset of these instabilities in an infinite horizontal layer with stress free boundaries is examined. This work is viewed as a first step in expanding previous results in solidification to the full problem of characterizing the effects of gravity modulation in thermosolutal convection during the directional solidification of binary alloys. Calculations carried out both with and without steady background acceleration are presented, the latter results being relevant to microgravity conditions.

Modulational instability of helicon waves in a magnetoactive semiconductor n-InSb

NASA Astrophysics Data System (ADS)

Salimullah, M.; Ferdous, T.

1984-03-01

In this paper the modulational instabilithy of a beam of high amplitude helicon wave in a magnetoactive piezoelectric semiconductor is studied. The nonlinear response of electrons in the semiconductor plasma has been found by following the fluid model of homogeneous plasmas. The low frequency nonlinearity has been taken through the ponderomotive force on electrons, whereas the nonlinearity in the scattered helicon waves arises through the nonlinear current densities of electrons. For typical plasma parameters in n-type indium antimonide and for a considerable power density (approximately 20 kW/sq cm) of the incident helicon beam, the growth rate of the modulational instability is quite high (approximately 10 to the 7th rad/s).

Spectrum-modulating fiber-optic sensors for aircraft control systems

NASA Technical Reports Server (NTRS)

Beheim, Glenn; Fritsch, Klaus

1987-01-01

A family of fiber-optic sensors for aircraft engine control systems is described. Each of these sensors uses a spectrum-modulation method to obtain an output which is largely independent of the fiber link transmissivity. A position encoder is described which uses a code plate to digitally modulate the sensor output spectrum. Also described are pressure and temperature sensors, each of which uses a Fabry-Perot cavity to modulate the sensor output spectrum as a continuous function of the measurand. A technique is described whereby a collection of these sensors may be effectively combined to perform a number of the measurements which are required by an aircraft-engine control system.

Stability of Initial Autism Spectrum Disorder Diagnoses in Community Settings

ERIC Educational Resources Information Center

Daniels, Amy M.; Rosenberg, Rebecca E.; Law, J. Kiely; Lord, Catherine; Kaufmann, Walter E.; Law, Paul A.

2011-01-01

The study's objectives were to assess diagnostic stability of initial autism spectrum disorder (ASD) diagnoses in community settings and identify factors associated with diagnostic instability using data from a national Web-based autism registry. A Cox proportional hazards model was used to assess the relative risk of change in initial ASD…

Investigating the anticipatory postural adjustment phase of gait initiation in different directions in chronic ankle instability patients.

PubMed

Ebrahimabadi, Zahra; Naimi, Sedigheh Sadat; Rahimi, Abbas; Sadeghi, Heydar; Hosseini, Seyed Majid; Baghban, Alireza Akbarzadeh; Arslan, Syed Asadullah

2018-01-01

The main objective of the present study was to analyze how supra spinal motor control mechanisms are altered in different directions during anticipatory postural phase of gait initiation in chronic ankle instability patients. It seems that supra spinal pathways modulate anticipatory postural adjustment phase of gait initiation. Yet, there is a dearth of research on the effect of chronic ankle instability on the anticipatory postural adjustment phase of gait initiation in different directions. A total of 20 chronic ankle instability participants and 20 healthy individuals initiated gait on a force plate in forward, 30° lateral, and 30° medial directions. According to the results of the present study, the peak lateral center of pressure shift decreased in forward direction compared to that in other directions in both groups. Also, it was found that the peak lateral center of pressure shift and the vertical center of mass velocity decreased significantly in chronic ankle instability patients, as compared with those of the healthy individuals. According to the results of the present study, it seems that chronic ankle instability patients modulate the anticipatory postural adjustment phase of gait initiation, compared with healthy control group, in order to maintain postural stability. These changes were observed in different directions, too. Copyright © 2017 Elsevier Ltd. All rights reserved.

Characterization of >100 T magnetic fields associated with relativistic Weibel instability in laser-produced plasmas

NASA Astrophysics Data System (ADS)

Mishra, Rohini; Ruyer, Charles; Goede, Sebastian; Roedel, Christian; Gauthier, Maxence; Zeil, Karl; Schramm, Ulrich; Glenzer, Siegfried; Fiuza, Frederico

2016-10-01

Weibel-type instabilities can occur in weakly magnetized and anisotropic plasmas of relevance to a wide range of astrophysical and laboratory scenarios. It leads to the conversion of a significant fraction of the kinetic energy of the plasma into magnetic energy. We will present a detailed numerical study, using 2D and 3D PIC simulations of the Weibel instability in relativistic laser-solid interactions. In this case, the instability develops due to the counter-streaming of laser-heated electrons and the background return current. We show that the growth rate of the instability is maximized near the critical density region on the rear side of the expanded plasma, producing up to 400 MG magnetic fields for Hydrogen plasmas. We have found that this strong field can be directly probed by energetic protons accelerated in rear side of the plasma by Target Normal Sheath Acceleration (TNSA). This allows the experimental characterization of the instability from the analysis of the spatial modulation of the detected protons. Our numerical results are compared with recent laser experiments with Hydrogen jets and show good agreement with the proton modulations observed experimentally. This work was supported by the DOE Office of Science, Fusion Energy Science (FWP 100182).

Gain modulation of the middle latency cutaneous reflex in patients with chronic joint instability after ankle sprain.

PubMed

Futatsubashi, Genki; Sasada, Shusaku; Tazoe, Toshiki; Komiyama, Tomoyoshi

2013-07-01

To investigate the neural alteration of reflex pathways arising from cutaneous afferents in patients with chronic ankle instability. Cutaneous reflexes were elicited by applying non-noxious electrical stimulation to the sural nerve of subjects with chronic ankle instability (n=17) and control subjects (n=17) while sitting. Electromyographic (EMG) signals were recorded from each ankle and thigh muscle. The middle latency response (MLR; latency: 70-120 ms) component was analyzed. In the peroneus longus (PL) and vastus lateralis (VL) muscles, linear regression analyses between the magnitude of the inhibitory MLR and background EMG activity showed that, compared to the uninjured side and the control subjects, the gain of the suppressive MLR was increased in the injured side. This was also confirmed by the pooled data for both groups. The degree of MLR alteration was significantly correlated to that of chronic ankle instability in the PL. The excitability of middle latency cutaneous reflexes in the PL and VL is modulated in subjects with chronic ankle instability. Cutaneous reflexes may be potential tools to investigate the pathological state of the neural system that controls the lower limbs in subjects with chronic ankle instability. Copyright © 2013 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

Characterization of complexities in combustion instability in a lean premixed gas-turbine model combustor.

PubMed

Gotoda, Hiroshi; Amano, Masahito; Miyano, Takaya; Ikawa, Takuya; Maki, Koshiro; Tachibana, Shigeru

2012-12-01

We characterize complexities in combustion instability in a lean premixed gas-turbine model combustor by nonlinear time series analysis to evaluate permutation entropy, fractal dimensions, and short-term predictability. The dynamic behavior in combustion instability near lean blowout exhibits a self-affine structure and is ascribed to fractional Brownian motion. It undergoes chaos by the onset of combustion oscillations with slow amplitude modulation. Our results indicate that nonlinear time series analysis is capable of characterizing complexities in combustion instability close to lean blowout.

Frequency Management Engineering Principles--Spectrum Measurements (Reference Order 6050.23).

DTIC Science & Technology

1982-08-01

Interference 22 (a) Dielectric Heater Example 22 (b) High Power FM Interference Examle 22 (c) Radar Interference Example 22 (d) ARSR Interference Example...Localizer 23 (i) Dielectric Heaters 23 (j) High Power TV/FM 23 (k) Power Line Noise 23 (1) Incidental Radiating Devices 23 (m) Super-regenerative...employing broad band power amplifiers or and random spectrum analyzer instabilities traveling wave tubes. The "cleanest" spectrums create drift problems

Detrimental Effect Elimination of Laser Frequency Instability in Brillouin Optical Time Domain Reflectometer by Using Self-Heterodyne Detection

PubMed Central

Li, Yongqian; Li, Xiaojuan; An, Qi; Zhang, Lixin

2017-01-01

A useful method for eliminating the detrimental effect of laser frequency instability on Brillouin signals by employing the self-heterodyne detection of Rayleigh and Brillouin scattering is presented. From the analysis of Brillouin scattering spectra from fibers with different lengths measured by heterodyne detection, the maximum usable pulse width immune to laser frequency instability is obtained to be about 4 µs in a self-heterodyne detection Brillouin optical time domain reflectometer (BOTDR) system using a broad-band laser with low frequency stability. Applying the self-heterodyne detection of Rayleigh and Brillouin scattering in BOTDR system, we successfully demonstrate that the detrimental effect of laser frequency instability on Brillouin signals can be eliminated effectively. Employing the broad-band laser modulated by a 130-ns wide pulse driven electro-optic modulator, the observed maximum errors in temperatures measured by the local heterodyne and self-heterodyne detection BOTDR systems are 7.9 °C and 1.2 °C, respectively. PMID:28335508

Generation of Langmuir wave supercontinuum by phase-preserving equilibration of plasmons with irreversible wave-particle interaction

NASA Astrophysics Data System (ADS)

Eiichirou, Kawamori

2018-04-01

We report the observation of supercontinuum of Langmuir plasma waves, that exhibits broad power spectrum having significant spatio-temporal coherence grown from a monochromatic seed-wave, in one-dimensional particle-in-cell simulations. The Langmuir wave supercontinuum (LWSC) is formed when the seed wave excites side-band fields efficiently by the modulational instabilities. Its identification is achieved by the use of the tricoherence analysis, which detects four wave mixings (FWMs) of plasmons (plasma wave quanta), and evaluation of the first order coherence, which is a measure of temporal coherence, of the wave electric fields. The irreversible evolution to the coherent LWSC from the seed wave is realized by the wave-particle interactions causing stochastic electron motions in the phase space and the coherence of LWSC is maintained by the phase-preserving FWMs of plasmons. The LWSC corresponds to a quasi Bernstein-Greene-Kruskal mode.

Climate Change, Instability and a Full Spectrum Approach to Conflict Prevention in Africa

DTIC Science & Technology

2009-10-23

commander to follow. 15. SUBJECT TERMS Climate Change, Global Warming , Security Cooperation, Stability, Instability, Stabilization, Security...note that global warming could also create similar impacts on resources.19 In modern times disputes over natural resources have erupted into conflict...16. Center for Naval Analysis, National Security and the Threat of Climate Change, 18. 17. Michael T. Klare, ― Global Warming Battlefields: How

Finite amplitude instability of second-order fluids in plane Poiseuille flow.

NASA Technical Reports Server (NTRS)

Mcintire, L. V.; Lin, C. H.

1972-01-01

The hydrodynamic stability of plane Poiseuille flow of second-order fluids to finite amplitude disturbances is examined using the method of Stuart and Watson as extended by Reynolds and Potter. For slightly non-Newtonian fluids subcritical instabilities are predicted. No supercritical equilibrium states are expected if the entire spectrum of disturbance wavelengths is present. Possible implications with respect to the Toms phenomenon are discussed.

Dust ion acoustic freak waves in a plasma with two temperature electrons featuring Tsallis distribution

NASA Astrophysics Data System (ADS)

Chahal, Balwinder Singh; Singh, Manpreet; Shalini; Saini, N. S.

2018-02-01

We present an investigation for the nonlinear dust ion acoustic wave modulation in a plasma composed of charged dust grains, two temperature (cold and hot) nonextensive electrons and ions. For this purpose, the multiscale reductive perturbation technique is used to obtain a nonlinear Schrödinger equation. The critical wave number, which indicates where the modulational instability sets in, has been determined precisely for various regimes. The influence of plasma background nonextensivity on the growth rate of modulational instability is discussed. The modulated wavepackets in the form of either bright or dark type envelope solitons may exist. Formation of rogue waves from bright envelope solitons is also discussed. The investigation indicates that the structural characteristics of these envelope excitations (width, amplitude) are significantly affected by nonextensivity, dust concentration, cold electron-ion density ratio and temperature ratio.

Mechanisms of femtosecond LIPSS formation induced by periodic surface temperature modulation

NASA Astrophysics Data System (ADS)

Gurevich, Evgeny L.

2016-06-01

Here we analyze the formation of laser-induced periodic surface structures (LIPSS) on metal surfaces upon single femtosecond laser pulses. Most of the existing models of the femtosecond LIPSS formation discuss only the appearance of a periodic modulation of the electron and ion temperatures. However the mechanism how the inhomogeneous surface temperature distribution induces the periodically-modulated surface profile under the conditions corresponding to ultrashort-pulse laser ablation is still not clear. Estimations made on the basis of different hydrodynamic instabilities allow to sort out mechanisms, which can bridge the gap between the temperature modulation and the LIPSS. The proposed theory shows that the periodic structures can be generated by single ultrashort laser pulses due to ablative instabilities. The Marangoni and Rayleigh-Bénard convection on the contrary cannot cause the LIPSS formation.

When linear stability does not exclude nonlinear instability

DOE PAGES

Kevrekidis, P. G.; Pelinovsky, D. E.; Saxena, A.

2015-05-29

We describe a mechanism that results in the nonlinear instability of stationary states even in the case where the stationary states are linearly stable. In this study, this instability is due to the nonlinearity-induced coupling of the linearization’s internal modes of negative energy with the continuous spectrum. In a broad class of nonlinear Schrödinger equations considered, the presence of such internal modes guarantees the nonlinear instability of the stationary states in the evolution dynamics. To corroborate this idea, we explore three prototypical case examples: (a) an antisymmetric soliton in a double-well potential, (b) a twisted localized mode in a one-dimensionalmore » lattice with cubic nonlinearity, and (c) a discrete vortex in a two-dimensional saturable lattice. In all cases, we observe a weak nonlinear instability, despite the linear stability of the respective states.« less

Modified jeans instability for dust grains in a plasma.

PubMed

Delzanno, G L; Lapenta, G

2005-05-06

An investigation of the properties of linear stability is conducted for a system consisting of particles having mass m and charge q, interacting through the gravitational and electrostatic force (Jeans instability). However, in light of recent works showing that dust particles in a plasma can have a Lennard-Jones-like shielding potential, a new set of equations has been derived, where the electrostatic interaction among the dust particles is Lennard-Jones-like instead of Coulomb-like. A new condition for the gravitational instability is derived, showing a broader spectrum of unstable modes with faster growth rates.

Many-body instabilities and mass generation in slow Dirac materials

NASA Astrophysics Data System (ADS)

Triola, Christopher; Zhu, Jianxin; Migliori, Albert; Balatsky, Alexander

2015-03-01

Some Kondo insulators are expected to possess topologically protected surface states with linear Dirac spectrum, the topological Kondo insulators. Because the bulk states of these systems typically have heavy effective electron masses, the surface states may exhibit extraordinarily small Fermi velocities that could force the effective fine structure constant of the surface states into the strong coupling regime. Using a tight-binding model we study the many-body instabilities of these systems and identify regions of parameter space for which antiferromagnetic, ferromagnetic and charge density wave instabilities occur. Work Supported by USDOE BES E304.

Holographic lens spectrum splitting photovoltaic system for increased diffuse collection and annual energy yield

NASA Astrophysics Data System (ADS)

Vorndran, Shelby D.; Wu, Yuechen; Ayala, Silvana; Kostuk, Raymond K.

2015-09-01

Concentrating and spectrum splitting photovoltaic (PV) modules have a limited acceptance angle and thus suffer from optical loss under off-axis illumination. This loss manifests itself as a substantial reduction in energy yield in locations where a significant portion of insulation is diffuse. In this work, a spectrum splitting PV system is designed to efficiently collect and convert light in a range of illumination conditions. The system uses a holographic lens to concentrate shortwavelength light onto a smaller, more expensive indium gallium phosphide (InGaP) PV cell. The high efficiency PV cell near the axis is surrounded with silicon (Si), a less expensive material that collects a broader portion of the solar spectrum. Under direct illumination, the device achieves increased conversion efficiency from spectrum splitting. Under diffuse illumination, the device collects light with efficiency comparable to a flat-panel Si module. Design of the holographic lens is discussed. Optical efficiency and power output of the module under a range of illumination conditions from direct to diffuse are simulated with non-sequential raytracing software. Using direct and diffuse Typical Metrological Year (TMY3) irradiance measurements, annual energy yield of the module is calculated for several installation sites. Energy yield of the spectrum splitting module is compared to that of a full flat-panel Si reference module.

Collective Beam Instabilities in the Taiwan Light Source

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

Chao, Alex W.

2002-08-12

The storage ring at Taiwan Light Source has experienced a strong collective instability since 1994. Various cures have been attempted to suppress this instability, including the use of damping antenna, tunable rf plungers, different filling patterns, and rf gap voltage modulation. So far these cures have improved the beam intensity, but the operation remains to be limited by the instability. The dominant phenomenon is the longitudinal coupled bunch instability. The major source of longitudinal impedance is from rf cavities of Doris type. The high-order modes of the cavity were numerically analyzed using a 3-D code GdfidL. The correlation of themore » observed phenomenon in user operation with high-order modes of rf cavities will be presented. Results of various attempts to suppress beam instabilities will be summarized. Proposed cures for beam instabilities will be discussed.« less

Nonlinear Stage of Modulation Instability for a Fifth-Order Nonlinear Schrödinger Equation

NASA Astrophysics Data System (ADS)

Jia, Hui-Xian; Shan, Dong-Ming

2017-10-01

In this article, a fifth-order nonlinear Schrödinger equation, which can be used to characterise the solitons in the optical fibre and inhomogeneous Heisenberg ferromagnetic spin system, has been investigated. Akhmediev breather, Kuzentsov soliton, and generalised soliton have all been attained via the Darbox transformation. Propagation and interaction for three-type breathers have been studied: the types of breather are determined by the module and complex angle of parameter ξ; interaction between Akhmediev breather and generalised soliton displays a phase shift, whereas the others do not. Modulation instability of the generalised solitons have been analysed: a small perturbation can develop into a rogue wave, which is consistent with the results of rogue wave solutions.

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.

The superradiant instability regime of the spinning Kerr black hole

NASA Astrophysics Data System (ADS)

Hod, Shahar

2016-07-01

Spinning Kerr black holes are known to be superradiantly unstable to massive scalar perturbations. We here prove that the instability regime of the composed Kerr-black-hole-massive-scalar-field system is bounded from above by the dimensionless inequality Mμ < m ṡ√{2(1 + γ) (1 -√ 1 -γ2) / -γ2 4γ2, where { μ , m } are respectively the proper mass and azimuthal harmonic index of the scalar field and γ ≡r- /r+ is the dimensionless ratio between the horizon radii of the black hole. It is further shown that this analytically derived upper bound on the superradiant instability regime of the spinning Kerr black hole agrees with recent numerical computations of the instability resonance spectrum.

Parallel proton fire hose instability in the expanding solar wind: Hybrid simulations

NASA Astrophysics Data System (ADS)

Matteini, Lorenzo; Landi, Simone; Hellinger, Petr; Velli, Marco

2006-10-01

We report a study of the properties of the parallel proton fire hose instability comparing the results obtained by the linear analysis, from one-dimensional (1-D) standard hybrid simulations and 1-D hybrid expanding box simulations. The three different approaches converge toward the same instability threshold condition which is in good agreement with in situ observations, suggesting that such instability is relevant in the solar wind context. We investigate also the effect of the wave-particle interactions on shaping the proton distribution function and on the evolution of the spectrum of the magnetic fluctuations during the expansion. We find that the resonant interaction can provide the proton distribution function to depart from the bi-Maxwellian form.

2D instabilities of surface gravity waves on a linear shear current

NASA Astrophysics Data System (ADS)

Francius, Marc; Kharif, Christian

2016-04-01

Periodic 2D surface water waves propagating steadily on a rotational current have been studied by many authors (see [1] and references therein). Although the recent important theoretical developments have confirmed that periodic waves can exist over flows with arbitrary vorticity, their stability and their nonlinear evolution have not been much studied extensively so far. In fact, even in the rather simple case of uniform vorticity (linear shear), few papers have been published on the effect of a vertical shear current on the side-band instability of a uniform wave train over finite depth. In most of these studies [2-5], asymptotic expansions and multiple scales method have been used to obtain envelope evolution equations, which allow eventually to formulate a condition of (linear) instability to long modulational perturbations. It is noted here that this instability is often referred in the literature as the Benjamin-Feir or modulational instability. In the present study, we consider the linear stability of finite amplitude two-dimensional, periodic water waves propagating steadily on the free surface of a fluid with constant vorticity and finite depth. First, the steadily propagating surface waves are computed with steepness up to very close to the highest, using a Fourier series expansions and a collocation method, which constitutes a simple extension of Fenton's method [6] to the cases with a linear shear current. Then, the linear stability of these permanent waves to infinitesimal 2D perturbations is developed from the fully nonlinear equations in the framework of normal modes analysis. This linear stability analysis is an extension of [7] to the case of waves in the presence of a linear shear current and permits the determination of the dominant instability as a function of depth and vorticity for a given steepness. The numerical results are used to assess the accuracy of the vor-NLS equation derived in [5] for the characteristics of modulational instabilities due to resonant four-wave interactions, as well as to study the influence of vorticity and nonlinearity on the characteristics of linear instabilities due to resonant five-wave and six-wave interactions. Depending on the dimensionless depth, superharmonic instabilities due to five-wave interactions can become dominant with increasing positive vorticiy. Acknowledgments: This work was supported by the Direction Générale de l'Armement and funded by the ANR project n°. ANR-13-ASTR-0007. References [1] A. Constantin, Two-dimensionality of gravity water flows of constant non-zero vorticity beneath a surface wave train, Eur. J. Mech. B/Fluids, 2011, 30, 12-16. [2] R. S. Johnson, On the modulation of water waves on shear flows, Proc. Royal Soc. Lond. A., 1976, 347, 537-546. [3] M. Oikawa, K. Chow, D. J. Benney, The propagation of nonlinear wave packets in a shear flow with a free surface, Stud. Appl. Math., 1987, 76, 69-92. [4] A. I Baumstein, Modulation of gravity waves with shear in water, Stud. Appl. Math., 1998, 100, 365-90. [5] R. Thomas, C. Kharif, M. Manna, A nonlinear Schrödinger equation for water waves on finite depth with constant vorticity, Phys. Fluids, 2012, 24, 127102. [6] M. M Rienecker, J. D Fenton, A Fourier approximation method for steady water waves , J. Fluid Mech., 1981, 104, 119-137 [7] M. Francius, C. Kharif, Three-dimensional instabilities of periodic gravity waves in shallow water, J. Fluid Mech., 2006, 561, 417-437

Machining of Two-Dimensional Sinusoidal Defects on Ignition-Type Capsules to Study Hydrodynamic Instability at the National Ignition Facility

DOE PAGES

Giraldez, E. M.; Hoppe Jr., M. L.; Hoover, D. E.; ...

2016-07-07

Hydrodynamic instability growth and its effects on capsule implosion performance are being studied at the National Ignition Facility (NIF). Experimental results have shown that low-mode instabilities are the primary culprit for yield degradation. Ignition type capsules with machined 2D sinusoidal defects were used to measure low-mode hydrodynamic instability growth in the acceleration phase of the capsule implosion. The capsules were imploded using ignition-relevant laser pulses and the ablation-front modulation growth was measured using x-ray radiography. The experimentally measured growth was in good agreement with simulations.

Rogue wave modes for a derivative nonlinear Schrödinger model.

PubMed

Chan, Hiu Ning; Chow, Kwok Wing; Kedziora, David Jacob; Grimshaw, Roger Hamilton James; Ding, Edwin

2014-03-01

Rogue waves in fluid dynamics and optical waveguides are unexpectedly large displacements from a background state, and occur in the nonlinear Schrödinger equation with positive linear dispersion in the regime of positive cubic nonlinearity. Rogue waves of a derivative nonlinear Schrödinger equation are calculated in this work as a long-wave limit of a breather (a pulsating mode), and can occur in the regime of negative cubic nonlinearity if a sufficiently strong self-steepening nonlinearity is also present. This critical magnitude is shown to be precisely the threshold for the onset of modulation instabilities of the background plane wave, providing a strong piece of evidence regarding the connection between a rogue wave and modulation instability. The maximum amplitude of the rogue wave is three times that of the background plane wave, a result identical to that of the Peregrine breather in the classical nonlinear Schrödinger equation model. This amplification ratio and the resulting spectral broadening arising from modulation instability correlate with recent experimental results of water waves. Numerical simulations in the regime of marginal stability are described.

Influence of two-stream relativistic electron beam parameters on the space-charge wave with broad frequency spectrum formation

NASA Astrophysics Data System (ADS)

Alexander, LYSENKO; Iurii, VOLK

2018-03-01

We developed a cubic non-linear theory describing the dynamics of the multiharmonic space-charge wave (SCW), with harmonics frequencies smaller than the two-stream instability critical frequency, with different relativistic electron beam (REB) parameters. The self-consistent differential equation system for multiharmonic SCW harmonic amplitudes was elaborated in a cubic non-linear approximation. This system considers plural three-wave parametric resonant interactions between wave harmonics and the two-stream instability effect. Different REB parameters such as the input angle with respect to focusing magnetic field, the average relativistic factor value, difference of partial relativistic factors, and plasma frequency of partial beams were investigated regarding their influence on the frequency spectrum width and multiharmonic SCW saturation levels. We suggested ways in which the multiharmonic SCW frequency spectrum widths could be increased in order to use them in multiharmonic two-stream superheterodyne free-electron lasers, with the main purpose of forming a powerful multiharmonic electromagnetic wave.

Fluctuations and correlations in modulation instability

NASA Astrophysics Data System (ADS)

Solli, D. R.; Herink, G.; Jalali, B.; Ropers, C.

2012-07-01

Stochastically driven nonlinear processes are responsible for spontaneous pattern formation and instabilities in numerous natural and artificial systems, including well-known examples such as sand ripples, cloud formations, water waves, animal pigmentation and heart rhythms. Technologically, a type of such self-amplification drives free-electron lasers and optical supercontinuum sources whose radiation qualities, however, suffer from the stochastic origins. Through time-resolved observations, we identify intrinsic properties of these fluctuations that are hidden in ensemble measurements. We acquire single-shot spectra of modulation instability produced by laser pulses in glass fibre at megahertz real-time capture rates. The temporally confined nature of the gain physically limits the number of amplified modes, which form an antibunched arrangement as identified from a statistical analysis of the data. These dynamics provide an example of pattern competition and interaction in confined nonlinear systems.

Fingering instabilities and pattern formation in a two-component dipolar Bose-Einstein condensate

NASA Astrophysics Data System (ADS)

Xi, Kui-Tian; Byrnes, Tim; Saito, Hiroki

2018-02-01

We study fingering instabilities and pattern formation at the interface of an oppositely polarized two-component Bose-Einstein condensate with strong dipole-dipole interactions in three dimensions. It is shown that the rotational symmetry is spontaneously broken by fingering instability when the dipole-dipole interactions are strengthened. Frog-shaped and mushroom-shaped patterns emerge during the dynamics due to the dipolar interactions. We also demonstrate the spontaneous density modulation and domain growth of a two-component dipolar BEC in the dynamics. Bogoliubov analyses in the two-dimensional approximation are performed, and the characteristic lengths of the domains are estimated analytically. Patterns resembling those in magnetic classical fluids are modulated when the number ratio of atoms, the trap ratio of the external potential, or tilted polarization with respect to the z direction is varied.

Controlled generation of high-intensity optical rogue waves by induced modulation instability

PubMed Central

Zhao, Saili; Yang, Hua; Chen, Nengsong; Zhao, Chujun

2017-01-01

Optical rogue waves are featured as the generation of high amplitude events at low probability in optical systems. Moreover, the formation of optical rogue waves is unpredictable and transient in photonic crystal fibers. In this paper, we put forward a method to generate high-intensity optical rogue waves in a more controlled way based on induced modulation instability, which can suppress the noise effect and hence play a leading role in the process of pulse evolution. Our numerical simulations indicate that the generation of rogue wave can be controlled when seeding at the optimal modulation frequency and the intensity of rogue wave can be enhanced with appropriate modulation depth. Further, high-intensity rogue wave can also be ejected in the fiber with a shorter propagation length by regulating the modulation depth. These results all provide a better understanding of optical rogue wave, which can contribute to the generation of tunable long-wavelength spectral components and selective excitation of mid-infrared supercontinuum. PMID:28051149

Controlled generation of high-intensity optical rogue waves by induced modulation instability.

PubMed

Zhao, Saili; Yang, Hua; Chen, Nengsong; Zhao, Chujun

2017-01-04

Optical rogue waves are featured as the generation of high amplitude events at low probability in optical systems. Moreover, the formation of optical rogue waves is unpredictable and transient in photonic crystal fibers. In this paper, we put forward a method to generate high-intensity optical rogue waves in a more controlled way based on induced modulation instability, which can suppress the noise effect and hence play a leading role in the process of pulse evolution. Our numerical simulations indicate that the generation of rogue wave can be controlled when seeding at the optimal modulation frequency and the intensity of rogue wave can be enhanced with appropriate modulation depth. Further, high-intensity rogue wave can also be ejected in the fiber with a shorter propagation length by regulating the modulation depth. These results all provide a better understanding of optical rogue wave, which can contribute to the generation of tunable long-wavelength spectral components and selective excitation of mid-infrared supercontinuum.

Modulation instability and dissipative rogue waves in ion-beam plasma: Roles of ionization, recombination, and electron attachment

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

Guo, Shimin, E-mail: gsm861@126.com; Mei, Liquan, E-mail: lqmei@mail.xjtu.edu.cn

The amplitude modulation of ion-acoustic waves is investigated in an unmagnetized plasma containing positive ions, negative ions, and electrons obeying a kappa-type distribution that is penetrated by a positive ion beam. By considering dissipative mechanisms, including ionization, negative-positive ion recombination, and electron attachment, we introduce a comprehensive model for the plasma with the effects of sources and sinks. Via reductive perturbation theory, the modified nonlinear Schrödinger equation with a dissipative term is derived to govern the dynamics of the modulated waves. The effect of the plasma parameters on the modulation instability criterion for the modified nonlinear Schrödinger equation is numericallymore » investigated in detail. Within the unstable region, first- and second-order dissipative ion-acoustic rogue waves are present. The effect of the plasma parameters on the characteristics of the dissipative rogue waves is also discussed.« less

Parametric instability, inverse cascade and the range of solar-wind turbulence

NASA Astrophysics Data System (ADS)

Chandran, Benjamin D. G.

2018-02-01

In this paper, weak-turbulence theory is used to investigate the nonlinear evolution of the parametric instability in three-dimensional low- plasmas at wavelengths much greater than the ion inertial length under the assumption that slow magnetosonic waves are strongly damped. It is shown analytically that the parametric instability leads to an inverse cascade of Alfvén wave quanta, and several exact solutions to the wave kinetic equations are presented. The main results of the paper concern the parametric decay of Alfvén waves that initially satisfy +\\gg e-$ , where +$ and -$ are the frequency ( ) spectra of Alfvén waves propagating in opposite directions along the magnetic field lines. If +$ initially has a peak frequency 0$ (at which +$ is maximized) and an `infrared' scaling p$ at smaller with , then +$ acquires an -1$ scaling throughout a range of frequencies that spreads out in both directions from 0$ . At the same time, -$ acquires an -2$ scaling within this same frequency range. If the plasma parameters and infrared +$ spectrum are chosen to match conditions in the fast solar wind at a heliocentric distance of 0.3 astronomical units (AU), then the nonlinear evolution of the parametric instability leads to an +$ spectrum that matches fast-wind measurements from the Helios spacecraft at 0.3 AU, including the observed -1$ scaling at -4~\\text{Hz}$ . The results of this paper suggest that the -1$ spectrum seen by Helios in the fast solar wind at -4~\\text{Hz}$ is produced in situ by parametric decay and that the -1$ range of +$ extends over an increasingly narrow range of frequencies as decreases below 0.3 AU. This prediction will be tested by measurements from the Parker Solar Probe.

Rossby and drift wave turbulence and zonal flows: The Charney-Hasegawa-Mima model and its extensions

NASA Astrophysics Data System (ADS)

Connaughton, Colm; Nazarenko, Sergey; Quinn, Brenda

2015-12-01

A detailed study of the Charney-Hasegawa-Mima model and its extensions is presented. These simple nonlinear partial differential equations suggested for both Rossby waves in the atmosphere and drift waves in a magnetically-confined plasma, exhibit some remarkable and nontrivial properties, which in their qualitative form, survive in more realistic and complicated models. As such, they form a conceptual basis for understanding the turbulence and zonal flow dynamics in real plasma and geophysical systems. Two idealised scenarios of generation of zonal flows by small-scale turbulence are explored: a modulational instability and turbulent cascades. A detailed study of the generation of zonal flows by the modulational instability reveals that the dynamics of this zonal flow generation mechanism differ widely depending on the initial degree of nonlinearity. The jets in the strongly nonlinear case further roll up into vortex streets and saturate, while for the weaker nonlinearities, the growth of the unstable mode reverses and the system oscillates between a dominant jet, which is slightly inclined to the zonal direction, and a dominant primary wave. A numerical proof is provided for the extra invariant in Rossby and drift wave turbulence-zonostrophy. While the theoretical derivations of this invariant stem from the wave kinetic equation which assumes weak wave amplitudes, it is shown to be relatively well-conserved for higher nonlinearities also. Together with the energy and enstrophy, these three invariants cascade into anisotropic sectors in the k-space as predicted by the Fjørtoft argument. The cascades are characterised by the zonostrophy pushing the energy to the zonal scales. A small scale instability forcing applied to the model has demonstrated the well-known drift wave-zonal flow feedback loop. The drift wave turbulence is generated from this primary instability. The zonal flows are then excited by either one of the generation mechanisms, extracting energy from the drift waves as they grow. Eventually the turbulence is completely suppressed and the zonal flows saturate. The turbulence spectrum is shown to diffuse in a manner which has been mathematically predicted. The insights gained from this simple model could provide a basis for equivalent studies in more sophisticated plasma and geophysical fluid dynamics models in an effort to fully understand the zonal flow generation, the turbulent transport suppression and the zonal flow saturation processes in both the plasma and geophysical contexts as well as other wave and turbulence systems where order evolves from chaos.

Evidence for Langmuir Envelope Solitons in Solar Type III Burst Source Regions

NASA Technical Reports Server (NTRS)

Thejappa, G.; Goldstein, M. L.; MacDowall, R. J.; Papadopoulos, K.; Stone, R. G.

1998-01-01

We present observational evidence for the generation of Langmuir envelope solitons in the source regions of solar type III radio bursts. The solitons appear to be formed by electron beams which excite either the modulational instability or oscillating two-stream instability (OTSI). Millisecond data from the Ulysses Unified Radio and Plasma Wave Experiment (URAP) show that Langmuir waves associated with type III bursts occur as broad intense peaks with time scales ranging from 15 to 90 milliseconds (6 - 27 km). These broad field structures have the properties expected of Langmuir envelope solitons, viz.: the normalized peak energy densities, W(sub L)/n(sub e)T(sub e) approximately 10(exp -5), are well above the modulational instability threshold; the spatial scales, L, which range from 1 - 5 Langmuir wavelengths, show a high degree of inverse correlation with (W(sub L)/n(sub e)T(sub e))(sup 1/2); and the observed widths of these broad peaks agree well with the predicted widths of envelope solitons. We show that the orientation of the Langmuir field structures is random with respect to the ambient magnetic field, indicating that they are probably isotropic structures that have evolved from initially pancake-like solitons. These observations suggest that strong turbulence processes, such as the modulational instability or the OTSI, stabilize the electron beams that produce type III bursts.

Modulation of Excitability in the Temporoparietal Junction Relieves Virtual Reality Sickness.

PubMed

Takeuchi, Naoyuki; Mori, Takayuki; Suzukamo, Yoshimi; Izumi, Shin-Ichi

2018-06-01

Virtual reality (VR) immersion often provokes subjective discomfort and postural instability, so called VR sickness. The neural mechanism of VR sickness is speculated to be related to visual-vestibular information mismatch and/or postural instability. However, the approaches proposed to relieve VR sickness through modulation of brain activity are poorly understood. Using transcranial direct current stimulation (tDCS), we aimed to investigate whether VR sickness could be relieved by the modulation of cortical excitability in the temporoparietal junction (TPJ), which is known to be involved in processing of both vestibular and visual information. Twenty healthy subjects received tDCS over right TPJ before VR immersion. The order of the three types of tDCS (anodal, cathodal, and sham) was counterbalanced across subjects. We evaluated the subjective symptoms, heart rate, and center of pressure at baseline, after tDCS, and after VR immersion. VR immersion using head-mounted displays provoked subjective discomfort and postural instability. However, anodal tDCS over right TPJ ameliorated subjective disorientation symptoms and postural instability induced by VR immersion compared with sham condition. The amelioration of VR sickness by anodal tDCS over the right TPJ might result from relief of the sensory conflict and/or facilitation of vestibular function. Our result not only has potential clinical implications for the neuromodulation approach of VR sickness but also implies a causal role of the TPJ in VR sickness.

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, this scheme would be implemented by the adaptive sliding phaser averaged control (ASPAC) algorithm, which requires very little detailed knowledge of the combustor dynamics. In the ASPAC algorithm, the power of the instability signal would be calculated from the wide-bandpass- filtered combustion-pressure signal and averaged over a period of time (typically of the order of a few hundredths of a second) corresponding to the controller updating cycle [not to be confused with the controller sampling cycle, which would be much shorter (typically of the order of 10(exp -4) second)].

Vector rogue waves and baseband modulation instability in the defocusing regime.

PubMed

Baronio, Fabio; Conforti, Matteo; Degasperis, Antonio; Lombardo, Sara; Onorato, Miguel; Wabnitz, Stefan

2014-07-18

We report and discuss analytical solutions of the vector nonlinear Schrödinger equation that describe rogue waves in the defocusing regime. This family of solutions includes bright-dark and dark-dark rogue waves. The link between modulational instability (MI) and rogue waves is displayed by showing that only a peculiar kind of MI, namely baseband MI, can sustain rogue-wave formation. The existence of vector rogue waves in the defocusing regime is expected to be a crucial progress in explaining extreme waves in a variety of physical scenarios described by multicomponent systems, from oceanography to optics and plasma physics.

Nonlinear mechanism for the generation of electromagnetic fields in a magnetized plasma by the beatings of waves

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

Aburjania, G. D.; Machabeli, G. Z.; Kharshiladze, O. A.

2006-07-15

The modulational instability in a plasma in a strong constant external magnetic field is considered. The plasmon condensate is modulated not by conventional low-frequency ion sound but by the beatings of two high-frequency transverse electromagnetic waves propagating along the magnetic field. The instability reduces the spatial scales of Langmuir turbulence along the external magnetic field and generates electromagnetic fields. It is shown that, for a pump wave with a sufficiently large amplitude, the effect described in the present paper can be a dominant nonlinear process.

Energy dynamics in a simulation of LAPD turbulence

NASA Astrophysics Data System (ADS)

Friedman, B.; Carter, T. A.; Umansky, M. V.; Schaffner, D.; Dudson, B.

2012-10-01

Energy dynamics calculations in a 3D fluid simulation of drift wave turbulence in the linear Large Plasma Device [W. Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)] illuminate processes that drive and dissipate the turbulence. These calculations reveal that a nonlinear instability dominates the injection of energy into the turbulence by overtaking the linear drift wave instability that dominates when fluctuations about the equilibrium are small. The nonlinear instability drives flute-like (k∥=0) density fluctuations using free energy from the background density gradient. Through nonlinear axial wavenumber transfer to k∥≠0 fluctuations, the nonlinear instability accesses the adiabatic response, which provides the requisite energy transfer channel from density to potential fluctuations as well as the phase shift that causes instability. The turbulence characteristics in the simulations agree remarkably well with experiment. When the nonlinear instability is artificially removed from the system through suppressing k∥=0 modes, the turbulence develops a coherent frequency spectrum which is inconsistent with experimental data. This indicates the importance of the nonlinear instability in producing experimentally consistent turbulence.

Unstable Behavior of Lasers and Other Optical Systems.

DTIC Science & Technology

1987-11-27

Isaacs, R.S. Gioggia, S.P. Adams, L.M. Narducci, L.A. Lugiato, Optical Instabilities, R.W. Boyd, M.G. Raymer , L.M. Narducci, Eds. (Cambridge...Instabilities, R.W. Boyd, M.G. Raymer , L.M. Narducci, Eds. (Cambridge University" Press, Cambridge, 1986), p. 34. "The Effect of Modulation in a Bistable System...Books "* " "OPTICAL INSTABILITIES", edited by R.W. Boyd, M.G. Raymer , and L.M. Narducci, Cambridge University Press, Cambridge, 1986. S P.-• 58

An experimental investigation of the power spectrum of phase modulation induced on a satellite radio signal by the ionosphere

NASA Technical Reports Server (NTRS)

Moser, D. T.

1972-01-01

The power spectrum of phase modulation imposed upon satellite radio signals by the inhomogeneous F-region of the ionosphere (100 - 500 km) was studied. Tapes of the S-66 Beacon B Satellite recorded during the period 1964 - 1966 were processed to yield or record the frequency of modulation induced on the signals by ionospheric dispersion. This modulation is produced from the sweeping across the receiving station as the satellite transits of the two dimensional spatial phase pattern are produced on the ground. From this a power spectrum of structure sizes comprising the diffracting mechanism was determined using digital techniques. Fresnel oscillations were observed and analyzed along with some comments on the statistical stationarity of the shape of the power spectrum observed.

Systems Characterization of Combustor Instabilities With Controls Design Emphasis

NASA Technical Reports Server (NTRS)

Kopasakis, George

2004-01-01

This effort performed test data analysis in order to characterize the general behavior of combustor instabilities with emphasis on controls design. The analysis is performed on data obtained from two configurations of a laboratory combustor rig and from a developmental aero-engine combustor. The study has characterized several dynamic behaviors associated with combustor instabilities. These are: frequency and phase randomness, amplitude modulations, net random phase walks, random noise, exponential growth and intra-harmonic couplings. Finally, the very cause of combustor instabilities was explored and it could be attributed to a more general source-load type impedance interaction that includes the thermo-acoustic coupling. Performing these characterizations on different combustors allows for more accurate identification of the cause of these phenomena and their effect on instability.

Affective Modulation of the Startle Eyeblink and Postauricular Reflexes in Autism Spectrum Disorder

ERIC Educational Resources Information Center

Dichter, Gabriel S.; Benning, Stephen D.; Holtzclaw, Tia N.; Bodfish, James W.

2010-01-01

Eyeblink and postauricular reflexes to standardized affective images were examined in individuals without (n = 37) and with (n = 20) autism spectrum disorders (ASDs). Affective reflex modulation in control participants replicated previous findings. The ASD group, however, showed anomalous reflex modulation patterns, despite similar self-report…

Investigation of hypersonic shock-induced combustion in a hydrogen-air system

NASA Technical Reports Server (NTRS)

Ahuja, J. K.; Tiwari, S. N.; Singh, D. J.

1992-01-01

A numerical study is conducted to simulate the ballistic range experiments at Mach 5.11 and 6.46. The flow field is found to be unsteady with periodic instabilities originating in the stagnation zone. The unsteadiness of the flow field decreased with increase in the Mach number, thus indicating that it is possible to stabilize such flow fields with a high degree of overdrive. The frequency of periodic instability is determined using Fourier power spectrum and is found to be in good agreement with the experimental data. The physics of the instability is explained by the wave interaction models available in the literature.

Genome instability: Linking ageing and brain degeneration.

PubMed

Barzilai, Ari; Schumacher, Björn; Shiloh, Yosef

2017-01-01

Ageing is a multifactorial process affected by cumulative physiological changes resulting from stochastic processes combined with genetic factors, which together alter metabolic homeostasis. Genetic variation in maintenance of genome stability is emerging as an important determinant of ageing pace. Genome instability is also closely associated with a broad spectrum of conditions involving brain degeneration. Similarities and differences can be found between ageing-associated decline of brain functionality and the detrimental effect of genome instability on brain functionality and development. This review discusses these similarities and differences and highlights cell classes whose role in these processes might have been underestimated-glia and microglia. Copyright © 2016. Published by Elsevier B.V.

Control of transversal instabilities in reaction-diffusion systems

NASA Astrophysics Data System (ADS)

Totz, Sonja; Löber, Jakob; Totz, Jan Frederik; Engel, Harald

2018-05-01

In two-dimensional reaction-diffusion systems, local curvature perturbations on traveling waves are typically damped out and vanish. However, if the inhibitor diffuses much faster than the activator, transversal instabilities can arise, leading from flat to folded, spatio-temporally modulated waves and to spreading spiral turbulence. Here, we propose a scheme to induce or inhibit these instabilities via a spatio-temporal feedback loop. In a piecewise-linear version of the FitzHugh–Nagumo model, transversal instabilities and spiral turbulence in the uncontrolled system are shown to be suppressed in the presence of control, thereby stabilizing plane wave propagation. Conversely, in numerical simulations with the modified Oregonator model for the photosensitive Belousov–Zhabotinsky reaction, which does not exhibit transversal instabilities on its own, we demonstrate the feasibility of inducing transversal instabilities and study the emerging wave patterns in a well-controlled manner.

Modulation instability in high power laser amplifiers.

PubMed

Rubenchik, Alexander M; Turitsyn, Sergey K; Fedoruk, Michail P

2010-01-18

The modulation instability (MI) is one of the main factors responsible for the degradation of beam quality in high-power laser systems. The so-called B-integral restriction is commonly used as the criteria for MI control in passive optics devices. For amplifiers the adiabatic model, assuming locally the Bespalov-Talanov expression for MI growth, is commonly used to estimate the destructive impact of the instability. We present here the exact solution of MI development in amplifiers. We determine the parameters which control the effect of MI in amplifiers and calculate the MI growth rate as a function of those parameters. The safety range of operational parameters is presented. The results of the exact calculations are compared with the adiabatic model, and the range of validity of the latest is determined. We demonstrate that for practical situations the adiabatic approximation noticeably overestimates MI. The additional margin of laser system design is quantified.

Composite rogue waves and modulation instability for the three-coupled Hirota system in an optical fiber

NASA Astrophysics Data System (ADS)

Chai, Han-Peng; Tian, Bo; Chai, Jun; Du, Zhong

2017-10-01

We investigate the three-coupled Hirota system, which is applied to model the long distance communication and ultrafast signal routing systems governing the propagation of light pulses. With the aid of the Darboux dressing transformation, composite rogue wave solutions are derived. Spatial-temporal structures, including the four-petaled structure for the three-coupled Hirota system, are exhibited. We find that the four-petaled rogue waves occur in two of the three components, whereas the eye-shaped rogue wave occurs in the other one. The composite rogue waves can split up into two or three single rogue waves. The corresponding conditions for the occurrence of such phenomena are discussed and presented. We find that the relative position of every single rogue wave is influenced by the ratios of certain parameters. Besides, the linear instability analysis is performed, and our results agree with those from the baseband modulation instability theory.

Temporal Processing Instability with Millisecond Accuracy Is a Cardinal Feature of Sensorimotor Impairments in Autism Spectrum Disorder: Analysis Using the Synchronized Finger-Tapping Task

ERIC Educational Resources Information Center

Morimoto, Chie; Hida, Eisuke; Shima, Keisuke; Okamura, Hitoshi

2018-01-01

To identify a specific sensorimotor impairment feature of autism spectrum disorder (ASD), we focused on temporal processing with millisecond accuracy. A synchronized finger-tapping task was used to characterize temporal processing in individuals with ASD as compared to typically developing (TD) individuals. We found that individuals with ASD…

Modulation of the Fibularis Longus Hoffmann Reflex and Postural Instability Associated With Chronic Ankle Instability

PubMed Central

Kim, Kyung-Min; Hart, Joseph M.; Saliba, Susan A.; Hertel, Jay

2016-01-01

Context: Individuals with chronic ankle instability (CAI) present with decreased modulation of the Hoffmann reflex (H-reflex) from a simple to a more challenging task. The neural alteration is associated with impaired postural control, but the relationship has not been investigated in individuals with CAI. Objective: To determine differences in H-reflex modulation and postural control between individuals with or without CAI and to identify if they are correlated in individuals with CAI. Design: Descriptive laboratory study. Setting: Laboratory. Patients or Other Participants: A total of 15 volunteers with CAI (9 males, 6 females; age = 22.6 ± 5.8 years, height = 174.7 ± 8.1 cm, mass = 74.9 ± 12.8 kg) and 15 healthy sex-matched volunteers serving as controls (9 males, 6 females; age = 23.8 ± 5.8 years, height = 171.9 ± 9.9 cm, mass = 68.9 ± 15.5 kg) participated. Intervention(s): Maximum H-reflex (Hmax) and motor wave (Mmax) from the soleus and fibularis longus were recorded while participants lay prone and then stood in unipedal stance. We assessed postural tasks of unipedal stance with participants' eyes closed for 10 seconds using a forceplate. Main Outcome Measure(s): We normalized Hmax to Mmax to obtain Hmax : Mmax ratios for the 2 positions. For each muscle, H-reflex modulation was quantified using the percentage change scores in Hmax : Mmax ratios calculated from prone position to unipedal stance. Center-of-pressure data were used to compute 4 time-to-boundary variables. Separate independent-samples t tests were performed to determine group differences. Pearson product moment correlation coefficients were calculated between the modulation and balance measures in the CAI group. Results: The CAI group presented less H-reflex modulation in the soleus (t26 = −3.77, P = .001) and fibularis longus (t25 = −2.59, P = .02). The mean of the time-to-boundary minima in the anteroposterior direction was lower in the CAI group (t28 = −2.06, P = .048). We observed a correlation (r = 0.578, P = .049) between the fibular longus modulation and mean of time-to-boundary minima in the anteroposterior direction. Conclusions: The strong relationship indicated that, as H-reflex amplitude in unipedal stance was less down modulated, unipedal postural control was more impaired. Given the deficits in H-reflex modulation and postural control in the CAI group, the relationship may provide insights into the neurophysiologic mechanism of postural instability. PMID:27583692

Glycine receptor modulating antibody predicting treatable stiff-person spectrum disorders.

PubMed

Hinson, Shannon R; Lopez-Chiriboga, A Sebastian; Bower, James H; Matsumoto, Joseph Y; Hassan, Anhar; Basal, Eati; Lennon, Vanda A; Pittock, Sean J; McKeon, Andrew

2018-03-01

Glycine receptor alpha-1 subunit (GlyRα1)-immunoglobulin G (IgG) is diagnostic of stiff-person syndrome (SPS) spectrum but has been reported detectable in other neurologic diseases for which significance is less certain. To assess GlyRα1-IgGs as biomarkers of SPS spectrum among patients and controls, specimens were tested using cell-based assays (binding [4°C] and modulating [antigen endocytosing, 37°C]). Medical records of seropositive patients were reviewed. GlyRα1-IgG (binding antibody) was detected in 21 of 247 patients with suspected SPS spectrum (8.5%) and in 8 of 190 healthy subject sera (4%) but not CSF. Among 21 seropositive patients, 20 had confirmed SPS spectrum clinically, but 1 was later determined to have a functional neurologic disorder. Sera from 9 patients with SPS spectrum , but not 7 controls, nor the functional patient, caused GlyRα1 modulation (100% specificity). SPS spectrum phenotypes included progressive encephalomyelitis with rigidity and myoclonus (PERM) (8), classic SPS (5), stiff limb (5), stiff trunk (1), and isolated exaggerated startle (hyperekplexia, 1). Neuropsychiatric symptoms present in 12 patients (60%) were anxiety (11), depression (6), and delirium (3). Anxiety was particularly severe in 3 patients with PERM. Objective improvements in SPS neurologic symptoms were recorded in 16 of 18 patients who received first-line immunotherapy (89%, 9/10 treated with corticosteroids, 8/10 treated with IVIg, 3/4 treated with plasma exchange, and 1 treated with rituximab). Treatment-sparing maintenance strategies were successful in 4 of 7 patients (rituximab [2/3], azathioprine [1/1], and mycophenolate [1/3]). GlyRα1-modulating antibody improves diagnostic specificity for immunologically treatable SPS spectrum disorders. This study provides Class IV evidence that GlyRα1-modulating antibody accurately identifies patients with treatable SPS spectrum disorders.

Method and apparatus configured for identification of a material

DOEpatents

Slater, John M.; Crawford, Thomas M.

2000-01-01

The present invention includes an apparatus configured for identification of a material, and methods of identifying a material. One embodiment of the invention provides an apparatus including a first region configured to receive a first sample, the first region being configured to output a first spectrum corresponding to the first sample and responsive to exposure of the first sample to radiation; a modulator configured to modulate the first spectrum according to a first frequency; a second region configured to receive a second sample, the second region being configured to output a second spectrum corresponding to the second sample and responsive to exposure of the second sample to the modulated first spectrum; and a detector configured to detect the second spectrum having a second frequency greater than the first frequency.

Direct-Sequence Spread Spectrum System

DTIC Science & Technology

1990-06-01

by directly modulating a conventional narrowband frequency-modulated (FM) carrier by a high rate digital code. The direct modulation is binary phase ...specification of the DSSS system will not be developed. The results of the evaluation phase of this research will be compared against theoretical...spread spectrum is called binary phase -shift keying 19 (BPSK). BPSK is a modulation in which a binary Ŕ" represents a 0-degree relative phase

An electromagnetic modulator based on electrically controllable metamaterial analogue to electromagnetically induced transparency.

PubMed

Fan, Yuancheng; Qiao, Tong; Zhang, Fuli; Fu, Quanhong; Dong, Jiajia; Kong, Botao; Li, Hongqiang

2017-01-16

Electromagnetically induced transparency (EIT) is a promising technology for the enhancement of light-matter interactions, and recent demonstrations of the EIT analogue realized in artificial micro-structured medium have remarkably reduced the extreme requirement for experimental observation of EIT spectrum. In this paper, we propose to electrically control the EIT-like spectrum in a metamaterial as an electromagnetic modulator. A diode acting as a tunable resistor is loaded in the gap of paired wires to inductively tune the magnetic resonance, which induces remarkable modulation on the EIT-like spectrum through the metamaterial sample. The experimental measurements confirmed that the prediction of electromagnetic modulation in three narrow bands on the EIT-like spectrum, and a modulation contrast of up to 31 dB was achieved on the transmission through the metamaterial. Our results may facilitate the study on active/dynamical technology in translational metamaterials, which connect extraordinary manipulations on the flow of light in metamaterials, e.g., the exotic EIT, and practical applications in industry.

Improper ferroelectricity: A theoretical and experimental investigation

NASA Astrophysics Data System (ADS)

Hardy, J. R.; Ullman, F. G.

1984-02-01

A combined theoretical and experimental study has been made of the origins and properties of the improper ferroelectricity associated with structural modulations of non-zero wavelengths. Two classes of materials have been studied: rare earth molybdates (specifically, gadolinium molybdate: GMO), and potassium selenate and its isomorphs. In the former, the modulation is produced by a zone boundary phonon instability, and in the latter by the instability of a phonon of wave vector approximately two-thirds of the way to the zone-boundary. In the second case the initial result is a modulated structure whose repeat distance is not a rational multiple of the basic lattice repeat distance. This result is a modulated polarization which, when the basic modulation locks in to a rational multiple of the lattice spacing, becomes uniform, and improper ferroelectricity results. The origins of these effects have been elucidated by theoretical studies, initially semi-empirical, but subsequently from first-principles. These complemented the experimental work, which primarily used inelastic light scattering, uniaxial stress, and hydrostatic pressure, to probe the balance between the interionic forces through the effects on the phonons and dielectric properties.

Appearance of ionization instability in a low-voltage arc

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

Kobelevskii, A.V.; Nastoyashchii, A.F.

1986-09-01

The conditions for the appearance of the ionization instability in a low-voltage arc are examined. On the basis of the model of a Knudsen arc a criterion is obtained for the appearance of the instability and the possible types of dispersion relations are analyzed. The possibility of ionization instability in a short arc in cesium vapor is discussed. The results of a numerical investigation of the appearance of ionization instability, including the nonlinear stage, in a two-dimensional formulation of the problem are presented. When the fluctuations in the elec tron temperature are in antiphase with the density fluctuations, stable (long-lived)more » two-dimensional structures, which are characterized by a high degree of modulation of the degree of ionization of the gas, can form.« less

How pattern is selected in drift wave turbulence: Role of parallel flow shear

NASA Astrophysics Data System (ADS)

Kosuga, Y.

2017-12-01

The role of parallel shear flow in the pattern selection problem in drift wave turbulence is discussed. Patterns of interest here are E × B convective cells, which include poloidally symmetric zonal flows and radially elongated streamers. The competition between zonal flow formation and streamer formation is analyzed in the context of modulational instability analysis, with the parallel flow shear as a parameter. For drift wave turbulence with k⊥ρs ≲ O (1 ) and without parallel flow coupling, zonal flows are preferred structures. While increasing the magnitude of parallel flow shear, streamer growth overcomes zonal flow growth. This is because the self-focusing effect of the modulational instability becomes more effective for streamers through density and parallel velocity modulation. As a consequence, the bursty release of free energy may result as the parallel flow shear increases.

The structure of lifetime manic-hypomanic spectrum.

PubMed

Cassano, G B; Mula, M; Rucci, P; Miniati, M; Frank, E; Kupfer, D J; Oppo, A; Calugi, S; Maggi, L; Gibbons, R; Fagiolini, A

2009-01-01

The observation that bipolar disorders frequently go unrecognized has prompted the development of screening instruments designed to improve the identification of bipolarity in clinical and non-clinical samples. Starting from a lifetime approach, researchers of the Spectrum Project developed the Mood Spectrum Self-Report (MOODS-SR) that assesses threshold-level manifestations of unipolar and bipolar mood psychopathology, but also atypical symptoms, behavioral traits and temperamental features. The aim of the present study is to examine the structure of mania/hypomania using 68 items of the MOODS-SR that explore cognitive, mood and energy/activity features associated with mania/hypomania. A data pool of 617 patients with bipolar disorders, recruited at Pittsburgh and Pisa, Italy was used for this purpose. Classical exploratory factor analysis, based on a tetrachoric matrix, was carried out on the 68 items, followed by an Item Response Theory (IRT)-based factor analytic approach. Nine factors were initially identified, that include Psychomotor Activation, Creativity, Mixed Instability, Sociability/Extraversion, Spirituality/Mysticism/Psychoticism, Mixed Irritability, Inflated Self-esteem, Euphoria, Wastefulness/Recklessness, and account overall for 56.4% of the variance of items. In a subsequent IRT-based bi-factor analysis, only five of them (Psychomotor Activation, Mixed Instability, Spirituality/Mysticism/Psychoticism, Mixed Irritability, Euphoria) were retained. Our data confirm the central role of Psychomotor Activation in mania/hypomania and support the definitions of pure manic (Psychomotor Activation and Euphoria) and mixed manic (Mixed Instability and Mixed Irritability) components, bearing the opportunity to identify patients with specific profiles for a better clinical and neurobiological definition.

Beyond the Rayleigh instability limit for multicharged finite systems: From fission to Coulomb explosion

PubMed Central

Last, Isidore; Levy, Yaakov; Jortner, Joshua

2002-01-01

We address the stability of multicharged finite systems driven by Coulomb forces beyond the Rayleigh instability limit. Our exploration of the nuclear dynamics of heavily charged Morse clusters enabled us to vary the range of the pair potential and of the fissibility parameter, which results in distinct fragmentation patterns and in the angular distributions of the fragments. The Rayleigh instability limit separates between nearly binary (or tertiary) spatially unisotropic fission and spatially isotropic Coulomb explosion into a large number of small, ionic fragments. Implications are addressed for a broad spectrum of dynamics in chemical physics, radiation physics of ultracold gases, and biophysics, involving the fission of clusters and droplets, the realization of Coulomb explosion of molecular clusters, the isotropic expansion of optical molasses, and the Coulomb instability of “isolated” proteins. PMID:12093910

A transverse separate-spin-evolution streaming instability

NASA Astrophysics Data System (ADS)

Iqbal, Z.; Andreev, Pavel A.; Murtaza, G.

2018-05-01

By using the separate spin evolution quantum hydrodynamical model, the instability of transverse mode due to electron streaming in a partially spin polarized magnetized degenerate plasma is studied. The electron spin polarization gives birth to a new spin-dependent wave (i.e., separate spin evolution streaming driven ordinary wave) in the real wave spectrum. It is shown that the spin polarization and streaming speed significantly affect the frequency of this new mode. Analyzing growth rate, it is found that the electron spin effects reduce the growth rate and shift the threshold of instability as well as its termination point towards higher values. Additionally, how the other parameters like electron streaming and Fermi pressure influence the growth rate is also investigated. Current study can help towards better understanding of the existence of new waves and streaming instability in the astrophysical plasmas.

Observations of enhanced ion line frequency spectrum during Arecibo ionospheric modification experiment

NASA Technical Reports Server (NTRS)

Hagfors, T.; Zamlutti, C. J.

1974-01-01

The Arecibo 430 MHz incoherent scatter radar (ISR) was used to monitor the effects of modifying the ionosphere by a high power HF transmitter feeding the 305 m reflector antenna. When in the ordinary magnetoionic mode parametric instabilities develop in the ionosphere near the reflection level. Manifestations of these instabilities are the strong enhancement of Langmuir oscillations in the direction of the ISR beam at a wavelength of 35 cm and the simultaneous much weaker enhancement of ion oscillations in that direction. The spectral analysis of the enhanced peak with a height resolution of 2.4 km shows that the ionic mode enhancement most often has a double humped frequency spectrum corresponding to up- and down-going ion acoustic waves. The shape of the frequency spectrum is interpreted in terms of a stable oscillation which is driven by a secondary electrostatic field caused by nonlinear interaction of Langmuir waves within a cone centered on the magnetic field and by the scattering of the pump field on stable Langmuir waves travelling along the direction of the ISR.

Dark solitons, modulation instability and breathers in a chain of weakly nonlinear oscillators with cyclic symmetry

NASA Astrophysics Data System (ADS)

Fontanela, F.; Grolet, A.; Salles, L.; Chabchoub, A.; Hoffmann, N.

2018-01-01

In the aerospace industry the trend for light-weight structures and the resulting complex dynamic behaviours currently challenge vibration engineers. In many cases, these light-weight structures deviate from linear behaviour, and complex nonlinear phenomena can be expected. We consider a cyclically symmetric system of coupled weakly nonlinear undamped oscillators that could be considered a minimal model for different cyclic and symmetric aerospace structures experiencing large deformations. The focus is on localised vibrations that arise from wave envelope modulation of travelling waves. For the defocussing parameter range of the approximative nonlinear evolution equation, we show the possible existence of dark solitons and discuss their characteristics. For the focussing parameter range, we characterise modulation instability and illustrate corresponding nonlinear breather dynamics. Furthermore, we show that for stronger nonlinearity or randomness in initial conditions, transient breather-type dynamics and decay into bright solitons appear. The findings suggest that significant vibration localisation may arise due to mechanisms of nonlinear modulation dynamics.

Academic Attainment in Students with Autism Spectrum Disorders in Distance Education

ERIC Educational Resources Information Center

Richardson, John T. E.

2017-01-01

This investigation studied attainment in students with autism spectrum disorders (ASDs) who were taking modules by distance learning with the UK Open University in 2012. Students with ASDs who had no additional disabilities were as likely as non-disabled students to complete the modules that they had taken, to pass the modules that they had…

Diagnosing Autism Spectrum Disorders in Adults: The Use of Autism Diagnostic Observation Schedule (ADOS) Module 4

ERIC Educational Resources Information Center

Bastiaansen, Jojanneke A.; Meffert, Harma; Hein, Simone; Huizinga, Petra; Ketelaars, Cees; Pijnenborg, Marieke; Bartels, Arnold; Minderaa, Ruud; Keysers, Christian; de Bildt, Annelies

2011-01-01

Autism Diagnostic Observation Schedule (ADOS) module 4 was investigated in an independent sample of high-functioning adult males with an autism spectrum disorder (ASD) compared to three specific diagnostic groups: schizophrenia, psychopathy, and typical development. ADOS module 4 proves to be a reliable instrument with good predictive value. It…

RApid Temporal Survey (RATS) - II. Followup observations of four newly discovered short-period variables

NASA Astrophysics Data System (ADS)

Ramsay, Gavin; Napiwotzki, Ralf; Hakala, Pasi; Lehto, Harry

2006-09-01

The Rapid Temporal Survey (RATS) is a survey to detect objects whose optical intensity varies on time-scales of less than ~70 min. In our pilot data set taken with the Isaac Newton Telescope and the Wide Field Camera in 2003 November, we discovered nearly 50 new variable objects. Many of these varied on time-scales much longer than 1 h. However, only four objects showed a modulation on a time-scale of 1 h or less. This paper presents followup optical photometry and spectroscopy of these four objects. We find that RATJ0455 + 1305 is a pulsating (on a period of 374 s) subdwarf B star of the EC14026 type. We have modelled its spectrum and determine Teff = 29200 +/- 1900K and logg = 5.2 +/- 0.3 which locates it on the cool edge of the EC14026 instability strip. It has a modulation amplitude which is one of the highest of any known EC14026 star. Based on their spectra, photometric variability and their infrared colours, we find that RATJ0449 + 1756, J0455 + 1254 and J0807 + 1510 are likely to be SX Phe stars - dwarf δ Sct stars. Our results show that our observing strategy is a good method for finding rare pulsating stars.

Harnessing rogue wave for supercontinuum generation in cascaded photonic crystal fiber.

PubMed

Zhao, Saili; Yang, Hua; Zhao, Chujun; Xiao, Yuzhe

2017-04-03

Based on induced modulation instability, we present a numerical study on harnessing rogue wave for supercontinuum generation in cascaded photonic crystal fibers. By selecting optimum modulation frequency, we achieve supercontinuum with a great improvement on spectrum stability when long-pulse is used as the pump. In this case, rogue wave can be obtained in the first segmented photonic crystal fiber with one zero dispersion wavelength in a controllable manner. Numerical simulations show that spectral range and flatness can be regulated in an extensive range by cascading a photonic crystal fiber with two zero dispersion wavelengths. Some novel phenomena are observed in the second segmented photonic crystal fiber. When the second zero dispersion wavelength is close to the first one, rogue wave is directly translated into dispersion waves, which is conducive to the generation of smoother supercontinuum. When the second zero dispersion wavelength is far away from the first one, rogue wave is translated into the form of fundamental soliton steadily propagating in the vicinity of the second zero dispersion wavelength. Meanwhile, the corresponding red-shifted dispersion wave is generated when the phase matching condition is met, which is beneficial to the generation of wider supercontinuum. The results presented in this work provide a better application of optical rogue wave to generate flat and broadband supercontinuum in cascaded photonic crystal fibers.

History of shoulder instability surgery.

PubMed

Randelli, Pietro; Cucchi, Davide; Butt, Usman

2016-02-01

The surgical management of shoulder instability is an expanding and increasingly complex area of study within orthopaedics. This article describes the history and evolution of shoulder instability surgery, examining the development of its key principles, the currently accepted concepts and available surgical interventions. A comprehensive review of the available literature was performed using PubMed. The reference lists of reviewed articles were also scrutinised to ensure relevant information was included. The various types of shoulder instability including anterior, posterior and multidirectional instability are discussed, focussing on the history of surgical management of these topics, the current concepts and the results of available surgical interventions. The last century has seen important advancements in the understanding and treatment of shoulder instability. The transition from open to arthroscopic surgery has allowed the discovery of previously unrecognised pathologic entities and facilitated techniques to treat these. Nevertheless, open surgery still produces comparable results in the treatment of many instability-related conditions and is often required in complex or revision cases, particularly in the presence of bone loss. More high-quality research is required to better understand and characterise this spectrum of conditions so that successful evidence-based management algorithms can be developed. IV.

Constraints on Nonlinear and Stochastic Growth Theories for Type 3 Solar Radio Bursts from the Corona to 1 AU

NASA Technical Reports Server (NTRS)

Cairns, Iver H.; Robinson, P. A.

1998-01-01

Existing, competing theories for coronal and interplanetary type III solar radio bursts appeal to one or more of modulational instability, electrostatic (ES) decay processes, or stochastic growth physics to preserve the electron beam, limit the levels of Langmuir-like waves driven by the beam, and produce wave spectra capable of coupling nonlinearly to generate the observed radio emission. Theoretical constraints exist on the wavenumbers and relative sizes of the wave bandwidth and nonlinear growth rate for which Langmuir waves are subject to modulational instability and the parametric and random phase versions of ES decay. A constraint also exists on whether stochastic growth theory (SGT) is appropriate. These constraints are evaluated here using the beam, plasma, and wave properties (1) observed in specific interplanetary type III sources, (2) predicted nominally for the corona, and (3) predicted at heliocentric distances greater than a few solar radii by power-law models based on interplanetary observations. It is found that the Langmuir waves driven directly by the beam have wavenumbers that are almost always too large for modulational instability but are appropriate to ES decay. Even for waves scattered to lower wavenumbers (by ES decay, for instance), the wave bandwidths are predicted to be too large and the nonlinear growth rates too small for modulational instability to occur for the specific interplanetary events studied or the great majority of Langmuir wave packets in type III sources at arbitrary heliocentric distances. Possible exceptions are for very rare, unusually intense, narrowband wave packets, predominantly close to the Sun, and for the front portion of very fast beams traveling through unusually dilute, cold solar wind plasmas. Similar arguments demonstrate that the ES decay should proceed almost always as a random phase process rather than a parametric process, with similar exceptions. These results imply that it is extremely rare for modulational instability or parametric decay to proceed in type III sources at any heliocentric distance: theories for type III bursts based on modulational instability or parametric decay are therefore not viable in general. In contrast, the constraint on SGT can be satisfied and random phase ES decay can proceed at all heliocentric distances under almost all circumstances. (The contrary circumstances involve unusually slow, broad beams moving through unusually hot regions of the Corona.) The analyses presented here strongly justify extending the existing SGT-based model for interplanetary type III bursts (which includes SGT physics, random phase ES decay, and specific electromagnetic emission mechanisms) into a general theory for type III bursts from the corona to beyond 1 AU. This extended theory enjoys strong theoretical support, explains the characteristics of specific interplanetary type III bursts very well, and can account for the detailed dynamic spectra of type III bursts from the lower corona and solar wind.

Frequency band of the f-mode Chandrasekhar-Friedman-Schutz instability

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

Zink, Burkhard; Korobkin, Oleg; Schnetter, Erik

2010-04-15

Rapidly rotating neutron stars can be unstable to the gravitational-wave-driven Chandrasekhar-Friedman-Schutz (CFS) mechanism if they have a neutral point in the spectrum of nonaxisymmetric f-modes. We investigate the frequencies of these modes in two sequences of uniformly rotating polytropes using nonlinear simulations in full general relativity, determine the approximate locations of the neutral points, and derive limits on the observable frequency band available to the instability in these sequences. We find that general relativity enhances the detectability of a CFS-unstable neutron star substantially, both by widening the instability window and enlarging the band into the optimal range for interferometric detectorsmore » like LIGO, VIRGO, and GEO-600.« less

Instability of the Superfluid Flow as Black-Hole Lasing Effect.

PubMed

Finazzi, S; Piazza, F; Abad, M; Smerzi, A; Recati, A

2015-06-19

We show that the critical velocity of a superfluid flow through a penetrable barrier coincides with the onset of the analog black-hole lasing effect. This dynamical instability is triggered by modes resonating in an effective cavity formed by two horizons enclosing the barrier. The location of the horizons is set by v(x)=c(x), with v(x),c(x) being the local fluid velocity and sound speed, respectively. We compute the critical velocity analytically and show that it is univocally determined by the configuration of the horizons. In the limit of broad barriers, the continuous spectrum at the origin of the Hawking-like radiation and of the Landau energetic instability is recovered.

Thermo-capillary effect on the linear temporal and spatial instability of viscous liquid jets falling under gravity

NASA Astrophysics Data System (ADS)

Alsharif, Abdullah M.; Althubaiti, Shadiah A.

2018-03-01

The thermal modulation of Newtonian liquid jets at the orifice causes a variation in surface tension, which propagates downstream inducing Marangoni instability. Therefore, the linear temporal and spatial instability should be investigated to predict the same size of producing small spherical pellets. In this paper, we consider a viscous liquid jet emerging from a nozzle subject to thermo-capillary effects falling under gravity. Moreover, we use the asymptotic approach to reduce the governing equation into one-dimensional (1-D). The steady state solutions have been found using a modified Newton's method, and then the linear instability analysis has been investigated of the resulting set of equations.

Quasilinear saturation of the aperiodic ordinary mode streaming instability

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

Stockem Novo, A., E-mail: anne@tp4.rub.de; Schlickeiser, R.; Yoon, P. H.

2015-09-15

In collisionless plasmas, only kinetic instabilities and fluctuations are effective in reducing the free energy and scatter plasma particles, preventing an increase of their anisotropy. Solar energetic outflows into the interplanetary plasma give rise to important thermal anisotropies and counterstreaming motions of plasma shells, and the resulting instabilities are expected to regulate the expansion of the solar wind. The present paper combines quasilinear theory and kinetic particle-in-cell simulations in order to study the weakly nonlinear saturation of the ordinary mode in hot counter-streaming plasmas with a temperature anisotropy as a follow-up of the paper by Seough et al. [Phys. Plasmasmore » 22, 082122 (2015)]. This instability provides a plausible mechanism for the origin of dominating, two-dimensional spectrum of transverse magnetic fluctuations observed in the solar wind. Stimulated by the differential motion of electron counterstreams the O mode instability may convert their free large-scale energy by nonlinear collisionless dissipation on plasma particles.« less

Spatio-temporal instabilities for counterpropagating waves in periodic media.

PubMed

Haus, Joseph; Soon, Boon Yi; Scalora, Michael; Bloemer, Mark; Bowden, Charles; Sibilia, Concita; Zheltikov, Alexei

2002-01-28

Nonlinear evolution of coupled forward and backward fields in a multi-layered film is numerically investigated. We examine the role of longitudinal and transverse modulation instabilities in media of finite length with a homogeneous nonlinear susceptibility c((3)). The numerical solution of the nonlinear equations by a beam-propagation method that handles backward waves is described.

Non-modal analysis of the diocotron instability: Cylindrical geometry

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

Mikhailenko, V. V.; Lee, Hae June; Mikhailenko, V. S.

2013-04-15

The temporal evolution of the linear diocotron instability of the cylindrical annular plasma column is investigated by employing the extension of the shearing modes methodology to the cylindrical geometry. It was obtained that the spatial time-dependent distortion of the electron density initial perturbations by shear flows leads to the non-modal evolution of the potential, which was referred to as the manifestation of the continuous spectrum. The evolution process leads toward the convergence to the phase-locking configuration of the mutually growing normal modes.

REVIEWS OF TOPICAL PROBLEMS: The nature of accretion disks of close binary stars: overreflection instability and developed turbulence

NASA Astrophysics Data System (ADS)

Fridman, A. M.; Bisikalo, D. V.

2008-06-01

The current status of the physics of accretion disks in close binary stars is reviewed, with an emphasis on the hydrodynamic overreflection instability, which is a factor leading to the accretion disk turbulence. The estimated turbulent viscosity coefficients are in good agreement with observations and explain the high angular momentum transfer rate and the measured accretion rate. Based on the observations, a power-law spectrum for the developed turbulence is obtained.

Continuous-wave modulation of a femtosecond oscillator using coherent molecules.

PubMed

Gold, D C; Karpel, J T; Mueller, E A; Yavuz, D D

2018-03-01

We describe a new method to broaden the frequency spectrum of a femtosecond oscillator in the continuous-wave (CW) domain. The method relies on modulating the femtosecond laser using four-wave mixing inside a Raman-based optical modulator. We prepare the modulator by placing deuterium molecules inside a high-finesse cavity and driving their fundamental vibrational transition using intense pump and Stokes lasers that are locked to the cavity modes. With the molecules prepared, any laser within the optical region of the spectrum can pass through the system and be modulated in a single pass. This constitutes a CW optical modulator at a frequency of 90 THz with a steady-state single-pass efficiency of ∼10 -6 and transient (10 μs-time-scale) single-pass efficiency of ∼10 -4 . Using our modulator, we broaden the initial Ti:sapphire spectrum centered at 800 nm and produce upshifted and downshifted sidebands centered at wavelengths of 650 nm and 1.04 μm, respectively.

Experimental study on rotating instability mode characteristics of axial compressor tip flow

NASA Astrophysics Data System (ADS)

Tian, Jie; Yao, Dan; Wu, Yadong; Ouyang, Hua

2018-04-01

This paper investigates the rotating instabilities that occurred on the single-stage axial compressor designed for aerodynamic performance validation, which was tested with two sets of circumferential measuring points in combination. Circumferential mode characteristics of compressors are usually too high to be captured experimentally, and aliasing of the circumferential mode order occurs when not enough sensors are used. A calibration and prediction method to capture the higher circumferential mode of unsteady flow in a compressor was proposed. Unsteady pressure fluctuations near the tip region in an axial compressor were studied, and high circumferential mode characteristics were captured on both the blade passing frequency (BPF) and the rotational instability frequency (RIF) under different flow rate conditions based on this novel method. The characteristic RI spectrum with a broadband hump was present in a large range of flow conditions. Both the frequency range and the dominant circumferential mode order decreased as the flow rate decreased. Based on the calibrated mode characteristics, a rotating aerodynamic source model is used to explain the side-by-side peak of RIF spectrum and rotating characteristics of RI. The calibration and prediction method of the high circumferential mode is beneficial for the research of unsteady flow in an axial compressor.

The instability of the spiral wave induced by the deformation of elastic excitable media

NASA Astrophysics Data System (ADS)

Ma, Jun; Jia, Ya; Wang, Chun-Ni; Li, Shi-Rong

2008-09-01

There are some similarities between the spiral wave in excitable media and in cardiac tissue. Much evidence shows that the appearance and instability of the spiral wave in cardiac tissue can be linked to one kind of heart disease. There are many models that can be used to investigate the formation and instability of the spiral wave. Cardiac tissue is excitable and elastic, and it is interesting to simulate the transition and instability of the spiral wave induced by media deformation. For simplicity, a class of the modified Fitzhugh-Nagumo (MFHN) model, which can generate a stable rotating spiral wave, meandering spiral wave and turbulence within appropriate parameter regions, will be used to simulate the instability of the spiral wave induced by the periodical deformation of media. In the two-dimensional case, the total acreage of elastic media is supposed to be invariable in the presence of deformation, and the problem is described with Lx × Ly = N × ΔxN × Δy = L'xL'y = N × Δx'N × Δy'. In our studies, elastic media are decentralized into N × N sites and the space of the adjacent sites is changed to simulate the deformation of elastic media. Based on the nonlinear dynamics theory, the deformation effect on media is simplified and simulated by perturbing the diffusion coefficients Dx and Dy with different periodical signals, but the perturbed diffusion coefficients are compensatory. The snapshots of our numerical results find that the spiral wave can coexist with the spiral turbulence, instability of the spiral wave and weak deformation of the spiral wave in different conditions. The ratio parameter ɛ and the frequency of deformation forcing play a deterministic role in inducing instability of the spiral wave. Extensive studies confirm that the instability of the spiral wave can be induced and developed only if an appropriate frequency for deformation is used. We analyze the power spectrum for the time series of the mean activator of four sampled sites which are selected symmetrically in different cases, such as the condition that the spiral wave coexists with the spiral turbulence, spiral wave without evident deformation, complete instability of the spiral wave (turbulence) and weak deformation of the spiral wave. It is found that more new peaks appear in the power spectrum and the distribution of frequency becomes sparser when the spiral wave encounters instability.

Defence Technology Strategy for the Demands of the 21st Century

DTIC Science & Technology

2006-10-01

understanding of human capability in the CBM role. Ownership of the intellectual property behind algorithms may be sovereign10, but implementation will...synchronisation schemes. · coding schemes. · modulation techniques. · access schemes. · smart spectrum usage . · low probability of intercept. · implementation...modulation techniques; access schemes; smart spectrum usage ; low probability of intercept Spectrum and bandwidth management · cross layer technologies to

Electrostatic and magnetic instabilities in the transition layer of a collisionless weakly relativistic pair shock

NASA Astrophysics Data System (ADS)

Dieckmann, M. E.; Bret, A.

2018-01-01

Energetic electromagnetic emissions by astrophysical jets like those that are launched during the collapse of a massive star and trigger gamma-ray bursts are partially attributed to relativistic internal shocks. The shocks are mediated in the collisionless plasma of such jets by the filamentation instability of counterstreaming particle beams. The filamentation instability grows fastest only if the beams move at a relativistic relative speed. We model here with a particle-in-cell simulation, the collision of two cold pair clouds at the speed c/2 (c: speed of light). We demonstrate that the two-stream instability outgrows the filamentation instability for this speed and is thus responsible for the shock formation. The incomplete thermalization of the upstream plasma by its quasi-electrostatic waves allows other instabilities to grow. A shock transition layer forms, in which a filamentation instability modulates the plasma far upstream of the shock. The inflowing upstream plasma is progressively heated by a two-stream instability closer to the shock and compressed to the expected downstream density by the Weibel instability. The strong magnetic field due to the latter is confined to a layer 10 electron skin depths wide.

Instability of liquid crystal elastomers

NASA Astrophysics Data System (ADS)

An, Ning; Li, Meie; Zhou, Jinxiong

2016-01-01

Nematic liquid crystal elastomers (LCEs) contract in the director direction but expand in other directions, perpendicular to the director, when heated. If the expansion of an LCE is constrained, compressive stress builds up in the LCE, and it wrinkles or buckles to release the stored elastic energy. Although the instability of soft materials is ubiquitous, the mechanism and programmable modulation of LCE instability has not yet been fully explored. We describe a finite element method (FEM) scheme to model the inhomogeneous deformation and instability of LCEs. A constrained LCE beam working as a valve for microfluidic flow, and a piece of LCE laminated with a nanoscale poly(styrene) (PS) film are analyzed in detail. The former uses the buckling of the LCE beam to occlude the microfluidic channel, while the latter utilizes wrinkling or buckling to measure the mechanical properties of hard film or to realize self-folding. Through rigorous instability analysis, we predict the critical conditions for the onset of instability, the wavelength and amplitude evolution of instability, and the instability patterns. The FEM results are found to correlate well with analytical results and reported experiments. These efforts shed light on the understanding and exploitation of the instabilities of LCEs.

Parametric Instability, Inverse Cascade, and the 1/f Range of Solar-Wind Turbulence.

PubMed

Chandran, Benjamin D G

2018-02-01

In this paper, weak turbulence theory is used to investigate the nonlinear evolution of the parametric instability in 3D low- β plasmas at wavelengths much greater than the ion inertial length under the assumption that slow magnetosonic waves are strongly damped. It is shown analytically that the parametric instability leads to an inverse cascade of Alfvén wave quanta, and several exact solutions to the wave kinetic equations are presented. The main results of the paper concern the parametric decay of Alfvén waves that initially satisfy e + ≫ e - , where e + and e - are the frequency ( f ) spectra of Alfvén waves propagating in opposite directions along the magnetic field lines. If e + initially has a peak frequency f 0 (at which fe + is maximized) and an "infrared" scaling f p at smaller f with -1 < p < 1, then e + acquires an f -1 scaling throughout a range of frequencies that spreads out in both directions from f 0 . At the same time, e - acquires an f -2 scaling within this same frequency range. If the plasma parameters and infrared e + spectrum are chosen to match conditions in the fast solar wind at a heliocentric distance of 0.3 astronomical units (AU), then the nonlinear evolution of the parametric instability leads to an e + spectrum that matches fast-wind measurements from the Helios spacecraft at 0.3 AU, including the observed f -1 scaling at f ≳ 3 × 10 -4 Hz. The results of this paper suggest that the f -1 spectrum seen by Helios in the fast solar wind at f ≳ 3 × 10 -4 Hz is produced in situ by parametric decay and that the f -1 range of e + extends over an increasingly narrow range of frequencies as r decreases below 0.3 AU. This prediction will be tested by measurements from the Parker Solar Probe .

Homogeneous wave turbulence driven by tidal flows

NASA Astrophysics Data System (ADS)

Favier, B.; Le Reun, T.; Barker, A.; Le Bars, M.

2017-12-01

When a moon orbits around a planet, the rotation of the induced tidal bulge drives a homogeneous, periodic, large-scale flow. The combination of such an excitation with the rotating motion of the planet has been shown to drive parametric resonance of a pair of inertial waves in a mechanism called the elliptical instability. Geophysical fluid layers can also be stratified: this is the case for instance of the Earth's oceans and, as suggested by several studies, of the upper part of the Earth's liquid Outer Core. We thus investigate the stability of a rotating and stratified layer undergoing tidal distortion in the limit where either rotation or stratification is dominant. We show that the periodic tidal flow drives a parametric subharmonic resonance of inertial (resp. internal) waves in the rotating (resp. stratified) case. The instability saturates into a wave turbulence pervading the whole fluid layer. In such a state, the instability mechanism conveys the tidal energy from the large scale tidal flow to the resonant modes, which then feed a succession of triadic resonances also generating small spatial scales. In the rotating case, we observe a kinetic energy spectrum with a k-2 slope for which the Coriolis force is dominant at all spatial scales. In the stratified case, where the timescale separation is increased between the tidal excitation and the Brunt-Väisälä frequencies, the temporal spectrum decays with a ω-2 power law up to the cut-off frequency beyond which waves do not exist. This result is reminiscent of the Garrett and Munk spectrum measured in the oceans and theoretically described as a manifestation of internal wave turbulence. In addition to revealing an instability driving homogeneous turbulence in geophysical fluid layers, our approach is also an efficient numerical tool to investigate the possibly universal properties of wave turbulence in a geophysical context.

Dust-acoustic waves modulational instability and rogue waves in a polarized dusty plasma

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

Bouzit, Omar; Tribeche, Mouloud

2015-10-15

The polarization force-induced changes in the dust-acoustic waves (DAWs) modulational instability (MI) are examined. Using the reductive perturbation method, the nonlinear Schrödinger equation that governs the MI of the DAWs is obtained. It is found that the effect of the polarization term R is to narrow the wave number domain for the onset of instability. The amplitude of the wave envelope decreases as R increases, meaning that the polarization force effects render weaker the associated DA rogue waves. The latter may therefore completely damp in the vicinity of R ∼ 1, i.e., as the polarization force becomes close to the electrostatic onemore » (the net force acting on the dust particles becomes vanishingly small). The DA rogue wave profile is very sensitive to any change in the restoring force acting on the dust particles. It turns out that the polarization effects may completely smear out the DA rogue waves.« less

Relativistic laser-plasma interactions in the quantum regime.

PubMed

Eliasson, Bengt; Shukla, P K

2011-04-01

We consider nonlinear interactions between a relativistically strong laser beam and a plasma in the quantum regime. The collective behavior of electrons is modeled by a Klein-Gordon equation, which is nonlinearly coupled with the electromagnetic wave through the Maxwell and Poisson equations. This allows us to study nonlinear interactions between arbitrarily large-amplitude electromagnetic waves and a quantum plasma. We have used our system of nonlinear equations to study theoretically the parametric instabilities involving stimulated Raman scattering and modulational instabilities. A model for quasi-steady-state propagating electromagnetic wave packets is also derived, and which shows possibility of localized solitary structures in a quantum plasma. Numerical simulations demonstrate collapse and acceleration of electrons in the nonlinear stage of the modulational instability, as well as possibility of the wake-field acceleration of electrons to relativistic speeds by short laser pulses at nanometer length scales. Our study is relevant for understanding the localization of intense electromagnetic pulses in a quantum plasma with extremely high electron densities and relatively low temperature.

Classification of instability modes in a model of aluminium reduction cells with a uniform magnetic field

NASA Astrophysics Data System (ADS)

Molokov, Sergei; El, Gennady; Lukyanov, Alexander

2011-10-01

A unified view on the interfacial instability in a model of aluminium reduction cells in the presence of a uniform, vertical, background magnetic field is presented. The classification of instability modes is based on the asymptotic theory for high values of parameter β, which characterises the ratio of the Lorentz force based on the disturbance current, and gravity. It is shown that the spectrum of the travelling waves consists of two parts independent of the horizontal cross-section of the cell: highly unstable wall modes and stable or weakly unstable centre, or Sele's modes. The wall modes with the disturbance of the interface being localised at the sidewalls of the cell dominate the dynamics of instability. Sele's modes are characterised by a distributed disturbance over the whole horizontal extent of the cell. As β increases these modes are stabilized by the field.

Effect of collisions on neutrino flavor inhomogeneity in a dense neutrino gas

DOE PAGES

Cirigliano, Vincenzo; Paris, Mark W.; Shalgar, Shashank

2017-09-25

We investigate the stability, with respect to spatial inhomogeneity, of a two-dimensional dense neutrino gas. The system exhibits growth of seed inhomogeneity due to nonlinear coherent neutrino self-interactions. In the absence of incoherent collisional effects, we also observe a dependence of this instability growth rate on the neutrino mass spectrum: the normal neutrino mass hierarchy exhibits spatial instability over a larger range of neutrino number density compared to that of the inverted case. Furthermore, we consider the effect of elastic incoherent collisions of the neutrinos with a static background of heavy, nucleon-like scatterers. At small scales, the growth of flavormore » instability can be suppressed by collisions. At large length scales we find, perhaps surprisingly, that for inverted neutrino mass hierarchy incoherent collisions fail to suppress flavor instabilities, independent of the coupling strength.« less

Simulation Study of Magnetic Fields Generated by the Electromagnetic Filamentation Instability

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Ramirez-Ruiz, E.; Hardee, P.; Hededal, C. B.; Mizuno, Y.; Fishman, G. J.

2007-01-01

We have investigated the effects of plasma instabilities driven by rapid e(sup plus or minus) pair cascades, which arise in the environment of GRB sources as a result of back-scattering of a seed fraction of the original spectrum. The injection of e(sup plus or minus) pairs induces strong streaming motions in the ambient medium. One therefore expects the pair-enriched medium ahead of the forward shock to be strongly sheared on length scales comparable to the radiation front thickness. Using three-dimensional particle-in-cell simulations, we show that plasma instabilities driven by these streaming e(sup plus or minus) pairs are responsible for the excitation of near-equipartition, turbulent magnetic fields. Our results reveal the importance of the electromagnetic filamentation instability in ensuring an effective coupling between e(sup plus or minus) pairs and ions, and may help explain the origin of large upstream fields in GRB shocks.

Filtering of non-linear instabilities. [from finite difference solution of fluid dynamics equations

NASA Technical Reports Server (NTRS)

Khosla, P. K.; Rubin, S. G.

1979-01-01

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 here that these problems can in fact 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 in some cases possibly eliminate the instability. These filtering procedures are equivalent to a weighted average of conservation and non-conservation differencing. The entire spectrum of filtered equations retains a three-point character as well as second-order spatial accuracy. Burgers equation has been considered as a model. Several filters are examined in detail, and smooth solutions have been obtained for extremely large cell Reynolds numbers.

Boundary-layer receptivity due to distributed surface imperfections of a deterministic or random nature

NASA Technical Reports Server (NTRS)

Choudhari, Meelan

1992-01-01

Acoustic receptivity of a Blasius boundary layer in the presence of distributed surface irregularities is investigated analytically. It is shown that, out of the entire spatial spectrum of the surface irregularities, only a small band of Fourier components can lead to an efficient conversion of the acoustic input at any given frequency to an unstable eigenmode of the boundary layer flow. The location, and width, of this most receptive band of wavenumbers corresponds to a relative detuning of O(R sub l.b.(exp -3/8)) with respect to the lower-neutral instability wavenumber at the frequency under consideration, R sub l.b. being the Reynolds number based on a typical boundary-layer thickness at the lower branch of the neutral stability curve. Surface imperfections in the form of discrete mode waviness in this range of wavenumbers lead to initial instability amplitudes which are O(R sub l.b.(exp 3/8)) larger than those caused by a single, isolated roughness element. In contrast, irregularities with a continuous spatial spectrum produce much smaller instability amplitudes, even compared to the isolated case, since the increase due to the resonant nature of the response is more than that compensated for by the asymptotically small band-width of the receptivity process. Analytical expressions for the maximum possible instability amplitudes, as well as their expectation for an ensemble of statistically irregular surfaces with random phase distributions, are also presented.

Ultra-Linear Polymer Modulator

DTIC Science & Technology

2006-05-01

Experimental Setup and Data 3.1 Erbium fiber laser ( EFL ) spectrum The EFL spectrum is measured using an HP 70950A optical spectrum analyzer (OSA...the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503 1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE...Boulder SFDR Test bed; Early results were limited by the optical loss of the polymer modulator and fiber coupling mechanisms used during the SFDR

Bandwidth tunable microwave photonic filter based on digital and analog modulation

NASA Astrophysics Data System (ADS)

Zhang, Qi; Zhang, Jie; Li, Qiang; Wang, Yubing; Sun, Xian; Dong, Wei; Zhang, Xindong

2018-05-01

A bandwidth tunable microwave photonic filter based on digital and analog modulation is proposed and experimentally demonstrated. The digital modulation is used to broaden the effective gain spectrum and the analog modulation is to get optical lines. By changing the symbol rate of data pattern, the bandwidth is tunable from 50 MHz to 700 MHz. The interval of optical lines is set according to the bandwidth of gain spectrum which is related to the symbol rate. Several times of bandwidth increase are achieved compared to a single analog modulation and the selectivity of the response is increased by 3.7 dB compared to a single digital modulation.

Hydrodynamic instability growth of three-dimensional modulations in radiation-driven implosions with “low-foot” and “high-foot” drives at the National Ignition Facility

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

Smalyuk, V. A.; Weber, C. R.; Robey, H. F.

Hydrodynamic instability growth has been studied using three-dimensional (3-D) broadband modulations by comparing “high-foot” and “low-foot” spherical plastic (CH) capsule implosions at the National Ignition Facility (NIF). The initial perturbations included capsule outer-surface roughness and capsule-mounting membranes (“tents”) that were similar to those used in a majority of implosions on NIF. The tents with thicknesses of 31-nm, 46-nm, and 109-nm were used in the experiments. The outer-surface roughness in the “low-foot” experiment was similar to the standard specification, while it was increased by ~4 times in the “high-foot” experiment to compensate for the reduced growth. The ablation-front instability growth wasmore » measured using a Hydrodynamic Growth Radiography platform at a convergence ratio of 3. The dominant capsule perturbations, generated by the tent mountings, had measured perturbation amplitudes comparable to the capsule thickness with the “low-foot” drive. These tent perturbations were reduced by ~3 to 10 times in implosions with the “high-foot” drive. Unexpectedly, the measured perturbations with initially thinner tents were either larger or similar to the measured perturbations with thicker tents for both “high-foot” and “low-foot” drives. While the measured instability growth of 3-D broadband perturbations was also significantly reduced by ~5 to 10 times with the “high-foot” drive, compared to the “low-foot” drive, the growth mitigation was stronger than expected based on previous “growth-factor” results measured with two-dimensional modulations. Lastly, one of the hypotheses to explain the results is based on the 3-D modulations of the oxygen content in the bulk of the capsule having a stronger effect on the overall growth of capsule perturbations than the outer-surface capsule roughness.« less

Hydrodynamic instability growth of three-dimensional modulations in radiation-driven implosions with “low-foot” and “high-foot” drives at the National Ignition Facility

DOE PAGES

Smalyuk, V. A.; Weber, C. R.; Robey, H. F.; ...

2017-04-11

Hydrodynamic instability growth has been studied using three-dimensional (3-D) broadband modulations by comparing “high-foot” and “low-foot” spherical plastic (CH) capsule implosions at the National Ignition Facility (NIF). The initial perturbations included capsule outer-surface roughness and capsule-mounting membranes (“tents”) that were similar to those used in a majority of implosions on NIF. The tents with thicknesses of 31-nm, 46-nm, and 109-nm were used in the experiments. The outer-surface roughness in the “low-foot” experiment was similar to the standard specification, while it was increased by ~4 times in the “high-foot” experiment to compensate for the reduced growth. The ablation-front instability growth wasmore » measured using a Hydrodynamic Growth Radiography platform at a convergence ratio of 3. The dominant capsule perturbations, generated by the tent mountings, had measured perturbation amplitudes comparable to the capsule thickness with the “low-foot” drive. These tent perturbations were reduced by ~3 to 10 times in implosions with the “high-foot” drive. Unexpectedly, the measured perturbations with initially thinner tents were either larger or similar to the measured perturbations with thicker tents for both “high-foot” and “low-foot” drives. While the measured instability growth of 3-D broadband perturbations was also significantly reduced by ~5 to 10 times with the “high-foot” drive, compared to the “low-foot” drive, the growth mitigation was stronger than expected based on previous “growth-factor” results measured with two-dimensional modulations. Lastly, one of the hypotheses to explain the results is based on the 3-D modulations of the oxygen content in the bulk of the capsule having a stronger effect on the overall growth of capsule perturbations than the outer-surface capsule roughness.« less

The N170 is not modulated by attention in autism spectrum conditions.

PubMed

Churches, Owen; Wheelwright, Sally; Baron-Cohen, Simon; Ring, Howard

2010-04-21

Face processing deficits are characteristic of autism spectrum conditions. However, event-related potential studies of autism spectrum conditions have found inconsistent results for the face selective N170 component. In this study, 15 adult males with autism spectrum conditions and 15 matched, typically developing controls completed a task in which pictures of faces were either attended to or ignored. In the control group, the N170 was larger when faces were attended to. However, there was no such modulation in the autism spectrum conditions group. This finding helps clarify the results from the earlier event-related potential studies of face processing in autism spectrum conditions and suggests that visual attention does not enhance face processing in autism spectrum conditions as it does in typical development.

Fast Transverse Instability and Electron Cloud Measurements in Fermilab Recycler

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

Eldred, Jeffery; Adamson, Philip; Capista, David

2015-03-01

A new transverse instability is observed that may limit the proton intensity in the Fermilab Recycler. The instability is fast, leading to a beam-abort loss within two hundred turns. The instability primarily affects the first high-intensity batch from the Fermilab Booster in each Recycler cycle. This paper analyzes the dynamical features of the destabilized beam. The instability excites a horizontal betatron oscillation which couples into the vertical motion and also causes transverse emittance growth. This paper describes the feasibility of electron cloud as the mechanism for this instability and presents the first measurements of the electron cloud in the Fermilabmore » Recycler. Direct measurements of the electron cloud are made using a retarding field analyzer (RFA) newly installed in the Fermilab Recycler. Indirect measurements of the electron cloud are made by propagating a microwave carrier signal through the beampipe and analyzing the phase modulation of the signal. The maximum betatron amplitude growth and the maximum electron cloud signal occur during minimums of the bunch length oscillation.« less

Quasiperiodic instability and chaos in the bad-cavity laser with modulated inversion: Numerical analysis of a Toda oscillator system

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

Ogawa, T.

The exact equivalence between a bad-cavity laser with modulated inversion and a nonlinear oscillator in a Toda potential driven by an external modulation is presented. The dynamical properties of the laser system are investigated in detail by analyzing a Toda oscillator system. The temporal characteristics of the bad-cavity laser under strong modulation are analyzed extensively by numerically investigating the simpler Toda system as a function of two control parameters: the dc component of the population inversion and the modulation amplitude. The system exhibits two kinds of optical chaos: One is the quasiperiodic chaos in the region of the intermediate modulationmore » amplitude and the other is the intermittent kicked chaos in the region of strong modulation and large dc component of the pumping. The former is well described by a one-dimensional discrete map with a singular invariant probability measure. There are two types of onset of the chaos: quasiperiodic instability (continuous path to chaos) and catastrophic crisis (discontinuous path). The period-doubling cascade of bifurcation is also observed. The simple discrete model of the Toda system is presented to obtain analytically the one-dimensional map function and to understand the effect of the asymmetric potential curvature on yielding chaos.« less

Development of Mirror Modules for the ART-XC Instrument aboard the Spectrum-Roentgen-Gamma Mission

NASA Technical Reports Server (NTRS)

Gubarev, Mikhail V.; Ramsey, Brian; O'Dell, Stephen L.; Elsner, Ronald F.; Kilaru, Kiranmayee; Atkins, Carolyn; Pavlinskiy, Mikhail N.; Tkachenko, Alexey V.; Lapshov, Igor Y.

2013-01-01

The Marshall Space Flight Center (MSFC) is developing x-ray mirror modules for the Astronomical Roengen Telescope- X-ray Concentrator (ART-XC) instrument on board the Spectrum-Roentgen-Gamma Mission. ART-XC will consist of seven co-aligned x-ray mirror modules with seven corresponding CdTe focal plane detectors. Each module provides an effective area of 65 sq cm at 8 keV, response out to 30 keV, and an angular resolution of 45 arcsec or better HPD. We will present a status of the ART x-ray module development at MSFC.

High Frequency Adaptive Instability Suppression Controls in a Liquid-Fueled Combustor

NASA Technical Reports Server (NTRS)

Kopasakis, George

2003-01-01

This effort extends into high frequency (>500 Hz), an earlier developed adaptive control algorithm for the suppression of thermo-acoustic instabilities in a liquidfueled combustor. The earlier work covered the development of a controls algorithm for the suppression of a low frequency (280 Hz) combustion instability based on simulations, with no hardware testing involved. The work described here includes changes to the simulation and controller design necessary to control the high frequency instability, augmentations to the control algorithm to improve its performance, and finally hardware testing and results with an experimental combustor rig developed for the high frequency case. The Adaptive Sliding Phasor Averaged Control (ASPAC) algorithm modulates the fuel flow in the combustor with a control phase that continuously slides back and forth within the phase region that reduces the amplitude of the instability. The results demonstrate the power of the method - that it can identify and suppress the instability even when the instability amplitude is buried in the noise of the combustor pressure. The successful testing of the ASPAC approach helped complete an important NASA milestone to demonstrate advanced technologies for low-emission combustors.

Enhanced accuracy of the microwave field strength measurement in a CW-EPR by pulsed modulation technique

NASA Astrophysics Data System (ADS)

Rakvin, B.; Carić, D.; Kveder, M.

2018-02-01

The microwave magnetic field strength, B1, in the cavity of a conventional continuous wave electron paramagnetic resonance, CW-EPR, spectrometer was measured by employing modulation sidebands, MS, in the EPR spectrum. MS spectrum in CW-EPR is produced by applying the modulation frequency, ωrf, which exceeds the linewidth, δB, given in frequency units. An amplitude-modulated CW-EPR, AM-CW-EPR, was selected as detection method. Theoretical description of AM-CW-EPR spectrum was modified by adding Bloch-Siegert-like shift obtained by taking into account the cumulative effect of the non-resonant interactions between the driving fields and the spin system. This approach enables to enhance the precision of B1 measurement. In order to increase the sensitivity of the method when saturation effects, due to higher intensity of B1, decrease the resolution of AM-CW-EPR spectrum, detection at the second harmonic of CW-EPR has been employed.

Enhanced accuracy of the microwave field strength measurement in a CW-EPR by pulsed modulation technique.

PubMed

Rakvin, B; Carić, D; Kveder, M

2018-02-01

The microwave magnetic field strength, B 1 , in the cavity of a conventional continuous wave electron paramagnetic resonance, CW-EPR, spectrometer was measured by employing modulation sidebands, MS, in the EPR spectrum. MS spectrum in CW-EPR is produced by applying the modulation frequency, ω rf , which exceeds the linewidth, δB, given in frequency units. An amplitude-modulated CW-EPR, AM-CW-EPR, was selected as detection method. Theoretical description of AM-CW-EPR spectrum was modified by adding Bloch-Siegert-like shift obtained by taking into account the cumulative effect of the non-resonant interactions between the driving fields and the spin system. This approach enables to enhance the precision of B 1 measurement. In order to increase the sensitivity of the method when saturation effects, due to higher intensity of B 1 , decrease the resolution of AM-CW-EPR spectrum, detection at the second harmonic of CW-EPR has been employed. Copyright © 2018 Elsevier Inc. All rights reserved.

Phase separation and long-wavelength charge instabilities in spin-orbit coupled systems

NASA Astrophysics Data System (ADS)

Seibold, G.; Bucheli, D.; Caprara, S.; Grilli, M.

2015-01-01

We investigate a two-dimensional electron model with Rashba spin-orbit interaction where the coupling constant g=g(n) depends on the electronic density. It is shown that this dependence may drive the system unstable towards a long-wavelength charge density wave (CDW) where the associated second-order instability occurs in close vicinity to global phase separation. For very low electron densities the CDW instability is nesting-induced and the modulation follows the Fermi momentum kF. At higher density the instability criterion becomes independent of kF and the system may become unstable in a broad momentum range. Finally, upon filling the upper spin-orbit split band, finite momentum instabilities disappear in favor of phase separation alone. We discuss our results with regard to the inhomogeneous phases observed at the LaAlO3/SrTiO3 or LaTiO3/SrTiO3 interfaces.

Secondary instability of high-speed flows and the influence of wall cooling and suction

NASA Technical Reports Server (NTRS)

El-Hady, Nabil M.

1992-01-01

The periodic streamwise modulation of the supersonic and hypersonic boundary layers by a two dimensional first mode or second mode wave makes the resulting base flow susceptible to a broadband spanwise-periodic three dimensional type of instability. The principal parametric resonance of this instability (subharmonic) was analyzed using Floquet theory. The effect of Mach number and the effectiveness of wall cooling or wall suction in controlling the onset, the growth rate, and the vortical nature of the subharmonic secondary instability are assessed for both a first mode and a second mode primary wave. Results indicate that the secondary subharmonic instability of the insulated wall boundary layer is weakened as Mach number increases. Cooling of the wall destabilizes the secondary subharmonic of a second mode primary wave, but stabilizes it when the primary wave is a first mode. Suction stabilizes the secondary subharmonic at all Mach numbers.

Static and Dynamic Water Motion-Induced Instability in Oxide Thin-Film Transistors and Its Suppression by Using Low-k Fluoropolymer Passivation.

PubMed

Choi, Seungbeom; Jo, Jeong-Wan; Kim, Jaeyoung; Song, Seungho; Kim, Jaekyun; Park, Sung Kyu; Kim, Yong-Hoon

2017-08-09

Here, we report static and dynamic water motion-induced instability in indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs) and its effective suppression with the use of a simple, solution-processed low-k (ε ∼ 1.9) fluoroplastic resin (FPR) passivation layer. The liquid-contact electrification effect, in which an undesirable drain current modulation is induced by a dynamic motion of a charged liquid such as water, can cause a significant instability in IGZO TFTs. It was found that by adopting a thin (∼44 nm) FPR passivation layer for IGZO TFTs, the current modulation induced by the water-contact electrification was greatly reduced in both off- and on-states of the device. In addition, the FPR-passivated IGZO TFTs exhibited an excellent stability to static water exposure (a threshold voltage shift of +0.8 V upon 3600 s of water soaking), which is attributed to the hydrophobicity of the FPR passivation layer. Here, we discuss the origin of the current instability caused by the liquid-contact electrification as well as various static and dynamic stability tests for IGZO TFTs. On the basis of our findings, we believe that the use of a thin, solution-processed FPR passivation layer is effective in suppressing the static and dynamic water motion-induced instabilities, which may enable the realization of high-performance and environment-stable oxide TFTs for emerging wearable and skin-like electronics.

Many-body instabilities and mass generation in slow Dirac materials

NASA Astrophysics Data System (ADS)

Triola, Christopher; Zhu, Jian-Xin; Migliori, Albert; Balatsky, Alexander V.

2015-07-01

Some Kondo insulators are expected to possess topologically protected surface states with linear Dirac spectrum: the topological Kondo insulators. Because the bulk states of these systems typically have heavy effective electron masses, the surface states may exhibit extraordinarily small Fermi velocities that could force the effective fine structure constant of the surface states into the strong coupling regime. Using a tight-binding model, we study the many-body instabilities of these systems and identify regions of parameter space in which the system exhibits spin density wave and charge density wave order.

Measuring the Binary Black Hole Mass Spectrum with an Astrophysically Motivated Parameterization

NASA Astrophysics Data System (ADS)

Talbot, Colm; Thrane, Eric

2018-04-01

Gravitational-wave detections have revealed a previously unknown population of stellar mass black holes with masses above 20 M ⊙. These observations provide a new way to test models of stellar evolution for massive stars. By considering the astrophysical processes likely to determine the shape of the binary black hole mass spectrum, we construct a parameterized model to capture key spectral features that relate gravitational-wave data to theoretical stellar astrophysics. In particular, we model the signature of pulsational pair-instability supernovae, which are expected to cause all stars with initial mass 100 M ⊙ ≲ M ≲ 150 M ⊙ to form ∼40 M ⊙ black holes. This would cause a cutoff in the black hole mass spectrum along with an excess of black holes near 40 M ⊙. We carry out a simulated data study to illustrate some of the stellar physics that can be inferred using gravitational-wave measurements of binary black holes and demonstrate several such inferences that might be made in the near future. First, we measure the minimum and maximum stellar black hole mass. Second, we infer the presence of a peak due to pair-instability supernovae. Third, we measure the distribution of black hole mass ratios. Finally, we show how inadequate models of the black hole mass spectrum lead to biased estimates of the merger rate and the amplitude of the stochastic gravitational-wave background.

Heating and Acceleration of Solar Wind Ions by Turbulent Wave Spectrum in Inhomogeneous Expanding Plasma

NASA Technical Reports Server (NTRS)

Ofman, Leon; Ozak, Nataly; Vinas, Adolfo F.

2016-01-01

Near the Sun (< 10Rs) the acceleration, heating, and propagation of the solar wind are likely affected by the background inhomogeneities of the magnetized plasma. The heating and the acceleration of the solar wind ions by turbulent wave spectrum in inhomogeneous plasma is studied using a 2.5D hybrid model. The hybrid model describes the kinetics of the ions, while the electrons are modeled as massless neutralizing fluid in an expanding box approach. Turbulent magnetic fluctuations dominated by power-law frequency spectra, which are evident from in-situ as well as remote sensing measurements, are used in our models. The effects of background density inhomogeneity across the magnetic field on the resonant ion heating are studied. The effect of super- Alfvenic ion drift on the ion heating is investigated. It is found that the turbulent wave spectrum of initially parallel propagating waves cascades to oblique modes, and leads to enhanced resonant ion heating due to the inhomogeneity. The acceleration of the solar wind ions is achieved by the parametric instability of large amplitude waves in the spectrum, and is also affected by the inhomogeneity. The results of the study provide the ion temperature anisotropy and drift velocity temporal evolution due to relaxation of the instability. The non-Maxwellian velocity distribution functions (VDFs) of the ions are modeled in the inhomogeneous solar wind plasma in the acceleration region close to the Sun.

Spatiotemporal character of the Bobylev-Pikin flexoelectric instability in a twisted nematic bent-core liquid crystal exposed to very low frequency fields.

PubMed

Krishnamurthy, K S

2014-05-01

The Bobylev-Pikin striped-pattern state induced by a homogeneous electric field is a volume flexoelectric instability, originating in the midregion of a planarly aligned nematic liquid crystal layer. We find that the instability acquires a spatiotemporal character upon excitation by a low frequency (0.5 Hz) square wave field. This is demonstrated using a bent-core liquid crystal, initially in the 90°-twisted planar configuration. The flexoelectric modulation appears close to the cathode at each polarity reversal and, at low voltage amplitudes, decays completely as the field becomes steady. Correspondingly, at successive polarity changes, the stripe direction switches between the alignment directions at the two substrates. For large voltages, the stripes formed nearly along the alignment direction at the cathode gradually reorient toward the midplane director. These observations are generally attributed to inhomogeneous and time-dependent field conditions that come to exist after each polarity reversal. Polarity dependence of the instability is attributed to the formation of intrinsic double layers that bring about an asymmetry in surface fields. Momentary field elevation near the cathode following a voltage sign reversal and concomitant gradient flexoelectric polarization are considered the key factors in accounting for the surfacelike modulation observed at low voltages.

Spectrum-Modulating Fiber-Optic Sensors

NASA Technical Reports Server (NTRS)

Beheim, Glenn; Fritsch, Klaus

1989-01-01

Family of spectrum-modulating fiber-optic sensors undergoing development for use in aircraft-engine control systems. Fiber-optic sensors offer advantages of small size, high bandwidth, immunity to electromagnetic interference, and light weight. Furthermore, they reduce number of locations on aircraft to which electrical power has to be supplied.

Glenohumeral Instability Related to Special Conditions: SLAP Tears, Pan-labral Tears, and Multidirectional Instability.

PubMed

Van Blarcum, Gregory S; Svoboda, Steven J

2017-09-01

Glenohumeral instability is one of the more common conditions seen by sports medicine physicians, especially in young, active athletes. The associated anatomy of the glenohumeral joint (the shallow nature of the glenoid and the increased motion it allows) make the shoulder more prone to instability events as compared with other joints. Although traumatic dislocations or instability events associated with acute labral tears (ie, Bankart lesions) are well described in the literature, there exists other special shoulder conditions that are also associated with shoulder instability: superior labrum anterior/posterior (SLAP) tears, pan-labral tears, and multidirectional instability. SLAP tears can be difficult to diagnose and arthroscopic diagnosis remains the gold standard. Surgical treatment as ranged from repair to biceps tenodesis with varying reports of success. Along the spectrum of SLAP tears, pan-labral tears consist of 360-degree injuries to the labrum. Patients can present complaining of either anterior or posterior instability alone, making the physical examination and advanced imaging a crucial component of the work up of the patients. Arthroscopic labral repair remains a good initial option for surgical treatment of these conditions. Multidirectional instability remains one of the more difficult conditions for the sports medicine physician to diagnose and treat. Symptoms may only be reported as vague pain versus frank instability making the diagnoses particularly challenging, especially in a patient with overall joint laxity. Conservative management to include physical therapy is the mainstay initial treatment in patients without an identifiable structural abnormality. Surgical management of this condition has evolved from open to arthroscopic capsular shifts with comparable results.

Manycast routing, modulation level and spectrum assignment over elastic optical networks

NASA Astrophysics Data System (ADS)

Luo, Xiao; Zhao, Yang; Chen, Xue; Wang, Lei; Zhang, Min; Zhang, Jie; Ji, Yuefeng; Wang, Huitao; Wang, Taili

2017-07-01

Manycast is a point to multi-point transmission framework that requires a subset of destination nodes successfully reached. It is particularly applicable for dealing with large amounts of data simultaneously in bandwidth-hungry, dynamic and cloud-based applications. As rapid increasing of traffics in these applications, the elastic optical networks (EONs) may be relied on to achieve high throughput manycast. In terms of finer spectrum granularity, the EONs could reach flexible accessing to network spectrum and efficient providing exact spectrum resource to demands. In this paper, we focus on the manycast routing, modulation level and spectrum assignment (MA-RMLSA) problem in EONs. Both EONs planning with static manycast traffic and EONs provisioning with dynamic manycast traffic are investigated. An integer linear programming (ILP) model is formulated to derive MA-RMLSA problem in static manycast scenario. Then corresponding heuristic algorithm called manycast routing, modulation level and spectrum assignment genetic algorithm (MA-RMLSA-GA) is proposed to adapt for both static and dynamic manycast scenarios. The MA-RMLSA-GA optimizes MA-RMLSA problem in destination nodes selection, routing light-tree constitution, modulation level allocation and spectrum resource assignment jointly, to achieve an effective improvement in network performance. Simulation results reveal that MA-RMLSA strategies offered by MA-RMLSA-GA have slightly disparity from the optimal solutions provided by ILP model in static scenario. Moreover, the results demonstrate that MA-RMLSA-GA realizes a highly efficient MA-RMLSA strategy with the lowest blocking probability in dynamic scenario compared with benchmark algorithms.

Optical solitons and modulation instability analysis of an integrable model of (2+1)-Dimensional Heisenberg ferromagnetic spin chain equation

NASA Astrophysics Data System (ADS)

Inc, Mustafa; Aliyu, Aliyu Isa; Yusuf, Abdullahi; Baleanu, Dumitru

2017-12-01

This paper addresses the nonlinear Schrödinger type equation (NLSE) in (2+1)-dimensions which describes the nonlinear spin dynamics of Heisenberg ferromagnetic spin chains (HFSC) with anisotropic and bilinear interactions in the semiclassical limit. Two integration schemes are employed to study the equation. These are the complex envelope function ansatz and the generalized tanh methods. Dark, dark-bright or combined optical and singular soliton solutions of the equation are derived. Furthermore, the modulational instability (MI) is studied based on the standard linear-stability analysis and the MI gain is got. Numerical simulation of the obtained results are analyzed with interesting figures showing the physical meaning of the solutions.

Calibration-free absolute frequency response measurement of directly modulated lasers based on additional modulation.

PubMed

Zhang, Shangjian; Zou, Xinhai; Wang, Heng; Zhang, Yali; Lu, Rongguo; Liu, Yong

2015-10-15

A calibration-free electrical method is proposed for measuring the absolute frequency response of directly modulated semiconductor lasers based on additional modulation. The method achieves the electrical domain measurement of the modulation index of directly modulated lasers without the need for correcting the responsivity fluctuation in the photodetection. Moreover, it doubles measuring frequency range by setting a specific frequency relationship between the direct and additional modulation. Both the absolute and relative frequency response of semiconductor lasers are experimentally measured from the electrical spectrum of the twice-modulated optical signal, and the measured results are compared to those obtained with conventional methods to check the consistency. The proposed method provides calibration-free and accurate measurement for high-speed semiconductor lasers with high-resolution electrical spectrum analysis.

Self-modulational formation of pulsar microstructures

NASA Technical Reports Server (NTRS)

Kennel, C. F.; Chian, A. C.-L.

1987-01-01

A nonlinear plasma theory for self modulation of pulsar radio pulses is discussed. A nonlinear Schroedinger equation is derived for strong electromagnetic waves propagating in an electron positron plasma. The nonlinearities arising from wave intensity induced particle mass variation may excite the modulational instability of circularly and linearly polarized pulsar radiation. The resulting wave envelopes can take the form of periodic wave trains or solitons. These nonlinear stationary waveforms may account for the formation of pulsar microstructures.

The University of Iowa Helios solar wind plasma wave experiment /E 5a/. [using spectrum analyzer-electric field antenna system

NASA Technical Reports Server (NTRS)

Gurnett, D. A.; Anderson, R. R.; Odem, D. L.

1975-01-01

This document describes the University of Iowa solar wind plasma wave experiment for the Helios missions (Experiment 5a). The objective of this experiment is the investigation of naturally occurring plasma instabilities and electromagnetic waves in the solar wind. To carry out this investigation, the experiment consists primarily of a 16-channel spectrum analyzer connected to the electric field antennas. The spectrum analyzer covers the frequency range from 20 Hz to 200 kHz and has an amplitude dynamic range which extends from .3 microvolts/m to 30 mV/m per channel. This spectrum analyzer, the antenna potential measurements, the shock alarm system and the supporting electronics are discussed in detail.

Spectrum of coherent transition radiation generated by a modulated electron beam

NASA Astrophysics Data System (ADS)

Naumenko, G. A.; Potylitsyn, A. P.; Karataev, P. V.; Shipulya, M. A.; Bleko, V. V.

2017-07-01

The spectrum of coherent transition radiation has been recorded with the use of a Martin-Puplett interferometer. It has been shown that the spectrum includes monochromatic lines that are caused by the modulation of an electron beam with the frequency of an accelerating radio-frequency field νRF and correspond to resonances at ν k = kνRF k ≤ 10. To determine the length of an electron bunch from the measurement of the spectrum from a single bunch, it is necessary to use a spectrometer with the resolution Δνsp > νRF.

On Instability of Geostrophic Current with Linear Vertical Shear at Length Scales of Interleaving

NASA Astrophysics Data System (ADS)

Kuzmina, N. P.; Skorokhodov, S. L.; Zhurbas, N. V.; Lyzhkov, D. A.

2018-01-01

The instability of long-wave disturbances of a geostrophic current with linear velocity shear is studied with allowance for the diffusion of buoyancy. A detailed derivation of the model problem in dimensionless variables is presented, which is used for analyzing the dynamics of disturbances in a vertically bounded layer and for describing the formation of large-scale intrusions in the Arctic basin. The problem is solved numerically based on a high-precision method developed for solving fourth-order differential equations. It is established that there is an eigenvalue in the spectrum of eigenvalues that corresponds to unstable (growing with time) disturbances, which are characterized by a phase velocity exceeding the maximum velocity of the geostrophic flow. A discussion is presented to explain some features of the instability.

Orbital angular momentum (OAM) spectrum correction in free space optical communication.

PubMed

Liu, Yi-Dong; Gao, Chunqing; Qi, Xiaoqing; Weber, Horst

2008-05-12

Orbital angular momentum (OAM) of laser beams has potential application in free space optical communication, but it is sensitive against pointing instabilities of the beam, i.e. shift (lateral displacement) and tilt (deflection of the beam). This work proposes a method to correct the distorted OAM spectrum by using the mean square value of the orbital angular momentum as an indicator. Qualitative analysis is given, and the numerical simulation is carried out for demonstration. The results show that the mean square value can be used to determine the beam axis of the superimposed helical beams. The initial OAM spectrum can be recovered.

Relationships between self-reported ankle function and modulation of Hoffmann reflex in patients with chronic ankle instability.

PubMed

Kim, Kyung-Min; Hart, Joseph M; Saliba, Susan A; Hertel, Jay

2016-01-01

To examine relationships between self-reported ankle function and Hoffmann (H) reflex modulation during changes in body positions in patients with chronic ankle instability (CAI). Observational. Laboratory. Thirty-one young adults with CAI (19 males, 12 females) participated. There were two subscales of Foot and Ankle Ability Measure (FAAM) to quantify self-reported ankle function during activities of daily living (ADL) and sports activities. Maximum H-reflexes (H-max) and motor waves (M-max) from soleus and fibularis longus were recorded while participants lied prone and stood in bipedal and unipedal stances. For each muscle, percent change scores in Hmax:Mmax ratios were calculated between each pair of positions: prone-to-bipedal, bipedal-to-unipedal, and prone-to-unipedal, and used as a measure of H-reflex modulation. Pearson correlation coefficients were calculated between FAAM and H-reflex modulation measures. There were significant correlations between: (1) FAAM-ADL and soleus prone-to-unipedal modulation (r = 0.384, p = 0.04), (2) FAAM-Sport and soleus prone-to-unipedal modulation (r = 0.505, p = 0.005), (3) FAAM-Sport and fibular bipedal-to-unipedal modulation (r = 0.377, p = 0.05), and (4) FAAM-Sport and fibular prone-to-unipedal modulation (r = 0.396, p = 0.04). CAI patients presented moderate, positive relationships between self-reported ankle function and H-reflex modulation during changes in body positions. Copyright © 2015 Elsevier Ltd. All rights reserved.

Implementation of STUD Pulses at the Trident Laser and Initial Results

NASA Astrophysics Data System (ADS)

Johnson, R. P.; Shimada, T.; Montgomery, D. S.; Afeyan, B.; Hüller, S.

2012-10-01

Controlling and mitigating laser-plasma instabilities such as stimulated Brillouin scattering, stimulated Raman scattering, and crossed-beam energy transfer is important to achieve high-gain inertial fusion using laser drivers. Recent theory and simulations show that these instabilities can be largely controlled using laser pulses consisting of spike trains of uneven duration and delay (STUD) by modulating the laser on a picosecond time scale [1,2]. We have designed and implemented a STUD pulse generator at the LANL Trident Laser Facility using Fourier synthesis to produce a 0.5-ns envelope of psec-duration STUD pulses using a spatial light modulator. Initial results from laser propagation tests and measurements as well as initial laser-plasma characterization experiments will be presented.[4pt] [1] B. Afeyan and S. H"uller, ``Optimal Control of Laser Plasma Instabilities using STUD pulses,'' IFSA 2011, P.Mo.1, to appear in Euro. Phys. J. Web of Conf. (2012).[2] S. H"uller and B. Afeyan, ``Simulations of drastically reduced SBS with STUD pulses,'' IFSA 2011, O.Tu8-1, to appear in Euro. Phys. J. Web of Conf. (2012).

Control of Thermo-Acoustics Instabilities: The Multi-Scale Extended Kalman Approach

NASA Technical Reports Server (NTRS)

Le, Dzu K.; DeLaat, John C.; Chang, Clarence T.

2003-01-01

"Multi-Scale Extended Kalman" (MSEK) is a novel model-based control approach recently found to be effective for suppressing combustion instabilities in gas turbines. A control law formulated in this approach for fuel modulation demonstrated steady suppression of a high-frequency combustion instability (less than 500Hz) in a liquid-fuel combustion test rig under engine-realistic conditions. To make-up for severe transport-delays on control effect, the MSEK controller combines a wavelet -like Multi-Scale analysis and an Extended Kalman Observer to predict the thermo-acoustic states of combustion pressure perturbations. The commanded fuel modulation is composed of a damper action based on the predicted states, and a tones suppression action based on the Multi-Scale estimation of thermal excitations and other transient disturbances. The controller performs automatic adjustments of the gain and phase of these actions to minimize the Time-Scale Averaged Variances of the pressures inside the combustion zone and upstream of the injector. The successful demonstration of Active Combustion Control with this MSEK controller completed an important NASA milestone for the current research in advanced combustion technologies.

A methodology to study the possible occurrence of chugging in liquid rocket engines during transient start-up

NASA Astrophysics Data System (ADS)

Leonardi, Marco; Nasuti, Francesco; Di Matteo, Francesco; Steelant, Johan

2017-10-01

An investigation on the low frequency combustion instabilities due to the interaction of combustion chamber and feed line dynamics in a liquid rocket engine is carried out implementing a specific module in the system analysis software EcosimPro. The properties of the selected double time lag model are identified according to the two classical assumptions of constant and variable time lag. Module capabilities are evaluated on a literature experimental set up consisting of a combustion chamber decoupled from the upstream feed lines. The computed stability map results to be in good agreement with both experimental data and analytical models. Moreover, the first characteristic frequency of the engine is correctly predicted, giving confidence on the use of the module for the analysis of chugging instabilities. As an example of application, a study is carried out on the influence of the feed lines on the system stability, correctly capturing that the lines extend the stable regime of the combustion chamber and that the propellant domes play a key role in coupling the dynamics of combustion chamber and feed lines. A further example is presented to discuss on the role of pressure growth rate and of the combustion chamber properties on the possible occurrence of chug instability during engine start-up and on the conditions that lead to its damping or growth.

A Meta-Analysis of Sensory Modulation Symptoms in Individuals with Autism Spectrum Disorders

ERIC Educational Resources Information Center

Ben-Sasson, Ayelet; Hen, Liat; Fluss, Ronen; Cermak, Sharon A.; Engel-Yeger, Batya; Gal, Eynat

2009-01-01

Sensory modulation symptoms are common in persons with autism spectrum disorders (ASD); however have a heterogeneous presentation. Results from 14 studies indicated a significant high difference between ASD and typical groups in the presence/frequency of sensory symptoms, with the greatest difference in under-responsivity, followed by…

Absolute versus convective helical magnetorotational instability in a Taylor-Couette flow.

PubMed

Priede, Jānis; Gerbeth, Gunter

2009-04-01

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 perturbations. First, we carry out a detailed conventional linear stability analysis with respect to perturbations in the form of Fourier modes that corresponds to the convective instability which is not in general self-sustained. The helical magnetic field is found to extend the instability to a relatively narrow range beyond its purely hydrodynamic limit defined by the Rayleigh line. There is not only a lower critical threshold at which HMRI appears but also an upper one at which it disappears again. The latter distinguishes the HMRI from a magnetically modified Taylor vortex flow. Second, we find an absolute instability threshold as well. In the hydrodynamically unstable regime before the Rayleigh line, the threshold of absolute instability is just slightly above the convective one although the critical wavelength of the former is noticeably shorter than that of the latter. Beyond the Rayleigh line the lower threshold of absolute instability rises significantly above the corresponding convective one while the upper one descends significantly below its convective counterpart. As a result, the extension of the absolute HMRI beyond the Rayleigh line is considerably shorter than that of the convective instability. The absolute HMRI is supposed to be self-sustained and, thus, experimentally observable without any external excitation in a system of sufficiently large axial extension.

Laser plasma interaction on rugby hohlraum on the Omega Laser Facility: Comparisons between cylinder, rugby, and elliptical hohlraums

NASA Astrophysics Data System (ADS)

Masson-Laborde, P. E.; Monteil, M. C.; Tassin, V.; Philippe, F.; Gauthier, P.; Casner, A.; Depierreux, S.; Neuville, C.; Villette, B.; Laffite, S.; Seytor, P.; Fremerye, P.; Seka, W.; Teychenné, D.; Debayle, A.; Marion, D.; Loiseau, P.; Casanova, M.

2016-02-01

Gas-filled rugby-shaped hohlraums have demonstrated high performances compared to a classical similar diameter cylinder hohlraum with a nearly 40% increase of x-ray drive, 10% higher measured peak drive temperature, and an increase in neutron production. Experimental comparisons have been done between rugby, cylinder, and elliptical hohlraums. The impact of these geometry differences on the laser plasma instabilities is examined. Using comparisons with hydrodynamic simulations carried out with the code FCI2 and postprocessed by Piranah, we have been able to reproduce the stimulated Raman and Brillouin scattering spectrum of the different beams. Using a methodology based on a statistical analysis for the gain calculations, we show that the behavior of the laser plasma instabilities in rugby hohlraums can be reproduced. The efficiency of laser smoothing techniques to mitigate these instabilities are discussed, and we show that while rugby hohlraums exhibit more laser plasma instabilities than cylinder hohlraum, the latter can be mitigated in the case of an elliptical hohlraum.

Interplay of phase sequence and electronic structure in the modulated martensites of Mn2NiGa from first-principles calculations

NASA Astrophysics Data System (ADS)

Kundu, Ashis; Gruner, Markus E.; Siewert, Mario; Hucht, Alfred; Entel, Peter; Ghosh, Subhradip

2017-08-01

We investigate the relative stability, structural properties, and electronic structure of various modulated martensites of the magnetic shape memory alloy Mn2NiGa by means of density functional theory. We observe that the instability in the high-temperature cubic structure first drives the system to a structure where modulation shuffles with a period of six atomic planes are taken into account. The driving mechanism for this instability is found to be the nesting of the minority band Fermi surface, in a similar way to that established for the prototype system Ni2MnGa . In agreement with experiments, we find 14M modulated structures with orthorhombic and monoclinic symmetries having energies lower than other modulated phases with the same symmetry. In addition, we also find energetically favorable 10M modulated structures which have not been observed experimentally for this system yet. The relative stability of various martensites is explained in terms of changes in the electronic structures near the Fermi level, affected mostly by the hybridization of Ni and Mn states. Our results indicate that the maximum achievable magnetic field-induced strain in Mn2NiGa would be larger than in Ni2MnGa . However, the energy costs for creating nanoscale adaptive twin boundaries are found to be one order of magnitude higher than that in Ni2MnGa .

On the nonlinear stability of a high-speed, axisymmetric boundary layer

NASA Technical Reports Server (NTRS)

Pruett, C. David; Ng, Lian L.; Erlebacher, Gordon

1991-01-01

The stability of a high-speed, axisymmetric boundary layer is investigated using secondary instability theory and direct numerical simulation. Parametric studies based on the temporal secondary instability theory identify subharmonic secondary instability as a likely path to transition on a cylinder at Mach 4.5. The theoretical predictions are validated by direct numerical simulation at temporally-evolving primary and secondary disturbances in an axisymmetric boundary-layer flow. At small amplitudes of the secondary disturbance, predicted growth rates agree to several significant digits with values obtained from the spectrally-accurate solution of the compressible Navier-Stokes equations. Qualitative agreement persists to large amplitudes of the secondary disturbance. Moderate transverse curvature is shown to significantly affect the growth rate of axisymmetric second mode disturbances, the likely candidates of primary instability. The influence of curvature on secondary instability is largely indirect but most probably significant, through modulation of the primary disturbance amplitude. Subharmonic secondary instability is shown to be predominantly inviscid in nature, and to account for spikes in the Reynolds stress components at or near the critical layer.

Analysis of shot noise suppression for electron beams

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

Ratner, Daniel; Huang, Zhirong; Stupakov, Gennady

2011-06-24

Shot noise can affect the performance of free-electron lasers (FELs) by driving instabilities (e.g., the microbunching instability) or by competing with seeded density modulations. Recent papers have proposed suppressing shot noise to enhance FEL performance. In this paper we use a onedimensional (1D) model to calculate the noise amplification from an energy modulation (e.g., electron interactions from space charge or undulator radiation) followed by a dispersive section. We show that, for a broad class of interactions, selecting the correct dispersive strength suppresses shot noise across a wide range of frequencies. The final noise level depends on the beam’s energy spreadmore » and the properties of the interaction potential. As a result, we confirm and illustrate our analytical results with 1D simulations.« less

Analysis of Shot Noise Suppression for Electron Beams

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

Ratner, Daniel; /Stanford U., Appl. Phys. Dept.; Huang, Zhirong

2012-05-07

Shot noise can affect the performance of free-electron lasers (FELs) by driving instabilities (e.g., the microbunching instability) or by competing with seeded density modulations. Recent papers have proposed suppressing shot noise to enhance FEL performance. In this paper we use a one-dimensional (1D) model to calculate the noise amplification from an energy modulation (e.g., electron interactions from space charge or undulator radiation) followed by a dispersive section. We show that, for a broad class of interactions, selecting the correct dispersive strength suppresses shot noise across a wide range of frequencies. The final noise level depends on the beam's energy spreadmore » and the properties of the interaction potential. We confirm and illustrate our analytical results with 1D simulations.« less

Optical solitons and modulation instability analysis with (3 + 1)-dimensional nonlinear Shrödinger equation

NASA Astrophysics Data System (ADS)

Inc, Mustafa; Aliyu, Aliyu Isa; Yusuf, Abdullahi; Baleanu, Dumitru

2017-12-01

This paper addresses the (3 + 1)-dimensional nonlinear Shrödinger equation (NLSE) that serves as the model to study the propagation of optical solitons through nonlinear optical fibers. Two integration schemes are employed to study the equation. These are the complex envelope function ansatz and the solitary wave ansatz with Jaccobi elliptic function methods, we present the exact dark, bright and dark-bright or combined optical solitons to the model. The intensity as well as the nonlinear phase shift of the solitons are reported. The modulation instability aspects are discussed using the concept of linear stability analysis. The MI gain is got. Numerical simulation of the obtained results are analyzed with interesting figures showing the physical meaning of the solutions.

Modulational-instability-induced supercontinuum generation with saturable nonlinear response

NASA Astrophysics Data System (ADS)

Raja, R. Vasantha Jayakantha; Porsezian, K.; Nithyanandan, K.

2010-07-01

We theoretically investigate the supercontinuum generation (SCG) on the basis of modulational instability (MI) in liquid-core photonic crystal fibers (LCPCF) with CS2-filled central core. The effect of saturable nonlinearity of LCPCF on SCG in the femtosecond regime is studied using an appropriately modified nonlinear Schrödinger equation. We also compare the MI induced spectral broadening with SCG obtained by soliton fission. To analyze the quality of the pulse broadening, we study the coherence of the SC pulse numerically. It is evident from the numerical simulation that the response of the saturable nonlinearity suppresses the broadening of the pulse. We also observe that the MI induced SCG in the presence of saturable nonlinearity degrades the coherence of the SCG pulse when compared to unsaturated medium.

Modulational-instability-induced supercontinuum generation with saturable nonlinear response

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

Raja, R. Vasantha Jayakantha; Porsezian, K.; Nithyanandan, K.

2010-07-15

We theoretically investigate the supercontinuum generation (SCG) on the basis of modulational instability (MI) in liquid-core photonic crystal fibers (LCPCF) with CS{sub 2}-filled central core. The effect of saturable nonlinearity of LCPCF on SCG in the femtosecond regime is studied using an appropriately modified nonlinear Schroedinger equation. We also compare the MI induced spectral broadening with SCG obtained by soliton fission. To analyze the quality of the pulse broadening, we study the coherence of the SC pulse numerically. It is evident from the numerical simulation that the response of the saturable nonlinearity suppresses the broadening of the pulse. We alsomore » observe that the MI induced SCG in the presence of saturable nonlinearity degrades the coherence of the SCG pulse when compared to unsaturated medium.« less

Excitation of MHD waves upstream of Jupiter by energetic sulfur or oxygen ions

NASA Technical Reports Server (NTRS)

Goldstein, M. L.; Wong, H. K.; Eviatar, A.

1986-01-01

Large fluxes of heavy ions have been reported upstream of Jupiter's bow shock as Voyager 1 approached the planet (Zwickl et al., 1981; Krimigis et al., 1985). Enhanced low-frequency magnetic wave activity was also observed during the particle events. The fluctuations are left-handed, elliptically polarized in the plasma frame. The spectrum of these fluctuations contains a peak close to the Doppler-shifted resonance frequency of a sulfur or oxygen beam with streaming energy of approximately 30 keV. These fluctuations are also present in the spectrum of the magnitude of the field. It is concluded that the observations result from an instability driven by an energetic beam of either sulfur or oxygen. The wave observations can be described by a heavy ion distribution with both a streaming anisotropy and a temperature anisotropy. This class of heavy ion streaming instabilities may also play a role in wave-particle interactions in the vicinity of comets.

Transport with Reversed Er in Gamma -10, LAPD and the Sao Paulo Tokamak

NASA Astrophysics Data System (ADS)

Fu, Sean; Morrison, P. J.; Horton, W.; Caldas, Ibere

2009-11-01

The understanding of how and when the reversed radial electric field produces an internal transport barrier is still poorly understood. There are two linked aspects to the problem: (i) the change in the plasma instabilities and thus the fluctuation spectrum from changes away from or towards the generalized Rayleigh condition for destabilizing the drift wave/ Rossby wave instabilities and (2) for a fixed fluctuation spectrum the role of the Er reversal in creating a layer where the resonant surfaces do not overlap so the condition for the onset of diffusion from overlapping resonances in phase space is not satisfied. We look at a model that is representative of the externally controlled Er shear in the G-10 Tsukuba tandem mirror and in the wall biasing experiments in the LAPD and the Sao Paulo Tokamak to ask when the effects are dominant and how they may compete with each other to determine the conditions for the transport suppression that is reported in numerous plasma experiments.

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.

Dynamics and Instabilities of the Shastry-Sutherland Model

NASA Astrophysics Data System (ADS)

Wang, Zhentao; Batista, Cristian D.

2018-06-01

We study the excitation spectrum in the dimer phase of the Shastry-Sutherland model by using an unbiased variational method that works in the thermodynamic limit. The method outputs dynamical correlation functions in all possible channels. This output is exploited to identify the order parameters with the highest susceptibility (single or multitriplon condensation in a specific channel) upon approaching a quantum phase transition in the magnetic field versus the J'/J phase diagram. We find four different instabilities: antiferro spin nematic, plaquette spin nematic, stripe magnetic order, and plaquette order, two of which have been reported in previous studies.

Ion acceleration from thin foil and extended plasma targets by slow electromagnetic wave and related ion-ion beam instability

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

Bulanov, S. V.; A. M. Prokhorov Institute of General Physics RAS, Moscow, 119991; Esirkepov, T. Zh.

When ions are accelerated by the radiation pressure of a laser pulse, their velocity cannot exceed the pulse group velocity which can be considerably smaller than the speed of light in vacuum. This is demonstrated in two cases corresponding to a thin foil target irradiated by high intensity laser light and to the hole boring produced in an extended plasma by the laser pulse. It is found that the beams of accelerated ions are unstable against Buneman-like and Weibel-like instabilities which results in the broadening of the ion energy spectrum.

Suppression of the Transit -Time Instability in Large-Area Electron Beam Diodes

NASA Astrophysics Data System (ADS)

Myers, Matthew C.; Friedman, Moshe; Swanekamp, Stephen B.; Chan, Lop-Yung; Ludeking, Larry; Sethian, John D.

2002-12-01

Experiment, theory, and simulation have shown that large-area electron-beam diodes are susceptible to the transit-time instability. The instability modulates the electron beam spatially and temporally, producing a wide spread in electron energy and momentum distributions. The result is gross inefficiency in beam generation and propagation. Simulations indicate that a periodic, slotted cathode structure that is loaded with resistive elements may be used to eliminate the instability. Such a cathode has been fielded on one of the two opposing 60 cm × 200 cm diodes on the NIKE KrF laser at the Naval Research Laboratory. These diodes typically deliver 600 kV, 500 kA, 250 ns electron beams to the laser cell in an external magnetic field of 0.2 T. We conclude that the slotted cathode suppressed the transit-time instability such that the RF power was reduced by a factor of 9 and that electron transmission efficiency into the laser gas was improved by more than 50%.

Theoretical studies of the solar atmosphere and interstellar pickup ions

NASA Technical Reports Server (NTRS)

1994-01-01

Solar atmosphere research activities are summarized. Specific topics addressed include: (1) coronal mass ejections and related phenomena; (2) parametric instabilities of Alfven waves; (3) pickup ions in the solar wind; and (4) cosmic rays in the outer heliosphere. Also included is a list of publications covering the following topics: catastrophic evolution of a force-free flux rope; maximum energy release in flux-rope models of eruptive flares; sheet approximations in models of eruptive flares; material ejection, motions of loops and ribbons of two-ribbon flares; dispersion relations for parametric instabilities of parallel-propagating; parametric instabilities of parallel-propagating Alfven waves; beat, modulation, and decay instabilities of a circularly-polarized Alfven wave; effects of time-dependent photoionization on interstellar pickup helium; observation of waves generated by the solar wind pickup of interstellar hydrogen ions; ion thermalization and wave excitation downstream of the quasi-perpendicular bowshock; ion cyclotron instability and the inverse correlation between proton anisotrophy and proton beta; and effects of cosmic rays and interstellar gas on the dynamics of a wind.

Ablative Rayleigh-Taylor and Richtmyer-Meshkov Instabilities in Laser-Accelerated Colliding Foils

NASA Astrophysics Data System (ADS)

Aglitskiy, Y.; Metzler, N.; Karasik, M.; Serlin, V.; Weaver, J.; Obenschain, S. P.; Oh, J.; Schmitt, A. J.; Velikovich, A. L.; Zalesak, S. T.; Gardner, J. H.; Harding, E. C.

2008-11-01

In our experiments done on the Nike KrF laser, we study instability growth at shock-decelerated interfaces in planar colliding-foil experiments. We use streaked monochromatic (1.86 keV) x-ray face-on imaging diagnostics to measure the areal mass modulation growth caused by the instability. Higher x-ray energies up to 5.25 keV are used to follow the shock propagation as well as the 1D dynamics of the collision. While a laser-driven foil is accelerated towards the stationary low-density foam layer, an ablative RT instability develops. Having reached a high velocity, the foil hits the foam layer. The impact generates strong shocks in the plastic and in the foam. The reflected shock wave re-shocks the ablation front, its acceleration stops, and so does the observed RT growth. This is followed by areal mass oscillations due to the ablative RM instability and feedout mechanisms, of which the latter dominates.

Heating and acceleration of solar wind ions by turbulent wave spectrum in inhomogeneous expanding plasma

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

Ofman, Leon, E-mail: Leon.Ofman@nasa.gov; NASA Goddard Space Flight Center, Greenbelt, MD; Visiting, Department of Geosciences, Tel Aviv University, Tel Aviv

Near the Sun (< 10R{sub s}) the acceleration, heating, and propagation of the solar wind are likely affected by the background inhomogeneities of the magnetized plasma. The heating and the acceleration of the solar wind ions by turbulent wave spectrum in inhomogeneous plasma is studied using a 2.5D hybrid model. The hybrid model describes the kinetics of the ions, while the electrons are modeled as massless neutralizing fluid in an expanding box approach. Turbulent magnetic fluctuations dominated by power-law frequency spectra, which are evident from in-situ as well as remote sensing measurements, are used in our models. The effects ofmore » background density inhomogeneity across the magnetic field on the resonant ion heating are studied. The effect of super-Alfvénic ion drift on the ion heating is investigated. It is found that the turbulent wave spectrum of initially parallel propagating waves cascades to oblique modes, and leads to enhanced resonant ion heating due to the inhomogeneity. The acceleration of the solar wind ions is achieved by the parametric instability of large amplitude waves in the spectrum, and is also affected by the inhomogeneity. The results of the study provide the ion temperature anisotropy and drift velocity temporal evolution due to relaxation of the instability. The non-Maxwellian velocity distribution functions (VDFs) of the ions are modeled in the inhomogeneous solar wind plasma in the acceleration region close to the Sun.« less

Modulational instability and higher-order rogue waves with parameters modulation in a coupled integrable AB system via the generalized Darboux transformation.

PubMed

Wen, Xiao-Yong; Yan, Zhenya

2015-12-01

We study higher-order rogue wave (RW) solutions of the coupled integrable dispersive AB system (also called Pedlosky system), which describes the evolution of wave-packets in a marginally stable or unstable baroclinic shear flow in geophysical fluids. We propose its continuous-wave (CW) solutions and existent conditions for their modulation instability to form the rogue waves. A new generalized N-fold Darboux transformation (DT) is proposed in terms of the Taylor series expansion for the spectral parameter in the Darboux matrix and its limit procedure and applied to the CW solutions to generate multi-rogue wave solutions of the coupled AB system, which satisfy the general compatibility condition. The dynamical behaviors of these higher-order rogue wave solutions demonstrate both strong and weak interactions by modulating parameters, in which some weak interactions can generate the abundant triangle, pentagon structures, etc. Particularly, the trajectories of motion of peaks and depressions of profiles of the first-order RWs are explicitly analyzed. The generalized DT method used in this paper can be extended to other nonlinear integrable systems. These results may be useful for understanding the corresponding rogue-wave phenomena in fluid mechanics and related fields.

Modulated wave formation in myocardial cells under electromagnetic radiation

NASA Astrophysics Data System (ADS)

Takembo, Clovis N.; Mvogo, A.; Ekobena Fouda, H. P.; Kofané, T. C.

2018-06-01

We exclusively analyze the onset and condition of formation of modulated waves in a diffusive FitzHugh-Nagumo model for myocardial cell excitations. The cells are connected through gap junction coupling. An additive magnetic flux variable is used to describe the effect of electromagnetic induction, while electromagnetic radiation is imposed on the magnetic flux variable as a periodic forcing. We used the discrete multiple scale expansion and obtained, from the model equations, a single differential-difference amplitude nonlinear equation. We performed the linear stability analysis of this equation and found that instability features are importantly influenced by the induced electromagnetic gain. We present the unstable and stable regions of modulational instability (MI). The resulting analytic predictions are confirmed by numerical experiments of the generic equations. The results reveal that due to MI, an initial steady state that consisted of a plane wave with low amplitude evolves into a modulated localized wave patterns, soliton-like in shape, with features of synchronization. Furthermore, the formation of periodic pulse train with breathing motion presents a disappearing pattern in the presence of electromagnetic radiation. This could provide guidance and better understanding of sudden heart failure exposed to heavily electromagnetic radiation.

The physical basis for estimating wave-energy spectra with the radar ocean-wave spectrometer

NASA Technical Reports Server (NTRS)

Jackson, Frederick C.

1987-01-01

The derivation of the reflectivity modulation spectrum of the sea surface for near-nadir-viewing microwave radars using geometrical optics is described. The equations required for the derivation are presented. The derived reflectivity modulation spectrum provides data on the physical basis of the radar ocean-wave spectrometer measurements of ocean-wave directional spectra.

Direct and quantitative broadband absorptance spectroscopy with multilayer cantilever probes

DOEpatents

Hsu, Wei-Chun; Tong, Jonathan Kien-Kwok; Liao, Bolin; Chen, Gang

2015-04-21

A system for measuring the absorption spectrum of a sample is provided that includes a broadband light source that produces broadband light defined within a range of an absorptance spectrum. An interferometer modulates the intensity of the broadband light source for a range of modulation frequencies. A bi-layer cantilever probe arm is thermally connected to a sample arm having at most two layers of materials. The broadband light modulated by the interferometer is directed towards the sample and absorbed by the sample and converted into heat, which causes a temperature rise and bending of the bi-layer cantilever probe arm. A detector mechanism measures and records the deflection of the probe arm so as to obtain the absorptance spectrum of the sample.

Rogue wave spectra of the Kundu-Eckhaus equation.

PubMed

Bayındır, Cihan

2016-06-01

In this paper we analyze the rogue wave spectra of the Kundu-Eckhaus equation (KEE). We compare our findings with their nonlinear Schrödinger equation (NLSE) analogs and show that the spectra of the individual rogue waves significantly differ from their NLSE analogs. A remarkable difference is the one-sided development of the triangular spectrum before the rogue wave becomes evident in time. Also we show that increasing the skewness of the rogue wave results in increased asymmetry in the triangular Fourier spectra. Additionally, the triangular spectra of the rogue waves of the KEE begin to develop at earlier stages of their development compared to their NLSE analogs, especially for larger skew angles. This feature may be used to enhance the early warning times of the rogue waves. However, we show that in a chaotic wave field with many spectral components the triangular spectra remain as the main attribute as a universal feature of the typical wave fields produced through modulation instability and characteristic features of the KEE's analytical rogue wave spectra may be suppressed in a realistic chaotic wave field.

On the maximum energy achievable in the first order Fermi acceleration at shocks

NASA Astrophysics Data System (ADS)

Grozny, I.; Diamond, P.; Malkov, M.

2002-11-01

Astrophysical shocks are considered as the sites of cosmic ray (CR) production. The primary mechanism is the diffusive shock (Fermi) acceleration which operates via multiple shock recrossing by a particle. Its efficiency, the rate of energy gain, and the maximum energy are thus determined by the transport mechanisms (confinement to the shock) of these particles in a turbulent shock environment. The turbulence is believed to be generated by accelerated particles themselves. Moreover, in the most interesting case of efficient acceleration the entire MHD shock structure is dominated by their pressure. This makes this problem one of the challenging strongly nonlinear problems of astrophysics. We suggest a physical model that describes particle acceleration, shock structure and the CR driven turbulence on an equal footing. The key new element in this scheme is nonlinear cascading of the MHD turbulence on self-excited (via modulational and Drury instability) sound-like perturbations which gives rise to a significant enrichment of the long wave part of the MHD spectrum. This is critical for the calculation of the maximum energy.

The contribution of microbunching instability to solar flare emission in the GHz to THz range of frequencies

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

Klopf, J. Michael; Kaufmann, Pierre; Raulin, Jean-Pierre

2014-07-01

Recent solar flare observations in the sub-terahertz range have provided evidence of a new spectral component with fluxes increasing for larger frequencies, separated from the well-known microwave emission that maximizes in the gigahertz range. Suggested interpretations explain the terahertz spectral component but do not account for the simultaneous microwave component. We present a mechanism for producing the observed "double spectra." Based on coherent enhancement of synchrotron emission at long wavelengths in laboratory accelerators, we consider how similar processes may occur within a solar flare. The instability known as microbunching arises from perturbations that produce electron beam density modulations, giving risemore » to broadband coherent synchrotron emission at wavelengths comparable to the characteristic size of the microbunch structure. The spectral intensity of this coherent synchrotron radiation (CSR) can far exceed that of the incoherent synchrotron radiation (ISR), which peaks at a higher frequency, thus producing a double-peaked spectrum. Successful CSR simulations are shown to fit actual burst spectral observations, using typical flaring physical parameters and power-law energy distributions for the accelerated electrons. The simulations consider an energy threshold below which microbunching is not possible because of Coulomb repulsion. Only a small fraction of the radiating charges accelerated to energies above the threshold is required to produce the microwave component observed for several events. The ISR/CSR mechanism can occur together with other emission processes producing the microwave component. It may bring an important contribution to microwaves, at least for certain events where physical conditions for the occurrence of the ISR/CSR microbunching mechanism are possible.« less

Rossby wave instability in astrophysical discs

NASA Astrophysics Data System (ADS)

Lovelace, R. V. E.; Romanova, M. M.

2014-08-01

A brief review is given of the Rossby wave instability in astrophysical discs. 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 disc surface mass-density. It gives rise to exponentially growing non-axisymmetric perturbation (\\propto \\exp \\,({ { i}}m\\phi ) , 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 proto-planetary discs. The Rossby vortices in the discs around stars and black holes may cause the observed quasi-periodic modulations of the disc's thermal emission.

Transverse mode coupling instability threshold with space charge and different wakefields

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

Balbekov, V.

Transverse mode coupling instability of a bunch with space charge and wake field is considered in frameworks of the boxcar model. Eigenfunctions of the bunch without wake are used as the basis for solution of the equations with the wake field included. Dispersion equation for the bunch eigentunes is obtained in the form of an infinite continued fraction. It is shown that influence of space charge on the instability essentially depends on the wake sign. In particular, threshold of the negative wake increases in absolute value until the space charge tune shift is rather small, and goes to zero atmore » higher space charge. The explanation of this behavior is developed by analysis of the bunch spectrum. As a result, a comparison of the results with published articles is represented.« less

Transverse mode coupling instability threshold with space charge and different wakefields

DOE PAGES

Balbekov, V.

2017-03-10

Transverse mode coupling instability of a bunch with space charge and wake field is considered in frameworks of the boxcar model. Eigenfunctions of the bunch without wake are used as the basis for solution of the equations with the wake field included. Dispersion equation for the bunch eigentunes is obtained in the form of an infinite continued fraction. It is shown that influence of space charge on the instability essentially depends on the wake sign. In particular, threshold of the negative wake increases in absolute value until the space charge tune shift is rather small, and goes to zero atmore » higher space charge. The explanation of this behavior is developed by analysis of the bunch spectrum. As a result, a comparison of the results with published articles is represented.« less

Effects of a semi-infinite stratification on the Rayleigh-Taylor instability in an interface with surface tension

NASA Astrophysics Data System (ADS)

de Andrea González, Ángel; González-Gutiérrez, Leo M.

2017-09-01

The Rayleigh-Taylor instability (RTI) in an infinite slab where a constant density lower fluid is initially separated from an upper stratified fluid is discussed in linear regime. The upper fluid is of increasing exponential density and surface tension is considered between both of them. It was found useful to study stability by using the initial value problem approach (IVP), so that we ensure the inclusion of certain continuum modes, otherwise neglected. This methodology includes the branch cut in the complex plane, consequently, in addition to discrete modes (surface RTI modes), a set of continuum modes (internal RTI modes) also appears. As a result, the usual information given by the normal mode method is now complete. Furthermore, a new role is found for surface tension: to transform surface RTI modes (discrete spectrum) into internal RTI modes belonging to a continuous spectrum at a critical wavenumber. As a consequence, the cut-off wavenumber disappears: i.e. the growth rate of the RTI surface mode does not decay to zero at the cut-off wavenumber, as previous researchers used to believe. Finally, we found that, due to the continuum, the asymptotic behavior of the perturbation with respect to time is slower than the exponential when only the continuous spectrum exists.

A Deeper Understanding of Stability in the Solar Wind: Applying Nyquist's Instability Criterion to Wind Faraday Cup Data

NASA Astrophysics Data System (ADS)

Alterman, B. L.; Klein, K. G.; Verscharen, D.; Stevens, M. L.; Kasper, J. C.

2017-12-01

Long duration, in situ data sets enable large-scale statistical analysis of free-energy-driven instabilities in the solar wind. The plasma beta and temperature anisotropy plane provides a well-defined parameter space in which a single-fluid plasma's stability can be represented. Because this reduced parameter space can only represent instability thresholds due to the free energy of one ion species - typically the bulk protons - the true impact of instabilities on the solar wind is under estimated. Nyquist's instability criterion allows us to systematically account for other sources of free energy including beams, drifts, and additional temperature anisotropies. Utilizing over 20 years of Wind Faraday cup and magnetic field observations, we have resolved the bulk parameters for three ion populations: the bulk protons, beam protons, and alpha particles. Applying Nyquist's criterion, we calculate the number of linearly growing modes supported by each spectrum and provide a more nuanced consideration of solar wind stability. Using collisional age measurements, we predict the stability of the solar wind close to the sun. Accounting for the free-energy from the three most common ion populations in the solar wind, our approach provides a more complete characterization of solar wind stability.

Control of secondary instability of the crossflow and Görtler-like vortices (Success and problems)

NASA Astrophysics Data System (ADS)

Kozlov, Viktor V.; Grek, Genrich R.

The secondary instability on a group of crossflow vortices developing in a swept wing boundary layer is described. It is shown that, for travelling waves, there is a region of linear development, and the growth rate of disturbances appreciably depends on the separation between the vortices. Methods of controlling the secondary instability of the vortices by a controlled wave and local suction are proposed and substantiated. The stability of a flat plate boundary layer modulated by G&ou ml;rtler-like stationary vortices is described. Vortices were generated inside the boundary layer by means of roughness elements arranged in a regular array along the spanwise (z) direction. Transition is not caused directly by these structures, but by the growth of small amplitude travelling waves riding on top of the steady vortices. This situation is analogous to the transition process in Görtler and cross-flows. The waves were found to amplify up to a stage where higher harmonics are gener ated, leading to turbulent breakdown and disintegration of the spanwise boundary layer structure. For strong modulations, the observed instability is quite powerful, and can be excited "naturally" by small uncontrollable background disturbances. Controlled oscillations were then introduced by means of a vibrating ribbon, allowing a detailed investigation of the wave characteristics. The instability seems to be associated with the spanwise gradients of the mean flow, , and at all z-positions, the maximum wave amplitude was found at a wall-normal position where the mean velocity is equal to the phase velocity of the wave, U(y)=c, i.e., at the local critical layer. Unstable waves were observed at frequency well above those for which Tollmien-Schlichting (TS) waves amplify in the Blasius boundary layer. Excitation at lower frequencies and milder basic flow modulation showed that TS-type waves may a lso develop. Study of the transition control in that flow by means of riblets shows that the effect of the riblets is to suppress longitudinal vortex structures in a boundary layer. The boundary layer becomes stable with respect to high-frequency travelling waves, which cause the transition in the absence of the riblets.

Amorphous-silicon module hot-spot testing

NASA Technical Reports Server (NTRS)

Gonzalez, C. C.

1985-01-01

Hot spot heating occurs when cell short-circuit current is lower than string operating current. Amorphous cell hot spot are tested to develop the techniques required for performing reverse bias testing of amorphous cells. Also, to quantify the response of amorphous cells to reverse biasing. Guidelines are developed from testing for reducing hot spot susceptibility of amorphous modules and to develop a qualification test for hot spot testing of amorphous modules. It is concluded that amorphous cells undergo hot spot heating similarly to crystalline cells. Comparison of results obtained with submodules versus actual modules indicate heating levels lower in actual modules. Module design must address hot spot testing and hot spot qualification test conducted on modules showed no instabilities and minor cell erosion.

Active Control of Combustor Instability Shown to Help Lower Emissions

NASA Technical Reports Server (NTRS)

DeLaat, John C.; Chang, Clarence T.

2002-01-01

In a quest to reduce the environmental impact of aerospace propulsion systems, extensive research is being done in the development of lean-burning (low fuel-to-air ratio) combustors that can reduce emissions throughout the mission cycle. However, these lean-burning combustors have an increased susceptibility to thermoacoustic instabilities, or high-pressure oscillations much like sound waves, that can cause severe high-frequency vibrations in the combustor. These pressure waves can fatigue the combustor components and even the downstream turbine blades. This can significantly decrease the safe operating life of the combustor and turbine. Thus, suppression of the thermoacoustic combustor instabilities is an enabling technology for lean, low-emissions combustors. Under the Aerospace Propulsion and Power Base Research and Technology Program, the NASA Glenn Research Center, in partnership with Pratt & Whitney and United Technologies Research Center, is developing technologies for the active control of combustion instabilities. With active combustion control, the fuel is pulsed to put pressure oscillations into the system. This cancels out the pressure oscillations being produced by the instabilities. Thus, the engine can have lower pollutant emissions and long life.The use of active combustion instability control to reduce thermo-acoustic-driven combustor pressure oscillations was demonstrated on a single-nozzle combustor rig at United Technologies. This rig has many of the complexities of a real engine combustor (i.e., an actual fuel nozzle and swirler, dilution cooling, etc.). Control was demonstrated through modeling, developing, and testing a fuel-delivery system able to the 280-Hz instability frequency. The preceding figure shows the capability of this system to provide high-frequency fuel modulations. Because of the high-shear contrarotating airflow in the fuel injector, there was some concern that the fuel pulses would be attenuated to the point where they would not be effective for control. Testing in the combustor rig showed that open-loop pulsing of the fuel was, in fact, able to effectively modulate the combustor pressure. To suppress the combustor pressure oscillations due to thermoacoustic instabilities, it is desirable to time the injection of the fuel so that it interferes with the instability. A closed-loop control scheme was developed that uses combustion pressure feedback and a phase-shifting controller to time the fuel-injection pulses. Some suppression of the pressure oscillations at the 280-Hz instability frequency was demonstrated (see the next figure). However, the overall peak-to- peak pressure oscillations in the combustor were only mildly reduced. Improvements to control hardware and control methods are being continued to gain improved closed-loop reduction of the pressure oscillations.pulse the fuel at

Fiber-optic temperature sensor using a spectrum-modulating semiconductor etalon

NASA Technical Reports Server (NTRS)

Beheim, Glenn; Anthan, Donald J.; Beheim, Glenn; Anthan, Donald J.

1987-01-01

Described is a fiber-optic temperature sensor that uses a spectrum modulating SiC etalon. The spectral output of this type of sensor may be analyzed to obtain a temperature measurement which is largely independent of the transmission properties of the sensor's fiber-optic link. A highly precise laboratory spectrometer is described in detail, and this instrument is used to study the properties of this type of sensor. Also described are a number of different spectrum analyzers that are more suitable for use in a practical thermometer.

Device for frequency modulation of a laser output spectrum

DOEpatents

Beene, James R.; Bemis, Jr., Curtis E.

1986-01-01

A device is provided for fast frequency modulating the output spectrum of multimode lasers and single frequency lasers that are not actively stabilized. A piezoelectric transducer attached to a laser cavity mirror is driven in an unconventional manner to excite resonance vibration of the transducer to rapidly, cyclicly change the laser cavity length. The result is a cyclic sweeping of the output wavelength sufficient to fill the gaps in the laser output frequency spectrum. When such a laser is used to excite atoms or molecules, complete absorption line coverage is made possible.

Device for frequency modulation of a laser output spectrum

DOEpatents

Beene, J.R.; Bemis, C.E. Jr.

1984-07-17

A device is provided for fast frequency modulating the output spectrum of multimode lasers and single frequency lasers that are not actively stabilized. A piezoelectric transducer attached to a laser cavity mirror is driven in an unconventional manner to excite resonance vibration of the tranducer to rapidly, cyclicly change the laser cavity length. The result is a cyclic sweeping of the output wavelength sufficient to fill the gaps in the laser output frequency spectrum. When a laser is used to excite atoms or molecules, complete absorption line coverage is made possible.

Smart radio: spectrum access for first responders

NASA Astrophysics Data System (ADS)

Silvius, Mark D.; Ge, Feng; Young, Alex; MacKenzie, Allen B.; Bostian, Charles W.

2008-04-01

This paper details the Wireless at Virginia Tech Center for Wireless Telecommunications' (CWT) design and implementation of its Smart Radio (SR) communication platform. The CWT SR can identify available spectrum within a pre-defined band, rendezvous with an intended receiver, and transmit voice and data using a selected quality of service (QoS). This system builds upon previous cognitive technologies developed by CWT for the public safety community, with the goal of providing a prototype mobile communications package for military and public safety First Responders. A master control (MC) enables spectrum awareness by characterizing the radio environment with a power spectrum sensor and an innovative signal detection and classification module. The MC also enables spectrum and signal memory by storing sensor results in a knowledge database. By utilizing a family radio service (FRS) waveform database, the CWT SR can create a new communication link on any designated FRS channel frequency using FM, BPSK, QPSK, or 8PSK modulations. With FM, it supports analog voice communications with legacy hand-held FRS radios. With digital modulations, it supports IP data services, including a CWT developed CVSD-based VoIP protocol. The CWT SR coordinates spectrum sharing between analog primary users and digital secondary users by applying a simple but effective channel-change protocol. It also demonstrates a novel rendezvous protocol to facilitate the detection and initialization of communications links with neighboring SR nodes through the transmission of frequency-hopped rendezvous beacons. By leveraging the GNU Radio toolkit, writing key modules entirely in Python, and utilizing the USRP hardware front-end, the CWT SR provides a dynamic spectrum test bed for future smart and cognitive radio research.

Parametric instability and wave turbulence driven by tidal excitation of internal waves

NASA Astrophysics Data System (ADS)

Le Reun, Thomas; Favier, Benjamin; Le Bars, Michael

2018-04-01

We investigate the stability of stratified fluid layers undergoing homogeneous and periodic tidal deformation. We first introduce a local model which allows to study velocity and buoyancy fluctuations in a Lagrangian domain periodically stretched and sheared by the tidal base flow. While keeping the key physical ingredients only, such a model is efficient to simulate planetary regimes where tidal amplitudes and dissipation are small. With this model, we prove that tidal flows are able to drive parametric subharmonic resonances of internal waves, in a way reminiscent of the elliptical instability in rotating fluids. The growth rates computed via Direct Numerical Simulations (DNS) are in very good agreement with WKB analysis and Floquet theory. We also investigate the turbulence driven by this instability mechanism. With spatio-temporal analysis, we show that it is a weak internal wave turbulence occurring at small Froude and buoyancy Reynolds numbers. When the gap between the excitation and the Brunt-V\\"ais\\"al\\"a frequencies is increased, the frequency spectrum of this wave turbulence displays a -2 power law reminiscent of the high-frequency branch of the Garett and Munk spectrum (Garrett & Munk 1979) which has been measured in the oceans. In addition, we find that the mixing efficiency is altered compared to what is computed in the context of DNS of stratified turbulence excited at small Froude and large buoyancy Reynolds numbers and is consistent with a superposition of waves.

Plasmon dispersion in strongly correlated superlattices

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

Lu, D.; Golden, K.I.; Kalman, G.

The dielectric response function of a strongly correlated superlattice is calculated in the quasilocalized charge (QLC) approximation. The resulting QLC static local-field correction, which contains both intralayer and interlayer pair-correlational effects, is identical to the correlational part of the third-frequency-moment sum-rule coefficient. This approximation treats the interlayer and intralayer couplings on an equal footing. The resulting dispersion relation is first analyzed to determine the effect of intralayer coupling on the out-of-phase acoustic-mode dispersion; in this approximation the interlayer coupling is suppressed and the mutual interaction of the layers is taken into account only through the average random-phase approximation (RPA) field.more » In the resulting mode dispersion, the onset of a finite-{ital k} ({ital k} being the in-plane wave number) reentrant low-frequency excitation developing (with decreasing {ital d}/{ital a}) into a dynamical instability is indicated ({ital a} being the in-plane Wigner-Seitz radius and {ital d} the distance between adjacent lattice planes). This dynamical instability parallels a static structural instability reported earlier both for a bilayer electron system and a superlattice and presumably indicates a structural change in the electron liquid. If one takes account of interlayer correlations beyond the RPA, the acoustic excitation spectrum is dramatically modified by the appearance of an energy gap which also has a stabilizing effect on the instability. We extend a previous energy gap study at {ital k}=0 [G. Kalman, Y. Ren, and K. I. Golden, Phys Rev. B {bold 50}, 2031 (1994)] to a calculation of the dispersion of the gapped acoustic excitation spectrum in the long-wavelength domain. {copyright} {ital 1996 The American Physical Society.}« less

THE EFFECTS OF KINETIC INSTABILITIES ON SMALL-SCALE TURBULENCE IN EARTH’S MAGNETOSHEATH

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

Breuillard, H.; Yordanova, E.; Vaivads, A.

2016-09-20

The Earth's magnetosheath is the region delimited by the bow shock and the magnetopause. It is characterized by highly turbulent fluctuations covering all scales from MHD down to kinetic scales. Turbulence is thought to play a fundamental role in key processes such as energy transport and dissipation in plasma. In addition to turbulence, different plasma instabilities are generated in the magnetosheath because of the large anisotropies in plasma temperature introduced by its boundaries. In this study we use high-quality magnetic field measurements from Cluster spacecraft to investigate the effects of such instabilities on the small-scale turbulence (from ion down tomore » electron scales). We show that the steepening of the power spectrum of magnetic field fluctuations in the magnetosheath occurs at the largest characteristic ion scale. However, the spectrum can be modified by the presence of waves/structures at ion scales, shifting the onset of the small-scale turbulent cascade toward the smallest ion scale. This cascade is therefore highly dependent on the presence of kinetic instabilities, waves, and local plasma parameters. Here we show that in the absence of strong waves the small-scale turbulence is quasi-isotropic and has a spectral index α ≈ −2.8. When transverse or compressive waves are present, we observe an anisotropy in the magnetic field components and a decrease in the absolute value of α . Slab/2D turbulence also develops in the presence of transverse/compressive waves, resulting in gyrotropy/non-gyrotropy of small-scale fluctuations. The presence of both types of waves reduces the anisotropy in the amplitude of fluctuations in the small-scale range.« less

Polar cap photoionization and the ten-hour clock at Jupiter

NASA Technical Reports Server (NTRS)

Goertz, C. K.; Baker, D. N.

1985-01-01

It is shown that the clock-like modulation of the spectral index of energetic electrons (greater than 2 MeV) in the outer Jovian magnetosphere is due to a periodic shift of the particle energy spectrum toward higher and lower energies. This shift results in a modulation of the spectral index when the spectrum is not a pure power law in energy. It is suggested that the periodic energization is due to a periodic modulation of the magnetic field in the outer magnetosphere. This modulation is caused by a variation of the longitudinally averaged Pedersen conductivity due to the asymmetric solar illumination of the trace of the magnetodisk in the high-latitude ionospheres. Such a modulation requires the presence of a surface magnetic anomaly.

Simulation and Spectrum Extraction in the Spectroscopic Channel of the SNAP Experiment

NASA Astrophysics Data System (ADS)

Tilquin, Andre; Bonissent, A.; Gerdes, D.; Ealet, A.; Prieto, E.; Macaire, C.; Aumenier, M. H.

2007-05-01

A pixel-level simulation software is described. It is composed of two modules. The first module applies Fourier optics at each active element of the system to construct the PSF at a large variety of wavelengths and spatial locations of the point source. The input is provided by the engineer's design program (Zemax). It describes the optical path and the distortions. The PSF properties are compressed and interpolated using shapelets decomposition and neural network techniques. A second module is used for production jobs. It uses the output of the first module to reconstruct the relevant PSF and integrate it on the detector pixels. Extended and polychromatic sources are approximated by a combination of monochromatic point sources. For the spectrum extraction, we use a fast simulator based on a multidimensional linear interpolation of the pixel response tabulated on a grid of values of wavelength, position on sky and slice number. The prediction of the fast simulator is compared to the observed pixel content, and a chi-square minimization where the parameters are the bin contents is used to build the extracted spectrum. The visible and infrared arms are combined in the same chi-square, providing a single spectrum.

Oscillations in the CMB from Axion Monodromy Inflation

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

Flauger, Raphael; /Texas U.; McAllister, Liam

2011-12-01

We study the CMB observables in axion monodromy inflation. These well-motivated scenarios for inflation in string theory have monomial potentials over super-Planckian field ranges, with superimposed sinusoidal modulations from instanton effects. Such periodic modulations of the potential can drive resonant enhancements of the correlation functions of cosmological perturbations, with characteristic modulations of the amplitude as a function of wavenumber. We give an analytical result for the scalar power spectrum in this class of models, and we determine the limits that present data places on the amplitude and frequency of modulations. Then, incorporating an improved understanding of the realization of axionmore » monodromy inflation in string theory, we perform a careful study of microphysical constraints in this scenario. We find that detectable modulations of the scalar power spectrum are commonplace in well-controlled examples, while resonant contributions to the bispectrum are undetectable in some classes of examples and detectable in others. We conclude that resonant contributions to the spectrum and bispectrum are a characteristic signature of axion monodromy inflation that, in favorable cases, could be detected in near-future experiments.« less

Combustion Instability Analysis and the Effects of Drop Size on Acoustic Driving Rocket Flow

NASA Technical Reports Server (NTRS)

Harper, Brent (Technical Monitor); Ellison, L. Renea; Moser, Marlow D.

2004-01-01

High frequency combustion instability, the most destructive kind, is generally solved on a per engine basis. The instability often is the result of compounding acoustic oscillations, usually from the propellant combustion itself. To counteract the instability the chamber geometry can be changed and/or the method of propellant injection can be altered. This experiment will alter the chamber dimensions slightly; using a cylindrical shape of constant diameter and the length will be varied from six to twelve inches in three-inch increments. The main flowfield will be the products of a high OF hydrogen/oxygen flow. The liquid fuel will be injected into this flowfield using a modulated injector. It will allow for varied droplet size, feed rate, spray pattern, and location for the mixture within the chamber. The response will be deduced from the chamber pressure oscillations.

The Time-Dependent Structure of the Electron Reconnection Layer

NASA Technical Reports Server (NTRS)

Hesse, Michael; Zenitani, Seiji; Kuznetsova, Masha; Klimas, Alex

2009-01-01

Collisionless magnetic reconnection is often associated with time-dependent behavior. Specifically, current layers in the diffusion region can become unstable to tearing-type instabilities on one hand, or to instabilities with current-aligned wave vectors on the other. In the former case, the growth of tearing instabilities typically leads to the production of magnetic islands, which potentially provide feedback on the reconnection process itself, as well as on the rate of reconnection. The second class of instabilities tend to modulate the current layer along the direction of the current flow, for instance generating kink-type perturbations, or smaller-scale turbulence with the potential to broaden the current layer. All of these processes contribute to rendering magnetic reconnection time-dependent. In this presentation, we will provide a summary of these effects, and a discussion of how much they contribute to the overall magnetic reconnection rate.

Harmonic plasma waves excitation and structure evolution of intense ion beams in background plasmas

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

Hu, Zhang-Hu, E-mail: zhanghu@dlut.edu.cn; Wang, You-Nian

2016-08-15

The long-term dynamic evolutions of intense ion beams in plasmas have been investigated with two-dimensional electromagnetic particle simulations, taking into account the effect of the two-stream instability between beam ions and plasma electrons. Depending on the initial beam radial density profile and velocity distribution, ring structures may be formed in the beam edge regions. At the later stage of beam-plasma interactions, the ion beams are strongly modulated by the two-stream instability and multiple density spikes are formed in the longitudinal direction. The formation of these density spikes is shown to result from the excitation of harmonic plasma waves when themore » instability gets saturated. Comparisons between the beam cases with initial flat-top and Gaussian radial density profiles are made, and a higher instability growth rate is observed for the flat-top profile case.« less

SPOP mutation leads to genomic instability in prostate cancer

PubMed Central

Boysen, Gunther; Barbieri, Christopher E; Prandi, Davide; Blattner, Mirjam; Chae, Sung-Suk; Dahija, Arun; Nataraj, Srilakshmi; Huang, Dennis; Marotz, Clarisse; Xu, Limei; Huang, Julie; Lecca, Paola; Chhangawala, Sagar; Liu, Deli; Zhou, Pengbo; Sboner, Andrea; de Bono, Johann S

2015-01-01

Genomic instability is a fundamental feature of human cancer often resulting from impaired genome maintenance. In prostate cancer, structural genomic rearrangements are a common mechanism driving tumorigenesis. However, somatic alterations predisposing to chromosomal rearrangements in prostate cancer remain largely undefined. Here, we show that SPOP, the most commonly mutated gene in primary prostate cancer modulates DNA double strand break (DSB) repair, and that SPOP mutation is associated with genomic instability. In vivo, SPOP mutation results in a transcriptional response consistent with BRCA1 inactivation resulting in impaired homology-directed repair (HDR) of DSB. Furthermore, we found that SPOP mutation sensitizes to DNA damaging therapeutic agents such as PARP inhibitors. These results implicate SPOP as a novel participant in DSB repair, suggest that SPOP mutation drives prostate tumorigenesis in part through genomic instability, and indicate that mutant SPOP may increase response to DNA-damaging therapeutics. DOI: http://dx.doi.org/10.7554/eLife.09207.001 PMID:26374986

Beam measurement of the high frequency impedance sources with long bunches in the CERN Super Proton Synchrotron

NASA Astrophysics Data System (ADS)

Lasheen, A.; Argyropoulos, T.; Bohl, T.; Esteban Müller, J. F.; Timko, H.; Shaposhnikova, E.

2018-03-01

Microwave instability in the Super Proton Synchrotron (SPS) at CERN is one of the main limitations to reach the requirements for the High Luminosity-LHC project (increased beam intensity by a factor 2). To identify the impedance source responsible of the instability, beam measurements were carried out to probe the SPS impedance. The method presented in this paper relies on measurements of the unstable spectra of single bunches, injected in the SPS with the rf voltage switched off. The modulation of the bunch profile gives information about the main impedance sources driving microwave instability, and is compared to particle simulations using the SPS impedance model to identify the most important contributions. This allowed us to identify the vacuum flanges as the main impedance source for microwave instability in the SPS, and to evaluate possible missing impedance sources.

Development of Mirror Modules for the ART-XC Instrument aboard the Spectrum-Roentgen-Gamma Mission

NASA Technical Reports Server (NTRS)

Gubarev, M; Ramsey, B.; O'Dell, S. L.; Elsner, R.; Kilaru, K.; McCracken, J.; Pavlinsky, M.; Tkachenko, A.; Lapshov, I.; Atkins, C.;

Development of mirror modules for the ART-XC instrument aboard the Spectrum-Roentgen-Gamma mission

NASA Astrophysics Data System (ADS)

Gubarev, M.; Ramsey, B.; O'Dell, S. L.; Elsner, R.; Kilaru, K.; McCracken, J.; Pavlinsky, M.; Tkachenko, A.; Lapshov, I.; Atkins, C.; Zavlin, V.

2013-09-01

The Marshall Space Flight Center (MSFC) is developing x-ray mirror modules for the ART-XC instrument on board the Spectrum-Roentgen Gamma Mission. Four of those modules are being fabricated under a Reimbursable Agreement between NASA and the Russian Space Research Institute (IKI.) An additional three flight modules and one spare for the ART-XC Instrument are produced under a Cooperative Agreement between NASA and IKI. The instrument will consist of seven co-aligned x-ray mirror modules with seven corresponding CdTe focal plane detectors. Each module consists of 28 nested thin Ni/Co shells giving an effective area of 65 cm2 at 8 keV, response out to 30 keV, and an angular resolution of 45 arcsec or better HPD. Delivery of the first four modules is scheduled for November 2013, while the remaining three modules will be delivered to IKI in January 2014. We present a status of the ART x-ray module development at MSFC.

The Marshall Space Flight Center Development of Mirror Modules for the ART-XC Instrument aboard the Spectrum-Roentgen-Gamma Mission

NASA Technical Reports Server (NTRS)

Gubarev, Mikhail V.; Ramsey, B.; ODell, S. L.; Elsner, R.; Kilaru, K.; McCracken, J.; Pavlinsky, M.; Tkachenko, A.; Lapshov, I.

2012-01-01

The Marshall Space Flight Center (MSFC) is developing x-ray mirror modules for the ART-XC instrument on board the Spectrum-Roentgen Gamma Mission under a Reimbursable Agreement between NASA and the Russian Space Research Institute (IKI.) ART-XC will consist of seven co-aligned x-ray mirror modules with seven corresponding CdTe focal plane detectors. Currently, four of the modules are being fabricated by the Marshall Space Flight Center (MSFC.) Each MSFC module consist of 28 nested Ni/Co thin shells giving an effective area of 65 sq cm at 8 keV, response out to 30 keV, and an angular resolution of 45 arcsec or better HPD. Delivery of these modules to the IKI is scheduled for summer 2013. We present a status of the ART x-ray modules development at the MSFC.

The Marshall Space Flight Center development of mirror modules for the ART-XC instrument aboard the Spectrum-Roentgen-Gamma mission

NASA Astrophysics Data System (ADS)

Gubarev, M.; Ramsey, B.; O'Dell, S. L.; Elsner, R.; Kilaru, K.; McCracken, J.; Pavlinsky, M.; Tkachenko, A.; Lapshov, I.

2012-09-01

The Marshall Space Flight Center (MSFC) is developing x-ray mirror modules for the ART-XC instrument on board the Spectrum-Roentgen-Gamma Mission under a Reimbursable Agreement between NASA and the Russian Space Research Institute (IKI.) ART-XC will consist of seven co-aligned x-ray mirror modules with seven corresponding CdTe focal plane detectors. Currently, four of the modules are being fabricated by the Marshall Space Flight Center (MSFC.) Each MSFC module consist of 28 nested Ni/Co thin shells giving an effective area of 65 cm2 at 8 keV, response out to 30 keV, and an angular resolution of 45 arcsec or better HPD. Delivery of these modules to the IKI is scheduled for summer 2013. We present a status of the ART x-ray modules development at the MSFC.

Comment on ‘AdS nonlinear instability: moving beyond spherical symmetry’ (2016 Class. Quantum Grav. 33 23LT01)

NASA Astrophysics Data System (ADS)

Rostworowski, Andrzej

2017-06-01

We argue that if the degeneracy of the spectrum of linear perturbations of AdS is properly taken into account, there are globally regular, time-periodic, asymptotically AdS solutions (geons) bifurcating from each linear eigenfrequency of AdS.

Discrete breathers dynamic in a model for DNA chain with a finite stacking enthalpy

NASA Astrophysics Data System (ADS)

Gninzanlong, Carlos Lawrence; Ndjomatchoua, Frank Thomas; Tchawoua, Clément

2018-04-01

The nonlinear dynamics of a homogeneous DNA chain based on site-dependent finite stacking and pairing enthalpies is studied. A new variant of extended discrete nonlinear Schrödinger equation describing the dynamics of modulated wave is derived. The regions of discrete modulational instability of plane carrier waves are studied, and it appears that these zones depend strongly on the phonon frequency of Fourier's mode. The staggered/unstaggered discrete breather (SDB/USDB) is obtained straightforwardly without the staggering transformation, and it is demonstrated that SDBs are less unstable than USDB. The instability of discrete multi-humped SDB/USDB solution does not depend on the number of peaks of the discrete breather (DB). By using the concept of Peierls-Nabarro energy barrier, it appears that the low-frequency DBs are more mobile.

Experimental study of the reversible behavior of modulational instability in optical fibers

NASA Astrophysics Data System (ADS)

van Simaeys, Gaetan; Emplit, Philippe; Haelterman, Marc

2002-03-01

We report what is to our knowledge the first clear-cut experimental evidence of the reversibility of modulational instability in dispersive Kerr media. It was possible to perform this experiment with standard telecommunication fiber because we used a specially designed 550-ps square-pulse laser source based on the two-wavelength configuration of a nonlinear optical loop mirror. Our observations demonstrate that reversibility is due to well-balanced and synchronous energy transfer among a significant number of spectral wave components. These results provide what we believe is the first evidence, in the field of nonlinear optics, of the universal Fermi-Pasta-Ulam recurrence phenomenon that has been predicted for a large number of conservative nonlinear systems, including those described by a nonlinear Schrödinger equation that is relevant to the context of the present study.

Design of a Single Channel Modulated Wideband Converter for Wideband Spectrum Sensing: Theory, Architecture and Hardware Implementation

PubMed Central

Liu, Weisong; Huang, Zhitao; Wang, Xiang; Sun, Weichao

2017-01-01

In a cognitive radio sensor network (CRSN), wideband spectrum sensing devices which aims to effectively exploit temporarily vacant spectrum intervals as soon as possible are of great importance. However, the challenge of increasingly high signal frequency and wide bandwidth requires an extremely high sampling rate which may exceed today’s best analog-to-digital converters (ADCs) front-end bandwidth. Recently, the newly proposed architecture called modulated wideband converter (MWC), is an attractive analog compressed sensing technique that can highly reduce the sampling rate. However, the MWC has high hardware complexity owing to its parallel channel structure especially when the number of signals increases. In this paper, we propose a single channel modulated wideband converter (SCMWC) scheme for spectrum sensing of band-limited wide-sense stationary (WSS) signals. With one antenna or sensor, this scheme can save not only sampling rate but also hardware complexity. We then present a new, SCMWC based, single node CR prototype System, on which the spectrum sensing algorithm was tested. Experiments on our hardware prototype show that the proposed architecture leads to successful spectrum sensing. And the total sampling rate as well as hardware size is only one channel’s consumption of MWC. PMID:28471410

Spread spectrum phase modulation for coherent X-ray diffraction imaging.

PubMed

Zhang, Xuesong; Jiang, Jing; Xiangli, Bin; Arce, Gonzalo R

2015-09-21

High dynamic range, phase ambiguity and radiation limited resolution are three challenging issues in coherent X-ray diffraction imaging (CXDI), which limit the achievable imaging resolution. This paper proposes a spread spectrum phase modulation (SSPM) method to address the aforementioned problems in a single strobe. The requirements on phase modulator parameters are presented, and a practical implementation of SSPM is discussed via ray optics analysis. Numerical experiments demonstrate the performance of SSPM under the constraint of available X-ray optics fabrication accuracy, showing its potential to real CXDI applications.

[Amplitude modulation in sound signals by mammals].

PubMed

Nikol'skiĭ, A A

2012-01-01

Periodic variations in amplitude of a signal, or amplitude modulation (AM), affect the structure of communicative messages spectrum. Within the spectrum of AM-signals, side frequencies are formed both above and below the carrier frequency that is subjected to modulation. In case of harmonic signal structure they are presented near fundamental frequency as well as near harmonics. Thus, AM may by viewed as a relatively simple mechanism for controlling the spectrum of messages transmitted by mammals. Examples of AM affecting the spectrum structure of functionally different sound signals are discussed as applied to representatives of four orders of mammals: rodents (Reodentia), duplicidentates (Lagomorpha), pinnipeds (Pinnipedia), and paridigitates (Artiodactia). For the first time, the classification of AM in animals' sound signals is given. Five forms of AM are picked out in sound signals by mammals: absence of AM, continuous AM, fragmented, heterogeneous, and multilevel one. AM presence/absence is related neither with belonging to any specific order nor with some particular function of a signal. Similar forms of AM can occur in different orders of mammals in parallel. On the contrary, different forms of AM can be detected in signals meant for similar functions. The assumption is made about AM-signals facilitating information encoding and jamprotection of messages transmitted by mammals. Preliminry analysis indicates that hard-driving amplitude modulation is incompatible with hard-driving frequency modulation.

Shapes, spectra and new methods in nonlinear spatial optics

NASA Astrophysics Data System (ADS)

Sun, Can

For a myriad of optical applications, the quality of the light source is poor and the beam is inherently spatially partially-coherent. For this broad class of systems, wave dynamics depends not only on the wave intensity, but also on its distribution of spatial frequencies. Unfortunately, this entire spectrum of problems has often been overlooked - for reasons of theoretical ease or experimental difficulties. Here, we remedy this by demonstrating a novel experimental setup which, for the first time, allows arbitrarily modulation of the spatial spectra of light to obtain any distribution of interest. Using modulation instability as an example, we isolate the effect of different spectral shapes and observe distinct beam dynamics. Next, we turn to a thermodynamic description of the long-term evolution of statistical fields. For quantum systems, a major consequence is Bose-Einstein Condensation. However, recent theoretical studies have suggested that quantum mechanics is not necessary for the condensation process: classical waves with random phases can also self-organize into a coherent state. Starting from a random ensemble, nonlinear interactions can lead to a turbulent energy cascade towards longer spatial scales. In complete analogy with the kinetics of a gas system, there is a statistical dynamics of waves in which particle velocities map to wavepacket k-vectors while collisions are mimicked by four-wave mixing. As with collisions, each wave interaction is formally reversible, yet entropy principles mandate that the ensemble evolves towards an equilibrium state of maximum disorder. The result is an equipartition of energy, in the form of a Rayleigh-Jeans spectrum, with information about the condensation process recorded in small-scale fluctuations. Here, we give the first experimental observation of the condensation of classical waves in any media. Using classical light in a self-defocusing photorefractive, we observe all aspects of the condensation process, including the population of a coherent state, spectral redistribution towards the Rayleigh-Jeans spectrum, and formal reversibility of the interactions. The latter is proved experimentally by introducing a digital "Maxwell's Demon" to reverse (phase-conjugate) the momentum of each wavepacket and recover the original "thermal cloud". The results integrate digital and physical methods of nonlinear processing, confirm fundamental ideas in wave turbulence, and greatly extend the range of Bose-Einstein theory.

Transition to chaos of natural convection between two infinite differentially heated vertical plates

NASA Astrophysics Data System (ADS)

Gao, Zhenlan; Sergent, Anne; Podvin, Berengere; Xin, Shihe; Le Quéré, Patrick; Tuckerman, Laurette S.

2013-08-01

Natural convection of air between two infinite vertical differentially heated plates is studied analytically in two dimensions (2D) and numerically in two and three dimensions (3D) for Rayleigh numbers Ra up to 3 times the critical value Rac=5708. The first instability is a supercritical circle pitchfork bifurcation leading to steady 2D corotating rolls. A Ginzburg-Landau equation is derived analytically for the flow around this first bifurcation and compared with results from direct numerical simulation (DNS). In two dimensions, DNS shows that the rolls become unstable via a Hopf bifurcation. As Ra is further increased, the flow becomes quasiperiodic, and then temporally chaotic for a limited range of Rayleigh numbers, beyond which the flow returns to a steady state through a spatial modulation instability. In three dimensions, the rolls instead undergo another pitchfork bifurcation to 3D structures, which consist of transverse rolls connected by counter-rotating vorticity braids. The flow then becomes time dependent through a Hopf bifurcation, as exchanges of energy occur between the rolls and the braids. Chaotic behavior subsequently occurs through two competing mechanisms: a sequence of period-doubling bifurcations leading to intermittency or a spatial pattern modulation reminiscent of the Eckhaus instability.

Modulational instability and dynamics of implicit higher-order rogue wave solutions for the Kundu equation

NASA Astrophysics Data System (ADS)

Wen, Xiao-Yong; Zhang, Guoqiang

2018-01-01

Under investigation in this paper is the Kundu equation, which may be used to describe the propagation process of ultrashort optical pulses in nonlinear optics. The modulational instability of the plane-wave for the possible reason of the formation of the rogue wave (RW) is studied for the system. Based on our proposed generalized perturbation (n,N - n)-fold Darboux transformation (DT), some new higher-order implicit RW solutions in terms of determinants are obtained by means of the generalized perturbation (1,N - 1)-fold DT, when choosing different special parameters, these results will reduce to the RW solutions of the Kaup-Newell (KN) equation, Chen-Lee-Liu (CLL) equation and Gerjikov-Ivanov (GI) equation, respectively. The relevant wave structures are shown graphically, which display abundant interesting wave structures. The dynamical behaviors and propagation stability of the first-order and second-order RW solutions are discussed by using numerical simulations, the higher-order nonlinear terms for the Kundu equation have an impact on the propagation instability of the RW. The method can also be extended to find the higher-order RW or rational solutions of other integrable nonlinear equations.

Natural History of Anterior Shoulder Instability.

PubMed

Carpinteiro, Eduardo Palma; Barros, Andre Aires

2017-01-01

The shoulder is the most complex joint in the body. The large freedom of motion in this joint is the main cause of instability. Instability varies in its degree, direction, etiology and volition and there is a large spectrum of conditions. Based on literature research and also in our own experience, we propose to elucidate the reader about the natural history of instability and its importance for the appropriate management of this pathology, by answering the following questions: What happens in the shoulder after the first dislocation? Which structures suffer damage? Who are the patients at higher risk of recurrence? How does the disease evolve without treatment? Will surgical treatment avoid future negative outcomes and prevent degenerative joint disease? Who should we treat and when? 80% of anterior-inferior dislocations occur in young patients. Recurrent instability is common and multiple dislocations are the rule. Instability is influenced by a large number of variables, including age of onset, activity profile, number of episodes,delay between first episode and surgical treatment. Understanding the disease and its natural evolution is determinant to decide the treatment in order to obtain the best outcome. It is crucial to identify the risk factors for recurrence. Delay in surgical treatment, when indicated, leads to worse results. Surgical technique should address the type and severity of both soft tissue and bone lesions, when present.

Three-dimensional single-mode nonlinear ablative Rayleigh-Taylor instability

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

Yan, R.; Aluie, H.; Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14627

The nonlinear evolution of the single-mode ablative Rayleigh-Taylor instability is studied in three dimensions. As the mode wavelength approaches the cutoff of the linear spectrum (short-wavelength modes), it is found that the three-dimensional (3D) terminal bubble velocity greatly exceeds both the two-dimensional (2D) value and the classical 3D bubble velocity. Unlike in 2D, the 3D short-wavelength bubble velocity does not saturate. The growing 3D bubble acceleration is driven by the unbounded accumulation of vorticity inside the bubble. The vorticity is transferred by mass ablation from the Rayleigh-Taylor spikes to the ablated plasma filling the bubble volume.

A second-order theory for transverse ion heating and momentum coupling due to electrostatic ion cyclotron waves

NASA Technical Reports Server (NTRS)

Miller, Ronald H.; Winske, Dan; Gary, S. P.

1992-01-01

A second-order theory for electrostatic instabilities driven by counterstreaming ion beams is developed which describes momentum coupling and heating of the plasma via wave-particle interactions. Exchange rates between the waves and particles are derived, which are suitable for the fluid equations simulating microscopic effects on macroscopic scales. Using a fully kinetic simulation, the electrostatic ion cyclotron instability due to counterstreaming H(+) beams has been simulated. A power spectrum from the kinetic simulation is used to evaluate second-order exchange rates. The calculated heating and momentum loss from second-order theory is compared to the numerical simulation.

Experimental Observation of the Stratified Electrothermal Instability on Aluminum with Thickness Greater than a Skin Depth

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

Hutchinson, Trevor M.; Hutchinson, Trevor M.; Awe, Thomas James

The first direct observation of the stratified electrothermal instability on the surface of thick metal is reported. Aluminum rods coated with 70 μm Parylene-N were driven to 1 MA in approximately 100 ns, with the metal thicker than the skin depth. The dielectric coating suppressed plasma formation, enabling persistent observation of discrete azimuthally-correlated stratified structures perpendicular to the current. Strata amplitudes grow rapidly, while their Fourier spectrum shifts toward longer wavelength. Assuming blackbody emission, radiometric calculations indicate strata are temperature perturbations that grow exponentially with rate γ = 0.04 ns -1 in 3000- 10,000 K aluminum.

Addendum to the User Manual for NASGRO Elastic-Plastic Fracture Mechanics Software Module

NASA Technical Reports Server (NTRS)

Gregg, M. Wayne (Technical Monitor); Chell, Graham; Gardner, Brian

2003-01-01

The elastic-plastic fracture mechanics modules in NASGRO have been enhanced by the addition of of the following: new J-integral solutions based on the reference stress method and finite element solutions; the extension of the critical crack and critical load modules for cracks with two degrees of freedom that tear and failure by ductile instability; the addition of a proof test analysis module that includes safe life analysis, calculates proof loads, and determines the flaw screening 1 capability for a given proof load; the addition of a tear-fatigue module for ductile materials that simultaneously tear and extend by fatigue; and a multiple cycle proof test module for estimating service reliability following a proof test.

e(sup +/-) Pair Loading and the Origin of the Upstream Magnetic Field in GRB Shocks

NASA Technical Reports Server (NTRS)

Ramirez-Ruiz, Enrico; Nishikawa, Ken-Ichi; Hededal, Christian B.

2006-01-01

We investigate here the effects of plasma instabilities driven by rapid e(sup +/-) pair cascades, which arise in the environment of GRB sources as a result of back-scattering of a seed fraction of their original spectrum. The injection of e(sup +/-) pairs induces strong streaming motions in the ambient medium. One therefore expects the pair-enriched medium ahead of the forward shock to be strongly sheared on length scales comparable to the radiation front thickness. Using three-dimensional particle-in-cell simulations, we show that plasma instabilities driven by these streaming e(sup +/-) pairs are responsible for the excitation of near-equipartition, turbulent magnetic fields. Our results reveal the importance of the electromagnetic filamentation instability in ensuring an effective coupling between e(sup +/-) pairs and ions, and may help explain the origin of large upstream fields in GRB shocks.

e+/- Pair Loading and the Origin of the Upstream Field in GRB Shocks

NASA Technical Reports Server (NTRS)

Ramirez-Ruiz, Enrico; Nishikawa, Ken-Ichi; Hededal, Christian B.

2006-01-01

We investigate here the effects of plasma instabilities driven by rapid e(sup plus or minus) pair cascades, which arise in the environment of GRB sources as a result of back-scattering of a seed fraction of their original spectrum. The injection of e(sup plus or minus) pairs induces strong streaming motions in the ambient medium. One therefore expects the pair-enriched medium ahead of the forward shock to be strongly sheared on length scales comparable to the radiation front thickness. Using three-dimensional particle-in-cell simulations, we show that plasma instabilities driven by these streaming e(sup plus or minus) pairs are responsible for the excitation of near-equipartition, turbulent magnetic fields. Our results reveal the importance of the electromagnetic filamentation instability in ensuring an effective coupling between e(sup plus or minus) pairs and ions, and may help explain the origin of large upstream fields in GRB shocks.

Instability of turing patterns in reaction-diffusion-ODE systems.

PubMed

Marciniak-Czochra, Anna; Karch, Grzegorz; Suzuki, Kanako

2017-02-01

The aim of this paper is to contribute to the understanding of the pattern formation phenomenon in reaction-diffusion equations coupled with ordinary differential equations. Such systems of equations arise, for example, from modeling of interactions between cellular processes such as cell growth, differentiation or transformation and diffusing signaling factors. We focus on stability analysis of solutions of a prototype model consisting of a single reaction-diffusion equation coupled to an ordinary differential equation. We show that such systems are very different from classical reaction-diffusion models. They exhibit diffusion-driven instability (turing instability) under a condition of autocatalysis of non-diffusing component. However, the same mechanism which destabilizes constant solutions of such models, destabilizes also all continuous spatially heterogeneous stationary solutions, and consequently, there exist no stable Turing patterns in such reaction-diffusion-ODE systems. We provide a rigorous result on the nonlinear instability, which involves the analysis of a continuous spectrum of a linear operator induced by the lack of diffusion in the destabilizing equation. These results are extended to discontinuous patterns for a class of nonlinearities.

Turbulent mixing noise from supersonic jets

NASA Technical Reports Server (NTRS)

Tam, Christopher K. W.; Chen, Ping

1994-01-01

There is now a substantial body of theoretical and experimental evidence that the dominant part of the turbulent noise of supersonic jets is generated directly by the large turbulence structures/instability waves of the jet flow. Earlier, Tam and Burton provided a description of the physical mechanism by which supersonically traveling instability waves can generate sound efficiently. They used the method of matched asymptotic expansions to construct an instability wave solution which is valid in the far field. The present work is an extension of the theory of Tam and Burton. It is argued that the instability wave spectrum of the jet may be regarded as generated by stochastic white noise excitation at the nozzle lip region. The reason why the excitation has white noise characteristics is that near the nozzle lip region the flow in the jet mixing layer has no intrinsic length and time scales. The present stochastic wave model theory of supersonic jet noise contains a single unknown multiplicative constant. Comparisons between the calculated noise directivities at selected Strouhal numbers and experimental measurements of a Mach 2 jet at different jet temperatures have been carried out. Favorable agreements are found.

Laser plasma interaction in rugby-shaped hohlraums

NASA Astrophysics Data System (ADS)

Masson-Laborde, P.-E.; Philippe, F.; Tassin, V.; Monteil, M.-C.; Gauthier, P.; Casner, A.; Depierreux, S.; Seytor, P.; Teychenne, D.; Loiseau, P.; Freymerie, P.

2014-10-01

Rugby shaped-hohlraum has proven to give high performance compared to a classical similar-diameter cylinder hohlraum. Due to this performance, this hohlraum has been chosen as baseline ignition target for the Laser MegaJoule (LMJ). Many experiments have therefore been performed during the last years on the Omega laser facility in order to study in details the rugby hohlraum. In this talk, we will discuss the interpretation of these experiments from the point of view of the laser plasma instability problem. Experimental comparisons have been done between rugby, cylinder and elliptical shape rugby hohlraums and we will discuss how the geometry differences will affect the evolution of laser plasma instabilities (LPI). The efficiency of laser smoothing techniques on these instabilities will also be discussed as well as gas filling effect. The experimental results will be compared with FCI2 hydroradiative calculations and linear postprocessing with Piranah. Experimental Raman and Brillouin spectrum, from which we can infer the location of the parametric instabilities, will be compared to simulated ones, and will give the possibility to compare LPI between the different hohlraum geometries.

Supersonic Coaxial Jets: Noise Predictions and Measurements

NASA Technical Reports Server (NTRS)

Dahl, Milo D.; Papamoschou, Dimitri; Hixon, Ray

1998-01-01

The noise from perfectly expanded coaxial jets was measured in an anechoic chamber for different operating conditions with the same total thrust, mass flow, and exit area. The shape of the measured noise spectrum at different angles to the jet axis was found to agree with spectral shapes for single, axisymmetric jets. Based on these spectra, the sound was characterized as being generated by large turbulent structures or fine-scale turbulence. Modeling the large scale structures as instability waves, a stability analysis was conducted for the coaxial jets to identify the growing and decaying instability waves in each shear layer and predict their noise radiation pattern outside the jet. When compared to measured directivity, the analysis identified the region downstream of the outer potential core, where the two shear layers were merging, as the source of the peak radiated noise where instability waves, with their origin in the inner shear layer, reach their maximum amplitude. Numerical computations were also performed using a linearized Euler equation solver. Those results were compared to both the results from the instability wave analysis and to measured data.

Temporal modulations in speech and music.

PubMed

Ding, Nai; Patel, Aniruddh D; Chen, Lin; Butler, Henry; Luo, Cheng; Poeppel, David

2017-10-01

Speech and music have structured rhythms. Here we discuss a major acoustic correlate of spoken and musical rhythms, the slow (0.25-32Hz) temporal modulations in sound intensity and compare the modulation properties of speech and music. We analyze these modulations using over 25h of speech and over 39h of recordings of Western music. We show that the speech modulation spectrum is highly consistent across 9 languages (including languages with typologically different rhythmic characteristics). A different, but similarly consistent modulation spectrum is observed for music, including classical music played by single instruments of different types, symphonic, jazz, and rock. The temporal modulations of speech and music show broad but well-separated peaks around 5 and 2Hz, respectively. These acoustically dominant time scales may be intrinsic features of speech and music, a possibility which should be investigated using more culturally diverse samples in each domain. Distinct modulation timescales for speech and music could facilitate their perceptual analysis and its neural processing. Copyright © 2017 Elsevier Ltd. All rights reserved.

Signatures of graviton masses on the CMB

NASA Astrophysics Data System (ADS)

Brax, Philippe; Cespedes, Sebastian; Davis, Anne-Christine

2018-03-01

The impact of the existence of gravitons with non-vanishing masses on the B-modes of the Cosmic Microwave Background (CMB) is investigated. We also focus on putative modifications to the speed of the gravitational waves. We find that a change of the graviton speed shifts the acoustic peaks of the CMB and then could be easily constrained. For the case of massive gravity, we show analytically how the B-modes are sourced in a manner differing from the massless case leading to a plateau at low l in the CMB spectrum. We also study the case when there are more than one graviton, and when pressure instabilities are present. The latter would occur in doubly coupled bigravity in the radiation era. We focus on the case where a massless graviton becomes tachyonic in the radiation era whilst a massive one remains stable. As the unstable mode decouples from matter in the radiation era, we find that the effects of the instability is largely reduced on the spectrum of B-modes as long as the unstable graviton does not grow into the non-linear regime. In all cases when both massless and massive gravitons are present, we find that the B-mode CMB spectrum is characterised by a low l plateau together with a shifted position for the first few peaks compared to a purely massive graviton spectrum, a shift which depends on the mixing between the gravitons in their coupling to matter and could serve as a hint in favour of the existence of multiple gravitons.

Robust phase-shifting interferometry resistant to multiple disturbances

NASA Astrophysics Data System (ADS)

Liu, Qian; Yue, Xiaobin; Li, Lulu; Zhang, Hui; He, Jianguo

2018-04-01

Phase-shifting interferometry (PSI) is sensitive to many disturbances, including the environmental vibration, laser instability, phase-shifting error and camera nonlinearity. A robust PSI (RPSI) based on the temporal spectrum analysis is proposed to suppress the effects of these common disturbances. RPSI retrieves wavefront phase from the temporal Fourier spectrum peak, which is identified by detecting the modulus of spectrum, and a referencing method is presented to improve the phase extracting accuracy. Simulations demonstrate the feasibility and effectiveness of RPSI. Experimental results indicate that RPSI is resistant to common disturbances in implementing PSI and achieves accuracy better than 0.03 rad in the disturbed environment. RPSI relaxes requirements on the hardware, environment and operator, and provides an easy-to-use design of an interferometer.

Power requirements reducing of FBG based all-optical switching

NASA Astrophysics Data System (ADS)

Scholtz, Ľubomír.; Solanská, Michaela; Ladányi, Libor; Müllerová, Jarmila

2017-12-01

Although Fiber Bragg gratings (FBGs) are well known devices, their using as all-optical switching elements has been still examined. Current research is focused on optimization of their properties for their using in future all-optical networks. The main problem are high switching intensities needed for achieving the changes of the transmission state. Over several years switching intensities have been reduced from hundreds of GW/cm2 to tens of MW/cm2 by selecting appropriate gratings and signal parameters or using suitable materials. Two principal nonlinear effects with similar power requirements can result in the bistable transmission/reflection of an input optical pulse. In the self-phase modulation (SPM) regime switching is achieved by the intense probe pulse itself. Using cross-phase modulation (XPM) a strong pump alters the FBG refractive index experienced by a weak probe pulse. As a result of this the detuning of the probe pulse from the center of the photonic band gap occurs. Using of XPM the effect of modulation instability is reduced. Modulation instability which is the main SPM degradation mechanism. We focused on nonlinear FBGs based on chalcogenide glasses which are very often used in various applications. Thanks to high nonlinear parameters chalcogenide glasses are suitable candidates for reducing switching intensities of nonlinear FBGs.

Extinction-ratio-independent electrical method for measuring chirp parameters of Mach-Zehnder modulators using frequency-shifted heterodyne.

PubMed

Zhang, Shangjian; Wang, Heng; Zou, Xinhai; Zhang, Yali; Lu, Rongguo; Liu, Yong

2015-06-15

An extinction-ratio-independent electrical method is proposed for measuring chirp parameters of Mach-Zehnder electric-optic intensity modulators based on frequency-shifted optical heterodyne. The method utilizes the electrical spectrum analysis of the heterodyne products between the intensity modulated optical signal and the frequency-shifted optical carrier, and achieves the intrinsic chirp parameters measurement at microwave region with high-frequency resolution and wide-frequency range for the Mach-Zehnder modulator with a finite extinction ratio. Moreover, the proposed method avoids calibrating the responsivity fluctuation of the photodiode in spite of the involved photodetection. Chirp parameters as a function of modulation frequency are experimentally measured and compared to those with the conventional optical spectrum analysis method. Our method enables an extinction-ratio-independent and calibration-free electrical measurement of Mach-Zehnder intensity modulators by using the high-resolution frequency-shifted heterodyne technique.

Diagnostic Stability of ICD/DSM First Episode Psychosis Diagnoses: Meta-analysis

PubMed Central

Fusar-Poli, Paolo; Cappucciati, Marco; Rutigliano, Grazia; Heslin, Margaret; Stahl, Daniel; Brittenden, Zera; Caverzasi, Edgardo; McGuire, Philip; Carpenter, William T.

2016-01-01

Background: Validity of current International Classification of Disease/Diagnostic and Statistical Manual of Mental Disorders (ICD/DSM) first episode psychosis diagnoses is essential in clinical practice, research, training and public health. Method: We provide a meta-analytical estimate of prospective diagnostic stability and instability in ICD-10 or DSM-IV first episode diagnoses of functional psychoses. Independent extraction by multiple observers. Random effect meta-analysis conducted with the “metaprop,” “metaninf,” “metafunnel,” “metabias,” and “metareg” packages of STATA13.1. Moderators were tested with meta-regression analyses. Heterogeneity was assessed with the I 2 index. Sensitivity analyses tested robustness of results. Publication biases were assessed with funnel plots and Egger’s test. Findings: 42 studies and 45 samples were included, for a total of 14 484 first episode patients and an average follow-up of 4.5 years. Prospective diagnostic stability ranked: schizophrenia 0.90 (95% CI 0.85–0.95), affective spectrum psychoses 0.84 (95% CI 0.79–0.89), schizoaffective disorder 0.72 (95% CI 0.61–0.73), substance-induced psychotic disorder 0.66 (95% CI 0.51–0.81), delusional disorder 0.59 (95% CI 0.47–0.71), acute and transient psychotic disorder/brief psychotic disorder 0.56 (95% CI 0.62–0.60), psychosis not otherwise specified 0.36 (95% CI 0.27–0.45, schizophreniform disorder 0.29 (95% CI 0.22–0.38). Diagnostic stability within schizophrenia spectrum psychoses was 0.93 (95% CI 0.89–0.97); changes to affective spectrum psychoses were 0.05 (95% CI 0.01–0.08). About 0.10 (95% CI 0.05–0.15) of affective spectrum psychoses changed to schizophrenia spectrum psychosis. Across the other psychotic diagnoses there was high diagnostic instability, mostly to schizophrenia. Interpretation: There is meta-analytical evidence for high prospective diagnostic stability in schizophrenia spectrum and affective spectrum psychoses, with no significant ICD/DSM differences. These results may inform the development of new treatment guidelines for early psychosis and impact drug licensing from regulatory agencies. PMID:26980142

Amplification of perpendicular and parallel magnetic fields by cosmic ray currents

NASA Astrophysics Data System (ADS)

Matthews, J. H.; Bell, A. R.; Blundell, K. M.; Araudo, A. T.

2017-08-01

Cosmic ray (CR) currents through magnetized plasma drive strong instabilities producing amplification of the magnetic field. This amplification helps explain the CR energy spectrum as well as observations of supernova remnants and radio galaxy hotspots. Using magnetohydrodynamic simulations, we study the behaviour of the non-resonant hybrid (NRH) instability (also known as the Bell instability) in the case of CR currents perpendicular and parallel to the initial magnetic field. We demonstrate that extending simulations of the perpendicular case to 3D reveals a different character to the turbulence from that observed in 2D. Despite these differences, in 3D the perpendicular NRH instability still grows exponentially far into the non-linear regime with a similar growth rate to both the 2D perpendicular and 3D parallel situations. We introduce some simple analytical models to elucidate the physical behaviour, using them to demonstrate that the transition to the non-linear regime is governed by the growth of thermal pressure inside dense filaments at the edges of the expanding loops. We discuss our results in the context of supernova remnants and jets in radio galaxies. Our work shows that the NRH instability can amplify magnetic fields to many times their initial value in parallel and perpendicular shocks.

Current driven instabilities of an electromagnetically accelerated plasma

NASA Technical Reports Server (NTRS)

Chouetri, E. Y.; Kelly, A. J.; Jahn, R. G.

1988-01-01

A plasma instability that strongly influences the efficiency and lifetime of electromagnetic plasma accelerators was quantitatively measured. Experimental measurements of dispersion relations (wave phase velocities), spatial growth rates, and stability boundaries are reported. The measured critical wave parameters are in excellent agreement with theoretical instability boundary predictions. The instability is current driven and affects a wide spectrum of longitudinal (electrostatic) oscillations. Current driven instabilities, which are intrinsic to the high-current-carrying magnetized plasma of the magnetoplasmadynmic (MPD) accelerator, were investigated with a kinetic theoretical model based on first principles. Analytical limits of the appropriate dispersion relation yield unstable ion acoustic waves for T(i)/T(e) much less than 1 and electron acoustic waves for T(i)/T(e) much greater than 1. The resulting set of nonlinear equations for the case of T(i)/T(e) = 1, of most interest to the MPD thruster Plasma Wave Experiment, was numerically solved to yield a multiparameter set of stability boundaries. Under certain conditions, marginally stable waves traveling almost perpendicular to the magnetic field would travel at a velocity equal to that of the electron current. Such waves were termed current waves. Unstable current waves near the upper stability boundary were observed experimentally and are in accordance with theoretical predictions. This provides unambiguous proof of the existence of such instabilites in electromagnetic plasma accelerators.

Modeling and Laboratory Investigations of Radiative Shocks

NASA Astrophysics Data System (ADS)

Grun, Jacob; Laming, J. Martin; Manka, Charles; Moore, Christopher; Jones, Ted; Tam, Daniel

2001-10-01

Supernova remnants are often inhomogeneous, with knots or clumps of material expanding in ambient plasma. This structure may be initiated by hydrodynamic instabilities occurring during the explosion, but it may plausibly be amplified by instabilities of the expanding shocks such as, for example, corrugation instabilities described by D’yakov in 1954, Vishniac in 1983, and observed in the laboratory by Grun et al. in 1991. Shock instability can occur when radiation lowers the effective adiabatic index of the gas. In view of the difficulty of modeling radiation in non-equilibrium plasmas, and the dependence of shock instabilities on such radiation, we are performing a laboratory experiment to study radiative shocks. The shocks are generated in a miniature, laser-driven shock tube. The gas density inside the tube at any instant in time is measured using time and space-resolved interferometry, and the emission spectrum of the gas is measured with time-resolved spectroscopy. We simulate the experiment with a 1D code that models time dependent post-shock ionization and non-equilibrium radiative cooling. S. P. D’yakov, Zhurnal Eksperimentalnoi Teoreticheskoi Fiziki 27, 288 (1954); see also section 90 in L.D. Landau and E.M. Lifshitz, Fluid Mechanics (Butterworth-Heinemann 1987); E.T. Vishniac, Astrophys. J. 236, 880 (1983); J. Grun, et al., Phys. Rev. Lett., 66, 2738 (1991)

Beam-Plasma Interaction and Instabilities in a 2D Yukawa Plasma

NASA Astrophysics Data System (ADS)

Kyrkos, S.; Kalman, G.; Rosenberg, M.

2008-11-01

In a complex plasma, penetrating charged particle beams may lead to beam-plasma instabilities. When either the plasma, the beam, or both, are strongly interacting [1], the features of the instability are different from those in a weakly coupled plasma. We consider the case when a 2D dusty plasma forms a lattice, and the beam is moving in the lattice plane. Both the grains and the beam particles interact through a Yukawa potential; the beam particles are weakly coupled to each other and to the lattice. The system develops both a longitudinal and a transverse instability. Based on the phonon spectrum of a 2D hexagonal Yukawa lattice [2], we determine and compare the transverse and longitudinal growth rates. As a function of the wavenumber, the growth rates exhibit remarkable gaps, where no instability is excited. The gap locations are governed by the ratio of the lattice and the beam plasma frequencies. The behavior of the growth rates also depends on the direction of the beam and on the relationship between the beam speed and the longitudinal and transverse sound speeds. [1] GJ Kalman, M Rosenberg, JPA 36, 5963 (2003). [2] T Sullivan, GJ Kalman, S Kyrkos, P Bakshi, M Rosenberg, Z Donko, JPA 39, 4607 (2006).

A non-linear theory of the parallel firehose and gyrothermal instabilities in a weakly collisional plasma

NASA Astrophysics Data System (ADS)

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

2011-05-01

Weakly collisional magnetized cosmic plasmas have a dynamical tendency to develop pressure anisotropies with respect to the local direction of the magnetic field. These anisotropies trigger plasma instabilities at scales just above the ion Larmor radius ρi and much below the mean free path λmfp. They have growth rates of a fraction of the ion cyclotron frequency, which is much faster than either the global dynamics or even local turbulence. Despite their microscopic nature, these instabilities dramatically modify the transport properties and, therefore, the macroscopic dynamics of the plasma. The non-linear evolution of these instabilities is expected to drive pressure anisotropies towards marginal stability values, controlled by the plasma beta βi. Here this non-linear evolution is worked out in an ab initio kinetic calculation for the simplest analytically tractable example - the parallel (k⊥= 0) firehose instability in a high-beta plasma. An asymptotic theory is constructed, based on a particular physical ordering and leading to a closed non-linear equation for the firehose turbulence. In the non-linear regime, both the analytical theory and the numerical solution predict secular (∝t) growth of magnetic fluctuations. The fluctuations develop a k-3∥ spectrum, extending from scales somewhat larger than ρi to the maximum scale that grows secularly with time (∝t1/2); the relative pressure anisotropy (p⊥-p∥)/p∥ tends to the marginal value -2/βi. The marginal state is achieved via changes in the magnetic field, not particle scattering. When a parallel ion heat flux is present, the parallel firehose mutates into the new gyrothermal instability (GTI), which continues to exist up to firehose-stable values of pressure anisotropy, which can be positive and are limited by the magnitude of the ion heat flux. The non-linear evolution of the GTI also features secular growth of magnetic fluctuations, but the fluctuation spectrum is eventually dominated by modes around a maximal scale ˜ρilT/λmfp, where lT is the scale of the parallel temperature variation. Implications for momentum and heat transport are speculated about. This study is motivated by our interest in the dynamics of galaxy cluster plasmas (which are used as the main astrophysical example), but its relevance to solar wind and accretion flow plasmas is also briefly discussed.

47 CFR 101.521 - Spectrum utilization.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 47 Telecommunication 5 2011-10-01 2011-10-01 false Spectrum utilization. 101.521 Section 101.521... SERVICES 24 GHz Service and Digital Electronic Message Service § 101.521 Spectrum utilization. All... contain detailed descriptions of the modulation method, the channel time sharing method, any error...

Constant-intensity waves and their modulation instability in non-Hermitian potentials

NASA Astrophysics Data System (ADS)

Makris, K. G.; Musslimani, Z. H.; Christodoulides, D. N.; Rotter, S.

2015-07-01

In all of the diverse areas of science where waves play an important role, one of the most fundamental solutions of the corresponding wave equation is a stationary wave with constant intensity. The most familiar example is that of a plane wave propagating in free space. In the presence of any Hermitian potential, a wave's constant intensity is, however, immediately destroyed due to scattering. Here we show that this fundamental restriction is conveniently lifted when working with non-Hermitian potentials. In particular, we present a whole class of waves that have constant intensity in the presence of linear as well as of nonlinear inhomogeneous media with gain and loss. These solutions allow us to study the fundamental phenomenon of modulation instability in an inhomogeneous environment. Our results pose a new challenge for the experiments on non-Hermitian scattering that have recently been put forward.

Mirror instability and origin of morningside auroral structure

NASA Technical Reports Server (NTRS)

Chiu, Y. T.; Schulz, M.; Fennell, J. F.; Kishi, A. M.

1983-01-01

Auroral optical imagery shows marked differences between auroral features of the evening and morning sectors: the separation between diffuse and discrete auroras in the evening sector is not distinct in the morning sector, which is dominated by auroral patches and multiple banded structures aligned along some direction. Plasma distribution function signatures also show marked differences: downward electron beams and inverted-V signatures prefer the evening sector, while the electron spectra on the morning sector are similar to the diffuse aurora. A theory of morningside auroras consistent with these features was constructed. The theory is based on modulation of the growth rates of electron cyclotron waves by the mirror instability, which is in turn driven by inward-convected ions that have become anisotropic. This modulation produces alternating bands of enhanced and reduced electron precipitation which approximate the observed multiple auroral bands and patches of the morning sector.

Modulational instability: Conservation laws and bright soliton solution of ion-acoustic waves in electron-positron-ion-dust plasmas

NASA Astrophysics Data System (ADS)

EL-Kalaawy, O. H.

2018-02-01

We consider the nonlinear propagation of non-planar (cylindrical and spherical) ion-acoustic (IA) envelope solitary waves in an unmagnetized plasma consisting of electron-positron-ion-dust plasma with two-electron temperature distributions in the context of the non-extensive statistics. The basic set of fluid equations is reduced to the modified nonlinear Schrödinger (MNLS) equation in cylindrical and spherical geometry by using the reductive perturbation method (RPM). It is found that the nature of the modulational instabilities would be significantly modified due to the effects of the non-extensive and other plasma parameters as well as cylindrical and spherical geometry. Conservation laws of the MNLS equation are obtained by Lie symmetry and multiplier method. A new exact solution (envelope bright soliton) is obtained by the extended homogeneous balance method. Finally, we study the results of this article.

Modulation instability, Fermi-Pasta-Ulam recurrence, rogue waves, nonlinear phase shift, and exact solutions of the Ablowitz-Ladik equation.

PubMed

Akhmediev, Nail; Ankiewicz, Adrian

2011-04-01

We study modulation instability (MI) of the discrete constant-background wave of the Ablowitz-Ladik (A-L) equation. We derive exact solutions of the A-L equation which are nonlinear continuations of MI at longer times. These periodic solutions comprise a family of two-parameter solutions with an arbitrary background field and a frequency of initial perturbation. The solutions are recurrent, since they return the field state to the original constant background solution after the process of nonlinear evolution has passed. These solutions can be considered as a complete resolution of the Fermi-Pasta-Ulam paradox for the A-L system. One remarkable consequence of the recurrent evolution is the nonlinear phase shift gained by the constant background wave after the process. A particular case of this family is the rational solution of the first-order or fundamental rogue wave.

Full load testing in the platform module prior to tow-out: A case history of subsynchronous instability

NASA Technical Reports Server (NTRS)

Fulton, J. W.

1984-01-01

An electric motor driven centrifugal compressor to supply gas for further compression and reinjection on a petroleum production platform in the North Sea was examined. The compressor design, raised concerns about susceptibility to subsynchronous instability. Log decrement, aerodynamic features, and the experience of other compressors with similar ratios of operating to critical speed ratio versus gas density led to the decision to full load test. Mixed hydrocarbon gas was chosen for the test to meet discharge temperature restrictions. The module was used as the test site. Subsynchronous vibrations made the compressor inoperable above approximately one-half the rated discharge pressure of 14500 kPa. Modifications, which includes shortening the bearing span, change of leakage inlet flow direction on the back to back labyrinth, and removal of the vaned diffusers on all stages were made simultaneously. The compressor is operating with satisfactory vibration levels.

Development and Calibration of the ART-XC Mirror Modules for the Spectrum Rontgen Gamma Mission

NASA Technical Reports Server (NTRS)

Ramsey, B.; Gubarev, M.; Elsner, R.; Kolodziejczak, J.; Odell, S.; Swartz, D.; Pavlinsky, M.; Tkachenko, A.; Lapshov, I.

2013-01-01

The Spectrum-Röntgen-Gamma (SRG) mission is a Russian-lead X-ray astrophysical observatory that carries two co-aligned X-ray telescope systems. The primary instrument is the German-led extended ROentgen Survey with an Imaging Telescope Array (eROSITA), a 7-module X-ray telescope system that covers the energy range from 0.2-12 keV. The complementary instrument is the Astronomical Roentgen Telescope -- X-ray Concentrator (ART-XC or ART), a 7-module Xray telescope system that provides higher energy coverage, up to 30 keV.

The routing, modulation level, and spectrum allocation algorithm in the virtual optical network mapping

NASA Astrophysics Data System (ADS)

Wang, Yunyun; Li, Hui; Liu, Yuze; Ji, Yuefeng; Li, Hongfa

2017-10-01

With the development of large video services and cloud computing, the network is increasingly in the form of services. In SDON, the SDN controller holds the underlying physical resource information, thus allocating the appropriate resources and bandwidth to the VON service. However, for some services that require extremely strict QoT (quality of transmission), the shortest distance path algorithm is often unable to meet the requirements because it does not take the link spectrum resources into account. And in accordance with the choice of the most unoccupied links, there may be more spectrum fragments. So here we propose a new RMLSA (the routing, modulation Level, and spectrum allocation) algorithm to reduce the blocking probability. The results show about 40% less blocking probability than the shortest-distance algorithm and the minimum usage of the spectrum priority algorithm. This algorithm is used to satisfy strict request of QoT for demands.

Electrical Energy Harvesting from Thermal Energy with Converged Infrared Light

NASA Astrophysics Data System (ADS)

Goh, S. Y.; Kok, S. L.

2017-06-01

Photovoltaics (PV) cell is a common energy harvester that had been used to harvest solar energy and convert it into electrical energy. However, the vast energy from the spectrum of sunlight is not fully harvested. Therefore, thermoelectric (TE) module that harvest electrical energy from heat is being proposed in this paper. Generally, the part of the sunlight spectrum that induce heat is in the spectrum band of infrared (IR). For the experimental set-up in this paper, infrared (IR) light bulb was being used to simulate the IR spectrum band of the sunlight. In order to maximize the heat energy collection, a convex lens was being used to converge the IR light and therefore focused the heat on an aluminium sheet and heat sink which was placed on top of the hot side of the TE module. The distance between convex lens and IR light bulb is varying in between 10cm and 55cm and the reading was taken at an interval of 5cm. Firstly, the temperature of the IR light and converged IR light were recorded and plotted in graph. The graph showed that the temperature of the converged IR light bulb is higher than the IR light bulb. Lastly, the voltage and power output of the TE module with different heat source was compared. The output voltage and power of the TE module increased inverse proportional to the distance between IR light bulb and TE module.

Minor shoulder instability.

PubMed

Castagna, Alessandro; Nordenson, Ulf; Garofalo, Raffaele; Karlsson, Jon

2007-02-01

The wide spectrum of shoulder instability is difficult to include in 1 classification. The distinction between traumatic, unidirectional, and atraumatic multidirectional instability is still widely used, even though this classification is not sufficiently precise to include all the different pathological findings of shoulder instability. We present "minor instability," which is a pathological condition causing a dysfunction of the glenohumeral articulation, especially in combination with microtrauma, repetitive or not, or after a period of immobilization or inactivity. When "minor shoulder instability" is suspected, the patient's history and detailed clinical examination represent the most important factors when establishing the diagnosis. In particular, the apprehension test stressing the middle glenohumeral ligament (MGHL)/labral complex in the position of midabduction and external rotation may be painful and may even reveal anterior instability or subluxation. Conventional radiographs are negative in most cases, as is magnetic resonance imaging arthrography. It is only after an accurate arthroscopic assessment that the pathological lesion can be found. The major pathological process can be identified at the level of the anterior superior labrum, in particular the MGHL complex, and appears as hyperemia, fraying, stretching, loosening, thinning, hypoplasia, or even absence. It may, however, be difficult to distinguish between a normal variant and a pathological lesion. Clinical symptoms and examination should always be correlated with arthroscopic findings. Recommended treatment is to restore shoulder stability and thereby prevent shoulder pain secondary to the increase in laxity. A reduction in range of motion should be expected during the postoperative phase, at least up to six to nine months. External rotation is usually permanently reduced by a few degrees.

A Novel Behavior of Pump Power in the Instability Induced Supercontinuum Generation of Saturable Nonlinear Media

NASA Astrophysics Data System (ADS)

Nithyanandan, K.; Porsezian, K.

2015-04-01

We investigate the modulational instability (MI) induced Supercontinuum generation (SCG) in exponential saturable nonlinearity. The pump power (P) is observed to behave in a unique way such that unlike the conventional Kerr case, the effective nonlinearity of saturable nonlinear system does not monotonously increases with an increase in power. The supercontinuum is observed at the shortest distance of propagation at power equal to the saturation power (Ps), whereas for all combinations of powers (P < Ps or P > Ps) spectral broadening occurs at longer distance.

Stability under scalar perturbations and quasinormal modes of 4D Einstein-Born-Infeld dilaton spacetime: exact spectrum

NASA Astrophysics Data System (ADS)

Destounis, Kyriakos; Panotopoulos, Grigoris; Rincón, Ángel

2018-02-01

We study the stability under scalar perturbations, and we compute the quasinormal modes of the Einstein-Born-Infeld dilaton spacetime in 1+3 dimensions. Solving the full radial equation in terms of hypergeometric functions, we provide an exact analytical expression for the spectrum. We find that the frequencies are purely imaginary, and we confirm our results by computing them numerically. Although the scalar field that perturbs the black hole is electrically neutral, an instability similar to that seen in charged scalar perturbations of the Reissner-Nordström black hole is observed.

Primordial perturbations with pre-inflationary bounce

NASA Astrophysics Data System (ADS)

Cai, Yong; Wang, Yu-Tong; Zhao, Jin-Yun; Piao, Yun-Song

2018-05-01

Based on the effective field theory (EFT) of nonsingular cosmologies, we build a stable model, without the ghost and gradient instabilities, of bounce-inflation (inflation is preceded by a cosmological bounce). We perform a full simulation for the evolution of scalar perturbation, and find that the perturbation spectrum has a large-scale suppression (as expected), which is consistent with the power deficit of the cosmic microwave background (CMB) TT-spectrum at low multipoles, but unexpectedly, it also shows itself one marked lower valley. The depth of valley is relevant with the physics around the bounce scale, which is model-dependent.

Correlation transfer and diffusion of ultrasound-modulated multiply scattered light.

PubMed

Sakadzić, Sava; Wang, Lihong V

2006-04-28

We develop a temporal correlation transfer equation (CTE) and a temporal correlation diffusion equation (CDE) for ultrasound-modulated multiply scattered light. These equations can be applied to an optically scattering medium with embedded optically scattering and absorbing objects to calculate the power spectrum of light modulated by a nonuniform ultrasound field. We present an analytical solution based on the CDE and Monte Carlo simulation results for light modulated by a cylinder of ultrasound in an optically scattering slab. We further validate with experimental measurements the numerical calculations for an actual ultrasound field. The CTE and CDE are valid for moderate ultrasound pressures and on a length scale comparable with the optical transport mean-free path. These equations should be applicable to a wide spectrum of conditions for ultrasound-modulated optical tomography of soft biological tissues.

Modules for Experiments in Stellar Astrophysics (MESA): Convective Boundaries, Element Diffusion, and Massive Star Explosions

NASA Astrophysics Data System (ADS)

Paxton, Bill; Schwab, Josiah; Bauer, Evan B.; Bildsten, Lars; Blinnikov, Sergei; Duffell, Paul; Farmer, R.; Goldberg, Jared A.; Marchant, Pablo; Sorokina, Elena; Thoul, Anne; Townsend, Richard H. D.; Timmes, F. X.

2018-02-01

We update the capabilities of the software instrument Modules for Experiments in Stellar Astrophysics (MESA) and enhance its ease of use and availability. Our new approach to locating convective boundaries is consistent with the physics of convection, and yields reliable values of the convective-core mass during both hydrogen- and helium-burning phases. Stars with M< 8 M⊙ become white dwarfs and cool to the point where the electrons are degenerate and the ions are strongly coupled, a realm now available to study with MESA due to improved treatments of element diffusion, latent heat release, and blending of equations of state. Studies of the final fates of massive stars are extended in MESA by our addition of an approximate Riemann solver that captures shocks and conserves energy to high accuracy during dynamic epochs. We also introduce a 1D capability for modeling the effects of Rayleigh-Taylor instabilities that, in combination with the coupling to a public version of the STELLA radiation transfer instrument, creates new avenues for exploring Type II supernova properties. These capabilities are exhibited with exploratory models of pair-instability supernovae, pulsational pair-instability supernovae, and the formation of stellar-mass black holes. The applicability of MESA is now widened by the capability to import multidimensional hydrodynamic models into MESA. We close by introducing software modules for handling floating point exceptions and stellar model optimization, as well as four new software tools - MESA-Web, MESA-Docker, pyMESA, and mesastar.org - to enhance MESA's education and research impact.

The spectrum of progressive derecho formation environments

NASA Astrophysics Data System (ADS)

Guastini, Corey T.

Progressive derechos are severe mesoscale convective systems that often form east of the Rocky Mountains during the warm season (May--August) and cause, by definition, straight-line wind damage along paths upwards of 400 km long. This study develops a subjective, seven-category classification scheme that spans the spectrum of progressive derecho formation environments from those dominated by robust upper-level ridges to those characterized by vigorous upper-level troughs. A climatology of 256 progressive derecho events is created for 1996--2013 and is categorized according to the developed classification scheme. Derecho initiation-relative composites are constructed for each of the seven groups using 0.5° Climate Forecast System Reanalysis data to document the environmental characteristics unique to each group as well as those shared among them. Finally, two in-depth case studies and five cursory case studies provide examples of the seven categories and reveal important nuances in mesoscale dynamic and thermodynamic structure inherent to all derecho cases. Results of the climatology show progressive derecho activity increases from 1 May through 1 July before decreasing again through the end of August and follows a northward trend in latitude from 1 May through 1 August before shifting slightly southward through the end of the warm season. Upslope flow in the vicinity of the Rocky Mountains initiates 28 percent of progressive derechos, upper-level troughs initiate 20 percent, 47 percent form in benign synoptic environments, and 5 percent are unclassifiable. Composite results show all progressive derecho initiation environments are marked by a long axis of instability caused by the overlap of high atmospheric moisture content and steep midlevel lapse rates, but the relative positions and strengths of upper-level troughs and ridges are crucial in determining how the instability axis develops and what its orientation in space will be. Case studies reveal instability axes forming in benign synoptic environments are generally zonally oriented and mainly the result of convergence of low-level moisture, whereas stronger synoptic-scale forcing forms meridionally oriented instability axes through the northward advection of Gulf moisture. The length and magnitude of these instability axes largely determines the duration and severity of a given progressive derecho.

Electro-optic modulator with ultra-low residual amplitude modulation for frequency modulation and laser stabilization.

PubMed

Tai, Zhaoyang; Yan, Lulu; Zhang, Yanyan; Zhang, Xiaofei; Guo, Wenge; Zhang, Shougang; Jiang, Haifeng

2016-12-01

The reduction of the residual amplitude modulation (RAM) induced by electro-optic modulation is essential for many applications of frequency modulation spectroscopy requiring a lower system noise floor. Here, we demonstrate a simple passive approach employing an electro-optic modulator (EOM) cut at Brewster's angle. The proposed EOM exhibits a RAM of a few parts per million, which is comparable with that achieved by a common EOM under critical active temperature and bias voltage controls. The frequency instability of a 10 cm cavity-stabilized laser induced by the RAM effect of the proposed EOM is below 3×10^-17 for integration times from 1 to 1000 s, and below 4×10^-16 for comprehensive noise contributions for integration times from 1 to 100 s.

A small-scale turbulence model

NASA Technical Reports Server (NTRS)

Lundgren, T. S.

1993-01-01

A previously derived analytical model for the small-scale structure of turbulence is reformulated in such a way that the energy spectrum may be computed. The model is an ensemble of two-dimensional (2D) vortices with internal spiral structure, each stretched by an axially symmetric strain flow. Stretching and differential rotation produce an energy cascade to smaller scales in which the stretching represents the effect of instabilities and the spiral structure is the source of dissipation at the end of the cascade. The energy spectrum of the resulting flow may be expressed as a time integration involving only the enstrophy spectrum of the time evolving 2D cross section flow, which may be obtained numerically. Examples are given in which a k exp -5/3 spectrum is obtained by this method. The k exp -5/3 inertial range spectrum is shown to be related to the existence of a self-similar enstrophy preserving range in the 2D enstrophy spectrum. The results are found to be insensitive to time dependence of the strain rate, including even intermittent on-or-off strains.

A Cognitive Agent for Spectrum Monitoring and Informed Spectrum Access

DTIC Science & Technology

2017-06-01

electromagnetic environments (EMEs) to understand what spectrum bands are accessed, when those bands are accessed, and how much energy is...recall. The cognitive agent in this report uses the second approach. The knowledge domain of the cognitive agent is the electromagnetic spectrum. The...Knowledge DTV digital television EME electromagnetic environments FM frequency modulated RF radio frequency VHF very high frequency

Modulational Instability of Dipolar Bose-Einstein Condensates in Optical Lattices with Three-Body Interactions

NASA Astrophysics Data System (ADS)

Qi, Wei; Li, Zi-Hao; Liang, Zhao-Xin

2018-01-01

Not Available Supported by the National Natural Science Foundation of China under Grant No 11647017, and the Science Research Fund of Shaanxi University of Science and Technology under Grant No BJ16-03.

Direct Evidence for Delocalization of Charge Carriers at the Fermi Level in a Doped Conducting Polymer

NASA Astrophysics Data System (ADS)

Zhuo, Jing-Mei; Zhao, Li-Hong; Chia, Perq-Jon; Sim, Wee-Sun; Friend, Richard H.; Ho, Peter K. H.

2008-05-01

The infrared absorption spectrum of the polaron charges at the Fermi level EF in a heavily p-doped conducting poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) film has been measured using interferogram-modulated Fourier-transform charge-modulation spectroscopy. The spectrum indicates softer phonons and weaker electron-phonon coupling riding on a strongly redshifted Drude-like electronic transition, different from the population-averaged “bulk” spectrum. This provides direct evidence that the EF holes are sufficiently delocalized even in such disordered materials to reside in an energy continuum (band states) while the rest of the hole population resides in self-localized gap states.

Auditory sensitivity may require dynamically unstable spike generators: evidence from a model of electrical stimulation.

PubMed

O'Gorman, David E; Colburn, H Steven; Shera, Christopher A

2010-11-01

The response of the auditory nerve to electrical stimulation is highly sensitive to small modulations (<0.5%). This report demonstrates that dynamical instability (i.e., a positive Lyapunov exponent) can account for this sensitivity in a modified FitzHugh-Nagumo model of spike generation, so long as the input noise is not too large. This finding suggests both that spike generator instability is necessary to account for auditory nerve sensitivity and that the amplitude of physiological noise, such as that produced by the random behavior of voltage-gated sodium channels, is small. Based on these results with direct electrical stimulation, it is hypothesized that spike generator instability may be the mechanism that reconciles high sensitivity with the cross-fiber independence observed under acoustic stimulation.

Energy spectrum control for modulated proton beams.

PubMed

Hsi, Wen C; Moyers, Michael F; Nichiporov, Dmitri; Anferov, Vladimir; Wolanski, Mark; Allgower, Chris E; Farr, Jonathan B; Mascia, Anthony E; Schreuder, Andries N

2009-06-01

In proton therapy delivered with range modulated beams, the energy spectrum of protons entering the delivery nozzle can affect the dose uniformity within the target region and the dose gradient around its periphery. For a cyclotron with a fixed extraction energy, a rangeshifter is used to change the energy but this produces increasing energy spreads for decreasing energies. This study investigated the magnitude of the effects of different energy spreads on dose uniformity and distal edge dose gradient and determined the limits for controlling the incident spectrum. A multilayer Faraday cup (MLFC) was calibrated against depth dose curves measured in water for nonmodulated beams with various incident spectra. Depth dose curves were measured in a water phantom and in a multilayer ionization chamber detector for modulated beams using different incident energy spreads. Some nozzle entrance energy spectra can produce unacceptable dose nonuniformities of up to +/-21% over the modulated region. For modulated beams and small beam ranges, the width of the distal penumbra can vary by a factor of 2.5. When the energy spread was controlled within the defined limits, the dose nonuniformity was less than +/-3%. To facilitate understanding of the results, the data were compared to the measured and Monte Carlo calculated data from a variable extraction energy synchrotron which has a narrow spectrum for all energies. Dose uniformity is only maintained within prescription limits when the energy spread is controlled. At low energies, a large spread can be beneficial for extending the energy range at which a single range modulator device can be used. An MLFC can be used as part of a feedback to provide specified energy spreads for different energies.

Transverse instabilities of stripe domains in magnetic thin films with perpendicular magnetic anisotropy

NASA Astrophysics Data System (ADS)

Ruth, Max E.; Iacocca, Ezio; Kevrekidis, Panayotis G.; Hoefer, Mark A.

2018-03-01

Stripe domains are narrow, elongated, reversed regions that exist in magnetic materials with perpendicular magnetic anisotropy. They appear as a pair of domain walls that can exhibit topology with a nonzero chirality. Recent experimental and numerical investigations identify an instability of stripe domains along the long direction as a means of nucleating isolated magnetic skyrmions. Here, the onset and nonlinear evolution of transverse instabilities for a dynamic stripe domain known as the bion stripe are investigated. Both nontopological and topological variants of the bion stripe are shown to exhibit a long-wavelength transverse instability with different characteristic features. In the former, small transverse variations in the stripe's width lead to a neck instability that eventually pinches the nontopological stripe into a chain of two-dimensional breathers composed of droplet soliton pairs. In the latter case, small variations in the stripe's center result in a snake instability whose topological structure leads to the nucleation of dynamic magnetic skyrmions and antiskyrmions as well as perimeter-modulated droplets. Quantitative, analytical predictions for both the early, linear evolution and the long-time, nonlinear evolution are achieved using an averaged Lagrangian approach that incorporates both exchange (dispersion) and anisotropy (nonlinearity). The method of analysis is general and can be applied to other filamentary structures.

The High Energy X-ray Spectrum of 4U1700-37 Observed from OSO-8

NASA Technical Reports Server (NTRS)

Dolan, J. F.; Coe, M. J.; Crannell, C. J.; Dennis, B. R.; Frost, K. J.; Maurer, G. S.; Orwig, L. E.

1979-01-01

The most intense hard X-ray source in the confused region in Scorpius is identified as 4U1700-37. The 3.4-day modulation is seen above 20 keV with the intensity during eclipse being consistent with zero flux. The photon-number spectrum from 20 to 150 keV is well represented by a single power law with a photo-number spectral index of -2.77 + or - 0.35 or by a thermal bremsstrahlung spectrum with kT = 27 96.8-min X-ray modulation previously reported at lower energies. Despite the difficulties in reconciling both the lack of periodic modulation in the emitted X-radiation and the orbital dynamics of the system with theories of the evolution and physical properties of neutron stars, the observed properties of 4U1700-37 are all consistent with the source being a spherically accreting neutron star rather than a black hole.

Simple analytical model for low-frequency frequency-modulation noise of monolithic tunable lasers.

PubMed

Huynh, Tam N; Ó Dúill, Seán P; Nguyen, Lim; Rusch, Leslie A; Barry, Liam P

2014-02-10

We employ simple analytical models to construct the entire frequency-modulation (FM)-noise spectrum of tunable semiconductor lasers. Many contributions to the laser FM noise can be clearly identified from the FM-noise spectrum, such as standard Weiner FM noise incorporating laser relaxation oscillation, excess FM noise due to thermal fluctuations, and carrier-induced refractive index fluctuations from stochastic carrier generation in the passive tuning sections. The contribution of the latter effect is identified by noting a correlation between part of the FM-noise spectrum with the FM-modulation response of the passive sections. We pay particular attention to the case of widely tunable lasers with three independent tuning sections, mainly the sampled-grating distributed Bragg reflector laser, and compare with that of a distributed feedback laser. The theoretical model is confirmed with experimental measurements, with the calculations of the important phase-error variance demonstrating excellent agreement.

Tuning the electrical and optical anisotropy of a monolayer black phosphorus magnetic superlattice

NASA Astrophysics Data System (ADS)

Li, X. J.; Yu, J. H.; Luo, K.; Wu, Z. H.; Yang, W.

2018-04-01

We investigate theoretically the effects of modulated periodic perpendicular magnetic fields on the electronic states and optical absorption spectrum in monolayer black phosphorus (phosphorene). We demonstrate that different phosphorene magnetic superlattice (PMS) orientations can give rise to distinct energy spectra, i.e. tuning the intrinsic electronic anisotropy. Rashba spin-orbit coupling (RSOC) develops a spin-splitting energy dispersion in this phosphorene magnetic superlattice. Anisotropic momentum-dependent carrier distributions along/perpendicular to the magnetic strips are demonstrated. The manipulations of these exotic electronic properties by tuning superlattice geometry, magnetic field and the RSOC term are addressed systematically. Accordingly, we find bright-to-dark transitions in the ground-state electron-hole pair transition rate spectrum and the PMS orientation-dependent anisotropic optical absorption spectrum. This feature offers us a practical way of modulating the electronic anisotropy in phosphorene by magnetic superlattice configurations and detecting this modulation capability by using an optical technique.

Frequency-Modulation Correlation Spectrometer

NASA Technical Reports Server (NTRS)

Margolis, J. S.; Martonchik, J. V.

1985-01-01

New type of correlation spectrometer eliminates need to shift between two cells, one empty and one containing reference gas. Electrooptical phase modulator sinusoidally shift frequencies of sample transmission spectrum.

Variability in Estrogen-Metabolizing Genes and Their Association with Genomic Instability in Untreated Breast Cancer Patients and Healthy Women

PubMed Central

Alves dos Santos, Raquel; Teixeira, Ana Cláudia; Mayorano, Mônica Beatriz; Carrara, Hélio Humberto Angotti; Moreira de Andrade, Jurandyr; Takahashi, Catarina Satie

2011-01-01

In the present study, we investigated the relationship between polymorphisms in the estrogen-metabolizing genes CYP17, CYP1B1, CYP1A1, and COMT and genomic instability in the peripheral blood lymphocytes of 62 BC patients and 62 controls considering that increased or prolonged exposure to estrogen can damage the DNA molecule and increase the genomic instability process in breast tissue. Our data demonstrated increased genomic instability in BC patients and that individuals with higher frequencies of MN exhibited higher risk to BC when belonging Val/Met genotype of the COMT gene. We also observed that CYP17 and CYP1A1 polymorphisms can modify the risk to BC depending on the menopause status. We can conclude that the genetic background in estrogen metabolism pathway can modulate chromosome damage in healthy controls and patients and thereby influence the risk to BC. These findings suggest the importance to ally biomarkers of susceptibility and effects to estimate risk groups. PMID:21716904

Weakly Nonlinear Analysis of Vortex Formation in a Dissipative Variant of the Gross--Pitaevskii Equation

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

Tzou, J. C.; Kevrekidis, P. G.; Kolokolnikov, T.

2016-05-10

For a dissipative variant of the two-dimensional Gross--Pitaevskii equation with a parabolic trap under rotation, we study a symmetry breaking process that leads to the formation of vortices. The first symmetry breaking leads to the formation of many small vortices distributed uniformly near the Thomas$-$Fermi radius. The instability occurs as a result of a linear instability of a vortex-free steady state as the rotation is increased above a critical threshold. We focus on the second subsequent symmetry breaking, which occurs in the weakly nonlinear regime. At slightly above threshold, we derive a one-dimensional amplitude equation that describes the slow evolutionmore » of the envelope of the initial instability. Here, we show that the mechanism responsible for initiating vortex formation is a modulational instability of the amplitude equation. We also illustrate the role of dissipation in the symmetry breaking process. All analyses are confirmed by detailed numerical computations« less

Generation of mesoscale magnetic fields and the dynamics of Cosmic Ray acceleration

NASA Astrophysics Data System (ADS)

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

The problem of the cosmic ray origin is discussed in connection with their acceleration in supernova remnant shocks. The diffusive shock acceleration mechanism is reviewed and its potential to accelerate particles to the maximum energy of (presumably) galactic cosmic rays (1018eV ) is considered. It is argued that to reach such energies, a strong magnetic field at scales larger than the particle gyroradius must be created as a result of the acceleration process, itself. One specific mechanism suggested here is based on the generation of Alfven wave at the gyroradius scale with a subsequent transfer to longer scales via interaction with strong acoustic turbulence in the shock precursor. The acoustic turbulence in turn, may be generated by Drury instability or by parametric instability of the Alfven waves. The generation mechanism is modulational instability of CR generated Alfven wave packets induced, in turn, by scattering off acoustic fluctuations in the shock precursor which are generated by Drury instability.

Three-dimensional single-mode nonlinear ablative Rayleigh-Taylor instability

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

Yan, R.; Betti, R.; Sanz, J.

The nonlinear evolution of the single-mode ablative Rayleigh-Taylor instability is studied in three dimensions. As the mode wavelength approaches the cutoff of the linear spectrum (short-wavelength modes), it is found that the three-dimensional (3D) terminal bubble velocity greatly exceeds both the two-dimensional (2D) value and the classical 3D bubble velocity. Unlike in 2D, the 3D short-wavelength bubble velocity does not saturate. The growing 3D bubble acceleration is driven by the unbounded accumulation of vorticity inside the bubble. As a result, the vorticity is transferred by mass ablation from the Rayleigh-Taylor spikes to the ablated plasma filling the bubble volume.

Fast saturation of the two-plasmon-decay instability for shock-ignition conditions

NASA Astrophysics Data System (ADS)

Weber, S.; Riconda, C.; Klimo, O.; Héron, A.; Tikhonchuk, V. T.

2012-01-01

Two-plasmon-decay (TPD) instability is investigated for conditions relevant for the shock-ignition (SI) scheme of inertial confinement fusion. Two-dimensional particle-in-cell simulations show that in a hot, large-scale plasma, TPD develops in concomitance with stimulated Raman scattering (SRS). It is active only during the first picosecond of interaction, and then it is rapidly saturated due to plasma cavitation. TPD-excited plasma waves extend to small wavelengths, above the standard Landau cutoff. The hot electron spectrum created by SRS and TPD is relatively soft, limited to energies below 100 keV, which should not be a danger for the fuel core preheat in the SI scenario.

Effects of radial electric fields on linear ITG instabilities in W7-X and LHD

NASA Astrophysics Data System (ADS)

Riemann, J.; Kleiber, R.; Borchardt, M.

2016-07-01

The impact of radial electric fields on the properties of linear ion-temperature-gradient (ITG) modes in stellarators is studied. Numerical simulations have been carried out with the global particle-in-cell (PIC) code EUTERPE, modelling the behaviour of ITG modes in Wendelstein 7-X and an LHD-like configuration. In general, radial electric fields seem to lead to a reduction of ITG instability growth, which can be related to the action of an induced E× B -drift. Focus is set on the modification of mode properties (frequencies, power spectrum, spatial structure and localization) to understand the observed growth rates as the result of competing stabilizing mechanisms.

Modulation for terrestrial broadcasting of digital HDTV

NASA Technical Reports Server (NTRS)

Kohn, Elliott S.

1991-01-01

The digital modulation methods used by the DigiCipher, DSC-HDTV, ADTV, and ATVA-P digital high-definition television (HDTV) systems are discussed. Three of the systems use a quadrature amplitude modulation method, and the fourth uses a vestigial sideband modulation method. The channel equalization and spectrum sharing of the digital HDTV systems is discussed.

Holding-time-aware asymmetric spectrum allocation in virtual optical networks

NASA Astrophysics Data System (ADS)

Lyu, Chunjian; Li, Hui; Liu, Yuze; Ji, Yuefeng

2017-10-01

Virtual optical networks (VONs) have been considered as a promising solution to support current high-capacity dynamic traffic and achieve rapid applications deployment. Since most of the network services (e.g., high-definition video service, cloud computing, distributed storage) in VONs are provisioned by dedicated data centers, needing different amount of bandwidth resources in both directions, the network traffic is mostly asymmetric. The common strategy, symmetric provisioning of traffic in optical networks, leads to a waste of spectrum resources in such traffic patterns. In this paper, we design a holding-time-aware asymmetric spectrum allocation module based on SDON architecture and an asymmetric spectrum allocation algorithm based on the module is proposed. For the purpose of reducing spectrum resources' waste, the algorithm attempts to reallocate the idle unidirectional spectrum slots in VONs, which are generated due to the asymmetry of services' bidirectional bandwidth. This part of resources can be exploited by other requests, such as short-time non-VON requests. We also introduce a two-dimensional asymmetric resource model for maintaining idle spectrum resources information of VON in spectrum and time domains. Moreover, a simulation is designed to evaluate the performance of the proposed algorithm, and results show that our proposed asymmetric spectrum allocation algorithm can improve the resource waste and reduce blocking probability.

Investigation of Combustion Control in a Dump Combustor Using the Feedback Free Fluidic Oscillator

NASA Technical Reports Server (NTRS)

Meier, Eric J.; Casiano, Matthew J.; Anderson, William E.; Heister, Stephen D.

2015-01-01

A feedback free fluidic oscillator was designed and integrated into a single element rocket combustor with the goal of suppressing longitudinal combustion instabilities. The fluidic oscillator uses internal fluid dynamics to create an unsteady outlet jet at a specific frequency. An array of nine fluidic oscillators was tested to mimic modulated secondary oxidizer injection into the combustor dump plane. The combustor has a coaxial injector that uses gaseous methane and decomposed hydrogen peroxide with an overall O/F ratio of 11.7. A sonic choke plate on an actuator arm allows for continuous adjustment of the oxidizer post acoustics enabling the study of a variety of instability magnitudes. The fluidic oscillator unsteady outlet jet performance is compared against equivalent steady jet injection and a baseline design with no secondary oxidizer injection. At the most unstable operating conditions, the unsteady outlet jet saw a 67% reduction in the instability pressure oscillation magnitude when compared to the steady jet and baseline data. Additionally, computational fluid dynamics analysis of the combustor gives insight into the flow field interaction of the fluidic oscillators. The results indicate that open loop high frequency propellant modulation for combustion control can be achieved through fluidic devices that require no moving parts or electrical power to operate.

Global and regional axial ocean angular momentum signals and length-of-day variations (1985-1996)

NASA Astrophysics Data System (ADS)

Ponte, Rui M.; Stammer, Detlef

2000-07-01

Changes in ocean angular momentum M about the polar axis are related to fluctuations in zonal currents (relative component Mr) and latitudinal shifts in mass (planetary component MΩ). Output from a 1° ocean model is used to calculate global Mr, MΩ, and M time series at 5 day intervals for the period January 1985 to April 1996. The annual cycle in Mr, MΩ, and M is larger than the semiannual cycle, and MΩ amplitudes are nearly twice those of Mr. Year-to-year modulation of the seasonal cycle is present, but interannual variability is weak. The spectrum of M is red (background slope between ω-1 and ω-2) at subseasonal periods, implying a white or blue spectrum for the external torque on the ocean. Comparisons with previous studies indicate the importance of direct atmospheric forcing in inducing subseasonal M signals, relative to instabilities and other internal sources of rapid oceanic signals. Regional angular momentum estimates show that seasonal variability tends to be larger at low latitudes, but many local maxima exist because of the spatial structure of zonal current and mass variability. At seasonal timescales, latitudes ~20°S-10°N contribute substantial variability to MΩ, while signals in Mr can be traced to Antarctic Circumpolar Current transports and associated circulation. Variability in M is found to be small when compared with similar time series for the atmosphere and the solid Earth, but ocean signals are significantly coherent with atmosphere-solid Earth residuals, implying a measurable oceanic impact on length-of-day variations.

Work-to-School Transitions in the Age of the Displaced Worker: A Psychology of Working Perspective

ERIC Educational Resources Information Center

Hees, Charles K.; Rottinghaus, Patrick J.; Briddick, William C.; Conrath, Julia A.

2012-01-01

Frank Parsons (1909) founded the vocational guidance movement more than 100 years ago within the context of a shift from an agricultural to an industrial workplace. Today, globalization, workforce diversity, and the financial instability related to the Great Recession present numerous challenges to workers across the economic spectrum. In addition…

Modulation of Core Turbulent Density Fluctuations by Large-Scale Neoclassical Tearing Mode Islands in the DIII-D Tokamak

DOE PAGES

Bardóczi, L.; Rhodes, T. L.; Carter, T. A.; ...

2016-05-26

We report the first observation of localized modulation of turbulent density uctuations en (via Beam Emission Spectroscopy) by neoclassical tearing modes (NTMs) in the core of the DIII-D tokamak. NTMs are important as they often lead to severe degradation of plasma confinement and disruptions in high-confinement fusion experiments. Magnetic islands associated with NTMs significantly modify the profiles and turbulence drives. In this experiment n was found to be modulated by 14% across the island. Gyrokinetic simulations suggest that en could be dominantly driven by the ion temperature gradient (ITG) instability.

Narrowband high temperature superconducting receiver for low frequency radio waves

DOEpatents

Reagor, David W.

2001-01-01

An underground communicating device has a low-noise SQUID using high temperature superconductor components connected to detect a modulated external magnetic flux for outputting a voltage signal spectrum that is related to the varying magnetic flux. A narrow bandwidth filter may be used to select a portion of the voltage signal spectrum that is relatively free of power line noise to output a relatively low noise output signal when operating in a portion of the electromagnetic spectra where such power line noise exists. A demodulator outputs a communication signal, which may be an FM signal, indicative of a modulation on the modulated external magnetic flux.

Convective stability in the Rayleigh-Benard and directional solidification problems - High-frequency gravity modulation

NASA Technical Reports Server (NTRS)

Wheeler, A. A.; Mcfadden, G. B.; Murray, B. T.; Coriell, S. R.

1991-01-01

The effect of vertical, sinusoidal, time-dependent gravitational acceleration on the onset of solutal convection during directional solidification is analyzed in the limit of large modulation frequency. When the unmodulated state is unstable, the modulation amplitude required to stabilize the system is determined by the method of averaging. When the unmodulated state is stable, resonant modes of instability occur at large modulation amplitude. These are analyzed using matched asymptotic expansions to elucidate the boundary-layer structure for both the Rayleigh-Benard and directional solidification configurations. Based on these analyses, a thorough examination of the dependence of the stability criteria on the unmodulated Rayleigh number, Schmidt number, and distribution coefficient, is carried out.

On the Two Components of Turbulent Mixing Noise from Supersonic Jets

NASA Technical Reports Server (NTRS)

Tam, Christopher K. W.; Golebiowski, Michel; Seiner, J. M.

1996-01-01

It is argued that because of the lack of intrinsic length and time scales in the core part of the jet flow, the radiated noise spectrum of a high-speed jet should exhibit similarity. A careful analysis of all the axisymmetric supersonic jet noise spectra in the data-bank of the Jet Noise Laboratory of the NASA Langley Research Center has been carried out. Two similarity spectra, one for the noise from the large turbulence structures/instability waves of the jet flow, the other for the noise from the fine-scale turbulence, are identified. The two similarity spectra appear to be universal spectra for axisymmetric jets. They fit all the measured data including those from subsonic jets. Experimental evidence are presented showing that regardless of whether a jet is supersonic or subsonic the noise characteristics and generation mechanisms are the same. There is large turbulence structures/instability waves noise from subsonic jets. This noise component can be seen prominently inside the cone of silence of the fine-scale turbulence noise near the jet axis. For imperfectly expanded supersonic jets, a shock cell structure is formed inside the jet plume. Measured spectra are provided to demonstrate that the presence of a shock cell structure has little effect on the radiated turbulent mixing noise. The shape of the noise spectrum as well as the noise intensity remain practically the same as those of a fully expanded jet. However, for jets undergoing strong screeching, there is broadband noise amplification for both turbulent mixing noise components. It is discovered through a pilot study of the noise spectrum of rectangular and elliptic supersonic jets that the turbulent mixing noise of these jets is also made up of the same two noise components found in axisymmetric jets. The spectrum of each individual noise component also fits the corresponding similarity spectrum of axisymmetric jets.

Formation of rogue waves from a locally perturbed condensate.

PubMed

Gelash, A A

2018-02-01

The one-dimensional focusing nonlinear Schrödinger equation (NLSE) on an unstable condensate background is the fundamental physical model that can be applied to study the development of modulation instability (MI) and formation of rogue waves. The complete integrability of the NLSE via inverse scattering transform enables the decomposition of the initial conditions into elementary nonlinear modes: breathers and continuous spectrum waves. The small localized condensate perturbations (SLCP) that grow as a result of MI have been of fundamental interest in nonlinear physics for many years. Here, we demonstrate that Kuznetsov-Ma and superregular NLSE breathers play the key role in the dynamics of a wide class of SLCP. During the nonlinear stage of MI development, collisions of these breathers lead to the formation of rogue waves. We present new scenarios of rogue wave formation for randomly distributed breathers as well as for artificially prepared initial conditions. For the latter case, we present an analytical description based on the exact expressions found for the space-phase shifts that breathers acquire after collisions with each other. Finally, the presence of Kuznetsov-Ma and superregular breathers in arbitrary-type condensate perturbations is demonstrated by solving the Zakharov-Shabat eigenvalue problem with high numerical accuracy.

Formation of rogue waves from a locally perturbed condensate

NASA Astrophysics Data System (ADS)

Gelash, A. Â. A.

2018-02-01

The one-dimensional focusing nonlinear Schrödinger equation (NLSE) on an unstable condensate background is the fundamental physical model that can be applied to study the development of modulation instability (MI) and formation of rogue waves. The complete integrability of the NLSE via inverse scattering transform enables the decomposition of the initial conditions into elementary nonlinear modes: breathers and continuous spectrum waves. The small localized condensate perturbations (SLCP) that grow as a result of MI have been of fundamental interest in nonlinear physics for many years. Here, we demonstrate that Kuznetsov-Ma and superregular NLSE breathers play the key role in the dynamics of a wide class of SLCP. During the nonlinear stage of MI development, collisions of these breathers lead to the formation of rogue waves. We present new scenarios of rogue wave formation for randomly distributed breathers as well as for artificially prepared initial conditions. For the latter case, we present an analytical description based on the exact expressions found for the space-phase shifts that breathers acquire after collisions with each other. Finally, the presence of Kuznetsov-Ma and superregular breathers in arbitrary-type condensate perturbations is demonstrated by solving the Zakharov-Shabat eigenvalue problem with high numerical accuracy.

Coherence-length-gated distributed optical fiber sensing based on microwave-photonic interferometry.

PubMed

Hua, Liwei; Song, Yang; Cheng, Baokai; Zhu, Wenge; Zhang, Qi; Xiao, Hai

2017-12-11

This paper presents a new optical fiber distributed sensing concept based on coherent microwave-photonics interferometry (CMPI), which uses a microwave modulated coherent light source to interrogate cascaded interferometers for distributed measurement. By scanning the microwave frequencies, the complex microwave spectrum is obtained and converted to time domain signals at known locations by complex Fourier transform. The amplitudes of these time domain pulses are a function of the optical path differences (OPDs) of the distributed interferometers. Cascaded fiber Fabry-Perot interferometers (FPIs) fabricated by femtosecond laser micromachining were used to demonstrate the concept. The experimental results indicated that the strain measurement resolution can be better than 0.6 µε using a FPI with a cavity length of 1.5 cm. Further improvement of the strain resolution to the nε level is achievable by increasing the cavity length of the FPI to over 1m. The tradeoff between the sensitivity and dynamic range was also analyzed in detail. To minimize the optical power instability (either from the light source or the fiber loss) induced errors, a single reflector was added in front of an individual FPI as an optical power reference for the purpose of compensation.

Energy-efficient routing, modulation and spectrum allocation in elastic optical networks

NASA Astrophysics Data System (ADS)

Tan, Yanxia; Gu, Rentao; Ji, Yuefeng

2017-07-01

With tremendous growth in bandwidth demand, energy consumption problem in elastic optical networks (EONs) becomes a hot topic with wide concern. The sliceable bandwidth-variable transponder in EON, which can transmit/receive multiple optical flows, was recently proposed to improve a transponder's flexibility and save energy. In this paper, energy-efficient routing, modulation and spectrum allocation (EE-RMSA) in EONs with sliceable bandwidth-variable transponder is studied. To decrease the energy consumption, we develop a Mixed Integer Linear Programming (MILP) model with corresponding EE-RMSA algorithm for EONs. The MILP model jointly considers the modulation format and optical grooming in the process of routing and spectrum allocation with the objective of minimizing the energy consumption. With the help of genetic operators, the EE-RMSA algorithm iteratively optimizes the feasible routing path, modulation format and spectrum resources solutions by explore the whole search space. In order to save energy, the optical-layer grooming strategy is designed to transmit the lightpath requests. Finally, simulation results verify that the proposed scheme is able to reduce the energy consumption of the network while maintaining the blocking probability (BP) performance compare with the existing First-Fit-KSP algorithm, Iterative Flipping algorithm and EAMGSP algorithm especially in large network topology. Our results also demonstrate that the proposed EE-RMSA algorithm achieves almost the same performance as MILP on an 8-node network.

Color instabilities in the quark-gluon plasma

NASA Astrophysics Data System (ADS)

Mrówczyński, Stanisław; Schenke, Björn; Strickland, Michael

2017-04-01

When the quark-gluon plasma (QGP) - a system of deconfined quarks and gluons - is in a nonequilibrium state, it is usually unstable with respect to color collective modes. The instabilities, which are expected to strongly influence dynamics of the QGP produced in relativistic heavy-ion collisions, are extensively discussed under the assumption that the plasma is weakly coupled. We begin by presenting the theoretical approaches to study the QGP, which include: field theory methods based on the Keldysh-Schwinger formalism, classical and quantum kinetic theories, and fluid techniques. The dispersion equations, which give the spectrum of plasma collective excitations, are analyzed in detail. Particular attention is paid to a momentum distribution of plasma constituents which is obtained by deforming an isotropic momentum distribution. Mechanisms of chromoelectric and chromomagnetic instabilities are explained in terms of elementary physics. The Nyquist analysis, which allows one to determine the number of solutions of a dispersion equation without explicitly solving it, and stability criteria are also discussed. We then review various numerical approaches - purely classical or quantum - to simulate the temporal evolution of an unstable quark-gluon plasma. The dynamical role of instabilities in the processes of plasma equilibration is analyzed.

Stability of Bose-Einstein condensates in a Kronig-Penney potential

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

Danshita, Ippei; Department of Physics, Waseda University, Okubo, Shinjuku, Tokyo 169-8555; Tsuchiya, Shunji

2007-03-15

We study the stability of Bose-Einstein condensates with superfluid currents in a one-dimensional periodic potential. By using the Kronig-Penney model, the condensate and Bogoliubov bands are analytically calculated and the stability of condensates in a periodic potential is discussed. The Landau and dynamical instabilities occur in a Kronig-Penney potential when the quasimomentum of the condensate exceeds certain critical values as in a sinusoidal potential. It is found that the onsets of the Landau and dynamical instabilities coincide with the point where the perfect transmission of low energy excitations through each potential barrier is forbidden. The Landau instability is caused bymore » the excitations with small q and the dynamical instability is caused by the excitations with q={pi}/a at their onsets, where q is the quasimomentum of excitation and a is the lattice constant. A swallow-tail energy loop appears at the edge of the first condensate band when the mean-field energy is sufficiently larger than the strength of the periodic potential. We find that the upper portion of the swallow-tail is always dynamically unstable, but the second Bogoliubov band has a phonon spectrum reflecting the positive effective mass.« less

Most-Critical Transient Disturbances in an Incompressible Flat-Plate Boundary Layer

NASA Astrophysics Data System (ADS)

Monschke, Jason; White, Edward

2015-11-01

Transient growth is a linear disturbance growth mechanism that plays a key role in roughness-induced boundary-layer transition. It occurs when superposed stable, non-orthogonal continuous spectrum modes experience algebraic disturbance growth followed by exponential decay. Algebraic disturbance growth can modify the basic state making it susceptible to secondary instabilities rapidly leading to transition. Optimal disturbance theory was developed to model the most-dangerous disturbances. However, evidence suggests roughness-induced transient growth is sub-optimal yet leads to transition earlier than optimal theory suggests. This research computes initial disturbances most unstable to secondary instabilities to further develop the applicability of transient growth theory to surface roughness. The main approach is using nonlinear adjoint optimization with solutions of the parabolized Navier-Stokes and BiGlobal stability equations. Two objective functions were considered: disturbance kinetic energy growth and sinuous instability growth rate. The first objective function was used as validation of the optimization method. Counter-rotating streamwise vortices located low in the boundary layer maximize the sinuous instability growth rate. The authors would like to acknowledge NASA and the AFOSR for funding this work through AFOSR Grant FA9550-09-1-0341.

The electron-cyclotron maser instability as a source of plasma radiation. [Solar radio bursts

NASA Technical Reports Server (NTRS)

Winglee, R. M.; Dulk, G. A.

1986-01-01

The generation of continuum bursts from the sun at dm and m wavelengths (in particular, type IV bursts) via the electron-cyclotron-maser instability is examined. The maser instability can be driven by an electron distribution with either a loss-cone anisotropy or a peak at large pitch angles. For omega(p)/Omega(e) much greater than 1, the maser emission is produced by electrons interacting through a harmonic (cyclotron) resonance and is electrostatic, being in the upper hybrid mode at frequencies approximately equal to omega(p). Coalescence processes are required to convert the electrostatic waves into transverse radiation which can escape from the source region. Whether the resultant spectrum is nearly a smooth continuum or has a zebra-stripe pattern (both of which occur in type IV bursts) depends on the form of the electron distribution, inhomogeneities in the density and magnetic field, and whether the maser reaches saturation. For at least the case of some type IV dm bursts with fine structure, comparison with observations seems to indicate that the electrons producing the emission are more likely to have a loss-cone distribution, and that the maser instability is not at saturation.

Color instabilities in the quark–gluon plasma

DOE PAGES

Mrówczyński, Stanisław; Schenke, Björn; Strickland, Michael

2017-04-09

When the quark–gluon plasma (QGP) – a system of deconfined quarks and gluons – is in a nonequilibrium state, it is usually unstable with respect to color collective modes. The instabilities, which are expected to strongly influence dynamics of the QGP produced in relativistic heavy-ion collisions, are extensively discussed under the assumption that the plasma is weakly coupled. Here, we begin by presenting the theoretical approaches to study the QGP, which include: field theory methods based on the Keldysh–Schwinger formalism, classical and quantum kinetic theories, and fluid techniques. The dispersion equations, which give the spectrum of plasma collective excitations, aremore » analyzed in detail. We pay particular attention to a momentum distribution of plasma constituents which is obtained by deforming an isotropic momentum distribution. Mechanisms of chromoelectric and chromomagnetic instabilities are explained in terms of elementary physics. The Nyquist analysis, which allows one to determine the number of solutions of a dispersion equation without explicitly solving it, and stability criteria are also discussed. We then review various numerical approaches – purely classical or quantum – to simulate the temporal evolution of an unstable quark–gluon plasma. The dynamical role of instabilities in the processes of plasma equilibration is analyzed.« less

Linear instabilities near the DIII-D edge simulated in fluid models

NASA Astrophysics Data System (ADS)

Bass, Eric; Holland, Christopher

2017-10-01

The linear instability spectrum is reported near the DIII-D edge (within the separatrix) for L-mode and H-mode shots using the new eigenvalue solver FluTES (Fluid Toroidal Eigenvalue Solver). FluTES circumvents difficulties with convergence to clean linear eigenmodes (required for diagnosis of nonlinear simulations in codes such as BOUT++) often encountered with fluid initial-value solvers. FluTES is well-verified in analytic cases and against a BOUT++/ELITE benchmark toroidal case. We report results for both a 3-field, one-fluid model (the well-known ``elm-pb'' model) and a 5-field, two-fluid model. For the peeling-ballooning-dominated H-mode, the two solutions are qualitatively the same. In the driftwave-dominated L-mode edge, only the two-fluid solution gives robust instabilities which occur primarily at n > 50 . FluTES is optimized for this regime (near-flutelike limit, toroidally spectral). Cross-separatrix, coupled fluid and drift instabilities may play a role in explaining the gyrokinetic L-mode edge transport shortfall. Extension of FluTES into the open-field-line region is underway. Prepared by UCSD under Contract Number DE-FG02-06ER54871.

Upstream and Downstream Influence in STBLI Instability

NASA Astrophysics Data System (ADS)

Martin, Pino; Priebe, Stephan; Helm, Clara

2016-11-01

Priebe and Martín (JFM, 2012) show that the low-frequency unsteadiness in shockwave and turbulent boundary layer interactions (STBLI) is governed by an inviscid instability. Priebe, Tu, Martín and Rowley (JFM, 2016) show that the instability is an inviscid centrifugal one, i.e Görtlerlike vortices. Previous works had given differing conclusions as to whether the low-frequency unsteadiness in STBLI is caused by an upstream or downstream mechanism. In this paper, we reconcile these opposite views and show that upstream and downstream correlations co-exist in the context of the nature of Görtler vortices. We find that the instability is similar to that in separated subsonic and laminar flows. Since the turbulence is modulated but passive to the global mode, the turbulent separated flows are amenable to linear global analysis. As such, the characteristic length and time scales, and the receptivity of the global mode might be determined, and low-order models that represent the low-frequency dynamics in STBLI might be developed. The centrifugal instability persists even under hypersonic conditions. This work is funded by the AFOSR Grant Number AF9550-15-1-0284 with Dr. Ivett Leyva.

Wrinkling instabilities in soft bilayered systems

PubMed Central

Budday, Silvia; Andres, Sebastian; Walter, Bastian

2017-01-01

Wrinkling phenomena control the surface morphology of many technical and biological systems. While primary wrinkling has been extensively studied, experimentally, analytically and computationally, higher-order instabilities remain insufficiently understood, especially in systems with stiffness contrasts well below 100. Here, we use the model system of an elastomeric bilayer to experimentally characterize primary and secondary wrinkling at moderate stiffness contrasts. We systematically vary the film thickness and substrate prestretch to explore which parameters modulate the emergence of secondary instabilities, including period-doubling, period-tripling and wrinkle-to-fold transitions. Our experiments suggest that period-doubling is the favourable secondary instability mode and that period-tripling can emerge under disturbed boundary conditions. High substrate prestretch can suppress period-doubling and primary wrinkles immediately transform into folds. We combine analytical models with computational simulations to predict the onset of primary wrinkling, the post-buckling behaviour, secondary bifurcations and the wrinkle-to-fold transition. Understanding the mechanisms of pattern selection and identifying the critical control parameters of wrinkling will allow us to fabricate smart surfaces with tunable properties and to control undesired surface patterns like in the asthmatic airway. This article is part of the themed issue ‘Patterning through instabilities in complex media: theory and applications.’ PMID:28373385

Off-axis holographic lens spectrum-splitting photovoltaic system for direct and diffuse solar energy conversion.

PubMed

Vorndran, Shelby D; Chrysler, Benjamin; Wheelwright, Brian; Angel, Roger; Holman, Zachary; Kostuk, Raymond

2016-09-20

This paper describes a high-efficiency, spectrum-splitting photovoltaic module that uses an off-axis volume holographic lens to focus and disperse incident solar illumination to a rectangular shaped high-bandgap indium gallium phosphide cell surrounded by strips of silicon cells. The holographic lens design allows efficient collection of both direct and diffuse illumination to maximize energy yield. We modeled the volume diffraction characteristics using rigorous coupled-wave analysis, and simulated system performance using nonsequential ray tracing and PV cell data from the literature. Under AM 1.5 illumination conditions the simulated module obtained a 30.6% conversion efficiency. This efficiency is a 19.7% relative improvement compared to the more efficient cell in the system (silicon). The module was also simulated under a typical meteorological year of direct and diffuse irradiance in Tucson, Arizona, and Seattle, Washington. Compared to a flat panel silicon module, the holographic spectrum splitting module obtained a relative improvement in energy yield of 17.1% in Tucson and 14.0% in Seattle. An experimental proof-of-concept volume holographic lens was also fabricated in dichromated gelatin to verify the main characteristics of the system. The lens obtained an average first-order diffraction efficiency of 85.4% across the aperture at 532 nm.

Novel Active Combustion Control Valve

NASA Technical Reports Server (NTRS)

Caspermeyer, Matt

2014-01-01

This project presents an innovative solution for active combustion control. Relative to the state of the art, this concept provides frequency modulation (greater than 1,000 Hz) in combination with high-amplitude modulation (in excess of 30 percent flow) and can be adapted to a large range of fuel injector sizes. Existing valves often have low flow modulation strength. To achieve higher flow modulation requires excessively large valves or too much electrical power to be practical. This active combustion control valve (ACCV) has high-frequency and -amplitude modulation, consumes low electrical power, is closely coupled with the fuel injector for modulation strength, and is practical in size and weight. By mitigating combustion instabilities at higher frequencies than have been previously achieved (approximately 1,000 Hz), this new technology enables gas turbines to run at operating points that produce lower emissions and higher performance.

Arthroscopic Findings in Anterior Shoulder Instability

PubMed Central

Hantes, Michael; Raoulis, Vasilios

2017-01-01

Background: In the last years, basic research and arthroscopic surgery, have improved our understanding of shoulder anatomy and pathology. It is a fact that arthroscopic treatment of shoulder instability has evolved considerably over the past decades. The aim of this paper is to present the variety of pathologies that should be identified and treated during shoulder arthroscopy when dealing with anterior shoulder instability cases. Methods: A review of the current literature regarding arthroscopic shoulder anatomy, anatomic variants, and arthroscopic findings in anterior shoulder instability, is presented. In addition, correlation of arthroscopic findings with physical examination and advanced imaging (CT and MRI) in order to improve our understanding in anterior shoulder instability pathology is discussed. Results: Shoulder instability represents a broad spectrum of disease and a thorough understanding of the pathoanatomy is the key for a successful treatment of the unstable shoulder. Patients can have a variety of pathologies concomitant with a traditional Bankart lesion, such as injuries of the glenoid (bony Bankart), injuries of the glenoid labrum, superiorly (SLAP) or anteroinferiorly (e.g. anterior labroligamentous periosteal sleeve avulsion, and Perthes), capsular lesions (humeral avulsion of the glenohumeral ligament), and accompanying osseous-cartilage lesions (Hill-Sachs, glenolabral articular disruption). Shoulder arthroscopy allows for a detailed visualization and a dynamic examination of all anatomic structures, identification of pathologic findings, and treatment of all concomitant lesions. Conclusion: Surgeons must be well prepared and understanding the normal anatomy of the glenohumeral joint, including its anatomic variants to seek for the possible pathologic lesions in anterior shoulder instability during shoulder arthroscopy. Patient selection criteria, improved surgical techniques, and implants available have contributed to the enhancement of clinical and functional outcomes to the point that arthroscopic treatment is considered nowadays the standard of care. PMID:28400880

DNA damage in cells exhibiting radiation-induced genomic instability

DOE PAGES

Keszenman, Deborah J.; Kolodiuk, Lucia; Baulch, Janet E.

2015-02-22

Cells exhibiting radiation induced genomic instability exhibit varied spectra of genetic and chromosomal aberrations. Even so, oxidative stress remains a common theme in the initiation and/or perpetuation of this phenomenon. Isolated oxidatively modified bases, abasic sites, DNA single strand breaks and clustered DNA damage are induced in normal mammalian cultured cells and tissues due to endogenous reactive oxygen species generated during normal cellular metabolism in an aerobic environment. While sparse DNA damage may be easily repaired, clustered DNA damage may lead to persistent cytotoxic or mutagenic events that can lead to genomic instability. In this study, we tested the hypothesismore » that DNA damage signatures characterised by altered levels of endogenous, potentially mutagenic, types of DNA damage and chromosomal breakage are related to radiation-induced genomic instability and persistent oxidative stress phenotypes observed in the chromosomally unstable progeny of irradiated cells. The measurement of oxypurine, oxypyrimidine and abasic site endogenous DNA damage showed differences in non-double-strand breaks (DSB) clusters among the three of the four unstable clones evaluated as compared to genomically stable clones and the parental cell line. These three unstable clones also had increased levels of DSB clusters. The results of this study demonstrate that each unstable cell line has a unique spectrum of persistent damage and lead us to speculate that alterations in DNA damage signaling and repair may be related to the perpetuation of genomic instability.« less

The charged black-hole bomb: A lower bound on the charge-to-mass ratio of the explosive scalar field

NASA Astrophysics Data System (ADS)

Hod, Shahar

2016-04-01

The well-known superradiant amplification mechanism allows a charged scalar field of proper mass μ and electric charge q to extract the Coulomb energy of a charged Reissner-Nordström black hole. The rate of energy extraction can grow exponentially in time if the system is placed inside a reflecting cavity which prevents the charged scalar field from escaping to infinity. This composed black-hole-charged-scalar-field-mirror system is known as the charged black-hole bomb. Previous numerical studies of this composed physical system have shown that, in the linearized regime, the inequality q / μ > 1 provides a necessary condition for the development of the superradiant instability. In the present paper we use analytical techniques to study the instability properties of the charged black-hole bomb in the regime of linearized scalar fields. In particular, we prove that the lower bound q/μ>√{rm /r- - 1/ rm /r+ - 1 } provides a necessary condition for the development of the superradiant instability in this composed physical system (here r± are the horizon radii of the charged Reissner-Nordström black hole and rm is the radius of the confining mirror). This analytically derived lower bound on the superradiant instability regime of the composed black-hole-charged-scalar-field-mirror system is shown to agree with direct numerical computations of the instability spectrum.

The effect of compliant walls on three-dimensional primary and secondary instabilities in boundary layer transition

NASA Astrophysics Data System (ADS)

Joslin, R. D.

1991-04-01

The use of passive devices to obtain drag and noise reduction or transition delays in boundary layers is highly desirable. One such device that shows promise for hydrodynamic applications is the compliant coating. The present study extends the mechanical model to allow for three-dimensional waves. This study also looks at the effect of compliant walls on three-dimensional secondary instabilities. For the primary and secondary instability analysis, spectral and shooting approximations are used to obtain solutions of the governing equations and boundary conditions. The spectral approximation consists of local and global methods of solution while the shooting approach is local. The global method is used to determine the discrete spectrum of eigenvalue without any initial guess. The local method requires a sufficiently accurate initial guess to converge to the eigenvalue. Eigenvectors may be obtained with either local approach. For the initial stage of this analysis, two and three dimensional primary instabilities propagate over compliant coatings. Results over the compliant walls are compared with the rigid wall case. Three-dimensional instabilities are found to dominate transition over the compliant walls considered. However, transition delays are still obtained and compared with transition delay predictions for rigid walls. The angles of wave propagation are plotted with Reynolds number and frequency. Low frequency waves are found to be highly three-dimensional.

Microwave assisted reconstruction of optical interferograms for distributed fiber optic sensing.

PubMed

Huang, Jie; Hua, Lei; Lan, Xinwei; Wei, Tao; Xiao, Hai

2013-07-29

This paper reports a distributed fiber optic sensing technique through microwave assisted separation and reconstruction of optical interferograms in spectrum domain. The approach involves sending a microwave-modulated optical signal through cascaded fiber optic interferometers. The microwave signal was used to resolve the position and reflectivity of each sensor along the optical fiber. By sweeping the optical wavelength and detecting the modulation signal, the optical spectrum of each sensor can be reconstructed. Three cascaded fiber optic extrinsic Fabry-Perot interferometric sensors were used to prove the concept. Their microwave-reconstructed interferogram matched well with those recorded individually using an optical spectrum analyzer. The application in distributed strain measurement has also been demonstrated.

Transient many-body instability in driven Dirac materials

NASA Astrophysics Data System (ADS)

Pertsova, Anna; Triola, Christopher; Balatsky, Alexander

The defining feature of a Dirac material (DM) is the presence of nodes in the low-energy excitation spectrum leading to a strong energy dependence of the density of states (DOS). The vanishing of the DOS at the nodal point implies a very low effective coupling constant which leads to stability of the node against electron-electron interactions. Non-equilibrium or driven DM, in which the DOS and hence the effective coupling can be controlled by external drive, offer a new platform for investigating collective instabilities. In this work, we discuss the possibility of realizing transient collective states in driven DMs. Motivated by recent pump-probe experiments which demonstrate the existence of long-lived photo-excited states in DMs, we consider an example of a transient excitonic instability in an optically-pumped DM. We identify experimental signatures of the transient excitonic condensate and provide estimates of the critical temperatures and lifetimes of these states for few important examples of DMs, such as single-layer graphene and topological-insulator surfaces.

Colliding winds from early-type stars in binary systems

NASA Technical Reports Server (NTRS)

Stevens, Ian R.; Blondin, John M.; Pollock, A. M. T.

1992-01-01

The dynamics of the wind and shock structure formed by the wind collision in early-type binary systems is examined by means of a 2D hydrodynamics code, which self-consistently accounts for radiative cooling, and represents a significant improvement over previous attempts to model these systems. The X-ray luminosity and spectra of the shock-heated region, accounting for wind attenuation and the influence of different abundances on the resultant level and spectra of X-ray emission are calculated. A variety of dynamical instabilities that are found to dominate the intershock region is examined. These instabilities are found to be particularly important when postshock material is able to cool. These instabilities disrupt the postshock flow and add a time variability of order 10 percent to the X-ray luminosity. The X-ray spectrum of these systems is found to vary with the nuclear abundances of winds. These theoretical models are used to study several massive binary systems, in particular V444 Cyg and HD 193793.

Temporal processing of speech in a time-feature space

NASA Astrophysics Data System (ADS)

Avendano, Carlos

1997-09-01

The performance of speech communication systems often degrades under realistic environmental conditions. Adverse environmental factors include additive noise sources, room reverberation, and transmission channel distortions. This work studies the processing of speech in the temporal-feature or modulation spectrum domain, aiming for alleviation of the effects of such disturbances. Speech reflects the geometry of the vocal organs, and the linguistically dominant component is in the shape of the vocal tract. At any given point in time, the shape of the vocal tract is reflected in the short-time spectral envelope of the speech signal. The rate of change of the vocal tract shape appears to be important for the identification of linguistic components. This rate of change, or the rate of change of the short-time spectral envelope can be described by the modulation spectrum, i.e. the spectrum of the time trajectories described by the short-time spectral envelope. For a wide range of frequency bands, the modulation spectrum of speech exhibits a maximum at about 4 Hz, the average syllabic rate. Disturbances often have modulation frequency components outside the speech range, and could in principle be attenuated without significantly affecting the range with relevant linguistic information. Early efforts for exploiting the modulation spectrum domain (temporal processing), such as the dynamic cepstrum or the RASTA processing, used ad hoc designed processing and appear to be suboptimal. As a major contribution, in this dissertation we aim for a systematic data-driven design of temporal processing. First we analytically derive and discuss some properties and merits of temporal processing for speech signals. We attempt to formalize the concept and provide a theoretical background which has been lacking in the field. In the experimental part we apply temporal processing to a number of problems including adaptive noise reduction in cellular telephone environments, reduction of reverberation for speech enhancement, and improvements on automatic recognition of speech degraded by linear distortions and reverberation.

Nonlinear excitation of long-wavelength modes in Hall plasmas

NASA Astrophysics Data System (ADS)

Lakhin, V. P.; Ilgisonis, V. I.; Smolyakov, A. I.; Sorokina, E. A.

2016-10-01

Hall plasmas with magnetized electrons and unmagnetized ions exhibit a wide range of small scale fluctuations in the lower-hybrid frequency range as well as low-frequency large scale modes. Modulational instability of lower-hybrid frequency modes is investigated in this work for typical conditions in Hall plasma devices such as magnetrons and Hall thrusters. In these conditions, the dispersion of the waves in the lower-hybrid frequency range propagating perpendicular to the external magnetic field is due to the gradients of the magnetic field and the plasma density. It is shown that such lower-hybrid modes are unstable with respect to the secondary instability of the large scale quasimode perturbations. It is suggested that the large scale slow coherent modes observed in a number of Hall plasma devices may be explained as a result of such secondary instabilities.

Periodic equivalence ratio modulation method and apparatus for controlling combustion instability

DOEpatents

Richards, George A.; Janus, Michael C.; Griffith, Richard A.

2000-01-01

The periodic equivalence ratio modulation (PERM) method and apparatus significantly reduces and/or eliminates unstable conditions within a combustion chamber. The method involves modulating the equivalence ratio for the combustion device, such that the combustion device periodically operates outside of an identified unstable oscillation region. The equivalence ratio is modulated between preselected reference points, according to the shape of the oscillation region and operating parameters of the system. Preferably, the equivalence ratio is modulated from a first stable condition to a second stable condition, and, alternatively, the equivalence ratio is modulated from a stable condition to an unstable condition. The method is further applicable to multi-nozzle combustor designs, whereby individual nozzles are alternately modulated from stable to unstable conditions. Periodic equivalence ratio modulation (PERM) is accomplished by active control involving periodic, low frequency fuel modulation, whereby low frequency fuel pulses are injected into the main fuel delivery. Importantly, the fuel pulses are injected at a rate so as not to affect the desired time-average equivalence ratio for the combustion device.

Hybrid spread spectrum radio system

DOEpatents

Smith, Stephen F.; Dress, William B.

2010-02-02

Systems and methods are described for hybrid spread spectrum radio systems. A method includes modulating a signal by utilizing a subset of bits from a pseudo-random code generator to control an amplification circuit that provides a gain to the signal. Another method includes: modulating a signal by utilizing a subset of bits from a pseudo-random code generator to control a fast hopping frequency synthesizer; and fast frequency hopping the signal with the fast hopping frequency synthesizer, wherein multiple frequency hops occur within a single data-bit time.

On the application of neural networks to the classification of phase modulated waveforms

NASA Astrophysics Data System (ADS)

Buchenroth, Anthony; Yim, Joong Gon; Nowak, Michael; Chakravarthy, Vasu

2017-04-01

Accurate classification of phase modulated radar waveforms is a well-known problem in spectrum sensing. Identification of such waveforms aids situational awareness enabling radar and communications spectrum sharing. While various feature extraction and engineering approaches have sought to address this problem, the use of a machine learning algorithm that best utilizes these features is becomes foremost. In this effort, a comparison of a standard shallow and a deep learning approach are explored. Experiments provide insights into classifier architecture, training procedure, and performance.

Marine asset security and tracking (MAST) system

DOEpatents

Hanson, Gregory Richard [Clinton, TN; Smith, Stephen Fulton [Loudon, TN; Moore, Michael Roy [Corryton, TN; Dobson, Eric Lesley [Charleston, SC; Blair, Jeffrey Scott [Charleston, SC; Duncan, Christopher Allen [Marietta, GA; Lenarduzzi, Roberto [Knoxville, TN

2008-07-01

Methods and apparatus are described for marine asset security and tracking (MAST). A method includes transmitting identification data, location data and environmental state sensor data from a radio frequency tag. An apparatus includes a radio frequency tag that transmits identification data, location data and environmental state sensor data. Another method includes transmitting identification data and location data from a radio frequency tag using hybrid spread-spectrum modulation. Another apparatus includes a radio frequency tag that transmits both identification data and location data using hybrid spread-spectrum modulation.

A Validation Study of the Compressible Rayleigh–Taylor Instability Comparing the Ares and Miranda Codes

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

Rehagen, Thomas J.; Greenough, Jeffrey A.; Olson, Britton J.

In this paper, the compressible Rayleigh–Taylor (RT) instability is studied by performing a suite of large eddy simulations (LES) using the Miranda and Ares codes. A grid convergence study is carried out for each of these computational methods, and the convergence properties of integral mixing diagnostics and late-time spectra are established. A comparison between the methods is made using the data from the highest resolution simulations in order to validate the Ares hydro scheme. We find that the integral mixing measures, which capture the global properties of the RT instability, show good agreement between the two codes at this resolution.more » The late-time turbulent kinetic energy and mass fraction spectra roughly follow a Kolmogorov spectrum, and drop off as k approaches the Nyquist wave number of each simulation. The spectra from the highest resolution Miranda simulation follow a Kolmogorov spectrum for longer than the corresponding spectra from the Ares simulation, and have a more abrupt drop off at high wave numbers. The growth rate is determined to be between around 0.03 and 0.05 at late times; however, it has not fully converged by the end of the simulation. Finally, we study the transition from direct numerical simulation (DNS) to LES. The highest resolution simulations become LES at around t/τ ≃ 1.5. Finally, to have a fully resolved DNS through the end of our simulations, the grid spacing must be 3.6 (3.1) times finer than our highest resolution mesh when using Miranda (Ares).« less

A Validation Study of the Compressible Rayleigh–Taylor Instability Comparing the Ares and Miranda Codes

DOE PAGES

Rehagen, Thomas J.; Greenough, Jeffrey A.; Olson, Britton J.

2017-04-20

In this paper, the compressible Rayleigh–Taylor (RT) instability is studied by performing a suite of large eddy simulations (LES) using the Miranda and Ares codes. A grid convergence study is carried out for each of these computational methods, and the convergence properties of integral mixing diagnostics and late-time spectra are established. A comparison between the methods is made using the data from the highest resolution simulations in order to validate the Ares hydro scheme. We find that the integral mixing measures, which capture the global properties of the RT instability, show good agreement between the two codes at this resolution.more » The late-time turbulent kinetic energy and mass fraction spectra roughly follow a Kolmogorov spectrum, and drop off as k approaches the Nyquist wave number of each simulation. The spectra from the highest resolution Miranda simulation follow a Kolmogorov spectrum for longer than the corresponding spectra from the Ares simulation, and have a more abrupt drop off at high wave numbers. The growth rate is determined to be between around 0.03 and 0.05 at late times; however, it has not fully converged by the end of the simulation. Finally, we study the transition from direct numerical simulation (DNS) to LES. The highest resolution simulations become LES at around t/τ ≃ 1.5. Finally, to have a fully resolved DNS through the end of our simulations, the grid spacing must be 3.6 (3.1) times finer than our highest resolution mesh when using Miranda (Ares).« less

Ion flux oscillations and ULF waves observed by ARASE satellite and their origin

NASA Astrophysics Data System (ADS)

Yamamoto, K.; Masahito, N.; Kasahara, S.; Yokota, S.; Keika, K.; Matsuoka, A.; Teramoto, M.; Nomura, R.; Fujimoto, A.; Tanaka, Y.; Shinohara, M.; Shinohara, I.; Yoshizumi, M.

2017-12-01

The ARASE satellite, which was launched on December 20, 2016, is now observing thenightside inner magnetosphere. The inclination of the orbit is larger than those of otherrecent spacecraft flying in the inner magnetosphere such as THMEIS and Van Allen Probes.This unique orbit provides us new information on ULF waves since ULF waves havelatitudinal structure and the antinode of magnetic fluctuations of fundamental mode is athigh magnetic latitudes.Although Pc pulsations are predominantly observed on the dayside, ARASE satellitesometimes observes Pc4-5 pulsations on the nightside. Some of these waves are accompaniedwith energetic particle flux modulations. We found 6 events of the particle flux modulationsaccompanying Pc pulsations on the dawnside and nightside. Theoretical studies suggest thatULF waves detected at afternoon are generated by plasma instabilities like drift-mirror instability [Hasegawa, 1969] and drift-bounce resonance [Southwood et al, 1969].These instabilities cause plasma pressure disturbances or flux modulation of ions. Nonresonant ion clouds injected on the duskside are also considered to be one of the candidates ofULF wave driver [Zolotukhina, 1974]. We therefore discuss whether the ULF waves observedby ARASE satellite are generated internally or externally, and the flux modulations arecreated by plasma instabilities or the other non-resonant effects.On March 31, 2017, Medium-Energy Particle Experiments - Ion Mass Analyzer (MEPi)onboard ARASE detected ion flux oscillations at 12-70 keV with a period of 120 seconds inthe normal (NML) mode observation. NML mode observation provides details of the directionof particle movements. The pitch angle distribution of proton flux showed isotropic fluxoscillations. At the same time, Pc4 pulsations with the same oscillation period were observed.These flux and field perturbations were seen on the dawnside (4.3-5.9 MLT).ARASE found oscillations of ion count with a period of 130 seconds in the time-of-flight(TOF) mode observation at midnight on May 29, 2017. Therefore, we used the list data, that is createdfor onboard calibrations, to make a pitch angle distribution of ion counts. The pitch angledistribution did not have clear fluctuations, so that the oscillations may beattributed to angyrotropic particle distributions.

Summer Study Program in Geophysical Fluid Dynamics, The Woods Hole Oceanographic Institution. Baroclinic Instability and Ocean Fronts.

DTIC Science & Technology

1983-11-01

spectrum of the linear stability theory has multiple roots with zero real parts. Then the general forms of the amplitude equations may be found for given...76 Dynamical Generation of Eastern Boundary Currents George eronis. .......................... 77 ..Amplitude Equations Edward...Associated Countercurrent. Benoit Cushman-Roisin ....... .................... ... 103 Turbulently Generated Eastern Boundary Currents Roger L. Hughes

Enhanced thermomechanical stability on laser-induced damage by functionally graded layers in quasi-rugate filters

NASA Astrophysics Data System (ADS)

Pu, Yunti; Ma, Ping; Lv, Liang; Zhang, Mingxiao; Lu, Zhongwen; Qiao, Zhao; Qiu, Fuming

2018-05-01

Ta2O5-SiO2 quasi-rugate filters with a reasonable optimization of rugate notch filter design were prepared by ion-beam sputtering. The optical properties and laser-induced damage threshold are studied. Compared with the spectrum of HL-stacks, the spectrum of quasi-rugate filters have weaker second harmonic peaks and narrower stopbands. According to the effect of functionally graded layers (FGLs), 1-on-1 and S-on-1 Laser induced damage threshold (LIDT) of quasi-rugate filters are about 22% and 50% higher than those of HL stacks, respectively. Through the analysis of the damage morphologies, laser-induced damage of films under nanosecond multi-pulse are dominated by a combination of thermal shock stress and thermomechanical instability due to nodules. Compared with catastrophic damages, the damage sits of quasi-rugate filters are developed in a moderate way. The damage growth behavior of defect-induced damage sites have been effectively restrained by the structure of FGLs. Generally, FGLs are used to reduce thermal stress by the similar thermal-expansion coefficients of neighboring layers and solve the problems such as instability and cracking raised by the interface discontinuity of nodular boundaries, respectively.

Effect of gain contouring in erbium-doped fiber amplifiers on bit error rate performance of wavelength-division multiplexing-based radio over fiber links

NASA Astrophysics Data System (ADS)

Jose, Tony; Narayanan, Vijayakumar

2018-03-01

Radio over fiber (RoF) systems use a large number of base stations (BSs) and a number of central stations (CSs), which are interlinked together to form the network. RoF systems use multiple wavelengths for communication between CSs or between CSs and BSs to facilitate the huge amount of data traffic due to the multiple services for a large number of users. When erbium-doped fiber amplifiers (EDFAs) are used as amplifiers in such wavelength-division multiplexed systems, the nonuniform gain spectrum of EDFAs causes instability to some of the channels while providing faithful amplification to other channels. To avoid this inconsistency, the gain spectrum of the amplifier needs to be uniform along the whole usable range of wavelengths. A gain contouring technique is proposed to provide uniform gain to all channels irrespective of wavelength. Optical add/drop multiplexers (OADMs) and different lengths of erbium-doped fibers are used to create such a gain contouring mechanism in the optical domain itself. The effect of a cascade of nonuniform gain amplifiers is studied, and the proposed system mitigates the adverse effects caused due to nonuniform gain-induced channel instability effectively.

Three-dimensional hybrid modeling of ion kinetic instabilities in space plasma

NASA Astrophysics Data System (ADS)

Ofman, L.

2017-12-01

Ion kinetic instabilities in space plasma are believed to play an imprortant role in energy transport, heating, dissipation of turbulence, as well as in generating of spectrum of magnetic fluctuations in the kinetic frequency range. The velocity distribution functions (VDFs) of unstable ion populations are generally non-Maxwellian and provide the free energy source that drives the waves. The VDFs were measured in-situ by satellites such as Helios, WIND, and would be obtained in the future Parkers' Solar Probe close to the Sun. In particular, temperature anisotropy provides a measure of VDF non-equilibroum structure, that together with parallel-beta determine the threshold of kinetic instabilities, such as mirror, ion-cyclotron, and firehose. Drifting population of alphas with respect to protons lead to the magnetosonic instability. So far, these isntabilities were studied primaraly using 1.5D or 2.5D particle-in-cell (PIC) or hybrid models (where electrons are modeled as a fluid), i.e., in 1 or 2 spatial dimensions with 3 components of velocity and magnetic field. I will present the results of recent full 3D hybrid models that studies these instabilities for heliospheric conditions and compare to previous modeling results. I will discuss the agreement and the differences between the 3D and more approximate models of the VDFs, the magnetic fluctuations spectra, and the temporal evolution of the anisotropy for typical instabilities relevant for space plasma. I will duscuss the use of the modeled VDFs for diagnostic of the physical processes that lead to space plasma energization from the observed VDFs in the heliospheric and magnetospheric plasma.

Causes of Combustion Instabilities with Passive and Active Methods of Control for practical application to Gas Turbine Engines

NASA Astrophysics Data System (ADS)

Cornwell, Michael D.

Combustion at high pressure in applications such as rocket engines and gas turbine engines commonly experience destructive combustion instabilities. These instabilities results from interactions between combustion heat release, fluid mechanics and acoustics. This research explores the significant affect of unstable fluid mechanics processes in augmenting unstable periodic combustion heat release. The frequency of the unstable heat release may shift to match one of the combustors natural acoustic frequencies which then can result in significant energy exchange from chemical to acoustic energy resulting in thermoacoustic instability. The mechanisms of the fluid mechanics in coupling combustion to acoustics are very broad with many varying mechanisms explained in detail in the first chapter. Significant effort is made in understanding these mechanisms in this research in order to find commonalities, useful for mitigating multiple instability mechanisms. The complexity of combustion instabilities makes mitigation of combustion instabilities very difficult as few mitigation methods have historically proven to be very effective for broad ranges of combustion instabilities. This research identifies turbulence intensity near the forward stagnation point and movement of the forward stagnation point as a common link in what would otherwise appear to be very different instabilities. The most common method of stabilization of both premixed and diffusion flame combustion is through the introduction of swirl. Reverse flow along the centerline is introduced to transport heat and chemically active combustion products back upstream to sustain combustion. This research develops methods to suppress the movement of the forward stagnation point without suppressing the development of the vortex breakdown process which is critical to the transport of heat and reactive species necessary for flame stabilization. These methods are useful in suppressing the local turbulence at the forward stagnation point, limiting dissipation of heat and reactive species significantly improving stability. Combustion hardware is developed and tested to demonstrate the stability principles developed as part of this research. In order to more completely understand combustion instability a very unique method of combustion was researched where there are no discrete points of combustion initiation such as the forward stagnation point typical in many combustion systems including swirl and jet wake stabilized combustion. This class of combustion which has empirical evidence of great stability and efficient combustion with low CO, NOx and UHC emissions is described as high oxidization temperature distributed combustion. This mechanism of combustion is shown to be stable largely because there are no stagnations points susceptible to fluid mechanic perturbations. The final topic of research is active combustion control by fuel modulation. This may be the only practical method of controlling most instabilities with a single technique. As there are many papers reporting active combustion control algorithms this research focused on the complexities of the physics of fuel modulation at frequencies up to 1000 Hz with proportionally controlled flow amplitude. This research into the physics of high speed fluid movement, oscillation mechanical mechanisms and electromagnetics are demonstrated by development and testing of a High Speed Latching Oscillator Valve.

The Marshall Space Flight Center Development of Mirror Modules for the ART-XC Ins1rument Aboard the Spectrum-Roentgen-Gamma Mission

NASA Technical Reports Server (NTRS)

Gubarev, M.; Ramsey, B.; ODell, S. L.; Elsner, R.; Kilaru, K.; McCracken, J.; Pavlinsky, M.; Tkachenko, A.; Lapshov, I.

2012-01-01

The Spectrum-Rontgen-Gamma (SRG) mission is a Russian-German X-ray astrophysical observatory that carries two co-aligned and complementary X-ray telescope systems. The primary instrument is the German-led extended ROentgen Survey with an Imaging Telescope Array (eROSITA), a 7-module X-ray telescope system that covers the energy range from 0.2-12 keV. The complementary instrument is the Russian-led Astronomical Roentgen Telescope -- X-ray Concentrator (ART-XC or ART), a 7-module X-ray telescope system that provides higher energy coverage, up to 30 keV (with limited sensitivity above 12 keV).

On the instability of hypersonic flow past a wedge

NASA Technical Reports Server (NTRS)

Cowley, Stephen; Hall, Philip

1988-01-01

The instability of a compressible flow past a wedge is investigated in the hypersonic limit. Particular attention is given to the Tollmien-Schlichting waves governed by triple-deck theory though some discussion of inviscid modes is given. It is shown that the attached shock has a significant effect on the growth rates of Tollmien-Schlichting waves. Moreover, the presence of the shock allows for more than one unstable Tollmien-Schlichting wave. Indeed, an infinite discrete spectrum of unstable waves is induced by the shock, but these modes are unstable over relatively small but high frequency ranges. The shock is shown to have little effect on the inviscid modes considered by previous authors and an asymptotic description of inviscid modes in the hypersonic limit is given.

Fingering and fracturing during multiphase flow in porous media (Invited)

NASA Astrophysics Data System (ADS)

Juanes, R.

2013-12-01

The displacement of one fluid by another in a porous medium give rise to a rich variety of hydrodynamic instabilities. Beyond their scientific value as fascinating models of pattern formation, unstable porous-media flows are essential to understanding many natural and man-made processes, including water infiltration in the vadose zone, carbon dioxide injection and storage in deep saline aquifers, and hydrocarbon recovery. Here, we review the pattern-selection mechanisms of a wide spectrum of porous-media flows that develop hydrodynamic instabilities, discuss their origin and the mathematical models that have been used to describe them. We point out many challenges that remain to be resolved in the context of multiphase flows, and suggest modeling approaches that may offer new quantitative understanding.

Transmit-reference methods in software defined radio platforms for communication in harsh propagation environments and systems thereof

DOEpatents

Dowla, Farid U; Nekoogar, Faranak

2015-03-03

A method for adaptive Radio Frequency (RF) jamming according to one embodiment includes dynamically monitoring a RF spectrum; detecting any undesired signals in real time from the RF spectrum; and sending a directional countermeasure signal to jam the undesired signals. A method for adaptive Radio Frequency (RF) communications according to another embodiment includes transmitting a data pulse in a RF spectrum; and transmitting a reference pulse separated by a predetermined period of time from the data pulse; wherein the data pulse is modulated with data, wherein the reference pulse is unmodulated. A method for adaptive Radio Frequency (RF) communications according to yet another embodiment includes receiving a data pulse in a RF spectrum; and receiving a reference pulse separated in time from the data pulse, wherein the data pulse is modulated with data, wherein the reference pulse is unmodulated; and demodulating the pulses.

Transmit-reference methods in software defined radio platforms for communication in harsh propagation environments and systems thereof

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

Dowla, Farid; Nekoogar, Faranak

A method for adaptive Radio Frequency (RF) jamming according to one embodiment includes dynamically monitoring a RF spectrum; detecting any undesired signals in real time from the RF spectrum; and sending a directional countermeasure signal to jam the undesired signals. A method for adaptive Radio Frequency (RF) communications according to another embodiment includes transmitting a data pulse in a RF spectrum; and transmitting a reference pulse separated by a predetermined period of time from the data pulse; wherein the data pulse is modulated with data, wherein the reference pulse is unmodulated. A method for adaptive Radio Frequency (RF) communications accordingmore » to yet another embodiment includes receiving a data pulse in a RF spectrum; and receiving a reference pulse separated in time from the data pulse, wherein the data pulse is modulated with data, wherein the reference pulse is unmodulated; and demodulating the pulses.« less

Transmission of 2.5 Gbit/s Spectrum-sliced WDM System for 50 km Single-mode Fiber

NASA Astrophysics Data System (ADS)

Ahmed, Nasim; Aljunid, Sayed Alwee; Ahmad, R. Badlisha; Fadil, Hilal Adnan; Rashid, Mohd Abdur

2011-06-01

The transmission of a spectrum-sliced WDM channel at 2.5 Gbit/s for 50 km of single mode fiber using an system channel spacing only 0.4 nm is reported. We have investigated the system performance using NRZ modulation format. The proposed system is compared with conventional system. The system performance is characterized as the bit-error-rate (BER) received against the system bit rates. Simulation results show that the NRZ modulation format performs well for 2.5 Gbit/s system bit rates. Using this narrow channel spectrum-sliced technique, the total number of multiplexed channels can be increased greatly in WDM system. Therefore, 0.4 nm channel spacing spectrum-sliced WDM system is highly recommended for the long distance optical access networks, like the Metro Area Network (MAN), Fiber-to-the-Building (FTTB) and Fiber-to-the-Home (FTTH).

p21/Cyclin E pathway modulates anticlastogenic function of Bmi-1 in cancer cells

PubMed Central

Deng, Wen; Zhou, Yuan; Tiwari, Agnes FY; Su, Hang; Yang, Jie; Zhu, Dandan; Lau, Victoria Ming Yi; Hau, Pok Man; Yip, Yim Ling; Cheung, Annie LM; Guan, Xin-Yuan; Tsao, Sai Wah

2015-01-01

Apart from regulating stem cell self-renewal, embryonic development and proliferation, Bmi-1 has been recently reported to be critical in the maintenance of genome integrity. In searching for novel mechanisms underlying the anticlastogenic function of Bmi-1, we observed, for the first time, that Bmi-1 positively regulates p21 expression. We extended the finding that Bmi-1 deficiency induced chromosome breaks in multiple cancer cell models. Interestingly, we further demonstrated that knockdown of cyclin E or ectopic overexpression of p21 rescued Bmi-1 deficiency-induced chromosome breaks. We therefore conclude that p21/cyclin E pathway is crucial in modulating the anticlastogenic function of Bmi-1. As it is well established that the overexpression of cyclin E potently induces genome instability and p21 suppresses the function of cyclin E, the novel and important implication from our findings is that Bmi-1 plays an important role in limiting genomic instability in cylin E-overexpressing cancer cells by positive regulation of p21. PMID:25131797

Superregular breathers, characteristics of nonlinear stage of modulation instability induced by higher-order effects

PubMed Central

Zhang, Jian-Hui; Liu, Chong

2017-01-01

We study the higher-order generalized nonlinear Schrödinger (NLS) equation describing the propagation of ultrashort optical pulse in optical fibres. By using Darboux transformation, we derive the superregular breather solution that develops from a small localized perturbation. This type of solution can be used to characterize the nonlinear stage of the modulation instability (MI) of the condensate. In particular, we show some novel characteristics of the nonlinear stage of MI arising from higher-order effects: (i) coexistence of a quasi-Akhmediev breather and a multipeak soliton; (ii) two multipeak solitons propagation in opposite directions; (iii) a beating pattern followed by two multipeak solitons in the same direction. It is found that these patterns generated from a small localized perturbation do not have the analogues in the standard NLS equation. Our results enrich Zakharov’s theory of superregular breathers and could provide helpful insight on the nonlinear stage of MI in presence of the higher-order effects. PMID:28413335

Vector semirational rogue waves and modulation instability for the coupled higher-order nonlinear Schrödinger equations in the birefringent optical fibers.

PubMed

Sun, Wen-Rong; Liu, De-Yin; Xie, Xi-Yang

2017-04-01

We report the existence and properties of vector breather and semirational rogue-wave solutions for the coupled higher-order nonlinear Schrödinger equations, which describe the propagation of ultrashort optical pulses in birefringent optical fibers. Analytic vector breather and semirational rogue-wave solutions are obtained with Darboux dressing transformation. We observe that the superposition of the dark and bright contributions in each of the two wave components can give rise to complicated breather and semirational rogue-wave dynamics. We show that the bright-dark type vector solitons (or breather-like vector solitons) with nonconstant speed interplay with Akhmediev breathers, Kuznetsov-Ma solitons, and rogue waves. By adjusting parameters, we note that the rogue wave and bright-dark soliton merge, generating the boomeron-type bright-dark solitons. We prove that the rogue wave can be excited in the baseband modulation instability regime. These results may provide evidence of the collision between the mixed ultrashort soliton and rogue wave.

Modulational instability, beak-shaped rogue waves, multi-dark-dark solitons and dynamics in pair-transition-coupled nonlinear Schrödinger equations.

PubMed

Zhang, Guoqiang; Yan, Zhenya; Wen, Xiao-Yong

2017-07-01

The integrable coupled nonlinear Schrödinger equations with four-wave mixing are investigated. We first explore the conditions for modulational instability of continuous waves of this system. Secondly, based on the generalized N -fold Darboux transformation (DT), beak-shaped higher-order rogue waves (RWs) and beak-shaped higher-order rogue wave pairs are derived for the coupled model with attractive interaction in terms of simple determinants. Moreover, we derive the simple multi-dark-dark and kink-shaped multi-dark-dark solitons for the coupled model with repulsive interaction through the generalizing DT. We explore their dynamics and classifications by different kinds of spatial-temporal distribution structures including triangular, pentagonal, 'claw-like' and heptagonal patterns. Finally, we perform the numerical simulations to predict that some dark solitons and RWs are stable enough to develop within a short time. The results would enrich our understanding on nonlinear excitations in many coupled nonlinear wave systems with transition coupling effects.

The modulational instability in the extended Hasegawa-Mima equation with a finite Larmor radius

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

Gallagher, S.; Hnat, B.; Rowlands, G.

2012-12-15

The effects of the finite Larmor radius on the generation of zonal flows by the four-wave modulational instability are investigated using an extended form of the Hasegawa-Mima equation. Growth rates of the zonal mode are quantified using analytical predictions from a four-mode truncated model, as well as from direct numerical simulation of the nonlinear extended Hasegawa-Mima equation. We not only consider purely zonal flows but also examine the generic oblique case and show that, for small Larmor radii, off-axis modes may become dominant. We find a key parameter M{sub {rho}} which characterises the behaviour of the system due to changesmore » in the Larmor radius. We find that, similarly to previous results obtained by changing the driving wave amplitude, two separate dynamical regimes can be accessed. These correspond to oscillatory energy transfer between zonal flows and a driving wave and the fully saturated zonal flow.« less

Laser plasma coupling with moderate Z, long scalelength underdense plasma

NASA Astrophysics Data System (ADS)

Kruer, William; Berger, Richard; Meezan, Nathaniel; Suter, Larry; Moody, John; Glenzer, Siegfried; Stevenson, R. M.; Oades, K.

2004-11-01

Recent experiments1,2 have focussed new attention on the coupling of laser light with moderate Z, long scalelength underdense plasmas. We discuss some intriguing features of these experiments, including a significant reduction of stimulated Raman and Brillouin scattering in higher Z plasmas, such as Krypton and Xenon. Threshold conditions for various instabilities are discussed, and potential consequences of thermal filamentation and self-focussing are explored. The presence of significant temperature modulations in the plasma can lead to a number of interesting effects not usually taken into account, such as ion wave refraction out of hot spots and instability reduction by the long wavelength modulations. We also consider the extrapolation of these results to the higher temperature regimes more relevant to ignition-scale hohlraums. 1. R. M. Stevenson, et. al, Phys. Plasmas 11, 2709 (2004) 2. J. Moody (to be published) Work performed under the auspices of the U.S. DOE by the Lawrence Livermore National Laboratory under Contract W-7405-ENG-48.

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

Bardóczi, L.; Rhodes, T. L.; Carter, T. A.

We report the first observation of localized modulation of turbulent density uctuations en (via Beam Emission Spectroscopy) by neoclassical tearing modes (NTMs) in the core of the DIII-D tokamak. NTMs are important as they often lead to severe degradation of plasma confinement and disruptions in high-confinement fusion experiments. Magnetic islands associated with NTMs significantly modify the profiles and turbulence drives. In this experiment n was found to be modulated by 14% across the island. Gyrokinetic simulations suggest that en could be dominantly driven by the ion temperature gradient (ITG) instability.

Extraordinary SEAWs under influence of the spin-spin interaction and the quantum Bohm potential

NASA Astrophysics Data System (ADS)

Andreev, Pavel A.

2018-06-01

The separate spin evolution (SSE) of electrons causes the existence of the spin-electron acoustic wave. Extraordinary spin-electron acoustic waves (SEAWs) propagating perpendicular to the external magnetic field have a large contribution of the transverse electric field. Its spectrum has been studied in the quasi-classical limit at the consideration of the separate spin evolution. The spin-spin interaction and the quantum Bohm potential give contribution in the spectrum extraordinary SEAWs. This contribution is studied in this paper. Moreover, it is demonstrated that the spin-spin interaction leads to the existence of the extraordinary SEAWs if the SSE is neglected. It has been found that the SSE causes the instability of the extraordinary SEAW at the large wavelengths, but the quantum Bohm potential leads to the full stabilization of the spectrum.

Fiber-distributed Ultra-wideband noise radar with steerable power spectrum and colorless base station.

PubMed

Zheng, Jianyu; Wang, Hui; Fu, Jianbin; Wei, Li; Pan, Shilong; Wang, Lixian; Liu, Jianguo; Zhu, Ninghua

2014-03-10

A fiber-distributed Ultra-wideband (UWB) noise radar was achieved, which consists of a chaotic UWB noise source based on optoelectronic oscillator (OEO), a fiber-distributed transmission link, a colorless base station (BS), and a cross-correlation processing module. Due to a polarization modulation based microwave photonic filter and an electrical UWB pass-band filter embedded in the feedback loop of the OEO, the power spectrum of chaotic UWB signal could be shaped and notch-filtered to avoid the spectrum-overlay-induced interference to the narrow band signals. Meanwhile, the wavelength-reusing could be implemented in the BS by means of the distributed polarization modulation-to-intensity modulation conversion. The experimental comparison for range finding was carried out as the chaotic UWB signal was notch-filtered at 5.2 GHz and 7.8 GHz or not. Measured results indicate that space resolution with cm-level could be realized after 3-km fiber transmission thanks to the excellent self-correlation property of the UWB noise signal provided by the OEO. The performance deterioration of the radar raised by the energy loss of the notch-filtered noise signal was negligible.

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

Reynoso, F; Cho, S

Purpose: To develop an external beam surrogate of the Yb-169 brachytherapy source applying a filter-based spectrum modulation technique to 250 kVp x-rays. In-vitro/vivo studies performed with the modulated 250 kVp beam will help gauge the benefits of implementing gold nanoparticle-aided radiotherapy with the Yb-169 source. Methods: A previously validated MCNP5 model of the Phillips RT-250 orthovoltage unit was used to obtain the percentage depth dose (PDD) and filtered photon spectra for a variety of filtration and irradiation conditions. Photon spectra were obtained using the average flux F4 tally in air right after all collimation. A 30 x 30 x 30more » cm{sup 3} water phantom was used to compute the PDD along the central axis (CAX) under the standards conditions of a 10 x 10 cm{sup 2} field size at 50 cm SSD. Cylindrical cells of 4 cm in diameter and the energy deposition F6 tally were used along the CAX to score the doses down to 20 cm depth. The number of particle history was set to 2 x 10{sup 8} in order to keep the relative uncertainty within each cell < 0.3%. The secondary electron spectrum within a gold-loaded tissue due to each photon spectrum was also calculated using EGSnrc and compared with that due to Yb-169 gamma rays. Results: Under the practical constraints for the spectrum modulation task, 250 kVp x-rays filtered by a 0.25 mm Erbium (Er) foil produced the best match with Yb-169 gamma rays, in terms of PDD and, more importantly, secondary electron spectrum. Conclusion: Modulation of 250kVp x-ray spectrum by an Er-filter was found effective in emulating the gamma ray spectrum of Yb-169. Possible benefits as predicted from the current MC model such as enhanced radiosensitization with the Er-filtered beam (as a surrogate of Yb-169) was confirmed with a separate in-vitro study. Supported by DOD/PCRP grant W81XWH-12-1-0198.« less

LSWS linked with the low-latitude Es and its implications for the growth of the R-T instability

NASA Astrophysics Data System (ADS)

Joshi, L. M.

2016-07-01

A comprehensive investigation of spread F irregularities over the Indian sector has been carried out using VHF radar and ionosonde observations. Two different categories of spread F observations, one where the onset of the range spread F (RSF) was concurrent with the peak h'F (category 1) and another where the RSF onset happened ~90 min after the peak h'F time (category 2), are presented. RSF in category 2 was preceded by the presence of oblique echoes in ionograms, indicating the irregularity genesis westward of Sriharikota. The average peak h'F in category 1 was ~30 km higher than that in category 2 indicating the presence of standing large-scale wave structure (LSWS). Occurrence of the blanketing Es during 19:30 to 20:30 Indian Standard Time in category 1 (category 2) was 0% (>50%). Model computation is also carried out to further substantiate the observational results. Model computation indicates that zonal variation of low-latitude Es can generate zonal modulation in the F layer height rise. It is found that the modulation of the F layer height, linked with the low-latitude Es, assists the equatorial spread F onset by modifying both the growth rate of the collisional Rayleigh-Taylor (R-T) instability and also its efficiency. A predominant presence of low-latitude Es has been observed, but the increase in the F layer height and the R-T instability growth in the evening hours will maximize with complete absence of low-latitude Es. A new mechanism for the generation of LSWS and its implications on R-T instability is discussed.

[Spectral analysis of fiber bragg grating modulated by double long period grating and its application in smart structure monitoring].

PubMed

Lu, Ji-Yun; Liang, Da-Kai; Zhang, Xiao-Li; Zhu, Zhu

2009-12-01

Spectrum of fiber bragg grating (FBG) sensor modulated by double long period grating (LPFG) is proposed in the paper. Double LPFG consists of two LPFGS whose center wavelengths are the same and reflection spectrum of FBG sensor is located in linear range of double LPFG transmission spectrum. Based on spectral analysis of FBG and double LPFG, reflection spectrum of FBG modulated by double LPFG is obtained and studied by use of band-hider filter characteristics for double LPFG. An FBG sensor is attached on the surface of thin steel beam, which is strained by bending, and the center wavelength of FBG sensor will shift. The spectral peak of FBG sensor modulated by double LPFG is changed correspondingly, and the spectral change will lead to variation in exit light intensity from double LPFG. Experiment demonstrates that the relation of filtering light intensity from double LPFG monitored by optical power meter to center wavelength change of FBG sensor is linear and the minimum strain of material (steel beam) detected by the modulation and demodulation system is 1.05 microepsilon. This solution is used in impact monitoring of optical fibre smart structure, and FBG sensor is applied for impulse response signal monitoring induced by low-velocity impact, when impact pendulum is loaded to carbon fiber-reinforced plastics (CFP). The acquired impact response signal and fast Fourier transform of the signal detected by FBG sensor agree with the measurement results of eddy current displacement meter attached to the FBG sensor. From the results, the present method using FBG sensor is found to be effective for monitoring the impact. The research provides a practical reference in dynamic monitoring of optical fiber smart structure field.

Kinetic Features in the Ion Flux Spectrum

NASA Astrophysics Data System (ADS)

Vafin, S.; Riazantseva, M.; Yoon, P. H.

2017-11-01

An interesting feature of solar wind fluctuations is the occasional presence of a well-pronounced peak near the spectral knee. These peaks are well investigated in the context of magnetic field fluctuations in the magnetosheath and they are typically related to kinetic plasma instabilities. Recently, similar peaks were observed in the spectrum of ion flux fluctuations of the solar wind and magnetosheath. In this paper, we propose a simple analytical model to describe such peaks in the ion flux spectrum based on the linear theory of plasma fluctuations. We compare our predictions with a sample observation in the solar wind. For the given observation, the peak requires ˜10 minutes to grow up to the observed level that agrees with the quasi-linear relaxation time. Moreover, our model well reproduces the form of the measured peak in the ion flux spectrum. The observed lifetime of the peak is about 50 minutes, which is relatively close to the nonlinear Landau damping time of 30-40 minutes. Overall, our model proposes a plausible scenario explaining the observation.

Fast Interrogation of Fiber Bragg Gratings with Electro-Optical Dual Optical Frequency Combs

PubMed Central

Posada-Roman, Julio E.; Garcia-Souto, Jose A.; Poiana, Dragos A.; Acedo, Pablo

2016-01-01

Optical frequency combs (OFC) generated by electro-optic modulation of continuous-wave lasers provide broadband coherent sources with high power per line and independent control of line spacing and the number of lines. In addition to their application in spectroscopy, they offer flexible and optimized sources for the interrogation of other sensors based on wavelength change or wavelength filtering, such as fiber Bragg grating (FBG) sensors. In this paper, a dual-OFC FBG interrogation system based on a single laser and two optical-phase modulators is presented. This architecture allows for the configuration of multimode optical source parameters such as the number of modes and their position within the reflected spectrum of the FBG. A direct read-out is obtained by mapping the optical spectrum onto the radio-frequency spectrum output of the dual-comb. This interrogation scheme is proposed for measuring fast phenomena such as vibrations and ultrasounds. Results are presented for dual-comb operation under optimized control. The optical modes are mapped onto detectable tones that are multiples of 0.5 MHz around a center radiofrequency tone (40 MHz). Measurements of ultrasounds (40 kHz and 120 kHz) are demonstrated with this sensing system. Ultrasounds induce dynamic strain onto the fiber, which generates changes in the reflected Bragg wavelength and, hence, modulates the amplitude of the OFC modes within the reflected spectrum. The amplitude modulation of two counterphase tones is detected to obtain a differential measurement proportional to the ultrasound signal. PMID:27898043

Fast Interrogation of Fiber Bragg Gratings with Electro-Optical Dual Optical Frequency Combs.

PubMed

Posada-Roman, Julio E; Garcia-Souto, Jose A; Poiana, Dragos A; Acedo, Pablo

2016-11-26

Optical frequency combs (OFC) generated by electro-optic modulation of continuous-wave lasers provide broadband coherent sources with high power per line and independent control of line spacing and the number of lines. In addition to their application in spectroscopy, they offer flexible and optimized sources for the interrogation of other sensors based on wavelength change or wavelength filtering, such as fiber Bragg grating (FBG) sensors. In this paper, a dual-OFC FBG interrogation system based on a single laser and two optical-phase modulators is presented. This architecture allows for the configuration of multimode optical source parameters such as the number of modes and their position within the reflected spectrum of the FBG. A direct read-out is obtained by mapping the optical spectrum onto the radio-frequency spectrum output of the dual-comb. This interrogation scheme is proposed for measuring fast phenomena such as vibrations and ultrasounds. Results are presented for dual-comb operation under optimized control. The optical modes are mapped onto detectable tones that are multiples of 0.5 MHz around a center radiofrequency tone (40 MHz). Measurements of ultrasounds (40 kHz and 120 kHz) are demonstrated with this sensing system. Ultrasounds induce dynamic strain onto the fiber, which generates changes in the reflected Bragg wavelength and, hence, modulates the amplitude of the OFC modes within the reflected spectrum. The amplitude modulation of two counterphase tones is detected to obtain a differential measurement proportional to the ultrasound signal.

Drive-amplitude-modulation atomic force microscopy: From vacuum to liquids

PubMed Central

Jaafar, Miriam; Cuenca, Mariano; Melcher, John; Raman, Arvind

2012-01-01

Summary We introduce drive-amplitude-modulation atomic force microscopy as a dynamic mode with outstanding performance in all environments from vacuum to liquids. As with frequency modulation, the new mode follows a feedback scheme with two nested loops: The first keeps the cantilever oscillation amplitude constant by regulating the driving force, and the second uses the driving force as the feedback variable for topography. Additionally, a phase-locked loop can be used as a parallel feedback allowing separation of the conservative and nonconservative interactions. We describe the basis of this mode and present some examples of its performance in three different environments. Drive-amplutide modulation is a very stable, intuitive and easy to use mode that is free of the feedback instability associated with the noncontact-to-contact transition that occurs in the frequency-modulation mode. PMID:22563531

Model-Based Self-Tuning Multiscale Method for Combustion Control

NASA Technical Reports Server (NTRS)

Le, Dzu, K.; DeLaat, John C.; Chang, Clarence T.; Vrnak, Daniel R.

2006-01-01

A multi-scale representation of the combustor dynamics was used to create a self-tuning, scalable controller to suppress multiple instability modes in a liquid-fueled aero engine-derived combustor operating at engine-like conditions. Its self-tuning features designed to handle the uncertainties in the combustor dynamics and time-delays are essential for control performance and robustness. The controller was implemented to modulate a high-frequency fuel valve with feedback from dynamic pressure sensors. This scalable algorithm suppressed pressure oscillations of different instability modes by as much as 90 percent without the peak-splitting effect. The self-tuning logic guided the adjustment of controller parameters and converged quickly toward phase-lock for optimal suppression of the instabilities. The forced-response characteristics of the control model compare well with those of the test rig on both the frequency-domain and the time-domain.

Understanding force-generating microtubule systems through in vitro reconstitution

PubMed Central

Kok, Maurits; Dogterom, Marileen

2016-01-01

ABSTRACT Microtubules switch between growing and shrinking states, a feature known as dynamic instability. The biochemical parameters underlying dynamic instability are modulated by a wide variety of microtubule-associated proteins that enable the strict control of microtubule dynamics in cells. The forces generated by controlled growth and shrinkage of microtubules drive a large range of processes, including organelle positioning, mitotic spindle assembly, and chromosome segregation. In the past decade, our understanding of microtubule dynamics and microtubule force generation has progressed significantly. Here, we review the microtubule-intrinsic process of dynamic instability, the effect of external factors on this process, and how the resulting forces act on various biological systems. Recently, reconstitution-based approaches have strongly benefited from extensive biochemical and biophysical characterization of individual components that are involved in regulating or transmitting microtubule-driven forces. We will focus on the current state of reconstituting increasingly complex biological systems and provide new directions for future developments. PMID:27715396

Stabilization of high-compression, indirect-drive inertial confinement fusion implosions using a 4-shock adiabat-shaped drive

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

MacPhee, A. G.; Peterson, J. L.; Casey, D. T.

Hydrodynamic instabilities and poor fuel compression are major factors for capsule performance degradation in ignition experiments on the National Ignition Facility. Using a recently developed laser drive profile with a decaying first shock to tune the ablative Richtmyer-Meshkov (ARM) instability and subsequent in-flight Rayleigh-Taylor growth, we have demonstrated reduced growth compared to the standard ignition pulse whilst maintaining conditions for a low fuel adiabat needed for increased compression. Using in-flight x-ray radiography of pre-machined modulations, the first growth measurements using this new ARM-tuned drive have demonstrated instability growth reduction of ∼4× compared to the original design at a convergence ratiomore » of ∼2. Corresponding simulations give a fuel adiabat of ∼1.6, similar to the original goal and consistent with ignition requirements.« less

Stabilization of high-compression, indirect-drive inertial confinement fusion implosions using a 4-shock adiabat-shaped drive

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

MacPhee, A. G.; Peterson, J. L.; Casey, D. T.

Hydrodynamic instabilities and poor fuel compression are major factors for capsule performance degradation in ignition experiments on the National Ignition Facility. Using a recently developed laser drive profile with a decaying first shock to tune the ablative Richtmyer-Meshkov (ARM) instability and subsequent in-flight Rayleigh-Taylor growth, we have demonstrated reduced growth compared to the standard ignition pulse whilst maintaining conditions for a low fuel adiabat needed for increased compression. Here, using in-flight x-ray radiography of pre-machined modulations, the first growth measurements using this new ARM-tuned drive have demonstrated instability growth reduction of ~4× compared to the original design at a convergencemore » ratio of ~2. Corresponding simulations give a fuel adiabat of ~1.6, similar to the original goal and consistent with ignition requirements.« less

Stabilization of high-compression, indirect-drive inertial confinement fusion implosions using a 4-shock adiabat-shaped drive

DOE PAGES

MacPhee, A. G.; Peterson, J. L.; Casey, D. T.; ...

2015-08-01

Hydrodynamic instabilities and poor fuel compression are major factors for capsule performance degradation in ignition experiments on the National Ignition Facility. Using a recently developed laser drive profile with a decaying first shock to tune the ablative Richtmyer-Meshkov (ARM) instability and subsequent in-flight Rayleigh-Taylor growth, we have demonstrated reduced growth compared to the standard ignition pulse whilst maintaining conditions for a low fuel adiabat needed for increased compression. Here, using in-flight x-ray radiography of pre-machined modulations, the first growth measurements using this new ARM-tuned drive have demonstrated instability growth reduction of ~4× compared to the original design at a convergencemore » ratio of ~2. Corresponding simulations give a fuel adiabat of ~1.6, similar to the original goal and consistent with ignition requirements.« less

Active optimal control strategies for increasing the efficiency of photovoltaic cells

NASA Astrophysics Data System (ADS)

Aljoaba, Sharif Zidan Ahmad

Energy consumption has increased drastically during the last century. Currently, the worldwide energy consumption is about 17.4 TW and is predicted to reach 25 TW by 2035. Solar energy has emerged as one of the potential renewable energy sources. Since its first physical recognition in 1887 by Adams and Day till nowadays, research in solar energy is continuously developing. This has lead to many achievements and milestones that introduced it as one of the most reliable and sustainable energy sources. Recently, the International Energy Agency declared that solar energy is predicted to be one of the major electricity production energy sources by 2035. Enhancing the efficiency and lifecycle of photovoltaic (PV) modules leads to significant cost reduction. Reducing the temperature of the PV module improves its efficiency and enhances its lifecycle. To better understand the PV module performance, it is important to study the interaction between the output power and the temperature. A model that is capable of predicting the PV module temperature and its effects on the output power considering the individual contribution of the solar spectrum wavelengths significantly advances the PV module edsigns toward higher efficiency. In this work, a thermoelectrical model is developed to predict the effects of the solar spectrum wavelengths on the PV module performance. The model is characterized and validated under real meteorological conditions where experimental temperature and output power of the PV module measurements are shown to agree with the predicted results. The model is used to validate the concept of active optical filtering. Since this model is wavelength-based, it is used to design an active optical filter for PV applications. Applying this filter to the PV module is expected to increase the output power of the module by filtering the spectrum wavelengths. The active filter performance is optimized, where different cutoff wavelengths are used to maximize the module output power. It is predicted that if the optimized active optical filter is applied to the PV module, the module efficiency is predicted to increase by about 1%. Different technologies are considered for physical implementation of the active optical filter.

Multimaterial Control of Instability in Soft Mechanical Metamaterials

NASA Astrophysics Data System (ADS)

Janbaz, Shahram; McGuinness, Molly; Zadpoor, Amir A.

2018-06-01

Soft mechanical metamaterials working on the basis of instability have numerous potential applications in the context of "machine materials." Controlling the onset of instability is usually required when rationally designing such metamaterials. We study the isolated and modulated effects of geometrical design and material distribution on the onset of instability in multimaterial cellular metamaterials. We use multimaterial additive manufacturing to fabricate cellular specimens whose unit cells are divided into void space, a square element, and an intermediate ligament. The ratio of the elastic modulus of the ligament to that of the square element [(EL)/(ES)] is changed by using different material types. Computational models are also developed, validated against experimental observations, and used to study a wide range of possible designs. The critical stress can be adjusted independently from the critical strain by changing the material type while keeping [(EL)/(ES)] constant. The critical strain shows a power-law relationship with [(EL)/(ES)] within the range [(EL)/(ES)]=0.1 - 10 . The void shape design alters the critical strain by up to threefold, while the combined effects of the void shape and material distribution cause up to a ninefold change in the critical strain. Our findings highlight the strong influence of material distribution on the onset of the instability and buckling mode.

Multi-dimensional dynamics of stimulated Brillouin scattering in a laser speckle: Ion acoustic wave bowing, breakup, and laser-seeded two-ion-wave decay

DOE PAGES

Albright, B. J.; Yin, L.; Bowers, K. J.; ...

2016-03-04

Two- and three-dimensional particle-in-cell simulations of stimulated Brillouin scattering(SBS) in laser speckle geometry have been analyzed to evaluate the relative importance of competing nonlinear processes in the evolution and saturation of SBS. It is found that ion-trapping-induced wavefront bowing and breakup of ion acoustic waves(IAW) and the associated side-loss of trapped ions dominate electron-trapping-induced IAW wavefront bowing and breakup, as well as the two-ion-wave decay instability over a range of ZT e/T i conditions and incident laser intensities. In the simulations, the latter instability does not govern the nonlinear saturation of SBS; however, evidence of two-ion-wave decay is seen, appearingmore » as a modulation of the ion acoustic wavefronts. This modulation is periodic in the laser polarization plane, anti-symmetric across the speckle axis, and of a wavenumber matching that of the incident laser pulse. Furthermore, a simple analytic model is provided for how spatial “imprinting” from a high frequency inhomogeneity (in this case, the density modulation from the laser) in an unstable system with continuum eigenmodes can selectively amplify modes with wavenumbers that match that of the inhomogeneity.« less

Bandwidth Dependence of Laser Plasma Instabilities Driven by the Nike KrF Laser

NASA Astrophysics Data System (ADS)

Weaver, J. L.; Oh, J.; Seely, J.; Kehne, D.; Brown, C. M.; Obenschain, S.; Serlin, V.; Schmitt, A. J.; Phillips, L.; Lehmberg, R. H.; McLean, E.; Manka, C.; Feldman, U.

2011-10-01

The Nike krypton-fluoride (KrF) laser at the Naval Research Laboratory operates in the deep UV (248 nm) and employs beam smoothing by induced spatial incoherence (ISI). In the first ISI studies at longer wavelengths (1054 nm and 527 nm) [Obenschain, PRL 62, 768(1989);Mostovych, PRL, 59, 1193(1987); Peyser, Phys. Fluids B 3, 1479(1991)], stimulated Raman scattering, stimulated Brillouin scattering, and the two plasmon decay instability were reduced when wide bandwidth ISI (δν / ν ~ 0.03-0.19%) pulses irradiated targets at moderate to high intensities (1014-1015W/cm2) . Recent Nike work showed that the threshold for quarter critical instabilities increased with the expected wavelength scaling, without accounting for the large bandwidth (δν ~ 1-3 THz). New experiments will compare laser plasma instabilities (LPI) driven by narrower bandwidth pulses to those observed with the standard operation. The bandwidth of KrF lasers can be reduced by adding narrow filters (etalons or gratings) in the initial stages of the laser. This talk will discuss the method used to narrow the output spectrum of Nike, the laser performance for this new operating mode, and target observations of LPI in planar CH targets. Work supported by DoE/NNSA.

Zakharov equations for viscous flow and their use in the blood clot formation

NASA Astrophysics Data System (ADS)

Zhou, Ai-Ping; Li, Xiao-Qing

2017-12-01

For theoretical study, blood can be regarded as a viscous electrically conducting fluid of negative ions and protons. Zakharov equations including viscosity are relevant for describing the behaviour of blood plasma. The dispersion formula is derived from the perturbation method and is solved numerically. It turns out that the imaginary part of one root of the perturbation frequency is greater than zero, and modulation instability occurs. This would lead to the formation of blood clot. The viscous force can suppress the occurrence of instability and prevent thrombosis. One can find that the chaotic state of blood signals human health.

Radiation pressure injection in laser-wakefield acceleration

NASA Astrophysics Data System (ADS)

Liu, Y. L.; Kuramitsu, Y.; Isayama, S.; Chen, S. H.

2018-01-01

We investigated the injection of electrons in laser-wakefield acceleration induced by a self-modulated laser pulse by a two dimensional particle-in-cell simulation. The localized electric fields and magnetic fields are excited by the counter-streaming flows on the surface of the ion bubble, owing to the Weibel or two stream like instability. The electrons are injected into the ion bubble from the sides of it and then accelerated by the wakefield. Contrary to the conventional wave breaking model, the injection of monoenergetic electrons are mainly caused by the electromagnetic process. A simple model was proposed to address the instability, and the growth rate was verified numerically and theoretically.

CUSP-PINCH DEVICE

DOEpatents

Baker, W.R.; Watteau, J.P.H.

1962-06-01

An ion-electron plasma heating device of the pinch tube class is designed with novel means for counteracting the instabilities of an ordinary linear pinch discharge. A plasma-forming discharge is created between two spacedapart coaxial electiodes through a gas such as deuterium. A pair of spaced coaxial magnetic field coils encircle the discharge and carry opposing currents so that a magnetic field having a cuspate configuration is created around the plasma, the field being formed after the plasma has been established but before significant instability arises. Thus, containment time is increased and intensified heating is obtained. In addition to the pinch compression heating additional heating is obtained by high-frequency magnetic field modulation. (AEC)

Excitation of terahertz radiation by an electron beam in a dielectric lined waveguide with rippled dielectric surface

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

Tripathi, Deepak; Uma, R.; Tripathi, V. K.

A relativistic electron beam propagating through a dielectric lined waveguide, with ripple on the dielectric surface, excites a free electron laser type instability where ripple acts as a wiggler. The spatial modulation of permittivity in the ripple region couples a terahertz radiation mode to a driven mode of lower phase velocity, where the beam is in Cerenkov resonance with the slow mode. Both the modes grow at the expanse of beam energy. The terahertz frequency increases as the beam velocity increases. The growth rate of the instability goes as one third power of beam density.

Spatially Developing Secondary Instabilities and Attachment Line Instability in Supersonic Boundary Layers

NASA Technical Reports Server (NTRS)

Li, Fei; Choudhari, Meelan M.

2008-01-01

This paper reports on progress towards developing a spatial stability code for compressible shear flows with two inhomogeneous directions, such as crossflow dominated swept-wing boundary layers and attachment line flows. Certain unique aspects of formulating a spatial, two-dimensional eigenvalue problem for the secondary instability of finite amplitude crossflow vortices are discussed. A primary test case used for parameter study corresponds to the low-speed, NLF-0415(b) airfoil configuration as tested in the ASU Unsteady Wind Tunnel, wherein a spanwise periodic array of roughness elements was placed near the leading edge in order to excite stationary crossflow modes with a specified fundamental wavelength. The two classes of flow conditions selected for this analysis include those for which the roughness array spacing corresponds to either the naturally dominant crossflow wavelength, or a subcritical wavelength that serves to reduce the growth of the naturally excited dominant crossflow modes. Numerical predictions are compared with the measured database, both as indirect validation for the spatial instability analysis and to provide a basis for comparison with a higher Reynolds number, supersonic swept-wing configuration. Application of the eigenvalue analysis to the supersonic configuration reveals that a broad spectrum of stationary crossflow modes can sustain sufficiently strong secondary instabilities as to potentially cause transition over this configuration. Implications of this finding for transition control in swept wing boundary layers are examined. Finally, extension of the spatial stability analysis to supersonic attachment line flows is also considered.

The anti-counterfeiting hologram of encryption processing in frequency domain

NASA Astrophysics Data System (ADS)

Bao, Nai K.; Chen, Zhongyu Y.

2004-09-01

This paper proposed a new encryption method using Computer Generated Fourier Hologram in frequency domain. When the main frequency spectrum, i.e. brand and an encrypted information frequency spectrum are mixed, it will not recognized and copied. We will use the methods of Dot Matrix (Digital) Hologram Modulation and the filter to get real signal. One new multi-modulated dot matrix hologram is introduced. It is encoded using several gratings. These gratings have different angles of inclination and different periods in same dot, to enable us in obtaining more information.

Influence of the cubic spectral phase of high-power laser pulses on their self-phase modulation

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

Ginzburg, V N; Kochetkov, A A; Yakovlev, I V

2016-02-28

Spectral broadening of high-power transform-limited laser pulses under self-phase modulation in a medium with cubic nonlinearity is widely used to reduce pulse duration and to increase its power. It is shown that the cubic spectral phase of the initial pulse leads to a qualitatively different broadening of its spectrum: the spectrum has narrow peaks and broadening decreases. However, the use of chirped mirrors allows such pulses to be as effectively compressed as transform-limited pulses. (nonlinear optical phenomena)

Active suppression of vortex-driven combustion instability using controlled liquid-fuel injection

NASA Astrophysics Data System (ADS)

Pang, Bin

Combustion instabilities remain one of the most challenging problems encountered in developing propulsion and power systems. Large amplitude pressure oscillations, driven by unsteady heat release, can produce numerous detrimental effects. Most previous active control studies utilized gaseous fuels to suppress combustion instabilities. However, using liquid fuel to suppress combustion instabilities is more realistic for propulsion applications. Active instability suppression in vortex-driven combustors using a direct liquid fuel injection strategy was theoretically established and experimentally demonstrated in this dissertation work. Droplet size measurements revealed that with pulsed fuel injection management, fuel droplet size could be modulated periodically. Consequently, desired heat release fluctuation could be created. If this oscillatory heat release is coupled with the natural pressure oscillation in an out of phase manner, combustion instabilities can be suppressed. To identify proper locations of supplying additional liquid fuel for the purpose of achieving control, the natural heat release pattern in a vortex-driven combustor was characterized in this study. It was found that at high Damkohler number oscillatory heat release pattern closely followed the evolving vortex front. However, when Damkohler number became close to unity, heat release fluctuation wave no longer coincided with the coherent structures. A heat release deficit area was found near the dump plane when combustor was operated in lean premixed conditions. Active combustion instability suppression experiments were performed in a dump combustor using a controlled liquid fuel injection strategy. High-speed Schlieren results illustrated that vortex shedding plays an important role in maintaining self-sustained combustion instabilities. Complete combustion instability control requires total suppression of these large-scale coherent structures. The sound pressure level at the excited dominant frequency was reduced by more than 20 dB with controlled liquid fuel injection method. Scaling issues were also investigated in this dump combustor to test the effectiveness of using pulsed liquid fuel injection strategies to suppress instabilities at higher power output conditions. With the liquid fuel injection control method, it was possible to suppress strong instabilities with initial amplitude of +/-5 psi down to the background noise level. The stable combustor operating range was also expanded from equivalence ratio of 0.75 to beyond 0.9.

Global and Regional Axial Ocean Angular Momentum Signals and Length-of-day Variations (1985-1996)

NASA Technical Reports Server (NTRS)

Ponte, Rui M.; Stammer, Detlef

2000-01-01

Changes in ocean angular momentum M about the polar axis are related to fluctuations in zonal currents (relative component M(sub tau) and latitudinal shifts in mass (planetary component M(sub Omega). Output from a 1 deg. ocean model is used to calculate global M(sub tau), (sub Omega), and M time series at 5 day intervals for the period January 1985 to April 1996. The annual cycle in M(sub tau), M(sub Omega), and M is larger than the semiannual cycle, and M(sub Omega) amplitudes are nearly twice those of M(sub tau). Year-to-year modulation of the seasonal cycle is present, but interannual variability is weak. The spectrum of M is red (background slope between omega(sup -1) and omega(sup -2) at sub-seasonal periods, implying a white or blue spectrum for the external torque on the ocean. Comparisons with previous studies indicate the importance of direct atmospheric forcing in inducing sub-seasonal M signals, relative to instabilities and other internal sources of rapid oceanic signals. Regional angular momentum estimates show that seasonal variability tends to be larger at low latitudes, but many local maxima exist because of the spatial structure of zonal current and mass variability. At seasonal timescales, latitudes approx. 20 deg. S - 10 deg. N contribute substantial variability to M(sub Omega), while signals in M(sub tau) can be traced to Antarctic Circumpolar Current transports and associated circulation. Variability in M is found to be small when compared with similar time series for the atmosphere and the solid Earth, but ocean signals are significantly coherent with atmosphere-solid Earth residuals, implying a measurable oceanic impact on length-of-day variations.

Global and Regional Axial Ocean Angular Momentum Signals and Length-of-Day Variations (1985-1996)

NASA Technical Reports Server (NTRS)

Ponte, Rui M.; Stammer, Detlef

1999-01-01

Changes in ocean angular momentum about the polar axis (M) are related to fluctuations in zonal currents (relative component M(sub r)) and latitudinal shifts in mass (planetary component M(sub Omega)). Output from a 1 deg ocean model is used to calculate global M(sub r), M(sub Omega), and M time series at 5-day intervals for the period January 1985-April 1996. The annual cycle in M(sub r), M(sub Omega), and M is larger than the semiannual cycle, and M(sub Omega) amplitudes are nearly twice those of M(sub r). Year-to-year modulation of the seasonal cycle is present, but interannual variability is weak. The spectrum of M is red (background slope between omega(sup (-1) and omega(sup -2)) at subseasonal periods, implying a white or blue spectrum for the external torque on the ocean. Comparisons with previous studies indicate the importance of direct atmospheric forcing in inducing subseasonal M signals, relative to instabilities and other internal sources of rapid oceanic signals. Regional angular momentum estimates show that seasonal variability tends to be larger at low latitudes but there are many local maxima due to the spatial structure of zonal current and mass variability. At seasonal timescales, latitudes approximately 20 S - 10 N contribute substantial variability to M(sub Omega), while signals in M(sub r) can be traced to Antarctic Circumpolar Current transports and associated circulation. Variability in M is found to be small when compared with similar time series for the atmosphere and the solid Earth, but ocean signals are significantly coherent with atmosphere-solid Earth residuals, implying a measurable oceanic impact on length-of-day variations.

A New Multi-dimensional General Relativistic Neutrino Hydrodynamics Code of Core-collapse Supernovae. III. Gravitational Wave Signals from Supernova Explosion Models

NASA Astrophysics Data System (ADS)

Müller, Bernhard; Janka, Hans-Thomas; Marek, Andreas

2013-03-01

We present a detailed theoretical analysis of the gravitational wave (GW) signal of the post-bounce evolution of core-collapse supernovae (SNe), employing for the first time relativistic, two-dimensional explosion models with multi-group, three-flavor neutrino transport based on the ray-by-ray-plus approximation. The waveforms reflect the accelerated mass motions associated with the characteristic evolutionary stages that were also identified in previous works: a quasi-periodic modulation by prompt post-shock convection is followed by a phase of relative quiescence before growing amplitudes signal violent hydrodynamical activity due to convection and the standing accretion shock instability during the accretion period of the stalled shock. Finally, a high-frequency, low-amplitude variation from proto-neutron star (PNS) convection below the neutrinosphere appears superimposed on the low-frequency trend associated with the aspherical expansion of the SN shock after the onset of the explosion. Relativistic effects in combination with detailed neutrino transport are shown to be essential for quantitative predictions of the GW frequency evolution and energy spectrum, because they determine the structure of the PNS surface layer and its characteristic g-mode frequency. Burst-like high-frequency activity phases, correlated with sudden luminosity increase and spectral hardening of electron (anti-)neutrino emission for some 10 ms, are discovered as new features after the onset of the explosion. They correspond to intermittent episodes of anisotropic accretion by the PNS in the case of fallback SNe. We find stronger signals for more massive progenitors with large accretion rates. The typical frequencies are higher for massive PNSs, though the time-integrated spectrum also strongly depends on the model dynamics.

Nuclear Chemistry, Science (Experimental): 5316.62.

ERIC Educational Resources Information Center

Williams, Russell R.

This nuclear chemistry module includes topics on atomic structure, instability of the nucleus, detection strengths and the uses of radioactive particles. Laboratory work stresses proper use of equipment and safe handling of radioactive materials. Students with a strong mathematics background may consider this course as advanced work in chemistry.…

Beneficial and paradoxical roles of selenium at nutritional levels of intake in healthspan and longevity

USDA-ARS?s Scientific Manuscript database

Accumulation of damage to the genome and macromolecules is a hallmark of aging, age-associated degeneration, and genome instability syndromes. Although the processes of aging are irreversible, they can be modulated by genome maintenance pathways and environmental factors such as diet. Selenium (Se) ...

Bubble-detector measurements of neutron radiation in the international space station: ISS-34 to ISS-37

PubMed Central

Smith, M. B.; Khulapko, S.; Andrews, H. R.; Arkhangelsky, V.; Ing, H.; Koslowksy, M. R.; Lewis, B. J.; Machrafi, R.; Nikolaev, I.; Shurshakov, V.

2016-01-01

Bubble detectors have been used to characterise the neutron dose and energy spectrum in several modules of the International Space Station (ISS) as part of an ongoing radiation survey. A series of experiments was performed during the ISS-34, ISS-35, ISS-36 and ISS-37 missions between December 2012 and October 2013. The Radi-N2 experiment, a repeat of the 2009 Radi-N investigation, included measurements in four modules of the US orbital segment: Columbus, the Japanese experiment module, the US laboratory and Node 2. The Radi-N2 dose and spectral measurements are not significantly different from the Radi-N results collected in the same ISS locations, despite the large difference in solar activity between 2009 and 2013. Parallel experiments using a second set of detectors in the Russian segment of the ISS included the first characterisation of the neutron spectrum inside the tissue-equivalent Matroshka-R phantom. These data suggest that the dose inside the phantom is ∼70 % of the dose at its surface, while the spectrum inside the phantom contains a larger fraction of high-energy neutrons than the spectrum outside the phantom. The phantom results are supported by Monte Carlo simulations that provide good agreement with the empirical data. PMID:25899609

Multi-dimensional PIC-simulations of parametric instabilities for shock-ignition conditions

NASA Astrophysics Data System (ADS)

Riconda, C.; Weber, S.; Klimo, O.; Héron, A.; Tikhonchuk, V. T.

2013-11-01

Laser-plasma interaction is investigated for conditions relevant for the shock-ignition (SI) scheme of inertial confinement fusion using two-dimensional particle-in-cell (PIC) simulations of an intense laser beam propagating in a hot, large-scale, non-uniform plasma. The temporal evolution and interdependence of Raman- (SRS), and Brillouin- (SBS), side/backscattering as well as Two-Plasmon-Decay (TPD) are studied. TPD is developing in concomitance with SRS creating a broad spectrum of plasma waves near the quarter-critical density. They are rapidly saturated due to plasma cavitation within a few picoseconds. The hot electron spectrum created by SRS and TPD is relatively soft, limited to energies below one hundred keV.

Screech tones from free and ducted supersonic jets

NASA Technical Reports Server (NTRS)

Tam, C. K. W.; Ahuja, K. K.; Jones, R. R., III

1994-01-01

It is well known that screech tones from supersonic jets are generated by a feedback loop. The loop consists of three main components. They are the downstream propagating instability wave, the shock cell structure in the jet plume, and the feedback acoustic waves immediately outside the jet. Evidence will be presented to show that the screech frequency is largely controlled by the characteristics of the feedback acoustic waves. The feedback loop is driven by the instability wave of the jet. Thus the tone intensity and its occurrence are dictated by the characteristics of the instability wave. In this paper the dependence of the instability wave spectrum on the azimuthal mode number (axisymmetric or helical/flapping mode, etc.), the jet-to-ambient gas temperature ratio, and the jet Mach number are studied. The results of this study provide an explanation for the observed screech tone mode switch phenomenon (changing from axisymmetric to helical mode as Mach number increases) and the often-cited experimental observation that tone intensity reduces with increase in jet temperature. For ducted supersonic jets screech tones can also be generated by feedback loops formed by the coupling of normal duct modes to instability waves of the jet. The screech frequencies are dictated by the frequencies of the duct modes. Super resonance, resonance involving very large pressure oscillations, can occur when the feedback loop is powered by the most amplified instability wave. It is proposed that the observed large amplitude pressure fluctuations and tone in the test cells of Arnold Engineering Development Center were generated by super resonance. Estimated super-resonance frequency for a Mach 1.3 axisymmetric jet tested in the facility agrees well with measurement.

Spectrum of perturbations in anisotropic inflationary universe with vector hair

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

Himmetoglu, Burak, E-mail: burak@physics.umn.edu

2010-03-01

We study both the background evolution and cosmological perturbations of anisotropic inflationary models supported by coupled scalar and vector fields. The models we study preserve the U(1) gauge symmetry associated with the vector field, and therefore do not possess instabilities associated with longitudinal modes (which instead plague some recently proposed models of vector inflation and curvaton). We first intoduce a model in which the background anisotropy slowly decreases during inflation; we then confirm the stability of the background solution by studying the quadratic action for all the perturbations of the model. We then compute the spectrum of the h{sub ×}more » gravitational wave polarization. The spectrum we find breaks statistical isotropy at the largest scales and reduces to the standard nearly scale invariant form at small scales. We finally discuss the possible relevance of our results to the large scale CMB anomalies.« less

Bayesian Analysis of the Power Spectrum of the Cosmic Microwave Background

NASA Technical Reports Server (NTRS)

Jewell, Jeffrey B.; Eriksen, H. K.; O'Dwyer, I. J.; Wandelt, B. D.

2005-01-01

There is a wealth of cosmological information encoded in the spatial power spectrum of temperature anisotropies of the cosmic microwave background. The sky, when viewed in the microwave, is very uniform, with a nearly perfect blackbody spectrum at 2.7 degrees. Very small amplitude brightness fluctuations (to one part in a million!!) trace small density perturbations in the early universe (roughly 300,000 years after the Big Bang), which later grow through gravitational instability to the large-scale structure seen in redshift surveys... In this talk, I will discuss a Bayesian formulation of this problem; discuss a Gibbs sampling approach to numerically sampling from the Bayesian posterior, and the application of this approach to the first-year data from the Wilkinson Microwave Anisotropy Probe. I will also comment on recent algorithmic developments for this approach to be tractable for the even more massive data set to be returned from the Planck satellite.

Ion dynamics during the parametric instabilities of a left-hand polarized Alfvén wave in a proton-electron-alpha plasma

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

Gao, Xinliang; Lu, Quanming; Hao, Yufei

2014-01-01

The parametric instabilities of an Alfvén wave in a proton-electron plasma system are found to have great influence on proton dynamics, where part of the protons can be accelerated through the Landau resonance with the excited ion acoustic waves, and a beam component along the background magnetic field is formed. In this paper, with a one-dimensional hybrid simulation model, we investigate the evolution of the parametric instabilities of a monochromatic left-hand polarized Alfvén wave in a proton-electron-alpha plasma with a low beta. When the drift velocity between the protons and alpha particles is sufficiently large, the wave numbers of themore » backward daughter Alfvén waves can be cascaded toward higher values due to the modulational instability during the nonlinear evolution of the parametric instabilities, and the alpha particles are resonantly heated in both the parallel and perpendicular direction by the backward waves. On the other hand, when the drift velocity of alpha particles is small, the alpha particles are heated in the linear growth stage of the parametric instabilities due to the Landau resonance with the excited ion acoustic waves. Therefore, the heating occurs only in the parallel direction, and there is no obvious heating in the perpendicular direction. The relevance of our results to the preferential heating of heavy ions observed in the solar wind within 0.3 AU is also discussed in this paper.« less

Immunotherapy and patients treated for cancer with microsatellite instability.

PubMed

Colle, Raphaël; Cohen, Romain; Cochereau, Delphine; Duval, Alex; Lascols, Olivier; Lopez-Trabada, Daniel; Afchain, Pauline; Trouilloud, Isabelle; Parc, Yann; Lefevre, Jérémie H; Fléjou, Jean-François; Svrcek, Magali; André, Thierry

2017-01-01

Microsatellite instability (MSI) is a tumor phenotype linked to somatic or germline (Lynch syndrome) inactivating alterations of DNA mismatch repair genes. A broad spectrum of neoplasms exhibits MSI phenotype, mainly colorectal cancer, endometrial cancer, and gastric cancer. MSI tumors are characterized by dense immune infiltration and high load of tumor neo-antigens. Growing evidence is accumulating on the efficacy of immune checkpoint inhibition for patients treated for MSI solid tumors. We present a comprehensive overview of MSI phenotype, its biological landscape and current diagnostic methods. Then we focus on MSI as a predictive biomarker of response to immune checkpoint inhibition in the context of colorectal cancer and non-colorectal tumors. Copyright © 2016 Société Française du Cancer. Published by Elsevier Masson SAS. All rights reserved.

All-polarization-maintaining, single-port Er:fiber comb for high-stability comparison of optical lattice clocks

NASA Astrophysics Data System (ADS)

Ohmae, Noriaki; Kuse, Naoya; Fermann, Martin E.; Katori, Hidetoshi

2017-06-01

All-polarization-maintaining, single-port Er:fiber combs offer long-term robust operation as well as high stability. We have built two such combs and evaluated the transfer noise for linking optical clocks. A uniformly broadened spectrum over 135-285 THz with a high signal-to-noise ratio enables the optical frequency measurement of the subharmonics of strontium, ytterbium, and mercury optical lattice clocks with the fractional frequency-noise power spectral density of (1-2) × 10-17 Hz-1/2 at 1 Hz. By applying a synchronous clock comparison, the comb enables clock ratio measurements with 10-17 instability at 1 s, which is one order of magnitude smaller than the best instability of the frequency ratio of optical lattice clocks.

Receiver Statistics for Cognitive Radios in Dynamic Spectrum Access Networks

DTIC Science & Technology

2012-02-28

SNR) are employed by many protocols and processes in direct-sequence ( DS ) spread-spectrum packet radio networks, including soft-decision decoding...adaptive modulation protocols, and power adjustment protocols. For DS spread spectrum, we have introduced and evaluated SNR estimators that employ...obtained during demodulation in a binary CDMA receiver. We investigated several methods to apply the proposed metric to the demodulator’s soft-decision

High data rate modem simulation for the space station multiple-access communications system

NASA Technical Reports Server (NTRS)

Horan, Stephen

1987-01-01

The communications system for the space station will require a space based multiple access component to provide communications between the space based program elements and the station. A study was undertaken to investigate two of the concerns of this multiple access system, namely, the issues related to the frequency spectrum utilization and the possibilities for higher order (than QPSK) modulation schemes for use in possible modulators and demodulators (modems). As a result of the investigation, many key questions about the frequency spectrum utilization were raised. At this point, frequency spectrum utilization is seen as an area requiring further work. Simulations were conducted using a computer aided communications system design package to provide a straw man modem structure to be used for both QPSK and 8-PSK channels.

Investigation of combustion control in a dump combustor using the feedback free fluidic oscillator

NASA Astrophysics Data System (ADS)

Meier, Eric J.

The feedback free fluidic oscillator uses the unsteady nature of two colliding jets to create a single oscillating outlet jet with a wide sweep angle. These devices have the potential to provide additional combustion control, boundary layer control, thrust vectoring, and industrial flow deflection. Two-dimensional computational fluid dynamics, CFD, was used to analyze the jet oscillation frequency over a range of operating conditions and to determine the effect that geometric changes in the oscillator design have on the frequency. Results presented illustrate the changes in jet oscillation frequency with gas type, gas temperature, operating pressure, pressure ratio across the oscillator, aspect ratio of the oscillator, and the frequency trends with various changes to the oscillator geometry. A fluidic oscillator was designed and integrated into single element rocket combustor with the goal of suppressing longitudinal combustion instabilities. An array of nine fluidic oscillators was tested to mimic modulated secondary oxidizer injection into the dump plane using 15% of the oxidizer flow. The combustor has a coaxial injector that uses gaseous methane and decomposed hydrogen peroxide at an O/F of 11.66. A sonic choke plate on an actuator arm allows for continuous adjustment of the oxidizer post acoustics for studying a variety of instability magnitudes. The fluidic oscillator unsteady outlet jet performance is compared with equivalent steady jet injection and a baseline design with no secondary oxidizer injection. At the most unstable operating conditions, the unsteady outlet jet saw a 60% reduction in the instability pressure oscillation magnitude when compared to the steady jet and baseline data. The results indicate open loop propellant modulation for combustion control can be achieved through fluidic devices that require no moving parts or electrical power to operate. Three-dimensional computational fluid dynamics, 3-D CFD, was conducted to determine the mechanism by which the fluidic oscillators were able to suppress the combustion instability. Results for steady jet secondary injection, showed a strong coupling between the jet injection and the combustion instability pressure pulse. The computational results were able to closely match the experimental results and previous CFD data. The model with the oscillating fluidic oscillator injection was unable to match the stable combustion seen in the experimental data. Further investigation is needed to determine the role higher order chemistry kinetics play in the process and the role of manifolds on the un-choked fuel and fluidic oscillator inlets. This research demonstrates the ability to modulate propellant injection and suppress combustion instabilities using fluidic devices that require no electrical power or moving parts. The advent of advanced manufacturing technologies such as direct metal laser sintering will allow for integration of fluidic devices into combustors to provide open loop active control with a high degree of reliability. Additionally, 2-D CFD analysis is demonstrated to be a valid tool for predicting the feedback free fluidic oscillator oscillation mechanism.

Multicasting based optical inverse multiplexing in elastic optical network.

PubMed

Guo, Bingli; Xu, Yingying; Zhu, Paikun; Zhong, Yucheng; Chen, Yuanxiang; Li, Juhao; Chen, Zhangyuan; He, Yongqi

2014-06-16

Optical multicasting based inverse multiplexing (IM) is introduced in spectrum allocation of elastic optical network to resolve the spectrum fragmentation problem, where superchannels could be split and fit into several discrete spectrum blocks in the intermediate node. We experimentally demonstrate it with a 1-to-7 optical superchannel multicasting module and selecting/coupling components. Also, simulation results show that, comparing with several emerging spectrum defragmentation solutions (e.g., spectrum conversion, split spectrum), IM could reduce blocking performance significantly but without adding too much system complexity as split spectrum. On the other hand, service fairness for traffic with different granularity of these schemes is investigated for the first time and it shows that IM performs better than spectrum conversion and almost as well as split spectrum, especially for smaller size traffic under light traffic intensity.

A model for chorus associated electrostatic bursts

NASA Technical Reports Server (NTRS)

Grabbe, C. L.

1984-01-01

The linear theory of the generation of electrostatic bursts of noise by electrons trapped in chorus wave packets is developed for a finite temperature electron beam and a Maxwellian elecron and ion background. The growth rates determined qualitatively in good agreement with those obtained by previous authors from a more idealized model. Two connected instability mechanisms seem to be occurring: a beam plasma (electron-ion two-stream) instability commonly associated with intensification of the chorus power levels, and a transitional or borderline resistive medium instability commonly associated with chorus hooks. The physical reasons for the two mechanisms is discussed. In the second case electron beams are difficult to identify in the particle data. An expression is obtained for the maximum growth rate in terms of the ratios of the beam and electron thermal velocities to the beam velocity, and of the beam density to plasma density. It is anticipated that this may allow the observed peak in the electrostatic noise spectrum to be used as a diagnostic for the beam characteristics. Previously announced in STAR as N84-12832

A two-fluid study of oblique tearing modes in a force-free current sheet

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

Akçay, Cihan, E-mail: akcay@lanl.gov; Daughton, William; Lukin, Vyacheslav S.

2016-01-15

Kinetic simulations have demonstrated that three-dimensional reconnection in collisionless regimes proceeds through the formation and interaction of magnetic flux ropes, which are generated due to the growth of tearing instabilities at multiple resonance surfaces. Since kinetic simulations are intrinsically expensive, it is desirable to explore the feasibility of reduced two-fluid models to capture this complex evolution, particularly, in the strong guide field regime, where two-fluid models are better justified. With this goal in mind, this paper compares the evolution of the collisionless tearing instability in a force-free current sheet with a two-fluid model and fully kinetic simulations. Our results indicatemore » that the most unstable modes are oblique for guide fields larger than the reconnecting field, in agreement with the kinetic results. The standard two-fluid tearing theory is extended to address the tearing instability at oblique angles. The resulting theory yields a flat oblique spectrum and underestimates the growth of oblique modes in a similar manner to kinetic theory relative to kinetic simulations.« less

Self-sustained oscillations of a sinusoidally-deformed plate

NASA Astrophysics Data System (ADS)

Muriel, Diego F.; Cowen, Edwin A.

2015-11-01

Motivated by energy harvesting, the oscillatory motion of a deformed elastic material with aspect ratio Length/Width=2, immerse in an incompressible flow is studied experimentally. To induce the wave-like deformation a polycarbonate sheet is placed under longitudinal compression with external forcing provided by equispaced tension lines anchored in a frame. No additional constrains are placed in the material. Based on quantitative image-based edge detection, ADV, and PIV measurements, we document the existence of three natural states of motion. Bellow a critical velocity, a stable state presents a sinusoidal-like deformation with weak small perturbations. Above a critical velocity, instability appears in the form of a traveling wave with predictable dominant frequency accompanied by higher-order harmonics. As the flow velocity increases the instability converges faster to its limit cycle in the phase plane (e.g., vertical velocity and position), until the stable oscillatory mode transitions to chaos showing a broad energy spectrum and unstable limit cycle. The underlying objective is to induce the onset of the instability at lower critical velocities for higher bending rigidities, promoting possible energy extraction and increasing the range at which stable oscillations appear.

Transient Modeling of Hybrid Rocket Low Frequency Instabilities

NASA Technical Reports Server (NTRS)

Karabeyoglu, M. Arif; DeZilwa, Shane; Cantwell, Brian; Zilliac, Greg

2003-01-01

A comprehensive dynamic model of a hybrid rocket has been developed in order to understand and predict the transient behavior including instabilities. A linearized version of the transient model predicted the low-frequency chamber pressure oscillations that are commonly observed in hybrids. The source of the instabilities is based on a complex coupling of thermal transients in the solid fuel, wall heat transfer blocking due to fuel regression rate and the transients in the boundary layer that forms on the fuel surface. The oscillation frequencies predicted by the linearized theory are in very good agreement with 43 motor test results obtained from the hybrid propulsion literature. The motor test results used in the comparison cover a very wide spectrum of parameters including: 1) four separate research and development programs, 2) three different oxidizers (LOX, GOX, N2O), 3) a wide range of motor dimensions (i.e. from 5 inch diameter to 72 inch diameter) and operating conditions and 4) several fuel formulations. A simple universal scaling formula for the frequency of the primary oscillation mode is suggested.

Langmuir instability in partially spin polarized bounded degenerate plasma

NASA Astrophysics Data System (ADS)

Iqbal, Z.; Jamil, M.; Murtaza, G.

2018-04-01

Some new features of waves inside the cylindrical waveguide on employing the separated spin evolution quantum hydrodynamic model are evoked. Primarily, the instability of Langmuir wave due to the electron beam in a partially spin polarized degenerate plasma considering a nano-cylindrical geometry is discussed. Besides, the evolution of a new spin-dependent wave (spin electron acoustic wave) due to electron spin polarization effects in the real wave spectrum is elaborated. Analyzing the growth rate, it is found that in the absence of Bohm potential, the electron spin effects or exchange interaction reduce the growth rate as well as k-domain but the inclusion of Bohm potential increases both the growth rate and k-domain. Further, we investigate the geometry effects expressed by R and pon and find that they have opposite effects on the growth rate and k-domain of the instability. Additionally, how the other parameters like electron beam density or streaming speed of beam electrons influence the growth rate is also investigated. This study may find its applications for the signal analysis in solid state devices at nanoscales.

A two-fluid study of oblique tearing modes in a force-free current sheet

DOE PAGES

Akçay, Cihan; Daughton, William; Lukin, Vyacheslav S.; ...

2016-01-01

Kinetic simulations have demonstrated that three-dimensional reconnection in collisionless regimes proceeds through the formation and interaction of magnetic flux ropes, which are generated due to the growth of tearing instabilities at multiple resonance surfaces. Because kinetic simulations are intrinsically expensive, it is desirable to explore the feasibility of reduced two-fluid models to capture this complex evolution, particularly, in the strong guide field regime, where two-fluid models are better justified. With this goal in mind, this paper compares the evolution of the collisionless tearing instability in a force-free current sheet with a two-fluid model and fully kinetic simulations. Our results indicatemore » that the most unstable modes are oblique for guide fields larger than the reconnecting field, in agreement with the kinetic results. The standard two-fluid tearing theory is extended to address the tearing instability at oblique angles. As a results this theory yields a flat oblique spectrum and underestimates the growth of oblique modes in a similar manner to kinetic theory relative to kinetic simulations.« less