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Sample records for geodesic acoustic mode

  1. On the dispersion of geodesic acoustic modes

    SciTech Connect

    Smolyakov, A. I.; Bashir, M. F.; Elfimov, A. G.; Yagi, M.; Miyato, N.

    2016-05-15

    The problem of dispersion of geodesic acoustic modes is revisited with two different methods for the solution of the kinetic equation. The dispersive corrections to the mode frequency are calculated by including the m = 2 poloidal harmonics. Our obtained results agree with some earlier results but differ in various ways with other previous works. Limitations and advantages of different approaches are discussed.

  2. Electromagnetic effects on geodesic acoustic modes

    SciTech Connect

    Bashir, M. F.; Smolyakov, A. I.; Elfimov, A. G.; Melnikov, A. V.; Murtaza, G.

    2014-08-15

    By using the full electromagnetic drift kinetic equations for electrons and ions, the general dispersion relation for geodesic acoustic modes (GAMs) is derived incorporating the electromagnetic effects. It is shown that m = 1 harmonic of the GAM mode has a finite electromagnetic component. The electromagnetic corrections appear for finite values of the radial wave numbers and modify the GAM frequency. The effects of plasma pressure β{sub e}, the safety factor q, and the temperature ratio τ on GAM dispersion are analyzed.

  3. Drift effects on electromagnetic geodesic acoustic modes

    SciTech Connect

    Sgalla, R. J. F.

    2015-02-15

    A two fluid model with parallel viscosity is employed to derive the dispersion relation for electromagnetic geodesic acoustic modes (GAMs) in the presence of drift (diamagnetic) effects. Concerning the influence of the electron dynamics on the high frequency GAM, it is shown that the frequency of the electromagnetic GAM is independent of the equilibrium parallel current but, in contrast with purely electrostatic GAMs, significantly depends on the electron temperature gradient. The electromagnetic GAM may explain the discrepancy between the f ∼ 40 kHz oscillation observed in tokamak TCABR [Yu. K. Kuznetsov et al., Nucl. Fusion 52, 063044 (2012)] and the former prediction for the electrostatic GAM frequency. The radial wave length associated with this oscillation, estimated presently from this analytical model, is λ{sub r} ∼ 25 cm, i.e., an order of magnitude higher than the usual value for zonal flows (ZFs)

  4. Perturbation analysis of electromagnetic geodesic acoustic modes

    SciTech Connect

    Ren, Haijun

    2014-06-15

    Lagrangian displacement and magnetic field perturbation response to the geodesic acoustic mode is analyzed by using the ideal magnetohydrodynamic equations in a large-aspect-ratio tokamak. δB{sub θ}, the poloidal component of magnetic field perturbation, has poloidal wave number m = 2 created by the poloidal displacement ξ{sub θ}. The parallel perturbation of magnetic field, δB{sub ∥}, has a poloidally asymmetric structure with m = 1 and is on the same order of magnitude with δB{sub θ} to the leading order. The radial displacement ξ{sub r} is of order O(βϵξ{sub θ}) but plays a significant role in determining δB{sub ∥}, where β is the plasma/magnetic pressure ratio and ϵ is the inverse aspect ratio.

  5. Global Geodesic Acoustic Modes in Tokamak Plasmas

    NASA Astrophysics Data System (ADS)

    Sorokina, Ekaterina; Ilgisonis, Viktor; Lakhin, Vladimir; Smolyakov, Andrey; Khalzov, Ivan

    2010-11-01

    Global Geodesic Acoustic Modes (GGAM) in Tokamak Plasmas are investigated in the framework of reduced ideal MHD. The axisymmetric eigenvalue problem for perturbed pressure and electrostatic potential is formulated as a recurrent set of equations for poloidal Fourier harmonics. For uniform safety factor q and temperature profile with a maximum at radius r=r0!=0 the analytical solution of this eigenvalue problem is obtained for a truncated set of equations taking into account the m=0 and m=2 poloidal harmonics of potential and the m=1 harmonic of pressure. This solution exists in wide range of βq^2. It is shown both analytically and numerically that the higher harmonics of pressure (m=3) and electrostatic potential (m=4) reduce the range of the parameters, in which GGAM exist, due to the resonance with continuum spectrum. The domain of GGAM existence in the (βq^2, r0)-plane is represented. Higher poloidal harmonics (m>4) are shown to weakly affect the GAM spectrum and do not lead to the appearance of other global eigenmodes. The work is supported in part by grant RBRF 10-02-01302 and by Ministry of Education and Science of the RF, contract 1.5-508-008-045.

  6. Geodesic Acoustic Propagation and Ballooning Mode Formalism

    NASA Astrophysics Data System (ADS)

    Li, M. B.; Diamond, P. H.; Young, G. G.; Arakawa, M.

    2005-10-01

    Relevance of ballooning formalism (BMF) in nonlinear interaction of toroidal electromagnetic drift waves in the presence of zonal flows and Geodesic Acoustic Oscillation (GAO) is critically examined from a physical argument of radial propagation of wave packets. To achieve the quasi-translational invariance of poloidal harmonics which is necessary for the BMF, the geodesic curvature induced transfer [1] of fluctuation energy in radial direction should occur faster than the time scale of physical interest. Of course, this does not happen necessarily in drift-Alfven (DALF) turbulence simulations [2]. This observation casts considerable doubts on the applicability of various codes based on the BMF concept to nonlinear electromagnetic problems. [1] B. Scott, Phys. Letters A 320 (2003) 53. [2] B. Scott, New J. Phys 7 (2005) 92.

  7. Geodesic acoustic modes with poloidal mode couplings ad infinitum

    NASA Astrophysics Data System (ADS)

    Singh, Rameswar; Gürcan, Ö. D.

    2017-02-01

    Geodesic acoustic modes (GAMs) are studied including all poloidal mode (m) couplings within a drift reduced Braginskii framework. An exact analytical formula for GAM frequency is given within the toroidal Hasegawa Mima model with the full finite larmor radius effect and poloidal mode couplings ad infinitum using a scalar continued fraction formulation, which results from reduction of the semi-infinite chain of interactions that is obtained from the nearest neighbor coupling pattern due to geodesic curvature. This pattern can be described by a semi-infinite chain model of the GAM with the mode-mode coupling matrix elements proportional to the radial wave number kr. In the more general case of multi-field description of the GAM, the infinite chain can be reduced to a renormalized bi-nodal chain with a matrix continued fraction formulation. The convergence study of the linear GAM dispersion with respect to kr and the m-spectra confirms that the coupling beyond m = 1 is sustained only when kr ≠ 0 and the higher m couplings become important with increasing kr and increasing ion to electron temperature ratio τi.

  8. Collisional damping of the geodesic acoustic mode with toroidal rotation. I. Viscous damping

    SciTech Connect

    Gong, Xueyu; Xie, Baoyi; Chen, You; Yu, Jiangmei; Yu, Jun; Guo, Wenfeng

    2016-03-15

    With the dispersion relation derived for the geodesic acoustic mode in toroidally rotating tokamak plasmas using the fluid model, the effect of the toroidal rotation on the collisional viscous damping of the geodesic acoustic mode is investigated. It is found that the collisional viscous damping of the geodesic acoustic mode has weak increase with respect to the toroidal Mach number.

  9. Electron collisionless damping of the geodesic acoustic mode in rotating tokamak plasmas

    NASA Astrophysics Data System (ADS)

    Xie, Baoyi; Guo, Wenfeng; Gong, Xueyu; Yu, Jun; Chen, You; Cao, Jinjia

    2016-12-01

    Collisionless damping of the geodesic acoustic mode due to electron dynamics in rotating tokamak plasmas is investigated. A dispersion relation of the geodesic acoustic mode with a non-adiabatic electron response in a rotating tokamak is derived and solved both analytically and numerically. It is found that the collisionless damping of the geodesic acoustic mode, due to electron dynamics, significantly increases with the increasing toroidal rotation, especially in the large safety factor regime. The rotation-induced frequency up-shift of the geodesic acoustic mode increases the resonant velocity, which enables a larger number of electrons to resonate with the geodesic acoustic mode. The significant increase of the number of the resonant electrons significantly enhances the collisionless damping of the geodesic acoustic mode. The result indicates that in rotating tokamak plasmas a more complete picture of the geodesic acoustic mode should include the electron dynamics.

  10. Landau damping of geodesic acoustic mode in toroidally rotating tokamaks

    SciTech Connect

    Ren, Haijun; Cao, Jintao

    2015-06-15

    Geodesic acoustic mode (GAM) is analyzed by using modified gyro-kinetic (MGK) equation applicable to low-frequency microinstabilities in a rotating axisymmetric plasma. Dispersion relation of GAM in the presence of arbitrary toroidal Mach number is analytically derived. The effects of toroidal rotation on the GAM frequency and damping rate do not depend on the orientation of equilibrium flow. It is shown that the toroidal Mach number M increases the GAM frequency and dramatically decreases the Landau damping rate.

  11. Excitation of geodesic acoustic modes by external fields.

    PubMed

    Hallatschek, K; McKee, G R

    2012-12-14

    It is planned to use external magnetic perturbations at acoustic frequencies at the DIII-D tokamak to attempt to drive geodesic acoustic modes (GAM) to modify the turbulent transport. We show that this might not only be possible--despite the well-known electrostatic nature of the GAMs--but might be a viable and efficient method to generate GAMs in magnetically confined plasmas, by developing an elegant analytic method which allows us to couple numerical dynamic equilibrium calculations with massively parallel non-Boussinesq turbulence code runs and yields practical estimates of the effectivity of the method.

  12. Onset condition of the subcritical geodesic acoustic mode instability in the presence of energetic-particle-driven geodesic acoustic mode

    SciTech Connect

    Itoh, K.; Itoh, S.-I.; Kosuga, Y.; Lesur, M.; Ido, T.

    2016-05-15

    An analytic model is developed for understanding the abrupt onset of geodesic acoustic mode (GAM) in the presence of chirping energetic-particle-driven GAM (EGAM). This abrupt excitation phenomenon has been observed on LHD plasma. Threshold conditions for the onset of abrupt growth of GAM are derived, and the period doubling phenomenon is explained. The phase relation between the mother mode (EGAM) and the daughter mode (GAM) is also discussed. This result contributes to the understanding of “trigger problems” of laboratory and nature plasmas.

  13. Onset condition of the subcritical geodesic acoustic mode instability in the presence of energetic-particle-driven geodesic acoustic mode

    NASA Astrophysics Data System (ADS)

    Itoh, K.; Itoh, S.-I.; Kosuga, Y.; Lesur, M.; Ido, T.

    2016-05-01

    An analytic model is developed for understanding the abrupt onset of geodesic acoustic mode (GAM) in the presence of chirping energetic-particle-driven GAM (EGAM). This abrupt excitation phenomenon has been observed on LHD plasma. Threshold conditions for the onset of abrupt growth of GAM are derived, and the period doubling phenomenon is explained. The phase relation between the mother mode (EGAM) and the daughter mode (GAM) is also discussed. This result contributes to the understanding of "trigger problems" of laboratory and nature plasmas.

  14. Fast excitation of geodesic acoustic mode by energetic particle beams

    NASA Astrophysics Data System (ADS)

    Cao, Jintao; Qiu, Zhiyong; Zonca, Fulvio

    2015-12-01

    A new mechanism for geodesic acoustic mode (GAM) excitation by a not fully slowed down energetic particle (EP) beam is analyzed to explain experimental observations in Large Helical Device. It is shown that the positive velocity space gradient near the lower-energy end of the EP distribution function can strongly drive the GAM unstable. The new features of this EP-induced GAM (EGAM) are: (1) no instability threshold in the pitch angle; (2) the EGAM frequency can be higher than the local GAM frequency; and (3) the instability growth rate is much larger than that driven by a fully slowed down EP beam.

  15. Fast excitation of geodesic acoustic mode by energetic particle beams

    SciTech Connect

    Cao, Jintao; Qiu, Zhiyong; Zonca, Fulvio

    2015-12-15

    A new mechanism for geodesic acoustic mode (GAM) excitation by a not fully slowed down energetic particle (EP) beam is analyzed to explain experimental observations in Large Helical Device. It is shown that the positive velocity space gradient near the lower-energy end of the EP distribution function can strongly drive the GAM unstable. The new features of this EP-induced GAM (EGAM) are: (1) no instability threshold in the pitch angle; (2) the EGAM frequency can be higher than the local GAM frequency; and (3) the instability growth rate is much larger than that driven by a fully slowed down EP beam.

  16. Geodesic acoustic mode frequencies in experimental tokamak equilibria

    NASA Astrophysics Data System (ADS)

    Hager, R.; Hallatschek, K.

    2013-03-01

    The geodesic acoustic mode (GAM) frequency is calculated for experimental equilibrium data from ASDEX Upgrade and NSTX discharges using an eigenvalue solver. For this purpose, a special algorithm is applied to generate precise, smooth flux-surfaces suitable for calculation of local equilibria from the coarse grained output of the equilibrium solver CLISTE. Since realistic magnetic geometries allow for more than one mode with the properties of a GAM, two-fluid turbulence computations are discussed to clarify the influence of the turbulence on the linear mode spectrum. Using equilibrium data from ASDEX Upgrade this approach is shown to be superior to the use of approximated flux-surface shapes and leads to better agreement with the experimental results.

  17. Radial structures and nonlinear excitation of geodesic acoustic modes

    NASA Astrophysics Data System (ADS)

    Zonca, F.; Chen, L.

    2008-08-01

    Geodesic acoustic modes (GAM) are shown to constitute a continuous spectrum due to radial inhomogeneities. The importance and theoretical as well as experimental implications of this fact are discussed in this work. The existence of a singular layer causes GAM to mode convert to short-wavelength kinetic GAM (KGAM) via finite ion Larmor radii; analogous to kinetic Alfvén waves (KAW). Furthermore, it is shown that KGAM can be nonlinearly excited by drift-wave (DW) turbulence via 3-wave parametric interactions, and the resultant driven-dissipative nonlinear system exhibits typical prey-predator self-regulatory dynamics, consistent with recent experimental observations on HL-2A. The degeneracy of GAM/KGAM with beta-induced Alfvén eigenmodes (BAE) is demonstrated and discussed, with emphasis on its important role in the complex self-organized behaviors of burning plasmas.

  18. Geodesic acoustic mode in anisotropic plasma with heat flux

    SciTech Connect

    Ren, Haijun

    2015-10-15

    Geodesic acoustic mode (GAM) in an anisotropic tokamak plasma is investigated in fluid approximation. The collisionless anisotropic plasma is described within the 16-momentum magnetohydrodynamic (MHD) fluid closure model, which takes into account not only the pressure anisotropy but also the anisotropic heat flux. It is shown that the GAM frequency agrees better with the kinetic result than the standard Chew-Goldberger-Low (CGL) MHD model. When zeroing the anisotropy, the 16-momentum result is identical with the kinetic one to the order of 1/q{sup 2}, while the CGL result agrees with the kinetic result only on the leading order. The discrepancies between the results of the CGL fluid model and the kinetic theory are well removed by considering the heat flux effect in the fluid approximation.

  19. Geodesic acoustic mode in toroidally rotating anisotropic tokamaks

    SciTech Connect

    Ren, Haijun

    2015-07-15

    Effects of anisotropy on the geodesic acoustic mode (GAM) are analyzed by using gyro-kinetic equations applicable to low-frequency microinstabilities in a toroidally rotating tokamak plasma. Dispersion relation in the presence of arbitrary Mach number M, anisotropy strength σ, and the temperature ration τ is analytically derived. It is shown that when σ is less than 3 + 2τ, the increased electron temperature with fixed ion parallel temperature increases the normalized GAM frequency. When σ is larger than 3 + 2τ, the increasing of electron temperature decreases the GAM frequency. The anisotropy σ always tends to enlarge the GAM frequency. The Landau damping rate is dramatically decreased by the increasing τ or σ.

  20. Geodesic acoustic mode in anisotropic plasma with heat flux

    NASA Astrophysics Data System (ADS)

    Ren, Haijun

    2015-10-01

    Geodesic acoustic mode (GAM) in an anisotropic tokamak plasma is investigated in fluid approximation. The collisionless anisotropic plasma is described within the 16-momentum magnetohydrodynamic (MHD) fluid closure model, which takes into account not only the pressure anisotropy but also the anisotropic heat flux. It is shown that the GAM frequency agrees better with the kinetic result than the standard Chew-Goldberger-Low (CGL) MHD model. When zeroing the anisotropy, the 16-momentum result is identical with the kinetic one to the order of 1/q2, while the CGL result agrees with the kinetic result only on the leading order. The discrepancies between the results of the CGL fluid model and the kinetic theory are well removed by considering the heat flux effect in the fluid approximation.

  1. Linear radial structure of reactive energetic geodesic acoustic modes

    NASA Astrophysics Data System (ADS)

    Qu, Z. S.; Hole, M. J.; Fitzgerald, M.

    2017-05-01

    In this paper we have developed a fluid model to study the radial mode structure of the reactive energetic geodesic acoustic modes (reactive EGAMs), a branch of GAM that becomes unstable in the presence of a cold fast ion beam. We have solved the resulting dispersion relationship, a second order ODE, both analytically in restricted cases and numerically in general. It is found that the reactive EGAM global mode structure is formed with the inclusion of fast ion finite drift orbit effects. In two cases with typical DIII-D parameters but different q profiles, the global EGAM frequency is slightly higher than the local EGAM extremum, located either on axis with a monotonic shear or at mid-radius with a reversed shear. The mode wavelength roughly scales with {L}{orbit}1/2 in the core and {L}{orbit} at the edge, though the dependency is more complicated for the reversed shear case when {L}{orbit}< 0.06a ({L}{orbit} is the fast ion drift orbit width and a the minor radius). Finally, the growth rate of the global mode is boosted by 50% to 100% when switching from co-beam to counter-beam, depending on the fast ion density, which may help to explain the more frequent occurrence of EGAMs with counter-injection in experiments.

  2. Geodesic acoustic mode in tokamaks: local consideration and eigenvalue analysis

    NASA Astrophysics Data System (ADS)

    Kolesnichenko, Ya I.; Lepiavko, B. S.; Lutsenko, V. V.

    2013-12-01

    A set of magnetohydrodynamic equations describing the geodesic acoustic mode (GAM) in tokamak plasmas is derived. The obtained equations take into account the presence of the energetic ions and allow to study energetic-ion-driven GAM instability perturbatively or non-perturbatively (EGAM mode). They are applicable to plasmas with \\bar{\\beta} q^2 \\lesssim 1 , where \\bar{\\beta} =\\beta_s/(1+\\beta_s) , \\beta_s=c_s^2/v_A^2 , cs is the sound velocity, vA is the Alfvén velocity, q is the tokamak safety factor. Using these equations, GAM/EGAM instability is studied in a local approach and by means of the eigenvalue analysis. It is shown that β-coupling (the coupling of Fourier harmonics of the perturbation due to finite β—ratio of the plasma pressure to the magnetic field pressure—and the curvature of the field lines) can be responsible for the radial structure of the GAM-mode. A conclusion is drawn that conditions for the GAM/EGAM instability to arise are mildest in the case of counter-injection of energetic ions with pitch angles χ2 < 0.6 and large ratio of Larmor radius of the energetic ions to a characteristic length of inhomogeneity of these ions. A numerical code solving the derived equations is developed. Specific calculations are carried out for tokamaks with a non-monotonic safety factor. On the other hand, it is found that due to the presence of the energetic ions the GAM/EGAM continuum can have an extremum even when the safety factor q(r) is monotonic, which indicates that global modes can exist also in this case.

  3. The magnetic component of geodesic acoustic modes in tokamak plasmas with a radial equilibrium electric field

    NASA Astrophysics Data System (ADS)

    Zhou, Deng

    2016-10-01

    The dispersion relation of geodesic acoustic modes with a magnetic perturbation in the tokamak plasma with an equilibrium radial electric field was derived. The dispersion relation was analyzed for very low field strength. The mode frequency decreases with increasing field strength, which is different from the electrostatic geodesic acoustic mode. There exists an m = 1 magnetic component that is very low when the radial electric field is absent. The ratio between the m = 1 and m = 2 magnetic components increases with strength of the radial electric field for low Mach numbers.

  4. Impact of Energetic-Particle-Driven Geodesic Acoustic Modes on Turbulence

    NASA Astrophysics Data System (ADS)

    Zarzoso, D.; Sarazin, Y.; Garbet, X.; Dumont, R.; Strugarek, A.; Abiteboul, J.; Cartier-Michaud, T.; Dif-Pradalier, G.; Ghendrih, Ph.; Grandgirard, V.; Latu, G.; Passeron, C.; Thomine, O.

    2013-03-01

    The impact on turbulent transport of geodesic acoustic modes excited by energetic particles is evidenced for the first time in flux-driven 5D gyrokinetic simulations using the Gysela code. Energetic geodesic acoustic modes (EGAMs) are excited in a regime with a transport barrier in the outer radial region. The interaction between EGAMs and turbulence is such that turbulent transport can be enhanced in the presence of EGAMs, with the subsequent destruction of the transport barrier. This scenario could be particularly critical in those plasmas, such as burning plasmas, exhibiting a rich population of suprathermal particles capable of exciting energetic modes.

  5. Impact of energetic-particle-driven geodesic acoustic modes on turbulence.

    PubMed

    Zarzoso, D; Sarazin, Y; Garbet, X; Dumont, R; Strugarek, A; Abiteboul, J; Cartier-Michaud, T; Dif-Pradalier, G; Ghendrih, Ph; Grandgirard, V; Latu, G; Passeron, C; Thomine, O

    2013-03-22

    The impact on turbulent transport of geodesic acoustic modes excited by energetic particles is evidenced for the first time in flux-driven 5D gyrokinetic simulations using the Gysela code. Energetic geodesic acoustic modes (EGAMs) are excited in a regime with a transport barrier in the outer radial region. The interaction between EGAMs and turbulence is such that turbulent transport can be enhanced in the presence of EGAMs, with the subsequent destruction of the transport barrier. This scenario could be particularly critical in those plasmas, such as burning plasmas, exhibiting a rich population of suprathermal particles capable of exciting energetic modes.

  6. Geodesic acoustic modes in tokamak plasmas with a radial equilibrium electric field

    SciTech Connect

    Zhou, Deng

    2015-09-15

    The dispersion relation of geodesic acoustic modes in the tokamak plasma with an equilibrium radial electric field is derived and analyzed. Multiple branches of eigenmodes have been found, similar to the result given by the fluid model with a poloidal mass flow. Frequencies and damping rates of both the geodesic acoustic mode and the sound wave increase with respect to the strength of radial electric field, while the frequency and the damping rate of the lower frequency branch slightly decrease. Possible connection to the experimental observation is discussed.

  7. Global geodesic acoustic mode in a tokamak with positive magnetic shear and a monotonic temperature profile

    NASA Astrophysics Data System (ADS)

    Ilgisonis, V. I.; Khalzov, I. V.; Lakhin, V. P.; Smolyakov, A. I.; Sorokina, E. A.

    2014-03-01

    The analytical solution for global geodesic acoustic modes (GGAMs) in a tokamak with a positive magnetic shear profile and a monotonic temperature profile is found in the framework of magnetohydrodynamic theory. The axisymmetric eigenvalue problem for perturbed pressure and electrostatic potential is formulated as a recurrent set of equations for poloidal Fourier harmonics. The integral condition for the existence of GGAMs is obtained. It is shown that the traditional paradigm of having a off-axis maximum of the local geodesic acoustic frequency is not necessary for the existence of GGAMs; a representative example is designed.

  8. Effect of toroidal rotation on the geodesic acoustic mode in magnetohydrodynamics

    SciTech Connect

    Ren Haijun

    2012-09-15

    Theoretical research on the geodesic acoustic mode (GAM) induced by equilibrium toroidal rotation flow in the tokamak plasmas is approached by using ideal magnetohydrodynamic model. The dispersion relation of the GAM is presented by taking into account magnetic field perturbations. It is shown that {beta} can decrease the frequency of the GAM.

  9. Properties of Geodesic Acoustic Modes and the Relation to Density Fluctuations

    SciTech Connect

    Kraemer-Flecken, A.; Soldatov, S.; Koslowski, H. R.; Zimmermann, O.

    2006-07-28

    The geodesic acoustic mode (GAM) is a high frequency branch of zonal flows, which is observed in toroidal plasmas. Because of toroidal curvature effects, density fluctuations are excited, which are investigated with the O-mode correlation reflectometer at TEXTOR. This Letter reports on the poloidal distribution of GAM induced density fluctuation and compares them with theoretical predictions. The influence of the GAM flows on the ambient turbulence is studied, too.

  10. Geodesic acoustic mode in anisotropic plasmas using double adiabatic model and gyro-kinetic equation

    SciTech Connect

    Ren, Haijun; Cao, Jintao

    2014-12-15

    Geodesic acoustic mode in anisotropic tokamak plasmas is theoretically analyzed by using double adiabatic model and gyro-kinetic equation. The bi-Maxwellian distribution function for guiding-center ions is assumed to obtain a self-consistent form, yielding pressures satisfying the magnetohydrodynamic (MHD) anisotropic equilibrium condition. The double adiabatic model gives the dispersion relation of geodesic acoustic mode (GAM), which agrees well with the one derived from gyro-kinetic equation. The GAM frequency increases with the ratio of pressures, p{sub ⊥}/p{sub ∥}, and the Landau damping rate is dramatically decreased by p{sub ⊥}/p{sub ∥}. MHD result shows a low-frequency zonal flow existing for all p{sub ⊥}/p{sub ∥}, while according to the kinetic dispersion relation, no low-frequency branch exists for p{sub ⊥}/p{sub ∥}≳ 2.

  11. Collisionless damping of geodesic acoustic mode in plasma with nonextensive distribution

    SciTech Connect

    Qiu, Hui-Bin; Song, Hai-Ying; Liu, Shi-Bing

    2014-06-15

    Geodesic acoustic mode (GAM) in collisionless toroidal plasmas with a constant electrostatic potential around a magnetic surface is investigated based on the linear gyrokinetic theory in context of nonextensive statistics mechanics. The damping rate of GAM is shown to be dependent on the nonextensive parameters of ions, and in the extensive limit, the result in Maxwellian distribution plasma is recovered. The damping rate is found to be enhanced as the nonextensive parameter of ion decreases.

  12. Radial structures and nonlinear excitation of Geodesic Acoustic Modes

    NASA Astrophysics Data System (ADS)

    Chen, Liu; Zonca, Fulvio

    2007-11-01

    In this paper, we show that GAMs constitute a continuous spectrum due to radial inhomogeneities. The existence of singular layer, thus, suggests linear mode conversion to short-wavelength kinetic GAM (KGAM) via finite ion Larmor radii. This result is demonstrated by derivations of the GAM mode structure and dispersion relation in the singular layer. At the lowest order in krρi, with kr the radial wave vector and ρi the ion Larmor radius, the well known kinetic dispersion relation of GAM is recovered. At the next relevant order, O(kr^2ρi^2), we show that KGAM propagates in the low-temperature and/or high safety-factor domain; i.e., typically, radially outward, and a corresponding damping rate is derived. In this work, we also show that, while KGAM is linearly stable due to ion Landau damping, it can be nonlinearly excited by finite-amplitude DW turbulence via 3-wave parametric interactions. The resultant 3-wave system exhibits the typical prey-predator self-regulatory dynamics.

  13. Collisional damping of the geodesic acoustic mode with toroidal rotation. II. Gyrokinetic formulation

    SciTech Connect

    Xie, Baoyi; Yu, Jun; Chen, You; Gong, Xueyu; Guo, Wenfeng

    2016-03-15

    The collisional damping of the geodesic acoustic mode (GAM) is analytically investigated in toroidally rotating tokamaks by using the gyrokinetic equation. It is found that the toroidal rotation could decrease the collisional damping of the GAM in the small safety factor region and increase the collisional damping of the GAM in the large safety factor region at low ion collision rate; while at high ion collision rate, the toroidal rotation will increase the collisional damping of the GAM with arbitrary safety factor. Furthermore, the change quantity of collisional damping rate of the GAM due to the toroidal rotation at high collision rate is larger than that at low collision rate.

  14. TEMPEST Simulations of Collisionless Damping of Geodesic-Acoustic Mode in Edge Plasma Pedestal

    SciTech Connect

    Xu, X; Xiong, Z; Nevins, W; McKee, G

    2007-05-31

    The fully nonlinear 4D TEMPEST gyrokinetic continuum code produces frequency, collisionless damping of geodesic-acoustic mode (GAM) and zonal flow with fully nonlinear Boltzmann electrons for the inverse aspect ratio {epsilon}-scan and the tokamak safety factor q-scan in homogeneous plasmas. The TEMPEST simulation shows that GAM exists in edge plasma pedestal for steep density and temperature gradients, and an initial GAM relaxes to the standard neoclassical residual, rather than Rosenbluth-Hinton residual due to the presence of ion-ion collisions. The enhanced GAM damping explains experimental BES measurements on the edge q scaling of the GAM amplitude.

  15. Experimental investigation of geodesic acoustic modes on JET using Doppler backscattering

    NASA Astrophysics Data System (ADS)

    Silva, C.; Hillesheim, J. C.; Hidalgo, C.; Belonohy, E.; Delabie, E.; Gil, L.; Maggi, C. F.; Meneses, L.; Solano, E.; Tsalas, M.; Contributors, JET

    2016-10-01

    Geodesic acoustic modes (GAMs) have been investigated in JET ohmic discharges using mainly Doppler backscattering. Characteristics and scaling properties of the GAM are studied. Time and spatial resolved measurements of the perpendicular velocity indicate that GAMs are located in a narrow layer at the edge density gradient region with amplitude corresponding to about 50% of the mean local perpendicular velocity. GAMs on JET appear to be regulated by the turbulence drive rather than by their damping rate. It is also shown that the GAM amplitude is ~20% larger in deuterium than in hydrogen plasmas.

  16. Simulation study of high-frequency energetic particle driven geodesic acoustic mode

    SciTech Connect

    Wang, Hao Ido, Takeshi; Osakabe, Masaki; Todo, Yasushi

    2015-09-15

    High-frequency energetic particle driven geodesic acoustic modes (EGAM) observed in the large helical device plasmas are investigated using a hybrid simulation code for energetic particles and magnetohydrodynamics (MHD). Energetic particle inertia is incorporated in the MHD momentum equation for the simulation where the beam ion density is comparable to the bulk plasma density. Bump-on-tail type beam ion velocity distribution created by slowing down and charge exchange is considered. It is demonstrated that EGAMs have frequencies higher than the geodesic acoustic modes and the dependence on bulk plasma temperature is weak if (1) energetic particle density is comparable to the bulk plasma density and (2) charge exchange time (τ{sub cx}) is sufficiently shorter than the slowing down time (τ{sub s}) to create a bump-on-tail type distribution. The frequency of high-frequency EGAM rises as the energetic particle pressure increases under the condition of high energetic particle pressure. The frequency also increases as the energetic particle pitch angle distribution shifts to higher transit frequency. It is found that there are two kinds of particles resonant with EGAM: (1) trapped particles and (2) passing particles with transit frequency close to the mode frequency. The EGAMs investigated in this work are destabilized primarily by the passing particles whose transit frequencies are close to the EGAM frequency.

  17. The effect of energetic particle induced geodesic acoustic modes on microturbulence

    NASA Astrophysics Data System (ADS)

    Schneller, Mirjam; Fu, Guoyong; Wang, Weixing; Chavdarovski, Ilija; Lauber, Philipp

    2016-10-01

    The control of turbulent transport reveals essential to achieve a successful fusion reactor. Together with turbulence, energetic particles are ubiquitous in present and future tokamaks due to heating systems and fusion reactions. Anisotropy in the distribution function of the energetic particle population is able to excite oscillations from the continuous spectrum of geodesic acoustic modes, which cannot be driven by plasma pressure gradients due to their toroidally and nearly poloidally symmetric structures. These oscillations are known as energetic particle-induced geodesic acoustic modes (EGAMs) [G.Y.Fu'08] and have been observed in recent experiments [R.Nazikian'08]. EGAMs are particularly attractive in the framework of turbulence regulation, since they lead to an oscillatory radial electric shear which can potentially saturate the turbulence. In recent years, numerical simulations have shown however, that turbulent transport could also be enhanced in the presence of EGAMs [D.Zarzoso'13]. For the presented work, the nonlinear gyrokinetic, electrostatic, particle-in-cell code GTS [W.X.Wang'06] has been extended to include an energetic particle population. With this new tool, the interaction of EGAMs with microturbulence is investigated in more detail. NERSC computing time is greatfully acknowledged.

  18. Synchronization of Geodesic Acoustic Modes and Magnetic Fluctuations in Toroidal Plasmas

    NASA Astrophysics Data System (ADS)

    Zhao, K. J.; Nagashima, Y.; Diamond, P. H.; Dong, J. Q.; Itoh, K.; Itoh, S.-I.; Yan, L. W.; Cheng, J.; Fujisawa, A.; Inagaki, S.; Kosuga, Y.; Sasaki, M.; Wang, Z. X.; Wei, L.; Huang, Z. H.; Yu, D. L.; Hong, W. Y.; Li, Q.; Ji, X. Q.; Song, X. M.; Huang, Y.; Liu, Yi.; Yang, Q. W.; Ding, X. T.; Duan, X. R.

    2016-09-01

    The synchronization of geodesic acoustic modes (GAMs) and magnetic fluctuations is identified in the edge plasmas of the HL-2A tokamak. Mesoscale electric fluctuations (MSEFs) having components of a dominant GAM, and m /n =6 /2 potential fluctuations are found at the same frequency as that of the magnetic fluctuations of m /n =6 /2 (m and n are poloidal and toroidal mode numbers, respectively). The temporal evolutions of the MSEFs and the magnetic fluctuations clearly show the frequency entrainment and the phase lock between the GAM and the m /n =6 /2 magnetic fluctuations. The results indicate that GAMs and magnetic fluctuations can transfer energy through nonlinear synchronization. Such nonlinear synchronization may also contribute to low-frequency zonal flow formation, reduction of turbulence level, and thus confinement regime transitions.

  19. A branch of energetic-particle driven geodesic acoustic modes due to magnetic drift resonance

    NASA Astrophysics Data System (ADS)

    Sasaki, M.; Kasuya, N.; Itoh, K.; Hallatschek, K.; Lesur, M.; Kosuga, Y.; Itoh, S.-I.

    2016-10-01

    Eigenmode analysis of geodesic acoustic modes (GAMs) driven by fast ions is performed, based on a set of gyrokinetic equations. Resonance to the magnetic drift of the fast ions can destabilize GAMs. A new branch is found in the family of GAMs, whose frequency is close to the magnetic drift frequency of the fast ions. The poloidal eigenfunction of this branch has bump structures in the poloidal direction where the resonance of the magnetic drift with the mode is strong. The ion heating rate by the GAMs is evaluated in the framework of quasi-linear theory. The heating is localized poloidally around the resonance locations. Owing to the bumps in the eigenfunction, the magnitude of the heating is much larger than that estimated without the magnetic drift resonance.

  20. Double adiabatic theory of driven collisionless geodesic acoustic modes (GAMs) in toroids

    NASA Astrophysics Data System (ADS)

    Hassam, Adil; Kleva, Robert

    2011-10-01

    The GAM is an axisymmetric oscillation of a toroidal magnetically confined plasma, resulting from an interplay between poloidal plasma rotation and perpendicular flux tube compression from the B field gradient. The frequency is super-parallel-sonic, ie, omega ~ (ion thermal speed)/R, greater than the parallel acoustic mode which is lower by a factor of q. Consequently, collisionless geodesic acoustic modes in tokamaks can be described by the Chew-Goldberger-Low double-adiabatic fluid closures. This allows a simpler nonlinear formulation. We use these equations to study driven, collisionless GAMs in tokamaks. The motivation for this study is a proposal by Hallatschek and McKee to drive GAMs on the D3D tokamak at resonance. The drivers in the CGL theory include external magnetic forces to effect flux surface displacements as well as sources to provide modulated non-axisymmetric ion heating. We show that the linear mode frequency from CGL theory agrees with previous kinetic results. Comparisons will be made between different approaches to resonate the mode. Nonlinear effects will be evaluated. A 2D toroidal numerical simulation of driven GAMs is in progress. Work supported by US-DOE.

  1. Double adiabatic theory of driven collisionless geodesic acoustic modes (GAMs) in toroids

    NASA Astrophysics Data System (ADS)

    Hassam, Adil; Kleva, Robert; Sengupta, Wrick

    2012-03-01

    The GAM is an axisymmetric oscillation of a toroidal magnetically confined plasma, resulting from an interplay between poloidal plasma rotation and perpendicular flux tube compression from the B field gradient. The frequency is super-parallel-sonic, ie, φ ˜ (ion thermal speed)/R, greater than the parallel acoustic mode which is lower by a factor of q. Consequently, collisionless geodesic acoustic modes in tokamaks can be described by the Chew-Goldberger-Low double-adiabatic fluid closures. This allows a simpler nonlinear formulation. We use these equations to study driven, collisionless GAMs in tokamaks. The motivation for this study is a proposal by Hallatschek and McKee to drive GAMs on the D3D tokamak at resonance. The drivers in the CGL theory include external magnetic forces to effect flux surface displacements as well as sources to provide modulated non-axisymmetric ion heating. We show that the linear mode frequency from CGL theory agrees with previous kinetic results. Comparisons will be made between different approaches to resonate the mode. Nonlinear effects will be evaluated. Results of a 2D toroidal numerical simulation of driven GAMs are described

  2. Toroidal momentum channeling of geodesic acoustic modes driven by fast ions

    NASA Astrophysics Data System (ADS)

    Sasaki, M.; Kasuya, N.; Itoh, K.; Kosuga, Y.; Lesur, M.; Hallatschek, K.; Itoh, S.-I.

    2017-03-01

    Toroidal momentum channeling by fast ion-driven geodesic acoustic mode (EGAM) is proposed based on a quasi-linear analysis. We focus on a branch due to the magnetic drift resonance. Without the magnetic drift resonance, the eigenfunction of the EGAM has up–down anti-symmetric property in the poloidal direction, and the toroidal momentum flux by the EGAM is zero. If the magnetic drift resonance is considered, the up–down anti-symmetry in the poloidal eigenfunction is violated, and, as a result, the toroidal momentum flux becomes finite. Comparing its magnitude to the other processes such as external momentum input, and the turbulent residual stress, the momentum flux induced by the EGAM is found to be significant in the total momentum balance. This suggests that EGAMs can be used as a control knob for the toroidal rotation.

  3. On Nonlinear Self-interaction of Geodesic Acoustic Mode Driven By Energetic Particles

    SciTech Connect

    G.Y. Fu

    2010-10-01

    It is shown that nonlinear self-interaction of energetic particle-driven Geodesic Acoustic Mode does not generate a second harmonic in radial electric field using the fluid model. However, kinetic effects of energetic particles can induce a second harmonic in the radial electric field. A formula for the second order plasma density perturbation is derived. It is shown that a second harmonic of plasma density perturbation is generated by the convective nonlinearity of both thermal plasma and energetic particles. Near the midplane of a tokamak, the second order plasma density perturbation (the sum of second harmonic and zero frequency sideband) is negative on the low field side with its size comparable to the main harmonic at low fluctuation level. These analytic predictions are consistent with the recent experimental observation in DIII-D.

  4. On Nonlinear Self-interaction of Geodesic Acoustic Mode Driven by Energetic Particles

    SciTech Connect

    G. Y. Fu

    2010-06-04

    It is shown that nonlinear self-interaction of energetic particle-driven Geodesic Acoustic Mode does not generate a second harmonic in radial electric field using the fluid model. However, kinetic effects of energetic particles can induce a second harmonic in the radial electric field. A formula for the second order plasma density perturbation is derived. It is shown that a second harmonic of plasma density perturbation is generated by the convective nonlinearity of both thermal plasma and energetic particles. Near the midplane of a tokamak, the second order plasma density perturbation (the sum of second harmonic and zero frequency sideband) is negative on the low field side with its size comparable to the main harmonic at low uctuation level. These analytic predictions are consistent with the recent experimental observation in DIII-D.

  5. Comprehensive comparisons of geodesic acoustic mode characteristics and dynamics between Tore Supra experiments and gyrokinetic simulations

    SciTech Connect

    Storelli, A. Vermare, L.; Hennequin, P.; Gürcan, Ö. D.; Singh, Rameswar; Morel, P.; Dif-Pradalier, G.; Sarazin, Y.; Garbet, X.; Grandgirard, V.; Ghendrih, P.; Görler, T.

    2015-06-15

    In a dedicated collisionality scan in Tore Supra, the geodesic acoustic mode (GAM) is detected and identified with the Doppler backscattering technique. Observations are compared to the results of a simulation with the gyrokinetic code GYSELA. We found that the GAM frequency in experiments is lower than predicted by simulation and theory. Moreover, the disagreement is higher in the low collisionality scenario. Bursts of non harmonic GAM oscillations have been characterized with filtering techniques, such as the Hilbert-Huang transform. When comparing this dynamical behaviour between experiments and simulation, the probability density function of GAM amplitude and the burst autocorrelation time are found to be remarkably similar. In the simulation, where the radial profile of GAM frequency is continuous, we observed a phenomenon of radial phase mixing of the GAM oscillations, which could influence the burst autocorrelation time.

  6. Intermittent Transport Associated with the Geodesic Acoustic Mode near the Critical Gradient Regime

    SciTech Connect

    Miki, K.; Kishimoto, Y.; Li, J. Q.; Miyato, N.

    2007-10-05

    Turbulent transport near the critical gradient in toroidal plasmas is studied based on global Landau-fluid simulations and an extended predator-prey theoretical model of ion temperature gradient turbulence. A new type of intermittent transport associated with the emission and propagation of a geodesic acoustic mode (GAM) is found near the critical gradient regime, which is referred to as GAM intermittency. The intermittency is characterized by new time scales of trigger, damping, and recursion due to GAM damping. During the recursion of intermittent bursts, stationary zonal flow increases with a slow time scale due to the accumulation of undamped residues and eventually quenches the turbulence, suggesting that a nonlinear upshift of the critical gradient, i.e., Dimits shift, is established through such a dynamical process.

  7. Excitation of kinetic geodesic acoustic modes by drift waves in nonuniform plasmas

    SciTech Connect

    Qiu, Z.; Chen, L.; Zonca, F.

    2014-02-15

    Effects of system nonuniformities and kinetic dispersiveness on the spontaneous excitation of Geodesic Acoustic Mode (GAM) by Drift Wave (DW) turbulence are investigated based on nonlinear gyrokinetic theory. The coupled nonlinear equations describing parametric decay of DW into GAM and DW lower sideband are derived and then solved both analytically and numerically to investigate the effects on the parametric decay process due to system nonuniformities, such as nonuniform diamagnetic frequency, finite radial envelope of DW pump, and kinetic dispersiveness. It is found that the parametric decay process is a convective instability for typical tokamak parameters when finite group velocities of DW and GAM associated with kinetic dispersiveness and finite radial envelope are taken into account. When, however, nonuniformity of diamagnetic frequency is taken into account, the parametric decay process becomes, time asymptotically, a quasi-exponentially growing absolute instability.

  8. Gyrokinetic simulation of turbulence driven geodesic acoustic modes in edge plasmas of HL-2A tokamak

    SciTech Connect

    Liu Feng; Zhao, K. J.; Lin, Z.; Dong, J. Q.

    2010-11-15

    Strong correlation between high frequency microturbulence and low frequency geodesic acoustic mode (GAM) has been observed in the edge plasmas of the HL-2A tokamak, suggesting possible GAM generation via three wave coupling with turbulence, which is in turn modulated by the GAM. In this work, we use the gyrokinetic toroidal code to study the linear and nonlinear development of the drift instabilities, as well as the generation of the GAM (and low frequency zonal flows) and its interaction with the turbulence for realistic parameters in the edge plasmas of the HL-2A tokamak for the first time. The simulation results indicate that the unstable drift wave drives strong turbulence in the edge plasma of HL-2A. In addition, the generation of the GAM and its interaction with the turbulence are all observed in the nonlinear simulation. The simulation results are in reasonable agreement with the experimental observations.

  9. Radial acceleration of geodesic acoustic modes in the presence of a temperature gradient

    NASA Astrophysics Data System (ADS)

    Palermo, F.; Poli, E.; Bottino, A.; Biancalani, A.; Conway, G. D.; Scott, B.

    2017-07-01

    The global dynamics of geodesic acoustic modes (GAMs) is studied analytically and by means of gyrokinetic simulations for several equilibria with flat and nonuniform profiles. In particular, the effects of phase mixing via the continuum spectrum in the presence of a temperature gradient are investigated. We show that the frequency of GAM is not constant but can evolve in time because of the increase of the radial wavenumber. As a consequence, also the radial velocity of GAM increases in time. Thus, this study reduces the discrepancy between the linear theory and the experiments, in which strong velocities of GAM are generally observed. An estimate of phase and group velocity is given for simulations performed with experimental parameter values.

  10. Kinetic effects on geodesic acoustic mode from combined collisions and impurities

    SciTech Connect

    Yang, Shangchuan; Xie, Jinlin Liu, Wandong

    2015-04-15

    The dispersion relation for geodesic acoustic mode (GAM) is derived by applying a gyrokinetic model that accounts for the effects from both collisions and impurities. Based on the dispersion relation, an analysis is performed for the non-monotonic behavior of GAM damping versus the characteristic collision rate at various impurity levels. As the effective charge increases, the maximum damping rate is found to shift towards lower collision rates, nearer to the parameter range of a typical tokamak edge plasma. The relative strengths of ion-ion and impurity-induced collision effects, which are illustrated by numerical calculations, are found to be comparable. Impurity-induced collisions help decrease the frequency of GAM, while their effects on the damping rate are non-monotonic, resulting in a weaker total damping in the high collision regime. The results presented suggest considering collision effects as well as impurity effects in GAM analysis.

  11. Toroidal symmetry of the geodesic acoustic mode zonal flow in a tokamak plasma.

    PubMed

    Zhao, K J; Lan, T; Dong, J Q; Yan, L W; Hong, W Y; Yu, C X; Liu, A D; Qian, J; Cheng, J; Yu, D L; Yang, Q W; Ding, X T; Liu, Y; Pan, C H

    2006-06-30

    The toroidal symmetry of the geodesic acoustic mode (GAM) zonal flows is identified with toroidally distributed three step Langmuir probes at the edge of the HuanLiuqi-2A (commonly referred to as HL-2A) tokamak plasmas for the first time. High coherence of both the GAM and the ambient turbulence for the toroidally displaced measurements along a magnetic field line is observed, in contrast with the high coherence of the GAM but low coherence of the ambient turbulence when the toroidally displaced measurements are not along the same field line. The radial and poloidal features of the flows are also simultaneously determined. The nonlinear three wave coupling between the high frequency turbulent fluctuations and the flows is demonstrated to be a plausible formation mechanism of the flows.

  12. Comprehensive comparisons of geodesic acoustic mode characteristics and dynamics between Tore Supra experiments and gyrokinetic simulations

    NASA Astrophysics Data System (ADS)

    Storelli, A.; Vermare, L.; Hennequin, P.; Gürcan, Ö. D.; Dif-Pradalier, G.; Sarazin, Y.; Garbet, X.; Görler, T.; Singh, Rameswar; Morel, P.; Grandgirard, V.; Ghendrih, P.

    2015-06-01

    In a dedicated collisionality scan in Tore Supra, the geodesic acoustic mode (GAM) is detected and identified with the Doppler backscattering technique. Observations are compared to the results of a simulation with the gyrokinetic code GYSELA. We found that the GAM frequency in experiments is lower than predicted by simulation and theory. Moreover, the disagreement is higher in the low collisionality scenario. Bursts of non harmonic GAM oscillations have been characterized with filtering techniques, such as the Hilbert-Huang transform. When comparing this dynamical behaviour between experiments and simulation, the probability density function of GAM amplitude and the burst autocorrelation time are found to be remarkably similar. In the simulation, where the radial profile of GAM frequency is continuous, we observed a phenomenon of radial phase mixing of the GAM oscillations, which could influence the burst autocorrelation time.

  13. The measurement of geodesic acoustic mode magnetic field oscillations in J-TEXT tokamak

    NASA Astrophysics Data System (ADS)

    Lan, T.; Wu, J.; Shen, H. G.; Deng, T. J.; Liu, A. D.; Xie, J. L.; Li, H.; Liu, W. D.; Yu, C. X.; Sun, Y.; Liu, H.; Chen, Z. P.; Zhuang, G.

    2014-10-01

    Geodesic acoustic mode (GAM) magnetic field oscillations have been investigated using three-dimension magnetic probe and Langmuir probe arrays in the edge of J-TEXT tokamak. The probe arrays are placed on the two top windows of tokamak, separated toroidally. Inside the LCFS, GAM shows apparent oscillations in floating potential. In contrast, GAM magnetic field oscillations are not significant in raw magnetic fields signals. Using toroidal correlation technique, the GAM magnetic field oscillations are distinguished from ambient magnetic field. The amplitudes of three dimension GAM magnetic field fluctuations, as well as the dependence with local plasma parameters such as safety factor and plasma beta, are coincident with theoretical predictions. And its toroidal symmetry mode structure, i.e. n = 0, is identified. Furthermore, the GAM current sheet, in which GAM oscillates, is firstly verified with magnetic probes arrays in different radial positions, which may help us to understand the radial structure of GAM. Supported by NNSFC (Nos. 10990210, 10990211, 10335060, 10905057 and 11375188), CPSF (No. 20080440104), YIF (No. WK2030040019) and KIPCAS (No. kjcx-yw-n28).

  14. Numerical modelling of geodesic acoustic mode relaxation in a tokamak edge

    DOE PAGES

    Dorf, M. A.; Cohen, R. H.; Dorr, M.; ...

    2013-05-08

    Here, the edge of a tokamak in a high confinement (H mode) regime is characterized by steep density gradients and a large radial electric field. Recent analytical studies demonstrated that the presence of a strong radial electric field consistent with a subsonic pedestal equilibrium modifies the conventional results of the neoclassical formalism developed for the core region. In the present work we make use of the recently developed gyrokinetic code COGENT to numerically investigate neoclassical transport in a tokamak edge including the effects of a strong radial electric field. The results of numerical simulations are found to be in goodmore » qualitative agreement with the theoretical predictions and the quantitative discrepancy is discussed. In addition, the present work investigates the effects of a strong radial electric field on the relaxation of geodesic acoustic modes (GAMs) in a tokamak edge. Numerical simulations demonstrate that the presence of a strong radial electric field characteristic of a tokamak pedestal can enhance the GAM decay rate, and heuristic arguments elucidating this finding are provided.« less

  15. Numerical modelling of geodesic acoustic mode relaxation in a tokamak edge

    SciTech Connect

    Dorf, M. A.; Cohen, R. H.; Dorr, M.; Rognlien, T.; Hittinger, J.; Compton, J.; Colella, P.; Martin, D.; McCorquodale, P.

    2013-05-08

    Here, the edge of a tokamak in a high confinement (H mode) regime is characterized by steep density gradients and a large radial electric field. Recent analytical studies demonstrated that the presence of a strong radial electric field consistent with a subsonic pedestal equilibrium modifies the conventional results of the neoclassical formalism developed for the core region. In the present work we make use of the recently developed gyrokinetic code COGENT to numerically investigate neoclassical transport in a tokamak edge including the effects of a strong radial electric field. The results of numerical simulations are found to be in good qualitative agreement with the theoretical predictions and the quantitative discrepancy is discussed. In addition, the present work investigates the effects of a strong radial electric field on the relaxation of geodesic acoustic modes (GAMs) in a tokamak edge. Numerical simulations demonstrate that the presence of a strong radial electric field characteristic of a tokamak pedestal can enhance the GAM decay rate, and heuristic arguments elucidating this finding are provided.

  16. Energetic-particle-induced electromagnetic geodesic acoustic mode in tokamak plasmas

    SciTech Connect

    Wang, Lingfeng He, Zhixiong; He, Hongda; Shen, Y.; Dong, J. Q.

    2014-07-15

    Energetic-particle-induced kinetic electromagnetic geodesic acoustic modes (EKEGAMs) are numerically studied in low β (=plasma pressure/magnetic pressure) tokamak plasmas. The parallel component of the perturbed vector potential is considered along with the electrostatic potential perturbation. The effects of finite Larmor radius and finite orbit width of the bulk and energetic ions as well as electron parallel dynamics are all taken into account in the dispersion relation. Systematic harmonic and ordering analysis are performed for frequency and growth rate spectra of the EKEGAMs, assuming (kρ{sub i})∼q{sup −3}∼β≪1, where q, k, and ρ{sub i} are the safety factor, radial component of the EKEGAMs wave vector, and the Larmor radius of the ions, respectively. It is found that there exist critical β{sub h}/β{sub i} values, which depend, in particular, on pitch angle of energetic ions and safety factor, for the mode to be driven unstable. The EKEGAMs may also be unstable for pitch angle λ{sub 0}B<0.4 in certain parameter regions. Finite β effect of the bulk ions is shown to have damping effect on the EKEGAMs. Modes with higher radial wave vectors have higher growth rates. The damping from electron dynamics is found decreasing with decrease of the temperature ratio T{sub e}/T{sub i}. The modes are easily to be driven unstable in low safety factor q region and high temperature ratio T{sub h}/T{sub i} region. The harmonic features of the EKEGAMs are discussed as well.

  17. Role of the geodesic acoustic mode shearing feedback loop in transport bifurcations and turbulence spreading

    SciTech Connect

    Miki, K.; Diamond, P. H.

    2010-03-15

    A theory of the effect of the geodesic acoustic mode (GAM) on turbulence is presented. Two synergistic issues are elucidated: namely, the physics of the zonal flow modulation and its role in the L-H transition, and the role of the GAM wave group propagation in turbulence spreading. Using a wavekinetic modulational analysis, the response of the turbulence intensity field to the GAM is calculated. This analysis differs from previous studies of zero-frequency zonal flows since it accounts for resonance between the drift wave group speed and the GAM strain field, which induces secularity. This mechanism is referred to as secular stochastic shearing. Finite real frequency and radial group velocity are intrinsic to the GAM, so its propagation can induce nonlocal phenomena at the edge and pedestal regions. To understand the effect of the GAM on turbulence and transition dynamics, a predator-prey model incorporating the dynamics of both turbulence and the GAMs is constructed and analyzed for stability around fixed points. Three possible states are identified, namely, an L-modelike stationary state, a reduced turbulence state, and a GAM limit-cycle state. The system is attracted to the state with the minimum turbulence level.

  18. Dynamics of turbulent transport dominated by the geodesic acoustic mode near the critical gradient regime

    SciTech Connect

    Miki, Kazuhiro; Kishimoto, Yasuaki; Li, Jiquan; Miyato, Naoaki

    2008-05-15

    The effects of geodesic acoustic modes (GAMs) on the toroidal ion temperature gradient turbulence and associated transport near the critical gradient regime in tokamak plasma are investigated based on global Landau-fluid simulations and extended predator-prey modeling analyses. A new type of intermittent dynamics of transport accompanied with the emission and propagation of the GAMs, i.e., GAM intermittency [K. Miki et al., Phys. Rev. Lett. 99, 145003 (2007)], has been found. The intermittent bursts are triggered by the onset of spatially propagating GAMs when the turbulent energy exceeds a critical value. The GAMs suffer collisionless damping during the propagation and nonlocally transfer local turbulence energy to wide radial region. The stationary zonal flows gradually increase due to the accumulation of non-damped residual part over many periods of quasi-periodic intermittent bursts and eventually quench the turbulence, leading to a nonlinear upshift of the linear critical gradient; namely, the Dimits shift. This process is categorized as a new class of transient dynamics, referred to as growing intermittency. The Dimits shift is found to be established through this dynamical process. An extended minimal predator-prey model with collisionless damping of the GAMs is proposed, which qualitatively reproduce the main features of the growing intermittency and approximately predict its various time scales observed in the simulations.

  19. Three dimensional measurements of Geodesic Acoustic Mode with correlation Doppler reflectometers

    NASA Astrophysics Data System (ADS)

    Zhong, W. L.; Shi, Z. B.; Xu, Y.; Zou, X. L.; Duan, X. R.; Chen, W.; Jiang, M.; Yang, Z. C.; Zhang, B. Y.; Shi, P. W.; Liu, Z. T.; Xu, M.; Song, X. M.; Cheng, J.; Ke, R.; Nie, L.; Cui, Z. Y.; Fu, B. Z.; Ding, X. T.; Dong, J. Q.; Liu, Yi.; Yan, L. W.; Yang, Q. W.; Liu, Yong; the HL-2A Team

    2015-10-01

    Correlation Doppler reflectometers have been newly developed in the HL-2A Tokamak. Owing to the flexibility of the diagnostic arrangements, the multi-channel systems allow us to study, simultaneously, the radial properties of edge turbulence and its long-range correlation in both the poloidal and toroidal direction. With these reflectometers, three-dimensional spatial structure of Geodesic Acoustic Mode (GAM) is surveyed, including the symmetric feature of Er fluctuations in both poloidal and toroidal directions, and the radial propagation of GAMs. The bi-coherence analysis for the Er fluctuations suggests that the three-wave nonlinear interaction could be the mechanism for the generation of GAM. The temporal evolution of GAM during the plasma density modulation experiments has been studied. The results show that the collisional damping plays a role in suppressing the GAM magnitudes, and hence, weakening the regulating effects of GAM on ambient turbulence. Three dimensional correlation Doppler measurements of GAM activity demonstrate that the newly developed correlation Doppler reflectometers in HL-2A are powerful tools for edge turbulence studies with high reliability. A shorter version of this contribution is due to be published in PoS at: ``1st EPS conference on Plasma Diagnostics''.

  20. Energetic particle driven geodesic acoustic mode in a toroidally rotating tokamak plasma

    NASA Astrophysics Data System (ADS)

    Ren, Haijun

    2017-01-01

    Energetic particle (EP) driven geodesic acoustic modes (EGAMs) in toroidally rotating tokamak plasmas are analytically investigated using the hybrid kinetic-fluid model and gyrokinetic equations. By ignoring high-order terms and ion Landau damping, the kinetic dispersion relation is reduced to the hybrid one in the large safety factor limit. There is one high-frequency branch with a frequency larger than {ωt0} , the transit frequency of EPs with initial energy, which is always stable. Two low-frequency solutions with a frequency smaller than {ωt0} are complex conjugates in the hybrid limit. In the presence of ion Landau damping, the growth rate of the unstable branch is decreased and the damping rate of the damped branch is increased. The toroidal Mach number is shown to increase {{ Ω }\\text{r}} , the normalized real frequency of both branches. Although not affecting the instability critical condition, the Mach number decreases the growth rate when {{ Ω }\\text{r}} is larger than a critical value Ω \\text{r}\\text{cri} and enlarges the growth rate when {{ Ω }\\text{r}}< Ω \\text{r}\\text{cri} . The ion Landau damping effect is negligible for large M. But the discrepancy between the kinetic dispersion relation and the hybrid one becomes ignorable only for q≳ 7 .

  1. Fully Nonlinear Edge Gyrokinetic Simulations of Kinetic Geodesic-Acoustic Modes and Boundary Flows

    SciTech Connect

    Xu, X Q; Belli, E; Bodi, K; Candy, J; Chang, C S; Cohen, B I; Cohen, R H; Colella, P; Dimits, A M; Dorr, M R; Gao, Z; Hittinger, J A; Ko, S; Krasheninnikov, S; McKee, G R; Nevins, W M; Rognlien, T D; Snyder, P B; Suh, J; Umansky, M V

    2008-09-18

    We present edge gyrokinetic neoclassical simulations of tokamak plasmas using the fully nonlinear (full-f) continuum code TEMPEST. A nonlinear Boltzmann model is used for the electrons. The electric field is obtained by solving the 2D gyrokinetic Poisson Equation. We demonstrate the following: (1) High harmonic resonances (n > 2) significantly enhance geodesic-acoustic mode (GAM) damping at high-q (tokamak safety factor), and are necessary to explain both the damping observed in our TEMPEST q-scans and experimental measurements of the scaling of the GAM amplitude with edge q{sub 95} in the absence of obvious evidence that there is a strong q dependence of the turbulent drive and damping of the GAM. (2) The kinetic GAM exists in the edge for steep density and temperature gradients in the form of outgoing waves, its radial scale is set by the ion temperature profile, and ion temperature inhomogeneity is necessary for GAM radial propagation. (3) The development of the neoclassical electric field evolves through different phases of relaxation, including GAMs, their radial propagation, and their long-time collisional decay. (4) Natural consequences of orbits in the pedestal and scrape-off layer region in divertor geometry are substantial non-Maxwellian ion distributions and flow characteristics qualitatively like those observed in experiments.

  2. Geodesic acoustic modes in toroidally rotating tokamaks with an arbitrary β

    SciTech Connect

    Ren, Haijun; Li, Ding; Chu, Paul K

    2013-07-15

    Theoretical research on the geodesic acoustic mode (GAM) induced by the equilibrium toroidal rotation flow (ETRF) in the tokamak plasmas with an arbitrary β is performed by using the ideal magnetohydrodynamic model, where β is the ratio of the plasma pressure and magnetic field pressure. Two equations determining the poloidal displacement ξ{sub θ} and the divergence of the Lagrangian perturbation are obtained and suitable for arbitrary cross-section tokamaks with large-aspect-ratios. The dispersion relations are then derived for two different coupling patterns by assuming ξ{sub ±2}=0 and ξ{sub ±4}=0, respectively, where ξ{sub m}=(1/2π)∫ξ{sub θ}e{sup imθ}dθ with θ being the poloidal angle under the circular cross-section condition. In both patterns, the ETRF will increase the frequencies of the GAMs but β can decrease them. The GAM for ξ{sub ±2}=0 has a larger frequency than GAM for ξ{sub ±4}=0.

  3. Exciting and propagating characteristics of two coexisting kinetic geodesic acoustic modes in the edge of plasma

    NASA Astrophysics Data System (ADS)

    Kong, D. F.; Liu, A. D.; Lan, T.; Yu, C. X.; Cheng, J.; Qiu, Z. Y.; Zhao, H. L.; Shen, H. G.; Yan, L. W.; Dong, J. Q.; Xu, M.; Zhao, K. J.; Duan, X. R.; Liu, Y.; Chen, R.; Zhang, S. B.; Sun, X.; Xie, J. L.; Li, H.; Liu, W. D.

    2017-04-01

    Coexisting dual kinetic geodesic acoustic modes (KGAMs) with similar characteristics have been observed with Langmuir probe arrays in the edge plasma of HL-2A tokamak with low density Ohmic discharge. The dual KGAMs are named a low-frequency GAM (LFGAM) and a high-frequency GAM (HFGAM), respectively. By changing the line averaged density from 1.0× {{10}19}~{{\\text{m}}-3} to 0.7× {{10}19}~{{\\text{m}}-3} , the study of n e and T e profiles indicate that collision damping rate plays a crucial role on exciting of dual KGAMs, especially for the higher frequency branch (HFGAM). With the application of modulating techniques, we provide direct proof that nonlinear interactions between GAMs and ambient turbulence (AT) show great difference at different radial positions. At the exciting position of GAM, the amplitude modulation of AT is dominant, indicating that GAM is generated in the energy-conserving triad interaction. After the exciting of GAMs, they will propagate both inward and outward. During the propagation, the phase modulation of AT is dominant, GAMs can rarely gain energy from AT, yet they can give back-reactions on AT through shearing effect.

  4. Observation of subcritical geodesic acoustic mode excitation in the large helical device

    NASA Astrophysics Data System (ADS)

    Ido, T.; Itoh, K.; Lesur, M.; Osakabe, M.; Shimizu, A.; Ogawa, K.; Nishiura, M.; Yamada, I.; Yasuhara, R.; Kosuga, Y.; Sasaki, M.; Ida, K.; Inagaki, S.; Itoh, S.-I.; the LHD Experiment Group

    2017-07-01

    The abrupt and strong excitation of the geodesic acoustic mode (GAM) has been found in the large helical device (LHD), when the frequency of a chirping energetic particle-driven GAM (EGAM) approaches twice that of the GAM frequency. The temporal evolution of the phase relation between the abrupt GAM and the chirping EGAM is common in all events. The result indicates a coupling between the GAM and the EGAM. In addition, the nonlinear evolution of the growth rate of the GAM is observed, and there is a threshold in the amplitude of the GAM for the appearance of nonlinear behavior. A threshold in the amplitude of the EGAM for the abrupt excitation of the GAM is also observed. According to one theory (Lesur et al 2016 Phys. Rev. Lett. 116 015003, Itoh et al 2016 Plasma Phys. Rep. 42 418) the observed abrupt phenomenon can be interpreted as the excitation of the subcritical instability of the GAM. The excitation of a subcritical instability requires a trigger and a seed with sufficient amplitude. The observed threshold in the amplitude of the GAM seems to correspond with the threshold in the seed, and the threshold in the amplitude of the EGAM seems to correspond with the threshold in the magnitude of the trigger. Thus, the observed threshold supports the interpretation that the abrupt phenomenon is the excitation of a subcritical instability of the GAM.

  5. Frequencies of the geodesic acoustic mode and Alfvén gap modes in high-q{sup 2}β plasmas with non-circular cross section

    SciTech Connect

    Fesenyuk, O. P.; Kolesnichenko, Ya. I.; Yakovenko, Yu. V.

    2013-12-15

    This work generalizes recent results [O. P. Fesenyuk et al., Plasma Phys. Controlled Fusion 54, 085014 (2012)] to plasmas with elongated cross section. It suggests new expressions for the frequencies of the geodesic acoustic mode and Alfvén gap modes in tokamaks, with a large ratio of the plasma pressure to the magnetic field pressure and a large safety factor (q≫1, which takes place in discharges with reversed-shear configuration and, especially, in hollow-current discharges)

  6. Multi-field characteristics and eigenmode spatial structure of geodesic acoustic modes in DIII-D L-mode plasmas

    SciTech Connect

    Wang, G.; Peebles, W. A.; Rhodes, T. L.; Doyle, E. J.; Hillesheim, J. C.; Schmitz, L.; Zeng, L.; Austin, M. E.; Yan, Z.; McKee, G. R.; La Haye, R. J.; Burrell, K. H.; Lanctot, M. J.; Petty, C. C.; Smith, S.; Strait, E. J.; Van Zeeland, M.; Nazikian, R.

    2013-09-15

    The geodesic acoustic mode (GAM), a coherent form of the zonal flow, plays a critical role in turbulence regulation and cross-magnetic-field transport. In the DIII-D tokamak, unique information on multi-field characteristics and radial structure of eigenmode GAMs has been measured. Two simultaneous and distinct, radially overlapping eigenmode GAMs (i.e., constant frequency vs. radius) have been observed in the poloidal E×B flow in L-mode plasmas. As the plasma transitions from an L-mode to an Ohmic regime, one of these eigenmode GAMs becomes a continuum GAM (frequency responds to local parameters), while the second decays below the noise level. The eigenmode GAMs occupy a radial range of ρ = 0.6–0.8 and 0.75–0.95, respectively. In addition, oscillations at the GAM frequency are observed for the first time in multiple plasma parameters, including n{sub e}, T{sub e}, and B{sub θ}. The magnitude of T(tilde sign){sub e}/T{sub e} at the GAM frequency (the magnitude is similar to that of ñ{sub e}/n{sub e}) and measured n{sub e}–T{sub e} cross-phase (∼140° at the GAM frequency) together indicate that the GAM pressure perturbation is not determined solely by ñ{sub e}. The magnetic GAM behavior, a feature only rarely reported, is significantly stronger (×18) on the high-field side of the tokamak, suggesting an anti-ballooning nature. Finally, the GAM is also observed to directly modify intermediate-wavenumber ñ{sub e} levels (kρ{sub s} ∼ 1.1). The simultaneous temperature, density, flow fluctuations, density-temperature cross-phase, and magnetic behavior present a new perspective on the underlying physics of the GAM.

  7. Plasma potential and geodesic acoustic mode evolution with Helium puffing in the ECRH regime on the T-10 tokamak

    NASA Astrophysics Data System (ADS)

    Zenin, V. N.; Subbotin, G. F.; Klyuchnikov, L. A.; Melnikov, A. V.

    2016-09-01

    The evolution of the Geodesic Acoustic Mode (GAM) and mean plasma electric potential were examined in the regime with short (5 ms) Helium puffing into Electron Cyclotron Resonance heated discharge of the T-10 tokamak. It was shown that a Helium pulse leads to temporal perturbation of the plasma electron temperature and density and concomitant evolution of the mean potential, happening in the diffusive time-scale ∼⃒ 30 ms. Afterwards, the potential restores to the new stationary level with the same time-scale. On top of that GAM amplitude reduces sharply (within 2-5 ms) and GAM frequency also decreases within 30 ms after Helium puffing. Afterwards GAM amplitude and frequency relax to a new stationary level within about 50-70 ms. The evolution of electron density, electron and ion temperatures, total stored energy and plasma density turbulence is discussed in order to clarify their links with potential and GAM evolution.

  8. Cross-code gyrokinetic verification and benchmark on the linear collisionless dynamics of the geodesic acoustic mode

    NASA Astrophysics Data System (ADS)

    Biancalani, A.; Bottino, A.; Ehrlacher, C.; Grandgirard, V.; Merlo, G.; Novikau, I.; Qiu, Z.; Sonnendrücker, E.; Garbet, X.; Görler, T.; Leerink, S.; Palermo, F.; Zarzoso, D.

    2017-06-01

    The linear properties of the geodesic acoustic modes (GAMs) in tokamaks are investigated by means of the comparison of analytical theory and gyrokinetic numerical simulations. The dependence on the value of the safety factor, finite-orbit-width of the ions in relation to the radial mode width, magnetic-flux-surface shaping, and electron/ion mass ratio are considered. Nonuniformities in the plasma profiles (such as density, temperature, and safety factor), electro-magnetic effects, collisions, and the presence of minority species are neglected. Also, only linear simulations are considered, focusing on the local dynamics. We use three different gyrokinetic codes: the Lagrangian (particle-in-cell) code ORB5, the Eulerian code GENE, and semi-Lagrangian code GYSELA. One of the main aims of this paper is to provide a detailed comparison of the numerical results and analytical theory, in the regimes where this is possible. This helps understanding better the behavior of the linear GAM dynamics in these different regimes, the behavior of the codes, which is crucial in the view of a future work where more physics is present, and the regimes of validity of each specific analytical dispersion relation.

  9. MHD-model for low-frequency waves in a tokamak with toroidal plasma rotation and problem of existence of global geodesic acoustic modes

    SciTech Connect

    Lakhin, V. P.; Sorokina, E. A. E-mail: vilkiae@gmail.com; Ilgisonis, V. I.; Konovaltseva, L. V.

    2015-12-15

    A set of reduced linear equations for the description of low-frequency perturbations in toroidally rotating plasma in axisymmetric tokamak is derived in the framework of ideal magnetohydrodynamics. The model suitable for the study of global geodesic acoustic modes (GGAMs) is designed. An example of the use of the developed model for derivation of the integral conditions for GGAM existence and of the corresponding dispersion relation is presented. The paper is dedicated to the memory of academician V.D. Shafranov.

  10. Geodesic acoustic modes in a fluid model of tokamak plasma: the effects of finite beta and collisionality

    NASA Astrophysics Data System (ADS)

    Singh, Rameswar; Storelli, A.; Gürcan, Ö. D.; Hennequin, P.; Vermare, L.; Morel, P.; Singh, R.

    2015-12-01

    Starting from the Braginskii equations, relevant for the tokamak edge region, a complete set of nonlinear equations for the geodesic acoustic modes (GAM) has been derived which includes collisionality, plasma beta and external sources of particle, momentum and heat. Local linear analysis shows that the GAM frequency increases with collisionality at low radial wave number {{k}\\text{r}} and decreases at high {{k}\\text{r}} . GAM frequency also decreases with plasma beta. Radial profiles of GAM frequency for two Tore Supra shots, which were part of a collisionality scan, are compared with these calculations. A discrepancy between experiment and theory is observed, which seems to be explained by a finite {{k}\\text{r}} for the GAM when flux surface averaged density < n> and temperature < T> are assumed to vanish. It is shown that this agreement is incidental and self-consistent inclusion of < n> and < T> responses enhances the disagreement more with {{k}\\text{r}} at high {{k}\\text{r}} . So the discrepancy between the linear GAM calculation and experiment, (which also persist for more ‘complete’ linear models such as gyrokinetics) can probably not be resolved by simply adding a finite {{k}\\text{r}} .

  11. Experimental investigation of geodesic acoustic mode spatial structure, intermittency, and interaction with turbulence in the DIII-D tokamak

    NASA Astrophysics Data System (ADS)

    Hillesheim, J. C.; Peebles, W. A.; Carter, T. A.; Schmitz, L.; Rhodes, T. L.

    2012-02-01

    Geodesic acoustic modes (GAMs) and zonal flows are nonlinearly driven, axisymmetric (m=0andn=0) E ×B flows, which are thought to play an important role in establishing the saturated level of turbulence in tokamaks. Results are presented showing the GAM's observed spatial scales, temporal scales, and nonlinear interaction characteristics, which may have implications for the assumptions underpinning turbulence models towards the tokamak edge (r /a>rsim0.75). Measurements in the DIII-D tokamak [Luxon, Nucl. Fusion 42, 614 (2002)] have been made with multichannel Doppler backscattering systems at toroidal locations separated by 180∘; analysis reveals that the GAM is highly coherent between the toroidally separated systems (γ>0.8) and that measurements are consistent with the expected m =0andn=0 structure. Observations show that the GAM in L-mode plasmas with ~2.5-4.5 MW auxiliary heating occurs as a radially coherent eigenmode, rather than as a continuum of frequencies as occurs in lower temperature discharges; this is consistent with theoretical expectations when finite ion Larmor radius effects are included. The intermittency of the GAM has been quantified, revealing that its autocorrelation time is fairly short, ranging from about 4 to about 15 GAM periods in cases examined, a difference that is accompanied by a modification to the probability distribution function of the E ×B velocity at the GAM frequency. Conditionally-averaged bispectral analysis shows the strength of the nonlinear interaction of the GAM with broadband turbulence can vary with the magnitude of the GAM. Data also indicate a wavenumber dependence to the GAM's interaction with turbulence.

  12. News from the Geodesic Acoustic Mode: Magnetic Shear-, q-, and Geometry Effect

    NASA Astrophysics Data System (ADS)

    Hallatschek, Klaus

    2006-04-01

    The generation of GAMs has been studied in greater depth by three-dimensional turbulence simulations. A change of the magnetic shear, in particular, a switch to negative shear profoundly affects the amplification mechanics of the GAMs. Essentially, negative shear flips the symmetry of the turbulence modes with respect to the shear flows, altering the sign of the Stringer-Winsor forces. The phenomenon readily suggests an experimental test, which would quantify the role of the Stringer-Winsor effect in comparison to the Reynolds stress in exciting the GAMs. The safety factor q controls the coupling of the GAMs to the parallel velocity, i.e., sound waves. Lowering q increases this coupling. Since the parallel sound waves in turn are heavily damped by the turbulence, they act as a loss channel. Thus sufficiently low q leads to a quench of the GAM activity, as has been found in recent experiments, too. Finally, the shape of the flux surfaces has great influence on the frequency of the modes and the relative strength of the Stringer-Winsor force. Again, the results suggest a relatively straightforward comparison with experiments. In all these cases one has to carefully differentiate between changes of the turbulence brought about by the parameters, and changed properties of the GAMs and their interaction with the turbulence.

  13. Generation of geodesic acoustic mode by nonlinear coupling of magnetic island and island-driven beta-induced Alfvén eigenmode

    NASA Astrophysics Data System (ADS)

    Marchenko, V. S.; Panwar, A.; Reznik, S. N.; Ryu, C. M.

    2017-09-01

    In a recent work, we have shown that the plasma flow around the magnetic island can excite the beta-induced Alfvén eigenmode (BAE) (Marchenko et al 2016 Nucl. Fusion 56 106021). In the present communication, it is shown that coupling of this primary BAE and magnetic island generates secondary geodesic acoustic mode (GAM), which has the frequency and mode structure identical to those of the primary BAE. The fixed GAM/BAE amplitude ratio, determined by the plasma neutrality, is comparable with the plasma/magnetic pressure ratio. This nonlinear coupling can be responsible for axis-symmetric modes, which accompany island-driven Alfvénic modes observed on HL-2A tokamak (Chen et al 2013 Nucl. Fusion 53 113010).

  14. Geodesic oscillations and the weakly coherent mode in the I-mode of ASDEX Upgrade

    NASA Astrophysics Data System (ADS)

    Manz, P.; Lauber, P.; Nikolaeva, V. E.; Happel, T.; Ryter, F.; Birkenmeier, G.; Bogomolov, A.; Conway, G. D.; Manso, M. E.; Maraschek, M.; Prisiazhniuk, D.; Viezzer, E.

    2015-08-01

    Density fluctuations in I-mode discharges in ASDEX Upgrade are studied. The I-mode specific weakly coherent mode (WCM) appears at the transition from the L to I-mode. The WCM but also the turbulence in general are strongly modulated by a low frequency mode which can be related to the geodesic acoustic mode (GAM). The GAM induces an energy transfer away from the central WCM frequency, indicating an underlying instability responsible for the WCM. During the I-mode magnetic fluctuations close to the WCM frequency are intensified, which can be assigned to the geodesic Alfvénic oscillation. The geodesic Alfvénic oscillation is already present in the L-mode, and does not follow changes of frequency of the WCM, therefore it is not responsible for the WCM.

  15. Geodesic mode instability driven by electron and ion fluxes in tokamaks

    SciTech Connect

    Elfimov, A. G. Camilo de Souza, F.; Galvão, R. M. O.

    2015-11-15

    The effect of the parallel electron current and plasma flux on Geodesic Acoustic Modes (GAM) in a tokamak is analyzed by kinetic theory taking into the account the ion Landau damping and diamagnetic drifts. It is shown that the electron current and plasma flow, modeled by shifted Maxwell distributions of electrons and ions, may overcome the ion Landau damping generating the GAM instability when the parallel electron current velocity is larger than the effective parallel GAM phase velocity of sidebands, Rqω. The instability is driven by the electron current and the parallel ion flux cross term. Possible applications to tokamak experiments are discussed. The existence of the geodesic ion sound mode due to plasma flow is shown.

  16. Geodesic mode instability driven by electron and ion fluxes during neutral beam injection in tokamaks

    NASA Astrophysics Data System (ADS)

    Camilo de Souza, F.; Elfimov, A. G.; Galvão, R. M. O.; Krbec, J.; Seidl, J.; Stöckel, J.; Hron, M.; Havlicek, J.; Mitosinkova, K.

    2017-09-01

    The effect of a minor concentration of energetic particles produced by parallel NB injection on Geodesic Acoustic Modes (GAM) spectrum is analyzed using fully kinetic equation. It is found that the GAM frequency is reduced by the effective mass renormalization due to that new energetic GAM appears with higher frequency. The electron current in combination with NB driven ion flow, modeled by shifted Maxwell distribution, may overcome the ion Landau damping thus resulting in the GAM instability when electron current velocity is larger than the effective parallel GAM phase velocity Rqω. Qualitative agreement of the theory with co/counter NB injection experiments in COMPASS tokamak is demonstrated.

  17. Radial propagation of geodesic acoustic modes

    SciTech Connect

    Hager, Robert; Hallatschek, Klaus

    2009-07-15

    The GAM group velocity is estimated from the ratio of the radial free energy flux to the total free energy applying gyrokinetic and two-fluid theory. This method is much more robust than approaches that calculate the group velocity directly and can be generalized to include additional physics, e.g., magnetic geometry. The results are verified with the gyrokinetic code GYRO[J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)], the two-fluid code NLET[K. Hallatschek and A. Zeiler, Phys. Plasmas 7, 2554 (2000)], and analytical calculations. GAM propagation must be kept in mind when discussing the windows of GAM activity observed experimentally and the match between linear theory and experimental GAM frequencies.

  18. Are eikonal quasinormal modes linked to the unstable circular null geodesics?

    NASA Astrophysics Data System (ADS)

    Konoplya, R. A.; Stuchlík, Z.

    2017-08-01

    In Cardoso et al. [6] it was claimed that quasinormal modes which any stationary, spherically symmetric and asymptotically flat black hole emits in the eikonal regime are determined by the parameters of the circular null geodesic: the real and imaginary parts of the quasinormal mode are multiples of the frequency and instability timescale of the circular null geodesics respectively. We shall consider asymptotically flat black hole in the Einstein-Lovelock theory, find analytical expressions for gravitational quasinormal modes in the eikonal regime and analyze the null geodesics. Comparison of the both phenomena shows that the expected link between the null geodesics and quasinormal modes is violated in the Einstein-Lovelock theory. Nevertheless, the correspondence exists for a number of other cases and here we formulate its actual limits.

  19. Passive Mode Carbon Nanotube Underwater Acoustic Transducer

    DTIC Science & Technology

    2016-09-20

    300151 1 of 14 PASSIVE MODE CARBON NANOTUBE UNDERWATER ACOUSTIC TRANSDUCER STATEMENT OF GOVERNMENT INTEREST [0001] The invention described...0003] The present invention is an acoustically transparent carbon nanotube transducer that can operate in a passive acoustic mode for data...acoustic carbon nanotube (CNT) yarn sheets capable of producing high acoustic output at low frequencies with broad bandwidth. An underwater acoustic

  20. Acoustic mode driven by fast electrons in TJ-II Electron Cyclotron Resonance plasmas

    NASA Astrophysics Data System (ADS)

    Sun, B. J.; Ochando, M. A.; López-Bruna, D.

    2016-08-01

    Intense harmonic oscillations in radiation signals (δ I/I∼ 5{%}) are commonly observed during Electron Cyclotron Resonance (ECR) heating in TJ-II stellarator plasmas at low line-averaged electron density, 0.15 < \\bar{n}e < 0.6 ×1019 \\text{m}-3 . The frequency agrees with acoustic modes. The poloidal modal structure is compatible with Geodesic Acoustic Modes (GAM) but an n \

  1. Comment on 'Acoustic plasma modes'

    NASA Technical Reports Server (NTRS)

    Oliva, J.; Ashcroft, N. W.

    1984-01-01

    In a recent treatment of the T = 0 acoustic plasma modes of a two-component Fermi liquid with Coulomb forces, Appel and Overhauser conclude that there exist three generally damped longitudinal acoustic branches. It is observed that this conclusion results from an inapplicable analytic continuation in their solution of the transport equations. There is only one longitudinal acoustic branch, and, in fact, when applied to the standard one-component Fermi-liquid model, the method of Appel and Overhauser also leads to the incorrect conclusion that there exist two longitudinal acoustic branches.

  2. Acoustic modes in fluid networks

    NASA Technical Reports Server (NTRS)

    Michalopoulos, C. D.; Clark, Robert W., Jr.; Doiron, Harold H.

    1992-01-01

    Pressure and flow rate eigenvalue problems for one-dimensional flow of a fluid in a network of pipes are derived from the familiar transmission line equations. These equations are linearized by assuming small velocity and pressure oscillations about mean flow conditions. It is shown that the flow rate eigenvalues are the same as the pressure eigenvalues and the relationship between line pressure modes and flow rate modes is established. A volume at the end of each branch is employed which allows any combination of boundary conditions, from open to closed, to be used. The Jacobi iterative method is used to compute undamped natural frequencies and associated pressure/flow modes. Several numerical examples are presented which include acoustic modes for the Helium Supply System of the Space Shuttle Orbiter Main Propulsion System. It should be noted that the method presented herein can be applied to any one-dimensional acoustic system involving an arbitrary number of branches.

  3. Is dust acoustic wave a new plasma acoustic mode?

    NASA Astrophysics Data System (ADS)

    Dwivedi, C. B.

    1997-09-01

    In this Brief Communication, the claim of the novelty of the dust acoustic wave in a dusty plasma within the constant dust charge model is questioned. Conceptual lacunas behind the claim have been highlighted and appropriate physical arguments have been forwarded against the claim. It is demonstrated that the so-called dust acoustic wave could better be termed as a general acoustic fluctuation response with a dominant characteristic feature of the acoustic-like mode (ALM) fluctuation response reported by Dwivedi et al. [J. Plasma Phys. 41, 219 (1989)]. It is suggested that both correct and more usable nomenclature of the ALM should be the so-called acoustic mode.

  4. Theory of Acoustic Raman Modes in Proteins

    NASA Astrophysics Data System (ADS)

    DeWolf, Timothy; Gordon, Reuven

    2016-09-01

    We present a theoretical analysis that associates the resonances of extraordinary acoustic Raman (EAR) spectroscopy [Wheaton et al., Nat. Photonics 9, 68 (2015)] with the collective modes of proteins. The theory uses the anisotropic elastic network model to find the protein acoustic modes, and calculates Raman intensity by treating the protein as a polarizable ellipsoid. Reasonable agreement is found between EAR spectra and our theory. Protein acoustic modes have been extensively studied theoretically to assess the role they play in protein function; this result suggests EAR spectroscopy as a new experimental tool for studies of protein acoustic modes.

  5. Empirical mode decomposition for analyzing acoustical signals

    NASA Technical Reports Server (NTRS)

    Huang, Norden E. (Inventor)

    2005-01-01

    The present invention discloses a computer implemented signal analysis method through the Hilbert-Huang Transformation (HHT) for analyzing acoustical signals, which are assumed to be nonlinear and nonstationary. The Empirical Decomposition Method (EMD) and the Hilbert Spectral Analysis (HSA) are used to obtain the HHT. Essentially, the acoustical signal will be decomposed into the Intrinsic Mode Function Components (IMFs). Once the invention decomposes the acoustic signal into its constituting components, all operations such as analyzing, identifying, and removing unwanted signals can be performed on these components. Upon transforming the IMFs into Hilbert spectrum, the acoustical signal may be compared with other acoustical signals.

  6. Is dust acoustic wave a new plasma acoustic mode?

    SciTech Connect

    Dwivedi, C.B.

    1997-09-01

    In this Brief Communication, the claim of the novelty of the dust acoustic wave in a dusty plasma within the constant dust charge model is questioned. Conceptual lacunas behind the claim have been highlighted and appropriate physical arguments have been forwarded against the claim. It is demonstrated that the so-called dust acoustic wave could better be termed as a general acoustic fluctuation response with a dominant characteristic feature of the acoustic-like mode (ALM) fluctuation response reported by Dwivedi {ital et al.} [J. Plasma Phys. {bold 41}, 219 (1989)]. It is suggested that both correct and more usable nomenclature of the ALM should be the so-called acoustic mode. {copyright} {ital 1997 American Institute of Physics.}

  7. Rotating Microphone Rake Measures Spinning Acoustic Modes

    NASA Technical Reports Server (NTRS)

    Konno, Kevin E.; Hausmann, Clifford R.

    1996-01-01

    Rotating rake of pressure transducers developed for use in experimental studies of sources and propagation of noise generated by subsonic fan engines. Pressure transducers used as microphones to measure acoustic modes generated by, and spin with, fans. Versatility of control software used in rake-drive system enables measurements of acoustic modes on wide range of test-engine configurations. Rake-drive hardware easily adapted to different engines because not mechanically coupled to engine under test.

  8. Drift and geodesic effects on the ion sound eigenmode in tokamak plasmas

    SciTech Connect

    Elfimov, A. G.; Smolyakov, A. I.; Melnikov, A. V.; Galvão, R. M. O.

    2016-05-15

    A kinetic treatment of geodesic acoustic modes (GAMs), taking into account ion parallel dynamics, drift and the second poloidal harmonic effects is presented. It is shown that first and second harmonics of the ion sound modes, which have respectively positive and negative radial dispersion, can be coupled due to the geodesic and drift effects. This coupling results in the drift geodesic ion sound eigenmode with a frequency below the standard GAM continuum frequency. Such eigenmode may be able to explain the split modes observed in some experiments.

  9. Ion Acoustic Modes in Warm Dense Matter

    NASA Astrophysics Data System (ADS)

    Hartley, Nicholas; Monaco, Guilio; White, Thomas; Gregori, Gianluca; Graham, Peter; Fletcher, Luke; Appel, Karen; Tschentscher, Thomas; Lee, Hae Ja; Nagler, Bob; Galtier, Eric; Granados, Eduardo; Heimann, Philip; Zastrau, Ulf; Doeppner, Tilo; Gericke, Dirk; Lepape, Sebastien; Ma, Tammy; Pak, Art; Schropp, Andreas; Glenzer, Siegfried; Hastings, Jerry

    2015-06-01

    We present results that, for the first time, show scattering from ion acoustic modes in warm dense matter, representing an unprecedented level of energy resolution in the study of dense plasmas. The experiment was carried out at the LCLS facility in California on an aluminum sample at 7 g/cc and 5 eV. Using an X-ray probe at 8 keV, shifted peaks at +/-150 meV were observed. Although the energy shifts from interactions with the acoustic waves agree with predicted values from DFT-MD models, a central (elastic) peak was also observed, which did not appear in modelled spectra and may be due to the finite timescale of the simulation. Data fitting with a hydrodynamic form has proved able to match the observed spectrum, and provide measurements of some thermodynamic properties of the system, which mostly agree with predicted values. Suggest for further experiments to determine the cause of the disparity are also given.

  10. Contour mode resonators with acoustic reflectors

    DOEpatents

    Olsson, Roy H.; Fleming, James G.; Tuck, Melanie R.

    2008-06-10

    A microelectromechanical (MEM) resonator is disclosed which has a linear or ring-shaped acoustic resonator suspended above a substrate by an acoustic reflector. The acoustic resonator can be formed with a piezoelectric material (e.g. aluminum nitride, zinc oxide or PZT), or using an electrostatically-actuated material. The acoustic reflector (also termed an acoustic mirror) uses alternating sections of a relatively low acoustic impedance Z.sub.L material and a relatively high acoustic impedance Z.sub.H material to isolate the acoustic resonator from the substrate. The MEM resonator, which can be formed on a silicon substrate with conventional CMOS circuitry, has applications for forming oscillators, rf filters, and acoustic sensors.

  11. Acoustic mode vibrational anharmonicity of hexahelometallate crystals

    NASA Astrophysics Data System (ADS)

    Jain, Sanjeev Kumar; Goyal, R. P.; Gupta, B. R. K.

    1992-11-01

    The vibrational anharmonicity and Grüneisen parameters of hexahelometallate A 2MX 6 single crystals have been determined theoretically by making use of phonon lattice theory. The potential model employed to calculate these properties consists of long range coulomb, three body interactions, short range overlap repulsion effective upto the nearest neighbour ions and phonon-lattice interactions. These antifluorite structure compounds contain large MX 2-6- ions and as the interionic spacings are much greater than those of the alkaline-earth fluorite structure halides, their elastic constants are correspondingly smaller. The hydrostatic pressure derivatives of the second order elastic constants (SOEC) calculated for K 2SnCl 6, K 2ReCl 6, (NH 4) 2SnCl 6, (NH 4) 2TeCl 6, (NH 4) 2SnBr 6, and (NH 4) 2TeBr 6, are found to be positive and close to the experimental values. The vibrational anharmonicities of the long-wavelength modes are explained in terms of the acoustic mode Grüneisen parameters.

  12. Matching Impedances and Modes in Acoustic Levitation

    NASA Technical Reports Server (NTRS)

    Barmatz, M. B.

    1985-01-01

    Temperature differences accommodated with tunable coupler. Report discusses schemes for coupling sound efficiently from cool outside atmosphere into hot acoustic-levitation chamber. Theoretical studies have practical implications for material-processing systems that employ acoustic levitation.

  13. Matching Impedances and Modes in Acoustic Levitation

    NASA Technical Reports Server (NTRS)

    Barmatz, M. B.

    1985-01-01

    Temperature differences accommodated with tunable coupler. Report discusses schemes for coupling sound efficiently from cool outside atmosphere into hot acoustic-levitation chamber. Theoretical studies have practical implications for material-processing systems that employ acoustic levitation.

  14. Soft acoustic mode in ferroelastic BiVO4

    NASA Astrophysics Data System (ADS)

    Benyuan, Gu; Copic, M.; Cummins, H. Z.

    1981-10-01

    Brillouin scattering spectroscopy of bismuth vanadate has revealed a soft acoustic mode which is characteristic of a proper ferroelastic phase transition. Raman scattering has revealed an optic mode which is doubly degenerate Eg in the paraelastic phase and splits into two Bg modes in the ferroelastic phase. The temperature dependence of the splitting is also consistent with a proper ferroelastic transition.

  15. Dust Acoustic Mode Manifestations in Earth's Dusty Ionosphere

    SciTech Connect

    Kopnin, S.I.; Popel, S.I.

    2005-10-31

    Dust acoustic mode manifestations in the dusty ionosphere are studied. The reason for an appearance of the low-frequency radio noises associated with such meteor fluxes as Perseids, Orionids, Leonids, and Gemenids is determined.

  16. TEMPEST Simulations of Collisionless Damping of Geodesic-Acoustic Mode in Edge Plasma Pedestal

    SciTech Connect

    Xu, X Q; Xiong, Z; Nevins, W M; McKee, G R

    2007-05-30

    The fully nonlinear (full-f) 4D TEMPEST gyrokinetic continuum code produces frequency, collisionless damping of GAM and zonal flow with fully nonlinear Boltzmann electrons for the inverse aspect ratio {epsilon}-scan and the tokamak safety factor q-scan in homogeneous plasmas. The TEMPEST simulation shows that GAM exists in edge plasma pedestal for steep density and temperature gradients, and an initial GAM relaxes to the standard neoclassical residual, rather than Rosenbluth-Hinton residual due to the presence of ion-ion collisions. The enhanced GAM damping explains experimental BES measurements on the edge q scaling of the GAM amplitude.

  17. Microwave-Field Driven Acoustic Modes in Selected DNA Molecules

    NASA Astrophysics Data System (ADS)

    Edwards, Glenn Steven

    The direct coupling of a microwave field to selected DNA molecules is demonstrated using standard dielectrometry. The absorption is resonant with a typical lifetime of 300 picoseconds. Such a long lifetime is unexpected for DNA in aqueous solution at room temperature and has interesting implications for microscopic considerations in future models of solvent damping. Resonant absorption at fundamental and harmonic frequencies for both supercoiled circular and linear DNA agrees with an acoustic mode model. Our associated acoustic velocities for linear DNA are very close to the acoustic velocity of the longitudinal acoustic mode independently observed on DNA fibers using Brillouin Spectroscopy. The difference in acoustic velocities for supercoiled circular and linear DNA is discussed in terms of a conformation dependent model. *This research has been funded by the Office of Naval Research, the Center for Devices and Radiological Health, and the National Science Foundation.

  18. Acoustic whispering gallery modes within the theory of elasticity

    NASA Astrophysics Data System (ADS)

    Sturman, Boris; Breunig, Ingo

    2015-07-01

    Investigations of nonlinear phenomena in optical whispering gallery mode (WGM) microresonators are booming because of rich physics and applications. Stimulated Brillouin scattering is one of the strongest processes in these devices. Here, the optical WGMs interact with acoustic counterparts. The acoustic WGMs are well known for resonators based on liquids and gases, where the sound waves are longitudinal. The situation with solid-state resonators is different because of the presence of the longitudinal (l) and transverse (t) sound waves with substantially different velocities v l , t . Moreover, the l- and t-parts of the acoustic displacement are coupled at the resonator surface breaking the separation of modes into longitudinal and transverse. Investigation of the acoustic WGMs is of high priority. Here, analytically and numerically we investigate the resonant frequencies and the eigenfunctions (displacement vector distributions) for acoustic WGMs in microresonators made of isotropic solid-state materials. Cylindrical and spherical resonators are considered. Each mode has the azimuth, radial, and orbital (for sphere) numbers m, q, and ℓ; its properties are controlled also by the ratio v l / v t . All modes are either transverse (t) or hybrid transverse-longitudinal (tl). Pure l-modes, providing the strongest interaction with optical modes in fibers and bulk crystals, are absent. The tl-modes include distorted Rayleigh waves, the modes with q ˜ 1 and dominating t-part, and pseudo-longitudinal modes with q ≫ 1 , closely spaced frequencies, and weakly localized t-part. They have no analogies to the optical WGMs and are of high relevance for Brillouin lasing in optical microresonators. The actual values of ℓ and m are 10 2 - 10 5 , and the lasing thresholds lie in the μW range. Our findings include exact dispersion equations for acoustic WGMs, which can be solved numerically for ℓ , m ≲ 10 4 , asymptotic tools for ℓ , m ≳ 10 3 , and particular

  19. Perturbations From Ducts on the Modes of Acoustic Thermometers

    PubMed Central

    Gillis, K. A.; Lin, H.; Moldover, M. R.

    2009-01-01

    We examine the perturbations of the modes of an acoustic thermometer caused by circular ducts used either for gas flow or as acoustic waveguides coupled to remote transducers. We calculate the acoustic admittance of circular ducts using a model based on transmission line theory. The admittance is used to calculate the perturbations to the resonance frequencies and half-widths of the modes of spherical and cylindrical acoustic resonators as functions of the duct’s radius, length, and the locations of the transducers along the duct's length. To verify the model, we measured the complex acoustic admittances of a series of circular tubes as a function of length between 200 Hz and 10 kHz using a three-port acoustic coupler. The absolute magnitude of the specific acoustic admittance is approximately one. For a 1.4 mm inside-diameter, 1.4 m long tube, the root mean square difference between the measured and modeled specific admittances (both real and imaginary parts) over this frequency range was 0.018. We conclude by presenting design considerations for ducts connected to acoustic thermometers. PMID:27504227

  20. Acoustic mode in numerical calculations of subsonic combustion

    SciTech Connect

    O'Rourke, P.J.

    1984-01-01

    A review is given of the methods for treating the acoustic mode in numerical calculations of subsonic combustion. In numerical calculations of subsonic combustion, treatment of the acoustic mode has been a problem for many researchers. It is widely believed that Mach number and acoustic wave effects are negligible in many subsonic combustion problems. Yet, the equations that are often solved contain the acoustic mode, and many numerical techniques for solving these equations are inefficient when the Mach number is much smaller than one. This paper reviews two general approaches to ameliorating this problem. In the first approach, equations are solved that ignore acoustic waves and Mach number effects. Section II of this paper gives two such formulations which are called the Elliptic Primitive and the Stream and Potential Function formulations. We tell how these formulations are obtained and give some advantages and disadvantages of solving them numerically. In the second approach to the problem of calculating subsonic combustion, the fully compressible equations are solved by numerical methods that are efficient, but treat the acoustic mode inaccurately, in low Mach number calculations. Section III of this paper introduces two of these numerical methods in the context of an analysis of their stability properties when applied to the acoustic wave equations. These are called the ICE and acoustic subcycling methods. It is shown that even though these methods are more efficient than traditional methods for solving subsonic combustion problems, they still can be inefficient when the Mach number is very small. Finally, a method called Pressure Gradient Scaling is described that, when used in conjunction with either the ICE or acoustic subcycling methods, allows for very efficient numerical solution of subsonic combustion problems. 11 refs.

  1. Nonlinear interactions among solar acoustic modes

    NASA Technical Reports Server (NTRS)

    Kumar, Pawan; Goldreich, Peter

    1989-01-01

    The rates at which nonlinear interactions transfer energy among the normal modes of a plane-parallel, stratified atmosphere are evaluated. It is shown that every p-mode in the 5-minute band is involved in many near-resonant triplets, and, as a consequence, the energy transfer rates are independent of the mode line widths. It is also found that nonlinear mode coupling cannot limit the growth of overstable p-modes, which favors the hypothesis that the sun's p-modes are stochastically excited by turbulent convection.

  2. Variational derivation of the dispersion relation of kinetic coherent modes in the acoustic frequency range in tokamaks

    SciTech Connect

    Nguyen, C.; Garbet, X.; Smolyakov, A. I.

    2008-11-15

    In the present paper, we compare two modes with frequencies belonging to the acoustic frequency range: the geodesic acoustic mode (GAM) and the Beta Alfven eigenmode (BAE). For this, a variational gyrokinetic energy principle coupled to a Fourier sidebands expansion is developed. High order finite Larmor radius and finite orbit width effects are kept. Their impact on the mode structures and on the Alfven spectrum is calculated and discussed. We show that in a local analysis, the degeneracy of the electrostatic GAM and the BAE dispersion relations is verified to a high order and based in particular on a local poloidal symmetry of the two modes. When a more global point of view is taken, and the full radial structures of the modes are computed, differences appear. The BAE structure is shown to have an enforced localization, and to possibly connect to a large magnetohydrodynamic structure. On the contrary, the GAM is seen to have a wavelike, nonlocalized structure, as long as standard slowly varying monotonic profiles are considered.

  3. Quantitative Determination of Lateral Mode Dispersion in Film Bulk Acoustic Resonators through Laser Acoustic Imaging

    SciTech Connect

    Ken Telschow; John D. Larson III

    2006-10-01

    Film Bulk Acoustic Resonators are useful for many signal processing applications. Detailed knowledge of their operation properties are needed to optimize their design for specific applications. The finite size of these resonators precludes their use in single acoustic modes; rather, multiple wave modes, such as, lateral wave modes are always excited concurrently. In order to determine the contributions of these modes, we have been using a newly developed full-field laser acoustic imaging approach to directly measure their amplitude and phase throughout the resonator. This paper describes new results comparing modeling of both elastic and piezoelectric effects in the active material with imaging measurement of all excited modes. Fourier transformation of the acoustic amplitude and phase displacement images provides a quantitative determination of excited mode amplitude and wavenumber at any frequency. Images combined at several frequencies form a direct visualization of lateral mode excitation and dispersion for the device under test allowing mode identification and comparison with predicted operational properties. Discussion and analysis are presented for modes near the first longitudinal thickness resonance (~900 MHz) in an AlN thin film resonator. Plate wave modeling, taking account of material crystalline orientation, elastic and piezoelectric properties and overlayer metallic films, will be discussed in relation to direct image measurements.

  4. Localization of acoustic modes in periodic porous silicon structures

    PubMed Central

    2014-01-01

    The propagation of longitudinal acoustic waves in multilayer structures based on porous silicon and the experimental measurement of acoustic transmission for the structures in the gigahertz range are reported and studied theoretically. The considered structures exhibit band gaps in the transmission spectrum and these are localized modes inside the band gap, coming from defect layers introduced in periodic systems. The frequency at which the acoustic resonances appear can be tuned by changing the porosity and/or thickness of the defect layer. PMID:25206317

  5. Spinning mode acoustic radiation from the flight inlet

    NASA Technical Reports Server (NTRS)

    Moss, W. F.

    1983-01-01

    A mathematical model was developed for spinning mode acoustic radiation from a thick wall duct without flow. This model is based on a series of experiments (with and without flow). A nearly pure azimuthal spinning mode was isolated and then reflection coefficients and far field pressure (amplitude and phase) were measured. In our model the governing boundary value problem for the Helmholtz equation is first converted into an integral equation for the unknown acoustic pressure over a disk, S1, near the mouth of the duct and over the exterior surface, S2, of the duct. Assuming a pure azimuthal mode excitation, the azimuthal dependence is integrated out which yields an integral equation over the generator C1 of S1 and the generator C2 of S2. The sound pressure on C1 was approximated by a truncated modal expansion of the interior acoustic pressure. Piecewise linear spline approximation on C2 was used.

  6. On Mode Correlation of Solar Acoustic Oscillations

    NASA Astrophysics Data System (ADS)

    Chang, Heon-Young

    2009-09-01

    In helioseismology it is normally assumed that p-mode oscillations are excited in a statistically independent fashion. Unfortunately, however, this issue is not clearly settled down in that two experiments exist, which apparently look in discrepancy. That is, Appourchaux et al.~(2000) looked at bin-to-bin correlation and found no evidence that the assumption is invalid. On the other hand, Roth (2001) reported that p-mode pairs with nearby frequencies tend to be anti-correlated, possibly by a mode-coupling effect. This work is motivated by an idea that one may test if there exists an excess of anticorrelated power variations of pairs of solar p-modes. We have analyzed a 72-day MDI spherical-harmonic time series to examine temporal variations of p-mode power and their correlation. The power variation is computed by a running-window method after the previous study by Roth (2001), and then distribution function of power correlation between mode pairs is produced. We have confirmed Roth's result that there is an excess of anti-correlated p-mode pairs with nearby frequencies. On the other hand, the amount of excess was somewhat smaller than the previous study. Moreover, the distribution function does not exhibit significant change when we paired modes with non-nearby frequencies, implying that the excess is not due to mode coupling. We conclude that the origin of this excess of anticorrelations may not be a solar physical process, by pointing out the possibility of statistical bias playing the central role in producing the excess.

  7. Refraction of acoustic duct waveguide modes by exhaust jets.

    NASA Technical Reports Server (NTRS)

    Mani, R.

    1973-01-01

    The refraction of acoustic duct waveguide modes emitted from the open end of a semiinfinite rectangular duct by a jet-like exhaust flow is studied theoretically. The problem is formulated as a Wiener-Hopf problem and is ultimately solved by an approximate method due to Carrier and Koiter. Continuity of transverse acoustic particle displacement and of acoustic pressure is assumed at the jet/still-air interface. The solution exhibits several features of the acoustics of moving media such as a source convection effect, zones of relative silence, and simple refraction. Plots of far-field directivity patterns are presented for several cases and show refraction effects to be important even at modest exhaust Mach numbers of order 0.3. Only subsonic exhaust Mach numbers are considered.

  8. An Acoustic Plate Mode Sensor for Biowarfare Toxins, Phase II

    DTIC Science & Technology

    1997-10-01

    Biological agents -- such as bacteria , bacterial toxins and viruses -- must be detected rapidly to allow their neutralization or the quick treatment of...Mode Sensor for Biowarfare Toxins PRINCIPAL INVESTIGATOR: Douglas J. McAllister, Ph.D. CONTRACTING ORGANIZATION: Biode, Incorporated Bangor, Maine...OF PAGES Acoustic Plate Mode, Biowarfare Toxins 54 16. PRICE CODE 17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION

  9. Zonal Flow Velocimetry in Spherical Couette Flow using Acoustic Modes

    NASA Astrophysics Data System (ADS)

    Adams, Matthew M.; Mautino, Anthony R.; Stone, Douglas R.; Triana, Santiago A.; Lekic, Vedran; Lathrop, Daniel P.

    2015-11-01

    We present studies of spherical Couette flows using the technique of acoustic mode Doppler velocimetry. This technique uses rotational splittings of acoustic modes to infer the azimuthal velocity profile of a rotating flow, and is of special interest in experiments where direct flow visualization is impractical. The primary experimental system consists of a 60 cm diameter outer spherical shell concentric with a 20 cm diameter sphere, with air or nitrogen gas serving as the working fluid. The geometry of the system approximates that of the Earth's core, making these studies geophysically relevant. A turbulent shear flow is established in the system by rotating the inner sphere and outer shell at different rates. Acoustic modes of the fluid volume are excited using a speaker and measured via microphones, allowingdetermination of rotational splittings. Preliminary results comparing observed splittings with those predicted by theory are presented. While the majority of these studies were performed in the 60 cm diameter device using nitrogen gas, some work has also been done looking at acoustic modes in the 3 m diameter liquid sodium spherical Couette experiment. Prospects for measuring zonal velocity profiles in a wide variety of experiments are discussed.

  10. Transportation control of microfluidic particles using mode switching between surface acoustic waves and plate waves

    NASA Astrophysics Data System (ADS)

    Hsu, Jin-Chen; Huang, Yeo-Wei; Hsu, Chih-Hsun

    2017-07-01

    In this study, we report the numerical and experimental results of guided acoustic mode switching between surface and plate acoustic waves (SAWs and PAWs) for manipulating microparticles suspended in a microfluidic channel. Numerical results show switchable acoustic pressure and acoustic radiation force fields for controlling particle motion in the microfluidic channel by acoustic mode switching. Acoustic mode switching can be achieved by designing an acoustic-wave device and by changing the frequencies of the input electrical signal. The working mechanisms of acoustic-mode-switchable manipulation are revealed. On the basis of numerical prediction, the feasibility of a mode-switchable acoustic microfluidic device is experimentally demonstrated, and the actuation of suspended microparticles using SAWs and PAWs is achieved. We note that this study provides access to mode-switching acoustophoresis.

  11. Light scattering from acoustic vibrational modes in confined structures

    NASA Astrophysics Data System (ADS)

    Bandhu, Rudra Shyam

    The acoustic vibrational modes and their light scattering intensities in confined structures such as supported films, double layer free-standing membrane and sub-micron sized wires on a free-standing membrane have been studied using Brillouin Light Scattering (BLS). Standing wave type acoustic phonons were recently observed in supported thin films of silicon oxy-nitride. We build upon this finding to study the acoustic modes in thin zinc selenide (ZnSe) films on gallium arsenide (GaAs). The surprising behaviour of the Brillouin intensities of the standing wave modes in ZnSe are explained in terms of interference of the elasto-optic scattering amplitudes from the film and substrate. Numerical calculations of the scattering cross-section, which takes into account ripple and elasto-optic scattering mechanism, agrees well with the experimental data. Light scattering studies of standing wave type modes in free-standing polymethyl methacrylate (PMMA) layer on Si3N4 were carried out. In these bilayer structures PMMA is much softer than Si3N 4, a property that leads to confinement of low frequency modes associated with the PMMA layer to within its boundaries. In addition, the flexural and the dilatational modes from the Si3N4 layer are observed and are found to hybridize with the standing wave modes from the PMMA layer. Our study of phonon modes in PMMA wires supported on a free-standing Si3N4 membrane extends our work on free-standing double layer membranes. In recent years there is much interest in the study of phonon modes in nano-scale structures such as wires or dots. Although much theoretical work has been carried out in this direction, no experiments exist that explore the dispersion of the phonon modes in such structures. Brillouin Light scattering is ideally suited for studying phonons in such reduced dimensions and our work represents the first effort in this direction. The spectra reveal modes which are quantized both along the width, as well along the thickness

  12. A violin shell model: vibrational modes and acoustics.

    PubMed

    Gough, Colin E

    2015-03-01

    A generic physical model for the vibro-acoustic modes of the violin is described treating the body shell as a shallow, thin-walled, guitar-shaped, box structure with doubly arched top and back plates. comsol finite element, shell structure, software is used to identify and understand the vibrational modes of a simply modeled violin. This identifies the relationship between the freely supported plate modes when coupled together by the ribs and the modes of the assembled body shell. Such coupling results in a relatively small number of eigenmodes or component shell modes, of which a single volume-changing breathing mode is shown to be responsible for almost all the sound radiated in the monopole signature mode regime below ∼1 kHz for the violin, whether directly or by excitation of the Helmholtz f-hole resonance. The computations describe the influence on such modes of material properties, arching, plate thickness, elastic anisotropy, f-holes cut into the top plate, the bass-bar, coupling to internal air modes, the rigid neck-fingerboard assembly, and, most importantly, the soundpost. Because the shell modes are largely determined by the symmetry of the guitar-shaped body, the model is applicable to all instruments of the violin family.

  13. Scattering of acoustic duct modes by axial liner splices

    NASA Astrophysics Data System (ADS)

    Tam, Christopher K. W.; Ju, Hongbin; Chien, Eugene W.

    2008-03-01

    Recent engine test data and results of computational analysis show that the engine inlet acoustic liner splices have a significant impact on aircraft flight noise certification and cabin noise levels. The phenomenon of scattering of acoustic duct modes by axial liner splices is investigated. Previous studies, invariably, follow the frequency-domain approach. The present study, however, uses the time-domain approach. It is demonstrated that time-domain computation yields results that are in close agreement with frequency-domain results. The scattering phenomenon under consideration is very complex. This study concentrates on the effects of four parameters. They are the width of the splices, the frequency of the incident duct mode, the number of splices and the length of splices. Based on the computed results, the conditions under which scattered wave modes would significantly increase the intensity of transmitted waves are identified. It is also found that surface scattering by liner splices has the tendency to distribute energy equally to all the cut-on scattered azimuthal modes. On the other hand, for each scattered azimuthal mode, the high-order cut-on radial mode, generally, has the highest intensity. Moreover, scattering by liner splices is a local phenomenon. It is confined primarily to an area of the duct adjacent to the junction between the hard wall near the fan face and the spliced liner.

  14. Dual mode acoustic wave sensor for precise pressure reading

    NASA Astrophysics Data System (ADS)

    Mu, Xiaojing; Kropelnicki, Piotr; Wang, Yong; Randles, Andrew Benson; Chuan Chai, Kevin Tshun; Cai, Hong; Gu, Yuan Dong

    2014-09-01

    In this letter, a Microelectromechanical system acoustic wave sensor, which has a dual mode (lateral field exited Lamb wave mode and surface acoustic wave (SAW) mode) behavior, is presented for precious pressure change read out. Comb-like interdigital structured electrodes on top of piezoelectric material aluminium nitride (AlN) are used to generate the wave modes. The sensor membrane consists of single crystalline silicon formed by backside-etching of the bulk material of a silicon on insulator wafer having variable device thickness layer (5 μm-50 μm). With this principle, a pressure sensor has been fabricated and mounted on a pressure test package with pressure applied to the backside of the membrane within a range of 0 psi to 300 psi. The temperature coefficient of frequency was experimentally measured in the temperature range of -50 °C to 300 °C. This idea demonstrates a piezoelectric based sensor having two modes SAW/Lamb wave for direct physical parameter—pressure readout and temperature cancellation which can operate in harsh environment such as oil and gas exploration, automobile and aeronautic applications using the dual mode behavior of the sensor and differential readout at the same time.

  15. Spinning mode sound propagation in ducts with acoustic treatment

    NASA Technical Reports Server (NTRS)

    Rice, E. J.

    1974-01-01

    Recent acoustic data have shown larger noise attenuations than predicted for acoustically treated aircraft engine inlets without splitter rings. These data have stimulated a more detailed theoretical study of the acoustic propagation of spinning modes in acoustically treated open circular ducts. In addition, the suppressor with splitter rings was modeled by using the rectangular approximation to the annular duct. The theoretical models were used to determine optimum impedance and maximum attenuation for several spinning lobe numbers from 0 to 50. It is found that for circular ducts the maximum possible attenuation and the optimum wall impedance are strong functions of the lobe number. For annular ducts the attenuation and optimum wall impedance are insensitive to the spinning lobe number for well cut-on modes. The results help explain why suppressors with splitter rings have been quite effective in spite of the lack of detailed information on the noise-source modal structure. Conversely, effective use of outer-wall treatment alone will require expanded knowledge of the noise-source structure. Approximate solutions are presented to help interpret the more exact theoretical results.

  16. Spinning mode sound propagation in ducts with acoustic treatment

    NASA Technical Reports Server (NTRS)

    Rice, E. J.

    1975-01-01

    Recent acoustic data show larger noise attenuations than predicted for acoustically treated aircraft engine inlets without splitter rings. A theoretical study of the acoustic propagation of spinning modes in acoustically treated open circular ducts is presented, and a suppressor with splitter rings was modeled by using the rectangular approximation to the annular duct. Theoretical models were used to determine optimum impedance and maximum attenuation for several spinning lobe numbers from 0 to 50. Results of the analysis indicate that for circular ducts the maximum possible attenuation and the optimum wall impedance are strong functions of the lobe number, and for annular ducts the attenuation and optimum wall impedance are insensitive to the spinning lobe number for well cut-on modes. These results explain why suppressors with splitter rings were quite effective in spite of the lack of detailed information on the noise source modal structure. Conversely, effective use of outer wall treatment alone will require expanded knowledge of the noise source structure. Approximate solutions are presented to help interpret the more exact theoretical results.

  17. Spinning mode sound propagation in ducts with acoustic treatment

    NASA Technical Reports Server (NTRS)

    Rice, E. J.

    1974-01-01

    A detailed theoretical study of the acoustic propagation of spinning modes in acoustically treated open circular ducts is described. The suppressor with splitter rings was modeled by using the rectangular approximation to the annular duct. The theoretical models were used to determine optimum impedance and maximum attenuation for several spinning lobe numbers from 0 to 50. Some interesting results of the analysis are that for circular ducts the maximum possible attenuation and the optimum wall impedance are strong functions of the lobe number. For annular ducts the attenuation and optimum wall impedance are insensitive to the spinning lobe number for well cut-on modes. The above results help explain why suppressors with splitter rings were quite effective in spite of the lack of detailed information on the noise source modal structure.

  18. Optimal Masks for Low-Degree Solar Acoustic Modes.

    PubMed

    Toutain; Kosovichev

    2000-05-10

    We suggest a solution to an important problem in observational helioseismology of the separation of lines of solar acoustic (p) modes of low angular degree in oscillation power spectra by constructing optimal masks for Doppler images of the Sun. Accurate measurements of oscillation frequencies of low-degree modes are essential for the determination of the structure and rotation of the solar core. However, these measurements for a particular mode are often affected by leakage of other p-modes arising when the Doppler images are projected on to spherical harmonic masks. The leakage results in overlapping peaks corresponding to different oscillation modes in the power spectra. In this Letter, we present a method for calculating optimal masks for a given (target) mode by minimizing the signals of other modes appearing in its vicinity. We apply this method to time series of 2 yr obtained from the Michelson Doppler Imager instrument on board the Solar and Heliospheric Observatory space mission and demonstrate its ability to reduce efficiently the mode leakage.

  19. Mode-locking of acoustic resonators and its application to vibration cancellation in acoustic heat engines

    SciTech Connect

    Spoor, P.S.; Swift, G.W. )

    1999-09-01

    Vibration induced in engine hardware by a working fluid can be very significant in high-power, high-amplitude acoustic heat engines, and is a serious impediment to their practical use. This vibration can cause fatigue and destruction of engine components as well as fuel lines, cooling lines, and sensor wires. The forces involved make anchoring such an engine to an [open quotes]immovable[close quotes] object impractical. Rigidly attaching two such engines together, and acoustically coupling them with a duct of such a length and diameter that the two engines mode-lock in antiphase (thus canceling the longitudinal vibration) appears to be an inexpensive, viable solution. This paper describes in detail experiments demonstrating the feasibility of this idea, and the underlying theory. [copyright] [ital 1999 Acoustical Society of America.] < --[HEB] -->

  20. Multimode filter composed of single-mode surface acoustic wave/bulk acoustic wave resonators

    NASA Astrophysics Data System (ADS)

    Huang, Yulin; Bao, Jingfu; Tang, Gongbin; Wang, Yiling; Omori, Tatsuya; Hashimoto, Ken-ya

    2017-07-01

    This paper discusses the possibility of realizing multimode filters composed of multiple single-mode resonators by using radio frequency surface and bulk acoustic wave (SAW/BAW) technologies. First, the filter operation and design principle are given. It is shown that excellent filter characteristics are achievable by combining multiple single-mode resonators with identical capacitance ratios provided that their resonance frequencies and clamped capacitances are set properly. Next, the effect of balun performance is investigated. It is shown that the total filter performance is significantly degraded by balun imperfections such as the common-mode rejection. Then, two circuits are proposed to improve the common-mode rejection, and their effectiveness is demonstrated.

  1. Prufer Transformations for the Normal Modes in Ocean Acoustics

    SciTech Connect

    Baggeroer, Arthur B.

    2010-09-06

    In 1926 Prufer introduced a method of transforming the second order Sturm-Liouville (SL) equation into two nonlinear first order differential equations for the phase oe and ''magnitude'', |oe{sup 2}+oe{sup 2}| for a Poincare phase space representation, (oe,oe). The useful property is the phase equation decouples from the magnitude one which leads to a nonlinear, two point boundary value problem for the eigenvalues, or SL numbers. The transformation has been used both theoretically, e.g. Atkinson, [1960] to prove certain properties of SL equations as well as numerically e.g Bailey [1978]. This paper examines the utility of the Prufer transformation in the context of numerical solutions for modes of the ocean acoustic wave equation. (Its use is certainly not well known in the ocean acoustics community.) Equations for the phase, oe, and natural logarithm of the ''magnitude'', ln(|oe{sup 2}+oe{sup 2}|) lead to same decoupling and a fast and efficient numerical solution with the SL eigenvalues mapping to the horizontal wavenubers. The Prufer transformation has stabilty problems for low order modes at high frequecies, so a numerically stable method of integrating the phase equation is derived. This seems to be the first time the these stability issues have been highlighted to provide a robust algorthim for the modes.

  2. Acoustic Propagation by Bottom Bounce Mode to the North East of Australia

    DTIC Science & Technology

    1994-07-01

    Washington, DC 20036. AUTHORITY DSTO Notice dtd 28 May 1999; Same THIS PAGE IS UNCLASSIFIED AD-CO 54 467 Acoustic Propagation by Bottom Bounce Mode to...TECHNOLOGY ORGANISATION CONFIDENTIAL Copy No. 2lof 45 Acoustic Propagation by Bottom Bounce Mode to the North East of Australia (U) M. W. Lawrence...8217 Acoustic Propagation by Bottom Bounce Mode to the North East of Australia (U) EXECUTIVE SUMMARY (U) Understanding the effectiveness of sonar systems

  3. Radiation of cylindrical duct acoustic modes with flow mismatch

    NASA Technical Reports Server (NTRS)

    Savkar, S. D.; Edelfelt, I. H.

    1975-01-01

    Calculations for the radiation of spinning acoustic modes, with or without a centerbody, and with or without flow temperature and velocity discontinuity, are presented. Solutions to the appropriate convected wave equations devised around Fourier transforms and Wiener-Hopf technique are presented. The decomposition of the asymmetric kernel, resulting from a flow and temperature mismatch, is carried out in part exactly and partially using the so-called Carrier-Koiter approximation procedure. The resulting solutions offer a good approximation to the radiation of both symmetric and asymmetric modes through a flow discontinuity represented as a plug flow jet issuing from a cylindrical duct. Besides the Koiter approximation, the major limitation on the calculation program is the difficulty of calculating the high order Bessel functions with sufficient accuracy.

  4. Acoustic mode coupling induced by nonlinear internal waves: evaluation of the mode coupling matrices and applications.

    PubMed

    Yang, T C

    2014-02-01

    This paper applies the mode coupling equation to calculate the mode-coupling matrix for nonlinear internal waves appearing as a train of solitons. The calculation is applied to an individual soliton up to second order expansion in sound speed perturbation in the Dyson series. The expansion is valid so long as the fractional sound speed change due to a single soliton, integrated over range and depth, times the wavenumber is smaller than unity. Scattering between the solitons are included by coupling the mode coupling matrices between the solitons. Acoustic fields calculated using this mode-coupling matrix formulation are compared with that obtained using a parabolic equation (PE) code. The results agree very well in terms of the depth integrated acoustic energy at the receivers for moving solitary internal waves. The advantages of using the proposed approach are: (1) The effects of mode coupling can be studied as a function of range and time as the solitons travel along the propagation path, and (2) it allows speedy calculations of sound propagation through a packet or packets of solitons saving orders of magnitude computations compared with the PE code. The mode coupling theory is applied to at-sea data to illustrate the underlying physics.

  5. Acoustic mode coupling of two facing, shallow cylindrical cavities

    NASA Astrophysics Data System (ADS)

    McCarthy, Philip; Ekmekci, Alis

    2016-11-01

    Cavity mode excitation by grazing flows is a well-documented source for noise generation. Similarly to their rectangular equivalents, single cylindrical cavities have been shown to exhibit velocity dependent self-sustaining feedback mechanisms that produce significant tonal noise. The present work investigates the effect of cavity mode coupling on the tonal noise generation for two facing, shallow cylindrical cavities. This geometric arrangement may occur for constrained flows, such as those within ducts, silencers or between aircraft landing gear wheels. For the latter configuration, the present study has observed that the tonal frequency dependence upon the freestream Mach number, associated with the single cavity feedback mechanism, no longer holds true. Instead, two simultaneously present and distinct large amplitude tones that are independent (in frequency) of speed, propagate to the far field. These two, fixed frequency tones are attributable to the first order transverse mode, and the first order transverse and azimuthal modes for the two combined cavities and the volume between them. Altering either the cavity aspect ratio or the inter-cavity spacing thus changes the acoustic resonant volume and translates the centre frequencies of the observed tones correspondingly. The authors would like to thank Bombardier and Messier-Bugatti-Dowty for their continued support.

  6. High-frequency acoustic modes in an ionic liquid.

    PubMed

    Ribeiro, Mauro C C

    2013-09-21

    High-frequency collective dynamics of the ionic liquid 1-hexyl-3-methylimidazolium bromide, [C6C1im]Br, has been investigated by molecular dynamics simulations. Time correlation functions of mass current fluctuations were calculated for several wavevectors and the dispersion curves of excitations, ω(k), for longitudinal and transverse acoustic sound modes were obtained at different temperatures and pressures. Two different thermodynamic states have the same high-frequency sound velocity irrespective of the temperature provided that both have the same density. Partial time correlation functions of mass currents were calculated for the atoms belonging to the polar or the non-polar domains resulting from the heterogeneous structure of [C6C1im]Br. The partial correlation functions indicate that the polar domains are stiffer than the non-polar domains of the simulated ionic liquid.

  7. NORM2L: An Interactive Computer Program for Acoustic Normal Mode Calculations for the Pekeris Model.

    DTIC Science & Technology

    1980-12-01

    although the formulae for the normal mode equations are scattered throughout the book. Chapter 9 of the newer book by Clay and Medwin [6] contains a... Medwin , Acoustical Oceanography, Wiley, 1977 7. F. Ingenito, "Measurements of mode attenuation coefficients in shallow water", J.Acoust.Soc.Am

  8. A numerical method for seeking the relationship between structural modes and acoustic radiation modes of complicated structures

    NASA Astrophysics Data System (ADS)

    Chang-wei, SU; Hai-chao, ZHU; Chang-geng, SHUAI; Rong-fu, MAO

    2016-09-01

    Both structural modes and acoustic radiation modes play important roles in the investigation of structure-borne sound. However, little work has been done for inherent relations between these two kinds of modes. Previous work has mainly dealt with simple and regular structures such as rectangular plates and single-layer cylindrical shells. Therefore, the relationship between structural modes and acoustic radiation modes of complicated structures which has great theory significance and utility value is an important problem that must be studied. This paper presents a numerical method for seeking the relationship between structural modes and acoustic radiation modes of complicated structures. First, a governing equation for relating these two kinds of modes is given based on the characteristics of the modes. Then, substitute the normal structural mode shape matrix and the acoustic radiation mode shape matrix which are obtained by FEM into the governing equation, the modal participating coefficients can be solved, thus we can get the corresponding relations between these two kinds of modes. Using the model of a simply supported truncated conical shell, a numerical example is presented with the numerical method which this paper has proposed. And then, the radiated sound power is calculated to verify the effectiveness of this method and the correctness of this conclusion. The results show that the numerical method proposed in this paper is feasible.

  9. Experimental determination of the particle motions associated with the low order acoustic modes in enclosures

    NASA Technical Reports Server (NTRS)

    Byrne, K. P.; Marshall, S. E.

    1983-01-01

    A procedure for experimentally determining, in terms of the particle motions, the shapes of the low order acoustic modes in enclosures is described. The procedure is based on finding differentiable functions which approximate the shape functions of the low order acoustic modes when these modes are defined in terms of the acoustic pressure. The differentiable approximating functions are formed from polynomials which are fitted by a least squares procedure to experimentally determined values which define the shapes of the low order acoustic modes in terms of the acoustic pressure. These experimentally determined values are found by a conventional technique in which the transfer functions, which relate the acoustic pressures at an array of points in the enclosure to the volume velocity of a fixed point source, are measured. The gradient of the function which approximates the shape of a particular mode in terms of the acoustic pressure is evaluated to give the mode shape in terms of the particle motion. The procedure was tested by using it to experimentally determine the shapes of the low order acoustic modes in a small rectangular enclosure.

  10. Envelope solitons of acoustic plate modes and surface waves.

    PubMed

    Mayer, Andreas P; Kovalev, Alexander S

    2003-06-01

    The problem of the existence of evelope solitons in elastic plates and at solid surfaces covered by an elastic film is revisited with special attention paid to nonlinear long-wave short-wave interactions. Using asymptotic expansions and multiple scales, conditions for the existence of envelope solitons are established and it is shown how their parameters can be expressed in terms of the elastic moduli and mass densities of the materials involved. In addition to homogeneous plates, weak periodic modulation of the plate's material parameters are also considered. In the case of wave propagation in an elastic plate, modulations of weakly nonlinear carrier waves are governed by a coupled system of partial differential equations consisting of evolution equations for the complex amplitude of the carrier wave (the nonlinear Schrödinger equation for envelope solitons and the Mills-Trullinger equations for gap solitons), and the wave equation for long-wavelength acoustic plate modes. In contrast to this situation, envelope solitons of surface acoustic waves in a layered structure are normally described by the nonlinear Schrödinger equation alone. However, at higher orders of the carrier wave amplitude, the envelope soliton is found to be accompanied by a quasistatic long-wavelength strain field, which may be localized at the surface with penetration depth into the substrate of the order of the inverse amplitude or which may radiate energy into the bulk. A new set of modulation equations is derived for the resonant case of the carrier wave's group velocity being equal to the phase velocity of long-wavelength Rayleigh waves of the uncoated substrate.

  11. High-order optical vortex generation in a few-mode fiber via cascaded acoustically driven vector mode conversion.

    PubMed

    Zhang, Wending; Huang, Ligang; Wei, Keyan; Li, Peng; Jiang, Biqiang; Mao, Dong; Gao, Feng; Mei, Ting; Zhang, Guoquan; Zhao, Jianlin

    2016-11-01

    We propose a method to generate the high-order optical vortex in a few-mode fiber via cascaded acoustically driven vector mode conversion. Theoretical analysis showed that the vector mode conversion induced by the acoustically induced fiber grating (AIFG) could occur between two HE modes with adjacent azimuthal numbers. In the experiment conducted at 532 nm, two AIFGs were simultaneously induced in the same segment of the fiber by a radio frequency source containing two different frequency components. One AIFG was used to convert the left- and right-handed circular polarization fundamental modes to the ±1-order vortex modes, which were then further converted to the ±2-order vortex modes by the other AIFG. The topological charges of the vortex modes were verified using both coaxial and off-axial interference methods, showing typical signature patterns of spiral forms and forklike fringes, respectively.

  12. Spherical geodesic mesh generation

    SciTech Connect

    Fung, Jimmy; Kenamond, Mark Andrew; Burton, Donald E.; Shashkov, Mikhail Jurievich

    2015-02-27

    In ALE simulations with moving meshes, mesh topology has a direct influence on feature representation and code robustness. In three-dimensional simulations, modeling spherical volumes and features is particularly challenging for a hydrodynamics code. Calculations on traditional spherical meshes (such as spin meshes) often lead to errors and symmetry breaking. Although the underlying differencing scheme may be modified to rectify this, the differencing scheme may not be accessible. This work documents the use of spherical geodesic meshes to mitigate solution-mesh coupling. These meshes are generated notionally by connecting geodesic surface meshes to produce triangular-prismatic volume meshes. This mesh topology is fundamentally different from traditional mesh topologies and displays superior qualities such as topological symmetry. This work describes the geodesic mesh topology as well as motivating demonstrations with the FLAG hydrocode.

  13. Metamorphic Geodesic Regression

    PubMed Central

    Hong, Yi; Joshi, Sarang; Sanchez, Mar; Styner, Martin; Niethammer, Marc

    2013-01-01

    We propose a metamorphic geodesic regression approach approximating spatial transformations for image time-series while simultaneously accounting for intensity changes. Such changes occur for example in magnetic resonance imaging (MRI) studies of the developing brain due to myelination. To simplify computations we propose an approximate metamorphic geodesic regression formulation that only requires pairwise computations of image metamorphoses. The approximated solution is an appropriately weighted average of initial momenta. To obtain initial momenta reliably, we develop a shooting method for image metamorphosis. PMID:23286131

  14. Geodesic measures of the landscape

    SciTech Connect

    Vanchurin, Vitaly

    2007-01-15

    We study the landscape models of eternal inflation with an arbitrary number of different vacua states, both recyclable and terminal. We calculate the abundances of bubbles following different geodesics. We show that the results obtained from generic timelike geodesics have dependence on initial conditions. In contrast, the predictions extracted from 'eternal' geodesics, which never enter terminal vacua, do not suffer from this problem. We derive measure equations for ensembles of geodesics and discuss possible interpretations of initial conditions in eternal inflation.

  15. Resonant mode interactions and the bifurcation of combustion-driven acoustic oscillations in resonance tubes

    SciTech Connect

    Margolis, S.B. . Combustion Research Facility)

    1994-12-01

    Acoustic oscillations in practical combustion devices such as pulse combustors and rocket motors, whether desirable or not, are properly interpreted as combustion instabilities. A nonlinear stability analysis of the corresponding fluid motions than shows that the nonsteady behavior is governed by infinitely coupled systems of nonlinear evolution equations for the amplitudes of the classical acoustic modes. However, under certain conditions, it has been conjectured that relatively low-order truncations can give qualitatively correct physical results. In the present work, one particular model of a pulse combustor is considered, and a parameter regime in the neighborhood of a primary acoustic bifurcation where either one or a pair of purely longitudinal acoustic modes achieves a positive linear growth rate is focused upon. In the first case, it is formally shown that a decoupling occurs such that a two-mode approximation consisting of the linearly unstable mode and its first resonant harmonic completely determines the dynamics of the oscillation. In the later case, it is again demonstrated that a decoupling occurs, and although mode interactions require the retention of additional modes besides the two linearly unstable modes and their first resonant harmonics, a relatively low-order dynamical system still governs the bifurcation behavior. The presence of two linearly unstable modes is then shown to lead to more complicated dynamics, including the stable secondary bifurcation of a multiperiodic acoustic oscillation from one of the single-period primary branches.

  16. Numerical study of acoustic modes in ducted shear flow

    NASA Astrophysics Data System (ADS)

    Vilenski, Gregory G.; Rienstra, Sjoerd W.

    2007-11-01

    The propagation of small-amplitude modes in an inviscid but sheared mean flow inside a duct is studied numerically. For isentropic flow in a circular duct with zero swirl and constant mean flow density the pressure modes are described in terms of the eigenvalue problem for the Pridmore-Brown equation. Since for sufficiently high Helmholtz and wavenumbers, which are of great interest for applications, the field equation is inherently stiff, special care is taken to insure the stability of the numerical algorithm designed to tackle this problem. The accuracy of the method is checked against the well-known analytical solution for uniform flow. The numerical method is shown to be consistent with the analytical predictions at least for Helmholtz numbers up to 100 and circumferential wavenumbers as large as 50, typical Mach numbers being up to 0.65. In order to gain further insight into the possible structure of the modal solutions and to obtain an independent verification of the robustness of the numerical scheme, comparison to the asymptotic solution of the problem based on the WKB method is performed. The asymptotic solution is also used as a benchmark for computations with high Helmholtz numbers, where numerical solutions of other authors are not available. The bulk of the analysis concentrates on the influence of the wall lining. The proposed numerical procedure is adapted in order to include Ingard-Myers boundary conditions. In parallel with this, the WKB solution is used to check the numerical predictions of the typical behaviour of the axial wavenumber in the complex plane, when the wall impedance varies in the complex plane. Numerical analysis of the problem with zero mean flow at the wall and acoustic lining shows that the use of Ingard-Myers condition in combination with an appropriate slip-stream approximation instead of the actual no-slip mean flow profile gives valid results in the limit of vanishing boundary-layer thickness, although the boundary layer

  17. Separation of acoustic modes in the Florida Straits using noise interferometry

    NASA Astrophysics Data System (ADS)

    Sergeev, S. N.; Shurup, A. S.; Godin, O. A.; Vedenev, A. I.; Goncharov, V. V.; Mukhanov, P. Yu.; Zabotin, N. A.; Brown, M. G.

    2017-01-01

    We consider separation of acoustic modes in an experiment carried out in the Florida Straits. The features of the approach are separation of modes using data from single hydrophones, not vertical mode arrays, and a passive scheme of noise interferometry in which the source consists of ocean noise. Processing made it possible to reliably separate the first four modes of the acoustic field. The results allow a conclusion on the possible use of this method for shallow-water monitoring under complex hydrological conditions.

  18. Acoustic total transmission and additional modes in the metamaterials embedded with defects

    NASA Astrophysics Data System (ADS)

    Ding, Erliang; Wang, Yangyang; Liu, Xiaozhou; Li, Yifeng

    2016-11-01

    Total reflection or transmission of waves has been explored extensively in different types of zero-index metamaterials (ZIMs). Almost all previous studies have shown that only monopole modes are excited inside the defects if they are cylindrical. However, the underlying physics for excited modes inside defects is wrongly ignored. In this work, we reveal that there is not only a monopole mode but also additional higher modes excited inside cylindrical defects by a system of two-dimensional waveguides. Actually, the total acoustic transmission and additional higher modes can occur simultaneously in a ZIM waveguide embedded with defects. We reveal the physical mechanism of excited higher modes, which will perfect the current perception of the excited modes in the acoustic metamaterials inside defects. Moreover, numerical simulations are carried out to demonstrate our finding concerning the additional modes.

  19. Acoustic band gaps due to diffraction modes in two-dimensional phononic crystals

    NASA Astrophysics Data System (ADS)

    Kang, Hwi Suk; Lee, Kang Il; Yoon, Suk Wang

    2017-06-01

    In this study, we experimentally and theoretically investigated acoustic band gap control with diffraction modes in two-dimensional (2D) phononic crystals (PCs) consisting of periodic arrays of stainless steel (SS) rods immersed in water. We could classify the acoustic band gaps into two types with diffraction modes in the reflection region, and control the center frequencies of the band gaps by varying the vertical lattice constants. Pressure transmission coefficients and acoustic pressure fields were calculated using the finite element method (FEM), to classify and control the acoustic band gaps. As the vertical lattice constants were varied, the center frequencies of the band gaps, where only normal reflection occurred, were almost constant while those of the band gaps, where additional reflected waves with different propagation directions occurred, decreased with increasing the vertical lattice constants. This work can be used to manipulate acoustic band gap adding, splitting, and shifting.

  20. A comparison between acoustic mode measurements and acoustic finite element analysis performed for SAAB SF 340

    NASA Astrophysics Data System (ADS)

    Goeransson, P.; Green, I.

    1986-03-01

    In order to verify an acoustic finite element package, measured and calculated eigenmodes and eigenfrequencies for Saab SF 340 cabin acoustics were compared. The measurements were performed in an acoustic mockup. For the analysis, a two dimensional model of the cross section of the fuselage was used. The comparison shows quite good agreement, the discrepancies being due to the representation of the flexible wall of the fuselage as rigid in the analysis.

  1. High sensitivity of p-modes near the acoustic cutoff frequency to solar model parameters

    NASA Technical Reports Server (NTRS)

    Guenther, D. B.

    1991-01-01

    The p-mode frequencies of low l have been calculated for solar models with initial helium mass fraction varying from Y = 0.2753-0.2875. The differences in frequency of the p-modes in the frequency range, 2500-4500 microHz, do not exceed 1-5 microHz among the models. But in the vicinity of the acoustic cutoff frequency, near 5000 microHz the p-mode frequency differences are enhanced by a factor of 4. The enhanced sensitivity of p-modes near the acoustic cutoff frequency was further tested by calculating and comparing p-mode frequencies of low l for two solar models one incorporating the Eddington T-tau relation and the other the Krishna Swamy T-tau relation. Again, it is found that p-modes with frequencies near the acoustic cutoff frequency show a significant increase in sensitivity to the different T-tau relations, compared to lower frequency p-modes. It is noted that frequencies above the acoustic cutoff frequency are complex, hence, cannot be modeled by the adiabatic pulsation code (assumes real eigenfrequencies) used in these calculations.

  2. Acoustic Eigenvalues of a Quasispherical Resonator: Second Order Shape Perturbation Theory for Arbitrary Modes

    PubMed Central

    Mehl, James B.

    2007-01-01

    The boundary-shape formalism of Morse and Ingard is applied to the acoustic modes of a deformed spherical resonator (quasisphere) with rigid boundaries. For boundary shapes described by r = a [1 − ε ℱ(θ, ϕ)], where ε is a small scale parameter and ℱ is a function of order unity, the frequency perturbation is calculated to order ε2. The formal results apply to acoustic modes whose angular dependence is designated by the indices ℓ and m. Specific examples are worked out for the radial (ℓ = 0) and triplet (ℓ = 1) modes, for prolate and oblate spheroids, and for triaxial ellipsoids. The exact eigenvalues for the spheroids, and eigenvalue determined with finite-element calculations, are shown to agree with perturbation theory through terms of order ε2. This work is an extension of the author’s previous papers on the acoustic eigenfrequencies of deformed spherical resonators, which were limited to the second-order perturbation for radial modes [J. Acoust. Soc. Am. 71, 1109-1113 (1982)] and the first order-perturbation for arbitrary modes [J. Acoust. Soc. Am. 79, 278–285 (1986)]. PMID:27110463

  3. Acoustic Eigenvalues of a Quasispherical Resonator: Second Order Shape Perturbation Theory for Arbitrary Modes.

    PubMed

    Mehl, James B

    2007-01-01

    The boundary-shape formalism of Morse and Ingard is applied to the acoustic modes of a deformed spherical resonator (quasisphere) with rigid boundaries. For boundary shapes described by r = a [1 - ε ℱ(θ, ϕ)], where ε is a small scale parameter and ℱ is a function of order unity, the frequency perturbation is calculated to order ε (2). The formal results apply to acoustic modes whose angular dependence is designated by the indices ℓ and m. Specific examples are worked out for the radial (ℓ = 0) and triplet (ℓ = 1) modes, for prolate and oblate spheroids, and for triaxial ellipsoids. The exact eigenvalues for the spheroids, and eigenvalue determined with finite-element calculations, are shown to agree with perturbation theory through terms of order ε (2). This work is an extension of the author's previous papers on the acoustic eigenfrequencies of deformed spherical resonators, which were limited to the second-order perturbation for radial modes [J. Acoust. Soc. Am. 71, 1109-1113 (1982)] and the first order-perturbation for arbitrary modes [J. Acoust. Soc. Am. 79, 278-285 (1986)].

  4. Quantum Computational Geodesics

    DTIC Science & Technology

    2010-01-01

    equation, a well-known nonlinear differential matrix equation, and L and iF (L) are Lax pairs (30–32). Some solutions to the geodesic equation...D2J j Dt2 +Rjikl ∂xi ∂t ∂xl ∂t Jk + Cj = 0, (91) the so-called “lifted Jacobi equation” (1). Nielsen and Dowling used the lifted Jacobi equation...quantum circuits (1, 28, 2). 27 6. References 1. Dowling , M. R.; Nielsen, M. A. The Geometry of Quantum Computation. Quantum Information and

  5. Deployable geodesic truss structure

    NASA Technical Reports Server (NTRS)

    Mikulas, Martin M., Jr. (Inventor); Rhodes, Marvin D. (Inventor); Simonton, J. Wayne (Inventor)

    1987-01-01

    A deployable geodesic truss structure which can be deployed from a stowed state to an erected state is described. The truss structure includes a series of bays, each bay having sets of battens connected by longitudinal cross members which give the bay its axial and torsional stiffness. The cross members are hinged at their mid point by a joint so that the cross members are foldable for deployment or collapsing. The bays are deployed and stabilized by actuator means connected between the mid point joints of the cross members. Hinged longerons may be provided to also connect the sets of battens and to collapse for stowing with the rest of the truss structure.

  6. Geodesics: a Tool in Manufacturing

    NASA Astrophysics Data System (ADS)

    Zantout, Rached Nabil

    In manufacturing nowadays, many applications await the development of computationally efficient, on-line, robotic systems that are able to mimic human capabilities. Robotic systems that are able to recognize or differentiate between a small number of objects have been developed over the past few years. The tools of choice for enabling a robot to recognize an object are almost always vision and touch. In this dissertation we re-introduce the concept of geodesics as useful curves to recognize a surface. We start by defining a geodesic and listing some of its properties. Then we introduce a new method to calculate geodesics using only digitized points on a surface. Geodesics are then proven to be useful in manufacturing by applying them to two areas. Geodesics are used to recognize the type and parameters of a surface based on its digitized points. Moreover, geodesics are used to calculate the material properties of a surface undergoing deformation. Many other applications are possible areas where geodesics can prove useful. We conclude this dissertation by talking about such applications and suggesting possible ways where geodesics can be used to improve those applications.

  7. The source of solar high-frequency acoustic modes - Theoretical expectations

    NASA Technical Reports Server (NTRS)

    Brown, Timothy M.

    1991-01-01

    The source exciting the solar p-modes is likely to be acoustic noise generated in the top part of the sun's convection zone. If so, then simple arguments suggest that most of the emitted energy may come from rare localized events that are well separated from one another in space and time. This note describes the acoustic emission that would be expected from such events, based on a ray-theory analysis. Most of the acoustic energy is found to emerge very close to the source, so that observations to identify emission events will require high spatial resolution.

  8. The source of solar high-frequency acoustic modes - Theoretical expectations

    NASA Technical Reports Server (NTRS)

    Brown, Timothy M.

    1991-01-01

    The source exciting the solar p-modes is likely to be acoustic noise generated in the top part of the sun's convection zone. If so, then simple arguments suggest that most of the emitted energy may come from rare localized events that are well separated from one another in space and time. This note describes the acoustic emission that would be expected from such events, based on a ray-theory analysis. Most of the acoustic energy is found to emerge very close to the source, so that observations to identify emission events will require high spatial resolution.

  9. Incompressible Modes Excited by Supersonic Shear in Boundary Layers: Acoustic CFS Instability

    NASA Astrophysics Data System (ADS)

    Belyaev, Mikhail A.

    2017-02-01

    We present an instability for exciting incompressible modes (e.g., gravity or Rossby modes) at the surface of a star accreting through a boundary layer. The instability excites a stellar mode by sourcing an acoustic wave in the disk at the boundary layer, which carries a flux of energy and angular momentum with the opposite sign as the energy and angular momentum density of the stellar mode. We call this instability the acoustic Chandrasekhar–Friedman–Schutz (CFS) instability, because of the direct analogy to the CFS instability for exciting modes on a rotating star by emission of energy in the form of gravitational waves. However, the acoustic CFS instability differs from its gravitational wave counterpart in that the fluid medium in which the acoustic wave propagates (i.e., the accretion disk) typically rotates faster than the star in which the incompressible mode is sourced. For this reason, the instability can operate even for a non-rotating star in the presence of an accretion disk. We discuss applications of our results to high-frequency quasi-periodic oscillations in accreting black hole and neutron star systems and dwarf nova oscillations in cataclysmic variables.

  10. Mode tomography using signals from the Long Range Ocean Acoustic Propagation EXperiment (LOAPEX)

    NASA Astrophysics Data System (ADS)

    Chandrayadula, Tarun K.

    Ocean acoustic tomography uses acoustic signals to infer the environmental properties of the ocean. The procedure for tomography consists of low frequency acoustic transmissions at mid-water depths to receivers located at hundreds of kilometer ranges. The arrival times of the signal at the receiver are then inverted for the sound speed of the background environment. Using this principle, experiments such as the 2004 Long Range Ocean Acoustic Propagation EXperiment have used acoustic signals recorded across Vertical Line Arrays (VLAs) to infer the Sound Speed Profile (SSP) across depth. The acoustic signals across the VLAs can be represented in terms of orthonormal basis functions called modes. The lower modes of the basis set concentrated around mid-water propagate longer distances and can be inverted for mesoscale effects such as currents and eddies. In spite of these advantages, mode tomography has received less attention. One of the important reasons for this is that internal waves in the ocean cause significant amplitude and travel time fluctuations in the modes. The amplitude and travel time fluctuations cause errors in travel time estimates. The absence of a statistical model and the lack of signal processing techniques for internal wave effects have precluded the modes from being used in tomographic inversions. This thesis estimates a statistical model for modes affected by internal waves and then uses the estimated model to design appropriate signal processing methods to obtain tomographic observables for the low modes. In order to estimate a statistical model, this thesis uses both the LOAPEX signals and also numerical simulations. The statistical model describes the amplitude and phase coherence across different frequencies for modes at different ranges. The model suggests that Matched Subspace Detectors (MSDs) based on the amplitude statistics of the modes are the optimum detectors to make travel time estimates for modes up to 250 km. The mean of the

  11. Influence of exit impedance on finite difference solutions of transient acoustic mode propagation in ducts

    NASA Technical Reports Server (NTRS)

    Baumeister, K. J.

    1981-01-01

    The time-dependent governing acoustic-difference equations and boundary conditions are developed and solved for sound propagation in an axisymmetric (cylindrical) hard-wall duct without flow and with spinning acoustic modes. The analysis begins with a harmonic sound source radiating into a quiescent duct. This explicit iteration method then calculates stepwise in real time to obtain the steady solutions of the acoustic field. The transient method did not converge to the steady-state solution for cutoff acoustic duct modes. This has implications as to its use in a variable-area duct, where modes may become cutoff in the smal-area portion of the duct. For single cutoff mode propagation the steady-state impedance boundary condition produced acoustic reflections during the initial transient that caused finite instabilities in the numerical calculations. The stability problem is resolved by reformulating the exit boundary condition. Example calculations show good agreement with exact analytical and numerical results for forcing frequencies above, below, and nearly at the cutoff frequency.

  12. Suppression of fatigue inducing cavity acoustic modes on turbo fan engines

    NASA Astrophysics Data System (ADS)

    Benner, R. H.

    1990-10-01

    This paper discusses several methods of suppressing shear layer excitation of cavity acoustic modes on turbofan engines. The methods include the use of a Helmholtz resonator, reducing the cavity impingement length with vane-like dividers, and drawing the shear layer into the cavity. Empirical data and closed-form solutions were used to design baseline structures employed in each method. Full scale turbofan engine tests were used to measure their effectiveness. Each method significantly reduced the level to which cavity acoustic modes were excited by shear layer flow.

  13. Acoustic plate mode propagation and interaction with ultraviolet light in periodic AIN-on-sapphire structure

    SciTech Connect

    Chivukula, Venkata; Shur, Michael; Ciplys, Daumantas; Jain, Rakesh; Yang Jinwei; Gaska, Remis

    2011-02-28

    AlN overlay featuring periodic columnar structure fabricated by epitaxial lateral overgrowth technique leads to excitation of acoustic plate modes (APMs) not observed in overlays without such periodic structure. The measured velocities of acoustic plate modes propagating in AlN-on-sapphire structure were verified by numerical simulation. The APM velocity is strongly modulated by UV illumination at wavelengths from 240 to 365 nm, and the corresponding phase response is sensitive to both the UV power and the wavelength with maximum sensitivity of 3.0 ppm/({mu}W/cm{sup 2}) at 240 nm.

  14. Poisson's ratio from polarization of acoustic zero-group velocity Lamb mode.

    PubMed

    Baggens, Oskar; Ryden, Nils

    2015-07-01

    Poisson's ratio of an isotropic and free elastic plate is estimated from the polarization of the first symmetric acoustic zero-group velocity Lamb mode. This polarization is interpreted as the ratio of the absolute amplitudes of the surface normal and surface in-plane components of the acoustic mode. Results from the evaluation of simulated datasets indicate that the presented relation, which links the polarization and Poisson's ratio, can be extended to incorporate plates with material damping. Furthermore, the proposed application of the polarization is demonstrated in a practical field case, where an increased accuracy of estimated nominal thickness is obtained.

  15. Quantized acoustic-phonon shear horizontal modes in an unbounded hexagonal nitride-based piezoelectric nanostructure

    NASA Astrophysics Data System (ADS)

    Mazouchi, M.; Dutta, M.; Stroscio, M. A.

    2017-05-01

    For the first time a quantum mechanics based theoretical description of acoustic-phonon shear horizontal modes in a class of piezoelectric media is proposed. The quantized acoustic modes that are needed in the transition from the microscale to the nanoscale are derived for a resonator with geometries of interest in optoelectronics and nanoelectronics. The acoustic-phonon frequency dispersion relations are obtained quantum mechanically for odd and even symmetry shear horizontal modes. It is shown that the derived dispersion relations are identical to the previously reported dispersion relations obtained classically as is expected. For each symmetry, the phonon-mode amplitude is derived in terms of the energy of the quantized vibrational mode, which is of great importance for modelling carrier-acoustic phonon interactions. Moreover, the product of quality factor and frequency (Q . f) have been estimated for AlN and GaN resonators by using the anharmonic phonon scattering theory. Furthermore, the electrical surface perturbation in the piezoelectric nanoresonator is studied and the resulting resonance frequency shift is determined.

  16. An improved method for the calculation of Near-Field Acoustic Radiation Modes

    NASA Astrophysics Data System (ADS)

    Liu, Zu-Bin; Maury, Cédric

    2016-02-01

    Sensing and controlling Acoustic Radiation Modes (ARMs) in the near-field of vibrating structures is of great interest for broadband noise reduction or enhancement, as ARMs are velocity distributions defined over a vibrating surface, that independently and optimally contribute to the acoustic power in the acoustic field. But present methods only provide far-field ARMs (FFARMs) that are inadequate for the acoustic near-field problem. The Near-Field Acoustic Radiation Modes (NFARMs) are firstly studied with an improved numerical method, the Pressure-Velocity method, which rely on the eigen decomposition of the acoustic transfers between the vibrating source and a conformal observation surface, including sound pressure and velocity transfer matrices. The active and reactive parts of the sound power are separated and lead to the active and reactive ARMs. NFARMs are studied for a 2D baffled beam and for a 3D baffled plate, and so as differences between the NFARMS and the classical FFARMs. Comparisons of the NFARMs are analyzed when varying frequency and observation distance to the source. It is found that the efficiencies and shapes of the optimal active ARMs are independent on the distance while that of the reactive ones are distinctly related on.

  17. Geodesic IO Library

    SciTech Connect

    2011-03-15

    GIO is an application programmer interface (API) or library for high performance IO that is designed for climate models that operate on a geodesic grid. GIO uses a combination of configuration files and API calls to define the mapping of internal model data to output variables in standard climate data formats. The mapping from model data to model output includes method of data slicing, aggregation, and linearization using a morton ordering approach. The data is then persisted through a standard interface that can be implemented using several different high level parallel libraries. Both Parallel NetCDF and NetCDF4 interfaces are provided. GIO is designed to run on supercomputing systems or multi-processor clusters with parallel file systems.

  18. Three-dimensional coupled mode analysis of internal-wave acoustic ducts.

    PubMed

    Shmelev, Alexey A; Lynch, James F; Lin, Ying-Tsong; Schmidt, Henrik

    2014-05-01

    A fully three-dimensional coupled mode approach is used in this paper to describe the physics of low frequency acoustic signals propagating through a train of internal waves at an arbitrary azimuth. A three layer model of the shallow water waveguide is employed for studying the properties of normal modes and their coupled interaction due to the presence of nonlinear internal waves. Using a robust wave number integration technique for Fourier transform computation and a direct global matrix approach, an accurate three-dimensional coupled mode full field solution is obtained for the tonal signal propagation through straight and parallel internal waves. This approach provides accurate results for arbitrary azimuth and includes the effects of backscattering. This enables one to provide an azimuthal analysis of acoustic propagation and separate the effects of mode coupled transparent resonance, horizontal reflection and refraction, the horizontal Lloyd's mirror, horizontal ducting and anti-ducting, and horizontal tunneling and secondary ducting.

  19. The Derivation and Quasinormal Mode Spectrum of Acoustic Anti-de Sitter Black Hole Analogues

    NASA Astrophysics Data System (ADS)

    Babb, James Patrick

    Dumb holes (also known as acoustic black holes) are fluid flows which include an "acoustic horizon": a surface, analogous to a gravitational horizon, beyond which sound may pass but never classically return. Soundwaves in these flows will therefore experience "effective geometries" which are identical to black hole spacetimes up to a conformal factor. By adjusting the parameters of the fluid flow, it is possible to create an effective geometry which is conformal to the Anti-de Sitter black hole spacetime---a geometry which has received a great deal of attention in recent years due to its conjectured holographic duality to Conformal Field Theories. While we would not expect an acoustic analogue of the AdS-CFT correspondence to exist, this dumb hole provides a means, at least in principle, of experimentally testing the theoretical properties of the AdS spacetime. In particular, I have calculated the quasinormal mode spectrum of this acoustic geometry.

  20. Computational Simulation of Acoustic Modes in Rocket Combustors

    NASA Technical Reports Server (NTRS)

    Harper, Brent (Technical Monitor); Merkle, C. L.; Sankaran, V.; Ellis, M.

    2004-01-01

    A combination of computational fluid dynamic analysis and analytical solutions is being used to characterize the dominant modes in liquid rocket engines in conjunction with laboratory experiments. The analytical solutions are based on simplified geometries and flow conditions and are used for careful validation of the numerical formulation. The validated computational model is then extended to realistic geometries and flow conditions to test the effects of various parameters on chamber modes, to guide and interpret companion laboratory experiments in simplified combustors, and to scale the measurements to engine operating conditions. In turn, the experiments are used to validate and improve the model. The present paper gives an overview of the numerical and analytical techniques along with comparisons illustrating the accuracy of the computations as a function of grid resolution. A representative parametric study of the effect of combustor mean flow Mach number and combustor aspect ratio on the chamber modes is then presented for both transverse and longitudinal modes. The results show that higher mean flow Mach numbers drive the modes to lower frequencies. Estimates of transverse wave mechanics in a high aspect ratio combustor are then contrasted with longitudinal modes in a long and narrow combustor to provide understanding of potential experimental simulations.

  1. The acoustic emission of a distributed mode loudspeaker near a porous layer.

    PubMed

    Prokofieva, E Yu; Horoshenkov, Kirill V; Harris, N

    2002-06-01

    Experimental and theoretical modeling of the vibro-acoustic performance of a distributed mode loudspeaker (DML) suggest that their acoustic emission can be significantly affected by the presence of a porous layer. The amplitude of the surface velocity of the panel and the acoustic pressure on the porous surface are reduced largely in the vicinity of structural resonances due to the additional radiation damping and visco-thermal absorption phenomenon in the porous layer. The experimental results suggest that a porous layer between a rigid base and a DML panel can considerably alter its acoustic emission in the near field and in the far field. This is illustrated by a reduction in the level of fluctuations in the emitted acoustic pressure spectra. These fluctuations are normally associated with the interference between the sound emitted by the front surface of the speaker and that emitted from the back. Another contribution comes from the pronounced structural resonances in the surface velocity spectrum. The results of this work suggest that the acoustic boundary conditions near a DML can be modified by the porous layer so that a desired acoustic output can be attained.

  2. Time-Resolved Studies of the Acoustic Vibrational Modes of Metal and Semiconductor Nano-objects.

    PubMed

    Major, Todd A; Lo, Shun Shang; Yu, Kuai; Hartland, Gregory V

    2014-03-06

    Over the past decade, there have been a number of transient absorption studies of the acoustic vibrational modes of metal and semiconductor nanoparticles. This Perspective provides an overview of this work. The way that the frequencies of the observed modes depend on the size and shape of the particles is described, along with their damping. Future research directions are also discussed, especially how these measurements provide information about the way nano-objects interact with their environment.

  3. Acoustic wave device using plate modes with surface-parallel displacement

    DOEpatents

    Martin, Stephen J.; Ricco, Antonio J.

    1992-01-01

    Solid-state acoustic sensors for monitoring conditions at a surface immersed in a liquid and for monitoring concentrations of species in a liquid and for monitoring electrical properties of a liquid are formed by placing interdigital input and output transducers on a piezoelectric substrate and propagating acoustic plate modes therebetween. The deposition or removal of material on or from, respectively, a thin film in contact with the surface, or changes in the mechanical properties of a thin film in contact with the surface, or changes in the electrical characteristics of the solution, create perturbations in the velocity and attenuation of the acoustic plate modes as a function of these properties or changes in them.

  4. Method and apparatus for acoustic plate mode liquid-solid phase transition detection

    DOEpatents

    Blair, Dianna S.; Freye, Gregory C.; Hughes, Robert C.; Martin, Stephen J.; Ricco, Antonio J.

    1993-01-01

    A method and apparatus for sensing a liquid-solid phase transition event is provided which comprises an acoustic plate mode detecting element placed in contact with a liquid or solid material which generates a high-frequency acoustic wave that is attenuated to an extent based on the physical state of the material is contact with the detecting element. The attenuation caused by the material in contact with the acoustic plate mode detecting element is used to determine the physical state of the material being detected. The method and device are particularly suited for detecting conditions such as the icing and deicing of wings of an aircraft. In another aspect of the present invention, a method is provided wherein the adhesion of a solid material to the detecting element can be measured using the apparatus of the invention.

  5. Acoustic wave device using plate modes with surface-parallel displacement

    DOEpatents

    Martin, S.J.; Ricco, A.J.

    1988-04-29

    Solid-state acoustic sensors for monitoring conditions at a surface immersed in a liquid and for monitoring concentrations of species in a liquid and for monitoring electrical properties of a liquid are formed by placing interdigital input and output transducers on a piezoelectric substrate and propagating acoustic plate modes therebetween. The deposition or removal of material on or from, respectively, a thin film in contact with the surface, or changes in the mechanical properties of a thin film in contact with the surface, or changes in the electrical characteristics of the solution, create perturbations in the velocity and attenuation of the acoustic plate modes as a function of these properties or changes in them. 6 figs.

  6. Method and apparatus for acoustic plate mode liquid-solid phase transition detection

    NASA Astrophysics Data System (ADS)

    Blair, D. S.; Frye, G. C.; Hughes, R. C.; Martin, S. J.; Ricco, A. J.

    1990-05-01

    A method and apparatus for sensing a liquid-solid phase transition event is provided which comprises an acoustic plate mode detecting element placed in contact with a liquid or solid material which generates a high-frequency acoustic wave that is attenuated to an extent based on the physical state of the material in contact with the detecting element. The attenuation caused by the material in contact with the acoustic plate mode detecting element is used to determine the physical state of the material being detected. The method and device are particularly suited for detecting conditions such as the icing and deicing of wings of an aircraft. In another aspect of the present invention, a method is provided wherein the adhesion of a solid material to the detecting element can be measured using the apparatus of the invention.

  7. Acoustic field enhancement and subwavelength imaging by coupling to slab waveguide modes

    NASA Astrophysics Data System (ADS)

    Christensen, J.; García de Abajo, F. J.

    2010-10-01

    We present a theoretical study on the amplification of evanescent sound waves produced by coupling to trapped modes hosted by a fluidic planar waveguide. Total internal reflection at interfaces of different refractive indexes can be frustrated by the introduction of a slow slab waveguide which is leading to a gigantic field enhancement, useful for sensitive transducers and acoustic shock lithotripsy. The mechanism behind the evanescent field coupling that is also known as tunnelling barrier penetration in quantum mechanics is here adopted for its use in an acoustic superlens. The higher spatial harmonics produced by a subwavelength object can couple to trapped modes of the slow waveguide and be reproduced as an image at a distant plane. We suggest a practical implementation of these ideas by means of a silicone rubber slab containing positive acoustic wave propagation parameters.

  8. Acoustic wave device using plate modes with surface-parallel displacement

    DOEpatents

    Martin, S.J.; Ricco, A.J.

    1992-05-26

    Solid-state acoustic sensors for monitoring conditions at a surface immersed in a liquid and for monitoring concentrations of species in a liquid and for monitoring electrical properties of a liquid are formed by placing interdigital input and output transducers on a piezoelectric substrate and propagating acoustic plate modes there between. The deposition or removal of material on or from, respectively, a thin film in contact with the surface, or changes in the mechanical properties of a thin film in contact with the surface, or changes in the electrical characteristics of the solution, create perturbations in the velocity and attenuation of the acoustic plate modes as a function of these properties or changes in them. 6 figs.

  9. Impact of acoustic airflow on intrasinus drug deposition: New insights into the vibrating mode and the optimal acoustic frequency to enhance the delivery of nebulized antibiotic.

    PubMed

    Leclerc, Lara; Merhie, Amira El; Navarro, Laurent; Prévôt, Nathalie; Durand, Marc; Pourchez, Jérémie

    2015-10-15

    We investigated the impact of vibrating acoustic airflow, the high frequency (f≥100 Hz) and the low frequency (f≤45 Hz) sound waves, on the enhancement of intrasinus drug deposition. (81m)Kr-gas ventilation study was performed in a plastinated human cast with and without the addition of vibrating acoustic airflow. Similarly, intrasinus drug deposition in a nasal replica using gentamicin as a marker was studied with and without the superposition of different modes of acoustic airflow. Ventilation experiments demonstrate that no sinus ventilation was observed without acoustic airflow although sinus ventilation occurred whatever the modes of acoustic airflow applied. Intrasinus drug deposition experiments showed that the high frequency acoustic airflow led to 4-fold increase in gentamicin deposition into the left maxillary sinus and to 2-fold deposition increase into the right maxillary sinus. Besides, the low frequency acoustic airflow demonstrated a significant increase of 4-fold and 2-fold in the right and left maxillary sinuses, respectively. We demonstrated the benefit of different modes of vibrating acoustic airflow for maxillary sinus ventilation and intrasinus drug deposition. The degree of gentamicin deposition varies as a function of frequency of the vibrating acoustic airflow and the geometry of the ostia. Copyright © 2015 Elsevier B.V. All rights reserved.

  10. Zonal Flow Velocimetry using Acoustic Modes in Experimental Models of a Planetary Core

    NASA Astrophysics Data System (ADS)

    Adams, M. M.; Mautino, A. R.; Stone, D.; Triana, S. A.; Lekic, V.; Lathrop, D. P.

    2015-12-01

    Rotating hydromagnetic experiments can serve as models of planetary cores, matching some of the dimensionless parameters relevant to planets. One challenge with such experiments is determining the flows present. The opacity of the fluids used in these experiments (e.g. liquid sodium) prevents direct flow visualization techniques from being employed. One method allowing determination of zonal flows in such experiments is acoustic mode velocimetry. In this technique, the rotational splittings of acoustic mode spectra are used to infer the azimuthal velocity profile of the flow. Here we present the use of this technique to study flows in experimental models of the Earth's core. Most of these results were obtained in a 60 cm diameter spherical Couette device, with a 20 cm diameter inner sphere, and using nitrogen gas as the working fluid. Turbulent flow is driven in the system via differential rotation of the outer shell and inner sphere. Acoustic modes are excited in the fluid volume using a speaker, and microphones are used to measure the frequencies and rotational splittings of the modes. We compare the observed splittings with those predicted by theory as a way of validating the method, and infer mean flows from these observations. We also present some preliminary results of acoustic studies in the 3 m diameter liquid sodium spherical Couette experiment. Finally, we discuss future prospects for this experimental technique.

  11. Mutual conversion between B-mode image and acoustic impedance image

    NASA Astrophysics Data System (ADS)

    Chean, Tan Wei; Hozumi, Naohiro; Yoshida, Sachiko; Kobayashi, Kazuto; Ogura, Yuki

    2017-07-01

    To study the acoustic properties of a B-mode image, two ways of analysis methods were proposed in this report. The first method is the conversion of an acoustic impedance image into a B-mode image (Z to B). The time domain reflectometry theory and transmission line model were used as reference in the calculation. The second method is the direct a conversion of B-mode image into an acoustic impedance image (B to Z). The theoretical background of the second method is similar to that of the first method; however, the calculation is in the opposite direction. Significant scatter, refraction, and attenuation were assumed not to take place during the propagation of an ultrasonic wave. Hence, they were ignored in both calculations. In this study, rat cerebellar tissue and human cheek skin were used to determine the feasibility of the first and second methods respectively. Some good results are obtained and hence both methods showed their possible applications in the study of acoustic properties of B-mode images.

  12. Measuring derived acoustic power of an ultrasound surgical device in the linear and nonlinear operating modes.

    PubMed

    Petosić, Antonio; Ivancević, Bojan; Svilar, Dragoljub

    2009-06-01

    The method for measuring derived acoustic power of an ultrasound point source in the form of a sonotrode tip has been considered in the free acoustic field, according to the IEC 61847 standard. The main objective of this work is measuring averaged pressure magnitude spatial distribution of an sonotrode tip in the free acoustic field conditions at different electrical excitation levels and calculation of the derived acoustic power at excitation frequency (f0 approximately 25 kHz). Finding the derived acoustic power of an ultrasonic surgical device in the strong cavitation regime of working, even in the considered laboratory conditions (anechoic pool), will enable better understanding of the biological effects on the tissue produced during operation with the considered device. The pressure magnitude spatial distribution is measured using B&K 8103 hydrophone connected with a B&K 2626 conditioning amplifier, digital storage oscilloscope LeCroy Waverunner 474, where pressure waveforms in the field points are recorded. Using MATLAB with DSP processing toolbox, averaged power spectrum density of recorded pressure signals in different field positions is calculated. The measured pressure magnitude spatial distributions are fitted with the appropriate theoretical models. In the linear operating mode, using the acoustic reciprocity principle, the sonotrode tip is theoretically described as radially oscillating sphere (ROS) and transversely oscillating sphere (TOS) in the vicinity of pressure release boundary. The measured pressure magnitude spatial distribution is fitted with theoretical curves, describing the pressure field of the considered theoretical models. The velocity and displacement magnitudes with derived acoustic power of equivalent theoretical sources are found, and the electroacoustic efficiency factor is calculated. When the transmitter is excited at higher electrical power levels, the displacement magnitude of sonotrode tip is increased, and nonlinear behaviour

  13. Dispersion relations of the acoustic modes in divalent liquid metals

    NASA Astrophysics Data System (ADS)

    Inui, Masanori; Kajihara, Yukio; Kimura, Koji; Matsuda, Kazuhiro; Miyatake, Tetsu; Chiba, Ayano; Hosokawa, Shinya; Tsutsui, Satoshi; Baron, Alfred Q. R.

    2017-08-01

    Collective dynamics in liquid Ca and liquid Cd was studied by inelastic x-ray scattering (IXS). Using our experimental technique to prepare proper sample cells and high performance of an IXS beamline (BL35XU) at SPring-8 in Japan, the dynamic structure factor with reasonable statistics was obtained for these divalent liquid metals. For both liquids, the dynamic structure factor at low Q exhibits a central peak with a shoulder or small hump clearly visible on each side, and the inelastic excitation energy determined using the model function composed of Lorentzian and the damped harmonic oscillator function disperses with increasing Q. The dispersion curves of these liquids were compared with that of the longitudinal acoustic phonon in each crystalline phase. From these results, clear difference in the interatomic interaction be- tween liquid Ca and liquid Cd was inferred.

  14. Inelastic ultraviolet scattering from high frequency acoustic modes in glasses.

    PubMed

    Masciovecchio, C; Gessini, A; Di Fonzo, S; Comez, L; Santucci, S C; Fioretto, D

    2004-06-18

    The dynamic structure factor of vitreous silica and glycerol has been measured as a function of temperature and of the momentum transfer up to Q=0.105 nm(-1) using a novel experimental technique, the inelastic ultraviolet scattering. As in the case of Brillouin light scattering and ultrasonic measurements, the temperature dependence of the acoustic attenuation shows a plateau below the glass transition whose amplitude scales as Q2. Moreover, a slight temperature dependence of attenuation has been found in vitreous silica at about 130 K, which seems to be reminiscent of the peak measured at lower Qs. These two findings strongly support the idea that anharmonicity is responsible for sound attenuation at ultrasonic and hypersonic frequencies. Finally, we demonstrate that the attenuation mechanism should show a change of regime between 0.105 and 1 nm(-1).

  15. Acoustic mode measurements in the inlet of a model turbofan using a continuously rotating rake

    NASA Astrophysics Data System (ADS)

    Heidelberg, Laurence J.; Hall, David G.

    1993-01-01

    Comprehensive measurements of the spinning acoustic mode structure in the inlet of the Advanced Ducted Propeller (ADP) have been completed. These measurements were taken using a unique and previously untried method which was first proposed by T.G. Sofrin. A continuously rotating microphone system was employed. The ADP model was designed and built by Pratt & Whitney and tested in the NASA Lewis 9- by 15-foot Anechoic Wind Tunnel. Three inlet configurations were tested with cut-on and cutoff stator vane sets. The cutoff stator was designed to suppress all modes at the blade passing frequency. Rotating rake measurements indicate that several extraneous circumferential modes were active. The mode orders suggest that their source was an interaction between the rotor and small interruptions in the casing tip treatment. The cut-on stator produced the expected circumferential modes plus higher levels of the unexpected modes seen with the cutoff stator.

  16. Acoustic Mode Measurements in the Inlet of a Model Turbofan Using a Continuously Rotating Rake

    NASA Technical Reports Server (NTRS)

    Heidelberg, Laurence J.; Hall, David G.

    1992-01-01

    Comprehensive measurements of the spinning acoustic mode structure in the inlet of the Advanced Ducted Propeller (ADP) have been completed. These measurements were taken using a unique and previously untried method which was first proposed by T.G. Sofrin. A continuously rotating microphone system was employed. The ADP model was designed and built by Pratt & Whitney and tested in the NASA Lewis 9- by 15-foot Anechoic Wind Tunnel. Three inlet configurations were tested with cut-on and cutoff stator vane sets. The cutoff stator was designed to suppress all modes at the blade passing frequency. Rotating rake measurements indicate that several extraneous circumferential modes were active. The mode orders suggest that their source was an interaction between the rotor and small interruptions in the casing tip treatment. The cut-on stator produced the expected circumferential modes plus higher levels of the unexpected modes seen with the cutoff stator.

  17. The model of local mode analysis for structural acoustics of box structures

    NASA Astrophysics Data System (ADS)

    Ngai, King-Wah

    Structure-borne noise is a new noise pollution problem emerging from railway concrete box structures in Hong Kong. Its low frequency noise with intermittent effect can cause considerable nuisance to neighborhoods. The tonal noise peaks in this low frequency range should be one of the important factors in structure-borne noise analysis. In the acoustic field, the deterministic analysis of all the resonant modes of vibration is generally considered as not practical. Many acoustic experts use the statistical energy analysis as the main tool for the noise investigation whereas the application of the experimental modal analysis in the structural acoustic problem is comparatively rare. In the past, most studies mainly focused on the structure-borne noise measurement and analysis. The detail study of the cause of structure-borne noise is lack, especially for the rectangular concrete box structure. In this dissertation, an experimental and analytical approach is adopted to study a typical concrete box model. This thesis aims at confirming the importance of modal analysis in the structure-borne noise study and then at identifying the local vibration modes along the cross-section of box structure. These local modes are responsible for the structure-borne noise radiation. The findings of this study suggest that the web of viaduct cross-section is not as rigid as assumed in the conventional viaduct design and the web face is likely to be more flexible in the vertical displacement of the concrete viaduct. Two types of local vibration modes along the cross-section are identified: the centre mode and the web mode. At the top panel of the viaduct, the centre mode has movement in the middle but not at the edges. The web mode has movement at the edges with the middle fixed. The combined centre and web mode has been found to be important in the structural acoustics of the concrete box structure. In the actual concrete viaduct, the coincidence frequency is especially low (often around

  18. Acoustical modes in lined ducts with flexible walls - A variational approach

    NASA Astrophysics Data System (ADS)

    Astley, R. J.

    A unified variational scheme is set forth for calculating axial wavenumbers, attenuations, and pressure distributions for acoustical modes propagating in flexible lined ducts. The technique accounts for the effects of bulk liners, flexible walls, and mean flow in the airway by describing a variational statement of the dispersion relationship for the propagation of fundamental modes. The variational statement can be applied as a Rayleigh-Ritz finite-element scheme to compute the eigenmodes for these ducts. The approach therefore unifies the computation of the fundamental dispersion relationships and the more complex modes described with high-resolution meshes. The approach is used to describe an experimental test duct without flow, and the Rayleigh-Ritz solution provides results that are similar to those of the full numerical solution. The present treatment is of practical interest to the design and fabrication of silencers and acoustically lined moving ductwork.

  19. Two true surface acoustic waves and other acoustic modes in (110) plane of Li2B4O7 substrate

    NASA Astrophysics Data System (ADS)

    Zhang, Victor Y.; Lefebvre, J. E.; Gryba, T.

    1999-09-01

    The surface acoustic waves (SAWs) and other acoustic modes propagating in the (110) plane of Li2B4O7 are investigated by means of the effective surface permittivity (ESP). It is demonstrated that the velocity of all piezoactive SAWs, both true and pseudo, as well as surface skimming bulk waves (SSBWs) can be numerically determined by computing the ESP as a function of acoustic trace slowness. A physical phenomenon not reported has been found for certain propagation directions, namely, simultaneous existence of two true SAWs, both being of the generalized Rayleigh type, together with a pseudo SAW of similar polarization. Propagation velocity, electromechanical coupling coefficient, and decay factor have been verified and confirmed by using two different sets of material constants and two numerical methods. The obtained values and accuracy of SAWs parameters are compared, and the validity conditions discussed. The generalized slowness diagram, plotted for the sagittal plane, enables to determine the total number of SSBW and to interpret the depth penetration properties of SAW. The Nyquist diagram of the ESP is shown to be a more helpful form for identifying a pseudo SAW and for distinguishing it from a SSBW.

  20. A new method to determine the asymptotic eigenfrequency equation of low-degree acoustic modes

    NASA Astrophysics Data System (ADS)

    Lopes, Ilídio P.

    2001-03-01

    The high accuracy of the observed solar spectra obtained from the space experiments GOLF and VIRGO has motivated us to develop a more precise asymptotic analysis of low-degree acoustic modes. Therefore we present a phase method to build an asymptotic solution to the equation of motion of acoustic oscillations. The principle consists of describing the oscillatory motion by a system of two first-order non-linear differential equations for the phase and amplitude. The equations are coupled only in the amplitude equation, leaving a single phase equation to determine the eigenfrequencies. We illustrate also the deficiency in the accuracy of standard asymptotic methods to determine the eigenfrequency, and highlight the advantages of this new method. The strength of this new technique is based on an accurate description of the phase dependence on the background state rather than on the wavefunction, as is done in standard asymptotic methods. This allows us to obtain a new asymptotic eigenvalue equation for low-degree acoustic modes, which is more accurate than the usual ones. In this case, the eigenfrequency equation is obtained without making the so-called Cowling approximation, i.e., by neglecting the Eulerian perturbation of the gravitational field. This allows us to obtain a new expression for the small separation, valid for the global acoustic modes of high and low radial orders.

  1. Vector Brillouin optical time-domain analyzer for high-order acoustic modes.

    PubMed

    Dossou, Michel; Bacquet, Denis; Szriftgiser, Pascal

    2010-11-15

    Thanks to a double-frequency phase modulation scheme, we report a vector Brillouin optical time-domain analyzer (BOTDA). This BOTDA has a high immunity level to noise, and it features a phase spectrogram capability. It is well suited for complex situations involving several acoustic resonances, such as high-order longitudinal modes. It has notably been used to characterize a dispersion-shifted fiber, allowing us to report spectrograms with multiple acoustic resonances. A very high 57 dB dynamic range is also reported for 100-ns-long pulses simultaneously with a 16 cm numerical resolution.

  2. Extremely high Q-factor mechanical modes in quartz bulk acoustic wave resonators at millikelvin temperature

    SciTech Connect

    Goryachev, M.; Creedon, D. L.; Ivanov, E. N.; Tobar, M. E.; Galliou, S.; Bourquin, R.

    2014-12-04

    We demonstrate that Bulk Acoustic Wave (BAW) quartz resonator cooled down to millikelvin temperatures are excellent building blocks for hybrid quantum systems with extremely long coherence times. Two overtones of the longitudinal mode at frequencies of 15.6 and 65.4 MHz demonstrate a maximum f.Q product of 7.8×10{sup 16} Hz. With this result, the Q-factor in such devices near the quantum ground state can be four orders of magnitude better than previously attained in other mechanical systems. Tested quartz resonators possess the ultra low acoustic losses crucial for electromagnetic cooling to the phonon ground state.

  3. Normal mode solutions for seismo-acoustic propagation resulting from shear and combined wave point sources.

    PubMed

    Nealy, Jennifer L; Collis, Jon M; Frank, Scott D

    2016-04-01

    Normal mode solutions to range-independent seismo-acoustic problems are benchmarked against elastic parabolic equation solutions and then used to benchmark the shear elastic parabolic equation self-starter [Frank, Odom, and Collis, J. Acoust. Soc. Am. 133, 1358-1367 (2013)]. The Pekeris waveguide with an elastic seafloor is considered for a point source located in the ocean emitting compressional waves, or in the seafloor, emitting both compressional and shear waves. Accurate solutions are obtained when the source is in the seafloor, and when the source is at the interface between the fluid and elastic layers.

  4. Damage Modes Recognition and Hilbert-Huang Transform Analyses of CFRP Laminates Utilizing Acoustic Emission Technique

    NASA Astrophysics Data System (ADS)

    WenQin, Han; Ying, Luo; AiJun, Gu; Yuan, Fuh-Gwo

    2016-04-01

    Discrimination of acoustic emission (AE) signals related to different damage modes is of great importance in carbon fiber-reinforced plastic (CFRP) composite materials. To gain a deeper understanding of the initiation, growth and evolution of the different types of damage, four types of specimens for different lay-ups and orientations and three types of specimens for interlaminar toughness tests are subjected to tensile test along with acoustic emission monitoring. AE signals have been collected and post-processed, the statistical results show that the peak frequency of AE signal can distinguish various damage modes effectively. After a AE signal were decomposed by Empirical Mode Decomposition (EMD) method, it may separate and extract all damage modes included in this AE signal apart from damage mode corresponding to the peak frequency. Hilbert-Huang Transform (HHT) of AE signals can clearly illustrate the frequency distribution of Intrinsic Mode Functions (IMF) components in time-scale in different damage stages, and can calculate accurate instantaneous frequency for damage modes recognition to help understanding the damage process.

  5. Variation of acoustic mode centroid frequencies over the solar cycle

    NASA Astrophysics Data System (ADS)

    Chaplin, W. J.; Appourchaux, T.; Elsworth, Y.; Isaak, G. R.; New, R.

    Together with a brief historical overview, we use high-quality helioseismic data collected by three different observational programmes during the declining phase of activity cycle 22, and a substantial portion of the rising phase of the current cycle (23), to study the phenomenological nature of the cycle-induced (centroid) eigenfrequencies. Our analyses (for 1600 ≤ ν ≤ 4000 μHz) make use of observations made by the ground-based GONG over the angular degree range 4 ≤ l ≤ 150; the ground-based BiSON over 0 ≤ l ≤ 2; and the VIRGO/LOI instrument on board the ESA/NASA SOHO satellite over 0 ≤ l ≤ 8. We show that GONG shifts averaged over different ranges in l, together with the BiSON and LOI data averaged over their full quoted ranges, all scale at a given frequency with the normalized mode inertia ratio Qnl (Christensen-Dalsgaard & Berthomieu 1991). This is to be expected if the time-dependent perturbation affecting the modes is confined in the surface layers; the excellent agreement also reflects favourably on the external consistency of the different observations. We have also analyzed the frequency dependence of the shifts by fitting a power-law of the form δν nl ∝ (ν nl/ Enl to the data (where the Enl are the mode inertias, and α is the power-law index to be extracted). Previous studies have suggested that a relation with α = 0 provides an adequate description of the shifts up to ν ≈ 3500 μHz. However, here we show that while nevertheless describing the shifts well up to ˜ 2500 μHz, the linear scaling breaks down conspicuously at higher frequencies. Above this threshold, the shifts follow a power-law dependence with α ˜ 2.

  6. An optical fibre sensor for acoustic wave mode decomposition

    NASA Astrophysics Data System (ADS)

    Rajic, N.; Davis, C.; Rosalie, C.

    2008-03-01

    This paper reports on the development of an optical fibre sensor comprising an array of uniformly distributed Bragg gratings that are configured to allow for the detection and modal decomposition of structural plate waves. Aspects of the design, fabrication and validation of the sensor are discussed. Laser vibrometry (LV) and advanced numerical modeling are used to demonstrate the fidelity of dynamic strain measurements furnished by a fibre Bragg grating. The sensor is applied in an experimental study involving a metal plate where it is shown that mode conversion of Lamb waves caused by a structural inhomogeneity is robustly measured.

  7. Modes of self-organization of diluted bubbly liquids in acoustic fields: One-dimensional theory.

    PubMed

    Gumerov, Nail A; Akhatov, Iskander S

    2017-02-01

    The paper is dedicated to mathematical modeling of self-organization of bubbly liquids in acoustic fields. A continuum model describing the two-way interaction of diluted polydisperse bubbly liquids and acoustic fields in weakly-nonlinear approximation is studied analytically and numerically in the one-dimensional case. It is shown that the regimes of self-organization of monodisperse bubbly liquids can be controlled by only a few dimensionless parameters. Two basic modes, clustering and propagating shock waves of void fraction (acoustically induced transparency), are identified and criteria for their realization in the space of parameters are proposed. A numerical method for solving of one-dimensional self-organization problems is developed. Computational results for mono- and polydisperse systems are discussed.

  8. Direct experimental investigations of acoustic modes guided by a solid{endash}solid interface using optical interferometry

    SciTech Connect

    Matteie, C.; Jia, X.; Quentin, G.

    1997-09-01

    This paper presents direct field measurements of acoustic modes guided by the interface between two transparent solids. The measurement technique is based on the acousto-optical interaction inside the solid between the acoustic field and the probe laser beam of an interferometer. The main advantage of the method is its ability to measure acoustic strain fields in areas of difficult access with the classic detection methods. Moreover, it gives complete information about the dilatation strain field inside the solid, e.g., amplitude and phase. The propagation of a real velocity mode (Stoneley wave) is first illustrated. Then the situation of complex velocity modes is investigated for a Plexiglas{endash}fused quartz slip interface. This material combination supports two possible interface modes theoretically. These modes are simultaneously observed and the differences between their behavior are measured. {copyright} {ital 1997 Acoustical Society of America.}

  9. A hybrid deconvolution approach to separate acoustic sources in multiple motion modes.

    PubMed

    Mo, Pinxi; Jiang, Weikang

    2017-07-01

    Motion mode is defined as a characteristic motion that a group of sources follow. If there are multiple groups of sources moving in the corresponding multiple motion modes, the beamforming map for a certain group of sources will be contaminated by the leakages from the other groups of sources. The original beamforming or deconvolution approaches fail to interpret the acoustic maps, as the source leakages may be mistaken for actual sources. A hybrid deconvolution approach is proposed to restrain the source leakages, so as to separate the acoustic sources in multiple motion modes. This approach simultaneously considers all the sources in the potential motion modes, and introduces equivalent sources in the corresponding motion modes to represent the sources. The equivalence between the actual sources and the equivalent sources leads to the construction of an expanded linear matrix equation. The sources in the respective motion modes are simultaneously extracted by solving the equation. The approach is shown effective by two numerical simulations and a practical experiment on two counter-rotating sources and one static source.

  10. A transversal substructuring mode matching method applied to the acoustic analysis of dissipative mufflers

    NASA Astrophysics Data System (ADS)

    Albelda, J.; Denia, F. D.; Torres, M. I.; Fuenmayor, F. J.

    2007-06-01

    To carry out the acoustic analysis of dissipative silencers with uniform cross-section, the application of the mode matching method at the geometrical discontinuities is an attractive option from a computational point of view. The consideration of this methodology assumes, in general, that the modes associated with the transversal geometry of each element with uniform cross-section are known for the excitation frequencies considered in the analysis. The calculation of the transversal modes is not, however, a simple task when the acoustic system involves perforated elements and absorbent materials. The current work presents a modal approach to calculate the transversal modes and the corresponding axial wavenumbers for dissipative mufflers of uniform (but arbitrary) cross-section. The proposed technique is based on the division of the transversal section into subdomains and the subsequent use of a substructuring procedure with two sets of modes to improve the convergence. The former set of modes fulfils the condition of zero pressure at the common boundary between transversal subdomains while the latter satisfies the condition of zero derivative in the direction normal to the boundary. The approach leads to a versatile methodology with a moderate computational effort that can be applied to mufflers commonly found in real applications. To validate the procedure presented in this work, comparisons are provided with finite element predictions and results available in the literature, showing a good agreement. In addition, the procedure is applied to an example of practical interest.

  11. Focal characteristics of spheroidal geodesic lenses for integrated optical processing

    NASA Technical Reports Server (NTRS)

    Vahey, D. W.; Wood, V. E.

    1977-01-01

    Aspheric shaping of geodesic lenses in optical waveguides is suggested as a means for correcting spherical aberrations. The technique is complementary to the method of Spiller and Harper, in which geodesic lens aberrations are reduced by thickening the waveguiding layer in the lens region. The properties of a family of oblate-spheroidal lenses with no third-order spherical aberrations are described theoretically. Diffraction-limited performance over apertures up to one-half the full lens aperture is predicted for lenses with true f/numbers (focal length divided by useful aperture) in the range 2-12. By combining spheroidal-shaping and mode-index correction techniques, geodesic lenses free from both third- and fifth-order aberrations can be designed. These lenses show diffraction-limited performance over apertures of a centimeter or more when true f/numbers are in the range 1.5-9.5.

  12. The first radial-mode Lorentzian Landau damping of dust acoustic space-charge waves

    SciTech Connect

    Lee, Myoung-Jae; Jung, Young-Dae

    2016-05-15

    The dispersion properties and the first radial-mode Lorentzian Landau damping of a dust acoustic space-charge wave propagating in a cylindrical waveguide dusty plasma which contains nonthermal electrons and ions are investigated by employing the normal mode analysis and the method of separation of variables. It is found that the frequency of dust acoustic space-charge wave increases as the wave number increases as well as the radius of cylindrical plasma does. However, the nonthermal property of the Lorentzian plasma is found to suppress the wave frequency of the dust acoustic space-charge wave. The Landau damping rate of the dust acoustic space-charge wave is derived in a cylindrical waveguide dusty plasma. The damping of the space-charge wave is found to be enhanced as the radius of cylindrical plasma and the nonthermal property increase. The maximum Lorentzian Landau damping rate is also found in a cylindrical waveguide dusty plasma. The variation of the wave frequency and the Landau damping rate due to the nonthermal character and geometric effects are also discussed.

  13. Studies of elasticity, sound propagation and attenuation of acoustic modes in granular media: final report

    SciTech Connect

    Makse, Hernan A.; Johnson, David L.

    2014-09-03

    This is the final report describing the results of DOE Grant # DE-FG02-03ER15458 with original termination date of April 31, 2013, which has been extended to April 31, 2014. The goal of this project is to develop a theoretical and experimental understanding of sound propagation, elasticity and dissipation in granular materials. The topic is relevant for the efficient production of hydrocarbon and for identifying and characterizing the underground formation for storage of either CO2 or nuclear waste material. Furthermore, understanding the basic properties of acoustic propagation in granular media is of importance not only to the energy industry, but also to the pharmaceutical, chemical and agricultural industries. We employ a set of experimental, theoretical and computational tools to develop a study of acoustics and dissipation in granular media. These include the concept effective mass of granular media, normal modes analysis, statistical mechanics frameworks and numerical simulations based on Discrete Element Methods. Effective mass measurements allow us to study the mechanisms of the elastic response and attenuation of acoustic modes in granular media. We perform experiments and simulations under varying conditions, including humidity and vacuum, and different interparticle force-laws to develop a fundamental understanding of the mechanisms of damping and acoustic propagation in granular media. A theoretical statistical approach studies the necessary phase space of configurations in pressure, volume fraction to classify granular materials.

  14. Resonant transmission and mode modulation of acoustic waves in H-shaped metallic gratings

    SciTech Connect

    Deng, Yu-Qiang; Fan, Ren-Hao; Zhang, Kun; Peng, Ru-Wen E-mail: dongxiang87@gmail.com; Qi, Dong-Xiang E-mail: dongxiang87@gmail.com

    2015-04-15

    In this work, we demonstrate that resonant full transmission of acoustic waves exists in subwavelength H-shaped metallic gratings, and transmission peaks can be efficiently tuned by adjusting the grating geometry. We investigate this phenomenon through both numerical simulations and theoretical calculations based on rigorous-coupled wave analysis. The transmission peaks are originated from Fabry-Perot resonances together with the couplings between the diffractive wave on the surface and the multiple guided modes in the slits. Moreover, the transmission modes can be efficiently tuned by adjusting the cavity geometry, without changing the grating thickness. The mechanism is analyzed based on an equivalent circuit model and verified by both the theoretical calculations and the numerical simulations. This research has potential application in acoustic-device miniaturization over a wide range of wavelengths.

  15. Effect of wind tunnel acoustic modes on linear oscillating cascade aerodynamics

    NASA Technical Reports Server (NTRS)

    Buffum, D. H.; Fleeter, S.

    1994-01-01

    The aerodynamics of a biconvex airfoil cascade oscillating in torsion is investigated using the unsteady aerodynamic influence coefficient technique. For subsonic flow and reduced frequencies as large as 0.9, airfoil surface unsteady pressures resulting from oscillation of one of the airfoils are measured using flush-mounted high-frequency-response pressure transducers. The influence coefficient data are examined in detail and then used to predict the unsteady aerodynamics of a cascade oscillating at various interblade phase angles. These results are correlated with experimental data obtained in the traveling-wave mode of oscillation and linearized analysis predictions. It is found that the unsteady pressure disturbances created by an oscillating airfoil excite wind tunnel acoustic modes, which have detrimental effects on the experimental results. Acoustic treatment is proposed to rectify this problem.

  16. Effect of wind tunnel acoustic modes on linear oscillating cascade aerodynamics

    NASA Technical Reports Server (NTRS)

    Buffum, Daniel H.; Fleeter, Sanford

    1993-01-01

    The aerodynamics of a biconvex airfoil cascade oscillating in torsion is investigated using the unsteady aerodynamic influence coefficient technique. For subsonic flow and reduced frequencies as large as 0.9, airfoil surface unsteady pressures resulting from oscillation of one of the airfoils are measured using flush-mounted high-frequency-response pressure transducers. The influence coefficient data are examined in detail and then used to predict the unsteady aerodynamics of a cascade oscillating at various interblade phase angles. These results are correlated with experimental data obtained in the traveling-wave mode of oscillation and linearized analysis predictions. It is found that the unsteady pressure disturbances created by an oscillating airfoil excite wind tunnel acoustic modes which have detrimental effects on the experimental data. Acoustic treatment is proposed to rectify this problem.

  17. Intensification of acoustic beams in crystals at mode conversion near total internal reflection

    NASA Astrophysics Data System (ADS)

    Alshits, V. I.; Bessonov, D. A.; Lyubimov, V. N.

    2017-07-01

    Geometrical conditions under which mode conversion occurs in a crystal near total internal reflection of an acoustic beam are found. In this case, the entire energy of an incident pump wave is spent on the excitation of a narrow intense reflected beam close in structure to an eigenmode. A consistent choice of orientations of the sagittal plane and surface that excludes the reflection of a parasitic wave of leakage is found.

  18. Geodesic self-organizing map

    NASA Astrophysics Data System (ADS)

    Wu, Yingxin; Takatsuka, Masahiro

    2005-03-01

    Self-Organizing map (SOM) is a widely used tool to find clustering and also to visualize high dimensional data. Several spherical SOMs have been proposed to create a more accurate representation of the data by removing the "border effect". In this paper, we compare several spherical lattices for the purpose of implementation of a SOM. We then introduce a 2D rectangular grid data structure for representing the geodesic dome. This new approach improves the neighborhood searching process in the spherical gird. The new Geodesic SOM and its data structure are tested using socio-demographic data. In the experiments, we try to create a notion of direction in the Geodesic SOM. The direction facilitates more consistent visual comparison of different datasets as well as to assist viewers building their mental maps.

  19. Time-warped geodesic regression.

    PubMed

    Hong, Yi; Singh, Nikhil; Kwitt, Roland; Niethammer, Marc

    2014-01-01

    We consider geodesic regression with parametric time-warps. This allows for example, to capture saturation effects as typically observed during brain development or degeneration. While highly-flexible models to analyze time-varying image and shape data based on generalizations of splines and polynomials have been proposed recently, they come at the cost of substantially more complex inference. Our focus in this paper is therefore to keep the model and its inference as simple as possible while allowing to capture expected biological variation. We demonstrate that by augmenting geodesic regression with parametric time-warp functions, we can achieve comparable flexibility to more complex models while retaining model simplicity. In addition, the time-warp parameters provide useful information of underlying anatomical changes as demonstrated for the analysis of corpora callosa and rat calvariae. We exemplify our strategy for shape regression on the Grassmann manifold, but note that the method is generally applicable for time-warped geodesic regression.

  20. Time-Warped Geodesic Regression

    PubMed Central

    Hong, Yi; Singh, Nikhil; Kwitt, Roland; Niethammer, Marc

    2016-01-01

    We consider geodesic regression with parametric time-warps. This allows, for example, to capture saturation effects as typically observed during brain development or degeneration. While highly-flexible models to analyze time-varying image and shape data based on generalizations of splines and polynomials have been proposed recently, they come at the cost of substantially more complex inference. Our focus in this paper is therefore to keep the model and its inference as simple as possible while allowing to capture expected biological variation. We demonstrate that by augmenting geodesic regression with parametric time-warp functions, we can achieve comparable flexibility to more complex models while retaining model simplicity. In addition, the time-warp parameters provide useful information of underlying anatomical changes as demonstrated for the analysis of corpora callosa and rat calvariae. We exemplify our strategy for shape regression on the Grassmann manifold, but note that the method is generally applicable for time-warped geodesic regression. PMID:25485368

  1. Rotating rake design for unique measurement of fan-generated spinning acoustic modes

    NASA Technical Reports Server (NTRS)

    Konno, Kevin E.; Hausmann, Clifford R.

    1993-01-01

    In light of the current emphasis on noise reduction in subsonic aircraft design, NASA has been actively studying the source of and propagation of noise generated by subsonic fan engines. NASA/LeRC has developed and tested a unique method of accurately measuring these spinning acoustic modes generated by an experimental fan. This mode measuring method is based on the use of a rotating microphone rake. Testing was conducted in the 9 x 15 Low-speed Wind Tunnel. The rotating rake was tested with the Advanced Ducted Propeller (ADP) model. This memorandum discusses the design and performance of the motor/drive system for the fan-synchronized rotating acoustic rake. This novel motor/drive design approach is now being adapted for additional acoustic mode studies in new test rigs as baseline data for the future design of active noise control for subsonic fan engines. Included in this memorandum are the research requirements, motor/drive specifications, test performance results, and a description of the controls and software involved.

  2. A generalized hydrodynamic model for acoustic mode stability in viscoelastic plasma fluid

    NASA Astrophysics Data System (ADS)

    Borah, B.; Haloi, A.; Karmakar, P. K.

    2016-05-01

    In this paper a generalized hydrodynamic (GH) model to investigate acoustic-mode excitation and stability in simplified strongly coupled bi-component plasma is proposed. The goal is centered in seeing the viscoelasticity-influences on the instability properties. The dispersive and nondispersive features are methodologically explored followed by numerical illustrations. It is seen that, unlike usual plasma acoustic mode, here the mode stability is drastically modified due to the considered viscoelastic effects contributed from both the electronic and ionic fluids. For example, it is found that there exists an excitation threshold value on angular wavenumber, K ≈3 in the K-space on the Debye scale, beyond which only dispersive characteristic features prevail. Further, it is demonstrated that the viscoelastic relaxation time plays a stabilizing influential role on the wave dynamics. In contrast, it is just opposite for the effective viscoelastic relaxation effect. Consistency with the usual viscoelasticity-free situations, with and without plasma approximation taken into account, is also established and explained. It is identified and conjectured that the plasma fluid viscoelasticity acts as unavoidable dispersive agency in attributing several new characteristics to acoustic wave excitation and propagation. The analysis is also exploited to derive a quantitative glimpse on the various basic properties and dimensionless numbers of the viscoelastic plasma. Finally, extended implications of our results tentative to different cosmic, space and astrophysical situations, amid the entailed facts and faults, are highlighted together with indicated future directions.

  3. Modelling the Influence of Acoustic Liner Non-Uniformities on Duct Modes

    NASA Astrophysics Data System (ADS)

    Regan, B.; Eaton, J.

    1999-02-01

    In most turbofan engine intakes, the acoustically lined region consists of several liner segments which are separated by longitudinal hard-walled intercostal strips or splices. Measurements indicate that the duct modal spectrum can be considerably altered by such circumferential variations in acoustic properties, with energy being transferred from an incident mode to several others. To investigate and quantify this phenomenon, a three-dimensional, frequency domain finite element method has been developed. The computational domain represents a length of infinite, hard-walled duct of circular cross-section fitted with a region of longitudinally spliced liner. A modal coupling scheme is used, in which complex modal input amplitudes are specified across a section at one end of the computational duct domain and the amplitudes and phases of the transmitted modes are captured at the other end. In addition, to model the convective effect of flow in the duct, a uniform, unidirectional flow field is treated. The method is verified by comparing predictions with analytical solutions and is then used to analyze a liner with splices. It is demonstrated that incident modes are significantly affected by the circumferential variations in impedance and as such, the influence of liner splices on the transmitted acoustic field ought to be further investigated.

  4. Influence of exit impedance on finite difference solutions of transient acoustic mode propagation in ducts

    NASA Technical Reports Server (NTRS)

    Baumeister, K. J.

    1981-01-01

    The cutoff mode instability problem associated with a transient finite difference solution to the wave equation is explained. The steady-state impedance boundary condition is found to produce acoustic reflections during the initial transient, which cause finite instabilities in the cutoff modes. The stability problem is resolved by extending the duct length to prevent transient reflections. Numerical calculations are presented at forcing frequencies above, below, and nearly at the cutoff frequency, and exit impedance models are presented for use in the practical design of turbofan inlets.

  5. Angular Momentum Transport and Variability in Boundary Layers of Accretion Disks Driven by Global Acoustic Modes

    NASA Astrophysics Data System (ADS)

    Belyaev, Mikhail A.; Rafikov, Roman R.; Stone, James M.

    2012-11-01

    Disk accretion onto a weakly magnetized central object, e.g., a star, is inevitably accompanied by the formation of a boundary layer near the surface, in which matter slows down from the highly supersonic orbital velocity of the disk to the rotational velocity of the star. We perform high-resolution two-dimensional hydrodynamical simulations in the equatorial plane of an astrophysical boundary layer with the goal of exploring the dynamics of non-axisymmetric structures that form there. We generically find that the supersonic shear in the boundary layer excites non-axisymmetric quasi-stationary acoustic modes that are trapped between the surface of the star and a Lindblad resonance in the disk. These modes rotate in a prograde fashion, are stable for hundreds of orbital periods, and have a pattern speed that is less than and of the order of the rotational velocity at the inner edge of the disk. The origin of these intrinsically global modes is intimately related to the operation of a corotation amplifier in the system. Dissipation of acoustic modes in weak shocks provides a universal mechanism for angular momentum and mass transport even in purely hydrodynamic (i.e., non-magnetized) boundary layers. We discuss the possible implications of these trapped modes for explaining the variability seen in accreting compact objects.

  6. ANGULAR MOMENTUM TRANSPORT AND VARIABILITY IN BOUNDARY LAYERS OF ACCRETION DISKS DRIVEN BY GLOBAL ACOUSTIC MODES

    SciTech Connect

    Belyaev, Mikhail A.; Stone, James M.; Rafikov, Roman R.

    2012-11-20

    Disk accretion onto a weakly magnetized central object, e.g., a star, is inevitably accompanied by the formation of a boundary layer near the surface, in which matter slows down from the highly supersonic orbital velocity of the disk to the rotational velocity of the star. We perform high-resolution two-dimensional hydrodynamical simulations in the equatorial plane of an astrophysical boundary layer with the goal of exploring the dynamics of non-axisymmetric structures that form there. We generically find that the supersonic shear in the boundary layer excites non-axisymmetric quasi-stationary acoustic modes that are trapped between the surface of the star and a Lindblad resonance in the disk. These modes rotate in a prograde fashion, are stable for hundreds of orbital periods, and have a pattern speed that is less than and of the order of the rotational velocity at the inner edge of the disk. The origin of these intrinsically global modes is intimately related to the operation of a corotation amplifier in the system. Dissipation of acoustic modes in weak shocks provides a universal mechanism for angular momentum and mass transport even in purely hydrodynamic (i.e., non-magnetized) boundary layers. We discuss the possible implications of these trapped modes for explaining the variability seen in accreting compact objects.

  7. Influence of material parameters on acoustic wave propagation modes in ZnO/Si bi-layered structures.

    PubMed

    Gao, Hui-dong; Zhang, Shu-Yi; Qi, Xue; Wasa, Kiyotaka; Wu, Hao-Dong

    2005-12-01

    The influences of material properties on acoustic wave propagation modes in ZnO/Si bi-layered structures are studied. The transfer matrix method is used to calculate dispersion relations, wave field distributions, and electromechanical coupling coefficients of acoustic wave propagation modes in ZnO/Si bi-layered systems, in which the thickness of the substrate is of the same order of magnitude as the wavelength of the propagating wave modes. The influences of the thin film parameters on the acoustic wave propagation modes and their electromechanical coupling coefficients of the wave modes also are obtained. In addition, some experimental results for characterizing the wave propagation modes and their frequencies have also been obtained, which agree well with the theoretical predictions.

  8. Geodesic behavior of sudden future singularities

    SciTech Connect

    Fernandez-Jambrina, L.; Lazkoz, Ruth

    2004-12-15

    In this paper we analyze the effect of recently proposed classes of sudden future singularities on causal geodesics of FLRW spacetimes. Geodesics are shown to be extendible and just the equations for geodesic deviation are singular, although tidal forces are not strong enough to produce a Big Rip. For the sake of completeness, we compare with the typical sudden future singularities of phantom cosmologies.

  9. On the acoustic radiation modes of compact regular polyhedral arrays of independent loudspeakers.

    PubMed

    Pasqual, Alexander Mattioli; Martin, Vincent

    2011-09-01

    Compact spherical loudspeaker arrays can be used to provide control over their directivity pattern. Usually, this is made by adjusting the gains of preprogrammed spatial filters corresponding to a finite set of spherical harmonics, or to the acoustic radiation modes of the loudspeaker array. Unlike the former, the latter are closely related to the radiation efficiency of the source and span the subspace of the directivities it can produce. However, the radiation modes depend on frequency for arbitrary distributions of transducers on the sphere, which yields complex directivity filters. This work focuses on the most common loudspeaker array configurations, those following the regular shape of the Platonic solids. It is shown that the radiation modes of these sources are frequency independent, and simple algebraic expressions are derived for their radiation efficiencies. In addition, since such modes are vibration patterns driven by electrical signals, the transduction mechanism of compact multichannel sources is also investigated, which is an important issue, especially if the transducers interact inside a shared cabinet. For Platonic solid loudspeakers, it is shown that the common enclosure does not lead to directivity filters that depend on frequency. © 2011 Acoustical Society of America

  10. Deformation pathways and breakup modes in acoustically levitated bicomponent droplets under external heating

    NASA Astrophysics Data System (ADS)

    Pathak, Binita; Basu, Saptarshi

    2016-03-01

    Controlled breakup of droplets using heat or acoustics is pivotal in applications such as pharmaceutics, nanoparticle production, and combustion. In the current work we have identified distinct thermal acoustics-induced deformation regimes (ligaments and bubbles) and breakup dynamics in externally heated acoustically levitated bicomponent (benzene-dodecane) droplets with a wide variation in volatility of the two components (benzene is significantly more volatile than dodecane). We showcase the physical mechanism and universal behavior of droplet surface caving in leading to the inception and growth of ligaments. The caving of the top surface is governed by a balance between the acoustic pressure field and the restrictive surface tension of the droplet. The universal collapse of caving profiles for different benzene concentration (<70 % by volume) is shown by using an appropriate time scale obtained from force balance. Continuous caving leads to the formation of a liquid membrane-type structure which undergoes radial extension due to inertia gained during the precursor phase. The membrane subsequently closes at the rim and the kinetic energy leads to ligament formation and growth. Subsequent ligament breakup is primarily Rayleigh-Plateau type. The breakup mode shifts to diffusional entrapment-induced boiling with an increase in concentration of the volatile component (benzene >70 % by volume). The findings are portable to any similar bicomponent systems with differential volatility.

  11. Acoustic emission localization in plates with dispersion and reverberations using sparse PZT sensors in passive mode

    NASA Astrophysics Data System (ADS)

    Perelli, Alessandro; De Marchi, Luca; Marzani, Alessandro; Speciale, Nicolò

    2012-02-01

    A strategy for the localization of acoustic emissions (AE) in plates with dispersion and reverberation is proposed. The procedure exploits signals received in passive mode by sparse conventional piezoelectric transducers and a three-step processing framework. The first step consists in a signal dispersion compensation procedure, which is achieved by means of the warped frequency transform. The second step concerns the estimation of the differences in arrival time (TDOA) of the acoustic emission at the sensors. Complexities related to reflections and plate resonances are overcome via a wavelet decomposition of cross-correlating signals where the mother function is designed by a synthetic warped cross-signal. The magnitude of the wavelet coefficients in the warped distance-frequency domain, in fact, precisely reveals the TDOA of an acoustic emission at two sensors. Finally, in the last step the TDOA data are exploited to locate the acoustic emission source through hyperbolic positioning. The proposed procedure is tested with a passive network of three/four piezo-sensors located symmetrically and asymmetrically with respect to the plate edges. The experimentally estimated AE locations are close to those theoretically predicted by the Cramèr-Rao lower bound.

  12. Electro-opto-mechanical radio-frequency oscillator driven by guided acoustic waves in standard single-mode fiber

    NASA Astrophysics Data System (ADS)

    London, Yosef; Diamandi, Hilel Hagai; Zadok, Avi

    2017-04-01

    An opto-electronic radio-frequency oscillator that is based on forward scattering by the guided acoustic modes of a standard single-mode optical fiber is proposed and demonstrated. An optical pump wave is used to stimulate narrowband, resonant guided acoustic modes, which introduce phase modulation to a co-propagating optical probe wave. The phase modulation is converted to an intensity signal at the output of a Sagnac interferometer loop. The intensity waveform is detected, amplified, and driven back to modulate the optical pump. Oscillations are achieved at a frequency of 319 MHz, which matches the resonance of the acoustic mode that provides the largest phase modulation of the probe wave. Oscillations at the frequencies of competing acoustic modes are suppressed by at least 40 dB. The linewidth of the acoustic resonance is sufficiently narrow to provide oscillations at a single longitudinal mode of the hybrid cavity. Competing longitudinal modes are suppressed by at least 38 dB as well. Unlike other opto-electronic oscillators, no radio-frequency filtering is required within the hybrid cavity. The frequency of oscillations is entirely determined by the fiber opto-mechanics.

  13. Accuracy of the Kirchhoff-approximation and Kirchhoff-ray-mode fish swimbladder acoustic scattering models.

    PubMed

    Macaulay, Gavin J; Peña, Héctor; Fässler, Sascha M M; Pedersen, Geir; Ona, Egil

    2013-01-01

    The acoustic backscatter from pressure release prolate spheroids and a three-dimensional representation of a fish swimbladder (Chilean jack mackerel, Trachurus symmetricus murphyi) was calculated using four target strength models (Kirchhoff-approximation, Kirchhoff-ray-mode, finite element solution of the Helmholtz equation, and prolate-spheroid-modal-series). Smoothly varying errors were found in the Kirchhoff-approximation and Kirchhoff-ray-mode model results when compared to the other models, and provide objective criteria for constraining the use of the KA and KRM models. A generic correction technique is also proposed for the prolate spheroid estimates and tentatively tested on a jack mackerel swimbladder, resulting in improvements to the target strength estimates from the Kirchhoff-approximation and Kirchhoff-ray-mode models.

  14. Properties of acoustic plate modes in YZ LiNbO₃.

    PubMed

    Soluch, Waldemar; Lysakowska, Magdalena

    2013-01-01

    Properties of acoustic plate modes (APMs) in YZ LiNbO₃ were calculated and measured. It was found that these modes have a dominant longitudinal component of mechanical motion concentrated near both surfaces of a plate. A delay line with double-electrode interdigital transducers (IDTs) was used for the measurements. Because of good matching to the load, strong triple-transit signals (TTS) were generated and insertion loss of about 7 dB was achieved at a frequency of about 131.4 MHz. Using water and glycerin solutions, insertion loss changes against viscosity were measured for this mode. In a viscosity range from about 1 mPa·s to 1000 mPa·s, an insertion loss change of about 16 dB was obtained. High sensitivity of viscosity measurement over a wide range makes the APMs in YZ LiNbO₃ attractive for application in viscosity sensors.

  15. Thin plate model for transverse mode analysis of surface acoustic wave devices

    NASA Astrophysics Data System (ADS)

    Tang, Gongbin; Han, Tao; Chen, Jing; Zhang, Benfeng; Omori, Tatsuya; Hashimoto, Ken-ya

    2016-07-01

    In this paper, we propose a physical model for the analysis of transverse modes in surface acoustic wave (SAW) devices. It is mostly equivalent to the scalar potential (SP) theory, but sufficiently flexible to include various effects such as anisotropy, coupling between multiple modes, etc. First, fundamentals of the proposed model are established and procedures for determining the model parameters are given in detailed. Then the model is implemented in the partial differential equation mode of the commercial finite element analysis software COMSOL. The analysis is carried out for an infinitely long interdigital transducer on the 128°YX-LiNbO3 substrate. As a demonstration, it is shown how the energy leakage changes with the frequency and the device design.

  16. The dependence of acoustic properties of a crack on the resonance mode and geometry

    USGS Publications Warehouse

    Kumagai, H.; Chouet, B.A.

    2001-01-01

    We examine the dependence of the acoustic properties of a crack containing magmatic or hydrothermal fluids on the resonance mode and geometry to quantify the source properties of long-period (LP) events observed in volcanic areas. Our results, based on spectral analyses of synthetic waveforms generated with a fluid-driven crack model, indicate that the basic features of the dimensionless frequency (??) and quality factor (Qr) for a crack containing various types of fluids are not strongly affected by the choice of mode, although the actual ranges of Q?? and ?? both depend on the mode. The dimensionless complex frequency systematically varies with changes in the crack geometry, showing increases in both Qr and ?? as the crack length to aperture ratio decreases. The present results may be useful for the interpretation of spatial and temporal variations in the observed complex frequencies of LP events.

  17. Generalized concept of shear horizontal acoustic plate mode and Love wave sensors

    NASA Astrophysics Data System (ADS)

    McHale, Glen

    2003-11-01

    An approach to mass and liquid sensitivity for both the phase velocity and insertion loss of shear mode acoustic wave sensors based on the dispersion equations for layered systems is outlined. The approach is sufficiently general to allow for viscoelastic guiding layers. An equation for the phase velocity and insertion loss sensitivities is given which depends on the slope of the complex phase velocity dispersion curves. This equation contains the equivalent of the Sauerbrey and Kanazawa equations for loading of a quartz crystal microbalance by rigid mass and Newtonian liquids, respectively, and also describes surface loading by viscoelastic layers. The theoretical approach can be applied to a four-layer system, with any of the four layers being viscoelastic, so that mass deposition from a liquid can also be modelled. The theoretical dispersion equation based approach to layer-guided shear horizontal acoustic wave modes on finite substrates presented in this work provides a unified view of Love wave and shear horizontal acoustic plate mode (SH-APM) devices, which have been generally regarded as distinct in sensor research. It is argued that SH-APMs with guiding layers possessing shear acoustic speeds lower than that of the substrate and Love waves are two branches of solution of the same dispersion equation. The layer guided SH-APMs have a phase velocity higher than that of the substrate and the Love waves a phase velocity lower than that of the substrate. Higher-order Love wave modes are continuations of the layer-guided SH-APMs. The generalized concept of SH-APMs and Love waves provides a basis for understanding the change in sensitivity with higher-frequency operation and the relationship between multiple modes in Love wave sensors. It also explains why a relatively thick layer of a high-loss polymer can be used as a waveguide layer and so extends the range of materials that can be considered experimentally. Moreover, it is predicted that a new type of sensor, a

  18. Fast scanning mode and its realization in a scanning acoustic microscope

    SciTech Connect

    Ju Bingfeng; Bai Xiaolong; Chen Jian

    2012-03-15

    The scanning speed of the two-dimensional stage dominates the efficiency of mechanical scanning measurement systems. This paper focused on a detailed scanning time analysis of conventional raster and spiral scan modes and then proposed two fast alternative scanning modes. Performed on a self-developed scanning acoustic microscope (SAM), the measured images obtained by using the conventional scan mode and fast scan modes are compared. The total scanning time is reduced by 29% of the two proposed fast scan modes. It will offer a better solution for high speed scanning without sacrificing the system stability, and will not introduce additional difficulties to the configuration of scanning measurement systems. They can be easily applied to the mechanical scanning measuring systems with different driving actuators such as piezoelectric, linear motor, dc motor, and so on. The proposed fast raster and square spiral scan modes are realized in SAM, but not specially designed for it. Therefore, they have universal adaptability and can be applied to other scanning measurement systems with two-dimensional mechanical scanning stages, such as atomic force microscope or scanning tunneling microscope.

  19. Fast scanning mode and its realization in a scanning acoustic microscope.

    PubMed

    Ju, Bing-Feng; Bai, Xiaolong; Chen, Jian

    2012-03-01

    The scanning speed of the two-dimensional stage dominates the efficiency of mechanical scanning measurement systems. This paper focused on a detailed scanning time analysis of conventional raster and spiral scan modes and then proposed two fast alternative scanning modes. Performed on a self-developed scanning acoustic microscope (SAM), the measured images obtained by using the conventional scan mode and fast scan modes are compared. The total scanning time is reduced by 29% of the two proposed fast scan modes. It will offer a better solution for high speed scanning without sacrificing the system stability, and will not introduce additional difficulties to the configuration of scanning measurement systems. They can be easily applied to the mechanical scanning measuring systems with different driving actuators such as piezoelectric, linear motor, dc motor, and so on. The proposed fast raster and square spiral scan modes are realized in SAM, but not specially designed for it. Therefore, they have universal adaptability and can be applied to other scanning measurement systems with two-dimensional mechanical scanning stages, such as atomic force microscope or scanning tunneling microscope.

  20. A new electromagnetic acoustic transducer design for generating torsional guided wave modes for pipe inspections

    NASA Astrophysics Data System (ADS)

    Hill, Samuel; Dixon, Steve; Sri Harsha Reddy, K.; Rajagopal, Prabhu; Balasubramaniam, Krishnan

    2017-02-01

    Guided waves inspection is a well-established method for the long-range ultrasonic inspection of pipes. Guided waves, used in a pulse-echo arrangement, can inspect a large range of the pipe from a single point as the pipe structure carries the waves over a large distance due to the relatively low attenuation of the wave modes. However, the complexity of the dispersion characteristics of these pipe guided wave modes are well known, and can lead to diffculty interpreting the obtained results. The torsional family of guided wave modes are generally considered to have much simpler dispersion characteristics; especially the fundamental T(0,1) mode, which is nominally non-dispersive, making it particularly useful for guided wave inspection. Torsional waves have been generated by a circumferential ring of transducers to approximate an axi-symmetric load to excite this T(0, 1) mode. Presented here is a new design of Electromagnetic Acoustic Transducer (EMAT) that can generate a T(0, 1) as a single transducer, rather than a circumferential array of transducers that all need to be excited in order to generate an axisymmetric force. The EMAT consists of a periodic permanent magnet array and a single meander coil, meaning that the excitation of the torsional mode is greatly simplified. The design parameters of this new EMAT are explored, and the ability to detect notch defects on a pipe is demonstrated.

  1. Investigation into mass loading sensitivity of sezawa wave mode-based surface acoustic wave sensors.

    PubMed

    Mohanan, Ajay Achath; Islam, Md Shabiul; Ali, Sawal Hamid; Parthiban, R; Ramakrishnan, N

    2013-02-06

    In this work mass loading sensitivity of a Sezawa wave mode based surface acoustic wave (SAW) device is investigated through finite element method (FEM) simulation and the prospects of these devices to function as highly sensitive SAW sensors is reported. A ZnO/Si layered SAW resonator is considered for the simulation study. Initially the occurrence of Sezawa wave mode and displacement amplitude of the Rayleigh and Sezawa wave mode is studied for lower ZnO film thickness. Further, a thin film made of an arbitrary material is coated over the ZnO surface and the resonance frequency shift caused by mass loading of the film is estimated. It was observed that Sezawa wave mode shows significant sensitivity to change in mass loading and has higher sensitivity (eight times higher) than Rayleigh wave mode for the same device configuration. Further, the mass loading sensitivity was observed to be greater for a low ZnO film thickness to wavelength ratio. Accordingly, highly sensitive SAW sensors can be developed by coating a sensing medium over a layered SAW device and operating at Sezawa mode resonance frequency. The sensitivity can be increased by tuning the ZnO film thickness to wavelength ratio.

  2. ANGULAR MOMENTUM TRANSPORT BY ACOUSTIC MODES GENERATED IN THE BOUNDARY LAYER. I. HYDRODYNAMICAL THEORY AND SIMULATIONS

    SciTech Connect

    Belyaev, Mikhail A.; Rafikov, Roman R.; Stone, James M.

    2013-06-10

    The nature of angular momentum transport in the boundary layers of accretion disks has been one of the central and long-standing issues of accretion disk theory. In this work we demonstrate that acoustic waves excited by supersonic shear in the boundary layer serve as an efficient mechanism of mass, momentum, and energy transport at the interface between the disk and the accreting object. We develop the theory of angular momentum transport by acoustic modes in the boundary layer, and support our findings with three-dimensional hydrodynamical simulations, using an isothermal equation of state. Our first major result is the identification of three types of global modes in the boundary layer. We derive dispersion relations for each of these modes that accurately capture the pattern speeds observed in simulations to within a few percent. Second, we show that angular momentum transport in the boundary layer is intrinsically nonlocal, and is driven by radiation of angular momentum away from the boundary layer into both the star and the disk. The picture of angular momentum transport in the boundary layer by waves that can travel large distances before dissipating and redistributing angular momentum and energy to the disk and star is incompatible with the conventional notion of local transport by turbulent stresses. Our results have important implications for semianalytical models that describe the spectral emission from boundary layers.

  3. Particle velocity gradient based acoustic mode beamforming for short linear vector sensor arrays.

    PubMed

    Gur, Berke

    2014-06-01

    In this paper, a subtractive beamforming algorithm for short linear arrays of two-dimensional particle velocity sensors is described. The proposed method extracts the highly directional acoustic modes from the spatial gradients of the particle velocity field measured at closely spaced sensors along the array. The number of sensors in the array limits the highest order of modes that can be extracted. Theoretical analysis and numerical simulations indicate that the acoustic mode beamformer achieves directivity comparable to the maximum directivity that can be obtained with differential microphone arrays of equivalent aperture. When compared to conventional delay-and-sum beamformers for pressure sensor arrays, the proposed method achieves comparable directivity with 70%-85% shorter apertures. Moreover, the proposed method has additional capabilities such as high front-back (port-starboard) discrimination, frequency and steer direction independent response, and robustness to correlated ambient noise. Small inter-sensor spacing that results in very compact apertures makes the proposed beamformer suitable for space constrained applications such as hearing aids and short towed arrays for autonomous underwater platforms.

  4. Enhanced acoustic mode coupling resulting from an internal solitary wave approaching the shelfbreak in the South China Sea.

    PubMed

    Chiu, Linus Y S; Reeder, D Benjamin; Chang, Yuan-Ying; Chen, Chi-Fang; Chiu, Ching-Sang; Lynch, James F

    2013-03-01

    Internal waves and bathymetric variation create time- and space-dependent alterations in the ocean acoustic waveguide, and cause subsequent coupling of acoustic energy between propagating normal modes. In this paper, the criterion for adiabatic invariance is extended to the case of an internal solitary wave (ISW) encountering a sloping bathymetry (i.e., continental shelfbreak). Predictions based on the extended criterion for adiabatic invariance are compared to experimental observations from the Asian Seas International Acoustics Experiment. Using a mode 1 starter field, results demonstrate time-dependent coupling of mode 1 energy to higher adjacent modes, followed by abrupt coupling of mode 5-7 energy to nonadjacent modes 8-20, produces enhanced mode coupling and higher received levels downrange of the oceanographic and bathymetric features. Numerical simulations demonstrate that increasing ISW amplitude and seafloor slope enhance the coupling of energy to adjacent and nonadjacent modes. This enhanced coupling is the direct result of the simultaneous influence of the ISW and its proximity to the shelfbreak, and, compared to the individual effect of the ISW or shelfbreak, has the capacity to scatter 2-4 times the amount of acoustic energy from below the thermocline into the upper water column beyond the shelfbreak in realistic environments.

  5. Using Acoustic Structure Quantification During B-Mode Sonography for Evaluation of Hashimoto Thyroiditis.

    PubMed

    Rhee, Sun Jung; Hong, Hyun Sook; Kim, Chul-Hee; Lee, Eun Hye; Cha, Jang Gyu; Jeong, Sun Hye

    2015-12-01

    This study aimed to evaluate the usefulness of Acoustic Structure Quantification (ASQ; Toshiba Medical Systems Corporation, Nasushiobara, Japan) values in the diagnosis of Hashimoto thyroiditis using B-mode sonography and to identify a cutoff ASQ level that differentiates Hashimoto thyroiditis from normal thyroid tissue. A total of 186 thyroid lobes with Hashimoto thyroiditis and normal thyroid glands underwent sonography with ASQ imaging. The quantitative results were reported in an echo amplitude analysis (Cm(2)) histogram with average, mode, ratio, standard deviation, blue mode, and blue average values. Receiver operating characteristic curve analysis was performed to assess the diagnostic ability of the ASQ values in differentiating Hashimoto thyroiditis from normal thyroid tissue. Intraclass correlation coefficients of the ASQ values were obtained between 2 observers. Of the 186 thyroid lobes, 103 (55%) had Hashimoto thyroiditis, and 83 (45%) were normal. There was a significant difference between the ASQ values of Hashimoto thyroiditis glands and those of normal glands (P < .001). The ASQ values in patients with Hashimoto thyroiditis were significantly greater than those in patients with normal thyroid glands. The areas under the receiver operating characteristic curves for the ratio, blue average, average, blue mode, mode, and standard deviation were: 0.936, 0.902, 0.893, 0.855, 0.846, and 0.842, respectively. The ratio cutoff value of 0.27 offered the best diagnostic performance, with sensitivity of 87.38% and specificity of 95.18%. The intraclass correlation coefficients ranged from 0.86 to 0.94, which indicated substantial agreement between the observers. Acoustic Structure Quantification is a useful and promising sonographic method for diagnosing Hashimoto thyroiditis. Not only could it be a helpful tool for quantifying thyroid echogenicity, but it also would be useful for diagnosis of Hashimoto thyroiditis. © 2015 by the American Institute of

  6. Surface Optomechanics: Calculating Optically Excited Acoustical Whispering Gallery Modes in Microspheres

    DTIC Science & Technology

    2011-07-18

    Spillane, and K. J. Vahala, “ Erbium - doped and Raman microlasers on a silicon chip fabricated by the sol-gel process,” Appl. Phys. Lett. 86(9), 091114 (2005...these acoustic whispering gallery modes is widely used in on- chip microdevices [2,3] to allow Raman- [4] and Erbium - [5] lasers , parametric...Ultralow-threshold Raman laser using a spherical dielectric microcavity,” Nature 415(6872), 621–623 (2002). 5. L. Yang, T. Carmon, B. Min, S. M

  7. Stability of geodesically complete cosmologies

    SciTech Connect

    Creminelli, Paolo; Pirtskhalava, David; Santoni, Luca; Trincherini, Enrico

    2016-11-22

    We study the stability of spatially flat FRW solutions which are geodesically complete, i.e. for which one can follow null (graviton) geodesics both in the past and in the future without ever encountering singularities. This is the case of NEC-violating cosmologies such as smooth bounces or solutions which approach Minkowski in the past. We study the EFT of linear perturbations around a solution of this kind, including the possibility of multiple fields and fluids. One generally faces a gradient instability which can be avoided only if the operator {sup (3)} RδN is present and its coefficient changes sign along the evolution. This operator (typical of beyond-Horndeski theories) does not lead to extra degrees of freedom, but cannot arise starting from any theory with second-order equations of motion. The change of sign of this operator prevents to set it to zero with a generalised disformal transformation.

  8. Stability of geodesically complete cosmologies

    NASA Astrophysics Data System (ADS)

    Creminelli, Paolo; Pirtskhalava, David; Santoni, Luca; Trincherini, Enrico

    2016-11-01

    We study the stability of spatially flat FRW solutions which are geodesically complete, i.e. for which one can follow null (graviton) geodesics both in the past and in the future without ever encountering singularities. This is the case of NEC-violating cosmologies such as smooth bounces or solutions which approach Minkowski in the past. We study the EFT of linear perturbations around a solution of this kind, including the possibility of multiple fields and fluids. One generally faces a gradient instability which can be avoided only if the operator (3) R δ N is present and its coefficient changes sign along the evolution. This operator (typical of beyond-Horndeski theories) does not lead to extra degrees of freedom, but cannot arise starting from any theory with second-order equations of motion. The change of sign of this operator prevents to set it to zero with a generalised disformal transformation.

  9. Protein-modified shear mode film bulk acoustic resonator for bio-sensing applications

    NASA Astrophysics Data System (ADS)

    Wang, Jingjing; Liu, Weihui; Xu, Yan; Chen, Da; Li, Dehua; Zhang, Luyin

    2014-09-01

    In this paper, we present a shear mode film bulk acoustic biosensor based on micro-electromechanical technology. The film bulk acoustic biosensor is a diaphragmatic structure consisting of a lateral field excited ZnO piezoelectric film piezoelectric stack built on an Si3N4 membrane. The device works at near 1.6 GHz with Q factors of 579 in water and 428 in glycerol. A frequency shift of 5.4 MHz and a small decline in the amplitude are found for the measurements in glycerol compared with those in water because of the viscous damping derived from the adjacent glycerol. For bio-sensing demonstration, the resonator was modified with biotin molecule to detect protein-ligand interactions in real-time and in situ. The resonant frequency of the biotin-modified device drops rapidly and gradually reaches equilibrium when exposed to the streptavidin solution due to the biotin-streptavidin interaction. The proposed film bulk acoustic biosensor shows promising applications for disease diagnostics, prognosis, and drug discovery.

  10. Investigation of a mercurous chloride acousto-optic cell based on longitudinal acoustic mode.

    PubMed

    Gupta, Neelam

    2009-03-01

    A number of spectral imagers using acousto-optic tunable filters (AOTFs) operating from the UV to the longwave infrared (LWIR) using KDP, MgF(2), TeO(2), and Tl(3)AsSe(3) crystals to cover different spectral regions have been developed. In the LWIR there is a lack of high quality acousto-optic (AO) materials. Mercurous halide (Hg(2)Cl(2) and Hg(2)Br(2)) crystals are highly anisotropic with a high AO figure of merit due to slow acoustic velocities and high photoelastic constants and are transparent over a wide spectral region from 0.35 to 20 mum for Hg(2)Cl(2) and from 0.4 to 30 mum for Hg(2)Br(2). AO modulators, deflectors, and AOTFs based on these crystals can operate over a wide spectral range. Single crystals of these materials are being grown and some prototype devices have been fabricated. Results are presented from device characterization for an AO cell fabricated in Hg(2)Cl(2) based on longitudinal acoustic mode propagation. This device was very useful in demonstrating the AO interaction as well as soundness of the transducer bonding technique. Acoustic phase velocity is calculated and measured, diffraction efficiency is obtained from experiments, and the AO figure of merit of the sample is evaluated.

  11. On the contribution of sunspots to the observed frequency shifts of solar acoustic modes

    NASA Astrophysics Data System (ADS)

    Santos, A. R. G.; Cunha, M. S.; Avelino, P. P.; Chaplin, W. J.; Campante, T. L.

    2016-09-01

    Activity-related variations in the solar oscillation properties have been known for 30 years. However, the relative importance of the different contributions to the observed variations is not yet fully understood. Our goal is to estimate the relative contribution from sunspots to the observed activity-related variations in the frequencies of the acoustic modes. We use a variational principle to relate the phase differences induced by sunspots on the acoustic waves to the corresponding changes in the frequencies of the global acoustic oscillations. From the sunspot properties (area and latitude as a function of time), we are able to estimate the spot-induced frequency shifts. These are then combined with a smooth frequency shift component, associated with long-term solar-cycle variations, and the results compared with the frequency shifts derived from the Global Oscillation Network Group data. The result of this comparison is consistent with a sunspot contribution to the observed frequency shifts of roughly 30 per cent, with the remaining 70 per cent resulting mostly from a global, non-stochastic variation, possibly related to the changes in the overall magnetic field. Moreover, analysis of the residuals obtained after the subtraction of the model frequency shifts from the observations indicates the presence of a 1.5-yr periodicity in the data in phase with the quasi-biennial variations reported in the literature.

  12. Acoustic performance of inlet suppressors on an engine generating a single mode

    NASA Technical Reports Server (NTRS)

    Heidelberg, L. J.; Rice, E. J.; Homyak, L.

    1981-01-01

    Three single degree of freedom liners with different open area ratio face sheets were designed for a single spinning mode in order to evaluate an inlet suppressor design method based on mode cutoff ratio. This mode was generated by placing 41 rods in front of the 28 blade fan of a JT15D turbofan engine. At the liner design this near cutoff mode has a theoretical maximum attenuation of nearly 200 dB per L/D. The data show even higher attenuations at the design condition than predicted by the theory for dissipation of a single mode within the liner. This additional attenuation is large for high open area ratios and should be accounted for in the theory. The data show the additional attenuation to be inversely proportional to acoustic resistance. It was thought that the additional attenuation could be caused by reflection and modal scattering at the hard to soft wall interface. A reflection model was developed, and then modified to fit the data. This model was checked against independent (multiple pure tone) data with good agreement.

  13. VizieR Online Data Catalog: Solar acoustic modes in period 1996-2014 (Salabert+, 2015)

    NASA Astrophysics Data System (ADS)

    Salabert, D.; Garcia, R. A.; Turck-Chieze, S.

    2015-03-01

    The central frequencies of the l = 0, 1, 2, and 3 acoustic modes of oscillations of the Sun between 1500{micro}Hz and 4000{micro}Hz and their associated formal 1σ uncertainties extracted from 365-day subseries of 18 years of the space-based, Sun-as-a-star GOLF/SoHO observations between 1996 April 11, and 2014 March 5 are presented. As a four-time overlap of 91.25 days was used, a total of 69 frequency tables are provided. We note that one of every four frequency tables contains frequencies extracted from independent subseries. Quality criteria were defined based on the fitted mode parameters and their associated uncertainties in order to remove outliers. An info file containing the associated starting date and duty cycle of each 365-day subseries is also provided. The corresponding mean 10.7cm radio flux is also given in the info file. (2 data files).

  14. Multiple-mode large deflection random response of beams with nonlinear damping subjected to acoustic excitation

    NASA Technical Reports Server (NTRS)

    Prasad, C. B.; Mei, Chuh

    1987-01-01

    Multiple-mode nonlinear analysis is carried out for beams subjected to acoustic excitation. Effects of both nonlinear damping and large-deflection are included in the analysis in an attempt to explain the experimental phenomena of aircraft panels excited at high sound pressure levels; that is the broadening of the strain response peaks and the increase of modal frequency. An amplitude dependent nonlinear damping model is used in the anlaysis to study the effects and interactions of multiple modes, nonlinear stiffness and nonlinear damping on the random response of beams. Mean square maximum deflection, mean square maximum strain, and spectral density function of maximum strain for simple supported and clamped beams are obtained. It is shown analytically that nonlinear damping contributes significantly to the broadening of the response peak and to the mean square deflection and strain.

  15. Properties of shear horizontal acoustic plate modes in BT-cut quartz.

    PubMed

    Soluch, Waldemar; Lysakowska, Magdalena

    2011-10-01

    Properties of shear horizontal acoustic plate modes (SHAPMs) in BT-cut quartz were calculated and measured. A delay line with a long interdigital transducer, deposited on -50.5°YX90°-oriented quartz plate, was used for the measurements. For one of the SHAPMs, at a frequency of about 100.4 MHz, insertion loss, turnover temperature, and quadratic temperature coefficient of frequency of about 10 dB, 15°C, and -30 ppb/(°C)(2) in air, respectively, were obtained. Using water and glycerin solutions, insertion loss changes against dynamic viscosity were measured for this mode. In a viscosity range from about 1 mPa·s to 1000 mPa·s, an insertion loss change of about 14 dB was obtained.

  16. Frequency Response of the Sample Vibration Mode in Scanning Probe Acoustic Microscope

    NASA Astrophysics Data System (ADS)

    Zhao, Ya-Jun; Cheng, Qian; Qian, Meng-Lu

    2010-05-01

    Based on the interaction mechanism between tip and sample in the contact mode of a scanning probe acoustic microscope (SPAM), an active mass of the sample is introduced in the mass-spring model. The tip motion and frequency response of the sample vibration mode in the SPAM are calculated by the Lagrange equation with dissipation function. For the silicon tip and glass assemblage in the SPAM the frequency response is simulated and it is in agreement with the experimental result. The living myoblast cells on the glass slide are imaged at resonance frequencies of the SPAM system, which are 20kHz, 30kHz and 120kHz. It is shown that good contrast of SPAM images could be obtained when the system is operated at the resonance frequencies of the system in high and low-frequency regions.

  17. Spinning mode sound propagation in ducts with acoustic treatment and sheared flow

    NASA Technical Reports Server (NTRS)

    Rice, E. J.

    1975-01-01

    The propagation of spinning mode sound was considered for a cylindrical duct with sheared steady flow. Calculations concentrated on the determination of the wall optimum acoustic impedance and the maximum possible attenuation. Both the least attenuated and higher radial modes for spinning lobe patterns were considered. A parametric study was conducted over a wide range of Mach numbers, spinning lobe numbers, sound frequency, and boundary layer thickness. A correlation equation was developed from theoretical considerations starting with the thin boundary layer approximation of Eversman. This correlation agrees well with the more exact calculations for inlets and provides a single boundary layer refraction parameter which determines the change in optimum wall impedance due to refraction effects.

  18. Spinning mode sound propagation in ducts with acoustic treatment and sheared flow

    NASA Technical Reports Server (NTRS)

    Rice, E. J.

    1975-01-01

    The propagation of spinning mode sound was considered for a cylindrical duct with sheared steady flow. The calculations concentrated on the determination of the wall optimum acoustic impedance and the maximum possible attenuation. Both the least attenuated and higher radial modes for spinning lobe patterns were considered. A parametric study was conducted over a wide range of Mach numbers, spinning lobe numbers, sound frequency, and boundary layer thickness. A correlation equation was developed from theoretical considerations starting with the thin boundary layer approximation of Eversman. This correlation agrees well with the more exact calculations for inlets and provides a single boundary layer refraction parameter which determines the change in optimum wall impedance due to refraction effects.

  19. Acoustic-wave-mode separation using a distributed Bragg grating sensor

    NASA Astrophysics Data System (ADS)

    Rajic, N.; Davis, C.; Thomson, A.

    2009-12-01

    This paper reports on the measurement and modal decomposition of structural plate waves using a single optical fibre sensor comprising an array of uniformly distributed Bragg gratings. Following a brief description of the design and fabrication of the sensor, numerical and experimental work is shown to demonstrate the fidelity of dynamic strain measurements furnished by the sensor at frequencies in excess of 200 kHz. The capacity of the sensor to provide a spatially resolved acoustic measurement represents an important advancement over conventional piezoelectric sensors as it allows for the decomposition of an elastic wave field into its constituent modes. This provides a potentially powerful diagnostic framework for structural health monitoring using guided waves. Experimental work on a metallic plate is presented to demonstrate the use of wave-mode conversion as a basis for the detection of structural damage, and its insensitivity to environmental effects.

  20. Interaction of High Frequency Acoustic Waves and Optical Waves Propagating in Single Mode Fibers.

    NASA Astrophysics Data System (ADS)

    de Paula, Ramon Perez

    This paper develops a frequency dependent model for the acousto-optic interaction with a single mode fiber of acoustic waves having wavelengths comparable to the fiber diameter. This paper also presents optical techniques for experimental observation and measurement of such effects. The acoustic waves are both normally and obliquelly incident on the fiber. The solutions to the elastic problem studied here are constructed using scalar and vector potentials. The principal strains induced by a plane wave propagating in a fluid is calculated through the solution of the wave equation and the associated boundary condition. The optical beam propagation is analyzed starting with Maxwell's, equations and the required solution for single mode (degenerate double mode) propagation is presented. For the perturbed fiber the anisotropic solution is discussed. The optical indicatrix is derived from the electric energy density, with the major axis parallel to the induced principal strains obtained from the solution of the elastic problem. The solution of the optical indicatrix equation (index ellipsoid) yields two independent propagation modes that are linear polarized plane waves with two different propagation velocities. The induced phase shift and birefringence are calculated from the index ellipsoid. The birefringence and phase shift are also measured experimentally using a fiber optic interferometer and a fiber optic polariscope. The experimental apparatus is discussed in detail and the techniques used to make the measurements are presented. The results are separated into two parts: first, the results for ultrasonic waves of normal incidence are presented, theoretical and experimental results are discussed, and the two compared; second, the results for angular incidence are presented in the same format as above, and compared with the results for perpendicular incidence.

  1. Direct imaging of delayed magneto-dynamic modes induced by surface acoustic waves.

    PubMed

    Foerster, Michael; Macià, Ferran; Statuto, Nahuel; Finizio, Simone; Hernández-Mínguez, Alberto; Lendínez, Sergi; Santos, Paulo V; Fontcuberta, Josep; Hernàndez, Joan Manel; Kläui, Mathias; Aballe, Lucia

    2017-09-01

    The magnetoelastic effect-the change of magnetic properties caused by the elastic deformation of a magnetic material-has been proposed as an alternative approach to magnetic fields for the low-power control of magnetization states of nanoelements since it avoids charge currents, which entail ohmic losses. Here, we have studied the effect of dynamic strain accompanying a surface acoustic wave on magnetic nanostructures in thermal equilibrium. We have developed an experimental technique based on stroboscopic X-ray microscopy that provides a pathway to the quantitative study of strain waves and magnetization at the nanoscale. We have simultaneously imaged the evolution of both strain and magnetization dynamics of nanostructures at the picosecond time scale and found that magnetization modes have a delayed response to the strain modes, adjustable by the magnetic domain configuration. Our results provide fundamental insight into magnetoelastic coupling in nanostructures and have implications for the design of strain-controlled magnetostrictive nano-devices.Understanding the effects of local dynamic strain on magnetization may help the development of magnetic devices. Foerster et al. demonstrate stroboscopic imaging that allows the observation of both strain and magnetization dynamics in nickel when surface acoustic waves are driven in the substrate.

  2. Variation of acoustic mode parameters with distance from a nearby active region

    NASA Astrophysics Data System (ADS)

    Rabello-Soares, M. Cristina; Bogart, Richard S.; Scherrer, Philip H.

    2017-08-01

    In a previous paper (Rabello-Soares, Bogart & Scherrer 2016), we quantified the influence of magnetic fields on acoustic mode parameters and flows in and around active regions by comparing the differences in the parameters in magnetically quiet regions when there is an active region in their vicinity with those of quiet regions at the same disc locations for which there are no neighboring active regions. Here we detail further our analysis by estimating how these differences vary with distance from the active region. We use ring diagram analysis from almost five years of HMI observations.In our first paper, we observed that the power reduction has a strong dependence on the wave direction but the amplitude enhacement (the `acoustic halo effect') has a very weak dependence on the wave propagation direction. We find that the effect on the amplitude decreases as the distance increases as expected. However, the dependence on the wave direction seems to reach a peak around 70 Mm from the active region. Very near the active region, the amplitude effects are independent of the direction of mode propagation.

  3. Cryogenic oxygen jet response to transverse acoustic excitation with the first transverse and the first combined longitudinal-transverse modes

    NASA Astrophysics Data System (ADS)

    Hardi, J. S.; Oschwald, M.

    2016-07-01

    The intact length of the dense oxygen core from an oxygen-hydrogen shear coaxial rocket injector was measured. The measurements were made in a rectangular rocket combustor with optical access and acoustic forcing. The combustor was operated at chamber pressures of 40 and 60 bar, with either ambient temperature or cryogenic hydrogen. The multielement injection spray is subjected to forced transverse gas oscillations of two different acoustic resonance modes; the first transverse (1T) mode at 4200 Hz and the first combined longitudinal-transverse (1L1T) at 5500 Hz. Intact core length is measured from high-speed shadowgraph imaging. The dependence of intact core length with increasing acoustic amplitude is compared for the two modes of excitation.

  4. On the exploitation of mode localization in surface acoustic wave MEMS

    NASA Astrophysics Data System (ADS)

    Hanley, T. H.; Gallacher, B. J.; Grigg, H. T. D.

    2017-05-01

    Mode localization sensing has been recently introduced as an alternative resonant sensing protocol. It has been shown to exhibit several advantages over other resonant methods, in particular a potential for higher sensitivity and rejection of common mode noise. This paper expounds the principles of utilising surface acoustic waves (SAW) to create a mode localization sensor. A generalised geometry consisting of a pair of coupled resonant cavities is introduced and an analytical solution found for the displacement fields within the cavities. The solution is achieved by coupling the internal cavity solutions using a ray tracing method. The results of the analytical solution are compared to a numerical solution found using commercial finite element method (FEM) software; exact agreement is found between the two solutions. The insight gained from the analytical model enables the determination of critical design parameters. A brief analysis is presented showing analogous operation to previous examples of mode localization sensors. The sensitivity of the device is shown to depend nonlinearly on the number of periods in the array coupling the two cavities.

  5. Energy trapping of thickness-extensional modes in thin film bulk acoustic wave filters

    NASA Astrophysics Data System (ADS)

    Zhao, Zinan; Qian, Zhenghua; Wang, Bin

    2016-01-01

    This paper presents the thickness-extensional vibration of a rectangular piezoelectric thin film bulk acoustic wave filter with two pairs of electrodes symmetrically deposited on the center of the zinc oxide film. The two-dimensional scalar differential equations which were first derived to describe in-plane vibration distribution by Tiersten and Stevens are employed. The Ritz method with trigonometric functions as basis functions is used based on a variational formulation developed in our previous paper. Free vibration resonant frequencies and corresponding modes are obtained. The modes may separate into symmetric and antisymmetric ones for such a structurally symmetric filter. Trapped modes with vibrations mainly under the driving electrodes are exhibited. The six corner-type regions of the filter neglected by Tiersten and Stevens for an approximation are taken into account in our analysis. Results show that their approximation can lead to an inaccuracy on the order of dozens of ppm for the fundamental mode, which is quite significant in filter operation and application.

  6. A vacuum spacetime with closed null geodesics

    SciTech Connect

    Sarma, Debojit Patgiri, Mahadev Ahmed, Faiz Uddin

    2013-02-15

    Here we present a vacuum spacetime with closed null geodesics (CNGs). These CNGs are obtained by analytically solving the geodesic equations. This spacetime is locally isometric to the plane wave spacetime and has very different global properties from metrics of the latter type. - Highlights: Black-Right-Pointing-Pointer Closed null geodesics are found in a vacuum spacetime. Black-Right-Pointing-Pointer These are obtained by analytically solving the geodesic equations. Black-Right-Pointing-Pointer The nature of the spacetime is fully analysed.

  7. Passive mode-locking of fiber ring laser at the 337th harmonic using gigahertz acoustic core resonances.

    PubMed

    Kang, M S; Joly, N Y; Russell, P St J

    2013-02-15

    We report the experimental demonstration of a passively mode-locked Er-doped fiber ring laser operating at the 337th harmonic (1.80 GHz) of the cavity. The laser makes use of highly efficient Raman-like optoacoustic interactions between the guided light and gigahertz acoustic resonances trapped in the micron-sized solid glass core of a photonic crystal fiber. At sufficient pump power levels the laser output locks to a repetition rate corresponding to the acoustic frequency. A stable optical pulse train with a side-mode suppression ratio higher than 45 dB was obtained at low pump powers (~60 mW).

  8. Wide Field-of-view and Broadband Terahertz Beam Steering Based on Gap Plasmon Geodesic Antennas

    NASA Astrophysics Data System (ADS)

    Liu, Kaipeng; Guo, Yinghui; Pu, Mingbo; Ma, Xiaoliang; Li, Xiong; Luo, Xiangang

    2017-01-01

    Despite a plethora of applications ranging from wireless communications to sensing and spectroscopy, the current terahertz beam steering technologies suffer from tremendous insert loss, stringent control of electric bias, limited scanning angle, relatively complicated configuration and narrow operation bandwidth, preventing further practical application. We propose and demonstrate a conceptually new approach for terahertz beam steering by virtue of gap plasmon geodesic antennas. By adjusting the geometric dimension of the gap plasmon geodesic antennas, all gap plasmon modes add coherently along a peculiar direction that depends on the geodesic mean surface. Consequently, high directive beams are generated through the antenna, whose direction could be changed within a wide-angle range spanning ±45° by lateral motion of the feed. Furthermore, an assembled antenna structure consisting of four-element geodesic antennas array is proposed for full 360° beam steering, which can operate in a broadband range from 0.8 THz to 1.2 THz.

  9. Wide Field-of-view and Broadband Terahertz Beam Steering Based on Gap Plasmon Geodesic Antennas.

    PubMed

    Liu, Kaipeng; Guo, Yinghui; Pu, Mingbo; Ma, Xiaoliang; Li, Xiong; Luo, Xiangang

    2017-01-30

    Despite a plethora of applications ranging from wireless communications to sensing and spectroscopy, the current terahertz beam steering technologies suffer from tremendous insert loss, stringent control of electric bias, limited scanning angle, relatively complicated configuration and narrow operation bandwidth, preventing further practical application. We propose and demonstrate a conceptually new approach for terahertz beam steering by virtue of gap plasmon geodesic antennas. By adjusting the geometric dimension of the gap plasmon geodesic antennas, all gap plasmon modes add coherently along a peculiar direction that depends on the geodesic mean surface. Consequently, high directive beams are generated through the antenna, whose direction could be changed within a wide-angle range spanning ±45° by lateral motion of the feed. Furthermore, an assembled antenna structure consisting of four-element geodesic antennas array is proposed for full 360° beam steering, which can operate in a broadband range from 0.8 THz to 1.2 THz.

  10. MODE CONVERSION BETWEEN DIFFERENT RADIAL ORDERS FOR SOLAR ACOUSTIC WAVES SCATTERED BY SUNSPOTS

    SciTech Connect

    Zhao, Hui; Chou, Dean-Yi

    2013-11-20

    We study the mode conversion between different radial orders for solar acoustic waves interacting with sunspots. Solar acoustic waves are modified in the presence of sunspots. The modification in the wave can be viewed as that the sunspot, excited by the incident wave, generates the scattered wave, and the scattered wave is added to the incident wave to form the total wave inside and around the sunspot. The wavefunction of the acoustic wave on the solar surface is computed from the cross-correlation function. The wavefunction of the scattered wave is obtained by subtracting the wavefunction of the incident wave from that of the total wave. We use the incident waves of radial order n = 0-5 to measure the scattered wavefunctions from n to another radial order n' for NOAAs 11084 and 11092. The strength of scattered waves decreases rapidly with |Δn|, where Δn ≡ n' – n. The scattered waves of Δn = ±1 are visible for n ≤ 1, and significant for n ≥ 2. For the scattered wave of Δn = ±2, only few cases are visible. None of the scattered waves of Δn = ±3 are visible. The properties of scattered waves for Δn = 0 and Δn ≠ 0 are different. The scattered wave amplitude relative to the incident wave amplitude decreases with n for Δn = 0, while it increases with n for Δn ≠ 0. The scattered wave amplitudes of Δn = 0 are greater for the larger sunspot, while those of Δn ≠ 0 are insensitive to the sunspot size.

  11. Evidence for temporal variation in the acoustic and f-mode eigenfrequency spectrum of the Sun

    NASA Astrophysics Data System (ADS)

    Oglesby, Paul H.; Hill, Henry A.; Rabaey, Gregory F.

    The power spectrum obtained from 1985 solar radiation intensity measurements was tested for evidence of frequency shifts of the low-order, low-degree acoustic modes and intermediate degree f-modes classified at SCLERA (Santa Catalina Laboratory for Experimental Relativity by Astrometry). These classifications were based on 1979 differential radius observations. Maxima in the coincidence rates between the peaks in the 1985 power spectrum and the classified frequency spectrum were found for frequency shifts (of the order of 0.05 microHz) that are dependent on degree. These shifts indicate a change in eigenfrequency spectrum over a 6 year period. The coincidence rates between the peaks in the 1985 power spectrum and the classified frequency spectrum for multiplets taken in subgroups of approx. 5 (same n and contiguous in lambda) were typically 3 to 5 sigma above the accidental coincidence rate. Since these modes primarily reside in the convection zone, details of temporal changes of these eigenfrequencies should yield interesting information about the level of variations in the properties of the convection zone over, for example, the solar cycle.

  12. On non-commutative geodesic motion

    NASA Astrophysics Data System (ADS)

    Ulhoa, S. C.; Amorim, R. G. G.; Santos, A. F.

    2014-07-01

    In this work we study the geodesic motion on a noncommutative space-time. As a result we find a non-commutative geodesic equation and then we derive corrections of the deviation angle per revolution in terms of the non-commutative parameter when we specify the problem of Mercury's perihelion. In this way, we estimate the noncommutative parameter based in experimental data.

  13. A Longitudinal Mode Electromagnetic Acoustic Transducer (EMAT) Based on a Permanent Magnet Chain for Pipe Inspection

    PubMed Central

    Cong, Ming; Wu, Xinjun; Qian, Chunqiao

    2016-01-01

    A new electromagnetic acoustic transducer (EMAT) design, employing a special structure of the permanent magnet chain, is proposed to generate and receive longitudinal guided waves for pipe inspection based on the magnetostriction mechanism. Firstly, a quantitative analysis of the excitation forces shows the influence of the radial component can be ignored. Furthermore, as the axial component of the static magnetic field is dominant, a method of solenoid testing coils connected in series is adopted to increase the signal amplitude. Then, two EMAT configurations are developed to generate and receive the L(0,2) guided wave mode. The experimental results show the circumferential notch can be identified and located successfully. Finally, a detailed investigation of the performance of the proposed EMATs is given. Compared to the conventional EMAT configuration, the proposed configurations have the advantages of small volume, light weight, easy installation and portability, which is helpful to improve inspection efficiency. PMID:27213400

  14. Quasi longitudinal Lamb acoustic modes along ZnO/Si/ZnO structures.

    PubMed

    Verona, E; Anisimkin, V I; Osipenko, V A; Voronova, N V

    2017-04-01

    A novel structure consisting of a Si plate sandwiched between two ZnO layers is suggested as propagation medium for Quasi Longitudinal (QL) acoustic Lamb waves. Considering a low-dispersive quasi-longitudinal mode as an example, the phase velocity v, electromechanical coupling constant k(2) and mechanical displacements U1, U3 versus plate and ZnO layers thicknesses have been calculated starting from uncoated plate through the same plate with one layer to the plate with two layers onto opposite faces. A remarkable increase in the electromechanical coupling, together with an essential decrease in the vertical displacement U3, at the ZnO surface, have been theoretically demonstrated and experimentally verified for definite combinations of the films/plate thicknesses. This property of the structure is attractive for applications to microwave liquid sensors.

  15. Acoustic Plate Mode sensing in liquids based on free and electrically shorted plate surfaces.

    PubMed

    Anisimkin, V I; Caliendo, C; Verona, E

    2016-05-01

    The sensing behavior to liquids for Acoustic Plate Modes (APMs) propagating along 64°Y, 90°X LiNbO3 plate was investigated vs. two electric boundary conditions. The changes in the APMs phase velocity and attenuation were measured upon exposure to different liquids wetting one of the surfaces of the plate, either free or electrically shorted by a thin conductive Al layer. The experimental data confirm that the presence of a metallic layer covering one of the plate surfaces affects the viscosity and temperature sensitivity of the device. The differences between the sensor response for various liquids, with free or metalized faces, are interpreted in terms of the APM polarization.

  16. Spatial evolution of nonlinear acoustic mode instabilities on hypersonic boundary layers

    NASA Technical Reports Server (NTRS)

    Goldstein, M. E.; Wundrow, D. W.

    1990-01-01

    The effects are considered of strong critical layer nonlinearity on the spatial evolution of an initially linear acoustic mode instability wave on a hypersonic flat plate boundary layer. The analysis shows that nonlinearity, which is initially confined to a thin critical layer, first becomes important when the amplitude of the pressure fluctuations become O(1/M exp 4 in M exp 2), where M is the free stream Mach number. The flow outside the critical layer is still determined by linear dynamics and therefore takes the form of a linear instability wave, but with its amplitude completely determined by the flow within the critical layer. The latter flow is determined by a coupled set of nonlinear equations, which were solved numerically.

  17. Spatial evolution of nonlinear acoustic mode instabilities on hypersonic boundary layers

    NASA Technical Reports Server (NTRS)

    Goldstein, M. E.; Wundrow, D. W.

    1989-01-01

    The effects are considered of strong critical layer nonlinearity on the spatial evolution of an initially linear acoustic mode instability wave on a hypersonic flat plate boundary layer. The analysis shows that nonlinearity, which is initially confined to a thin critical layer, first becomes important when the amplitude of the pressure fluctuations become 0(1/M exp 4 In M exp 2), where M is the free stream Mach number. The flow outside the critical layer is still determined by linear dynamics and therefore takes the form of a linear instability wave, but with its amplitude completely determined by the flow within the critical layer. The latter flow is determined by a coupled set of nonlinear equations, which were solved numerically.

  18. Modeling and experimental study on near-field acoustic levitation by flexural mode.

    PubMed

    Liu, Pinkuan; Li, Jin; Ding, Han; Cao, Wenwu

    2009-12-01

    Near-field acoustic levitation (NFAL) has been used in noncontact handling and transportation of small objects to avoid contamination. We have performed a theoretical analysis based on nonuniform vibrating surface to quantify the levitation force produced by the air film and also conducted experimental tests to verify our model. Modal analysis was performed using ANSYS on the flexural plate radiator to obtain its natural frequency of desired mode, which is used to design the measurement system. Then, the levitation force was calculated as a function of levitation distance based on squeeze gas film theory using measured amplitude and phase distributions on the vibrator surface. Compared with previous fluid-structural analyses using a uniform piston motion, our model based on the nonuniform radiating surface of the vibrator is more realistic and fits better with experimentally measured levitation force.

  19. Focusing of the lowest-order antisymmetric Lamb mode behind a gradient-index acoustic metalens with local resonators

    NASA Astrophysics Data System (ADS)

    Zhao, Jinfeng; Bonello, Bernard; Boyko, Olga

    2016-05-01

    We have investigated the focusing of the lowest-order antisymmetric Lamb mode (A0) behind a positive gradient-index (GRIN) acoustic metalens consisting of air holes drilled in a silicon plate with silicon pillars erected on one face of the lens. We have analyzed the focusing in the near field as the result of the coupling between the flexural resonant mode of the pillars and the vibration mode of the air/silicon phononic crystal. We highlight the role played by the polarization coherence between the resonant mode and the vibration of the plate. We demonstrate both numerically and experimentally the focusing behind the lens over a spot less than half a wavelength, paving a way for performance of acoustic lenses beyond the diffraction limit. Our findings can be easily extended to other types of elastic wave.

  20. Dual-mode thin film bulk acoustic wave resonators for parallel sensing of temperature and mass loading.

    PubMed

    García-Gancedo, L; Pedrós, J; Zhao, X B; Ashley, G M; Flewitt, A J; Milne, W I; Ford, C J B; Lu, J R; Luo, J K

    2012-01-01

    Thin film bulk acoustic wave resonator (FBAR) devices supporting simultaneously multiple resonance modes have been designed for gravimetric sensing. The mechanism for dual-mode generation within a single device has been discussed, and theoretical calculations based on finite element analysis allowed the fabrication of FBARs whose resonance modes have opposite reactions to temperature changes; one of the modes exhibiting a positive frequency shift for a rise of temperature whilst the other mode exhibits a negative shift. Both modes exhibit negative frequency shift for a mass load and hence by monitoring simultaneously both modes it is possible to distinguish whether a change in the resonance frequency is due to a mass load or temperature variation (or a combination of both), avoiding false positive/negative responses in gravimetric sensing without the need of additional reference devices or complex electronics.

  1. Contactless transport of matter in the first five resonance modes of a line-focused acoustic manipulator.

    PubMed

    Foresti, Daniele; Nabavi, Majid; Poulikakos, Dimos

    2012-02-01

    The first five resonance modes for transport of matter in a line-focused acoustic levitation system are investigated. Contactless transport was achieved by varying the height between the radiating plate and the reflector. Transport and levitation of droplets in particular involve two limits of the acoustic forces. The lower limit corresponds to the minimum force required to overcome the gravitational force. The upper limit corresponds to the maximum acoustic pressure beyond which atomization of the droplet occurs. As the droplet size increases, the lower limit increases and the upper limit decreases. Therefore to have large droplets levitated, relatively flat radiation pressure amplitude during the translation is needed. In this study, using a finite element model, the Gor'kov potential was calculated for different heights between the reflector and the radiating plate. The application of the Gor'kov potential was extended to study the range of droplet sizes for which the droplets can be levitated and transported without atomization. It was found that the third resonant mode (H(3)-mode) represents the best compromise between high levitation force and smooth pattern transition, and water droplets of millimeter radius can be levitated and transported. The H(3)-mode also allows for three translation lines in parallel. © 2012 Acoustical Society of America

  2. Near-Field Acoustical Imaging using Lateral Bending Mode of Atomic Force Microscope Cantilevers

    NASA Astrophysics Data System (ADS)

    Caron, A.; Rabe, U.; Rödel, J.; Arnold, W.

    Scanning probe microscopy techniques enable one to investigate surface properties such as contact stiffness and friction between the probe tip and a sample with nm resolution. So far the bending and the torsional eigenmodes of an atomic force microscope cantilever have been used to image variations of elasticity and shear elasticity, respectively. Such images are near-field images with the resolution given by the contact radius typically between 10 nm and 50 nm. We show that the flexural modes of a cantilever oscillating in the width direction and parallel to the sample surface can also be used for imaging. Additional to the dominant in-plane component of the oscillation, the lateral modes exhibit a vertical component as well, provided there is an asymmetry in the cross-section of the cantilever or in its suspension. The out-of-plane deflection renders the lateral modes detectable by the optical position sensors used in atomic force microscopes. We studied cracks which were generated by Vickers indents, in submicro- and nanocrystalline ZrO2. Images of the lateral contact stiffness were obtained by vibrating the cantilever close to a contact-resonance frequency. A change in contact stiffness causes a shift of the resonant frequency and hence a change of the cantilever vibration amplitude. The lateral contact-stiffness images close to the crack faces display a contrast that we attribute to altered elastic properties indicating a process zone. This could be caused by a stress-induced phase transformation during crack propagation. Using the contact mode of an atomic force microscope, we measured the crack-opening displacement as a function of distance from the crack tip, and we determined the crack-tip toughness Ktip. Furthermore, K1c was inferred from the length of radial cracks of Vickers indents that were measured using classical scanning acoustic microscopy

  3. Acoustic anomalies in Tb2(MoO4)3 and the "missing" A1 optic mode

    NASA Astrophysics Data System (ADS)

    Fleury, P. A.; Lyons, K. B.; Katiyar, R. S.

    1982-12-01

    Anomalies in both the acoustic- and optic-phonon spectra associated with the ferroelectric and ferroelastic phase transition in terbium molybdate have been quantitatively measured by simultaneous Brillouin and Raman spectroscopy. The most striking singular behavior observed is the divergent damping of both the A1 optic phonon and the C11 acoustic phonon upon approach to T0 from below. T0 was determined to be 159°C for our sample by measurement of the pyroelectric response. The A1-mode frequency determined from the Raman spectrum shows little temperature dependence, while the C11 elastic constant determined from the Brillouin spectra decreases by about 60% between room temperature and T0. There is no evidence of a dynamic central peak. The observed anomalies in the acoustic velocity and damping are incompatible with a model based on bilinear coupling between the acoustic mode and the A1 mode seen in the Raman spectrum. However, a satisfactory account of all the experimental observations (including the anomalies in C~11 and C22) can be obtained by assuming the presence of a second A1 optic phonon with a negligible Raman scattering cross section. We note that the dynamic variables below T0 are not simply related to the distortion, as has often been assumed previously. On the basis of this model we use the acoustic velocities and damping to determine the frequency and damping parameters of this unseen mode. It is emphasized that the singular behavior of the damping of the observed A1 mode has yet to receive adequate theoretical explanation.

  4. Acoustic Efficiency of Azimuthal Modes in Jet Noise Using Chevron Nozzles

    NASA Technical Reports Server (NTRS)

    Brown, Clifford A.; Bridges, James

    2006-01-01

    The link between azimuthal modes in jet turbulence and in the acoustic sound field has been examined in cold, round jets. Chevron nozzles, however, impart an azimuthal structure on the jet with a shape dependent on the number, length and penetration angle of the chevrons. Two particular chevron nozzles, with 3 and 4 primary chevrons respectively, and a round baseline nozzle are compared at both cold and hot jet conditions to determine how chevrons impact the modal structure of the flow and how that change relates to the sound field. The results show that, although the chevrons have a large impact on the azimuthal shape of the mean axial velocity, the impact of chevrons on the azimuthal structure of the fluctuating axial velocity is small at the cold jet condition and smaller still at the hot jet condition. This is supported by results in the azimuthal structure of the sound field, which also shows little difference in between the two chevron nozzles and the baseline nozzle in the distribution of energy across the azimuthal modes measured.

  5. Acoustic Reflection and Transmission of 2-Dimensional Rotors and Stators, Including Mode and Frequency Scattering Effects

    NASA Technical Reports Server (NTRS)

    Hanson, Donald B.

    1999-01-01

    A reduced order modeling scheme has been developed for the unsteady acoustic and vortical coupling between blade rows of a turbomachine. The essential behavior of the system is governed by modal scattering coefficients (i.e., reflection and transmission coefficients) of the rotor, stator, inlet and nozzle, which are calculated as if they were connected to non-reflecting ducts. The objective of this report is to identify fundamental behavior of these scattering coefficients for a better understanding of the role of blade row reflection and transmission in noise generation. A 2D flat plate unsteady cascade model is used for the analysis with the expectation that the general behavior presented herein will carry over to models that include more realistic flow and geometry. It is shown that stators scatter input waves into many modes at the same frequency whereas rotors scatter on frequency, or harmonic order. Important cases are shown here the rotor reflection coefficient is greater than unity; a mode at blade passing frequency (BPF) traveling from the stator with unit sound power is reflected by the rotor with more than unit power at 2xBPF and 3xBPE Analysis is presented to explain this unexpected phenomenon. Scattering curves are presented in a format chosen for design use and for physical interpretation. To aid in interpretation of the curves, formulas are derived for special condition where waveforms are parallel to perpendicular to the rotor.

  6. Noncontact excitation of guided waves (A0 mode) using an electromagnetic acoustic transducer (EMAT)

    NASA Astrophysics Data System (ADS)

    Fromme, Paul

    2016-02-01

    Fatigue damage can develop in aircraft structures at locations of stress concentration, such as fasteners, and has to be detected before reaching a critical size to ensure safe aircraft operation. Guided ultrasonic waves offer an efficient method for the detection and characterization of such defects in large aerospace structures. Electromagnetic acoustic transducers (EMAT) for the noncontact excitation of guided ultrasonic waves were developed. The transducer development for the specific excitation of the A0 Lamb wave mode with an out-of-plane Lorentz force is explained. The achieved radial and angular dependency of the excited guided wave pulses were measured using a noncontact laser interferometer. Based on the induced eddy currents in the plate a theoretical model was developed. The application of the developed transducers for defect detection in aluminum components using fully noncontact guided wave measurements was demonstrated. Excitation of the A0 Lamb wave mode was achieved using the developed EMAT transducer and the guided wave propagation and scattering was measured using a noncontact laser interferometer.

  7. Acoustics

    NASA Technical Reports Server (NTRS)

    Goodman, Jerry R.; Grosveld, Ferdinand

    2007-01-01

    The acoustics environment in space operations is important to maintain at manageable levels so that the crewperson can remain safe, functional, effective, and reasonably comfortable. High acoustic levels can produce temporary or permanent hearing loss, or cause other physiological symptoms such as auditory pain, headaches, discomfort, strain in the vocal cords, or fatigue. Noise is defined as undesirable sound. Excessive noise may result in psychological effects such as irritability, inability to concentrate, decrease in productivity, annoyance, errors in judgment, and distraction. A noisy environment can also result in the inability to sleep, or sleep well. Elevated noise levels can affect the ability to communicate, understand what is being said, hear what is going on in the environment, degrade crew performance and operations, and create habitability concerns. Superfluous noise emissions can also create the inability to hear alarms or other important auditory cues such as an equipment malfunctioning. Recent space flight experience, evaluations of the requirements in crew habitable areas, and lessons learned (Goodman 2003; Allen and Goodman 2003; Pilkinton 2003; Grosveld et al. 2003) show the importance of maintaining an acceptable acoustics environment. This is best accomplished by having a high-quality set of limits/requirements early in the program, the "designing in" of acoustics in the development of hardware and systems, and by monitoring, testing and verifying the levels to ensure that they are acceptable.

  8. Ion wake field effects on the dust-ion-acoustic surface mode in a semi-bounded Lorentzian dusty plasma

    SciTech Connect

    Lee, Myoung-Jae; Jung, Young-Dae

    2016-03-15

    The dispersion relation for the dust ion-acoustic surface waves propagating at the interface of semi-bounded Lorentzian dusty plasma with supersonic ion flow has been kinetically derived to investigate the nonthermal property and the ion wake field effect. We found that the supersonic ion flow creates the upper and the lower modes. The increase in the nonthermal particles decreases the wave frequency for the upper mode whereas it increases the frequency for the lower mode. The increase in the supersonic ion flow velocity is found to enhance the wave frequency for both modes. We also found that the increase in nonthermal plasmas is found to enhance the group velocity of the upper mode. However, the nonthermal particles suppress the lower mode group velocity. The nonthermal effects on the group velocity will be reduced in the limit of small or large wavelength limit.

  9. Analytical Study of the Propagation of Fast Longitudinal Modes along wz-BN/AlN Thin Acoustic Waveguides

    PubMed Central

    Caliendo, Cinzia

    2015-01-01

    The propagation of the fundamental symmetric Lamb mode S0 along wz-BN/AlN thin composite plates suitable for telecommunication and sensing applications is studied. The investigation of the acoustic field profile across the plate thickness revealed the presence of modes having longitudinal polarization, the Anisimkin Jr. plate modes (AMs), travelling at a phase velocity close to that of the wz-BN longitudinal bulk acoustic wave propagating in the same direction. The study of the S0 mode phase velocity and coupling coefficient (K2) dispersion curves, for different electrical boundary conditions, has shown that eight different coupling configurations are allowable that exhibit a K2 as high as about 4% and very high phase velocity (up to about 16,700 m/s). The effect of the thickness and material type of the metal floating electrode on the K2 dispersion curves has also been investigated, specifically addressing the design of an enhanced coupling device. The gravimetric sensitivity of the BN/AlN-based acoustic waveguides was then calculated for both the AMs and elliptically polarized S0 modes; the AM-based sensor velocity and attenuation shifts due to the viscosity of a surrounding liquid was theoretically predicted. The performed investigation suggests that wz-BN/AlN is a very promising substrate material suitable for developing GHz band devices with enhanced electroacoustic coupling efficiency and suitable for application in telecommunications and sensing fields. PMID:25625904

  10. Acoustic mode measurements in the inlet of a model turbofan using a continuously rotating rake - Data collection/analysis techniques

    NASA Technical Reports Server (NTRS)

    Hall, David G.; Heidelberg, Laurence; Konno, Kevin

    1993-01-01

    The rotating microphone measurement technique and data analysis procedures are documented which are used to determine circumferential and radial acoustic mode content in the inlet of the Advanced Ducted Propeller (ADP) model. Circumferential acoustic mode levels were measured at a series of radial locations using the Doppler frequency shift produced by a rotating inlet microphone probe. Radial mode content was then computed using a least squares curve fit with the measured radial distribution for each circumferential mode. The rotating microphone technique is superior to fixed-probe techniques because it results in minimal interference with the acoustic modes generated by rotor-stator interaction. This effort represents the first experimental implementation of a measuring technique developed by T. G. Sofrin. Testing was performed in the NASA Lewis Low Speed Anechoic Wind Tunnel at a simulated takeoff condition of Mach 0.2. The design is included of the data analysis software and the performance of the rotating rake apparatus. The effect of experiment errors is also discussed.

  11. Analytical study of the propagation of fast longitudinal modes along wz-BN/AlN thin acoustic waveguides.

    PubMed

    Caliendo, Cinzia

    2015-01-23

    The propagation of the fundamental symmetric Lamb mode S0 along wz-BN/AlN thin composite plates suitable for telecommunication and sensing applications is studied. The investigation of the acoustic field profile across the plate thickness revealed the presence of modes having longitudinal polarization, the Anisimkin Jr. plate modes (AMs), travelling at a phase velocity close to that of the wz-BN longitudinal bulk acoustic wave propagating in the same direction. The study of the S0 mode phase velocity and coupling coefficient (K2) dispersion curves, for different electrical boundary conditions, has shown that eight different coupling configurations are allowable that exhibit a K2 as high as about 4% and very high phase velocity (up to about 16,700 m/s). The effect of the thickness and material type of the metal floating electrode on the K2 dispersion curves has also been investigated, specifically addressing the design of an enhanced coupling device. The gravimetric sensitivity of the BN/AlN-based acoustic waveguides was then calculated for both the AMs and elliptically polarized S0 modes; the AM-based sensor velocity and attenuation shifts due to the viscosity of a surrounding liquid was theoretically predicted. The performed investigation suggests that wz-BN/AlN is a very promising substrate material suitable for developing GHz band devices with enhanced electroacoustic coupling efficiency and suitable for application in telecommunications and sensing fields.

  12. Acoustic mode measurements in the inlet of a model turbofan using a continuously rotating rake: Data collection/analysis techniques

    NASA Technical Reports Server (NTRS)

    Hall, David G.; Heidelberg, Laurence; Konno, Kevin

    1993-01-01

    The rotating microphone measurement technique and data analysis procedures are documented which are used to determine circumferential and radial acoustic mode content in the inlet of the Advanced Ducted Propeller (ADP) model. Circumferential acoustic mode levels were measured at a series of radial locations using the Doppler frequency shift produced by a rotating inlet microphone probe. Radial mode content was then computed using a least squares curve fit with the measured radial distribution for each circumferential mode. The rotating microphone technique is superior to fixed-probe techniques because it results in minimal interference with the acoustic modes generated by rotor-stator interaction. This effort represents the first experimental implementation of a measuring technique developed by T. G. Sofrin. Testing was performed in the NASA Lewis Low Speed Anechoic Wind Tunnel at a simulated takeoff condition of Mach 0.2. The design is included of the data analysis software and the performance of the rotating rake apparatus. The effect of experiment errors is also discussed.

  13. Acoustic mode measurements in the inlet of a model turbofan using a continuously rotating rake - Data collection/analysis techniques

    NASA Technical Reports Server (NTRS)

    Hall, David G.; Heidelberg, Laurence; Konno, Kevin

    1993-01-01

    The rotating microphone measurement technique and data analysis procedures are documented which are used to determine circumferential and radial acoustic mode content in the inlet of the Advanced Ducted Propeller (ADP) model. Circumferential acoustic mode levels were measured at a series of radial locations using the Doppler frequency shift produced by a rotating inlet microphone probe. Radial mode content was then computed using a least squares curve fit with the measured radial distribution for each circumferential mode. The rotating microphone technique is superior to fixed-probe techniques because it results in minimal interference with the acoustic modes generated by rotor-stator interaction. This effort represents the first experimental implementation of a measuring technique developed by T. G. Sofrin. Testing was performed in the NASA Lewis Low Speed Anechoic Wind Tunnel at a simulated takeoff condition of Mach 0.2. The design is included of the data analysis software and the performance of the rotating rake apparatus. The effect of experiment errors is also discussed.

  14. Quantum frictionless trajectories versus geodesics

    NASA Astrophysics Data System (ADS)

    Barbado, Luis C.; Barceló, Carlos; Garay, Luis J.

    2015-10-01

    Moving particles outside a star will generally experience quantum friction caused by the Unruh radiation reaction. There exist however radial trajectories that lack this effect (in the outgoing radiation sector, and ignoring backscattering). Along these trajectories, observers perceive just stellar emission, without further contribution from the Unruh effect. They turn out to have the property that the variations of the Doppler and the gravitational shifts compensate each other. They are not geodesics, and their proper acceleration obeys an inverse square law, which means that it could in principle be generated by outgoing stellar radiation. In the case of a black hole emitting Hawking radiation, this may lead to a buoyancy scenario. The ingoing radiation sector has little effect and seems to slow down the fall even further.

  15. Anatomy of geodesic Witten diagrams

    NASA Astrophysics Data System (ADS)

    Chen, Heng-Yu; Kuo, En-Jui; Kyono, Hideki

    2017-05-01

    We revisit the so-called "Geodesic Witten Diagrams" (GWDs) [1], proposed to be the holographic dual configuration of scalar conformal partial waves, from the perspectives of CFT operator product expansions. To this end, we explicitly consider three point GWDs which are natural building blocks of all possible four point GWDs, discuss their gluing procedure through integration over spectral parameter, and this leads us to a direct identification with the integral representation of CFT conformal partial waves. As a main application of this general construction, we consider the holographic dual of the conformal partial waves for external primary operators with spins. Moreover, we consider the closely related "split representation" for the bulk to bulk spinning propagator, to demonstrate how ordinary scalar Witten diagram with arbitrary spin exchange, can be systematically decomposed into scalar GWDs. We also discuss how to generalize to spinning cases.

  16. Strain coupling, microstructure dynamics, and acoustic mode softening in germanium telluride

    NASA Astrophysics Data System (ADS)

    Yang, D.; Chatterji, T.; Schiemer, J. A.; Carpenter, M. A.

    2016-04-01

    GeTe is a material of intense topical interest due to its potential in the context of phase-change and nanowire memory devices, as a base for thermoelectric materials, and as a ferroelectric. The combination of a soft optic mode and a Peierls distortion contributes large strains at the cubic-rhombohedral phase transition near 625 K and the role of these has been investigated through their influence on elastic and anelastic properties by resonant ultrasound spectroscopy. The underlying physics is revealed by softening of the elastic constants by ˜30%-45%, due to strong coupling of shear and volume strains with the driving order parameter and consistent with an improper ferroelastic transition which is weakly first order. The magnitude of the softening is permissive of the transition mechanism involving a significant order/disorder component. A Debye loss peak in the vicinity of 180 K is attributed to freezing of the motion of ferroelastic twin walls and the activation energy of ˜0.07 eV is attributed to control by switching of the configuration of long and short Ge-Te bonds in the first coordination sphere around Ge. Precursor softening as the transition is approached from above can be described with a Vogel-Fulcher expression with a similar activation energy, which is attributed to coupling of acoustic modes with an unseen central mode that arises from dynamical clusters with local ordering of the Peierls distortion. The strain relaxation and ferroelastic behavior of GeTe depend on both displacive and order/disorder effects but the dynamics of switching will be determined by changes in the configuration of distorted GeT e6 octahedra, with a rather small activation energy barrier.

  17. A numerical model for ocean ultra-low frequency noise: wave-generated acoustic-gravity and Rayleigh modes.

    PubMed

    Ardhuin, Fabrice; Lavanant, Thibaut; Obrebski, Mathias; Marié, Louis; Royer, Jean-Yves; d'Eu, Jean-François; Howe, Bruce M; Lukas, Roger; Aucan, Jerome

    2013-10-01

    The generation of ultra-low frequency acoustic noise (0.1 to 1 Hz) by the nonlinear interaction of ocean surface gravity waves is well established. More controversial are the quantitative theories that attempt to predict the recorded noise levels and their variability. Here a single theoretical framework is used to predict the noise level associated with propagating pseudo-Rayleigh modes and evanescent acoustic-gravity modes. The latter are dominant only within 200 m from the sea surface, in shallow or deep water. At depths larger than 500 m, the comparison of a numerical noise model with hydrophone records from two open-ocean sites near Hawaii and the Kerguelen islands reveal: (a) Deep ocean acoustic noise at frequencies 0.1 to 1 Hz is consistent with the Rayleigh wave theory, in which the presence of the ocean bottom amplifies the noise by 10 to 20 dB; (b) in agreement with previous results, the local maxima in the noise spectrum support the theoretical prediction for the vertical structure of acoustic modes; and (c) noise level and variability are well predicted for frequencies up to 0.4 Hz. Above 0.6 Hz, the model results are less accurate, probably due to the poor estimation of the directional properties of wind-waves with frequencies higher than 0.3 Hz.

  18. Elasticity of Stishovite and Acoustic Mode Softening Under High Pressure by Brillouin Scattering

    SciTech Connect

    Jiang, F.; Gwanmesia, G; Dyuzheva, T; Duffy, T

    2009-01-01

    Brillouin scattering measurements on single-crystal stishovite, a high-pressure polymorph of SiO2, were carried out to 22 GPa. Acoustic velocities in three 30-em thick crystal platelets of synthetic stishovite were measured in a forward symmetric scattering geometry, and the full set of elastic constants were retrieved to 12 GPa. The measured velocity data were fit to Christoffel's equation, yielding ambient-pressure elastic constants of C11 = 455(1) GPa, C33 = 762(2) GPa, C12 = 199(2) GPa, C13 = 192(2) GPa, C44 = 258(1) GPa, and C66 = 321(1) GPa. The elastic modulus (C11 - C12)/2 was observed to decrease with pressure, indicating acoustic mode softening, consistent with theoretical predications for the behavior of stishovite as it approaches the transition to the CaCl2-type phase. The bounds on the aggregate adiabatic bulk and shear moduli are KS0 = 315(1) GPa, G0 = 240(1) GPa for the Voigt bound, KS0 = 301(1) GPa, G0 = 216(1) GPa for the Reuss bound. Pressure derivatives of aggregate bulk and shear moduli were constrained to be (?KS/?P)T0 = 4.34(16) and (?G/?P)0 = 0.7(1) for the Reuss bound, and (?KS/?P)T0 = 4.0(1) and (?G/?P)0 = 1.1(1) for the Voigt-Reuss-Hill (VRH) average, respectively, by fitting the data to Eulerian finite strain equations. The volume compression curve obtained from our Brillouin measurement is in very good agreement with previous compression studies up to 50 GPa.

  19. Acoustic emission detection for composite damage assessment using embedded ordinary single-mode fiber-optic interferometric sensors

    NASA Astrophysics Data System (ADS)

    Liu, Kexing; Ferguson, Suzanne M.; McEwen, Keith; Tapanes, Edward; Measures, Raymond M.

    1990-12-01

    An interferometric fiber optic sensor using ordinary single-mode fibers is developed to detect acoustic emission (AE) for damage assessment of composite materials. This fiber sensor has been embedded in both graphite/epoxy and Kevlar/epoxy composite specimens and used to produce the fast direct correlation of acoustic emission with their concomitant forms of damage, such as matrix crack or material fiber rupture. Applications of the sensor for assessment of damage due to impact and out-of-plane loading are presented. Limitations of the sensor are also discussed.

  20. Multichannel image regularization using anisotropic geodesic filtering

    SciTech Connect

    Grazzini, Jacopo A

    2010-01-01

    This paper extends a recent image-dependent regularization approach introduced in aiming at edge-preserving smoothing. For that purpose, geodesic distances equipped with a Riemannian metric need to be estimated in local neighbourhoods. By deriving an appropriate metric from the gradient structure tensor, the associated geodesic paths are constrained to follow salient features in images. Following, we design a generalized anisotropic geodesic filter; incorporating not only a measure of the edge strength, like in the original method, but also further directional information about the image structures. The proposed filter is particularly efficient at smoothing heterogeneous areas while preserving relevant structures in multichannel images.

  1. Stability of perturbed geodesics in nD axisymmetric spacetimes

    NASA Astrophysics Data System (ADS)

    Coimbra-Araújo, C. H.; Anjos, R. C.

    2016-09-01

    The effect of self-gravity of a disk matter is evaluated by the simplest modes of oscillation frequencies for perturbed circular geodesics. We plotted the radial profiles of free oscillations of an equatorial circular geodesic perturbed within the orbital plane or in the vertical direction. The calculation is carried out to geodesics of an axisymmetric n-dimensional spacetime. The profiles are computed by examples of disks embeded in five-dimensional or six-dimensional spacetime, where we studied the motion of free test particles for three axisymmetric cases: (i) the Newtonian limit of a general proposed 5D and 6D axisymmetric spacetime; (ii) a simple Randall-Sundrum (RS) 5D spacetime; (iii) general 5D and 6D RS spacetime. The equation of motion of such particles is derived and the stability study is computed for both horizontal and vertical directions, to see how extra dimensions could affect the system. In particular, we investigate a disk constructed from Miyamoto-Nagai and Chazy-Curzon with a cut parameter to generate a disk potential. Those solutions have a simple extension for extra dimensions in case (i), and by solving vacuum Einstein field equations for a kind of RS-Weyl metric in cases (ii) and (iii). We find that it is possible to compute a range of possible solutions where such perturbed geodesics are stable. Basically, the stable solutions appear, for the radial direction, in special cases when the system has 5D and in all cases when the system has 6D and, for the axial direction, in all cases when the system has both 5D or 6D.

  2. Acoustic far-field of shroud-lip-scattered instability modes of supersonic co-flowing jets

    NASA Astrophysics Data System (ADS)

    Samanta, Arnab; Freund, Jonathan B.

    2013-11-01

    We consider the acoustic radiation of instability modes in dual-stream jets, with the inner nozzle buried within the outer shroud, particularly the upstream scattering into acoustic modes that occurs at the shroud lip. For supersonic core jets, several families of instability waves are possible, beyond the regular Kelvin-Helmholtz (K-H) mode, with very different modal shapes and propagation characteristics, which are candidates for changing the sound character of very high-speed jets. The co-axial shear layers are modeled as vortex sheets, with the Wiener-Hopf method used to compute these modes coupled with an asymptotic solution for the far-field radiation. A broadband mode spectra as well as single propagating modes are considered as incident and scattered waves. The resulting far-field directivity patterns are quantified, to show the efficiency of some of these radiation mechanisms, particularly in the upstream direction, which is not directly affected by the Mach-wave-like sound that is radiated from these modes irrespective of any scattering surface. A full Kutta condition, which provides the usual boundary condition at the shroud lip, is altered to examine how vortex shedding, perhaps controllable at the lip, affects the radiated sound.

  3. Distance Functions and Geodesics on Points Clouds

    DTIC Science & Technology

    2005-01-01

    An algorithm for computing intrinsic distance functions and geodesics on sub-manifolds vector r(sup d) given by point clouds is introduced in this...and geodesics on point clouds while skipping the manifold reconstruction step. The case of point clouds representing noisy samples of a sub-manifold of...boundaries, and obtain also for the case of intrinsic distance functions on sub-manifolds of vector r(sup d), a computationally optimal approach. For point

  4. Geodesics in the static Mallett spacetime

    SciTech Connect

    Olum, Ken D.

    2010-06-15

    Mallett has exhibited a cylindrically symmetric spacetime containing closed timelike curves produced by a light beam circulating around a line singularity. I analyze the static version of this spacetime obtained by setting the intensity of the light to zero. Some null geodesics can escape to infinity, but all timelike geodesics in this spacetime originate and terminate at the singularity. Freely falling matter originally at rest quickly attains relativistic velocity inward and is destroyed at the singularity.

  5. Mode coupling and wave particle interactions for unstable ion acoustic waves

    NASA Technical Reports Server (NTRS)

    Martin, P.; Fried, B. D.

    1972-01-01

    A theory for the spatial development of linearly unstable, coupled waves is presented in which both quasi-linear and mode coupling effects are treated in a self-consistent manner. Steady state excitation of two waves is assumed at the boundary x = 0, the plasma being homogeneous in the y and z directions. Coupled equations are derived for the x dependence of the amplitudes of the primary waves and the secondary waves, correct through second order terms in the wave amplitude, but without usual approximation of small growth rates. This general formalism is then applied to the case of coupled ion acoustic waves driven unstable by an ion beam streaming in the direction of the x axis. If the modifications of the ion beam by the waves (quasi-linear effects) are ignored, explosive instabilities (singularities in all of the amplitudes at finite x) are found, even when all of the waves have positive energy. If these wave-particle interactions are included, the solutions are no longer singular, and all of the amplitudes have finite maxima.

  6. Use of multiple acoustic wave modes for assessment of long bones: Model study

    PubMed Central

    Tatarinov, Alexey; Sarvazyan, Noune; Sarvazyan, Armen

    2010-01-01

    Multiple acoustic wave mode method has been proposed as a new modality in axial bone QUS. The new method is based on measurement of ultrasound velocity at different ratio of wavelength to the bone thickness, and taking into account both bulk and guided waves. It allows assessment of changes in both the material properties related to porosity and mineralization as well as the cortical thickness influenced by resorption from inner layers, which are equally important in diagnostics of osteoporosis and other bone osteopenia. Developed method was validated in model studies using a dual-frequency (100 and 500 kHz) ultrasound device. Three types of bone phantoms for long bones were developed and tested: (1) tubular specimens from polymer materials to model combined changes of material stiffness and cortical wall thickness; (2) layered specimens to model porosity in compact bone progressing from endosteum towards periosteum; (3) animal bone specimens with both cortical and trabecular components. Observed changes of the ultrasound velocity of guided waves at 100 kHz followed gradual changes in the thickness of the intact cortical layer. On the other hand, the bulk velocity at 500 kHz remained nearly constant at the different cortical layer thickness but was affected by the material stiffness. Similar trends were observed in phantoms and in fragments of animal bones. PMID:15982472

  7. A new mode of acoustic NDT via resonant air-coupled emission

    NASA Astrophysics Data System (ADS)

    Solodov, Igor; Dillenz, Alexander; Kreutzbruck, Marc

    2017-06-01

    Resonant modes of non-destructive testing (NDT) which make use of local damage resonance (LDR) have been developed recently and demonstrated a significant increase in efficiency and sensitivity of hybrid inspection techniques by laser vibrometry, ultrasonic thermography, and shearography. In this paper, a new fully acoustic version of resonant NDT is demonstrated for defects in composite materials relevant to automotive and aviation applications. This technique is based on an efficient activation of defect vibrations by using a sonic/ultrasonic wave matched to a fundamental LDR frequency of the defect. On this condition, all points of the faulty area get involved in synchronous out-of-plane vibrations which produce a similar in-phase wave motion in ambient air. This effect of resonant air-coupled emission results in airborne waves emanating from the defect area, which can be received by a commercial microphone (low LDR frequency) or an air-coupled ultrasonic transducer (high frequency LDR). A series of experiments confirm the feasibility of both contact and non-contact versions of the technique for NDT and imaging of simulated and realistic defects (impacts, delaminations, and disbonds) in composites.

  8. Mode-coupling and wave-particle interactions for unstable ion-acoustic waves.

    NASA Technical Reports Server (NTRS)

    Martin, P.; Fried, B. D.

    1972-01-01

    A theory for the spatial development of linearly unstable, coupled waves is presented in which both quasilinear and mode-coupling effects are treated in a self-consistent manner. Steady-state excitation of two waves is assumed at the boundary x = 0, the plasma being homogeneous in the y and z directions. Coupled equations are derived for the x dependence of the amplitudes of the primary waves and the secondary waves, correct through terms of second order in the wave amplitude, but without the usual approximation of small growth rates. This general formalism is then applied to the case of coupled ion-acoustic waves driven unstable by an ion beam streaming in the direction of the x axis. If the modifications of the ion beam by the waves (quasilinear effects) are ignored, explosive instabilities (singularities in all of the amplitudes at finite x) are found even when all of the waves have positive energy. If these wave-particle interactions are included, the solutions are no longer singular, and all of the amplitudes have finite maxima.

  9. Interfacial slip on a transverse-shear mode acoustic wave device

    NASA Astrophysics Data System (ADS)

    Ellis, Jonathan S.; Hayward, Gordon L.

    2003-12-01

    This article describes a mathematical relationship between the slip parameter α and the slip length b for a slip boundary condition applied to the transverse-shear model for a quartz-crystal acoustic wave device. The theory presented here reduces empirical determination of slip to a one-parameter fit. It shows that the magnitude and phase of the slip parameter, which describes the relative motion of the surface and liquid in the transverse-shear model, can be linked to the slip length. Furthermore, the magnitude and phase of the slip parameter are shown to depend on one another. An experiment is described to compare the effects of liquid-surface affinity on the resonant properties of a transverse-shear mode wave device by applying different polar and nonpolar liquids to surfaces of different polarity. The theory is validated with slip values determined from the transverse-shear model and compared to slip length values from literature. Agreement with literature values of slip length is within one order of magnitude.

  10. On-chip temperature-compensated Love mode surface acoustic wave device for gravimetric sensing

    NASA Astrophysics Data System (ADS)

    Liu, Q.; Flewitt, A. J.

    2014-11-01

    Love mode surface acoustic wave (SAW) sensors have been recognized as one of the most sensitive devices for gravimetric sensors in liquid environments such as bio sensors. Device operation is based upon measuring changes in the transmitted (S21) frequency and phase of the first-order Love wave resonance associated with the device upon on attachment of mass. However, temperature variations also cause a change in the first order S21 parameters. In this work, shallow grooved reflectors and a "dotted" single phase unidirectional interdigitated transducer (D-SPUDT) have been added to the basic SAW structure, which promote unidirectional Love wave propagation from the device's input interdigitated transducers. Not only does this enhance the first-order S21 signal but also it allows propagation of a third-order Love wave. The attenuation coefficient of the third-order wave is sufficiently great that, whilst there is a clear reflected S11 signal, the third-order wave does not propagate into the gravimetric sensing area of the device. As a result, whilst the third-order S11 signal is affected by temperature changes, it is unaffected by mass attachment in the sensing area. It is shown that this signal can be used to remove temperature effects from the first-order S21 signal in real time. This allows gravimetric sensing to take place in an environment without the need for any other temperature measurement or temperature control; this is a particular requirement of gravimetric biosensors.

  11. Assessing the horizontal refraction of ocean acoustic tomography signals using high-resolution ocean state estimates.

    PubMed

    Dushaw, Brian D

    2014-07-01

    The analysis of signals for acoustic tomography sent between a source and a receiver most often uses the unrefracted geodesic path, an approximation that is justified from theoretical considerations, relying on estimates of horizontal gradients of sound speed, or on simple theoretical models. To quantify the effects of horizontal refraction caused by a realistic ocean environment, horizontal refractions of long-range signals were computed using global ocean state estimates for 2004 from the Estimating the Circulation and Climate of the Ocean (ECCO2) project. Basin-scale paths in the eastern North Pacific Ocean and regional-scale paths in the Philippine Sea were used as examples. At O(5 Mm) basin scales, refracted geodesic and geodesic paths differed by only about 5 km. Gyre-scale features had the greatest refractive influence, but the precise refractive effects depended on the path geometry with respect to oceanographic features. Refraction decreased travel times by 5-10 ms and changed azimuthal angles by about 0.2°. At O(500 km) regional scales, paths deviated from the geodesic by only 250 m, and travel times deviated by less than 0.5 ms. Such effects are of little consequence in the analysis of tomographic data. Refraction details depend only slightly on mode number and frequency.

  12. Development and Application of a Three-Dimensional Seismo-Acoustic Coupled-Mode Model

    DTIC Science & Technology

    2015-09-30

    comparison to measured data. RESULTS Modeling acoustic data recorded in a scale model experiment Three-dimensional modeling of data recorded in a 1:7500... acoustic field in 3D, and the time domain signals were beamformed for comparison with the measured data. The modeled time series are generated by...Muir, “Laboratory P- and S-wave measurements of a reconstituted muddy sediment with comparison to card-house theory,” Journal of the Acoustical

  13. Depolarization of surface-attached hypothalamic mouse neurons studied by acoustic wave (thickness shear mode) detector.

    PubMed

    Cheung, Shilin; Fick, Laura J; Belsham, Denise D; Thompson, Michael

    2010-02-01

    Isolation of neurons from animal tissue is an important aspect of understanding basic biochemical processes such as the action of hormones and neurotransmitters. In the present work, the focus is on an effort to evaluate the utility of acoustic wave physics for the study of such cells. Immortalised hypothalamic neuronal cells from mouse embryos were cultured on the surface of the gold electrode of a 9.0 MHz thickness-shear mode acoustic wave sensor. These cells, which are clonal, are imposed on the surface of the device at a confluence in the range of 80-100%. The coated sensor is incorporated into a flow-injection configuration such that electrolytes can be introduced in order to examine their effects through measurement by network analysis. Both series resonance frequency, fs, and motional resistance, R(m), were measured in a number of experiments involving the injection of KCl and NaCl into the sensor-neuron system. The various responses to these electrolytes were interpreted in terms of changes in cellular structure associated with the depolarization process. The sensor-neuron system was found to elicit different responses to the addition of KCl and NaCl. Preliminary findings indicate that the TSM sensor does not purely measure changes in the membrane potential upon KCl addition. Typical changes in fs for 15 mM, 30 mM and 60 mM KCl additions were 54 +/- 15, 80 +/- 26 and 142 +/- 58 Hz (mean +/- standard deviation) respectively. Typical changes in R(m) for these KCl additions were 7 +/- 3, 13 +/- 4 and 23 +/- 6 Omega, respectively. These results were concluded after 17 runs at each concentration. Despite the large relative standard deviations, the dependence of f(s) and R(m) with respect to concentration was apparent. Controls performed by coating the TSM sensor with laminin or a cell attachment matrix showed no significant changes in either f(s) or R(m) for the same solutions tested on the sensor-neuron system.

  14. Nonlinear Excitation of Acoustic Modes by Large Amplitude Alfvén waves in the Large Plasma Device (LAPD)

    NASA Astrophysics Data System (ADS)

    Dorfman, S. E.; Carter, T. A.; Pribyl, P.; Tripathi, S.; Van Compernolle, B.; Vincena, S. T.; Sydora, R. D.

    2013-12-01

    Alfvén waves, a fundamental mode of magnetized plasmas, are ubiquitous in space plasmas. While the linear behavior of these waves has been extensively studied [1], non-linear effects are important in many real systems, including the solar corona and solar wind. In particular, a parametric decay process in which a large amplitude Alfvén wave decays into an ion acoustic wave and backward propagating Alfvén wave may play an important role in the coronal heating problem. Specifically, the decay of large-amplitude Alfvén waves propagating outward from the photosphere could lead to heating of the corona by the daughter ion acoustic modes [2]. As direct observational evidence of parametric decay is limited [3], laboratory experiments may play an important role in validating simple theoretical predictions and aiding in the interpretation of space measurements. Recent counter-propagating Alfvén wave experiments in the Large Plasma Device (LAPD) have recorded the first laboratory observation of the Alfvén-acoustic mode coupling at the heart of this parametric decay instability [4]. A resonance in the beat wave response produced by the two launched Alfvén waves is observed and is identified as a damped ion acoustic mode based on the measured dispersion relation. Other properties of the interaction including the spatial profile of the beat mode and response amplitude are also consistent with theoretical predictions for a three-wave interaction driven by a nonlinear ponderomotive force. Strong damping observed after the pump Alfvén waves are turned off is under investigation; a novel ion acoustic wave launcher is under development to launch the mode directly for damping studies. New experiments also aim to identify decay instabilities from a single large-amplitude Alfvén wave. In conjunction with these experiments, gyrokinetic simulation efforts are underway to scope out the relevant parameter space. [1] W. Gekelman, et. al., Phys. Plasmas 18, 055501 (2011). [2] F

  15. Acoustic mode radiation from the termination of a truncated nonlinear internal gravity wave duct in a shallow ocean area.

    PubMed

    Lin, Ying-Tsong; Duda, Timothy F; Lynch, James F

    2009-10-01

    Horizontal ducting of sound between short-wavelength nonlinear internal gravity waves in coastal environments has been reported in many theoretical and experimental studies. Important consequences arising at the open end of an internal wave duct (the termination) are examined in this paper with three-dimensional normal mode theory and parabolic approximation modeling. For an acoustic source located in such a duct and sufficiently far from the termination, some of the propagating sound may exit the duct by penetrating the waves at high grazing angles, but a fair amount of the sound energy is still trapped in the duct and propagates toward the termination. Analysis here shows that the across-duct sound energy distribution at the termination is unique for each acoustic vertical mode, and as a result the sound radiating from the termination of the duct forms horizontal beams that are different for each mode. In addition to narrowband analysis, a broadband simulation is made for water depths of order 80 m and propagation distances of 24 km. Situations occur with one or more modes absent in the radiated field and with mode multipath in the impulse response. These are both consistent with field observations.

  16. 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.

  17. Craniofacial reconstruction evaluation by geodesic network.

    PubMed

    Zhao, Junli; Liu, Cuiting; Wu, Zhongke; Duan, Fuqing; Wang, Kang; Jia, Taorui; Liu, Quansheng

    2014-01-01

    Craniofacial reconstruction is to estimate an individual's face model from its skull. It has a widespread application in forensic medicine, archeology, medical cosmetic surgery, and so forth. However, little attention is paid to the evaluation of craniofacial reconstruction. This paper proposes an objective method to evaluate globally and locally the reconstructed craniofacial faces based on the geodesic network. Firstly, the geodesic networks of the reconstructed craniofacial face and the original face are built, respectively, by geodesics and isogeodesics, whose intersections are network vertices. Then, the absolute value of the correlation coefficient of the features of all corresponding geodesic network vertices between two models is taken as the holistic similarity, where the weighted average of the shape index values in a neighborhood is defined as the feature of each network vertex. Moreover, the geodesic network vertices of each model are divided into six subareas, that is, forehead, eyes, nose, mouth, cheeks, and chin, and the local similarity is measured for each subarea. Experiments using 100 pairs of reconstructed craniofacial faces and their corresponding original faces show that the evaluation by our method is roughly consistent with the subjective evaluation derived from thirty-five persons in five groups.

  18. Craniofacial Reconstruction Evaluation by Geodesic Network

    PubMed Central

    Zhao, Junli; Liu, Cuiting; Wu, Zhongke; Duan, Fuqing; Wang, Kang; Jia, Taorui; Liu, Quansheng

    2014-01-01

    Craniofacial reconstruction is to estimate an individual's face model from its skull. It has a widespread application in forensic medicine, archeology, medical cosmetic surgery, and so forth. However, little attention is paid to the evaluation of craniofacial reconstruction. This paper proposes an objective method to evaluate globally and locally the reconstructed craniofacial faces based on the geodesic network. Firstly, the geodesic networks of the reconstructed craniofacial face and the original face are built, respectively, by geodesics and isogeodesics, whose intersections are network vertices. Then, the absolute value of the correlation coefficient of the features of all corresponding geodesic network vertices between two models is taken as the holistic similarity, where the weighted average of the shape index values in a neighborhood is defined as the feature of each network vertex. Moreover, the geodesic network vertices of each model are divided into six subareas, that is, forehead, eyes, nose, mouth, cheeks, and chin, and the local similarity is measured for each subarea. Experiments using 100 pairs of reconstructed craniofacial faces and their corresponding original faces show that the evaluation by our method is roughly consistent with the subjective evaluation derived from thirty-five persons in five groups. PMID:25214890

  19. Numerical inverse method predicting acoustic spinning modes radiated by a ducted fan from free-field test data.

    PubMed

    Lewy, Serge

    2008-07-01

    Spinning modes generated by a ducted turbofan at a given frequency determine the acoustic free-field directivity. An inverse method starting from measured directivity patterns is interesting in providing information on the noise sources without requiring tedious spinning-mode experimental analyses. According to a previous article, equations are based on analytical modal splitting inside a cylindrical duct and on a Rayleigh or a Kirchhoff integral on the duct exit cross section to get far-field directivity. Equations are equal in number to free-field measurement locations and the unknowns are the propagating mode amplitudes (there are generally more unknowns than equations). A MATLAB procedure has been implemented by using either the pseudoinverse function or the backslash operator. A constraint comes from the fact that squared modal amplitudes must be positive which involves an iterative least squares fitting. Numerical simulations are discussed along with several examples based on tests performed by Rolls-Royce in the framework of a European project. It is assessed that computation is very fast and it well fits the measured directivities, but the solution depends on the method and is not unique. This means that the initial set of modes should be chosen according to any known physical property of the acoustic sources.

  20. Contrast Enhanced Superharmonic Imaging for Acoustic Angiography Using Reduced Form-Factor Lateral Mode Transmitters for Intravascular and Intracavity Applications.

    PubMed

    Wang, Zhuochen; Heath Martin, K; Huang, Wenbin; Dayton, Paul A; Jiang, Xiaoning

    2017-02-01

    Techniques to image the microvasculature may play an important role in imaging tumor-related angiogenesis and vasa vasorum associated with vulnerable atherosclerotic plaques. However, the microvasculature associated with these pathologies is difficult to detect using traditional B-mode ultrasound or even harmonic imaging due to small vessel size and poor differentiation from surrounding tissue. Acoustic angiography, a microvascular imaging technique that utilizes superharmonic imaging (detection of higher order harmonics of microbubble response), can yield a much higher contrast-to-tissue ratio than second harmonic imaging methods. In this paper, two dual-frequency transducers using lateral mode transmitters were developed for superharmonic detection and acoustic angiography imaging in intracavity applications. A single element dual-frequency intravascular ultrasound transducer was developed for concept validation, which achieved larger signal amplitude, better contrast-to-noise ratio (CNR), and pulselength compared to the previous work. A dual-frequency [Pb(Mg1/3Nb2/3)O3]-x[PbTiO3] array transducer was then developed for superharmonic imaging with dynamic focusing. The axial and lateral sizes of the microbubbles in a 200- [Formula: see text] tube were measured to be 269 and [Formula: see text], respectively. The maximum CNR was calculated to be 22 dB. These results show that superharmonic imaging with a low frequency lateral mode transmitter is a feasible alternative to thickness mode transmitters when the final transducer size requirements dictate design choices.

  1. On the instability of time-domain acoustic boundary element method due to the static mode in interior problems

    NASA Astrophysics Data System (ADS)

    Jang, Hae-Won; Ih, Jeong-Guon

    2013-11-01

    In the analysis of interior acoustic problems, the time domain boundary element method (TBEM) suffers the monotonically increasing instability when using the direct Kirchhoff integral. This instability is related to the non-oscillatory static acoustic mode describing the constant spatial response in an enclosure. In this work, nonphysical natures of non-oscillatory static mode influencing the instability of TBEM calculation are investigated, and a method for stabilization is studied. In TBEM calculation, the static mode is represented by two non-oscillatory eigenmodes with different eigenvalues. The monotonically increasing instability is caused by the unstable poles of non-oscillatory eigenmodes as well as very small, very low frequency noise of an input signal. Interior problems with impedance boundary condition also exhibit the monotonically increasing instability stemming from its pseudo non-oscillatory static mode due to the lack of dissipation at very low frequencies. Calculation of transient sound fields within rigid and lined boxes provides numerical evidences. It is noted that the stabilization effort by modifying the coefficient matrix based on the spectral decomposition can be used only for correcting the unstable pole. The filtering method based on the eigen-analysis must be additionally used to avoid the remaining instability caused by very low frequency noise of input signal.

  2. Dynamic exchange via spin currents in acoustic and optical modes of ferromagnetic resonance in spin-valve structures

    NASA Astrophysics Data System (ADS)

    Timopheev, A. A.; Pogorelov, Yu. G.; Cardoso, S.; Freitas, P. P.; Kakazei, G. N.; Sobolev, N. A.

    2014-04-01

    Two ferromagnetic (FM) layers magnetically decoupled by a thick, normal metal spacer layer can be dynamically coupled via spin currents emitted by the spin pump and absorbed through the spin-torque effects at the neighboring interfaces. A decrease of damping in both layers due to a partial compensation of the angular momentum leakage in each layer was previously observed at the coincidence of the two FM resonances. In the case of nonzero magnetic coupling, such a dynamic exchange will depend on the mutual precession of the magnetic moments in the layers. A difference in the linewidth of the resonance peaks is expected for the acoustic and optical regimes of precession. However, the interlayer coupling (IC) hybridizes the resonance responses of the layers and therefore can also change their linewidths. The interplay between the two mechanisms has never been considered before. In the present work, the joint influence of the hybridization and nonlocal damping on the linewidth has been studied in weakly coupled NiFe/CoFe/Cu/CoFe/MnIr spin-valve multilayers. It has been found that the dynamic exchange by spin currents is different in the optical and acoustic modes, and this difference is dependent on the IC strength. In contrast to the acoustic precession mode, the dynamic exchange in the optical mode works as an additional damping source. A simulation in the framework of the Landau-Lifshitz-Gilbert formalism for two FM layers coupled magnetically and by spin currents has been done to separate the effects of the nonlocal damping from the resonance modes hybridization. In our samples, both mechanisms bring about linewidth changes of the same order of magnitude but lead to a distinctly different angular behavior. The obtained results are relevant for a broad class of coupled magnetic multilayers with ballistic regime of the spin transport.

  3. Dual-mode resonant instabilities of the surface dust-acoustic wave in a Lorentzian plasma slab

    SciTech Connect

    Lee, Myoung-Jae; Jung, Young-Dae

    2015-08-15

    The dual-mode resonant instabilities of the dust-acoustic surface wave propagating at the plasma-vacuum interfaces of the generalized Lorentzian dusty plasma slab are kinetically investigated. The dispersion relation is derived for the two propagation modes: symmetric and anti-symmetric waves. We have found that the temporal growth rate of the resonant instability increases with an increase of the slab thickness for both modes. Especially, the nonthermality of plasmas enhances the growth rate of the anti-symmetric resonant wave, and the nonthermal effect is enhanced as the slab thickness is increased. It is also found that the growth rate increases with increasing angular frequency of the rotating dust grain due to the enhanced resonant energy exchange.

  4. Pulsed-laser excitation of acoustic modes in open high-Q photoacoustic resonators for trace gas monitoring: results for C2H4

    NASA Astrophysics Data System (ADS)

    Brand, Christian; Winkler, Andreas; Hess, Peter; Miklós, András; Bozóki, Zoltán; Sneider, János

    1995-06-01

    The pulsed excitation of acoustic resonances was studied with a continuously monitoring photoacoustic detector system. Acoustic waves were generated in C2H4/N 2 gas mixtures by light absorption of the pulses from a transversely excited atmospheric CO2 laser. The photoacoustic part consisted of high-Q cylindrical resonators (Q factor 820 for the first radial mode in N2) and two adjoining variable acoustic filter systems. The time-resolved signal was Fourier transformed to a frequency spectrum of high resolution. For the first radial mode a Lorentzian profile was fitted to the measured data. The outside noise suppression and the signal-to-noise ratio were investigated in a normal laboratory environment in the flow-through mode. The acoustic and electric filter system combined with the

  5. Development and Application of a Three-dimensional Seismo-acoustic Coupled-mode Model

    DTIC Science & Technology

    2014-09-30

    of coral reef fish need to locate a reef , and sound emanating from reefs may act as a cue to guide them. Using acoustic data collected from Bahia...Almirante on the north coast of Panama, this study examines the distances from potential settlement sites for which reef sounds can be detected by reef ...fish larvae. Maps of signal excess are created using source levels measured at the reef , transmission loss calculated with range-dependent acoustic

  6. Geodesic Monte Carlo on Embedded Manifolds

    PubMed Central

    Byrne, Simon; Girolami, Mark

    2013-01-01

    Markov chain Monte Carlo methods explicitly defined on the manifold of probability distributions have recently been established. These methods are constructed from diffusions across the manifold and the solution of the equations describing geodesic flows in the Hamilton–Jacobi representation. This paper takes the differential geometric basis of Markov chain Monte Carlo further by considering methods to simulate from probability distributions that themselves are defined on a manifold, with common examples being classes of distributions describing directional statistics. Proposal mechanisms are developed based on the geodesic flows over the manifolds of support for the distributions, and illustrative examples are provided for the hypersphere and Stiefel manifold of orthonormal matrices. PMID:25309024

  7. A Riemannian approach to Randers geodesics

    NASA Astrophysics Data System (ADS)

    Brody, Dorje C.; Gibbons, Gary W.; Meier, David M.

    2016-08-01

    In certain circumstances tools of Riemannian geometry are sufficient to address questions arising in the more general Finslerian context. We show that one such instance presents itself in the characterisation of geodesics in Randers spaces of constant flag curvature. To achieve a simple, Riemannian derivation of this special family of curves, we exploit the connection between Randers spaces and the Zermelo problem of time-optimal navigation in the presence of background fields. The characterisation of geodesics is then proven by generalising an intuitive argument developed recently for the solution of the quantum Zermelo problem.

  8. Double-mode lateral-field-excitation bulk acoustic wave characteristics of Ca3TaGa3Si2O14 crystals.

    PubMed

    Ma, Tingfeng; Zhang, Qiong; Yu, Fapeng; Xie, Chao; Wang, Ji; Du, Jianke; Huang, Bin; Huang, Jiahan; Zhang, Chao

    2017-08-01

    The double-mode lateral-field-excitation (LFE) bulk acoustic wave characteristics of Ca3TaGa3Si2O14 (CTGS) crystals are investigated. It is found that LFE devices based on (yxl)-57° CTGS crystals can work on both pure-LFE and pseudo-LFE modes when the driving electric field direction is normal to the crystallographic x axis of the piezoelectric substrate. Several double-mode LFE bulk acoustic wave devices based on CTGS crystals are designed and tested. The experimental results conform to the theoretical prediction well. Being able to operate in pure-LFE and pseudo-LFE modes, the double-mode LFE sensors show high sensitivity to both mechanical and electrical property changes of analytes. The results provide the crystal cut for double-mode LFE sensors, which is a critical basis of designing high-performance chemical and biological sensors by using double-mode LFE devices.

  9. The Main Principles of Formation of the Transverse Modes in the Multilayered Waveguides of Surface Acoustic Waves

    NASA Astrophysics Data System (ADS)

    Sveshnikov, B. V.; Bagdasaryan, A. S.

    2016-07-01

    We develop a self-consistent model allowing one to analyze the properties of the interdigital transducer of the surface acoustic waves as a symmetric five-layered waveguide on a piezoelectric substrate with three possible values of the phase velocity of the acoustic-wave propagation along the longitudinal axis of the system. The transcendental dispersion relation for describing the waves in such a system is derived and the method for its instructive graphic analysis is proposed. The condition under which only the fundamental transverse mode is excited in the waveguide is formulated. The method for calculating the normalized power and the transverse distribution of the field of the continuous-spectrum waves radiated from the considered waveguide is described. It is shown that the characteristic spatial scale of the longitudinal damping of the amplitude of this field at the waveguide center can be a qualitative estimate of the transverse-mode formation length. The efficiency of a new method for suppressing the higher-order transverse waveguide modes is demonstrated.

  10. Deformation and Brittle Failure of Folded Gneiss in Triaxial Compression: Failure Modes, Acoustic Signatures and Microfabric Controls

    NASA Astrophysics Data System (ADS)

    Agliardi, F.; Vinciguerra, S.; Dobbs, M. R.; Zanchetta, S.

    2014-12-01

    Fabric anisotropy is a key control of rock behavior in different geological settings and over different timescales. However, the effect of tectonically folded fabrics on the brittle strength and failure mode of metamorphic rocks is poorly understood. Recent data, obtained from uniaxial compression experiments on folded gneiss (Agliardi et al., 2014), demonstrated that their brittle failure modes depend upon the arrangement of two anisotropies (i.e. foliation and fold axial planes) and that rock strength correlates with failure mode. Since lithostatic pressure may significantly affect this rock behavior, we investigated its effect in triaxial compression experiments. We tested the Monte Canale Gneiss (Italian Alps), characterized by low phyllosilicate content and compositional layering folded at the cm-scale. We used a servo-controlled hydraulic loading system to test 19 air-dry cylindrical specimens (ø = 54 mm) that were characterized both in terms of fold geometry and orientation of foliation and fold axial planes to the axial load direction. The specimens were instrumented with direct contact axial and circumferential strain gauges. Acoustic emissions and P- and S-wave velocities were measured by piezoelectric transducers mounted in the compression platens. The tests were performed at confining pressures of 40 MPa and axial strain rates of 5*10-6 s-1. Post-failure study of fracture mechanisms and related microfabric controls was undertaken using X-ray CT, optical microscopy and SEM. Samples failed in three distinct brittle modes produced by different combinations of fractures parallel to foliation, fractures parallel to fold axial planes, or mm-scale shear bands. The failure modes, consistent with those described in uniaxial compression experiments, were found to be associated with distinct stress-strain and acoustic emission signatures. Failure modes involving quartz-dominated axial plane anisotropy correspond to higher peak strength and axial strain, less

  11. Geodesic Dome Activity Provides Serious Fun!

    ERIC Educational Resources Information Center

    Anderson, Richard

    2009-01-01

    After the author's class completed last year's 44'-long timber-framed covered bridge project, he was pondering what other learning challenge he could pose to his students. He came across an article on geodesic dome construction in the September 2007 issue of "Tech Directions" and, he had his answer. In this article, the author and his…

  12. Horndeski scalar-tensor black hole geodesics

    NASA Astrophysics Data System (ADS)

    Tretyakova, Darya; Melkoserov, Dmitry; Adyev, Timur

    2016-10-01

    We examine massive particles and null geodesics for the scalar-tensor black hole in the Horndeski-Galileon framework. Our analysis shows that first kind relativistic orbits, corresponding to circular and elliptic orbits, are absent for the black hole solution with the static scalar field. This is a highly pathological behavior contradicting to the black hole accretion and Solar System observations.

  13. Geodesic curvature driven surface microdomain formation.

    PubMed

    Adkins, Melissa R; Zhou, Y C

    2017-09-15

    Lipid bilayer membranes are not uniform and clusters of lipids in a more ordered state exist within the generally disorder lipid milieu of the membrane. These clusters of ordered lipids microdomains are now referred to as lipid rafts. Recent reports attribute the formation of these microdomains to the geometrical and molecular mechanical mismatch of lipids of different species on the boundary. Here we introduce the geodesic curvature to characterize the geometry of the domain boundary, and develop a geodesic curvature energy model to describe the formation of these microdomains as a result of energy minimization. Our model accepts the intrinsic geodesic curvature of any binary lipid mixture as an input, and will produce microdomains of the given geodesic curvature as demonstrated by three sets of numerical simulations. Our results are in contrast to the surface phase separation predicted by the classical surface Cahn-Hilliard equation, which tends to generate large domains as a result of the minimizing line tension. Our model provides a direct and quantified description of the structure inhomogeneity of lipid bilayer membrane, and can be coupled to the investigations of biological processes on membranes for which such inhomogeneity plays essential roles.

  14. Geodesic curvature driven surface microdomain formation

    NASA Astrophysics Data System (ADS)

    Adkins, Melissa R.; Zhou, Y. C.

    2017-09-01

    Lipid bilayer membranes are not uniform and clusters of lipids in a more ordered state exist within the generally disorder lipid milieu of the membrane. These clusters of ordered lipids microdomains are now referred to as lipid rafts. Recent reports attribute the formation of these microdomains to the geometrical and molecular mechanical mismatch of lipids of different species on the boundary. Here we introduce the geodesic curvature to characterize the geometry of the domain boundary, and develop a geodesic curvature energy model to describe the formation of these microdomains as a result of energy minimization. Our model accepts the intrinsic geodesic curvature of any binary lipid mixture as an input, and will produce microdomains of the given geodesic curvature as demonstrated by three sets of numerical simulations. Our results are in contrast to the surface phase separation predicted by the classical surface Cahn-Hilliard equation, which tends to generate large domains as a result of the minimizing line tension. Our model provides a direct and quantified description of the structure inhomogeneity of lipid bilayer membrane, and can be coupled to the investigations of biological processes on membranes for which such inhomogeneity plays essential roles.

  15. Energy loss to intravalley acoustic modes in nano-dimensional wire structures at low temperatures

    NASA Astrophysics Data System (ADS)

    Nag, S.; Das, B.; Basu, A.; Das, J.; Bhattacharya, D. P.; Sarkar, C. K.

    2017-03-01

    The theory of rate of loss of energy of non-equilibrium electrons due to inelastic interaction with the intravalley acoustic phonons in a nano-dimensional semiconductor wire has been developed under the condition of low lattice temperature, when the approximations of the well known traditional theory are not valid. Numerical results are obtained for narrow-channel GaAs-GaAlAs wires structures. On comparison with other available results it is revealed that the finite energy of the intravalley acoustic phonons and, the use of the full form of the phonon distribution without truncation to the equipartition law, produce significant changes in the energy loss characteristics at low temperatures.

  16. On the possibility of representing an acoustic field in shallow water as the sum of normal modes and quasimodes

    NASA Astrophysics Data System (ADS)

    Grigor'ev, V. A.; Petnikov, V. G.

    2016-11-01

    Using the example of a shallow-water acoustic waveguide with a homogeneous water layer of constant thickness H lying on a homogeneous fluid absorbing half-space (bottom), we obtain estimates of distance r from a source, for which it is possible to ignore the continuous spectrum for the mode description of the depth dependence of the intensity of a low-frequency sound field in the bottom layer. We have compared two discrete representations of the field using (1) the total set of normal modes and (2) the total set of normal modes and quasimodes. It is shown that in the case when there is at least one normal mode in the channel, additional allowance for quasimodes makes it possible by an order of magnitude to approximate the boundary of applicability of mode theory and on average establish it at a level of r H or less. We explain the functional dependences of the contribution of the continuous spectrum to the total field on the waveguide parameters and find the conditions of its minimization. We present examples of description of the field in the bottom, where the advantage of using quasimodes at short distances is also demonstrated.

  17. Non-linear Alfvén wave interaction leading to resonant excitation of an acoustic mode in the laboratory

    SciTech Connect

    Dorfman, S.; Carter, T. A.

    2015-05-15

    The nonlinear three-wave interaction process at the heart of the parametric decay process is studied by launching counter-propagating Alfvén waves from antennas placed at either end of the Large Plasma Device [W. Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)]. A resonance in the beat wave response produced by the two launched Alfvén waves is observed and is identified as a damped ion acoustic mode based on the measured dispersion relation. Other properties of the interaction including the spatial profile of the beat mode and response amplitude are also consistent with theoretical predictions for a three-wave interaction driven by a nonlinear ponderomotive force. A simple damped, driven oscillator model making use of the MHD equations well-predicts most of the observations, but the width of the resonance curve is still under investigation.

  18. Acoustic Modeling Using a Three-Dimensional Coupled-Mode Model

    DTIC Science & Technology

    2013-09-30

    a comparison of the 3D coupled-mode solution to a finite element method ( FEM ) solution, (2) ranging estimates from horizontal multipath in a...mode code for environments with elastic layers. RESULTS Comparison of the 3D coupled-mode solution to a FEM solution As described above, in...assumption are examined by comparing the solution from the 3D coupled-mode model to a solution obtained using a FEM model applied with the

  19. VLP seismicity from resonant modes of acoustic-gravity waves in a conduit-crack system filled with multiphase magma

    NASA Astrophysics Data System (ADS)

    Liang, C.; Prochnow, B. N.; OReilly, O. J.; Dunham, E. M.; Karlstrom, L.

    2016-12-01

    Oscillation of magma in volcanic conduits connected to cracks (dikes and sills) has been suggested as an explanation for very long period (VLP) seismic signals recorded at active basaltic volcanoes such as. Kilauea, Hawaii, and Erebus, Antarctica. We investigate the VLP seismicity using a linearized model for waves in and associated eigenmodes of a coupled conduit-crack system filled with multiphase magma, an extension of the Karlstrom and Dunham (2016) model for acoustic-gravity waves in volcanic conduits. We find that the long period surface displacement (as recorded on broadband seismometers) is dominated by opening/closing of the crack rather than the deformation of the conduit conduit walls. While the fundamental eigenmode is sensitive to the fluid properties and the geometry of the magma plumbing system, a closer scrutiny of various resonant modes reveals that the surface displacement is often more sensitive to higher modes. Here we present a systematic analysis of various long period acoustic-gravity wave resonant modes of a coupled conduit-crack system that the surface displacement is most sensitive to. We extend our previous work on a quasi-one-dimensional conduit model with inviscid magma to a more general axisymmetric conduit model that properly accounts for viscous boundary layers near the conduit walls, based on the numerical method developed by Prochnow et al. (submitted to Computers and Fluids, 2016). The surface displacement is dominated by either the fundamental or higher eigenmodes, depending on magma properties and the geometry of conduit and crack. An examination of the energetics of these modes reveals the complex interplay of different restoring forces (magma compressibility in the conduit, gravity, and elasticity of the crack) driving the VLP oscillations. Both nonequilibrium bubble growth and resorption and viscosity contribute to the damping of VLP signals. Our models thus provide a means to infer properties of open-vent basaltic volcanoes

  20. Liquid density analysis of sucrose and alcoholic beverages using polyimide guided Love-mode acoustic wave sensors

    NASA Astrophysics Data System (ADS)

    Turton, Andrew; Bhattacharyya, Debabrata; Wood, David

    2006-02-01

    A liquid density sensor using Love-mode acoustic waves has been developed which is suitable for use in the food and drinks industries. The sensor has an open flat surface allowing immersion into a sample and simple cleaning. A polyimide waveguide layer allows cheap and simple fabrication combined with a robust chemically resistant surface. The low shear modulus of polyimide allows thin guiding layers giving a high sensitivity. A dual structure with a smooth reference device exhibiting viscous coupling with the wave, and a patterned sense area to trap the liquid causing mass loading, allows discrimination of the liquid density from the square root of the density-viscosity product (ρη)0.5. Frequency shift and insertion loss change were proportional to (ρη)0.5 with a non-linear response due to the non-Newtonian nature of viscous liquids at high frequencies. Measurements were made with sucrose solutions up to 50% and different alcoholic drinks. A maximum sensitivity of 0.13 µg cm-3 Hz-1 was achieved, with a linear frequency response to density. This is the highest liquid density sensitivity obtained for acoustic mode sensors to the best of our knowledge.

  1. Collective acoustic modes as renormalized damped oscillators: unified description of neutron and x-ray scattering data from classical fluids.

    PubMed

    Bafile, Ubaldo; Guarini, Eleonora; Barocchi, Fabrizio

    2006-06-01

    In the Q range where inelastic x-ray and neutron scattering are applied to the study of acoustic collective excitations in fluids, various models of the dynamic structure factor S(Q, omega) generalize in different ways the results obtained from linearized-hydrodynamics theory in the Q-->0 limit. Here we show that the models most commonly fitted to experimental S(Q, omega) spectra can be given a unified formulation. In this way, direct comparisons among the results obtained by fitting different models become now possible to a much larger extent than ever. We also show that a consistent determination of the dispersion curve and of the propagation Q range of the excitations is possible, whichever model is used. We derive an exact formula which describes in all cases the dispersion curve and allows for the first quantitative understanding of its shape, by assigning specific and distinct roles to the various structural, thermal, and damping effects that determine the Q dependence of the mode frequencies. The emerging picture describes the acoustic modes as Q-dependent harmonic oscillators whose characteristic frequency is explicitly renormalized in an exact way by the relaxation processes, which also determine, through the widths of both the inelastic and the elastic lines, the whole shape of collective-excitation spectra.

  2. Elastic parabolic equation and normal mode solutions for seismo-acoustic propagation in underwater environments with ice covers.

    PubMed

    Collis, Jon M; Frank, Scott D; Metzler, Adam M; Preston, Kimberly S

    2016-05-01

    Sound propagation predictions for ice-covered ocean acoustic environments do not match observational data: received levels in nature are less than expected, suggesting that the effects of the ice are substantial. Effects due to elasticity in overlying ice can be significant enough that low-shear approximations, such as effective complex density treatments, may not be appropriate. Building on recent elastic seafloor modeling developments, a range-dependent parabolic equation solution that treats the ice as an elastic medium is presented. The solution is benchmarked against a derived elastic normal mode solution for range-independent underwater acoustic propagation. Results from both solutions accurately predict plate flexural modes that propagate in the ice layer, as well as Scholte interface waves that propagate at the boundary between the water and the seafloor. The parabolic equation solution is used to model a scenario with range-dependent ice thickness and a water sound speed profile similar to those observed during the 2009 Ice Exercise (ICEX) in the Beaufort Sea.

  3. Bolt axial stress measurement based on a mode-converted ultrasound method using an electromagnetic acoustic transducer.

    PubMed

    Ding, Xu; Wu, Xinjun; Wang, Yugang

    2014-03-01

    A method is proposed to measure the stress on a tightened bolt using an electromagnetic acoustic transducer (EMAT). A shear wave is generated by the EMAT, and a longitudinal wave is obtained from the reflection of the shear wave due to the mode conversion. The ray paths of the longitudinal and the shear wave are analyzed, and the relationship between the bolt axial stress and the ratio of time of flight between two mode waves is then formulated. Based on the above outcomes, an EMAT is developed to measure the bolt axial stress without loosening the bolt, which is required in the conventional EMAT test method. The experimental results from the measurement of the bolt tension show that the shear and the mode-converted longitudinal waves can be received successfully, and the ratio of the times of flight of the shear and the mode-converted longitudinal waves is linearly proportional to the bolt axial tension. The non-contact characteristic of EMAT eliminates the effect of the couplant and also makes the measurement more convenient than the measurement performed using the piezoelectric transducer. This method provides a promising way to measure the stress on tightened bolts.

  4. GeodesicViewer - A tool for exploring geodesics in the theory of relativity

    NASA Astrophysics Data System (ADS)

    Müller, Thomas; Grave, Frank

    2010-02-01

    The GeodesicViewer realizes exocentric two- and three-dimensional illustrations of lightlike and timelike geodesics in the general theory of relativity. By means of an intuitive graphical user interface, all parameters of a spacetime as well as the initial conditions of the geodesics can be modified interactively. This makes the GeodesicViewer a useful instrument for the exploration of geodesics in four-dimensional Lorentzian spacetimes. Program summaryProgram title: GeodesicViewer Catalogue identifier: AEFP_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEFP_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 168 868 No. of bytes in distributed program, including test data, etc.: 6 076 202 Distribution format: tar.gz Programming language: C++, Qt, Qwt, OpenGL Computer: All platforms with a C++ compiler, Qt, Qwt, OpenGL Operating system: Linux, Mac OS X RAM: 24 Mbytes Classification: 1.5 External routines:Gnu Scientific Library (GSL) ( http://www.gnu.org/software/gsl/) Motion4D (included in the package). The Motion4D library can also be downloaded from CPC. Catalogue identifier: AEEX Qt ( http://qt.nokia.com/downloads) Qwt ( http://qwt.sourceforge.net/) OpenGL ( http://www.opengl.org/) Nature of problem: Illustrate geodesics in four-dimensional Lorentzian spacetimes. Solution method: Integration of ordinary differential equations. 3D-Rendering via OpenGL. Running time: Interactive. The examples given take milliseconds.

  5. Finite element analysis for the inhibition of electromagnetic acoustic testing (EMAT) Lamb waves multi-modes

    NASA Astrophysics Data System (ADS)

    Liu, Suzhen; Zhang, Yanwei; Zhang, Chuang; Yang, Qingxin

    2017-02-01

    Lamb waves are widely used in nondestructive testing (NDT) and structural health monitoring (SHM) for its obvious advantages, such as good directionality, longer-range propagation and lower loss etc. However, it is difficult to analysis and to interpret the echo signals because of its multi-modes and dispersion. In this paper, the properties of single-mode Lamb waves which were excited by double EMAT were studied based on the principles of multi-modes and the characteristics of wave structure. Simulation results show that the double transducer excitation structure can stimulate single-mode Lamb waves and eliminate the extra modes, which are produced by modal conversion at ends of the specimen. The single-mode excitation of Lamb waves is beneficial to reduce the difficulty of signal processing and provide reliable information to locate the defect. The researches in this paper can be used as a theoretical basis to design double transducer excitation system.

  6. Discrete-Mode Source Development and Testing for New Seismo-Acoustic Sonar

    DTIC Science & Technology

    1998-03-01

    the English scientist, Lord Rayleigh (J.W. Strutt ) [Ref. 6] demonstrated theoretically that there exist waves that can propagate over the planar...and T.G. Muir, Aug. 1994. 6. Rayleigh , Lord (J.W. Strutt ), "On Waves Propagated along the Plane Surface of an Elastic Solid," Proceedings London...13. ABSTRACT (maximum 200 words) A seismo-acoustic sonar concept that uses guided interface waves ( Rayleigh or Schölte) is being developed to

  7. Wide Field-of-view and Broadband Terahertz Beam Steering Based on Gap Plasmon Geodesic Antennas

    PubMed Central

    Liu, Kaipeng; Guo, Yinghui; Pu, Mingbo; Ma, Xiaoliang; Li, Xiong; Luo, Xiangang

    2017-01-01

    Despite a plethora of applications ranging from wireless communications to sensing and spectroscopy, the current terahertz beam steering technologies suffer from tremendous insert loss, stringent control of electric bias, limited scanning angle, relatively complicated configuration and narrow operation bandwidth, preventing further practical application. We propose and demonstrate a conceptually new approach for terahertz beam steering by virtue of gap plasmon geodesic antennas. By adjusting the geometric dimension of the gap plasmon geodesic antennas, all gap plasmon modes add coherently along a peculiar direction that depends on the geodesic mean surface. Consequently, high directive beams are generated through the antenna, whose direction could be changed within a wide-angle range spanning ±45° by lateral motion of the feed. Furthermore, an assembled antenna structure consisting of four-element geodesic antennas array is proposed for full 360° beam steering, which can operate in a broadband range from 0.8 THz to 1.2 THz. PMID:28134324

  8. On the Geodesic Hypothesis in General Relativity

    NASA Astrophysics Data System (ADS)

    Yang, Shiwu

    2014-02-01

    In this paper, we give a rigorous derivation of Einstein's geodesic hypothesis in general relativity. We use small material bodies governed by the nonlinear Klein-Gordon equations to approximate the test particle. Given a vacuum spacetime , we consider the initial value problem for the Einstein-scalar field system. For all sufficiently small ɛ and δ ≤ ɛ q , q > 1, where δ, ɛ are the amplitude and size of the particle, we show the existence of the solution to the Einstein-scalar field system with the property that the energy of the particle is concentrated along a timelike geodesic. Moreover, the gravitational field produced by is negligibly small in C 1, that is, the spacetime metric g is C 1 close to the given vacuum metric h. These results generalize those obtained by Stuart in (Ann Sci École Norm Sup (4) 37(2):312-362, 2004, J Math Pures Appl (9) 83(5):541-587, 2004).

  9. Acoustic phonon modes in asymmetric AlxGa1-xN/GaN/AlyGa1-yN quantum wells

    NASA Astrophysics Data System (ADS)

    Zan, Y. H.; Ban, S. L.; Chai, Y. J.; Qu, Y.

    2017-02-01

    Using an elastic continuum model, the dispersion relations and phonon modes of propagating, confined, half space and interface acoustic phonons in asymmetric AlxGa1-xN/GaN/Al1-yGayN quantum wells (QWs) have been solved theoretically with the varieties of Al components x and y. Contrary to the previous conclusions, some regulations for the existence of the above different acoustic phonons are revealed as well as the transition conditions among these modes are also discussed. With increase of wave vectors, the dispersion relations split into several groups. Because the classification of these groups is related to the eigen frequencies of bulk materials forming QWs, phonon modes in these groups will be confined or propagating in different layers of QWs. Furthermore, the gradients of the dispersion relations' asymptotes are the velocities of longitudinal and the transverse acoustic phonons propagating in bulk materials in turns. The properties of the dispersion relations and their phonon modes are also analyzed in depth based on the cut-off conditions. By the changing of Al components x and y, the bottom of these groups will be modified to adjust eigen frequencies of AlxGa1-xN or Al1-yGayN layers. But the propagation properties of acoustic phonon modes will remain unchanged in each section.

  10. Geodesic denoising for optical coherence tomography images

    NASA Astrophysics Data System (ADS)

    Shahrian Varnousfaderani, Ehsan; Vogl, Wolf-Dieter; Wu, Jing; Gerendas, Bianca S.; Simader, Christian; Langs, Georg; Waldstein, Sebastian M.; Schmidt-Erfurth, Ursula

    2016-03-01

    Optical coherence tomography (OCT) is an optical signal acquisition method capturing micrometer resolution, cross-sectional three-dimensional images. OCT images are used widely in ophthalmology to diagnose and monitor retinal diseases such as age-related macular degeneration (AMD) and Glaucoma. While OCT allows the visualization of retinal structures such as vessels and retinal layers, image quality and contrast is reduced by speckle noise, obfuscating small, low intensity structures and structural boundaries. Existing denoising methods for OCT images may remove clinically significant image features such as texture and boundaries of anomalies. In this paper, we propose a novel patch based denoising method, Geodesic Denoising. The method reduces noise in OCT images while preserving clinically significant, although small, pathological structures, such as fluid-filled cysts in diseased retinas. Our method selects optimal image patch distribution representations based on geodesic patch similarity to noisy samples. Patch distributions are then randomly sampled to build a set of best matching candidates for every noisy sample, and the denoised value is computed based on a geodesic weighted average of the best candidate samples. Our method is evaluated qualitatively on real pathological OCT scans and quantitatively on a proposed set of ground truth, noise free synthetic OCT scans with artificially added noise and pathologies. Experimental results show that performance of our method is comparable with state of the art denoising methods while outperforming them in preserving the critical clinically relevant structures.

  11. Acoustic waves generated from seismic surface waves: propagation properties determined from Doppler sounding observations and normal-mode modelling

    NASA Astrophysics Data System (ADS)

    Artru, Juliette; Farges, Thomas; Lognonné, Philippe

    2004-09-01

    Since 1960, experiments have shown that perturbations of the ionosphere can occur after earthquakes, by way of dynamic coupling between seismic surface waves and the atmosphere. The atmospheric wave is amplified exponentially while propagating upwards due to the decrease of density, and interaction with the ionospheric plasma leads to clearly identified signals on both ground-based or satellite ionospheric measurements. In 1999 and 2000, after an upgrade of the HF Doppler sounder, the Commisariat à l'Énergie Atomique systematically recorded these effects in the ionosphere with the Francourville (France) network, by measuring vertical oscillations of ionospheric layers with the Doppler technique. Normal-mode theory extended to a solid Earth with an atmosphere allows successful modelling of such signals, even if this 1-D approach is probably too crude, especially in the solid Earth, where 20 s surface waves see large lateral variations in the crust. The combination of observations and simulations provides a new tool to determine acoustic gravity wave propagation characteristics from the ground to ionospheric height. Observed velocity and amplification of the atmospheric waves show good agreement from the ground up to moderate sounding altitudes (140-150 km); however, at higher altitudes the propagation speed is found to be much smaller than predicted and attenuation is underestimated. This shows that the standard formalism of acoustic gravity waves in the atmosphere cannot efficiently describe propagation in the ionized atmosphere. Further work is needed to characterize the propagation of acoustic waves in this altitude range: we believe that seismic waves can provide a well-constrained source for such study.

  12. Prefrontal oxygenation and the acoustic startle eyeblink response during exercise: A test of the dual-mode model.

    PubMed

    Tempest, Gavin D; Parfitt, Gaynor

    2017-03-30

    The interplay between the prefrontal cortex and amygdala is proposed to explain the regulation of affective responses (pleasure/displeasure) during exercise as outlined in the dual-mode model. However, due to methodological limitations the dual-mode model has not been fully tested. In this study, prefrontal oxygenation (using near-infrared spectroscopy) and amygdala activity (reflected by eyeblink amplitude using acoustic startle methodology) were recorded during exercise standardized to metabolic processes: 80% of ventilatory threshold (below VT), at the VT, and at the respiratory compensation point (RCP). Self-reported tolerance of the intensity of exercise was assessed prior to, and affective responses recorded during exercise. The results revealed that, as the intensity of exercise became more challenging (from below VT to RCP), prefrontal oxygenation was larger and eyeblink amplitude and affective responses were reduced. Below VT and at VT, larger prefrontal oxygenation was associated with larger eyeblink amplitude. At the RCP, prefrontal oxygenation was greater in the left than right hemisphere, and eyeblink amplitude explained significant variance in affective responses (with prefrontal oxygenation) and self-reported tolerance. These findings highlight the role of the prefrontal cortex and potentially the amygdala in the regulation of affective (particularly negative) responses during exercise at physiologically challenging intensities (above VT). In addition, a psychophysiological basis of self-reported tolerance is indicated. This study provides some support of the dual-mode model and insight into the neural basis of affective responses during exercise.

  13. Quantifying Image Quality Improvement Using Elevated Acoustic Output in B-Mode Harmonic Imaging.

    PubMed

    Deng, Yufeng; Palmeri, Mark L; Rouze, Ned C; Trahey, Gregg E; Haystead, Clare M; Nightingale, Kathryn R

    2017-10-01

    Tissue harmonic imaging has been widely used in abdominal imaging because of its significant reduction in acoustic noise compared with fundamental imaging. However, tissue harmonic imaging can be limited by both signal-to-noise ratio and penetration depth during clinical imaging, resulting in decreased diagnostic utility. A logical approach would be to increase the source pressure, but the in situ pressures used in diagnostic ultrasound are subject to a de facto upper limit based on the U.S. Food and Drug Administration guideline for the mechanical index (<1.9). A recent American Institute of Ultrasound in Medicine report concluded that an effective mechanical index ≤4.0 could be warranted without concern for increased risk of cavitation in non-fetal tissues without gas bodies, but would only be justified if there were a concurrent improvement in image quality and diagnostic utility. This work evaluates image quality differences between normal and elevated acoustic output hepatic harmonic imaging using a transmit frequency of 1.8 MHz. The results indicate that harmonic imaging using elevated acoustic output leads to modest improvements (3%-7%) in contrast-to-noise ratio of hypo-echoic hepatic vessels and increases in imaging penetration depth on the order of 4 mm per mechanical index increase of 0.1 for a given focal depth. Difficult-to-image patients who suffer from poor ultrasound image quality exhibited larger improvements than easy-to-image study participants. Copyright © 2017 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

  14. Stable Vortex Generation in Liquid Filled Wells by Mode Conversion of Surface Acoustic Waves

    NASA Astrophysics Data System (ADS)

    Landskron, Johannes; Schmidt, Katrin; Kufner, Maria; Lindner, Gerhard

    The formation of stable vortex flow pattern has been observed at liquid filled aluminum wells of 15 to 30 mm diameter when Lamb waves are excited on the bottom of the wells by piezoelectric transducers operated at a frequency of 1 MHz. The shape of the vortex pattern changed with the position of the transducer. Strong differences in mixing times were observed between water and ethanol when the filling level was changed and a remarkable reduction of mixing time was achieved by the addition of a small amount of detergent to water at small filling levels. Besides mixing of liquids thermal equilibration within a liquid volume was accelerated by acoustic streaming.

  15. Acoustic normal modes using the propagator matrix technique for a stratified ocean overlaying an inhomogeneous anisotropic porous bed

    NASA Astrophysics Data System (ADS)

    Badiey, M.; Yamamoto, T.

    1986-01-01

    Propogation of acoustic normal modes at excitation frequencies of 50 to 50000 Hz in a shallow stratified ocean overlaying a transverse isotropic poro-elastic sediment bed is modeled. The Biot-Willis stiffness matrix of the poro-elastic anisotropy is defined in terms of physical properties of sediments to model the bed. Propagator matrix method is used to solve the differential equations for the motion stress vectors in both layered sediment and water. The effects of sediment properties on the dispersion and attenuation of acoustic waves are examined numerically. Using the relaxation principle it is observed that the energy loss is maximum at frequency referred to as relaxation frequency of the porous media given by f sub ri = (beta)(nu)/3 pi k (sub si), where beta is the porosity, nu is the kinematic viscosity of the pore fluid and k (sub si) is the anisotropic permeability coefficient. The phase speed of compressional and shear waves in the sediment becomes highly dispersive around this frequency. The sandy bottom's relaxation frequency is the range of several hundred hertz to several kilo hertz. This report presents the derivation of the mathematical expressions used in the model and a complete description of the computer program. Four examples of numerical calculations are provided.

  16. Horizontal rays and vertical modes method for the computation of the vertical propagation of acoustic-gravity waves

    NASA Astrophysics Data System (ADS)

    Lahaye, Noé; Smith, Stefan Llewellyn

    2016-04-01

    We consider the vertical propagation of acoustic-gravity waves generated by a finite-size perturbation at the bottom, through a moving inhomogeneous atmosphere. Under the hypothesis of weak inhomogeneities in the horizontal direction, an approximate solution is obtained in terms of normal modes and horizontal rays. The problem is thus reduced to a depth-separated equation very similar to the standard Taylor-Goldstein equation, with weak dependence of the parameters on the horizontal coordinates, and to ray equations along the horizontal -- thus decreasing the computational resources needed. One advantage of this method is to retain the signal that is partially transmitted across reflecting regions that may exist due to the background wind jet, contrary to standard ray tracing that would predict pure reflexion. In addition, the limitation to an homogeneous medium along the horizontal coordinates that applies to other standard methods based on spectral integral transforms is released with the current approach. An idealized configuration is investigated, where numerical results are shown. Finally, a more general formulation in terms of approximate adiabatic spectral integral transform is presented. Implications for the computation of the propagation of Tsunami-generated acoustic-gravity waves, and more generally waves generated at the bottom of an inhomogeneous moving fluid, are discussed.

  17. Acoustic emission pattern: an indicator of mode of failure in geologic materials as affected by their natural imperfections

    SciTech Connect

    Khair, A.W.

    1984-01-01

    Two types of geologic materials, granite and coal, containing irregularities (different grain sizes and shapes in granite) and discontinuities (face and butt cleats in coal) were tested under different loading conditions. Deformation and acoustic emission characteristics of these materials under stress were recorded. In this study, for the first type of geologic material, beam specimens of approximately 4'' x 8'' x 2.5'' were prepared from four different types of granite namely, Honesboro Granite, Mason Granite, New Hampshire Pink, and Milford Pink. These were tested under constant loading rates according to the Standard Test Method for modulus of rupture of natural building stone. For the second type of geologic material, cylindrical specimens of coal were tested under a uniaxial compressive load at a constant rate of deformation. The tested coal specimens were from the Illinois number5 coal seam located in the Niantic Coal Field in southern Illinois. In both cases an MTS electrohydraulic loading system was used. Mode of failure in each material was characterized by the acoustic emission pattern and the results were substantiated by the deformation characteristics of the materials during failure.

  18. Geodesics dynamics in the Linet-Tian spacetime with

    NASA Astrophysics Data System (ADS)

    Brito, Irene; Da Silva, M. F. A.; Mena, Filipe C.; Santos, N. O.

    2014-03-01

    We investigate the geodesics' kinematics and dynamics in the Linet-Tian metric with and compare with the results for the Levi-Civita metric, when . This is used to derive new stability results about the geodesics' dynamics in static vacuum cylindrically symmetric spacetimes with respect to the introduction of . In particular, we find that increasing always increases the minimum and maximum radial distances to the axis of any spatially confined planar null geodesic. Furthermore, we show that, in some cases, the inclusion of any breaks the geodesics' orbit confinement of the metric, for both planar and non-planar null geodesics, which are therefore unstable. Using the full system of geodesics' equations, we provide numerical examples which illustrate our results.

  19. Surface modes and acoustic scattering of microspheres and ultrasound contrast agents.

    PubMed

    Falou, Omar; Jafari Sojahrood, Amin; Kumaradas, J Carl; Kolios, Michael C

    2012-09-01

    Surface modes of spherical objects subject to ultrasound excitation have been recently proposed to explain experimental measurements of scattering from microspheres and ultrasound contrast agents (UCAs). In this work, the relationship between surface modes and resonance frequencies of microspheres and UCAs is investigated. A finite-element model, built upon the fundamentals of wave propagation and structural mechanics, was introduced and validated against analytical solutions (error <5%). Numerical results showed the existence of a systematic relationship between resonance frequencies and surface modes of a 30 μm microsphere driven at 1-70 MHz. On the contrary, for a 100 nm shelled, 4 μm diameter UCA, no clear relationship between the resonance frequencies and the surface modes was found in the frequency range examined. Instead, the UCA exhibited a collection of complex oscillations, which appear to be a combination of various surface modes and displacements. A study of the effects of varying the shell properties on the backscatter showed the presence of peaks in the backscatter of thick-shelled UCAs, which are not predicted by previous models. In summary, this work presents a systematic effort to examine scattering and surface modes from ultrasound contrast agents using finite-element models.

  20. Experimental setup for measurement of acoustic power dissipation in lined ducts for higher order modes propagation with air mean-flow conditions.

    PubMed

    Ville, Jean-Michel; Foucart, Felix

    2003-10-01

    A flow duct acoustic facility was developed to measure liner efficiency in attenuating higher order acoustic duct modes propagation conditions with mean air flow. The method is based on measurement, upstream and downstream of a liner, of the acoustic power produced by a periodic source. Directly measured total or modal acoustic powers are deduced from the local measurement, in both cross sections, of acoustic pressure, axial acoustic particle velocity, and axial mean flow velocity which are supplied by a probe made of a microphone and a single hot film. In this paper, the equipment, signal processing, and the data treatment process of this facility are first described. Then, information on the accuracy of the methodology is provided by a validation test performed with a rigid wall duct section. Finally, the results of an experiment carried out with a locally reacting liner and a mean flow velocity of 20 m/s will be presented. Measurements of the main attenuation frequency and of the main total acoustic power dissipated agree with the values for which the liner was designed. These results point out the limitations of the method presented to sources with high-level periodic sounds to provide a sufficient signal-to-noise ratio, the noise being produced by fluctuations of the turbulent flow.

  1. A Dual-Mode Magnetic-Acoustic System for Monitoring Fluid Intake Behavior in Animals.

    PubMed

    Sargolzaei, Saman; Elahi, Hassan; Sokoloff, Alan; Ghovanloo, Maysam

    2017-09-01

    We have developed an unobtrusive magnetic-acoustic fluid intake monitoring (MAFIM) system using a conventional stainless-steel roller-ball nipple to measure licking and drinking behavior in animals. Movements of a small permanent magnetic tracer attached to stainless-steel roller balls that operate as a tongue-actuated valve are sensed by a pair of three-axial magnetometers, and transformed into a time-series indicating the status of the ball (up or down), using a Gaussian mixture model based data-driven classifier. The sounds produced by the rise and fall of the roller balls are also recorded and classified to substantiate the magnetic data by an independent modality for a more robust solution. The operation of the magnetic and acoustic sensors is controlled by an embedded system, communicating via Universal Serial Bus (USB) with a custom-designed user interface, running on a PC. The MAFIM system has been tested in vivo with minipigs, accurately measuring various drinking parameters and licking patterns without constraints imposed by current lick monitoring systems, such as nipple access, animal-nipple contact, animal training, and complex parameter settings.

  2. High contrast air-coupled acoustic imaging with zero group velocity lamb modes.

    PubMed

    Holland, Stephen D; Chimenti, D E

    2004-04-01

    The well known zero in the group velocity of the first-order symmetric (S1) plate wave mode has been exploited in air-coupled ultrasonic imaging to obtain significantly higher sensitivity than can be achieved in conventional air-coupled scanning. At the zero group velocity point at the frequency minimum of the S1 mode, a broad range of wavenumbers couple into the first-order symmetric mode at nearly a constant frequency, greatly enhancing transmission at that frequency. Coupled energy remains localized near the coupling point because the group velocity is zero. We excite the mode with a broadband, focussing, air-coupled transducer at the frequency of the zero group velocity point in the S1 mode. By exploiting the efficient coupling at the zero group velocity frequency, we have easily imaged a single layer of Scotch tape attached to a 6.4-mm thick Plexiglas plate and 3.2-mm Teflon inserts in a composite laminate.

  3. NEW APPLICATIONS IN THE INVERSION OF ACOUSTIC FULL WAVEFORM LOGS - RELATING MODE EXCITATION TO LITHOLOGY.

    USGS Publications Warehouse

    Paillet, Frederick L.; Cheng, C.H.; Meredith, J.A.

    1987-01-01

    Existing techniques for the quantitative interpretation of waveform data have been based on one of two fundamental approaches: (1) simultaneous identification of compressional and shear velocities; and (2) least-squares minimization of the difference between experimental waveforms and synthetic seismograms. Techniques based on the first approach do not always work, and those based on the second seem too numerically cumbersome for routine application during data processing. An alternative approach is tested here, in which synthetic waveforms are used to predict relative mode excitation in the composite waveform. Synthetic waveforms are generated for a series of lithologies ranging from hard, crystalline rocks (Vp equals 6. 0 km/sec. and Poisson's ratio equals 0. 20) to soft, argillaceous sediments (Vp equals 1. 8 km/sec. and Poisson's ratio equals 0. 40). The series of waveforms illustrates a continuous change within this range of rock properties. Mode energy within characteristic velocity windows is computed for each of the modes in the set of synthetic waveforms. The results indicate that there is a consistent variation in mode excitation in lithology space that can be used to construct a unique relationship between relative mode excitation and lithology.

  4. Gauge-invariant coupled gravitational, acoustical, and electromagnetic modes on most general spherical space-times

    NASA Astrophysics Data System (ADS)

    Gerlach, Ulrich H.; Sengupta, Uday K.

    1980-09-01

    The coupled Einstein-Maxwell system linearized away from an arbitrarily given spherically symmetric background space-time is reduced from its four-dimensional to a two-dimensional form expressed solely in terms of gauge-invariant geometrical perturbation objects. These objects, which besides the gravitational and electromagnetic, also include mass-energy degrees of freedom, are defined on the two-manifold spanned by the radial and time coordinates. For charged or uncharged arbitrary matter background the odd-parity perturbation equations for example, reduce to three second-order linear scalar equations driven by matter and charge inhomogeneities. These three equations describe the intercoupled gravitational, electromagnetic, and acoustic perturbational degrees of freedom. For a charged black hole in an asymptotically de Sitter space-time the gravitational and electromagnetic equations decouple into two inhomogeneous scalar wave equations.

  5. Acoustic Modeling Using a Three-Dimensional Coupled-Mode Model

    DTIC Science & Technology

    2012-09-30

    the 3D coupled-mode solution can also be observed in the semi-analytic solution by the wider shadow behind the seamount and by the interference...propagation around a shallow-water seamount , (2) the addition of a 3D rough sea surface in the model with comparison to solution calculated with a 3D...Propagation around a conical seamount The 3D coupled-mode model described above is applied to calculate propagation around a conical seamount in shallow

  6. Acoustic fatigue life prediction for nonlinear structures with multiple resonant modes

    NASA Technical Reports Server (NTRS)

    Miles, R. N.

    1992-01-01

    This report documents an effort to develop practical and accurate methods for estimating the fatigue lives of complex aerospace structures subjected to intense random excitations. The emphasis of the current program is to construct analytical schemes for performing fatigue life estimates for structures that exhibit nonlinear vibration behavior and that have numerous resonant modes contributing to the response.

  7. Acoustic fatigue life prediction for nonlinear structures with multiple resonant modes

    NASA Astrophysics Data System (ADS)

    Miles, R. N.

    1992-03-01

    This report documents an effort to develop practical and accurate methods for estimating the fatigue lives of complex aerospace structures subjected to intense random excitations. The emphasis of the current program is to construct analytical schemes for performing fatigue life estimates for structures that exhibit nonlinear vibration behavior and that have numerous resonant modes contributing to the response.

  8. Guided wave mode dispersion of transient acoustic emission on copper pipes-Its visualisation and application to source location

    NASA Astrophysics Data System (ADS)

    Wang, Chao; Joe Au, Y. H.; Li, Lin; Cheng, Kai

    2016-03-01

    In this paper is presented an improved method for locating a transient acoustic emission (AE) source on a pipeline with two broad-band AE sensors. Using Short Time Fourier Transform (STFT), the method identifies a flexural wave mode, F(1,1), in the two AE signals detected, notes its respective arrival times at different frequencies, and determines the location of the AE source based on the arrival times. Due to velocity dispersion, the arrival time of the wave mode varies with frequency. The method has three main advantages: that the wave speed is not required in the calculation, that it is insensitive to threshold setting for arrival time estimation, and that, at least in theory, the accuracy of the source location can be made as high as desired. The paper first demonstrates, by way of an experiment, the inadequacy of threshold-crossing as a method for identifying the first arrival time of the AE wave. The paper then presents the theory of the proposed method and of the estimated error inherent in the theory and an explanation on how the error can be reduced. The method is then verified experimentally using results obtained from a 3-m long copper pipe of 22 mm diameter.

  9. Elastic constants and softening of acoustic modes in A2MX6-crystals observed by Brillouin scattering

    NASA Astrophysics Data System (ADS)

    Henkel, W.; Pelzl, J.; Höck, K. H.; Thomas, H.

    1980-12-01

    Room-temperature Brillouin-scattering measurements of the longitudinal and transverse sound velocities for the cubic crystals K2SnCl6, K2ReCl6, (NH4)2SnCl6 and (NH4)2SiF6 are presented. The elastic constants c 11, c 12 and c 44 are determined from the angular variation of the Brillouin line shifts. Furthermore, for K2SnCl6 the sound velocities in the [100]- and [111]-direction are investigated as a function of temperature, 256K≦ T≦330K. A strong softening of the c 11 c 12 mode is observed in the para-distortive phase as the temperature approaches the phase transition temperature T c1=262K from above, while c 44 shows no anomaly within the experimental error. These acoustic anomalies are interpreted theoretically by a mechanism based on the coupling of the elastic strain field to the fluctuations of the soft-mode coordinates.

  10. Coupled-mode theory for the interaction between acoustic waves and spin waves in magnonic-phononic crystals: Propagating magnetoelastic waves

    NASA Astrophysics Data System (ADS)

    Graczyk, Piotr; Krawczyk, Maciej

    2017-07-01

    We have investigated codirectional and contradirectional couplings between spin wave and acoustic wave in a one-dimensional periodic structure (the so-called magphonic crystal). The system consists of two ferromagnetic layers alternating in space. We have taken into consideration materials commonly used in magnonics: yttrium iron garnet, CoFeB, permalloy, and cobalt. The coupled mode theory (CMT) formalism has been successfully implemented to describe the magnetoelastic interaction as a periodic perturbation in the magphonic crystal. The results of CMT calculations have been verified by more rigorous simulations with the frequency-domain plane-wave method and the time-domain finite-element method. The presented resonant coupling in the magphonic crystal is an active in-space mechanism which spatially transfers energy between propagating spin and acoustic modes, thus creating a propagating magnetoelastic wave. We have shown that CMT analysis of the magnetoelastic coupling is an useful tool to optimize and design a spin wave-acoustic wave transducer based on magphonic crystals. The effect of spin-wave damping has been included to the model to discuss the efficiency of such a device. Our model shows that it is possible to obtain forward conversion of the acoustic wave to the spin wave in case of codirectional coupling and backward conversion in case of contradirectional coupling. That energy transfer may be realized for broadband coupling and for generation of spin waves which are of different wavelength (in particular, shorter) than exciting acoustic waves.

  11. The SQG Equation as a Geodesic Equation

    NASA Astrophysics Data System (ADS)

    Washabaugh, Pearce

    2016-12-01

    We demonstrate that the surface quasi-geostrophic (SQG) equation given by θ_t + < u, nabla θrangle = 0,quad θ = nabla × (-Δ)^{-1/2} u, is the geodesic equation on the group of volume-preserving diffeomorphisms of a Riemannian manifold M in the right-invariant {dot{H}^{-1/2}} metric. We show by example, that the Riemannian exponential map is smooth and non-Fredholm, and that the sectional curvature at the identity is unbounded of both signs.

  12. Focal properties of geodesic waveguide lenses

    NASA Technical Reports Server (NTRS)

    Verber, C. M.; Vahey, D. W.; Wood, V. E.

    1976-01-01

    The focal properties of uncorrected geodesic lenses in ion-exchanged glass waveguides are reported. A 13.8-mm-focal-length lens resolved beams with an angular separation of 27.6 mrad, while a 28-mm-focal-length lens resolved beams with an angular separation of only 3.3 mrad. Intensity profiles of the focal region of the former lens revealed a 40-micron spot size when the input aperture was 5 mm, and a spot size of 7.7 microns when the aperture was reduced to 1 mm. This value is close to the diffraction-limited spot size of 5.7 microns.

  13. Geodesic least squares regression on information manifolds

    SciTech Connect

    Verdoolaege, Geert

    2014-12-05

    We present a novel regression method targeted at situations with significant uncertainty on both the dependent and independent variables or with non-Gaussian distribution models. Unlike the classic regression model, the conditional distribution of the response variable suggested by the data need not be the same as the modeled distribution. Instead they are matched by minimizing the Rao geodesic distance between them. This yields a more flexible regression method that is less constrained by the assumptions imposed through the regression model. As an example, we demonstrate the improved resistance of our method against some flawed model assumptions and we apply this to scaling laws in magnetic confinement fusion.

  14. Solar-cycle variations of large frequency separations of acoustic modes: implications for asteroseismology

    NASA Astrophysics Data System (ADS)

    Broomhall, A.-M.; Chaplin, W. J.; Elsworth, Y.; New, R.

    2011-06-01

    We have studied solar-cycle changes in the large frequency separations that can be observed in Birmingham Solar Oscillations Network (BiSON) data. The large frequency separation is often one of the first outputs from asteroseismic studies because it can help constrain stellar properties like mass and radius. We have used three methods for estimating the large separations: use of individual p-mode frequencies, computation of the autocorrelation of frequency-power spectra, and computation of the power spectrum of the power spectrum. The values of the large separations obtained by the different methods are offset from each other and have differing sensitivities to the realization noise. A simple model was used to predict solar-cycle variations in the large separations, indicating that the variations are due to the well-known solar-cycle changes to mode frequency. However, this model is only valid over a restricted frequency range. We discuss the implications of these results for asteroseismology.

  15. Phononic crystal surface mode coupling and its use in acoustic Doppler velocimetry.

    PubMed

    Cicek, Ahmet; Salman, Aysevil; Kaya, Olgun Adem; Ulug, Bulent

    2016-02-01

    It is numerically shown that surface modes of two-dimensional phononic crystals, which are Bloch modes bound to the interface between the phononic crystal and the surrounding host, can couple back and forth between the surfaces in a length scale determined by the separation of two surfaces and frequency. Supercell band structure computations through the finite-element method reveal that the surface band of an isolated surface splits into two bands which support either symmetric or antisymmetric hybrid modes. When the surface separation is 3.5 times the lattice constant, a coupling length varying between 30 and 48 periods can be obtained which first increases linearly with frequency and, then, decreases rapidly. In the linear regime, variation of coupling length can be used as a means of measuring speeds of objects on the order of 0.1m/s by incorporating the Doppler shift. Speed sensitivity can be improved by increasing surface separation at the cost of larger device sizes.

  16. Acoustic Levitation With Less Equipment

    NASA Technical Reports Server (NTRS)

    Barmatz, M. B.; Jacobi, N.

    1983-01-01

    Certain chamber shapes require fewer than three acoustic drivers. Levitation at center of spherical chamber attained using only one acoustic driver. Exitation of lowest spherical mode produces asymmetric acoustic potential well.

  17. Studying Null and Time-Like Geodesics in the Classroom

    ERIC Educational Resources Information Center

    Muller, Thomas; Frauendiener, Jorg

    2011-01-01

    In a first course of general relativity, it is usually quite difficult for students to grasp the concept of a geodesic. It is supposed to be straight (auto-parallel) and yet it "looks" curved. In these situations, it is very useful to have some explicit examples available which show the different behaviour of geodesics. In this paper, we present…

  18. Studying Null and Time-Like Geodesics in the Classroom

    ERIC Educational Resources Information Center

    Muller, Thomas; Frauendiener, Jorg

    2011-01-01

    In a first course of general relativity, it is usually quite difficult for students to grasp the concept of a geodesic. It is supposed to be straight (auto-parallel) and yet it "looks" curved. In these situations, it is very useful to have some explicit examples available which show the different behaviour of geodesics. In this paper, we present…

  19. Energy-loss rate of hot electrons due to confined acoustic phonon modes in a semiconductor quantum wire under transverse electric field

    NASA Astrophysics Data System (ADS)

    Stepanyan, A.; Yeranosyan, M.; Vardanyan, L.; Asatryan, A.; Kirakosyan, A.; Vartanian, A.

    2017-08-01

    The hot-electron energy-loss rate via the acoustic-phonons in an embedded semiconductor quantum wire of circular cross section in the presence of external electric field has been investigated using deformation potential theory. Dimensional confinement effect on modifying acoustic-phonon modes are taken into account. The energy-loss rate as a function of electric field strength, electron density and electron temperature is obtained. Our calculations show that the electric field applied perpendicularly to the wire axis can be used as an important tool for the control of the energy-loss processes in nanowires.

  20. A Dynamical Systems Approach to Geodesics in Bianchi Cosmologies

    NASA Astrophysics Data System (ADS)

    Nilsson, Ulf S.; Uggla, Claes; Wainwright, John

    2000-10-01

    To understand the observational properties of cosmological models, in particular, the temperature of the cosmic microwave background radiation, it is necessary to study their null geodesics. Dynamical systems theory, in conjunction with the orthonormal frame approach, has proved to be an invaluable tool for analyzing spatially homogeneous cosmologies. It is thus natural to use such techniques to study the geodesics of these models. We therefore augment the Einstein field equations with the geodesic equations, all written in dimensionless form, obtaining an extended system of first-order ordinary differential equations that simultaneously describes the evolution of the gravitational field and the behavior of the associated geodesics. It is shown that the extended system is a powerful tool for investigating the effect of space-time anisotropies on the temperature of the cosmic microwave background radiation, and that it can also be used for studying geodesic chaos.

  1. One-step thickness shear mode acoustic assay for plasminogen activators.

    PubMed

    Ghazali, Mirnader; Hayward, Gordon L

    2008-07-01

    A new procedure is presented for the measurement of plasminogen activators using a thickness shear mode sensor and a modified version of the fibrin plate assay at the micro-scale. Separate, well-mixed solutions of the substrates fibrinogen and plasminogen, and enzymes thrombin and the plasminogen activator sample were mixed together and placed on the sensor surface. The temperature and evaporation were controlled during the assay. The clot dissolution time correlated well with the quantity of the plasminogen activator in the sample. The average relative standard deviation was 12.5%.

  2. High-frequency acoustic modes in liquid gallium at the melting point.

    PubMed

    Scopigno, T; Filipponi, A; Krisch, M; Monaco, G; Ruocco, G; Sette, F

    2002-12-16

    The microscopic dynamics in liquid gallium at melting has been studied by inelastic x-ray scattering. We demonstrate the existence of acousticlike modes up to wave vectors above one-half of the first maximum of the static structure factor, at variance with earlier results from inelastic neutron scattering [F. J. Bermejo et al., Phys. Rev. E 49, 3133 (1994)]. Despite structural (extremely rich polymorphism) and electronic (mixed valence) peculiarities, the collective dynamics is strikingly similar to the one of van der Waals and metallic fluids. This result speaks in favor of the universality of the short time dynamics in monatomic liquids rather than of system-specific dynamics.

  3. β-Suppression of Alfvén Cascade Modes in the National Spherical Torus Experiment

    SciTech Connect

    Fredrickson, E D; Gorelenkov, N N; Heidbrink, W W; Kubota, S; Levinton, F M; Yuh, H; Menard, J E

    2007-06-29

    The coupling of Alfvén Cascade (AC) modes or reversed-shear Alfvén eigenmodes (rsAE) to Geodesic Acoustic Modes (GAM) implies that the range of the AC frequency sweep is reduced as the electron β is increased. This model provides an explanation for the otherwise surprising absence of AC modes in reverse shear NSTX plasmas, given the rich spectrum of beam-driven instabilities typically seen in NSTX. In experiments done at very low β to investigate this prediction, AC modes were seen, and as the βe was increased from shot to shot, the range of the AC frequency sweep was reduced, in agreement with this theoretical prediction.

  4. GeodesicViewer - A tool for exploring geodesics in the theory of relativity

    NASA Astrophysics Data System (ADS)

    Müller, Thomas

    2011-06-01

    The GeodesicViewer realizes exocentric two- and three-dimensional illustrations of lightlike and timelike geodesics in the general theory of relativity. By means of an intuitive graphical user interface, all parameters of a spacetime as well as the initial conditions of the geodesics can be modified interactively. New version program summaryProgram title: GeodesicViewer Catalogue identifier: AEFP_v2_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEFP_v2_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 76 202 No. of bytes in distributed program, including test data, etc.: 1 722 290 Distribution format: tar.gz Programming language: C++, OpenGL Computer: All platforms with a C++ compiler, Qt, OpenGL Operating system: Linux, Mac OS X, Windows RAM: 24 MBytes Classification: 1.5 External routines: Motion4D (included in the package) Gnu Scientific Library (GSL) ( http://www.gnu.org/software/gsl/) Qt ( http://qt.nokia.com/downloads) OpenGL ( http://www.opengl.org/) Catalogue identifier of previous version: AEFP_v1_0 Journal reference of previous version: Comput. Phys. Comm. 181 (2010) 413 Does the new version supersede the previous version?: Yes Nature of problem: Illustrate geodesics in four-dimensional Lorentzian spacetimes. Solution method: Integration of ordinary differential equations. 3D-Rendering via OpenGL. Reasons for new version: The main reason for the new version was to visualize the parallel transport of the Sachs legs and to show the influence of curved spacetime on a bundle of light rays as is realized in the new version of the Motion4D library ( http://cpc.cs.qub.ac.uk/summaries/AEEX_v3_0.html). Summary of revisions: By choosing the new geodesic type "lightlike_sachs", the parallel transport of the Sachs basis and the integration of the Jacobi equation

  5. Effect of turbulent eddy viscosity on the unstable surface mode above an acoustic liner

    NASA Astrophysics Data System (ADS)

    Marx, David; Aurégan, Yves

    2013-07-01

    Lined ducts are used to reduce noise radiation from ducts in turbofan engines. In certain conditions they may sustain hydrodynamic instabilities. A local linear stability analysis of the flow in a 2D lined channel is performed using a numerical integration of the governing equations. Several model equations are used, one of them taking into account turbulent eddy viscosity, and a realistic turbulent mean flow profile is used that vanishes at the wall. The stability analysis results are compared to published experimental results. Both the model and the experiments show the existence of an unstable mode, and the importance of taking into account eddy viscosity in the model is shown. When this is done, quantities such as the growth rate and the velocity eigenfunctions are shown to agree correctly.

  6. High-Frequency Acoustic Modes in Liquid Gallium at the Melting Point

    NASA Astrophysics Data System (ADS)

    Scopigno, T.; Filipponi, A.; Krisch, M.; Monaco, G.; Ruocco, G.; Sette, F.

    2002-12-01

    The microscopic dynamics in liquid gallium at melting has been studied by inelastic x-ray scattering. We demonstrate the existence of acousticlike modes up to wave vectors above one-half of the first maximum of the static structure factor, at variance with earlier results from inelastic neutron scattering [F. J. Bermejo et al.,

    Phys. Rev. EPLEEE81063-651X 49, 3133 (1994)
    ]. Despite structural (extremely rich polymorphism) and electronic (mixed valence) peculiarities, the collective dynamics is strikingly similar to the one of van der Waals and metallic fluids. This result speaks in favor of the universality of the short time dynamics in monatomic liquids rather than of system-specific dynamics.

  7. Modeling stochastic excitation of acoustic modes in stars: present status and perspectives

    NASA Astrophysics Data System (ADS)

    Samadi, R.; Belkacem, K.; Goupil, M.-J.; Ludwig, H.-G.; Dupret, M.-A.

    2008-12-01

    Solar-like oscillations have now been detected for more than ten years and their frequencies measured for a still growing number of stars with various characteristics (e.g. mass, chemical composition, evolutionary stage ...). Excitation of such oscillations is attributed to turbu- lent convection and takes place in the uppermost part of the convective envelope. Since the pioneering work of Goldreich & Keely (1977), more sophisticated theoretical models of stochastic excitation were developed, which differ from each other both by the way turbulent convection is modeled and by the assumed sources of excitation. We briefly review here the different underlying approximations and assumptions of those models. A second part shows that computed mode excitation rates crucially depend on the way time-correlations between eddies are described but also on the surface metal abundance of the star.

  8. Generation of coherent ion acoustic solitary waves in inhomogeneous plasma by odd-symmetric trapped mode in an electron hole

    NASA Astrophysics Data System (ADS)

    Dokgo, K.; Woo, M.; Choi, C.; Min, K. W.; Hwang, J.

    2015-12-01

    The generation of coherent ion acoustic solitary waves (IASWs) due to interactions between an electron hole (EH) and density gradient of plasma is investigated by both 1D particle-in-cell (PIC) simulation and theory. In our simulation, an EH is generated by plasma blob injection at the beginning. When the EH passes density gradient region, two features are observed: one is oscillations of EH bipolar field and another is IASWs generation. We found that these E field oscillations correspond to odd-symmetric trapped mode in the EH (OSTM). Using theoretical formalism introduced by Lewis, we theoretically derived the structure and the dispersion relation of OSTM. The OSTM structures calculated from simulation and theory are in good agreement. In the presence of density gradient, OSTM structure is distorted and become spatially asymmetric; its potential is weak in the higher density side and strong in the lower density side. Ions are pulled and pushed by the OSTM potential. As a results of potential difference, ions are accelerated to the lower density side then they formed IASWs. These process are repeated in the density gradient region when EH are passing, so IASWs are generated coherently.

  9. Particle-area dependence of mineral dust in the immersion mode: investigations with freely suspended drops in an acoustic levitator

    NASA Astrophysics Data System (ADS)

    Diehl, K.; Debertshäuser, M.; Eppers, O.; Schmithüsen, H.; Mitra, S. K.; Borrmann, S.

    2014-05-01

    The heterogeneous freezing temperatures of supercooled drops were measured by using an acoustic levitator. This technique allows to freely suspending single drops in air without electrical charges thereby avoiding any electrical influences which may affect the freezing process. Heterogeneous nucleation caused by several mineral dust particles (montmorillonite, two types of illite) was investigated in the immersion mode. Drops of 1 \\unit{mm} in radius were monitored by a video camera during cooling down to -28 °C to simulate the tropospheric temperature range. The surface temperature of the drops was remotely determined with an infra-red thermometer so that the onset of freezing was indicated. For comparisons, measurements with one particle type were additionally performed in the Mainz vertical wind tunnel with drops of 340 \\unit{{μ}m} radius freely suspended. The data were interpreted regarding the particle surfaces immersed in the drops. Immersion freezing was observed in a temperature range between -13 and -26 °C in dependence of particle type and surface area per drop. The results were evaluated by applying two descriptions of heterogeneous freezing, the stochastic and the singular model.

  10. MR-monitored focused ultrasound using the acoustic-coupling water bath as an intrinsic high-mode dielectric resonator.

    PubMed

    Webb, A G

    2014-06-01

    The conventional set-up for MR-monitored focused ultrasound surgery includes a piezoelectric transducer and an acoustic-coupling water bath integrated into the MR patient table; a large surface RF coil is placed close to the patient or, alternatively, the body coil is used as the MR receiver. Potential disadvantages of this approach are that the body coil has low sensitivity because of its low filling factor and the local RF coil can interfere with and cause reflections of the ultrasound irradiation. In this article, a completely new approach is presented, in which an MR transmit/receive coil is not needed at all. Instead, the dimensions of the water bath are adjusted so that a high-order dielectric mode is excited, resulting in efficient MR excitation and reception at the transducer focal point. An example of monitoring ultrasound-mediated heating in a phantom is shown on a 7-T human system, although the new method can also be applied at lower fields. Copyright © 2014 John Wiley & Sons, Ltd.

  11. Scanning-mode 2D acoustic radiation force impulse (s2D-ARFI) imaging based on GPU acceleration.

    PubMed

    Wang, Congzhi; Zeng, Bo; Qiu, Weibao; Zheng, Hairong

    2014-01-01

    Acoustic radiation force impulse (ARFI) technique is a quantitative method for tissue stiffness assessment. It has been proved to be less operator dependent than the quasi-static elastography, and has more simple hardware architecture than the supersonic shearwave imaging (SSI) technique, which make it easier to be miniaturized for some special clinical applications. However, unlike the SSI, ARFI cannot provide real-time 2D images of tissue stiffness distribution mainly due to its data-intensive and time-consuming algorithms. In this study, the algorithms of ARFI were modified and improved to fit for the parallel computation on graphics processing unit (GPU), and the quasi-real-time scanning-mode 2D ARFI images (s2D-ARFI) were implemented on a self-developed compact system. High ratio of the time consumptions between the algorithms using CPU and using GPU has been verified, and it was also proved that there was no distinct difference between the stiffness images obtained by these two methods. The s2D-ARFI provides us an additional choice for quantitatively imaging the tissue stiffness, and has a potential to be miniaturized and used in the emergency treatments in field first-aid and the donor evaluation for organ transplantation.

  12. Acoustic radiation from out-of-plane modes of an annular disk using thin and thick plate theories

    NASA Astrophysics Data System (ADS)

    Lee, Hyeongill; Singh, Rajendra

    2005-04-01

    Out-of-plane (flexural) vibration is a major source of sound radiation from many mechanical or structural components having annular or circular disk shape. The typical thickness of practical components is often beyond the thin plate theory limit and it may have considerable effect on sound radiation. But, traditionally, thin annular disk models have been employed for such structures neglecting the thickness effect. In this article, structural eigensolutions for the out-of-plane modes and sound radiation from the modal vibration of a thick annular disk with free-free boundaries have been calculated using both thick and thin plate theories. A new analytical formulation is proposed for the sound radiation problem. In addition, the same problem has been solved by a semi-analytical procedure in which the disk surface velocity is numerically defined by a finite-element model and sound radiation is then analytically obtained using a modified circular radiator model. Also, the effects of radii and thickness ratios on the structural and acoustic radiation characteristics are investigated using the analytical procedure. Finally, the effect of boundary conditions is briefly examined.

  13. Long range acoustic measurements of an undersea volcano.

    PubMed

    Heaney, Kevin D; Campbell, Richard L; Snellen, Mirjam

    2013-10-01

    A seamount 8 km southeast of Sarigan Island erupted on 29 May 2010 and was visually observed. The recordings on two sets of hydrophones, operated by International Monitoring System (IMS) of the Comprehensive Test Ban Treaty Organization (CTBTO) are analyzed. Each array is a triplet of axial single hydrophones deployed as a 2 km triangle. Measurements of acoustic intensity for the path to the southern triplet are on the order of 6 dB lower than those received on the northern triplet. Temporal cross-correlation beamforming estimation is performed and the estimated arrival angles for the two arrays, 265° and 267° were consistent with the predicted geodesic arrival of 264.6° and 267.8°, respectively. Cross-correlation between single phones on the northern and southern arrays reveals a peak at 266°, with a cross-correlation of 0.1. Nx2D parabolic equation modeling predicts complete blockage due to seamount interaction along the geodesic path. Overprediction of the seamount blockage indicates that the 2D approximation is incorrect, and three-dimensional propagation must be used to explain the observations. This is demonstrated by the computation of the Adiabatic Mode Parabolic Equation Transmission Loss, which predicts a 5-10 dB lower reception at the southern site.

  14. Multiple-Component Crystal Fabric Measurements from Acoustically-Generated Normal Modes in Borehole

    NASA Astrophysics Data System (ADS)

    Kluskiewicz, D. J.; Waddington, E. D.; McCarthy, M.; Anandakrishnan, S.; Voigt, D.; Matsuoka, K.

    2014-12-01

    Sound wave velocities in ice are a proxy of crystal orientation fabric. Because p- and s-waves respectively travel faster and slower in the direction of an ice crystal c-axis, the velocities of these waves in a fabric are related to the clustering of ice crystal c-axes in the direction of wave propagation. Previous sonic logs at Dome C, NGRIP, WAIS, and NEEM have inferred a single component fabric description from the velocities of vertically-propagating p-waves around each ice core borehole. These records supplement thin-section measurements of crystal fabric by sampling larger numbers of crystals in a depth-continuous log. Observations of azimuthally anisotropic vertical-girdle fabrics at ice-core sites such as WAIS, NGRIP, and EDML underly a benefit for logging methods that are sensitive to such fabrics. We present a theoretical framework for using borehole flexural modes to measure azimuthal crystal-fabric anisotropy, and describe ongoing efforts to develop a sonic logging tool for this purpose. We also present data from p-wave logs and thin section measurements at the WAIS Divide, and describe how a flexural wave log could supplement the existing measurements.

  15. An Algorithm for Constructing Principal Geodesics in Phylogenetic Treespace.

    PubMed

    Nye, Tom M W

    2014-01-01

    Most phylogenetic analyses result in a sample of trees, but summarizing and visualizing these samples can be challenging. Consensus trees often provide limited information about a sample, and so methods such as consensus networks, clustering and multidimensional scaling have been developed and applied to tree samples. This paper describes a stochastic algorithm for constructing a principal geodesic or line through treespace which is analogous to the first principal component in standard principal components analysis. A principal geodesic summarizes the most variable features of a sample of trees, in terms of both tree topology and branch lengths, and it can be visualized as an animation of smoothly changing trees. The algorithm performs a stochastic search through parameter space for a geodesic which minimizes the sum of squared projected distances of the data points. This procedure aims to identify the globally optimal principal geodesic, though convergence to locally optimal geodesics is possible. The methodology is illustrated by constructing principal geodesics for experimental and simulated data sets, demonstrating the insight into samples of trees that can be gained and how the method improves on a previously published approach. A java package called GeoPhytter for constructing and visualizing principal geodesics is freely available from www.ncl.ac.uk/ ntmwn/geophytter.

  16. Diffeomorphometry and geodesic positioning systems for human anatomy

    PubMed Central

    Miller, Michael I.; Younes, Laurent; Trouvé, Alain

    2014-01-01

    The Computational Anatomy project has largely been a study of large deformations within a Riemannian framework as an efficient point of view for generating metrics between anatomical configurations. This approach turns D’Arcy Thompson’s comparative morphology of human biological shape and form into a metrizable space. Since the metric is constructed based on the geodesic length of the flows of diffeomorphisms connecting the forms, we call it diffeomorphometry. Just as importantly, since the flows describe algebraic group action on anatomical submanifolds and associated functional measurements, they become the basis for positioning information, which we term geodesic positioning. As well the geodesic connections provide Riemannian coordinates for locating forms in the anatomical orbit, which we call geodesic coordinates. These three components taken together — the metric, geodesic positioning of information, and geodesic coordinates — we term the geodesic positioning system. We illustrate via several examples in human and biological coordinate systems and machine learning of the statistical representation of shape and form. PMID:24904924

  17. On a nonlinear gravitational wave. Geodesics

    NASA Astrophysics Data System (ADS)

    Culetu, Hristu

    2016-12-01

    An exact, plane-wave solution of the gravitational field equations is investigated. The source stress tensor is represented by an anisotropic null fluid with energy flux to which the energy density ρ and all pressures are finite throughout the spacetime. They depend on a constant length (taken of the order of the Planck length) and acquire Planck values close to the null surface t-z=0, the z-axis being the direction of propagation. However, ρ and p become positive when a cross-polarization term is introduced in the line element. The timelike geodesics of a test particle are contained in a plane whose normal has constant direction and the null trajectories are comoving with a plane of fixed direction.

  18. Geodesic Regression for Image Time-Series

    PubMed Central

    Niethammer, Marc; Huang, Yang; Vialard, François-Xavier

    2014-01-01

    Registration of image-time series has so far been accomplished (i) by concatenating registrations between image pairs, (ii) by solving a joint estimation problem resulting in piecewise geodesic paths between image pairs, (iii) by kernel based local averaging or (iv) by augmenting the joint estimation with additional temporal irregularity penalties. Here, we propose a generative model extending least squares linear regression to the space of images by using a second-order dynamic formulation for image registration. Unlike previous approaches, the formulation allows for a compact representation of an approximation to the full spatio-temporal trajectory through its initial values. The method also opens up possibilities to design image-based approximation algorithms. The resulting optimization problem is solved using an adjoint method. PMID:21995085

  19. Efficiently computing exact geodesic loops within finite steps.

    PubMed

    Xin, Shi-Qing; He, Ying; Fu, Chi-Wing

    2012-06-01

    Closed geodesics, or geodesic loops, are crucial to the study of differential topology and differential geometry. Although the existence and properties of closed geodesics on smooth surfaces have been widely studied in mathematics community, relatively little progress has been made on how to compute them on polygonal surfaces. Most existing algorithms simply consider the mesh as a graph and so the resultant loops are restricted only on mesh edges, which are far from the actual geodesics. This paper is the first to prove the existence and uniqueness of geodesic loop restricted on a closed face sequence; it contributes also with an efficient algorithm to iteratively evolve an initial closed path on a given mesh into an exact geodesic loop within finite steps. Our proposed algorithm takes only an O(k) space complexity and an O(mk) time complexity (experimentally), where m is the number of vertices in the region bounded by the initial loop and the resultant geodesic loop, and k is the average number of edges in the edge sequences that the evolving loop passes through. In contrast to the existing geodesic curvature flow methods which compute an approximate geodesic loop within a predefined threshold, our method is exact and can apply directly to triangular meshes without needing to solve any differential equation with a numerical solver; it can run at interactive speed, e.g., in the order of milliseconds, for a mesh with around 50K vertices, and hence, significantly outperforms existing algorithms. Actually, our algorithm could run at interactive speed even for larger meshes. Besides the complexity of the input mesh, the geometric shape could also affect the number of evolving steps, i.e., the performance. We motivate our algorithm with an interactive shape segmentation example shown later in the paper.

  20. Geodesic Witten diagrams with an external spinning field

    NASA Astrophysics Data System (ADS)

    Nishida, Mitsuhiro; Tamaoka, Kotaro

    2017-05-01

    We explore AdS/CFT correspondence between geodesic Witten diagrams and conformal blocks (conformal partial waves) with an external symmetric traceless tensor field. We derive an expression for the conformal partial wave with an external spin-1 field and show that this expression is equivalent to the amplitude of the geodesic Witten diagram. We also show the equivalence by using a conformal Casimir equation in embedding formalism. Furthermore, we extend the construction of the amplitude of the geodesic Witten diagram to an external arbitrary symmetric traceless tensor field. We show that our construction agrees with the known result of the conformal partial waves.

  1. Acoustic mode coupling induced by shallow water nonlinear internal waves: sensitivity to environmental conditions and space-time scales of internal waves.

    PubMed

    Colosi, John A

    2008-09-01

    While many results have been intuited from numerical simulation studies, the precise connections between shallow-water acoustic variability and the space-time scales of nonlinear internal waves (NLIWs) as well as the background environmental conditions have not been clearly established analytically. Two-dimensional coupled mode propagation through NLIWs is examined using a perturbation series solution in which each order n is associated with nth-order multiple scattering. Importantly, the perturbation solution gives resonance conditions that pick out specific NLIW scales that cause coupling, and seabed attenuation is demonstrated to broaden these resonances, fundamentally changing the coupling behavior at low frequency. Sound-speed inhomogeneities caused by internal solitary waves (ISWs) are primarily considered and the dependence of mode coupling on ISW amplitude, range width, depth structure, location relative to the source, and packet characteristics are delineated as a function of acoustic frequency. In addition, it is seen that significant energy transfer to modes with initially low or zero energy involves at least a second order scattering process. Under moderate scattering conditions, comparisons of first order, single scattering theoretical predictions to direct numerical simulation demonstrate the accuracy of the approach for acoustic frequencies upto 400 Hz and for single as well as multiple ISW wave packets.

  2. Observation of acoustic-phonon-like mode driven by magnetic imbalance between neighboring Fe atoms in Fe1+yTe (y < 0 . 12)

    NASA Astrophysics Data System (ADS)

    Fobes, David; Zaliznyak, Igor; Xu, Zhijun; Gu, Genda; Tranquada, John M.; He, Xu-Gang; Ku, Wei; Garlea, Ovidiu

    2014-03-01

    We have studied the evolution with temperature of the low-energy inelastic spectra of Fe1+yTe (y < 0 . 12), a parent compound of the iron-chalcogenide superconductor family, revealing an acoustic mode at an unexpected position. Recently, we found evidence for the formation of a bond-order wave leading to ferro-orbital order in the monoclinic phase, in part due to the observation of an elastic structural peak at (100) in the low-temperature monoclinic phase [D. Fobes, et al., arXiv:1307.7162]. In the inelastic spectra we observe a sharp acoustic-phonon-like mode dispersing out of the (100) position in the monoclinic phase. Surprisingly, the mode survives in the tetragonal phase, despite the absence of a Bragg peak at (100); such a peak is forbidden by symmetry. LDA calculations suggest this mode could involve significant magnetic scattering. By assuming in-phase virtual displacement of the Fe atoms from their equilibrium position in a frozen phonon calculation, we have found a small but significant imbalance in the magnetic moments between the two Fe atoms within the unit cell, suggesting magnetic contribution to the mode. Work at BNL supported by Office of Basic Energy Sciences, US DOE, under Contract No. DE-AC02-98CH10886. Research conducted at ORNL Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US DOE.

  3. Adiabatic Normal-Mode Theory of Low-Frequency Sound Transmission in a Shallow Range-Dependent Ocean with Seismo-Acoustic Effects from the Elastic Bottom Sediments.

    NASA Astrophysics Data System (ADS)

    Arvelo, Juan Ismael, Jr.

    The theory of normal modes has been extended to incorporate the effects of shear waves in the elastic ocean floor. The effect of absorption has also been included as the imaginary component of the shear and compressional wave numbers. The eigenvalues of the multilayered wave guide are searched in the complex k-plane by the Levenberg -Marquardt minimization of the magnitude of the complex characteristic equation. The liquid layers of the water column are represented by a wave number squared linear with depth to better simulate the sound speed profile. It has been found that the compressional sound speed in an elastic layer can also be represented by a wave number squared which varies linearly with depth and still lead to solvable wave equations. A semi-infinite elastic bottom basement layer with compressional and shear absorption has been included in the normal mode model and it has been found that absorption causes the wave number spectrum of the radiating modes to be inherently discrete, hence the number of radiating modes is drastically reduced. The range dependence of the acoustic properties and of the boundaries of the ocean has been included by a modified version of the adiabatic normal mode theory. This newly developed version handles the shear wave contribution and the fact that the eigenvalues and depth functions are complex. The coherent transmission loss in the elastic layers is computed using the magnitude of the acoustic intensity vector whose value in decibels is widely used in determining the performance of active and passive sonar systems. Comparisons are made with experimental measurements of the transmission loss of underwater explosives producing very good agreement for frequencies above 100 Hz. At lower frequencies, sound penetrates deeper into the bottom where no data on the acoustic properties are available. Hence, this model is used for inverse scattering predictions of the unknown properties.

  4. Poisson disk sampling in geodesic metric for DEM simplification

    NASA Astrophysics Data System (ADS)

    Hou, Wenguang; Zhang, Xuming; Li, Xin; Lai, Xudong; Ding, Mingyue

    2013-08-01

    To generate highly compressed digital elevation models (DEMs) with fine details, the method of Poisson disk sampling in geodesic metric is proposed. The main idea is to uniformly pick points from DEM nodes in geodesic metric, resulting in terrain-adaptive samples in Euclidean metric. This method randomly selects point from mesh nodes and then judges whether this point can be accepted in accordance with the related geodesic distances from the sampled points. The whole process is repeated until no more points can be selected. To further adjust the sampling ratios in different areas, weighted geodesic distance, which is in relation to terrain characteristics, are introduced. In addition to adaptability, sample distributions are well visualised. This method is simple and easy to implement. Cases are provided to illustrate the feasibility and superiority of the proposed method.

  5. Turbulence characteristics of the I-mode confinement regime in ASDEX Upgrade

    NASA Astrophysics Data System (ADS)

    Manz, P.; Happel, T.; Ryter, F.; Bernert, M.; Birkenmeier, G.; Conway, G. D.; Dunne, M.; Guimarais, L.; Hennequin, P.; Hetzenecker, A.; Honoré, C.; Lauber, P.; Maraschek, M.; Nikolaeva, V. E.; Prisiazhniuk, D.; Stroth, U.; Viezzer, E.; ASDEX Upgrade Team2, The

    2017-08-01

    Besides strong geodesic acoustic mode (GAM) activity, turbulence in the I-mode confinement regime of ASDEX Upgrade exhibits two prominent features, the weakly coherent mode (WCM) and strongly intermittent solitary density perturbations. The nonlinear interaction between these structures is studied in detail by means of a conditional averaged wavelet-bicoherence analysis. The wavelet analysis reveals that these density perturbations are at the WCM frequency. The GAM is coupled to all frequency scales of the velocity fluctuations via a modulational instability. The WCM shows coupling to higher frequencies prior to the bursts, indicating a process resembling wave-steepening. A possible mechanism for the generation of such solitary density perturbations by a Korteweg-de Vries-like nonlinearity is discussed.

  6. Marginally bound (critical) geodesics of rapidly rotating black holes

    NASA Astrophysics Data System (ADS)

    Hod, Shahar

    2013-10-01

    One of the most important geodesics in a black hole spacetime is the marginally bound spherical orbit. This critical geodesic represents the innermost spherical orbit which is bound to the central black hole. The radii rmb(a¯) of the marginally bound equatorial circular geodesics of rotating Kerr black holes were found analytically by Bardeen et al. more than four decades ago (here a¯≡J/M2 is the dimensionless angular momentum of the black hole). On the other hand, no closed-form formula exists in the literature for the radii of generic (nonequatorial) marginally bound geodesics of the rotating Kerr spacetime. In the present study, we analyze the critical (marginally bound) orbits of rapidly rotating Kerr black holes. In particular, we derive a simple analytical formula for the radii rmb(a¯≃1;cos⁡i) of the marginally bound spherical orbits, where cos⁡i is an effective inclination angle (with respect to the black hole equatorial plane) of the geodesic. We find that the marginally bound spherical orbits of rapidly rotating black holes are characterized by a critical inclination angle, cos⁡i=2/3, above which the coordinate radii of the geodesics approach the black hole radius in the extremal a¯→1 limit. It is shown that this critical inclination angle signals a transition in the physical properties of the orbits: in particular, it separates marginally bound spherical geodesics which lie a finite proper distance from the black hole horizon from marginally bound geodesics which lie an infinite proper distance from the horizon.

  7. The Lorentzian oscillator group as a geodesic orbit space

    SciTech Connect

    Batat, W.; Gadea, P. M.; Oubina, J. A.

    2012-10-15

    We prove that the four-dimensional oscillator group Os, endowed with any of its usual left-invariant Lorentzian metrics, is a Lorentzian geodesic (so, in particular, null-geodesic) orbit space with some of its homogeneous descriptions corresponding to certain homogeneous Lorentzian structures. Each time that Os is endowed with a suitable metric and an appropriate homogeneous Lorentzian structure, it is a candidate for constructing solutions in d-dimensional supergravity with at least 24 of the 32 possible supersymmetries.

  8. Adaptive Riemannian Metrics for Improved Geodesic Tracking of White Matter

    PubMed Central

    Hao, Xiang; Whitaker, Ross T.; Fletcher, P. Thomas

    2011-01-01

    We present a new geodesic approach for studying white matter connectivity from diffusion tensor imaging (DTI). Previous approaches have used the inverse diffusion tensor field as a Riemannian metric and constructed white matter tracts as geodesics on the resulting manifold. These geodesics have the desirable property that they tend to follow the main eigenvectors of the tensors, yet still have the flexibility to deviate from these directions when it results in lower costs. While this makes such methods more robust to noise, it also has the serious drawback that geodesics tend to deviate from the major eigenvectors in high-curvature areas in order to achieve the shortest path. In this paper we formulate a modification of the Riemannian metric that results in geodesics adapted to follow the principal eigendirection of the tensor even in high-curvature regions. We show that this correction can be formulated as a simple scalar field modulation of the metric and that the appropriate variational problem results in a Poisson’s equation on the Riemannian manifold. We demonstrate that the proposed method results in improved geodesics using both synthetic and real DTI data. PMID:21761642

  9. Geodesic active contours with adaptive neighboring influence.

    PubMed

    Liu, Huafeng; Chen, Yunmei; Ho, Hon Pong; Shi, Pengcheng

    2005-01-01

    While geometric deformable models have brought tremendous impacts on shape representation and analysis in medical image analysis, some of the remaining problems include the handling of boundary leakage and the lack of global understanding of boundaries. We present a modification to the geodesic active contour framework such that influence from local neighbors of a front point is explicitly incorporated, and it is thus capable of robustly dealing with the boundary leakage problem. The fundamental power of this strategy rests with the local integration of evolution forces for each front point within its local influence domain, which is adaptively determined by the local level set geometry and image/prior information. Due to the combined effects of internal and external constraints on a point and the interactions with those of its neighbors, our method allows stable boundary detection when the edge information is noisy and possibly discontinuous (e.g. gaps in the boundaries) while maintaining the abilities to handle topological changes, thanks to the level set implementation. The algorithm has been implemented using the meshfree particle domain representation, and experimental results on synthetic and real images demonstrate its superior performance.

  10. Brain extraction using geodesic active contours

    NASA Astrophysics Data System (ADS)

    Huang, Albert; Abugharbieh, Rafeef; Tam, Roger; Traboulsee, Anthony

    2006-03-01

    Extracting the brain cortex from magnetic resonance imaging (MRI) head scans is an essential preprocessing step of which the accuracy greatly affects subsequent image analysis. The currently popular Brain Extraction Tool (BET) produces a brain mask which may be too smooth for practical use. This paper presents a novel brain extraction tool based on three-dimensional geodesic active contours, connected component analysis and mathematical morphology. Based on user-specified intensity and contrast levels, the proposed algorithm allows an active contour to evolve naturally and extract the brain cortex. Experiments on synthetic MRI data and scanned coronal and axial MRI image volumes indicate successful extraction of tight perimeters surrounding the brain cortex. Quantitative evaluations on both synthetic phantoms and manually labeled data resulted in better accuracy than BET in terms of true and false voxel assignment. Based on these results, we illustrate that our brain extraction tool is a robust and accurate approach for the challenging task of automatically extracting the brain cortex in MRI data.

  11. Multi-object geodesic active contours (MOGAC).

    PubMed

    Lucas, Blake C; Kazhdan, Michael; Taylor, Russell H

    2012-01-01

    An emerging topic is to build image segmentation systems that can segment hundreds to thousands of objects (i.e. cell segmentation\\tracking, full brain parcellation, full body segmentation, etc.). Multi-object Level Set Methods (MLSM) perform this task with the benefit of sub-pixel precision. However, current implementations of MLSM are not as computationally or memory efficient as their region growing and graph cut counterparts which lack sub-pixel precision. To address this performance gap, we present a novel parallel implementation of MLSM that leverages the sparse properties of the algorithm to minimize its memory footprint for multiple objects. The new method, Multi-Object Geodesic Active Contours (MOGAC), can represent N objects with just two functions: a label mask image and unsigned distance field. The time complexity of the algorithm is shown to be O((M (power)d)/P) for M (power)d pixels and P processing units in dimension d = {2,3}, independent of the number of objects. Results are presented for 2D and 3D image segmentation problems.

  12. Geodesics and Acceleration in Influence Theory

    NASA Astrophysics Data System (ADS)

    Walsh, James; Knuth, Kevin

    Influence theory is concerned with a foundational approach where it is assumed that particles influence one another in a discrete one-to-one fashion. This results in a partially ordered set of influence events, called the influence network, where particles are represented by totally ordered chains of events. Information physics considers physical laws to result from consistent quantification of physical phenomena. Knuth and Bahreyni (2014) demonstrated that the mathematics of spacetime emerges from consistent quantification of influence events by embedded coordinated observers. Knuth (2014) showed that in 1 +1 dimensions observer-based predictions about a free (uninfluenced) particle result in the Dirac equation. Here, we show that when a particle in 1 +1 dimensions is influenced, it is uniquely and consistently described in terms of relativistic acceleration for constant rate of influence and in general obeys equations of the form of the geodesic equations of general relativity. This suggests that Influence Theory can also account for forces (like gravity), which give rise to well-known relativistic effects such as time dilation.

  13. Dust-acoustic solitary modes in plasmas with isothermal and nonthermal ions: Polarity switches and coexistence domains

    SciTech Connect

    Verheest, Frank

    2011-08-15

    Large dust-acoustic waves are investigated in a multispecies plasma model consisting of cold negative dust in the presence of cooler Boltzmann and hotter nonthermal Cairns positive ions, in a Sagdeev pseudopotential formalism. Use of the pseudopotential at the acoustic speed itself yields in a systematic way compositional parameter values where negative/positive solitons interchange polarities and also where both polarities coexist. The latter requires that solitons at the acoustic speed exist, with finite amplitudes, compared to superacoustic solitons of the opposite polarity. The coexistence region starts when the pseudopotential at the acoustic speed has a negative root at the limit of infinite dust compression and ends when a positive double root is encountered. Outside the coexistence domain, only negative or positive superacoustic solitons can exist. Thus, the discussion and numerical evaluations are guided by precise physical and analytic arguments rather than mere numerical experimentation. Graphs of relevant Sagdeev pseudopotentials illustrate the link with the analytical constraints.

  14. The normal modes of a resonant cavity containing discrete inhomogeneities - The influence of fibril magnetic fields on the solar acoustic oscillations

    NASA Technical Reports Server (NTRS)

    Bogdan, Thomas J.; Cattaneo, Fausto

    1989-01-01

    Motivated by considerations of the interaction between fibril magnetic fields and solar p-modes, the acoustic spectrum of a cylindrical cavity filled with ideal gas in which a number of magnetic flux tubes are embedded is studied. A formalism, based on the T-matrix approach to acoustic scattering, is developed which can be used to determine the eigenfrequencies and eigenfunctions for any arbitrary distribution of flux tubes. For weak scatterers, the frequency shifts and velocity eigenfunctions are calculated using perturbation theory for the cases of a single flux tube and a random distribution of up to 100 flux tubes. The results of this 'exact' approach are used to give a critical appraisal of the predictions of theories based on some form of averaging, such as the one discussed recently by Bogdan and Zweibel (1987).

  15. Active Control of Fan Noise: Feasibility Study. Volume 5; Numerical Computation of Acoustic Mode Reflection Coefficients for an Unflanged Cylindrical Duct

    NASA Technical Reports Server (NTRS)

    Kraft, R. E.

    1996-01-01

    A computational method to predict modal reflection coefficients in cylindrical ducts has been developed based on the work of Homicz, Lordi, and Rehm, which uses the Wiener-Hopf method to account for the boundary conditions at the termination of a thin cylindrical pipe. The purpose of this study is to develop a computational routine to predict the reflection coefficients of higher order acoustic modes impinging on the unflanged termination of a cylindrical duct. This effort was conducted wider Task Order 5 of the NASA Lewis LET Program, Active Noise Control of aircraft Engines: Feasibility Study, and will be used as part of the development of an integrated source noise, acoustic propagation, ANC actuator coupling, and control system algorithm simulation. The reflection coefficient prediction will be incorporated into an existing cylindrical duct modal analysis to account for the reflection of modes from the duct termination. This will provide a more accurate, rapid computation design tool for evaluating the effect of reflected waves on active noise control systems mounted in the duct, as well as providing a tool for the design of acoustic treatment in inlet ducts. As an active noise control system design tool, the method can be used preliminary to more accurate but more numerically intensive acoustic propagation models such as finite element methods. The resulting computer program has been shown to give reasonable results, some examples of which are presented. Reliable data to use for comparison is scarce, so complete checkout is difficult, and further checkout is needed over a wider range of system parameters. In future efforts the method will be adapted as a subroutine to the GEAE segmented cylindrical duct modal analysis program.

  16. Scalar self-force on eccentric geodesics in Schwarzschild spacetime: A time-domain computation

    SciTech Connect

    Haas, Roland

    2007-06-15

    We calculate the self-force acting on a particle with scalar charge moving on a generic geodesic around a Schwarzschild black hole. This calculation requires an accurate computation of the retarded scalar field produced by the moving charge; this is done numerically with the help of a fourth-order convergent finite-difference scheme formulated in the time domain. The calculation also requires a regularization procedure, because the retarded field is singular on the particle's world line; this is handled mode-by-mode via the mode-sum regularization scheme first introduced by Barack and Ori. This paper presents the numerical method, various numerical tests, and a sample of results for mildly eccentric orbits as well as ''zoom-whirl'' orbits.

  17. Focusing of geodesic congruences in an accelerated expanding Universe

    SciTech Connect

    Albareti, F.D.; Cembranos, J.A.R.; Cruz-Dombriz, A. de la E-mail: cembra@fis.ucm.es

    2012-12-01

    We study the accelerated expansion of the Universe through its consequences on a congruence of geodesics. We make use of the Raychaudhuri equation which describes the evolution of the expansion rate for a congruence of timelike or null geodesics. In particular, we focus on the space-time geometry contribution to this equation. By straightforward calculation from the metric of a Robertson-Walker cosmological model, it follows that in an accelerated expanding Universe the space-time contribution to the Raychaudhuri equation is positive for the fundamental congruence, favoring a non-focusing of the congruence of geodesics. However, the accelerated expansion of the present Universe does not imply a tendency of the fundamental congruence to diverge. It is shown that this is in fact the case for certain congruences of timelike geodesics without vorticity. Therefore, the focusing of geodesics remains feasible in an accelerated expanding Universe. Furthermore, a negative contribution to the Raychaudhuri equation from space-time geometry which is usually interpreted as the manifestation of the attractive character of gravity is restored in an accelerated expanding Robertson-Walker space-time at high speeds.

  18. Acoustic transducer for acoustic microscopy

    DOEpatents

    Khuri-Yakub, B.T.; Chou, C.H.

    1990-03-20

    A shear acoustic transducer-lens system is described in which a shear polarized piezoelectric material excites shear polarized waves at one end of a buffer rod having a lens at the other end which excites longitudinal waves in a coupling medium by mode conversion at selected locations on the lens. 9 figs.

  19. Acoustic transducer for acoustic microscopy

    DOEpatents

    Khuri-Yakub, Butrus T.; Chou, Ching H.

    1990-01-01

    A shear acoustic transducer-lens system in which a shear polarized piezoelectric material excites shear polarized waves at one end of a buffer rod having a lens at the other end which excites longitudinal waves in a coupling medium by mode conversion at selected locations on the lens.

  20. Accurate Anisotropic Fast Marching for Diffusion-Based Geodesic Tractography

    PubMed Central

    Jbabdi, S.; Bellec, P.; Toro, R.; Daunizeau, J.; Pélégrini-Issac, M.; Benali, H.

    2008-01-01

    Using geodesics for inferring white matter fibre tracts from diffusion-weighted MR data is an attractive method for at least two reasons: (i) the method optimises a global criterion, and hence is less sensitive to local perturbations such as noise or partial volume effects, and (ii) the method is fast, allowing to infer on a large number of connexions in a reasonable computational time. Here, we propose an improved fast marching algorithm to infer on geodesic paths. Specifically, this procedure is designed to achieve accurate front propagation in an anisotropic elliptic medium, such as DTI data. We evaluate the numerical performance of this approach on simulated datasets, as well as its robustness to local perturbation induced by fiber crossing. On real data, we demonstrate the feasibility of extracting geodesics to connect an extended set of brain regions. PMID:18299703

  1. Paraconformal structures, ordinary differential equations and totally geodesic manifolds

    NASA Astrophysics Data System (ADS)

    Kryński, Wojciech

    2016-05-01

    We construct point invariants of ordinary differential equations of arbitrary order that generalise the Tresse and Cartan invariants of equations of order two and three, respectively. The vanishing of the invariants is equivalent to the existence of a totally geodesic paraconformal structure which consists of a paraconformal structure, an adapted GL(2 , R) -connection and a two-parameter family of totally geodesic hypersurfaces on the solution space. The structures coincide with the projective structures in dimension 2 and with the Einstein-Weyl structures of Lorentzian signature in dimension 3. We show that the totally geodesic paraconformal structures in higher dimensions can be described by a natural analogue of the Hitchin twistor construction. We present a general example of Veronese webs that generalise the hyper-CR Einstein-Weyl structures in dimension 3. The Veronese webs are described by a hierarchy of integrable systems.

  2. Shape change along geodesics with application to cleft lip surgery

    PubMed Central

    Faraway, Julian J.; Trotman, Carroll-Ann

    2012-01-01

    Summary Continuous shape change is represented as curves in the shape space. A method for checking the closeness of these curves to a geodesic is presented. Three large databases of short human motions are considered and shown to be well approximated by geodesics. The motions are thus approximated by two shapes on the geodesic and the rate of progress along the path. An analysis of facial motion data taken from a study of subjects with cleft lip or cleft palate is presented that allows the motion to be considered independently from the static shape. Inferential methods for assessing the change in motion are presented. The construction of predicted animated motions is discussed. PMID:22639469

  3. Superintegrability of geodesic motion on the sausage model

    NASA Astrophysics Data System (ADS)

    Arutyunov, Gleb; Heinze, Martin; Medina-Rincon, Daniel

    2017-06-01

    Reduction of the η-deformed sigma model on AdS_5× S5 to the two-dimensional squashed sphere (S^2)η can be viewed as a special case of the Fateev sausage model where the coupling constant ν is imaginary. We show that geodesic motion in this model is described by a certain superintegrable mechanical system with four-dimensional phase space. This is done by means of explicitly constructing three integrals of motion which satisfy the sl(2) Poisson algebra relations, albeit being non-polynomial in momenta. Further, we find a canonical transformation which transforms the Hamiltonian of this mechanical system to the one describing the geodesic motion on the usual two-sphere. By inverting this transformation we map geodesics on this auxiliary two-sphere back to the sausage model. This paper is a tribute to the memory of Prof Petr Kulish.

  4. Integrable geodesic flows and super polytropic gas equations

    NASA Astrophysics Data System (ADS)

    Guha, Partha

    2003-06-01

    The polytropic gas equations are shown to be the geodesic flows with respect to an L2 metric on the semidirect product space Diff( S1)⊙ C∞( S1), where Diff( S1) is the group of orientation preserving diffeomorphisms of the circle. We also show that the N=1 supersymmetric polytropic gas equation constitute an integrable geodesic flow on the extended Neveu-Schwarz space. Recently other kinds of supersymmetrizations have been studied vigorously in connection with superstring theory and are called supersymmetric-B (SUSY-B) extension. In this paper we also show that the SUSY-B extension of the polytropic gas equation form a geodesic flow on the extension of the Neveu-Schwarz space.

  5. (Non-)geodesic motion in chameleon Brans Dicke model

    NASA Astrophysics Data System (ADS)

    Saaidi, K.

    2013-06-01

    Based on Das and Banerjee (Phys. Rev D 78:043512, 2008), we assume there is a non-minimal coupling between scalar field and matter in the Brans-Dicke model. We analyzes the motion of different matter such as, massless scalar field, photon, massless perfect fluid (dust), massive perfect fluid and point particle matter in this study. We show that the motion of massless scalar field and photon can satisfy null geodesic motion only in high frequency limit. Also we find that the motion of the dust and massive perfect fluid is geodesic for L m =- P and it is non-geodesic for L m = ρ. Finally, we study the motion of point particle and show that the motion of this kind of matter is like massive perfect fluid.

  6. Spherical null geodesics of rotating Kerr black holes

    NASA Astrophysics Data System (ADS)

    Hod, Shahar

    2013-01-01

    The non-equatorial spherical null geodesics of rotating Kerr black holes are studied analytically. Unlike the extensively studied equatorial circular orbits whose radii are known analytically, no closed-form formula exists in the literature for the radii of generic (non-equatorial) spherical geodesics. We provide here an approximate formula for the radii rph (a / M ; cos i) of these spherical null geodesics, where a / M is the dimensionless angular momentum of the black hole and cos i is an effective inclination angle (with respect to the black-hole equatorial plane) of the orbit. It is well-known that the equatorial circular geodesics of the Kerr spacetime (the prograde and the retrograde orbits with cos i = ± 1) are characterized by a monotonic dependence of their radii rph (a / M ; cos i = ± 1) on the dimensionless spin-parameter a / M of the black hole. We use here our novel analytical formula to reveal that this well-known property of the equatorial circular geodesics is actually not a generic property of the Kerr spacetime. In particular, we find that counter-rotating spherical null orbits in the range (3√{ 3} -√{ 59}) / 4 ≲ cos i < 0 are characterized by a non-monotonic dependence of rph (a / M ; cos i =const) on the dimensionless rotation-parameter a / M of the black hole. Furthermore, it is shown that spherical photon orbits of rapidly-rotating black holes are characterized by a critical inclination angle, cos i =√{ 4 / 7 }, above which the coordinate radii of the orbits approach the black-hole radius in the extremal limit. We prove that this critical inclination angle signals a transition in the physical properties of the spherical null geodesics: in particular, it separates orbits which are characterized by finite proper distances to the black-hole horizon from orbits which are characterized by infinite proper distances to the horizon.

  7. Study of the influence of semiconductor material parameters on acoustic wave propagation modes in GaSb/AlSb bi-layered structures by Legendre polynomial method

    NASA Astrophysics Data System (ADS)

    Othmani, Cherif; Takali, Farid; Njeh, Anouar; Ben Ghozlen, Mohamed Hédi

    2016-09-01

    The propagation of Rayleigh-Lamb waves in bi-layered structures is studied. For this purpose, an extension of the Legendre polynomial (LP) method is proposed to formulate the acoustic wave equation in the bi-layered structures induced by thin film Gallium Antimonide (GaSb) and with Aluminum Antimonide (AlSb) substrate in moderate thickness. Acoustic modes propagating along a bi-layer plate are shown to be quite different than classical Lamb modes, contrary to most of the multilayered structures. The validation of the LP method is illustrated by a comparison between the associated numerical results and those obtained using the ordinary differential equation (ODE) method. The convergency of the LP method is discussed through a numerical example. Moreover, the influences of thin film GaSb parameters on the characteristics Rayleigh-Lamb waves propagation has been studied in detail. Finally, the advantages of the Legendre polynomial (LP) method to analyze the multilayered structures are described. All the developments performed in this work were implemented in Matlab software.

  8. A two-way coupled mode formalism that satisfies energy conservation for impedance boundaries in underwater acoustics.

    PubMed

    Stotts, Steven A; Koch, Robert A

    2015-11-01

    This paper shows that energy conservation and the derivation of the two-way coupled mode range equations can be extended in three dimensions to complex mode functions and eigenvalues. Furthermore, the energy in the coupled mode formulation is conserved for finite thickness fluid ocean waveguides with a penetrable bottom boundary beneath any range dependence. The derivations rely on completeness and a modified orthonormality statement. The mode coupling coefficients are specified solely and explicitly by the waveguide range dependence. The statement of energy conservation is applied to a numerical coupled mode calculation.

  9. An Efficient Geodesic Path Solution for Prolate Spheroids

    DTIC Science & Technology

    1979-07-01

    unit tangent vector is determinr 4, the other relevant parameter in the ray analysis , namely, the unit binprmal vector 6 can readily be obtained via...geodesic shown in Fig. S . Recall that the unit tangent vectors for the geodesic are given by Equations (1l)-(15). Assuming at a particular point (e )on the...Aeronautics and Space Adi&inistration, ’,,ashington, D.C. 20546. [3] M.M. Lipschutz, Theory and Problems of Di-fferentia-l_(eni ret-rv, Schaums Outline

  10. Geodesic-loxodromes for diffusion tensor interpolation and difference measurement.

    PubMed

    Kindlmann, Gordon; Estépar, Raúl San José; Niethammer, Marc; Haker, Steven; Westin, Carl-Fredrik

    2007-01-01

    In algorithms for processing diffusion tensor images, two common ingredients are interpolating tensors, and measuring the distance between them. We propose a new class of interpolation paths for tensors, termed geodesic-loxodromes, which explicitly preserve clinically important tensor attributes, such as mean diffusivity or fractional anisotropy, while using basic differential geometry to interpolate tensor orientation. This contrasts with previous Riemannian and Log-Euclidean methods that preserve the determinant. Path integrals of tangents of geodesic-loxodromes generate novel measures of over-all difference between two tensors, and of difference in shape and in orientation.

  11. The linear and non-linear characterization of dust ion acoustic mode in complex plasma in presence of dynamical charging of dust

    SciTech Connect

    Bhattacharjee, Saurav Das, Nilakshi

    2015-10-15

    A systematic theoretical investigation has been carried out on the role of dust charging dynamics on the nature and stability of DIA (Dust Ion Acoustic) mode in complex plasma. The study has been made for both linear and non-linear scale regime of DIA mode. The observed results have been characterized in terms of background plasma responses towards dust surface responsible for dust charge fluctuation, invoking important dusty plasma parameters, especially the ion flow speed and dust size. The linear analyses confirm the nature of instability in DIA mode in presence of dust charge fluctuation. The instability shows a damping of DIA mode in subsonic flow regime followed by a gradual growth in instability in supersonic limit of ion flow. The strength of non-linearity and their existence domain is found to be driven by different dusty plasma parameters. As dust is ubiquitous in interstellar medium with plasma background, the study also addresses the possible effect of dust charging dynamics in gravito-electrostatic characterization and the stability of dust molecular clouds especially in proto-planetary disc. The observations are influential and interesting towards the understanding of dust settling mechanism and formation of dust environments in different regions in space.

  12. Observation of guided longitudinal acoustic modes and nondestructive characterization of the elastic properties of hard films/coatings

    SciTech Connect

    Chirita, M.; Sooryakumar, R.; Xia, Hua; Monteiro, O. R.; Brown, I. G.

    1999-12-02

    We report on a new high frequency excitation, identified as a longitudinal guided mode, supported in a hard isotropic film deposited on a substrate. The observation of this mode allows for a direct determination of the C{sub 11} elastic constant of the film. The remaining constant, C{sub 44}, was determined through a least square fit to the dispersion of the pseudo surface wave. Properties of the observed excitations were investigated by evaluating their mode density and polarization characteristics.

  13. Acoustic Translation of an Acoustically Levitated Sample

    NASA Technical Reports Server (NTRS)

    Barmatz, M. B.; Allen, J. L.

    1986-01-01

    Acoustic-levitation apparatus uses only one acoustic mode to move sample from one region of chamber to another. Sample heated and cooled quickly by translation between hot and cold regions of levitation chamber. Levitated sample is raised into furnace region by raising plunger. Frequency of sound produced by transducers adjusted by feedback system to maintain (102) resonant mode, which levitates sample midway between transducers and plunger regardless of plunger position.

  14. Optical detection of folded mini-zone-edge coherent acoustic modes in a doped GaAs/AlAs superlattice

    NASA Astrophysics Data System (ADS)

    Beardsley, R.; Akimov, A. V.; Glavin, B. A.; Maryam, W.; Henini, M.; Kent, A. J.

    2010-07-01

    A coherent phonon mode with frequency corresponding to the first mini Brillouin-zone edge stop gap is observed in ultrafast pump-probe measurements on a doped semiconductor superlattice structure. It is proposed that the optical detection of the mode is facilitated by interactions with the free carriers present in the superlattice.

  15. Acoustic biosensors

    PubMed Central

    Fogel, Ronen; Seshia, Ashwin A.

    2016-01-01

    Resonant and acoustic wave devices have been researched for several decades for application in the gravimetric sensing of a variety of biological and chemical analytes. These devices operate by coupling the measurand (e.g. analyte adsorption) as a modulation in the physical properties of the acoustic wave (e.g. resonant frequency, acoustic velocity, dissipation) that can then be correlated with the amount of adsorbed analyte. These devices can also be miniaturized with advantages in terms of cost, size and scalability, as well as potential additional features including integration with microfluidics and electronics, scaled sensitivities associated with smaller dimensions and higher operational frequencies, the ability to multiplex detection across arrays of hundreds of devices embedded in a single chip, increased throughput and the ability to interrogate a wider range of modes including within the same device. Additionally, device fabrication is often compatible with semiconductor volume batch manufacturing techniques enabling cost scalability and a high degree of precision and reproducibility in the manufacturing process. Integration with microfluidics handling also enables suitable sample pre-processing/separation/purification/amplification steps that could improve selectivity and the overall signal-to-noise ratio. Three device types are reviewed here: (i) bulk acoustic wave sensors, (ii) surface acoustic wave sensors, and (iii) micro/nano-electromechanical system (MEMS/NEMS) sensors. PMID:27365040

  16. Acoustic biosensors.

    PubMed

    Fogel, Ronen; Limson, Janice; Seshia, Ashwin A

    2016-06-30

    Resonant and acoustic wave devices have been researched for several decades for application in the gravimetric sensing of a variety of biological and chemical analytes. These devices operate by coupling the measurand (e.g. analyte adsorption) as a modulation in the physical properties of the acoustic wave (e.g. resonant frequency, acoustic velocity, dissipation) that can then be correlated with the amount of adsorbed analyte. These devices can also be miniaturized with advantages in terms of cost, size and scalability, as well as potential additional features including integration with microfluidics and electronics, scaled sensitivities associated with smaller dimensions and higher operational frequencies, the ability to multiplex detection across arrays of hundreds of devices embedded in a single chip, increased throughput and the ability to interrogate a wider range of modes including within the same device. Additionally, device fabrication is often compatible with semiconductor volume batch manufacturing techniques enabling cost scalability and a high degree of precision and reproducibility in the manufacturing process. Integration with microfluidics handling also enables suitable sample pre-processing/separation/purification/amplification steps that could improve selectivity and the overall signal-to-noise ratio. Three device types are reviewed here: (i) bulk acoustic wave sensors, (ii) surface acoustic wave sensors, and (iii) micro/nano-electromechanical system (MEMS/NEMS) sensors.

  17. Haustral loop extraction for CT colonography using geodesics.

    PubMed

    Liu, Yongkai; Duan, Chaijie; Liang, Jerome; Hu, Jing; Lu, Hongbing; Luo, Mingyue

    2017-03-01

    The human colon has complex geometric structures because of its haustral folds, which are thin flat protrusions on the colon wall. The haustral loop is the curve (approximately triangular in shape) that encircles the highly convex region of the haustral fold, and is regarded as the natural landmark of the colon, intersecting the longitude of the colon in the middle. Haustral loop extraction can assist in reducing the structural complexity of the colon, and the loops can also serve as anatomic markers for computed tomographic colonography (CTC). Moreover, haustral loop sectioning of the colon can help with the performance of precise prone-supine registration. We propose an accurate approach of extracting haustral loops for CT virtual colonoscopy based on geodesics. First, the longitudinal geodesic (LG) connecting the start and end points is tracked by the geodesic method and the colon is cut along the LG. Second, key points are extracted from the LG, after which paired points that are used for seeking the potential haustral loops are calculated according to the key points. Next, for each paired point, the shortest distance (geodesic line) between the paired points twice is calculated, namely one on the original surface and the other on the cut surface. Then, the two geodesics are combined to form a potential haustral loop. Finally, erroneous and nonstandard potential loops are removed. To evaluate the haustral loop extraction algorithm, we first utilized the algorithm to extract the haustral loops. Then, we let the clinicians determine whether the haustral loops were correct and then identify the missing haustral loops. The extraction algorithm successfully detected 91.87% of all of the haustral loops with a very low false positive rate. We believe that haustral loop extraction may benefit many post-procedures in CTC, such as supine-prone registration, computer-aided diagnosis, and taenia coli extraction.

  18. Acoustic neuroma

    MedlinePlus

    Vestibular schwannoma; Tumor - acoustic; Cerebellopontine angle tumor; Angle tumor; Hearing loss - acoustic; Tinnitus - acoustic ... Acoustic neuromas have been linked with the genetic disorder neurofibromatosis type 2 (NF2). Acoustic neuromas are uncommon.

  19. Nonlinear coupling of acoustic and shear mode in a strongly coupled dusty plasma with a density dependent viscosity

    NASA Astrophysics Data System (ADS)

    Garai, S.; Janaki, M. S.; Chakrabarti, N.

    2016-09-01

    The nonlinear propagation of low frequency waves, in a collisionless, strongly coupled dusty plasma (SCDP) with a density dependent viscosity, has been studied with a proper Galilean invariant generalized hydrodynamic (GH) model. The well known reductive perturbation technique (RPT) has been employed in obtaining the solutions of the longitudinal and transverse perturbations. It has been found that the nonlinear propagation of the acoustic perturbations govern with the modified Korteweg-de Vries (KdV) equation and are decoupled from the sheared fluctuations. In the regions, where transversal gradients of the flow exists, coupling between the longitudinal and transverse perturbations occurs due to convective nonlinearity which is true for the homogeneous case also. The results, obtained here, can have relative significance to astrophysical context as well as in laboratory plasmas.

  20. Optimal design of geodesically stiffened composite cylindrical shells

    NASA Technical Reports Server (NTRS)

    Gendron, G.; Gurdal, Z.

    1992-01-01

    An optimization system based on general-purpose finite element code CSM Testbed and optimization program ADS is described. The system can be used to obtain minimum-mass designs of composite shell structures with complex stiffening arrangements. Ply thicknesses, ply orientations, and stiffener heights can be used as design variables. Buckling, displacement, and material failure constraints can be imposed on the design. The system is used to conduct a preliminary design study of geodesically stiffened shells. For comparison purposes, optimal designs of unstiffened shells, and ring and longitudinal stringer stiffened shells are also studied. Trends in the design of geodesically stiffened shells are identified. Features that enhance the capabilities and efficiency of the design system are described.

  1. MAGNETOHYDRODYNAMIC MODELING OF SOLAR SYSTEM PROCESSES ON GEODESIC GRIDS

    SciTech Connect

    Florinski, V.; Guo, X.; Balsara, D. S.; Meyer, C.

    2013-04-01

    This report describes a new magnetohydrodynamic numerical model based on a hexagonal spherical geodesic grid. The model is designed to simulate astrophysical flows of partially ionized plasmas around a central compact object, such as a star or a planet with a magnetic field. The geodesic grid, produced by a recursive subdivision of a base platonic solid (an icosahedron), is free from control volume singularities inherent in spherical polar grids. Multiple populations of plasma and neutral particles, coupled via charge-exchange interactions, can be simulated simultaneously with this model. Our numerical scheme uses piecewise linear reconstruction on a surface of a sphere in a local two-dimensional 'Cartesian' frame. The code employs Haarten-Lax-van-Leer-type approximate Riemann solvers and includes facilities to control the divergence of the magnetic field and maintain pressure positivity. Several test solutions are discussed, including a problem of an interaction between the solar wind and the local interstellar medium, and a simulation of Earth's magnetosphere.

  2. Geodesics in the field of a rotating deformed gravitational source

    NASA Astrophysics Data System (ADS)

    Boshkayev, K. A.; Quevedo, H.; Abutalip, M. S.; Kalymova, Zh. A.; Suleymanova, Sh. S.

    2016-01-01

    We investigate equatorial geodesics in the gravitational field of a rotating and deformed source described by the approximate Hartle-Thorne metric. In the case of massive particles, we derive within the same approximation analytic expressions for the orbital angular velocity, the specific angular momentum and energy, and the radii of marginally stable and marginally bound circular orbits. Moreover, we calculate the orbital angular velocity and the radius of lightlike circular geodesics. We study numerically the frame dragging effect and the influence of the quadrupolar deformation of the source on the motion of test particles. We show that the effects originating from the rotation can be balanced by the effects due to the oblateness of the source.

  3. Bayesian principal geodesic analysis in diffeomorphic image registration.

    PubMed

    Zhang, Miaomiao; Fletcher, P Thomas

    2014-01-01

    Computing a concise representation of the anatomical variability found in large sets of images is an important first step in many statistical shape analyses. In this paper, we present a generative Bayesian approach for automatic dimensionality reduction of shape variability represented through diffeomorphic mappings. To achieve this, we develop a latent variable model for principal geodesic analysis (PGA) that provides a probabilistic framework for factor analysis on diffeomorphisms. Our key contribution is a Bayesian inference procedure for model parameter estimation and simultaneous detection of the effective dimensionality of the latent space. We evaluate our proposed model for atlas and principal geodesic estimation on the OASIS brain database of magnetic resonance images. We show that the automatically selected latent dimensions from our model are able to reconstruct unseen brain images with lower error than equivalent linear principal components analysis (LPCA) models in the image space, and it also outperforms tangent space PCA (TPCA) models in the diffeomorphism setting.

  4. Newtonian potential and geodesic completeness in infinite derivative gravity

    NASA Astrophysics Data System (ADS)

    Edholm, James; Conroy, Aindriú

    2017-08-01

    Recent study has shown that a nonsingular oscillating potential—a feature of infinite derivative gravity theories—matches current experimental data better than the standard General Relativity potential. In this work, we show that this nonsingular oscillating potential can be given by a wider class of theories which allows the defocusing of null rays and therefore geodesic completeness. We consolidate the conditions whereby null geodesic congruences may be made past complete, via the Raychaudhuri equation, with the requirement of a nonsingular Newtonian potential in an infinite derivative gravity theory. In doing so, we examine a class of Newtonian potentials characterized by an additional degree of freedom in the scalar propagator, which returns the familiar potential of General Relativity at large distances.

  5. Time travel in transformation optics: Metamaterials with closed null geodesics

    NASA Astrophysics Data System (ADS)

    Boston, S. Reece

    2015-06-01

    We apply the methods of transformation optics to theoretical descriptions of spacetimes that support closed null geodesic curves. The metric used is based on frame dragging spacetimes, such as the van Stockum dust or the Kerr black hole. Through transformation optics, this metric is analogous to a material that in theory should allow for communication between past and future. Presented herein is a derivation and description of the spacetime and the resulting permeability, permittivity, and magnetoelectric couplings that a material would need in order for light in the material to follow closed null geodesics. We also address the paradoxical implications of such a material and demonstrate why such a material would not actually result in a violation of causality. A full derivation of the Plebanski equations is also included.

  6. All stationary vacuum solutions with geodesic shearfree eigenrays.

    NASA Astrophysics Data System (ADS)

    Horvath, I.; Lukacs, B.; Szello, L.

    1997-12-01

    The Kerr solution, which is the general vacuum black hole solution in general relativity, belongs to the class of geodesic shearfree eigenrays, but it is somehow isolated within the class. For better orientation in future Kerr generalisation one would like to map completely the σ = κ = 0 class. Therefore in this paper the authors methodically look for all possible subclasses of solutions in the said class, and explicitly treat their connections with each other.

  7. Approximate analytical calculations of photon geodesics in the Schwarzschild metric

    NASA Astrophysics Data System (ADS)

    De Falco, Vittorio; Falanga, Maurizio; Stella, Luigi

    2016-10-01

    We develop a method for deriving approximate analytical formulae to integrate photon geodesics in a Schwarzschild spacetime. Based on this, we derive the approximate equations for light bending and propagation delay that have been introduced empirically. We then derive for the first time an approximate analytical equation for the solid angle. We discuss the accuracy and range of applicability of the new equations and present a few simple applications of them to known astrophysical problems.

  8. A Few Endpoint Geodesic Restriction Estimates for Eigenfunctions

    NASA Astrophysics Data System (ADS)

    Chen, Xuehua; Sogge, Christopher D.

    2014-07-01

    We prove a couple of new endpoint geodesic restriction estimates for eigenfunctions. In the case of general 3-dimensional compact manifolds, after a TT* argument, simply by using the L 2-boundedness of the Hilbert transform on , we are able to improve the corresponding L 2-restriction bounds of Burq, Gérard and Tzvetkov (Duke Math J 138:445-486, 2007) and Hu (Forum Math 6:1021-1052, 2009). Also, in the case of 2-dimensional compact manifolds with nonpositive curvature, we obtain improved L 4-estimates for restrictions to geodesics, which, by Hölder's inequality and interpolation, implies improved L p -bounds for all exponents p ≥ 2. We do this by using oscillatory integral theorems of Hörmander (Ark Mat 11:1-11, 1973), Greenleaf and Seeger (J Reine Angew Math 455:35-56, 1994) and Phong and Stein (Int Math Res Notices 4:49-60, 1991), along with a simple geometric lemma (Lemma 3.2) about properties of the mixed-Hessian of the Riemannian distance function restricted to pairs of geodesics in Riemannian surfaces. We are also able to get further improvements beyond our new results in three dimensions under the assumption of constant nonpositive curvature by exploiting the fact that, in this case, there are many totally geodesic submanifolds.

  9. Geodesic completeness in a wormhole spacetime with horizons

    NASA Astrophysics Data System (ADS)

    Olmo, Gonzalo J.; Rubiera-Garcia, D.; Sanchez-Puente, A.

    2015-08-01

    The geometry of a spacetime containing a wormhole generated by a spherically symmetric electric field is investigated in detail. These solutions arise in high-energy extensions of general relativity formulated within the Palatini approach and coupled to Maxwell electrodynamics. Even though curvature divergences generically arise at the wormhole throat, we find that these spacetimes are geodesically complete. This provides an explicit example where curvature divergences do not imply spacetime singularities.

  10. Bayesian principal geodesic analysis for estimating intrinsic diffeomorphic image variability.

    PubMed

    Zhang, Miaomiao; Fletcher, P Thomas

    2015-10-01

    In this paper, we present a generative Bayesian approach for estimating the low-dimensional latent space of diffeomorphic shape variability in a population of images. We develop a latent variable model for principal geodesic analysis (PGA) that provides a probabilistic framework for factor analysis in the space of diffeomorphisms. A sparsity prior in the model results in automatic selection of the number of relevant dimensions by driving unnecessary principal geodesics to zero. To infer model parameters, including the image atlas, principal geodesic deformations, and the effective dimensionality, we introduce an expectation maximization (EM) algorithm. We evaluate our proposed model on 2D synthetic data and the 3D OASIS brain database of magnetic resonance images, and show that the automatically selected latent dimensions from our model are able to reconstruct unobserved testing images with lower error than both linear principal component analysis (LPCA) in the image space and tangent space principal component analysis (TPCA) in the diffeomorphism space. Copyright © 2015 Elsevier B.V. All rights reserved.

  11. Adaptive geodesic transform for segmentation of vertebrae on CT images

    NASA Astrophysics Data System (ADS)

    Gaonkar, Bilwaj; Shu, Liao; Hermosillo, Gerardo; Zhan, Yiqiang

    2014-03-01

    Vertebral segmentation is a critical first step in any quantitative evaluation of vertebral pathology using CT images. This is especially challenging because bone marrow tissue has the same intensity profile as the muscle surrounding the bone. Thus simple methods such as thresholding or adaptive k-means fail to accurately segment vertebrae. While several other algorithms such as level sets may be used for segmentation any algorithm that is clinically deployable has to work in under a few seconds. To address these dual challenges we present here, a new algorithm based on the geodesic distance transform that is capable of segmenting the spinal vertebrae in under one second. To achieve this we extend the theory of the geodesic distance transforms proposed in1 to incorporate high level anatomical knowledge through adaptive weighting of image gradients. Such knowledge may be provided by the user directly or may be automatically generated by another algorithm. We incorporate information 'learnt' using a previously published machine learning algorithm2 to segment the L1 to L5 vertebrae. While we present a particular application here, the adaptive geodesic transform is a generic concept which can be applied to segmentation of other organs as well.

  12. Investigation of the Coupling of Unsteady Lift to Low Order Acoustic Duct Modes in an Axial Flow Fan.

    DTIC Science & Technology

    1982-06-17

    Standing Wave Frequencies for the (0,0) and (1,0) Modes . ......... ... 57 21. Fourier Harmonics of 8-Cycle Screen versus Mean Axial Flow Velocity for...Current Work .... ............ ... 60 22. Fourier Harmonics of 9-Cycle Screen versus Mean Axial Flow Velocity for Current Work .... ............ ... 61 23... Fourier Harmonics of 10-Cycle Screen versus Mean Axial Flow Velocity for Current Work .... ............ ... 62 24. SPL versus Microphone Position with

  13. Comparison of ultrasound B-mode, strain imaging, acoustic radiation force impulse displacement and shear wave velocity imaging using real time clinical breast images

    NASA Astrophysics Data System (ADS)

    Manickam, Kavitha; Machireddy, Ramasubba Reddy; Raghavan, Bagyam

    2016-04-01

    It has been observed that many pathological process increase the elastic modulus of soft tissue compared to normal. In order to image tissue stiffness using ultrasound, a mechanical compression is applied to tissues of interest and local tissue deformation is measured. Based on the mechanical excitation, ultrasound stiffness imaging methods are classified as compression or strain imaging which is based on external compression and Acoustic Radiation Force Impulse (ARFI) imaging which is based on force generated by focused ultrasound. When ultrasound is focused on tissue, shear wave is generated in lateral direction and shear wave velocity is proportional to stiffness of tissues. The work presented in this paper investigates strain elastography and ARFI imaging in clinical cancer diagnostics using real time patient data. Ultrasound B-mode imaging, strain imaging, ARFI displacement and ARFI shear wave velocity imaging were conducted on 50 patients (31 Benign and 23 malignant categories) using Siemens S2000 machine. True modulus contrast values were calculated from the measured shear wave velocities. For ultrasound B-mode, ARFI displacement imaging and strain imaging, observed image contrast and Contrast to Noise Ratio were calculated for benign and malignant cancers. Observed contrast values were compared based on the true modulus contrast values calculated from shear wave velocity imaging. In addition to that, student unpaired t-test was conducted for all the four techniques and box plots are presented. Results show that, strain imaging is better for malignant cancers whereas ARFI imaging is superior than strain imaging and B-mode for benign lesions representations.

  14. Low frequency acoustic microscope

    DOEpatents

    Khuri-Yakub, Butrus T.

    1986-11-04

    A scanning acoustic microscope is disclosed for the detection and location of near surface flaws, inclusions or voids in a solid sample material. A focused beam of acoustic energy is directed at the sample with its focal plane at the subsurface flaw, inclusion or void location. The sample is scanned with the beam. Detected acoustic energy specularly reflected and mode converted at the surface of the sample and acoustic energy reflected by subsurface flaws, inclusions or voids at the focal plane are used for generating an interference signal which is processed and forms a signal indicative of the subsurface flaws, inclusions or voids.

  15. Amplitude modulation of quantum-ion-acoustic wavepackets in electron-positron-ion plasmas: Modulational instability, envelope modes, extreme waves

    SciTech Connect

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

    2015-02-15

    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.

  16. Mapping dynamical mechanical properties of osteonal bone by scanning acoustic microscopy in time-of-flight mode.

    PubMed

    Blouin, Stéphane; Puchegger, Stephan; Roschger, Andreas; Berzlanovich, Andrea; Fratzl, Peter; Klaushofer, Klaus; Roschger, Paul

    2014-06-01

    An important determinant of mechanical properties of bone is Young's modulus and its variation in individual osteons of cortical bone tissue. Its mechanical behavior also depends on deformation rate owing to its visco- or poroelastic properties. We developed a method to measure dynamical mechanical properties of bulk bone tissue at osteonal level based on scanning acoustic microscopy (SAM) using time-of-flight (TOF) measurements in combination with quantitative backscattered electron imaging (qBEI). SAM-TOF yields local sound velocities and qBEI corresponding material densities together providing elastic properties. Osteons (n=55) were measured in three human femoral diaphyseal ground bone sections (∼ 30 µm in thickness). In addition, subchondral bone and mineralized articular cartilage were investigated. The mean mineral contents, the mean sound velocities, and the mean elastic modulus of the osteons ranged from 20 to 26 wt%, from 3,819 to 5,260 m/s, and from 21 to 44 GPa, respectively. There was a strong positive correlation between material density and sound velocity (Pearson's r=0.701; p<0.0001) of the osteons. Sound velocities between cartilage and bone was similar, though material density was higher in cartilage (+4.46%, p<0.0001). These results demonstrate the power of SAM-TOF to estimate dynamic mechanical properties of the bone materials at the osteonal level.

  17. Acoustic metric of the compressible draining bathtub

    SciTech Connect

    Cherubini, C.; Filippi, S.

    2011-10-15

    The draining bathtub flow, a cornerstone in the theory of acoustic black holes, is here extended to the case of exact solutions for compressible nonviscous flows characterized by a polytropic equation of state. Investigating the analytical configurations obtained for selected values of the polytropic index, it is found that each of them becomes nonphysical at the so called limiting circle. By studying the null geodesics structure of the corresponding acoustic line elements, it is shown that such a geometrical locus coincides with the acoustic event horizon. This region is characterized also by an infinite value of space-time curvature, so the acoustic analogy breaks down there. Possible applications for artificial and natural vortices are finally discussed.

  18. Wavefront modulation and subwavelength diffractive acoustics with an acoustic metasurface.

    PubMed

    Xie, Yangbo; Wang, Wenqi; Chen, Huanyang; Konneker, Adam; Popa, Bogdan-Ioan; Cummer, Steven A

    2014-11-24

    Metasurfaces are a family of novel wavefront-shaping devices with planar profile and subwavelength thickness. Acoustic metasurfaces with ultralow profile yet extraordinary wave manipulating properties would be highly desirable for improving the performance of many acoustic wave-based applications. However, designing acoustic metasurfaces with similar functionality to their electromagnetic counterparts remains challenging with traditional metamaterial design approaches. Here we present a design and realization of an acoustic metasurface based on tapered labyrinthine metamaterials. The demonstrated metasurface can not only steer an acoustic beam as expected from the generalized Snell's law, but also exhibits various unique properties such as conversion from propagating wave to surface mode, extraordinary beam-steering and apparent negative refraction through higher-order diffraction. Such designer acoustic metasurfaces provide a new design methodology for acoustic signal modulation devices and may be useful for applications such as acoustic imaging, beam steering, ultrasound lens design and acoustic surface wave-based applications.

  19. Wavefront modulation and subwavelength diffractive acoustics with an acoustic metasurface

    NASA Astrophysics Data System (ADS)

    Xie, Yangbo; Wang, Wenqi; Chen, Huanyang; Konneker, Adam; Popa, Bogdan-Ioan; Cummer, Steven A.

    2014-11-01

    Metasurfaces are a family of novel wavefront-shaping devices with planar profile and subwavelength thickness. Acoustic metasurfaces with ultralow profile yet extraordinary wave manipulating properties would be highly desirable for improving the performance of many acoustic wave-based applications. However, designing acoustic metasurfaces with similar functionality to their electromagnetic counterparts remains challenging with traditional metamaterial design approaches. Here we present a design and realization of an acoustic metasurface based on tapered labyrinthine metamaterials. The demonstrated metasurface can not only steer an acoustic beam as expected from the generalized Snell’s law, but also exhibits various unique properties such as conversion from propagating wave to surface mode, extraordinary beam-steering and apparent negative refraction through higher-order diffraction. Such designer acoustic metasurfaces provide a new design methodology for acoustic signal modulation devices and may be useful for applications such as acoustic imaging, beam steering, ultrasound lens design and acoustic surface wave-based applications.

  20. Acoustic Levitation With One Transducer

    NASA Technical Reports Server (NTRS)

    Barmatz, Martin B.

    1987-01-01

    Higher resonator modes enables simplification of equipment. Experimental acoustic levitator for high-temperature containerless processing has round cylindrical levitation chamber and only one acoustic transducer. Stable levitation of solid particle or liquid drop achieved by exciting sound in chamber to higher-order resonant mode that makes potential well for levitated particle or drop at some point within chamber.

  1. Nonlinear excitation of subcritical fast ion-driven modes

    NASA Astrophysics Data System (ADS)

    Lesur, M.; Itoh, K.; Ido, T.; Itoh, S.-I.; Kosuga, Y.; Sasaki, M.; Inagaki, S.; Osakabe, M.; Ogawa, K.; Shimizu, A.; Ida, K.; the LHD experiment Group

    2016-05-01

    In collisionless plasma, it is known that linearly stable modes can be destabilized (subcritically) by the presence of structures in phase-space. The growth of such structures is a nonlinear, kinetic mechanism, which provides a channel for free-energy extraction, different from conventional inverse Landau damping. However, such nonlinear growth requires the presence of a seed structure with a relatively large threshold in amplitude. We demonstrate that, in the presence of another, linearly unstable (supercritical) mode, wave-wave coupling can provide a seed, which can lead to subcritical instability by either one of two mechanisms. Both mechanisms hinge on a collaboration between fluid nonlinearity and kinetic nonlinearity. If collisional velocity diffusion is low enough, the seed provided by the supercritical mode overcomes the threshold for nonlinear growth of phase-space structure. Then, the supercritical mode triggers the conventional subcritical instability. If collisional velocity diffusion is too large, the seed is significantly below the threshold, but can still grow by a sustained collaboration between fluid and kinetic nonlinearities. Both of these subcritical instabilities can be triggered, even when the frequency of the supercritical mode is rapidly sweeping. These results were obtained by modeling the subcritical mode kinetically, and the impact of the supercritical mode by simple wave-wave coupling equations. This model is applied to bursty onset of geodesic acoustic modes in an LHD experiment. The model recovers several key features such as relative amplitude, timescales, and phase relations. It suggests that the strongest bursts are subcritical instabilities, with sustained collaboration between fluid and kinetic nonlinearities.

  2. Experimental investigation of the radial structure of energetic particle driven modes

    NASA Astrophysics Data System (ADS)

    Horváth, L.; Papp, G.; Lauber, Ph.; Por, G.; Gude, A.; Igochine, V.; Geiger, B.; Maraschek, M.; Guimarais, L.; Nikolaeva, V.; Pokol, G. I.; the ASDEX Upgrade Team

    2016-11-01

    Alfvén eigenmodes (AEs) and energetic particle modes (EPMs) are often excited by energetic particles (EPs) in tokamak plasmas. One of the main open questions concerning EP driven instabilities is the non-linear evolution of the mode structure. The aim of the present paper is to investigate the properties of beta-induced AEs (BAEs) and EP driven geodesic acoustic modes (EGAMs) observed in the ramp-up phase of off-axis NBI heated ASDEX Upgrade (AUG) discharges. This paper focuses on the changes in the mode structure of BAEs/EGAMs during the non-linear chirping phase. Our investigation has shown that in the case of the observed down-chirping BAEs the changes in the radial structure are smaller than the uncertainty of our measurement. This behaviour is most probably the consequence of the fact that BAEs are normal modes, thus their radial structure strongly depends on the background plasma parameters rather than on the EP distribution. In the case of rapidly upward chirping EGAMs the analysis consistently shows shrinkage of the mode structure. The proposed explanation is that the resonance in the velocity space moves towards more passing particles which have narrower orbit widths.

  3. Generalized acoustic energy density.

    PubMed

    Xu, Buye; Sommerfeldt, Scott D; Leishman, Timothy W

    2011-09-01

    The properties of acoustic kinetic energy density and total energy density of sound fields in lightly damped enclosures have been explored thoroughly in the literature. Their increased spatial uniformity makes them more favorable measurement quantities for various applications than acoustic potential energy density (or squared pressure), which is most often used. In this paper, a generalized acoustic energy density (GED), will be introduced. It is defined by introducing weighting factors into the formulation of total acoustic energy density. With an additional degree of freedom, the GED can conform to the traditional acoustic energy density quantities, or it can be optimized for different applications. The properties of the GED will be explored in this paper for individual room modes, a diffuse sound field, and a sound field below the Schroeder frequency. © 2011 Acoustical Society of America

  4. Juxta-vascular nodule segmentation based on flow entropy and geodesic distance.

    PubMed

    Sun, Shenshen; Guo, Yang; Guan, Yubao; Ren, Huizhi; Fan, Linan; Kang, Yan

    2014-07-01

    Computed aided diagnosis of lung CT data is a new quantitative analysis technique to distinguish malignant nodules from benign ones. Nodule growth rate is a key indicator to discriminate between benign and malignant nodules. Accurate nodule segmentation is the essential for calculating the nodule growth rate. However, it is difficult to segment juxta-vascular nodules, due to the similar gray levels in nodule and attached blood vessels. To distinguish the nodule region from the adjacent vessel region, a flowing direction feature, referred to as the direction of the normal vector for a pixel, is introduced. Since blood is flowing in one single direction through a vessel, the normal vectors of pixels in the vessel region typically point in similar orientations while the directions of those in the nodule region can be viewed as disorganized. The entropy value of the flowing direction features in a neighboring region for a vessel pixel is smaller than that for a nodule pixel. Moreover, vessel pixels typically have a larger geodesic distance to the nodule center than nodule pixels. Based on k -means clustering method, the flow entropy, combined with the geodesic distance, is used to segment vessel attached nodules. The validation of the proposed segmentation algorithm was carried out on juxta-vascular nodules, identified in the Chinalung-CT screening trial and on Lung Image Database Consortium (LIDC) dataset. In fully automated mode, accuracies of 92.9% (26/28), 87.5%(7/8), and 94.9% (149/157) are reached for the outlining of juxta-vascular nodules in the Chinalung-CT, and the first and second datasets of LIDC, respectively. Furthermore, it is demonstrated that the proposed method has low time complexity and high accuracies.

  5. B-mode and acoustic radiation force impulse (ARFI) imaging of prostate zonal anatomy: comparison with 3T T2-weighted MR imaging.

    PubMed

    Palmeri, Mark L; Miller, Zachary A; Glass, Tyler J; Garcia-Reyes, Kirema; Gupta, Rajan T; Rosenzweig, Stephen J; Kauffman, Christopher; Polascik, Thomas J; Buck, Andrew; Kulbacki, Evan; Madden, John; Lipman, Samantha L; Rouze, Ned C; Nightingale, Kathryn R

    2015-01-01

    Prostate cancer (PCa) is the most common non-cutaneous malignancy among men in the United States and the second leading cause of cancer-related death. Multi-parametric magnetic resonance imaging (mpMRI) has gained recent popularity to characterize PCa. Acoustic Radiation Force Impulse (ARFI) imaging has the potential to aid PCa diagnosis and management by using tissue stiffness to evaluate prostate zonal anatomy and lesions. MR and B-mode/ARFI in vivo imaging datasets were compared with one another and with gross pathology measurements made immediately after radical prostatectomy. Images were manually segmented in 3D Slicer to delineate the central gland (CG) and prostate capsule, and 3D models were rendered to evaluate zonal anatomy dimensions and volumes. Both imaging modalities showed good correlation between estimated organ volume and gross pathologic weights. Ultrasound and MR total prostate volumes were well correlated (R(2) = 0.77), but B-mode images yielded prostate volumes that were larger (16.82% ± 22.45%) than MR images, due to overestimation of the lateral dimension (18.4% ± 13.9%), with less significant differences in the other dimensions (7.4% ± 17.6%, anterior-to-posterior, and -10.8% ± 13.9%, apex-to-base). ARFI and MR CG volumes were also well correlated (R(2) = 0.85). CG volume differences were attributed to ARFI underestimation of the apex-to-base axis (-28.8% ± 9.4%) and ARFI overestimation of the lateral dimension (21.5% ± 14.3%). B-mode/ARFI imaging yielded prostate volumes and dimensions that were well correlated with MR T2-weighted image (T2WI) estimates, with biases in the lateral dimension due to poor contrast caused by extraprostatic fat. B-mode combined with ARFI imaging is a promising low-cost, portable, real-time modality that can complement mpMRI for PCa diagnosis, treatment planning, and management. © The Author(s) 2014.

  6. B-Mode and Acoustic Radiation Force Impulse (ARFI) Imaging of Prostate Zonal Anatomy: Comparison with 3T T2-Weighted MR Imaging

    PubMed Central

    Palmeri, Mark L.; Miller, Zachary A.; Glass, Tyler J.; Garcia-Reyes, Kirema; Gupta, Rajan T.; Rosenzweig, Stephen J.; Kauffman, Christopher; Polascik, Thomas J.; Buck, Andrew; Kulbacki, Evan; Madden, John; Lipman, Samantha L.; Rouze, Ned C.; Nightingale, Kathryn R.

    2015-01-01

    Prostate cancer (PCa) is the most common non-cutaneous malignancy among men in the United States and the second leading cause of cancer-related death. Multi-parametric magnetic resonance imaging (mpMRI) has gained recent popularity to characterize PCa. Acoustic Radiation Force Impulse (ARFI) imaging has the potential to aid PCa diagnosis and management by using tissue stiffness to evaluate prostate zonal anatomy and lesions. MR and B-mode/ARFI in vivo imaging datasets were compared with one another and with gross pathology measurements made immediately after radical prostatectomy. Images were manually segmented in 3D Slicer to delineate the central gland (CG) and prostate capsule, and 3D models were rendered to evaluate zonal anatomy dimensions and volumes. Both imaging modalities showed good correlation between estimated organ volume and gross pathologic weights. Ultrasound and MR total prostate volumes were well correlated (R2 = 0.77), but B-mode images yielded prostate volumes that were larger (16.82% ± 22.45%) than MR images, due to overestimation of the lateral dimension (18.4% ± 13.9%), with less significant differences in the other dimensions (7.4% ± 17.6%, anterior-to-posterior, and −10.8% ± 13.9%, apex-to-base). ARFI and MR CG volumes were also well correlated (R2 = 0.85). CG volume differences were attributed to ARFI underestimation of the apex-to-base axis (−28.8% ± 9.4%) and ARFI overestimation of the lateral dimension (21.5% ± 14.3%). B-mode/ARFI imaging yielded prostate volumes and dimensions that were well correlated with MR T2-weighted image (T2WI) estimates, with biases in the lateral dimension due to poor contrast caused by extraprostatic fat. B-mode combined with ARFI imaging is a promising low-cost, portable, real-time modality that can complement mpMRI for PCa diagnosis, treatment planning, and management. PMID:25060914

  7. A three-dimensional coupled-mode model for the acoustic field in a two-dimensional waveguide with perfectly reflecting boundaries

    NASA Astrophysics Data System (ADS)

    Luo, Wen-Yu; Yu, Xiao-Lin; Yang, Xue-Feng; Zhang, Ze-Zhong; Zhang, Ren-He

    2016-12-01

    This paper presents a three-dimensional (3D) coupled-mode model using the direct-global-matrix technique as well as Fourier synthesis. This model is a full wave, two-way three-dimensional model, and is therefore capable of providing accurate acoustic field solutions. Because the problem of sound propagation excited by a point source in an ideal wedge with perfectly reflecting boundaries is one of a few three-dimensional problems with analytical solutions, the ideal wedge problem is chosen in this work to validate the presented three-dimensional model. Numerical results show that the field results by analytical solutions and those by the presented model are in excellent agreement, indicating that the presented model can serve as a benchmark model for three-dimensional sound propagation problems involving a planar two-dimensional geometry as well as a point source. Project supported by the National Natural Science Foundation of China (Grant Nos. 11125420, 11434012, and 41561144006) and the Knowledge Innovation Program of the Chinese Academy of Sciences.

  8. Particle surface area dependence of mineral dust in immersion freezing mode: investigations with freely suspended drops in an acoustic levitator and a vertical wind tunnel

    NASA Astrophysics Data System (ADS)

    Diehl, K.; Debertshäuser, M.; Eppers, O.; Schmithüsen, H.; Mitra, S. K.; Borrmann, S.

    2014-11-01

    The heterogeneous freezing temperatures of supercooled drops were measured using an acoustic levitator. This technique allows one to freely suspend single drops in the air without any wall contact. Heterogeneous nucleation by two types of illite (illite IMt1 and illite NX) and a montmorillonite sample was investigated in the immersion mode. Drops of 1 mm in radius were monitored by a video camera while cooled down to -28 °C to simulate freezing within the tropospheric temperature range. The surface temperature of the drops was contact-free, determined with an infrared thermometer; the onset of freezing was indicated by a sudden increase of the drop surface temperature. For comparison, measurements with one particle type (illite NX) were additionally performed in the Mainz vertical wind tunnel with drops of 340 μm radius freely suspended. Immersion freezing was observed in a temperature range between -13 and -26 °C as a function of particle type and particle surface area immersed in the drops. Isothermal experiments in the wind tunnel indicated that after the cooling stage freezing still proceeds, at least during the investigated time period of 30 s. The results were evaluated by applying two descriptions of heterogeneous freezing, the stochastic and the singular model. Although the wind tunnel results do not support the time-independence of the freezing process both models are applicable for comparing the results from the two experimental techniques.

  9. On the failure mode in dry and hygrothermally aged short fiber-reinforced injection-molded polyarylamide composites by acoustic emission

    NASA Astrophysics Data System (ADS)

    Czigány, T.; Mohd Ishak, Z. A.; Karger-Kocsis, J.

    1995-09-01

    The failure mode in injection-molded short glass (GF) and carbon fiber (CF) reinforced polyarylamide (PAR) composites was studied on compact tension (CT) specimens in as-received (AR), hygrothermally aged (HA) and re-dried (RD) states, respectively, using acoustic emission (AE) and fractography. A significant difference was revealed in the failure manner characterized by the cumulative run, amplitude and energy distribution of the AE events as a function of the water content of the composites. Furthermore, a correlation was found between the cumulative AE events up to the maximum load and the fracture toughness of the composites. It was shown that the fracture response and thus the failure behavior of the water-saturated PAR composites can be restored by drying. This fact indicates that the water absorption and desorption are of a purely physical nature, i.e. they are reversible processes. It was established that chopped fiber-reinforced PAR composites fail by matrix deformation along with fiber/matrix debonding in the crack initiation, whereas fiber pull-out becomes dominant in the crack propagation range. Water uptake shifts both the AE amplitude and energy curves toward lower values, a phenomenon attributed to plastification of the PAR matrix by water.

  10. Polytropic spheres containing regions of trapped null geodesics

    NASA Astrophysics Data System (ADS)

    Novotný, Jan; Hladík, Jan; Stuchlík, Zdeněk

    2017-02-01

    We demonstrate that in the framework of standard general relativity, polytropic spheres with properly fixed polytropic index n and relativistic parameter σ , giving a ratio of the central pressure pc to the central energy density ρc , can contain a region of trapped null geodesics. Such trapping polytropes can exist for n >2.138 , and they are generally much more extended and massive than the observed neutron stars. We show that in the n - σ parameter space, the region of allowed trapping increases with the polytropic index for intervals of physical interest, 2.138 geodesics increases with both increasing n and σ >0.677 from the allowed region. In order to relate the trapping phenomenon to astrophysically relevant situations, we restrict the validity of the polytropic configurations to their extension rextr corresponding to the gravitational mass M ˜2 M⊙ of the most massive observed neutron stars. Then, for the central density ρc˜1 015 g cm-3 , the trapped regions are outside rextr for all values of 2.138 geodesics is located close to the polytrope center and could have a relevant influence on the cooling of such polytropes or binding of gravitational waves in their interior.

  11. Simulation of Alfvén frequency cascade modes in reversed shear-discharges using a Landau-closure model

    NASA Astrophysics Data System (ADS)

    Spong, D. A.

    2013-05-01

    The dynamics of energetic particle destabilized Alfvén frequency sweeping modes in tokamak reversed-shear safety factor discharges are modelled using a new Landau-closure model that includes coupling to geodesic acoustic wave dynamics and closure relations optimized for energetic particle-Alfvén mode resonances. Profiles and equilibria are based upon reconstructions of a DIII-D discharge (#142111) in which a long sequence of frequency sweeping modes were observed. This model (TAEFL) has recently been included in a verification and validation study of n = 3 frequency sweeping modes for this case along with two gyrokinetic codes, GTC and GYRO. This paper provides a more detailed documentation of the equations and methods used in the TAEFL model and extends the earlier calculation to a range of toroidal mode numbers: n = 2 to 6. By considering a range of toroidal mode numbers and scanning over a range of safety factor profiles with varying qmin, both up-sweeping frequency (reversed-shear Alfvén eigenmode) and down-sweeping frequency (toriodal Alfvén eigenmode) modes are present in the results and show qualitative similarity with the frequency variations observed in the experimental spectrograms.

  12. Simulation of Alfv n frequency cascade modes in reversed shear discharges using a Landau-closure model

    SciTech Connect

    Spong, Donald A

    2013-01-01

    The dynamics of energetic particle destabilized Alfve n frequency sweeping modes in tokamak reversed-shear safety factor discharges are modelled using a new Landau-closure model that includes coupling to geodesic acoustic wave dynamics and closure relations optimized for energetic particle Alfve n mode resonances. Profiles and equilibria are based upon reconstructions of a DIII-D discharge (#142111) in which a long sequence of frequency sweeping modes were observed. This model (TAEFL) has recently been included in a verification and validation study of n = 3 frequency sweeping modes for this case along with two gyrokinetic codes, GTC and GYRO. This paper provides a more detailed documentation of the equations and methods used in the TAEFL model and extends the earlier calculation to a range of toroidal mode numbers: n = 2 to 6. By considering a range of toroidal mode numbers and scanning over a range of safety factor profiles with varying qmin, both up-sweeping frequency (reversed-shear Alfve n eigenmode) and down-sweeping frequency (toriodal Alfve n eigenmode) modes are present in the results and show qualitative similarity with the frequency variations observed in the experimental spectrograms.

  13. Diffeomorphic registration using geodesic shooting and Gauss–Newton optimisation

    PubMed Central

    Ashburner, John; Friston, Karl J.

    2011-01-01

    This paper presents a nonlinear image registration algorithm based on the setting of Large Deformation Diffeomorphic Metric Mapping (LDDMM), but with a more efficient optimisation scheme — both in terms of memory required and the number of iterations required to reach convergence. Rather than perform a variational optimisation on a series of velocity fields, the algorithm is formulated to use a geodesic shooting procedure, so that only an initial velocity is estimated. A Gauss–Newton optimisation strategy is used to achieve faster convergence. The algorithm was evaluated using freely available manually labelled datasets, and found to compare favourably with other inter-subject registration algorithms evaluated using the same data. PMID:21216294

  14. Geodesic Motion in General Relativity:. Lares in Earth's Gravity

    NASA Astrophysics Data System (ADS)

    Ciufolini, I.; Gurzadyan, V. G.; Penrose, R.; Paolozzi, A.

    2013-11-01

    According to General Relativity, as distinct from Newtonian gravity, motion under gravity is treated by a theory that deals, initially, only with test particles. At the same time, satellite measurements deal with extended bodies. We discuss the correspondence between geodesic motion in General Relativity and the motion of an extended body by means of the Ehlers-Geroch theorem, and in the context of the recently launched LAser RElativity Satellite (LARES). Being possibly the highest mean density orbiting body in the Solar system, this satellite provides the best realization of a test particle ever reached experimentally and provides a unique possibility for testing the predictions of General Relativity.

  15. Time adaptive variational integrators: A space-time geodesic approach

    NASA Astrophysics Data System (ADS)

    Nair, Sujit

    2012-02-01

    The goal of this paper is to show that the space-time geodesic approach of classical mechanics can be used to generate a time adaptive variational integration scheme. The only assumption we make is that the Lagrangian for the system is in a separable form. The geometric structure which is preserved in the integration scheme is made explicit and the algorithm is illustrated with simulation for a compact case, a non-compact case, a chaotic system which arises as a perturbation of an integrable system and the figure eight solution for a three body problem.

  16. Analyzing the radial geodesics of the Campanelli-Lousto solutions

    NASA Astrophysics Data System (ADS)

    Formiga, J. B.

    2015-12-01

    When dealing with a spacetime, one usually searches for singularities, black holes, white holes and wormholes due to their importance to the motion of particles. There is a family of solution of the Brans-Dicke vacuum equations that has not been fully studied from this perspective. In this paper, I study some properties of this family and find the complete set of solutions that avoids singularity at the point where the metric diverges or degenerates. The possible changes in the metric signature when passing through this point is analyzed. In addition, I also study the radial geodesics and obtain the solutions of some particular cases.

  17. On geodesics of the rotation group SO(3)

    NASA Astrophysics Data System (ADS)

    Novelia, Alyssa; O'Reilly, Oliver M.

    2015-11-01

    Geodesics on SO(3) are characterized by constant angular velocity motions and as great circles on a three-sphere. The former interpretation is widely used in optometry and the latter features in the interpolation of rotations in computer graphics. The simplicity of these two disparate interpretations belies the complexity of the corresponding rotations. Using a quaternion representation for a rotation, we present a simple proof of the equivalence of the aforementioned characterizations and a straightforward method to establish features of the corresponding rotations.

  18. Curbing-The Metallic Mode In-between: An empirical study qualifying and categorizing restrained sounds known as Curbing based on audio perception, laryngostroboscopic imaging, acoustics, LTAS, and EGG.

    PubMed

    Thuesen, Mathias Aaen; McGlashan, Julian; Sadolin, Cathrine

    2017-09-01

    This study aims to study the categorization Curbing from the pedagogical method Complete Vocal Technique as a reduced metallic mode compared with the full metallic modes Overdrive and Edge by means of audio perception, laryngostroboscopic imaging, acoustics, long-term average spectrum (LTAS), and electroglottography (EGG). Twenty singers were recorded singing sustained vowels in a restrained character known as Curbing. Two studies were performed: (1) laryngostroboscopic examination using a videonasoendoscopic camera system and the Laryngostrobe program; and (2) simultaneous recording of EGG and acoustic signals using Speech Studio. Images were analyzed based on consensus agreement. Statistical analysis of acoustic, LTAS, and EGG parameters was undertaken using Student paired t tests. The reduced metallic singing mode Curbing has an identifiable laryngeal gesture. Curbing has a more open setting than Overdrive and Edge, with high visibility of the vocal folds, and the false folds giving a rectangular appearance. LTAS showed statistically significant differences between Curbing and the full metallic modes, with less energy across all spectra, yielding a high second and a low third harmonic. Statistically significant differences were identified on Max Qx, Average Qx, Shimmer+, Shimmer-, Shimmer dB, normalized noise energy, cepstral peak prominence, harmonics-to-noise ratio, and mean sound pressure level (P ≤ 0.05). Curbing as a voice production strategy is statistically significantly different from Overdrive and Edge, and can be categorized based on audio perception. This study demonstrates consistently different laryngeal gestures between Curbing and Overdrive and Edge, with high corresponding differences in LTAS, EGG and acoustic measures. Copyright © 2017 The Voice Foundation. Published by Elsevier Inc. All rights reserved.

  19. Unruh-DeWitt detector response along static and circular-geodesic trajectories for Schwarzschild-anti-de Sitter black holes

    NASA Astrophysics Data System (ADS)

    Ng, Keith K.; Hodgkinson, Lee; Louko, Jorma; Mann, Robert B.; Martín-Martínez, Eduardo

    2014-09-01

    We present novel methods to numerically address the problem of characterizing the response of particle detectors in curved spacetimes. These methods allow for the integration of the Wightman function, at least in principle, in rather general backgrounds. In particular we will use this tool to further understand the nature of conformal massless scalar Hawking radiation from a Schwarzschild black hole in anti-de Sitter space. We do that by studying an Unruh-DeWitt detector at rest above the horizon and in circular-geodesic orbit. The method allows us to see that the response rate shows peaks at certain characteristic frequencies, which correspond to the quasinormal modes of the spacetime. It is in principle possible to apply these techniques to more complicated and interesting physical scenarios, e.g., geodesic infall or multiple detector entanglement evolution, or the study of the behavior of quantum correlations in spacetimes with black hole horizons.

  20. Dome, Sweet Dome--Geodesic Structures Teach Math, Science, and Technology Principles

    ERIC Educational Resources Information Center

    Shackelford, Ray; Fitzgerald, Michael

    2007-01-01

    Today, geodesic domes are found on playgrounds, homes, over radar installations, storage facilities, at Disney's Epcot Center, and at World's Fairs. The inventor of the design, Buckminster Fuller, thought that geodesic domes could be used to cover large areas and even designed one to cover all of New York's Manhattan Island. This article details…

  1. Dome, Sweet Dome--Geodesic Structures Teach Math, Science, and Technology Principles

    ERIC Educational Resources Information Center

    Shackelford, Ray; Fitzgerald, Michael

    2007-01-01

    Today, geodesic domes are found on playgrounds, homes, over radar installations, storage facilities, at Disney's Epcot Center, and at World's Fairs. The inventor of the design, Buckminster Fuller, thought that geodesic domes could be used to cover large areas and even designed one to cover all of New York's Manhattan Island. This article details…

  2. Measurement and analysis of the electromagnetic scattering of a geodesic array of triangular trihedral corner reflectors

    NASA Astrophysics Data System (ADS)

    Hamilton, Richard E.

    1990-03-01

    This thesis investigated the EM scattering of a geodesic array consisting of a cluster of 20 trihedral corner reflectors held together by hinges. This target was designed to provide a large radar return with a spatial coverage greater than that due to an array of 8 corner reflectors. RCS, or echo area, was chosen as a means of investigating the EM scattering of a scaled model version of geodesic array. The RCS of the individual components of the geodesic array (i.e., the single corner reflectors) and the RCS of the geodesic array were measured using a continuous wave measurement technique. For the purpose of comparison, the RCS of an 8 corner reflector array was also measured. In order to gather as much spatial scattering information as possible, a unique target support mount was designed, constructed, and used to collect conical cut RCS patterns. Measured RCS patterns of the targets are included in the appendixes. A comparative analysis between the measured RCS of the geodesic array and that of the 8 corner reflector array was performed to determine how well the geodesic array met its designed goal. It was found that in almost all cases, the measured spatial RCS coverage for the geodesic array was equal to or better than the measured spatial RCS coverage of the array of 8 corner reflectors. The only exception was for broadside incidence for which the geodesic array spatial coverage was slightly less.

  3. Mechanical and spatial determinants of cytoskeletal geodesic dome formation in cardiac fibroblasts

    PubMed Central

    Bien, Harold

    2015-01-01

    This study tests the hypothesis that the cell cytoskeletal (CSK) network can rearrange from geodesic dome type structures to stress fibers in response to microenvironmental cues. The CSK geodesic domes are highly organized actin microarchitectures within the cell, consisting of ordered polygonal elements. We studied primary neonatal rat cardiac fibroblasts. The cues used to trigger the interconversion between the two CSK architectures (geodesic domes and stress fibers) included factors affecting spatial order and the degree of CSK tension in the cells. Microfabricated three-dimensional substrates with micrometre sized grooves and peaks were used to alter the spatial order of cell growth in culture. CSK tension was modified by 2,3-butanedione 2-monoxime (BDM), cytochalasin D and the hyphae of Candida albicans. CSK geodesic domes occurred spontaneously in about 20% of the neonatal rat cardiac fibroblasts used in this study. Microfabricated structured surfaces produced anisotropy in the cell CSK and effectively converted geodesic domes into stress fibers in a dose-dependent manner (dependence on the period of the features). Affectors of actin structure, inhibitors of CSK tension and cell motility, e.g. BDM, cytochalasin D and the hyphae of C. albicans, suppressed or eliminated the geodesic domes. Our data suggest that the geodesic domes, similar to actin stress fibers, require maintenance of CSK integrity and tension. However, microenvironments that promote structural anisotropy in tensed cells cause the transformation of the geodesic domes into stress fibers, consistent with topographic cell guidance and some previous CSK model predictions. PMID:20023805

  4. Geodesics in the sub-Riemannian problem on the group SO(3)

    NASA Astrophysics Data System (ADS)

    Beschatnyi, I. Yu; Sachkov, Yu L.

    2016-07-01

    Geodesics of left-invariant sub-Riemannian structures are considered on the group SO(3). A complete description of periodic geodesics, their elementary properties, certain necessary conditions for minimality and estimates for the cut time and the diameter of the metric are presented. Bibliography: 32 titles.

  5. Axisymmetric oscillations at L-H transitions in JET: M-mode

    NASA Astrophysics Data System (ADS)

    Solano, Emilia R.; Vianello, N.; Delabie, E.; Hillesheim, J. C.; Buratti, P.; Réfy, D.; Balboa, I.; Boboc, A.; Coelho, R.; Sieglin, B.; Silburn, S.; Drewelow, P.; Devaux, S.; Dodt, D.; Figueiredo, A.; Frassinetti, L.; Marsen, S.; Meneses, L.; Maggi, C. F.; Morris, J.; Gerasimov, S.; Baruzzo, M.; Stamp, M.; Grist, D.; Nunes, I.; Rimini, F.; Schmuck, S.; Lupelli, I.; Silva, C.; contributors, JET

    2017-02-01

    L to H transition studies at JET have revealed an n  =  0, m  =  1 magnetic oscillation starting immediately at the L to H transition (called M-mode for brevity). While the magnetic oscillation is present a weak ELM-less H-mode regime is obtained, with a clear increase of density and a weak electron temperature pedestal. It is an intermediate state between L and H-mode. In ICRH heated plasmas or low density NBI plasmas the magnetic mode and the pedestal can remain steady (with small oscillations) for the duration of the heating phase, of order 10 s or more. The axisymmetric magnetic oscillation has period ~0.5-2 ms, and poloidal mode number m  =  1: it looks like a pedestal localised up/down oscillation, although it is clearly a natural oscillation of the plasma, not driven by the position control system. Electron cyclotron emission, interferometry, reflectometry and fast Li beam measurements locate the mode in the pedestal region. D α , fast infrared camera and Langmuir probe measurements show that the mode modulates heat and particle fluxes to the target. The mode frequency appears to scale with the poloidal Alfvén velocity, and not with sound speed (i.e. it is not a geodesic acoustic mode). A heuristic model is proposed for the frequency scaling of the mode. We discuss the relationship between the M-mode and other related observations near the L-H transition.

  6. Behavior of causal geodesics on a Kerr-de Sitter spacetime

    NASA Astrophysics Data System (ADS)

    Salazar, J. Felix; Zannias, Thomas

    2017-07-01

    We analyze the behavior of causal geodesics on a Kerr-de Sitter spacetime with particular emphasis on their completeness property. We set up an initial value problem of which the solutions lead to a global understanding of causal geodesics on these spacetimes. Causal geodesics that avoid the rotation axis are complete except the ones that hit the ringlike curvature singularity and those that encounter the ring singularity are necessary equatorial ones. We also show the existence of geodesics that cross or lie on the rotation axis. The equations governing the latter family show the repulsive nature of the ring singularity. The results of this work show that, as far as properties of causal geodesics are concerned, Kerr-de Sitter spacetimes behave in a similar manner as the family of Kerr spacetimes.

  7. Optimal design of geodesically stiffened composite cylindrical shells

    NASA Technical Reports Server (NTRS)

    Gendron, G.; Guerdal, Z.

    1992-01-01

    An optimization system based on the finite element code Computations Structural Mechanics (CSM) Testbed and the optimization program, Automated Design Synthesis (ADS), is described. The optimization system can be used to obtain minimum-weight designs of composite stiffened structures. Ply thickness, ply orientations, and stiffener heights can be used as design variables. Buckling, displacement, and material failure constraints can be imposed on the design. The system is used to conduct a design study of geodesically stiffened shells. For comparison purposes, optimal designs of unstiffened shells and shells stiffened by rings and stingers are also obtained. Trends in the design of geodesically stiffened shells are identified. An approach to include local stress concentrations during the design optimization process is then presented. The method is based on a global/local analysis technique. It employs spline interpolation functions to determine displacements and rotations from a global model which are used as 'boundary conditions' for the local model. The organization of the strategy in the context of an optimization process is described. The method is validated with an example.

  8. Robust Diffeomorphic Mapping via Geodesically Controlled Active Shapes

    PubMed Central

    Tward, Daniel J.; Ma, Jun; Miller, Michael I.; Younes, Laurent

    2013-01-01

    This paper presents recent advances in the use of diffeomorphic active shapes which incorporate the conservation laws of large deformation diffeomorphic metric mapping. The equations of evolution satisfying the conservation law are geodesics under the diffeomorphism metric and therefore termed geodesically controlled diffeomorphic active shapes (GDAS). Our principal application in this paper is on robust diffeomorphic mapping methods based on parameterized surface representations of subcortical template structures. Our parametrization of the GDAS evolution is via the initial momentum representation in the tangent space of the template surface. The dimension of this representation is constrained using principal component analysis generated from training samples. In this work, we seek to use template surfaces to generate segmentations of the hippocampus with three data attachment terms: surface matching, landmark matching, and inside-outside modeling from grayscale T1 MR imaging data. This is formulated as an energy minimization problem, where energy describes shape variability and data attachment accuracy, and we derive a variational solution. A gradient descent strategy is employed in the numerical optimization. For the landmark matching case, we demonstrate the robustness of this algorithm as applied to the workflow of a large neuroanatomical study by comparing to an existing diffeomorphic landmark matching algorithm. PMID:23690757

  9. Robust Diffeomorphic Mapping via Geodesically Controlled Active Shapes.

    PubMed

    Tward, Daniel J; Ma, Jun; Miller, Michael I; Younes, Laurent

    2013-01-01

    This paper presents recent advances in the use of diffeomorphic active shapes which incorporate the conservation laws of large deformation diffeomorphic metric mapping. The equations of evolution satisfying the conservation law are geodesics under the diffeomorphism metric and therefore termed geodesically controlled diffeomorphic active shapes (GDAS). Our principal application in this paper is on robust diffeomorphic mapping methods based on parameterized surface representations of subcortical template structures. Our parametrization of the GDAS evolution is via the initial momentum representation in the tangent space of the template surface. The dimension of this representation is constrained using principal component analysis generated from training samples. In this work, we seek to use template surfaces to generate segmentations of the hippocampus with three data attachment terms: surface matching, landmark matching, and inside-outside modeling from grayscale T1 MR imaging data. This is formulated as an energy minimization problem, where energy describes shape variability and data attachment accuracy, and we derive a variational solution. A gradient descent strategy is employed in the numerical optimization. For the landmark matching case, we demonstrate the robustness of this algorithm as applied to the workflow of a large neuroanatomical study by comparing to an existing diffeomorphic landmark matching algorithm.

  10. Geodesic invariant feature: a local descriptor in depth.

    PubMed

    Liu, Yazhou; Lasang, Pongsak; Siegel, Mel; Sun, Quansen

    2015-01-01

    Different from the photometric images, depth images resolve the distance ambiguity of the scene, while the properties, such as weak texture, high noise, and low resolution, may limit the representation ability of the well-developed descriptors, which are elaborately designed for the photometric images. In this paper, a novel depth descriptor, geodesic invariant feature (GIF), is presented for representing the parts of the articulate objects in depth images. GIF is a multilevel feature representation framework, which is proposed based on the nature of depth images. Low-level, geodesic gradient is introduced to obtain the invariance to the articulate motion, such as scale and rotation variation. Midlevel, superpixel clustering is applied to reduce depth image redundancy, resulting in faster processing speed and better robustness to noise. High-level, deep network is used to exploit the nonlinearity of the data, which further improves the classification accuracy. The proposed descriptor is capable of encoding the local structures in the depth data effectively and efficiently. Comparisons with the state-of-the-art methods reveal the superiority of the proposed method.

  11. Gravitational Self-Force: Orbital Mechanics Beyond Geodesic Motion

    NASA Astrophysics Data System (ADS)

    Barack, Leor

    The question of motion in a gravitationally bound two-body system is a longstanding open problem of General Relativity. When the mass ratio η is small, the problem lends itself to a perturbative treatment, wherein corrections to the geodesic motion of the smaller object (due to radiation reaction, internal structure, etc.) are accounted for order by order in η, using the language of an effective gravitational self-force. The prospect for observing gravitational waves from compact objects inspiralling into massive black holes in the foreseeable future has in the past 15 years motivated a program to obtain a rigorous formulation of the self-force and compute it for astrophysically interesting systems. I will give a brief survey of this activity and its achievements so far, and will identify the challenges that lie ahead. As concrete examples, I will discuss recent calculations of certain conservative post-geodesic effects of the self-force, including the O(η ) correction to the precession rate of the periastron. I will highlight the way in which such calculations allow us to make a fruitful contact with other approaches to the two-body problem.

  12. Spectral segmentation via midlevel cues integrating geodesic and intensity.

    PubMed

    Lu, Huchuan; Zhang, Ruixuan; Li, Shifeng; Li, Xuelong

    2013-12-01

    Image segmentation still remains as a challenge in image processing and pattern recognition when involving complex natural scenes. In this paper, we present a new affinity model for spectral segmentation based on midlevel cues. In contrast to most existing methods that operate directly on low-level cues, we first oversegment the image into superpixel images and then integrate the geodesic line edge and intensity cue to form the similarity matrix W so that it more accurately describes the similarity between data. The geodesic line edge could avoid strong boundary and represent the true boundary between two superpixels while the mean red green blue vector could describe the intensity of superpixels better. As far as we know, this is a totally new kind of affinity model to represent superpixels. Based on this model, we use the spectral clustering in the superpixel level and then achieve the image segmentation in the pixel level. The experimental results show that the proposed method performs steadily and well on various natural images. The evaluation comparisons also prove that our method achieves comparable accuracy and significantly performs better than most state-of-the-art algorithms.

  13. Acoustic confinement in superlattice cavities

    NASA Astrophysics Data System (ADS)

    Garcia-Sanchez, Daniel; Déleglise, Samuel; Thomas, Jean-Louis; Atkinson, Paola; Lagoin, Camille; Perrin, Bernard

    2016-09-01

    The large coupling rate between the acoustic and optical fields confined in GaAs/AlAs superlattice cavities makes them appealing systems for cavity optomechanics. We have developed a mathematical model based on the scattering matrix that allows the acoustic guided modes to be predicted in nano and micropillar superlattice cavities. We demonstrate here that the reflection at the surface boundary considerably modifies the acoustic quality factor and leads to significant confinement at the micropillar center. Our mathematical model also predicts unprecedented acoustic Fano resonances on nanopillars featuring small mode volumes and very high mechanical quality factors, making them attractive systems for optomechanical applications.

  14. Acoustic Neuroma

    MedlinePlus

    ... search IRSA's site Unique Hits since January 2003 Acoustic Neuroma Click Here for Acoustic Neuroma Practice Guideline ... to microsurgery. One doctor's story of having an acoustic neuroma In August 1991, Dr. Thomas F. Morgan ...

  15. Gyrokinetic δ particle simulation of trapped electron mode driven turbulence

    NASA Astrophysics Data System (ADS)

    Lang, Jianying

    2007-11-01

    Turbulent transport driven by collisionless trapped electron modes (CTEM) is systematically studied using gyrokinetic delta-f particle-in-cell simulation. Scaling with local plasma parameters, including density gradient, electron temperature gradient, magnetic shear, temperature ratio and aspect ratio, is investigated. Simulation results are compared with previous simulations and theoretical predictions. Nonlinearly the transport level increases with increasing magnetic shear. We explain the nonlinear magnetic shear scaling by differences in the radial correlation lengths caused by toroidal coupling. The turbulence is more radially elongated at higher magnetic shear compared with low magnetic shear. We show that the suppression effect of zonal flow on CTEM transport depends on both the electron temperature gradient and the electron to ion temperature ratio. This helps explain the previous contradictory conclusions on the importance of zonal flows in different parameter regimes.ootnotetextT. Dannert, F. Jenko, Phys. Plasmas 12, 072309 (2005); D. Ernst, et al., Phys. Plasmas 11, 2637 (2004). Zonal flow suppression is consistent with the rate of EXB shearing from the ambient turbulence as well as the radial broadening of the spectra. Strong geodesic acoustic modes (GAMs) are generated along with zonal flows and the frequency of the GAMs agrees well with kinetic theory.ootnotetextT. Watari, et al., Phys. Plasmas 13, 062504 (2006). We further explore the nonlinear saturation mechanism when the zonal flows are not important. We find that when only a single toroidal mode (and its conjugate) is kept, reasonable nonlinear saturation is obtained. Investigating a range of n, modes with larger mode number n saturate at a higher level relative to lower n modes, indicating a turbulent inverse cascade process.

  16. Levitation With a Single Acoustic Driver

    NASA Technical Reports Server (NTRS)

    Barmatz, M. B.; Gaspar, M. S.; Allen, J. L.

    1986-01-01

    Pair of reports describes acoustic-levitation systems in which only one acoustic resonance mode excited, and only one driver needed. Systems employ levitation chambers of rectangular and cylindrical geometries. Reports first describe single mode concept and indicate which modes used to levitate sample without rotation. Reports then describe systems in which controlled rotation of sample introduced.

  17. Off-Resonance Acoustic Levitation Without Rotation

    NASA Technical Reports Server (NTRS)

    Barmatz, M. B.; Allen, J. L.

    1984-01-01

    Orthogonal acoustic-levitation modes excited at slightly different frequencies to control rotation. Rotation of object in square cross-section acoustic-levitation chamber stopped by detuning two orthogonal (x and y) excitation drivers in plane of square cross section. Detuning done using fundamental degenerate modes or odd harmonic modes.

  18. Acoustically Induced Vibration of Structures: Reverberant Vs. Direct Acoustic Testing

    NASA Technical Reports Server (NTRS)

    Kolaini, Ali R.; O'Connell, Michael R.; Tsoi, Wan B.

    2009-01-01

    Large reverberant chambers have been used for several decades in the aerospace industry to test larger structures such as solar arrays and reflectors to qualify and to detect faults in the design and fabrication of spacecraft and satellites. In the past decade some companies have begun using direct near field acoustic testing, employing speakers, for qualifying larger structures. A limited test data set obtained from recent acoustic tests of the same hardware exposed to both direct and reverberant acoustic field testing has indicated some differences in the resulting structural responses. In reverberant acoustic testing, higher vibration responses were observed at lower frequencies when compared with the direct acoustic testing. In the case of direct near field acoustic testing higher vibration responses appeared to occur at higher frequencies as well. In reverberant chamber testing and direct acoustic testing, standing acoustic modes of the reverberant chamber or the speakers and spacecraft parallel surfaces can strongly couple with the fundamental structural modes of the test hardware. In this paper data from recent acoustic testing of flight hardware, that yielded evidence of acoustic standing wave coupling with structural responses, are discussed in some detail. Convincing evidence of the acoustic standing wave/structural coupling phenomenon will be discussed, citing observations from acoustic testing of a simple aluminum plate. The implications of such acoustic coupling to testing of sensitive flight hardware will be discussed. The results discussed in this paper reveal issues with over or under testing of flight hardware that could pose unanticipated structural and flight qualification issues. Therefore, it is of paramount importance to understand the structural modal coupling with standing acoustic waves that has been observed in both methods of acoustic testing. This study will assist the community to choose an appropriate testing method and test setup in

  19. Acoustically Induced Vibration of Structures: Reverberant Vs. Direct Acoustic Testing

    NASA Technical Reports Server (NTRS)

    Kolaini, Ali R.; O'Connell, Michael R.; Tsoi, Wan B.

    2009-01-01

    Large reverberant chambers have been used for several decades in the aerospace industry to test larger structures such as solar arrays and reflectors to qualify and to detect faults in the design and fabrication of spacecraft and satellites. In the past decade some companies have begun using direct near field acoustic testing, employing speakers, for qualifying larger structures. A limited test data set obtained from recent acoustic tests of the same hardware exposed to both direct and reverberant acoustic field testing has indicated some differences in the resulting structural responses. In reverberant acoustic testing, higher vibration responses were observed at lower frequencies when compared with the direct acoustic testing. In the case of direct near field acoustic testing higher vibration responses appeared to occur at higher frequencies as well. In reverberant chamber testing and direct acoustic testing, standing acoustic modes of the reverberant chamber or the speakers and spacecraft parallel surfaces can strongly couple with the fundamental structural modes of the test hardware. In this paper data from recent acoustic testing of flight hardware, that yielded evidence of acoustic standing wave coupling with structural responses, are discussed in some detail. Convincing evidence of the acoustic standing wave/structural coupling phenomenon will be discussed, citing observations from acoustic testing of a simple aluminum plate. The implications of such acoustic coupling to testing of sensitive flight hardware will be discussed. The results discussed in this paper reveal issues with over or under testing of flight hardware that could pose unanticipated structural and flight qualification issues. Therefore, it is of paramount importance to understand the structural modal coupling with standing acoustic waves that has been observed in both methods of acoustic testing. This study will assist the community to choose an appropriate testing method and test setup in

  20. Radial localization of edge modes in Alcator C-Mod pedestals using optical diagnostics

    NASA Astrophysics Data System (ADS)

    Theiler, C.; Terry, J. L.; Edlund, E.; Cziegler, I.; Churchill, R. M.; Hughes, J. W.; LaBombard, B.; Golfinopoulos, T.; the Alcator C-Mod Team

    2017-02-01

    Dedicated experiments in ion cyclotron range heated enhanced D-alpha (EDA) H-mode and I-mode plasmas have been performed on Alcator C-Mod to identify the location of edge fluctuations inside the pedestal and to determine their plasma frame phase velocity. For this purpose, measurements from gas puff imaging (GPI) and gas puff charge exchange recombination spectroscopy (GP-CXRS) have been collected using the same optical views. The data suggest that the EDA H-mode-specific quasi-coherent mode (QCM) is centered near the radial electric field (E r) well minimum and propagates along the ion diamagnetic drift direction in the plasma frame. The weakly coherent mode (WCM) and the geodesic acoustic mode observed in I-mode, on the other hand, are found to be located around the outer shear layer of the E r well. This results in a weak plasma frame phase velocity mostly along the electron diamagnetic drift direction for the WCM. The findings in these EDA H-mode plasmas differ from probe measurements in ohmic EDA H-mode (LaBombard et al 2014 Phys. Plasmas 21 056108), where the QCM was identified as an electron drift-wave located several mm outside the E r well minimum in a region of positive E r. To explore if instrumental effects of the optical diagnostics could be the cause of the difference, a synthetic diagnostic for GPI is introduced. This diagnostic reproduces amplitude ratios and relative radial shifts of the mode profiles determined from poloidally and toroidally oriented optics and, if instrumental effects related to GP-CXRS are also included, indicates that the measured location of the QCM and WCM relative to the E r well reported here is only weakly affected by instrumental effects.

  1. Rational first integrals of geodesic equations and generalised hidden symmetries

    NASA Astrophysics Data System (ADS)

    Aoki, Arata; Houri, Tsuyoshi; Tomoda, Kentaro

    2016-10-01

    We discuss novel generalisations of Killing tensors, which are introduced by considering rational first integrals of geodesic equations. We introduce the notion of inconstructible generalised Killing tensors, which cannot be constructed from ordinary Killing tensors. Moreover, we introduce inconstructible rational first integrals, which are constructed from inconstructible generalised Killing tensors, and provide a method for checking the inconstructibility of a rational first integral. Using the method, we show that the rational first integral of the Collinson-O’Donnell solution is not inconstructible. We also provide several examples of metrics admitting an inconstructible rational first integral in two and four-dimensions, by using the Maciejewski-Przybylska system. Furthermore, we attempt to generalise other hidden symmetries such as Killing-Yano tensors.

  2. Geodesic-light-cone coordinates and the Bianchi I spacetime

    NASA Astrophysics Data System (ADS)

    Fleury, Pierre; Nugier, Fabien; Fanizza, Giuseppe

    2016-06-01

    The geodesic-light-cone (GLC) coordinates are a useful tool to analyse light propagation and observations in cosmological models. In this article, we propose a detailed, pedagogical, and rigorous introduction to this coordinate system, explore its gauge degrees of freedom, and emphasize its interest when geometric optics is at stake. We then apply the GLC formalism to the homogeneous and anisotropic Bianchi I cosmology. More than a simple illustration, this application (i) allows us to show that the Weinberg conjecture according to which gravitational lensing does not affect the proper area of constant-redshift surfaces is significantly violated in a globally anisotropic universe; and (ii) offers a glimpse into new ways to constrain cosmic isotropy from the Hubble diagram.

  3. CUDA-Accelerated Geodesic Ray-Tracing for Fiber Tracking.

    PubMed

    van Aart, Evert; Sepasian, Neda; Jalba, Andrei; Vilanova, Anna

    2011-01-01

    Diffusion Tensor Imaging (DTI) allows to noninvasively measure the diffusion of water in fibrous tissue. By reconstructing the fibers from DTI data using a fiber-tracking algorithm, we can deduce the structure of the tissue. In this paper, we outline an approach to accelerating such a fiber-tracking algorithm using a Graphics Processing Unit (GPU). This algorithm, which is based on the calculation of geodesics, has shown promising results for both synthetic and real data, but is limited in its applicability by its high computational requirements. We present a solution which uses the parallelism offered by modern GPUs, in combination with the CUDA platform by NVIDIA, to significantly reduce the execution time of the fiber-tracking algorithm. Compared to a multithreaded CPU implementation of the same algorithm, our GPU mapping achieves a speedup factor of up to 40 times.

  4. Light-cone coordinates based at a geodesic world line

    SciTech Connect

    Preston, Brent; Poisson, Eric

    2006-09-15

    Continuing work initiated in an earlier publication [Phys. Rev. D 69, 084007 (2004)], we construct a system of light-cone coordinates based at a geodesic world line of an arbitrary curved spacetime. The construction involves (i) an advanced-time or a retarded-time coordinate that labels past or future light cones centered on the world line (ii) a radial coordinate that is an affine parameter on the null generators of these light cones, and (iii) angular coordinates that are constant on each generator. The spacetime metric is calculated in the light-cone coordinates, and it is expressed as an expansion in powers of the radial coordinate in terms of the irreducible components of the Riemann tensor evaluated on the world line. The formalism is illustrated in two simple applications, the first involving a comoving world line of a spatially flat cosmology, the other featuring an observer placed on the axis of symmetry of Melvin's magnetic universe.

  5. A hierarchical scheme for geodesic anatomical labeling of airway trees.

    PubMed

    Feragen, Aasa; Petersen, Jens; Owen, Megan; Lo, Pechin; Thomsen, Laura H; Wille, Mathilde M W; Dirksen, Asger; de Bruijne, Marleen

    2012-01-01

    We present a fast and robust supervised algorithm for labeling anatomical airway trees, based on geodesic distances in a geometric tree-space. Possible branch label configurations for a given tree are evaluated based on distances to a training set of labeled trees. In tree-space, the tree topology and geometry change continuously, giving a natural way to automatically handle anatomical differences and noise. The algorithm is made efficient using a hierarchical approach, in which labels are assigned from the top down. We only use features of the airway centerline tree, which are relatively unaffected by pathology. A thorough leave-one-patient-out evaluation of the algorithm is made on 40 segmented airway trees from 20 subjects labeled by 2 medical experts. We evaluate accuracy, reproducibility and robustness in patients with chronic obstructive pulmonary disease (COPD). Performance is statistically similar to the inter- and intra-expert agreement, and we found no significant correlation between COPD stage and labeling accuracy.

  6. From laboratory experiments to LISA Pathfinder: achieving LISA geodesic motion

    NASA Astrophysics Data System (ADS)

    Antonucci, F.; Armano, M.; Audley, H.; Auger, G.; Benedetti, M.; Binetruy, P.; Boatella, C.; Bogenstahl, J.; Bortoluzzi, D.; Bosetti, P.; Brandt, N.; Caleno, M.; Cavalleri, A.; Cesa, M.; Chmeissani, M.; Ciani, G.; Conchillo, A.; Congedo, G.; Cristofolini, I.; Cruise, M.; Danzmann, K.; De Marchi, F.; Diaz-Aguilo, M.; Diepholz, I.; Dixon, G.; Dolesi, R.; Dunbar, N.; Fauste, J.; Ferraioli, L.; Fertin, D.; Fichter, W.; Fitzsimons, E.; Freschi, M.; García Marin, A.; García Marirrodriga, C.; Gerndt, R.; Gesa, L.; Giardini, D.; Gibert, F.; Grimani, C.; Grynagier, A.; Guillaume, B.; Guzmán, F.; Harrison, I.; Heinzel, G.; Hewitson, M.; Hollington, D.; Hough, J.; Hoyland, D.; Hueller, M.; Huesler, J.; Jeannin, O.; Jennrich, O.; Jetzer, P.; Johlander, B.; Killow, C.; Llamas, X.; Lloro, I.; Lobo, A.; Maarschalkerweerd, R.; Madden, S.; Mance, D.; Mateos, I.; McNamara, P. W.; Mendes, J.; Mitchell, E.; Monsky, A.; Nicolini, D.; Nicolodi, D.; Nofrarias, M.; Pedersen, F.; Perreur-Lloyd, M.; Perreca, A.; Plagnol, E.; Prat, P.; Racca, G. D.; Rais, B.; Ramos-Castro, J.; Reiche, J.; Romera Perez, J. A.; Robertson, D.; Rozemeijer, H.; Sanjuan, J.; Schleicher, A.; Schulte, M.; Shaul, D.; Stagnaro, L.; Strandmoe, S.; Steier, F.; Sumner, T. J.; Taylor, A.; Texier, D.; Trenkel, C.; Tombolato, D.; Vitale, S.; Wanner, G.; Ward, H.; Waschke, S.; Wass, P.; Weber, W. J.; Zweifel, P.

    2011-05-01

    This paper presents a quantitative assessment of the performance of the upcoming LISA Pathfinder geodesic explorer mission. The findings are based on the results of extensive ground testing and simulation campaigns using flight hardware, flight control and operations algorithms. The results show that, for the central experiment of measuring the stray differential acceleration between the LISA test masses, LISA Pathfinder will be able to verify the overall acceleration noise to within a factor 2 of the LISA requirement at 1 mHz and within a factor 6 at 0.1 mHz. We also discuss the key elements of the physical model of disturbances, coming from LISA Pathfinder and ground measurement that will guarantee the LISA performance.

  7. CUDA-Accelerated Geodesic Ray-Tracing for Fiber Tracking

    PubMed Central

    van Aart, Evert; Sepasian, Neda; Jalba, Andrei; Vilanova, Anna

    2011-01-01

    Diffusion Tensor Imaging (DTI) allows to noninvasively measure the diffusion of water in fibrous tissue. By reconstructing the fibers from DTI data using a fiber-tracking algorithm, we can deduce the structure of the tissue. In this paper, we outline an approach to accelerating such a fiber-tracking algorithm using a Graphics Processing Unit (GPU). This algorithm, which is based on the calculation of geodesics, has shown promising results for both synthetic and real data, but is limited in its applicability by its high computational requirements. We present a solution which uses the parallelism offered by modern GPUs, in combination with the CUDA platform by NVIDIA, to significantly reduce the execution time of the fiber-tracking algorithm. Compared to a multithreaded CPU implementation of the same algorithm, our GPU mapping achieves a speedup factor of up to 40 times. PMID:21941525

  8. About some diophantine equation and the resulting chaos in geodesics

    NASA Astrophysics Data System (ADS)

    Perrine, Serge

    2001-06-01

    We announce results about a complete Markoff theory for the diophantine equation: x2+y2+z2=3xyz+2x All its solutions can be computed. For positive integers, they are organized in two trees. With them, we build a new tree thanks to related continued fractions, and associated binary quadratic forms. In an infinite number of cases, the corresponding approximation and Markoff constants have the form: ((m-2)/√9m2-4 ) For other cases, we conjecture the expression of the constants. All of them converge towards (1/3) by lower values, similarly but differently from the classical Markoff theory. We conclude considering very briefly the link between such equations and geodesics on some Riemann surfaces.

  9. The LISA Pathfinder Mission. Tracing Einstein's Geodesics in Space

    NASA Astrophysics Data System (ADS)

    Racca, Giuseppe D.; McNamara, Paul W.

    2010-03-01

    LISA Pathfinder, formerly known as SMART-2, is the second of the European Space Agency’s Small Missions for Advance Research and Technology, and is designed to pave the way for the joint ESA/NASA Laser Interferometer Space Antenna (LISA) mission, by testing the core assumption of gravitational wave detection and general relativity: that free particles follow geodesics. The new technologies to be demonstrated in a space environment include: inertial sensors, high precision laser interferometry to free floating mirrors, and micro-Newton proportional thrusters. LISA Pathfinder will be launched on a dedicated launch vehicle in late 2011 into a low Earth orbit. By a transfer trajectory, the sciencecraft will enter its final orbit around the first Sun-Earth Lagrange point. First science results are expected approximately 3 months thereafter. Here, we give an overview of the mission including the technologies being demonstrated.

  10. Gravitational instability of polytropic spheres containing region of trapped null geodesics: a possible explanation of central supermassive black holes in galactic halos

    NASA Astrophysics Data System (ADS)

    Stuchlík, Zdeněk; Schee, Jan; Toshmatov, Bobir; Hladík, Jan; Novotný, Jan

    2017-06-01

    We study behaviour of gravitational waves in the recently introduced general relativistic polytropic spheres containing a region of trapped null geodesics extended around radius of the stable null circular geodesic that can exist for the polytropic index N > 2.138 and the relativistic parameter, giving ratio of the central pressure pc to the central energy density ρc, higher than σ = 0.677. In the trapping zones of such polytropes, the effective potential of the axial gravitational wave perturbations resembles those related to the ultracompact uniform density objects, giving thus similar long-lived axial gravitational modes. These long-lived linear perturbations are related to the stable circular null geodesic and due to additional non-linear phenomena could lead to conversion of the trapping zone to a black hole. We give in the eikonal limit examples of the long-lived gravitational modes, their oscillatory frequencies and slow damping rates, for the trapping zones of the polytropes with N in (2.138,4). However, in the trapping polytropes the long-lived damped modes exist only for very large values of the multipole number l > 50, while for smaller values of l the numerical calculations indicate existence of fast growing unstable axial gravitational modes. We demonstrate that for polytropes with N >= 3.78, the trapping region is by many orders smaller than extension of the polytrope, and the mass contained in the trapping zone is about 10-3 of the total mass of the polytrope. Therefore, the gravitational instability of such trapping zones could serve as a model explaining creation of central supermassive black holes in galactic halos or galaxy clusters.

  11. Analytic treatment of complete and incomplete geodesics in Taub-NUT space-times

    SciTech Connect

    Kagramanova, Valeria; Kunz, Jutta; Hackmann, Eva; Laemmerzahl, Claus

    2010-06-15

    We present the complete set of analytical solutions of the geodesic equation in Taub-NUT space-times in terms of the Weierstrass elliptic functions. We systematically study the underlying polynomials and characterize the motion of test particles by its zeros. Since the presence of the 'Misner string' in the Taub-NUT metric has led to different interpretations, we consider these in terms of the geodesics of the space-time. In particular, we address the geodesic incompleteness at the horizons discussed by Misner and Taub [C. W. Misner and A. H. Taub, Sov. Phys. JETP 28, 122 (1969) [Zh. Eksp. Teor. Fiz. 55, 233 (1968)

  12. Diffraction-free acoustic detection for optoacoustic depth profiling of tissue using an optically transparent polyvinylidene fluoride pressure transducer operated in backward and forward mode.

    PubMed

    Jaeger, Michael; Niederhauser, Joël J; Hejazi, Marjaneh; Frenz, Martin

    2005-01-01

    An optoacoustic detection method suitable for depth profiling of optical absorption of layered or continuously varying tissue structures is presented. Detection of thermoelastically induced pressure transients allows reconstruction of optical properties of the sample to a depth of several millimeters with a spatial resolution of 24 mum. Acoustic detection is performed using a specially designed piezoelectric transducer, which is transparent for optical radiation. Thus, ultrasonic signals can be recorded at the same position the tissue is illuminated. Because the optoacoustical sound source is placed in the pulsed-acoustic near field of the pressure sensor, signal distortions commonly associated with acoustical diffraction are eliminated. Therefore, the acoustic signals mimic exactly the depth profile of the absorbed energy. This is illustrated by imaging the absorption profile of a two-layered sample with different absorption coefficients, and of a dye distribution while diffusing into a gelatin phantom.

  13. Virtual Acoustics

    NASA Astrophysics Data System (ADS)

    Lokki, Tapio; Savioja, Lauri

    The term virtual acoustics is often applied when sound signal is processed to contain features of a simulated acoustical space and sound is spatially reproduced either with binaural or with multichannel techniques. Therefore, virtual acoustics consists of spatial sound reproduction and room acoustics modeling.

  14. Acoustic Levitation With One Driver

    NASA Technical Reports Server (NTRS)

    Wang, T. G.; Rudnick, I.; Elleman, D. D.; Stoneburner, J. D.

    1985-01-01

    Report discusses acoustic levitation in rectangular chamber using one driver mounted at corner. Placement of driver at corner enables it to couple effectively to acoustic modes along all three axes. Use of single driver reduces cost, complexity and weight of levitation system below those of three driver system.

  15. iPGA: Incremental Principal Geodesic Analysis with Applications to Movement Disorder Classification★

    PubMed Central

    Salehian, Hesamoddin; Vaillancourt, David

    2014-01-01

    The nonlinear version of the well known PCA called the Principal Geodesic Analysis (PGA) was introduced in the past decade for statistical analysis of shapes as well as diffusion tensors. PGA of diffusion tensor fields or any other manifold-valued fields can be a computationally demanding task due to the dimensionality of the problem and thus establishing motivation for an incremental PGA (iPGA) algorithm. In this paper, we present a novel iPGA algorithm that incrementally updates the current Karcher mean and the principal sub-manifolds with any newly introduced data into the pool without having to recompute the PGA from scratch. We demonstrate substantial computational and memory savings of iPGA over the batch mode PGA for diffusion tensor fields via synthetic and real data examples. Further, we use the iPGA derived representation in an NN classifier to automatically discriminate between controls, Parkinson’s Disease and Essential Tremor patients, given their HARDI brain scans. PMID:25485449

  16. Multi-reflective acoustic wave device

    DOEpatents

    Andle, Jeffrey C.

    2006-02-21

    An acoustic wave device, which utilizes multiple localized reflections of acoustic wave for achieving an infinite impulse response while maintaining high tolerance for dampening effects, is disclosed. The device utilized a plurality of electromechanically significant electrodes disposed on most of the active surface. A plurality of sensors utilizing the disclosed acoustic wave mode device are also described.

  17. YNOGKM: Time-like geodesics in the Kerr-Newmann Spacetime calculations

    NASA Astrophysics Data System (ADS)

    Yang, Xiao-lin; Wang, Jian-cheng

    2014-03-01

    YNOGKM (Yun-Nan observatories geodesic in a Kerr-Newman spacetime for massive particles) performs fast calculation of time-like geodesics in the Kerr-Newman (K-N) spacetime; it is a direct extension of YNOGK (Yun-Nan observatories geodesic Kerr) calculating null geodesics in a Kerr spacetime. The four Boyer-Lindquis coordinates and proper time are expressed as functions of a parameter p semi-analytically by using the Weierstrass' and Jacobi's elliptic functions and integrals. The elliptic integrals are computed by Carlson's elliptic integral method, which guarantees the fast speed of the code. The source Fortran file ynogkm.f90 contains three modules: constants, rootfind, ellfunction, and blcoordinates.

  18. Geodesics without differential equations: general relativistic calculations for introductory modern physics classes

    NASA Astrophysics Data System (ADS)

    Rowland, D. R.

    2006-01-01

    Introductory courses covering modern physics sometimes introduce some elementary ideas from general relativity, though the idea of a geodesic is generally limited to shortest Euclidean length on a curved surface of two spatial dimensions rather than extremal aging in spacetime. It is shown that Epstein charts provide a simple geometric picture of geodesics in one space and one time dimension and that for a hypothetical uniform gravitational field, geodesics are straight lines on a planar diagram. This means that the properties of geodesics in a uniform field can be calculated with only a knowledge of elementary geometry and trigonometry, thus making the calculation of some basic results of general relativity accessible to students even in an algebra-based survey course on physics.

  19. Thermodynamic geodesics of a Reissner Nordström black hole

    NASA Astrophysics Data System (ADS)

    Farrugia, Christine; Sultana, Joseph

    2017-01-01

    Starting from a Geometrothermodynamics metric for the space of thermodynamic equilibrium states in the mass representation, we use numerical techniques to analyse the thermodynamic geodesics of a supermassive Reissner Nordström black hole in isolation. Appropriate constraints are obtained by taking into account the processes of Hawking radiation and Schwinger pair-production. We model the black hole in line with the work of Hiscock and Weems (Phys Rev D 41:1142-1151, 1990). It can be deduced that the relation which the geodesics establish between the entropy S and electric charge Q of the black hole extremises changes in the black hole's mass. Indeed, the expression for the entropy of an extremal black hole is an exact solution to the geodesic equation. We also find that in certain cases, the geodesics describe the evolution brought about by the constant emission of Hawking radiation and charged-particle pairs.

  20. Sets of medians in the non-geodesic pseudometric space of unsigned genomes with breakpoints

    PubMed Central

    2014-01-01

    Background The breakpoint median in the set Sn of permutations on n terms is known to have some unusual behavior, especially if the input genomes are maximally different to each other. The mathematical study of the set of medians is complicated by the facts that breakpoint distance is not a metric but a pseudo-metric, and that it does not define a geodesic space. Results We introduce the notion of partial geodesic, or geodesic patch between two permutations, and show that if two permutations are medians, then every permutation on a geodesic patch between them is also a median. We also prove the conjecture that the input permutations themselves are medians. PMID:25571965